A PROJECT ON Analysis and Development of a Pay Per Click Advertising System : Chapter Two

Chapter 2 Internet & Network Programming 1. What is internet? 2. World Wide Web (WWW) 3. What is HTML? 4. Web Server 5. Apache Web Server 6. Web Browser 7. DNS Server 8.DHCP Server 9. Dynamic Host Configaration Protocol(DHCP) 10. The Universal Resource Locator (URL) 11. Client Side programming 12. Server Side programming 13. Web Based Application 2.1 What is Internet? Internet is an interconnection between several computers of different types belonging to various networks all over the globe. It is a network of networks. A group of computer networks that distribute www, email and ftp news groups etc services around the world. To send or receive data to some placed beyond pacific within in a second was unthinkable before advent of Internet. The Internet is making a major impact on the information technology industry . 2.2 World Wide Web (WWW) The World Wide Web (WWW) is a distributed information system based on hypertext. World Wide Web is not the Internet. The WWW is a giant hypertext system (text, graphics and other multimedia goodies) a series of millions of documents linked to each other all of which reside same place on the Internet and written in HTML, DHTML, VbScript, JavaScript, ASP/Perl/PHP etc. One can view a web document in a web browser or web client software (Internet Explorer, Netscape Navigator, Opera etc.) and the web client requests are responded by web servers such as PWS, IIS, Apache and JSDK etc. The standard of www is maintained by w3c (World Wide Web Consortium). Documents stored under the Web can be one of several types. The most common type hypertext documents are formatted according to the Hyper Text Markup Language (HTML), which itself is based on the Standard Generalized Markup Language (SGML). HTML documents contain text, font specifications, and other formatting instructions. Link to other documents (whether remote or local) can be associated with regions of the text. The HTML documents are displayed with an appropriate Web Browser. The World Wide Web is an architectural framework for accessing linked documents spread out over thousands of Machines all over the Internet. An Internet or Web address (sometimes called a URL or Uniform Resource Locator) typically is composed of four parts : • A protocol name (a protocol is a set of rules and standards that enable computers to exchange information. • The location of the site. • The name of the organization that maintain the site. • A suffix that identifies what kind of organization it is (such as .com for commercial organization). 2.3 What is HTML? HTML is the acronym for Hyper Text Markup Language. Web pages are written with HTML. HTML has two essential features: Hypertext and Universality. Hyper text means we can create a link in a web page that leads the visitors to any other web page or to practically any thing else on the Internet. It means that the information on the web can be accessed from many different directions. Universality means that because HTML documents are saved as ASCII or Text Only files, virtually any computer can read a web page. It does not matter if visitors have Macintosh, Windows or UNIX machines. HTML is a general-purpose hypertext display language, based on SGML. It specifies a document format that allows text-formatting commands, as well as hypertext-link like commands, and image display commands. HTML also provides a limited input features. For example, an HTML document can specify that a form should be displayed. The HTML display program (that is, the Web client) allows the user to fill entries in the form to select a menu item. When a user has finished entering values, he can press a “submit” button . 2.4 Web Server The web server has what seems to be a fairly straightforward job. Basically, the job of a web server is to hold lots of web pages on its hard drive. Then when a browser (web client) usually on a different computer, requests a web page that is contained on that web server, the web server loads from its own hard drive or native hard drive and then passes the page back to the requesting computer via a special communication protocol called Hyper Text Transfer Protocol (HTTP) . There are many web server but mainly three web servers dominate the market. They are Apache, MS Personal Web Server (PWS) for Windows 98 and MS Internet Information Server (IIS) for Windows 2000 Professional. HTTP provides powerful features, beyond the simple transfer of documents, such as encryption of security. The document name in a URL may identify an executable program that, when run, generates an HTML document. When a HTTP server receives a request for such a document, it executes the program, and sends back the HTML document that is generated. Further, the web the client can pass extra argument with the name of the document; they are then passed as arguments when the program is executed. Thus the generated document can depend on the arguments that were passed in. As a result of these features, a web server can easily serve as a front-end to a variety of information services. To install a new service on the web, a person needs only to create and install an executable program that provides the service. The language supported by the web, HTML, provides a graphical user interface to the information service. 2.5 Apache Web Server A web server is the program that runs on a web site and is responsible for replying to web browser request for files. You need a web server to publish documents on the web. When we use a browser to request a page on a web site, that browser makes a web connection to a server (using the HTTP protocol). The server accepts the contents of the files that were requested, and then closes the connection. The browser then formats the information it got from the server. On the server side, many different browsers may connect to the same server. The web server is responsible for handling all these requests. Web servers do more than just deposit files. They are also responsible for managing from input for linking forms and browsers with programs such as databases running on the server. The main features of the apache web server include: 1. The stability and rapid development cycle associated with a large group of cooperative volunteer programmers. 2. Full source code, downloadable at no charge. 3. Ease of configuration using plaintext files. 4. Access-control based on client host name IP address or user name password combinations. 5. Support for server-side scripting as well as CGI scripts. 6. A custom API that enables external modules to be utilized by the server daemon. 7. Support IPV6 8. Have support SSL 2.6 Web Browser A program that enables someone views the contents of pages on the web, the graphical portion of the Internet. In other word, it is an application that makes HTTP request and formats the resultant HTML documents for the user. Most web browsers understand all Internet protocol. Some most popular web browsers are: Mozilla, Fast Browser, Opera, MS Internet Explorer etc . 2.7 DNS server DNS service provides name resolution for clients running Windows 2003. With name resolution, users can access servers by name rather than having to use IP addresses that are difficult to remember. DNS servers host records of a distributed DNS database and use the records they host to resolve DNS name queries sent by DNS client computers, such as queries for the names of Web sites or computers in your network or on the Internet. If you plan to use this computer to answer DNS queries for computers in your network, then add the DNS server role. 2.8 DHCP server A computer running the Microsoft DHCP service that offers dynamic configuration of IP addresses and related information to DHCP-enabled clients. 2.9 Dynamic Host Configuration Protocol (DHCP) A TCP/IP service protocol that offers dynamic leased configuration of host IP addresses and distributes other configuration parameters to eligible network clients. DHCP provides safe, reliable, and simple TCP/IP network configuration prevents address conflicts, and helps conserve the use of client IP addresses on the network. DHCP uses a client/server model where the DHCP server maintains centralized management of IP addresses that are used on the network. DHCP-supporting clients can then request and obtain lease of an IP address from a DHCP server as part of their network boot process. 2.10 The Universal Resource Locator (URL) A hypertext system must be able to store pointers to documents. In the web, the functionality of pointer is provided by the Universal Resource Locators (URLs). The following is an example URL: http://www.microsoft.com/admin/customerservice The first part of the URL indicates how the document to be accessed: “http” indicates that the document is to be accessed using hypertext transfer protocol, which is a protocol for transferring html documents. The second part gives a unique name of a machine on the Internet. It is actually an address of the machine on the Internet. The rest of the URL is the name of the file on the machine. Thus the URLs provide a globally unique name for each document that can be accessed from a web system . 2.11 Client Side Programming In client side programming, we need to develop program that are executed by the appropriate web browser on the client machine of a computer network. The client machine sends a request to the web server for a document in which the program is integrated. The document then carries all necessary information of the program, travels in the network and after reaching to the client machine; it is executed by the web browser. 2.12 Server Side Programming In case of server side programming, we need to develop programs that are to be executed by the server. The client computer of a computer network sends request to the server with necessary information (input) by using HTML or other accepted document. This information then retrieved by the server side program, produces result and sends back the result to the client machine . 2.13 Web Based Application A web application is computer software, which provides a query interface, transmit user-defined query, perform server-side processing, send message data, transmit query results and perform client-side processing. A web application performs its tasks by using following steps: • User instructs web browser through HTML or other accepted document, • The web browser contact a web server using the HTTP protocol, • The web server process that data send by the user with PHP, • Connecting to a data file and search data based upon the user query, • Sending back the results to display in the web browser window as a table. The following figure shows the architecture of web application. Fig 2.1: Architecture of the Web Application. The following four most important conceptual categories part are: • The display layer or graphical user interface (GUI) layer • The communication layer • The middle-ware layer and • The data layer. The GUI or Display Layer: The display layer or GUI Layer, sometimes called the “frontend”, balanced upon the tenuous border between the world of computers and the world of people. It performs the often-complex task of translating between human and computer languages. In its role as translator, the GUI is responsible for two things. First, the GUI translates the desires, intentions, needs, and wants of people into executable, logical machine instructions. At the same time, the GUI also translates computer-generated data into meaningful human-readable information. At its core, a web browser is a software program that knows how to contact a web server using the HTTP protocol, request a given document from that web server, and display that document returned by the server to a human user. The Communication Layer: After the user into GUI submits the needed information, the information is transmitted from the web browser to the web server. The Communication Layer performs the transmission of information. In the communication layer, information goes from one software program on one computer to another software program on another computer. Since there are many types of computers and many software packages that must communicate, it is required to follow very rigorous standards of communications called protocols. Protocols guarantee that each participant of the discussion can understand the other. For the purpose of the web, there are three types of communication protocols: 1. Computer to computer communication 2. Encryption of plain text over the wires 3. Software to software communication Communication between client and sever through the communication layer occurs through TCP/IP connection to exchange data between software programs. Once the TCP/IP connection is opened, the software communicates via HTTP or SSL. The actual data exchanged may or may not be encrypted. TCP/IP (The Transmission Control Protocol/Internet Protocol) is the protocol suite that drives the Internet. The middle-ware Layer: The user requests are gathered by the GUI Layers and they are sent across the wire to a web server by the communication layer. The web application on the other end of the wire from the web browser is a web server. The web server is the entry point to the middle-ware layer. The purpose of the middle-ware layer is to accept incoming requests and process them, using the resources provided by the web server, the machine that the web server runs on, or by the network or servers and resources that the web server is connected to. The middle-ware 1) creates an executable script that the web server may call on demand, 2) pass incoming HTTP GET or POST data to the script, and 3) generates answers back to the browser. The data Layer: The most basic part of a web application is the data itself. As all web applications allow a user to submit instructions on how the web application should message a bit of data on the web server. This might involve searching a database, creating a shopping cart of products, or emailing some information to someone. Regardless, the data, which is being manipulated, all have some basic characteristics. Those are: 1) Data have values; 2) Data have types; 3) Data have descriptions; and 4) Data have formats. All of the web technologies at the Data layer define, describe, or standardize one or more of these characteristics. Generally, a database is used for this purpose.

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