1. Enforce Collaboration in Mobile Ad Hoc Network Ning Jiang School of EECS University of Central Florida njiang@cs.ucf.edu

2. Outline Mobile Ad Hoc Network Existing Techniques DSG Approach Conclusion

3. Mobile Ad Hoc Network A collection of devices equipped with wireless communications and networking capability Devices heterogeneity Palm, laptop, mobile phone, etc. Infrastructureless Self-organizing and adaptive Nodes relay data packets for each other Energy critical

4. Mobile Ad Hoc Network

5. Mobile Ad Hoc Network Applications In the office Traveling Wireless home network Location/context based services Battlefield

6. Collaboration in Mobile Ad Hoc Network Routing Dynamic Source Routing Routing Request Routing Reply Packet forwarding

7. Detecting Selfish Nodes Marti et al. ACM MOBICOM, 2001 Watchdog Each node in promiscuous mode Each node verifies whether its downstream node forwards packets Packet loss threshold Inform the source node of the misbehaving node Path Rater Nodes select paths without selfish nodes

8. Drawbacks of the Approach No punishment to selfish nodes Each packet should be monitored Slow propagation of warning information Selfish nodes have no chance to rejoin

9. Packet Purse Model Hubaux et al. IEEE/ACM Workshop on Mobile Ad Hoc Networking and Computing Reward the packet forwarding service The originator loads each packet with a number of “nuggets” Each forwarding node acquires one or more nuggets Packets with insufficient nuggets are discarded Selfish nodes are detected and fined Relies on a temper resistant security module Cryptographic techniques are applied to prevent abuse

10. Packet Purse Model Advantages Secure Nodes are motivated to collaborate Selfish nodes are punished Node enjoin enabled Disadvantages Still monitor each packet Generally, nodes have no knowledge of selfish nodes Cryptographic overhead

11. CONFIDANT Protocol Birds and Mobile Ad Hoc Network Sucker birds Cheating birds Grudger birds Interesting observation: starting with a majority of cheating birds, grudger birds finally win over Can Mobile Ad Hoc nodes also act like grudger birds? – Yes!!

12. CONFIDANT Protocol Sonja et al. MOBIHOC 2002 Monitor Neighbor watch Reputation System Evaluates selfish behaviors

13. CONFIDANT Protocol Trust Manager Sends alarms to “friend” nodes A friend list Checks the trustiness of incoming alarms Several levels of trustiness Maintains a trust table of nodes Path Manager Path ranking and management

14. CONFIDANT Protocol Drawbacks Only informs friends about the malicious nodes Control overhead Need to manage complex trust relationships Rejoin not addressed

15. DSG Approach Main idea Let the cheating bird inform others! Assumptions Omni-directional antenna Security Module (smart card) There are TCP traffics

16. DSG Approach Finite State Model Normal Detecting Penalized Rejoin States stored in the security module

17. DSG Approach – Detecting Mechanism Initially all nodes in Normal state Source monitors its TCP traffic No acknowledgement -> Detecting immediate downstream node Two possibilities: Neighboring node forwards packets -> detecting propagate Neighboring node discards packets -> Marked as penalized, does not forward source node!

18. DSG Approach – Selfish Node Avoidance Selfish nodes are recognized and their states switched to penalized Security Module marks DSR Routing packets Penalized bit Source node picks the best path

19. DSG Approach – Node Rejoin Selfish nodes switch to rejoin state after certain timeout A rejoining node broadcasts to inform its neighbors Each neighboring node monitors the target rejoining node The node is switched back to Normal state if it forwards enough packets

20. DSG Approach - Analysis On-demand selfish node detection Saves energy Instant selfish node avoidance Minimum control packets transmission No need to inform nodes about a selfish node Node rejoin supported

21. DSG Approach - FSM Penalize packet received Normal Rejoin Detecting Penalized Too many packets lost, or detecting packet received Enough packets forwarded, or timeout Penalize packet received timeout Random time, or selfish node detected

22. Experiment Preliminary experimental results illustrate a 60% increase in throughput under 30% malicious nodes configuration Most of the TCP sessions closed

23. Conclusion Collaboration is vital to the good performance of Mobile Ad Hoc network Existing techniques cannot solve the problem well enough DSG Approach incurs minimum overhead, requires minimum energy consumption