Queueing Analysis of a Butterfly Network for Comparing Network Coding to Classical Routing

Network coding has gained significant attention in recent years as a means to improve throughput, especially in multicast scenarios. These capacity gains are achieved by combining packets algebraically at various points in the network, thereby alleviating local congestion at the nodes. The benefits of network coding are greatest when the network is heavily utilized or, equivalently, when the sources are saturated so that there is data to send at every scheduling opportunity. Yet, when a network supports delay-sensitive applications, traffic is often bursty and congestion becomes undesirable. The lighter loads typical of real-time traffic with variable sources tend to reduce the returns of network coding. This work seeks to identify the potential benefits of network coding in the context of delay-sensitive applications. As a secondary objective, this paper also studies the cost of establishing network coding in wireless environments. For a network topology to be suitable for coding, links need to possess a proper structure. The cost of establishing this structure may require excessive radio resources in terms of bandwidth and transmit power. Bursty traffic together with structural cost tend to decrease the potential benefits of network coding. This paper describes how, for real-time applications over wireless networks, there exist network topologies for which it may be best not to establish a network structure tailored to network coding.