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Selfish MAC Layer Misbehavior in Wireless Networks

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Selfish MAC Layer Misbehavior in Wireless Networks. Pradeep Kyasanur and Nitin H. Vaidya 2005 IEEE Reviewed by Dean Chiang. How is network contention resolved? . Distributed Contention Function (DCF) Relies on protocol adherence from all of the network.

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Selfish MAC Layer Misbehavior in Wireless Networks

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  1. Selfish MAC Layer Misbehavior in Wireless Networks Pradeep Kyasanur and Nitin H. Vaidya 2005 IEEE Reviewed by Dean Chiang

  2. How is network contention resolved? • Distributed Contention Function (DCF) • Relies on protocol adherence from all of the network. Ok everyone better wait the same amount! I’m transmitting guys! …What if I don’t want to…? You got it!

  3. Selfish Host Backoff = rand[1,1] Problem Definition Normal Host Backoff = rand[0,CW] t Normal Channel Usage t Channel Usage with a Selfish Host

  4. Problem Challenges • Difference between a small backoff and differing usage by each node? • Node channel conditions are different. A node can claim an idle channel.

  5. Solution • Modified MAC Protocol • Goal: retain performance of 802.11 while ensuring detection of misbehavior in a short interval • Assumptions: • Misbehaving senders only. Receivers are assumed to be trusted. • No collusion between sender and receiver

  6. Protocol Modifications - Backoff • Receiver assigns random backoff and sends it in the CTS and ACK. Receiver is in control.

  7. Protocol Modifications - Retransmission • Sender adds attempt number to RTS • Receiver estimates expected backoff from attempt number.

  8. Penalty Scheme • Penalize if: • B_actual < Alpha * B_expected (Alpha = 0.8) • Penalty • Add to next backoff by an amount proportional to deviation and then some. • Still not adhering? Identify as a selfish host. (Last W packets that deviated over total threshold T slots) • Receiver is in control. Misbehavior with backoff cannot be spoofed by senders.

  9. What happens after identification? • Possibilities • MAC Layer • Receiver exiles sender by not responding to RTS. • Network Layer • Network routes around host.

  10. Misdiagnosis • Receiver senses a busy channel from 2 hops away when sender does not. • Sender sends to receiver, receiver thinks sender did not adhere to assigned backoff. • Solution: receiver does not count a busy channel for transmission, only during overheard RTS/CTS.

  11. Results: Diagnostic Accuracy • Notes: • Low misdiagnosis rate • Does not fully resolve selfish behavior problem. Only alleviates high end of deviation. • Notice there is a threshold of misbehavior that can go undetected.

  12. Results: Throughput • Throughput comparison to 802.11 • Adheres closely to throughput of 802.11

  13. Results: Fairness • Fairness Index comparison to 802.11 • Fairness decreases with # of nodes • Fairness deviates more when background traffic is high (TWO-FLOW)

  14. Results: What about crafty clients? Correct Diagnosis % Protocol is worse at detecting adaptive misbehavior HOWEVER Throughput gain is not large because of penalty scheme

  15. Pros and Cons • Pros • Fast diagnosis, no need to collect tons of data • Low Misdiagnosis rate • Retains fairness and throughput of 802.11 • Reduces workaround potential • Cons • Additional overhead • Backwards compatibility • Spoofed MAC addresses

  16. Addendum: Optimal Threshold • Authors show a proof for an optimal threshold • Threshold T is a function of assigned back-off value and # of slots. • However, authors chose a static threshold in simulations. This suggests the data could be better.

  17. Discussion/Consideration • What does the police do? • Why did the government create a police force? • At what intrinsic layer does the government’s control end? http://www.thunderroadlaser.com/images/thunderimages/05_Police%20Badge%20-%2072dpi.jpg

  18. Discussion/Consideration • Is this really the best place to handle selfish behavior? Base Station PC, Driver Wireless Network Adapter Not Regulated by IEEE Regulated by IEEE Regulated by IEEE http://images.belkin.com/F6D3000/PRN1_F6D3000.jpg http://store.madtux.org/images/PC319a.jpg http://compuplus.com.mx/tienda/images/WAP54G.jpg

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