1. 2-Hop TorrentSmell A distributed tracking algorithm name:Raynor Vliegendhart date:July 10, 2009 event:Tribler Dev Meeting

2. Research Question How to decentralize Peer Discovery Functionality with hooks for Security and Scalability? 2

3. Central Tracker 3 Request Peerlist

4. Central Tracker 4 Peer List

5. Central Tracker 5 Connect to Download Swarm

6. Central Tracker 6 Keep in touch with tracker to 1.discover new peers; 2.announce your presence.

7. Distributed Tracking How do we… track peers in the swarm? find the distributed trackers tracking the swarm? 7

8. Distributed Tracking Algorithm How do we… track peers in the swarm? RePEX find the distributed trackers tracking the swarm? Extended Remote Content Search 8 2-Hop TorrentSmell

9. Peer Exchange 9 Modern BitTorrent clients can exchange their neighbourhood sets through Peer Exchange (PEX) 136.12.5.59 8.33.232.4 65.1.5.212

10. Peer Exchange 10 Modern BitTorrent clients can exchange their neighbourhood sets through Peer Exchange (PEX) 136.12.5.59 8.33.232.4 65.1.5.212

11. Peer Exchange 11 Modern BitTorrent clients can exchange their neighbourhood sets through Peer Exchange (PEX) 136.12.5.59 8.33.232.4 65.1.5.212 65.1.5.212, 8.33.232.4

12. RePEX Reconnect to PEX peers encountered before. Discover new and reliable peers. Goal: Each peer has a local list of peers in the swarm. 12

13. Which swarms to track? How often? How many peers to store? RePEX Research Questions 13

14. 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. RePEX Research Questions 14

15. Remote Content Search Currently implemented in Tribler: 15 “Obama”

16. Remote Content Search 16 obama.mp3 SHA1 obama.avi SHA1 X Tribler peers respond with matching torrent files

17. Extended Remote Content Search + RePEX 17 “Obama” RePEX Tribler Peer

18. Extended Remote Content Search + RePEX 18 RePEX Tribler Peer obama.mp3 SHA1 obama.avi SHA1 X +136.12.5.59, 8.33.232.4, … A RePEX peer includes swarm peers in the response

19. 2-Hop TorrentSmell 19 Tribler peers already announce their download profile through BuddyCast We can use this to further extend Remote Content Search

20. 2-Hop TorrentSmell 20 “Obama” 212.13.153.124 The user issues a query as normally

21. 2-Hop TorrentSmell 21 212.13.153.124 The responding Tribler peer knows who has downloaded obama.avi obama.avi SHA1 +RePEX: 212.13.153.124, …

22. 2-Hop TorrentSmell 22 212.13.153.124 So the user can reissue the query to that peer “Obama”

23. 2-Hop TorrentSmell 23 212.13.153.124 Finally, the RePEX peer responds with a list of swarm peers obama.avi SHA1 +Swarm: 136.12.5.59, 8.33.232.4, …

24. Algorithm Summary 24 2 Hops needed using Extended RCS RePEX used for tracking

25. Research Questions Recap How often do we have to revisit swarms? How many peers should we store per swarm? What’s the churn rate? Etc… 25

26. Additional Research Questions But also: Do peers lie about PEX capabilities? What’s the PEX “response time” of non-Tribler peers? 26