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Impact of Incentives in BitTorrent

Impact of Incentives in BitTorrent. By Jenny Liu and Seth Cooper. Peer to Peer Networks. Multiple independent peers connect to share resources with each other. Incentives. But what reason does one peer have to share its resources with another?. ?. Incentives.

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Impact of Incentives in BitTorrent

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  1. Impact of Incentives in BitTorrent By Jenny Liu and Seth Cooper

  2. Peer to Peer Networks • Multiple independent peers connect to share resources with each other

  3. Incentives • But what reason does one peer have to share its resources with another? ?

  4. Incentives • Does a peer need something in return?

  5. Incentives • Or is simple altruism enough?

  6. BitTorrent • Torrent file directs peers to a tracker, which helps to coordinate peers Torrent Tracker

  7. BitTorrent • Initial peer, known as a “seed,” begins with the complete file. Torrent Tracker Seed

  8. BitTorrent • Peers trade pieces of the file amongst themselves, uploading pieces to the peers they are downloading the fastest from. When a peer finishes, it becomes a new seed. Torrent Tracker Seed

  9. Motivation • Other P2P networks (Napster, Kazaa) have become successful relying on altruism alone.

  10. Motivation ? • It is often claimed that freeloading on P2P networks is a problem, and many attempts have been made to find an effective incentive, but is one necessary?

  11. Motivation • How effective is BitTorrent? Are incentives necessary? How do greedy peers affect the network? Are incentives an unnecessary overheard? ?

  12. System • Modify BitTorrent source to remove incentives, and compare efficiency with unmodified BitTorrent vs

  13. System • Assign each peer a strategy: greedy or altruistic.

  14. Metrics • Client side: average download time

  15. Metrics • Server side: percent of unicast

  16. Trials • Measure data from several trials of one seed distributing a file to a set of peers. Start with a default network setting and vary parameters to see their effect on the two types of networks. Seed

  17. Trials • We varied: delay between peer connections.

  18. Trials • We varied: minimum number of uploads for each peer.

  19. Results • Not much difference.

  20. Trials • We varied: total number of peers.

  21. Results • Number of peers has an effect on download time when the incentive is removed.

  22. Trials • We varied: percentage of greedy peers.

  23. Results • Percentage of greedy peers has an effect on both metrics when the incentive is removed.

  24. Trials • We varied: size of network and tried different percentages of greedy hosts

  25. Results 10 Peers 20 Peers • As the network gets bigger, a larger percentage of greedy hosts can be supported

  26. Conclusions • Q: How efficient is BitTorrent? • A: Very.

  27. Conclusions • Q: Are incentives necessary? • A: It depends.

  28. Conclusions • Q: How do greedy peers affect the network? • A1: Not much. • A2: Not much up to a point. • A3: Quite a lot after that.

  29. Conclusions • Q: Are incentives an unnecessary overhead? A: No!

  30. Future Work • Conduct experiments on more heterogeneous networks. • Try UDP. • Address other negative aspects of BitTorrent, such as content lifetime.

  31. The End

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