HOW THE WEB BROWSER DISPLAY A HOMEPAGE OR WEBPAGE

A web browser thus deal with web server . Actually , a server is a computer that provides services to other computer programs in the same or other computers . The computer that a server program runs on is also frequently referred to as a server (thought it may contain a number of server and client programs) . Client / server describes the relationship between two computer program which one program , the client , make a service request from another program , the server , which fulfills the request . In a network , the client / server model provides a convenient way to interconnect programs that are distributed efficiently across the network.
A web browser is a piece of computer software that runs on a computer connected to internet . It can respond to a browser’s request for a page , and deliver the page to the web browser through the internet . Every computer on the internet that contains , or hosts , a website must have a web server program . The most popular web server are Microsoft’s Internet Information Server , which comes with the Windows NT server , Netscape FastTrack and Enterprise servers , and Apache , a web server for UNIX-based operating system(web server).
In the usual client / server model , one server , somestimes called a daemon , is activated and awaits client requests . Typically , multiple client programs share the services for a common server program . Both client programs and server programs are often part of the larger program or application . In the context of the internet , your web browser is a client program that requests services from the web server in another computer somewhere on the internet . Similarly , your computer with Transmission Control Protocol (TCP) / Internet Protocol (IP) installed allows you to make client request for files from File Transfer Protocol (FTP) servers in other computers on the internet.

The Basic Process

To access a website we need to know its file address , or URL(Uniform Resource Locator) . Suppose you type the URL http://www.dis.strath.ac.uk into your browser and press . Then , no matter where that website is , the page pops us on your screen.


Several things happened here behind the scene:

Step 1
The browser divided URL into three parts:
• The protocol (http)
• Server name (www.dis.strath.ac.uk)
• File name (courses/buscomp)

Step 2
The browser communicated with a Domain Name Server (DNS) to translate the server name into an IP address , which it uses to connect to the server machine . Each machine on the internet is assigned a unique IP address . These are 32-bit number normally expressed as four octets in a dotted decimal number . A typical IP address looks like this :
216.27.61.137
An octet is a number between 0 and 255 (2³ possibilities per octet) . A server has a static IP address that does not change very often . A home machine that uses a dial-up connection through a modem often has an IP address that is assigned by the ISP( Internet Service Provider) when you dial in . That IP address is unique for a given session , but many be different the next time you dial in . The DNS system is a very large distributed database system that keeps track of each and every IP address on the internet . Whenever we type a URL on our browser , it send a message to a DNS to get IP address for the domain for which we have typed a URL . Domain name servers not only provide the correct IP address for a domain , but also keep track of new domain names as well as changes in domain names . This massive distributed database system has possibly the largest number of transactions everyday.

Step 3
After obtaining the IP address , the browser formed a connection to the server at that IP address on port 80 . Any server machine makes its service available to the internet using numbered ports , one of each service that is available on the serve r. For example , if a server machine is running a web 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.

Step 4
Following the hypertext transfer protocol , the browser sent a GET request to the server , asking for the file named corses / buscomp . At this stage , cookies may be sent from browser to server with the GET request . A cookies is a piece of text that a web server can store on a user’s hard disk . Cookies allow a website to store information on a user’s machine and later retrieve it . The piece of information are stored as name – value pairs . Using cookies , sites can determine how many visitor arrive , how many are new visitors , how often a visitor has visited , and so on.


Step 5
The server then sent the HTML text for the web page to the browser

Step 6
The browser read the HTML tags , formatted the page accordingly and displayed it on your screen