A Measurement Study of Peer-to-Peer File Sharing Systems

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A Measurement Study of Peer-to-Peer File
SharingSystems

• Stefan Saroiu, P. Krishna Gummadi, Steven D.
  Gribble
• Presented by Zhengxiang Pan
• March 18th, 2003

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Introduction

• Napster Gnutella
• Population of users
• Bottleneck bandwidth of hosts latencies
• Duration time of remain connected
• Number of files shared downloaded

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Methodology-architecture

• Napsters architecture
• A cluster of central servers
• Each peer connects to one server
• Servers cooperate to process query
• Gnutellas architecture
• No centralized servers
• Peers form overlay network
• Send a query by a controlled flood

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Methodology-crawler

• Napster crawler
• A larger number of connections to a single server
• Issue popular queries in parallel
• Captured 40-60 local users
• Gnutella crawler
• Iteratively send ping messages with large TTLs
• Discover new hosts by receiving pong messages.
• Capture 25-50 of the total population

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Methodology-directly measure characteristics

• Latency
• Measure the time spent by exchanging a 40-byte
  TCP packet.
• Lifetime
• Offline not respond to TCP SYN packets
• Inactive respond with TCP RST
• Active accept the connection
• Bottleneck bandwidth
• Approximate to available bandwidth
• Actively measure upstream and downstream using a
  few TCP packets

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Results-bandwidth
Downstream upstream bottleneck bandwidth -50
in Napster 60 in Gnutella use broadband
connections -25 in Napster 8 in Gnutella use
modems -20 in Napster 30 in Gnutella have
high bandwidth (gt3Mbps)
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Result-reported bandwidth
22 in Napster report unknown bandwidth
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Result- latency
Latencies for Gnutella users -Unstructured,
ad-hoc, a substantial fraction suffer from
high-lantency -Difference in trans-oceanic peers
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Result- availability
-only 20 peers had an IP-level uptime of 93 or
more -Median session duration 60 minutes
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Result-files
-25 in Gnutella do not share any files -40-60
peers share 5-20 of the shared files
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Result-download upload
the percentage of peers in each bandwidth class
is roughly the same as the percentage of files
shared by that bandwidth class.
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Result- cooperate
-30 of the users that report their bandwidth as
64 Kbps or less actually have a significantly
greater bandwidth. -10 of the users reporting
high bandwidth (3Mbps or higher) in reality have
significantly lower bandwidth.
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Result-resilience of Gnutella overlay
Although highly resilient in the face of random
breakdowns, Gnutella is nevertheless highly
vulnerable in the face of well-orchestrated,
targeted attacks.
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Conclusion

• Heterogeneity of hosts
• Carefully delegate responsibilities
• Clearly evidence of client-like and server-like
  behaviors
• Peers tend to misreport information if there is
  an incentive to do so
• Built-in incentive for telling the truth
• Verify reported information