Multicast group membership management in high speed wide area networks

Multicast services, assisted by special hardware, are being considered as part of high-speed wide area networks in order to support new generations of multi-user applications. This paper describes an application multicast service for high-speed WANs which is capable of exploiting multicast hardware. Indeed, this research was conducted in context of the spanning tree hardware structure of IBM Networking Broad Band Services (NBBS) architecture announced recently, as well as by the tree broadcast in experimental predecessors to NBBS named PARIS and plaNET. The results of the research described here influenced the development of the multicasting facility in NBBS. Similarly, the assumptions our design is based on hold for NBBS, as well as for multiple other networks. We achieve modularity and low cost by assigning to distinct components the separate problems of (1) naming groups, (2) finding group members in a network, (3) configuring multicast hardware, and (4) delivering multicast messages in sequence. We present the overall organization of our service, and then describe in detail the methods used to solve the first two subproblems. In particular we present a novel algorithm to maintain dynamic trees, such that each spans a dynamically changing subset of the set of the wide area network nodes. The algorithm withstands failures and recoveries of software, sites and communication. As far as we know this algorithm was the first algorithm of its kind. A node not in such a subset may at any time be instructed by one of its local processes to join. At that point the node has to look for the other nodes currently belonging to that subset, and we provide efficient mechanisms for that. Similarly, nodes may leave, and the network may partition. As an added feature, our algorithm also provides answers to a query asking for the current membership list of such a subset.