Brocade: Landmark Routing on Overlay Networks

1. Brocade: Landmark Routing on Overlay Networks To P2P or not to P2P? http://www.cs.berkeley.edu/~duan/prjs/cs262/ CS262A Fall 2001 Yitao Duan and Ling Huang duan@cs.berkeley.edu, hlion@newton.berkeley.edu

2. Motivation • Problems with existing P2P Network • Constrained by the theoretical approach adopted, nodes are treated uniformly[1, 2, 3, 4] • Routing algorithms are decoupled from underlying topology and node capability • Result: inefficient routing • Reality: Nodes are not born equal • Bandwidth, Connectivity, Storage, Processing Power. • Administrative Constraints

3. Brocade: Discrimination Justified • A philosophy: A system is more efficient when it is organized – e.g., IP routing on Internet • 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. • Construct a hierarchy out of flat network

4. Brocade Original Route Brocade Route AS-3 AS-1 S D AS-2 P2P Network Brocade Architecture

5. Overlay nodes are grouped by their supernodes – Cover Set • Supernodes treat their overlay nodes as objects that they possess • Routing on Brocade => Object Location. Use your favorite • mechanism: Tapestry[1], CAN[3], Chord[2], Pastry[4] … • Message filtering: only send inter-domain messages to Brocade.

6. Case Study - Brocade On Tapestry • Tapestry: A novel wide-area fault-tolerant location and routing infrastructure[1] • Construction • Gateway routers or machines close by as supernodes • Existing connections among supernodes as Brocade links • Routing: object location Tapestry style • Each supernode advertises the IDs of overlay nodes in its cover set as IDs of objects it “stores”. • Destination’s supernode can be found using Tapestry’s object location mechanism • Remaining issue: How to get onto Brocade?

7. Get onto the Super Highway • 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

8. Yes Ordinary Tapestry Routing Destination is in my cover set? No Send to supernode • 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

9. Simulation Results Fig 1. Hops Based RDP Fig 2. Aggregate bandwidth used per message

10. Optimizing Object Location on Brocade • Routing latency could be high if latencies on Brocade links are high and object • location on Brocade is not optimized(Fig 3) • Optimization: Bloom Filter - Membership query and group ID problem Fig 3. Weighted latency RDP w/o optimization Fig 4. Weighted latency RDP with Bloom Filter Brocade link latency/Ordinary link latency = 8 : 1

11. Conclusion and Future work • Brocade: powerful idea that can achieve near optimal performance • General enough to be applied to other (P2P) networks • Future research: • Study the effect of different supernodes selection and distribution • Further optimization of object location on Brocade overlay • Latent Brocade • Brocade benefits from aggregation of info • Bias some nodes in the network so they will be favored by others while selecting route - an implicit Brocade

12. References [1] ZHAO, B. Y., KUBIATOWICZ, J. D., AND JOSEPH, A. D. Tapestry: An infrastructure for fault-tolerant wide-area location and routing. Tech. Rep. UCB/CSD-01-1141, University of California at Berkeley, Computer Science Division, April 2001. [2] STOICA, I., MORRIS, R., KARGER, D., KAASHOEK, M. F., AND BALAKRISHNAN, H. Chord: A scalable peer-to-peer lookup service for internet applications. In Proceedings of SIGCOMM (August2001), ACM. [3] RATNASAMY, S., FRANCIS, P., HANDLEY, M., KARP, R., AND SCHENKER, S. A scalable content-addressable network. In Proceedings of SIGCOMM (August 2001), ACM. [4] ROWSTRON, A., AND DRUSCHEL, P. Pastry: Scalable, distributed object location and routing for large-scale peer-to-peer systems. In Proceedings of IFIP/ACM Middleware 2001 (November 2001). [5] TSUCHIYA, P. F. The landmark hierarchy: A new hierarchy for routing in very large networks. Computer Communication Review 18, 4 (August 1988), 35–42.