In this paper, we discuss the efficiency of tunneling techniques which are expected to accelerate multicast deployment. Our motivation is that, despite the proposal of many tunneling techniques, no paper has studied their impact on multicast efficiency. Through detailed computer experiments, we find that there is a critical size of multicast island, above which the loads imposed on tunneling endpoints are suddenly diminished. In addition, multicast islands equaling or exceeding 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 on using tunneling when deploying multicast systems. A possible explanation for our findings is uncovered by a simple analysis. Our work is the first to evaluate the impact of tunneling and clarify conditions in which multicast deployment is well supported by tunneling.

In this paper, we examine the efficiency of tunneling techniques since they will accelerate multicast deployment. Our motivation is that, despite the many proposals focused on tunneling techniques, their impact on multicast efficiency has yet to be assessed sufficiently. First, the structure of multicast delivery trees is examined based on the seminal work of Phillips et al. [26]. We then quantitatively assess the impact of tunneling, such as loads imposed on the tunnel endpoints and redundant traffic. We also formulate a critical size of multicast island, above which the loads are suddenly diminished. Finally, a unique delivery tree model is introduced, which is so simple yet practical, to better understand the performance of the multicast-related protocols. This paper is the first to formulate the impact of tunneling.