Client–Server Architecture of the World Wide Web (WWW)

Introduction

The World Wide Web (WWW) is a distributed client–server application that allows users to access information stored on web servers across the Internet.

The Web was first proposed by Tim Berners-Lee in 1989 at CERN to enable researchers at different locations to share research documents. Commercial use of the Web began in the early 1990s.

The Web is a repository of information where documents, called web pages, are distributed across servers worldwide and connected through hyperlinks.

Features of the World Wide Web

The popularity of the Web is mainly due to two important features:

1. Distributed

  • Web pages are stored on different servers around the world.
  • Any organization can add new web pages without affecting existing servers.
  • This allows the Web to grow continuously.

2. Linked

  • Web pages are connected using hyperlinks.
  • A web page can reference another page stored on the same server or a different server.
  • Clicking a hyperlink retrieves the linked document automatically.

Initially, linked text documents were called hypertext. Today, since web pages may contain text, images, audio, video, and animations, the term hypermedia is used.

WWW Client–Server Architecture

The World Wide Web follows the client–server paradigm.

It consists of two main components:

  1. Web Client (Browser)
  2. Web Server

The communication between them uses the HTTP protocol over the Internet.

+-----------------+            HTTP Request            +-----------------+
|   Web Browser   | --------------------------------> |   Web Server    |
|     (Client)    |                                   |                 |
|                 | <-------------------------------- |                 |
+-----------------+           HTTP Response           +-----------------+

Web Client (Browser)

The web browser is the client application that requests web pages from a web server and displays them to the user.

Main Functions

  • Accepts user input through the keyboard or mouse.
  • Sends requests to the web server.
  • Receives web pages.
  • Interprets and displays web pages.

Components of a Browser

According to the textbook, a browser consists of three components:

1. Controller

  • Receives user input.
  • Controls browser operations.
  • Uses client protocols to communicate with servers.

2. Client Protocols

Responsible for communicating with different servers.

Examples include:

  • HTTP
  • FTP
  • SMTP
  • SSH

3. Interpreters

Interpret and display the received documents.

Examples:

  • HTML
  • Java
  • JavaScript

Popular Web Browsers

Examples include:

  • Microsoft Internet Explorer
  • Netscape Navigator
  • Mozilla Firefox


Web Server

A web server stores web pages and responds to requests from browsers.

Whenever a browser requests a web page:

  1. The server locates the requested file.
  2. It sends the file back to the browser.
  3. The browser displays the page.

Features of a Web Server

Storage

Stores web pages as files.

Caching

Frequently requested web pages are stored in memory (cache).

Advantages:

  • Faster access
  • Reduced disk access
  • Improved performance

Multithreading / Multiprocessing

A web server can process multiple client requests simultaneously.

Advantages:

  • Supports many users at the same time
  • Improves response time

Popular Web Servers

Examples:

  • Apache Web Server
  • Microsoft Internet Information Server (IIS)

Working of Client–Server Architecture

The communication process is as follows:

  1. The user enters a URL or clicks a hyperlink.
  2. The browser sends an HTTP request to the web server.
  3. The server searches for the requested web page.
  4. The server returns the web page to the browser.
  5. The browser interprets the page using HTML, JavaScript, etc.
  6. The web page is displayed to the user.

Retrieval of Linked Documents

A web page may contain links to other documents stored on the same or different servers.

For example:

  • File A – Main web page
  • File B – Image stored on the same server
  • File C – Text file stored on another server

To retrieve all content:

  1. The browser first requests File A.
  2. If the user clicks the image link, it requests File B.
  3. If the user clicks the text link, it requests File C.

Each file is an independent web page with its own address and is retrieved through a separate client–server transaction.




Advantages of WWW Client–Server Architecture

  • Centralized storage of web pages.
  • Supports distributed information sharing.
  • Easy access through browsers.
  • Scalable architecture.
  • Supports multimedia content (text, images, audio, video).
  • Allows multiple users to access the same server simultaneously.

Summary

The World Wide Web is a distributed client–server application in which a web browser (client) requests web pages from a web server. The browser consists of a controller, client protocols, and interpreters, while the server stores web pages, processes client requests, and returns the requested documents. Web pages distributed across different servers are connected through hyperlinks, enabling users to seamlessly access information from anywhere on the Internet.

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