Source-Coded Multicast for Efficient Content Delivery

Network coding is both necessary and sufficient to utilize at full capacity a single-source multicast network. For this purpose, intermediate nodes must linearly encode and then forward their incoming packets, generally, using a code which has to be known to all the nodes and that depends on the topology. Consequently, realizing the benefits of network coding in large multicast networks can be challenging. In this paper, we propose restricting the use of multicast packet encoding to the source of the multicast distribution tree, while the remaining nodes only forward packets. Although this reduces the opportunities for exploiting multicast in overlapped paths, we show that implementing network coding only at the source is both practical and useful for a large class of networks, and that it realizes a substantial part of the gain in bandwidth achievable with full network coding. Our numerical results show that source-coded multicast (SCM) is optimal or nearly optimal in a large fraction of network topologies, and overcomes the complexity of deploying a network-wide code across all the forwarding nodes.