1. Highly-Resilient, Energy-Efficient Multipath Routing in Wireless Sensor Networks Computer Science Department, UCLA International Computer Science Institute, Berkeley ACIRI, Berkeley

2. About Periodic low-rate flooding of data in order to allow recovery from failure. Multipaths for energy efficient recovery Disjoint multipath scheme Braided multipath scheme Braided multipaths are viable alternative for energy-efficient recovery from isolated and patterned failures

3. Introduction Directed Diffusion Earlier work has explored the design of mechanisms for single-path routing in sensor networks To route around failed nodes, this work assumed periodic, low-rate, flooding of events that enabled local re-routing around failed nodes

4. Introduction Multipath routing Disjoint multipath Braided multipath Resilience Maintenance Overhead Evaluating the two mechanisms: isolated node failures and patterned failures

5. Direct Diffusion Directed Diffusion

6. Direct Diffusion Using directed diffusion to perform energy-efficient and robust dissemination of surveillance data samples from sources to sinks Low rate samples Path reinforcement Recovery from failure along reinforcement path The problem is low-rate flooding scheme

7. Direct Diffusion Direct Diffusion for energy-efficient data samples from source to sinks.

8. Multipath Routing Classic Multipath Routing usage Using multipath routing in this paper Primary path Construct and maintain a small number of alternate paths (without periodic flooding) When primary path is set up, alternate paths also sets up multipaths which data is send low-rate No network wide flooding needed

9. Disjoint Multipaths Small number of alternate paths that are node-disjoint with the primary path, and with each other How do we realize node disjoint multipaths using localized information alone, and not relying on global topology information? Primary and alternate path reinforcement Localized disjoint multipaths are differ from idealized multipaths

10. Construction of Localized Disjoint Paths

11. Braided Multipaths Disjoint multipaths can be energy inefficient Alternate paths in a braid are partially disjoint from the primary path, not completely node-disjoint For each node on the primary path, find the best path from source to sink that does not contain that node All paths are called idealized braided

12. Braided Multipaths Localized technique for constructing braids. Nodes send reinforcement to route neighbours. The alternate paths can rejoin the primary path

13. Braided Multipaths

15. Qualitative Comparison Energy/resilience tradeoffs of the two multipath schemes The energy cost of alternate disjoint paths depends on the network density The resilience of these multipaths to failure (isolated failures and patterned failures) Disjoint paths give us independence, but the failure of a single node on each alternate path results in the failure of the multipath.

16. Qualitative Comparison By contrast, in braided multipaths, the various alternate paths are not independent, and a combination of failures on the primary path could sever all alternate paths How much additional energy must one expend in order to increase resilience by a fixed amount? How does the energy/resilience tradeoff vary with density or with the extent and frequency of patterned failures? How closely do the localized schemes approximate their idealized counterparts?

17. Evaluation Methodology Maintenance overhead Resilience Failure models for which we evaluated the resilience of our multipath mechanisms

18. Isolated Failures Patterned Failures Failures

19. Details of Methodology The idealized and localized constructions of disjoint and braided multipath in ns-2 Uniformly distributing a number of sensor nodes on a finite plane of dimension 400 meters square Node transmission radius: 40 meters Density The spatial separation between source and sink (represented by the length of the shortest-hop path between the two

20. Details of Methodology The failure probability for isolated failures pi the arrival rate of patterned failures is lamda p Radius of patterned failures R Each run of our experiment corresponded to one choice of number of nodes N and and spatial separation between source and sink d In each run, we randomly selected a large number of source-sink pairs separated by d hops

21. Simulation Results Impact of failure probability on resilience: 400 nodes, 6- hop source-sink separation

22. Simulation Results Resilience to Isolated Failures

23. Simulation Results The impact of density and source-sink separation on resilience to isolated failure

24. Simulation Results Resilience to Patterned Failures

25. Simulation Results The impact of density and source-sink separation on resilience to patterned failure

26. Simulation Results Maintenance Overhead - Density

27. Simulation Results Maintenance Overhead – Path Length

28. Conclusions Multipath routing for energy-efficient recovery No need network-wide flooding for path discory on failure Disjoint and braided multipaths are similar, but braided multipaths have about %50 higher resilience to isolated failures It is harder to design localized energy-efficient mechanisms for constructing disjoint alternate paths, because the localized algorithms lack the information to find low latency disjoint paths Increasing the number of disjoint paths does increase the resilince but this needs higher energy cost.

29. Questions ?