A Skype case study (2011)

1. P2P VoIP Applications:P2P VoIP Applications: “A Skype case-study”“A Skype case-study” Vasia Kalavri (vasia@ac.upc.edu) EMDC 2011 – Decentralized Systems Universitat Politècnica de Catalunya

2. 2 OutlineOutline ● Introduction ● The Skype P2P System ● Explaining Supernodes ● NAT Traversal ● Discussing outages ● Skype Security ● Conclusions

4. 4 P2P VoIP OverviewP2P VoIP Overview ● Communication Over IP Networks ● Free calls among Internet users ● Usually mixed centralized and P2P scheme ● Requirements ● Resource location ● Session establishment ● Session management ● Presence Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

5. 5 P2P VoIP ChallengesP2P VoIP Challenges ● Best-effort Internet ● Transmission delays ● Delay variations ● Packet loss ● Network failures ● NATs and Firewalls Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

7. 7 Skype: why so popular?Skype: why so popular? ● Easy-to-use ● Works behind NATs and Firewalls (always?) ● More than 50 million users! ● Offers three services ● VoIP ● IM ● File transfer Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

8. 8 System Design: A KaZaASystem Design: A KaZaA extension?extension? ● Several studies conclude that Skype is related to Kazaa ● Founded by the same individuals ● Overlap of technical staff ● Use of the “supernode” hierarchical P2P network scheme ● KaZaA V 3.0 included a Skype client Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

9. 9 Skype Peer-to-Peer NetworkSkype Peer-to-Peer Network ● Supernodes ● Must be publicly reachable ● Run the regular Skype software ● Form an overlay among themselves ● Also act as ordinary nodes ● Ordinary Nodes ● Connect to one or more supernodes ● Issue queries through supernodes Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

11. 11 Explaining SupernodesExplaining Supernodes Image Source: http://www.disruptivetelephony.com/2010/12/understanding-todays-skype-outage-explaining-supernodes.htmlImage Source: http://www.disruptivetelephony.com/2010/12/understanding-todays-skype-outage-explaining-supernodes.html Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

12. 12 The complete imageThe complete image Image Source: http://www.disruptivetelephony.com/2010/12/understanding-todays-skype-outage-explaining-supernodes.htmlImage Source: http://www.disruptivetelephony.com/2010/12/understanding-todays-skype-outage-explaining-supernodes.html Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

13. 13 System Design AdvantagesSystem Design Advantages ● High scalability ● Use of processing and networking power of the end-users ● Reduce costs ● Reliability by self-healing Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

14. 14 Self-healingSelf-healing Image Source: http://www.disruptivetelephony.com/2010/12/understanding-todays-skype-outage-explaining-supernodes.htmlImage Source: http://www.disruptivetelephony.com/2010/12/understanding-todays-skype-outage-explaining-supernodes.html Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

15. 15 Becoming a Supernode: How will itBecoming a Supernode: How will it affect my connection?affect my connection? ● Negligible additional processing power, memory and storage compared to an ordinary node Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

17. 17 NAT TraversalNAT Traversal ● If one client is behind NAT ● Connection Reversal ● Hole Punching ● If both clients are behind NATs ● STUN ● If STUN fails ● TURN Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

18. 18 NAT Traversal: Connection ReversalNAT Traversal: Connection Reversal Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

19. 19 NAT Traversal: Hole PunchingNAT Traversal: Hole Punching Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

21. 21 Self-healing - revisitedSelf-healing - revisited Image Source: http://www.disruptivetelephony.com/2010/12/understanding-todays-skype-outage-explaining-supernodes.htmlImage Source: http://www.disruptivetelephony.com/2010/12/understanding-todays-skype-outage-explaining-supernodes.html What could possibly go wrong? Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

22. 22 11stst major outage: August 2007major outage: August 2007 ● The number of on-line users started falling unexpectedly ● Users faced login problems or slow services ● Problems lasted for more than 48h Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

23. 23 11stst major outage:major outage: ● Skype's Official Explanation ● A Microsoft Windows Update caused Supernodes to restart all at once ● Self-healing failed because too many users were chasing too few Supernodes ““Supernodes not so super”Supernodes not so super” ● Skype's Solution ● The system self-recovered completely after almost 48 hours. Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

24. 24 11stst major outagemajor outage Image Source: http://www.disruptivetelephony.com/2010/12/understanding-todays-skype-outage-explaining-supernodes.htmlImage Source: http://www.disruptivetelephony.com/2010/12/understanding-todays-skype-outage-explaining-supernodes.html Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

25. 25 11stst major outage:major outage: ● Questions raised ““Blame it on Microsoft!”Blame it on Microsoft!” ● Why this particular Tuesday? – Microsoft has been releasing security fixes on the 2nd Tuesday of each month since October 2003 ● Why at the same time? – Updates are downloaded and installed at 3am in the PC's local time – At the very least, systems would have rebooted time zone by time zone! ● Microsoft: “The disruption was caused by a bug in their software.” Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

26. 26 22ndnd major outage: December 2010major outage: December 2010 ● The network became unstable ● Suffered a critical failure ● The outage lasted for 24h approx. Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

27. 27 22ndnd major outage:major outage: ““Supernodes fail again”Supernodes fail again” ● A cluster of servers became overloaded... ● In version 5.0.0152 of Skype Windows client, the delayed responses caused crashes... ● 50% of all Skype users globally were running this version... ● Including 25–30% of the publicly available Supernodes! Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

28. 28 22ndnd major outage:major outage: Permanent Solutions?Permanent Solutions? ● Fixing software bugs ● Building a more resistant core-system ● Suggestions? ● Can we rely on user-Supernodes only? ● How can we recover faster next time? Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

30. 30 Skype SecuritySkype Security ● Privacy: Does the Skype system allow an outsider to eavesdrop on a conversation? I don't mean a person in the next room! Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

31. 31 Skype Security: PrivacySkype Security: Privacy Login behind the scenes Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

32. 32 Skype Security: PrivacySkype Security: Privacy ● Skype uses encryption ● Specific algorithms not publicly available ● Key-exchange mechanisms not known ● Secure against casual snooping ● Packets can be observed but are undecipherable ● Searches are observable ● Unknown security level against sophisticated attacks Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

33. 33 Skype Security: PrivacySkype Security: Privacy Security PSTN VoIP Skype VoIP over VPN Silence ;) Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

34. 34 Skype Security: AuthenticitySkype Security: Authenticity ● Email-based Identification and Authentication ● username/password ● Registered e-mail address ● The network is involved → attacks are possible! Authentication security level: AOL, Webmail Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

36. 36 Conclusions on SkypeConclusions on Skype ● Gained popularity and offers good quality despite Internet limitations ● Good performance and user satisfaction ● Supernodes increase availability but also fail ● Not clear Security level ● Encryption, network involvement ● As secure as webmail Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

37. 37 General ConclusionsGeneral Conclusions ● VoIP over P2P is challenging but works ● Cost reduction sharing resources ● Fault Tolerance ● Increase call quality over best-effort Internet Introduction - Supernodes - NAT Traversal - Outages - Security - Conclusions

38. 38 ReferencesReferences ● [1] Barbosa R, Kamienski C., Mariz D., Callado A., Fernandes S. Sadok D., “Performance evaluation os P2P VoIP applications” ● [2] Garfinkel, S.L. “VoIP and Skype Security”, Jan. 2005 ● [3] Saikat G., Daswani N., Jain R., “An Experimental study of the Skype Peer-to-Peer VoIP System”, February 2006 ● [4] Baset, S. A., And Schrulzrinne, H. “An Analysis of the Skype Peer-to-Peer Internet Telephony Protocol”, April 2006 ● [5] Liang, J., Kumar, R. and Ross, K. W., “ The kazaa overlay: A measurement study” ● [6] Haiyong Xie, Yang R. Yang, “A Measurement-based Study of the Skype Peer-to-Peer VoIP Performance”. ● [7] David A. Bryan, Bruce B. Lowerkamp, “SOSIMPLE: A SIP/SIMPLE Based P2P VoIP and IM System” ● [8] Ford B., Srisuresh P., Kegel D., “Peer-to-Peer Communication Across Network Address Translators” ● [9] http://blogs.skype.com/en/2010/12/cio_update.html ● [10] http://www.disruptivetelephony.com ● [11] http://news.techworld.com