Agenda Module Ii (2 Sessions)

Agenda Module II (2 sessions) • • • • •

Internet Architecture The Life Cycle Approach Overview of different Phases The Network Information transfer

The Internet and the WWW

What is the Internet? • A loosely configured global wide-area network. • Includes more than 31,000 different networks in over 100 different countries. • Millions of people visit and contribute to the Internet, through e-mail and the World Wide Web. • Began as a Department of Defense project. • For detailed information about the history of the Internet, see: http://dir.yahoo.com/Computers_and_internet/Internet/History/

Early history of the Internet • In the 1950s the U.S. Department of Defense became concerned that a nuclear attack could disable its computing (and thus planning and coordinating) capabilities. • By 1969 the Advanced Research Projects Agency Network (ARPANet) had been constructed. • The first computers to be connected were ones at the University of California at Los Angeles, SRI International, the University of California at Santa Barbara, and the University of Utah.

The changing Internet Early on researchers began to find new uses for the Internet, beyond its original purpose of controlling weapons systems. These new applications included the following: • Electronic mail • File transfer protocol • Telnet • User’s News Network (Usenet)

The new uses • In 1972 a researcher wrote a program that could send and receive messages over the Internet. E-mail was quickly adopted by Internet users. • File transfer protocol (FTP) allowed researchers using the Internet to transfer files easily across great distances. • Telnet allows users of the Internet to log into their computer accounts from remote sites. • All three of these applications are still widely used. We will discuss them again later.

Usenet • In 1979 a group of students and programmers at Duke and the University of North Carolina started Usenet, short for User News Network. • Usenet allows anyone who connects to the network to read and post articles on a variety of subjects. • Usenet survives today in what are called newsgroups.

Newsgroups There are several thousand newsgroups covering a highly varied groups of subjects. Examples: – alt.cats  – comp.databases  – rec.climbing  – soc.penpals  The first part of the name of each group tells you what type of group it is and the remaining parts indicate the subject matter.

Terminology • A hypertext server is a computer that stores files written in hypertext markup language (HTML) and lets other computers connect to it and read those files. It is now called a Web server. • A hyperlink is a special tag that contains a pointer to another location in the same or in a different HTML document. • HTML is based on Standard Generalized Markup Language (SGML), which organizations have used for many years to manage large document filing systems.

Early Web browsers • A Web browser is a software interface that lets users read (or browse) HTML documents. • Early web browsers were text based. • Although the Web caught on quickly in the research community, broader acceptance was slow to materialize. • Part of the problem was that the early browsers were difficult to use.

GUI Web browsers • In 1993, Marc Andressen led a team of researchers and developed the first software with a graphical user interface for viewing pages over the Web. • This first GUI browser was named Mosaic. • Mosaic widened the appeal of the Web by making access easier and adding multimedia capabilities. • Andressen later went on to develop the Netscape Navigator browser.

Control of the Internet • No one organization currently controls the Internet. • Several groups oversee aspects of the development of the Internet. – Internet Engineering Task Force (IETF) Oversees the evolution of Internet protocols

– Internet Registries (InterNIC) Maintain and allocate Internet domains

– World Wide Web Consortium (W3C) Develops standards for the WWW • See the Internet Standardization Organizations.

Internet 2 A project to develop another Internet, Internet2, is is being led by over 170 U.S. universities working in partnership with industry and government. This new network is designed to allow development and deployment of advanced network applications and technologies. For more information see: http://www.internet2.edu/

A model for networking • The world’s telephone companies were the early models for networked computers because the networks used leased telephone company lines. • Telephone companies at the time established a single connection between sender and receiver for each telephone call. • Once a connection was established, data traveled along that path.

Circuit switching • Telephone company switching equipment (both mechanical and computerized) selected the phone lines, or circuits, to connect in order to create the path between caller and receiver. • This centrally controlled, single connection model is known as circuit switching. • Using circuit switching does not work well for sending data across a large network. • Point-to-point connections for each sender/ receiver pair is expensive and hard to manage.

A different approach • The Internet uses a less expensive and more easily managed technique than circuit switching. • Files and messages are broken down into packets that are labeled with codes that indicate their origin and destination. • Packets travel from computer to computer along the network until they reach their destination. • The destination computer reassembles the data from the packets it receives. • This is called a packet switching network.

Packet switching • In a packet-switched network, (some of) the computers that an individual packet encounters determine the best way to move the packet to its destination. • Computers performing this determination are called routers. • The programs that the computers use to determine the path are called routing algorithms.

Benefits of packet switching There are benefits to packing switching: • Long streams of data can be broken down into small manageable data chunks, allowing the small packets to be distributed over a wide number of possible paths to balance traffic. • It is relatively inexpensive to replace damaged data packets after they arrive, since if a data packet is altered in transit only a single packet must be retransmitted.

Open architecture When it was being developed, the people working on ARPANet adhered to the following principles: 3. Independent networks should not require any internal changes in order to be connected. 4. The router computers do not retain information about the packets that they handle. 5. Packets that do not arrive at their destinations must be retransmitted from their source network. 6. No global control exists over the network.

Most popular Internet protocols The most popular Internet protocols include: • TCP/IP • HTTP (Hypertext transfer protocol) • E-mail protocols (SMTP, POP, IMAP) • FTP (File transfer protocol) Each protocol is used for a different purpose, but all of them are important.

TCP/IP • The protocols that underlie the basic operation of the Internet are TCP (transmission control protocol) and IP (Internet protocol). • Developed by Internet pioneers Vinton Cerf and and Robert Kahn, these protocols establish rules about how data are moved across networks and how network connections are established and broken. • Four layer architecture

Purposes of each protocol • TCP controls the assembly of a message into smaller packets before it is transmitted over the network. It also controls the reassembly of packets once they reach their destination. • The IP protocol includes rules for routing individual data packets from their source to their destination. It also handles all addressing details for each packet.

Network layers The work done by communications software is broken into multiple layers, each of which handles a different set of tasks. Each layer is responsible for a specific set of tasks and works as one unit with the other layers when delivering information over the Internet. Each layer provides services for the layer above it.

TCP/IP architecture There are five layers in the Internet model: 1. Application 2. Transport 3. Internet 4. Network interface 5. Hardware The lowest layer is the hardware layer that handles the individual pieces of equipment attached to the network. The highest layer is the application layer where various network applications run.

Positioning within the layers A full discussion of the Internet model is beyond the scope of this class. It is, however, useful to know where each protocol resides. TCP operates in the transport layer and IP in the Internet layer. See Figure 2-2 on page 38. Some of the application layer protocols include HTTP, SMTP, POP, IMAP, and FTP. (Telnet also operates in the application layer).

Web System Architecture

Web Clients

Internet

Web Server and Application Server

Database

Web System Architecture Web Browser : It is client interface. Web Server : it is one of the main components of the service system,. It interacts with the web clients as well as backend system. Application Server : It hosts the e-commerce application software.

HTTP • HTTP (hypertext transfer protocol) is the protocol responsible for transferring and displaying Web pages. • It has continued to evolve since being introduced. • Like other Internet protocols, HTTP uses the client/ server model of computing. Thus, to understand how HTTP works, we need to first discuss the client/server model. HTTP/1.0 HTTP/1.1

HTTP Request Method in HTML • Get • Head • Post

Client/server model • In the client/server model there are two roles: the client and the server. • The client process makes requests of the server. The client is only capable of sending a request to the server and then waiting for the reply. • The server satisfies the requests of the client. It usually has access to a resource, such as data, that the client wants. When the resource that the client wants becomes available, it sends a message to the client. • This model simplifies communication.

HTTP and client/server • With HTTP the client is the user’s Web browser and the server is the Web server. • To open a session, the browser sends a request to the server that holds the desired web page. • The server replies by sending back the page or an error message if the page could not be found. • After the client verifies that the response sent was correct, the TCP/IP connection is closed and the HTTP session ends. • Each new page that is desired will result in a new HTTP session and another TCP/IP connection.

One page, multiple requests • If a Web page contains objects such as movies, sound, or graphics, a client must make a request for each object. • For example, a Web page containing a background sound and three graphics will result in five separate server request messages to retrieve the four objects plus the page itself.

Internet addresses Internet addresses are represented in several ways, but all the formats are translated to a 32-bit number called an IP address. The increased demand for IP addresses will soon make 32-bit addresses too small, and they will be replaced with 128-bit addresses in the near future. See the links page for more information. How does increasing the number of bits in the address help with increasing demand?

Dotted quads • IP numbers appear as a series of up to 4 separate numbers delineated by a period. • Examples: students.depaul.edu: 140.192.1.100 condor.depaul.edu: 140.192.1.6 facweb.cs.depaul.edu: 140.192.33.6 • Each of the four numbers can range from 0 to 255, so the possible IP addresses range from 0.0.0.0 to 255.255.255.255

Domain names • Since IP numbers can be difficult for humans to remember, domain names are associated with each IP address. • Examples: students.depaul.edu: 140.192.1.100 facweb.cs.depaul.edu: 140.192.33.6 • A domain name server is responsible for the mapping between domain names and IP addresses.

Uniform resource locator • People on the Web use a naming convention called the uniform resource locator (URL). • A URL consists of at least two and as many as four parts. • A simple two part URL contains the protocol used to access the resource followed by the location of the resource. Example: http://www.cs.depaul.edu/ • A more complex URL may have a file name and a path where the file can be found.

A URL deconstructed http://facweb.cs.depaul.edu/asettle/ect250/section602/hw/assign2.htm

hypertext transfer protocol

domain

path that indicates the location of the document in the host’s file system

document name

Anatomy of an e-mail address asettle @ cs . depaul . edu

Handle

Host/Server Others: • students • hawk • condor

Domain

Domain Type

Domain types • edu: educational • com: commercial • net: originally for telecommunications • org: organizations (non-profit) • gov: U.S. government • ja, uk, de, … : Nations other than the U.S. • New additions: info, biz, name, pro, museum, coop, aero, tv. See links page for a related news story.

Internet utility programs TCP/IP supports a variety of utility programs that allow people to use the Internet more efficiently. These utility programs include: • Finger • Ping

Architecture of A Web Based E-Commerce System

E-Commerce hardware and Software

Revisiting the Three Tier Model

First Tier – Web Client It provides a web based GUI displayed through a web browser in the client computer .

Second Tier – Server side Applications It consists of server side applications that run on a web server or a dedicated application server . These application implement the business logic of the web system. Major Factors : Efficiency , Security , cost effectiveness and Compatibility CGI : Common Gateway Interface ASP : Active Server Page Java Servlet

Third Tier – Database Management System It provides data storage / retrieval services for the second tier so that dynamic web pages can be created. It may consist of one database or group of databases. For this we need database connectivity. One of the most popular method is by means of JDBC – ODBC bridge . Others are Proprietary Network Protocol Drivers and Native API drivers. To communicate with a database , we used SQL.

Web servers • The components of a web server are: – Hardware – Software • When determining what sort of server hardware and software to use you have to consider: – Size of the site – Purpose of the site – Traffic on the site • A small, noncommercial Web site will require less resources than a large, commercial site.

The role of a web server • Facilitates business – Business to business transactions – Business to customer transactions • Hosts company applications • Part of the communications infrastructure Poor decisions about web server platforms can have a negative impact on a company. This is particularly true for purely online (“click and mortar”) companies.

Hosting considerations Will the site be hosted in-house or by a provider? Factors to consider: • The bandwidth and availability needed for the expected size, traffic, and sales of the site • Scalability: If the Web site needs to grow or has a sudden increase in traffic, can the provider still handle it? • Personnel requirements or restraints • Budget and cost effectiveness of the solution • Target audience: Business-to-customer (B2C) or business-to-business (B2B)

Types of Web sites • Development sites: A test site; low-cost • Intranets: Available internally only • B2B and B2C commerce sites • Content delivery site Each type of site has a different purpose, requires different hardware and software, and incurs varying costs.

Commerce sites Commerce sites must be available 24 hours a day, 7 days a week. Requirements include: • Reliable servers • Backup servers for high availability • Efficient and easily upgraded software • Security software • Database connectivity B2B sites also require certificate servers to issue and analyze electronic authentication information.

Content delivery site • Examples:  USA Today  New York Times  ZDNet • Sell and deliver content: news, summaries, histories, other digital information. • Hardware requirements are similar to the commerce sites. • Database access must be efficient.

What is Web hosting? Web hosts are Internet service providers who also allow access to: • E-commerce software • Storage space • E-commerce expertise You can choose: • Managed hosting: the service provider manages the operation and oversight of all servers • Unmanaged hosting: the customer must maintain and oversee all servers

Benefits • Cost effective for small companies or those without in-house technical staff. • May require less investment in hardware/software. • Can eliminate the need to hire and oversee technical personnel. • Make sure that the site is scalable.

Services provided • Access to hardware, software, personnel • Domain name, IP address • Disk storage • Template pages to use for designing the site • E-mail service • Use of FTP to upload and download information • Shopping cart software • Multimedia extensions (sound, animation, movies) • Secure credit card processing

Summary • ISPs have Web hosting expertise that small or medium-sized companies may not. • Creating and maintaining a Web site using an existing network can be difficult. • With the exception of large companies with large Web sites and in-house computer experts, it is almost always cheaper to use outside Web hosting services.

Examples • EZ Webhost • Interland • HostPro • HostIndex  Managed hosting  Other hosting options • TopHosts.com