Content distribution in overlay multicast

Multicast is an important communication paradigm, upon which many distribution applications are built, such as video-on-demand, live broadcasting, teleconferencing, large-volume content dis-semination, etc. The efforts to support multicast at IP layer, however, have proved to be slow and painful, due to factors such as ISP’s lack of incentives, shortage of address space, difficulty to support reliable transmission and congestion control, and others. Recently proposed overlay multicast[16] appears to be a more practical solution to address above problems. In this approach, end hosts, instead of routers, organize themselves into a logical overlay network and relay data to each other via unicast transport services. The fundamental dif-ference between these two approaches, is that in IP multicast, the data forwarding/replication task is performed by the routers, while in overlay multicast, the same task is performed by participating end hosts of the overlay network. Although seemingly it just elevates the multicast functionality into application layer, overlay network actually revolutionizes the way network applications can be built. In IP network, except for nodes at the edge, the network is composed of routers, whose task is no more than forwarding packets. In contrast, each node in overlay network is an intelligen