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Selfish MAC Layer Misbehavior in Wireless Networks

Selfish MAC Layer Misbehavior in Wireless Networks. Nitin Vaidya and Pradeep Kyasanur. ECE 299, Karthik Balasubramanian February 8, 2007. The problem: a game theory approach. Node B. Node A. Need incentive structure to prevent cheating. Review: contention schemes.

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Selfish MAC Layer Misbehavior in Wireless Networks

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  1. Selfish MAC Layer Misbehavior in Wireless Networks Nitin Vaidya and Pradeep Kyasanur ECE 299, Karthik Balasubramanian February 8, 2007

  2. The problem: a game theory approach Node B Node A Need incentive structure to prevent cheating

  3. Review: contention schemes Point Contention Function (PCF) • Centralized controller required • No ad-hoc networks • 802.11 optional feature Distributed Contention Function (DCF) • Suitable for ad-hoc networks • Suitable for fluctuating number of nodes and hosts • Uses Carrier Sense Multiple Access/Collision Avoidance • What paper focuses on

  4. B1=20 B1=15 B1=0 S1 Transmit wait CW=31 S2 wait Transmit B2=25 B2=10 B2=10 Review: collision avoidance and backoff • Randomly choose backoff value B in range [0,CW] • CW is the Contention Window • Count down backoff by 1 every idle slot Source: Pradeep Kyasanur and Nitin Vaidya, UIUC

  5. Cheating What if I always choose B=1? B1 = 1 B1 = 1 Misbehaving node Transmit Transmit Well-behaved node wait wait B2 = 20 B2 = 19 Good for me, bad for you Source: Pradeep Kyasanur and Nitin Vaidya, UIUC

  6. Goal 1: detect cheating • Method: Sender backoff data collection • Measure actual backoff durations of individual nodes • If backoff from skewed distribution, cheating suspected • Method weaknesses • Cheating cannot be immediately diagnosed • High chance for misdiagnosis if small sample size • Requires significant computation Current 802.11 not sufficient for good detection

  7. B Sender S CTS ACK(B) DATA RTS RTS Receiver R 802.11 modification: B selected by receiver 1. R provides backoff B to S in ACK B selected from [0,CWmin] 2. S uses B for backoff Source: Pradeep Kyasanur and Nitin Vaidya, UIUC

  8. Backoff Sender S ACK(B) RTS Receiver R Bobsr Detection • Receiver counts number of idle slots Bobsr Condition for detecting deviations: Bobsr <  B 0 <  <= 1 Source: Pradeep Kyasanur and Nitin Vaidya, UIUC

  9. Goal 2: punish cheating • Punishment • Must be effective deterrent • Must not hinder overall throughput • If Σ(deviations) > threshold, cheater identified • Pass on to higher layers: “telling Daddy on you” • Appropriate action can be taken

  10. Actual backoff < B Sender S ACK(B) CTS ACK(B+P) DATA RTS Receiver R Bobsr Punishment • When Bobsr < B, penalty P added • P proportional to  B– Bobsr • Total backoff assigned = B + P Source: Pradeep Kyasanur and Nitin Vaidya, UIUC

  11. Misbehaving Node Simulation Setup Source: Pradeep Kyasanur and Nitin Vaidya, UIUC

  12. Diagnosis Correct Diagnosis Percentage Misdiagnosis Percentage of Misbehavior (of misbehaving node) Source: Pradeep Kyasanur and Nitin Vaidya, UIUC

  13. 802.11 Avg. with penalty Proposed Scheme Throughput (Kbps per node) Avg. with 802.11 Percentage of Misbehavior Throughput Source: Pradeep Kyasanur and Nitin Vaidya, UIUC

  14. Proposed Scheme Throughput (Kbps per node) 802.11 Number of sender nodes Throughput with no misbehavior Source: Pradeep Kyasanur and Nitin Vaidya, UIUC

  15. Discussion/Limitations • Requires 802.11 modification for efficient detection • Breakdown at high cheating levels • No enforcement mechanism presented • Questions?

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