SKR 5302: Advanced Distributed Computing

9.6. Peer-to-Peer Networks: Gnutella

Peer-to-Peer Networks: Gnutella

• Gnutella history
• 2000: J. Frankel & T. Pepper released Gnutella
• Soon after: many other clients (e.g., Morpheus, Limewire, Bearshare)
• 2001: protocol enhancements, e.g., “ultrapeers”

• Query flooding
• Join: contact a few nodes to become neighbors
• Publish: no need!
• Search: ask neighbors, who ask their neighbors
• Fetch: get file directly from another node
  
  

Gnutella: Query Flooding

• Fully distributed
  • No central server
• Public domain protocol
• Many Gnutella clients implementing protocol
• Overlay network: graph
  • Edge between peer X and Y if there’s a TCP connection
  • All active peers and edges is overlay net
  • Given peer will typically be connected with < 10 overlay neighbors

Gnutella: Protocol

• Query message sent over existing TCPconnections
• Peers forward Query message
• QueryHit sent over reverse path

Gnutella: Peer Joining

• Joining peer X must find some other peer in Gnutella network: use list of candidate peers
• X sequentially attempts to make TCP with peers on list until connection setup with Y
• X sends Ping message to Y; Y forwards Ping message. 
• All peers receiving Ping message respond with Pong message
• X receives many Pong messages. It can then setup additional TCP connections

Gnutella: Pros and Cons

• Advantages
  • Fully decentralized
  • Search cost distributed
  • Processing per node permits powerful search semantics
• Disadvantages
  • Search scope may be quite large
  • Search time may be quite long
  • High overhead and nodes come and go often