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SKR 5302: Advanced Distributed Computing

9. Chapter 9: Peer-to-peer networks

9.8. P2P Case study: Skype

P2P Case study: Skype

  • inherently P2P: pairs of users communicate.
  • proprietary application-layer protocol (inferred via reverse engineering) 
  • hierarchical overlay with SNs
  • Index maps usernames to IP addresses; distributed over SNs

Peers as relays

  • Problem when both Alice and Bob are behind  “NATs”. 
    • NAT prevents an outside peer from initiating a call to insider peer
  • Solution:
    • Using Alice’s and Bob’s SNs, Relay is chosen
    • Each peer initiates session with relay. 
    • Peers can now communicate through NATs via relay