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Tianbo Kuang and Carey Williamson Department of Computer Science University of Calgary

A Bidirectional Multi-channel MAC Protocol for Improving TCP Performance on Multihop Wireless Ad Hoc Networks. Tianbo Kuang and Carey Williamson Department of Computer Science University of Calgary ACM MSWiM 2004 (Modeling, Analysis and Simulation of Wireless and Mobile Systems). Outline.

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Tianbo Kuang and Carey Williamson Department of Computer Science University of Calgary

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  1. A Bidirectional Multi-channel MAC Protocol for Improving TCP Performance on Multihop Wireless Ad Hoc Networks Tianbo Kuang and Carey Williamson Department of Computer Science University of Calgary ACM MSWiM 2004 (Modeling, Analysis and Simulation of Wireless and Mobile Systems)

  2. Outline • Introduction • Bi-MCMAC • Extensions • Simulations • Throughput • Fairness • Transfer delay • Conclusions

  3. Introduction • A well-known problem of multihop ad hoc wireless networks is the hidden node problem • IEEE 802.11 MAC Protocol attempts to solve the problem by using RTS/CTS handshake • But RTS collisionandExposed node problem are not completely solved.

  4. Introduction (cont.) • For a transport-layer protocol working above RTS/CTS based protocol, the problems described above will affect the network performance

  5. Problem description • Hidden node • When data packets travel in the same direction transmission RTS collision 1 2 3 4 5 sender receiver interference hidden

  6. Problem description (cont.) • Exposed node • When data packets travel in opposite direction transmission 1 2 3 4 5 RTS sender receiver interference no transmission

  7. Problem description (cont.) • Capture effect • Unfairness can occur between different TCP flows hidden transmission RTS collision 1 2 3 4 5 interference sender sender receiver receiver

  8. Related works • C. Cordeiro, S. Das, and D. Agrawal. COPAS: Dynamic contention-balancing to enhance the performance of TCP over multi-hop wireless networks. In Proceedings of ICCCN’02, pages 382–387. Miami, FL, USA, October 2002.

  9. Goal • Design a multi-channel MAC protocol to reduce TCP DATA-DATA collision • Use bidirectional RTS/CTS channel reservations to reduce TCP DATA-ACK contention

  10. Bi-MCMAC • Static multihop wireless ad hoc networks • One control channel, K-1 data channels • Single transceiver • Extends the RTS/CTS handshake to do the bidirectional channel reservation • CRN (Channel Reservation Notification) control frame

  11. Bi-MCMAC (cont.) • Channel state is included in RTS/CTS frames • CRN frame is sent after the sender receives CTS, containing the channel and reservationduration information • Subsequent data frame sent by receiver is indicated as MAC-layer ACK

  12. Bi-MCMAC(cont.) Announce channel 7 and CRN NAV Channel: 1,5,7,11 Indicated as MAC-layer ACK Channel: 2,6,7,11 Choose 7

  13. Extension • Head-of-Line (HOL) blocking • If the first packet in the buffer is not destined to the sender • Per-neighbor queue • Multi-channel Hidden Terminal Problem • Receiver always selects the channel used for the last successful transmission

  14. Further work • Heterogeneous channel rates • If all the data channel are 54Mbps and the control channel is 1Mbps, then the control channel may become congested

  15. Simulations • Throughput • Fairness • Strict sense • General sense • Transfer delay • 100 nodes • 300 seconds, 50 repetition • Chain topology • Grid topology • Random topology • Sparse (500*500) • Dense (250*250)

  16. Environmental parameters Data packet size: Ld Control packet size: Lc Maximum number of channels should not exceed Ld/3Lc Ex: 1000/3*64

  17. Throughput in chain topology

  18. Collisions in chain topology

  19. Throughput in grid topology

  20. Throughput in sparse random topology

  21. Throughput in dense random topology

  22. Fairness • Strict sense • Similar path and competition • General sense • Share the same channels regardless of their local contention Jain’s Fairness Index (FI)

  23. Strict sense fairness

  24. General sense fairness in grid topology

  25. General sense fairness in sparse random topology

  26. General sense fairness in dense random topology

  27. Web transfer time

  28. Web transfer time (cont.)

  29. Conclusions • The Bi-MCMAC protocol is explicitly designed to improve TCP performance over a static multihop wireless ad hoc network • Bi-MCMAC extends IEEE 802.11 RTS/CTS handshake to do bidirectional channel reservations

  30. Conclusions (cont.) • Subsequent data frame resolves the TCP DATA-ACK problem • Simulations show that • Throughput improved • Lower transfer delay • Good fairness • Its unfairness in thesingle-cell caseis a minor disadvantage

  31. Thank you !

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