Nemo: Resilient Peer-to-Peer Multicast without the Cost

Stefan Birrer and Fabián E. Bustamante
Tech. Report NWU-CS-04-36, Department of Computer Science, Northwestern University, 2004.

Department of Computer Science
Northwestern University
Evanston, IL 60201, USA
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One of the most important challenges of peer-to-peer multicast protocols is the ability to efficiently deal with the high degree of transiency inherent to their environment. As multicast functionality is pushed to autonomous, unpredictable peers, significant performance losses can result from group membership changes and the higher failure rates of end-hosts when compared to routers. Achieving high delivery ratios without sacrificing end-to-end latencies or incurring additional costs has proven to be a challenging task.

This paper introduces Nemo, a novel peer-to-peer multicast protocol that aims at achieving this elusive goal. Based on two simple techniques: (1) co-leaders to minimize dependencies and, (2) triggered negative acknowledgments (NACKs) to detect lost packets, Nemo s design emphasizes conceptual simplicity and minimum dependencies, thus achieving performance characteristics capable of withstanding the natural instability of its target environment. We present an extensive comparative evaluation of our protocol through simulation and wide-area experimentation.

We compare the scalability and performance of Nemo with that of three alternative protocols: Narada, Nice and Nice-PRM. Our results show that Nemo can achieve delivery ratios (up to 99.9%) similar to those of comparable protocols under high failure rates, but at a fraction of their cost in terms of duplicate packets (reductions > 90%) and control-related traffic (reductions > 20%).