The HyperText Transfer Protocol (HTTP), the Web';s application-layer jprotocol is at the
heart of the Web. HTTP is implemented in two programs: a client program and a server program. The client program
and server program, exzecuting on different end systems, talk to each other by exchanging HTTP messages. HTTP defines
the structure of these messages and how the client and server exchange the message.
A Web page(also called a document) consists of objects. An object is
simply a file--such as an HTML file, a JPEG image, a GIF image, a Java applet, an audio clip, ans so on--that is addressable
by a single URL. Most Web pages consist of a base HTML file and several referenced objects.
A browser is a user agent for the Web; it displays the requested Web page to the user and
provides numberous navigational and configuration features. Because Web browsers also implement the client side of HTTP,
in the context of the Web, we will use the words browser and client interchangeablye.
A Web server
houses Web objects, each addressabvle by a URL. Web servers also implement the server side of HTTP.
HTTP defines how Web clients request Web pages from Web servers and how servers transfer Web pages to clients.
HTTP uses TCP as its underlying transport protocol. The HTTP client first initiates a TCP connection
with the server. Once the connection is established, the browser and the server processes access TCP through their socket
interfaces.
