A Measurement Study of Napster and Gnutella Krishna P. Gummadi, Stefan Saroiu and Steven D. Gribble – U. of Washington 1. Motivation 2. Measurement Methodology Lots of research and industrial excitement: Chord [MIT], Tapestry,CAN [UCB], Jxta [SUN], Herald, Past [MSR], Publius [AT&T] A distributed infrastructure largely comprised of voluntary, dynamic ad-hoc membership by peers. Peers have symmetric roles (serving, downloading and routing) throughout system. No knowledge regarding the fundamental characteristics of peers participating in the network This knowledge can help in evaluating the effectiveness of different schemes. Our measurements proceeded in three stages: Periodically crawl Napster and Gnutella: discover peers, IP’s. overlay topology, and whatever metadata about peers Feed output from crawl into custom measurement tools: measure bottleneck bandwidth to/from peers using SProbe. measure IP latency to/from peers track content and degree of sharing, where possible Sub-sample population to measure lifetime: Track availability of peers at application and IP level 3. Results How many peers have server-like behavior ? High upstream bandwidth ? Low latency ? High availability ? Majority of the peers (>50%) connect through Cable or DSL modems. On average, peers have low upstream bandwidths compared to downstream bandwidths, a feature more representative of a client than a server. Large variation in IP level latencies. For a fraction of peers (~20%) transmission delay << latency, implying congestion. Session durations strikingly similar in both systems. Median session: ~60 mins. Hence, content on a peer unlikely to be available without replication. How many peers lie about their bandwidth ? What is the extent of free-riding ? A large fraction of peers (~25%) choose not to report their bandwidth, they are either unaware of it of have no incentive to report it. Peers have an incentive to report lower bandwidths, a significant fraction do so. Lack of knowledge is universal. Modem (<64 Kbps) users share less files and do more downloads compared to broad band users. Sharing less files: Top 7% of nodes share more than bottom 75% in Gnutella. 40-60% of peers in Napster share only 10-15% of files. 4. Conclusions 5. Future Work Peers’ characteristics are very heterogeneous. A system should delegate responsibilities to its peers based on their characteristics. The system should measure the characteristics of a peer rather than rely on self-reports from the peers themselves. Apply the results of these measurements to evaluate several proposed distributed index systems. Analyze content life time patterns, and geographical distribution of the content and peers 6. More Information A more complete analysis of the measurements is to appear in Multimedia Computing and Networking (MMCN) 2002. A tech report is available online at: http://www.cs.washington.edu/homes/gummadi/p2ptechreport.pdf