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Vincent Matossian September 21st 2001 ECE 579

An Overview of Decentralized Discovery mechanisms. Vincent Matossian September 21st 2001 ECE 579. Decentralized Discovery mechanisms. Centralized indexes and repositories Flooding broadcast of queries Selective forwarding/routing of queries Decentralized hashing index systems

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Vincent Matossian September 21st 2001 ECE 579

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

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

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

  6. 128.1.2.3 xyz.mp3 ? Central Napster server Napster 3 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. Gnutella step 1 From Sylvia Ratnasamy Berkeley

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

  12. Gnutella step 3 From Sylvia Ratnasamy Berkeley

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

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

  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. Concept N2 N1 N3 Client N4 Lookup(“title”) Publisher Key=“title” Value=MP3 data… N6 N8 N7 N9 From Robert Morris MIT

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

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

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

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

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

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

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

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

  30. Example: Octal digits, 218 namespace, 005712  627510 005712 340880 727510 627510 943210 387510 834510 0 0 0 0 0 0 0 1 1 1 1 1 1 1 2 2 2 2 2 2 2 4 4 4 4 4 4 4 5 5 5 5 5 5 5 7 7 7 7 7 7 7 3 3 3 3 3 3 3 6 6 6 6 6 6 6 Neighbor Map For “5712” (Octal) 005712 340880 943210 0712 x012 xx02 xxx0 1712 x112 5712 xxx0 834510 2712 x212 xx22 5712 3712 x312 xx32 xxx3 387510 4712 x412 xx42 xxx4 5712 x512 xx52 xxx5 6712 x612 xx62 xxx6 727510 7712 5712 xx72 xxx7 4 3 2 1 Routing Levels 627510 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 Chord CAN Pastry Tapestry • Properties • Parameter • Logical Path Length • Neighbor-state • Routing Overhead (RDP) • Messages to insert • Mutability • Load-balancing Base b None Dimen d Base b LogbN O(d*N1/d) LogbN Log2N bLogbN bLogbN+O(b) Log2N O(d) O(1) ? O(1)? O(1) O(1) O(Log22N) O(d*N1/d) O(Logb2N) O(LogbN) App-dep. ??? App-dep Immut. Good Good Good Good Designed as P2P Indices

  33. Drawbacks Advantages • Scalable • Fault Tolerant • No keyword search • Susceptible of malicious activities • 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 • Low latency delivery of content • Cuts ISP’s bandwidth costs • Load balancing • QoS is possible • Centrally managed, pre-installed network • Infrastructure difficult to setup • Cost • Cache Coherence • “Slash-Dot” effect

  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

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