Varun

A Report on Practical training

YAGYAVALKYA INSTITUTE OF TECHNOLOGY JAIPUR, RAJASTHAN.

WHAT IS A NETWORK? A network consists of two or more computers that are linked in order to share resources (such as printers and CD-ROMs), exchange files, or allow electronic communications. The computers on a network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.

TYPES OF NETWORK 1. LAN (LOCAL AREA NETWORK) 1. CAN (CAMPUS AREA NETWORK) 1. MAN (METROPOLITAN AREA NETWORK) 1. WAN (WIDE AREA NETWORK)

CABLES AND STANDARDS USED FOR LAN NETWORK CAT 3, 4 AND 5 IBM TYPE 1-9 CABLING STANDARDS EIA568A AND 568B ETHERNET CABLING STANDARDS: IEEE 802.3 (10base5), IEEE 802.3a (10base2) IEEE 802.3i (10baset)  UNSHEILDED TWISTED PAIR (UTP)  SHIELDED TWISTED PAIR (STP)  CONNECTORS: RJ-45, RJ-11, RS-232, BNC    

HARDWARE DEVICES USED IN LAN NICs (NETWORK INTERFACE CARDS) REPEATERS ETHERNET HUBS TOKEN RING BRIDGES BROUTERS ROUTERS GATEWAYS PRINT SERVERS FILE SERVERS SWITCHES

PEER to PEER NETWORK Peer-to-peer network operating systems allow users to share resources and files located on their computers and to access shared resources found on other computers. However, they do not have a file server or a centralized management source (See the figure below). In a peer-to-peer network, all computers are considered equal; they all have the same abilities to use the resources available on the network. Peer-to-peer networks are designed primarily for small to medium local area networks.

Client/Server Client/server network operating systems allow the network to centralize functions and applications in one or more dedicated file servers (See the figure below). The file servers become the heart of the system, providing access to resources and providing security. Individual workstations (clients) have access to the resources available on the file servers. The network operating system provides the mechanism to integrate all the components of the network and allow multiple users to simultaneously share the same resources irrespective of physical location

CAMPUS AREA NETWORK Campus Area Network or CAN is a network spread over a limited geographical area such as a university. Cables as the communication medium, and a device that can interface various patches of LANs across the campus. Once such device is the LAN extender. Cable 1: Power adapter Cable 2: RJ45 Ethernet port. You could either connect the LAN extender directly to a PC using a cross-over cable, or connect it to an Ethernet hub or switch using a straight through cable. Cable 3: Console port. Initial configuration of the LAN Extender is done by connecting it to a free COM port on your PC using a RS232 cable. Cable 4: RJ11 Telephone cable. A plain two-wire telephone cable serves as the WAN link between the two LAN Extenders. MAN (METROPOLITAN AREA NETWORK) METROPOLITAN AREA NETWORKS (MAN) ARE NETWORKS THAT CONNECT LANS TOGETHER WITHIN A CITY. THE PROTOCOLS USED FOR MAN ARE :RS-232, V-35 X.25 (56KBPS), PACKET ASSEMBLETS AND DISSEMBLERS FRAME RELAY ASYNCHRONOUS TRANSFER MODE (ATM) ISDN (INTEGRATED SERVICES DIGITAL NETWORK)

A typical use of MANs to provide shared access to a wide area network is shown in the Figure below:

WAN (WIDE AREA NETWORK) Wide Area Networks (WANs) connect larger geographic areas, such as Florida, the United States, or the world. Dedicated transoceanic cabling or satellite uplinks may be used to connect this type of network. Using a WAN, schools in Florida can communicate with places like Tokyo in a matter of minutes, without paying enormous phone bills. A WAN is complicated. It uses multiplexers to connect local and metropolitan networks to global communications networks like the Internet. To users, however, a WAN will not appear to be much different than a LAN or a MAN.

OSI REFERENCE MODEL When computers were first linked together into networks, moving information between different types of computers was a very difficult task. In the early 1970s, the International Organization of Standards (ISO) recognized the need for a standard network model. This would help vendors to create interpretable network devices. The Open Systems Interconnection (OSI) reference model, released in 1984, addressed this need. The OSI model describes how information makes its way from application programs through a network medium to another application program in another computer. It divides this one big problem into seven smaller problems. Each of these seven problems is reasonably self-contained and therefore more easily solved without excessive reliance on external information. Each problem is addressed by one of the seven layers of the OSI model.

The Seven Layers of the OSI model • Application • Presentation • Session • Transport • Network • Data-link • Physical The lower two OSI model layers are implemented with hardware and software.

APPLICATION LAYER The application layer of the OSI model is the layer that is closest to the user. Instead of providing services to other OSI layers, it provides services to application programs outside the scope of the OSI model. It's services are often part of the application process. Main functions are:• identifies and establishes the availability of the intended communication partner. • synchronizes the sending and receiving applications. • establishes agreement on procedures for error recovery and control of data integrity. • determines whether sufficient resources for the intended communications exist.

Devices:• Browsers • Search engines • E-mail programs • Newsgroup and chat programs • Transaction services • Audio/video conferencing • Telnet • SNMP

PRESENTATION LAYER It ensures that information sent by the application layer of one system will be readable by the application layer of another system. It provides a common format for transmitting data across various systems, so that data can be understood, regardless of the types of machines involved. The presentation layer concerns itself not only with the format and representation of actual user data, but also with data structure used by programs. Therefore, the presentation layer negotiates data transfer syntax for the application layer.

Devices:• Encryption • EBCDIC and ASCII • GIF & JPEG

SESSION LAYER The main function of the OSI model's session layer is to control "sessions", which are logical connections between network devices. A session consists of a dialog, or data communications conversation, between two presentation entities. Dialogs can be • Simplex (one-way) • half-duplex (alternate) • full-duplex (bi-directional) Simplex conversations are rare on networks. Half-duplex conversations require a good deal of session layer control, because the start and end of each transmission need to be monitored. Most networks are of course capable of full-duplex transmission, but in fact many conversations are in practice half-duplex.

Devices:Some examples of session layer protocols and interfaces are: • Network File System (NFS) • Concurrent database access • X-Windows System • Remote Procedure Call (RPC) • SQL • NetBIOS Names • AppleTalk Session Protocol (ASP) • Digital Network Architecture

TRANSPORT LAYER You can think of the transport layer of the OSI model as a boundary between the upper and lower protocols. The transport layer provides a data transport service that shields the upper layers from transport implementation issues such as the reliability of a connection. The transport layer provides mechanisms for:• multiplexing upper layer applications • the establishment, maintenance, and orderly termination of virtual circuits • information flow control • transport fault detection and recovery

Devices:• TCP, UDP, SPX and Sliding Windows.

NETWORK LAYER Layer three of the OSI model is the network layer. • The network layer sends packets from source network to destination network. • It provides consistent end-to-end packet delivery services to its user, the transport layer. In wide area networking a substantial geographic distance and many networks can separate two end systems that wish to communicate. Between the two end systems the data may have to be passed through a series of widely distributed intermediary nodes. These intermediary nodes are normally routers. Routers are special stations on a network, capable of making complex routing decisions. • The network layer is the domain of routing. Routing protocols select optimal paths through the series of interconnected networks. Network layer protocols then move information along these paths. • One of the functions of the network layer is "path determination". Path determination enables the router to evaluate all available paths to a destination and determine which to use. It can also establish the preferred way to handle a packet. After the router determines which path to use it can proceed with switching the packet. It takes the packet it has accepted on one interface and forwards it to another interface or port that reflects the best path to the packet's destination.

Devices:• IP, IPX, Routers, Routing Protocols (RIP, IGRP, OSPF, BGP etc), ARP, RARP, ICMP.

DATA-LINK LAYER Layer two of the OSI reference model is the data-link layer. This layer is responsible for providing reliable transit of data across a physical link. The data-link layer is concerned with • Physical addressing; Bridges, Transparent Bridges, Layer 2 Switches • network topology; CDP • line discipline (how end systems will use the network link) • error notification • ordered delivery of frames • flow control • Frame Relay, PPP, SDLC, X.25, 802.3, 802.3, 802.5/Token Ring, FDDI.

PHYSICAL LAYER Layer one of the OSI model is the physical layer. The physical layer is concerned with the interface to the transmission medium. At the physical layer, data is transmitted onto the medium (e.g. coaxial cable or optical fiber) as a stream of bits. So, the physical layer is concerned, not with networking protocols, but with the transmission media on the network. The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. This layer puts 1's & 0's onto the wire. Characteristics specified by the physical layer include • voltage levels • timing of voltage changes • physical data rates • maximum transmission distances • physical connectors Devices:• Hubs, FDDI Hardware, Fast Ethernet, Token Ring Hardware.

NETWORK TOPOLOGIES What is a Topology? The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations. Logical topology will be discussed in the Protocol Chapter.

Main Types of Physical Topologies Linear Bus Star Ring Tree 5. Mesh 6. Hybrid 1. 2. 3. 4.

Linear Bus A linear bus topology consists of a main run of cable with a terminator at each end (See fig. 1). All nodes (file server, workstations, and peripherals) are connected to the linear cable. Ethernet and Local Talk networks use a linear bus topology. Nodes

Nodes

Advantages of a Linear Bus Topology Easy to connect a computer or peripheral to a linear bus. Requires less cable length than a star topology. Disadvantages of a Linear Bus Topology Entire network shuts down if there is a break in the main cable. Terminators are required at both ends of the backbone cable. Difficult to identify the problem if the entire network shuts down.

Not meant to be used as a stand-alone solution in a large building

Star A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub or concentrator (See fig. 2). Data on a star network passes through the hub or concentrator before continuing to its destination. The hub or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable. Advantages of a Star Topology Easy to install and wire. No disruptions to the network then connecting or removing devices. Easy to detect faults and to remove parts. Disadvantages of a Star Topology Requires more cable length than a linear topology. If the hub or concentrator fails, nodes attached are disabled. More expensive than linear bus topologies because of the cost of the concentrators. The protocols used with star configurations are usually Ethernet or LocalTalk. Token Ring uses a similar topology, called the star-wired ring.

Ring Topology A star-wired ring topology may appear (externally) to be the same as a star topology. Internally, the MAU (multi station access unit) of a star-wired ring contains wiring that allows information to pass from one device to another in a circle or ring. The Token Ring protocol uses a star-wired ring topology. nodes

Tree A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Advantages of a Tree Topology Point-to-point wiring for individual segments. Supported by several hardware and software venders. Disadvantages of a Tree Topology Overall length of each segment is limited by the type of cabling used. If the backbone line breaks, the entire segment goes down. More difficult to configure and wire than other topologies

MESH TOPOLOGY nodes

HYBRID

Hierarchical Topology

Physical Topology

Common Cable

Common Protocol

Linear Bus

Twisted Pair Coaxial Fiber

Ethernet LocalTalk

Star

Twisted Pair Fiber

Ethernet LocalTalk

Star-Wired Ring Twisted Pair

Token Ring

Tree

Ethernet

Twisted Pair Coaxial Fiber

NETWORK TECHNOLOGY ETHERNET The term Ethernet refers to the family of local-area network (LAN) products covered by the IEEE 802.3 standard that defines what is commonly known as the CSMA/CD protocol. Three data rates are currently defined for operation over optical fiber and twisted-pair cables: • 10 Mbps—10Base-T Ethernet • 100 Mbps—Fast Ethernet • 1000 Mbps—Gigabit Ethernet 10-Gigabit Ethernet is under development and will likely be published as the IEEE 802.3ae supplement to the IEEE 802.3 base standard in late 2001 or early 2002. Other technologies and protocols have been touted as likely replacements, but the market has spoken. Ethernet has survived as the major LAN technology (it is currently used for approximately 85 percent of the world's LAN-connected PCs and workstations) because its protocol has the following characteristics: • Is easy to understand, implement, manage, and maintain

• Allows low-cost network implementations • Provides extensive topological flexibility for network installation • Guarantees successful interconnection and operation of standardscompliant products, regardless of manufacturer Ethernet Network Elements Ethernet LANs consist of network nodes and interconnecting media. The network nodes fall into two major classes: • Data terminal equipment (DTE)—Devices that are either the source or the destination of data frames. DTEs are typically devices such as PCs, workstations, file servers, or print servers that, as a group, are all often referred to as end stations. • Data communication equipment (DCE)—Intermediate network devices that receive and forward frames across the network. DCEs may be either standalone devices such as repeaters, network switches, and routers, or communications interface units such as interface cards and modems. Throughout this chapter, standalone intermediate network devices will be referred to as either intermediate nodes or DCEs. Network interface cards will be referred to as NICs. The current Ethernet media options include two general types of copper cable: unshielded twisted-pair (UTP) and shielded twisted-pair (STP), plus several types of optical fiber cable

802.3 (Ethernet) This standard specifies a network that uses a bus topology, base band signaling, and a CSMA/CD network access method. This standard was developed to match the Digital, Intel, and Xerox (DIX) Ethernet networking technology. So many people implemented the 802.3 standard, which resembles the DIX Ethernet, that people just started calling it Ethernet. It is the most widely implemented of all the 802 standards because of its simplicity and low cost. Ethernet

Speeds Access Topologies Media

-

10, 100, or 1000 Mbps CSMA/CD Logical bus Coaxial or UTP

The IEEE 802.3 Logical Relationships to the ISO Reference Model Figure below shows the IEEE 802.3 logical layers and their relationship to the OSI reference model. As with all IEEE 802 protocols, the ISO data link layer is divided into two IEEE 802 sublayers, the Media Access Control (MAC) sublayer and the MAC-client sublayer. The IEEE 802.3 physical layer corresponds to the ISO physical layer.

The MAC-client sublayer may be one of the following:

• Logical Link Control (LLC), if the unit is a DTE. This sublayer provides the interface between the Ethernet MAC and the upper layers in the protocol stack of the end station. The LLC sublayer is defined by IEEE 802.2 standards. • Bridge entity, if the unit is a DCE. Bridge entities provide LAN-to-LAN interfaces between LANs that use the same protocol (for example, Ethernet to Ethernet) and also between different protocols (for example, Ethernet to Token Ring). Bridge entities are defined by IEEE 802.1 standards. Because specifications for LLC and bridge entities are common for all IEEE 802 LAN protocols, network compatibility becomes the primary responsibility of the particular network protocol. Figure shows different compatibility requirements imposed by the MAC and physical levels for basic data communication over an Ethernet link.

The Basic Ethernet Frame Format The IEEE 802.3 standard defines a basic data frame format that is required for all MAC implementations, plus several additional optional formats that are used to extend the protocol's basic capability. The basic data frame format contains the seven fields shown in Figure. • Preamble (PRE)—Consists of 7 bytes. The PRE is an alternating pattern of ones and zeros that tells receiving stations that a frame is coming, and that provides a means to synchronize the frame-reception portions of receiving physical layers with the incoming bit stream. • Start-of-frame delimiter (SOF)—Consists of 1 byte. The SOF is an alternating pattern of ones and zeros, ending with two consecutive 1-bits indicating that the next bit is the left-most bit in the left-most byte of the destination address. • Destination address (DA)—Consists of 6 bytes. The DA field identifies which station(s) should receive the frame. The left-most bit in the DA field indicates whether the address is an individual address (indicated by a 0) or a group address (indicated by a 1). The second bit from the left indicates whether the DA is globally administered (indicated by a 0) or locally administered (indicated by a 1). The remaining 46 bits are a uniquely assigned value that identifies a single station, a defined group of stations, or all stations on the network.

• Source addresses (SA)—Consists of 6 bytes. The SA field identifies the sending station. The SA is always an individual address and the left-most bit in the SA field is always 0. • Length/Type—Consists of 2 bytes. This field indicates either the number of MAC-client data bytes that are contained in the data field of the frame, or the frame type ID if the frame is assembled using an optional format. If the Length/Type field value is less than or equal to 1500, the number of LLC bytes in the Data field is equal to the Length/Type field value. If the Length/Type field value is greater than 1536, the frame is an optional type frame, and the Length/Type field value identifies the particular type of frame being sent or received. • Data—Is a sequence of n bytes of any value, where n is less than or equal to 1500. If the length of the Data field is less than 46, the Data field must be extended by adding a filler (a pad) sufficient to bring the Data field length to 46 bytes. • Frame check sequence (FCS)—Consists of 4 bytes. This sequence contains a 32-bit cyclic redundancy check (CRC) value, which is created by the sending MAC and is recalculated by the receiving MAC to check for damaged frames. The FCS is generated over the DA, SA, Length/Type, and Data fields

Frame Transmission

Whenever an end station MAC receives a transmit-frame request with the accompanying address and data information from the LLC sublayer, the MAC begins the transmission sequence by transferring the LLC information into the MAC frame buffer. • The preamble and start-of-frame delimiter are inserted in the PRE and SOF fields. • The destination and source addresses are inserted into the address fields. • The LLC data bytes are counted, and the number of bytes is inserted into the Length/Type field. • The LLC data bytes are inserted into the Data field. If the number of LLC data bytes is less than 46, a pad is added to bring the Data field length up to 46. • An FCS value is generated over the DA, SA, Length/Type, and Data fields and is appended to the end of the Data field. After the frame is assembled, actual frame transmission will depend on whether the MAC is operating in half-duplex or full-duplex mode. The IEEE 802.3 standard currently requires that all Ethernet MACs support half-duplex operation, in which the MAC can be either transmitting or receiving a frame, but it cannot be doing both simultaneously. Full-duplex operation is an optional MAC capability that allows the MAC to transmit and receive frames simultaneously

Half-Duplex Transmission—the CSMA/CD Access Method The CSMA/CD access rules are summarized by the Protocol’s acronym: Carrier sense— each station continuously listens for traffic on the medium to determine when gaps between frame transmissions occur. Multiple accesses—Stations may begin transmitting any time they detect that the network is quiet (There is no traffic). Collision detect—If two or more stations in the same CSMA/CD network (collision domain)begin transmitting at approximately the same time, the bit streams from the transmitting stations will interfere (collide) with each other, and both transmissions will be unreadable. If that happens, each transmitting station must be capable of detecting that a Collision has occurred before it has finished sending its frame.

Full Duplex Operation

Full-duplex operation is an optional MAC capability that allows simultaneous two-way transmission over point-to-point links. Full duplex transmission is functionally much simpler than half-duplex transmission because it involves no media contention, no collisions, no need to schedule retransmissions, and no need for extension bits on the end of short frames. The result is not only more time available for transmission, but also an effective doubling of the link bandwidth because each link can now support full-rate, simultaneous, two-way transmission. Transmission can usually begin as soon as frames are ready to send. The only restriction is that there must be a minimum-length inter-frame gap between successive frames, as shown in Figure, and each frame must conform to Ethernet frame format standards

NETWORK CABLING What is Network Cabling? Cable is the medium through which information usually moves from one network device to another. There are several types of cable which are commonly used with LANs. In some cases, a network will utilize only one type of cable, other networks will use a variety of cable types. The type of

cable chosen for a network is related to the network's topology, protocol, and size. Understanding the characteristics of different types of cable and how they relate to other aspects of a network is necessary for the development of a successful network. The types of cables used in networks Unshielded Twisted Pair (UTP) Cable Shielded Twisted Pair (STP) Cable Coaxial Cable Fiber Optic Cable Wireless LANs

Unshielded twisted pair (UTP) is the most popular and is generally the best option for school networks The quality of UTP may vary from telephone-grade wire to extremely highspeed cable. The cable has four pairs of wires inside the jacket. Each pair is twisted with a different number of twists per inch to help eliminate interference from adjacent pairs and other electrical devices. The tighter the twisting, the higher the supported transmission rate and the greater the cost per foot. The EIA/TIA (Electronic Industry Association/Telecommunication Industry Association) has established standards of UTP and rated five categories of wire Shielded Twisted Pair (STP) Cable A disadvantage of UTP is that it may be susceptible to radio and electrical frequency interference. Shielded twisted pair (STP) is suitable for environments with electrical interference; however, the extra shielding can make the cables quite bulky. Shielded twisted pair is often used on networks using Token Ring topology. Coaxial Cable Coaxial cabling has a single copper conductor at its center. A plastic layer provides insulation between the center conductor and a braided metal shield the metal shield helps to block any outside interference from fluorescent lights, motors, and other computers Although coaxial cabling is difficult to install, it is highly resistant to signal interference. In addition, it can support greater cable lengths between network devices than twisted pair cable. The two types of coaxial cabling are thick coaxial and thin coaxial.

Thin coaxial cable is also referred to as thinnet. 10Base2 refers to the specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to the approximate maximum segment length being 200 meters. In actual fact the maximum segment length is 185 meters. Thin coaxial cable is popular in school networks, especially linear bus networks. Thick coaxial cable is also referred to as thicknet. 10Base5 refers to the specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to the maximum segment length being 500 meters. Thick coaxial cable has an extra protective plastic cover that helps keep moisture away from the center conductor. This makes thick coaxial a great choice when running longer lengths in a linear bus network. One disadvantage of thick coaxial is that it does not bend easily and is difficult to install.

Fiber Optic Cable Fiber optic cabling consists of a center glass core surrounded by several layers of protective materials. It transmits light rather than electronic signals eliminating the problem of electrical interference. This makes it ideal for certain environments that contain a large amount of electrical interference. It has also made it the standard for connecting networks between buildings, due to its immunity to the effects of moisture and lighting. Fiber optic cable has the ability to transmit signals over much longer distances than coaxial and twisted pair. It also has the capability to carry information at vastly greater speeds. This capacity broadens communication possibilities to include services such as video conferencing and interactive services. The cost of fiber optic cabling is comparable to copper cabling; however, it is more difficult to install and modify. 10BaseF refers to the specifications for fiber optic cable carrying Ethernet signals. 10BaseT Unshielded Twisted Pair 100 meters 10Base2 Thin Coaxial 185 meters 10Base5 Thick Coaxial l500 meters 10BaseF Fiber Optic 2000 meters 100BaseT Unshielded Twisted Pair 100 meters 100BaseTX Unshielded Twisted Pair 220 meters

Wireless LANs

Not all networks are connected with cabling; some networks are wireless. Wireless LANs use high frequency radio signals, infrared light beams, or lasers to communicate between the workstations and the file server or hubs. Each workstation and file server on a wireless network has some sort of transceiver/antenna to send and receive the data. Information is relayed between transceivers as if they were physically connected. For longer distance, wireless communications can also take place through cellular telephone technology, microwave transmission, or by satellite.

Hubs The term ‘hub’ is sometimes used to refer to any piece of network equipment that connects PCs together, but it actually refers to a multi-port repeater. This type of device simply passes on (repeats) all the information it receives, so that all devices connected to its ports receive that information. Hubs repeat everything they receive and can be used to extend the network. However, this can result in a lot of unnecessary traffic being sent to all devices on the network. Hubs pass on traffic to the network regardless of the intended destination; the PCs to which the packets are sent use the address information in each packet to work out which packets are meant for them. In a small network repeating is not a problem but for a larger, more heavily used network, another piece of networking equipment (such as a switch) may be required to help reduce the amount of unnecessary traffic being generated.

ROUTER

A router is a computer networking device that forwards data packets toward their destinations through a process known as routing. Routing occurs at layer 3 of the OSI seven-layer model.

Router Responsibilities 1. Optimizing the Routing Paths. 2. Switching Router Features Use dynamic routing Operate at the protocol level Remote administration Support complex networks The more filtering done, the lower the performance Provides security Segment networks logically Broadcast storms can be isolated

Often provide bridge functions also More complex routing protocols used [such as RIP, IGRP, OSPF]

Bridges A data-link bridge is a device that connects two similar networks or divides one network into two. It takes frames from one network and puts them on the other, and vice versa. As it does this, it regenerates the signal strength of the frames, allowing data to travel further. In this sense, a data-link bridge incorporates the functionality of a repeater, which also regenerates frames to extend a LAN. But a bridge does more than a repeater. A bridge is more intelligent than a repeater. It can look at each frame and decide on which of the two networks it belongs. Repeaters simply forward every frame from one network to the other, without looking at them. A bridge looks at each frame as it passes, checking the source and destination addresses. If a frame coming from Station 1 on LAN A is destined for Station 5 on LAN B, the bridge will pass the frame onto LAN B. If a frame coming from Station 1 on LAN A is destined for Station 3 on LAN A, the bridge will not forward it; that is, it will filter it. Bridges know which frames belong where by looking at the source and destination addresses in the Medium Access Control (MAC) layer information carried in the frame. The MAC layer, which is part of the second layer of OSI Model, defines how frames get on the network without bumping into each other. It also contains information about where the frame came from and where it should go. Because bridges use this level of information, they have several advantages over other forms of interconnecting LANs.

Bridge Features  Operate at the MAC layer (layer 2 of the OSI model)  Can reduce traffic on other segments  Broadcasts are forwarded to every segment  Most allow remote access and configuration  Small delays introduced  Fault tolerant by isolating fault segments and  Reconfiguring paths in the event of failure  Not efficient with complex networks  Redundant paths to other networks are not used (would be useful if the major path being used was overloaded)  Shortest path is not always chosen by spanning tree algorithm

SWITCHES Switches are smart hubs that send data directly to the destination rather than everywhere within a network. Switches also allow components of different speeds to communicate. Switches divide the network into smaller collision domains [a collision domain is a group of workstations that contend for the same bandwidth]. Each segment into the switch has its own collision domain (where the bandwidth is competed for by workstations in that segment). As packets arrive at the switch, it looks at the MAC address in the header, and decides which segment to forward the packet to. Higher protocols like IPX and

TCP/IP are buried deep inside the packet, so are invisible to the switch. Once the destination segment has been determined, the packet is forwarded without delay. Different forwarding techniques:1. Cut-through Switches 2. Store-Forward Switches

MODEM The word "modem" stands for "modulator-demodulator". A modem's purpose is to convert digital information to analog signals (modulation), and to convert analog signals back into useful digital information (demodulation).

JACK

MAC Address MAC addresses are also known as hardware addresses or physical addresses. They uniquely identify an adapter on a LAN. Short for Media Access Control address. This is OSI layer 2 hardware addresses defined by IEEE standard and is used to deliver packets in the

local network. It is sequence of six two-digits hexadecimal numbers separated by colons, example: 00:2f:21:c1:11:0a MM:MM:MM:SS: SS:SS MM-MM-MM-SS-SS-SS The first half of a MAC address contains the ID number of the adapter manufacturer. These IDs are regulated by an Internet standards body. The second half of a MAC address represents the serial number assigned to the adapter by the manufacturer

IP ADDRESS IP Addressing Requirements Each Device that uses TCP/IP needs at least one! Computer/Host (each Network Interface Card) Routers (each port or connection) Other Devices Each Device needs a Unique IP Address An Example: 206.77.105.9 Configured in TCP/IP Software What is an IP Address? 32-bit Binary Number (Address) 11000000101010000111000100010011 Divided into 4, 8-bit Octets 11000000.10101000.01110001.00010011 Converted to Decimal Numbers See: Binary Math 192.168.113.19 Decimal range of an Octet: 0-255 It contains the device’s Network ID and Host ID Network ID and Host ID Network ID Shared or common to all computers on the same physical segment Unique on the Entire Network “Area Code” Host ID Identifies a specific device (Host) within a physical segment Unique on the physical segment “Phone Number” 192.176.11.201

IP Addressing Rules  Each Device (Host) Needs at Least One Unique IP Address  All Devices on the Same Physical Segment Share a Common Network ID (Subnet Mask)  Each Physical Segment Has a Unique Network ID (Subnet Mask)

Class full IP Addressing Traditional Manner of Addressing Class A Class B Class C Address Classes Specify Which Octets of the IP Address are the Network-ID and which are the Host-ID Address Classes Specify Network Sizes (Number of Hosts) Address Classes Class A Network. Host. Host. Host Class B Network. Network. Host. Host Class C Network. Network. Network. Host Class D & E

Class A Network: The Definition per Specification: 1st Octet is the Network ID 2nd, 3rd, 4th Octets are the Host ID In Binary – Any address that starts with a “0” in the first bit! First Class A Network Address: 00000001.00000000.0000000.00000000 (Binary) 1.0.0.0 (Decimal) Last Class A Network Address: 01111111.00000000.00000000.00000000 (Binary) 127.0.0.0 (Decimal) (Loop back Address)

Network IDs 1st Octet is the Network ID 0.0.0.0 (Invalid) 1.0.0.0 2.0.0.0 3.0.0.0 ~~~~ 127.0.0.0 (Loop back) 2nd, 3rd, 4th Octets are the Host IDs An Assigned Class A Network Address: 33.0.0.0 (Specifies the Network) 2nd, 3rd, 4th Octets are the Host IDs Specified by Network Administrators The Number of Networks 1st Octet is the Network ID 1-126 = 126 Possible Class A Network IDs 2nd, 3rd, 4th Octets are the Host IDs Each of the three Octets has a possible 256 Host IDs Number of Host IDs from three Octets: 256 * 256 * 256 = 16,777,216 (minus 2) = 16,777,214 Always Subtract 2 from the number of Host IDs Host IDs cannot be all 1’s (reserved for broadcast address) Host IDs cannot be all 0’s (reserved for “this network only” address) Host ID Addresses 33.0.0.0 (An Assigned Class A Address) All devices would share the 33 network ID. The Administrator would number the IP devices: 33.0.0.1 – 33.0.0.255 (255 Addresses) 33.0.1.0 – 33.0.1.255 (256 Addresses) ~~~~ 33.0.255.0 -- 33.0.255.255 (256 Addresses) (A Total of 65,535 Addresses) 33.1.0.0 -- 33.1.255.255 (65,536 Addresses) 33.2.0.0 -- 33.2.255.255 (65,536 Addresses)

~~~~ 33.255.0.0 -- 33.255.255.254 (65,535 Addresses) ( Total Addresses: 16.7 Million)

Class B Networks: The Definition per Specification: 1st and 2nd Octets are the Network ID 3rd, 4th Octets are the Host IDs In Binary – Any address that starts with a “10” in the first two bits of the first octet! First Class B Network Address: 10000000.00000000.0000000.00000000 (Binary) 128.0.0.0 (Decimal) Last Class B Network Address: 10111111.11111111.00000000.00000000 (Binary) 191.255.0.0 (Decimal) Network IDs 1st and 2nd Octets are the Network IDs 128.0.0.0 128.1.0.0 ~~~~ 128.255.0.0 129.0.0.0 129.1.0.0 ~~~~ 191.255.0.0 3rd, 4th Octets are the Host IDs An Assigned Class B Network Addresses 153.11.0.0 3rd, 4th Octets are the Host IDs Specified by Network Administrators The Number of Networks 1st and 2nd Octets are the Network IDs

1st Octet 128 -- 191 = 64 Possible Network IDs 2nd Octet 0 – 255 = 256 Possible Network IDs Total Class B Network IDs 64 * 256 = 16,384 3rd, 4th Octets are the Host IDs Each of the Two Octets has a possible 256 Host IDs Number of Host IDs from Two Octets: 256 * 256 = 65,536 (minus 2) = 65,534 Always Subtract 2 from the number of Host IDs Host ID cannot be all 1’s (reserved for broadcast address) Host ID cannot be all 0’s (reserved for “this network only” address) Host ID Addresses An Assigned Class B Address 153.11.0.0 All devices would share the 153.11 Network ID. The Administrator would number the IP devices: 153.11.0.1 -- 153.11.0.255 (255 Addresses) 153.11.1.0 -- 153.11.1.255 (256 Addresses) 153.11.2.0 -- 153.11.2.255 (256 Addresses) ~~~~ 153.11.255.0 -- 153.11.255.254 (255 Addresses) Total Addresses: 65,534

The DefinitionPer Specification: 1st, 2nd, 3rd Octets are the Network ID 4th Octet is the Host ID In Binary – Any address that starts with a “110” in the first three bits of the first octet! First Class C Network Address: 11000000.00000000.0000000.00000000 (Binary) 192.0.0.0 (Decimal) Last Class C Network Address: 11011111.11111111.11111111.00000000 (Binary) 223.255.255.0 (Decimal)

Network IDs 1st, 2nd, 3rd Octets are the Network IDs 192.0.0.0 – 192.0.255. 0 192.1.0.0 – 192.1.255.0 ~~~~ 192.255.0.0 – 192.255.255.0 193.0.0.0 – 193.255.255.0 ~~~~ 223.0.0.0 – 223.255.255.0 4th Octet is the Host IDs An Assigned Class C Network Address 201.11.206.0 4th Octet is the Host IDs Specified by Network Administrators The Number of Networks 1st, 2nd, 3rd Octets are the Network IDs 1st Octet 192 -- 223 = 31 Possible IDs 2nd Octet 0 – 255 = 256 Possible IDs 3nd Octet 0 – 255 = 256 Possible IDs Total Class C Network IDs 32 * 256 *256 = 2,097,152 4th Octet is the Host ID An Octet has a possible 256 IDs Number of Host IDs an Octet: 256 (minus 2) = 254 Always Subtract 2 from the number of Host IDs Host ID cannot be all 1’s (reserved for broadcast address) Host ID cannot be all 0’s (reserved for “this network only” address) Host ID Addresses An Assigned Class C Address 201.11.206.0 All devices would share the 201.11.206.0 Network ID. The Administrator would number the IP devices: 201.11.206.1, 201.11.206.2, ~~~~ 201.11.206.254

Class D & E Class D Used by Multicast Applications Shared Addresses 224.0.0.0 – 239.255.255.255 Class E Experimental 240.0.0.0 + Address Class Summary 1st Class A Class B Class C

Networks Octet

1-127 128-191 192-223

126 16,384 2,097,152

Hosts IDs IDs /Network 16,777,214 65,534 254

Subnetting and Creating Custom Subnet Masks Introduction: Why Custom Subnet Masks? What are Subnet IDs? Step 1 – Design the Physical Network Step 2 – Choose a Custom Subnet Mask Step 3 – Determining the Subnet IDs Step 4 – Determining the Host IDs What is a Subnet Mask? An Address the accompanies an IP address that indicates which portion of the IP address is the Network ID and which portion of the IP address is the Host ID. 152.107.102.7 (IP Address) 255.255.255.0 (Subnet Mask) The IP Address and Subnet Mask (SNM) are interrelated and each only has meaning in the context of the other! IP Address and SNM are the minimum IP addressing requirements.

What Makes up a Subnet Mask (SNM)? In Binary: 1’s represent what portion of the IP address is the Network ID 0’s represent what portion of the IP address is the Host ID For Example: 207.23.106.99 (Class C Address) Net . Net . Net . Host 11111111 . 11111111 . 11111111 . 00000000 (SNM in Binary) 255.255.255.0 (SNM in Decimal) Default Subnet Masks (SNM) Class A (Net.Host.Host.Host) 11111111.00000000.00000000.00000000 255.0.0.0 Class B (Net.Net.Host.Host) 11111111.11111111.00000000.00000000 255.255.0.0 Class C (Net.Net.Net.Host) 11111111.11111111.11111111.00000000 255.255.255.0 Why Custom Subnet Masks? Default Subnet Masks Class A (1 Network – 16.7M Hosts) Class B (1 Network – 65K Hosts) Class C (1 Network – 254 Hosts) Addressing an IP Network Assigned an IP Network Address 152.77.0.0 (IP Address) 255.255.0.0 (Subnet Mask) All Devices/Hosts on the Same Physical Segment Must have the Same Network ID One Network ID Supports Only One Physical Segment!

What are Subnets? A Subnet is a portion or subdivision of the IP Addresses that are associated with an assigned Network ID.The Range of IP Addresses included in a subnet is determined by the Subnet Mask. Subnets must be meticulously numbered for network communication to be successful. Custom Subnetting: The Steps Design Physical Network Determine the Number of Physical Segments Determine the Maximum Number of Hosts per Physical Segment Choose a Subnet Mask that creates the number of: Subnet-IDs >= Physical Segments Host-IDs/Subnet-ID >= Hosts/Physical Segment Determine and Number Subnet IDs (SN ID) Determine and Number Host IDs Subnet IDs Portions of the Assigned Network ID are Defined by Subnet IDs 152.77.0.0 (Network IP Address) 255.255.0.0 (Default Subnet Mask) Network . Network . Host . Host (Default SNM) Network . Network . SN-ID . Host (Custom SNM) All Device/Hosts Share the Assigned Network ID (All Physical Segments) Each Physical Segment of the Network has a Unique Subnet-ID and the Subnet ID is Common to All Hosts on a Physical Segment Each Host on the Network has a Host ID Unique to its Subnet ID

Domain Naming System DNS as a Service IP Address needed by programs 100.109.23.144 The DNS Service Provides IP Name Resolution DNS is a distributed database of Domain Names and their corresponding IP Addresses Domain Naming System A hierarchical naming system used to give each server on the Internet a unique name. www.varun.com (URL or FQDN) HostName.Domain.TLD HostName and the Domain Name = Fully Qualified Domain Name (FQDN) DNS keeps a complete listing of all FQDNs and their associated IP address

Domain Name Structure (Organizational Structure) Root

NET

COM

IIHT

COMPAQ

GOV

SEC

Org, us, ca, etc

DNS Software Resolver Built into Client TCP/IP Software Ask Designated Name Server for IP Address When Client Enters FQDN (URL) Name Server DNS Server (Available with Most OS) Retrieves IP Addresses for Clients Supplies IP Address to other Name Servers Provided by the Internet, ISP, or business

COMMUNICATION PROTOCOLS This is an agreed upon format for transmitting data between two devices (eg, Transmission Control Protocol/Internet Protocol (TCP/IP). The protocol may determine, for example, the type of error checking and data compression method used. Protocol Is a set of rules or standards which govern communication between computers and peripherals? Protocol Stack A complete set of protocols that work together to enable communication on a network. Compare protocol suite Internet Protocol Suite The Internet Protocol suite, usually referred to as "TCP/IP," is a full set of internetworking protocols that operate in the network layer, the transport layer, and the application layer. While TCP/IP refers to two separate protocols called TCP and IP, Internet Protocol suite refers to the entire set of protocols developed by the Internet community. Still, most people just say "TCP/IP" when they are referring to the Internet Protocol suite.

The global Internet is a success because of TCP/IP. It is hard to believe that there ever was a "protocol war," but during the 1980s and early 1990s, many organizations were indecisive about which protocols to use. TCP/IP was popular in academic, military, and scientific communities, but many businesses had installed LANs using Novell SPX/IPX and Microsoft's NetBEUI/NetBIOS, or were tied to legacy protocols such as IBM SNA. The Internet protocols have been universally accepted because they support scalable internetworking, for which the global Internet is the best example.

TCP/IP SUITE LAYERS  APPLICATION LAYER  TRANSPORT LAYER  INTERNETWORK LAYER  NETWORK ACCESS LAYER Network Access Layer The design of TCP/IP hides the function of this layer from users—it is concerned with getting data across a specific type of physical network (such as Ethernet, Token Ring, etc.). This design reduces the need to rewrite higher levels of a TCP/IP stack when new physical network technologies are introduced (such as ATM and Frame Relay). The functions performed at this level include encapsulating the IP datagrams into frames that are transmitted by the network. It also maps the IP addresses to the physical addresses used by the network. One of the strengths of TCP/IP is its addressing scheme, which uniquely identifies every computer on the network. This IP address must be converted into whatever address is appropriate for the physical network over which the datagram is transmitted. Data to be transmitted is received from the internetwork layer. The network access layer is responsible for routing and must add its routing information to the data. The network access layer information is added in the form of a header, which is appended to the beginning of the data.

Internetwork Layer The best known TCP/IP protocol at the internetwork layer is the Internet Protocol (IP), which provides the basic packet delivery service for all TCP/IP networks. In addition to the physical node addresses used at the network access layer, the IP protocol implements a system of logical host addresses called IP addresses. The IP addresses are used by the internetwork and higher layers to identify devices and to perform internetwork routing. The Address Resolution Protocol (ARP) enables IP to identify the physical address that matches a given IP address. IP is used by all protocols in the layers above and below it to deliver data, which means all TCP/IP data flows through IP when it is sent and received, regardless of its final destination. Host-to-Host Transport Layer The protocol layer just above the internetwork layer is the host-to-host layer. It is responsible for end-to-end data integrity. The two most important protocols employed at this layer are the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). TCP provides reliable, full-duplex connections and reliable service by ensuring that data is resubmitted when transmission results in an error (endto-end error detection and correction). Also, TCP enables hosts to maintain multiple, simultaneous connections. When error correction is not required, UDP provides unreliable datagram service (connectionless) that enhances network throughput at the host-to-host transport layer. Both protocols deliver data between the application layer and the internetwork layer. Applications programmers can choose the service that is most appropriate for their specific applications. Application Layer The most widely known and implemented TCP/IP application layer protocols are listed below: File Transfer Protocol (FTP). Telnet. Simple Mail Transfer Protocol (SMTP). Hypertexts Transfer Protocol (HTTP). Domain Name Service (DNS). Routing Information Protocol (RIP). Simple Network Management Protocol (SNMP). Network File System (NFS).

IPv4 header format

Version. 4 bits. Specifies the format of the IP packet header. IHL, Internet Header Length. 4 bits. Specifies the length of the IP packet header in 32 bit words. The minimum value for a valid header is 5 TOS, Type of Service. 8 bits. Specifies the parameters for the type of service requested. The parameters may be utilized by networks to define the handling of the datagram during transport. The M bit was added to this field Total length. 16 bits. Contains the length of the datagram Identification. 16 bits. Used to identify the fragments of one datagram from those of another. The originating protocol module of an internet datagram sets the identification field to a value that must be unique for that source-destination pair and protocol for the time the datagram will be active in the internet system. The originating protocol module of a complete datagram clears the MF bit to zero and the Fragment Offset field to zero Flags. 3 bits. Fragment Offset. 13 bits. Used to direct the reassembly of a fragmented datagram TTL, Time to Live. 8 bits. A timer field used to track the lifetime of the datagram. When the TTL field is decremented down to zero, the datagram is discarded. Protocol. 8 bits. This field specifies the next encapsulated protocol.

Header checksum. 16 bits. A 16 bit one's complement checksum of the IP header and IP options. Source IP address. 32 bits. IP address of the sender. Destination IP address. 32 bits. IP address of the intended receiver. Options. Variable length. Padding. Variable length. Used as a filler to guarantee that the data starts on a 32 bit boundary. BOOTSTRAP PROTOCOL The Bootstrap Protocol (BOOTP) allows a client system to discover its own IP address, the address of a BOOTP server, and the name of a file to be loaded into memory and executed. DHCP Short for Dynamic Host Configuration Protocol, a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device's IP address can even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses.

WAN TECHNOLOGIES WAN A WAN is a data communications network that covers a relatively broad geographic area and that often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer. Circuit Switching Switched circuits allow data connections that can be initiated when needed and terminated when communication is complete. This works much like a normal telephone line works for voice communication. Integrated Services Digital Network (ISDN) is a good example of circuit switching. When a router has data for a remote site, the switched circuit is initiated with the circuit number of the remote network. In the case of ISDN circuits, the device actually places a call to the telephone number of the remote ISDN circuit. When the Two networks are connected and authenticated, they can transfer data. When the data transmission is complete, the call can be terminated. Packet Switching Packet switching is a WAN technology in which users share common carrier resources. Because this allows the carrier to make more efficient use of its infrastructure, the cost to the customer is generally much better than with point-to-point lines. In a packet switching setup, networks have connections into the carrier's network, and many customers share the carrier's network. The carrier can then create virtual circuits between customers' sites by which packets of data are delivered from one to the other through the network. The section of the carrier's network that is shared is often referred to as a cloud. Some examples of packet-switching networks include Asynchronous Transfer Mode (ATM), Frame Relay

ISDN Integrated Services Digital Network, a circuit-switching network used for voice, data and video transfer over existing copper telephone lines. ISDN is a bit similar to the normal telephone system but it is faster and needs less time to setup a call. There are 2 types of services associated with ISDN: BRI PRI ISDN BRI Service The ISDN Basic Rate Interface (BRI) service offers 2 B channels and one D channel. BRI B-channel service operates at 64 kbps and is meant to carry user data; BRI D-channel service operates at 16 kbps and is meant to carry control and signaling information, although it can support user data transmission under certain circumstances. ISDN PRI Service ISDN Primary Rate Interface service offers 23 B channels and 1 D channel in North America and Japan, Yielding a total bit rate of 1.544 Mbps (The PRI D channel runs at 64 kbps). ISDN PRI in Europe, Australia and other parts of the world provides 30 B channels plus one 64-kbps D channel and a total interface rate of 2.048 Mbps. Advantages of ISDN Speed Multiple Devices Signaling

Asynchronous Transfer Mode (ATM) Asynchronous Transfer Mode (ATM) is an International Telecommunication Union-Telecommunications Standards Section (ITU-T) standard for cell relay wherein information for multiple service types, such as voice, video, or data, is conveyed in small, fixed-size cells. ATM networks are connectionoriented.

ATM Devices and the Network Environment ATM is a cell-switching and multiplexing technology that combines the benefits of circuit switching (guaranteed capacity and constant transmission delay) with those of packet switching (flexibility and efficiency for intermittent traffic). It provides scalable bandwidth from a few megabits per second (Mbps) to many gigabits per second (Gbps). Because of its asynchronous nature, ATM is more efficient than synchronous technologies, such as time-division multiplexing (TDM). With TDM, each user is assigned to a time slot, and no other station can send in that time slot. If a station has much data to send, it can send only when its time slot comes up, even if all other time slots are empty. However, if a station has nothing to transmit when its time slot comes up, the time slot is sent empty and is wasted. Because ATM is asynchronous, time slots are available on demand with information identifying the source of the transmission contained in the header of each ATM cell. ATM Devices An ATM network is made up of an ATM switch and ATM endpoints. An ATM switch is responsible for cell transit through an ATM network. The job of an ATM switch is well defined: It accepts the incoming cell from an ATM endpoint or another ATM switch. It then reads and updates the cell header information and quickly switches the cell to an output interface toward its destination. An ATM endpoint (or end system) contains an ATM network interface adapter. Examples of ATM endpoints are workstations, routers, digital service units (DSUs), LAN switches, and video coder-decoders (CODECs).

FRAME RELAY Frame Relay is a simplified form of Packet Switching, similar in principle to X.25, in which synchronous frames of data are routed to different destinations depending on header information. Frame Relay Devices Devices attached to a Frame Relay WAN fall into the following two general categories: • Data terminal equipment (DTE) • Data circuit-terminating equipment (DCE) DTEs generally are considered to be terminating equipment for a specific network and typically are located on the premises of a customer. In fact, they

may be owned by the customer. Examples of DTE devices are terminals, personal computers, routers, and bridges. DCEs are carrier-owned internetworking devices. The purpose of DCE equipment is to provide clocking and switching services in a network, which are the devices that actually transmit data through the WAN. In most cases, these are packet switches. Figure 10-1 shows the relationship between the two categories of devices

SONET Short for Synchronous Optical Network The transport network using SONET provides much more powerful networking capabilities than existing asynchronous systems.