The Hypertext Transfer Protocol (HTTP) is an application-level protocolfor transferring hypertext files (Web pages) over the Internet. HTTP is the most important protocol used in the World Wide Web.
HTTP communication usually takes place over TCP/IP connections.
The HTTP protocol is a request/response protocol between clients and servers. When a web browser (client) wants to display a web page, it connects to the Web server mentioned in the Uniform Resource Locations (URL) to retrieve the page contents. As soon as the TCP connection is established, the browser sends an HTTP request asking the web server to provide the desired page. The Web server sends a reply containing the page contents, and closes the connection.
This design makes HTTP ideal for the World Wide Web, where pages regularly link to pages on other servers. It can occasionally pose problems for Web developers, as the lack of a persistent connection requires other methods of maintaining a user’s "state". Many of these methods involve the use of "cookies".
Version 1.0 of HTTP caused considerable overhead to Web downloads. For example, if the document contained hypertext that referenced embedded contents, such as images, for each image a new protocol connection was established between the browser and the server.
In HTTP Version 1.1, a persistent connection allows multiple downloads. The connection may remain open for some time to allow multiple requests with less TCP overhead.
Also to reduce download times, there are two types of web caches: local and shared.
The local cache is managed by the browser itself. When the browser requests a document from the Web server, it often stores a copy in the disk. If a new request for the same page is made, the browser may choose to view the local copy rather than send a second request to the server.
A shared cache, or proxy cache, is typically a server within the local area network. All users in the organisation browse the web though this server. A proxy cache helps reduce the internet traffic and improves the speed of web requests.
A secure version of HTTP exists called HTTPS.
Now that both HTTP extensions and HTTP/1.1 are stable specifications, W3C has ceased HTTP Activity. The Activity has achieved its goal of creating a successful standard that addresses the weaknesses of earlier HTTP versions.
W3C has started new protocol-related work on XML Protocol Activity, the XML Protocol Working Group will define an HTTP binding for XML Protocol, which is a higher-level protocol.
