A Transport Protocol For Reliable Multicast Over IP-Multicast Capable Networks

We present a transport protocol that uses IP multicasting to provide reliable multicast transport services for distributed applications. The Transport Protocol for Reliable Multicast (TRM) has a receiver{ oriented style of deening group membership and the lack of group information at the source. The distributed nature of the group membership information within TRM ensures scalability, which we believe is an important requirement. TRM uses a many{to{many communication model in which any of the participants can become a source of data. TRM guarantees the statistical reliability of message delivery without any guarantee of the reliability of the group membership. Group management and group membership functions are assumed to be handled by the session layer and the application. TRM delegates the responsibility of ensuring reliable message delivery to the receivers, which use a negative acknowledgment (NACK){based scheme with message damping to request retransmissions of missing data. The sources send heartbeats periodically (to the multicast group) to let every member of the group know about its own state when there is no data to transmit. TRM also supports late joins, early leaves, and source{speciic joins.