Cisco Systems

Abstract

Pragmatic General Multicast (PGM) is a reliable multicast transport protocol that runs over a best effort datagram service, such as IP multicast. PGM obtains scalability via hierarchy, forward error correction, NAK (negative acknowledgement) elimination, and NAK suppression. It employs a novel polling scheme for NAK delay tuning to facilitate scaling up and down. This paper describes the architecture of PGM and discusses performance and security issues. We show that PGM has supports asymmetric networks, achieves high network utilization, and is capable of high-speed (>100 Mbps) operation. PGM is currently an IETF experimental RFC that has been implemented in both commercial and academic settings.