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Brocade Landmark Routing on P2P Networks

Brocade Landmark Routing on P2P Networks. Gisik Kwon April 9, 2002. Motivation. Problems with existing P2P systems Existing systems : CAN, Chord, Tapestry, Pastry Constrained by the theoretical approach adopted, nodes are treated uniformly

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Brocade Landmark Routing on P2P Networks

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  1. BrocadeLandmark Routing on P2P Networks Gisik KwonApril 9, 2002

  2. Motivation • Problems with existing P2P systems • Existing systems : CAN, Chord, Tapestry, Pastry • Constrained by the theoretical approach adopted, nodes are treated uniformly • Routing algorithms are decoupled from underlying topology and node capability • Result: Sub-optimal performance • Due to 1) the asymmetry of nodes in reality • Less powerful nodes can be overloaded • Due to 2) the lack of structure • No advantage of the aggregated knowleges of the network • P2P does not need to operate in the pure P2P style • A secondary overlay network on top of existing system(e.g., Tapestry)

  3. Brocade • A philosophy: A system is more efficient when it is organized • Respect the differences and take advantage of those that are more powerful – Supernodes! • Fast/well-connected/situated near network access points • Supernodes have better knowledge of underlying network characteristics. Benefit from aggregation.

  4. Network in reality • Transit-stub topology, disparate resources per node • Result: Inefficient inter-domain routing AS-3 AS-1 S R AS-2 P2P Overlay Network

  5. Landmark Routing • Goals • Eliminate unnecessary wide-area hops for inter-domain messages • Eliminate traffic going through high latency, congested stub links • Reduce wide-area bandwidth utilization

  6. Brocade Architecture Brocade Layer Original Route Brocade Route AS-3 AS-1 S R AS-2 P2P Network

  7. Intuitive mechanisms • Intuition: route quickly to destination domain • Organize group of supernodes into secondary overlay • Sender (S) sends message to local supernode SN1 • SN1 finds and routes message to supernode SN2 near receiver R • SN1 uses Tapestry object location to find SN2 • SN2 sends message to R via normal routing

  8. Overlay nodes are grouped by their supernodes • Supernodes treat their overlay nodes as objects that they possess • Routing on Brocade => Object Location. Use your favorite • mechanism: Tapestry, CAN, Chord, Pastry • Message filtering: only send inter-domain messages to Brocade.

  9. Case Study - Brocade On Tapestry • Tapestry: A novel wide-area fault-tolerant location and routing infrastructure • Construction • Supernode selection • Significant processing power • Minimum number of ip hops to wide-area network • High bandwidth outgoing link  So, gateway routers or machines close by those • Existing connections among supernodes as Brocade links

  10. AS-1 Classifying Traffic S • Brocade not useful for intra-domain messages • P2P layer should exploit some locality (Tapestry) • Undesirable processing overhead • Classifying traffic by destination • Proximity caches: - Every overlay node keeps list of nodes it knows to be local- Need not be optimal • Cover set:- Supernode keeps list of all nodes in its domain- Acts as authority on local vs. distant traffic

  11. Entering the Brocade • Route: Sender  Supernode • Naïve Brocade:Tapestry routing unchanged. Message gets onto the Brocade overlay if a supernode is encountered on its route. • Advantage: simple, no modification to ordinary nodes. • Disadvantage: possibility of hitting a supernode in Tapestry routing small. • IP Snooping Brocade: Supernodes snoop IP packets to intercept Tapestry messages. • Advantage: - No modification to ordinary nodes. - High possibility of encountering supernodes because supernodes are situated near the edge of local networks. • Disadvantage: difficult to implement

  12. Yes Ordinary Tapestry Routing Destination is in my cover set? No Send to supernode Entering the Brocade • Directed Brocade: Each overlay node keep info about • its supernode and decides by its own whether to send a • message to supernode directly. • Feasible: only local information required • Decision Engine: • A small cache storing most frequently used nodes in its cover set will do the trick. • Query locality will make hit rate high • Consequences of mistakes aren’t expensive

  13. Inter-supernode Routing • Route: Supernode (sender)  Supernode (receiver) • Locate receiver’s supernode given destination nodeID • Use Tapestry object location or Bloom filter • Tapestry • Routing mesh w/ built in proximity metrics • Location exploits locality (finds closer objects faster) • Finding supernodes • Supernode “publishes” cover set on brocade layer as locally stored objects • To route to node N, locate server on brocade storing N

  14. Brocade Summary • P2P systems assume uniformity • Extraneous hops through backbone to domains • Routing across congested stubs links • Constrain inter-domain routing • Remove unnecessary routing through stubs • Reduce expected inter-domain hops • Result: lower latency, less bandwidth utilization

  15. Appendix • Tapestry • Bloom filter

  16. Brief Tapestry • Suffix matching ( similar to Plaxton ) • Incrementally routing digital by digital 7598 B4F8 Msg to 4598 4598 9098 6789 B437 • Maximum hops : logb(N)

  17. Routing : Neighbor maps • A table with b*logb(N) entries • The i-th level neighbor share (i-1) suffix chunks • Entry( i, j ) • Pointer to the neighbor • “ j” + (i-1) suffix 0642

  18. Locating : basic procedure • 4 phrases locating • Map the Object ID to a “virtual” Node ID • Route the request to that node • Arrive the surrogate or“root for the object • Direct to the server 6234 <O:1234,S:B4F8> B234 F734 8724 Surrogate Routing Server : B4F8 Client : B4F8 1234

  19. Publishing : basic procedure • Similar to locating • Server send msg and pretends to locate the object • Find the surrogate node as the “root” for the Obj. • Save the related info there, such as <O,S> 6234 <O:1234,S:B4F8> B234 F734 8724 Surrogate Routing Server :B4F8 1234

  20. Insert a new node: basic procedure • Get an Node ID • Begin with a “Gateway node” G • Pretends to route to itself • Establish nearly optimal neighbor map during the “pseudo routing” by coping & Choosing nearest ones. • Go back and notify neighbors 6234 B234 F734 8724 Surrogate Routing Gateway node : B4F8 New node : 1234

  21. Bloom filter(1) •Set S •Query: is x in S? •If filter says no, x is not in S. •If filter says yes, x is probably in S. •Set is bitmap: 010110 •Sequence of hash functions f(x, i) –Independent on x, i –F(x,i) = 0 or 1 •If f(x,i) is 1 for i values: –0,2,3 not present –2,4 probably present

  22. Bloom filter(2) Procedure BloomFilter(set A, hash_functions, integer m) returns filter filter = allocate m bits initialized to 0 foreach ai in A: foreach hash function hj: filter[hj(ai)] = 1 end foreach end foreach return filter Procedure MembershipTest (elm, filter, hash_functions) returns yes/no foreach hash function hj: if filter[hj(elm)] != 1 return No end foreach return Yes

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