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Effect of links on DHT routing algorithms

Effect of links on DHT routing algorithms. Zou FuTai zoufutai@cs.sjtu.edu.cn Internet Computing Lab 12/5/2003. Outline. 1.What is DHT? 2.Motivation and goals 3.Links in current DHT routing algorithms 4.The effect of links on routing performance 5.Improved CAN 6.Conclusions

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Effect of links on DHT routing algorithms

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  1. Effect of links on DHT routing algorithms Zou FuTai zoufutai@cs.sjtu.edu.cn Internet Computing Lab 12/5/2003

  2. Outline • 1.What is DHT? • 2.Motivation and goals • 3.Links in current DHT routing algorithms • 4.The effect of links on routing performance • 5.Improved CAN • 6.Conclusions • 7.Ongoing works 2

  3. 1.What is DHT? • Distributed Hash Table (DHT) • DHT is structured overlays that offer • extreme scalability • hash-table-like lookup interface • Ideal substrate for many distributed applications • file-systems, storage, backups, event-notification, e-mail, chat, databases, sensor networks ... • Applications need reliable and efficient DHT routing 3

  4. 2.Motivation • DHT routing algorithms have been proposing such as Chord,CAN, Pastry, Tapestry,Koorde,Symphony,… • Each has different performances: path hops, resilience, load balance….. • What makes them different? What could be the direction for the improvement of the routing performance? 4

  5. Goals • Understand the basic principles of designing DHT routing DHT. • Provide the insight into the improvement of the routing performances and the feasible approach to design new DHT routing algorithms. 5

  6. 3.Links in DHT • A structured geometry presented by DHT routing algorithms • Chord: circle, CAN: hypercube, Tapestry:tree • Each node can determinedly be routed to any other nodes in the geometry. • However, it is a dynamic geometry, So we use the link to catch its characteristics. • Link: A link is referred to an edge but it is very different the edge from the dynamic characteristic. The link can be dynamically adjusted according to the change of peer’s neighbors and it reflects how well the peer senses the system. 6

  7. Links in DHT • Three kinds of links exist in the geometry from the view of the distance and are maintained by each peer. • Basic short link • Redundant short link • Long link • The distance: • Distance d=Xdest - Xsrc (Xdest,Xsrc is node ID) • Hamming Distance: h=the number of 1’s in Xdest XOR Xsrc 7

  8. Model • No loss of generality, considering a cycle graph on n nodes where vertices are labeled 1, 2, . . . , n, we use links to express the relation between nodes. • A message can be routed clockwise from a node to any other node according to these links. 8

  9. Basic short link: 1 • Redundant short link: 2, 3 • Long link: 4, 5 9

  10. 4.The effect of links on routing performance • 1.Average Path Length:the average hops between every pair of nodes.It identifies how quickly a request is forwarded to the destination. • It is a tradeoff between the number of links and the maintaining overheads. Average path length can vary from 1 to n. • The key is how to arrange long links. There are diversified approaches. 10

  11. 2.Resilience: measure the extent to which DHT can route around failure even without the aid of recovery mechanisms that fix the failure. • Short links is the key. . It can improve the resilience by adding the redundant short links. 11

  12. Current DHT Routing Algorithms 12

  13. 5.Improved CAN • 1.Add long links • 2.Add redundant short links 13

  14. Add long links • Case one: add additional 2 long links to CAN and compare it with the original CAN. • Case two: add additional 4 long links to 4 dimensional CAN and compare it with 6 dimensional CAN. In this way, both have the same number of links. 14

  15. Path Hops vs. Long Links (Case One) 15

  16. Path Hops vs. Long Links (Case Two) 16

  17. Add redundant short links • Case one: add redundant short links to 2 dimensional CAN. The number of additional short links is varied form 0 to 4 . • Case two: add 2 additional redundant short links to 2,4,6 dimensional CAN respectively. 17

  18. Resilience vs. Redundant Short Links (Case One) 18

  19. Resilience vs. Redundant Short Links (Case Two) 19

  20. 6.Conclusions • 1. Links has great effects on the performances of DHT routing algorithms • 2. According to the analysis of links in current DHT routing algorithms, the possible improvement of routing performances can be suggested . • 3. New DHT routing algorithms should take the effect of links into account. 20

  21. 7.Ongoing Works • 1.Fixed Links vs. Randomized Links • 2.More performance arguments need to be investigated such as load balance, delay…. 21

  22. Thank You! 22

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