The Web is a good example ofa two-tier client-server architecture. Each client computer needs an application layer software package called a Web browser. There are many different browsers, such as Microsoft's Internet Explorer. Each server on the network that will act as a Web server needs an application layer software package called a Web server. There are many different Web servers, such as those produced by Microsoft and Apache.
To get a page from the Web, the user must type the Internet uniform resource locator (URL) for the page he or she wants (e.g., www.yahoo.com) or click on a link that provides the URL. The URL specifies the internet address of the Web server and the directory and name of the specific page wanted. If no directory and page are specified, the Web server will provide whatever page has been defined as the site's home page.
For the requests from the Web browser to be understood by the Web server, they must use the same standard protocol or language. If there were no standard and each Web browser used a different protocol to request pages, then it would be impossible for a Microsoft Web browser to communicate with an Apache Web server, for example.
The standard protocol for communication between a Web browser and a Web server is
Hypertext Transfer Protocol (HTTP). To get a page from a Web server, the Web browser issues a special packet called an HTTP request that contains the URL and other information about the Web page requested (see Figure 2- l O). Once the server receives the HTTP request,