1. Brocade: Landmark Routing on Overlay Networks
To P2P or not to P2P?
CS262A Fall 2001
Yitao Duan and Ling Huang

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

5. Message filtering: only send inter-domain messages to Brocade.
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. 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
Destination is in my cover set?
Send to supernode
Ordinary Tapestry Routing No
Yes

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