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 Introduction Bi-MCMAC Bi-MCMAC Extensions Extensions Simulations Simulations Throughput Throughput Fairness Fairness Transfer delay Transfer delay Conclusions Conclusions

3. Introduction A well-known problem of multihop ad hoc wireless networks is the hidden node problem 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 IEEE 802.11 MAC Protocol attempts to solve the problem by using RTS/CTS handshake But RTS collision and Exposed node problem are not completely solved. But RTS collision and Exposed 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 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 Hidden node When data packets travel in the same direction When data packets travel in the same direction 12345 senderreceiver RTS interference transmission hidden collision

6. Problem description (cont.) Exposed node Exposed node When data packets travel in opposite direction When data packets travel in opposite direction 12345 senderreceiver RTS interference no transmission transmission

7. Problem description (cont.) Capture effect Capture effect Unfairness can occur between different TCP flows Unfairness can occur between different TCP flows 12345 senderreceiver RTS interference transmission sender receiver hidden collision

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

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

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

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

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

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

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

16. Environmental parameters Data packet size: L d Control packet size: L c Maximum number of channels should not exceed L d /3L c 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 Strict sense Similar path and competition Similar path and competition General sense General sense Share the same channels regardless of their local contention 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 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 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 Subsequent data frame resolves the TCP DATA-ACK problem Simulations show that Simulations show that Throughput improved Throughput improved Lower transfer delay Lower transfer delay Good fairness Good fairness Its unfairness in the single-cell case is a minor disadvantage Its unfairness in the single-cell case is a minor disadvantage

31. Thank you !