1. A Measurement Study of Peer-to-Peer File Sharing Systems Presented by Hakim Weatherspoon CS294-4: Peer-to-Peer Systems By Stefan Saroiu, P. Krishna Gummadi, Steven D. Gribble University of Washington P P PP P P SS SS Q R D P P PP P P Q R P Q Q NapsterGnutella

2. P2P Systems 2003©2003 Hakim Weatherspoon/UC BerkeleyMeasurement Study:2 What is definition of P2P? Debatable –Systems that lack dedicated, centralized infrastructure. –Depend on voluntary participation of peers to contribute resources. –Membership is ad hoc and dynamic Challenge –Organize peers such that they can cooperate to provide a useful service to the community.

3. P2P Systems 2003©2003 Hakim Weatherspoon/UC BerkeleyMeasurement Study:3 Big Idea Measure current P2P systems –Extract common peer and organizational characteristics Surprising, no one else thought of measure first. –Current P2P designers building with “P2P Purist” ideals

4. P2P Systems 2003©2003 Hakim Weatherspoon/UC BerkeleyMeasurement Study:4 Measurement Methodology Crawl –Snapshot of system –Gathered IP address and reported characteristics Probe –Several days –Measured properties Bottleneck bw: Proportional to capacity of slowest link Latency: RTT of 40B TCP packet Lifetime: active, inactive, offline number of files to share (not measured) Flaw – one vantage point –Measurements taken from Seattle, WA.

5. P2P Systems 2003©2003 Hakim Weatherspoon/UC BerkeleyMeasurement Study:5 Napster and Gnutella Architecture Napster –Send query to centralized server –Contact peer to download –Server store index and peer characteristics Gnutella –Contact a gateway (e.g. limewire.com) –Perform a constrained flood to find new peers and perform queries. P P PP P P SS SS Q R D P P PP P P Q R P Q Q NapsterGnutella

6. P2P Systems 2003©2003 Hakim Weatherspoon/UC BerkeleyMeasurement Study:6 Crawling the P2P Systems Napters –Look all most popular songs –Identified 40-60% of total users contributed 85-90% of system resources Gnutella –Ping/Pong with large TTL Discovered 8-10,000 peers (i.e. 25-50% of total population) P P PP P P SS SS Q R D P P PP P P Q R P Q Q NapsterGnutella

7. P2P Systems 2003©2003 Hakim Weatherspoon/UC BerkeleyMeasurement Study:7 Measurement Characteristics Bottleneck bw –Proportional to capacity of slowest link between two hosts Latency –RTT of 40B TCP packet Lifetime –active, inactive, offline –Combinations of TCP SYN, TCP RST, Connection Established, Timeout Flaw – one vantage point –Measurements taken from Seattle, WA. Note: number of files to share (not measured)

8. P2P Systems 2003©2003 Hakim Weatherspoon/UC BerkeleyMeasurement Study:8 Measurement Questions High bandwidth, low latency profile of a server? High availability profile of a server? Accurate reported bw? No sharing, always downloading profile of client? Number of shared files? Resilience in face of attach?

9. P2P Systems 2003©2003 Hakim Weatherspoon/UC BerkeleyMeasurement Study:9 Measurement Results Server Peers –High BW, Low Latency, and High availability 78% have downstream bw of at least 100Kpbs 22% have upstream bw of less than 100Kbps Peers lie so that resources are not over used. –Identified free users. Bottomline –Undesirable and detrimental if download capacity exceeds upload bw of system. Gnutella has few low bw peers –Flooding to expensive –Users for technically savvy???

10. P2P Systems 2003©2003 Hakim Weatherspoon/UC BerkeleyMeasurement Study:10 Key takeaways Significant amount of heterogeneity –BW, latency, availability, degree of sharing –Over five orders of magnitude differences Client/Server model is reality –Even though systems designed with symmetric responsibility Peers lie!

11. P2P Systems 2003©2003 Hakim Weatherspoon/UC BerkeleyMeasurement Study:11 Result P2P systems must take into account the suitability of a given peer for a specific task.