Issues in Overlay Multicast Networks: Dynamic Routing and Communication Cost

Overlay networks are becoming a popular vehicle for deploying advanced services in the Internet. One such service is multicast. Unlike conventional IP multicast, which requires universal deployment of network layer mechanisms, the overlay multicast model leverages the existing unicast mechanism and offers many service flexibilities to applications. Implementing multicast without requiring network support eliminates many deployment complexities that IP multicast has faced. However, it also raises new issues in efficient network design. In an earlier paper, we studied multicast routing algorithms designed to optimize resource usage in overlay networks, when multicast session membership is static. In this paper, we study the routing performance in sessions where members can join and leave dynamically. In order to prevent service interruptions, routing in dynamic sessions cannot be as optimized as in the static case, resulting in possible performance degradation. We quantify this effect and show how it can be partially mitigated using a limited form of session rearrangement. We also study the impact of the overlay multicast approach on underlying networks, in order to quantify the difference in cost and performance of overlay multicast and “native” multicast. We demonstrate that overlay multicast is reasonably efficient. Indeed, in many cases it makes more efficient use of network resources than native IP multicast.