A Case for End System Multicast *

The conventional wisdom has been that IP is the natural protocol layer for implementing multicast related function-ality. However, ten years after its initial proposal, IP Multi-cast is still plagued with concerns pertaining to scalability, network management, deployment and support for higher layer functionality such as error, flow and congestion con-trol. In this paper, we explore an alternative architecture for small and sparse groups, where end systems implement all multicast related functionality including membership man-agement and packet replication. We call such a scheme End System Multicast. This shifting of multicast support from routers to end systems has the potential to address most problems associated with IP Multicast. However, the key concern is the performance penalty associated with such a model. In particular, End System Multicast introduces du-plicate packets on physical links and incurs larger end-to-end delay than IP Multicast. In this paper, we study this question in the context of the Narada protocol. In Narada, end systems serf-organize into an overlay structure using a fully distributed protocol. In addition, Narada attempts to optimize the efficiency of the overlay based on end-to-end measurements. We present details of Narada and evaluate it using both simulation and Internet experiments. Prelimi-nary results are encouraging. In most simulations and Inter-net experiments, the delay and bandwidth penalty are low. We believe the potential benefits of repartitioning multicast functionality between end systems and routers significantly outweigh the performance penalty incurred. 1