The CODIS Content Delivery Network

In this paper we describe the CODIS content delivery network (CDN) which has been set up and run by our consortium within an IST project sponsored by the European Commission. A CDN may be implemented as an overlay network over existing WANs, or may use its private WAN links. Its purpose is to bring content to the network edges, close to the actual users, as retrieving content from a nearby source usually results in a user experienced quality of service (QoS) being much better compared to retrieving content from sources far away. When distributing the content from one source to several replicating sites (caches), using multicast is much more efficient than using unicast. Here CODIS uses the natural multicasting/broadcasting capabilities of a GEO satellite. We describe the architecture of CODIS, the types of sites producing and storing content, and end-user-focused QoS which has been measured in various experiments.