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Sharing in BitTorrent communities

Miranda Mowbray, HP LabsNazareno Andrade, UFCG BrazilMatei Ripeanu, UBC CanadaAliandro Lima+Gustavo Wagner, UFCG Brazil

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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

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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

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Lifecycle of a BitTorrent peer

Downloader

Seeder

Finishes download

Leaves

Rejoins

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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 defaultTit-for-tat incentive

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

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Seeding over time• Results for etree over 10 days

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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 M

B

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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

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Seeding: legal / illegal content

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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

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Sharing Ratio enforcement

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Broadcatching

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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

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Vampire bats• Need to drink 50-100% 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

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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

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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, 2000.

• Idea: upload only to “generous” peers

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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

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Motivations for sharing in P2P systems• Altruistic

− 58% of SETI@home 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

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Reduce the effort required for sharing• Increase the effectiveness of sharing

This also increases some types of motivation

• Make sharing safeReduce 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

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Questions?

miranda.mowbray@hp.com