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An Experimental Study of the Skype Peer-to-Peer VoIP System

An Experimental Study of the Skype Peer-to-Peer VoIP System. Saikat Guha, Cornell University Neil DasWani, Google Ravi Jain, Google IPTPS ’ 06 Presenter: Te-Yuan. What do they want to know?. What makes Skype so successful? Compare with File-sharing P2P network By Observing Skype ’ s

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An Experimental Study of the Skype Peer-to-Peer VoIP System

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  1. An Experimental Study of the Skype Peer-to-Peer VoIP System Saikat Guha, Cornell University Neil DasWani, Google Ravi Jain, Google IPTPS’06 Presenter: Te-Yuan

  2. What do they want to know? • What makes Skype so successful? • Compare with • File-sharing P2P network • By Observing Skype’s • User behavior • Node Session Time • Overlay Network Traffic • SuperNode overlay network • Overall utilization & resource consumption

  3. Skype • Three Services • two-way audio streams & conference call up to 4 users • Instant Message • file-transfer • Structure • Alike KaZaA – SuperNode-based • Ordinary Node (ON) • Super Node (SN)

  4. Outline - Experiments • Expt. 1: Basic operation • Expt. 2: Promotion to supernode • Expt. 3: Supernode network activity • Expt. 4: Supernode and client population • Expt. 5: Supernode presence

  5. Expt. 1: Basic operation • To Answer: How do two Skype clients connect to each other? • Normally, • ON send control traffic through SN-p2p • Including • Availability information • Instant messages • Request for VoIP & File-transfer • What if ON is behind NAT/Firewall?

  6. Expt. 1: Basic operation – Cont. • NAT Traversal in Skype: • Level 0: Initiator NAT’ed • Level 1: Recipient NAT'ed • Level 2: Both NAT'ed (well-behaved NATs) • Level 3: Both NAT'ed

  7. Expt. 1: Basic operation – Cont. • Level 0: Initiator NAT’ed

  8. Expt. 1: Basic operation – Cont. • Level 1: Recipient NAT’ed

  9. Expt. 1: Basic operation – Cont. • Level 2: Both NAT'ed (well-behaved NATs)

  10. Expt. 1: Basic operation – Cont. • Level 3: Both NAT'ed

  11. Expt. 1: Basic operation – Cont. Level 0 Level 1 Level 2 Level 3

  12. Outline - Experiments • Expt. 1: Basic operation • Expt. 2: Promotion to supernode • Expt. 3: Supernode network activity • Expt. 4: Supernode and client population • Expt. 5: Supernode presence

  13. Expt. 2: Promotion to supernode • To Answer: What kind of node will be promote to SN? • Setup several Skype clients • One behind a saturated network uplink • One behind a NAT • One with a 10 Mbps connection & public IP • Key to be SN • plenty of spare bandwidth • publicly reachable

  14. Outline - Experiments • Expt. 1: Basic operation • Expt. 2: Promotion to supernode • Expt. 3: Supernode network activity • Expt. 4: Supernode and client population • Expt. 5: Supernode presence

  15. Expt. 3: Supernode network activity • Goal: To observe the network traffic of a Skype supernode • Duration: 135 days (Sep. 1, 2005 to Jan. 14, 2006) • Data captured: 13GB with ethereal

  16. Expt. 4: Supernode and client population • Goal: Collect SN & client IP/port • Duration:2005/7/25 – 2005/10/12 • Result: • Crawl 150K SN • Collect 250K SN info

  17. Expt. 4: Supernode and client population Connect to a SN A list of SN Save the list Connect to a SN from the list A list of SN

  18. Expt. 4: Supernode and client population • Collect client info • Collect the number reported by skype client

  19. Expt. 5: Supernode presence • Goal: how many SN online at a give time • Flow • Randomly Select 6000 SN - from the list collected by expt. 4 • Send “application-layer Ping” • Repeat every 30 mins for a month

  20. Expt. 5: Supernode presence - Cont Num. of SuperNode is more Stable diurnal behaviorof SN Weekend

  21. Expt. 5: Supernode presence - Cont • Geographic Distribution of Active SuperNodes 15-25% 20-25% 45--60% peak at 11am UTC (Europe mid-day)

  22. Expt. 5: Supernode presence - Cont • SuperNode Session Time Median is 5.5h

  23. Expt. 5: Supernode presence - Cont • Fraction of supernodes joining or departing Node arrival concentrated toward morning Skype usage is correlated with working hours Different from P2P file-sharing Node departureconcentrated toward evening

  24. Expt. 5: Supernode presence - Cont • Node Arrival dependent on Time • Not Poisson or Uniform process • Poisson process with varying hourly rate Node arrival concentrated toward morning Node departureconcentrated toward evening

  25. VoIP in Skype: Preliminary Observation 90.4%SN no need to relay VoIP traffic • SuperNode Traffic

  26. VoIP in Skype: Preliminary Observation • VoIP Relayed Session Arrival Behavior • Inter arrival time of Relayed VoIP/File sessions may be Poisson

  27. VoIP in Skype: Preliminary Observation • VoIP Session Length Behavior Skype: Median: 2m50s Average: 12m53s Longest: 3h 26s Traditional: Average: 3m Fraudulent: Average: 9m

  28. VoIP in Skype: Preliminary Observation • File-transfer sizes File size: Median: 346kB

  29. Conclusion • First measurement study of Skype VoIP system • Skype differs significantly from file-sharing P2P • User Behavior • Diurnal & Work-week • Calls are significantly longer • File transferred are significantly smaller • SuperNode of Skype • Consume little bandwidth • Relatively stable

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