How Web Browsers and Web Servers Communicate

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Web browsers like Internet Explorer, Firefox, Chrome, and Safari rank among the most popular network applications in the world. People use them for basic information browsing but also for various other needs including online shopping and casual gaming. Web servers supply content to Web browsers via Internet network connections.

Client-Server Network Design and the Web

Web browsers and Web servers together function as a client-server system.

In computer networking, client-server is a standard method for designing applications where data is kept in central locations (server computers) and efficiently shared with any number of other computers (the clients) on request. Web browsers all function as clients that request information from Web sites (servers).

Numerous Web browser clients may request data from one Web site. Requests can happen at all different times or simultaneously. Client-server systems conceptually call for all requests to the same site to be handled by one server. In practice, however, because the volume of requests to Web servers can sometimes grow very large, Web servers are often built as a distributed pool of multiple server computers. (For very large Web sites popular in different countries around the world, this Web server pool is geographically distributed to help improve the response time to browsers.)

Network Protocols for Web Browsers and Servers

Web browsers and servers communicate via TCP/IP.

Hypertext Transfer Protocol (HTTP) is the standard application protocol on top of TCP/IP supporting Web browser requests and server responses. Web browsers also rely on the DNS to work with URLs like ‘http://wireless.about.com/’. These protocol standards enable different brands of Web browsers to communicate with different brands of Web servers without requiring special logic for each combination.

A basic Web browsing session works as follows:

  • the user specifies a URL in their browser (either from a bookmark or by typing)
  • the browser initiates a TCP connection to the Web server (or server pool) via its IP address as published in DNS. (Web servers by default use TCP port 80 to service incoming requests.). As part of this process, the browser also makes DNS lookup requests to convert the URL to an IP address
  • after the server completes acknowledgment of its side of the TCP connection, the browser sends HTTP requests to the server to retrieve content for the URL.
  • after the server replies with content for the Web page, the browser retrieves the content from the HTTP packets and display it accordingly. Content can include embedded URLs for advertising banners or other third-party content, that in turn triggers the browser to issue new TCP connection requests to those locations. The browser may also save temporary information about its connections to local files on the client computer called cookies.

Web browser and server connections normally run through a series of intermediate network routers as does most other Internet traffic.