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  P2P is alternative to client-server model  Peers send/receive information from each other  Utilize the bandwidth of all users  3 paradigms…

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

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

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

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

Kazaa Screen Shot Source: HowStuffWorks.com

Kazaa Screen Shot Source: atFile.com

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

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

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

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

Kazaa Network Topology Source: HowStuffWorks.com

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

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

Topology of BitTorrent Source: BitTorrent.com

Looking for Torrents

BitTorrent Screen Shot Source: Sciencemedia.com

BitTorrent In Action

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