Ramp: A Reliable Adaptive Multicast Protocol

The specifications and performance of RAMP, a Reliable Adaptive Multicast Protocol, are presented. Initially described in IETF RFC 1458 [1], RAMP has been enhanced for use over an all-optical, circuit-switched, gigabit network under our ARPA-sponsored Testbed for Optical NEtworking (TBONE) project. RAMP uses immediate, receiver-initiated, NAK-based error notification combined with originator-based unicast retransmission. The approach is motivated by the loss characteristics of the TBONE network, where extremely low bit-error rates (10e-12 or better) and circuit switching make packet losses almost entirely a result of receiver buffer overflows. Hence, multicast retransmission would hinder performance through unnecessary receiver processing of redundant packets, and delayed NAKs would increase both latency and the likelihood of buffer overflow. Interestingly, TBONE loss characteristics resemble those of switched virtual circuit ATM networks and packet-switched networks employing reservation services. Hence, RAMP’s design is also relevant for conventional networks.