RMTP: A Reliable Multicast Transport Protocol

This paper describes the design and implementation of a multicast transport protocol called RMTP. RMTP provides sequenced, lossless delivery of bulk data from one sender to a group of receivers. RMTP achieves reliability by using a packet based selective repeat retransmission scheme, in which each acknowledgment (ACK) packet carries a sequence number and a bitmap. ACK handling is based on a multi-level hierarchical approach, in which the receivers are grouped into a hierarchy of local regions, with a Designated Receiver (DR) in each local region. Receivers in each local region periodically send ACKs to their corresponding DR, DRs send ACKs to the higher-level DRs, until the DRs in the highest level send ACKs to the sender, thereby avoiding the ACK-implosion problem. DRs cache received data and respond to retransmission requests of the receivers in their corresponding local regions, thereby decreasing end-to-end latency and improving resource usage. This paper also provides the measurements of RMTP’s performance with receivers located at various sites in the Internet.