Research On Application Level Multicast Protocol Matching Physical Topoplogy

Since it is hard to widely deploy IP multicast over Internet, application level multicast(ALM) has become a perfect alternative approach and the research on it has got substantial productions after years of great efforts.The substance of ALM network is an virtual mesh which is build over physical underlying network based on the self-organizing of the end-hosts through unicast. A lot of ALM protocols or systems didn't think much of the location meaning of nodes, hence are hard to ensure topology matching between logical overlay network and physical underlying network. If there is mismatching problem, the actual length of transmission path among the nodes would be longer causing longer link latency and a large volume of redundant traffic in the network, as a result, the system would afford lower running efficiency because of larger cost and load.Firstly, we study the mismatching problem between logical overlay network and physical underlying network and point out some reasons causing the problem and their aftereffects. Secondly, we analyze the potential problem of mesh-first method used for building ALM network. And then we discuss the low-cost shortest path tree(SPT) issue by analyzing the improvement needed for classical Dijkstra SPT algorithm, compare the basic ideas of some low-cost SPT algorithms and further indicate their limitation.Based on the study above, we present a new ALM protocol named UnionCast with topology matching attribute.The aim of UnionCast is to support middle scale multi-source multicast application.In order to build multicast network matching physical topology and realize highly efficient data distribution, UnionCast uses a new algorithm called TMLC-SPT to create multicast tree. TMLC-SPT can create shortest path tree matching physical underlying network and the cost of the tree is minimal compared with that of other shortest path trees composed of same nodes.For efficient monitoring on multicast network, UnionCast adopts a new method called multi-tree intersection to build overlay. The method can get matchable overlay based on multicast tree created by TMLC-SPT. With the overlay, UnionCast further provides efficient mechanism for monitoring multicast network, that is, every node can find whether the multicast network had changed or occured exception only by checking few instant neighbors with very low overhead.For making the multicast system can not only afford the effect caused by the quit of few nodes, but also respond the notable change of the multicast network in time, UnionCast combines the temporary attaching mechanism, the failure recovery mechanism and the reconstruction mechanism, which are specially designed, to maintain the stabilization of multicast system. The temporary attaching mechanism aims at reducing the time needed to join the multicast session for new node. The failure recovery mechanism can ensure the connectedness of multicast tree when some node quits or collapses. And the reconstruction mechanism can rightly refresh the multicast tree and overly to have multicast network keep matching with physical underlying network.Based on the protocol design, we also introduce the software architecture and the realization details of UnionCast prototype.