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Chih-He Chiang, Wanjiun Liao, Tehuang Liu, Iam Kin Chan, and Hsi-Lu Chao

Adaptive Downlink and Uplink Channel Split Ratio Determination for TCP-Based Best Effort Traffic in TDD-Based WiMAX Networks. Chih-He Chiang, Wanjiun Liao, Tehuang Liu, Iam Kin Chan, and Hsi-Lu Chao National Taiwan University

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Chih-He Chiang, Wanjiun Liao, Tehuang Liu, Iam Kin Chan, and Hsi-Lu Chao

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  1. Adaptive Downlink and Uplink Channel Split Ratio Determination for TCP-Based Best Effort Traffic in TDD-Based WiMAX Networks Chih-He Chiang, Wanjiun Liao, Tehuang Liu, Iam Kin Chan, and Hsi-Lu Chao National Taiwan University IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, VOL. 27, NO. 2, FEBRUARY 2009

  2. Outline • Introduction • Adaptive bandwidth allocation for DL and UL • Simulation • Conclusion

  3. Introduction

  4. Introduction • To determine the ratio of downlink to uplink bandwidth capacities between the BS and SSs is a challenge. • The last mile access for residential users tends to be asymmetric • more demands on downloading and less on uploading. • An equal split between the uplink and downlink channels may lead to inefficient bandwidth utilization. • Ex: TCP traffic

  5. BS BS Data Ack Data Ack SS SS Introduction_ Goal ?

  6. Adaptive bandwidth allocation for DL and UL • Overview • Bandwidth Asymmetry Ratio for TCP over a Direct Link • Bandwidth Asymmetry Ratio for TCP over WiMAX • Adaptive Channel Split Ratio Adjustment Mechanism

  7. Adaptive bandwidth allocation for DL and UL_ Overview asymmetry ratio k for one-way TCP transfers the average delay for an SS sending twoconsecutive packetsout from the queue derive the asymmetryratio for downloading users, denoted by ηd derive derive

  8. Adaptive bandwidth allocation for DL and UL_ Overview derive derive Total number of time slots allocated for downlink channel Total number of time slots allocated for uplink channel (do not contain contention slots) Total number of time slots allocated for uplink channel (contain contention slots) derive Total number of time slots allocated for downlink channel

  9. Adaptive bandwidth allocation for DL and UL

  10. Adaptive bandwidth allocation for DL and UL_ Bandwidth Asymmetry Ratio for TCP over a Direct Link The downlink channel capacity in terms of bps ÷ The size of one TCP data packet in terms of bits derive asymmetry ratio k for one-way TCP transfers K≧1, TCP operates normally

  11. Adaptive bandwidth allocation for DL and UL_ Bandwidth Asymmetry Ratio for TCP over WiMAX asymmetry ratio k for one-way TCP transfers d is the delayed ACK parameter (i.e., sending one ACK packet per d data packets) the average delay for an SS sending two consecutive packets out from the queue the asymmetryratio for downloading users, denoted by ηd The number of downloading TCP transfers

  12. Adaptive bandwidth allocation for DL and UL BS BS Data Ack Data Ack SS SS

  13. Adaptive bandwidth allocation for DL and UL _ Bandwidth Asymmetry Ratio for TCP over WiMAX One slot time in terms of sec Total number of time slots

  14. Adaptive bandwidth allocation for DL and UL 2 1 3 4 2+12 * +2 +12 Ex: 2

  15. Adaptive bandwidth allocation for DL and UL _ Bandwidth Asymmetry Ratio for TCP over WiMAX The goal is to make ηd ≤ 1 and ηu ≤ 1.

  16. Adaptive bandwidth allocation for DL and UL derive

  17. Adaptive bandwidth allocation for DL and UL derive

  18. Adaptive bandwidth allocation for DL and UL

  19. Adaptive Channel Split Ratio Adjustment Mechanism BS ndSS and nuSS SS SS SS SS • Step1: • BS retrieves the information about ndSS and nuSS • Step2: • Ensure that the bandwidth asymmetry ratios for both downloading and uploading TCP transfers are each equal to one • Step3: • After the ratio of n to m is determined at Step 2, we can adjust the split between uplink and downlink

  20. Simulation • NS2 simulator • Link capacity is 25.4 Mbps, • Time slot is 0.5 μs, • Nc = 650, and Nf = 10000 slots. • Each TCP packet has a fixed length of 1000 bytes • The size of ACK packet is 40 bytes.

  21. Simulation_ scenario 1(downloading FTP)

  22. Simulation_ scenario 1(downloading FTP)

  23. Simulation_ scenario 1(downloading FTP)

  24. Simulation_ scenario 2(DL and UL FTP) To fix the total number of TCP transfers at 20

  25. Simulation_ scenario 2(DL and UL FTP)

  26. Simulation_ scenario 2(DL and UL FTP)

  27. Conclusions • Adaptive Split Ratio (ASR) scheme is proposed to adjust the downlink to uplink capacity ratio adaptively • ASR can cooperate with the BS scheduler to throttle the TCP source when acknowledgements are transmitted infrequently

  28. Thank you~

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