© 2006 Hewlett-Packard Development Company, L.P. You’re welcome to copy, distribute or use these slides, provided that you retain this notice Sharing in BitTorrent communities Miranda Mowbray, HP Labs Nazareno Andrade, UFCG Brazil Matei Ripeanu, UBC Canada Aliandro Lima+Gustavo Wagner, UFCG Brazil

2 Sharing in BitTorrent communities BitTorrent How sharing varies between different BitTorrent communities Ideas from animals for improving BitTorrent clients Encouraging sharing in P2P systems Conclusions + Questions

3 BitTorrent BitTorrent is a cooperative publishing tool −Downloading peers share bandwidth ~30% of all Internet traffic at end 2004 CacheLogic, Peer to Peer in 2005 Open source software, pirate movies, videos of lectures, podcasts, TV episodes, Warner Bros trial… Tit-for-tat incentive for uploading −No incentive for seeding

4 Lifecycle of a BitTorrent peer Downloader Seeder Finishes download Leaves Rejoins

5 Freeriders (peers who upload nothing) Results from etree, alluvion, easytree Freeriders: < 6% −Most firewalled (in the sites where we could tell) −Much younger than other peers Gnutella: 13% - 85% Most BitTorrent clients don’t have a zero-upload option Uploading as default Tit-for-tat incentive

6 Freeriders don’t always have slower download times Discovered by Gustavo + Aliandro

7 Seeding over time Results for etree over 10 days

8 Seeding vs Size of file Piratebay: 13,054 files Similar for all 6 sites we looked at # seeders / # peers per torrent size of file in MB

9 Sharing in BitTorrent communities BitTorrent How sharing varies between different BitTorrent communities Ideas from animals for improving BitTorrent clients Encouraging sharing in P2P systems Conclusions + Questions

10 Seeding: legal / illegal content

11 Extra mechanisms Use BitTorrent community’s centralized component Sharing ratio enforcement −Sharing ratio = upload/download −Incentive to seed Broadcatching −RSS + regular expressions: “Download any new episode from Dr Who” −Automatic download −Requires user interaction to stop seeding

12 Sharing Ratio enforcement

13 Broadcatching

14 Sharing in BitTorrent communities BitTorrent Influences on the amount of sharing in BitTorrent communities Ideas from animals for improving BitTorrent clients Encouraging sharing in P2P systems Conclusions + Questions

15 Vampire bats Need to drink % of their weight in blood each night −If they don’t get blood for 60 hours, they die −Estimated one-year survival rate 16% −Actual survival rate 76% Share blood meals with unrelated bats close to starvation G. S. Wilkinson, “Reciprocal food sharing in the vampire bat”, Nature 308:183, 1984 Idea: harsh environment for uncooperative BitTorrent peers Idea: preferentially seed files with peers closer to starvation

16 Ophryotrocha diadema Aquatic worm −Hermaphroditic, not self-fertilizing −Alternates roles in mating, tit-for-tat-like −Apparently no punishment of cheats −Long courtship ritual (for a worm) Gabriella Sella and M. Cristina Lorenzi, “Partner fidelity and egg reciprocation in the simultaneously hermaphroditic polychaete worm Ophryotrocha diadema”, Behavioural Ecology 11:260-4, 2000 Idea: hysteresis for BitTorrent uploading

17 Brown Capuchin Monkeys Tit-for-tat-like behaviour in food sharing −Remembers whether a particular monkey was generous in the past, behaves accordingly −But doesn’t remember exact amount of food shared Frans de Waal, “Attitudinal reciprocity in food sharing among brown capuchin monkeys”. Animal Behaviour 60:253-61, Idea: upload only to “generous” peers

18 Sharing in BitTorrent communities BitTorrent Influences on the amount of sharing in BitTorrent communities Ideas from animals for improving BitTorrent clients Encouraging sharing in P2P systems Conclusions + Questions

19 Motivations for sharing in P2P systems Altruistic −58% of contributors did it “for the good of humanity” Social −social norm not leave BitTorrent client open a while Ideological −promoting a particular type of music or software Indirect reciprocation −resource pooling, promotional gifts Trading −uploading while downloading in BitTorrent, sharing CPU in Grids Avoiding punishment −sharing ratio enforcement Byproduct −btefnet seeding, Skype, addition to Napster index

20 Reduce the effort required for sharing Increase the effectiveness of sharing This also increases some types of motivation Make sharing safe Reduce risk: legal/ethical/security Make sharing the default, or a byproduct of actions carried out by users for their own benefit Default sharing in BitTorrent => most peers upload Allow different kinds of sharing with different levels of effort Uploading while downloading vs. seeding vs. providing new content

21 Questions?