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Sustaining Cooperation in Multi-Hop Wireless Networks

Sustaining Cooperation in Multi-Hop Wireless Networks. Ratul Mahajan, Maya Rodrig , David Wetherall, John Zahorjan University of Washington. Multi-hop networks are real. Incentives to free-ride. Personal bandwidth maximization Power conservation It’s easy! You’ll get away with it.

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Sustaining Cooperation in Multi-Hop Wireless Networks

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  1. Sustaining Cooperation in Multi-Hop Wireless Networks Ratul Mahajan, Maya Rodrig, David Wetherall, John Zahorjan University of Washington

  2. Multi-hop networks are real Sustaining Cooperation in Multi-Hop Wireless Networks

  3. Incentives to free-ride • Personal bandwidth maximization • Power conservation • It’s easy! • You’ll get away with it Sustaining Cooperation in Multi-Hop Wireless Networks

  4. The impact of free-riding • Using multi-hop routes improves throughput • Per-node delivery rate improvement of 25% on average • Free-riders gain at the expense of cooperative nodes • Free-riders’ throughput increased 4X • Cooperative nodes’ throughput decreased by 25% • In our testbed, 60% chance of network partition with only 20% free-riding nodes Sustaining Cooperation in Multi-Hop Wireless Networks

  5. Challenge in detecting free-riding Wireless range is not a simple function of distance and can be asymmetric Sustaining Cooperation in Multi-Hop Wireless Networks

  6. Free-riding Lack of connectivity Challenge in detecting free-riding Free-rider pretends to be out of range and drops the packet Sustaining Cooperation in Multi-Hop Wireless Networks

  7. Free-riding Lack of connectivity Challenge in detecting free-riding A cooperative node does not receive the packet Sustaining Cooperation in Multi-Hop Wireless Networks

  8. Free-riding Lack of connectivity Challenge in detecting free-riding Hard to differentiate the two cases given asymmetric, lossy links Sustaining Cooperation in Multi-Hop Wireless Networks

  9. Catch • Two main challenges: • Determining when a node is free-riding • Getting its neighbors to agree to punish it • Solution: • Detecting wireless connectivity • Monitoring packet relaying behavior • Punishing selfish misbehavior Sustaining Cooperation in Multi-Hop Wireless Networks

  10. Proposed solutions Catch Deployed protocols Tradeoffs between approaches Overhead Protection Applicability Sustaining Cooperation in Multi-Hop Wireless Networks

  11. 1. Detecting wireless connectivity • Nodes want to connect to at least one neighbor • Send anonymous connectivity probes Sustaining Cooperation in Multi-Hop Wireless Networks

  12. 2. Monitoring packet relaying behavior • Watchdog: relayed packets should be overheard [Marti et al, 2000] • Use statistical tests to compare success rate of anonymous probes and data packets Sustaining Cooperation in Multi-Hop Wireless Networks

  13. 3. Punishing selfish misbehavior • Leverage the cooperative majority to collectively deter free-riders • Use anonymous probes, one-way hash functions, and signaling by absence Sustaining Cooperation in Multi-Hop Wireless Networks

  14. 184 ft Our testbed • In-building experimental testbed • 15 802.11b nodes • 10 APs on same floor • A real wireless setting • Many asymmetric links • Frequent packet losses • ~20% loss rate Sustaining Cooperation in Multi-Hop Wireless Networks

  15. Catch evaluation • Speed and accuracy of detection • Effectiveness of isolation • Overhead Sustaining Cooperation in Multi-Hop Wireless Networks

  16. 1 2 3 Epochs to Detection Total Drop Rate Speed and accuracy of detection client server • Rapid detection with few false positives • Detection is quicker for more egregious free-riding • 1 false positive in 10 hrs across testbed Sustaining Cooperation in Multi-Hop Wireless Networks

  17. Effectiveness of isolation Isolation period Elapsed Time (minutes) • Isolation is successful despite asymmetric, lossy links • Throughput of free-riders is curbed Sustaining Cooperation in Multi-Hop Wireless Networks

  18. Overhead • Bandwidth: Only 24Kbps per node in our testbed • CPU: Maintain packet counters, but no crypto operations per data packet Sustaining Cooperation in Multi-Hop Wireless Networks

  19. Future work: Signal strength attacks • Physical layer hints can undermine anonymity • Catch already offers some protection Sustaining Cooperation in Multi-Hop Wireless Networks

  20. Conclusion • Catch is a lightweight solution to deter free-riding • Modest overheads • No restrictive requirements • Key insights: • Using anonymous probes to detect connectivity and communicate via free-riders • Leveraging cooperative majority to detect and punish free-riders • Testbed evaluation shows that Catch is effective in a real wireless environment Sustaining Cooperation in Multi-Hop Wireless Networks

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