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Spotlighting Decentralized P2P File Sharing

Spotlighting Decentralized P2P File Sharing. Archie Kuo and Ethan Le Department of Computer Science San Jose State University. Agenda. P2P overview The Three Paradigms Kazaa and BitTorrent Conclusion Q & A. What is P2P?. Tradition dictates a client-server model

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Spotlighting Decentralized P2P File Sharing

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  1. Spotlighting Decentralized P2P File Sharing Archie Kuo and Ethan Le Department of Computer Science San Jose State University

  2. Agenda • P2P overview • The Three Paradigms • Kazaa and BitTorrent • Conclusion • Q & A

  3. What is P2P? • Tradition dictates a client-server model • P2P is alternative to client-server model • Peers send/receive information from each other • Utilize the bandwidth of all users • 3 paradigms…

  4. Centralized Directory • Central server • Advantages: • Simple • Easy to maintain • Disadvantages • Single point of failure • Single point of prosecution • Bottleneck effect Source: Kurose and Ross, 2003

  5. Decentralized Directory • AKA Super decentralized network • No central server • Advantages • Distributed contents • Smaller databases • Harder to track • Disadvantages • Bootstrap node • Complex protocol • Peers are ranked Source: Kurose and Ross, 2003

  6. Query Flooding • AKA Equal decentralized network • All are created equal • Advantages • Flat • No central directory • Disadvantages • Scalability • Does not search entire network Source: Kurose and Ross, 2003

  7. Kazaa Overview • 3 million users • Definitive decentralized network • No central agent • No central agent means no need for a central point of management • At one point Kazaa held 76% of all the P2P traffic

  8. Kazaa Screen Shot Source: HowStuffWorks.com

  9. Kazaa Screen Shot Source: atFile.com

  10. How does Kazaa achieve decentralization? • Users are categorized into two categories: • Ordinary Nodes (ON) • Super Nodes (SN) • Users are designated as ON or SN based on their system capabilities • Network connection • Bandwidth • Processing capabilities • Designation process is done without users knowledge • Result is that users do not know if they have been designated ON or SN

  11. Super Decentralized (Revisted) Source: Kurose and Ross, 2003

  12. Super Nodes • Kazaa has approximately 30,000 SNs • Each SN is like a traffic hub that processes requests from ONs • Each SN serves approximately 60-150 ONs at a time • Each SN keeps a database of all the files that it’s ONs are sharing

  13. User Requests • User requests are propagated to the SN which communicates with other SNs • Those other SNs communicate with their ONs with a search depth of 7 (similar to TTL) • When correct file is located the transfer occurs directly between the two nodes without SN intervention

  14. Kazaa Network Topology Source: HowStuffWorks.com

  15. User Request in detail • Query containing keywords is sent out over a TCP connection from ON to its SN • For each match the SN returns the IP address and metadata of the matching node • SNs will maintain a TCP connection between SNs creating an overlay network • Query is sent to one or more of the directly connected nodes between SNs • SNs will shuffle their directly connected nodes every 10 minutes in order to allow for a larger area of the network to be reached

  16. Kazaa’s competion: BitTorrent • Kazaa is declining in popularity while BitTorrent is rising rapidly in popularity. • BitTorrent: User receives data from multiple sources at once • Data is split up into chunks • Each chunk is received from source with the best connection • Chunks are received randomly but can be reassembled • Separate channel available for uploading, even while downloading • Kazaa: User receives data from node that it has established connection with • Data is split up into chunks • Data is received in order

  17. Topology of BitTorrent Source: BitTorrent.com

  18. Looking for Torrents

  19. BitTorrent Screen Shot Source: Sciencemedia.com

  20. BitTorrent In Action

  21. Conclusion • Centralized approach offers easy maintenance but too many legal and performance issues • Decentralized approach has a longer lifetime and more reliable service

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