Resource and topology discovery for IP multicast using a fan-out decrement mechanism

As the use of IP multicast sessions becomes widespread, the potential benefits derived from currently unavailable topological information on multicast distribution trees may become increasingly critical. We propose a framework for discovering the topology of shared multicast trees based on a novel fan-out decrement mechanism analogous to time-to-live (TTL) decrementing in IP. We propose an algorithm for topology discovery based on the matrix of path/fan-out distances among a set of E session members-the algorithm's computational complexity is O(|E|/sup 2/). We exhibit sufficient conditions for topology discovery based on a reduced distance matrix, and propose a practical protocol to acquire this information requiring the exchange of 2|E| multicast messages of size O(|E|). Finally, we show how the same approach permits nodes to discover the multicast distribution tree associated with members within their fan-out/TTL scoped neighborhoods. This permits one to reduce the computational costs while making the communication costs proportional to the size of neighborhoods.