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Adaptive Fair Channel Allocation for QoS Enhancement in IEEE 802.11 WLANs

Adaptive Fair Channel Allocation for QoS Enhancement in IEEE 802.11 WLANs. Mohammad Malli Qiang Ni, Thierry Turletti, Chadi Barakat PLANETE group, INRIA Sophia-Antipolis. Outline. Introduction : MAC methods Motivation : limitations of EDCF Our scheme: Adaptive Fair EDCF

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Adaptive Fair Channel Allocation for QoS Enhancement in IEEE 802.11 WLANs

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  1. Adaptive Fair Channel Allocation for QoS Enhancement in IEEE 802.11 WLANs Mohammad Malli Qiang Ni, Thierry Turletti, Chadi BarakatPLANETE group, INRIA Sophia-Antipolis

  2. Outline • Introduction : MAC methods • Motivation : limitations of EDCF • Our scheme: Adaptive Fair EDCF • Simulation Results in NS-2 • Conclusions June, 2004

  3. MAC Methods • IEEE 802.11 MAC: • DCF : Distributed Coordination Function to support asynchronous data transmissions • PCF: Point Coordination Function for time-bounded multimedia applications • Upcoming IEEE 802.11e MAC for Service Differentiation : • EDCF : Enhanced Distributed Coordination Function provides asynchronous data transmissions & service differentiation support • HCF : Hybrid Coordination Function has controlled channel access mechanism & it is used in infrastructure networks June, 2004

  4. Enhanced DCF AC3 AC2 AC1 AC0 DCF EDCF CW[ACi] CW AIFS[ACi] DIFS Virtual Collision Handler Transmission attempt Transmission attempt June, 2004

  5. Motivation • EDCF main limitations : • High collision rate especially in high load case • Wasted idle slots especially in the moderate load case • So, our goal is to : • Design an efficient channel access algorithm that reduces the impact of the above limitations by adapting itself to the channel status June, 2004

  6. EDCF June, 2004

  7. FCR (Fast Collision Resolution) • Proposed by Y. Kwon et al. (Infocom ’03) • no service differentiation • Linear + exponential backoff decrease separated by a constant backoff threshold value June, 2004

  8. AEDCF • Proposed by L. Romdhani et al. (WCNC ’03) • increase CW[i] by a multiplicative factor larger than 2 after each collision • slow CW[i] decrease after each successful transmission June, 2004

  9. Our approach: Adaptive Fair EDCF Goals : 1. increase the total throughput in all channel status 2. improve the QoS for multimedia applications in high load 3. increase the fairnessbeween the same priority flows in high load Idea : (1) = reduce idle time & avoid collisions (2) = provide multimedia flows much more transmission opportunity than low priority flows in high load (3) = the same priority queues must have similar transmission opportunity June, 2004

  10. Adaptive Fair EDCF: 1st extension • 2 Backoff states : • Linear decrease (old) • Exponential decrease (new) How can we have a Backoff Threshold function which : • Adapts to the channel status • Differentiate between traffic classes Linear state exponential state Slot T. Backoff_Time Backoff_Threshold 0 Backoff_Counter decrease June, 2004

  11. Adaptive Fair EDCF: 1st extension • CW[i] => Backoff_Threshold : • CW[i] = CWmin[i] : only exponential backoff decrease • CW[i] = CWmax[i] : only linear backoff decrease June, 2004

  12. Adaptive Fair EDCF : 2nd extension When the channel is sensed busy, during deferring periods : CW[pri] = min ( 2 * CW[pri], CWmax[pri] ) Priority 0 1 2 3 CWmax 1023 1023 31 15 • Low priority flows will be punished • High priority flows will be protected • CW[i] values converge rapidly to CWmax[i] during high contention periods => better fairness June, 2004

  13. Simulations Topology Audio Audio Video Video Node0 Node n Node 1 Background Background Audio Background Video Node2 Medium Bandwidth = 4.5 Mbytes/s June, 2004

  14. Parameters MAC parameters for the three flows June, 2004

  15. Adaptive Fair EDCF: total goodput • The Total goodput is higher about 55 % more than with EDCF in high load June, 2004

  16. Adaptive Fair EDCF: flows goodput • Good multimedia flow performance even in high load case • Also, Background flows have better throughput than in EDCF case EDCF Adaptive Fair EDCF June, 2004

  17. Adaptive Fair EDCF: latency EDCF :delay of 90 % audio pkts = 11ms & for video pkts = 700ms& for background pkts = 7 s Our scheme :delay of 90 % audio pkts = 1.5ms & for video pkts = 4ms& for background pkts = 1.7 s Load = 80 % Adaptive Fair EDCF EDCF June, 2004

  18. Adaptive Fair EDCF: channel usage Load = 100 % : Adaptive Fair EDCF improves the channel utilization compared to EDCF by 34 % & reduces the collision rate by more than 5 times less than EDCF June, 2004

  19. Adaptive Fair EDCF: Fairness index EDCF AEDCF Adaptive Fair EDCF June, 2004

  20. Conclusions • QoS support in IEEE 802.11 and 802.11e WLANs can be improved • We propose an extension to the proposed 802.11e EDCF: Adaptive Fair EDCF • Uses adaptive backoff threshold to separate linear and exponential backoff decrease states • improves the performance in case of high load : Provides more transmission opportunity to multimedia applications & higher total throughput & better fairness between the same priority flows • Future work: Analytic modeling & Real Experimentation June, 2004

  21. Q & A Thank you Mohammad.Malli@sophia.inria.fr June, 2004

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