From RFC 3208:
- 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.
With the release of an open source implementation of PGM, PGM might qualify as an alternate multicast transport for PSYC. The General PGM Disadvantages mentioned on OpenPGM_Critique actually fit the requirements of PSYC, since PSYC provides some of those layers, and a higher latency is inevitable. Using PGM with PSYC would make PSYC reliability extensions such as packet ids unnecessary to implement. Some of the other disadvantages specific to Novell's implementation might pose a problem, however.
Also, after reading more of the RFC it turns out PGM is based upon IP Multicast, thus it is probably not workable for PSYC. Why didn't they say so much earlier in the various documents!? As if IP Multicast was a good choice for multicasting.