HTTP - HyperText Transfer Protocol

Woman sitting on sofa using laptop
AMV Photo/Digital Vision/Getty Images

HTTP (Hypertext Transfer Protocol) provides a network protocol standard that Web browsers and servers use to communicate.

History of HTTP

Tim Berners-Lee created the initial HTTP in the early 1990s as part of his work in defining the original World Wide Web.  Three primary versions were widely deployed during the 1990s

  • HTTP 0.9 (for support of basic hypertext documents)
  • HTTP 1.0 (extensions to support rich Web sites and scalability)
  • HTTP 1.1 (developed to address performance limitations of HTTP 1.0, specified in Internet RFC 2068)

The latest version - HTTP 2.0 - became an approved standard in 2015. It maintains backward compatibility with HTTP 1.1 but offers additional performance enhancements.

While standard HTTP does not encrypt traffic sent over a network, the HTTPS standard was developed to add encryption to HTTP via the use of (orignially) Secure Sockets Layer (SSL) or (later) Transport Layer Security (TLS).

How HTTP Works

HTTP is an application layer protocol built on top of TCP that uses a client-server communication model. HTTP clients (such as Web browsers) and Web servers communicate via HTTP request and response messages. The three main HTTP message types are GET, POST, and HEAD.

HTTP GET messages sent to a Web server contain only a URL. Zero or more optional data parameters may be appended to the end of the URL.

 The HTTP server processes the optional data portion of the URL if present and returns the result (a Web page or element of a Web page) to the browser.

HTTP POST messages place any optional data parameters in the body of the request message rather than adding them to the end of the URL.

HTTP HEAD request work the same as GET requests.

Instead of replying with the full contents of the URL, the Web server sends back only the Web page header information (contained inside the HTML <HEAD> section).

The browser initiates communication with an HTTP server by initiating a TCP connection to the server. Web browsing sessions use server port 80 by default although other ports such as 8080 are sometimes used instead.

Once a session is established, users of Web browsers trigger the sending and receiving of HTTP messages by visiting Web pages that have HTTP (or HTTPS) URLs. More - Web Searching Using HTTP and HTTPS.

Issues with HTTP

Messages transmitted over HTTP can fail to be delivered successfully for several reasons:

  • user error
  • malfunction of the Web browser
  • malfunction of  the Web server
  • errors in creation of Web pages
  • temporary Internet network glitches

When these failures occur, the protocol captures the cause of the failure (if possible) and reports an error code back to the browser. Error 404 ("Page not found"), for example, became famous in the early days of the Internet when issues with Web pages and navigation were more common.

More -  HTTP Status and Error Codes Explained