Multicast TCP via concast merged acknowledgments

Abstract

One of the challenges in reliable multicast is approximating or replicating TCP's congestion control algorithm. This has led to various proposals to adapt TCP itself for use over multicast. The drawback of these multicast TCP services is that they place significant processing load on the sender and they fail to deal with the problem of ACK implosion. This paper shows how concast, a network-layer aggregation service, can be used in conjunction with a standard (unmodified) TCP implementation to support reliable multicast while avoiding ACK implosion and offloading ACK processing. Our prototype implementation shows that, even for relatively small groups, distributing the ACK processing and reducing ACK losses translates into significant improvements in end-to-end transmission rates.