Scalable fair reliable multicast using active services

Scalability is of paramount importance in the design of reliable multicast transport protocols, and requires careful consideration of a number of prob lems such as feedback implosion, retransmission scoping, distributed loss r ecovery, and congestion control. In this article, we present a reliable mul ticast architecture that invokes active services at strategic locations ins ide the network to comprehensively address these challenges. Active service s provide the ability to quickly and efficiently recover from loss at the p oint of loss. They also exploit the physical hierarchy for feedback aggrega tion and effective retransmission scoping with minimal router support. We p resent two protocols, one for packet loss recovery and another for congesti on control, and describe an experimental testbed where these have been impl emented. Analytical and experimental results are used to demonstrate that t he active services architecture improves resource usage, reduces latency fo r loss recovery, and provides TCP-friendly congestion control.