4.4. The HTTP Message Exchange
The basic HTTP interaction includes a client request and a server response. The simplicity of the protocol results from its being stateless: it does not require either the client or the server to record any information beyond the boundaries of this simple interaction.
An HTTP exchange can generally be carried over any Layer 4 protocol. However, for all practical purposes, TCP is used in the Internet environment. Figure 4.7a shows the message exchanges between the client and the server in the simplest HTTP interaction, which is also the only possible case for HTTP 0.9. In this example, the client downloads the page index.html from the server and then image.gif that is embedded into this page.
Figure 4.7. The TCP-level ...
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