Making Application Layer Multicast Reliable is Feasible

Application layer multicast (ALM henceforth) was proposed as a substitute for network layer multicast (IP multicast). However, the end users, who take the responsibility to replicate and forward data in ALM, are not as stable as routers in IP multicast. Therefore, reliability has become the major concern in ALM. This paper presents a new tree construction algorithm and demonstrates that making ALM reliable is achievable, even when a single-tree based multicast structure is used. It exploits the property that participating users´ lifetime follow a Pareto distribution which has the used better than new (UBTN) feature, and dynamically adjusts the multicast tree. Participating nodes are organized into a hierarchy and the hierarchy is organized in such a way that it reflects the relative stability among participating nodes. The proposed approach achieves reliability enhancement for ALM by using a very low overhead and no a priori knowledge about users´ lifetime is required. A minimum reduction of 50% can be achieved in terms of service disruption frequency. Detailed mathematical analysis and simulation results reveal that making ALM reliable is feasible