A Locating-First Approach for Scalable Overlay Multicast

Recent proposals in multicast overlay networks have demonstrated the importance of exploiting underlying network topology data to construct efficient overlays. While they avoid virtual coordinates embedding and fixed landmarks measurements, these topology-aware proposals often rely on incremental and periodic refinements to improve each node's position in the delivery tree. We claim that there are barriers for the scalability of existing overlay multicast protocols. In fact, periodical refinement and control processes induce additional overhead and high communication cost. On the other hand, users attending a video conferencing session or an event broadcast expect an acceptable quality as soon as they join the multicast session. It is then important to overcome an efficiency problem from which almost all current overlay multicast proposals suffer. This problem is the long convergence time to reach a stabilized quality state in the overlay delivery tree. We propose a novel overlay multicast tree construction scheme, called LCC : Locate, Cluster and Conquer, designed to address the aforementioned scalability and efficiency issues. The scheme consists in two phases: a selective locating phase and an overlay construction phase. Using partial knowledge of location-information for participating nodes, the selective locating phase algorithm consists in locating the closest existing set of nodes (cluster) in the overlay for a newcomer. It allows then to avoid initially randomly-connected structures without using virtual coordinates system embedding nor fixed landmarks measurements. Then, on the basis of this locating process, the overlay construction phase consists in building and managing a topology-aware clustered hierarchical overlay.