Serving dynamic groups in application-level multicast

We propose an ALM framework for dynamic groups (such as stock-quote application) in this paper, where users may hop from one multicast group to another quite frequently even though the total pool of users in the system may remain quite stable. Our approach efficiently maintains multiple multicast trees for dynamic subsets of end-hosts, and hence is called subset-ALM (SALM). SALM first builds a relatively stable mesh consisting of all endhosts for control messaging, which is used to efficiently guide the construction of dynamic overlay trees for data multicast. We choose Delaunay Triangulation (DT) as an example for mesh formation, and study various tree construction mechanisms based on the degree of embedding of the tree branches in the mesh (embedded, bypass and intermediate trees). Using simulation on Internet-like topologies, we show that SALM achieves low costs in terms of relative delay penalty and physical link stress, even for large multicast groups (in excess of a thousand end-hosts).