Distributed center-location algorithms: proposals and comparisons

Multicast routing protocol proposals such as PIM and CBT have been based on the notion of group-shared trees. Since the construction of a minimal-cost tree spanning all members of a group is difficult, they rely on center-based trees, and distribute packets from all sources over a single shortest-path tree rooted at some center. While PIM and CBT provisionally use administrative selection of centers or trivial heuristics for locating the center of a group, they do not preclude the use of other methods as long as they provide an ordered list of centers. Other previously proposed heuristics typically require knowledge of the complete network topology, a requirement which is not always practical for a distributed problem such as Internet routing. In this paper we investigate the problem of finding a good center in distributed fashion, study various heuristics for automating center selection, and examine their applicability to real-world networks. We also propose several new algorithms which we feel to be more practical than existing methods. We present simulation results showing that of the methods potentially feasible in the Internet multicast backbone, ours offer the best results in terms of cost and delay.