For more information, refer to:
http://www.w3.org/Protocols/rfc2616/rfc2616.txt
RFC 2616, "Hypertext Transfer Protocol," by R. Fielding, J. Gettys, J. Mogul, H. Frystyk, L. Mastinter, P. Leach, and T. Berners-Lee.
HTTP Pocket Reference
Clintin Wong, O'Reilly & Associates, Inc.
http://www.w3.org/Protocols/
The W3C architecture page for HTTP.