Hypertext Transfer Protocol

Specifics of HTTP

HTTP is an application layer of the Internet and relies on a transport layer such as Transmission Control Protocol to function. The resources that HTTP provides are identified on the web by Uniform Resource Locators. Early Uniform Resource Locator addresses contained HTTP at the beginning, but this practice was dropped as it became the default mode of communication.

HTTP functions as a request-response protocol in the classic client-server model of computing. Clients are usually browsers and servers are web servers. For example, a web browser acting as a client may submit a request to a server, which then responds. Every browser contains software that waits for HTTP requests, processes them when they arrive, and then sends a response. An HTTP session is a sequence of network request-response transactions. Browsers often contain an HTTP cache that stores responses to reduce response times.

Requests and responses usually contain one or more lines of header information that conveys email address of the person making the request, authorization data, the name of the client software, the date the document was last modified, the type of document being sent, the length and type of the document, and how the document was compressed.

When user or webpage errors, browser or server malfunctions, or Internet glitches occur, HTTP attempts to identify the problem and sends an error message to the browser.

The History of HTTP

[Page 434]The story of HTTP began when it was proposed by Tim Berners-Lee, the “father of the World Wide Web,” who coauthored the first version in 1989 at the CERN nuclear laboratory. At first, it could only request a page from a server. The first documented version appeared in 1991, HTTP/0.9. In 1995, Dave Raggett, leader of the HTTP Working Group, expanded the protocol in several ways, including more meta-information, leading to the second version, HTTP/1.0, in 1996. It was rapidly adopted by the expanding browser market, including Netscape and Mosaic.

Over time, HTTP has gone through several updates and clarifications, including syntax and routing, semantics, conditional requests, caching, and authentication. The latest version, HTTP/1.1, was released in 1997 and uses a variety of request methods (e.g., GET, POST, PUT, and HEAD) to indicate desired actions. Unlike HTTP/1.0, in which a separate connection was needed (a situation called “stateless”), in HTTP/1.1, the connection can be reused multiple times (a “persistent connection”). Version 1.1 also allows for decompression of HTML files by client browsers and multiple domain names sharing the same IP address. HTTP/1.1 improves performance by reusing a prior response message to satisfy a current request.

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