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Section C.2. Internet Communication Between Client and Server

C.2. Internet Communication Between Client and Server

C.2.1. The HTTP Server

On the Internet, communication is also handled by a TCP/IP connection. The Web is based on this model. The server side responds to client (browser) requests and provides feedback by sending back a document, by executing a CGI program, or by issuing an error message. The network protocol that is used by the Web so that the server and client know how to talk to each other is the Hypertext Transport Protocol, or HTTP. This does not preclude the TCP/IP protocol being implemented. HTTP objects are mapped onto the transport data units, a process that is beyond the scope of this discussion; it is a simple, straightforward process that is unnoticed by the typical Web user. (See www.cis.ohio-state.edu/cgi-bin/rfc/rfc2068.html for a technical description of HTTP.) The HTTP protocol was built for the Web to handle hypermedia information; it is object-oriented and stateless. In object-oriented terminology, the documents and files are called objects and the operations that are associated with the HTTP protocol are called methods. When a protocol is stateless, neither the client nor the server stores information about each other, but manages its own state information.

Once a TCP/IP connection is established between the Web server and client, the client will request some service from the server. Web servers are normally located at well-known TCP port 80. The client tells the server what type of data it can handle by sending Accept statements with its requests. For example, one client may accept only HTML text, whereas another client might accept sounds and images as well as text. The server will try to handle the request (requests and responses are in ASCII text) and send back whatever information it can to the client (browser).


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