On the Internet, content delivery is the service of copying the pages of a Web site to geographically dispersed servers. When a page is requested, content is dynamically identified and served from the closest server to the user, enabling faster delivery. Typically, Internet Service Providers (ISPs) and the owners of high-traffic Web sites hire the services of a company to provide content delivery. A common content delivery approach is the placement of cache servers at major Internet access points around the world. A special routing code redirects a Web page 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, sending it to the cache server closest 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 mirroring of a Web site to geographically dispersed servers.