Evaluating the Impact of Tunneling on Multicast Efficiency

In this paper, we discuss the efficiency of tunneling techniques that should accelerate multicast deployment. Our motivation is that, despite the many proposals focused on tunneling techniques, their impact on multicast efficiency has not yet revealed sufficiently. Through detailed computer experiments, we examine the behavior of some metrics that represent the impact of tunneling on multicast efficiency, such as loads on tunneling endpoints, redundant links, and forwarding states on routers. Experiments are conducted on realistic topologies with hundreds of thousands routers, which were sampled from the Internet in 1999 and 2004. We calculate the metrics for thousands of multicast delivery paths with tunnels, and note several interesting findings; there is a critical size of multicast island, above which the negative impact of tunneling is suddenly diminished. In addition, multicast islands equaling the critical size reduce the overhead of forwarding states on routers. We also find a scaling law between the critical size and group size. Based on these findings, we present simple guidelines for the use of tunneling when deploying multicast systems