CDN (Content delivery network)

Content delivery networks (CDN) deliver Web-based content from geographically dispersed servers that sit on the edge of various networks and deliver content according to the proximity of the Web surfer. A Web surfer viewing a Web site on a computer in California most likely will get content delivered from servers on the West Coast; a Boston viewer would get images from a server on the East Coast, for example.

CDNs typically sit on ISP networks, where traffic to each server is limited only by the capacity of that network's bandwidth, and overflow traffic is routed among the CDN's servers.

So, when some sites are busy and others aren't, the busy sites get the capacity they need. As a result, CDN users don't have to worry about increasing bandwidth or hardware to handle spikes in traffic; all that is done automatically by the CDN that determines which server is best able to handle the load.