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

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 As the network gets bigger, a larger percentage of greedy hosts can be supported 10 Peers20 Peers

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? A 1 : Not much. A 2 : Not much up to a point. A 3 : 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