A reliable multicast protocol is a computer networking protocol that provides a reliable sequence of packets to multiple recipients simultaneously, making it suitable for applications like multi-receiver file transfer or streaming media.
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Overview
Multicast is a network addressing method for the delivery of information to a group of destinations simultaneously using the most efficient strategy to deliver the messages over each link of the network only once, creating copies only when the links to the multiple destinations split (typically network switchs and routers). However, like the User Datagram Protocol, multicast does not guarantee the delivery of a message stream. Messages may be dropped, delivered multiple times, or delivered out of order. A reliable multicast protocol adds the ability for receivers to detect lost and/or out-of-order messages and take corrective action (similar in principle to TCP), resulting in a gap-free, in-order message stream.
Reliability
The exact meaning of reliability depends on the specific protocol instance. A minimal definition of reliable multicast is eventual delivery of all the data to all the group members, without enforcing any particular delivery order[1]. However, not all reliable multicast protocols ensure this level of reliability; many of them trade efficiency for reliability, in different ways. For example, while TCP makes the sender responsible for transmission reliability, multicast NAK-based protocols shift the responsibility to receivers: the sender does never know for sure that all the receivers have in fact received all the data[2]. RFC 2887 explores the design space for bulk data transfer, with a brief discussion on the various issues and some hints at the possible different meanings of reliable.
Existing or proposed protocols
- Pragmatic General Multicast (PGM)
- Tibco Software's TRDP (part of RV). Note: when Tibco acquired Talarian, they inherited a PGM implementation with SmartSockets (SmartPGM). TRDP pre-dates the development of SmartPGM
- 29West's LBT-RM protocol (part of LBM/UME)
- RTI's reliable multicast protocol (part of NDDS)
- OpenDDS as an open source implementation since their 0.12 release
- Reliable Multicast Transport Protocol (RMTP)
- Scalable Reliable Multicast (SRM)
- QuickSilver Scalable Multicast (QSM)
- SMART Multicast (Secure Multicast for Advanced Repeating of Television)
- NACK-Oriented Reliable Multicast Protocol (NORM)
References
- ^ Floyd, Sally; Jacobson, Van; Liu, C.; McCanne, S.; Zhang, L. (December), "A Reliable Multicast Framework for Light-weight Sessions and Application Level Framing", IEEE/ACM Transactions on Networking 5 (6): 784–803, http://www.icir.org/floyd/srm-paper.html
- ^ Diot, C; Dabbous, W; Crowcroft, Jon (1997), "Multipoint communication: a survey of protocols, functions, and mechanisms", IEEE Journal on Selected Areas in Communications 15 (3): 277–290, doi:, http://www-sop.inria.fr/rodeo/personnel/Walid.Dabbous/jsac.ps.gz
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