content delivery (content distribution, content distribution delivery, or content caching)

On the Internet, content delivery (sometimes called content distribution , content distribution delivery , or content caching ) is the service of copying the pages of a Web site to geographically dispersed server s and, when a page is requested, dynamically identifying and serving page content from the closest server to the user, enabling faster delivery. Typically, high-traffic Web site owners and Internet service providers ( ISP s) hire the services of the company that provides content delivery.

A common content delivery approach involves the placement of cache servers at major Internet access points around the world and the use of a special routing code that redirects a Web page request (technically, a Hypertext Transfer Protocol - HTTP - request) to the closest server. When the Web user clicks on a URL that is content-delivery enabled, the content delivery network re-routes that user's request away from the site's originating server to a cache server closer to the user. The cache server determines what content in the request exists in the cache, serves that content, and retrieves any non-cached content from the originating server. Any new content is also cached locally. Other than faster loading times, the process is generally transparent to the user, except that the URL served may be different than the one requested.

The three main techniques for content delivery are: HTTP redirection, Internet Protocol (IP) redirection, and domain name system ( DNS ) redirection. In general, DNS redirection is the most effective technique.

Content delivery can also be used for specific high-traffic events such as live Web broadcasts by continually dispersing content from the originating server to other servers via satellite links.

Content delivery is similar to but more selective and dynamic than the simple copying or mirror site of a Web site to one or several geographically dispersed servers.