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Service differentiation mechanisms for IEEE 802.11-based wireless networks

Service differentiation mechanisms for IEEE 802.11-based wireless networks. Srikant Kuppa , Ravi Prakash University of Texas at Dallas WCNC2004. Outline. Instruction Possible MAC policies for Service Differentiation SAB (schedule after backoff) SBB (schedule before backoff)

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Service differentiation mechanisms for IEEE 802.11-based wireless networks

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  1. Service differentiation mechanisms forIEEE 802.11-based wireless networks Srikant Kuppa , Ravi Prakash University of Texas at Dallas WCNC2004

  2. Outline • Instruction • Possible MAC policies for Service Differentiation • SAB (schedule after backoff) • SBB (schedule before backoff) • Comparative Performance Evaluation • Conclusions

  3. Instruction • 802.11 DCF • All nodes contest for the medium for each transmitted frame • Simplicity • Offer only best-effort service • No QoS guarantee

  4. Instruction • Two MAC policies SAB/SBB are proposed and intend to • offer some “guarantees” for high-priority data • Prevent starvation of low-priority traffic

  5. Possible MAC policies for Service Differentiation (SAB) • Schedule after backoff (SAB) policy • 802.11e Enhanced DCF(EDCF) is based on SAB policy • a node accesses the medium depending on AC of the frame • Access Category (AC) mechanism is used to realize service differentiation • Four ACs (AC 3 > AC 2 > AC 1 > AC 0) • Different IFS for different ACs • Shorter CWfor high-priority frames

  6. Backoff instances for each ACs Possible MAC policies for Service Differentiation (SAB)

  7. Possible MAC policies for Service Differentiation (SAB) • Schedule after backoff (SAB) policy • Each AC with the nodes behaves like a virtual node • Arbitration IFS(AIFS) is used • AIFS = DIFS + some time slot • Internal collision: solve by frame-scheduler • External collision • Problem: Under high lodes , EDCF suffer high collision and starve low-priority traffic [7]

  8. Possible MAC policies for Service Differentiation (SBB) • Schedule before backoff (SBB) policy • provides service differentiation without maintaining concurrent backoff instances • 2 Steps • selection of the next frame to transmit • RR / WRR (weight Round Robin) • channel access functionality for the selected frame • VCW (Various CW )

  9. Possible MAC policies for Service Differentiation (SBB)

  10. Performance Evaluation • Simulator NS-2.26 • Single hops / Stationary • Simulation time = 110s

  11. Performance Evaluation • Scenario A • Saturation traffic • Traffic flows = 4 * n • Constant Bit Rate • Frame Size = 512 byte • Date Rate = 1Mbps • Scenario B • Non-Saturation traffic • Traffic flows = 2 * n

  12. Performance Evaluation

  13. Performance Evaluation

  14. Performance Evaluation • improve the chances of successful transmission in High contention environment • larger values of CW • more number of backoff stages

  15. Performance Evaluation

  16. Performance Evaluation

  17. Performance Evaluation ：the effective bandwidth used for successful transmissions and does not include bandwidth spent on collided or retransmitted frames

  18. Conclusions • Service differentiation in IEEE 802.11-based wireless ad hoc networks • SAB =>EDCF：AC + AIFS • SBB => RR/WRR + VCW • Through simulation experiments： • EDCF starves low-priority frames under high loads of high-priority traffic. • Reasonable performance guarantees shown by schemes WRR and WRR with VCW

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