|  | 15.1 | Basics of the Application Layer
| 15.1.2 | Direct network applications

Most applications that work in a networked environment are classified as client-server applications. These applications, such as FTP, web browsers, and e-mail, all have two components, which allow them to function - the client side, and the server side. The client side is located on the local computer and is the requestor of the services. The server side is located on a remote computer and provides services in response to the client’s requests.

A client-server application works by constantly repeating the following looped routine: client-request, server-response; client-request, server-response; etc. For example, a web browser accesses a web page by requesting a uniform resource locator (URL), or web address, on a remote web server. After it locates the URL, the web server that is identified by that URL responds to the request. Then, based on the information received from the web server, the client can request more information from the same web server, or can access another web page from a different web server.

The World Wide Web, Netscape Navigator, and Internet Explorer, are probably the most commonly used network applications. An easy way to understand a Web browser is to compare it to a television remote control. A remote control gives you the ability to directly control a TV's functions: volume, channels, brightness, etc. For the remote control to function properly, you do not need to understand how the remote control functions electronically. The same is true of a Web browser, in that the browser gives you the ability to navigate through the Web by clicking on hyperlinks. For the Web browser to function properly, it is not necessary for you to understand how the lower layer OSI protocols work and interact.

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Client/Server Frequently Asked Questions