Since the original version, HTTP/0.9, there have only been two revisions of the HTTP standard. HTTP/1.0 was released as RFC-1945[A] in May 1996 and HTTP/1.1 as RFC-2616 in June 1999.
[A] Request for Comments, or RFCs, are submitted to the RFC editor (http://www.rfc-editor.org
) usually by authors attached to organizations such as the Internet Engineering Task Force (IETF athttp://www.ietf.org
). RFCs date back to the early ARPAnet days and are used to present networking protocols, procedures, programs, and concepts. They also include meeting notes, opinions, bad poems, and other humor: RFC-2324 describes the Hypertext Coffee Pot Control Protocol.
Request and Response Model
HTTP is simple: a client-most conspicuously a web browser-sends a request for some resource to a HTTP server, and the server sends back a response. The HTTP response carries the resource-the HTML document or image or whatever-as its payload back to the client. This simple request-response model is shown in Figure B-2.
Figure B-2. Browser makes a request and the HTTP server responds
The term HTTP server is the correct description for what is more commonly called a web server. Technically, a web browser is an example of a user agent. Other user agents include proxy servers, applications that can provide services such as caching of responses, and access control.