1. Distributed Monitoring and Aggregation in Wireless Sensor Networks INFOCOM 2010 Changlei Liu and Guohong Cao Speaker: Wun-Cheng Li

2. Outline Introduction Goal Distributed Poller Selection Algorithms ▫ Randomized Algorithm ▫ Deterministic Algorithm ▫ Hybrid Algorithm Performance evaluation Conclusion 2

3. Introduction As sensor nodes usually operate in an unattended harsh environment, they are prone to failure and may run out of battery To make sensor network reliable as well as adaptable, sensor status has to be closely monitored ▫ liveness ▫ density estimation ▫ residue energy 3

4. Introduction In distributed systems, the only way to learn the status of a node is through receiving messages from the node ▫ Poller-Pollee structure has been widely used for network management 4

5. Introduction Compared with the wired networks, designing monitoring mechanisms for sensor networks has more challenges. ▫ Dynamic topology ▫ sensors need to self-organize themselves into a monitoring architecture 5

6. If the number of pollers is too small then false alarm rate may increase as a consequence ▫ pollees will be too far away from the poller Problem 6

7. To reduce the monitoring overhead, we take the hop- by-hop aggregation opportunities in sensor networks. Problem 7 poller s ： aggregation ratio

8. Goal Strike a balance between the number of Pollers and false alarm rate ▫ Minimum Poller Selection 8

9. Two widely used operational modes of the poller- pollee structure System model 9 Poller Pollee 2reply/s 2poll/s Poller Pollee 2reply/s

10. System model The poller-pollee based monitoring. ▫ Failure rate f i 10 T d ： detection time t ： polling time interval

11. Distributed Poller Selection Algorithms Randomized Algorithm ▫ Each node elects itself as a poller with probability ρ 11 1 2 9 10 3 7 5 4 6 11 8 2 9 10 3 7 5 4 11 8 6 1 poller pollee Unlabeled node

12. Distributed Poller Selection Algorithms Deterministic Algorithm ▫ Uses two parameters k 1, k 2 to guide a better distribution of poller and pollee ▫ No two pollers are less than k 1 hops away from each other ▫ No pollee is more than k 2 hops away from its poller. 12

13. Distributed Poller Selection Algorithms Deterministic Algorithm ▫ k 1 =k 2 =1 13 1 2 9 10 3 7 5 4 6 11 8 poller pollee Unlabeled node 2 9 10 7 5 4 6 11 8 1 3 2 9 10 7 4 6 8 3 5 11 1

14. Distributed Poller Selection Algorithms Hybrid Algorithm ▫ k 1 =k 2 =1 14 1 2 9 10 3 7 5 4 6 11 8 poller pollee Unlabeled node 3 1 9 10 7 5 4 11 8 2 6 1 9 10 7 5 4 6 11 8 2 3 1 9 10 7 4 6 8 2 3 5 11

15. Performance evaluation C++ 15 Parameter Settings Randomly Deployed region20 × 20 Nodes1000~1500 transmission range1 Failure rate f i 0.05 Detection time T d 2t2t

16. Performance evaluation 16

17. Performance evaluation 17

18. Performance evaluation 18 Randomized algorthmHybrid algorthm

19. Performance evaluation 19 Randomized algorthmHybrid algorthm

20. Performance evaluation 20

21. Conclusions This paper proposed a fully distributed algorithms to select the minimum number of pollers while bounding the false alarm rate. Simulations results the hybrid algorithm can reduce the message overhead significantly 21

22. Thank you! 22