INTERNET TECHNOLOGY AND WEB PROGRAMMING

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CONTENTS LESSON I: Introduction to Networking · Networking concepts and Technology (LANs and WANs) .. . . . . . . . · Serial Networking (SLIP, PPP) . . . .. . . . . . . . . . . . . · Internet Protocol (IP) and Domain Name System (DNS) .. . . . . . . . · What is the Internet . . . . . . .. . . . . . . . . . . . . LESSON II: Internet Access Hardware and Media · HARDWARE: Modems, Terminal Adapters, Routers . . . . . . . . . . · MEDIA: PTSN, ISDN, Kilostream . . . . . . . . . . . . . . . . LESSON III: Internet Services · Electronic Mail; Newsgroups . . . . . . . . . . . . . . . . . . · File Transfer Protocol (FTP) and Hypertext Transfer Protocol (HTTP) . . . . . · Internet databases: WAIS, Archie, gopher, WWW search databases . . . . . LESSON IV: Using E-Mail and other Clients · Electronics Mail . . . . . . . . . . . . . . . . . . . . · Other Internet Clients . . . . . . . . . . . . . . . . . . . . · FTP . . . . . . . . . . . . . . . . . . · Newsgroups . . . . . . . . . . . . . . . . · Telnet . . . . . . . . . . . . . . . . . .

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LESSON V: Media & Active Content · Object & Active Content . . . . . . . . .

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Types of Browser Plug-ins . . . . . . . . . . .

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Additional Media File Formats . . . . . . . . . . . . Images File Formats . . . . . . . . . . . . . .

LESSON VI: Internetworking Servers · Server Implementation . . . . . . . . . . . . . . · Content Servers . . . . . . . . . . . . . . . . · Performance Servers . . . . . . . . . . . . . . · Database Servers . . . . . . . . . . . . . . . · Mirrored Servers . . . . . . . . . . . . . . . . · Popular Server Products . . . . . . . . . . . . .

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LESSON VII: Web Servers and Databases · Databases . . . . . . . . . . . . . . . . . . . . . . . · Introduction to Database Gateways for Web Servers . . . . . . . . . . · Common Gateway Interface (CGI) . . . . . . . . . . . . . . . . · Server Application Programming Interfaces (SAPIs) . . . . . . . . . . · JavaScript . . . . . . . . . . . . . . . . . . . · ASP . . . . . . . . . . . . . . . . . . . . . · PHP . . . . . . . . . . . . . . . . . . . . . . · HTML . . . . . . . . . . . . . . . . . . . . . · Java & Java Service . . . . . . . . . . . . . . . . · JSP . . . . . . . . . . . . . . . . . . . . . · ColdFusion . . . . . . . . . . . . . . . . . . . · Database Connectivity

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ODBC . . . . JDBC . . . .

LESSON VIII: Internet Security · What is Security? . . . . . . . . . . . · · · · · ·

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The cracker Process . . . . . . . . . . . . . Types of Attacks . . . . . . . . . . . . . . Defending Your Networks . . . . . . . . . . . Firewalls . . . . . . . . . . . . . . . . Defending Your Computer . . . . . . . . . . . Defending Your Transmitted . . . . . . . . . .

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Lesson I: (Introduction to Networking) 1. Network concepts and Technology (LANs and WANs)

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LANs, WANs, and Other Area Networks

Computer networks come in many different shapes and sizes. Over the years, the networking industry has coined terms like "LAN" and "WAN" attempting to define sensible categories for the major types of network designs. The precise meaning of this terminology remains lost on the average person, however. Area Networks For historical reasons, the industry refers to nearly every type of network as an "area network." The most commonly-discussed categories of computer networks include the following ·

Local Area Network (LAN)

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Wide Area Network (WAN)

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Metropolitan Area Network (MAN)

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Storage Area Network (SAN)

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System Area Network (SAN)

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Server Area Network (SAN)

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Small Area Network (SAN)

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Personal Area Network (PAN)

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Desk Area Network (DAN)

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Controller Area Network (CAN)

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Cluster Area Network (CAN)

LANs and WANs were the original flavors of network design. The concept of "area" made good sense at this time, because a key distinction between a LAN and a WAN involves the physical distance that the network spans. A third category, the MAN, also fit into this scheme as it too is centered on a distance-based concept.

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LAN Basics

A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs, and occasionally a LAN will span a group of nearby buildings. In IP networking, one can conceive of a LAN as a single IP subnet (though this is not necessarily true in practice). Besides operating in a limited space, LANs include several other distinctive features. LANs are typically owned, controlled, and managed by a single person or organization. They also use certain specific connectivity technologies, primarily Ethernet and Token Ring.

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WAN Basics

As the term implies, a wide-area network spans a large physical distance. A WAN like the Internet spans most of the world! A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN. In IP networking, the router maintains both a LAN address and a WAN address. WANs differ from LANs in several important ways. Like the Internet, most WANs are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs use technology like ATM, Frame Relay and X.25 for connectivity.

LANs and WANs at Home Home net workers with cable modem or DSL service already have encountered LANs and WANs in practice, though they may not have noticed. A cable/DSL router like those in the Links family join the home LAN to the WAN link maintained by one's ISP. The ISP provides a WAN IP address used by the router, and all of the computers on the home network use private LAN addresses. On a home network, like many LANs, all computers can communicate directly with each other, but they must go through a central gateway location to reach devices outside of their local area. What About MAN, SAN, PAN, DAN, and CAN? Future articles will describe the many other types of area networks in more detail. After LANs and WANs, one will most commonly encounter the following three network designs: A Metropolitan Area Network (MAN) connects an area larger than a LAN but smaller than a WAN, such as a city, with dedicated or high-performance hardware. A Storage Area Network (SAN) connects servers to data storage devices through a technology like Fibre Channel. A System Area Network (SAN) connects high-performance computers with high-speed connections in a cluster configuration.

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Conclusion To the uninitiated, LANs, WANs, and the other area network acronyms appear to be just more alphabet soup in a technology industry already drowning in terminology. The names of these networks are not nearly as important as the technologies used to construct them, however. A person can use the categorizations as a learning tool to better understand concepts like subnets, gateways, and routers.

A Simple Computer Network for File Sharing Illustration: 1

This diagram illustrates the simplest possible kind of computer network. In a simple network, two computers (or other networkable devices) make a direct connection with each and communicate over a wire or cable. Simple networks like this have existed for decades. A common use for these networks is file sharing.

A Local Area Network (LAN)

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Illustration: 2

This diagram illustrates a typical local area network (LAN) environment. Local area networks often feature a group of computers located in a home, school, or part of an office building. Like a simple network, computers on a LAN share files and printers. Computers on one LAN can also share connections with other LANs and with the internet.

A Hypothetical Wide Area Network Illustration: 3

This diagram illustrates a hypothetical wide area network (WAN) configuration that joins LANs in three metropolitan locations. Wide area networks cover a large geographic area like a city, a country or multiple countries. WANs normally connect multiple LANs and other smaller-scale area networks. WANs are built by large telecommunication companies and other corporations using highly-specialized equipment not found in consumer stores. The Internet is an example of a WAN that joins local and metropolitan area networks across most of the world.

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Wiring in Computer Networks Illustration: 4

This diagram illustrates s e v e r a l c o m m o n forms of wiring in computer networks. In many homes, twisted-pair Ethernet cables are often used to connect computers. Phone or cable TV lines in turn connect the home LAN to the Internet Service Provider (ISP). ISPs, larger schools and businesses often stack their computer equipment in racks (as shown), and they use a mix of different kinds of cable to join this equipment to LANs and to the Internet. Much of the Internet uses high-speed fiber optic cable to send traffic long distances underground, but twisted pair and coaxial cable can also be used for leased lines and in more remote areas.

Network Topologies Bus, ring, star, and all the rest

In networking, the term topology refers to the layout of connected devices on a network. This article introduces the standard topologies of computer networking. Topology in Network Design One can think of a topology as a network's "shape" . This shape does not necessarily correspond to the actual physical layout of the devices on the network. For example, the computers on a home LAN may be arranged in a circle, but it would be highly unlikely to find an actual ring topology there. Network topologies are categorized into the following basic types:

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bus

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ring

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star

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·

tree

·

mesh

More complex networks can be built as hybrids of two or more of the above basic topologies.

Illustration: 5

Bus Topology diagram

Bus Topology Bus networks (not to be confused with the system bus of a computer) use a common backbone to connect all devices. A single cable, the backbone functions as a shared communication medium, that devices attach or tap into with an interface connector. A device wanting to communicate with another device on the network sends a broadcast

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message onto the wire that all other devices see, but only the intended recipient actually accepts and processes the message. Ethernet bus topologies are relatively easy to install and don't require much cabling compared to the alternatives. 10Base-2 ("ThinNet") and 10Base-5 ("ThickNet") both were popular Ethernet cabling options years ago. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable. Ring Topology Diagram

Illustration: 6

Ring Topology In a ring network, every device has exactly two neighbors for communication purposes. All messages travel through a ring in the same direction (effectively either "clockwise" or "counterclockwise"). A failure in any cable or device breaks the loop and can take down the entire network.

To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology. Rings are found in some office buildings or school campuses. Star Topology Diagram

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Illustration: 7

Star Topology Many home networks use the star topology. A star network features a central connection point called a "hub" that may be an actual hub or a switch. Devices typically connect to the hub with Unshielded Twisted Pair (UTP) Ethernet. Compared to the bus topology, a star network generally requires more cable, but a failure in any star network cable will only take down one computer's network access and not the entire LAN. (If the hub fails, however, the entire network also fails.)

Tree Topology Diagram Illustrati on: 8

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Tree Topology Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of devices. This bus/star hybrid approach supports future expandability of the network much better than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star (limited by the number of hub ports) alone.

Mesh Topology Diagram Illustration: 9

Mesh Topology Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages sent on a mesh network can take any of several possible paths from source to destination. (Recall that in a ring, although

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two cable paths exist, messages can only travel in one direction.) Some WANs, like the Internet, employ mesh routing.

Conclusion Topologies remain an important part of network design theory. You can probably build a home or small business network without understanding the difference between a bus design and a star design, but understanding the concepts behind these gives you a deeper understanding of important elements like hubs, broadcasts, ports, and routes

Serial Networking (SLIP) What is SLIP? The Shared Land Information Platform is a shared information delivery service which provides fast and easy access to the state’s spatial information. SLIP is the platform connecting WA Government spatial information. Driven by the Department of Land Information in Western Australia (DLI), SLIP is a ground-breaking project revolutionizing the way government spatial (land and property) information is used and shared, providing numerous benefits to government, business, industry and the community. SLIP delivers online real-time access to spatial information in a seamless cross-Government manner, thereby overcoming the agency run-around currently experienced by industry and the public. Spatial information underpins and links a range of government activities, including planning, land use and development, environmental sustainability and emergency management. SLIP makes it easier to locate and use this information. The implementation plan for SLIP was developed and endorsed by the WA Government in November 2004. SLIP involves the engagement of over 200 people across more than 20 State Government agencies, as well as local government, community groups and industry bodies. SLIP works with WALIS (WA Land Information System) to facilitate widespread engagement and collaboration. SLIP is the platform connecting WA Government Spatial Information, with the endorsed program-of-work also pursuing four cross-agency whole-of-government business opportunities - emergency management, natural resource management, land development and register of interests. The SLIP platform is implemented using an enabling framework built on current DLI infrastructure. The platform has been funded to connect fifteen (15) State Government agencies, provide access to a minimum of 60 data services (with access to up to 200 data services available when all business opportunities are fully implemented), together with services for security, management, metering, cataloguing and viewing of data. SLIP Benefits

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SLIP facilitates improvement of business processes and systems which use spatial information across networked government. Through the use of SLIP, Government agencies, local government, community groups, industry and private citizens will have a single point of access to spatial information. This improved information access will facilitate greater sharing of information amongst diverse groups; more consistent use of information; resulting in better management decisions; and the ability to more effectively "value-add" new information using a range of information sources. Systems using spatial information will be able to be implemented with a reduced infrastructure overhead and at lower cost than otherwise previously achievable. Data integrity will improve through access to the single and most recent "authorities" source of spatial information, in an online real-time basis. The right information can be made available to the right people at the right time.

1. Serial Networking (PPP)

The Point-to-Point Protocol (PPP) originally emerged as an encapsulation protocol for transporting IP traffic over point-to-point links. PPP also established a standard for the assignment and management of IP addresses asynchronous (start/stop) and bit-oriented synchronous encapsulation, network protocol multiplexing, link configuration, link quality testing, error detection, and option negotiation for such capabilities as network layer address negotiation and data-compression negotiation. PPP supports these functions by providing an extensible Link Control Protocol (LCP) and a family of Network Control Protocols (NCPs) to negotiate optional configuration parameters and facilities. In addition to IP, PPP supports other protocols, including Novell's Internet work Packet Exchange (IPX) and DECnet. PPP Components PPP provides a method for transmitting diagrams over serial point-to-point links. PPP contains three main components: • A method for encapsulating datagram’s over serial links. PPP uses the High-Level Data Link Control (HDLC) protocol as a basis for encapsulating diagrams over point-to-point links. "Synchronous Data Link Control and Derivatives," forzaxyzaxy more information on HDLC.) •

An extensible LCP to establish, configure, and test the data link connection.

• A family of NCPs for establishing and configuring different network layer protocols. PPP is designed to allow the simultaneous use of multiple network layer protocols. General Operation To establish communications over a point-to-point link, the originating PPP first sends LCP frames to configure and (optionally) test the data link. After the link has been established and optional facilities have been negotiated as needed by the LCP, the originating PPP sends NCP frames to choose and configure one or more network layer protocols. When each of the chosen network layer protocols has been configured, packets from each network layer

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protocol can be sent over the link. The link will remain configured for communications until explicit LCP or NCP frames close the link, or until some external event occurs (for example, an inactivity timer expires or a user intervenes). Physical Layer Requirements PPP is capable of operating across any DTE/DCE interface. Examples include EIA/TIA-232-C (formerly RS-232-C), EIA/TIA-422 (formerly RS-422), EIA/TIA-423 (formerly RS-423), and International Telecommunication Union Telecommunication Standardization Sector (ITU-T) (formerly CCITT) V.35. The only absolute requirement imposed by PPP is the provision of a duplex circuit, either dedicated or switched, that can operate in either an asynchronous or synchronous bit-serial mode, transparent to PPP link layer frames. PPP does not impose any restrictions regarding transmission rate other than those imposed by the particular DTE/DCE interface in use. PPP Link Layer PPP uses the principles, terminology, and frame structure of the International Organization for Standardization (ISO) HDLC procedures (ISO 3309-1979), as modified by ISO 3309:1984/PDAD1 "Addendum 1: Start/Stop Transmission." ISO 3309-1979 specifies the HDLC frame structure for use in synchronous environments. ISO 3309:1984/PDAD1 specifies proposed modifications to ISO 3309-1979 to allow its use in asynchronous environments. The PPP control procedures use the definitions and control field encodings standardized in ISO 4335-1979 and ISO 4335-1979/Addendum 1-1979. Six Fields Make Up the PPP Frame Illustration: 10 T h e f ol lo w in g d escriptions summarize the PPP frame fields. • Flag—A single byte that indicates the beginning or end of a frame. The flag field consists of the binary sequence 01111110. • Address—A single byte that contains the binary sequence 11111111, the standard broadcast address. PPP does not assign individual station addresses. • Control—A single byte that contains the binary sequence 00000011, which calls for transmission of user data in an subsequences frame. A connectionless link service similar to that of Logical Link Control (LLC) Type 1 is provided. (For more information about LLC types and frame types, refer to Chapter 16.) • Protocol—Two bytes that identify the protocol encapsulated in the information field of the frame. The most up-to-date values of the protocol field are specified in the most recent Assigned Numbers Request For Comments (RFC).

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• Data—Zero or more bytes that contain the datagram for the protocol specified in the protocol field. The end of the information field is found by locating the closing flag sequence and allowing 2 bytes for the FCS field. The default maximum length of the information field is 1,500 bytes. By prior agreement, consenting PPP implementations can use other values for the maximum information field length. • Frame check sequence (FCS)—normally 16 bits (2 bytes). By prior agreement, consenting PPP implementations can use a 32-bit (4-byte) FCS for improved error detection. The LCP can negotiate modifications to the standard PPP frame structure. Modified frames, however, always will be clearly distinguishable from standard frames. PPP Link-Control Protocol The PPP LCP provides a method of establishing, configuring, maintaining, and terminating the point-to-point connection. LCP goes through four distinct phases. First, link establishment and configuration negotiation occur. Before any network layer datagram’s (for example, IP) can be exchanged, LCP first must open the connection and negotiate configuration parameters. This phase is complete when a configuration-acknowledgment frame has been both sent and received. This is followed by link quality determination. LCP allows an optional link quality determination phase following the link-establishment and configuration-negotiation phase. In this phase, the link is tested to determine whether the link quality is sufficient to bring up network layer protocols. This phase is optional. LCP can delay transmission of network layer protocol information until this phase is complete. At this point, network layer protocol configuration negotiation occurs. After LCP has finished the link quality determination phase, network layer protocols can be configured separately by the appropriate NCP and can be brought up and taken down at any time. If LCP closes the link, it informs the network layer protocols so that they can take appropriate action. Finally, link termination occurs. LCP can terminate the link at any time. This usually is done at the request of a user but can happen because of a physical event, such as the loss of carrier or the expiration of an idle-period timer. Three classes of LCP frames exist. Link-establishment frames are used to establish and configure a link. Link-termination frames are used to terminate a link, and link-maintenance frames are used to manage and debug a link. These frames are used to accomplish the work of each of the LCP phases.

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Internet Protocols

The Internet protocols are the world's most popular open-system (nonproprietary) protocol suite because they can be used to communicate across any set of interconnected networks and are equally well suited for LAN and WAN communications. The Internet protocols consist of a suite of communication protocols, of which the two best known are the Transmission Control Protocol (TCP) and the Internet Protocol (IP). The Internet protocol suite not only includes lower-layer protocols (such as TCP and IP), but it also specifies common applications such as electronic mail, terminal emulation, and file transfer. This chapter provides a broad introduction to specifications that comprise the Internet protocols. Discussions include IP addressing and key upper-layer protocols used in the Internet. Specific routing protocols are addressed individually later in this document.

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Internet protocols were first developed in the mid-1970s, when the Defense Advanced Research Projects Agency (DARPA) became interested in establishing a packet-switched network that would facilitate communication between dissimilar computer systems at research institutions. With the goal of heterogeneous connectivity in mind, DARPA funded research by Stanford University and Bolt, Beranek, and Newman (BBN). The result of this development effort was the Internet protocol suite, completed in the late 1970s. TCP/IP later was included with Berkeley Software Distribution (BSD) UNIX and has since become the foundation on which the Internet and the World Wide Web (WWW) are based. Documentation of the Internet protocols (including new or revised protocols) and policies are specified in technical reports called Request For Comments (RFCs), which are published and then reviewed and analyzed by the Internet community. Protocol refinements are published in the new RFCs. To illustrate the scope of the Internet protocols, maps many of the protocols of the Internet protocol suite and their corresponding OSI layers. This chapter addresses the basic elements and operations of these and other key Internet protocols.

Internet protocols span the complete range of OSI model layers. Illustration: 11

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Internet Protocol (IP) The Internet Protocol (IP) is a network-layer (Layer 3) protocol that contains addressing information and some control information that enables packets to be routed. IP is documented in RFC 791 and is the primary network-layer protocol in the Internet protocol suite. Along with the Transmission Control Protocol (TCP), IP represents the heart of the Internet protocols. IP has two primary responsibilities: providing connectionless, best-effort delivery of datagram’s through an internetwork; and providing fragmentation and reassembly of datagram’s to support data links with different maximum-transmission unit (MTU) sizes.

IP Packet Format Illustration: 12

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Fourteen fields comprise an IP packet.

The following discussion describes the IP packet fields illustrated in : •

Version—indicates the version of IP currently used.

•

IP Header Length (IHL)—Indicates the datagram header length in 32-bit words.

• Type-of-Service—specifies how an upper-layer protocol would like a current datagram to be handled, and assigns datagram’s various levels of importance. • Total Length—specifies the length, in bytes, of the entire IP packet, including the data and header. • Identification—contains an integer that identifies the current datagram. This field is used to help piece together datagram fragments. • Flags—consist of a 3-bit field of which the two low-order (least-significant) bits control fragmentation. The low-order bit specifies whether the packet can be fragmented. The middle bit specifies whether the packet is the last fragment in a series of fragmented packets. The third or high-order bit is not used. • Fragment Offset—indicates the position of the fragment's data relative to the beginning of the data in the original datagram, which allows the destination IP process to properly reconstruct the original datagram. • Time-to-Live—maintains a counter that gradually decrements down to zero, at which point the datagram is discarded. This keeps packets from looping endlessly.

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• Protocol—Indicates which upper-layer protocol receives incoming packets after IP processing is complete. •

Header Checksum—helps ensure IP header integrity.

•

Source Address—specifies the sending node.

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Destination Address—specifies the receiving node.

•

Options—Allows IP to support various options, such as security.

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Data—Contains upper-layer information.

IP Addressing As with any other network-layer protocol, the IP addressing scheme is integral to the process of routing IP datagrams through an internetwork. Each IP address has specific components and follows a basic format. These IP addresses can be subdivided and used to create addresses for subnetworks, as discussed in more detail later in this chapter. Each host on a TCP/IP network is assigned a unique 32-bit logical address that is divided into two main parts: the network number and the host number. The network number identifies a network and must be assigned by the Internet Network Information Center (InterNIC) if the network is to be part of the Internet. An Internet Service Provider (ISP) can obtain blocks of network addresses from the InterNIC and can itself assign address space as necessary. The host number identifies a host on a network and is assigned by the local network administrator. IP Address Format The 32-bit IP address is grouped eight bits at a time, separated by dots, and represented in decimal format (known as dotted decimal notation). Each bit in the octet has a binary weight (128, 64, 32, 16, 8, 4, 2, 1). The minimum value for an octet is 0, and the maximum value for an octet is 255. Illustration: 13 An

IP

address

consists

of

32

bits,

grouped

into

four

octets.

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IP Address Classes IP addressing supports five different address classes: A, B, C, D, and E. Only classes A, B, and C are available for commercial use. The left-most (high-order) bits indicate the network class. Provides reference information about the five IP address classes. Illustration: 14 Reference Information About the Five IP Address Classes I P Address Class Format

Purpose

Hig hOrder No. Bits Bit(s) Address Range Network/Host M a x . Hosts

A

large 0 N.H .H .H Few organizations 1

1.0.0.0 126.0.0.0

to 7/24

16777214 2 (224 - 2)

B

N.N.H.H

Medium-size 1, 0 organizations

128.1.0.0 191.254.0.0

to 14/16

6 5 5 3 4 (2 16 - 2)

C

N.N.N.H

R e l a t i v e l y 1, 1, 0 192.0.1.0 to 21/8 s m a l l 223.255.254.0 organizations

D

N/A

M u l t i c a s t 1, 1, 224.0.0.0 to N/A (not for N/A groups (RFC 1, 0 239.255.255.255 c o m m e r c i a l 1112) use)

E

N/A

Experimental 1, 1, 240.0.0.0 to N/A 1, 1 254.255.255.255

254 (2 8 2)

N/A

N= network number, H= host number. One address is reserved for the broadcast address, and one address is reserved for the network.

Illustrates the format of the commercial IP address classes. (Note the high-order bits in each class.)

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The class of address can be determined easily by examining the first octet of the address and mapping that value to a class range in the following table. In an IP address of 172.31.1.2, for example, the first octet is 172. Because 172 falls between 128 and 191, 172.31.1.2 is a Class B address. Summarizes the range of possible values for the first octet of each address class. Illustration: 15 A range of possible values exists for the first octet of each address class.

IP Subnet Addressing

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IP networks can be divided into smaller networks called subnetworks (or subnets). Subnetting provides the network administrator with several benefits, including extra flexibility, more efficient use of network addresses, and the capability to contain broadcast traffic (a broadcast will not cross a router). Subnets are under local administration. As such, the outside world sees an organization as a single network and has no detailed knowledge of the organization's internal structure. A given network address can be broken up into many subnetworks. For example, 172.16.1.0, 172.16.2.0, 172.16.3.0, and 172.16.4.0 are all subnets within network 171.16.0.0. (All 0s in the host portion of an address specifies the entire network.) IP Subnet Mask A subnet address is created by "borrowing" bits from the host field and designating them as the subnet field. The number of borrowed bits varies and is specified by the subnet mask. Shows how bits are borrowed from the host address field to create the subnet address field.

Illustration: 16 Bits are borrowed from the host address field to create the subnet address field.

Subnet masks use the same format and representation technique as IP addresses. The subnet mask, however, has binary 1s in all bits specifying the network and subnetwork fields, and binary 0s in all bits specifying the host field.

Illustration: 17 A sample subnet mask consists of all binary 1s and 0s.

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Subnet mask bits should come from the high-order (left-most) bits of the host field, as illustrates. Details of Class B and C subnet mask types follow. Class A addresses are not discussed in this chapter because they generally are subnetted on an 8-bit boundary. Illustration: 18 Subnet mask bits come from the high-order bits of the host field.

Vari ous types of subnet masks exist for Class B and C subnets. The default subnet mask for a Class B address that has no subnetting is 255.255.0.0, while the subnet mask for a Class B address 171.16.0.0 that specifies eight bits of subnetting is 255.255.255.0. The reason for this is that eight bits of subnetting or 2 8 - 2 (1 for the network address and 1 for the broadcast address) = 254 subnets possible, with 28 - 2 = 254 hosts per subnet. The subnet mask for a Class C address 192.168.2.0 that specifies five bits of subnetting is 255.255.255.248.With five bits available for subnetting, 2 5 - 2 = 30 subnets possible, with 23 - 2 = 6 hosts per subnet. The reference charts shown in table 30-2 and table 30-3 can be used when planning Class B and C networks to determine the required number of subnets and hosts, and the appropriate subnet mask.

Illustration: 19

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Class B Subnetting Reference Chart Number of Bits

Number of Subnets

Subnet Mask

Number of Hosts

2

255.255.192.0

2

16382

3

255.255.224.0

6

8190

4

255.255.240.0

14

4094

5

255.255.248.0

30

2046

6

255.255.252.0

62

1022

7

255.255.254.0

126

510

8

255.255.255.0

254

254

9

255.255.255.128 510

126

10

255.255.255.192 1022

62

11

255.255.255.224 2046

30

12

255.255.255.240 4094

14

13

255.255.255.248 8190

6

14

255.255.255.252 16382

2

Illustration: 20 Class C Subnetting Reference Chart Number of Bits Subnet Mask

Number of Subnets

Number of Hosts

2

255.255.255.192

2

62

3

255.255.255.224

6

30

4

255.255.255.240

14

14

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5

255.255.255.248

30

6

6

255.255.255.252

62

2

How Subnet Masks are Used to Determine the Network Number The router performs a set process to determine the network (or more specifically, the subnetwork) address. First, the router extracts the IP destination address from the incoming packet and retrieves the internal subnet mask. It then performs a logical AND operation to obtain the network number. This causes the host portion of the IP destination address to be removed, while the destination network number remains. The router then looks up the destination network number and matches it with an outgoing interface. Finally, it forwards the frame to the destination IP address. Specifics regarding the logical AND operation are discussed in the following section. Logical AND Operation Three basic rules govern logically "ANDing" two binary numbers. First, 1 "ANDed" with 1 yields 1. Second, 1 "ANDed" with 0 yields 0. Finally, 0 "ANDed" with 0 yields 0. The truth table provided in illustration 21 illustrate the rules for logical AND operations. Illustration: 21 Rules for Logical AND Operations Input

Input

Output

1

1

1

1

0

0

0

1

0

0

0

0

Two simple guidelines exist for remembering logical AND operations: Logically "ANDing" a 1 with a 1 yields the original value, and logically "ANDing" a 0 with any number yields 0. Illustrates that when a logical AND of the destination IP address and the subnet mask is performed, the subnetwork number remains, which the router uses to forward the packet.

Illustration: 22 Applying a logical AND the destination IP address and the subnet mask produces the subnetwork number.

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Address Resolution Protocol (ARP) Overview For two machines on a given network to communicate, they must know the other machine's physical (or MAC) addresses. By broadcasting Address Resolution Protocols (ARPs), a host can dynamically discover the MAC-layer address corresponding to a particular IP network-layer address. After receiving a MAC-layer address, IP devices create an ARP cache to store the recently acquired IP-to-MAC address mapping, thus avoiding having to broadcast ARPS when they want to recontact a device. If the device does not respond within a specified time frame, the cache entry is flushed. In addition to the Reverse Address Resolution Protocol (RARP) is used to map MAC-layer addresses to IP addresses. RARP, which is the logical inverse of ARP, might be used by diskless workstations that do not know their IP addresses when they boot. RARP relies on the presence of a RARP server with table entries of MAC-layer-to-IP address mappings. Internet Routing Internet routing devices traditionally have been called gateways. In today's terminology, however, the term gateway refers specifically to a device that performs application-layer protocol translation between devices. Interior gateways refer to devices that perform these protocol functions between machines or networks under the same administrative control or authority, such as a corporation's internal network. These are known as autonomous systems. Exterior gateways perform protocol functions between independent networks. Routers within the Internet are organized hierarchically. Routers used for information exchange within autonomous systems are called interior routers, which use a variety of Interior Gateway Protocols (IGPs) to accomplish this purpose. The Routing Information Protocol (RIP) is an example of an IGP. Routers that move information between autonomous systems are called exterior routers. These routers use an exterior gateway protocol to exchange information between autonomous systems. The Border Gateway Protocol (BGP) is an example of an exterior gateway protocol. IP Routing IP routing protocols are dynamic. Dynamic routing calls for routes to be calculated automatically at regular intervals by software in routing devices. This contrasts with static routing, where routers are established by the network administrator and do not change until the network administrator changes them.

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An IP routing table, which consists of destination address/next hop pairs, is used to enable dynamic routing. An entry in this table, for example, would be interpreted as follows: to get to network 172.31.0.0, send the packet out Ethernet interface 0 (E0). IP routing specifies that IP datagram’s travel through internetworks one hop at a time. The entire route is not known at the onset of the journey, however. Instead, at each stop, the next destination is calculated by matching the destination address within the datagram with an entry in the current node's routing table. Each node's involvement in the routing process is limited to forwarding packets based on internal information. The nodes do not monitor whether the packets get to their final destination, nor does IP provide for error reporting back to the source when routing anomalies occur. This task is left to another Internet protocol, the Internet Control-Message Protocol (ICMP), which is discussed in the following section.

·

The Domain Name System (DNS)

The initial solution for name resolution on the Internet was a file named Hosts.txt that was used on the now obsolete Advanced Research Projects Agency network (ARPANET), the predecessor of the modern day Internet. When the number of hosts on the ARPANET was small, the Hosts.txt file was easy to manage because it consisted of unstructured names and their corresponding IPv4 addresses. Computers on the ARPANET periodically downloaded Hosts.txt from a central location and used it for local name resolution. As the ARPANET grew into the Internet, the number of hosts began to increase dramatically and the centralized administration and manual distribution of a text file containing the names for computers on the Internet became unwieldy. The replacement for the Hosts.txt file needed to be distributed, to allow for a hierarchical name space, and require minimal administrative overhead. The original design goal for DNS was to replace the existing cumbersome, centrally administered text file with a lightweight, distributed database that would allow for a hierarchical name space, delegation and distribution of administration, extensible data types, virtually unlimited database size, and reasonable performance. DNS defines a namespace and a protocol for name resolution and database replication: 2.

The DNS namespace is based on a hierarchical and logical tree structure.

3.

The DNS protocol defines a set of messages sent over either User Datagram Protocol (UDP) port 53 or Transmission Control Protocol (TCP) port 53. Hosts that originate DNS queries send name resolution queries to servers over UDP first because it is faster. These hosts, known as DNS clients, resort to TCP only if the returned data is truncated. Hosts that store portions of the DNS database, known as DNS servers, use TCP when replicating database information.

Historically, the most popular implementation of the DNS protocol is Berkeley Internet Name Domain (BIND), which was originally developed at the University of California at Berkeley for the 4.3 Berkeley Software Distribution release of the UNIX operating system.

DNS Components

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Requests for Comments (RFCs) 974, 1034, and 1035 define the primary specifications for DNS. From RFC 1034, DNS comprises the following three components:

1. The domain namespace and resource records DNS defines a specification for a structured namespace as an inverted tree in which each node and leaf of the tree names a set of information. Resource records are records in the DNS database that can be used to configure the DNS database server (such as the Start of Authority [SOA] record) or to contain information of different types to process client queries (such as Address [A] records or Mail Exchanger [MX] records). Typical resource records contain resources by name and their IP addresses. Name queries to DNS database servers are attempts to extract information of a certain type from the namespace. The name query requests a name of interest and a specific type of record. For example, a name query would provide a host name and ask for the corresponding IPv4 or IPv6 address. 2. Name servers Name servers store resource records and information about the domain tree structure and attempt to resolve received client queries. DNS database servers, hereafter referred to as name servers or DNS servers, either contain the requested information in their resource records or have pointer records to other name servers that can help resolve the client query. If the name server contains the resource records for a given part of the namespace, the server is said to be authoritative for that part of the namespace. Authoritative information is organized into units called zones. 3. Resolvers Resolvers are programs that run on DNS clients and DNS servers and that create queries to extract information from name servers. A DNS client uses a resolver to create a DNS name query. A DNS server uses a resolver to contact other DNS servers to resolve a name on a DNS client's behalf. Resolvers are usually built into utility programs or are accessible through library functions, such as the Windows Sockets gethostbyname () or getaddrinfo () functions. DNS Names DNS names have a very specific structure, which identifies the location of the name in the DNS namespace. A fully qualified domain name (FQDN) is a DNS domain name that has been constructed from its location relative to the root of the namespace (known as the root domain). FQDNs have the following attributes: ·

FQDNs consist of the series of names from the name of the host or computer to the root domain.

·

A period character separates each name.

·

Each FQDN ends with the period character, which indicates the root domain.

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·

Each name within the FQDN can be no more than 63 characters long.

·

The entire FQDN can be no more than 255 characters long.

·

FQDNs are not case-sensitive.

·

RFC 1034 requires the names that make up a FQDN to use only the characters a-z, A-Z, 0-9, and the dash or minus sign (-). RFC 2181 allows additional characters and is supported by the DNS Server service in Microsoft® Windows Server™ 2003 operating systems.

Domains and Subdomains The DNS namespace is in the form of a logical inverted tree structure. Each branch point (or node) in the tree is given a name that is no more than 63 characters long. Each node of the tree is a portion of the namespace called a domain. A domain is a branch of the tree and can occur at any point in the tree structure. Domains can be further partitioned at node points within the domain into subdomains for the purposes of administration or load balancing. The domain name identifies the domain's position in the DNS hierarchy. The FQDN identifies the domain relative to the root. You create domain names and FQDNs by combining the names of the nodes from the designated domain node back to the root and separating each node with a period (.). The root of the tree has the special reserved name of "" (null), which you indicate by placing a final period at the end of the domain name (such as www.sales.example.com.). Domains and subdomains are grouped into zones to allow for distributed administration of the DNS namespace. Illustration: 23 Shows the DNS namespace as it exists for the Internet.

Shows a few of the top-level domains and example hosts in the "microsoft.com." domain. A trailing period designates a domain name of a host relative to the root domain. To connect to that host, a user would specify the name "www.microsoft.com." If the user does not specify the final period, the DNS resolver automatically adds it to the specified name. Individual organizations manage second-level domains (subdomains of the top level domains) and their name servers. For example, Microsoft manages the "microsoft.com." domain.

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DNS Servers and the Internet Domains define different levels of authority in a hierarchical structure. The top of the hierarchy is called the root domain. The DNS namespace on the Internet ·

Root domain

·

Top-level domains

·

Second-level domains

The root domain uses a null label, which you write as a single period (.). In the United States, the Internet Assigned Names Authority (IANA) manages several root domain name servers. The next level in the hierarchy is divided into a series of nodes called the top-level domains. The top-level domains are assigned by organization type and by country/region. Some of the more common top-level domains are the following: · · · · · · · · ·

com – Commercial organizations in the United States (for example, microsoft.com for the Microsoft Corporation). edu – Educational organizations in the United States. gov – United States governmental organizations. int – International organizations. mil – United States military organizations. net - Networking organizations. org – Noncommercial organizations. xx – Two-letter country code names that follow the International Standard 3166. For example, “.fr” is the country code for France. arpa – Used to store information for DNS reverse queries.

Each top-level domain has name servers that IANA administers. Top-level domains can contain second-level domains and hosts. Second-level domains contain the domains and names for organizations and countries/regions. The names in second-level domains are administered by the organization or country/region either directly (by placing its own DNS server on the Internet) or by using an Internet service provider (ISP) who manages the names for an organization or country/region on its customer's behalf. Zones A zone is a contiguous portion of a domain of the DNS namespace whose database records exist and are managed in a particular DNS database file stored on one or multiple DNS servers. You can configure a single DNS server to manage one or multiple zones. Each zone is anchored at a specific domain node, referred to as the zone's root domain. Zone files do not necessarily contain the complete branch (that is, all subdomains) under the zone's root domain. For example, you can partition a domain into several subdomains, which are controlled by separate DNS servers. You might break up domains across multiple zone files if you want to distribute management of the domain across different groups or make data replication more efficient. Illustration: 24 Shows the difference between domains and zones.

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In the example, "microsoft.com" is a domain (the entire branch of the DNS namespace that starts with the microsoft.com. node), but the entire domain is not controlled by one zone file. Part of the domain is in a zone for "microsoft.com." and part of the domain is in a zone for the "dev.microsoft.com." domain. These zones correspond to different DNS database files that can reside on the same or different DNS servers.

Name Resolution The two types of queries that a DNS resolver (either a DNS client or another DNS server) can make to a DNS server are the following: ·

Recursive queries In a recursive query, the queried name server is requested to respond with the requested data or with an error stating that data of the requested type or the specified domain name does not exist. The name server cannot just refer the DNS resolver to a different name server. A DNS client typically sends this type of query.

·

Iterative queries

In an iterative query, the queried name server can return the best answer it currently has back to the DNS resolver. The best answer might be the resolved name or a referral to another name server that is closer to fulfilling the DNS client's original request. DNS servers typically send iterative queries to query other DNS servers. DNS Name Resolution Example To show how recursive and iterative queries are used for common DNS name resolutions, consider a computer running a Microsoft Windows® XP operating system or Windows Server 2003 connected to the Internet. A user types http://www.example.com in the Address

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field of their Internet browser. When the user presses the ENTER key, the browser makes a Windows Sockets function call, either gethostbyname () or getaddrinfo(), to resolve the name http://www.example.com to an IP address. For the DNS portion of the Windows host name resolution process, the following occurs: ·

The DNS resolver on the DNS client sends a recursive query to its configured DNS server, requesting the IP address corresponding to the name "www.example.com". The DNS server for that client is responsible for resolving the name and cannot refer the DNS client to another DNS server. The DNS server that received the initial recursive query checks its zones and finds no zones corresponding to the requested domain name; the DNS server is not authoritative for the example.com domain. Because the DNS server has no information about the IP addresses of DNS servers that are authoritative for example.com. or com., it sends an iterative query for www.example.com. to a root name server.

·

The DNS server that received the initial recursive query checks its zones and finds no zones corresponding to the requested domain name; the DNS server is not authoritative for the example.com domain. Because the DNS server has no information about the IP addresses of DNS servers that are authoritative for example.com. or com., it sends an iterative query for www.example.com. to a root name server.

3. The root name server is authoritative for the root domain and has information about name servers that are authoritative for top-level domain names. It is not authoritative for the example.com. Domain. Therefore, the root name server replies with the IP address of a name server for the com. top-level domain. 4. The DNS server of the DNS client sends an iterative query for www.example.com. to the name server that is authoritative for the com. top-level domain. 5. The com. name server is authoritative for the com. domain and has information about the IP addresses of name servers that are authoritative for second-level domain names of the com. domain. It is not authoritative for the example.com. domain. Therefore, the com. name server replies with the IP address of the name server that is authoritative for the example.com. domain. 6. The DNS server of the DNS client sends an iterative query for www.example.com. to the name server that is authoritative for the example.com. domain. 7. The example.com. name server replies with the IP address corresponding to the FQDN www.example.com. 8. The DNS server of the DNS client sends the IP address of www.example.com to the DNS client. Illustration: 25 Example of recursive and iterative queries in DNS name resolution

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All DNS queries are DNS Name Query Request messages. All DNS replies are DNS Name Query Response messages. In practice, DNS servers cache the results of queries on an ongoing basis. If a DNS server finds an entry matching the current request in its cache, it does not send an iterative DNS query. This example assumes that no cache entries were in any of the DNS servers to prevent the sending of the iterative name queries. Forward lookups are queries in which a DNS client attempts to resolve an FQDN to its corresponding IP address. Zones that contain FQDN-to-IP address mappings are known as forward lookup zones. Reverse Queries In a reverse query, instead of supplying a name and asking for an IP address, the DNS client provides the IP address and requests the corresponding host name. Reverse queries are also known as reverse lookups, and zones that contain IP address-to-FQDN mappings are known as reverse lookup zones. Because you cannot derive the IP address from a domain name in the DNS namespace, only a thorough search of all domains could guarantee a correct answer. To prevent an exhaustive search of all domains for a reverse query, reverse name domains and pointer (PTR) resource records were created. An example of an application that uses reverse queries is the Tracert tool, which by default uses reverse queries to display the names of the routers in a routing path. If you are going to use reverse queries, you must create reverse lookup zones and PTR records when you administer a DNS server so that reverse queries can be satisfied. Reverse Queries for IPv4 Addresses

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To support reverse lookups for IPv4 addresses, a special domain named in-addr.arpa. was created. Nodes in the in-addr.arpa domain are named after the numbers in the dotted decimal representation of IPv4 addresses. But because IPv4 addresses get more specific from left to right and domain names get more specific from right to left, the order of IPv4 address octets must be reversed when building the in-addr.arpa domain name corresponding to the IPv4 address. For example, for the generalized IPv4 address w.x.y.z, the corresponding reverse query name is z.y.x.w.in-addr.arpa. IANA delegates responsibility for administering the reverse query namespace below the in-addr.arpa domain to organizations as they are assigned IPv4 address prefixes. Illustration: 26 Shows an example of the reverse lookup portion of the DNS namespace.

Within the in-addr.arpa domain, special pointer (PTR) resource records are added to associate the IPv4 addresses to their corresponding host names. To find a host name for the IPv4 address 157.54.200.2, a DNS client sends a DNS query for a PTR record for the name 2.200.54.157.in-addr.arpa. Reverse queries use the same name resolution process previously described for forward lookups (a combination of recursive and iterative queries). The DNS server finds the PTR record that contains the FQDN that corresponds to the IPv4 address 157.54.200.2 and sends that FQDN back to the DNS client.

Reverse Queries for IPv6 Addresses IPv6 reverse lookups use the ip6.arpa. domain. To create the domains for reverse queries, each hexadecimal digit in the fully expressed 32-digit IPv6 address becomes a separate level in the reverse domain hierarchy in inverse order. For example, the reverse lookup domain name for the address 3ffe:ffff::1:2aa:ff:fe3f:2a1c (fully expressed as 3ffe:ffff:0000:0001:02aa:00ff:fe3f:2a1c) is c.1.a.2.f.3.e.f.f.f.0.0.a.a.2.0.1.0.0.0.0.0.0.0.f.f.f.f.e.f.f.3.ip6.arpa.Just as in IPv4 addresses, PTR records in the reverse IPv6 domain map IPv6 addresses to FQDNs.

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Caching and TTL For each resolved query (either recursive or iterative), the DNS resolver caches the returned information for a time that is specified in each resource record in the DNS response. This is known as positive caching. The amount of time in seconds to cache the record data is referred to as the Time To Live (TTL). The network administrator of the zone that contains the record decides on the default TTL for the data in the zone. Smaller TTL values help ensure that data about the domain is more consistent across the network if the zone data changes often. However, this practice also increases the load on name servers because positive cache entries time out more quickly. After a DNS resolver caches data, it must start counting down from the received TTL so that it will know when to remove the data from its cache. For queries that can be satisfied by this cached data, the TTL that is returned is the current amount of time left before the data is flushed from the DNS cache. DNS client resolvers also have data caches and honor the TTL value so that they know when to remove the data.The DNS Client service in Windows XP and Windows Server 2003 and the DNS Server service in Windows Server 2003 support positive caching. Negative Caching As originally defined in RFC 1034, negative caching is the caching of failed name resolutions. A failed name resolution occurs when a DNS server returns a DNS Name Query Response message with an indication that the name was not found. Negative caching can reduce response times for names that DNS cannot resolve for both the DNS client and DNS servers during an iterative query process. Like positive caching, negative cache entries eventually time out and are removed from the cache based on the TTL in the received DNS Name Query Response message. The DNS Client service in Windows XP and Windows Server 2003 and the DNS Server service in Windows Server 2003 support negative caching. Round Robin Load Balancing DNS Name Query Response messages can contain multiple resource records. For example, for a simple forward lookup, the DNS Name Query Response message can contain multiple Address (A) records that contain the IPv4 addresses associated with the desired host. When multiple resource records for the same resource record type exist, the following issues arise:

· ·

For the DNS server, how to order the resource records in the DNS Name Query Response message For the DNS client, how to choose a specific resource record in the DNS Name Query Response message

To address these issues, RFC 1794 describes a mechanism named round robin or load sharing to share and distribute loads for network resources. The central assumption of RFC 1794 is that when multiple resource records for the same resource record type and the same name exist, multiple servers are offering the same type of service to multiple users. For example, the www.microsoft.com Web site is actually hosted by multiple Web servers with different IPv4 addresses. To attempt to distribute the load of servicing all the users who access www.microsoft.com, the DNS servers that are authoritative for microsoft.com modify the order of the resource records for the www.microsoft.com name in successive DNS Name

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Query Response messages. The DNS client uses the data in the first resource record in the response. For example, if there were three A records for www.microsoft.com with the IPv4 addresses of 131.107.0.99, 131.107.0.100, and 131.107.0.101, the round robin scheme works as follows: 1.

For the first request, the order of the resource records in the DNS Name Query Response message is 131.107.0.99-131.107.0.100-131.107.0.101. For the second request, the order of the resource records in the DNS Name Query Response message is 131.107.0.100-131.107.0.101-131.107.0.99. For the third request, the order of the resource records in the DNS Name Query Response message is 131.107.0.101-131.107.0.99-131.107.0.100.

2. 3.

The pattern repeats for subsequent queries. For an arbitrary number of resource records, the rotation process cycles through the list of resource records. A DNS server running Windows Server 2003 that is responding to a recursive query by default attempts to order the resource records according to the addresses that most closely match the IP address of the originating DNS client, and you can configure that server for round robin according to RFC 1794. To determine the addresses that are the closest match to the IPv4 address of the DNS client, the DNS Server service in Windows Server 2003 orders the addresses by using a high-order bit-level comparison of the DNS client's IPv4 address and the IPv4 addresses associated with the queried host name. This comparison technique is similar to the route determination process, in which IPv4 or IPv6 examines the IPv4 or IPv6 routing table to determine the route that most closely matches the destination address of a packet being sent or forwarded. Name Server Roles DNS servers store information about portions of the domain namespace. When name servers have one or more zones for which they are responsible, they are said to be authoritative servers for those zones. Using the example in Figure 8-2, the name server containing the dev.microsoft.com zone is an authoritative server for dev.microsoft.com. Configuration of a DNS server includes adding name server (NS) resource records for all the other name servers that are in the same domain. Using the example on the previous page, if the two zones were on different name servers, each would be configured with an NS record about the other. These NS records provide pointers to the other authoritative servers for the domain.

DNS defines two types of name servers, each with different functions: ·

Primary

A primary name server gets the data for its zones from locally stored and maintained files. To change a zone, such as adding subdomains or resource records, you change the zone file at the primary name server. ·

Secondary

A secondary name server gets the data for its zones across the network from another name server (either a primary name server or another secondary name server). The process of

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obtaining this zone information (that is, the database file) across the network is referred to as a zone transfer. Zone transfers occur over TCP port 53. The following are reasons to have secondary name servers within an enterprise network: ·

Redundancy: At least two DNS servers, a primary and at least one secondary, serving each zone are needed for fault tolerance.

·

Remote locations: Secondary name servers (or other primary servers for subdomains) are needed in remote locations that have a large number of DNS clients. Clients should not have to communicate across slower wide area network (WAN) links for DNS queries.

·

Load distribution: Secondary name servers reduce the load on the primary name server.

Because information for each zone is stored in separate files, the primary or secondary name server designation is defined at a zone level. In other words, a specific name server may be a primary name server for certain zones and a secondary name server for other zones. When defining a zone on a secondary name server, you configure the zone with the name server from which the zone information is to be obtained. The source of the zone information for a secondary name server is referred to as a master name server. A master name server can be either a primary or secondary name server for the requested zone.

Illustration:27 Shows the relationship between primary, secondary, and master name servers.

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When a secondary name server starts up, it contacts the master name server and initiates a zone transfer for each zone for which it is acting as a secondary name server. Zone transfers also can occur periodically (provided that data on the master name server has changed) as specified in the SOA record of the zone file. The "Resource Records and Zones" section of this chapter describes the SOA resource record. Forwarders When a DNS server receives a query, it attempts to locate the requested information within its own zone files. If this attempt fails because the server is not authoritative for the domain of the requested name and it does not have the record cached from a previous lookup, it must communicate with other name servers to resolve the request. On a globally connected network such as the Internet, DNS queries for names that do not use the second-level domain name of the organization might require interaction with DNS servers across WAN links outside of the organization. To prevent all the DNS servers in the organization from sending their queries over the Internet, you can configure forwarders. A forwarder sends queries across the Internet. Other DNS servers in the organization are configured to forward their queries to the forwarder.

Illustration: 28 Shows an example of intranet servers using a forwarder to resolve Internet names.

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A name server can use a forwarder in non-exclusive or exclusive mode. Forwarders in Non-exclusive Mode In non-exclusive mode, when a name server receives a DNS query that it cannot resolve through its own zone files, it sends a recursive query to its forwarder. The forwarder attempts to resolve the query and returns the results to the requesting name server. If the forwarder is unable to resolve the query, the name server that received the original query attempts to resolve the query using iterative queries. A name server using a forwarder in non-exclusive mode does the following when attempting to resolve a name: 1. 2. 3. 4.

Checks its local cache. Checks its zone files. Sends a recursive query to a forwarder. Attempts to resolve the name through iterative queries to other DNS servers.

Forwarders in Exclusive Mode In exclusive mode, name servers rely on the name-resolving ability of the forwarders. When a name server in exclusive mode receives a DNS query that it cannot resolve through its own zone files, it sends a recursive query to its designated forwarder. The forwarder then carries out whatever communication is necessary to resolve the query and returns the results to the originating name server. If the forwarder is unable to resolve the request, the originating name server returns a query failure to the original DNS client. Name servers in exclusive

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mode make no attempt to resolve the query on their own if the forwarder is unable to satisfy the request. A name server using a forwarder in exclusive mode does the following when attempting to resolve a name: 1. Checks its local cache. 2. Checks its zone files. 3. Sends a recursive query to a forwarder. Caching-Only Name Servers Although all DNS servers cache queries that they have resolved, caching-only servers are DNS servers that only perform queries, cache the answers, and return the results. Caching-only servers are not authoritative for any domains and contain only the information that they have cached while attempting to resolve queries. When caching-only servers are started, they do not perform any zone transfers because they have no zones and no entries exist in their caches. Initially, the caching-only server must forward queries until the cache has been built up to a point where it can service commonly used queries by just using its cache entries. Resource Records and Zones If your organization is connected to the Internet, in many cases you do not need to maintain a DNS infrastructure. For small networks, DNS name resolution is simpler and more efficient by having the DNS client query a DNS server that is maintained by an ISP. Most ISPs will maintain domain information for a fee. If your organization wants to have control over its domain or not incur the costs of using an ISP, you can set up your organization's own DNS servers. In both cases, either going through an ISP or setting up separate DNS servers, the IANA must be informed of the domain name of the organization and the IP addresses of at least two DNS servers on the Internet that service the domain. An organization can also set up DNS servers within itself independent of the Internet. At least two computers as DNS servers are recommended for reliability and redundancy—a primary and a secondary name server. The primary name server maintains the database of information, which is then replicated from the primary name server to the secondary name server. This replication allows name queries to be serviced even if one of the name servers is unavailable. Replication is scheduled based on how often names change in the domain. Replication should be frequent enough so that changes are reflected on both servers. However, excessive replication can have a negative impact on the performance of the network and name servers. Resource Record Format Resource records have the following format: owner ·

TTL

type

class

RDATA

owner The domain name of the resource record.

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·

TTL (Time to Live) The length of time in seconds that a DNS resolver should wait before it removes from its cache an entry that corresponds to the resource record.

·

type The type of resource record.

·

class The protocol family in use, which is typically IN for the Internet class.

·

RDATA The resource data for the resource record type. For example, for an address (A) resource record, RDATA is the 32-bit IPv4 address that corresponds to the FQDN in the owner field.

Resource records are represented in binary form in DNS request and response messages. In text-based DNS database files, most resource records are represented as a single line of text. For readability, blank lines and comments are often inserted in the database files and are ignored by the DNS server. Comments always start with a semicolon (;) and end with a carriage return. The following is an example A resource record stored in a DNS database file: srv1.dev.microsoft.com.

3600

A

IN

157.60.221.205

Each resource record starts with the owner in the first column (srv1.dev.microsoft.com.). If the first column is blank, then it is assumed that the owner for this record is the owner of the previous record. The owner is followed by the TTL (3600 seconds = 1 hour), type (A = Address record), class (IN = Internet), and then the RDATA (Resource Data = 157.60.221.205). If the TTL value is not present, the DNS server sets the value to the TTL specified in the SOA (Start of Authority) record of the zone. Resource Record Types The DNS standards define many types of resource records. The most commonly used resource records are the following: ·

SOA Identifies the start of a zone of authority. Every zone contains an SOA resource record at the beginning of the zone file, which stores information about the zone, configures replication behavior, and sets the default TTL for names in the zone.

·

A Maps an FQDN to an IPv4 address.

·

AAAA Maps an FQDN to an IPv6 address.

·

NS Indicates the servers that are authoritative for a zone. NS records indicate primary and secondary servers for the zone specified in the SOA resource record, and they indicate the servers for any delegated zones. Every zone must contain at least one NS record at the zone root.

·

PTR Maps an IP address to an FQDN for reverse lookups.

·

CNAME Specifies an alias (synonymous name).

·

MX Specifies a mail exchange server for a DNS domain name. A mail exchange server is a host that receives mail for the DNS domain name.

·

SRV Specifies the IP addresses of servers for a specific service, protocol, and DNS domain.

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RFCs 1035, 1034, 1183, and others define less frequently used resource records. The DNS Server service in Windows Server 2003 is fully compliant with RFCs 1034, 1035, and 1183. The DNS Server service in Windows Server 2003 also supports the following resource record types that are Microsoft-specific: ·

WINS Indicates the IPv4 address of a Windows Internet Name Service (WINS) server for WINS forward lookup. The DNS Server service in Windows Server 2003 can use a WINS server for looking up the host portion of a DNS name.

·

WINS-R Indicates the use of WINS reverse lookup, in which a DNS server uses a NetBIOS Adapter Status message to find the host portion of the DNS name given its IPv4 address.

ATMA Maps DNS domain names to Asynchronous Transfer Mode (ATM) addresses. For detailed information about the structure and contents of various types of DNS resource records, see the topic titled "Resource records reference" in Help and Support for Windows Server 2003. Delegation and Glue Records You add delegation and glue records to a zone file to indicate the delegation of a subdomain to a separate zone. For example, in Figure 8-2, the DNS server that is authoritative for the microsoft.com zone must be configured so that, when resolving names for the dev.microsoft.com, the DNS server can determine the following: ·

That a separate zone for that domain exists. A delegation is an NS record in the parent zone that lists the name server that is authoritative for the delegated zone.

·

Where the zone for that domain resides.

A glue record is an A record for the name server that is authoritative for the delegated zone. The name server for the microsoft.com. Domain has delegated authority for the dev.microsoft.com zone to the name server devdns.dev.microsoft.com at the IPv4 address of 157.60.41.59. In the zone file for the microsoft.com. Zone, the following records must be added: dev.microsoft.com. IN NS devdns.dev.microsoft.com. devdns.dev.microsoft.com. IN A 157.60.41.59 Without the delegation record for dev.microsoft.com, queries for all names ending in dev.microsoft.com would fail. Glue records are needed when the name of the name server that is authoritative for the delegated zone is in the domain of the name server attempting name resolution. In the example above, we need the A record for devdns.dev.microsoft.com. Because that FQDN is within the microsoft.com. Portion of the DNS namespace. Without this A record, the microsoft.com. DNS server would be unable to locate the name server for the dev.microsoft.com. Zone, and all name resolutions for names in the dev.microsoft.com domain would fail. A glue record is not needed when the name of the authoritative name server for the delegated zone is in a domain that is different than the domain of the zone file. In this case, the DNS server would use normal iterative queries to resolve the name to an IP

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address. The DNS Server service in Windows Server 2003 automatically adds delegation and glue records when you delegate a subdomain. The Root Hints File The root hints file, also known as the cache file, contains the names and addresses of root name servers. For resolving domain names on the Internet, the default file provided with the DNS Server service in Windows Server 2003 has the records for the root servers of the Internet. For installations not connected to the Internet, the file should be replaced to contain the name servers authoritative for the root of the private network. This file is named Cached and is stored in the systemroot/System32/Dns folder. Zone Transfers Secondary name servers obtain zone files from a master name server using a zone transfer. The zone transfer replicates the set of records in the zone file from the master server to the secondary server. Zone transfers occur for all zones for which a DNS server is a secondary name server upon startup and on an ongoing basis to ensure that the most current information about the zone is reflected in the local zone file. The two types of zone transfers are full and incremental. Full Zone Transfer The original DNS RFCs defined zone transfers as a transfer of the entire zone file, regardless of how the file has changed since the last time it was transferred. In a full zone transfer, the following process occurs: · The secondary server waits until the next refresh time (as specified in the SOA resource record) and then queries the master server for the SOA resource record for the zone. 2. The master server responds with the SOA resource record. 3. The secondary server checks the Serial Number field of the returned SOA resource record. If the serial number in the SOA resource record is higher than the serial number of the SOA resource record of the locally stored zone file, then there have been changes to the zone file on the master server and a zone transfer is needed. Whenever a resource record is changed on the master name server, the serial number in the SOA resource record is updated. The secondary server sends an AXFR request (a request for a full zone transfer) to the master server. 4. The secondary server initiates a TCP connection with the master server and requests all of the records in the zone database. After the zone transfer, the Serial Number field in the SOA record of the local zone file matches the Serial Number field in the SOA record of the master server.

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Illustration: 29 Full zone transfer

If the secondary server does not receive a response to the SOA query, it retries SOA queries using a retry time interval specified in the SOA resource record in the local zone file. The secondary server continues to retry until the time elapsed since attempting to perform a zone transfer reaches an expiration time specified in the SOA resource record in the local zone file. After the expiration time, the secondary server closes the zone file and does not use it to answer subsequent queries. The secondary server keeps attempting to perform the zone transfer. When the zone transfer succeeds, the local zone file is opened and used for subsequent queries. Incremental Zone Transfer In a full zone transfer, the entire zone file is transferred. This can consume a substantial portion of processing resources and network bandwidth when the zone files are large and when zone records are frequently changed. To minimize the amount of information that is sent in a zone transfer for changes to zone records, RFC 1995 specifies a standard method of performing incremental zone transfers. In an incremental zone transfer, only the resource records that have changed (been added, deleted, or modified) are sent during the zone transfer. In an incremental zone transfer, the secondary server performs the same query for the SOA record of the master server and comparison of the Serial Number field. If changes exist, the secondary server sends an IXFR request (a request for an incremental zone transfer) to the master server. The master server sends the records that have changed, and the secondary server builds a new zone file from the records that have not changed and the records in the incremental zone transfer. Illustration: 30 An incremental zone transfer

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For the master server to determine the records that have changed, it must maintain a history database of changes made to its zone files. The zone file changes are linked to a serial number so that the master server can determine which changes were made to the zone past the serial number indicated in the IXFR request from the secondary server. The DNS Server service in Windows Server 2003 supports incremental zone transfer. DNS Notify For both full and incremental zone transfers, the secondary server always initiates the zone transfer based on periodically querying the master server for its SOA record. The original DNS RFCs do not define a notification mechanism if the master server wanted to immediately propagate a large number of changes to its secondary servers. To improve the consistency of data among secondary servers, RFC 1996 specifies DNS Notify, an extension of DNS that allows master servers to send notifications to secondary servers that a zone transfer might be needed. Upon receipt of a DNS notification, secondary servers request the SOA record of their master server and initiate a full or incremental zone transfer as needed.

Illustration: 31 Shows the DNS notify process.

To determine the secondary servers to which notifications should be sent, the master server maintains a notify list (a list of IP addresses) for each zone. The master server sends notifications to only the servers in the notify list when the zone is updated.The DNS Server service in Windows Server 2003 supports the configuration of a notify list (a list of IPv4 addresses) for each zone. DNS Dynamic Update

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DNS was originally defined as a name resolution scheme for relatively static names and addresses; DNS records contained information about servers, whose name and address configuration did not change often. Therefore, the manual administration of resource records in zone files was manageable. These original assumptions work well for an environment that is based on server and client computers that are statically configured, in which the client computers communicate only with the server computers and address configuration does not change. With the advent of peer-to-peer communications and applications and the Dynamic Host Configuration Protocol (DHCP), both of the assumptions of static DNS are challenged. In a Windows-based environment, client computers often communicate directly with each other and are automatically configured using DHCP. To communicate with each other, client computers must be able to resolve each other's names; therefore they must have corresponding DNS resource records. With DHCP, the address configuration of client computers could change every time they start. Manually administering DNS records for this environment is obviously impractical. Therefore, RFC 2136 defines DNS dynamic update to provide an automated method to populate the DNS namespace with the current names and addresses for client and server computers by dynamically updating zone data on a zone's primary server. With DNS dynamic update, DNS records are automatically created, modified, and removed by either host computers or DHCP servers on their behalf. For example, a client computer that supports DNS dynamic update sends UPDATE messages to its DNS server to automatically add A, AAAA, and PTR records. The DNS server, which must also support DNS dynamic update, verifies that the sender is permitted to make the updates and then updates its local zone files. The DNS Client service in Windows XP and Windows Server 2003 and the DNS Server service in Windows Server 2003 support DNS dynamic update. ·

What is the Internet

The Internet was the result of some visionary thinking by people in the early 1960s who saw great potential value in allowing computers to share information on research and development in scientific and military fields. J.C.R. Licklider of MIT, first proposed a global network of computers in 1962, and moved over to the Defense Advanced Research Projects Agency (DARPA) in late 1962 to head the work to develop it. Leonard Kleinrock of MIT and later UCLA developed the theory of packet switching, which was to form the basis of Internet connections. Lawrence Roberts of MIT connected a Massachusetts computer with a California computer in 1965 over dial-up telephone lines. It showed the feasibility of wide area networking, but also showed that the telephone line's circuit switching was inadequate. Kleinrock's packet switching theory was confirmed. Roberts moved over to DARPA in 1966 and developed his plan for ARPANET. These visionaries and many more left unnamed here are the real founders of the Internet. When Senator Ted Kennedy heard in 1968 that the pioneering Massachusetts Company BBN had won the ARPA contract for an "interface message processor (IMP)," he sent a congratulatory telegram to BBN for their ecumenical spirit in winning the "interfaith message processor" contract. The Internet, then known as ARPANET, was brought online in 1969 under a contract let by the renamed Advanced Research Projects Agency (ARPA) which initially connected four major computers at universities in the southwestern US (UCLA, Stanford Research Institute, UCSB, and the University of Utah). The contract was carried out by BBN of Cambridge, MA under Bob Kahn and went online in December 1969. By June 1970, MIT, Harvard, BBN, and Systems Development Corp (SDC) in Santa Monica, Cal. were added. By January 1971,

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Stanford, MIT's Lincoln Labs, Carnegie-Mellon, and Case-Western Reserve U were added. In months to come, NASA/Ames, Mitre, Burroughs, RAND, and the U of Illinois plugged in. After that, there were far too many to keep listing here. Who was the first to use the Internet? Charley Kline at UCLA sent the first packets on ARPANet as he tried to connect to Stanford Research Institute on Oct 29, 1969. The system crashed as he reached the G in LOGIN! The Internet was designed in part to provide a communications network that would work even if some of the sites were destroyed by nuclear attack. If the most direct route was not available, routers would direct traffic around the network via alternate routes. The early Internet was used by computer experts, engineers, scientists, and librarians. There was nothing friendly about it. There were no home or office personal computers in those days, and anyone who used it, whether a computer professional or an engineer or scientist or librarian, had to learn to use a very complex system. Did Al Gore invent the Internet? According to a CNN transcript of an interview with Wolf Blitzer, Al Gore said, "During my service in the United States Congress, I took the initiative in creating the Internet." Al Gore was not yet in Congress in 1969 when ARPANET started or in 1974 when the term Internet first came into use. Gore was elected to Congress in 1976. In fairness, Bob Kahn and Vint Cerf acknowledge in a paper titled Al Gore and the Internet that Gore has probably done more than any other elected official to support the growth and development of the Internet from the 1970's to the present. E-mail was adapted for ARPANET by Ray Tomlinson of BBN in 1972. He picked the @ symbol from the available symbols on his teletype to link the username and address. The telnet protocol, enabling logging on to a remote computer, was published as a Request for Comments (RFC) in 1972. RFC's are a means of sharing developmental work throughout community. The ftp protocol, enabling file transfers between Internet sites, was published as an RFC in 1973, and from then on RFC's were available electronically to anyone who had use of the ftp protocol. Libraries began automating and networking their catalogs in the late 1960s independent from ARPA. The visionary Frederick G. Kilgour of the Ohio College Library Center (now OCLC, Inc.) led networking of Ohio libraries during the '60s and '70s. In the mid 1970s more regional consortia from New England, the Southwest states, and the Middle Atlantic states, etc., joined with Ohio to form a national, later international, network. Automated catalogs, not very user-friendly at first, became available to the world, first through telnet or the awkward IBM variant TN3270 and only many years later, through the web. Ethernet, a protocol for many local networks, appeared in 1974, an outgrowth of Harvard student Bob Metcalfe's dissertation on "Packet Networks." The dissertation was initially rejected by the University for not being analytical enough. It later won acceptance when he added some more equations to it. The Internet matured in the 70's as a result of the TCP/IP architecture first proposed by Bob Kahn at BBN and further developed by Kahn and Vint Cerf at Stanford and others throughout the 70's. It was adopted by the Defense Department in 1980 replacing the earlier Network Control Protocol (NCP) and universally adopted by 1983. The Unix to Unix Copy Protocol (UUCP) was invented in 1978 at Bell Labs. Usenet was started in 1979 based on UUCP. Newsgroups, which are discussion groups focusing on a topic, followed, providing a means of exchanging information throughout the world. While Usenet is not considered as part of the Internet, since it does not share the use of TCP/IP, it linked UNIX systems around the world, and many Internet sites took advantage of the availability of newsgroups. It was a significant part of the community building that took place on the networks. Similarly, BITNET (Because It's Time Network) connected IBM mainframes around

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the educational community and the world to provide mail services beginning in 1981. Listserv software was developed for this network and later others. Gateways were developed to connect BITNET with the Internet and allowed exchange of e-mail, particularly for e-mail discussion lists. These listservs and other forms of e-mail discussion lists formed another major element in the community building that was taking place. In 1986, the National Science Foundation funded NSFNet as a cross country 56 Kbps backbone for the Internet. They maintained their sponsorship for nearly a decade, setting rules for its non-commercial government and research uses. As the commands for e-mail, FTP, and telnet were standardized, it became a lot easier for non-technical people to learn to use the nets. It was not easy by today's standards by any means, but it did open up use of the Internet to many more people in universities in particular. Other departments besides the libraries, computer, physics, and engineering departments found ways to make good use of the nets--to communicate with colleagues around the world and to share files and resources. While the number of sites on the Internet was small, it was fairly easy to keep track of the resources of interest that were available. But as more and more universities and organizations--and their libraries-- connected, the Internet became harder and harder to track. There was more and more need for tools to index the resources that were available. The first effort, other than library catalogs, to index the Internet was created in 1989, as Peter Deutsch and his crew at McGill University in Montreal, created an archiver for ftp sites, which they named Archie. This software would periodically reach out to all known openly available ftp sites, list their files, and build a searchable index of the software. The commands to search Archie were UNIX commands, and it took some knowledge of unix to use it to its full capability. McGill University, which hosted the first Archie, found out one day that half the Internet traffic going into Canada from the United States was accessing Archie. Administrators were concerned that the University was subsidizing such a volume of traffic, and closed down Archie to outside access. Fortunately, by that time, there were many more Archies available.At about the same time, Brewster Kahle, then at Thinking Machines, Corp. developed his Wide Area Information Server (WAIS), which would index the full text of files in a database and allow searches of the files. There were several versions with varying degrees of complexity and capability developed, but the simplest of these were made available to everyone on the nets. At its peak, Thinking Machines maintained pointers to over 600 databases around the world which had been indexed by WAIS. They included such things as the full set of Usenet Frequently Asked Questions files, the full documentation of working papers such as RFC's by those developing the Internet's standards, and much more. Like Archie, its interface was far from intuitive, and it took some effort to learn to use it well. Peter Scott of the University of Saskatchewan, recognizing the need to bring together information about all the telnet-accessible library catalogs on the web, as well as other telnet resources, brought out his Hytelnet catalog in 1990. It gave a single place to get information about library catalogs and other telnet resources and how to use them. He maintained it for years, and added HyWebCat in 1997 to provide information on web-based catalogs. In 1991, the first really friendly interface to the Internet was developed at the University of Minnesota. The University wanted to develop a simple menu system to access files and information on campus through their local network. A debate followed between mainframe adherents and those who believed in smaller systems with client-server architecture. The mainframe adherents "won" the debate initially, but since the client-server advocates said they could put up a prototype very quickly, they were given the go-ahead to do a demonstration system. The demonstration system was called a gopher after the U of Minnesota mascot--the golden gopher. The gopher proved to be very prolific, and within a few years there were over 10,000 gophers around the world. It takes no knowledge of unix or

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computer architecture to use. In a gopher system, you type or click on a number to select the menu selection you want. Gopher's usability was enhanced much more when the University of Nevada at Reno developed the VERONICA searchable index of gopher menus. It was purported to be an acronym for Very Easy Rodent-Oriented Net wide Index to Computerized Archives. A spider crawled gopher menus around the world, collecting links and retrieving them for the index. It was so popular that it was very hard to connect to, even though a number of other VERONICA sites were developed to ease the load. Similar indexing software was developed for single sites, called JUGHEAD (Jonzy's Universal Gopher Hierarchy Excavation And Display). Peter Deutsch, who developed Archie, always insisted that Archie was short for Archiver, and had nothing to do with the comic strip. He was disgusted when VERONICA and JUGHEAD appeared. In 1989 another significant event took place in making the nets easier to use. Tim Berners-Lee and others at the European Laboratory for Particle Physics, more popularly known as CERN, proposed a new protocol for information distribution. This protocol, which became the World Wide Web in 1991, was based on hypertext--a system of embedding links in text to link to other text, which you have been using every time you selected a text link while reading these pages. Although started before gopher, it was slower to develop. The development in 1993 of the graphical browser Mosaic by Marc Andreessen and his team at the National Center for Supercomputing Applications (NCSA) gave the protocol its big boost. Later, Andreessen moved to become the brains behind Netscape Corp., which produced the most successful graphical type of browser and server until Microsoft declared war and developed its Microsoft Internet Explorer. MICHAEL 1936-2001

DERTOUZOS

The early days of the web was a confused period as many developers tried to put their personal stamp on ways the web should develop. The web was threatened with becoming a mass of unrelated protocols that would require different software for different applications. The visionary Michael Dertouzos of MIT's Laboratory for Computer Sciences persuaded Tim Berners-Lee and others to form the World Wide Web Consortium in 1994 to promote and develop standards for the Web. Proprietary plug-ins still abounds for the web, but the Consortium has ensured that there are common standards present in every browser. Since the Internet was initially funded by the government, it was originally limited to research, education, and government uses. Commercial uses were prohibited unless they directly served the goals of research and education. This policy continued until the early 90's, when independent commercial networks began to grow. It then became possible to route traffic across the country from one commercial site to another without passing through the government funded NSFNet Internet backbone. Delphi was the first national commercial online service to offer Internet access to its subscribers. It opened up an email connection in July 1992 and full Internet service in November 1992. All pretenses of limitations on commercial use disappeared in May 1995 when the National Science Foundation ended its sponsorship of the Internet backbone, and all traffic relied on commercial networks. AOL, Prodigy, and CompuServe came online. Since commercial usage was so widespread by this time and educational institutions had been paying their own way for some time, the loss of NSF funding had no appreciable effect on costs. Today, NSF funding has moved beyond supporting the backbone and higher educational institutions to building the K-12 and local public library accesses on the one hand, and the research on the massive high volume connections on the other.

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Microsoft's full scale entry into the browser, server, and Internet Service Provider market completed the major shift over to a commercially based Internet. The release of Windows 98 in June 1998 with the Microsoft browser well integrated into the desktop shows Bill Gates' determination to capitalize on the enormous growth of the Internet. Microsoft's success over the past few years has brought court challenges to their dominance. We'll leave it up to you whether you think these battles should be played out in the courts or the marketplace. During this period of enormous growth, businesses entering the Internet arena scrambled to find economic models that work. Free services supported by advertising shifted some of the direct costs away from the consumer--temporarily. Services such as Delphi offered free web pages, chat rooms, and message boards for community building. Online sales have grown rapidly for such products as books and music CDs and computers, but the profit margins are slim when price comparisons are so easy, and public trust in online security is still shaky. Business models that have worked well are portal sites that try to provide everything for everybody, and live auctions. AOL's acquisition of Time-Warner was the largest merger in history when it took place and shows the enormous growth of Internet business! The stock market has had a rocky ride, swooping up and down as the new technology companies, the dot.com's encountered good news and bad. The decline in advertising income spelled doom for many dot.coms, and a major shakeout and search for better business models took place by the survivors. A current trend with major implications for the future is the growth of high speed connections. 56K modems and the providers who supported them spread widely for a while, but this is the low end now. 56K is not fast enough to carry multimedia, such as sound and video except in low quality. But new technologies many times faster, such as cable modems and digital subscriber lines (DSL) are predominant now. Wireless has grown rapidly in the past few years, and travelers search for the wi-fi "hot spots" where they can connect while they are away from the home or office. Many airports, coffee bars, hotels and motels now routinely provide these services, some for a fee and some for free. The next big growth area is the surge towards universal wireless access, where almost everywhere is a "hot spot". Municipal wi-fi or city-wide access, wiMAX offering broader ranges than wi-fi, Verizon's EV-DO, and other formats will joust for dominance in the USA in the months ahead. The battle is both economic and political.Another trend that is beginning to affect web designers is the growth of smaller devices to connect to the Internet. Small tablets, pocket PCs, smart phones, game machines, and even GPS devices are now capable of tapping into the web on the go, and many web pages are not designed to work on that scale.

Lesson II: Internet Hardware and Media ·

HARDWARE: MODEMS

Short for Modulator Demodulator, a modem is a hardware device that enables a computer to transmit and receive information over telephone lines. The modem is responsible for

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converting the digital data used by your computer into an analog signal used on phone lines and then converting it back once received on the other end. Because of the speed limitations of modems, many users are upgrading to a broadband connection such as a cable modem or DSL, which offer a faster download and upload speed when compared to the modem.

MODEM ABCs Short for Modulator / Demodulator, which describes the method used to convert digital data used by computers into analog signals used by the phones and then back into digital data once received by the other computer. Illustration: 32

The above pictures help represent a digital signal and an analog signal. All computer data is stored and transmitted within the computer in digital format 1s and 0s. In order for this data to be transmitted over analog phone lines, the data must be transmitted into an analog signal which is the noise you hear when connecting to another computer. Once the other computer receives this signal, it will then translate the signal back into its original digital format. Typical modems are referred to as an asynchronous device, meaning that the device transmits data in an intermittent stream of small packets. Once received, the receiving system then takes the data in the packets and reassembles it into a form the computer can use. Illustration: 33 S t o 1 bit P a 10 bits

pD a 8 bits c

t

aS t 1 bit k

a e

r

tS t o 1 bit tP a 10 bits

pD a 8 bits c

t

aS t 1 bit k

a e

r

t t

The above chart represents how an asynchronous transmission would be transmitted over a phone line. In asynchronous communication, 1 byte (8 bits) is transferred within 1 packet, which is equivalent to one character. However, for the computer to receive this information each packet must contain a Start and a Stop bit; therefore, the complete packet would be 10 bits. An example of what the above chart would transmit is the word HI which is equivalent to 2 bytes (16 bits). There are two types of modems used in all computers.

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Internal: Modem which would be plugged into a slot located within or on the computer. External: Modem which is located within a box and is hooked up externally to the computer, generally VIA the Serial Ports.

·

Hardware: Terminal Adapters

A terminal adapter (TA) is a hardware interface between a computer and an Integrated Services Digital Network line. It's what replaces a modem when you are using an ISDN connection. Unlike "plain old telephone service," which carries signal in analog (voice) form between your computer and the telephone company's office, ISDN carries signals in digital form so there is no need to modulate and demodulate between analog and digital signals. The terminal adapter is what you have to install on a computer so that data can be fed directly into the ISDN line in digital form. Since ISDN service is not available from telephone companies in all areas, the terminal adapter is not usually built into a computer. You purchase and install it when you sign up for ISDN service. ·

Hardware: Router

There are other important types of network devices besides the router, but understanding how a router works will go a long way toward your understanding the whole of internetworking. Before you can learn how to configure and manage routers, however, you need to know the basics of what makes one up. This chapter gives a general review of Cisco router hardware and software. A dizzying array of hardware, software, telecommunications media, and technical expertise goes into internetworking. Switches, hubs, firewalls, packets, gateways, ports, access servers, interfaces, layers, protocols, serial lines, ISDN, frames, topologies—the list can seem endless. But there is a way to simplify things. A single, tangible entity makes sense of it all: the router. In the most basic terms, internetworking is about nothing more than linking machines and people through a maze of intermediary telecommunications lines and computing devices. This takes routing, which in essence involves just two fundamental missions: determine a path along which a link can be made and transmit packets across that path. It is within these two functions—which take place inside the router—that internetworking becomes easier to understand. This is because the router itself must cut all the complexity down to a level it can deal with. The router does this by working with everything, one IP packet at a time. Looked at in this way, the router is the basic fabric of internetworks. Indeed, without the router, the Internet as we know it couldn’t even exist. This is because of the router’s unique and powerful capabilities: ·

Routers can simultaneously support different protocols (such as Ethernet, Token Ring, ISDN, and others), effectively making virtually all computers compatible at the internetwork level.

·

They seamlessly connect local area networks (LANs) to wide area networks (WANs), which makes it feasible to build large-scale internetworks with minimum centralized planning—sort of like Lego™ sets.

·

Routers filter out unwanted traffic by isolating areas in which messages can be “broadcast” to all users in a network.

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·

They act as security gates by checking traffic against access permission lists

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Routers assure reliability by providing multiple paths through internetworks.

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They automatically learn about new paths and select the best ones, eliminating artificial constraints on expanding and improving internetworks.

In other words, routers make internetworks possible. They do so by providing a unified and secure environment in which large groups of people can connect. However, there are obstacles to bringing users together on internetworks, whether on a corporate intranet, a virtual private network, or the Internet itself. Figure 4-1 depicts how routing technology is the key to overcoming these obstacles. Routers are like mini Towers of Babel. The router’s ability to support different protocols simultaneously is probably its most important feature because this capability lets otherwise incompatible computers talk with one another regardless of operating system, data format, or communications medium. The computer industry spent decades and billions of dollars struggling to attain compatibility between proprietary systems and met with limited success. Yet, in less than a decade, TCP/IP internetworking has built a common platform across which virtually all computer and network architectures can freely exchange information.

Illustration: 34

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The router’s ability to filter out unwanted traffic is also important to internetworking. If users are bombarded with volumes of unwanted messages or if they feel their systems can be easily broken into, they will resist linking up to internetworks. Traffic filtering and access control provided by routers give users sufficient privacy and confidence to participate in internetworks. There are other important types of network devices besides the router, but understanding how a router works will go a long way toward your understanding the whole of internetworking. Before you can learn how to configure and manage routers, however, you need to know the basics of what makes one up. This chapter gives a general review of Cisco router hardware and software. In a nutshell, routers do exactly what their name says: They route data from a LAN to another router, then another router, and so on until data is received at its destination. Routers also act as traffic cops, allowing only authorized machines to transmit data into the local network so that private information can remain secure. In addition to supporting these dial-in and leased connections, routers also handle errors, keep network usage statistics, and handle security issues. Routing for Efficiency When you send an e-mail to your Aunt Sadie on the other side of the country, it’s routing technology that ensures she and she alone gets the message, and not every computer hooked up to the Internet. Routers direct the flow of traffic among, rather than within, networks. For instance, let’s consider how routers can be used within a LAN to keep information flowing. Design-O-Rama, as shown in Illustration: 34, is a computer graphics company. The company’s LAN is divvied into two smaller LANs — one for the animators and one for the administration and support staff. The two subdivisions are connected with a router. Design-O-Rama employs eight people — four animators and four other staffers. When one animator sends a file to another, the large file will use a great deal of the network’s capacity. This results in performance problems for the others on the network.

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Illustration: 35

NOTE: Remember how Ethernet works. A single user can have such a dramatic impact on the network because each information packet sent by one computer is broadcast to all the other computers on the LAN. Then each computer examines the packet and decides if it was meant for them. To keep the animators from constantly slowing down the network, the network was divided into two—one for the animators and one for everybody else. A router links the two networks and connects them both to the Internet. The router is the only device on the network that sees every message sent by any computer on either network. When an animator sends a file to a colleague, the router looks at the recipient’s address and keeps that piece of traffic isolated on that LAN. On the other hand, if the animator wants to query the human relations department about vacation time, the router knows to let that piece of traffic through to the HR department. Routers and the Internet In our previous example, we examined how a router could be used locally. Now, let’s broaden the scope of what routers do to include their functionality across the entire Internet. For the sake of comparison, let’s first talk about how a telephone call is routed across the country. Say it’s Aunt Sadie’s birthday and rather than send an e-mail, you want to call her. When you make a long-distance call, the telephone system establishes a stable circuit between your telephone and Aunt Sadie’s. The circuit may involve hopping through a number of steps, including fiber-optics, copper wires, and satellites. This end-to-end chain ensures that the quality of the line between you and Aunt Sadie will be constant. However, if the satellite goes offline or work crews cut the fiber-optic cable, your conversation with Aunt Sadie will be cut short. The Internet avoids this problem by making its “calls” in an entirely different way. Whatever information is sent across the Internet (e-mail, Web page, and so on) is first broken into 1,500-byte packets. The packets are transmitted across a number of routers, each one sending the packet to the destination device. The packets will be transmitted via the best available route. This type of network is called a packet-switched network. Each

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packet could take the same route, or none of the packets could take the same route. Once the packets show up at the destination computer, they are reassembled. This process goes so quickly that you wouldn’t even know that the file was chopped into 1,500-byte packets and then reassembled. In illustration: 35, illustrates how a packet-switched network operates. The routers in the Internet are linked together in a web. The packets follow the path of least resistance to ensure they arrive at their destination in a reasonable amount of time. It seems logical that the packets would go through the least number of routers to get to its destination. However, sometimes that isn’t feasible, because there may be congestion clogging the ideal path. Routers send the traffic around the congested portions of the Internet for increased speed and efficiency. Illustration: 36

This may seem like a very complicated system—as compared to the process followed when placing a telephone call—but the system works for two important reasons: The network can balance the load across different pieces of equipment on a millisecond-by-millisecond basis. If there is a problem with one piece of equipment in the network while a message is being transmitted, packets can be routed around the problem to ensure that the entire message is received. The routers that make up the main back bone of the Internet can reconfigure the paths that packets take because they look at all the information surrounding the data packet, and they tell each other about line conditions, like problems sending and receiving data on various parts of the Internet.

All Shapes and Sizes Not every router is responsible for the fate of packets whizzing across the Internet. Routers come in different sizes and do more or less, depending on how big and sophisticated they

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are. For instance: If you have enabled Internet Connection Sharing between two Windows XP-based computers, the computer that is connected to the Internet is acting as a simple router. This router does very little—it just looks at data to see which computer it’s meant for. ■ Routers that are used to connect small offices to the Internet do more. They enforce rules about security for the office LAN, and they generally handle enough traffic that they tend to be stand-alone devices. ▲ The biggest routers (the ones used to handle data at the major traffic points on the Internet) handle a lot of information—millions of packets each second. These are stand-alone devices that look more like Maytag made them than a computer company. Let’s consider the medium-sized router—it’s probably something humming away in a small room at your business. This router only has two networks to deal with—you’re LAN and the Internet. The office LAN connects to the router via an Ethernet connection. The router might also have two connections to your company’s ISP—a T3 and an ISDN connection. For the most part, your traffic comes and goes via the T3 line. However, the ISDN line is used in the event something goes awry with the T3 line. In fact, the router is configured to send data across the ISDN line, because the configuration table has been programmed to switch over in case of an emergency. This router is also tasked with another function—it’s a layer of security against outside attacks. Although firewalls are routinely used to prevent attacks, the router is also configured to keep the bad people out. However, the backbone of the Internet uses the third kind of router we listed. Cisco’s Gigabit Switch Router 12000 Series of routers is the kind of equipment used to run the Internet. These routers are designed and built like supercomputers. For instance, the 12000 Series uses 200 MHz MIPS R5000 processors, which are the same kind of processors used in the computers that make special effects for the movies. Cisco’s largest router—the 12816—can handle up to 1.28 trillion bits of information per second In a conventional internetwork, information would be transmitted across great distances using twisted-pair copper wire, across a WAN or even a LAN. As useful and utilitarian as twisted-pair cabling and an electrical network have been, fiber-optics allow information to be transferred at immensely higher rates. In the past, when computers shared only brief conversations across the miles, electrical networks could handle the load. But now, as information is shared as it has never been shared before, there is a clear need for an upgrade in network capacities. Comparing the bit rates in electrical networks to optical networks is like putting Woody Allen in a prison yard fist fight with Mike Tyson—there’s just no comparison. The greatest thing that optical networking has going for it is raw speed.

Illustration: 37

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Common WAN links that move across electrical networks are T-1 (1.544 Mbps) and T-3 (45 Mbps). On the LAN front, things get a little better. Most organizations use 10 or 100 Mbps Ethernet. The top-of-the-line Ethernet clocks in at 10 Gbps. However, once fi-ber-optics gets into the race, look out. At their slowest, fiber-optic networks speed along much faster than a T-1 or a T-3. Once fiber shifts out of first gear, there ceases to be a comparison. When discussing optical networking speeds, you’ll hear the terminology change from T-1 or T-3 to OC. OC stands for opticalcarrier.OC takes over where T leaves off. Once the optical carrier gets involved, speeds not only reach 1 Gbps but even leave 1 Gbps in the rearview mirror. Table 4-1 shows how optical networking line speeds increase. As you can see, the speed rates in optical networks (not to mention their development) are increasing at an amazing velocity. Thanks to dense wavelength division multiplexing (DWDM) optical bandwidth will only increase, because more than one stream of data can be introduced on a single run of fiber. More on that in a moment. Optical Technologies There are two prevalent technologies in the world of optical routing: SONET and DWDM. SONET is the oldest and most popular technology, while DWDM is somewhat of a new kid on the block, but supports capacities much greater than SONET. Let’s examine these technologies in a little more depth. SONET -- The most basic and popular architecture for an optical network is the Synchronous Optical Network (SONET). SONET is a standard for optical telecommunications transport developed by the Exchange Carriers Standards Association (ECSA) for the American National Standards Institute (ANSI), the body that sets industry standards in the U.S. for telecommunications and other industries. The comprehensive SONET standard is expected to provide the transport infrastructure for worldwide telecommunications for at least the next two or three decades. NOTE: In Europe, SONET is known by another acronym, SDH, which is short for Synchronous Digital Hierarchy. SONET is so speedy that you could transmit an entire 650MB CD-ROM from New York to Seattle in less than one second. Not only is SONET fast, but it’s also rather versatile. Voice calls from one office to another can be multiplexed along with data and fired out across the same fiber. Further, because of the generous bandwidth SONET affords, compression and encapsulation into Internet Protocol (IP) packets is unnecessary. For comparison’s sake, a single OC-3 connection can carry more than 2,000 simultaneous voice calls. Further, all types of data can be multiplexed alongside the calls.

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SONET offers a top-end bandwidth of OC-192 (9.952 Gbps) and can carry a diverse range of information. In addition to high speeds, SONET features bit-error rates of one error in 10 billion bits. Compare this with copper transmission methods that have bit-error rates of one error in 1 million bits. DWDM -- In its beginning, SONET delivered bandwidth that was previously unimaginable. At the time, delivering OC-3 levels (155.52 Mbps) provided more bandwidth than anyone knew what to do with. Of course, those were in the mid-1980s, a decade before the Internet and high-bandwidth applications. Technology kept delivering faster and faster optical carriers. After OC-3, there were OC-12, OC-48, and beyond. OC-48 (2.5 Gbps) is a popular speed for SONET; however, the next level, OC-192 (10 Gbps) is about the best SONET will be able to deliver. Sure, ten years ago no one knew what a gigabit was, but now we do and we can’t get enough of them. The problem is that 10 Gbps is about Sonnet’s limit. The solution is to jump to DWDM. DWDM is a technique in which multiple signals can traverse a single strand of optical fiber. The lasers used in optical networking can be tuned to different wavelengths (think of them as different colors). As such, it is possible to put multiple colors on a single fiber. When the receiving router sees the various colors, it knows which colors to separate out for which data streams. Illustration: 38

Cisco’s Optical Offerings Cisco utilizes both SONET and DWDM with its optical routers. For example, the Cisco ONS 15808 optical router supports DWDM technology. This carrier class router supports speeds between 2.5 and 10 Gbps and is capable of transmitting up to 2,000 kilometers. The router is able to be upgraded so that 160 channels are transmitted across the fiber with speeds up to 40 Gbps. Cisco also provides a certain level of modularity with its devices. Rather than make a few models with a predetermined number of ports set up for Gigabit Ethernet and another amount dedicated to SONET or DWDM, the company has developed cards and modules that can be plugged into a router, making it customizable. That is, you can decide to load the router with SONET modules, DWDM modules, or any combination of optical and electrical you please. Communicating with router

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Most users of internetworks don’t communicate with routers, they communicate through them. Network administrators, however, must deal directly with individual routers in order to install and manage them. Routers are purpose-built computers dedicated to internetwork processing. They are important devices that individually serve hundreds or thousands of users—some serve even more. When a router goes down, or even just slows down, users howl and network managers jump. As you might imagine then, network administrators demand foolproof ways to gain access to the routers they manage in order to work on them. Routers don’t come with a monitor, keyboard, or mouse, so you must communicate with them in one of three other ways: ▼ From a terminal that’s in the same location as the router and is connected to it via a cable (the terminal is usually a PC or workstation running in terminal mode). ■ From a terminal that’s in a different location as the router and is connected to it via a modem that calls a modem connected to the router with a cable. ▲ Via the network on which the router sits. In large networks, network administrators are often physically removed from routers and must access them via a network. However, if the router is unreachable due to a network problem, or if there’s no modem attached to the router itself, someone must go to its location and log directly into the router. The three ways to gain administrative access to routers are depicted in illustration: 39 Even when network administrators manage routers in the same building, they still prefer to access them by network. It doesn’t make sense to have a terminal hooked up to each router, especially when there are dozens of them stacked in a data closet or computer room. Also, it’s much more convenient to manage them all from a single PC or workstation.

Illustration: 40

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There is several ways to communicate with a router each made possible by a particular communications protocol. The protocol, and how each is used. Router Security Routers aren’t very visible on internetworks, mainly because they usually don’t have addresses such as www.yahoo.com or www.amazon.com. Routers don’t need to have hu man-friendly addresses, because normal internetwork users never need to know that a router is there; they just need the connectivity it provides them. The only people who ever need to log directly into a router are members of the network team responsible for managing it. In TCP/IP networks—the protocol on which most internetworks run—routers identify themselves to internetworks only with their IP addresses. For this reason, to log into a router you must first know that it exists and then what its IP address is. The network administrators responsible for the router will, of course, know this information. The potential for abuse by hackers still exists. As you will learn in Chapter 14, routers constantly send messages to one another in order to update and manage the internetworks on which they operate. With the proper skills and enough determination, a hacker could discover a router’s IP address and then attempt to establish a Telnet connection to it. Given that routers are the links that stitch internetworks together, it’s easy to understand why Cisco and other internetwork equipment manufacturers design many security measures into their products. As shown in illustration: 41, security must restrict access to areas within an internetwork and to individual devices.

Illustration: 41

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NOTE: Router passwords only control entry to the router devices themselves. Don’t confuse router passwords with passwords normal internetwork users must type in to enter certain Web sites or to gain admittance to intranets (private internetworks). Restrictions put on normal users are administered through firewalls and access lists Router Passwords Router passwords aren’t intended only to keep out hackers. Password protection is administered on a router-by-router basis. Passwords to get into a router are stored inside the router itself in most cases. Large internetworks have dozens or even hundreds of routers— some more critical to network operations than others—so it’s a common practice for network managers to allow only select network team members access to certain routers, or even to command levels within routers. In illustration: 42 list router passwords and what they do.

llustration: 42

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I n routers, passwords are used to control access to

Cisco

▼ The router device itself ■ The Privileged EXEC (enable mode) portion of the IOS software environment ▲ The use of specific IOS commands Line Passwords Line passwords are used to control who can log into a router. They are used to set password protection on the console terminal line, the AUX (auxiliary) line, and any or all of the five virtual terminal (VTY) lines. You must set at least one password for the router’s VTY lines. If no Line password is set, when you attempt to log into the router via Telnet, you will be stopped by the error message “password required but none set.” Remember, anyone on the Internet can conceivably Telnet into any router, so setting Line passwords will stop all but the best hackers from getting a foothold. Here, IOS is prompting for a password: User Access Verification P a Router>>

s

s

w

o

r

d

:

When you enter passwords into IOS, no asterisks appear to mask the letters typed— something to which most of us are accustomed. In the preceding example, at the prompt Router>> (the router’s host name in this example), the correct password was entered, the host router was successfully logged into, but no asterisks appear to the right of the password prompt. This might throw you off at first, but you’ll grow accustomed to it. NOTE: You may have noticed that the password examples in this chapter are not made person-specific with usernames. While it is possible to have usernames with Enable and Enable Secret passwords, it is rarely done. This is because Enable and Enable Secret passwords are stored in router configuration files. Network managers find it more practical to simply issue generic passwords to avoid the administrative nightmare of maintaining

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username/passwords across dozens or even hundreds of routers. Refer to Chapter 8 to find out how user accounts and passwords can be centrally maintained using TACACS+ and Cisco Secure. Enable and Enable Secret Password Once you get past the Line password, you are logged into the router’s IOS software environment. IOS is divided into two privilege levels, EXEC and Privileged EXEC (which is usually called enable mode). The EXEC level contains only basic, nondestructive commands. Being in enable mode provides access to more commands. EXEC-level commands basically allow you to view a router. Enable mode commands are more powerful in that they let you reconfigure the router’s settings. These commands are potentially destructive commands, the erase command being a good example. Two types of passwords can be used to restrict access to Privileged EXEC (enable mode): the Enable password and the Enable Secret password. The idea of a “secret password” seems silly at first. Ofcourseall passwords are secret, or at least they should be. What the Cisco engineers are alluding to here is the level of encryption used to mask the password from unauthorized users. The Privileged EXEC Level of IOS Enable and Enable Secret passwords both do the same thing: they restrict access to Privileged EXEC (enable mode). The difference between the two is in the level of encryption supported. Encryption is a technique used to scramble data, making it incomprehensible to those who don’t have a key to read it. Enable Secret passwords are scrambled using an advanced encryption algorithm based on 128 bits for which there is no known decoding technique. Encryption for the Enable password relies on a less powerful algorithm. Cisco strongly recommends using Enable Secret instead of the Enable password. Enable Secret was introduced in 1997, so a fair amount of hardware and software that can support only Enable passwords is still in use, and servers storing backup IOS images frequently service both old and new routers. When both are set, the Enable Secret password always takes precedence over the Enable password. IOS will only put the Enable password to use when running an old version of IOS software. IOS passwords are stored in the configuration file for a router. Configuration files routinely cross networks as routers are updated and backed up. Having an Enable Secret password means that a hacker using a protocol analyzer (a test device that can read packets) will have a tougher time decoding your password. The following sample configuration file illustrates this: Version service service service Hostname Enable secret enable password 7 0012000F

11.2 password-encryption udp-small-servers tcp-small-servers ! Router! 5 $1$C/q2$ZhtujqzQIuJrRGqFwdwn71

Note that the encryption mask of the Enable password on the last line is much shorter than the encryption mask of the Enable Secret password (on the second-to-last line).

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The Service Password-Encryption Command Certain types of passwords, such as Line passwords, by default appear in clear text in the configuration file. You can use the service password-encryption command to make them more secure. Once this command is entered, each password configured is automatically encrypted and thus rendered illegible inside the configuration file (much as the Enable/Enable Secret passwords are). Securing Line passwords is doubly important in networks on which TFTP servers are used, because TFTP backup entails routinely moving config files across networks—and config files, of course, contain Line passwords. Router Hardware and Memory At first glance, routers seem a lot like a PC. They have a CPU, memory, and, on the back, ports and interfaces to hook up peripherals and various communications media. They sometimes even have a monitor to serve as a system console. But there’s one defining difference from a PC: routers are diskless. They don’t even have floppy disks. If you think about it, this makes sense. A router exists to do just that: route. They don’t exist to create or display information or to store it, even temporarily. Routers have as their sole mission the task of filtering incoming packets and routing them outbound to their proper destinations. Another difference is in the kind of add-on modules that can be plugged into routers. Whereas the typical PC contains cards for video, sound, graphics, or other purposes, the modules put into routers are strictly for networking (for obvious reasons). These are called interface modules, or just plain interfaces. When people or documents refer to a router interface, they mean an actual, physical printed circuit board that handles a particular networking protocol. EO and E1, for example, probably mean Ethernet interface numbers 1 and 2 inside a router. Interface modules are always layer-2 protocol specific. There is one protocol per interface. Interfaces are added according to the network environment in which they will work. For example, a router might be configured with interface modules only for Ethernet. A router serving in a mixed-LAN environment, by contrast, would have interfaces for both the Ethernet and Token Ring protocols, and if that router were acting as a LAN-to-WAN juncture, it might also have an ISDN module. There is one last difference between routers and general-purpose computers—a more subtle one. Computer product lines are almost always based on a common central processor (CPU) architecture, for example, Wintel PCs on the venerable Intel x86 architecture, Apple’s Motorola 68000 variants, Sun’s SPARC, and so on. In contrast, Cisco routers use a variety of CPUs, each chosen to fit a particular mis- sion. Cisco SOHO 70 Series routers, for example, employ 50 MHz CPUs. Cisco probably made this selection because the 70 Series is designed for small office or home office use, where activity loads are light. The Motorola MPC 855T RISC chip is reliable; capable of handling the job; and, perhaps most important, inexpensive. Moving up the router product line, Cisco uses progressively more powerful general-purpose processors from Motorola, Silicon Graphics, and other chip makers.

Router Memory

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Routers use various kinds of memory to operate and manage themselves. Figure 4-9 depicts the layout of a motherboard in a Cisco 4500 router (a good example because it’s one of the most widely used routers in the world today). All Cisco router motherboards use four types of memory, each dedicated to performing specific roles. Illustration: 43

Each Cisco router ships with at least a factory default minimum amount of DRAM and flash memory. Memory can be added at the factory or upgraded in the field. As a general rule, the amount of DRAM can be doubled or quadrupled (depending on the spe- cific model), and the amount of flash can be doubled. If traffic loads increase over time, DRAM can be upgraded to increase a router’s throughput capacity. RAM/DRAM RAM/DRAM stands for random access memory/dynamic random access memory. Also called working storage, RAM/DRAM is used by the router’s central processor to do its work, much like the memory in your PC. When a router is in operation, its RAM/DRAM contains an image of the Cisco IOS software, the running configuration file, the routing table, other tables (built by the router after it starts up), and the packet buffer. Don’t be thrown by the two parts in RAM/DRAM. The acronym is a catch-all. Virtually all RAM/DRAM in Cisco routers is DRAM—dynamic random access memory. Nondynamic memory, also called static memory, became obsolete years ago. But the term RAM is still so widely used that it’s included in the literature to avoid confusion on the subject. Cisco’s smallest router, the 70 Series, ships with a minimum of 16MB of DRAM. At the other end of the spectrum, the 12816-gigabit switch router, one of Cisco’s largest, supports up to 4GB. NOTE: Shared memory (also called packet memory) is a specialized type of DRAM. Shared memory DRAM is dedicated to handling the router’s packet buffer. Cisco’s designers separate out shared memory to help assure I/O throughput. Shared memory is even physically nearer to the interface modules to further boost performance. NVRAM NVRAM stands for nonvolatile RAM. Nonvolatile means memory that will retain information after losing power. Cisco routers store a copy of the router’s configuration file in NVRAM (configuration files are covered later in this chapter). When the router is intentionally turned off, or if power is lost, NVRAM enables the router to restart in its proper configuration. Flash Memory

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Flash memory is also nonvolatile. It differs from NVRAM in that it can be erased and reprogrammed as needed. Originally developed by Intel, flash memory is in wide use in computers and other devices. In Cisco routers, flash memory is used to store one or more copies of the IOS software. This is an important feature because it enables network managers to stage new versions of IOS on routers throughout an internetwork and then upgrade them all at once to a new version from flash memory. ROM ROM stands for read-only memory. It, too, is nonvolatile. Cisco routers use ROM to hold a so-called bootstrapprogram, which is a file that can be used to boot to a minimum configuration state after a catastrophe. ROM is also referred to as ROMMON. In fact, when you boot from ROM, the first thing you’ll see is the rommon>> prompt. ROMMON (for ROM monitor) harks back to the early days of the UNIX operating system, which relied on ROMMON to reboot a computer to the point at which commands could at least be typed into the system console monitor. In smaller Cisco routers, ROM holds a bare-bones subset of the Cisco IOS software. ROM in some high-end Cisco routers holds a full copy of IOS. Router Ports and Modules A router’s window to the internetwork is through its ports and modules. Without them, a router is a useless box. The ports and modules that are put into a router define what it can do. Internetworking can be intimidating, with the seemingly endless combinations of products, protocols, media, feature sets, standards—you name it. The acronyms come so fast and so hard that it might seem hopeless to learn how to properly configure a router. But choosing the right router product can be boiled down to manageable proportions. Table 4-4 lays out five major requirement areas that, if met, will lead you to the best router solution. Cisco obviously can’t manufacture a model of router to match every customer’s specific requirements. To make them more flexible to configure, routers come in two major parts: ▼ Chassis The actual box and basic components inside it, such as power supply, fans, rear and front faceplates, indicator lights, and slots ▲ Ports and modules the printed circuit boards that slide into the router box Cisco’s router product-line structure tries to steer you to a product—or at least to a reasonably focused selection of products—meeting all five requirement areas in Table

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Finding the right router for your needs is basically a three-step process. The following illustrates the process of selecting a router for a large branch office operation:] Illustration: 44

First, Cisco’s routers are grouped into product families called series. Choosing a router product series is usually a matter of budget, because each series reflects a price/ performance tier. Models within series are generally based on the same chassis, which is the metal frame and basic components (power supply, fans, and so on) around which the router is built. We’ll select the Cisco 2000 Series because it fits both the purchase budget and performance requirements for our large branch office. Illustration: 45

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From the 2000 Series, we’ll take the Cisco 2600 Series. The 2600 chassis is versatile enough to fit a lot of situations, making it a popular brand of branch office router. Illustration: 46

Third, we’ll select the Cisco 2650 because it has two Ethernet ports; and our imaginary branch office will operate two subnets, one for the customer service office and another for

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the front office. The two Ethernet ports will let us separate the two departments, thereby isolating traffic. NOTE: The term “port” can cause confusion if you’re not careful. When speaking of hardware, port means a physical connection through which I/O can pass(a serial port, for example), but there are also so-called ports at the transport layer of network protocols. These “ports” are actually port numbers used to identify what network application packets contain. These ports (port numbers) are also referred to as TCP ports or “listeners,” because they inform the receiver what’s inside the message. Example TCP-defined port numbers include Port 25 for Simple Mail Transfer Protocol and Port 80 for HTTP. Refer to Chapter 2’s section, “The Transport Layer,” for more on TCP ports. Router Packaging Three major categories of modules can be configured into Cisco routers to support either LAN or WAN connectivity: ▼ Ethernet modules To support any of the many Ethernet LAN variants on the market, including Novell NetWare, Banyan VINES, and AppleTalk. ■ Token Ring modules IBM’s LAN technology, which is well established in banks, insurance companies, and other Fortune 1000 corporate environments. ▲ WAN connectivity modules To support a wide variety of WAN protocols, some old and some new. Example WAN technologies include newer protocols such as ISDN, Frame Relay, Asynchronous Transfer Mode (ATM), and legacy protocols such as SDLC and X.25. Configuration options depend mainly on the specific Cisco router: ▼ Lower-end routers tend to be “fixed configuration” in that the modules are factory integrated only (preconfigured). ■ Midrange routers, such as the Cisco 3600 Series, are “modular” in that they can accept a variety of modules, often packaging different protocols in the same box. Interface modules are plugged into this class of routers’ motherboards. ▲ High-end routers, the Cisco 7300 Series and Cisco 12000 Series, have buses (also called backplanes). Bus-based routers accept larger modules—usually referred to as blades or cards—that are effectively self-contained routers (they have their own CPUs, memory units, and so on). In illustration 47, is a view of the back of a Cisco 4500 configured with two Token Ring modules (Ring A and Ring B) and four serial ports. Notice that an empty slot is available on the right. It’s a common practice to purchase a router model with room for adding an interface as network traffic grows.

Illustration: 47

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Media: PSTN The Beginning of the PSTN The first voice transmission, sent by Alexander Graham Bell, was accomplished in 1876 through what is called a ring-down circuit. A ring-down circuit means that there was no dialing of numbers; Instead, a physical wire connected two devices. Basically, one person picked up the phone and another person was on the other end (no ringing was involved). Over time, this simple design evolved from a one-way voice transmission, by which only one user could speak, to a bi-directional voice transmission, whereby both users could speak. Moving the voices across the wire required a carbon microphone, a battery, an electromagnet, and an iron diaphragm. It also required a physical cable between each location that the user wanted to call. The concept of dialing a number to reach a destination, however, did not exist at this time. To further illustrate the beginnings of the PSTN, see the basic four-telephone network. Illustration: 48 As you can see, a physical cable exists between each location.

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Place a physical cable between every household requiring access to a telephone, however, and you’ll see that such a setup is neither cost-effective nor feasible. To Determine how many lines you need to your house, think about everyone you call as a value of N and use the following equation: N× (N–1)/2. As such, if you want to call 10 people, you need 45 pairs of lines running into your house. Illustration: 49

Due to the cost concerns and the impossibility of running a physical cable between

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Everyone on Earth who wanted access to a telephone, another mechanism was developed that could map any phone to another phone. With this device, called a switch , the telephone users needed only one cable to the centralized switch office, instead of seven. At first, a telephone operator acted as the switch. This operator asked callers where they wanted to dial and then manually connected the two voice paths. Shows how the four-phone network example would look today with a centralized operator to switch the calls. Illustration: 50 Centralized Operator: The Human Switch

Now, skip ahead 100 years or so—the human switch is replaced by electronic switches. At this point, you can learn how the modern PSTN network is built. Understanding PSTN Basics Although it is difficult to explain every component of the PSTN, this section explains the most important pieces that make the PSTN work. The following sections discuss how your voice is transmitted across a digital network, basic circuit-switching concepts, and why your phone number is 10 digits long. Analog and Digital Signaling Everything you hear, including human speech, is in analog form. Until several decades ago, the telephony network was based on an analog infrastructure as well. Although analog communication is ideal for human interaction, it is neither robust nor efficient at recovering from line noise. ( Line noise is normally caused by the introduction of static into a voice network.) In the early telephony network, analog transmission was passed through amplifiers to boost the signal. But, this practice amplified not just the voice, but the line noise as well. This line noise resulted in an often unusable connection. Analog communication is a mix of time and amplitude. Illustration: 51 Analog Waveform

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If you were far away from the end office switch (which provides the physical cable to your home), an amplifier might be required to boost the analog transmission (your voice). Analog signals that receive line noise can distort the analog waveform and cause garbled reception. This is more obvious to the listener if many amplifiers are located between your home and the end office switch. In illustration 51, a show that an amplifier does not clean the signal as it amplifies, but simply amplifies the distorted signal. This process of going through several amplifiers with one voice signal is called accumulated noise. Illustration: 52 Analog Line Distortion

In digital networks, line noise is less of an issue because repeaters not only amplify the signal, but clean it to its original condition. This is possible with digital communication because such communication is based on 1s and 0s. Illustration: 52 Digital Line Distortion

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Therefore, when signals are repeated, a clean sound is maintained. When the benefits of this digital representation became evident, the telephony network migrated to pulse code modulation (PCM). Digital Voice Signals PCM is the most common method of encoding an analog voice signal into a digital stream of 1s and 0s. All sampling techniques use the Nyquist theorem , which basically states that if you sample at twice the highest frequency on a voice line, you achieve good-quality voice transmission. The PCM process is as follows: •Analog waveforms are put through a voice frequency filter to filter out anything greater than 4000 Hz. These frequencies are filtered to 4000 Hz to limit the amount of crosstalk in the voice network. Using the Nyquist theorem, you need to sample at 8000 samples per second to achieve good-quality voice transmission. • The filtered analog signal is then sampled at a rate of 8000 times per second. •After the waveform is sampled, it is converted into a discrete digital form. This sample is represented by a code that indicates the amplitude of the waveform at the instant the sample was taken. The telephony form of PCM uses eight bits for the code and a logarithm compression method that assigns more bits to lower-amplitude signals. If you multiply the eight-bit words by 8000 times per second, you get 64,000 bits per second (bps). The basis for the telephone infrastructure is 64,000 bps (or 64 kbps). Two basic variations of 64 kbps PCM are commonly used:ì-law, the standard used in North America; and a-law, the standard used in Europe. The methods are similar in that both use logarithmic compression to achieve from 12 to 13 bits of linear PCM quality in only eight-bit words, but they differ in relatively minor details. The ì-law method has a slight advantage over the a-law method in terms of low-level signal-to noise ratio performance, for instance. Local Loops, Trunks, and Inters witch Communication The telephone infrastructure starts with a simple pair of copper wires running to your home. This physical cabling is known as a local loop. The local loop physically connects your home

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telephone to the central office switch (also known as a Class 5 switch or end office switch). The communication path between the central office switch and your home is known as the phone line, and it normally runs over the local loop. The communication path between several central office switches is known as a trunk . Just as it is not cost-effective to place a physical wire between your house and every other house you want to call, it is also not cost-effective to place a physical wire between every central office switch. Illustration: 53 Meshed Network versus Hierarchical Network

Switches are currently deployed in hierarchies. End office switches (or central office switches) interconnect through trunks to tandem switches (also referred to as Class 4 switches). Higher layer tandem switches connect local tandem switches. Illustration: 54 Circuit-Switching Hierarchy

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Central office switches often directly connect to each other. Where the direct connections occur between central office switches depends to a great extent on call patterns. If enough traffic occurs between two central office switches, a dedicated circuit is placed between the two switches to offload those calls from the local tandem switches. Some portions of the PSTN use as many as five levels of switching hierarchy. Now that you know how and why the PSTN is broken into a hierarchy of switches, you need to understand how they are physically connected, and how the network communicates. PSTN Signaling Generally, two types of signaling methods run over various transmission media. The signaling methods are broken into the following groups: • User-to-network signaling—this is how an end user communicates with the PSTN. • Network-to-network signaling—this is generally how the switches in the intercommunicate. User-to-Network signaling generally, when using twisted copper pair as the transport,

PSTN

User-to-Network Signaling Generally, when using twisted copper pair as the transport, a user connects to the PSTN through analog, Integrated Services Digital Network (ISDN), or through a T1 carrier. The most common signaling method for user-to-network analog communication is Dual Tone Multi-Frequency (DTMF. DTMF is known as in-band signaling because the tones are carried through the voice path. Illustration: 55 Dual Tone Multi-Frequency

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When you pick up your telephone handset and press the digits the tone that passes from your phone to the central office switch to which you are connected tells the switch what number you want to call. ISDN uses another method of signaling known as out-of-band. With this method, the signaling is transported on a channel separate from the voice. The channel on which the voice is carried is called a bearer (or B channel) and is 64 kbps. The channel on which the signal is carried is called a data channel (D channel) and is 16 kbps. Illustration: 56 Basic Rate Interface

Out-of-band signaling offers benefits, including the following:

many

• Signaling is multiplexed (consolidated) into a common channel. • Glare is reduced (glare occurs when two people on the same circuit seize opposite ends of that circuit at the same time). • A lower post dialing delay. • Additional features, such as higher bandwidth, are realized. • Because setup messages are not subject to the same line noise as DTMF tones, call completion is greatly increased. In-band signaling suffers from a few problems, the largest of which is the possibility for lost tones. This occurs when signaling is carried across the voice path and it is a common reason why you can sometimes experience problems remotely accessing your voice mail. Network-to-Network Signaling Network-to-network communication is normally carried across the following transmission media: •T1/E1 carrier over twisted pair T1 is a 1.544-Mbps digital transmission link normally used in North America and Japan. E1 is a 2.048-Mbps digital transmission link normally used in Europe. •T3/E3, T4 carrier over coaxial cable T3 carries 28 T1s or 672 64-kbps connections and is 44.736 Mbps. E3 carries 16 E1s or 512 64-kbps connections and is 34.368 Mbps.

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T4 handles 168 T1 circuits or 4032 4-kbps connections and is 274.176 Mbps. •T3, T4 carrier over a microwave link •Synchronous Optical Network (SONET) across fiber media SONET is normally deployed in OC-3, OC-12, and OC-48 rates, which are 155.52 Mbps, 622.08 Mbps, and 2.488 Gbps, respectively. Network-to-network signaling types include in-band signaling methods such as MultiFrequency (MF) and Robbed Bit Signaling (RBS). These signaling types can also be used to network signaling methods. Digital carrier systems (T1, T3) use A and B bits to indicate on/off hook supervision. The A/B bits are set to emulate Single Frequency (SF) tones (SF typically uses the presence or absence of a signal to signal A/B bit transitions). These bits might be robbed from the information channel or multiplexed in a common channel (the latter occurs mainly in Europe). More information on these signaling types is found in Chapter 3, “Basic Telephony Signaling.” MF is similar to DTMF, but it utilizes a different set of frequencies. As with DTMF, MF tones are sent in-band. But, instead of signaling from a home to an end office switch, MF signals from switch to switch. Network-to-network signaling also uses an out-of-band signaling method known as Signaling System7 (SS7) (Or C7 in European countries). NOTE: SS7 is beneficial because it is an out-of-band signaling method and it interconnects to the Intelligent Network (IN). Connection to the IN enables the PSTN to offer Custom Local Area Signaling Services (CLASS) services. SS7 is a method of sending messages between switches for basic call control and for CLASS. These CLASS services still rely on the end-office switches and the SS7 network. SS7 is also used to connect switches and databases for network-based services (for example, 800-number services and Local Number Portability [LNP]). Some of the benefits of moving to an SS7 network are as follows: •Reduced post-dialing delay There is no need to transmit DTMF tones on each hop of the PSTN. The SS7 network transmits all the digits in an initial setup message that includes the entire calling and called number. When using in-band signaling, each MF tone normally takes 50 ms to transmit. This means you have at least a .5-second post-dialing delay per PSTN hop. This number is based on 11-digit dialing (11 MF tones × 50 ms = 550 ms). • Increased call completion SS7 is a packet-based, out-of-band signaling protocol, compared to the DTMF or MF in-band signaling types. Single packets containing all the necessary information (phone numbers, services, and so on) are transmitted faster than tones generated one at a time across an in-band network. •Connection to the IN This connection provides new applications and services transparently across multiple vendors’ switching equipment as well as the capability to create new services and applications more quickly. To further explain the PSTN, visualize a call from my house to my Grandma’s house 10 miles away. This call traverses an end office switch, the SS7 network (signaling only), and a second end office switch.

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Illustration: 58 PSTN Call Flow to Grandma’s House

To better explain the diagram let’s walk through the flow of the call: 1. 2. 3. 4.

I pick up the phone and send an off-hook indication to the end office switch. The switch sends back a dial tone. I dial the digits to call Grandma’s house (they are sent in-band through DTMF). The switch interprets the digits and sends an Initial Address Message (IAM, or setup message) to the SS7 network. 5. The SS7 network reads the incoming IAM and sends a new IAM to Grandma’s switch. 6. Grandma’s switch sends a setup message to Grandma’s phone (it rings her phone). 7. An alerting message (alerting is the same as the phone ringing) is sent from Grandma’s switch (not from her phone) back to the SS7 network through an Address Complete Message (ACM). 8. The SS7 network reads the incoming ACM and generates an ACM to my switch. 9. I can hear a ringing sound and know that Grandma’s phone is ringing. (The ringing is not synchronized; your local switch normally generates the ringing when the ACM is received from the SS7 network.) 10 . Grandma picks up her phone, sending an off-hook indication to her switch. 11. Grandma’s switch sends an ANswer Message (ANM) that is read by the SS7, and a new ANM is generated to my switch. 12. A connect message is sent to my phone (only if it’s an ISDN phone) and a connect acknowledgment is sent back (again, only if it’s an ISDN phone). (If it is not an ISDN phone, then on-hook or off-hook representations signal the end office switch.) 13. I can now talk to Grandma until I hang up the phone (on-hook indication).

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If Grandma’s phone was busy, I could use an IN feature by which I could park on her line and have the PSTN call me back after she got off the phone. Now that you have a basic understanding of how the PSTN functions, the next section discusses services and applications that are common in the PSTN. New PSTN Network Infrastructure Model As discussed in the previous sections, the new infrastructure will focus on the ability to separate the old stagnant infrastructure into a model by which multiple vendors can develop applications and features quickly for the consumer. In the illustration clearly shows the relationship between all three layers as well as the relationship between these layers and the components that would be used in a live network. Carriers will enjoy this method, as it means they won’t be locked into a single solution for any of their layers. They will be able to mix and match all three layers to offer the services, functionality, and time-to-market that they need. Illustration: 59 Illustration of Elements of Packet Telephony

Some carriers might be hesitant to utilize more than one equipment vendor to cut down on their integration timeframe, but many service providers will partner with a minimum of two vendors to ensure competition. The reality of the illustration is that the bearers, connection plane, or media transport will be either IP gateways or ATM gateways, or a combination of both. Multiple vendors will be in this space initially, but most likely, they will consolidate to three to five major players. The call-control plane is an extremely important piece of the new PSTN network infrastructure model, as it must gracefully coexist with both the connection plane and the service (application) layers. Many vendors are building MGC technology. In fact, the authors are working with approximately 15 vendors to ensure compatibility from the connection plane into the call-control and service/application plane.

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Many vendors will continue to be in the call-control plane, as service providers will more than likely use several vendors for this key technology, depending upon what service they decide to deploy. The onus on the Call Agent vendors will be to ensure compatibility from one Call Agent to another. Call Agent interoperability is one of the components that could keep service providers from using large-scale, packet based voice networks. The service or application plane is where the innovation in the network will happen. One major issue affecting the service plane is its reliance upon soft-switch vendors to open APIs that are useful enough to develop services. For this reason, you will see many application vendors attempting to develop Call Agent technology until APIs into the top Call Agent vendors are fully open and service-friendly. The service plane is where thousands of ISVs will converge to develop new and revenue enhancing applications. This is comparable to the client/server revolution in which Microsoft removed the barriers of having to code video drivers, and so on, and enabled ISVs to concentrate on applications. This same revolution is happening in the PSTN today and will change the way services and telephony/multimedia networks are designed, built, and deployed.

ISDN A long time ago, the entire telephone network was analog. This was bad, because as a voice went farther down the line, and through more switches, the quality became worse and worse as noise crept in. And there was no way to eliminate the noise, no way to know what the signal was supposed to be. Digital encoding promised a way to encode the audio such that you'd know what the signal was supposed to be. As noise crept in, you could eliminate it throught the phone network, assuming it wasn't worse than the variation between different digital encoding levels. With the transistor revolution, this theory became possible, and the phone companies began converting their own networks over to digital. Today, you have to search pretty hard to find a phone company switch that isn't digital. They call their network the Integrated Digital Network, or IDN. This solved many of the phone company's problems. However for a variety of reasons, it has been attractive to make the phone network completely digital, from end to end. For computer users, this is ideal, because we can eliminate those clumsy modems, and will hopefully benefit from higher speed. For the phone companies, they can eliminate the last of the noise and loss from the audio data. And for dreamers, this will enable a wide variety of different services to be delivered to the customer over a single interface. What is ISDN? ISDN stands for Integrated Services Digital Network. It is a design for a completely digital telephone/telecommunications network. It is designed to carry voice, data, images, video, everything you could ever need. It is also designed to provide a single interface (in terms of both hardware and communication protocols) for hooking up your phone, your fax machine, your computer, your videophone, your video-on-demand system (someday), and your microwave. ISDN is about what the future phone network, and information superhighway, will look like (or would have looked like). ISDN was originally envisioned as a very fast service, but this was a long time ago when it was hoped to have fiber all the way to your house. It turned out that running all that fiber would be too expensive, so they designed ISDN to run on the copper wiring that you already

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have. Unfortunately, that slowed things down considerably - too slow for quality video, for instance. ISDN has been very slow in coming. The standards organizations have taken their time in coming up with the standards. In fact, many people consider them to be out of date already. But on the other side of the coin, the phone companies (especially in the U.S.) have been very slow at designing products and services, or marketing them with ISDN in mind. Things are starting to pick up, but still very slowly. ISDN is available now in many places, but it is not widely used. Further most of the products and services that people have forecast for ISDN still aren't available. For this reason many people say that ISDN also stands for "It Still Does Nothing". B-ISDN That brings is to B-ISDN. B-ISDN is Broadband ISDN. (The older ISDN is often called Narrowband ISDN.) This is not simply faster ISDN, or ISDN with the copper to your home finally upgraded to fiber. B-ISDN is a complete redesign. It is still capable of providing all the integrated services (voice, data, video, etc.) through a single interface just like ISDN was supposed to. But it will do it a lot faster than ISDN could. Of course, that copper to your house will still have to be replaced with fiber. But B-ISDN is still in development - it seems to be moving faster than ISDN, but it is still quite a ways off. Fitting things together In order to understand what ISDN is, you have to understand a bit about modern telephony. You'll invariably find lots of buzzwords, or in most cases buzz-acronyms, that seem to overlap in a terribly complex way. That's because they do overlap considerably. Nevertheless you can generalize about how certain things fit together. Hopefully I can sum it all up in a few almost correct categories. There are two parts of a telephone network: the phone company's part, and the customer's part. The customer's part today is largely just the telephone, some house wiring, and some connectors. The phone company's part is lots more wire, fiber, switches, computers, and lots of expensive and complicated stuff. ISDN is concerned (almost) entirely with the customer's part of the network. ISDN gets the data from you, to the phone company in a standard way. What they do with it in order to get it to its destination is entirely up to them. This is a very simple, important concept. If you understand this, then when someone says something like "SONET is the future of the modern telephone network" you'll know that they're talking (mostly) about what goes on inside the phone company, and between phone companies. They are probably right, but it is also true that "ISDN is the future of the modern telephone network" especially if you mean B-ISDN. They're just the future of different parts of the telephone network. Media: Kilo stream Kilo stream: Private Services are specially designed for businesses which rely heavily on communications. They provide permanently connected analogue and digital, voice and data circuits, between different sites, for the exclusive use of the business. Speech Line and Key Line analogue circuits are used for straightforward voice or low-speed data applications. However, once you are regularly in touch with the same locations, making increased use of e-mail or exchanging larger and larger data files, then switching to KiloStream or the KiloStream N (the fastest KiloStream service for speech or data) digital services should result in substantial cost savings. In fact, because KiloStream circuits are leased for a fixed tariff, the more you use them, the more cost effective they become.

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KiloStream comes in a range of different speeds, from 2.4kbit/s to 1,024kbit/s, to suit the needs and the budget of any business customer. KiloStream services offer a resilient, high quality connection, and are available with a range of added-value packages to deliver an average performance target of 99.95%.

Key benefits of KiloStream include;

·

Physical point-to-point connectivity - assuring high levels of security

·

A state of the art network - providing very high levels of reliability and circuit availability

·

Geographical coverage - extending over 99% of the UK

·

2-week provision

·

Absence of modems - saving cost and adding reliability

·

Connectivity applications, including data, voice and image; and, with suitable multiplexers, a mixture of all three.

Key features of KiloStream N include;

·

Cost effectiveness where ordinary KiloStream is insufficient

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A smooth evolution path for network growth

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Easy accommodation video-conferencing

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High quality transmission, performance and reliability

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Resilience - both separation/diversity & disaster recovery service available

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Total Care support

·

Nation-wide geographical coverage

·

6 week provision

of

specialist

applications

such

as

CAD/CAM

and

The Private Service you choose will depend on the volume and kind of information you wish to communicate Analogue or digital circuits up to 64kbit/s are mainly used for low-speed voice or data applications, such as PC terminal users at branch offices who need on-line access to a host computer for electronic data interchange (EDI), file transfer or remote printing facilities. At 64kbit/s, you can transmit voice and data, linking together local area networks (LANs) for order processing and stock control, or make Internet access more widely available. And at speeds of 128kbit/s and above, KiloStream N can be used for voice or data applications, to connect complete systems, for high speed faxing, or video conferences. Finally, when you decide that you need more bandwidth, you'll find it simple to migrate to the MegaStream service, enabling your business to access even more applications as it grows. There is a Private Service to suit your precise geographical and traffic requirements. Whether

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you work across the country or around the world, you will benefit from a single, seamless private network which is right for your business. The cost of upgrading from analogue to digital private services, and from KiloStream to KiloStream N has reduced in real terms, making it more affordable for smaller businesses. There are a variety of discounts and a range of term-based contracts available to suit any business, and a bandwidth-based option with discount levels which increase in line with usage. All of which will help you to keep your costs down. With the right Private Service, reliability comes as standard. With KiloStream you can expect a resilient and high quality connection, achieving an average network performance target of 99.95% error free seconds a year. There is even the option of KiloStream Assured Restore automatic back-up which offers very high levels of circuit availability. Moreover, with KiloStream, you get BT's Total Care maintenance service within tariff. That means for no extra cost, you will have the peace of mind of a guaranteed fault response time of 4 hours, any time, any day - or night. KiloStream coverage is global and seamless. You can be sure of cost-effective migration into even faster bandwidths when you want them. KiloStream is your fast track into the future of telecoms.

Lesson III: Internet Services Electronic Mail Electronic Mail every day, the citizens of the Internet send each other billions of e-mail messages. If you are online a lot, you yourself may send a dozen or more e-mails each day without even thinking about it. Obviously, e-mail has become an extremely popular communication tool. Have you ever wondered how e-mail gets from your desktop to a friend halfway around the world? What is a POP3 server, and how does it hold your mail? The answers may surprise you, because it turns out that e-mail is an incredibly simple system at its core. In this article, we'll take an in-depth look at e-mail and how it works. An E-mail Message According to Darwin Magazine: Prime Movers, the first e-mail message was sent in 1971 by an engineer named Ray Tomlinson. Prior to this, you could only send messages to users on a single machine. Tomlinson's breakthrough was the ability to send messages to other machines on the Internet, using the @ sign to designate the receiving machine. An e-mail message has always been nothing more than a simple text message -- a piece of text sent to a recipient. In the beginning and even today, e-mail messages tend to be short pieces of text, although the ability to add attachments now makes many e-mail messages quite long. Even with attachments, however, e-mail messages continue to be text messages -- we'll see why when we get to the section on attachments. E-mail Clients

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You have probably already received several e-mail messages today. To look at them, you use some sort of e-mail client. Many people use well-known stand-alone clients like Microsoft Outlook, Outlook Express, Eudora or Pegasus. People who subscribe to free e-mail services like Hotmail or Yahoo use an e-mail client that appears in a Web page. If you are an AOL customer, you use AOL's e-mail reader. No matter which type of client you are using, it generally does four things: ·

It shows you a list of all of the messages in your mailbox by displaying the message headers. The header shows you who sent the mail, the subject of the mail and may also show the time and date of the message and the message size. · It lets you select a message header and read the body of the e-mail message. · It lets you create new messages and send them. You type in the e-mail address of the recipient and the subject for the message, and then type the body of the message. · Most e-mail clients also let you add attachments to messages you send and save the attachments from messages you receive. Sophisticated e-mail clients may have all sorts of bells and whistles, but at the core, this is all that an e-mail client does. A Simple E-mail Server

Given that you have an e-mail client on your machine, you are ready to send and receive e-mail. All that you need is an e-mail server for the client to connect to. Let's imagine what the simplest possible e-mail server would look like in order to get a basic understanding of the process. Then we will look at the real thing. There are Web servers, FTP servers, telnet servers and e-mail servers running on millions of machines on the Internet right now. These applications run all the time on the server machine and they listen to specific ports, waiting for people or programs to attach to the port. The simplest possible e-mail server would work something like this:

· · ·

·

It would have a list of e-mail accounts, with one account for each person who can receive e-mail on the server. My account name might be mbrain; John Smith's might be jsmith, and so on. It would have a text file for each account in the list. So the server would have a text file in its directory named MBRAIN.TXT, another named JSMITH.TXT, and so on. If someone wanted to send me a message, the person would compose a text message ("Marshall, Can we have lunch Monday? John") in an e-mail client, and indicate that the message should go to mbrain. When the person presses the Send button, the e-mail client would connect to the e-mail server and pass to the server the name of the recipient (mbrain), the name of the sender (jsmith) and the body of the message. The server would format those pieces of information and append them to the bottom of the MBRAIN.TXT file. The entry in the file might look like this: · From: jsmith · To: mbrain · Marshall, · Can we have lunch Monday? · John

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There are several other pieces of information that the server might save into the file, like the time and date of receipt and a subject line; but overall, you can see that this is an extremely simple process. As other people sent mail to mbrain, the server would simply append those messages to the bottom of the file in the order that they arrived. The text file would accumulate a series of five or 10 messages, and eventually I would log in to read them. When I wanted to look at my e-mail, my e-mail client would connect to the server machine. In the simplest possible system, it would:

· · · · ·

Ask the server to send a copy of the MBRAIN.TXT file Ask the server to erase and reset the MBRAIN.TXT file Save the MBRAIN.TXT file on my local machine Parse the file into the separate messages (using the word "From:" as the separator) Show me all of the message headers in a list

When I double-clicked on a message header, it would find that message in the text file and show me its body. You have to admit that this is a very simple system. Surprisingly, the real e-mail system that you use every day is not much more complicated than this. The Real E-mail System For the vast majority of people right now, the real e-mail system consists of two different servers running on a server machine. One is called the SMTP server, where SMTP stands for Simple Mail Transfer Protocol. The SMTP server handles outgoing mail. The other is either a POP3 server or an IMAP server, both of which handle incoming mail. POP stands for Post Office Protocol, and IMAP stands for Internet Mail Access Protocol. A typical e-mail server looks like this: Illustration: 60

The SMTP server listens on well-known port number 25, POP3 listens on port 110 and IMAP uses port 143, The SMTP Server Whenever you send a piece of e-mail, your e-mail client interacts with the SMTP server to

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handle the sending. The SMTP server on your host may have conversations with other SMTP servers to actually deliver the e-mail. Illustration: 61

Let's assume that I want to send a piece of e-mail. My e-mail ID is brain, and I have my account on howstuffworks.com. I want to send e-mail to [email protected]. I am using a stand-alone e-mail client like Outlook Express. When I set up my account at howstuffworks, I told Outlook Express the name of the mail server -- mail.howstuffworks.com. When I compose a message and press the Send button, here is what happens:

· · ·

Outlook Express connects to the SMTP server at mail.howstuffworks.com using port 25. Outlook Express has a conversation with the SMTP server, telling the SMTP server the address of the sender and the address of the recipient, as well as the body of the message. The SMTP server takes the "to" address ([email protected]) and breaks it into two parts: 1. The recipient name (jsmith) 2. The domain name (mindspring.com) If the "to" address had been another user at howstuffworks.com, the SMTP server would simply hand the message to the POP3 server for howstuffworks.com (using a little program called the delivery agent). Since the recipient is at another domain, SMTP needs to communicate with that domain.

·

·

The SMTP server has a conversation with a Domain Name Server. It says, "Can you give me the IP address of the SMTP server for mindspring.com?" The DNS replies with the one or more IP addresses for the SMTP server(s) that Mind spring operates. The SMTP server at howstuffworks.com connects with the SMTP server at Mind spring using port 25. It has the same simple text conversation that my e-mail client had with the SMTP server for HowStuffWorks, and gives the message to the Mind spring server. The Mind spring server recognizes that the domain name for jsmith is at Mind spring, so it hands the message to Mind spring’s POP3 server, which puts the message in jsmith's mailbox.

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If, for some reason, the SMTP server at HowStuffWorks cannot connect with the SMTP server at Mind spring, then the message goes into a queue. The SMTP server on most machines uses a program called send mail to do the actual sending, so this queue is called the send mail queue. Send mail will periodically try to resend the messages in its queue. For example, it might retry every 15 minutes. After four hours, it will usually send you a piece of mail that tells you there is some sort of problem. After five days, most send mail configurations give up and return the mail to you undelivered. The actual conversation that an e-mail client has with an SMTP server is incredibly simple and human readable. It is specified in public documents called Requests For Comments (RFC), and a typical conversation looks something like this: Hello test250 mx1.mindspring.com Hello abc.sample.com [220.57.69.37], pleased to meet you Mail from: [email protected] 250 2.1.0 [email protected]... Senders ok Rcpt to: [email protected] 250 2.1.5 jsmith... Recipient ok Data 354 Enter mail, end with "." on a line by itself from: [email protected] to:[email protected] Subject: testing John, I am testing.... 250 2.0.0 e1NMajH24604 Message accepted for delivery Quit 221 2.0.0 mx1.mindspring.com closing connection Connection closed by foreign host. What the e-mail client says is in blue, and what the SMTP server replies is in green. The e-mail client introduces itself, indicates the "from" and "to" addresses, delivers the body of the message and then quits. You can, in fact, telnet to a mail server machine at port 25 and have one of these dialogs yourself -- this is how people "spoof" e-mail. You can see that the SMTP server understands very simple text commands like HELO, MAIL, RCPT and DATA. The most common commands are:

· · · · · · · · · · ·

HELO - introduce yourself EHLO - introduce yourself and request extended mode MAIL FROM: - specify the sender RCPT TO: - specify the recipient DATA - specify the body of the message (To:, From: and Subject: should be the first three lines.) RSET - reset QUIT - quit the session HELP - get help on commands VRFY - verify an address EXPN - expand an address VERB - verbose

Newsgroup Newsgroups are electronic meeting places where people with a similar interest have conversations. These conversations occur over a period of time - often days or weeks. Each newsgroup usually has a specific topic or focus that is reflected in its name. Users post questions with the hope that someone in the group has the knowledge and expertise to assist them and will reply. Messages posted on a subject that is not the focus of the group are

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know as off-topic posts and are frowned upon by the membership. Newsgroups can be significant sources of information and access to other people’s knowledge. This is the reason a newsgroup reader is part of the Knowledge Workshop tool set. Conversations around a particular topic or question are called threads. They start with a single post and grow as others contribute messages. The reply to the first message appears below and indented from it in the displayed list. Other replies to the first message are listed directly below and in line with the first reply. Users may post a reply to a reply, creating an indented message beneath it, and so on. Newsgroup messages are stored on a news server maintained by the organization that created the newsgroup. Many newsgroups are public but some have restricted access and require you to enter a username and password issued by the newsgroup host. The server may host many different newsgroups. To see the list of newsgroups you must first connect to the news server and request the list. You then choose the newsgroups you are interested in and subscribe to them. Once subscribed, you can open the newsgroup in Knowledge Workshop. The first time you open the newsgroup the most current messages (up to 300) are copied to your computer where you can read and reply to them.

FTP FTP or File Transfer Protocol is used to connect two computers over the Internet so that the user of one computer can transfer files and perform file commands on the other computer. Specifically, FTP is a commonly used protocol for exchanging files over any network that supports the TCP/IP protocol (such as the Internet or an intranet). There are two computers involved in an FTP transfer: a server and a client. The FTP server, running FTP server software, listens on the network for connection requests from other computers. The client computer, running FTP client software, initiates a connection to the server. Once connected, the client can do a number of file manipulation operations such as uploading files to the server, download files from the server, rename or delete files on the server and so on. Any software company or individual programmer is able to create FTP server or client software because the protocol is an open standard. Virtually every computer platform supports the FTP protocol. This allows any computer connected to a TCP/IP based network to manipulate files on another computer on that network regardless of which operating systems are involved (if the computers permit FTP access). There are many existing FTP client and server programs. FTP runs exclusively over TCP. FTP servers by default listen on port 21 for incoming connections from FTP clients. A connection to this port from the FTP Client forms the control stream on which commands are passed to the FTP server from the FTP client and on occasion from the FTP server to the FTP client. For the actual file transfer to take place, a different

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connection is required which is called the data stream. Depending on the transfer mode, the process of setting up the data stream is different. In active mode, the FTP client opens a random port (> 1023), sends the FTP server the random port number on which it is listening over the control stream and waits for a connection from the FTP server. When the FTP server initiates the data connection to the FTP client it binds the source port to port 20 on the FTP server. In passive mode, the FTP Server opens a random port (> 1023), sends the FTP client the port on which it is listening over the control stream and waits for a connection from the FTP client. In this case the FTP client binds the source port of the connection to a random port greater than 1023. While data is being transferred via the data stream, the control stream sits idle. This can cause problems with large data transfers through firewalls which time out sessions after lengthy periods of idleness. While the file may well be successfully transferred, the control session can be disconnected by the firewall, causing an error to be generated. When FTP is used in a UNIX environment, there is an often-ignored but valuable command; "reget" (meaning "get again") that will cause an interrupted "get" command to be continued, hopefully to completion, after a communications interruption. The principle is obvious—the receiving station has a record of what it got, so it can spool through the file at the sending station and re-start at the right place for a seamless splice. The converse would be "reput" but is not available. Again, the principle is obvious: The sending station does not know how much of the file was actually received, so it would not know where to start. The objectives of FTP, as outlined by its RFC, are:

·

To promote sharing of files (computer programs and/or data).

·

To encourage indirect or implicit use of remote computers.

·

To shield a user from variations in file storage systems among different hosts.

·

To transfer data reliably, efficiently.

Criticism of FTP 1.

Passwords and file contents are sent in clear text, which can be intercepted by eavesdroppers. There are protocol enhancements that circumvent this.

2.

Multiple TCP/IP connections are used, one for the control connection, and one for each download, upload, or directory listing. Firewall software needs additional logic to account for these connections.

3.

It is hard to filter active mode FTP traffic on the client side by using a firewall, since the client must open an arbitrary port in order to receive the connection. This problem is largely resolved by using passive mode FTP.

4.

It is possible to abuse the protocol's built-in proxy features to tell a server to send data to an arbitrary port of a third computer; see FXP.

5.

FTP is a high latency protocol due to the number of commands needed to initiate a transfer.

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6.

No integrity check on the receiver side. If transfer is interrupted the receiver has no way to know if the received file is complete or not. It is necessary to manage this externally for example with MD5 sums or cyclic redundancy checking.

7.

No error detection. FTP relies on the underlying TCP layer for error control, which uses a weak checksum by modern standards.

8.

No date/timestamp attribute transfer. Uploaded files are given a new current timestamp, unlike other file transfer protocols such as SFTP, which allow attributes to be included. There is no way in the standard FTP protocol to set the time-last-modified (or time-created) date stamp that most modern file systems preserve. There is a draft of a proposed extension that adds new commands for this, but as of yet, most of the popular FTP servers do not support it.

Security problems The original FTP specification is an inherently insecure method of transferring files because there is no method specified for transferring data in an encrypted fashion. This means that under most network configurations, user names, passwords, FTP commands and transferred files can be "sniffed" or viewed by anyone on the same network using a packet sniffer. This is a problem common to many Internet protocol specifications written prior to the creation of SSL such as HTTP, SMTP and Telnet. The common solution to this problem is to use either SFTP (SSH File Transfer Protocol), or FTPS (FTP over SSL), which adds SSL or TLS encryption to FTP as specified in RFC 4217 FTP return codes FTP server return codes indicate their status by the digits within them. Brief explanations of various digits’ meanings are given below: 1.

1yz: Positive Preliminary reply. The action requested is being initiated but there will be another reply before it begins.

2.

2yz: Positive Completion reply. The action requested has been completed. The client may now issue a new command.

3.

3yz: Positive Intermediate reply. The command was successful, but a further command is required before the server can act upon the request.

4.

4yz: Transient Negative Completion reply. The command was not successful, but the client is free to try the command again as the failure is only temporary.

5.

5yz: Permanent Negative Completion reply. The command was not successful and the client should not attempt to repeat it again.

·

x0z: The failure was due to a syntax error.

·

x1z: This response is a reply to a request for information.

·

x2z: This response is a reply relating to connection information.

·

x3z: This response is a reply relating to accounting and authorization.

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·

x4z: Unspecified as yet

·

x5z: These responses indicate the status of the Server file system vis-a-vis the requested transfer or other file system action

Many sites that run FTP servers enable so-called "anonymous ftp". Under this arrangement, users do not need an account on the server. The user name for anonymous access is typically 'anonymous' or 'ftp'. This account does not need a password. Although users are commonly asked to send their email addresses as their passwords for authentication, usually there is trivial or no verification, depending on the FTP server and its configuration. Internet Gopher has been suggested as an alternative to anonymous FTP, as well as Trivial File Transfer Protocol. Data format While transferring data over the network, several data representations can be used. The two most common transfer modes are:

·

ASCII mode

·

Binary mode

The two types differ in the way they send the data. When a file is sent using an ASCII-type transfer, the individual letters, numbers, and characters are sent using their ASCII character codes. The receiving machine saves these in a text file in the appropriate format (for example, a Unix machine saves it in a Unix format, a Macintosh saves it in a Mac format). Hence if an ASCII transfer is used it can be assumed plain text is sent, which is stored by the receiving computer in its own format. Translating between text formats entails substituting the end of line and end of file characters used on the source platform with those on the destination platform, e.g. a Windows machine receiving a file from a Unix machine will replace the line feeds with carriage return-line feed pairs. ASCII transfer is also marginally faster, as the highest-order bit is dropped from each byte in the file. Sending a file in binary mode is different. The sending machine sends each file bit for bit and as such the recipient stores the bit stream as it receives it. Any form of data that is not plain text will be corrupted if this mode is not used. By default, most FTP clients use ASCII mode. Some clients try to determine the required transfer-mode by inspecting the file's name or contents. The FTP specifications also list the following transfer modes: 1.

EBCDIC mode

2.

Local mode

In practice, these additional transfer modes are rarely used. They are however still used by some legacy mainframe systems. FTP and web browsers Most recent web browsers and file managers can connect to FTP servers, although they may lack the support for protocol extensions such as FTPS. This allows manipulation of remote files over FTP through an interface similar to that used for local files. This is done via an FTP URL, which takes the form ftp(s):// (e.g., [2]). A password can optionally be given in the URL, e.g.:

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ftp(s)://:<password>@:<port>. Most web-browsers require the use of passive mode FTP, which not all FTP servers are capable of handling. Some browsers allow only the downloading of files, but offer no way to upload files to the server.

FTP over SSH FTP over SSH refers to the practice of tunneling a normal FTP session over an SSH connection. Because FTP uses multiple TCP connections (unusual for a TCP/IP protocol that is still in use), it is particularly difficult to tunnel over SSH. With many SSH clients, attempting to set up a tunnel for the control channel (the initial client-to-server connection on port 21) will only protect that channel; when data is transferred, the FTP software at either end will set up new TCP connections (data channels) which will bypass the SSH connection, and thus have no confidentiality, integrity protection, etc. If the FTP client is configured to use passive mode and to connect to a SOCKS server interface that many SSH clients can present for tunneling, it is possible to run all the FTP channels over the SSH connection. Otherwise, it is necessary for the SSH client software to have specific knowledge of the FTP protocol, and monitor and rewrite FTP control channel messages and autonomously open new forwarding for FTP data channels. Version 3 of SSH Communications Security's software suite, and the GPL licensed FONC are two software packages that support this mode. FTP over SSH is sometimes referred to as secure FTP; this should not be confused with other methods of securing FTP, such as with SSL/TLS (FTPS). Other methods of transferring files using SSH that are not related to FTP include SFTP and SCP; in each of these, the entire conversation (credentials and data) is always protected by the SSH protocol.

HTTP The Hypertext Transfer Protocol (HTTP) is the foundation protocol of the World Wide Web (WWW). The name is somewhat misleading in that HTTP is not a protocol for transferring hypertext; rather, it's a protocol for transmitting information with the efficiency necessary for making hypertext jumps. The data transferred by the protocol can be plain text, hypertext, audio, images, or any type of Internet-accessible information.HTTP is a transaction-oriented client/server protocol. The most typical use of HTTP is between a web browser and a web server. To provide reliability, HTTP makes use of TCP. Nevertheless, HTTP is a "stateless" protocol; each transaction is treated independently. A typical implementation creates a new TCP connection between client and server for each transaction and then terminates the connection as soon as the transaction completes, although the specification doesn't dictate this one-to-one relationship between transaction and connection lifetimes.The stateless nature of HTTP is well suited to its typical application. A normal session of a user with a web browser involves retrieving a sequence of web pages and documents. Ideally, the sequence is performed rapidly, and the locations of the various pages and documents may include a number of widely distributed servers. Another important feature of HTTP is flexibility in the formats that it can handle. When a client issues a request to a server, it may include a prioritized list of formats that it can handle, and the server replies with the appropriate format. For example, a lynx browser can't handle images, so a web server need not transmit any images on web pages to this browser.

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This arrangement prevents the transmission of unnecessary information and provides the basis for extending the set of formats with new standardized and proprietary specifications. Illustration: 62 Illustrates three examples of HTTP operation.

Examples of HTTP operation. The simplest case is one in which a user agent establishes a direct connection with an origin server. The user agent is the client that initiates the request, such as a web browser being run on behalf of an end user. The origin server is the server on which a resource of interest resides; an example is a web server at which a desired home page resides. For this case, the client opens a TCP connection that's end-to-end between the client and the server. The client then issues an HTTP request. The request consists of a specific command (referred to as a method), a URL, and a message containing request parameters, information about the client, and perhaps some additional content information.When the server receives the request, it attempts to perform the requested action and then returns an HTTP response. The response includes status information, a success/error code, and a message containing information about the server, information about the response itself, and possibly body content. The TCP connection is then closed.The middle part of shows a case in which there is no end-to-end TCP connection between the user agent and the origin server. Instead, there are one or more intermediate systems with TCP connections between logically adjacent systems. Each intermediate system acts as a relay, so that a request initiated by the client is relayed through the intermediate systems to the server, and the response from the server is relayed back to the client. Three forms of intermediate system are defined in the HTTP specification: proxy, gateway, and tunnel. Illustration: 63

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Intermediate HTTP systems.

Proxy A proxy acts on behalf of other clients, presenting requests from the other clients to a server. The proxy acts as a server in interacting with a client and as a client in interacting with a server. Several scenarios call for the use of a proxy: 1. Firewall. The client and server may be separated by a firewall, with the proxy on the client side of the firewall. Typically, the client is part of a network secured by the firewall and the server is external to the secured network. In this case, the server must authenticate itself to the firewall to set up a connection with the proxy. The proxy accepts responses after they have passed through the firewall. 2. Different versions of HTTP. If the client and server are running different versions of HTTP, the proxy can implement both versions and perform the required mapping. In summary, a proxy is a forwarding agent—receiving a request for a URL object, modifying the request, and forwarding the request toward the server identified in the URL.

Gateway A gateway is a server that appears to the client as if it were an origin server. It acts on behalf of other servers that may not be able to communicate directly with a client. There are several scenarios in which servers can be used:

·

Firewall. The client and server may be separated by a firewall, with the gateway on the server side of the firewall. Typically, the server is connected to a network

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protected by a firewall, with the client external to the network. In this case, the client must authenticate itself to the proxy, which can then pass the request to the server.

·

Non–HTTP server. Web browsers have a built-in capacity to contact servers for protocols other than HTTP, such as FTP and Gopher servers. This capability can also be provided by a gateway. The client makes an HTTP request to a gateway server. The gateway server then contacts the relevant FTP or Gopher server to obtain the desired result. This result is then converted into a form suitable for HTTP and transmitted back to the client.

Tunnel Unlike the proxy and the gateway, the tunnel performs no operations on HTTP requests and responses. Instead, a tunnel is simply a relay point between two TCP connections, and the HTTP messages are passed unchanged—as if there were a single HTTP connection between user agent and origin server. Tunnels are used when there must be an intermediary system between client and server but it's unnecessary for that system to understand the contents of any messages. An example is a firewall in which a client or server external to a protected network can establish an authenticated connection, and then maintain that connection for purposes of HTTP transactions.

Cache Returning to the lowest portion of the figure shows an example of a cache. A cache is a facility that may store previous requests and responses for handling new requests. If a new request arrives that's the same as a stored request, the cache can supply the stored response rather than accessing the resource indicated in the URL. The cache can operate on a client or server or on an intermediate system other than a tunnel. In intermediary B has cached a request/response transaction, so that a corresponding new request from the client need not travel the entire chain to the origin server, but instead is handled by B. Not all transactions can be cached, and a client or server can dictate that a certain transaction may be cached only for a given time limit.

Request Messages A request message is sent by an agent to a server to request some action. These are the possible actions, called methods: Method

Description

OPTIONS

A request for information about the options available.

GET

A request to retrieve information.

HEAD

Like a GET except that the server's response must not include an entity body; all of the header fields in the response are the same

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as if the entity body were present. This enables a client to get information about a resource without transferring the entity body. POST

A request to accept the attached entity as a new subordinate to the identified URL.

PUT

A request to accept the attached entity and store it under the supplied URL. This may be a new resource with a new URL, or a replacement of the contents of an existing resource with an existing URL.

DELETE

Requests that the origin server delete a resource.

TRACE

Requests that the server return whatever is received as the entity body of the response. This can be used for testing and diagnostic purposes.

Response Messages A response message is returned by a server to an agent in response to a request message. It may include an entity body containing hypertext-based information. In addition, the response message must specify a status code, which indicates the action taken on the corresponding request. Status codes are organized into the following categories: Category

Description

Informational

The request has been received and processing continues. No entity body accompanies this response.

Successful

The request was successfully received, understood, and accepted.

Redirection

Further action is required to complete the request.

Client Error

The request contains a syntax error or the request cannot be fulfilled.

Server Error

The server failed to fulfill an apparently valid request.

Internet Databases WAIS

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A wide area interoperability system (WAIS) interconnects communications systems over existing network infrastructure - allowing users of disparate radios, telephones, satellite phones, and dispatch centers to communicate with each other locally, Regionally, or in systems that span entire states. Benefits ·

Provides a wide area interoperability communications platform for critical incident command and control that is easily scalable.

·

Allows efficient use of existing network resources with commercial- off-the-shelf (COTS) equipment and proven Radio over IP (RoIP)/ Voice over IP (VoIP) technology.

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Provides remote access from any point on the network. Authorized users may configure, control, and monitor unselected audio and communicate with any entity via selected audio.

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Allows disparate radio systems to be connected locally, regionally, statewide, or in a cross nation network.

·

WAIS Controller software’s user-friendly interface presents clearly the state of the system and allows operators to make and break connections swiftly.

The JPSWAIS is a wide area interoperability solution that links multiple communication devices through an IP network. The system is managed via the WAIS Controller software, the system’s graphical user interface (GUI). AWAIS may range in size from just a few sites to an entire statewide system or larger. Fixed sites and mobile platforms can be integrated, provided they have an access point into the network. Any number of control points, equipped with the WAIS Controller, can be installed; each may control the entire system or any portion of it. Operators stationed at the control points can easily monitor communications and form or disband multiple user talk groups anywhere on the system. Each control point can have its own password-protected permission set, customized to include the specific sites or modules that they need to control. As a safety feature, system administrators may be given full authorization, allowing them to control the entire system or temporarily take over for another operator from any control station. WAIS Architecture Most WAIS end users interface the system via the industry standard radio interoperability gateway, the JPS ACU-1000. The ACU-1000 is the centerpiece for local interoperability; its modular design is customizable to accommodate disparate communication devices. Any number of these fully functional independent local systems, along with dispatch positions and other communications assets, are linked over a network to create a WAIS. The number of network audio links from each local interoperability system (LIS) may be adjusted to suit system requirements. Single, independent users, dispatchers, operators or radio Systems not part of an LIS can connect to the WAIS using JPS’s NXU-2A. WAIS Controller Software A PC application called WAIS Controller provides the GUI for the WAIS. It monitors all system elements to keep operators apprised on the state of the entire system in real time. The WAIS Controller software provides an Overview screen, which manages connections among any set of sites desired, or the operator can switch to the Local View at times when it is necessary to

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focus on activity for a single site. Making and breaking connections are simple using the point and- click interface. All sites in the WAIS can have their own graphical icon, making it easy to identify each site at a glance. The WAIS Controller has a library of preset icons, but custom icons can be added. Capabilities

· · · · · · ·

LAN, WAN, or the Internet can be used to link sites Multiple vocoders available; allows optimization of bandwidth used versus features required Distributed design approach eliminates single points of failure and Ensures reliable communications New control points or system users can be added at any time to any point in the network Local Interoperability Systems remain operational in the event of network failure Pre-installed icon library to customize software interface Software password protection for controlled access

Illustration: 64

Photo caption: Upper: A WAIS local interoperability site featuring the ACU-1000 Middle: A local view WAIS Controller GUI screen. Bottom:WAIS sample block diagram. Illustration: 65

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Internet Databases: Archie Archie was the first search engine ever invented, designed to index FTP archives, allowing people to find specific files. The original implementation was written in 1990 by Alan Emtage, Bill Heelan, and Peter J. Deutsch, then students at McGill University in Montreal. The earliest versions of Archie simply contacted a list of FTP archives on a regular basis (contacting each roughly once a month, so as not to waste too much resources on the remote servers) and requested a listing. These listings were stored in local files to be searched using the UNIX grep command. Later, more efficient front- and back-ends were developed, and the system spread from a local tool, to a network-wide resource, to a popular service available from multiple sites around the Internet. Such archie servers could be accessed in multiple ways: using a local client (such as archie or xarchie); telneting to a server directly; sending queries by electronic mail; and later via World Wide Web interfaces. The name derives from the word "archive", but is also associated with the comic book series of the same name. This was not originally intended, but it certainly acted as the inspiration for the names of Jughead and Veronica, both search systems for the Gopher protocol, named after other characters from the same comics.

Internet Databases: Gopher Gopher is a distributed document search and retrieval network protocol designed for the Internet. Its goal is to function as an improved form of Anonymous FTP, with features similar to that of the World Wide Web. The Gopher protocol offers some features not natively supported by the Web and imposes a much stronger hierarchy on information stored on it. Its text menu interface is well-suited to

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computing environments that rely heavily on remote computer terminals, common in universities at the time of its creation. Some consider it to be the superior protocol for storing and searching large repositories of information. The World Wide Web was in its infancy in 1991, and Gopher services quickly became established. However, by the late 1990s, Gopher had almost disappeared. Insofar as information management is concerned, the progress from Gopher to the web as a standard can be seen simply as a natural progression from text-based to graphical interfaces. Several other factors contributed to the acceleration of Gopher's decline: ·

In February of 1993, the University of Minnesota announced that it would charge licensing fees for the use of its implementation of the Gopher server. As a consequence of this some users suspected that a licensing fee would be also charged for independent implementations. In contrast, there was no such limitation on the World Wide Web. The University of Minnesota eventually re-licensed its Gopher software under the GNU GPL.

·

Gopher's functionality was quickly duplicated by early Web browsers, such as Mosaic. Furthermore, the greater flexibility of the Web's HTML, and particularly its integration of text and graphics, encouraged the migration of content from Gopher to the World Wide Web.

·

Gopher has an inflexible structure when compared to the free-form HTML of the Web. With Gopher, every document has a defined format and type, and the typical user must navigate through a single server-defined menu system to get to a particular document. Many people did not like the artificial distinction between menu and fixed document in the Gopher system, and found the Web's open-ended flexibility much more useful for constructing interrelated sets of documents and interactive applications.

Availability of Gopher today As of 2006, there are fewer than 1000 gopher servers on the internet. Many of them are owned by universities in various parts the world. Most of them are neglected and rarely updated except for the ones run by enthusiasts of the protocol. A handful of new servers are set up every year by hobbyists - 25 have been set up and added to Flood gap’s list since 1999 and possibly some more that haven't been added. Today Gopher exists as an almost forgotten corner of the internet - one can publish email addresses in plaintext without having to worry about spam, and publish large amounts of files without the risk of the server's bandwidth becoming saturated, while at the same time people do still browse the gopher servers regularly. Some have suggested that the bandwidth-sparing simple interface of Gopher would be a good match for mobile phones and Personal digital assistants (PDAs), but so far, the market prefers Wireless Markup Language (WML)/Wireless Application Protocol (WAP), DoCoMo i-mode, XHTML Basic or other adaptations of HTML and XML. The PyGopherd server, however, provides a built-in WML front-end to Gopher sites served with it. The Microsoft Windows Vista operating system (2007) has dropped support for the Gopher protocol. Gopher characteristics

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A Gopher system consists of a series of hierarchical menus. The choice of menu items and titles is set by the administrator of the server. Illustration: 66

The top level menu of a Gopher server. Selecting the "Fun and Games" menu item...

Illustration: 67

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... takes the user to the "Fun and Games" menu.

Similar to a file on a Web server, a file on a Gopher server can be linked to as a menu item from any other Gopher server. Many servers take advantage of this inter-server linking to provide a directory of other servers that the user can access. Illustration: 68

Gopher support in Web browsers

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Mozilla Fire fox 1.5 displaying the top-level menu of the Floodgap gopher server Gopher support was disabled in Internet Explorer versions 5.* and 6 for Windows in June 2002 by a patch meant to fix a security vulnerability in the browser's Gopher protocol handler; however, it can be re-enabled by editing the Windows registry. In Internet Explorer 7, Gopher support was removed on the WinINET level. Internet Explorer for Mac (only on PowerPC architecture and in End-of-life) still supports Gopher. Other browsers, including Mozilla and AOL, still support the protocol, but incompletely — the most obvious deficiency is that they cannot display the informational text found on many Gopher menus. Konqueror needs a plug-in to be installed for full Gopher support. Mozilla Firefox has full Gopher support as of release 1.5 and partial support in previous versions. The Sea Monkey Internet suite, successor of the Mozilla all-in-one suite, also supports Gopher fully, as does Camino, a browser based on Mozilla's engine. Such Mozilla based browsers are able to display embedded images from a gopher server on an HTTP-based HTML document and follow download links to a gopher server. However, the most extensive gopher support is offered in Lynx, a text based browser. The Safari Web browser does not support Gopher at all while Opera requires the use of a proxy such as Squid. UNIX Gopher client A purpose-made open source gopher client for gopher exists. This is simply called gopher and is available in most Linux software repositories and source packages are available on the internet as well as some gopher servers. This client has the ability to fetch additional details about the files such as their size and their owner. Gopher to HTTP gateways Users of Web browsers that have incomplete or no support for Gopher can access content on Gopher servers via a server gateway that converts Gopher menus into HTML. One such server is at Floodgap.com. By default any Squid cache proxy server will act as a Gopher to HTTP gateway. Some Gopher servers, like PyGopherd, also have built-in Gopher to HTTP interfaces.

What is the “World Wide Web?” The World Wide Web is a global, seamless environment in which all information (text, images, audio, video, computational services) that is accessible from the Internet can be accessed in a consistent and simple way by using a standard set of naming and access conventions Whew! Quite a statement, but it is true, and it exists today. You are on the Web now consider.... You can access sites all over the world. You can connect from your desktop to thousands of Web servers simply by "clicking" on a selection (the underlined words), or by entering a specific address. You can connect to many different types of systems - and not be aware of the differences

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You can access many different types of information - text, images (like the heading on this page, and the diagrams we'll use), audio, video, computational services again, usually with no extra work on your part You are using a single Web-browser to do this. One tool accessing many different types of systems, information across the world! Already we can see some of the unique aspects of the Web that make it so popular:

·

it is easy to use

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it is easy to move from place to place

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it combines words, graphics....even sound and movies - any data type!

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there are many tools (like this browser) that make the Web easy to use

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it is easy to publish information

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and there are millions of people using it now - and more every day!

The Web was initially conceived by Tim Berners-Lee and others at CERN. The scientists at CERN needed access to a wide variety of information on many different, distributed, computers. Berners-Lee had this idea of universal readership, which is that any client should be able to read any information. Berners-Lee developed the basis ideas, which others have since added to. Then those involved agreed to work by a common set of principles: 1.

There would be no central control. The Web works because people work within the agreed-to guidelines. As part of this the Web ethic is that anyone can publish, and anyone (who is authorized) can read information.

2.

All Web servers would use the same protocols/mechanisms....

3.

1.

http, a fast, stateless, extensible transport mechanism would be used to communicate within the Web

2.

http, or http daemons, would be the base Web server - receiving messages and providing data as requested

3.

URLs (Universal addressing

4.

all Web browsers would use the same basic language - Hypertext Markup Language HTML

Resource

Locator)

would

be

used

for

network-wide

And built into the mechanisms is support for format negotiation. Web clients tell servers what formats they can handle, and Web viewers allow basic browsers to use different formats

We'll look at those mechanisms in more detail in a few minutes. But one of the most important factors in the success of the Web is that it is built on the Internet, so next we'll look at the relationship between the Web and the Internet. The Web and the Internet

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The basis for the Web is the Internet. The Web is built on the Internet, and makes use of many of the mechanisms the Internet provides. The Internet is the physical aspects - computers, networks, services. It allows us to connect to thousands of other computers across the world. But it doesn't mean that those systems users' can look at, and understand, the information there. The Web is an abstraction and common set of services on top of the Internet. It is the set of protocols and tools that let us share information with each other. The Web was developed with the concept of "universal readership" any participating system should be able to read the information on any connected system using a common set of tools browsers servers/gateways addressing schemes common protocols format negotiation Illustration: 69

This is a generalized picture, but shows many aspects of the physical net. Your system, which has a unique number assigned to it (an IP address), is connected to an Internet Service Provider, possibly through a dial-in modem, or by a direct connection. There are currently about 2,300 of these ISPs in the States, most of which run local networks of their own with multiple Points of Presences (POPs), allowing you to dial in to a local number, even if your ISP is not located nearby. The ISP in turn is connected to other providers, and eventually to one of the big carriers, who have huge networks that use fiber optic cables running at 45 mb/second (these are referred to as T3s). At the other end there is probably an ISP who gets a request you made to a specific web address, and who will route it to the server at that address, which then does its magic, and sends you back what you asked for - again using the various pieces of the network we just went through. How the Web is Used Today

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The Web is used in many creative and interesting ways today, and new uses are being introduced nearly daily. This page contains links to some examples of how the Web is used. Many of these pages are available for you to use at any t ime, as a part of Web Central:

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By companies all over the World ·

for external communication...

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to share product information

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to learn about the marketplace

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to share in process work with business partners

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and for internal sharing of information....

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by business people....

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for education at all levels....

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by technical people....

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for reference Information

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for online news...

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to provide financial information...

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by lawyers....

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for library information...

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for government information...

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for personal services...

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and for information about the Web itself!

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..and for some unusual reasons...

Illustration: 70

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Let's look at that simplified view in a little more detail. This has the same basic components, but we've now added a new server path, which can be one that goes through a firewall, and/or which accesses applications. A firewall is a mechanism to control access to and from Web servers. Most companies have firewalls set up to prevent access to their internal servers from external clients.

Illustration: 71

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There are many different clients, such as Netscape or Microsoft's Explorer. The Web client usually sends an http message, but as the diagram shows it can send any Internet message (e.g. ftp, file, gopher, wais). The servers can be behind a firewall, which is a way to prevent access to a server. Servers can include gateways which allow them to "talk" to applications. These gateways can be in any computing language, the most common being perl and TCL, but C and other languages are also used. Finally, the components know how to find documents because they all use a standard addressing scheme, or URLs. Note that there is no central control. Anyone can create a Web server, and for the most part anyone can read what is online. The reason it all works is because everyone is using the same set of "standards".

Illustration: 72

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World Wide Web Servers The phrase "World-Wide Web" is often used to refer to the collective network of servers speaking HTTP as well as the global body of information available using the protocol. In a May 1996 survey Netcraft found 193,150 servers on the Web (and who knows how many more exist behind corporate firewalls?). A Web client (or browser) sends requests to a Web server. Every retrievable piece of information on the Web is identified by a URL, which includes the name of the object, where it is located, and the protocol used to get it. Only information on a server (or your local system) is part of the Web. You need to "publish it" (i.e. put it on a Web server) to make it accessible. The Web server is responsible for document storage and retrieval. It sends the document requested (or an error message) back to the requesting client. The client interprets and presents the document. The client is responsible for document presentation. The language that Web clients and servers use to communicate with each other is called the Hypertext Transfer Protocol (HTTP). All Web clients and servers must be able to speak

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HTTP in order to send and receive hypermedia documents. For this reason, Web servers are often called HTTP servers, or HTTP Daemons (HTTPD).

A Sample Web Request

·

In this example you are using a browser (Netscape, or Mosaic, or some other browser) and you click on a reference to Webmaster Magazine Online. The browser is able to figure out that what you really want (in Web terminology) is the object the Web knows as http://www.cio.com/WebMaster/wmhome.html - the Web address (or URL) for Webmaster Magazine Online.

Illustration: 73

A typical transaction between Web servers and clients.

·

The browser sends your request to the right server. How it figures out what that machine is, and where it is, is beyond this discussion, but gets us into looking at name servers and other tools which keep track of domain names, address names, and phys ical locations. Let's trust that some bit of magic occurs, and the browser can send your request off to the machine that handles requests for www.cio.com. In the message it sends there is a lot of information you don't need to see, like the method to be used, the URL, possibly parameters (used when you want to pass a search string, for example), and other information.

·

When it gets to the server the Web server, also known as the http (which stands for http daemon) takes over. It knows where it stores Web objects, and it tracks down the one you asked for. It might pass your request off to another process (like a sea rich engine or an application), and wait for a reply. When it gets what it asked for, it sends the object back to your browser.

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If the document contains several Web objects (for example, this document includes several different graphic files as well as the HTML you are reading, each of which is a separate object), the server will send each of these objects back individually.

·

Your browser collects together the different pieces you requested. A Web page can have references to objects all over the net, and may include objects that are on your local system (for example objects that it cached earlier). It pulls them all together , and presents the finished product to you.

Lesson IV 1. Electronic Mail Electronic mail, also known as e-mail, is probably the most common method of using the Internet. You must have access to the Internet to use e-mail. Many teachers can access the Internet through their home institution. This access appears to be "free," but someone, somewhere is paying for the connection. You can also have access from free net systems (similar to a public broadcasting operation where user donations support the system) or commercial providers (e.g., CompuServe, AOL, Prodigy). Many of the latter exist, and you need to shop wisely to get the most service and access for your money. Once you have access, you also need software so that your computer can talk to other computers; this involves sending commands, receiving and sending mail, and any other general communication functions computers do. You need to install the software, set the parameters, and begin sending and receiving mail. Several e-mail programs exist, and the way they function differs, so it is best to (1) read the instructions and, if they make little or no sense to you, then (2) get someone who already knows how to do this to help you set it up. How does e-mail work? You can send and receive original messages, include parts of messages in other messages, reply to messages, forward messages, and save your messages to a file. These functions are all done by commands, which differ from system to system. It is, therefore, very important to understand how your system works so you do not forward a message to someplace you wish you hadn't. If you hit the "reply" button, make sure you know to what address the message is headed. E-mail addresses are a bit like a teeter-totter with the "@" sign as the fulcrum:

Other Internet Clients: [File Transfer Protocol] ABOUT FTP FTP is short for File Transfer Protocol, this page contains additional information about the FTP command and help using that command in Unix and MS-DOS (Windows). Windows FTP From the MS-DOS prompt or shell type in FTP, once typed in you will have access to the FTP command line. In this command line type: open ftp.address.domain

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Where address is the name of the server and the domain is the domain such as .COM, .NET... In addition, the IP address can be typed in, such as 255.255.255.0. Once connected you will be asked for a username and password; if done successfully, you will have access to transfer files between computers.

FTP Commands Depending upon the version of FTP and the Operating System being used, each of the below commands may or may not work. Generally typing -help or a ? will list the commands available to you. Command !

? abor append ascii bell binary bye cd cdup close cwd dele delete debug dir

disconnect get glob hash help lcd list literal ls

Information Using this command you will have the capability of toggling back and forth between the operating system and ftp. Once back in the Operating System generally typing exit will take you back to the FTP command line. Access the Help screen. Abort Transfer Append text to a local file. Switch to ASCII transfer mode Turns bell mode on / off. Switches to binary transfer mode. Exits from FTP. Changes directory. Change to parent directory on remote system Exits from FTP. Change working directory on remote system Delete file on remote system Deletes a file. Sets debugging on / off. Lists files if connected. dir -C = Will list the files in wide format. dir -1 = Lists the files in bare format in alphabetic order dir -r = Lists directory in reverse alphabetic order. dir -R = Lists all files in current directory and sub directories. dir -S = Lists files in bare format in alphabetic order. Exits from FTP. Get file from the computer connected to. Sets globbing on / off. Sets hash mark printing on / off Access the Help screen and displays information about command if command typed after help. Displays local directory or if path typed after lcd will change local directory. Send a list of file names in the current directory on the remote system on the data connection. Sends command line Lists files if connected.

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mdelete mdir mget mkd mkdir mls mode mput nlst open pass port prompt put pwd quit quote recv retr remotehelp rename rmdir send status trace type user verbose

Multiple delete Lists contents of multiple remote directories Get multiple files Make directory. Make directory. Lists contents of multiple remote directories. Specifies the transfer mode. Available parameters are generally S, B or C. Sent multiple files Send a full directory listing of the current directory on the remote system on the data connection. Opens address. Supplies a user password. Specify the client port number. Enables/disables prompt. Send one file Print working directory Exits from FTP. Send arbitrary ftp command Receive file Get file from remote system. Get help from remote server Renames a file Removes a directory Send single file Shows status of currently enabled / disabled options Toggles packet tracing Set file transfer type Send new user information Sets verbose on / off.

Newsgroup

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Although most of the hype and attention that the Internet gets today is about e-commerce and business, there are two main reasons that most of us use it: communication and information. We rely on the Internet to send e-mail and instant messages, and search through the World Wide Web to find information for work or play.

Illustration: 74

Microsoft's Outlook Express contains a newsgroup client. One source of both information and communication is newsgroups. A newsgroup is a continuous public discussion about a particular topic. You can join a newsgroup at any time to become part of a huge conversation between hundreds or even thousands of people. Newsgroups originated in North Carolina back in 1979. That's when a couple of Duke University students hooked a few computers together to start an exchange of information with other UNIX users. Just down the road at the University of North Carolina in Chapel Hill, another student was writing software that could be used to distribute the information. Eventually, the work of these three students became the first bastion of newsgroups, termed Usenet. Talk Amongst Yourselves Along with e-mail, newsgroups are one of the oldest communication methods on the Internet. But there are many ways to communicate on the Web. You probably use more than one method, depending on your needs. Let's take a look at the different methods and when you might use them: · E-mail - By far the most popular means of communicating over the Internet, e-mail allows you to send a message directly to another person or group of people. Messages can range from short to long and may include quotes or attached files. You can learn more about e-mail in the article How E-mail Works. E-mail is most effective when:

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· · · ·

·

You don't need an immediate answer. You are communicating with a single person or specific group of people. You know with whom you wish to communicate. You need to attach a file or provide extensive information.

Chat - Chat is a conversation between two or more people that takes place in a chat room. The chat room software allows a group of people to type in messages that are seen by everyone in the "room." Chat rooms can be found all over the Internet, including on the America Online service and the Web site TalkCity.com. Chat is most effective when:

· · · · ·

You need an immediate answer. You want to communicate with more than one person. You can communicate in brief messages the information you need to know or wish to provide. You want to meet new people.

Instant messages - Instant messaging is something of a cross between chat and e-mail. It allows you to maintain a list of people that you wish to interact with. You can send messages to any of the people in your list, as long as that person is online. Sending a message opens up a small window where you and your friend can type in messages that each of you can see. Instant messages are most effective when:

· · · · ·

You You You You

need an immediate answer. only need to communicate with a single person or small group. know with whom you wish to communicate. need to communicate in real time.

Newsgroup - As stated earlier, a newsgroup is a continuous public discussion about a particular topic. Newsgroups are decentralized, which means that the messages are not maintained on a single server, but are replicated to hundreds of servers around the world. Newsgroups are most effective when:

· ·

You don't need an immediate answer. You want to communicate with more than one person.

·

You want to communicate with a group of people interested in the same topic. You need or want to provide extensive information about that topic.

· ·

Forum/Discussion Board - Forums and discussion boards are very similar to newsgroups, with one major difference: Most forums and discussions boards are kept on a single server maintained by the owner or originator of the forum or discussion board. Forums or discussion boards are most effective when:

· ·

You don't need an immediate answer. You want to participate in a community that is discussing a particular topic.

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· · ·

You want to communicate with a group of people interested in the same topic. You need or want to provide extensive information about that topic.

Listserv - Most of us probably belong to one listserv or another. Every time you register for a newsletter, such as the free HowStuffWorks newsletter, you are placed on a listserv. Basically, this is a type of broadcast e-mail. Information on a listserv is sent to everyone who is listed in the e-mail group on the server. The biggest difference between a listserv and a newsgroup is that listservs are not interactive. Listservs are most effective when:

· · · ·

You don't need an immediate answer. You want or need regularly updated information about a particular topic. You want to receive information from a group of people interested in the same topic.

Conferencing - Conferencing is like a chat room on steroids. The conference software, such as Microsoft Netmeeting, allows you to have a real-time chat with one or more other users. It also allows you to do such things as share an electronic whiteboard or a software application. Most conferencing-software packages provide several means of communication, including text only, audio and even video. Conferencing is most effective when:

· · · · ·

You need an immediate answer. You want to communicate with more than one person. You can communicate in brief messages the information you need to know or wish to provide. You want to attach files or use the whiteboard function in addition to sending and receiving traditional text messages.

Video - Some users take advantage of a fast connection, such as a cable modem or DSL, in conjunction with a Webcam to communicate by way of video. This method of communication is not common yet, but will probably increase in popularity as the number of users with high-speed connections increases. Video is most effective when:

·

· · ·

You need an immediate answer. You want to visually demonstrate or display information. You and the people you are connecting to have fast connections. IP Telephony - Another emerging communications technology is IP telephony, which uses the Internet in much the same way that a regular telephone uses a phone line. Most IP telephony software requires that each person who wishes to talk have a computer, Internet connection and special software. But some companies, such as Net2Phone, provide software that allows you to call someone directly over the Internet and connect to that person's normal phone. IP telephony is most effective when:

·

You need an immediate answer.

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You have the appropriate equipment (speakers, sound card and microphone). The information you are providing or requesting is easier to convey through talking than through text messaging.

Most of the methods described above require some type of client software on your computer. In most cases, the client software is either free or integrated with another software application. For example, Netscape Navigator and Microsoft's Internet Explorer and Outlook Express each includes a newsgroup reader client that you can use to subscribe to newsgroups. We'll talk more about subscribing to newsgroups later. The News Newsgroups use a lot of special terms to describe the newsgroup process: · Usenet - The primary exchange and listing of newsgroups · Feed or Newsfeed - The group of messages that make up a single newsgroup, sent from one server to another server or to a subscriber · Posting - Entering a message into a newsgroup · Posts or Articles - The messages that are entered into a newsgroup Illustration: 75

Similar to most e-mail programs, you normally can click on the title of a newsgroup post in order to read the message.

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Thread or Threaded discussion - A post and the series of messages replying to it Hierarchies - Category information provided in the name of the newsgroup Newsgroups are categorized according to interest. The name of the newsgroup provides the category information, going from general to specific (left to right). For example, comp.lang.java.programmer is a newsgroup for Java programmers, in the Java section of the language category, which is part of the overall computer category.

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Big Eight - Usenet's original eight newsgroup categories Now, there are thousands of newsgroups in hundreds of categories, but Usenet originally divided newsgroups into one of eight major categories: · · · · · · · ·

comp (computers) humanities (arts and culture) misc (miscellaneous) news (news and current events) rec (recreational) sci (science) soc (social) talk (general discussion)

Ironically, alt (alternate), which is now the biggest general newsgroup category, was not part of the original eight.

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Moderated - A newsgroup that has a person or persons who read all messages before they are posted to the general group and reserve the right to reject a message that they deem inappropriate for the newsgroup Unmoderated - A newsgroup in which any message posted is immediately incorporated into the newsgroup (more common) Flame - A criticism of someone else's post News server - A server that maintains an archive of the messages posted to a newsgroup or series of newsgroups Network News Transfer Protocol (NNTP) - The protocol typically used to transmit newsgroup messages over the Internet UNIX-to-UNIX Copy Protocol (UUCP) - A protocol occasionally used for direct connections between some UNIX servers Newsreader - The client software used to read the posts in a newsgroup, often combined with other software Online - Type of newsreader that maintains a live connection to the news server while it is open Offline - Type of newsreader that connects to the news server just long enough to download the new messages in any newsgroups you subscribe to and then disconnects, reconnecting when you're ready to send new messages

Illustration: 76

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Forte' Incorporated's FreeAgent newsreader is a good example of an offline newsgroup client. The Newsgroup Process A newsgroup begins on a single news server, but is eventually replicated to hundreds or thousands of other servers. News servers provide the infrastructure that makes newsgroups work. Each news server has special software that maintains a file for each newsgroup serviced by that server. Here's what happens when you access a newsgroup:

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Your newsreader, using NNTP, connects to the news server designated in your configuration. Typically, the news server's connection information is provided to you by your Internet Service Provider (ISP). If your ISP does not have a news server, you can refer to a list of publicly accessible news servers. Once the connection is established, your newsreader downloads all of the new messages posted in the newsgroups that you are subscribed to. You read through the messages and decide to reply to a couple. You also decide to start a new thread with a post of your own.

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Illustration: 77

Replying to a post in a newsgroup is as easy as replying to an e-mail.

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Your newsreader sends your messages to the news server. (If it's an offline newsreader, it must first reconnect to the news server via NNTP). The news server saves your messages in the file for that newsgroup. Newsgroup files are large text files, meaning that each new message is simply appended to the end of the text file. As the file reaches a certain size, or after a certain length of time, the messages at the beginning of the file are removed and placed in a newsgroup-archive text file. The news server connects to one or more other news servers using NNTP (or UUCP) and sends the updated information. Each news server compares its own file for the newsgroup with the files it receives for that same newsgroup. It adds any differences that it finds -- this is important, because if the news server simply saved the received file over the one it already had, it would lose any messages posted to it during the update. By comparing the files, it can extract the new messages and add them to the file it has, without losing any new postings. The news server then sends the combined file to the other news servers. The newsgroup changes are replicated to each news server until all of them have the updated information. This process is ongoing, and most large newsgroups change so quickly that the updating is virtually continuous. Other subscribers read your messages, plus all the others posted since the last time they looked at the newsgroup, and reply. You see their replies and new messages, and the process repeats.

Other Internet Clients: Telnet

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All Windows versions include Telnet Client and Telnet Server components. Using Telnet Client and Server, you can create a remote command console session on a host. You can run command line programs, shell commands, and scripts in a remote command console session just as though you were locally logged on to the host and using a local command prompt window. Windows Server 2003 Telnet Client and Server are well suited for troubleshooting and configuring remote computers, especially in mixed environments that require interoperability between different operating systems. For example, you can use Telnet Client to connect to a Telnet server that is running on another operating system such as UNIX. Likewise, you can use a Telnet client that is running on UNIX to connect to a computer running Telnet Server. Windows Server 2003 Telnet Client and Server are also ideal in situations where memory and processor resources are minimal on a client or host or where network bandwidth is limited. This is because computers running Telnet clients and servers use less memory and processor time than other remote management tools, and Telnet clients and servers transmit only plaintext (unencrypted characters) across the network. Understanding Telnet Before using the Windows Server 2003 Telnet tools, you should consider the following: 2.

Windows Server 2003 Telnet Client and Server are based on the Telnet protocol, which specifies a method for transmitting and receiving unencrypted ASCII characters (plaintext) across a network. Understanding how the protocol works, and how Telnet clients and servers use the Telnet protocol, helps you manage Telnet connections.

3.

The Windows Server 2003 Telnet tools have several inherent limitations that affect the types of remote management tasks you can perform and the level of security that is in effect when you perform those tasks. Understanding these limitations helps you determine when and when not to use the Telnet tools.

4.

You can configure Telnet Server settings by using the Windows Server 2003 Telnet administration tool (Tlntadmn.exe) and the registry editor (Regedit.exe). Although the default Telnet Server settings are sufficient for most Telnet client connections, you might need to change the default settings to better suit your organization. Examples of Telnet Server settings include: authentication type, default port assignment for Telnet connections, maximum number of client connections, and maximum number of failed logon attempts.

5.

By default, members of the local administrators group can log on to a Telnet server. However, you might not want all Telnet users to have full administrative control of the host they log on to. In this case, you can use a Telnet clients group to grant users Telnet logon rights without granting them any administrative rights on the host. To configure these user rights from the graphical user interface, you must use the Active Directory Users and Groups snap-in or the Local Users and Groups snap-in. You can also use the Net User and Net Group commands to configure user rights from the command line.

6.

You can configure several optional settings when you use Telnet Client to establish a Telnet session on a host. Depending on the type of Telnet server you are logging on to, and how the Telnet server is configured, you might need to enable or change some of these optional settings. Examples of Windows Server 2003 Telnet Client

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settings include: client-side logging, terminal type, port assignment, and alternate user name for logon.

Note: The information in this document refers to the Telnet Client and Telnet Server components that are installed by default with Windows Server 2003 and Windows XP Professional operating systems. Telnet Architecture Most network operating systems provide a Telnet client and a Telnet server. Telnet clients and servers are small executable programs that allow a local computer (a client) to access services and programs on a remote computer (a host). Telnet clients and servers, including Windows Server 2003 Telnet Client and Telnet Server, are based on the Telnet protocol, which is a subset of the TCP/IP suite and is described in RFC 854. The Telnet protocol specifies two general mechanisms: how Telnet clients and servers establish a connection across a network and how they transmit and receive information across a network. You usually run a Telnet client program on a local computer: for example, a workstation that you are logged on to. You usually run a Telnet server program on a remote computer: for example, a host you want to administer. Telnet client programs initiate connections with Telnet servers. Telnet servers run in the background on a host, listening for Telnet clients to request a connection. Common Telnet Features Because Telnet clients and servers are based on the same standard protocol, all Telnet clients and servers have several features in common. These common features are what make Telnet clients and servers well suited for performing remote administration tasks in environments that require interoperability among disparate operating systems. In short, the Telnet protocol makes it possible for you to connect a computer running Windows Server 2003 Telnet Client to a UNIX Telnet server. The key features that make this interoperability possible include the following: Common communication protocols All Telnet clients and servers use TCP/IP as the underlying communication protocol. This makes Telnet clients and servers particularly useful for remotely administering computers across the Internet or within wide area networks (WANs) that are connected to the Internet. If your network does not support TCP/IP, you will not be able to use a Telnet client or server. Common communication ports TCP port 23 is reserved for Telnet client and server communication. By default, most Telnet clients initiate communication on port 23, and most Telnet servers listen on port 23 for connection requests. You can change the default port assignments with some Telnet client and server software, such as Windows Server 2003 Telnet Client and Server, but port 23 is the universally accepted port for Telnet communication. Common character set for communication

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All Telnet clients and servers are capable of transmitting and receiving a predefined character set consisting of standard ASCII character codes and ASCII control codes. All Telnet clients and servers transmit the ASCII codes across a network in unencrypted form (plaintext).

Common implementation of the Network Virtual Terminal All Telnet clients and servers implement a network virtual terminal (NVT). The NVT is responsible for translating operating system-specific instructions (keyboard codes or display codes) into a consistent set of codes that all Telnet clients and servers can transmit and receive. The NVT is what makes Telnet clients and servers capable of communicating with each other regardless of which operating system they are using. Creating a Telnet Connection To create a Telnet connection between a Telnet client and a Telnet server, you must do the following:

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Start the Telnet Server program on the host. On Windows Server 2003, Telnet Server (Tlntsvr.exe) runs as a service. You can start the service manually every time you want to connect to a host, or you can configure the service so that it starts every time your computer starts. Telnet clients cannot connect to a host unless a Telnet server program (or service) is running and listening for connection requests.

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Run the Telnet Client program on the local computer. When you run Windows Server 2003 Telnet Client (Telnet.exe), you must specify the host to which you want to connect. You can also configure several optional connection settings and features.

When you run a Telnet client, it makes a connection request to the host. If a Telnet server responds to the request, the Telnet client and server negotiate the details of the connection, such as flow control settings, window size, and terminal type. After the connection details are successfully negotiated, and logon credentials are validated, the Telnet server program creates a Telnet command console session. On Windows Server 2003, each Telnet command console session consists of two processes: Tlntsess.exe and Cmd.exe. Tlntsess.exe is responsible for managing the Telnet session. Cmd.exe is the command interpreter, or shell program, that runs commands, programs, or scripts on the host. Note: Cmd.exe is the default command interpreter for a Windows Server 2003 Telnet command console session. However, you can configure the Windows Server 2003 Telnet Server program to use as a default any command interpreter or shell program that is installed on the host.

Running Programs Remotely Using a Telnet Connection After you establish a Telnet connection with Telnet Server, the following message appears in the command prompt window on the client:

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*= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Welcome to Microsoft Telnet Server. *= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = This message indicates that your credentials are valid and that you have an active Telnet session with Telnet Server. Assuming you have the appropriate administrative user rights, you can use this session to remotely run command-line programs, shell commands, and scripts on a host. Telnet client and server processes rely on the Telnet network virtual terminal (NVT) to translate operating system-specific keyboard and display codes to Telnet character codes that all Telnet clients and servers can understand.

Telnet Limitations Telnet connections have several limitations. You can address many of these limitations by changing Windows Server 2003 security and Group Policy settings, but the following limitation cannot be eliminated or modified. You cannot run GUI tools over a Telnet connection Telnet is a character-based communication protocol. It is not designed to transmit cursor movements or graphical user interface information. Because of this, you can only run command line programs, shell commands, scripts, and batch files over a Telnet connection. Some editing programs, such as vi and Edit, can be run over a Telnet connection; however, these interactive programs are not true GUI programs because cursor movement is controlled by the keyboard, not the mouse.

Lesson V: Media & Active Content 7. Object & Active Content The growing popularity of the internet for a wide variety of information exchange and the features that have been developed to meet the demand for increased browser-based functionality have led to growing concern within organizations about their vulnerability to worms, viruses and Trojan horses. In particular, there is concern that these and other types of malicious code can be delivered covertly in programs that contain everything they need to run without requiring the intervention of the user. This type of program has come to be defined as ‘active content’, a term that refers to an object’s ability to act upon and change the way in which a user’s computer operates. The threat In the past there was always a distinction between static data and the programs by which it was called. Today many data objects such as web pages, mail and documents can interleave data and code, allowing dynamic execution of the program and giving external computers a way into the user’s computer. The transparency of the execution and the fact that the program is often called by a browser from a server on a remote website are seen as major potential security risks. Current concern centres round the security question of what happens if the code is malicious. Fears exist about the ability of active content to deliver, for instance,

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Trojans that lie dormant and undetected until triggered to cause widespread damage to an organization’s networks and business credibility, perhaps by stealing passwords, sending email, transferring money and so on – and destroying any information about where they came from. The threat can be summarized as follows: – I send you a program and you run it to get my message. – The running program may be able to do other things with your rights. Users’ fears are exacerbated by the claims of some vendors using terms like ‘the silent killer’ and other hyperbole to talk up the risks associated with code that carries a material threat and exploits other security vulnerabilities of operating systems and weak network design. Delivery of active content The two main technologies associated with the term ‘active content’ are ActiveX controls and Java which provide additional functionality to web pages, both of which are described later in this paper. In fact, the concept of active content goes back much further than either of these technologies. One of the earliest scripting languages, the page description language, PostScript, goes back in its current form to 1982 and is a classic example of active content, offloading the processing and interpretation of the presentation of documents to the printer. The commands are language statements in ASCII text that are translated into the printer’s machine language by a PostScript interpreter built into the printer. In an early example of the inappropriate use of active content, an attacker sent codes that altered the passwords on the receiving printer. Any subsequent jobs not using the password could not print. However, it is through the increased functionality of the browser – the client for web and other Internet servers – that active content has been able to flourish. Browsers and active content Browsers allow code to run in one of three ways. 1 Browser-initiated code In some cases a file can be started by the browser to be executed by the operating system. In this case the browser might download a .DOC file and automatically run Word to process it without the user knowing, unless the “Confirm open after download” has been selected in Windows Explorer, under Options.

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2 Browser-extending codes Some programs are installed on to the hard disk to extend the browser. These include ActiveX controls and Netscape Navigator plug-ins which enable active content by allowing browsers to support different types of content such as audio, video and interactive animation. Some programs exist as both plug-ins and ActiveX controls and this seems likely to increase as Internet Explorer for Windows, versions 5.5 SP 2 and 6.0 no longer supports plug-ins. 3 Browser-interpreted code This third type of browser-using code operates functionally within the browser and includes Java applets, HTML interpreters and interpreters for scripting languages. There is much focus on this area as web pages, which are written in HTML – and increasingly in more powerful XML-based languages, can have embedded within them programs written in scripting languages such as VBScript or JavaScript. Although such languages do not themselves have full access to the system’s resources, they can create a vulnerability as they can invoke, or attempt to invoke, ActiveX controls and/or Java applets as well as other software components such as plug-ins, document macros and other executable files. Because they execute on the browser’s side of the connection instead of the server’s they “move the security risk squarely from the server to the client, thus bringing the problem of security right down to the user’s desktop. In addition, the close binding of the browser to related functionality such as email capability or the underlying operating system means that the security that one might have expected in confining scripting languages to the boundaries of the web browser is not realized. Many people disable “Active scripting”, ie the ability for web pages to run scripts, but in doing so the tradeoff between security and functionality must be carefully weighed.

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Similar security can be achieved by turning off the Windows Scripting Host unless it is specifically needed for running stand-alone scripts. ActiveX ActiveX, announced in March 1996, is built on Microsoft’s COM (Component Object Model) and is a development of its OLE (Object Linking and Embedding) technology for transferring and sharing information among applications. ActiveX allows for the automation of many background tasks and consists of a set of technologies that enable software components to interact with one another in a networked environment, regardless of the language in which the they were created. Although ActiveX can be used in desktop applications and other programs, its primary aim is to allow desktop applications to interact with Microsoft’s Internet Explorer web browser. Netscape Navigator users can also use ActiveX controls but only via plug-ins. ActiveX ‘controls’ are reusable software components based on ActiveX technology. They are executable programs, compiled separately for each target operating system – which are installed on the user’s computer to extend the functionality of the browser by allowing applications to communicate with each other. ActiveX controls can be written in several different languages including Java, C++ and Visual Basic and run in an application program that uses the Component Object Model program interfaces. The controls perform many functions and can be invoked by web pages. They can be downloaded over the web, but many are pre-installed with Windows. When an ActiveX control is called by a web script, email or document, the browser checks to see if it is already installed on the user’s computer. If it is not, the embedded script calls the remote server on which the control is stored in order to download a copy. The browser can be configured to prevent ActiveX controls from being downloaded. However, if the downloading is allowed, the add-on program code is stored locally on the user’s machine and can then be used automatically by local programs or by an HTML page on that machine. It then remains on the client machine. Once an ActiveX control is installed on a user’s system, it has full access to more or less all the system resources, including those relating to the hardware. That a document, usually via an embedded script, can call upon a remote site for its program which is then rendered on the user’s computer causes legitimate worries about security. Germany’s Chaos Computer Club alleged that they had demonstrated a control that could check for the presence of a popular financial package and transfer money from an unknowing user’s bank account to another in Switzerland. Digital signatures ActiveX places no restrictions on what a control can do. Rather it relies on a number of security features built in to the browser and works on the basis that as long as users are as careful about installing ActiveX controls as they should be with .EXE files, the ActiveX should not endanger their system. Web browsers come with a pre-installed list of certifying

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authorities that they trust, the most well-known being VeriSign. The certificates in the list can be viewed, activated/deactivated, installed and deleted.

Internet Explorer’s Authenticode feature, used in conjunction with VeriSign and other certification authorities, allows vendors of ActiveX controls to attach digital signatures to their products. Since version 4.0 which allowed customization, users of Internet Explorer can automatically check whether the certificate has been revoked and can choose to download unsigned software. A company creating an ActiveX control registers with VeriSign or another approved certification authority. After checking the credentials of the company, VeriSign issues a unique certificate to the company using a private key supplied by that company. When the company creates the program it wishes to sign, it activates the signing process by using the key and then appending the certificate. When a browser attempts to invoke the program, it first checks that the program is signed, and if it is, then checks that it comes from a ‘trusted’ company. Recent versions of Internet Explorer allow customization of what ActiveX controls can do, such as preventing scripting languages from interacting with them, and allow users to download controls automatically, disable them or be prompted with a dialog box, based on whether or not they are signed. Indeed, as stated above, the browser can be set to refuse all ActiveX controls.

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The system of digital signatures was introduced so that users can feel certain that the software they are installing is safe by letting them know the publisher and underwriter. This remains, however, essentially a trust model and there remains a risk even if the ActiveX control is digitally signed. The certification process ensures that the control cannot be anonymous (allowing users to trace it back to the owner) and cannot be tampered with by third parties after its publication. However, it does not certify that it is safe. Even if it is issued, owned and used in good faith, just because it is signed does not mean that it does not have a virus. The Exploder ActiveX control developed – and later withdrawn – by Fred McLain was certified but performs a clean shutdown of any Windows 95 machine that downloads it. The weakness in the system is that although additional cryptographic information can be added to a digital signature to add confidence, the company which creates the ActiveX control is the person who initially signs it and sends it for authorisation, and controls can be fraudulently signed. In March 2001, VeriSign revoked two digital certificates that it had issued two months earlier to someone falsely claiming to be a representative of Microsoft. “In this scenario, it is possible that the fraudulent party could create a destru ctive program or ActiveX control, then sign it using either certificate and host it on a web site or distribute it to other web sites. Safe for scripting A further measure of security can be imposed on ActiveX controls to prevent unsafe controls from being initialized or scripted through a feature called ‘safe for scripting’. Controls not marked ‘safe for scripting’ cannot be launched, linked to or invoked from unsafe places like web pages. It was asserted in May 2001 that “of the thousand or so registered controls only 50 to 100 have the marked designation as safe for scripting” ‘Safe for scripting’ allows an ActiveX object to be given a discretionary marker to indicate to the operating system that code such as scripts from other people’s web pages can call it because it does not do anything Permanent, dangerous or dubious. As with digital signatures, not only is the user trusting the author not to have any ill intent, but is also assuming that the code cannot be subverted by others. Another problem is that Microsoft themselves ship their operating system with important and pre-installed ActiveX objects, which users have little choice but to trust. Some ActiveX objects implement an interface – a set of services that can be called from another script or program – with tens or hundreds of functions which users can invoke. Some of these have sub services, such as creating a pop up window, and all the functions need to be safe for the control itself to be safe. It is not surprising that some of the more obscure ones might be overlooked and later abused. This situation of controls believed to be secure and signed as such, but in fact turning out not to be represents a real threat. The VBS/Kakworm virus took advantage of just such a mistake, using a security hole in two Microsoft installed ActiveX controls (scriptlet.typelib and Eyedog) to write an infected file into the Windows startup folder so that it runs on starting Windows. The other danger is that someone can create some

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malicious code, sign it as secure and incorporate a dialog box which will trick users into using it by relying on the well-proven fact that when presented with an OK button as the default option, many users will ignore the ‘Warning’ message and simply click on OK.

Indeed, this is how many Word macro viruses have been successfully spread – relying on what Russel Sanders has referred to as “the blind indifference with which end users treat dialogue boxes that appear to inform them of impending doom.”[2] This is echoed by Chess and Morar who state that “years of security experience show that users are all too ready to push ‘OK’ on a prompt that they do not understand, just to get it out of the way so they can get on with their jobs. Java Java is a cross-platform programming language created by Sun Microsystems in 1995, the ability of its applications to run on many different types of hardware platform being an example of so-called “mobile code”. Java programs are compiled into byte code which does not rely on platform specific instructions (as ActiveX does). They run in a special interpreted software environment called the Java Virtual Machine. Java applications are generally large, full-blown programs which, like other programs, can access any system resources allowed by an organization’s security. Java applets, however, are small programs which are stored on the server side of the connection. It is these which are usually called by web pages, referenced with the tag within HTML documents. Java applets are generally considered to be much safer than ActiveX controls. This is because the Java Virtual Machine within which they execute is inside the browser which creates a protected, limited environment – called the sandbox – where the downloaded applets can run without risking damage to the rest of the system. The applets are restricted in what they are allowed to do by the Java Security Manager. It is possible to have two conflicting sets of security technologies if a web page is hosting two different Java applets running under two different Java Virtual Machines. Applets are not allowed to open network connections to any computer, except for the host that provided the .class (the fundamental unit of Java code) files. Neither can an applet loaded from the web start programs on the client. If an attempt is made to read or write a file, the Java Security Manager determines whether or not it is allowed. It is not possible, for instance, for data to be written to the hard disk. This “software computer” environment allows users to build in controls and because the applet cannot write to the system, one applet cannot leave its mark behind to affect the next applet. Side-effects such as writing to a real hard disk or finding out about the real operating system environment simply are not available. So it cannot, for instance, start some rogue process on the PC to list the contents of the file system. This is why running an application – like the Strange Brew virus – in a browser does not work, because it needs to, but cannot, interact with the real system. Even within the boundaries of the sandbox, however, hostile applets can exist. On 5 August 2000 Dan Brumleve posted the following to the BugTraqmailing list: “I’ve found some security holes in Java and Netscape that allow arbitrary network access and read-access for local files and directories. As a demonstration I’ve written Brown Orifice HTTPD, a web server and file

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sharing tool that runs in Netscape Communicator on all tested platforms.” The flaw allows programmers to tell a Java applet included in the browser to display a directory of what is on the victim’s hard drive. A greater risk, however, comes from the need to allow wider functionality. So although the original scenario meant that untrusted programs can be run but not read/write or access system services, applets can now be digitally signed as safe to run outside the sandbox. The resources a signed applet can access are bounded by ‘permissions’ which are assigned primarily based on where the code came from and the name of the developer. In this case the risks become very similar to those associated with ActiveX controls. As with the these controls, the browser can be set to allow/disallow different functions and permissions, or can disallow all applets.

Approaches to blocking malicious code Although the threats arrive from the outside, the vulnerability is at the desktop and this is where the security mechanisms are focused. The dilemma is how to achieve maximum browser-based, ie client-side, functionality, while protecting the systems from security vulnerabilities. At the browser In reality, in looking at browser security we are talking about the security available through Internet Explorer (although Netscape Navigator provides very similar mechanisms)*. Security models in leading browsers and in the operating systems themselves can provide layers of protection, both in terms of physical security and by assigning/denying access right to particular users or groups of users. Different security settings in the browser give network and systems administrators a great deal of control over what can be received by whom. One caveat is that browsers assume the privileges of whoever logged in – so if this was an administrator, a script – malicious or otherwise – will run with the administrator’s privileges.

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Questions of the security mechanisms, such as digital signatures, built into active content have been dealt with above. These mechanisms are designed to trap any content which might be suspect and to prevent it accessing and compromising the system. Some vendors of content scanning packages believe that this is not sufficient and advocate that the only way that an organization can be secure against malicious code is to install software which will examine the behavior of all traffic on its networks. The argument is that as code such as ActiveX controls can be referenced in a stream of content in web pages, mail and news, the downloaded code should be monitored in real time and the program blocked if a security policy has been violated. While this behavioural analysis approach does have legitimacy, it is also wellknown to lead to completely safe files being falsely identified as malicious and vice-versa. It also brings greater overhead, and slows down performance. There are many other ways in which companies can protect their networks, not least of which is applying operating system patches immediately they are issued by Microsoft. Scanning email at the gateway will prevent malicious code from entering an organization’s network as will blocking certain file types or all files with double extensions, eg by writing a script at the email server, buying specific software which will do it, or requiring one’s ISP (Internet Service Provider) to do it. Installing and keeping up to date anti-virus software at the desktop will provide complete protection at the point of access. Viruses and Trojans, for instance, will each have their own identity and as soon as an attempt is made to run them, the program will be prevented from running. Some vendors raise the concern that PE (Portable Executable) compression utilities such as UPX and Petite can compress files, including of course malicious code, which when unpacked runs directly in memory, thus bypassing anti-virus software. Furthermore, when unpacked the resulting file is not an exact copy of the original, making detection even more difficult. Nevertheless each manifestation will have its own identity – in exactly the same way that variants of other viruses have their own identities – and will be prevented from running as soon as an attempt is made to launch it. A full description of other means by which systems can be protected against malicious code can be found in.

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8. What are the types of Browser Plug-ins The Web Browser Plug-in section of Web Tools contains direct links to information about the most widely used plug-ins and helper applications. A list of online resources is also provided which contains detailed information on these and other plug-ins and helper applications not specifically addressed in this section. Browser Netscape Inline Plug-ins

Watch’s

Plug-In

Plaza!

The Web Browser Plug-in section of Web Tools contains direct links to information about the most widely used plug-ins and helper applications. A list of online resources is also provided which contains detailed information on these and other plug-ins and helper applications not specifically addressed in this section. Plug-ins Below is a compiled list of the most widely used web browser plug-ins. Each direct link contains detailed information specific to each of the plug-ins. Download information is also provided at these sites.

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Beatnik Beatnik delivers high-quality interactive sound from websites. It is provided by Headspace, Inc. and is available for Netscape Navigator and Communicator on both Macintosh PowerPC and Windows 95/NT. The Headspace website offers detailed information on Beatnik, as well as an array of sites that showcase the plug-in's capabilities. Quick Time QuickTime, a product of Apple, Inc., is capable of delivering multimedia such as movies, audio, MIDI soundtracks, 3D animation, and virtual reality. It is available to Macintosh and Windows 3.x/95/NT. The QuickTime package contains a plug-in and helper applications. The

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QuickTime Plug-in allows QuickTime and QuickTime VR content to be viewed directly within a browser. The Movie Player and Picture Viewer, helper applications, allow all QuickTime multimedia to be played (file creation and editing can be completed with QuickTime. RealPlayer RealPlayer is a live and on-demand RealAudio and Real Video player which functions without download delays. It is provided by Real Networks, Inc. and is available for Macintosh, Unix, and Windows 3.1/95/NT as both a plug-in and helper application. To test your RealPlayer plug-in, visit any of the sites listed in their showcase. The plug-in is compatible with many popular browsers. For a complete listing visit the RealPlayer system requirements page. Shockwave The Shockwave plug-in, provided by Macromedia, Inc., allows multimedia files created using Macromedia's Director, Author ware, and Flash to be viewed directly in your web browser. The plug-in is compatible with Netscape Navigator 2.0 or later and Internet Explorer 3.0 or later on Macintosh and Windows 3.1/95/NT platforms. The Macromedia site also provides detailed information about Shockwave, including a section called Shock zone where users can view Shockwave in action. Vivo Active Player Vivo Active Player delivers on-demand video and audio from any website offering Vivo Active content. This product, provided by Vivo Software, Inc., is available for Netscape Navigator and Microsoft Internet Explorer browsers on Power Macintosh and Windows 3.x/95/NT platforms. Learn more about the Vivo Active Player and test its capabilities at the Vivo Software website. 9. Additional file format -

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10. Image file format

Image Which to use?

File

Formats

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Briefly, the three most common image file formats, the most important for general purposes today, are TIF, JPG and GIF. I propose we also consider the new PNG format too. Best file types for these general purposes:

Photographic Images

Graphics, Logos or Line art

including

Properties

Continuous tones, 24 bit color or 8 bit Gray, no text, few lines and edges

Solid colors, up to 256 colors, with text or lines and sharp edges

Best Quality for Archived Master

TIF or (no JPG artifacts)

PNG or GIF (no JPG artifacts)

Smallest File Size

JPG with a higher Quality factor can be decent (JPG is questionable quality for archiving master copies)

TIF LZW or GIF or PNG (graphics/logos usually permit reducing to 2 to 16 colors for smallest file size)

M a x i m u m C omp atib ilit y (PC, Mac, Unix)

TIF or JPG (the simplest programs may not read TIF LZW)

TIF or GIF

Worst Choice

256 color GIF is very limited color, and is a larger file than 24 bit JPG

JPG compression adds artifacts, smears text and lines and edges

PNG

or

without

TIF

LZW

These are not the only choices, but they are good and reasonable choices. TIF file format is the undisputed leader when best quality is required. TIF is very commonly used in commercial printing or professional environments. Web pages require JPG or GIF or PNG image types, because that is all that browsers can show. On the web, JPG is the best choice (smallest file) for photo images, and GIF is most common for graphic images. A common question is "How do I make my image files smaller?". The JPG section following attempts to explain why the wonderfully small JPG files are NOT the best choice to be the master copy of your important image. However JPG cannot be beat for emailing photographs to friends, and for web page use. The JPG file format is the smallest by far, and a JPG copy should be used for such purposes (when file size is all important). For Line art and graphic files (as opposed to photographic images), then GIF files have historically been best, both for smallest size and for best quality. But note that lowering scan resolution to reasonable values for the purpose is often the best file size improvement you can make.

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The Next button will browse through the descriptions on the next pages, or you can use these shortcut links directly: PNG - Portable Network Graphics (.PNG file extension, the pronunciation 'Ping' is specifically mentioned in the PNG Specification). PNG needs to be mentioned. PNG is not the number one file format, but you will want to know about it. PNG is not so popular yet, but it's appeal is growing as people discover what it can do. PNG was designed recently, with the experience advantage of knowing all that went before. The original purpose of PNG was to be a royalty-free GIF and LZW replacement (see LZW next page). However PNG supports a large set of technical features, including superior lossless compression from LZ77. Compression in PNG is called the ZIP method, and is like the 'deflate" method in PKZIP (and is royalty free). But the big deal is that PNG incorporates special preprocessing filters that can greatly improve the lossless compression efficiency, especially for typical gradient data found in 24 bit photographic images. This filter preprocessing causes PNG to be a little slower than other formats when reading or writing the file (but all types of compression require processing time). Photoshop 7 and Elements 2.0 correct this now, but earlier Adobe versions did not store or read the ppi number to scale print size in PNG files (Adobe previously treated PNG like GIF in this respect, indicated 72 ppi regardless). The ppi number never matters on the video screen or web, but it was a serious usability flaw for printing purposes. Without that stored ppi number, we must scale the image again every time we print it. If we understand this, it should be no big deal, and at home, we probably automatically do that anyway (digital cameras do the same thing with their JPG files). But sending a potentially unsized image to a commercial printer is a mistake, and so TIF files should be used in that regard. Most other programs do store and use the correct scaled resolution value in PNG files. PNG stores resolution internally as pixels per meter, so when calculating back to pixels per inch, some programs may show excessive decimal digits, perhaps 299.999 ppi instead of 300 ppi (no big deal). PNG has additional unique features, like an Alpha channel for a variable transparency mask (any RGB or Grayscale pixel can be say 79% transparent and other pixels may individually have other transparency values). If indexed color, palette values may have similar variable transparency values. PNG files may also contain an embedded Gamma value so the image brightness can be viewed properly on both Windows and Macintosh screens. These should be wonderful features, but in many cases these extra features are not implemented properly (if at all) in many programs, and so these unique features must be ignored for web pages. However, this does not interfere with using the standard features, specifically for the effective and lossless compression. Netscape 4.04 and MS IE 4.0 browsers added support for PNG files on web pages, not to replace JPG, but to replace GIF for graphics. For non-web and non-graphic use, PNG would compete with TIF. Most image programs support PNG, so basic compatibility is not an issue. You may really like PNG. PNG may be of great interest, because it's lossless compression is well suited for master copy data, and because PNG is a noticeably smaller file than LZW TIF. Perhaps about 25% smaller

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than TIF LZW for 24 bit files, and perhaps about 10% to 30% smaller than GIF files for indexed data. Different images will have varying compression sizes, but PNG is an excellent replacement for GIF and 24 bit TIFF LZW files. PNG does define 48 bit files, but I don't know of any programs that support 48 bit PNG (not too many support 48 bit in any form). Here are some representative file sizes for a 9.9 megabyte 1943x1702 image: File type

File size

TIFF

9 . megs

9

T I F F LZW

8 . megs

4

PNG

6 . megs

5

JPG

1 . megs

0

BMP

9 . megs

9

24-bit RGB color

(1.0 / 9.9) is 10% file size

Seems to me that PNG is an excellent replacement for TIFF too. TIFF - Tag Image File Format (.TIF file extension, pronounced Tif) TIFF is the format of choice for archiving important images. TIFF is THE leading commercial and professional image standard. TIFF is the most universal and most widely supported format across all platforms, Mac, Windows, Unix. Data up to 48 bits is supported. TIFF supports most color spaces, RGB, CMYK, YCbCr, etc. TIFF is a flexible format with many options. The data contains tags to declare what type of data follows. New types are easy to invent, and this versatility can cause incompatibly, but about any program anywhere will handle the standard TIFF types that we might encounter. TIFF can store data with bytes in either PC or Mac order (Intel or Motorola CPU chips differ in this way). This choice improves efficiency (speed), but all major programs today can read TIFF either way, and TIFF files can be exchanged without problem. Several compression formats are used with TIF. TIF with G3 compression is the universal standard for fax and multi-page line art documents.

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TIFF image files optionally use LZW lossless compression. Lossless means there is no quality loss due to compression. Lossless guarantees that you can always read back exactly what you thought you saved, bit-for-bit identical, without data corruption. This is a critical factor for archiving master copies of important images. Most image compression formats are lossless, with JPG and Kodak PhotoCD PCD files being the main exceptions. Compression works by recognizing repeated identical strings in the data, and replacing the many instances with one instance, in a way that allows unambiguous decoding without loss. This is fairly intensive work, and any compression method makes files slower to save or open. LZW is most effective when compressing solid indexed colors (graphics), and is less effective for 24 bit continuous photo images. Featureless areas compress better than detailed areas. LZW is more effective for grayscale images than color. It is often hardly effective at all for 48 bit images (VueScan 48 bit TIF LZW is an exception to this, using an efficient data type that not all others use ). LZW is Lempel-Ziv-Welch, named for Israeli researchers Abraham Lempel and Jacob Zif who published IEEE papers in 1977 and 1978 (now called LZ77 and LZ78) which were the basis for most later work in compression. Terry Welch built on this, and published and patented a compression technique that is called LZW now. This is the 1984 Unisys patent (now Sperry) involved in TIF LZW and GIF (and V.42bis for modems). There was much controversy about a royalty for LZW for GIF, but royalty was always paid for LZW for TIF files and for v.42bis modems. International patents recently expired in mid-2004. Image programs of any stature will provide LZW, but simple or free programs often do not pay LZW patent royalty to provide LZW, and then its absence can cause an incompatibility for compressed files. It is not necessary to say much about TIF. It works, it's important, it's great, it's practical, it's the standard universal format for high quality images, it simply does the best job the best way. Give TIF very major consideration, both for photos and documents, especially for archiving anything where quality is important. But TIF files for photo images are generally pretty large. Uncompressed TIFF files are about the same size in bytes as the image size in memory. Regardless of the novice view, this size is a plus, not a disadvantage. Large means lots of detail, and it's a good thing. 24 bit RGB image data is 3 bytes per pixel. That is simply how large the image data is, and TIF LZW stores it with recoverable full quality in a lossless format (and again, that's a good thing). $200 today buys BOTH a 320 GB 7200 RPM disk and 512 MB of memory so it is quite easy to plan for and deal with the size. There are situations for less serious purposes when the full quality may not always be important or necessary. JPEG files are much smaller, and are suitable for non-archival purposes, like photos for read-only email and web page use, when small file size may be more important than maximum quality. JPG has its important uses, but be aware of the large price in quality that you must pay for the small size of JPG, it is not without cost. JPEG - Joint Photographic Experts Group (.JPG file extension, pronounced Jay Peg). This is the right format for those photo images which must be very small files, for example, for web sites or for email. JPG is often used on digital camera memory cards, but RAW or TIF format may be offered too, to avoid it. The JPG file is wonderfully small, often compressed to perhaps only 1/10 of the size of the original data, which is a good thing when modems are involved. However, this fantastic compression

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efficiency comes with a high price. JPG uses lossy compression (lossy meaning "with losses to quality"). Lossy means that some image quality is lost when the JPG data is compressed and saved, and this quality can never be recovered. File compression methods for most other file formats are lossless, and lossless means "fully recoverable". Lossless compression always returns the original data, bit-for-bit identical without any question about differences (losses). We are used to saving data to a file, and getting it all back when we next open that file. Our Word and Excel documents, our Quicken data, any data at all, we cannot imagine NOT getting back exactly the original data. TIF, PNG, GIF, BMP and most other image file formats are lossless too. This integrity requirement does limit efficiency, limiting compression of photo image data to maybe only 10% to 40% reduction in practice (graphics can be smaller). But most compression methods have full lossless recoverability as the first requirement. JPG files don't work that way. JPG is a big exception. JPG compression is not lossless. JPG compression is lossy. Lossy means "with losses" to image quality. JPG compression has very high efficiency (relatively tiny files) because it is intentionally designed to be lossy, designed to give very small files without the requirement for full recoverability. JPG modifies the image pixel data (color values) to be more convenient for its compression method. Tiny detail that doesn't compress well (minor color changes) can be ignored (not retained). This allows amazing size reductions on the remainder, but when we open the file and expand the data to access it again, it is no longer the same data as before. This lost data is like lost purity or integrity. It can vary in degree, it can be fairly good, but it is always unrecoverable corruption of the data. This makes JPG be quite different from all the other usual file format choices. This will sound preachy, but if your use is critical, you need a really good reason to use JPG. There are times and places this compromise is an advantage. Web pages and email files need to be very small, to be fast through the modem, and some uses may not need maximum quality. In some cases, we are willing to compromise quality for size, sacrificing for the better good. And this is the purpose of JPG. There is no magic answer providing both high compression and high quality. We don't get something for nothing, and the small size has a cost in quality. Still, mild quality losses may sometimes be acceptable for less critical purposes. The sample JPG images on next page show the kind of problem to expect from excessive compression. Even worse, more quality is lost every time the JPG file is compressed and saved again, so ever editing and saving a JPG image again is a questionable decision. You should instead just discard the old JPG file and start over from your archived lossless TIF master, saving that change as the new JPG copy you need. JPG compression can be selected to be better quality in a larger file, or to be lesser quality in a smaller file. When you save a JPG file, your FILE SAVE AS dialog box should have an option for the degree of file compression. Many programs (Photoshop, Elements, PhotoImpact, PhotoDeluxe) call this setting JPG Quality. Other programs (Paint Shop Pro and Corel) call it JPG Compression, which is the same thing, except Quality runs numerically the opposite direction from Compression. High Quality corresponds to Low Compression. Typical values might be 85 Quality, or 15 Compression. These numbers are relative and have no absolute meaning. Compression in one program will vary from another even at the same number. The number is also not a percentage of anything, and Quality 100 does NOT mean no compression, it is just an arbitrary starting point. JPG will always compress, and Quality 90 is not so different from Quality 100 in practice. There's very little improvement over 95. Digital cameras also offer JPG quality choices too. Large image files do fill memory cards fast. You can buy more and larger cards, or you can compromise by sacrificing image quality for small file size (but I hope you won't go overboard with this). The camera menu will have two

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kinds of resizing choices. One size choice actually creates a smaller image size (pixels), resampled smaller from the original standard size of the CCD chip, for example perhaps to half size in pixel dimensions. The correct image size in pixels is related to your goal for using the image. For example you may need enough pixels to print 8x10 inches on paper (6 megapixels), or you may only want a small image for video screen viewing (1 megapixel). Regardless of that selected image size in pixels, the camera menu will also offer a smaller file size choice in bytes, related to quality, via JPG file compression. This menu will offer a best quality setting which is the largest file, and maybe intermediate sizes, and a smallest but worst quality choice. My Nikon D70 offers three JPG file size choices of Fine (about 1/4 size in bytes), Norm (about 1/8 size in bytes), or Basic (about 1/16 size in bytes), comparing compressed file size to the uncompressed size. The best (largest) JPG file size will still contain JPG artifacts, but very mild, essentially undetectable, vastly better than the smallest file choice. Even better, some cameras also offer a RAW or TIF format to bypass JPG problems all together. These images may be large, but memory cards are becoming less expensive ($100 for 1 GB), and larger or multiple cards are by far the best quality solution. With either scanner or camera images, individual image JPG file sizes will vary a little, because detail in the individual image greatly affects compressibility. Large featureless areas (skies, walls, etc.) compress much better (smaller) than images containing much tiny detail all over (a tree full of leaves). Therefore images of the same size in pixels and using the same JPG quality setting, but with differing image content, will vary a little in JPG file size, with extremes perhaps over a 2 to 1 range around the average size. Since each image varies a little, the file size is only a crude indicator of JPG quality, however it is a rough guide. For ordinary color images (24 bit RGB), the uncompressed image size when opened in memory is always 3 bytes per pixel. For example, an image size of 3000x2000 pixels is 6 mega pixels, and therefore by definition, when uncompressed (when opened), this memory size is 3X that in bytes, or 18 MB. That is simply how large the 24 bit data is. The compressed JPG file size will be smaller (same pixels, but fewer bytes). A High quality JPG file size might be compressed to 50% to 25% uncompressed size (bytes). A JPG file size only 10% of that image's size in memory would the general ballpark for a fair tradeoff of quality vs. file size for color images of web page quality (but not best quality). The 10% size is not very precise, but of course only refers roughly to the average image size, since each individual image varies a little. Color compresses better than grayscale files, so grayscale doesn't decrease as much. These are very rough guidelines, your image, your photo program, your purpose, and your personal criteria or tolerance will all be a little different. It is difficult to describe the JPG quality losses, except by seeing an example image (next page). JPG does not discard pixels. Instead it changes the color detail of some pixels in an abstract mathematical way. JPG is mathematically complex and requires considerable CPU processing power to decompress an image. JPG also allows several parameters, and programs don't all use the same JPG rules. Programs vary, some programs take shortcuts to load JPG faster but with less quality (browsers for example), and other programs load JPG slower with better quality. Final image quality can depend on the image details, on the degree of compression, on the method used by the compressing JPG program, and on the method used by the viewing JPG program.

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JPEG Artifacts I am sent JPG images with questions why they appear "bad" and very "unclear", when the only problem is excessive JPG compression, too much, or saved too many times, or both. Too little Quality or too much Compression will affect JPG image quality visibly. It can be awful. You can and should learn to recognize this bad effect yourself. It's easy to recognize, almost trivial, after you've seen it once. Then you will know if it is acceptable or not, and you will know that you have choices. How to see JPG artifacts the first time If using a digital camera, shoot the same scene as the best file format you have, a RAW or TIF file, or at least at the best JPG quality setting (largest file). Also shoot exactly the same scene at the lowest JPG quality setting (smallest file). If using a scanner, scan a new photo image and save it as a TIF file. Then, after that, also save the same image as a JPG file using more compression than usual, a lower JPG quality setting this one time to help learn to see it. Then close that JPG image, and reopen that file to be sure you are viewing the contents of the file image you actually wrote (instead of the uncompressed image on the screen that you thought you wrote). Then examine both large and small file images side by side on the same screen, by zooming in to about 4 times size (400%, huge) on both. You will have to scroll around on them, but the 400% is to help you learn to recognize the artifacts this first time. The differences you see are the JPG artifacts of compression. The visible signs of excessive JPG compression are JPG artifacts, which include: ·

Areas of similar color (generally featureless areas like skies or walls) become "blocky", with tile-like squares that are 8x8 pixel blocks of one color (compresses well), or which may contain horizontal or vertical patterns at extremes. You see the 8x8 squares, like big pixels, but at 400% zoom, you can recognize the size difference in the pixels (jaggies) and the 8x8 pixel blocks.

·

The sharp contrasting edges in the image will have "vague dark smudges" surrounding the sharp edges. This is normally the worst effect in most images, it obsures detail. Excessive JPG compression is tough on all sharp edges in the image (especially so for text and graphic images). This is very counterproductive to apparent sharpness and fine detail.

·

Some false color or color changes.

Here are samples below, zoomed large, but same size and side by side for comparison, to better learn to recognize the JPG artifacts (that is a cookie jar at left, with a little reflection on it)

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Original TIF image ABOVE, zoomed to 300% size Low Quality JPG image BELOW, zoomed to 300% size

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Not that it seems necessary, but I have marked a few of the 8x8 pixel blocks seen in areas of similar color, and also some of the smudging around sharp edges (all edges). You can find more almost any place in the image. Notice the missing detail at the ridged knob marked in blue. The two power cords behind the fruit are nearly obscured by JPG artifacts. The tiny jaggies in the TIF are the original pixels zoomed to 300%. Their size is a guide to show the larger JPG 8x8 pixel blocks are clearly a different artifact. Zooming to 300% size is not the normal thing to do, but it does help to recognize these JPG artifacts the first time. After you learn what you are looking for, then you can recognize them at 100% size too. This sample shows what is meant by "lossy compression" in JPG - the losses are from deteriorating image quality due to the JPG artifacts. Using a Higher JPG Quality setting to produce a larger JPG file improves the JPG image quality. Using a Lower JPG Quality setting to produce a smaller file makes it worse. That seems straight-forward. A High JPG Quality setting of 8 or 9 (assuming a 1-10 scale, but 80 or 90 on a 1-100 scale is used by some software - same thing) is normally a pretty good image, normally not much problem for read-only uses, like viewing or printing (both zoomed images above are in a High quality JPG now for web presentation). The problem then is when you want to edit the image and save it yet again as JPG (additional JPG artifacts accumultate each time). We should only save a JPG image ONE TIME. Note that most other types of image file compression (for example PNG or TIF LZW) are lossless compression, meaning that there is absolutely no loss of quality due to compression (zero loss), so that then file quality is simply not an isssue at all, and the most critical user

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need not ever worry about it. The TIF file above used LZW compression. However lossless file compression is less effective, meaning that it can not produce files so drastically small as JPG. The lossless file size is closer to the actual size of the color data, perhaps 70% or 80% instead of 5% to 20%. I want to call this JPG an extreme example, and it is poor, but it is not extreme. You ought to see some of the images that people send me asking why their images are so poor. This JPG was done in Photoshop, and Adobe's lowest quality settings are conservative, and won't let us make them as extreme and poor as some other programs will. The JPG quality numbers like 8 or 9 are NOT absolute values, instead they are relative to the JPG properties that each program chooses to individually use. JPG artifacts do vary, and this will be of more concern when you do this same test on your own images. Once you realize what you are looking for, then JPG artifacts are easy to see and recognize at 100% size. Some people are more critical than others, asking "How good can I make it?" instead of "How small can I make it"? Your priorities are your own, but after you are able to recognize JPG artifacts, you will be able to judge how much of this you want in your own images. Use a higher JPG Quality factor to minimize these effects (or don't use JPG at all if maximum quality is important). Less JPG Quality is more JPG compression, a smaller file, but worse artifacts. Normally you may detect some artifacts even at high Quality factors, and you can learn to recognize this easier if you zoom in to about 400% size. But the image can still be very usable size if the compression is mild. Now you know what to look for, and how to look for it, and how to judge if you want it or not. The JPG artifacts become part of the image data, and it cannot be removed. Sharpening again after JPG compression (next time) will emphasize these JPG artifacts, so be careful with that. Actually, very slight intentional softening or blurring before JPG compression will help minimize the effect of the JPG artifacts (and will slightly reduce JPG file size too). JPG normally should not be used for text or graphic images. It obscures the sharp edges too much, and the results are typically poor. TIF LZW, PNG, and GIF are vastly better for line art or graphic images, and these will normally compress text and graphics effectively. The way to make a scanned text document PDF file smaller is to scan in Line art mode and use compression. Acrobat will use G4 compression which is very small for line art, but LZW is good too. For text, line art will be smaller and better result than a JPG grayscale file. JPG cannot handle line art or indexed color anyway, JPG requires 8 bit grayscale or 24 bit color. However for continuous tone photo images, as opposed to text or graphics, then files with high JPG Quality (low compression) are normally acceptable for viewing (read-only purposes), and the small file size is extremely desirable for modems. Due to the quality concerns, JPG compression is generally NOT suitable for archiving the important master copy of your image. With only mild compression, it might view OK, but you should grit your teeth, hold your breath, and cross your fingers for luck, if you ever have the need to modify and save a JPG file again. Because this will lower the quality of that image even more, every time you save the file. By "save", I mean to select the FILE - SAVE or FILE - SAVE AS or FILE - SAVE FOR WEB menu with JPG format from an image program. That SAVE step does the JPG compression again. Note that downloading, or copying, or opening and viewing JPG files is no problem at all. This does not save the file again, and it does not alter the file in any way, so it does not create more artifacts. You can open and view a JPG file a jillion times without any concern (a web page for example). The artifacts are created only when the data is compressed for saving it

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as a JPG file. This happens only at the menus FILE - SAVE or FILE - SAVE AS or FILE - SAVE FOR WEB when you select JPG format. Archive your important master copy images in a non-lossy format (TIF LZW and PNG are very good, and compress moderately), and then also make a JPG copy if needed for view-only purposes that need it to be smaller, like email and web pages. You won't gain any quality by converting JPG to TIF now, because that image copy will still contain the JPG artifacts it had before. It is part of the image now, there is no way to improve it again. However, if you do need to edit a JPG, then saving it as TIF will prevent adding more artifacts by not doing another JPG Save, so TIF would be a good plan then. If you find that you must edit the JPG image and must save it as JPG again, at least try to use the same program and same value of Quality or Compression every time you save the file. Using different values will use different parameters that will aggravate the damage due the lossy compression. I am certainly not suggesting repeated saving of JPG files with the same parameters is a good thing, but only that there are even worse ways to do it. JPEG Lossless Rotation Sometimes for viewing, we need to rotate an image beween horizontal or vertical (Landscape or Portrait), without needing any other editing operations. But if you save that rotated image as JPG, that is another SAVE operation and additional JPG artifacts. But there are image programs that can rotate a JPG file image exactly 90 or 180 degrees, and then save it again without additional loss, by rotating it without uncompressing and recompressing it first, thus preventing any additional JPG artifacts. This option merely rearranges the row and column data, without uncompressing that data. So while the JPG file itself is still lossy, the lossless rotation does not create additional artifacts. Jpegclub.org has a list of programs that support this lossless rotation feature. Standard photo editor programs typically do not provide this option, but a few of the better known programs that can do this are IrfanView Free, Windows GraphicConverter Trail available, Macintosh ThumbsPlus Trial available, Windows IrfranView needs its free extra JPG plugin package to provide lossless rotation, which is then found at menu Options - Lossless JPG Operations when the JPG file is open. Irfanview also shows the JPG EXIF information well (Exchangeable Image File Format) - extra file data added by cameras showing information like camera name, date, f-stop, and shutter speed, exposure compensation, metering and flash used, etc. More Preaching, but it is important JPG format has a magic status for us. JPG is wonderful when the purpose is right, but we need to understand we pay a cost in quality. I know you surely will consider using JPG for master copies; everyone does at first, because the JPG file is so small, and the idea is frightfully appealing. But it's a high price paid in lost quality, and you will eventually come around to appreciate the quality of TIF files. I hope that happens before you have damaged important images that you cannot scan again. Some people argue that high quality JPG masters are not so bad. That's OK with me, it's your file, but the file size is one property of an image, and quality is another. You can choose either way, and I hope you choose Highest Quality, at least for your master copies. My goal is that you understand the effects of your choice in regard to your valuable master copies.

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If you simply must use JPG for your master copy (if file size is the most important property of this image), then at least use the best Quality you can. Aim for a average JPG file size at least as large as 25% of its true memory size. For web images, file size is indeed important, and absolute quality is less important, and a JPG file size 10% of uncompressed size is often a good tradeoff of quality for size for color images, but that is too extreme for any notion of a master copy. Grayscale images do not compress as much as color at the same settings. Grayscale is already 1/3 the size of color, and grayscale JPG files won't compress as much. Then keep a master copy that you never rewrite. For any purpose, always start with a copy of that JPG master and never modify that JPG master itself. Saving that JPG master image again causes more artifacts, even more loss, permanent loss, so simply don't do it. If you simply need to rotate to vertical, or to scale for printing, consider not saving that simple change at all if it is trivial to do again. Save any change to a different file, and never make your one master copy worse. Or save the change to a TIF file, so as to not create more JPG artifacts. You could of course just use a TIF master instead, and sleep better at night. And be aware that lowering scan resolution to reasonable values for the purpose is often the best size reduction you can make. Judge your own common sense periodically. Why can't we see that a decent JPG image compressed to be only 25% of original size (1/4 size, still amazingly small, and still with mild artifacts), is more useful, and a much better deal, than one at 5% size that is simply too awful to use? I know, the macho types are saying "but I can get it down to 3%". Then go for it man! For emailing and for web pages, JPG file format is the smallest by far, and the best goal by far (for photo images). JPG is acceptable for such read-only "viewing" use, and a JPG copy normally is used for such purposes. JPG is NOT very acceptable for "editing" use, when you may need to edit and save the image again (we always do). JPG is best only for photographic images. For line art and graphic files (characterized by containing graphic sharp edges and very few but solid colors), then TIF LZW or PNG is good, or GIF files too, which have historically been used for graphics on web pages. The process of saving a JPG file to disk first compresses the image data to make the file be much smaller. This JPG compression affects the image quality, because JPG compression uses a very different technique than does PKZIP or TIF LZW or PNG file compression (lossy vs. lossless). JPG compression is extremely effective, because it does not attempt to be 100% faithful to the original image data. If parts of the image data are a problem for it, the JPG compression simply modifies that data to make it conform better. That means when we read that JPG file later, we don't get back the same original image data (that is the meaning of lossy, losses of image quality). Also the software opening that JPG image does a similar thing when it reads it. It does not necessarily show exactly what is in the file, it can also take similar liberties. Web browsers for example are not the best JPG image viewers, but they are the fastest JPG viewers. Every time we save a JPG file (menu FILE - SAVE AS - JPG), it compresses again, and image quality is lost. This loss is variable, depending on the JPG Quality factor used, but it is never zero. If we edit the JPG file image and save it again, then quality is lost again. Even if we save it at a much higher quality setting the second time, it is still a second compression and another loss. Every time we compress a JPG file, we add more JPG artifacts and lose a little more quality. Artifacts are always a one way trip, there is no recovery. The damage is done. Most other file formats (say TIF or PNG) use lossless compression. These files are larger than JPG because they use milder, fully recoverable (lossless) compression to carefully preserve all of the original image data. These file formats remain full quality at all times, no matter how

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many times we might save them to a file, which is of course exactly what is needed for a master copy. The small JPG file size is great, but it has a big price of reduced quality. There are proper times and places one would use it, and also major reasons one would not. There's nothing wrong with creating a JPG image using a moderate to high Quality factor to put a photo image on a web page or to send it via email. It's the only practical way. However there is an additional quality loss when we try to edit and save that JPG file a second time, so JPG is usually inappropriate for important archived master copies. The risk if you make this mistake now is that you cannot undo it in the future, so now is the best time to understand the situation. Progressive JPG is a web option that quickly shows the entire image in very low quality, and the quality fills in and improves as the file download completes. JPEG 2000 A new JPEG 2000 file format is available now in many newer program versions, with various file extensions, normally .jp2 (or .jpg, with option extensions). JPEG 2000 uses a wavelet compression method. It has a lossless option (to perhaps 65% size). Otherwise it is lossy, size comparable to regular JPG files, but different... slower then JPG, but arguably perhaps better quality. Extremes of compression have few detectable artifacts; however JPEG 2000 images become noticeably soft with greater compression. Paint Shop Pro 8 and Photo Impact 8 started including JPEG 2000. Adobe Elements 3.0 includes JPEG 2000. Elements 2.0 have an update to add JPEG 2000 - at the How To palette, Select a Recipe, Download New Adobe Recipes, then (very important) the BACK button and you will see it. Photoshop has an optional JPEG 2000 plug-in from CD; see JPEG 2000 at the CS or CS2 Help menu. Note that web browsers do NOT support JPEG 2000 yet, and so compatibility is still a very significant issue. Therefore it seems important to stay with the original JPG format for now, at least if you want others to be able to open your files. More Preaching, but it is important JPG format has a magic status for us. JPG is wonderful when the purpose is right, but we need to understand we pay a cost in quality. I know you surely will consider using JPG for master copies, everyone does at first, because the JPG file is so small, and the idea is frightfully appealing. But it's a high price paid in lost quality, and you will eventually come around to appreciate the quality of TIF files. I hope that happens before you have damaged important images that you cannot scan again. Some people argue that high quality JPG masters are not so bad. That's OK with me, it's your file, but the file size is one property of an image, and quality is another. You can choose either way, and I hope you choose Highest Quality, at least for your master copies. My goal is that you understand the effects of your choice in regard to your valuable master copies. If you simply must use JPG for your master copy (if file size is the most important property of this image), then at least use the best Quality you can. Aim for a average JPG file size at least as large as 25% of its true memory size. For web images, file size is indeed important, and absolute quality is less important, and a JPG file size 10% of uncompressed size is often a good tradeoff of quality for size for color images, but that is too extreme for any notion of a master copy. Grayscale images do not compress as much as color at the same settings. Grayscale is already 1/3 the size of color, and grayscale JPG files won't compress as much. Then keep a master copy that you never rewrite. For any purpose, always start with a copy of that JPG master and never modify that JPG master itself. Saving that JPG master image again

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causes more artifacts, even more loss, permanent loss, so simply don't do it. If you simply need to rotate to vertical, or to scale for printing, consider not saving that simple change at all if it is trivial to do again. Save any change to a different file, and never make your one master copy worse. Or save the change to a TIF file, so as to not create more JPG artifacts. You could of course just use a TIF master instead, and sleep better at night. And be aware that lowering scan resolution to reasonable values for the purpose is often the best size reduction you can make. Judge your own common sense periodically. Why can't we see that a decent JPG image compressed to be only 25% of original size (1/4 size, still amazingly small, and still with mild artifacts), is more useful, and a much better deal, than one at 5% size that is simply too awful to use? I know, the macho types are saying "but I can get it down to 3%". Then go for it man! For emailing and for web pages, JPG file format is the smallest by far, and the best goal by far (for photo images). JPG is acceptable for such read-only "viewing" use, and a JPG copy normally is used for such purposes. JPG is NOT very acceptable for "editing" use, when you may need to edit and save the image again (we always do). JPG is best only for photographic images. For line art and graphic files (characterized by containing graphic sharp edges and very few but solid colors), then TIF LZW or PNG is good, or GIF files too, which have historically been used for graphics on web pages. The process of saving a JPG file to disk first compresses the image data to make the file be much smaller. This JPG compression affects the image quality, because JPG compression uses a very different technique than does PKZIP or TIF LZW or PNG file compression (lossy vs. lossless). JPG compression is extremely effective, because it does not attempt to be 100% faithful to the original image data. If parts of the image data are a problem for it, the JPG compression simply modifies that data to make it conform better. That means when we read that JPG file later, we don't get back the same original image data (that is the meaning of lossy, losses of image quality). Also the software opening that JPG image does a similar thing when it reads it. It does not necessarily show exactly what is in the file, it can also take similar liberties. Web browsers for example are not the best JPG image viewers, but they are the fastest JPG viewers. Every time we save a JPG file (menu FILE - SAVE AS - JPG), it compresses again, and image quality is lost. This loss is variable, depending on the JPG Quality factor used, but it is never zero. If we edit the JPG file image and save it again, then quality is lost again. Even if we save it at a much higher quality setting the second time, it is still a second compression and another loss. Every time we compress a JPG file, we add more JPG artifacts and lose a little more quality. Artifacts are always a one way trip, there is no recovery. The damage is done. Most other file formats (say TIF or PNG) use lossless compression. These files are larger than JPG because they use milder, fully recoverable (lossless) compression to carefully preserve all of the original image data. These file formats remain full quality at all times, no matter how many times we might save them to a file, which is of course exactly what is needed for a master copy. The small JPG file size is great, but it has a big price of reduced quality. There are proper times and places one would use it, and also major reasons one would not. There's nothing wrong with creating a JPG image using a moderate to high Quality factor to put a photo image on a web page or to send it via email. It's the only practical way. However there is an additional quality loss when we try to edit and save that JPG file a second time, so JPG is usually inappropriate for important archived master copies. The risk if you make this mistake now is that you cannot undo it in the future, so now is the best time to understand the situation.

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Progressive JPG is a web option that quickly shows the entire image in very low quality, and the quality fills in and improves as the file download completes. JPEG 2000 A new JPEG 2000 file format is available now in many newer program versions, with various file extensions, normally .jp2 (or .jpx, with option extensions). JPEG 2000 uses a wavelet compression method. It has a lossless option (to perhaps 65% size). Otherwise it is lossy, size comparable to regular JPG files, but different... slower then JPG, but arguably perhaps better quality. Extremes of compression have few detectable artifacts; however JPEG 2000 images become noticeably soft with greater compression. Paint Shop Pro 8 and Photo Impact 8 started including JPEG 2000. Adobe Elements 3.0 includes JPEG 2000. Elements 2.0 have an update to add JPEG 2000 - at the How To palette, Select a Recipe, Download New Adobe Recipes, then (very important) the BACK button, and you will see it. Photoshop has an optional JPEG 2000 plug-in from CD, see JPEG 2000 at the CS or CS2 Help menu. Note that web browsers do NOT support JPEG 2000 yet, and so compatibility is still a very significant issue. Therefore it seems important to stay with the original JPG format for now, at least if you want others to be able to open your files. Graphic Interchange Format (GIF) (.GIF file extension) There have been raging debates about the pronunciation. The designers of GIF say it is correctly pronounced to sound like Jiff. But that seems counter-intuitive, and up in my hills, we say it sounding like Gift (without the t). GIF was developed by CompuServe to show images online (in 1987 for 8 bit video boards, before JPG and 24 bit color was in use). GIF uses indexed color, which is limited to a palette of only 256 colors (next page). GIF was a great match for the old 8 bit 256 color video boards, but is inappropriate for today's 24 bit photo images. GIF files do NOT store the image's scaled resolution ppi number, so scaling is necessary every time one is printed. This is of no importance for screen or web images. GIF file format was designed for CompuServe screens, and screens don't use ppi for any purpose. Our printers didn't print images in 1987, so it was useless information, and CompuServe simply didn't bother to store the printing resolution in GIF files. GIF is still an excellent format for graphics, and this is its purpose today, especially on the web. Graphic images (like logos or dialog boxes) use few colors. Being limited to 256 colors is not important for a 3 color logo. A 16 color GIF is a very small file, much smaller, and clearer than any JPG, and ideal for graphics on the web. Graphics generally use solid colors instead of graduated shades, which limits their color count drastically, which is ideal for GIF's indexed color. GIF uses lossless LZW compression for relatively small file size, as compared to uncompressed data. GIF files offer optimum compression (smallest files) for solid color graphics, because objects of one exact color compress very efficiently in LZW. The LZW compression is lossless, but of course the conversion to only 256 colors may be a great loss. JPG is much better for 24 bit photographic images on the web. For those continuous tone images, the JPG file is also very much smaller (although lossy). But for graphics, GIF files will be smaller, and better quality, and (assuming no dithering) pure and clear without JPG artifacts.

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If GIF is used for continuous tone photo images, the limited color can be poor, and the 256 color file is quite large as compared to JPG compression, even though it is 8 bit data instead of 24 bits. Photos might typically contain 100,000 different color values, so the image quality of photos is normally rather poor when limited to 256 colors. 24 bit JPG is a much better choice today. The GIF format may not even be offered as a save choice until you have reduced the image to 256 colors or less. So for graphic art or screen captures or line art, GIF is the format of choice for graphic images on the web. Images like a company logo or screen shots of a dialog box should be reduced to 16 colors if possible and saved as a GIF for smallest size on the web. A complex graphics image that may look bad at 16 colors might look very good at say 48 colors (or it may require 256 colors if photo-like). But often 16 colors is fine for graphics, with the significance that the fewer number of colors, the smaller the file, which is extremely important for web pages. GIF optionally offers transparent backgrounds, where one palette color is declared transparent, so that the background can show through it. The GIF File - Save As dialog box usually has an Option Button to specify which one GIF palette index color is to be transparent. Interlacing is an option that quickly shows the entire image in low quality, and the quality sharpens as the file download completes. Good for web images, but it makes the file slightly larger. GIF files use a palette of indexed colors, and if you thought 24 bit RGB color was kinda complicated, then you isn’t seen nothing' yet. For GIF files, a 24 bit RGB image requires conversion to indexed color. More specifically, this means conversion to 256 colors, or less. Indexed Color can only have 256 colors maximum. There are however selections of different ways to convert to 256 colors. Indexed Color and Palettes What's an Index? What's a Palette? This topic of Indexed Color is NOT unique to GIF. TIF and PNG files can save Indexed color too, but GIF requires it, GIF has no other mode. We speak of GIF files here, but it could be TIF or PNG too. File formats like TIF and JPG store a 24 bit RGB value for each of the millions of image pixels. But GIF files only store a 4 or 8 bit index at each pixel, so that the image data is 1/6 or 1/3 the size of 24 bits. Indexed Color is limited to 256 colors, which can be any 256 from the set of 16.7 million 24 bit colors. Each color used is a 24 bit RGB value. Each such image file contains its own color palette, which is a list of the selected 256 colors (or 16 colors in a smaller palette). Images are called indexed color because the actual image color data for each pixel is the index into this palette. Each pixel's data is a number that specifies one of the palette colors, like maybe "color number 82", where 82 is the index into the palette, the 82nd color in the palette list of colors. We have to go to the palette to see what color is there. The palette is stored in the file with the image. The index is typically a 4 bit value (16 colors) or 8 bit value (256 colors) for each pixel, the idea being that this is much smaller than storing 24 bits for every pixel. But an 8 bit number can only contain a numerical value of 0 to 255, so only 256 colors can be in the palette of possible colors. The size of most graphics files can be limited to use 16 colors, which only uses 4 bit indexes, making the file smaller yet, half the 8 bit size for the index for each pixel. The file also contains the palette too, which is the table of the selected 24 bit colors, or 3 bytes of RGB overhead for each color in the palette (768 bytes for 256 colors). The first RGB

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color in the table is index 0, the second RGB color is index 1, etc. There can be at most only 256 colors in the palette. So indexed files have 24 bits stored for each palette color, but not for each pixel. Each pixel only stores either a 4 bit or 8 bit index to specify which palette color is used. Image programs will show the palette for indexed images, and can modify palette colors. There are various ways to create the palette, to choose the possible color choices that it will contain. This palette choice affects the image greatly. Converting to 16 or 256 colors There are several ways to convert to indexed color. Two choices are required, to specify a palette of colors, and also a choice how to dither or show colors not in that limited palette.

The dithering choices might be: Dithering - Dithering means representing a color by combinations of dots of other colors. Dots are pretty much the definition. If the one exact shade of pink is not in the palette, then dots of other palette colors are mixed to simulate the color. Dithering often causes a visible and objectionable dotted or speckled image. But that simulated color may be much closer than a nearest color approximation. Nearest Color - This selection is the same as disabling dithering, or no dots. If the exact shade of pink is not in the palette, then the closest color in the palette is used, which might not be very pink at all. Sometimes exact color is not important. No dithering means no visible dots. Choices for a palette often have many names, but are of two main types, Standard or Adaptive: Adaptive or Optimized or Perceptual Palette These custom palettes are created from the 256 most representative colors within the one specific current image. The gradient image below is red graduated to white, originally over 5000 shades of pink and white. It is pretty much all red.

The Photo Impact optimized palette at right for this image includes 8 system colors, including black, but this palette specifically has 248 shades of pink to be appropriate for this specific image. That is enough shades of pink that the quality of the GIF image does not show any banding or dithering in this case (one color). However only 256 colors is often pretty bad for normal photos (too few indexed colors for photos, which typically need up to maybe 100,000 colors, not 256). Since most colors in this graphic image are red, this optimized palette appropriately contains mostly red, so it is a much easier case than a normal photo. Optimized

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and Adaptive (two words for same thing) means optimized for the specific image, instead of being optimized for the old Windows 8 bit Palette Manager. Standard Web Browser Palette The Standard Palette (often called the Netscape palette or Web palette) always contains the same colors for any image. It is sometimes called 6-6-6, because it contains six standard evenly spaced colors for each of Red, Green, and Blue. Those 6x6x6 color combinations create 6x6x6 = 216 standard color combinations, which are independent of any specific image (used for any image). The remaining 40 colors are standard colors reserved for the Windows or Macintosh desktop.

The Standard Palette always contains combinations of the following 6 tones for each of the Red, Green, Blue primaries: 6 colors, Hexadecimal (0-ff) 00

33

66

99

CC

FF

6 colors, Decimal (0-255) 0

51

102

153

204

255

The 216 combinations of these 18 colors above (six shades of the three RGB colors, 6x6x6 = 216) produce the Standard web-safe palette below (this one is the standard "Web" palette from Elements 2.0)

The 6x6x6 standard colors are intended to be somewhat suitable for ANY generic image, but of course, it is not correct (not precise) for any normal image. For example, this very GIF

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image uses that same palette, and notice that 6 shades of blue are insufficient to show the Title bar without banding. This standard palette was very important for old 8 bit video cards. The situation used to be (in historic times, ten years ago) that 8 bit video card drivers had only one Windows video Palette Manager, requiring ALL images on that desktop to share ONE palette simultaneously. We used to see bizarre psychedelic colors when the palette of a new image reloaded that palette and affected all other images on the desktop. Perhaps palette Index 82 changed from pink to green, correct for the one image, but very wrong for all other images on the desktop. When the WWW started showing web pages with multiple images on the one web page, it was awful. Netscape standardized the 216 color palette as a workaround. Using one standard palette for all GIF images was better than the alternative, even if that generic palette was far from optimum for any image. This standard 216 color palette is that palette, one generic palette for all indexed images, even if not best for any image. But this concept of a Standard Palette or web-safe palette is obsolete today, now that we all have 24 bit video cards. Today, using the Standard Netscape 216 color web-safe palette only helps those still using ancient 8 bit video cards. Using the standard 216 colors means old 8 bit video systems can show them without adding additional dithering (dotted color). This used to be important several years ago when we all had 8 bit video boards. There are two schools of thought about this ·

the belief that this might somehow still be important, and

·

Why bother anymore? Why be artificially limited for no current reason?

My opinion is that the so-called web-safe palette is an obsolete concept, no longer useful today, and is instead outright detrimental today. There is no Windows Palette Manager anymore (except in drivers for obsolete 8 bit video boards). Today's 24 bit video boards can show any possible palette color, even when in 256 color mode (easy to test). We don't see dithered colors (speckled dotted colors) in 256 color mode anymore, unless the images were created that way in the first place by using a so-called web-safe palette. The GIF problems today are mostly all self-inflicted due to still trying to be limited to obsolete concepts (the use of non-optimum palettes). There is no magic in 216 colors on today's computers with 24 bit video. Adaptive palettes (instead of web-safe 216 color palettes) give better images, and makes creating poor images unnecessary in indexed color. A non-dithered Adaptive palette is hard to beat. Most of the GIF graphic images on this site (screen captured dialogs, etc) use a 16 color Adaptive palette from Nearest Color. The exact shade of color was not very important, but the small file size for the web was important (however where there was embedded photo content of many colors, the image may have been sliced, mostly GIF portions with a little JPG portion). The few users still using ten year old 8 bit boards, if any, are frankly used to poor color, it's nothing they haven't seen before, and they can upgrade if they wish. Why make the overwhelming majority, those with the now standard 24 bit boards capable of good color, see poor color because it used to be that not everyone could? Personally, I ignore web-safe today, and I go out of my way to use the optimized or adaptive palettes for GIF files. The images are much better, without dithering dots to ruin them.

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For the other side of it, Microsoft has a good write-up about Safety Palettes, about dithering and the standard 216 color web-safe browser palette. Note it is dated 1996, and it was still important then, but modern 24 bit video cards have changed the world now. A little more, to be sure you understand Adaptive palettes: GIF, particularly 16 colors GIF, is ideal for web pages for logos and similar simple graphics without continuous tones. The files can be very small (assuming solid color graphics). The next example shows how a 16 color GIF file with Adaptive palette can be better than a 256 color GIF file with Standard palette. The 16 color Optimized GIF file enlarged 4 times, and its palette.

OK, it's a special case, but since most of this image's colors are red, the optimized palette contains mostly red also. Since we only have 16 colors, and since 16 colors is insufficient for this graduated image, then many of the pinks are combined into the same few colors, and we see some dots (pixels, this is shown at 4x size). In the image below with the Standard palette (above was Adaptive Palette), we do have the standard 216 colors available, but very few of them are the Reds that we need for THIS image, so the results are not even as good as the 16 color Optimized palette in this case. This graduated image was ill-suited for 16 colors, but 16 colors of Red is still more than 6 colors of Red. This graduated image would be better as a 256 color GIF, or a JPG. The JPG file would be smaller, but not likely better than 256 color Adaptive in THIS case, because 24 bit color only has 256 shades of Red too, and red is about all we need here.

Most graphics (logos, dialog boxes, etc) don't have more than 16 colors anyway. In those cases, 16 bit GIF files can be much smaller than 256 color GIF files. -

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LESSON VI: Internetworking Servers

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11. Server Implementation DHCP

Server

General

Implementation

and

Management

Issues

DHCP is a client/server protocol, relying on both server and client to fulfill certain responsibilities. Of the two device roles, the DHCP server is arguably the more important, because it is in the server that most of the functionality of DHCP is actually implemented. The server maintains the configuration database, keeps track of address ranges and manages leases. For this reason, DHCP servers are also typically much more complex than DHCP clients. In essence, without a DHCP server, there really is no DHCP. Thus, deciding how to implement DHCP servers is a large part of implementing the protocol. This overall chapter is about describing the function of protocols like DHCP and not getting into details of how to implement them. However, I feel it is useful to look at some of the general issues related to how DHCP servers are set up and used, to help put into perspective how the protocol really works. DHCP Server Implementations A “classical” DHCP server consists of DHCP server software running on a server hardware platform of one sort or another. A DHCP server usually will not be a dedicated computer except on very large networks. It is more common for a hardware server to provide DHCP services along with performing other functions, such as acting as an application server, general database server, providing DNS services and so forth. So, a DHCP server need not be a special computer; any device that can run a DHCP server implementation can act as a server. In fact, the DHCP server may not even need to be a host computer at all. Today, many routers include DHCP functionality. Programming a router to act as a DHCP server allows clients that connect to the router to be automatically assigned IP addresses. This provides numerous potential advantages in an environment where a limited number of public IP addresses is shared amongst multiple clients, or where IP Network Address Translation (NAT) is used to dynamically share a small number of addresses. Since DHCP requires a database, a router that acts as a DHCP server requires some form of permanent storage. This is often implemented using flash memory on routers, while “true” servers of course use hard disk storage. Virtually all modern operating systems include support for DHCP, including most variants of UNIX, Linux, newer versions of Microsoft Windows, Novell NetWare and others. In some cases, you may need to run the “server version” of the operating system to have a host act as a DHCP server. For example, while Microsoft Windows XP supports DHCP, I don't believe that a DHCP server comes in “Windows XP Home”, the “home user” version. (Of course, you could install one yourself!) DHCP Server Software Features In most networks you will choose the operating system based on a large number of factors. The choice of OS will then dictate what options you have for selecting DHCP server software. Most common operating systems have a number of options available for software. While all will implement the core DHCP protocol, they will differ in terms of the usual software attributes: cost, performance, ease of use and so. They may also differ in terms of their features, such as the following:

·

How they allow address ranges (scopes) to be defined.

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·

How clients can be grouped and managed.

·

The level of control an administrator has over parameters returned to a client.

·

The level of control an administrator has over general operation of the protocol, such as specification of the T1 and T2 timers and other variables, and how leases are allocated and renewals handled.

·

Security features.

·

Ability to interact with DNS to support dynamic device naming.

·

Optional features such as BOOTP support, conflict detection, and automatic private IP addressing.

Choosing the Number of Servers In setting up DHCP for a network, there are a number of important factors to consider and decisions to be made. One of the most critical is the number of servers you want to have. In theory, each network requires only one DHCP server; in practice, this is often not a great idea. Servers sometimes experience hardware or software failures, or have to be taken down for maintenance. If there is only one server and clients can't reach it, no DHCP clients will be able to get addresses. For this reason, two or more servers are often used. If you do use more than one server, you have to carefully plan how you will configure each one. One of the first decisions you will need to make is which servers will be responsible for which addresses and clients. You have to determine whether you want the servers to have distinct or overlapping address pools, as discussed in the topic on DHCP address ranges. Distinct pools ensure that addresses remain unique but result in unallocatable addresses if a server fails; overlapping addresses are more flexible, but risk address conflicts unless a feature like conflict detection is used. Server Placement, Setup and Maintenance Once you know how many servers you want, you have to determine on which part of the network you want to place them. If you have many physical networks, you may also need to use DHCP relaying to allow all clients to reach a server. Of course, the structure of the network may affect the number of servers you use, so many of these decisions are interrelated. You must make policy decisions related to all the DHCP operating parameters we earlier. The two biggies are deciding on the size and structure of the address making lease policy decisions such as lease length and the settings for the T1 and You also must decide what clients will be dynamically allocated addresses manually-configured clients will be handled.

have seen pool, and T2 timers. and how

Finally, it's essential for the administrator to remember that an organization's DHCP server is a database server and must be treated accordingly. Like any database server, it must be maintained and managed carefully. Administrative policies must be put into place to ensure the security and efficient operation of the server. Also, unlike certain other types of database systems, the DHCP database is not automatically replicated; the server database should therefore be routinely backed up, and using RAID storage is also a good idea.

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12. Content server Content Server Business users in today’s organizations require timely and relevant information to make effective decisions on a daily basis. Inmagic, Inc. has offered content and information management tools and applications for information-intensive organizations for close to two decades. Unlike more complex content management systems that often require extensive support from internal technical staff as well as a significant commitment of both time and money, Inmagic® Content Server offers a self-managed system that can be deployed quickly and cost-effectively, with only minimal ongoing support from IT. With Inmagic Content Server YOU are in the driver’s seat. Content Server enables you to: • Create content as well as integrate existing content from internal and external sources • Deploy that content to Web pages on intranets, extranets and the Internet • Organize and manage the information flow and have the databases you create drive the content that end users access. Inmagic Content Server [CS] combines the advantages of a robust and flexible database management environment with high speed search and categorization, making finding relevant information fast, easy and precise. Web publishing capabilities are built into Inmagic CS, offering a better way to publish, access, and maintain information on corporate intranets and the Internet. Scalable and Extensible Architecture Content Server is built on the Microsoft® SQL Server™ database, ensuring that Inmagic can offer you a range of content management solutions; from the single department or workgroup to global deployment of an enterprise-wide system. From Content Server Workgroup to Content Server Enterprise, you are able to take advantage of the unparalleled scalability and reliability of this industry-standard database. Inmagic CS makes extensive use of other industry and open standards, including XML. Content Server easily integrates internal, external and licensed content providing a single access point for your users. Content from internal data repositories can be combined with dynamic content from Web sites to provide up-to the- minute information on competitive intelligence, business intelligence and other critical content management tasks. Content Server for the Web uses XML and SOAP to enable you to: • Publish content via a Web browser • Add, edit and delete content directly from the browser • Create interactive Web forms using standard third-party tools • Tightly integrate content from your Content Server databases with other applications. Powerful Database Capabilities Combined With Search Accuracy Inmagic Content Server includes a Windows client – CS/Text Works – that allows you to set up and modify databases, independent of direct support from the IT group. While using SQL Server as its data store, Content Server includes a Text base Engine that greatly enhances the database and search capabilities of the standard SQL database. This allows you to create new databases easily and quickly without requiring support from a DBA or Systems Administrator. The Text base Engine provides features such as support for fields and records with no size limitations – an entire document can be stored in a record without utilizing large objects. Repeating fields – such as multiple authors or descriptive terms – are supported without the user having to design additional tables. And, you have complete control over

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indexing fields for fast retrieval. These capabilities make Inmagic Content Server ideally suited to manage unstructured content with maximum flexibility and complete local control.

CS/Text Works also supports a drag-and-drop forms designer to create reports. Full data entry capabilities include a built-in spell checker and thesaurus as well as validation controls. Password protection at the database, field or record level provide inherent security and full-text searching – including keyword, term, phrase, Boolean, proximity and comparison searches – complement the database design capabilities of Inmagic Content Server. The Importance of Local Control Research conducted by Wallace and Washburn Inc. Marketing of Boston clearly demonstrates that business users look to content management systems to provide the right people with the right information. They want such systems to make accessing information, navigating varying information resources and updating content easy and fast. They also want to have greater control of the content at the local level — in their business units and departments — without requiring extensive integration or support from a vendor or IT personnel. Inmagic Content Server meets these requirements for local control and self-management — databases can be set up and modified independent of support from a database administrator. The product’s non programming database design and development environment allow rapid applications development to ensure quick turnaround of product that meets the unique needs of the business group. Inmagic often works with customers to develop specialized content management solutions in a matter of weeks or months. And, even if your organization has invested in an enterprise-wide portal or information system, standards such as XML and SOAP allow Content Server to complement and interface with other corporate systems. You have a local solution that meets your distinct content and information requirements while still integrating effectively within the enterprise-wide system.

For DB/TextWorks Customers Inmagic Content Server is an extension of Inmagic’s DB/Text® product line, currently installed in over 7,000 organizations around the world. Because of its proprietary database architecture, DB/Text Works® is used primarily in small or mid-size information intensive departments such as corporate libraries and document centers, museums, archives, etc. DB/ Text Works is used to manage content collections ranging from litigation support documents to Technical reports, digital and image libraries and all manner of Web-based resources. By upgrading to Inmagic Content Server, current DB/TextWorks customers can expand their information and content management solutions more widely within their enterprises. The extensive compatibility between DB/ Text Works and Inmagic CS ensure that all databases currently built using DB/TextWorks as well as all Web sites developed using the DB/Text® Web Publisher products will run seamlessly in the Inmagic Content Server environment, requiring only that the text base records be exported from DB/Text Works and imported into Content Server. And, because the Windows and Web user interfaces are nearly identical, your users will be able to use Inmagic CS without additional training. About Inmagic

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Inmagic is a global provider of content and information management software and services that organize and deliver enterprise content, seamlessly integrate both internal and external content sources, and deploy business-critical information to corporate portals, intranets, extranets, and the Web. Specific applications include market, business, and competitive intelligence, library automation, litigation support, and Web publishing. Inmagic’s information management solutions are installed in more than 7,000 organizations in over 50 countries.

13. Performance server

The What, Why, and Whether If part of your job is measuring your Web server's performance-or measuring prospective servers against each other-you may want to turn to Web server benchmarking tools to gather the data you need. This article talks about benchmarks: what tools are available, what people are saying about them, and why, if your site handles moderate traffic, you may not need them at all. What is a Benchmark? A benchmark is simply a way to measure system performance. Benchmarks aren't new. Engineers have used them for years. Designing benchmarks to measure chip performance, for example, is a science unto itself. The idea behind benchmarking is simple enough. Perform a process that is typical of what the system you're testing will be expected to perform. Execute and time the process, then perform the exact same test on different systems and measure your results. The devil, in this case, is in the details. As an analogy, say Zolo the Great and Omar are competing knife throwers at the carnival. As Webmaster, er, ringmaster, you have to decide who has the better act, so you decide to benchmark their performance. The first step is to make sure test conditions are identical. Are the models of the same height, in the same position, and standing perfectly still? If they're not standing perfectly still, is the amount of wincing and squirming the same for both throwers? Are the number and position of balloons (or other markers) constant? Is the lighting the same (Omar might just cry foul, for example, if he had to test in the afternoon when the sun was in his eyes.) Once you've set up and run the tests (more than once, of course, to allow for statistical variations) the job is far from over. You now have to interpret the results. Which elements of the performance are the most important? Omar may claim precision should be the determinant, while Zolo the Great argues number of knives thrown per minute is the true measure of skill. Third parties, such as the model, may have different opinions altogether. How Do We Measure Server Performance? When we turn to analyzing Web server performance, deciding what to measure is certainly the first step in benchmarking. Right now the leading benchmarks tend to focus on two measurements of performance: throughput-the rate at which the server can process HTTP requests; and response time-the time a server spends processing a single request. A typical approach is to configure the benchmarking software to simulate a large number of clients, and then to request a set of pages of varying lengths, so you can see results for both small and large files.

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To give you an idea of what kind of results you'd be looking at, just below are SPECweb96's benchmark results for Digital's Alpha server 4000 5/400 running Zeus 1.1.5. Full details of this performance evaluation are at open.specbench.org/osg/web/results/res96q4/web96-961125- 01539.html (see below for a description of SPECweb96).

Throughput (Ops/sec) 117 234 351 468 586 703 820 937 1054 1157

Response (msec) 9.0 8.9 8.9 9.4 10.5 11.5 13.1 15.4 19.8 30.2

There are a number of Web server benchmarking programs available. One of the main ways in which they differ lies in the ability of the user running the test to configure the test parameters. Silicon Graphic Inc.'s WebStone, the first benchmarking software specifically developed to measure HTTP performance, is highly configurable. The idea is that the results are more meaningful if they are tailored to a specific configuration. Why measure retrieval time for a generic 10 KB HTML document when you can measure the time for the actual document itself? The flip side of this argument is that standard tests better allow administrators to analyze comparison data. Standard Performance Evaluation Corp. (SPEC) calls this "apples-to-apples" comparison.

Comparing Benchmarks The descriptions below summarize and compare the benchmarking resources scouted for this article. Availability ranges from free (WebStone is an open, non-proprietary benchmark you can download source code for) to none (the Web66 GStone benchmarks results are available, but not the software itself). SGI's WebStone WebStone, from SGI, was the first available benchmarking software for the Web. It measures throughput and latency for HTTP GET requests, and simulates the load from a varying number of clients. It gives you either statistical output or (if requested) data for each transaction. WebStone also reports transaction failures, and touts itself as being highly customizable, so you can get results that measure how your particular setup will perform. WebStone is an open (some say de facto-Ed.) standard and is available free for download. Ziff-Davis' Web Bench WebBench was developed by the Ziff-Davis Benchmark Operation for use in Ziff-Davis publications' evaluations. It produces two overall scores, one for requests per second, and one for throughput as measured in bytes per second. WebBench includes an additional, dynamic test suite which uses CGI operations, but these tests are platform-dependent. Output is in the form of an Excel workbook, and shows both overall statistics and data for the individual clients. Clients for WebBench must run on Windows 95 or Windows NT systems.

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The software is licensed-but free for download, or you can order the CD for a nominal cost ($5, ZDBOp, 1001 Aviation Parkway, Suite 400, Morrisville, NC 27560). The SPEC's SPECweb96 SPECweb96 is the benchmark for The Standard Performance Evaluation Corporation (SPEC), a non-profit body that develops standards for workstation performance measurements. Unlike WebStone, SPECweb96 doesn't let you customize the workload configuration. The workloads were established by studying representative Internet sites and include a range of file sizes from 1 KB to 1 MB. People who are shopping for a potential server can study the benchmark results (www.specbench.org/osg/web96/results/) submitted by member companies and know they're getting an even comparison. If you want to buy the software to run the test yourself, the cost is $800. 14. Database server -

-

-

Database is simply an organized set of information. Strictly speaking, there's no need for it to even be in computerized form - address books are often used as a simple example of a database, since they contain large volumes of information organized into categories (name, address, and phone number). Despite this, most people now take the term 'database' to refer to information stored electronically. Note also that the general definition of a database given here could encompass many common PC applications, such as electronic mail (which can be organized by recipient or sender) or information in a spreadsheet (which tends to be structured mathematically). In practice, the term 'database' is most commonly used to refer to highly structured information (examples might include order forms or medical information). Most business databases will contain a carefully planned set of information that can be analyzed to indicate overall trends, as well as providing a historical record of past transactions and activities. A basic database system simply allows you to enter and search for information (a process often known as querying). Most modern databases also support the development of specific applications that run on top of the database, which enable you to access the features you need without having to worry about all the complexities of the system. For instance, within one company general staff might have access to an order entry system, while financial staff have access to automatic reporting systems that provide sales summaries and other information. Both use a database server to store information, but the means of entering this, and the ability to change it after entry, will vary between the different applications.

What is a database server?

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A single-person business could run database software on just one PC quite easily. However, in most businesses data will need to be accessed by multiple staff across a network, often simultaneously. Database server software handles this task, making databases available to all relevant employees. This is not simply a matter of creating network connections. Database server software must ensure that information isn't modified by multiple staff members at once, index and sort the information that is entered so it can be easily searched, and allow analysis of the information stored in the database to produce reports. It also allows different applications to use the same centralised storage mechanism. With appropriate hardware, a database server can handle as many of these options as are needed. Staff may use different applications to access this information, but the server will handle the core data storage. Since databases were one of the earliest computer applications to be developed, they have become highly sophisticated over the years. Modern database servers can handle huge volumes of information and present it in a variety of formats, including automatically outputting Web pages from stored data and allowing the placing of orders and other electronic commerce tasks. For many businesses, a database server in some form will lie at the heart of most daily activities. A note about the word server is in order here. Database server software is distinct both from server hardware (which is the physical machine or machines used to run a network) and the server operating system (which runs on the server hardware and provides an interface between it and specific applications, of which a database server is one example). Despite this distinction, in practice all three will work together closely, and your choice of database server will influence your server OS and hardware choices. The types of databases available As database software has evolved, a number of different approaches to storing and linking information have emerged. Some of the more common include: Relational databases. A relational database creates formal definitions of all the included items in a database, setting them out in tables, and defines the relationship between them. For instance, a typical business database would include tables for defining both customers and orders. Using ids or keys, the two tables can be related together. Such databases are called 'relational' because they explicitly define these connections (an order form can look up customer details from the customer table rather than having to store the information twice). Most relational databases now make use of SQL to handle queries (discussed in more detail below). Currently these are the most common form of database. Object databases. Object databases store data in discreet, self-contained units - objects. These objects have specific data, attributes and behaviours associated with them. An

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extremely simple example might be a product database with a shirt object, which has attributes such as size, colour, and price. In practical use, the main difference between object and relational databases is the way in which data is accessed. Programmers use object-oriented programming languages to access the data objects from the object database by calling methods in their code. This takes much of the information that would have resided in the application code and transfers that information to the object database. Thus the application code is simplified. However, at the same time the fact that the database and application are tightly entwined can make accessing the data outside of the application more complex. Object-relational databases. Object-relational databases attempt to combine object and relational approaches. This allows the benefits of using objects where necessary to be tied to the strengths of relational databases. Hierarchical databases. While relational databases arrange data in tabular format, hierarchical databases arrange them in a tree format, with a parent node leading to further child nodes (which in turn may have further nodes of their own). The model is very similar to the way in which a program such as Windows Explorer displays the contents of a hard drive (double-clicking on a parent directory leads down the tree to further information, and so on down the directory tree). This allows for multiple types of subsidiary data, but makes it difficult to identify complex multiple relationships between individual data items (just as there is no obvious link between two subdirectories on a hard drive). Until recently, hierarchical databases have been more common in computer science fields than in real-world applications. However, hierarchical methods have become more popular with the emergence of XML (Extensible Markup Language), which uses a hierarchical structure, as a common data exchange format.

What do I need to know about SQL? SQL (Structured Query Language) is used by relational databases to define queries and help generate reports. First developed in 1976, it provides a standardized means of sending queries to relational databases. SQL also defines more fundamental elements of databases, such as data types. SQL has become a dominant standard in the world of database development, since it allows developers to use the same basic constructions to query data from a wide variety of systems. The central functions of SQL have been defined by international standards organizations: originally the American National Standards Institute (ANSI), and subsequently the International Standards Organization (ISO). Like most computer-based standards, SQL also comes in a number of flavors. The two most recent iterations are SQL-99 (also sometimes known as SQL-3) and SQL-92, both named for the

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years in which they were first released. (SQL-99 had been originally planned for release in 1996). While SQL-92 defined three individual levels of compliance (basic, intermediate and advanced), SQL-99 reverted to the model used in previous versions of providing just one large feature list. More importantly, SQL-99 also added some basic support for object features, extending SQL's usefulness and blurring the distinction between relational and object approaches to databases. It is comparatively rare for vendors to implement the precise standards laid down for SQL, which is a complex standard running into thousands of pages. Several companies choose not to implement every aspect of the existing standards, arguing that the functions in question are rarely if ever needed by developers or users. Simultaneously, many provide additional, functions (known as extensions) to make particular tasks easier. Despite what you might suspect, many companies will simultaneously add their own extensions while ignoring some aspects of the basic standard. Whether these additions and exclusions are important to your business will depend on the exact mix of applications you wish to run or develop, and what existing applications you already have in place.

What other features should I look for in a database? When choosing a database server, the most important consideration will be whether it can deliver the specific application functions you require. These may be supplied in the form of pre-packaged software, or you may choose to develop your own (or more likely hire a consultant to do so). This may involve considerable expenditure, but this needs to be balanced against improved staff productivity and the ability to more accurately analyze your business. Standards compliance. As discussed above, SQL support varies widely between database server suppliers. Databases which comply with SQL should allow relatively straightforward data exchange, so SQL compliance is important, especially in environments running more than one operating system. Security systems. Databases often store highly valuable and sensitive commercial information, so it's important that there is some security system in place, even if this is only a basic username/password system. Most database servers will provide audit trails, allowing you to see who has entered, accessed or modified information. If your database server is going to be exposed to the Internet, then security mechanisms will need to be more robust and you will need to consider whether other mechanisms (such as encryption) are necessary as well.

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Performance features. Databases are generally critical applications, and even a brief outage can be harmful to your business. To help prevent this, modern database servers have borrowed many features from the world of general network operating systems, including fault tolerance (systems to keep the server running in the event of unexpected errors) and load balancing (which allows database queries on high-volume systems to be handled by multiple servers, improving performance and response times). These are unlikely to be needed if you're just running a single database server, but as your needs expand they are likely to become more crucial considerations. If your database server is used for e-commerce applications, these availability issues will take on a heightened degree of importance. While you may not require all these features immediately, you should consider future needs as well as your current plans. Retrofitting these features to your system is likely to be more difficult than installing a database server that supports them from the beginning, even if it takes time for you to actively deploy them. XML: If you will be doing data interchange now or in the future you may want to look for a database that allows extraction of data as XML. This may make using XML as a data interchange format simpler. the database players Reflecting its long heritage, literally dozens of companies offer database server solutions. Some are tailored to individual markets; some are designed to work closely with existing application and OS software; some are aimed at people building their own specific applications, while others have many commercial add-on applications available. A partial, alphabetized list of major companies in the space would include Borland, IBM, Informix, Microsoft, My SQL, Oracle, Red Hat, SAP and Sybase. Many other companies supply applications that will work with database servers from these providers.

What hardware will I need? There's no single answer to this question. You will need to work out how many staff members are likely to connect to the database, and how many transactions (looking up existing data, modifying it or entering new information) will take place. These will provide you with broad parameters for selecting an appropriate database server, and in turn give you a good indication of what your server requirements will be. As with many computing tasks, the more memory, processing power and disk storage you can provide on the server, the better. Don't neglect network connection speeds, either; if you have a high-powered server but a poorly configured network, you'll lose most of the advantage waiting for data to be sent back to you.

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How much should I expect to pay? This is also a difficult question. Database server prices vary hugely. At one end of the spectrum, open source database solutions are available for no up-front cost. At the other extreme, specialized database solutions can cost hundreds of thousands of dollars. Two broad parameters will guide cost: the number of supported features, and the number of connected users. A system that is designed to serve just a few dozen staff and with minimal security features should be cheaper than one that handles thousands of simultaneous transactions and also powers a number of Web sites. The other important factor to consider is the degree to which your database accessing application will be customized. If you can make use of an off-the-shelf application, this will generally be cheaper than having a developer build a custom system for your business. Even a 'free' database system using readily available software will still require an investment in training for your staff, however.

15. Mirrored server -

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16. Popular server products

Popular Server Products

The Netserver X 1000 in Brief There’s little that can beat Giacom’s NetServer XL 1000 dedicated server in terms if price and performance. If these you’re first dedicated server or you’re searching for the most cost-effective solution, then this is the server for you. Prices start from only £99 per month, and there are no set-up fees. You get access to the desktop of your own Windows 2003 Server for your online use. Simply connect to the server from your PC or Mac, and you’ll have complete control over the vast array of on-board features such as the unlimited domain web server, FTP server, full unlimited mail server, stats server, and a place to launch your online applications. And exclusive to Giacom, all NetServers are individually protected by their own hardware firewall providing second-to-none security and protection at no extra cost.

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Netserver XL 1000 specification Processor HDD Memory O/S

: : : :

Server

: : : :

Domains

:

Network

:

Training

:

Intel Core 2 Duo E6300 Processor 250 GB SATAII Hard Disk 512MB DDRII RAM Windows 2003 Server- Web edition (Upgrade to Windows 2003 Standard edition available. 1 static IP address Full remote administration access Giacom managed DNS No domain import / export charges Load balanced network Free domains imports Free domain exports Giacom managed DNS 24x7 network 100% network Load balanced datacenter Server training

monitoring SLA

Pricing THE NETSERVER XL1000 Bandwidth (GB)

10

15

20

30

40

60

Per month

£99

£149

£199

£269

£339

£469

Setup

Free

Free

Free

Free

Free

Free

THE NETSERVER XL1400 So you’re looking for server performance? The NetServer XL1400 definitely comes with excellent credentials – centered around the fast Core 2 Duo E6600 processor, this is Giacom’s most popular power server. Prices start from only £139 per month, with only £99 set-up. You get access to the desktop of your own Windows 2003 Server for your online use. Simply connect to the server from your PC or Mac, and you’ll have complete control over the vast array of on-board features such as the unlimited domain web server, FTP server, full unlimited mail server, stats server, and a place to launch your online applications. And exclusive to Giacom, all NetServers are individually protected by their own hardware firewall providing second-to-none security and protection at no extra cost. Netserver XL 1400 Specification Processor

:

Processor

HDD

:

320GB SATAII hard disk

Memory

:

1 GB DDRII RAM

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O/S

: Windows 2003 Server – Web edition : (Upgrade to Windows 2003 Server edition available.) Server : Free VPN hardware Firewall : 1 static IP address : Full remote administration access : Giacom managed : No domain import / export : Load balanced network Domains : Free domain imports : Free domain exports : Giacom managed DNS Network : 24x7 network : 100% network : Load balanced datacenter Support : Training :

DNS charges

monitoring SLA

Giacom dedicated : Free priority pager service Server Training

support

PRICING Bandwidth (GB)

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Per month

£139

£189

£239

£309

£379

£509

Setup

£99

£99

£99

£99

£99

£99

THE NETSERVER XL1600 Giacom’s flagship dedicated server, the NetServer XL1600 provides ultra fast performance using its Intel Core 2 Extreme processor backed up by twin RAID1 duplicated hard drives. Prices start from only £199 per month, with only £599 set-up. You get access to the desktop of your own Windows 2003 Server for your online use. Simply connect to the server from your PC or Mac, and you’ll have complete control over the vast array of on-board features such as the unlimited domain web server, FTP server, full unlimited mail server, stats server, and a place to launch your online applications. And exclusive to Giacom, all NetServers are individually protected by their own hardware firewall providing second-to-none security and protection at no extra cost. Netserver XL 1600 specification Processor Memory

: :

Intel Core 2 Extreme 2.6Ghz (Quad Core) 400Gb SATAII hard disk x 2 RAID 1

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O/S Server

: :

Domains

: : : : : : : : : : : : :

Network Support Training

2GB DDRII 800 RAM Windows 2003 Server – Web edition (Upgrade to Windows 2003 Standard edition available.) RAID 1 Free VPN hardware Firewall 1 static IP Full remote administration Giacom managed No domain import / export Load balanced network 24x7 network 100% network Load balanced datacenter Giacom dedicated Free priority pager service Server training

address access DNS charges monitoring SLA support

PRICING Bandwidth (GB)

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£199

£249

£299

£369

£439

£569

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£599

£599

£599

£599

£599

£599

UNIVERSAL SERVER FEATURES Microsoft Windows 2003 Server Microsoft IIS web and ftp SmarterMail mail SmarterStats website SmarterTicket website support F-Prot Dedicated Hardware Domain name 100% network Service Level Fully managed Hardware fault Priority Secure remote desktop administration

OS server server statistics system anti-virus Firewall management Agreement DNS management support

YOUR SERVER WILL BE PROTECTED BY ITS OWN DEDICATED VPN FIREWALL

We believe all dedicated servers should be protected fully when exposed to the Internet, that's why we only supply our servers with an accompanying Dedicated Hardware Firewall as standard. This Stateful Packet Inspection Firewall sits between your server and the rest of our network and, of course, the Internet. You have full individual control over the firewall settings allowing specific rules to be set should you need extra protection. What's more, the firewall is installed as standard with no extra cost to you. CONNECT USING A VIRTUAL PRIVATE NETWORK (VPN)

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Communication across the Internet can be insecure, so you can connect to your Dedicated Server using the on-board VPN. From your network or PC, using high-level encryption, you'll create a data-tunnel protecting the information you pass to and from your server. FIREWALL SPECIFICATION Firewall

High performance hardware VPN firewall

Type

Stateful Packet Inspection

VPN

2x VPN (IPSec) endpoints and pass-through support DES (56 bit) and 3DES (168 bit) encryption Auto Internet Key Exchange (IKE)

Management

Remote management via Server desktop only Menu-driven user interface for easy server management System performance and status monitoring

NAT

One-to-One

Lesson VII: Web Server and Databases ·

Databases

What is a Database?

Wondering what a database is? Well, this is the right place to be. Basically, a database is a collection of data organized for easy storage and access. Data is a single piece of information, and can include, but is not limited to, text, images, numbers, and media clips! Databases help to organize data in a coherent way to help us in our everyday lives. Every single day, we can accumulate tons of data. Without a way to organize all of this, the world would be a complete mess of little pieces of scattered information! You might not know it, but you frequently use databases in your everyday lives. Have you ever checked a dictionary for the spelling of some unknown word? Well, dictionaries are large databases of words! They organize words and their definitions in such a way to make it easy for us to use! Your local library is also an example of a database. They store hundreds upon hundreds of books in a logical order. There's the children's section and the adult's section, the nonfiction and fiction sections, the paperback and hardcover sections, and so on. Within these sections, books are placed in alphabetical order or in the order denoted by the Dewey Decimal System. All of this is a coherent way to organize books! Libraries and dictionaries are both paper-based databases. This means that these databases are not computerized, but instead are written down on paper. Paper-based databases have often presented dozens of problems. They are cumbersome and hard to transport from one place to another. It is also quite easy to misplace a page or a portion of the database! That is why some brilliant scientists have introduced computerized databases. These are databases

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that rely on computers to organize and store data. They are fast, compact, durable, and extremely reliable! Ever since computerized databases have been introduced, they have played an integral part in record keeping and in the storage of data. These databases are often used by the government, by universities and colleges, and by businesses to keep track of data. Most of these databases are private and of no interest to the general public. However, there is also a variety of databases, both commercial and non-profit, for the public. Anybody could access these databases, providing that they had the proper software and hardware. As the years have progressed, databases have begun to play an important role in the Internet. They are vital components of many websites, especially on-line stores, like Amazon or Barnes and Noble. Databases are also vital components of search engines like Yahoo and Google. They enable the search engines to keep track of the millions of websites so that you can access them quickly and efficiently. Also, there is what is called an on-line database. These are databases that are available to anybody that has a modem, computer, and a telephone line- basically, anybody with Internet access! The user merely connects to the database, type in the data it wants to access, and voila, the data is displayed on the computer screen Parts of a Database

Now that you know what a database is, you might be wondering how exactly these things work. Databases are divided into three main parts: 1. Data: Of course, as databases are specially designed to organize data, data is one of the key parts of a database! As you probably already know, data is a small bit of information. It could be in the form of pictures, text, numeric values, media, or audio samples. Any information that you gather can be considered data. For example, pretend that you are growing sunflowers in science class. Your teacher has told you to measure the plant to see how much it has grown. Your measurements are a type of data! The data is the information that is placed in a database. Here is a database that we are all familiar with- an address book. Pretend that you have an address book that is set up to resemble a table: Name John Cook Matthew Smith Emily Coffey Mary France

Address 255 Main St. 43 First Ave. 2 Meadow Ln. 43 Strawberry Rd.

Phone Number 543-7885 423-4567 978-2346 231-5926

E-mail [email protected] [email protected] [email protected] [email protected]

All of the names, addresses, phone numbers, and e-mail addresses are called data. 2. Field: Fields are where the data goes when it is entered into a database. Recall the address book that we mentioned above. Each of the columns would be called a field. The words in bold are called Field Names, because they describe the information that is to

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be contained in the field. All fields can contain different types of information. For example, the "Name" field above contains the names of the people, while the "Address" field contains the people's addresses. Some fields can contain text, some numeric values, some images, some a short movie clip, some an audio file- the list goes on and on. Sometimes, you can control the type of data that can be placed in a certain field. For example, say you want to limit the "Name" field in the above address book to only letters. There are "attribute" tags you can add to each field that restrict the kind of data that is to be placed in the field. For example, there are "attribute" tags that might say that you can only place letters in a field and other "attribute" tags that might say you can only place numbers in the field. There is also another type of attribute tag that can limit the number of characters that you can place in a field. For example, a certain attribute tag might say that you can only type in a maximum of 10 letters in a certain field. Finally, there is a type of attribute tag that is called "required, optional, or calculated." These attribute tags control the amount of data to be placed in a certain field. If a field is given the "required" attribute tag, that means that the field is mandatory- meaning that you must put data in the field. You cannot leave it empty. On the other hand, a field with an "optional" attribute tag does not have to be filled in. Finally, the "calculated" attribute tag means that the user is not supposed to fill it in. The computer will later fill in this field after it has performed the necessary calculations. 3. Records Just as fields would be the columns in the address book above, the records would be the rows. If you take a look at the address book that we mentioned above, a record would be a row of data. However, keep in mind that the first row is NOT called a record because it contains the field names. Thus, records begin with the second row.

Database Files: As you might know, computer files are collections of data. For example, the word document I typed this article on would be a text file. The picture of my cat that I scanned onto my computer would be saved as a graphic file, while the MP3 that I downloaded off the Internet would be stored in an MP3 file. There are also special types of files that are used to store the data in databases. These are called database files. Database files are composed of all of the fields, records, and data that are found in a typical database. The more files that are found in a single database, the larger the database will be! Types of Databases

As with just about everything else in the world, there are many different types of databases. There are also different ways to classify these types of databases. Two popular ways to

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differentiate between databases is by the function of the database and by the data model of the database. Function: First, we shall take a look at classifying by the function of the database. There are different databases that are used for different tasks and jobs. The two categories here are analytic databases and operational databases: Analytic Databases: Analytic databases, also called On Line Analytical Processing (OLAP), are databases that are primarily used to keep track of statistics. Usually, they are read-only, meaning that you can only retrieve data, but you can't modify the data in any way. They are often used by stores as inventory catalogs. They keep track of the company's sales, and then can be read and analyzed to determine how and when more products are sold. These databases can hold all sorts of descriptive information about the goods stored in a company's inventory. Operational Databases: Operational databases, also called On Line Transaction Processing (OLTP), are databases that have a completely different job. These databases, unlike the analytic databases, let you actually change and manipulate the data. While analytic databases only let you view the data, these databases let you modify the data in any way you would like- you can add data, delete data, or even change the data. Data Model: Another way of classifying databases is by their data model. So, what's a data model? A data model is the intangible form in which data is stored. It is kind of like the structure of a database, but data models are only a theoretical idea; they are abstract concepts that you cannot touch. Data models are used to describe how the data is stored and retrieved in a database. Now, we will discuss a few of the types of data models.

Flat-file Database Model: The flat-file data model is generally used by the old paper-based databases. In this system, data was stored in numerous files. However, the files were not linked, so often, data might be repeated in more than one file. This caused everything to be quite redundant. The original "database," flat-file databases inspired scientists to find a way to link files so that they would not be repetitive. Hierarchical Database Model: The hierarchical database model took steps to get rid of the repetitiveness of the flat-file database model, but although it was somewhat successful, it did not completely succeed. There is still a level of redundant data in hierarchical databases. A hierarchical database consists of a series of databases that are grouped together to resemble a family tree:

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Each of the boxes in the diagram represents one database. The top database in the hierarchical model is called the "parent" database. The databases under it are called "child" databases. One "parent" can have many "children," but a "child" can only have one "parent." The child databases are all connected to the parent database via links called "pointers." To get to a child database in the hierarchical database model, you must first go through the parent database, and then through the levels above it. If you have Microsoft Windows, you might realize that this is how Windows Explorer works. First, you open up a file- usually it's "My Computer." Under "My Computer," you can then choose from a list of drives. Pretend you clicked on the "Disk Drive C" icon. Then, under this, you can choose from a series of folders. After opening one folder, you can open another folder, and another, until you reach the file that you want. Notice in the diagram above how the child databases on the same level are not connected. This presents a problem in the hierarchical database model and makes searching for data extremely difficult. Another problem is that data cannot be entered into the child databases until that field has been added to the parent database. This method was quite inefficient. Thus, although the hierarchical database model reduced some repetitiveness of data, it also presented many new problems. Network Database Model: The network database model was designed to help resolve some of the hierarchical database model's problems. For one thing, it allowed for links between the child databases. This no only reduces the chance of redundant data, but also makes searching for data much easier! Another improvement of the network database model over the hierarchical model is that while in the hierarchical model a child database can only have one parent, in the network model, a child database can have more than one parent! However, the network database model still had its share of problems. For one thing, it was difficult to execute and maintain. Only database experts could successfully use these databases. It was difficult for the general public to use network databases for real-life applications. Relational Database Model: The relational database model came in at full swing during the 1980s. Modeled after the work of Dr. E. F. Codd of IBM, the relational database model is extremely popular because it solved many of the problems displayed in the hierarchical and network database models.

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The relational database model is different from the hierarchical and network database models in that there are no "parent" and "child" databases. Rather, all of the databases in the relational database model are equal. Data can be stored in any number of separate databases. Then, these databases are connected by a "key" field. A key field is a field (in case you don't remember, a field is the columns in the database where the data is stored- see "Parts of a Database" for more details) that is found in all of the databases that are being linked together. All of the databases can be used to hold different types of data. For example, let's pretend that we have an address book, which is a paper-based database. If we were to use the relational database model, then we would store all of the data in separate databases. One database could hold a person's address; another could hold the person's phone number, etc. However, all of the databases might have one field that is the same, like, for example, the person's name. This makes it easy to search for and extract data from the databases. It is also very efficient and easy to use. No wonder why this database model is so popular! Object-oriented Databases: You might realize that databases can not only store text and numeric values, but that there are special databases that can also store photos, sounds, videos, and all sorts of graphics. How is this possible? Well, I can tell you one thing, the old hierarchical, network, and relational databases couldn't store all of these types of data! As a matter of fact, this is where the object-oriented database models come in. Object-oriented database models let databases store and manipulate not only text, but also sounds, images, and all sorts of media clips! They are extremely useful, but unfortunately, they are large in size and are extremely expensive. Thus, they are only found in large commercial or governmental organizations. Client/Server Databases As you probably know, the Internet is one of the most popular usages of a computer. Client/server databases are the databases that you will use for the Internet and for the World Wide Web. The database is left on 24 hours a day, 7 days a week. This is so that users, or clients, can access the web sites or whatever other data is contained in the database at any time they want. This is especially necessary if you want to make the applications available to anybody, anywhere in the world. There is a special type of interface that lets the clients submit certain data requests from the database. Then, the database will handle and process the requests!

How Databases Work

In previous sections, we have described what databases are, what the parts of a database are, and what the types of databases are. But how do you interact with a database? How do you add, change, or delete data? There are two ways to connect to a database.

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1. Command Shell: The first way to connect to a database is by using a command shell. These are devices that gives you access to the data in a database. First, you need to log on, after which you will be able manipulate data and receive the output of your actions. Command-shells come in many different forms. Some can be quite simple, while others are quite fancy, complete with graphics and icons! 2. Network Sockets: The second way to connect to a database is through sockets over a network, like the Internet. This way lets you connect to a database by using a local-area network (LAN) or a wide-area network (WAN). Thus, you can access a database in Seattle, Washington while at a business conference across the country in Philadelphia, Pennsylvania!

SQL: As with computers, people, and animals, databases have a type of language. The most common language used by relational databases is SQL, or Structured Query Language. As you may or may not know, databases are arranged in table-like structures. The columns are called fields, while the rows are called records. (See Parts of a Database for more details.) It is in these fields and records that data is stored. You can use commands in the SQL language to access and manipulate the data in the fields and records of a database. How does SQL keep track of all of these tables? Well, SQL databases have "data dictionaries." These are merely tables that keep track of all of the data tables! You will type in the name of the table where the data you want access to is held, and the database will search through its data dictionary until it comes up with your table. When you type in a command to an SQL database, you first must type in the name of the table you want. Then, you can give the database the specific details that you want. The database will search through its data dictionaries until it finds the correct piece of data. The database will then produce a "view," or result, of the information that you specified! It's as simple as that. ·

Introduction to database gateways for web servers

The Recital Universal Application Server comes complete with the Recital Relational Database Management System. It can also be extended via database gateways to give full access to other data sources and SQL based RDBMSs. Gateways are available to ODBC data sources, such as Microsoft Access or SQL Server, to JDBC data sources via third party JDBC drivers, to MySQL, PostgreSQL, Informix, Ingres and Oracle and to Recital itself.

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Once a connection is established to the server, there are two ways for the Universal Application Server (UAS to access the data: 1. ‘Pass Through’ technology. This allows full access to all data related commands provided by the server. The UAS passes SQL statements through to the server without parsing them, so the SQL statements issued must be valid for that particular server. The Remote Data Connectivity Functions can be used to provide automatic cursor creation and fetching when using Pass Through SQL. Please see the SQL Reference Manual for details. 2. Recital/4GL. A subset of the Recital work surfaces and 4GL commands and functions can be used against the data source. The SET GATEWAY and LOGIN commands can each be used to establish a connection to a gateway server. SET GATEWAY SET GATEWAY TO [ | <expC1>] [IN <work area/alias>] [ALIAS <expC2>] The gateway is defined using a predefined gateway file (.gtw) or a character expression, <expC1>. If | <expC1> is not included with the SET GATEWAY command, the connection in that workarea will be detached. An optional ALIAS <expC2> keyword can be used to specify an alias name for the workarea that is currently connected. Note: Gateway files can be created using the CREATE CONNECTION or CREATE GATEWAY (Recital Terminal Developer work surface) commands. Please see the Commands and SQL references manuals for more details. The basic format of <expC1> is as follows: server@machinename:username/password-database.protocol

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// Connect to Ingres server set gateway to “ing@sun5:inguser1/ingpass1-accounts.tcpip” For server-specific variations, please see below: JDBC server@machinename:username/password-driver path;url

// Connect to Recital JDBC Driver set gateway “jdbc@linux:jdbuser1/jdbpass1-/usr/java/lib/RecitalJDBC/Recital/sql/RecitalDriver;” + ; “jdbc:Recital:SERVERNAME=linux1;DIRECTORY=/usr/recital/ud/demo” ODBC server@machinename:username/password-datasource

the datasource name as specified in the ODBC Data Source Administrator. // short format for local ODBC data source set gateway to “odbc:Northwind” // long format set gateway to “odbc@host1:user1/pass1-Northwind” ORACLE server@machinename:username/password-service

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to

// Connect to Oracle server set gateway to “ora@host2:scott/tiger-orasamples” LOGIN LOGIN [<server>,<nodename>,<username>,<password>[, | | <service> | ]] The LOGIN command allows you to connect to database gateway server via the Recital Universal Application Server. In Character Mode environments, the login command can be issued without specifying all the connection parameters. In this case, a dialog box labeled “LOGIN TO DATABASE SERVER” will be displayed on the screen prompting for the missing parameters.

Example // Recital Gateway login “recital”, “hp5”, “hpuser1”, “hppass1”, “/usr/recital/data/southwind” // Recital JDBC Driver server = “jdbc” nodename = “host2” username = “user1” password = “pass1” database = “/usr/java/lib/RecitalJDBC/Recital/sql/RecitalDriver;" + ; “jdbc:Recital:SERVERNAME=host2;DIRECTORY=/usr/recital/ud/demo”

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login server,nodename,username,password,database // Oracle Gateway login “oracle”, “orahost”, “scott”, “tiger”, “orasamples”

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Common Gateways Interface

The Common Gateway Interface (CGI) is a standard for interfacing external applications with information servers, such as HTTP or Web servers. A plain HTML document that the Web daemon retrieves is static, which means it exists in a constant state: a text file that doesn't change. A CGI program, on the other hand, is executed in real-time, so that it can output dynamic information. For example, let's say that you wanted to "hook up" your Unix database to the World Wide Web, to allow people from all over the world to query it. Basically, you need to create a CGI program that the Web daemon will execute to transmit information to the database engine, and receive the results back again and display them to the client. This is an example of a gateway, and this is where CGI, currently version 1.1, got its origins. The database example is a simple idea, but most of the time rather difficult to implement. There really is no limit as to what you can hook up to the Web. The only thing you need to remember is that whatever your CGI program does, it should not take too long to process. Otherwise, the user will just be staring at their browser waiting for something to happen.

Specifics Since a CGI program is executable, it is basically the equivalent of letting the world run a program on your system, which isn't the safest thing to do. Therefore, there are some security precautions that need to be implemented when it comes to using CGI programs. Probably the one that will affect the typical Web user the most is the fact that CGI programs need to reside in a special directory, so that the Web server knows to execute the program rather than just display it to the browser. This directory is usually under direct control of the webmaster, prohibiting the average user from creating CGI programs. There are other ways to allow access to CGI scripts, but it is up to your webmaster to set these up for you. At this point, you may want to contact them about the feasibility of allowing CGI access. If you have a version of the NCSA HTTPd server distribution, you will see a directory called /cgi-bin. This is the special directory mentioned above where all of your CGI programs currently reside. A CGI program can be written in any language that allows it to be executed on the system, such as: ·

C/C++

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Fortran

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PERL

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TCL

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Any Unix shell

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·

Visual Basic

·

AppleScript

It just depends what you have available on your system. If you use a programming language like C or Fortran, you know that you must compile the program before it will run. If you look in the /cgi-src directory that came with the server distribution, you will find the source code for some of the CGI programs in the /cgi-bin directory. If, however, you use one of the scripting languages instead, such as PERL, TCL, or a Unix shell, the script itself only needs to reside in the /cgi-bin directory, since there is no associated source code. Many people prefer to write CGI scripts instead of programs, since they are easier to debug, modify, and maintain than a typical compiled program.

How do I get information from the server? Each time a client requests the URL corresponding to your CGI program, the server will execute it in real-time. The output of your program will go more or less directly to the client. A common misconception about CGI is that you can send command-line options and arguments to your program, such as command% myprog -qa blorf CGI uses the command line for other purposes and thus this is not directly possible. Instead, CGI uses environment variables to send your program its parameters. The two major environment variables you will use for this purpose are:

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QUERY_STRING QUERY_STRING is defined as anything which follows the first ? in the URL. This information could be added either by an ISINDEX document, or by an HTML form (with the GET action). It could also be manually embedded in an HTML anchor which references your gateway. This string will usually be an information query, i.e. what the user wants to search for in the archie databases, or perhaps the encoded results of your feedback GET form. This string is encoded in the standard URL format of changing spaces to +, and encoding special characters with %xx hexadecimal encoding. You will need to decode it in order to use it. If your gateway is not decoding results from a FORM, you will also get the query string decoded for you onto the command line. This means that each word of the query string will be in a different section of ARGV. For example, the query string "forms rule" would be given to your program with argv[1]="forms" and argv[2]="rule". If you choose to use this, you do not need to do any processing on the data before using it.

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PATH_INFO CGI allows for extra information to be embedded in the URL for your gateway which can be used to transmit extra context-specific information to the scripts. This information is usually made available as "extra" information after the path of your gateway in the URL. This information is not encoded by the server in any way. The most useful example of PATH_INFO is transmitting file locations to the CGI program. To illustrate this, let's say I have a CGI program on my server called /cgi-bin/foobar that can process files residing in the DocumentRoot of the server. I

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need to be able to tell foobar which file to process. By including extra path information to the end of the URL, foobar will know the location of the document relative to the DocumentRoot via the PATH_INFO environment variable, or the actual path to the document via the PATH_TRANSLATED environment variable which the server generates for you. How do I send my document back to the client? I have found that the most common error in beginners' CGI programs is not properly formatting the output so the server can understand it. CGI programs can return a myriad of document types. They can send back an image to the client, and HTML document, a plaintext document, or perhaps even an audio clip. They can also return references to other documents. The client must know what kind of document you're sending it so it can present it accordingly. In order for the client to know this, your CGI program must tell the server what type of document it is returning. In order to tell the server what kind of document you are sending back, whether it be a full document or a reference to one, CGI requires you to place a short header on your output. This header is ASCII text, consisting of lines separated by either linefeeds or carriage returns (or both) followed by a single blank line. The output body then follows in whatever native format.

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A full document with a corresponding MIME type In this case, you must tell the server what kind of document you will be outputting via a MIME type. Common MIME types are things such as text/html for HTML, and text/plain for straight ASCII text. For example, to send back HTML to the client, your output should read: Content-type: text/html <TITLE>output of HTML from CGI script

Sample output

What do you think of <STRONG>this?

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A reference to another document Instead of outputting the document, you can just tell the browser where to get the new one, or have the server automatically output the new one for you. For example, say you want to reference a file on your Gopher server. In this case, you should know the full URL of what you want to reference and output something like: Content-type: text/html Location: gopher://httprules.foobar.org/0 <TITLE>Sorry...it moved

Go to gopher instead

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Now available at a new location On our gopher server. However, today's browsers are smart enough to automatically throw you to the new document, without ever seeing the above since. If you get lazy and don't want to output the above HTML, NCSA HTTP will output a default one for you to support older browsers. If you want to reference another file (not protected by access authentication) on your own server, you don't have to do nearly as much work. Just output a partial (virtual) URL, such as the following: Location: /dir1/dir2/myfile.html The server will act as if the client had not requested your script, but instead requestedhttp://yourserver/dir1/dir2/myfile.html. It will take care of most everything, such as looking up the file type and sending the appropriate headers. Just be sure that you output the second blank line. If you do want to reference a document that is protected by access authentication, you will need to have a full URL in the Location:, since the client and the server need to re-transact to establish that you access to the referenced document. Advanced usage: If you would like to output headers such as Expires or Content-encoding, you can if your server is compatible with CGI/1.1. Just output them along with Location or Content-type and they will be sent back to the client. Writing secure CGI scripts Any time that a program is interacting with a networked client, there is the possibility of that client attacking the program to gain unauthorized access. Even the most innocent looking script can be very dangerous to the integrity of your system. With that in mind, we would like to present a few guidelines to making sure your program does not come under attack.

·

Beware the eval statement Languages like PERL and the Bourne shell provide an eval command which allow you to construct a string and have the interpreter execute that string. This can be very dangerous. Observe the following statement in the Bourne shell: eval `echo $QUERY_STRING | awk 'BEGIN{RS="&"} {printf "QS_%s\n",$1}' ` This clever little snippet takes the query string, and convents it into a set of variable set commands. Unfortunately, this script can be attacked by sending it a query string which starts with a ;. See what I mean about innocent-looking scripts being dangerous?

·

Do not trust the client to do anything A well-behaved client will escape any characters which have special meaning to the Bourne shell in a query string and thus avoid problems with your script misinterpreting the characters. A mischievous client may use special characters to confuse your script and gain unauthorized access.

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·

Be careful with popen and system. If you use any data from the client to construct a command line for a call to popen() or system(), be sure to place backslashes before any characters that have special meaning to the Bourne shell before calling the function. This can be achieved easily with a short C function.

·

Turn off server-side includes If your server is unfortunate enough to support server-side includes, turn them off for your script directories!!!. The server-side includes can be abused by clients which prey on scripts which directly output things they have been sent.

·

Server Application Programming Interfaces (SAPIs) ·

JavaScript

JavaScript is a scripting language used in many websites. A scripting language is a language, which is easy and fast to learn. So is this reference. A scripting language is interpreted in run-time. It is not compiled like other languages as C++, C#, VB.NET etc. JavaScript is a client side language and it runs on the client browser. Netscape developed it and because of its simplicity it is one of the most known scripting languages. However JavaScript can be also used on the server-side. JavaScript can be used on all most known browsers. It can be easily used to interact with HTML elements. You can validate text fields, disable buttons, validate forms, or change the background color of your page. All this is possible with JavaScript. Like each programming language, it contains variables, arrays, functions, operators, objects and much more which can be help you to create better scripts for your pages. On the server side you can use JavaScript for example to manage your database entry. JavaScript code can be inserted directly in the HTML or you can place it in a separate file with the .js extension and link the web page with the .js file. Is JavaScript a lighter version of Java? Many who haven’t worked before with java or scripting languages think that JavaScript is the same as Java or a lighter version of it. This is not true. Java is a different language developed by Sun Micro Systems. Java is much more complex then JavaScript. In Java you have to declare each variable with the type, in JavaScript you don’t need to do that. All variables are declared when you first time use them. Furthermore in Java you have to declare all variables, functions and classes. In JavaScript you don’t even need to think about these things. Java is compiled to byte codes on the server and the result is send to the client. JavaScript is interpreted on the client side it doesn’t require any compilation. Usage of JavaScript Usually web-designers design pages and coders code applications. However with JavaScript a designer has the possibility to create a client side application with very less efforts. He can easily create some kind of dynamic pages – i.e.: you can easily show a prompt box and asks the user to enter his name whenever the page loads for the first time. He can then use the entered value to create a welcome string. These procedures are called events. Events can be used and called when something occurs – like loading the page for the first time. You could also write another event which is called whenever the page is closed. JavaScript is also mostly used to validate text fields. For example in asp.net you have the possibility to validate

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your controls with some validator controls. These validator controls are basically nothing more then a JavaScript file. This validation can be easily written with JavaScript to verify if a text field is empty or not. JavaScript Functions Introduction Functions are an important part in any programming language. A function is a block of commands, which can be executed again and again, by the calling the name. JavaScript contains some inbuilt functions, which can be used freely and you can create your own functions. A function contains of a name and a body. Each function starts with the keyword function and then the name of the function. After that you can put your required commands in the body part which must be enclosed with the {} brackets. Once you have created your function you can call it with the name of the function. JavaScript Simple Function <script type="text/javascript"> // Create a function function X() { document.write("This is a simple function.
") } // Call the function X()

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Output

JavaScript Functions with Parameters The above example displays a simple function, however you can also pass arguments to a function. For that you have to define the parameter in the in the brackets of the function name. Once you have declared your parameter you can simply pass the value when calling the function. The following example demonstrates it. Example …function CalculcatePI(number){ document.write("This is a function with parameters.
") var PI = 3.14 document.write(number*PI+"
")} // Call function and pass 5 as a parameter Calculate(5)… Output

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JavaScript Functions with Return Values Functions can also return the value instead of displaying it. This can be useful if you need to do some more processing with the variable returned by the function. The following example demonstrates it. Example …function ReturnPIValue(number){ document.write("This is a function with parameters and a return value.
") var PI = 3.14 return number*PI// Call function, which will return a value.var x = ReturnPIValue(5) document.write(x)… Output

·

ASP

Active Server Pages or ASP is a technology developed by Microsoft to further the ability to write applications for the web. Active Server Pages can be written in Visual Basic Script or Javascript and contain the ability to be dynamic. What this means is that a few lines of code can create pages that can change minute to minute. For instance, many applications that access and manipulate data in databases are now being written in ASP and as the database is updated the web pages are also updated. In this tutorial we will focus on the Visual Basic Scripting side of ASP and demonstrate how a few functions work within this technology. In order to properly utilize Active Server Pages technology you must either have a Windows NT 4.0 Server or greater with IIS 3.0 or greater or Windows NT 4.0 Workstation or greater with PWS installed. Once this service is installed and running we must find the root web directory. For ease we will the default web site that is normally installed. Multiple websites can later be added to this. The default directory for these pages is c:\inetpub\wwwroot\. When we place files in this directory they should be able to be accessed via this directory. As an example place a simple text file in this directory and then using the server console try to access this file by typing http://localhost/filename.txt where filename.txt is the file that you

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placed in this directory. If this succeeds you have placed the file in the proper location and have the server software correctly installed. We want to now create dynamic web pages. Let's start with the basics. First off all ASP 3.0 pages are designated with the file extension of .asp. This tells the server to access the asp.dll library to process the page. Secondly all ASP code must fall between these two designators: <% %> The <% %> tells the server to process that information as ASP.

The next line after the initial <% needs to be: @Language=VBScript This tells the server that the language that will be used to create these pages is VBScript. We can now Visual Basic Scripting code within these brackets. An easy and useful element to begin with is the write method of the response object. Response.write has the ability to display on the page either a string or a value from a variable. For instance: Response. Write ("Hello!") This would output: Hello! At this point it would obviously be faster to just create an HTML page to do the same thing. However, perhaps we want to display Hello! five times in a row. By using a for-next loop the ASP code would be three lines: For i = 1 to 5 response.write ("Hello!
") Next i Whereas the HTML code would be five lines: Hello!
Hello!
Hello!
Hello!
Hello!
This is a very simplistic and unstructured example, but it shows where a working knowledge of ASP can cut down on our coding and make our lives easier. In the previous examples a variable of "i" is used to move through the for-next loop. All variables in ASP should be declared by using a "Dim" statement: Dim i This declares the "i" variable as a variant type. A variant type of variable means that "i" can contain an integer, float, string, etc. All constants must be declared using the "Const" statement: Const t=5 To make sure all variables are declared an "Option Explicit" should be one of the first lines in the code. By the way, many programmers do not include this statement and create variables on the fly. The previous for-next loop example would work without first declaring "i" but it is considered bad, unstructured programming. In the rest of the examples it will be assumed that "Option Explicit" proceeds the example as does the variable declarations. Loop-the-Loop

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Active Server Pages contains various loops that can be used to process data. These loops include: If-Then-Else For-Next For-Each-Next Do-While/Until While-Wend Loop

Loop Loop Loop Loop

We will now discuss each of these loop types individually. If-Then-Else Loop This loop allows for checking of code, if a statement is found then certain processing occurs, otherwise something else is processed. If name="Joe" then Response.write ("Hello Joe!") else Response.write("I don't think we have met.") End If In this example if the variable "name" is equal to the value "Joe" then the "Hello Joe!" string is outputted. Otherwise, the script will output "I don't think we have met." For-Next Loop The For-Next loop allows for code to be processed until a specific goal is reached. We have already seen one example of the for-next loop. Here is another example: For i=1 to 20 response.write (i) Next This example outputs the value of "i" 20 times, each time incrementing it once. This would produce: 1234567891011121314151617181920. This allows for code to be run a multiple of times very easily. At any time in a For-Next Loop the loop can exit using an "Exit For" statement. y=7 for i=1 to 20 response.write (i) if i=y then exit for next In this example when "i" equals "y" the For-Next Loop will not continue and the rest of the page will process. For-Each-Next Loop The For-Each-Next Loop is specifically designed for arrays, collections, or dictionaries. This allows for processing to occur on each value in one of these types of situations. If you had an array, for example, you could process for each value in the array. Dim x (20) For Each g in x

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response.write (g) Next The "Exit For" statement works the same way in this situation as it does in the previous For-Next Loop. Do-While/Until Loop The Do-While/Until Loop allows for bits of code to be run Until a goal is attained or While a goal is not attended. x=1 Do While x<10 Response.write ("Hi There!
") x=x+1 Loop This outputs Hi There!
to the page each time incrementing "x". Once x has reached the value of "10" the loop is broken and the page continues processing. Do-Until loops basically work the same way, but instead of proceeding through the loop while a value remains true, it procedures through the loop until something becomes true. At any time in a Do-While/Until Loop the loop can exit using an "Exit Do" statement. x=10 y=7 Do Until x<5 response.write("hello") x=x-1 if x=y then Exit Do Loop In this example when "x" equals "y" the loop will not continue and the rest of the page will process. While-Wend Loop The final loop type we will discuss is the While-Wend. The While-Wend loop will process given statements until a goal or condition is achieved. This type of loop is very similar to the Do-While Loop and generally not thought of as structured as the Do-While Loop. x=1 While x<10 Response.write ("Hi There!
") x=x+1 Wend This outputs Hi There!
and increments "x". Once x has reached the value of "10" the While-Wend loop is broken and the page continues processing. Make a Statement! Now that we have gone over the common loops found in ASP we need to talk about a couple of other useful statements. Select-Case Statement

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First of, the Select-Case statement is a very effective means of executing statements based on the value of a given variable. Job Type="Programmer" Select Case Job Type Select "Graphics Designer" Response.write ("I am a Graphics Designer") Select "Network Engineer" Response.write ("I am a Network Engineer") Select "Programmer" Response.write ("I am a Programmer") End Select In this example the statement "I am a Programmer" would be outputted to the page. A "Case Else" statement can be added so if the condition is not met a selected set of statements are then executed. The Select-Case statement is useful for a greater degree of control, ease of use, and ease of reading than several If-Then-Else statements. With Statement The With statement enables several statements to be performed on an object without the object being requalified every time. With Color Scheme .Trim="Green" .Main Color="Red" .PinStrips="Yellow" End With Nesting Statements All the previous loops and statements have the ability to be nested within each other and within themselves. For instance: If x=y then do until x=8 x=x+1 loop End If In this instance if "x" is equal to "y" a Do-Until Loop is executed until "x" is equal to "8". Where's the Function? Of course, one of the major strengths of any language is the ability to create functions for tasks and then call on those functions whenever necessary. In Visual Basic Script a function is declared by simply calling "Function" a name and any variable names that will get passed into the function. g=total amount (1,5) Function Total Amount(x,y) Total Amount=x+y End Function In this function the values x and y are passed into the function, added and then final result is passed back to the original call. This was an example of a function that returned a value.

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Functions can just as easily process a few lines and then return without sending back any results. Call Write This Function Write This Response. Write ("Hello!") Response. Write ("This is a function!") End Function The function "WriteTshis" was called using the Call statement, it processed the two response. write statements and then returned. No variable was needed since it did not need any values from outside the function. This is not SUB Par! Subs are very close to Functions with one major exception, Subs cannot return any values. This means values can be sent to them, they can process statements within them, they can call other functions or subs, but they cannot send back any results. Remember that "g=total amount(1,5)" that called the total amount function and made the variable "g" equal to the result. That cannot occur with Subs. An error would occur. Subs can only be called by using the Call Statement, like the second function example previously. Call WhatColorisThis (8) Sub WhatColorisThis(x) Select Case x Case 2 Response.write ("Yellow") Case 4 Response.write ("Blue") Case 6 Response.write ("Red") Case 8 Response.write ("Green") End Sub By calling this sub the response of "Green" is outputted to the page and the rest of the processing of the Visual Basic Script occurs. I am ready to write a script! Now that we have gone over the basics we can write a full script. We will create a page and designate it default. asp. Create the file in the c:\inetpub\wwwroot\ directory. Open the file using any text editor, my editor of choice is notepad because of the fact it is installed on every Microsoft Windows machine in the world. In this file place the following code: <% @Language=VBScript Option Explicit Dim Final Result Dim Number1 Dim Number2

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Final Result=NumberstoMultiply (5, 6) Function NumberstoMultiply (Number1, Number2) NumberstoMultiply=5*6 End Function Response. Write ("Your Final Result is” & Final Result & ".") %> Save the file and then open a web browser on the server and go to the URL: http://localhost/default.asp, or replace local host with the ip address or name of the server. This should process your page. With any luck the output of the page would be: Your Final Result is 30. As you can see from the previous example, the response. Write method outputted a string and the variable result followed by. This is done by using the apersand (&) in between the string declaration and variable. I want more! This example is simplistic example of what we can accomplish using ASP. With our arsenal of statements and loops that we discussed we can begin to create much more complex ASP scripts that will make our web lives easier. We can pull data from a database, perform computations, even pull data from other websites. Feel free to try out each loop, it takes practice and experience to learn what loop and statement needs to be used where. ASP is designed to be easy and robust at the same time. ·

PHP

What is PHP? PHP, which stands for "Hypertext Preprocessor", is a server-side, HTML embedded scripting language used to create dynamic Web pages. Much of its syntax is borrowed from C, Java and Perl with some unique features thrown in. The goal of the language is to allow Web developers to write dynamically generated pages quickly. In an HTML page, PHP code is enclosed within special PHP tags. When a visitor opens the page, the server processes the PHP code and then sends the output (not the PHP code itself) to the visitor's browser. It means that, unlike JavaScript, you don't have to worry that someone can steal your PHP script. PHP offers excellent connectivity to many databases including MySQL, Informix, Oracle, Sybase, Solid, PostgreSQL, and Generic ODBC. The popular PHP-MySQL combination (both are open-source products) is available on almost every UNIX host. Being web-oriented, PHP also contains all the functions to do things on the Internet - connecting to remote servers, checking email via POP3 or IMAP, url encoding, setting cookies, redirecting, etc. What do PHP code look like? PHP is a rather simple language. Much of its syntax is borrowed from C except for dealing with the types of variables. You don't need to think of the types of variables at all - you just

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work with their values, not their types. And you don't have to declare variables before you use them. Basic Syntax

·

F

i

l

e

n

a

m

e

:

You should save your file with the extension .php (earlier versions used the extensions .php3 and .phtml).

·

C

o

m

m

//This comment extends to the the

e end

n

t

s

:

of

line.

/* This is a multi-line comment */

·

Escaping

from HTML:

A PHP code block starts with "". A PHP code block can be placed anywhere in the HTML document.

·

Instruction separation: Each separate instruction must end with a semicolon. The PHP closing tag (?>) also implies the end of the instruction.

Here's a small PHP example... < h t m l > < h e a d > < t i t l e > E x a m p l e < / t i t l e > < / h e a d > < b o d y >

< ? p h p $txt = "This is my first PHP script"; /* This line creates the variable $txt and gives it the initial value. Variables in PHP are represented by a dollar sign followed by the name of the variable. The variable name is case-sensitive. */ echo <

/

b

o

d

y

$txt;?> >

Simple PHP mail script This script is not only educational, but also applicable for practical Web development. It allows you to place a simple form for sending emails on any HTML page. The script shows you how to gather user input, perform form validation with PHP, and send an email. First, make the form page mail.html (you may call it whatever you like)... < h y >

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< <

E b b

action="mail.php" m a i l < type="text" > S u b j e type="text" > M e s s a cols=40 rows=10 type="submit" f o b o

method="POST"> / b > < b r > name="email" size=40> c t < / b > < b r > name="subject" size=40> g e < / b > < b r > name="message"> value=" Send "> r m > d y >

The form contains the necessary text fields Email, Subject, Message, and the Send button. The line tells the browser which PHP file will process the form and what method to use for sending data. When the user fills in the form and hits the Send button, the mail.php file is called... < h y > h p

automatically passed to the PHP script through the array */ = $HTTP_POST_VARS['email']; = $HTTP_POST_VARS['subject']; = $HTTP_POST_VARS['message'];

/* PHP form validation: the script checks that the Email field contains a valid email address and the Subject field isn't empty. Preg_match performs a regular expression match. It's a very powerful PHP function to validate form fields and other strings - see PHP manual for details. */ if (!preg_match("/\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+ ([-.]\w+)*/", $email)) { echo "

Invalid email address

"; echo "Back"; } else if ($subject == "") { echo "

No subject

"; echo "Back"; } /* Sends the mail and outputs the "Thank you" string if the mail is successfully sent, or the error string otherwise. */ else if (mail ($email,$subject,$message)) { echo "

Thank you for sending email

"; } else { echo "

Can't send email to $email

"; } ? > < / b o d y > As you see, the script is simply one if ... elseif ... else statement. At first, it validates the required form fields. Note that PHP form validation is performed on the server, after sending

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all the data. Therefore, it would be a good idea to combine server-side form validation with PHP and client-side form validation with JavaScript in order to avoid unnecessary data sending. If the email address is valid and subject isn't empty, the script sends the mail and displays the corresponding message. Note how the variable $email is included into the output string. You can also use this script to implement the safe "Contact Us" function on your website. Your visitors will be able to send you a message, but your email address won't be displayed on the page and spam bots, that parse pages looking for potential email addresses, won't get it. Just remove the Email text field from the form and replace the first line of the script with something like... $email = '[email protected]'; And, of course, you don't need to validate the email address in this case. ·

HMTL

HTML is initials that stand for Hyper Text Markup Language

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Hyper is the opposite of linear. It used to be that computer programs had to move in a linear fashion. This before this, this before this, and so on. HTML does not hold to that pattern and allows the person viewing the World Wide Web page to go anywhere, any time they want.

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Text is what you will use. English letters, just like you use everyday..

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Markup is what you will do. You will write in plain English and then mark up what you wrote.

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Language. Some may argue that technically html is a code, but you write html in plain, everyday English language.

HTML is the code behind your webpage and is what your browser looks for to display a webpage, the way the webdesigner intended it to look, and is a series of tags that tells the browser where to display what. It is really a series of simple commands that you give to the browser, just like telling your dog to sit, and because it is in plain English it is easy to learn. For example, if you want your text to show in a bold type, you command it to be bold text , it really is that easy. Keep this in mind: HTML documents must be text only. When you save a HTML document, you must save only the text, nothing else. HTML browsers can only read text. Look at your keyboard. See the letters and numbers and little signs like % and @ and *? There are 128 in all (read upper- and lowercase letters as two). That's text. That's what the browser reads. It simply doesn't understand anything else. Remember that if you are using Notepad, Wordpad, or Simple Text, the document will be saved as text with no extra prompting. Just choose SAVE. If you are going to start learning to write HTML, it is a good idea to learn to look at other authors' HTML pages. The actual html potion of the page behind the pretty page you see in front of you now.

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Looking at another's html code helps you learn how things are done and you can copy the style of pages that you like. Please do not just steal and copy the pages, but no one will be upset if you make the style in much the same way. For example, if you were going to build a house, you would look around to see what styles you like before deciding on your own design. Same thing here, look around the web and see what styles you like and apply them to your own ideas. Here's how you look at an HTML document (known as the "source code")

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When you find a page you like, click on VIEW at the top of the screen.

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Choose SOURCE from the menu.

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The HTML document will appear on the screen.

Try it with this page. Click on VIEW and then choose the SOURCE. It will look like mumbo jumbo right now, but soon it'll be readable and you'll be able to find exactly how a certain HTML presentation was performed. What are HTML Tags? HTML works in a very simple, very logical, format. It reads like you do, top to bottom, left to right. HTML is written with TEXT. What you use to set certain sections apart as bigger text, smaller text, bold text, underlined text, is a series of tags. Think of tags as commands. For example if you want a line of text to be bold. You will put a tag at the exact point you want the bold lettering to start and another tag where you want the bold lettering to stop. There you have an example of how tags make commands and tell the browser how to display the text. Just like telling a dog to sit. You give the command. All tags that are opened must correspondingly be closed, just as if you are writing a quoted statement with those "inverted commas". A tag is closed this way therefore we open a new tag and close the tag HTML

Tags

to

help

you

create

your

own

website

design

Below are the most common used html tags used in website design and a short description of the function of each. Some have examples of how they are used with their html codes. Website HTML tags are arranged in alphabetical order.

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this element is what the hyperlinked structure of the World Wide Web is based on. It is used in two ways: 1. Create a hyperlink to another anchor (Link to another page or website) 2. Create an anchor in a document.

·

Identifies that the content is an abbreviated form of some kind.

·

Identifies that some text is an acronym.

·

Specifies information such as authorship and contact details for the current document. Browsers should render the content with

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paragraph-breaks

before

and

after.

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<APPLET>

Embed a Java applet into your website document.

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Used to implement a client-side image map.

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This element displays the audioscope, the graphical display of the amplitude of the current sound over time.

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Change your website or <strong> can also be used.

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Supply a base address that must be used for resolving relative URI's to absolute URI's.

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Change the appearance of the default font that is used to draw the text.

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This element overrides the bidirectional algorithm, the default algorithm to resolve the direction to show the text.

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Play a background sound when your webpage is opened. This element must be placed in the HEAD section of the document .

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Increase the current size of the font by 1. The maximum size is 7.

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This element will render the text in a double-weight boldface font.

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Changes the text to blinking. Drives people insane. *smiles*

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This is used to enclose larger quotations from other works in the page. See working example.

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This element contains the body of your website document. If a section is present in the page then the body must be placed after this section.

·

This element is an alias of the blockquote element.

·


Line Break. Break the current line and continue on the next line.

·

This attribute creates a button that the user can push.

text

to

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bold.

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Specify the caption of a table. This element is only valid inside the TABLE element.

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Centers everything inside the opening and closing element. This tag is equivalent to

.

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Used for citations or references to other sources.

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Used for source code examples.

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This element sets the attribute values for one or more columns.

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This tag creates a column group and sets attribute values for all the columns in this group.

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Used to insert comments in the HTML source which will be ignored by the browser. All HTML elements inside the comment will be ignored. You can use this code to put comments in your pages, which can help you when you have to edit the source later. HTML generating programs sometimes store program-specific information inside c o m m e n t s , so they will not be visible, but still available to the program. This code is not a container, but inside it you can put one or more comments, by surrounding with "--". The end of the code is indicated with the sequence -->.

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The description of a term in a definition list.

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This is a tag that is used to indicate webpage text that has been deleted.

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This is a element that is used to indicate a word or phrase that is being defined.

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Create a directory list.

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HTML DIV tags. This element is a general container for a part of the contents of a page. Through the DIV element you can add attributes, like style information, to this whole division. The DIV element will not show anything when used without any other attribute. A division will terminate a paragraph opened with the P element.

is the same as the deprecated element.

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Create a definition list. This is a list where each item consists of two parts.

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<EM> Put "emphasis" on the enclosed text.

203 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327

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<EMBED> The EMBED element lets you display output from a plug-in application in an HTML document.

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Group a set of related controls in a form together. HTML font tags change the font which is used to draw the text.

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HTML form tags. Create a form inside a document.

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In a page with frames, this element defines how the a specific frame looks and what is initially shown inside the frame, when the framed page is loaded. This element is only allowed inside a FRAMESET element.

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Container for creating a document that consists of several frames.

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The elements H1, H2, H3, H4, H5 and H6 are used to create several levels of headers, with H1 as the most important header and H6 as the least important.

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Container for elements describing the current document. This section contains no contents the browser should display in the body of the text. The following elements are allowed inside the HEAD section : B B B I L M S S TITLE

A A

S

S G S

E S I I E

C

F

O

O N R

U D N T

N E

I

T

E T D X K A T E

N

P

Y

L

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---

Draw a horizontal rule.

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The container for a complete HTML document.

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Change can also be used.

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<IFRAME> This element is a container to create an inline or floating frame. A floating frame is a frame in which the contents of another HTML document can be seen.

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With this element you can create several layers of content on a page. These layers can be stacked on top of each other, showing parts of underlying layers through non-occupied space.

the

text

to

italic.

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HTML image tag. Place an image in the document.

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Create a control for a form. A control is an element which the user can use to enter data, like textboxes, radiobuttons and checkboxes and is only valid inside the FORM element.

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This element will show an text input field. After pressing the <Enter> key the browser will construct a new URL, with the current address, a question mark and the text the user entered in the text field, and send it to the server

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This is used to identify text that a user is supposed to enter.

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Attach information to a specific field of a form.

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With this element you can create several layers of content on a page. These layers can be stacked on top of each other, showing parts of underlying layers through non-occupied space.

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Give the caption for a group of related controls, created with the FIELDSET element. See working example

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List tags Identify an item in a list.

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<MAP> this element is a container for the map that is used in a client-side image map.

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<MARQUEE> HTML marquee tag. This element is a container that enables you to create a scrolling text marquee.

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<MENU> A container for a list of menu items.

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<META> This element supplies meta-information about the current document.

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The NOBR element stands for NO BReak. This means all the text between the start and end of the NOBR elements cannot have line breaks inserted between them.

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This element defines content within EMBED content that is to be ignored by browsers that can activate the EMBED plug-in application.

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This element provides a way to create alternative content that is intended for browsers that can't show frames, or are configured not to show them. A browser that displays the frames ignores the contents of the NOFRAMES element.

205 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327

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The object element allows the author to embed an object into the document. This element also replaces the APPLET element.

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This describes an option in a list box of a form.

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This indicates a paragraph in the document. It is a container but most browsers allow you to omit the closing element.

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This element is for supplying parameters to a JAVA applet or another object and is only valid inside the APPLET and OBJECT elements.

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</PLAINTEXT> All HTML elements inside this container are ignored by the browser, and shown as they were only text.<br /> <br /> ·<br /> <br /> <PRE></PRE> This element allows you to show preformatted text as it is, using the supplied whitespace of the text.<br /> <br /> ·<br /> <br /> <Q></Q> This is used to enclose short quotations from other works in the page.<br /> <br /> ·<br /> <br /> &lt;S></S> Render text as strikethrough.<br /> <br /> ·<br /> <br /> &lt;SAMP></SAMP> this element describes text that is output from a program.<br /> <br /> ·<br /> <br /> &lt;SCRIPT></SCRIPT> this element adds the possibility of programming inside a HTML document by using a scripting language.<br /> <br /> ·<br /> <br /> &lt;SELECT></SELECT> this element lets you create a list box as an input field on a f o r m .<br /> <br /> ·<br /> <br /> &lt;SERVER></SERVER> This element is used to write JavaScript’s that will be executed on the server, in the process of serving the page to the browser.<br /> <br /> ·<br /> <br /> &lt;SMALL></SMALL> Draw the text using a smaller font than the one that is used for normal text.<br /> <br /> ·<br /> <br /> &lt;SPACER> With a spacer you can control the horizontal whitespace that appears between words in a line, the vertical whitespace that appears between lines on a page, or set up rectangular spacing elements.<br /> <br /> ·<br /> <br /> &lt;SPAN></SPAN> this element is used to create a structure in a document. By using this element you can give a part of the document a name, or apply style sheet information to the part.<br /> <br /> ·<br /> <br /> &lt;STRIKE></STRIKE> Render text as strikethrough. Same as the &lt;S> tag.<br /> <br /> 206 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> ·<br /> <br /> &lt;STRONG></STRONG> Render the text with strong emphasis.<br /> <br /> ·<br /> <br /> &lt;STYLE></STYLE> This element is a container for style sheet elements to use with this document.<br /> <br /> ·<br /> <br /> &lt;SUB></SUB> This is a container for text that should be displayed as a subscript, and, if practical, using a smaller font (compared with normal text).<br /> <br /> ·<br /> <br /> &lt;SUP></SUP> Display the text as a superscript.<br /> <br /> ·<br /> <br /> < T A B L E > < / T A B L E > HTML table tags. Create a table layout which can contain cells in rows and columns. The cells of a table are specified with the TR, TH and TD elements.<br /> <br /> ·<br /> <br /> < T B O D Y > < This element defines the body part of a table.<br /> <br /> ·<br /> <br /> < T D > < / T D > HTML table tags. The container for a cell in a table. Inside this you can put all the HTML coding you want to appear in the cell.<br /> <br /> ·<br /> <br /> < T E X T A R E A > < / T E X T A R E A > Define a multiline text field in a form. This element is only valid inside the FORM element.<br /> <br /> ·<br /> <br /> < T F O O T > < This element defines the footer of a table.<br /> <br /> ·<br /> <br /> < T I T L E > < / T I T L E > Specify the title of the HTML document. This element is only allowed inside the HEAD element.<br /> <br /> ·<br /> <br /> < T R Define a row inside a table.<br /> <br /> ·<br /> <br /> < U Underline your text.<br /> <br /> ·<br /> <br /> < U L > < / U L > Create an unordered list of items, where unordered means the individual items are not numbered, but have a bullet in front of them. If you want numbered items use an ordered list. The items in the list are identified with the LI element. See working example<br /> <br /> ><br /> <br /> ><br /> <br /> <<br /> <br /> <<br /> <br /> /<br /> <br /> T<br /> <br /> /<br /> <br /> B<br /> <br /> T<br /> <br /> O<br /> <br /> F<br /> <br /> /<br /> <br /> D<br /> <br /> O<br /> <br /> O<br /> <br /> T<br /> <br /> /<br /> <br /> Y<br /> <br /> T<br /> <br /> R<br /> <br /> U<br /> <br /> 207 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> ><br /> <br /> ><br /> <br /> ><br /> <br /> ><br /> <br /> ·<br /> <br /> < V A R > < / V A R > Used to describe a metasyntactic variable, where the user is to replace the variable with a specific instance. Typically displayed in italics.<br /> <br /> ·<br /> <br /> < W B The WBR element stands for Word Break.<br /> <br /> ·<br /> <br /> R<br /> <br /> ><br /> <br /> Java and Java service<br /> <br /> What Can Java Technology Do? The general-purpose, high-level Java programming language is a powerful software platform. Every full implementation of the Java platform gives you the following features:<br /> <br /> ·<br /> <br /> Development Tools: The development tools provide everything you'll need for compiling, running, monitoring, debugging, and documenting your applications. As a new developer, the main tools you'll be using are the javac compiler, the java launcher, and the javadoc documentation tool.<br /> <br /> ·<br /> <br /> Application Programming Interface (API): The API provides the core functionality of the Java programming language. It offers a wide array of useful classes ready for use in your own applications. It spans everything from basic objects, to networking and security, to XML generation and database access, and more. The core API is very large; to get an overview of what it contains, consult the Java SE Development Kit 6 (JDKTM 6) documentation.<br /> <br /> ·<br /> <br /> Deployment Technologies: The JDK software provides standard mechanisms such as the Java Web Start software and Java Plug-In software for deploying your applications to end users.<br /> <br /> ·<br /> <br /> User Interface Toolkits: The Swing and Java 2D toolkits make it possible to create sophisticated Graphical User Interfaces (GUIs).<br /> <br /> ·<br /> <br /> Integration Libraries: Integration libraries such as the Java IDL API, JDBC TM API, Java Naming and Directory InterfaceTM ("J.N.D.I.") API, Java RMI, and Java Remote Method Invocation over Internet Inter-ORB Protocol Technology (Java RMI-IIOP Technology) enable database access and manipulation of remote objects.<br /> <br /> How Will Java Technology Change My Life? We can't promise you fame, fortune, or even a job if you learn the Java programming language. Still, it is likely to make your programs better and requires less effort than other languages. We believe that Java technology will help you do the following:<br /> <br /> ·<br /> <br /> Get started quickly: Although the Java programming language is a powerful object-oriented language, it's easy to learn, especially for programmers already familiar with C or C++.<br /> <br /> ·<br /> <br /> Write less code: Comparisons of program metrics (class counts, method counts, and so on) suggest that a program written in the Java programming language can be four times smaller than the same program written in C++.<br /> <br /> 208 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> ·<br /> <br /> Write better code: The Java programming language encourages good coding practices, and automatic garbage collection helps you avoid memory leaks. Its object orientation, its JavaBeans TM component architecture, and its wide-ranging, easily extendible API let you reuse existing, tested code and introduce fewer bugs.<br /> <br /> ·<br /> <br /> Develop programs more quickly: The Java programming language is simpler than C++, and as such, your development time could be up to twice as fast when writing in it. Your programs will also require fewer lines of code.<br /> <br /> ·<br /> <br /> Avoid platform dependencies: You can keep your program portable by avoiding the use of libraries written in other languages.<br /> <br /> ·<br /> <br /> Write once, run anywhere: Because applications written in the Java programming language are compiled into machine-independent byte codes, they run consistently on any Java platform.<br /> <br /> ·<br /> <br /> Distribute software more easily: With Java Web Start software, users will be able to launch your applications with a single click of the mouse. An automatic version check at startup ensures that users are always up to date with the latest version of your software. If an update is available, the Java Web Start software will automatically update their installation.<br /> <br /> Lesson: The "Hello World!" Application The sections listed below provide detailed instructions for compiling and running a simple "Hello World!" application. The first section provides information on getting started with the NetBeans IDE, an integrated development environment that greatly simplifies the software development process. The NetBeans IDE runs on all of the platforms listed below. The remaining sections provide platform-specific instructions for getting started without an integrated development environment. If you run into problems, be sure to consult the common problems section; it provides solutions for many issues encountered by new users. "Hello World!" for the NetBeans IDE These instructions are for users of the NetBeans IDE. The NetBeans IDE runs on the Java platform, which means that you can use it with any operating system for which there is a JDK 6 available. These operating systems include Microsoft Windows, Solaris OS, Linux, and Mac OS X. We recommend using the NetBeans IDE instead of the command line whenever possible. "Hello World!" for Microsoft Windows These command-line instructions are for users of Windows XP Professional, Windows XP Home, Windows Server 2003, Windows 2000 Professional, and Windows Vista. "Hello World!" for Solaris OS and Linux These command-line instructions are for users of Solaris OS and Linux. Common Problems (and Their Solutions) Consult this page if you have problems compiling or running your application.<br /> <br /> ·<br /> <br /> JSP<br /> <br /> ·<br /> <br /> What is JSP? Describe its concept. JSP is a technology that combines HTML/XML markup languages and elements of Java programming Language to return dynamic<br /> <br /> 209 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> content to the Web client, It is normally used to handle Presentation logic of a web application, although it may have business logic.<br /> <br /> ·<br /> <br /> What are the lifecycle phases of a JSP? JSP page looks like a HTML page but is a servlet. When presented with JSP page the JSP engine does the following 7 phases. ·<br /> <br /> Page translation: -page is parsed, and a java file which is a servlet is created.<br /> <br /> ·<br /> <br /> Page compilation: page is compiled into a class file<br /> <br /> ·<br /> <br /> Page loading : This class file is loaded.<br /> <br /> ·<br /> <br /> Create an instance :- Instance of servlet is created<br /> <br /> ·<br /> <br /> jspInit() method is called<br /> <br /> ·<br /> <br /> _jspService is called to handle service calls<br /> <br /> ·<br /> <br /> _jspDestroy is called to destroy it when the servlet is not required.<br /> <br /> ·<br /> <br /> What is a translation unit? JSP page can include the contents of other HTML pages or other JSP files. This is done by using the include directive. When the JSP engine is presented with such a JSP page it is converted to one servlet class and this is called a translation unit, Things to remember in a translation unit is that page directives affect the whole unit, one variable declaration cannot occur in the same unit more than once, the standard action jsp:useBean cannot declare the same bean twice in one unit.<br /> <br /> ·<br /> <br /> How is JSP used in the MVC model? JSP is usually used for presentation in the MVC pattern (Model View Controller ) i.e. it plays the role of the view. The controller deals with calling the model and the business classes which in turn get the data, this data is then presented to the JSP for rendering on to the client.<br /> <br /> ·<br /> <br /> What are context initialization parameters? Context initialization parameters are specified by the <context-param> in the web.xml file, these are initialization parameter for the whole application and not specific to any servlet or JSP.<br /> <br /> ·<br /> <br /> What is a output comment? A comment that is sent to the client in the viewable page source. The JSP engine handles an output comment as un-interpreted HTML text, returning the comment in the HTML output sent to the client. You can see the comment by viewing the page source from your Web browser.<br /> <br /> ·<br /> <br /> What is a Hidden Comment? A comment that documents the JSP page but is not sent to the client. The JSP engine ignores a hidden comment, and does not process any code within hidden comment tags. A hidden comment is not sent to the client, either in the displayed JSP page or the HTML page source. The hidden comment is useful when you want to hide or “comment out” part of your JSP page.<br /> <br /> ·<br /> <br /> What is a Expression? Expressions are act as place holders for language expression, expression is evaluated each time the page is accessed.<br /> <br /> ·<br /> <br /> What is a Declaration? It declares one or more variables or methods for use later in the JSP source file. A declaration must contain at least one complete declarative statement. You can declare any number of variables or methods within one<br /> <br /> 210 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> declaration tag, as long as semicolons separate them. The declaration must be valid in the scripting language used in the JSP file.<br /> <br /> ·<br /> <br /> What is a Scriptlet? A scriptlet can contain any number of language statements, variable or method declarations, or expressions that are valid in the page scripting language. Within scriptlet tags, you can declare variables or methods to use later in the file, write expressions valid in the page scripting language, use any of the JSP implicit objects or any object declared with a &lt;jsp:useBean>.<br /> <br /> ·<br /> <br /> What are the implicit objects? List them. Certain objects that are available for the use in JSP documents without being declared first. These objects are parsed by the JSP engine and inserted into the generated servlet. The implicit objects are: 1.<br /> <br /> request<br /> <br /> 2.<br /> <br /> response<br /> <br /> 3.<br /> <br /> page Context<br /> <br /> 4.<br /> <br /> session<br /> <br /> 5.<br /> <br /> application<br /> <br /> 6.<br /> <br /> out<br /> <br /> 7.<br /> <br /> config<br /> <br /> 8.<br /> <br /> page<br /> <br /> 9.<br /> <br /> exception<br /> <br /> 2. What’s the difference between forward and send Redirect? When you invoke a forward request, the request is sent to another resource on the server, without the client being informed that a different resource is going to process the request. This process occurs completely with in the web container And then returns to the calling method. When a send Redirect method is invoked, it causes the web container to return to the browser indicating that a new URL should be requested. Because the browser issues a completely new request any object that are stored as request attributes before the redirect occurs will be lost. This extra round trip a redirect is slower than forward. 3. What are the different scope values for the &lt;jsp: useBean>? The different scope values for &lt;jsp:useBean> are: 1.<br /> <br /> page<br /> <br /> 2.<br /> <br /> request<br /> <br /> 3.<br /> <br /> session<br /> <br /> 4.<br /> <br /> application<br /> <br /> 4. Why are JSP pages the preferred API for creating a web-based client program? Because no plug-ins or security policy files are needed on the client systems(applet does). Also, JSP pages enable cleaner and more module application design because they provide a way to separate applications programming from web<br /> <br /> 211 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> page design. This means personnel involved in web page design do not need to understand Java programming language syntax to do their jobs. 5. Is JSP technology extensible? Yes, it is. JSP technology is extensible through the development of custom actions, or tags, which are encapsulated in tag libraries. 6. What is difference between custom JSP tags and beans? Custom JSP tag is a tag you defined. You define how a tag, its attributes and its body are interpreted, and then group your tags into collections called tag libraries that can be used in any number of JSP files. Custom tags and beans accomplish the same goals — encapsulating complex behavior into simple and accessible forms. There are several differences:<br /> <br /> ·<br /> <br /> 1.<br /> <br /> Custom tags can manipulate JSP content; beans cannot.<br /> <br /> 2.<br /> <br /> Complex operations can be reduced to a significantly simpler form with custom tags than with beans.<br /> <br /> 3.<br /> <br /> Custom tags require quite a bit more work to set up than do beans.<br /> <br /> 4.<br /> <br /> Custom tags usually define relatively self-contained behavior, whereas beans are often defined in one servlet and used in a different servlet or JSP page.<br /> <br /> 5.<br /> <br /> Custom tags are available only in JSP 1.1 and later, but beans can be used in all JSP 1.x versions.<br /> <br /> Coldfusion<br /> <br /> What is Coldfusion? Initially, developing highly interactive and data-rich sites was a difficult process. Writing custom Web-based applications was a job for experienced programmers only. A good working knowledge of Unix was a prerequisite, and experience with traditional development or scripting languages was a must. But all that has changed. Macromedia's ColdFusion enables you to create sites every bit as powerful and capable as those listed earlier, without a long and painful learning curve. In fact, rather than being painful, the process is actually fun! So, what exactly is ColdFusion? Simply put, ColdFusion is an application server—one of the very best out there (as well as the very first one out there; ColdFusion actually created the Application Server category back in 1995).ColdFusion does not require coding in traditional programming languages, although traditional programming constructs and techniques are fully supported. Instead, you create applications by extending your standard HTML files with high-level formatting functions, conditional operators, and database commands. These commands are instructions to the ColdFusion processor and form the building blocks on which to build industrial-strength applications. This method of creating Web applications has significant advantages over conventional application development. Advantages include 7.<br /> <br /> COLDFUSION APPLICATIONS CAN BE DEVELOPED RAPIDLY BECAUSE NO CODING, OTHER THAN USE OF SIMPLE HTML STYLE TAGS, IS REQUIRED.<br /> <br /> 8.<br /> <br /> COLDFUSION APPLICATIONS ARE EASY TO TEST AND ROLL OUT.<br /> <br /> 212 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> 9.<br /> <br /> THE COLDFUSION LANGUAGE CONTAINS ALL THE PROCESSING AND FORMATTING FUNCTIONS YOU'LL NEED (AND THE CAPABILITY TO CREATE YOUR OWN FUNCTIONS IF YOU REALLY RUN INTO A DEAD END).<br /> <br /> 10. COLDFUSION APPLICATIONS ARE EASY TO MAINTAIN BECAUSE NO COMPILATION OR LINKING STEP IS REQUIRED (FILES ACTUALLY ARE COMPILED, BUT THAT HAPPENS TRANSPARENTLY AS I'LL EXPLAIN SHORTLY). THE FILES YOU CREATE ARE THE FILES USED BY COLDFUSION. 11. COLDFUSION PROVIDES ALL THE TOOLS YOU NEED TO TROUBLESHOOT AND DEBUG APPLICATIONS, INCLUDING A POWERFUL DEVELOPMENT ENVIRONMENT AND DEBUGGER. 12. COLDFUSION COMES WITH ALL THE HOOKS NECESSARY TO LINK TO ALMOST ANY DATABASE APPLICATION AND ANY OTHER EXTERNAL SYSTEM. 13. COLDFUSION IS FAST, THANKS SERVICE-BASED ARCHITECTURE.<br /> <br /> TO<br /> <br /> ITS<br /> <br /> SCALABLE,<br /> <br /> MULTITHREADED,<br /> <br /> 14. COLDFUSION IS BUILT ON INDUSTRY STANDARD JAVA ARCHITECTURE, AND SUPPORTS ALL MAJOR STANDARDS AND INITIATIVES.<br /> <br /> ColdFusion and Your Intranet or Extranet Although we've been discussing Internet sites, the benefits of ColdFusion apply to intranets and extranets, too. Most companies have masses of information stored in various systems. Users often don't know what information is available or even how to access it. ColdFusion bridges the gap between existing and legacy applications and your employees. It empowers employees with the tools to work more efficiently. ColdFusion Explained You're now ready to take a look at ColdFusion so you can understand what it is and how it works its magic.And if you're wondering why you went through all this discussion about the Internet and Web servers, here's where it will all fit together.<br /> <br /> The ColdFusion Application Server ColdFusion is an application server—a piece of software that (usually) resides on the same computer as your Web server, enabling the Web server to do things it would not normally know how to do. ColdFusion is actually made up of several pieces of software (applications on Windows; and daemons on Linux, Solaris, and HP-UX). The ColdFusion Application Server is the program that actually parses (reads and compiles) and processes any supplied instructions. Instructions are passed to ColdFusion using templates. A template looks much like any HTML file, with one big difference. Unlike HTML files, ColdFusion templates can contain special tags that instruct ColdFusion to perform specific operations. This is a sample ColdFusion template; it is one that you'll use later in this book. <! --- Get movies sorted by release date ---><br /> <br /> 213 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> <CFQUERY DATASOURCE="ows" NAME="movies"> SELECT Movie Title, DateInTheaters FROM Films ORDER BY DateInTheaters </CFQUERY> <! --- Create HTML page ---> <HTML> <HEAD> &lt;TITLE>Movies by Release Date</TITLE> </HEAD> <BODY> <H1>Movies by Release Date</H1> <! --- Display movies in list format ---> <UL> <CFOUTPUT QUERY="movies"> <LI><B>#Trim (Movie Title) #</B> - #Date Format (DateInTheaters)#</LI> </CFOUTPUT> </UL> </BODY> </HTML> Earlier in this chapter, it was stated that Web servers typically return the contents of a Web page without paying any attention to the file contents. That's exactly what ColdFusion does not do. When ColdFusion receives a request, it parses through the template looking for special ColdFusion tags (they all begin with CF) or ColdFusion variables and functions (always surrounded by pound signs). Any HTML or plain text is left alone and is output to the Web server untouched. Any ColdFusion instructions are processed, and any existing results are sent to the Web server. The Web server can then send the entire output back to the requester's browser. As explained earlier, the request file type tells the Web server that a request is to be handled by an application server. All ColdFusion files have an extension of .cfm or .cfml, like this: http://www.forta.com/books/index.cfm When ColdFusion is installed, it configures your Web server so it knows that any file with an extension of .cfm (or .cfml) is a ColdFusion file. Then, whenever a ColdFusion file is requested, the Web server knows to pass the file to ColdFusion for processing rather than return it. TIP As ColdFusion is bound to a Web server, ColdFusion can be used to process any and all requests sent to a Web server, regardless of which host or virtual host it is sent to. But, ColdFusion is only ever bound to a single Web server, and so if you have multiple Web servers installed only one of them will be usable with ColdFusion (unless you plan to do lots of tweaking, a process not recommended at all). So, if you need to support multiple hosts, use a single Web server with IP or DNS based virtual hosts rather than multiple Web servers. It is worth noting that ColdFusion MX actually does not need a Web server because it has one built in. So as not to conflict with any other installed Web servers (like Apache and Microsoft<br /> <br /> 214 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> IIS) the internal Web server runs on port 8500 (instead of the default port 80). During ColdFusion MX installation you'll be asked whether you want to run ColdFusion in standalone mode (bound to the integrated Web server) or using an existing Web server. If you opt to use the internal Web server you'll need to specify the port number in all URLs.<br /> <br /> TIP Macromedia does not recommend that the internal Web server (standalone mode) be used on production boxes. ColdFusion MX's integrated HTTP server is intended for use on development boxes only.<br /> <br /> The ColdFusion Markup Language Earlier it was stated that ColdFusion is an application server, which is true, but that is not all Cold-Fusion is. In fact, ColdFusion is two distinct technologies:<br /> <br /> ·<br /> <br /> The ColdFusion Application Server<br /> <br /> ·<br /> <br /> The CFML language<br /> <br /> And although the ColdFusion Application Server itself is important, ColdFusion's power comes from its capable and flexible language. ColdFusion Markup Language (CFML) is modeled after HTML, which makes it very easy to learn. CFML extends HTML by adding tags with the following capabilities:<br /> <br /> ·<br /> <br /> Read data from, and update data to, databases and tables<br /> <br /> ·<br /> <br /> Create dynamic data-driven pages<br /> <br /> ·<br /> <br /> Perform conditional processing<br /> <br /> ·<br /> <br /> Populate forms with live data<br /> <br /> ·<br /> <br /> Process form submissions<br /> <br /> ·<br /> <br /> Generate and retrieve email messages<br /> <br /> ·<br /> <br /> Interact with local files<br /> <br /> ·<br /> <br /> Perform HTTP and FTP operations<br /> <br /> ·<br /> <br /> Perform credit-card verification and authorization<br /> <br /> ·<br /> <br /> Read and write client-side cookies<br /> <br /> And that's not even the complete list. The majority of this book discusses ColdFusion pages (often called templates) and the use of CFML.<br /> <br /> Linking to External Applications<br /> <br /> 215 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> One of ColdFusion's most powerful features is its capability to connect to data created and maintained in other applications. You can use ColdFusion to retrieve or update data in many applications, including the following:<br /> <br /> ·<br /> <br /> Corporate databases<br /> <br /> ·<br /> <br /> Client/server database systems (such as Microsoft SQL Server and Oracle)<br /> <br /> ·<br /> <br /> Spreadsheets<br /> <br /> ·<br /> <br /> XML data<br /> <br /> ·<br /> <br /> Contact-management software<br /> <br /> ·<br /> <br /> ASCII-delimited files<br /> <br /> ·<br /> <br /> Java beans, JSP tag libraries, and EJBs<br /> <br /> ·<br /> <br /> Web Services<br /> <br /> ColdFusion accesses these applications via database drivers (JDBC and ODBC).<br /> <br /> Extending ColdFusion As installed, ColdFusion will probably do most of what you need, interacting with most of the applications and technologies you'll be using. But in the event that you need something more, ColdFusion provides all the hooks and support necessary to communicate with just about any application or service in existence. Integration is made possible via:<br /> <br /> ·<br /> <br /> C and C++<br /> <br /> ·<br /> <br /> Java<br /> <br /> ·<br /> <br /> COM<br /> <br /> ·<br /> <br /> CORBA<br /> <br /> ·<br /> <br /> Web Services<br /> <br /> These technologies and their uses are beyond the scope of this book and are covered in detail in the sequel Advanced ColdFusion MX Application Development (Macromedia Press, ISBN: 0321127102).<br /> <br /> Beyond the Web As was explained earlier, the Web and the Internet are not one and the same. The Web is an application that runs on top of the Internet, one of many applications. Others do exist, and you can use and take advantage of many of them.One of the most exciting new technologies is Wireless Application Protocol (WAP), which can be used to power applications accessed via wireless devices (such as phones and PDAs).<br /> <br /> 216 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> As explained earlier, Web servers (and thus application servers) send content back to requesters without paying attention to what that content is. The requester (known as the client or user agent) is typically a Web browser, but it need not be. In fact, WAP browsers (the Internet browsers built into WAP devices) can also make requests to Web servers. WAP and generating WAP content using ColdFusion are discussed in Chapter 32, "Generating Non-HTML Content."In other words, although ColdFusion is primarily used to generate Web content, it is not limited to doing so in any way, shape, or form. The same server can generate content for the Web, WAP, email, and more. ColdFusion is client independent and can generate content for many types of clients, not just Web browsers.<br /> <br /> Inside ColdFusion MX ColdFusion MX is the most remarkable ColdFusion to date, and is the first completely redesigned and rebuilt ColdFusion since the product was first created back in 1995. While understanding the inner workings of ColdFusion MX are not a prerequisite to using the product, understanding what ColdFusion is doing under the hood will help you to better leverage this remarkable product. As already explained ColdFusion is a page preprocessor — it processes pages and returns the results as opposed to the page itself. To do this ColdFusion has to read each file, check and validate the contents, and then perform the desired operations. But there is actually much more to it than that—in fact, within ColdFusion is a complete J2EE (Java 2 Enterprise Edition) server that provides the processing power ColdFusion needs. NOTE Don't worry; you need know no Java at all to use ColdFusion. First, a clarification. When people talk about Java they generally mean two very different things:<br /> <br /> ·<br /> <br /> The Java language is just that, a programming language. It is powerful and not at all easy to learn or use.<br /> <br /> ·<br /> <br /> The Java platform, a complete set of building blocks and technologies to build rich and powerful applications.<br /> <br /> 217 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Of the two, the former is of no interest (well, maybe little interest) to ColdFusion developers. After all, why write complex code in Java to do what CFML can do in a single tag? But Java the platform, now that is compelling. The Java platform provides the wherewithal to:<br /> <br /> ·<br /> <br /> Access all sorts of databases<br /> <br /> ·<br /> <br /> Interact with legacy systems<br /> <br /> ·<br /> <br /> Support mobile devices<br /> <br /> ·<br /> <br /> Use directory services<br /> <br /> ·<br /> <br /> Create multilingual and internationalized applications<br /> <br /> ·<br /> <br /> Leverage transactions, queuing, and messaging<br /> <br /> ·<br /> <br /> Create robust and highly scalable applications<br /> <br /> In the past you'd have had to write Java code in order to leverage the Java platform, but not anymore. ColdFusion MX runs on top of the Java platform, providing the power of underlying Java made accessible via the simplicity of CFML. NOTE By default, the Java engine running ColdFusion MX is Macromedia's own award-winning J2EE server, JRun. ColdFusion MX can also be run on top of third party J2EE servers like IBM's Web Sphere and BEA's Web Logic. See Appendix A, "Installing ColdFusion MX and Dreamweaver MX" for more information. But don't let the CFML (and CFM files) fool you—when you create a ColdFusion application you are actually creating a Java application. In fact, when ColdFusion MX processes your CFM pages it actually creates Java source code and compiles it into Java byte code for you, all in the background. This behavior is new to ColdFusion MX, and is part of why this is the most important new Cold-Fusion to date. Using ColdFusion MX you can truly have the best of both worlds—the power of Java, and the simplicity of ColdFusion, and all without having to make any sacrifices at all.<br /> <br /> ·<br /> <br /> Database Connectivity 1.<br /> <br /> ODBC<br /> <br /> In computing, Open Database Connectivity (ODBC) provides a standard software API method for using database management systems (DBMS). The designers of ODBC aimed to make it independent of programming languages, database systems, and operating systems. The ODBC specification offers a procedural API for using SQL queries to access data. An implementation of ODBC will contain one or more applications, a core ODBC library, and one or more "database drivers". The core library, independent of the applications and DBMS systems, acts as an "interpreter" between the applications and the database drivers, whereas the database drivers contain the DBMS-specific details. Thus a programmer can write applications that use standard types and features without concern for the specifics of each DBMS that the applications may encounter. Likewise, database driver implementors need only know how to attach to the core library. This makes ODBC modular.<br /> <br /> 218 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> To write ODBC code that exploits DBMS-specific features requires more advanced programming. An application must use introspection, calling ODBC metadata functions that return information about supported features, available types, syntax, limits, isolation levels, driver capabilities and more. Even when programmers use adaptive techniques, however, ODBC may not provide some advanced DBMS features. The ODBC 3.x API operates well with traditional SQL applications such as OLTP, but it has not evolved to support richer types introduced by SQL:1999 and SQL:2003. ODBC provides the standard of ubiquitous data access because hundreds of ODBC drivers exist for a large variety of data sources. ODBC operates with a variety of operating systems and drivers exist for non-relational data such as spreadsheets, text and XML files. Because ODBC dates back more than ten years, it offers connectivity to a wider variety of data sources than other data-access APIs. More drivers exist for ODBC than drivers or providers exist for newer APIs such as OLE DB, JDBC, and ADO.NET. Despite the benefits of ubiquitous connectivity and platform-independence, ODBC has certain drawbacks. Administering a large number of client machines can involve a diversity of drivers and DLLs. This complexity can increase system administration overhead. Large organizations with thousands of PCs have often turned to ODBC server technology to simplify the administration problem. The layered architecture of ODBC can introduce a minor performance penalty. However, the overhead of executing an additional layer of code generally appears insignificant compared to network latency and other factors that influence query performance. Driver architecture may also affect performance. Many first-generation ODBC drivers operated with database client libraries supplied by a DBMS vendor. An ODBC driver for Oracle, for example, would use Oracle's network library (SQL*Net, Oracle Net) and OCI client library. Similarly, drivers for Sybase or for Microsoft SQL Server would use a vendor-supplied network library to emit Tabular Data Stream (TDS) packets. Some vendors provide wire protocol drivers that do not use database client libraries. These drivers communicate using protocols such as TDS, TNS, and DRDA without needing database client libraries, but the actual database vendor might not always support the direct use of these protocols. Differences between drivers and driver maturity can also raise important issues. Newer ODBC drivers do not always have the stability of drivers already deployed for years. Years of testing and deployment mean a driver may contain fewer bugs. Developers needing features or types not accessible with ODBC can use other SQL APIs. When not aiming for platform-independence, developers can use proprietary APIs. If developers need to produce portable, platform-independent, albeit language specific code, they can use the JDBC API. History ODBC uses as its basis the various Call Level Interface (CLI) specifications from the SQL Access Group, X/Open (now part of The Open Group), and the ISO/IEC. Microsoft, in partnership with Simba Technologies, created ODBC by adapting the SQL Access Group CLI. It released ODBC 1.0 in September 1992. After ODBC 2.0, Microsoft decided to align ODBC 3.0 with the CLI specification making its way through X/Open and ISO. In 1995, SQL/CLI became part of the international SQL standard. JDBC-ODBC bridges A JDBC-ODBC bridge consists of a JDBC driver which employs the ODBC driver to connect to the database. This driver translates JDBC method calls into ODBC function calls. Programmers usually use such a bridge when a particular database lacks a JDBC driver. Sun included one such bridge in the JVM, but viewed it as a stop-gap measure while few JDBC Drivers existed. Sun never intended its bridge for production environments, and generally<br /> <br /> 219 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> recommends against its use. Independent data-access vendors now deliver JDBC-ODBC bridges which support current standards for both mechanisms, and which far outperform the JVM built-in. ODBC-JDBC bridges An ODBC-JDBC bridge consists of an ODBC driver which uses the services of a JDBC driver to connect to a database. This driver translates ODBC function calls into JDBC method calls. Programmers usually use such a bridge when they lack an ODBC driver for a particular database but have access to a JDBC driver. Implementations ODBC implementations run on many operating systems, including Microsoft Windows, Unix, Linux, OS/2, and Mac OS X. Hundreds of ODBC drivers exist, including drivers for Oracle, DB2, Microsoft SQL Server, Sybase, Pervasive SQL, MySQL, PostgreSQL, and desktop database products such as FileMaker, Alpha Five, and Microsoft Access. Microsoft ODBC Microsoft released the first ODBC product as a set of DLLs for Microsoft Windows. As of 2006, Microsoft ships its own ODBC with every supported version of Windows: compare Microsoft Data Access Components. 2.<br /> <br /> JDBC<br /> <br /> JDBC is an API for the Java programming language that defines how a client may access a database. It provides methods for querying and updating data in a database. JDBC is oriented towards relational databases.The Java Platform, Standard Edition includes the JDBC API together with an ODBC implementation of the API enabling connections to any relational database that supports ODBC. This driver is native code and not Java, and is closed source. JDBC has been part of the Java Standard Edition since the release of JDK 1.1. The JDBC classes are contained in the Java package java.sql. Starting with version 3.0, JDBC has been developed under the Java Community Process. JSR 54 specifies JDBC 3.0 (included in J2SE 1.4), JSR 114 specifies the JDBC Row set additions, and JSR 221 is the specification of JDBC 4.0 (included in Java SE 6). JDBC allows multiple implementations to exist and be used by the same application. The API provides a mechanism for dynamically loading the correct Java packages and registering them with the JDBC Driver Manager. The Driver Manager is used as a connection factory for creating JDBC connections.JDBC connections support creating and executing statements. These statements may be update statements such as SQL INSERT, UPDATE and DELETE or they may be query statements using the SELECT statement. Additionally, stored procedures may be invoked through a statement. Statements are one of the following types:<br /> <br /> ·<br /> <br /> Statement – the statement is sent to the database server each and every time.<br /> <br /> ·<br /> <br /> Prepared Statement – the statement is cached and then the execution path is pre determined on the database server allowing it to be executed multiple times in an efficient manner.<br /> <br /> ·<br /> <br /> Callable Statement – used for executing stored procedures on the database.<br /> <br /> 220 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Update statements such as INSERT, UPDATE and DELETE return an update count that indicates how many rows were affected in the database. These statements do not return any other information. Query statements return a JDBC row result set. The row result set is used to walk over the result set. Individual columns in a row are retrieved either by name or by column number. There may be any number of rows in the result set. The row result set has metadata that describes the names of the columns and their types. There is an extension to the basic JDBC API in the javax.sql package that allows for scrollable result sets and cursor support among other things. Example The method Class.forName (String) is used to load the JDBC driver class. The line below causes the JDBC driver from some jdbc vendor to be loaded into the application. (Some JVMs also require the class to be instantiated with .new Instance ().) Class.forName (“com.somejdbcvendor.TheirJdbcDriver" ); When a Driver class is loaded, it creates an instance of itself and registers it with the Driver Manager. This can be done by including the needed code in the driver class's static block. e.g. DriverManager.registerDriver (Driver driver) Now when a connection is needed, one of the DriverManager.getConnection () methods is used to create a JDBC connection. Connection conn = DriverManager.getConnection ( "Jdbc: somejdbcvendor: other data needed by some jdbc vendor", "My Login", "My Password”); The URL used is dependent upon the particular JDBC driver. It will always begin with the "jdbc:" protocol, but the rest is up to the particular vendor. Once a connection is established, a statement must be created. Statement stmt = conn.createStatement (); Try { stmt.executeUpdate ( "INSERT INTO My Table( name ) VALUES ( 'my name' ) " ); } finally { //It's important to close the statement when you are done with it stmt.close (); } Note that connections, statements, and result sets often tie up operating system resources such as sockets or file descriptors. In the case of connections to remote database servers, further resources are tied up on the server, e.g. Cursors for currently open result sets. It is vital to close () any JDBC object as soon as it has played its part; garbage collection shall not be relied upon. Forgetting to close () things properly results in spurious errors and misbehavior. The above try-finally construct is a recommended code pattern to use with JDBC objects. Data is retrieved from the database using a database query mechanism. The example below shows creating a statement and executing a query. Statement stmt = conn.createStatement (); Try { Result Set rs = stmt.executeQuery ( "SELECT * FROM My Table" ); Try { While (rs.next ()) { Int numColumns = rs.getMetaData ().getColumnCount ();<br /> <br /> 221 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> for ( int i = 1 ; i <= numColumns ; i++ ) { //Column numbers start at 1. //Also there are many methods on the result set to return // the column as a particular type. Refer to the Sun documentation // for the list of valid conversions. System.out.println (“COLUMN” + i + " = " + rs.getObject (i)); } } } finally { rs.close (); } } finally { stmt.close (); } Typically, however, it would be rare for a seasoned Java programmer to code in such a fashion. The usual practice would be to abstract the database logic into an entirely different class and to pass preprocessed strings (perhaps derived themselves from a further abstracted class) containing SQL statements and the connection to the required methods. Abstracting the data model from the application code makes it more likely that changes to the application and data model can be made independently. An example of a Prepared Statement query. Using conn and class from first example. Prepared Statement ps = conn.prepareStatement (“SELECT i.*, j.* FROM Omega i, Zappa j" + "WHERE i =? AND j =?”); Try { // In the prepared statement ps, the question mark denotes variable input, // which can be passed through a parameter list, for example. // the following replaces the question marks, // with the string or int, before sending it to SQL. // The first parameter corresponds to the nth occurrence of the? // the second parameter tells Java to replace it with // the second item. ps.setString (1, "Poor Yorick"); ps.setInt (2, 8008); // The ResultSet rs, receives the SQL Query response. ResultSet rs = ps.executeQuery (); Try { While (rs.next ()) { Int numColumns = rs.getMetaData ().getColumnCount (); For ( int i = 1 ; i <= numColumns ; i++ ) { //Column numbers start at 1. //Also there are many methods on the result set to return // the column as a particular type. Refer to the Sun documentation // for the list of valid conversions. System.out.println ( "COLUMN " + i + " = " + rs.getObject(i) ); } // for } // while } finally { rs.close (); } } finally { Psychoses; } // try<br /> <br /> 222 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> When a database operation fails, a SQLException is raised. There is typically very little one could do to recover from such an error, apart from logging it with as much detail as possible. It is recommended that the SQLException be translated into an application domain exception (an unchecked one) that eventually results in a transaction rollback and a notification to the user. Here are examples of host database types, Java can convert to with a function. setXXX ()Methods Oracle type<br /> <br /> Data setXXX()<br /> <br /> CHAR<br /> <br /> setString()<br /> <br /> VARCHAR2<br /> <br /> setString()<br /> <br /> NUMBER<br /> <br /> setBigDecimal( ) setBoolean() setByte() setShort() setInt() setLong() setFloat() setDouble()<br /> <br /> INTEGER<br /> <br /> setInt()<br /> <br /> FLOAT<br /> <br /> setDouble()<br /> <br /> CLOB<br /> <br /> setClob()<br /> <br /> BLOB<br /> <br /> setBlob()<br /> <br /> RAW<br /> <br /> setBytes()<br /> <br /> LONGRAW<br /> <br /> setBytes()<br /> <br /> DATE<br /> <br /> setDate() setTime() setTimestamp( )<br /> <br /> For an example of a CallableStatement (to call stored procedures in the database.)<br /> <br /> Lesson VIII: Internet Security<br /> <br /> 223 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> ·<br /> <br /> What is security<br /> <br /> Internet Security Focus This handbook is designed to help companies consider the issues involved with getting connected to the Internet. It is assumed that companies are already aware of general security issues such as designing a security policy, making regular backups, scanning for viruses, securing the computers physically, and ensuring appropriate personnel security. Instead, the handbook focuses on identifying the new security issues involved with getting connected to the Internet. Overall Security That said, it is important to remember that uninformed people mainly cause security problems. People need to be aware of the security policy and understand the importance of maintaining a secure system. Having technically elaborate security does little good if employees are not aware of the need to keep their passwords secret. Since there are many ways an attacker can get information a company wants to protect, it is wise for a company to not focus on one single area of security while neglecting others. Internet security is only one component in an overall security program* . What are you trying to protect?" To establish a security policy, it is important to identify what you are trying to protect. When you connect to the Internet, you risk your data stored on your computers, your computing resources themselves, and your reputation. Your Data There are three aspects of data security:<br /> <br /> ·<br /> <br /> Confidentiality: keeping other people from knowing your data.<br /> <br /> ·<br /> <br /> Integrity: keeping other people from changing your data.<br /> <br /> ·<br /> <br /> Availability: keeping other people from preventing you from accessing your data.<br /> <br /> Many organizations focus their security efforts on keeping sensitive data secret. Often the importance of integrity and availability are overlooked. It may be costly (in terms of time, money, as well as others' confidence in your organization) to reconstruct data that has been altered or destroyed. Your Resources You also want to protect your computing resources, such as computing time and disk space. Any computing resources used by an attacker are resources that are not available to you. Types of Attacks There are many ways a system can be attacked. These attacks can be broken into three categories: denial-of-service, intrusion, and theft of information. Denial of Service<br /> <br /> 224 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> A denial of service attack aims to prevent you from using your own computer. This is usually done by an attacker overloading the system with so many messages, network requests, and/or processes that no resources are left for you. This can also be accomplished by exploiting flaws in software that causes the system to hang. Intrusion An intrusion involves an attacker using your computers as if he were a legitimate user. This is often done by using the user name and password of a legitimate user. Passwords can be guessed by using "password crackers". They can be captured as they traverse the network using "packet sniffers". And, finally, they can be talked out of an employee using "social engineering". Information Theft An attacker does not necessarily need access to your computer to steal information. There are many types of network services, such as ftp, which are designed to disseminate information. Many of these services have security holes that an attacker can exploit to get these services to divulge more information than you intend. "Packet sniffers" can also be used to steal information as it traverses the network. Types of Attackers There are many types of attackers and many ways to categorize them. Attacks originating from within an organization include disgruntled employees and hackers. Unintentional losses are also caused from within an organization by accidents and users stupidity. Attackers originating outside the organization include former employees, hackers, vendors, and corporate spies. Methods to Secure Your Site There are a few approaches that can be taken to secure a site. The most straightforward form of protection is physical isolation - not connecting internal and external networks at all. This denies users the benefits of connecting to the Internet such as Email, World Wide Web, and newsgroups. As more computers are connected to the Internet, the value of the information accessible from the Internet increases. Unfortunately, the threat of attacks originating from the Internet also increases. The risks of being connected must be balanced against the rewards. Assuming you want to connect to external networks, there are four approaches that can be taken to secure a site:<br /> <br /> ·<br /> <br /> Ignore Security: The simplest approach is to ignore security altogether and to simply use whatever minimal security your vendor provides by default. This method is rarely acceptable for obvious reasons.<br /> <br /> ·<br /> <br /> Security through Obscurity: People who assume that a system is secure because nobody knows about it are practicing security through obscurity. Given the time and resourcefulness of an attacker, a system is not likely to remain obscure for long.<br /> <br /> ·<br /> <br /> Host Security: A third approach is to provide host security in which security is enforced separately on each particular host. This approach works well when a small number of hosts are involved. But, it becomes unwieldy to secure all the holes in the host hardware, software, and operating systems in a multiplatform environment with a large number of hosts. The problem is that there are different security problems<br /> <br /> 225 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> associated with each hardware, software, and operating system; they may be configured differently, which may affect the security of the host.<br /> <br /> ·<br /> <br /> Network Security: Network Security is enforced on the network access to the hosts and on the services the hosts offer, rather than on securing each individual host. The main advantage of network security is that it allows a security policy to be enforced from a single firewalled gateway. One problem with enforcing network security at a gateway between two networks is that it can only enforce the security policy on network traffic that traverse the gateway. It cannot prevent an attack on an internal network that originates from within the internal network. For this reason, host security should still be enforced on the most important hosts, such as servers.<br /> <br /> User Authentication Computer systems perform many different operations such as generating reports, updating accounting tables, and transferring funds between bank accounts. The decision about whether a certain operation should be allowed is often based on the identity of the requesting user. It is therefore crucial to accurately identify this user. This problem is called "user authentication". The most common approach to identifying users in a computer system is with passwords. Each user has a secret password; presenting the password is considered proof of the user's identity. Despite the popularity of this approach, there are a number of problems with passwords:<br /> <br /> ·<br /> <br /> Users have difficulty remembering passwords; they therefore tend to choose easy-to-remember passwords, such as a name, a date, or a short phrase like "iloveyou". Unfortunately, easy-to-remember passwords are often easy for an attacker to guess.<br /> <br /> ·<br /> <br /> Using standard software, such as web-based email, passwords are sent over the Internet as clear text. Such clear text passwords can be captured or "sniffed" by attackers.<br /> <br /> ·<br /> <br /> Some standard software packages are automatically installed with default passwords and accounts. A list of commonly attacked default accounts on UNIX systems is given on page 227 of Garfinkle and Spafford. If system administrators do not change such passwords and accounts, attackers can use the default password to log into the system.<br /> <br /> Mechanisms do exist to address the problems with password authentication. Organizations can adopt (and enforce) a policy on choosing hard-to-guess passwords. Such policies could include guidelines such as "do not use anyone's name as your password" and "do not use a date as your password". System administrators should change all default passwords. Further, software alternatives (such as Secure Shell [SSH]) are available that allow users to log into a system over the Internet without sending their password as clear text. Alternately, an organization can adopt a mechanism that completely replaces passwords. Possible mechanisms include hand-held authenticators and one-time password generators. These mechanisms, while more secure, are hardware-based, so they require additional expense.<br /> <br /> 226 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Insecure Communication When connecting to the Internet, it is essential to realize the standard Internet communication software provides no security whatsoever. Messages sent over the Internet can be intercepted, redirected, modified, or even fabricated by attackers. In particular, when a message is received, it is possible the apparent sender (e.g. the sender's name in an email message) may not be the real sender; further, the message may have been read and/or modified by attackers in transit. There are many ways attackers may accomplish the above attacks. The most common techniques are known as "packet sniffing" (for reading messages) and "IP spoofing" (for fabricating messages). Fortunately, all such attacks can be foiled with the large body of techniques known as "cryptography". In particular, many Internet applications make use of "public key/private key pairs", "encryption", and "digital signatures". Typically, each user has its own public key/private key pair. The public key can be given to all other users, whereas the private key should never be revealed. Messages intended to be read only by a particular user can be encrypted with that user's public key. The user can decrypt the message using the corresponding private key, but no one else (because he does not have that key) can decrypt or otherwise read the message. In a similar way, a user can compute a digital signature for a given message using his private key. No one else (who does not have that key) can forge the digital signature. Digital signatures (sent over the Internet) are the mechanism used to ensure that a given user has made some statement, such as an agreement to purchase particular goods for a particular price. Further, other users can verify the digital signature by a computation involving the signer's public key and the original message. That is, cryptographic techniques can be employed to ensure:<br /> <br /> ·<br /> <br /> Attackers cannot read messages sent over the Internet.<br /> <br /> ·<br /> <br /> When a message is received, the apparent sender is in fact the actual sender and the message was received exactly as sent.<br /> <br /> Software packages are available that provide cryptographic capabilities for various applications. PGP (Pretty Good Privacy) is a popular free encryption package. Netscape Mail and Microsoft Outlook support reception and delivery of secure encrypted mail. An important consideration in evaluating the suitability of a particular encryption package for a particular application is the "encryption key length". The lengthier the encoding key, the harder it is for an assailant to guess the right key to use to unlock your secret. For a public key/private key pair, standard practice is to use keys of length 1024 bits and larger. For symmetric key pair encryption like Digital Encryption Standard (DES), a US standard, the key is 56 bits. The small key size of DES does pose a problem. An attacker (such as a large criminal organization) with a budget around HK $750,000 could use Application-specific Integrated Circuits (ASICs) to design and build a DES key-cracking machine that would crack keys in a few hours. Therefore, in an application where millions of dollars are at stake, 56-bit encryption is still insufficient. Beyond 56-bit keys, three well-known symmetric encryption algorithms are "triple DES" (providing 112-bit keys), IDEA (providing 128-bit keys), and RC5 (also 128-bit keys).<br /> <br /> 227 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Another important consideration in evaluation an encryption algorithm is the amount of scrutiny subjected to the algorithm. For example, world-class cryptographers may not have scrutinized proprietary algorithms whose details are not publicly available. In fact, such algorithms may have obvious weaknesses if an attacker ever obtains a description of the algorithm. It is therefore prudent to make use of encryption algorithms whose details are publicly available and thus subject to the most rigorous scrutiny. Flawed Software Unintentional software flaws, such as network operating system bugs and application design flaws, are vulnerable when connecting to the Internet. Some applications, such as early versions of sendmail, were never designed with security in mind and have security holes that may be exploited to gain unauthorized access. Additionally, some security holes are intentional and may be introduced by viruses or vendors. Viruses and Other Rouge Programs Viruses are computer programs that propagate by copying themselves. Viruses are commonly found on boot disks and executable files. Some viruses are harmless while others wreak havoc on a system. They can modify or erase the contents of files, and consume vast quantities of system resources. Viruses are most commonly spread by infected disks from outside an organization, although they can also propagate by attaching themselves to files that are transferred via a network. A Trojan horse is an innocent-looking program that performs some unwanted action. Much like the Trojan horse that carried enemy soldiers into Troy, a computer Trojan horse can carry viruses that might alter data, record passwords, or capture network traffic. It can also create a trap door that an attacker can exploit later. Trojan Horses can be installed in host systems as well as in bridges, routers, and gateways. The best way to combat viruses is with an anti-virus policy. This policy should aim to prevent infection of your software (by obtaining software from reliable sources), detect a virus if your software does get infected (by using up-to-date anti-virus software such as McAfee VirusScan), control contamination if files are infected so the virus does not spread (by isolating the system), and recover from infection by removing the virus or by using backups. Anti-virus software can support the policy by watching for suspect activity, checking the integrity of files for contamination, and scanning for signatures left by a virus. Operating System Weaknesses Improperly configured software often results in security holes. Most operating systems have adequate built-in security features; however, these features are often ignored or used improperly. For example, Unix and Windows NT have extensive user and group permissions that can be set on files or directories to regulate users access only to the files they need. Setting directory access permissions can limit not only the users' access to data and applications, but a virus' access as well. When configured correctly, most modern operating systems are able to track login failures, create an audit trail, and restrict or monitor logins from different locations. Tools, such as Nessus or Retina from eye Digital Security, can be used to scan for network vulnerabilities so they can be corrected. The best defense against OS weaknesses is to use the security features provided by the OS and to understand its limitations and weaknesses. Tools can also increase the security of a system. Vendors regularly release software patches to fix new security holes as they are discovered. So, it is important to use only the most current versions of system, client, and<br /> <br /> 228 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> patch software. If software is not updated, known security holes can be exploited by attackers to gain unauthorized access to your system. Vendor's "Back Doors" Some software vendors include "back doors" which allow their technical support personnel access to the system for maintenance purposes. Sometimes the vendor does not inform the customer of the existence of these back doors, which allow the vendor to change the software without the customer's knowledge. Vendors, as well as hackers, can exploit these "back doors" to gain unauthorized entry and are therefore a security risk. Unauthorized Modification of System Files In most cases of interest, system security depends on a large number of system files, including programs, configuration files, and data files. Normally, these security-relevant files are stored on ordinary disk drives along with all other files. The first time attackers break into a system, it is common for them to modify such security-relevant files. In this way, it will be easier for them to break in subsequent times. It is therefore important to identify exactly which system files are security-relevant and take precautions to ensure that in the event these files are modified, system administrators are alerted and can take appropriate actions. A useful tool in this regard is the freely available software package called tripwire. This software package allows system administrators to compute and store a "cryptographic hash" of every security-relevant file. Cryptographic hashes provide an "electronic fingerprint" of the file. The idea is that all cryptographic hashes are placed into the "tripwire database". System administrators periodically re-compute all cryptographic hashes and compare them to the tripwire database. If any security-relevant file has been modified, this comparison will fail, thus alerting the system administrators. Tripwire depends on the tripwire software and the tripwire database. If attackers replace the tripwire software or database at the same time they are replacing other security-relevant files, then the modifications may not be detected. It is therefore important to take special precautions with the tripwire software and database. These can be placed on a special-purpose write-once disk. Unauthorized Reading of System Files In some environments, computers may be used to store confidential data. After connecting to the Internet, it becomes especially important to protect such data from being read by attackers. The simplest technique to protect such data is to store it on removable media, such as floppy disks. Whenever that data is not in use, it is removed from the system and thus protected against unauthorized reading. When storing files on removable media is impractical or inconvenient, use encryption to keep the data confidential. If this approach is taken, it is important to realize there are many encryption algorithms, some of which are excellent and some of which are entirely worthless. One example is crypt's enciphering algorithm. Crypt is a standard part of most UNIX distribution. Unfortunately, there is another widely available piece of software called Code Breaker's Workbench (CBW) that can be used to easily decrypt any file encrypted with crypt. In other words, do not use crypt to encrypt confidential files. For information on good encryption algorithms and appropriate key lengths,<br /> <br /> 229 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Unauthorized Data Flow between Network Domain Host security focuses on protecting an individual host from a hostile network. Tools such as SSH can provide secure communication within a hostile network. In addition to protecting individual hosts and communication channels within a network from attack, most organizations opt to protect an entire internal network from external attacks. Firewalls provide a degree of isolation between an internal and an external network. Firewalls are most often used as a gateway between the Internet and an internal network. They can also be placed between two parts of an internal network. A firewall prevents an attacker on the Internet from gaining direct access to the internal network. They provide a certain level of security if they are correctly chosen, installed, configured, and maintained. Fundamentally, firewalls restrict the flow of information between two networks. A firewall policy specifies what kinds of data are allowed to pass through the firewall. Many firewalls have default policies that specify that anything that is not expressly permitted is prohibited. Using this strategy, you authorize the specific message types that are allowed to pass through the firewall. Only the services that are needed by your organization can be permitted and other services can be denied. An alternative default policy is that anything that is not expressly prohibited is permitted. With this approach, the message types that you know to be dangerous can be prohibited while all others are permitted. A firewall has many uses in addition to providing access control. They can block access to particular Internet sites, monitor the network traffic across the firewall, eavesdrop on communication, and form a virtual private network (VPN) by automatically encrypting data. Firewall Techniques There are basically three techniques used to build firewalls:<br /> <br /> ·<br /> <br /> Packet Filtering: Routers can implement packet filtering. Packet filters look at the TCP/IP header that contains minimal routing information such as the packet source and destination address. If packets have source or destination addresses that are prohibited by your access list, the packet is thrown away. Advantages of using packet-filtering routers are that they are easier to set up than most other firewall configurations. They also use simple equipment that many companies already own. They are somewhat flexible, since they allow access to be accepted or denied from and/or to a particular host or network. The disadvantages of packet filters are that they have rudimentary systems for logging traffic and break-in attempts, their access lists can get so complex that they are difficult to maintain, and it is difficult for them to support some particular services. Additionally, packet filters have several security-related design weaknesses. Attackers can use "IP spoofing" attacks to fool packet filters by forging IP headers. Finally, if the security of a packet filter is compromised, an attacker has access to the entire network.<br /> <br /> ·<br /> <br /> Circuit Level Gateways: There are two types of gateway firewalls: circuit-level gateways and application gateways. Circuit level gateways relay Internet connections. Outbound connections destined for the Internet head to a relay gateway. The gateway reads the destination address of the request and creates a link to the destination. The gateway then passes information between the internal connection request and the external destination link. The internal connection request never talks directly with the external destination. Therefore, the external destination believes it is just communicating with the relay gateway. Everything behind the relay<br /> <br /> 230 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> gateway is hidden. Network Address Translation (NAT) is used to hide knowledge about hosts behind the gateway. NAT can relay the connection with a new Internet address. NAT can hide an entire intranet behind one Internet address (this is also known as masquerading). Or, NAT can use a range of Internet addresses assigned to the organization running the g a t e w a y . Circuit level gateway's main disadvantage is it relies on static rules to determine whether to relay a connection. Applications that rely on random destination addresses for services are not supported in a circuit level gateway's pre-defined access control list. As a result, services like FTP, Microsoft Netmeeting, Mirabilis ICQ, and AOL Instant Messenger (AIM), conflict with the access control of circuit gateways. In order to support dynamic destination services, the circuit level gateway must disable destination-based filtration.<br /> <br /> ·<br /> <br /> Application Gateways: Instead of filtering traffic based only on the information in the packet header, application gateways use specially written code for each specific application. They are able to examine and interpret the data within the packet, not just the packet header. A physical application gateway uses proxy servers, code which represents both clients and servers. Since application gateways filter at the application layer, they have strong control of incoming and outgoing traffic. They can also hide host names and IP address, enabling outsiders to only see the gateway. The routing and filtering rules are simplified since traffic only needs to be sent to the gateway and the rest is rejected. One drawback to using proxy servers is that they require specific code for each service. Fortunately, many corporations with proprietary applications, like RealAudio have written proxies for their own software. They make the proxies freely available for download. Another drawback is that ready-made proxies may not be immediately available for new Internet applications. Applications may also require modified clients since they may need to first connect to the gateway, and then transferred to the host.<br /> <br /> Firewall Configurations Packet filters, applications gateways and circuit-level gateways can be configured in several different ways to meet the security needs of an organization. Depending on the configuration, a firewall may be implemented on a single machine or may include multiple machines and routers. There are four firewall configurations:<br /> <br /> ·<br /> <br /> Packet Filtering: A packet filtering firewall simply filters packets. Based on the packet header information, including the source and destination addresses and port numbers, the packet filter can pass some packets while blocking others. A packet filter is often implemented using a screening router that can be programmed, for example, to block all packets from a particular untrusted system or to block all incoming connections except those for email and FTP. Packet filtering is available on all routers and a variation can be implemented on hosts running UNIX, WinNT/2000/XP, and MacOS X.<br /> <br /> ·<br /> <br /> Stateful Inspection Packet Filtering: An alternative to simple packet filtering is Stateful Inspection. This method also filters on packet header information. Stateful inspection looks at the packet to see whether it is the beginning of a session, a continuation of a session, or the termination of a session. It builds up a table containing information about the current status of each Internet session. Based on the current state of a session, the packet may or may not be allowed to pass. Because of the table, stateful inspection prevents IP spoofing. Stateful inspection is<br /> <br /> 231 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> usually implemented as an add-on product of most routers. It is also available as an add-on package called, IP-Filter, for UNIX systems.<br /> <br /> ·<br /> <br /> Screened-Host: A screened-host firewall allows only trusted services to bypass the gateway. A screening router or firewall appliance is used to ensure that a host on an external network can only communicate with a bastion host that is attached to an internal network. The bastion host can communicate with other computers on the Internet network. The screened-host configuration allows only certain types of connections. Using the screened-host architecture, for example, direct connections between internal hosts and external hosts can be disallowed, or direct connections may be allowed, but only for select services. The advantages of the screened-host configuration are that it provides strong security, as long as it is working. The problem is that there is a single point of failure. Since the bastion host is on an internal network, if the host or the router is compromised, all the internal hosts can be directly attacked.<br /> <br /> ·<br /> <br /> Screened-Subnet or Demilitarized Zone (DMZ): The screened-subnet firewall has the advantages of a screened host, but is more secure. Instead of connecting to an internal network, the bastion host is connected to a perimeter network or DMZ. This DMZ is connected to the internal network and to an external network through screening routers or a firewall appliance. The main advantage with this configuration is that there is no single point of failure. If the bastion host fails, an attacker must still get through the screening routers/firewall appliance in order to access internal hosts. With the availability of firewall systems that support NAT, many screened-subnets use private network numbers to further enhance security. Since private network numbers are never to be routed around the Internet, most Internet Service Providers discard those packets. Companies that employ private network numbers use NAT to translate the private source address to a public source address assigned to the company. Internet resource servers can only communicate with the public source address. Therefore, connections from the Internet can never directly access the private hosts of the company since the private addresses are never revealed.<br /> <br /> ·<br /> <br /> Multi-homed Host: A multi-homed host firewall provides the highest-level of security because it allows absolutely no access to internal systems. A dual-homed host firewall is a single computer with at least two interface cards. A host on the internal network can communicate with the firewall, as can a host on an external network; however, hosts inside and outside the firewall cannot directly communicate with each other. The multi-homed hosts do not route packets directly from one network to another, although they could be configured to do so. Packets can go from one network to another only after being inspected, authenticated, authorized, and proxied.<br /> <br /> ·<br /> <br /> The crackers process<br /> <br /> Police, prosecutors and most of the press call them "hackers." Computer cognoscenti prefer the term "crackers." Both sides are talking about the same people, typically young men, whose fascination with computers leads them to gain access to computers where they don't belong. A few crackers make headlines, like Robert T. Morris Jr., son of a top computer security expert for the super secret National Security Agency, who let loose a "worm" program on a national network of university, research and government computers in 1988. There are also notorious crackers like Kevin Mitnick, who was under investigation at the age of 13 for illegally obtaining free long-distance phone calls and was sentenced to prison<br /> <br /> 232 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> i n 1989 for computer break-ins. Then there are legions of far more ordinary crackers who simply use their knowledge of computers to "explore" intriguing corporate or government computers or simply to go for the electronic equivalent of a joy ride and impress their friends. But they all share something: an air of mystery. How do they do it? At a recent conference on computer freedom and privacy, computer expert Russell L. Brand gave a four-hour lecture on the inner workings of computer cracking. His basic message: Cracking is not as hard as it seems to an outsider, and it often goes undetected by legitimate users of "cracked" computers.” Just because you don't see a problem is no reason to think a problem hasn't occurred," Brand said. "Generally it's a month to six weeks before (operators) notice anything happened and usually because the cracker accidentally broke something." Home computers aren't in danger from crackers because they aren't accessible to outsiders--and because they aren't interesting to crackers. Instead, they target mainframes and minicomputers that support many users and are connected to telephone lines and large networks. Understanding how crackers work and what security weaknesses they exploit can help system managers prevent many break-ins, Brand said. And the biggest problem is carelessness.” When I started looking at break-ins, I had the assumption that technical problems were at fault," he said. "But the problem is human beings."The "Cracker": Most crackers are not bent on stealing either money or secrets but will target a particular computer for entry because of the bragging rights they will enjoy with fellow crackers once they prove they broke in. Typically, the computer belongs to a corporation or the government and is considered in cracking circles to be hard to penetrate. Often, it is connected to the nationwide NSFNet computer network. The attack: Crackers can attack the target computer from home, using a modem and a telephone line. Or they can visit a publicly accessible terminal room, like one on a college campus, using the school's computer to attack the target through a network. At home, the cracker works undisturbed and unseen for hours, but phone calls might be traced. The resources: If the target computer is nearby, the cracker may look through the owner's trash for valuable information, a practice called "dumpster was diving." Discarded printouts, manuals or other paper may contain lists of accounts, some passwords, or technical data more sophisticated crackers can exploit. The target: The easiest way to enter the target is with an account name and its password. Passwords are often the weakest link in a computer's security system: Many are easy to guess, and some accounts have no password at all. Sophisticated crackers use their personal computers to quickly try thousands of potential passwords for a match. The cover: To make calls from home harder to trace, crackers might use stolen telephone credit-card numbers to place a series of calls through different long-distance carriers or corporate switchboards before calling the target computer’s modem. The way in: Many crackers take advantage of "holes" in the operating system, the software that controls the basic operations of the machine. The holes are like secret doors that either let crackers make their own "super" accounts or just bypass accounts and passwords altogether. Five holes in the Unix operating system account for the bulk of computer break-ins--yet many installations have failed to patch them. The network: Most large computers are connected to several others through networks, a chief point of attack. Computers erect barriers to people but often completely trust other computers, so attacking a computer through another computer on the network can be easier than attacking it with a personal computer and a modem. Ill-used<br /> <br /> passwords<br /> <br /> let<br /> <br /> many<br /> <br /> pass<br /> <br /> 233 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Passwords are the security linchpin for most computer systems. But these supposedly secret keys to computer access are easily obtained by a determined cracker. The main reason: Users and system managers often are so careless with passwords that they are as easy to find as a door key left under the welcome mat. Part of the problem is the proliferation of computers and computer like devices such as automated teller machines, all of which require passwords or personal identification numbers. Many people must now remember half a dozen or more such secret codes, encouraging them to make each one short and simple. Often, that means making their passwords the same as their account name, which in turn is often the user's own first or last name. Such identical combinations are called "Joe" accounts, and according to computer expert Russell L. Brand, they are “the single most common cause of password problems in the world." These `secret' keys to computer access are easily obtained by a determined cracker. The main reason: Users and system managers often are so careless with passwords that they are as easy to find as a key left under the welcome mat. Knowing there are Joes, a cracker can simply try a few dozen common English names with a reasonable chance that one will work. Armed with an easily obtained company directory of employees, the task can be even easier. Joe accounts also crop up when the system manager creates an account for a new employee, expecting that the user will immediately change the given password from his or her name to aren't told how. Sometimes, they never use the account at all, providing not only easy access for the cracker but an account where the owner won't notice any illicit activity. Even if crackers can't find a "Joe" on the computer they want to enter, there are several other common ways for them to find a password that will work. - Many systems have accounts with no passwords or have accounts for occasional visitors use where the ID and password are both GUEST. - Outdated operator's manuals retrieved from the trash often list the account name and standard password provided by the operating system for use by maintenance programmers. Although it can and should be changed, the password seldom is. - "Social engineering"--in effect, persuading someone, usually by telephone, to divulge account names, passwords or both--is a common ploy used by crackers. then use the first two letters of each word as the password. As added protection, users who are able should mix uppercase and lowercaseletters in their passwords or use a punctuation mark in the middle of the word.--Rory J. O'Connor to<br /> <br /> The<br /> <br /> rights<br /> <br /> of<br /> <br /> bits<br /> <br /> Constitutional scholar Laurence H. Tribe, widely considered the first choice for any Supreme Court vacancy that might arise under a Democratic administration, proposed a fairly radical idea recently: a constitutional amendment covering computers. Tribe's proposal for a 27th Amendment would specifically extend First and Fourth Amendment protections to the rapidly growing and increasingly pervasive universe of computing. Those rights would be "construed as fully applicable without regard to the technological method or medium through which information content is generated, stored, altered, transmitted or controlled," in the words of the proposed amendment. I am not a constitutional scholar, but I have to believe that what's needed is not a change in the Constitution, but instead a change in the thinking of judges in particular and the public in general. Tribe acknowledges that he doesn't take amendments lightly, pointing to the ridiculous brouhaha over a flag-burning amendment as an example of what not to do to the basic law of the land. But like many people who are more deeply involved in the world of computers, Tribe sees the issue of civil liberties in an information society as a crucial one.<br /> <br /> 234 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> The question is not whether the civil liberties issue is serious enough to be addressed by some fundamental legal change. The question is really how to get people to see that communicating with a computer is speech, and that to search a computer and seize details the same as searching a house and seizing the contents of my filing cabinet. People seem to have trouble making these connections when computers are involved, even though they wouldn't have trouble recognizing a private telephone conversation as protected speech. Yet most telephone calls in this country are, at some time in their transmission, nothing more than a stream of computer bits traveling between sophisticated computers. Admittedly, computers do make for some complications where things like search and seizure are concerned. Let's say the FBI gets a search warrant for a computer bulletin board, looking for a specific set of messages about an illegal drug business. Because a single hard disk drive on a bulletin board system can contain thousands of messages from different users, the normal method for police will be to take the whole disk, and probably the computer as well, back to the lab to look for the suspect messages. Of course, that exposes other, supposedly confidential messages to police scrutiny. It also interrupts the legitimate operation of what is, in effect, an electronic printing press. Certainly, in the case of a real printing press that used paper, such police activity would never be allowed. But a computer is involved here which to some appears to make the existing rules inapplicable. But in a case like this, we don't need a new amendment, just the proper application of the Bill of Rights. As a more practical matter, the chances of amending the Constitution are slight. It was the intent of the framers to make the task difficult, to prevent just such trivial things as flag-burning amendments from being tacked onto the document. Even the far more substantial Equal Rights Amendment did not survive the rocky road from proposal to adoption. I doubt Tribe's &nbs<br /> <br /> ·<br /> <br /> Types of attack<br /> <br /> Types of attack<br /> <br /> ·<br /> <br /> Password guessing/cracking<br /> <br /> ·<br /> <br /> Denial of service<br /> <br /> ·<br /> <br /> Spoofing/masquerading<br /> <br /> ·<br /> <br /> System break-in<br /> <br /> ·<br /> <br /> Eavesdropping<br /> <br /> ·<br /> <br /> Viruses, Trojan horses<br /> <br /> Password attacks (1)<br /> <br /> ·<br /> <br /> Social engineering and user mistakes Hello, my name is John Smith and I forgot my password. I need it really urgently can you set it to ‘js1234’ and I’ll change it myself? Certainly, sir. If there’s anything else we can do, don’t hesitate to call.<br /> <br /> 235 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Password attacks (2)<br /> <br /> ·<br /> <br /> Guessing weak passwords ·<br /> <br /> Name of partner, child, pet, favorite movie, book title, band name, birthdays,…<br /> <br /> ·<br /> <br /> guesses based on known previous passwords<br /> <br /> ·<br /> <br /> keyboard sequences<br /> <br /> Password attacks (3)<br /> <br /> ·<br /> <br /> Dictionary attacks (UNIX Crack, L0pht Crack for Windows NT) Original password<br /> <br /> Password attacks (4)<br /> <br /> ·<br /> <br /> Cached passwords in cleartext ·<br /> <br /> storing cleartext passwords in temporary files<br /> <br /> ·<br /> <br /> caching passwords on servers<br /> <br /> ·<br /> <br /> weak XOR encryption<br /> <br /> Denial of service<br /> <br /> ·<br /> <br /> Network floods (ICMP, UDP, SYN flood), possibly with spoofed source address<br /> <br /> ·<br /> <br /> Crashing servers with carefully constructed requests<br /> <br /> ·<br /> <br /> Redirecting network traffic on the backbone<br /> <br /> ·<br /> <br /> Mail bombs<br /> <br /> Spoofed ping floods A B C ICMP ECHO REQUEST Source: C, Destination: B ICMP ECHO REPLY Source: B, Destination: C Smurf attack Subnet B C ICMP ECHO REQUEST Source: C, Dest.: subnet B Broadcast address A<br /> <br /> 236 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Smurf attack Subnet B C ICMP ECHO REPLY Source: whole subnet B, Destination’s<br /> <br /> TCP three-way handshake SYN (A) ACK (A+1) SYN(B) ACK (B+1)<br /> <br /> SYN flood<br /> <br /> ·<br /> <br /> Send a flood of SYN packets to target host<br /> <br /> ·<br /> <br /> Target host allocates a buffer for each requests and replies with SYN|ACK packets<br /> <br /> ·<br /> <br /> Target host waits for ACKs that don’t come<br /> <br /> ·<br /> <br /> If you’re quick enough, target hosts runs out of available buffers and denies all further connections until connection attempts reach timeout<br /> <br /> Spoofing<br /> <br /> ·<br /> <br /> inserting false source IP address<br /> <br /> ·<br /> <br /> obscures real source of attack<br /> <br /> ·<br /> <br /> possible session hijacking<br /> <br /> ·<br /> <br /> two-way communication with spoofing must employ redirection of replies<br /> <br /> Spoofing trusted hosts SYN (A) SYN flood Trusted hosts<br /> <br /> Spoofing trusted hosts ACK (A+1) SYN (B) SYN flood Unable to process and send RST<br /> <br /> Spoofing trusted hosts ACK (B+1) SYN flood Sequence number predicted From “legitimate” connections<br /> <br /> 237 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Preventing spoofing A<br /> <br /> ·<br /> <br /> The only real prevention is by ISPs filtering spoofed packets on backbone routers<br /> <br /> System break-in<br /> <br /> ·<br /> <br /> Common break-in scenario: ·<br /> <br /> gain unauthorized user level access<br /> <br /> ·<br /> <br /> transition from user level to privileged access<br /> <br /> ·<br /> <br /> hide your presence<br /> <br /> Break-in consequences<br /> <br /> ·<br /> <br /> System can be used as a source of attacks to other sites on the Internet<br /> <br /> ·<br /> <br /> Information can be lost, altered or stolen<br /> <br /> ·<br /> <br /> Blackmail<br /> <br /> ·<br /> <br /> The system, local network, all users and maybe even your organization may be at the mercy of the attacker<br /> <br /> Ways to gain unauthorised access<br /> <br /> ·<br /> <br /> Poor or no authentication<br /> <br /> ·<br /> <br /> Weak, sniffed or stolen passwords<br /> <br /> ·<br /> <br /> “Forgotten” services<br /> <br /> ·<br /> <br /> Server buffer overruns<br /> <br /> ·<br /> <br /> Backdoors, Trojan horses and poor implementation of OS code and services<br /> <br /> ·<br /> <br /> Spoofing trusted hosts<br /> <br /> Common scenario of the attack<br /> <br /> ·<br /> <br /> Find a scanner for latest OS/server vulnerabilities and scan a wide range of address space<br /> <br /> ·<br /> <br /> Use available exploits to gain access<br /> <br /> ·<br /> <br /> Hide yourself on attacked host<br /> <br /> ·<br /> <br /> Install sniffers to collect passwords on remote sites<br /> <br /> 238 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Rootkit<br /> <br /> ·<br /> <br /> Tools for removing log entries<br /> <br /> ·<br /> <br /> Substitutes for original binaries<br /> <br /> ·<br /> <br /> ·<br /> <br /> login (accepts special usernames with root privileges)<br /> <br /> ·<br /> <br /> ps, ls, netstat, du (hide processes and files)<br /> <br /> ·<br /> <br /> ifconfig (hides promiscuous mode - sniffer)<br /> <br /> includes a user-friendly sniffer<br /> <br /> Buffer overruns<br /> <br /> ·<br /> <br /> Result of programming errors<br /> <br /> ·<br /> <br /> Arguments or requests exceed server’s buffer length<br /> <br /> ·<br /> <br /> Can cause crash of server program or even execution of arbitrary code<br /> <br /> ·<br /> <br /> Most notorious examples: UNIX send mail, POP/IMAP servers, BIND<br /> <br /> MS IE buffer overrun<br /> <br /> Netscape buffer overrun<br /> <br /> Sniffer<br /> <br /> ·<br /> <br /> Listens to all traffic on a local network<br /> <br /> ·<br /> <br /> Privileged access needed on UNIX systems (Windows 95/98: every user is a “privileged” users)<br /> <br /> ·<br /> <br /> Specialized sniffers grab and log passwords in nice human-readable form<br /> <br /> ·<br /> <br /> Generally undetectable over network<br /> <br /> Detection and prevention<br /> <br /> ·<br /> <br /> Use clean tools (commands on the system can be replaced by attacker) to check for “promiscuous mode” of network interface<br /> <br /> ·<br /> <br /> Use Ethernet switches (expensive…)<br /> <br /> ·<br /> <br /> Use session encryption (e.g. Secure Shell)<br /> <br /> ·<br /> <br /> Use one-time passwords (e.g. S/Key)<br /> <br /> 239 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Viruses and trojan horses<br /> <br /> ·<br /> <br /> A wide range of benign and malicious viruses, including MS Word macro viruses attached to documents sent by email<br /> <br /> ·<br /> <br /> Trojan horses are programs disguised as useful tools<br /> <br /> ·<br /> <br /> Platform/OS specific<br /> <br /> Prevention measures<br /> <br /> ·<br /> <br /> Antiviral tools (with regular updates)<br /> <br /> ·<br /> <br /> User education ·<br /> <br /> problems with downloads from untrusted sites<br /> <br /> ·<br /> <br /> be careful with received executable content<br /> <br /> Trojan horses<br /> <br /> ·<br /> <br /> BackOrifice, BO2k, NetBus, DeepThroat, Girlfriend ·<br /> <br /> target MS Windows systems<br /> <br /> ·<br /> <br /> install as a service at boot time<br /> <br /> ·<br /> <br /> accepts network connections (some encrypt their traffic)<br /> <br /> ·<br /> <br /> allow full access to the system (specialised commands for grabbing dial-up passwords)<br /> <br /> Proactive measures<br /> <br /> ·<br /> <br /> establish a site security policy<br /> <br /> ·<br /> <br /> install latest versions of software and apply recommended patches<br /> <br /> ·<br /> <br /> Strip down default services<br /> <br /> ·<br /> <br /> Restrict access to hosts<br /> <br /> ·<br /> <br /> Stay current with new security issues<br /> <br /> ·<br /> <br /> Apply OS and server patches immediately<br /> <br /> ·<br /> <br /> Do regular backups<br /> <br /> ·<br /> <br /> Monitor system activity and integrity<br /> <br /> 240 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> ·<br /> <br /> Implement a firewall Connect the system to your network<br /> <br /> Site security policy<br /> <br /> ·<br /> <br /> Who is authorized to use specific services from where (and when)?<br /> <br /> ·<br /> <br /> Who is given privileged access?<br /> <br /> ·<br /> <br /> Plan division of your network to public and private segments<br /> <br /> ·<br /> <br /> Inform users of risks<br /> <br /> ·<br /> <br /> Seek approval of your policy<br /> <br /> ·<br /> <br /> depending your network<br /> <br /> IDG) -- ParaProtect, a network security portal in Alexandria, Va., reports that 90 percent of the security breaches its technicians work on are based on attacks from within. Even more shocking is that upwards of 50 percent are caused by the company's own network administrators. So what can you do to protect your network? Here's a list of tips culled from industry analysts, security experts, corporate executives and agents of the U.S. Secret Service: MESSAGE BOARD Insurgency<br /> <br /> ·<br /> <br /> Make sure no one person is controlling the system front to back.<br /> <br /> ·<br /> <br /> Require every person logging on to use a password.<br /> <br /> ·<br /> <br /> Assign supervisory rights to as few people as possible.<br /> <br /> ·<br /> <br /> Back up all systems weekly.<br /> <br /> ·<br /> <br /> Have a strict sign-in/sign-out system for backup tapes.<br /> <br /> ·<br /> <br /> Always have a current copy of the backup tape stored remotely.<br /> <br /> ·<br /> <br /> Do backups of desktops and laptops as well as servers.<br /> <br /> 241 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> ·<br /> <br /> Rotate backup tapes - don't keep using the same one over and over again.<br /> <br /> ·<br /> <br /> Change passwords every three months.<br /> <br /> ·<br /> <br /> Keep servers in a secured area.<br /> <br /> ·<br /> <br /> Stay up-to-date on software patches.<br /> <br /> ·<br /> <br /> Use intrusion-detection software that alerts you when you are being hit.<br /> <br /> ·<br /> <br /> Make sure two pairs of eyes have checked code before it is entered into the system.<br /> <br /> ·<br /> <br /> Have an information security department (at least one person and then one other for every 1,000 users) that is separate from the IT department and reports directly to the chief information officer.<br /> <br /> ·<br /> <br /> Spend at least 3% to 5% of the IS budget on information security. Train information security personnel to be aware of any employee who shows signs of being troubled or disgruntled, particularly if that employee holds an information-critical position.<br /> <br /> ·<br /> <br /> Beef up security during certain events, such as mergers or downsizings, that could upset workers and cause them to lash out at the company.<br /> <br /> ·<br /> <br /> Monitor the network - set up software that will alert you if the person is working in a different part of the network or at a different time than usual.<br /> <br /> ·<br /> <br /> Scan e-mail to see what's going out of the company, double-check backup tapes and have someone else do the backups if that person is the one in question.<br /> <br /> ·<br /> <br /> Make sure the person in charge of the system is not the same person in charge of the backup.<br /> <br /> ·<br /> <br /> Have specific policies and punishments built into employee contracts.<br /> <br /> ·<br /> <br /> Make sure critical IS workers are bonded.<br /> <br /> 242 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> How to protect your system if you're firing a network administrator:<br /> <br /> ·<br /> <br /> Change everyone's passwords so he/she can't use them to break into the system.<br /> <br /> ·<br /> <br /> Verify that your backup tapes are where they should be; make sure the information has been saved correctly and the tape is functioning properly.<br /> <br /> ·<br /> <br /> Do a new backup.<br /> <br /> ·<br /> <br /> Lock down every system that person had access to on the day of termination.<br /> <br /> ·<br /> <br /> Have a new network administrator ready to step into the open position immediately.<br /> <br /> ·<br /> <br /> Go up on the system and check user names and passwords, looking for anything unusual.<br /> <br /> ·<br /> <br /> Make sure every logon has a password for it.<br /> <br /> ·<br /> <br /> Lock down all the inside doors, such as the file servers, application servers and mail servers.<br /> <br /> ·<br /> <br /> Look for backdoors on the system, such as Back Orifice on Windows NT.<br /> <br /> ·<br /> <br /> Make sure there aren't any known vulnerabilities that haven't been patched - the administrator could have left those holes behind so he could get back in.<br /> <br /> ·<br /> <br /> Strengthen your intrusion-detection system.<br /> <br /> ·<br /> <br /> Set a trip wire - software that alerts the administrator to system anomalies, such as the size of a file changing.<br /> <br /> ·<br /> <br /> Firewall<br /> <br /> If you have been using the Internet for any length of time, and especially if you work at a larger company and browse the Web while you are at work, you have probably heard the<br /> <br /> 243 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> term firewall used. For example, you often hear people in companies say things like, "I can't use that site because they won't let it through the firewall." If you have a fast Internet connection into your home (either a DSL connection or a cable modem), you may have found yourself hearing about firewalls for your home network as well. It turns out that a small home network has many of the same security issues that a large corporate network does. You can use a firewall to protect your home network and family from offensive Web sites and potential hackers.<br /> <br /> Basically, a firewall is a barrier to keep destructive forces away from your property. In fact, that's why its called a firewall. Its job is similar to a physical firewall that keeps a fire from spreading from one area to the next. As you read through this article, you will learn more about firewalls, how they work and what kinds of threats they can protect you from.<br /> <br /> What It Does A firewall is simply a program or hardware device that filters the information coming through the Internet connection into your private network or computer system. If an incoming packet of information is flagged by the filters, it is not allowed through. If you have read the article How Web Servers Work, then you know a good bit about how data moves on the Internet, and you can easily see how a firewall helps protect computers inside a large company. Let's say that you work at a company with 500 employees. The company will therefore have hundreds of computers that all have network cards connecting them together. In addition, the company will have one or more connections to the Internet through something like T1 or T3 lines. Without a firewall in place, all of those hundreds of computers are directly accessible to anyone on the Internet. A person who knows what he or she is doing can probe those computers, try to make FTP connections to them, try to make telnet connections to them and so on. If one employee makes a mistake and leaves a security hole, hackers can get to the machine and exploit the hole. With a firewall in place, the landscape is much different. A company will place a firewall at every connection to the Internet (for example, at every T1 line coming into the company). The firewall can implement security rules. For example, one of the security rules inside the company might be:<br /> <br /> 244 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Out of the 500 computers inside this company, only one of them is permitted to receive public FTP traffic. Allow FTP connections only to that one computer and prevent them on all others. A company can set up rules like this for FTP servers, Web servers, Telnet servers and so on. In addition, the company can control how employees connect to Web sites, whether files are allowed to leave the company over the network and so on. A firewall gives a company tremendous control over how people use the network. Firewalls use one or more of three methods to control traffic flowing in and out of the network:<br /> <br /> · · ·<br /> <br /> Packet filtering - Packets (small chunks of data) are analyzed against a set of filters. Packets that make it through the filters are sent to the requesting system and all others are discarded. Proxy service - Information from the Internet is retrieved by the firewall and then sent to the requesting system and vice versa. Stateful inspection - A newer method that doesn't examine the contents of each packet but instead compares certain key parts of the packet to a database of trusted information. Information traveling from inside the firewall to the outside is monitored for specific defining characteristics, then incoming information is compared to these characteristics. If the comparison yields a reasonable match, the information is allowed through. Otherwise it is discarded.<br /> <br /> Making the Firewall Fit Firewalls are customizable. This means that you can add or remove filters based on several conditions. Some of these are: · IP addresses - Each machine on the Internet is assigned a unique address called an IP address. IP addresses are 32-bit numbers, normally expressed as four "octets" in a "dotted decimal number." A typical IP address looks like this: 216.27.61.137. For example, if a certain IP address outside the company is reading too many files from a server, the firewall can block all traffic to or from that IP address. · Domain names - Because it is hard to remember the string of numbers that make up an IP address, and because IP addresses sometimes need to change, all servers on the Internet also have human-readable names, called domain names. For example, it is easier for most of us to remember www.howstuffworks.com than it is to remember 216.27.61.137. A company might block all access to certain domain names, or allow access only to specific domain names. · Protocols - The protocol is the pre-defined way that someone who wants to use a service talks with that service. The "someone" could be a person, but more often it is a computer program like a Web browser. Protocols are often text, and simply describe how the client and server will have their conversation. The http in the Web's protocol. Some common protocols that you can set firewall filters for include: · IP (Internet Protocol) - the main delivery system for information over the Internet · TCP (Transmission Control Protocol) - used to break apart and rebuild information that travels over the Internet · HTTP (Hyper Text Transfer Protocol) - used for Web pages · FTP (File Transfer Protocol) - used to download and upload files · UDP (User Datagram Protocol) - used for information that requires no response, such as streaming audio and video<br /> <br /> 245 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> · · · ·<br /> <br /> ICMP (Internet Control Message Protocol) - used by a router to exchange the information with other routers SMTP (Simple Mail Transport Protocol) - used to send text-based information (e-mail) SNMP (Simple Network Management Protocol) - used to collect system information from a remote computer Telnet - used to perform commands on a remote computer<br /> <br /> A company might set up only one or two machines to handle a specific protocol and ban that protocol on all other machines.<br /> <br /> ·<br /> <br /> Ports - Any server machine makes its services available to the Internet using numbered ports. For example, if a server machine is running a Web (HTTP) server and an FTP server, the Web server would typically be available on port 80, and the FTP server would be available on port 21. A company might block port 21 access on all machines but one inside the company. · Specific words and phrases - This can be anything. The firewall will sniff (search through) each packet of information for an exact match of the text listed in the filter. For example, you could instruct the firewall to block any packet with the word "X-rated" in it. The key here is that it has to be an exact match. The "X-rated" filter would not catch "X rated" (no hyphen). But you can include as many words, phrases and variations of them as you need. Some operating systems come with a firewall built in. Otherwise, a software firewall can be installed on the computer in your home that has an Internet connection. This computer is considered a gateway because it provides the only point of access between your home network and the Internet. With a hardware firewall, the firewall unit itself is normally the gateway. A good example is the Linksys Cable/DSL router. It has a built-in Ethernet card and hub. Computers in your home network connect to the router, which in turn is connected to either a cable or DSL modem. You configure the router via a Web-based interface that you reach through the browser on your computer. You can then set any filters or additional information. Hardware firewalls are incredibly secure and not very expensive. Home versions that include a router, firewall and Ethernet hub for broadband connections can be found for well under $100. What It Protects You From There are many creative ways that unscrupulous people use to access or abuse unprotected computers: · Remote login - When someone is able to connect to your computer and control it in some form. This can range from being able to view or access your files to actually running programs on your computer. · Application backdoors - Some programs have special features that allow for remote access. Others contain bugs that provide a backdoor, or hidden access, that provides some level of control of the program. · SMTP session hijacking - SMTP is the most common method of sending e-mail over the Internet. By gaining access to a list of e-mail addresses, a person can send unsolicited junk e-mail (spam) to thousands of users. This is done quite often by redirecting the e-mail through the SMTP server of an unsuspecting host, making the actual sender of the spam difficult to trace. · Operating system bugs - Like applications, some operating systems have backdoors. Others provide remote access with insufficient security controls or have bugs that an experienced hacker can take advantage of.<br /> <br /> 246 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> ·<br /> <br /> Denial of service - You have probably heard this phrase used in news reports on the attacks on major Web sites. This type of attack is nearly impossible to counter. What happens is that the hacker sends a request to the server to connect to it. When the server responds with an acknowledgement and tries to establish a session, it cannot find the system that made the request. By inundating a server with these unanswerable session requests, a hacker causes the server to slow to a crawl or eventually crash. · E-mail bombs - An e-mail bomb is usually a personal attack. Someone sends you the same e-mail hundreds or thousands of times until your e-mail system cannot accept any more messages. · Macros - To simplify complicated procedures, many applications allow you to create a script of commands that the application can run. This script is known as a macro. Hackers have taken advantage of this to create their own macros that, depending on the application, can destroy your data or crash your computer. · Viruses - Probably the most well-known threat is computer viruses. A virus is a small program that can copy itself to other computers. This way it can spread quickly from one system to the next. Viruses range from harmless messages to erasing all of your data. · Spam - Typically harmless but always annoying, spam is the electronic equivalent of junk mail. Spam can be dangerous though. Quite often it contains links to Web sites. Be careful of clicking on these because you may accidentally accept a cookie that provides a backdoor to your computer. · Redirect bombs - Hackers can use ICMP to change (redirect) the path information takes by sending it to a different router. This is one of the ways that a denial of service attack is set up. · Source routing - In most cases, the path a packet travels over the Internet (or any other network) is determined by the routers along that path. But the source providing the packet can arbitrarily specify the route that the packet should travel. Hackers sometimes take advantage of this to make information appear to come from a trusted source or even from inside the network! Most firewall products disable source routing by default. Some of the items in the list above are hard, if not impossible, to filter using a firewall. While some firewalls offer virus protection, it is worth the investment to install anti-virus software on each computer. And, even though it is annoying, some spam is going to get through your firewall as long as you accept e-mail. The level of security you establish will determine how many of these threats can be stopped by your firewall. The highest level of security would be to simply block everything. Obviously that defeats the purpose of having an Internet connection. But a common rule of thumb is to block everything, then begin to select what types of traffic you will allow. You can also restrict traffic that travels through the firewall so that only certain types of information, such as e-mail, can get through. This is a good rule for businesses that have an experienced network administrator that understands what the needs are and knows exactly what traffic to allow through. For most of us, it is probably better to work with the defaults provided by the firewall developer unless there is a specific reason to change it. One of the best things about a firewall from a security standpoint is that it stops anyone on the outside from logging onto a computer in your private network. While this is a big deal for businesses, most home networks will probably not be threatened in this manner. Still, putting a firewall in place provides some peace of mind.<br /> <br /> 247 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> ·<br /> <br /> Depending your computer<br /> <br /> 10 Steps to Protecting Your Computer Everyone must read this! Don't skip it...don't tell yourself that you are safe... Your inaction could cause great harm... At home, your identity, your money, and your personal information could be at risk. At work, your patient's medical information could be at risk! No, these are not "the sky is falling" rants...they are serious facts about today's computer world...and they directly affect each member of the Society of Diagnostic Medical Sonography (SDMS). Most computer users don't give security a second thought but the reality is that failure to take some simple steps could result in identity theft or worse. Hackers have thousands of tools at their disposal to take advantage of you including tools such as keystroke loggers. Keystroke loggers record every single keystroke you type on your computer...this includes your private email messages, your bank account password, and your credit card number! If you are connected to the Internet via a high-speed connection (DSL or cable), hackers can turn your computer into a "zombie" to launch attacks against thousands of other users and computers. This article focuses on Microsoft Windows users since the majority of computer users today use a version of this operating system on their home and/or office computers. And while not as frequent targets of hackers, alternative operating systems such as Mac OS and Linux are also vulnerable to attack. 10 Steps you can take to protect yourself:<br /> <br /> ·<br /> <br /> Update your computer - Stop using computers with insecure operating systems such as Microsoft Windows 95, Windows 98, and Windows ME. These versions of Microsoft Windows are now so old and outdated, they cannot be considered secure. Every day you use your computer may put you at risk. Upgrade your computer to Windows XP Service Pack 2 (or consider buying a new PC with it already installed). UPDATE 02/01/2007: Microsoft has now released a new operating system - Vista - which is designed to replace Windows XP and is supposed to be more secure.<br /> <br /> ·<br /> <br /> Update Microsoft Windows - Even with the newest computer, there are updates to be applied. There have been significant security holes discovered in all versions of Windows so it's important to update your computer's operating system as soon as possible. Regardless of the version of Windows you use, visit the Microsoft's Windows Update website (http://windowsupdate.microsoft.com) and install all "critical patches." You should also consider installing the recommended and driver patches. Note: It's always a good idea to backup your important data before installing updates (see Step #9). Keep in mind that even with Windows XP, there may be more than 80 patches that need to be installed...although the process is fairly automated, downloading the patches could take many hours on a dial-up Internet account. You may not be able to install patches for Windows on your work computer (requires administrator privileges) but you should ask your network administrator about their plans to keep your work computer up-to-date.<br /> <br /> 248 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> ·<br /> <br /> Use antivirus software - No one should be without antivirus software on their computer. There are many commercial products that can help protect your computer from various viruses, worms, Trojans and other hacker tools. But antivirus software works based on known viruses...the software must be configured to update its database of what to look for...be sure to configure your anti-virus software to update itself at least daily. And plan to run a complete system check of your computer's hard disks at least once per month to make sure nothing slipped in between antivirus software updates. Antivirus Software ·<br /> <br /> http://free.grisoft.com (AVG Antivirus Free)<br /> <br /> ·<br /> <br /> http://www.symantec.com/nav/nav_9xnt/ (Norton Antivirus)<br /> <br /> ·<br /> <br /> http://www.sophos.com/products/sav/ (Sophos Antivirus)<br /> <br /> ·<br /> <br /> http://www.pandasoftware.com/home/default.asp (Titanium Antivirus)<br /> <br /> ·<br /> <br /> http://www.trendmicro.com/en/home/us/personal.htm (Trend Micro PC-cillin)<br /> <br /> ·<br /> <br /> http://www.mcafee.com (McAfee VirusScan)<br /> <br /> Online Antivirus Checkups<br /> <br /> ·<br /> <br /> ·<br /> <br /> ·<br /> <br /> http://housecall.trendmicro.com/<br /> <br /> ·<br /> <br /> http://www.pandasoftware.com/products/activescan.htm<br /> <br /> Block Spyware - spyware and viruses often go hand-in-hand but can take many forms. Some 'hijack' your web browser and redirects you to their website. Others quietly download and install trojans, keylogger programs, etc. to your computer so hackers can take control of your computer later. Install and run an anti-spyware program such as: ·<br /> <br /> http://www.safer-networking.org/en/download/index.html (Spybot Search & Destroy)<br /> <br /> ·<br /> <br /> http://www.webroot.com/consumer/products/spysweeper/ (Spy Sweeper)<br /> <br /> ·<br /> <br /> http://www.lavasoft.com/products/ad-aware_se_personal.php (Ad-aware SE Personal)<br /> <br /> Keep your software up-to-date Microsoft Office: Many computer users use a version of the popular Microsoft Office suite (Outlook, Word, Excel, Powerpoint, or Publisher). Microsoft has released many patches for the Microsoft Office suite including some for "critical" security issues as well as "stability and performance enhancements." Note that you may need your original Microsoft Office installation CD to complete the updates. ·<br /> <br /> http://office.microsoft.com/officeupdate/default.aspx (Microsoft Office)<br /> <br /> 249 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Adobe Reader: Acrobat PDF files are used extensively on the SDMS website and throughout the Internet. Adobe Reader 8 can be used to view/print these files. You should not be using older versions - a free upgrade is available. ·<br /> <br /> http://www.adobe.com/products/acrobat/readstep2.html (Acrobat Reader)<br /> <br /> Flash: Adobe Flash Player is used on many website, including the ARDMS, to provide a more interactive web experience. Serious security issues have been found in older versions of the Flash viewer. ·<br /> <br /> ·<br /> <br /> ·<br /> <br /> http://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version =ShockwaveFlash (Adobe Flash Player)<br /> <br /> Use a firewall - A firewall simply tries to block hackers from entering or using your computer. If you are using cable or DSL connections to the Internet, a hacker can attempt to break-in to your computer 24x7! Make sure you have a router/firewall properly installed and configured. The most common mistake home users make is buying a router/firewall but never resetting the default password...it's like leaving the keys in the door! You can also use a software-based firewall to protect your computer from hackers. Microsoft's scheduled release of its Service Pack #2 for Windows XP in August will include a simple software-based firewall designed to better protect your computer. Some software-based firewalls include: ·<br /> <br /> http://www.zonealarm.com (ZoneAlarm)<br /> <br /> ·<br /> <br /> http://www.mcafee.com (McAfee Personal Firewall)<br /> <br /> ·<br /> <br /> http://www.symantec.com/sabu/nis/npf/ (Norton Personal Firewall)<br /> <br /> Use complex passwords - whether at work or at home, use complex passwords (and never write them down!). Using a password longer than 8 characters can greatly reduce the chance that someone will guess your password. Hackers don't usually sit there and try to guess your password one at a time. They use automated brute force tools that can break a simple password in a few minutes to a few hours. Here's an example of a complex password: 1mSdM5m3MbEr (Hint: I am SDMS member) You should change your password at least every 3 months and never reuse old passwords...be creative, come up with something new! Tip: Never use the same (or similar) password at home and work...if one is compromised, then both are compromised... Tips for Creating Secure Passwords<br /> <br /> ·<br /> <br /> ·<br /> <br /> http://www.microsoft.com/athome/security/privacy/password.mspx<br /> <br /> ·<br /> <br /> http://www.us-cert.gov/cas/tips/ST04-002.html<br /> <br /> ·<br /> <br /> http://www.symantec.com/homecomputing/library/pass_w.html<br /> <br /> Use "Personal Biometric Devices" - If you use the Internet for online banking, purchases, etc., remembering all your passwords can be difficult. Personal biometric devices that use fingerprints are great tools to assist you in protecting your computer and easily storing your passwords ($50 to $150).<br /> <br /> 250 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> ·<br /> <br /> http://www.apc.com/resource/include/techspec_index.cfm?base_sku=BIOPO D (APC's Personal Biometric USB Pod)<br /> <br /> ·<br /> <br /> http://www.digitalpersona.com/products/personal.html U.Are.U Personal)<br /> <br /> ·<br /> <br /> http://www.microsoft.com/hardware/mouseandkeyboard/productdetails.aspx ?pid=093 (Microsoft Fingerprint Reader)<br /> <br /> (Digital<br /> <br /> Persona's<br /> <br /> ·<br /> <br /> Backup your important data often - Diskettes are no longer practical for backup a CD recordable (CD-R) drive can help quickly backup your important data (700 MB per disc or equivalent to 485 diskettes). DVD recordable drives are also available (~7 times as much as a CD or equivalent to 3200 diskettes!) Other options include external USB hard drives to store all of your "data", documents, photos, music as well as USB "thumb" drives that you can carry on your keychain.<br /> <br /> ·<br /> <br /> Enlist the support of experts - all this can be scary...hackers and even unexpected problems with security patches could potentially mess up your system rendering it unusable! And it's time consuming...with over 80 patches to Windows XP, the download and installations can take hours. Don't be afraid to enlist the assistance of experts. Check with your local computer or electronics store. There are many companies that specialize in providing home user support such as Geeks on Call: http://www.geeksoncall.com/resserv.htm<br /> <br /> ·<br /> <br /> Depending your transmnitting data<br /> <br /> I am sure that anyone that has been listening to the news for the past year has realized that corporations need to do more to protect their data. Security breaches at financial institutions and credit card processing centers demonstrate the risk of exposing non-public personal information to a hacker. Also with Mobile Devices when they contain all your contacts, imagine what damage a competitor can do with your list? A critical component to the solution to protecting your company’s data on your mobile device is encryption. Even though your company may have security standards, you should be aware of these controls and ensure that your data is secure. This article covers where you can use encryption to restrict access to the data stored on or transmitted from your device. What<br /> <br /> is<br /> <br /> Encryption?<br /> <br /> Encryption is a way to make data unreadable to others however still allows users to access it. It requires the user or system to have a specific key and software to decrypt the data. There are a couple of standards for encryption you should be aware of in this discussion. Encryption uses the CPU of the computer intensively to perform the encryption and decryption. So when you use encryption the computer system is slowed by performing the encryption and decryption and the size of the data may increase. These are the main reasons why all data is not encrypted today. Generally the longer the encryption key the harder it is for the encryption to be broken by trying all possible permutations of the key. What<br /> <br /> Encryption<br /> <br /> is<br /> <br /> Used<br /> <br /> when<br /> <br /> you<br /> <br /> access<br /> <br /> a<br /> <br /> Website?<br /> <br /> When you visit a website that uses HTTPS (or SSL), it is using a digital certificate issued by an authorized company to allow you to access the website. This is accomplished using a digital signature with the certificate which you can see on your desktop by clicking File – Properties and click on the Certificates button. Originally the web browsers supported 56 bit and 128 bit encryption keys because the United States restricted the export of 128 bit<br /> <br /> 251 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> encryption however today the standard is 128 bits. Also some companies now use locally signed certificates. These locally signed certificates need to be installed on each Pocket PC or Smartphone to access internal websites or Exchange 2003. What<br /> <br /> is<br /> <br /> the<br /> <br /> 3DES<br /> <br /> Encryption<br /> <br /> Standard?<br /> <br /> Triple Data Encryption Standard (3DES) is the most common encryption standard used in the enterprise today. 3DES is where 3 different 56 bit keys are used to encrypt the data three times. Since 3DES uses a 168 bit key which is long enough that it is not easy break. It is most commonly used in Virtual Private Networks. What<br /> <br /> is<br /> <br /> the<br /> <br /> AES<br /> <br /> Encryption<br /> <br /> Standard?<br /> <br /> AES is the Advanced Encryption Standard. It uses 128 bit symmetrical blocks to encrypt the data. So you can have AES128, AES256 AES384, etc. by increasing the key size by 128 bits. It has been adopted by the United States Government as the official standard for encrypting d a t a . What<br /> <br /> is<br /> <br /> the<br /> <br /> Blowfish<br /> <br /> Encryption<br /> <br /> Standard?<br /> <br /> Blowfish is an open source encryption standard that is used in Linux applications such as Secure Shell. It supports encryption keys of varying lengths with 512 and 1024 being commonly used values. It is optimized to run on 32 bit operating systems so it is faster to encrypt and decrypt than other encryption standards. Since it is an open source solution many developers have adopted it. What<br /> <br /> Are<br /> <br /> Wi-Fi<br /> <br /> Encryption<br /> <br /> Standards?<br /> <br /> Wired Equivalent Privacy (WEP) is the minimum encryption standard for Wi-Fi. It supports both 64 and 128 bit encryption. However it can easily be broken due to a limitation in the design of the protocol. This is the reason why Wired Protected Access (WPA) was created. WPA uses the temporal key integrity protocol which provides the keys with an integrity check to ensure they are not tampered with. What<br /> <br /> Built-In<br /> <br /> Applications<br /> <br /> can<br /> <br /> use<br /> <br /> Encryption?<br /> <br /> On the Pocket PC and Smartphone, you can use the SSL encryption when visiting a website. Additionally the Pocket PC supports the use of 3DES encryption to access a Virtual Private Network as well. Also, you should be aware that with Pocket PC 2002 and Windows Mobile 2003 and Windows Mobile 2003 Second Edition you can install additional root and local certificates. Also, with Windows Mobile 2003 and later Microsoft now supports encrypting Wi-Fi connections using WEP, WPA and EAP. Beyond theses examples, Microsoft provides the CryptoAPIs to allow developers to create custom applications to support encryption. These APIs provide support for DES and 3DES encryption. 3rd<br /> <br /> Party<br /> <br /> Applications<br /> <br /> that<br /> <br /> use<br /> <br /> Encryption<br /> <br /> For example, you can use 3rd party Virtual Private Network clients from Cisco, Checkpoint and AnthaVPN/MovianVPN to allow you to securely access your company’s network when you are out of the office. You can also use encryption to protect files stored on your Pocket PC or storage card. Examples include Pretty Good Privacy (PGP), Air Scanner Mobile Encrypted. Also, there are 3rd party applications to encrypt all data stored on your Pocket PC. These applications include Sentry 2020, Crypto Storage, Asynchrony: PDADefense, F-Secure: File Crypto Enterprise, Pointsec Mobile Technologies: Pointsec for Pocket PC 2.0, Trust Digital: PDASecure, and Utimaco: Safe Guard PDA. Also, you can use Secure Shell (SSH) to access a<br /> <br /> 252 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327<br /> <br /> Linux Go<br /> <br /> computer, ahead<br /> <br /> router and<br /> <br /> or<br /> <br /> firewall.<br /> <br /> Use<br /> <br /> it!<br /> <br /> Whenever you are storing or transmitting data that needs to be kept confidential, I highly recommend using encryption. As with any security mechanism, periodically you will need to reevaluate the level of security that the encryption provides. Over time, I expect that users will have the option to encrypt all data and that vendors will focus on providing easier tools to enable them to encrypt data.<br /> <br /> 253 F.C Ledesma Avenue, San Carlos City, Negros Occidental Tel. #: (034) 312-6189/(034) 729-4327 </div> </div> <hr /> <h4>Related Documents</h4> <div class="row"> <div class="col-lg-2 col-md-4 col-sm-6 col-6"> <div class="card item-doc mb-4"> <a href="https://pdfcoke.com/documents/internet-web-programming-v8z1x258v3ry" class="d-block"><img class="card-img-top" src="https://pdfcoke.com/img/crop/300x300/v8z1x258v3ry.jpg" alt=""/></a> <div class="card-body text-left"> <h5 class="card-title"><a href="https://pdfcoke.com/documents/internet-web-programming-v8z1x258v3ry" class="text-dark">Internet & Web Programming</a></h5> <small class="text-muted float-left"><i class="fas fa-clock"></i> November 2019</small> <small class="text-muted float-right"><i class="fas fa-eye"></i> 10</small> <div class="clearfix"></div> </div> </div> </div> <div class="col-lg-2 col-md-4 col-sm-6 col-6"> <div class="card item-doc mb-4"> <a href="https://pdfcoke.com/documents/web-programming-48ojp6v87wo1" class="d-block"><img class="card-img-top" src="https://pdfcoke.com/img/crop/300x300/48ojp6v87wo1.jpg" alt=""/></a> <div class="card-body text-left"> <h5 class="card-title"><a href="https://pdfcoke.com/documents/web-programming-48ojp6v87wo1" class="text-dark">Web Programming</a></h5> <small class="text-muted float-left"><i class="fas fa-clock"></i> June 2020</small> <small class="text-muted float-right"><i class="fas fa-eye"></i> 11</small> <div class="clearfix"></div> </div> </div> </div> <div class="col-lg-2 col-md-4 col-sm-6 col-6"> <div class="card item-doc mb-4"> <a href="https://pdfcoke.com/documents/web-programming-j6o4l420jkzx" class="d-block"><img class="card-img-top" src="https://pdfcoke.com/img/crop/300x300/j6o4l420jkzx.jpg" alt=""/></a> <div class="card-body text-left"> <h5 class="card-title"><a href="https://pdfcoke.com/documents/web-programming-j6o4l420jkzx" class="text-dark">Web Programming</a></h5> <small class="text-muted float-left"><i class="fas fa-clock"></i> June 2020</small> <small class="text-muted float-right"><i class="fas fa-eye"></i> 20</small> <div class="clearfix"></div> </div> </div> </div> <div class="col-lg-2 col-md-4 col-sm-6 col-6"> <div class="card item-doc mb-4"> <a href="https://pdfcoke.com/documents/internet-web-09352qvjvd3e" class="d-block"><img class="card-img-top" src="https://pdfcoke.com/img/crop/300x300/09352qvjvd3e.jpg" alt=""/></a> <div class="card-body text-left"> <h5 class="card-title"><a href="https://pdfcoke.com/documents/internet-web-09352qvjvd3e" class="text-dark">Internet-web</a></h5> <small class="text-muted float-left"><i class="fas fa-clock"></i> June 2020</small> <small class="text-muted float-right"><i class="fas fa-eye"></i> 11</small> <div class="clearfix"></div> </div> </div> </div> <div class="col-lg-2 col-md-4 col-sm-6 col-6"> <div class="card item-doc mb-4"> <a href="https://pdfcoke.com/documents/internet-programming-php-4d3782190ezx" class="d-block"><img class="card-img-top" src="https://pdfcoke.com/img/crop/300x300/4d3782190ezx.jpg" alt=""/></a> <div class="card-body text-left"> <h5 class="card-title"><a href="https://pdfcoke.com/documents/internet-programming-php-4d3782190ezx" class="text-dark">Internet Programming-php</a></h5> <small class="text-muted float-left"><i class="fas fa-clock"></i> June 2020</small> <small class="text-muted float-right"><i class="fas fa-eye"></i> 9</small> <div class="clearfix"></div> </div> </div> </div> <div class="col-lg-2 col-md-4 col-sm-6 col-6"> <div class="card item-doc mb-4"> <a href="https://pdfcoke.com/documents/internet-programming-css-xlo67ld8k136" class="d-block"><img class="card-img-top" src="https://pdfcoke.com/img/crop/300x300/xlo67ld8k136.jpg" alt=""/></a> <div class="card-body text-left"> <h5 class="card-title"><a href="https://pdfcoke.com/documents/internet-programming-css-xlo67ld8k136" class="text-dark">Internet Programming - 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