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Incentives Build Robustness in BitTorrent

Incentives Build Robustness in BitTorrent. Author: Bram Cohen Presenter: Brian Liao. About Bram Cohen. Live in Berkeley Only publish one paper: Noise Strategies for Local Search Interest : Complexity theory Multi-agent systems Usability . What is BitTorrent?.

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Incentives Build Robustness in BitTorrent

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  1. Incentives Build Robustness in BitTorrent Author: Bram Cohen Presenter: Brian Liao

  2. About Bram Cohen • Live in Berkeley • Only publish one paper: Noise Strategies for Local Search • Interest : • Complexity theory • Multi-agent systems • Usability

  3. What is BitTorrent? New file-sharing strategy: • Minimize the file hosting cost • Increase scalability

  4. Traditional File Hosting

  5. BitTorrent Strategy

  6. Technical Framework • Publishing Content • Peer Distribution • Pipelining • Piece Selection

  7. Technical Framework • Publishing Content • Peer Distribution • Pipelining • Piece Selection

  8. Publishing Content • Distribute .torrent file over the web. • Contains file info, name, hash info, url for a tracker

  9. Technical Framework • Publishing Content • Peer Distribution • Pipelining • Piece Selection

  10. Peer Distribution • Standard tracker algorithm will return a random list of peers. • cut files into pieces of fixed size for easy bookkeeping

  11. Technical Framework • Publishing Content • Peer Distribution • Pipelining • Piece Selection

  12. Pipelining • Avoid delay between pieces so a pipeline is required. • Further breaking pieces into sub-pieces (usually 16 kilobytes) to put in the pipeline. • Usually 5 sub-pieces pipelined at once.

  13. Technical Framework • Publishing Content • Peer Distribution • Pipelining • Piece Selection

  14. Piece Selection • Strict Priority • Rarest First • Random First Piece • Endgame Mode

  15. Strict Priority • Finish complete piece as quickly as possible

  16. Rarest First • Download pieces which all others want • Better performance • Prevent rarest piece missing

  17. Randnom First Piece & Endgame Mode • Random First Piece • For the initial stage of download • Endgame Mode • Multiple requests for sub-pieces to prevent delay.

  18. Choking Algorithms • Punishment to selfish users • Utilize available resources & provide consistent service

  19. Pareto Efficiency • Def: no two parties can exchange resource and make both happier. • Local optimization –> global optima

  20. Choke & Unchoke • Purely based on download rate • Every 10 seconds calculate who to choke • Unchoke limit is 4

  21. Optimistic Unchoking • Discover unused connection • Rotate every 30 seconds

  22. Upload only • After finish download, only upload to high upload rate users.

  23. My thought on implementing a price scheme for BT • DC: download charge • Static price base on content or fixed per download fee • SC: service charge • Negatively proportion to the contribution to the network. • Goal: encourage more seeds

  24. Price Paid = DC + SC Price paid DC Finish download

  25. Price Measurement • Local measurement • Periodically report to host

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