1. Backup Path Allocation Based on A Link Failure Probability Model in Overlay Networks Weidong Cui, Ion Stoica, and Randy H. Katz EECS, UC Berkeley {wdc, istoica, randy}@EECS.Berkeley.EDU

2. Motivation The Internet is actually a BIG overlay network. Link failures in an overlay network usually are not independent because they may share same links/nodes in the lower level network. Having two orthogonal service/communication paths (a primary path and a backup path) can improve service availability. This project studies the problem of how to find and set up two orthogonal paths based on a correlated link failure model in overlay networks.

3. A Link Failure Probability Model in Overlay Networks The link failure probability model has Single link failure probabilities Double link failure probabilities Assumption: probabilities are SMALL! Path failure probabilities Single path failure probability Double path failure probability How to obtain the link failure probabilities?

4. Backup Path Routing Algorithms Probability Cost Routing Algorithm Goal: find a backup path such that it minimizes the joint path failure probability given a shortest path as the primary path Probability cost for link used in the backup path is: Second Shortest Routing Algorithm Find a second shortest path as the backup path which is disjoint from the primary path

5. Backup Path Bandwidth Allocation Algorithms Duplicate Bandwidth Allocation Same bandwidth on backup paths as on primary paths Single-Link-Failure Bandwidth Allocation Allocate bandwidth on backup paths such that it can recover from a single link failure Zero Bandwidth Allocation A baseline for comparison.

6. Simulation Experiments Use GT-ITM to generate random network topology. Assume the link failures in the lower level network are independent. Calculate the link failure probabilities in the overlay network based on the link failure probabilities in the lower level network. Simulate the link failures in the lower level network

7. Results: Robustness

8. Results: Efficiency

9. Results: Fault Tolerance

10. Conclusion and Future Work Probability-cost routing algorithm and single- link-failure bandwidth allocation algorithm have good performance on robustness and efficiency. Probability-cost routing algorithm is fault tolerant to noise of overlay link failure probabilities. Future Work Test the algorithms both in NISTNet emulation testbed and in a real overlay network Study how to obtain overlay link failure probabilities in real networks.