On the Multimessage Capacity Region for Undirected Ring Networks

The ??Japanese?? theorem is extended to multiple multicast sessions in an arbitrary network to characterize the routing capacity region by the intersection of an infinite collection of halfspaces. An elimination technique is developed to simplify this infinite description into a finite one based upon the shortest routing paths and trees in the network graph. This result is used as a step in providing the capacity regions for two multimessage multicast problems on undirected ring networks; in the first case only unicast and broadcast sessions are considered, and in the second case multicast sessions where the source and destination vertices form lines of adjacent vertices are studied. Network coding is generally necessary to achieve network capacity, but for our multimessage multicast problems, new arguments are used to demonstrate that routing can achieve network coding bounds.