Leveraging Social Networks for Increased BitTorrent Robustness Wojciech Galuba, Karl Aberer EPFL,...
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Transcript of Leveraging Social Networks for Increased BitTorrent Robustness Wojciech Galuba, Karl Aberer EPFL,...
Leveraging Social Networks for Increased BitTorrent Robustness
Wojciech Galuba, Karl AbererEPFL, Switzerland
Zoran Despotovic, Wolfgang Kellerer Docomo Euro-Labs, Munich, Germany
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Motivation 1
BitTorrent relies on cooperative behavior But freeriding possible
15-80% of peers are freeriders
Freerider
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Current solution: Tit-for-tat
Tit-for-tat (TFT) strategy:Reward good uploaders by giving them higher
priority TFT defense ineffective:
Large-view exploitSeeders don’t download all peers look
equal to seeders
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Friend-to-Friend (F2F) systems
Source of the problem In P2P nets everyone is
a stranger A solution: connect to friends’
computers only Reliable, stable identities
Take advantage of existing social trust Cooperation more likely
Social network
P2P network
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Motivation 2
How can we leverage the social network to solve freeriding?
Is the social network a good content distribution medium?
BitTorrent
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The social BitTorrent
Approach BitTorrent on top of a social network Friends’ computers added to the peer list Protocol unchanged
Communication only along the social links Mutually authenticated Can be encrypted for privacy
Friend discovery We use a centralized friend server Possible decentralized implementation:
PGP Jabber/XMPP
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Freeriding disincentiveUser interface:
AliceUpload/download: 1.2
BobUL/DL: 2.5
CarolUL/DL: 0.9
DanielUL/DL: 1.2
EveUL/DL: 0.02
Users unlikely to freeride on friends
Hmmm... I need to talk to Eve
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Evaluated systems
BT – BitTorrent implementation Using trackers to discover peers
SBT – the social BitTorrent Only friend connections
HBT – hybrid implementation Both on peer list:
friend peers peers obtained from the trackers
Friend uploads have absolute priority
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Experimental setup Simulated in protopeer.net Tit-for-tat (TFT), downloaders ordered by:
TFT on: how much they upload TFT off: how much they download
1024 peers, 25 MB file, single initial seeder Mixture of peers with 0.5, 1 and 2Mbit/s upload
bandwidth Social net generated based on MSN Messenger data
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Social network alone is an efficient content distribution medium Though: long-tail problem
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Swarm density
Def: Fraction of peers in the social network interested in downloading a file
Low swarm density distribution graph becomes disconnected
Source
No access to source
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Low swarm density many failed downloads Trackers (in BT and HBT) solve the problem
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Social links give HBT advantage only if swarm density > 2%
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Linear scaling with content size
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O(logN) scaling with the number of peers
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Open problems
We assumed uniform distribution of interested peers In reality interest clustered in social nets
Even better performance?
Content discoveryCan friends-of-friends be trusted?
Social BT geo locality less inter-AS traffic?
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Conclusions
Social network alone an efficient and scalable content distribution medium
Social BitTorrent Increased robustness to freeridingAs long as swarm density >2%
F2F approach to content distribution:Authenticated connections, trust Increased privacy