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Data link layer protocol for wireless TCP

Data link layer protocol for wireless TCP. K.S. Chan EEE Department The University of Hong Kong. Outlines. Introduction Multi-dimensional zigzag code Data link layer protocol Performance evaluation Automatic adaptation Conclusions. Introduction. Packet loss in wireless TCP:

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Data link layer protocol for wireless TCP

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  1. Data link layer protocol for wireless TCP K.S. Chan EEE Department The University of Hong Kong

  2. Outlines • Introduction • Multi-dimensional zigzag code • Data link layer protocol • Performance evaluation • Automatic adaptation • Conclusions

  3. Introduction • Packet loss in wireless TCP: • congestion: TCP reacts properly • Random loss: reducing congestion window will cause performance degradation • New schemes differentiating congestion packet loss and random loss needed • Existing schemes: • Wireless aware TCP: two connections • TCP modification needed • Wireless unaware TCP: • Link layer: airmail, unlimited ARQ • Split connection: I-TCP, M-TCP • Proxy: snoop, new snoop

  4. TCP aware solution Control connection • Same fraction of ACKs received: packet loss due to congestion • Acknowledged fraction significantly different, random loss user connection

  5. Introduction • Packet loss in wireless TCP: • congestion: TCP reacts properly • Random loss: reducing congestion window will cause performance degradation • New schemes differentiating congestion packet loss and random loss needed • Existing schemes: • Wireless aware TCP: two connections • TCP modification needed • Wireless unaware TCP: • Link layer: airmail, unlimited ARQ • Split connection: I-TCP, M-TCP • Proxy: snoop, new snoop

  6. TCP unaware solution: airmail TCP DLC with strong FEC • Not efficient

  7. Introduction • Packet loss in wireless TCP: • congestion: TCP reacts properly • Random loss: reducing congestion window will cause performance degradation • New schemes differentiating congestion packet loss and random loss needed • Existing schemes: • Wireless aware TCP: two connections • TCP modification needed • Wireless unaware TCP: • Link layer: airmail, unlimited ARQ • Split connection: I-TCP, M-TCP • Proxy: snoop, new snoop

  8. TCP unaware solution: I-TCP TCP TCP or other protocols • TCP end-to-end semantics violated • Huge buffer at base station

  9. Introduction • Packet loss in wireless TCP: • congestion: TCP reacts properly • Random loss: reducing congestion window will cause performance degradation • New schemes differentiating congestion packet loss and random loss needed • Existing schemes: • Wireless aware TCP: two connections • TCP modification needed • Wireless unaware TCP: • Link layer: airmail, unlimited ARQ • Split connection: I-TCP, M-TCP • Proxy: snoop, new snoop

  10. TCP unaware solution: snoop TCP Snoop module • Function for snoop module: • Buffer new packets from sender • Suppress duplicated ACK and retransmit lost packets

  11. Introduction (cont’d) • Our scheme: • Link layer • Hybrid ARQ with limited re-transmission times • No transport layer activities • Adaptive to time-varying channel conditions TCP DLC with limited retransmission of hybrid ARQ

  12. Multidimensional Zigzag code d(1,1) d(1,2) d(1,3) d(1,4) d(1,5) d(2,3) d(2,4) p(1) d(2,5) d(2,1) d(2,2) p(2) d(3,2) d(3,3) d(3,4) d(3,5) d(3,1) p(3) p(I-1) d(I,2) d(I,3) d(I,4) d(I,1) d(I,5) p(I)

  13. An example of zigzag code 1 0 1 1 0 1 p(1)=1 I=55 0 1 0 0 p(2)=1 1 1 0 1 0 p(3)=0 T 1 1 P=[11010] 1 1 p(4)=1 1 0 1 0 1 p(5)=0 1

  14. Multi-dimensional zigzag code J J J D1 P1 D2 DN PN P2 (a) I I I J D I (b) P1 P2 PN

  15. DLC Protocol Description Mobile terminal Base station User process TCP IP IP Wireless DLC Wireless DLC Wireless MAC Wireless MAC High-speed radio High-speed radio

  16. Hybrid ARQ for TCP connections b n (a) Physical preamble MAC header W-DLC header TCP packet CRC1 CRC2 (b) Physical preamble MAC header CRC2 Level 2 Level m Level 1 J G1 G2 Gm D I P1 P2 Pm1 Pm1+1 Pm2 Pm2+1 PN

  17. Operation • Estimate the allowed retransmission times • When a new packet is received, encode it N-dimensional zigzag codeword, and divide the N parity vectors into m groups • Transmission counter set to 0 • Level 1 transmission: increase the transmission counter by 1, and transmit the information matrix with parity vector group 1 • Level i, 1<i<m+1: increase the counter by 1. If the retransmission limit is met, end. Otherwise, transmit the parity vector in group i.

  18. An example for ARQ b 12,000 G1 (a) Physical preamble W-MAC header W-DLC header TCP packet CRC1 CRC2 (b) Physical preamble W-MAC header CRC2 G2 G1 G2 80 D 150 P1 P2 P7 P8 P9

  19. Performance Evaluation 1.544Mbps 1.544Mbps 100 m 200 m • Additive White Gaussian channel • Server-client connection: 32Mbytes, packet size: 12,000bits • Goodput measurement

  20. Goodput for different SNRs

  21. Goodput for different coding schemes SNR: 5 dB

  22. Automatic Channel Adaptation • Small number of possible states • A state suitable for a wide range of channel conditions • Un-match detectable

  23. Adaptation • 8 states • Two level transmission • criteria for state change: • If consecutively 100 information packets can be correctly decoded by only (L1-1) parity check vectors, increase the state by 1 • Information part of 5 packets out of 100 consecutive packets needed to be retransmitted, decrease the state by 1

  24. state k1 k2 I N 1 2 100 7 9 2 100 5 1 6 3 100 4 2 6 5 2 4 50 7 4 1 5 50 5 2 25 6 5 7 20 4 7 3 7 8 20 4 3 1 Table 1: the encoder states for non-real-time services

  25. Example for adaptation • A FEC connection • if 3 packets out of consecutively 60 packets are discarded, state is decreased by 1 • if consecutively 40 packets can be decoded with less than Nr parity vectors, state is increased by 1 • simulation condition: • SNR=5.4dB, coding state: 1 (coding rate: 0.36) • SNR change 0.1dB roughly per 150 packets sent

  26. state Nr I 1 100 9 2 100 6 3 50 7 5 4 50 7 5 25 20 6 7 7 20 4 Table 2: the encoder states for real-time services

  27. Encoder’s adaptation in the time-varying channel.

  28. Conclusions • Data link layer protocol for TCP over wireless links proposed • Hybrid ARQ with limited retransmission times • Adaptive

  29. Thank You

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