...
One of possible implementations is based on geo-located Domain Name Server System (DNS) service that responds to a user’s domain lookup query indicating the IP address of the proxy (edge) server that is the “nearest” for the user. Then, the user communicates with the edge server and, if the edge server has the desired content (cache), no transfer to and from the origin server is needed. Otherwise, the edge server fetches first the content from the origin server, and the first user requesting this particular piece of data waits for the response a little bit longer.
Various benefits can come from using CDN. From end-user perspective, it is an increased Quality of Experience: data download time and latency are reduced, and availability of the service is improved (if a desired data is available in an edge server then a downtime of the origin server does not prevent users to access the data). From the network perspective, CDN provides better network performance: the number of hops during the data transfers is reduced, possibility of bandwidth saturation is lowered, and the traffic in backbone network is also reduced. From the content provider perspective CDN causes lower costs: less network load and reduced possibility of service downtime.
...