Pragmatic General Multicast (PGM) is a reliable multicast transport protocol for applications that require ordered or unordered, duplicate-free, multicast data delivery from multiple sources to multiple receivers. PGM guarantees that a receiver in the group either receives all data packets from transmissions and repairs, or is able to detect unrecoverable data packet loss. PGM is specifically intended as a workable solution for multicast applications with basic reliability requirements. Its central design goal is simplicity of operation with due regard for scalability and network efficiency.

PGM is now an experimental RFC, and has shipped in Windows XP and Cisco routers. It is used by Microsoft' MSMQ. Tibco also shipped a client

Speakman, T., Crowcroft, J., Gemmell, J., Farinacci, D. , Lin, S., Leshchiner, D., Luby, M., Montgomery, T. , Rizzo, L., Tweedly, A., Bhaskar, N., Edmonstone, R., Sumanasekera, R., Vicisano, L., PGM Reliable Transport Protocol Specification, RFC 3208, December 2001.
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Much easier to read than the RFC, is this paper:
Gemmell, Jim, Montgomery, Todd, Speakman, Tony, Bhaskar, Nidhi, and Crowcroft, Jon, The PGM Reliable Multicast Protocol, IEEE Network special issue on "Multicasting: An Enabling Technology", Vol. 17, No. 1, Jan/Feb 2003, pp. 16-22. Word (232KB)  PDF (266 KB)

Public implementation of PGM

ECSRM stands for Erasure Correcting Scalable Reliable Multicast. ECSRM uses NAK suppression and FEC to scale. The work on ECSRM has been merged into the PGM protocol.

Gemmell, Jim, Scalable Reliable Multicast Using Erasure-Correcting Re-sends, June 1997, Microsoft Research Technical Report, MSR-TR-97-20, June 1997.Word   postscript

Abstract

Reliable multicast schemes often cannot scale to large receiver sets due to the problems of state explosion and message implosion. In this paper we propose Erasure Correcting Scalable Reliable Multicast, ECSRM. ECSRM is based on the SRM framework proposed by Floyd et. al., which utilizes NACK suppression to reduce message implosion. ECSRM makes a number of modifications to SRM to addressed enhanced scalability and rate control. Most notably, instead of re-sending lost packets, erasure-correcting encoded packets are sent in response to NACK messages.

Related work: PGMCC adds congestion control to PGM. Paper: citeseer pdf  IETF draft draft-ietf-rmt-bb-pgmcc-03.txt (expired) text  postscript
 

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