1. Vincent Matossian September 21st 2001 ECE 579 An Overview of Decentralized Discovery mechanisms

2. Decentralized Discovery mechanisms Centralized indexes and repositories Flooding broadcast of queries Selective forwarding/routing of queries Decentralized hashing index systems Distributed indexes and repositories

3. Centralized indexes and repositories

4. Napster 1 Central Napster server (xyz.mp3, 128.1.2.3) 128.1.2.3 From Sylvia Ratnasamy Berkeley

5. Napster 2 Central Napster server xyz.mp3 ? 128.1.2.3 From Sylvia Ratnasamy Berkeley

6. Napster 3 Central Napster server 128.1.2.3 xyz.mp3 ? From Sylvia Ratnasamy Berkeley

7. Drawbacks Advantages Single point of failure Scalability Cost increases with popularity Lawsuits Performance Control of accesses

8. Decentralized Discovery mechanisms Centralized indexes and repositories Flooding broadcast of queries Selective forwarding/routing of queries Decentralized hashing index systems Distributed indexes and repositories

9. Flooding broadcast

10. From Sylvia Ratnasamy Berkeley Gnutella step 1

11. xyz.mp3 ? From Sylvia Ratnasamy Berkeley Gnutella step 2

12. Gnutella step 3 From Sylvia Ratnasamy Berkeley

13. xyz.mp3 Gnutella step 4 From Sylvia Ratnasamy Berkeley

14. Drawbacks Advantages Message broadcasting becomes a problem as popularity increases due to bandwidth requirements Susceptible to malicious attacks Simple Efficient Flexible query interpretation Reliable in small networks

15. Decentralized Discovery mechanisms Centralized indexes and repositories Flooding broadcast of queries Selective forwarding/routing of queries Decentralized hashing index systems Distributed indexes and repositories

16. Clip2 Reflector (Gnutella) CANCELLED

17. FastTrack (KaZaA Morpheus) Nodes become supernodes automatically if they have sufficient bandwidth and processing power.

18. Drawbacks Advantages Susceptible to malicious activities Too much importance on Super Nodes Each peer must contain additional information used to route or direct queries received. Performance Scalability Fault-Tolerance

19. Decentralized Discovery mechanisms Centralized indexes and repositories Flooding broadcast of queries Selective forwarding/routing of queries Decentralized hashing index systems Distributed indexes and repositories

20. Selective forwarding of queries Chord Ion Stoica, Robert Morris, David Karger, M. Frans Kaashoek, and Hari Balakrishnan; MIT Content-Addressable Networks Sylvia Ratnasamy, Paul Francis, Mark Handley, Richard Karp, Scott Shenker; UC Berkeley Pastry Antony Rowstron (Rice University) and Peter Druschel (Microsoft) Tapestry Ben Y. Zhao, John Kubiatowicz and Anthony D.Joseph UC Berkeley

21. N4N4 Publisher Client N6N6 N9N9 N7N7 N8N8 N3N3 N2N2 N1N1 Lookup(“title”) Key=“title” Value=MP3 data… Concept From Robert Morris MIT

22. Chord 1 N32 N90 N105 K80 K20 K5 Circular 7-bit ID space Key 5 Node 105 A key is stored at its successor: node with next higher ID

23. Chord 2 N32 N90 N105 N60 N10 N120 K80 “Where is key 80?” “N90 has K80”

24. Content-Addressable Networks - CAN hash(K) = (a,b) (K,V) retrieve (K) insert (K,V) (a,b)

25. Bootstrap node 1) Discover some node “I” already in CAN new node CAN Node Insertion

26. I Bootstrap node new node 1) Discover some node “I” already in CAN CAN Node Insertion

27. 2) pick random point in space I (p,q) new node CAN Node Insertion

28. (p,q) 3) I routes to (p,q), discovers node J I J new node CAN Node Insertion

29. new J 4) split J’s zone in half… new owns one half CAN Node Insertion

30. Example: Octal digits, 2 18 namespace, 005712  627510 005712 340880 943210 387510 834510 727510 627510 Neighbor Map For “5712” (Octal) Routing Levels 1234 xxx0 5712 xxx0 xxx3 xxx4 xxx5 xxx6 xxx7 xx02 5712 xx22 xx32 xx42 xx52 xx62 xx72 x012 x112 x212 x312 x412 x512 x612 5712 0712 1712 2712 3712 4712 5712 6712 7712 005712 012 3 45 6 7 340880 012 3 45 6 7 943210 012 3 45 6 7 834510 012 3 45 6 7 387510 012 3 45 6 7 727510 012 3 45 6 7 627510 012 3 45 6 7 Plaxton Rajamaran Richa

31. PASTRY TAPESTRY Based on Plaxton Rajamaran Richa algorithm but have additional support for dynamic node insertion and deletion. Node insertion: Node N requests a new ID and contacts a Gateway G. Neighbor maps tables are updated along each hop. Minor differences in object replications and routing distances calculation.

32. Comparing Key Metrics Properties –Parameter –Logical Path Length –Neighbor-state –Routing Overhead (RDP) –Messages to insert –Mutability –Load-balancing Tapestry ChordCANPastry Log b N Log 2 N O(d*N 1/d ) O(d) Base b bLog b N O(1)  O(1) O(1) ? App-dep. App-depImmut. ??? Good Log b N Log 2 N NoneDimen dBase b bLog b N+O(b) O(Log 2 2 N)O(d*N 1/d ) Good O(Log b 2 N)O(Log b N) Designed as P2P Indices

33. Drawbacks Advantages No keyword search Susceptible of malicious activities Scalable Fault Tolerant Common Applications: Storage systems Application-level multicasts Event Notification

34. Decentralized Discovery mechanisms Centralized indexes and repositories Flooding broadcast of queries Selective forwarding/routing of queries Decentralized hashing index systems Distributed indexes and repositories

35. Clients Content Broker Content Distribution Networks

36. Drawbacks Advantages Infrastructure difficult to setup Cost Cache Coherence “Slash-Dot” effect Low latency delivery of content Cuts ISP’s bandwidth costs Load balancing QoS is possible Centrally managed, pre- installed network

37. Conclusion Not one system fits-all Drawbacks for all systems include malicious activities Business-oriented and Research discovery mechanisms will merge Links: http://cubicmetercrystal.com/alpine/discovery.html http://www.caip.rutgers.edu/~vincentm/p2p.html