Reliable Multicast Transport Protocol (RMTP)

ABSTRACT
Reliable Multicast Transport Protocol (RMTP) provides sequenced, lossless delivery of a data stream from one sender to a group of receivers on Internet/Intranets. RMTP 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 acknowledgments (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. RMTP uses a packet-based selective repeat retransmission scheme for higher throughput. We have also developed some scaleable multicast flow control procedures.
RMTP has been implemented on the MBone (Multicast Backbone), and its performance measurements on the Internet are very encouraging. A version of RMTP/UDP/IP implementation is operational in AT&T's core billing network which uses only IP-Multicast routers, in contrast to MBone, which uses IP tunneling.
RMTP software is available for Solaris, HP-UX, SUNOS, SVR4, Windows NT, and Windows 95. More information about RMTP and free binaries of RMTP code can be obtained from the website http://www.bell-labs.com/e-cast/