The purpose of multicast routing is to reduce the communication costs for applications that send the same data to multiple recipients, Existing multicast routing mechanisms were intended for use within regions where a group is widely represented or bandwidth is universally plentiful, When group members, and senders to those group members, are distributed sparsely across a wide area, these schemes are not efficient; data packets or membership report information are occasionally sent over many links that do not lead to receivers or senders, respectively, We have developed a multicast routing architecture that efficiently establishes distribution trees across wide area internets, where many groups will be sparsely represented, Efficiency is measured in terms of the router state, control message processing, and data packet processing, required across the entire network in order to deliver data packets to the members of the group, Our protocol independent multicast (PIM) architecture: a) maintains the traditional IP multicast service model of receiver-initiated membership, b) supports both shared and source-specific (shortest-path) distribution trees, c) is not dependent on a specific unicast routing protocol, and d) uses soft-state mechanisms to adapt to underlying network conditions and group dynamics, The robustness, flexibility, and scaling properties of this architecture make it well-suited to large heterogeneous internetworks.
