OpenPGM is an open source implementation of the Pragmatic General
Multicast (PGM) specification in RFC 3208 available at www.ietf.org.
PGM is a reliable and scalable multicast protocol that enables
receivers to detect loss, request retransmission of lost data, or
notify an application of unrecoverable loss.  PGM is a
receiver-reliable protocol, which means the receiver is responsible
for ensuring all data is received, absolving the sender of reception
responsibility.  PGM runs over a best effort datagram service,
currently OpenPGM uses IP multicast but could be implemented above
switched fabrics such as InfiniBand.

PGM is appropriate for applications that require duplicate-free
multicast data delivery from multiple sources to multiple receivers.
PGM does not support acknowledged delivery, nor does it guarantee
ordering of packets from multiple senders.

PGM is primarly used on internal networks to help integrate disparate
systems through a common communication platform.  A lack of IPv4
multicast-enabled infrastructure leads to limited capability for
internet applications, IPv6 promotes multicast to be a part of the
core functionality of IP but may still be disabled on core routers.
Support of Source-Specific Multicast (SSM) allows for improved WAN
deployment by allowing end-point router filtering of unwanted source
traffic.