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Selfish MAC Layer Misbehavior in Wireless Networks

Selfish MAC Layer Misbehavior in Wireless Networks. Author: Pradeep Kyasanur and Nitin H. Vaidya Some slides are borrowed from the author and others Reviewed by Xuan Bao. 2. 3. 4. 1. Problem Definition. Proposed Methods. Modification. Simulation Result. Index.

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Selfish MAC Layer Misbehavior in Wireless Networks

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  1. Selfish MAC Layer Misbehavior in Wireless Networks Author: Pradeep Kyasanur and Nitin H. Vaidya Some slides are borrowed from the author and others Reviewed by Xuan Bao

  2. 2 3 4 1 Problem Definition Proposed Methods Modification Simulation Result Index Company Logo

  3. Review of Details about DCF Company Logo

  4. Calculation of Contention Window (CW) • A host with data to transmit selects a random backoff counter from range [0, CW] • The backoff counter will decrease by one when the channel is idle for one time slot. • A host may access the channel when the counter reaches 0. • If a transmission is successful, CW is reset to the minimum value. Otherwise, CW is doubled, subject to the maximum value. Company Logo

  5. Opportunities of Misbehavior Using analogy, the contention process is like throwing a dice and the competitor with the least points gets channel access. Fairness is achieved because the loser in earlier contention will decrease their backoff counter and therefore has better chance to win the contention later. Company Logo

  6. Selfish Host Backoff = rand[1,1] Opportunities of Misbehavior A selfish host can choose a small backoff counter by: 1 Choosing the backoff counter from a smaller region than [0, CW] 2 Do not increase CW after collision Normal Host Backoff = rand[0,CW] Company Logo

  7. The Reason Behind Misbehavior Opportunities • Senders, while participating in contention, maintain the CW value by themselves. Therefore, they are in fact both the regulator and participator in this game. Company Logo

  8. Conclusion on Definition of Misbehavior in This Paper • In this paper, selfish misbehavior only consider the sender’s behavior intending to obtain unfair share of channel access. • Does not consider high layer solutions. • Does not consider malicious attacks. Company Logo

  9. 2 3 4 1 Problem Definition Proposed Methods Methods Simulation Results Index Company Logo

  10. Basic Frame • The receiver calculates and assign backoff counter to senders. • The receiver monitors the time interval between ACK and the next RTS. It identifies misbehavior based on the deviation between this interval and the assigned backoff counter. Company Logo

  11. B Sender S CTS ACK(B) DATA RTS RTS Receiver R Illustration Graph • R provides backoff B to S in ACK • S uses B for backoff • NewBackoff = f(backoff, ID, attempt)*CW Company Logo

  12. Penalty Scheme • Penalty is introduced in two time scale: per transmission and for the last w transmissions. Company Logo

  13. Penalty Scheme • For each transmission, a penalty proportional to the deviation D is added to the next backoff counter. • D = max (a*Bexp – Bact, 0) (misdiagnose) • For nodes keeps deviating more than a threshold T for the last W transmissions. • Further punishment such as refusal of accepting further packets. Company Logo

  14. Tradeoff Here • Choice of parameters as factor a, threshold T. • Misdiagnose may lead to unwanted performance degrading especially when refuse accepting further transmission or drop packets. Company Logo

  15. 2 4 1 3 Problem Definition Proposed Methods Modifications Simulation Result Index Company Logo

  16. Problems and Consequence • Problem: • Receiver may sense the channel under a different status than the sender. • Consequence: • Unjustified penalty to well behaved nodes. Company Logo

  17. Scenario • Classic Hidden Terminal Scenario S reduces its backoff counter now, which will be considered as misbehavior later. M Y S D X K Company Logo

  18. Solution • The receiver only classifies a slot to be busy when an overheard RTS/CTS has reserved the slot or a packet is being received. • Assumptions behind this: Deep carrier sensing. Carrier sensing range = 2 * Communication range Company Logo

  19. 2 1 4 3 Problem Definition Proposed Methods Modifications Simulation Results Index Company Logo

  20. Proposed Scheme Throughput (Kbps \ node) 802.11 Number of sender nodes Throughput – no misbehavior

  21. Correct Diagnosis Percentage Misdiagnosis Percentage of Misbehavior (of misbehaving node) Persistent Misbehavior -Diagnosis Accuracy

  22. 802.11 Avg. with proposed scheme Proposed Scheme Throughput (Kbps) Avg. with 802.11 Percentage of Misbehavior Persistent Misbehavior- throughput

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