2Hop TorrentSmell A distributed tracking algorithm

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2-Hop TorrentSmellA distributed tracking
algorithm
name Raynor Vliegendhartdate July 10,
2009event Tribler Dev Meeting
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Research Question

• How to decentralizePeer Discovery Functionality
• with hooks for
• Security
• and Scalability?

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Central Tracker
Request Peerlist
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Central Tracker
Peer List
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Central Tracker
Connect to Download Swarm
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Central Tracker

• Keep in touch with tracker to
• discover newpeers
• announceyour presence.

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Distributed Tracking

• How do we
• track peers in the swarm?
• find the distributed trackerstracking the swarm?

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Distributed Tracking Algorithm

• How do we
• track peers in the swarm?
• RePEX
• find the distributed trackerstracking the swarm?
• Extended Remote Content Search

2-Hop TorrentSmell
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Peer Exchange

• Modern BitTorrent clients can exchange their
  neighbourhood sets throughPeer Exchange (PEX)

65.1.5.212
8.33.232.4
136.12.5.59
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Peer Exchange

• Modern BitTorrent clients can exchange their
  neighbourhood sets throughPeer Exchange (PEX)

65.1.5.212
136.12.5.59
8.33.232.4
136.12.5.59
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Peer Exchange

• Modern BitTorrent clients can exchange their
  neighbourhood sets throughPeer Exchange (PEX)

65.1.5.212
65.1.5.212, 8.33.232.4
8.33.232.4
136.12.5.59
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RePEX

• Reconnect to PEX peers encountered before.
• Discover new and reliable peers.
• Goal
• Each peer has a local list of peers in the swarm.

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RePEX Research Questions

• Which swarms to track?
• How often? How many peers to store?

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RePEX Research Questions

• Which swarms to track?
• Last 25 downloads, since we have been
• in those swarms before
• How often? How many peers to store?
• Yet unknown
• Measurements needed to determine churn,
  online status, connectivity, etc.

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Remote Content Search

• Currently implementedin Tribler

Obama
Obama
Obama
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Remote Content Search
obama.mp3 SHA1
obama.avi SHA1
X

• Tribler peers respond with matching torrent files

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Extended Remote Content Search RePEX
Obama
Obama
RePEX Tribler Peer
Obama
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Extended Remote Content Search RePEX
obama.mp3 SHA1
obama.avi SHA1
136.12.5.59, 8.33.232.4,
RePEX Tribler Peer
X

• A RePEX peer includes swarm peers in the response

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2-Hop TorrentSmell

• Tribler peers already announce their download
  profile through BuddyCast
• We can use this to further extendRemote Content
  Search

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2-Hop TorrentSmell
Obama
212.13.153.124

• The user issues a query as normally

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2-Hop TorrentSmell
obama.avi SHA1
RePEX 212.13.153.124,
212.13.153.124

• The responding Tribler peer knows who has
  downloaded obama.avi

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2-Hop TorrentSmell
Obama
212.13.153.124

• So the user can reissue the query to that peer

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2-Hop TorrentSmell
obama.avi SHA1
Swarm 136.12.5.59, 8.33.232.4,
212.13.153.124

• Finally, the RePEX peer responds with a list of
  swarm peers

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Algorithm Summary

• 2 Hops needed using Extended RCS
• RePEX used for tracking

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Research Questions Recap

• How often do we have to revisit swarms?
• How many peers should we store per swarm?
• Whats the churn rate?
• Etc

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Additional Research Questions

• But also
• Do peers lie about PEX capabilities?
• Whats the PEX response timeof non-Tribler
  peers?
• ltyour input?gt