PLANETE group, INRIA Sophia-Antipolis July 1, 2003

1. Université de Nice Sophia-Antipolis Ecole Doctorale STIC DEA Réseaux et Systèmes Distribués Adaptive Channel allocation for QoS Enhancement in IEEE 802.11 Wireless LANs Presented by:Mohammad Malli Advisors:Qiang Ni, Thierry Turletti, and Chadi Barakat PLANETE group, INRIA Sophia-AntipolisJuly 1, 2003

2. Outline • IEEE 802.11 and 802.11e • Problems and Solutions • Simulation Topologies and Parameters • Our scheme: Adaptive EDCF • Our scheme: Adaptive DCF • Conclusions and Future Work July 1, 2003

3. IEEE 802.11 New technology • Provide end-users the benefits of increased mobility & productivity • Enable network connectivity at locations where cabling is either difficult or costly to install IEEE 802.2 Logical Link Control (LLC) IEEE 802.11 Media Access Control (MAC) IEEE 802.11 Physical Layer (FHSS, DSSS, IR) July 1, 2003

4. IEEE 802.11 MAC MAC layer uses twokinds of protocols to access to the medium • DCF : Distributed Coordination Function is used to support asynchronous data transmissions • PCF: Point Coordination Function is designed for time-bounded multimedia applications July 1, 2003

5. CSMA/CA Data Data Time Source SIFS Ack Destination DIFS Backoff Time Others Defer Access Backoff_Time = Rand(0, CW) * aSlotTime Backoff Counter must be decreased each slot time by one slot time whenever the channel is idle • CW is initially set to CWmin • CW is doubled after a failed transmission • CW is set to Cwmin, when the packet is successfully transmitted July 1, 2003

6. DCF Limitations DCF is unsuitable for real time applications because it doesn’t support service differentiation  DCF suffers from significant throughput degradation and high delay at high load due to high collision rate and wasted number of idle slots in each backoff contention cycle  Collisions DIFS DIFS SIFS ACK DIFS SIFS ACK DIFS Virtual transmission time Idle backoff slots (at each contention period) July 1, 2003

7. FCR (Fast Collision Resolution) • Proposed by Florida U. (Infocom ’03) • Extends the basic DCF (no service differentiation), to improve the throughput • Main features: - Static Backoff Threshold value = 2 * (CWmin + 1) - 1 - Increasing CW when the channel is busy during deferring periods • Weakness: • Backoff Threshold must be adapted to the medium state because during high load, the period of exponential state must be shorter to reduce aggressivity • When the channel is busy, it is better that the node waits with its remaining backoff time because doubling the CW during deferring periods increases the number of idle slots in low and medium load cases July 1, 2003

8. IEEE 802.11e Extends the basic DCF to support service differentiation • Upcoming IEEE 802.11e MAC: • HCF: Hybrid Coordination Function has Controlled Channel Access Mechanism, it is used in infrastructure network • EDCF: Enhanced Distributed Coordination Function doesn’t need a central coordinator point, it is used in Ad-hoc network July 1, 2003

9. EDCF - Enhanced DCF Class1 Class0 Class2 Class7 TC0 TC1 TC2 TC7 CW[TCi] CW DIFS AIFS[TCi] Internal Scheduler (Resolve Virtual Collisions) Transmission attempt EDCF Transmission attempt DCF Many classes provide per flow differentiation July 1, 2003

10. EDCF Limitations EDCF fails to provide QoS at high load Bad Video Quality Low Total Throughput   Audio Video Background Throughput (in B/s) Time (in sec) July 1, 2003

11. Our approach: Adaptive EDCF (1) Goals : • improve the QoS for multimedia applications in all medium states • increase the total throughput in all medium states Idea : • To protect Audio and Video transmissions, best effort queue increases its CW larger and reset a new backoff time, when it senses the channel is busy, during deferring periods • To decrease the wasted number of idle slots due to backoff in each contention cycle, a queue must decrease faster its backoff time after it senses the channel idle during a certain time • Each extension will help to realize the above goals July 1, 2003

12. AEDCF(2): 1st extension Our Solution : • First,extend the Fast Backoff mechanism, proposed for DCF in Florida U., to an adapted approach that differentiates between the different priority levels • 2 Backoff states : • Linear decrease (old) • Exponential decrease (new) - Adapted to medium state - Differentiate between traffic classes Linear state exponential state Slot T. Backoff_Time Backoff_Threshold 0 Backoff_Counter decrease July 1, 2003

13. AEDCF (3): 2nd extension • Second, increase the contention window size and reset a new backoff time, when the channel is sensed busy, during deferring periods : CW[pri] = min(CWmax[pri], 2 * CW[pri]) Priority 0 1 2 3 CWmax 1023 1023 31 15 • Low priority flows will be punished • High priority flows will be protected July 1, 2003

14. Simulations Topology and parameters (1) Medium Bandwidth = 4.5 Mbytes/s Audio Audio Video Video Node0 Node n Node 1 Background Background Audio Background Video Low load : n = 5, 1 Mbytes/s Medium load : n = 11, 2.5 Mbytes/s High load : n = 15, 3.5 Mbytes/s Node2 July 1, 2003

15. Simulation Topologies and parameters (2) MAC parameters for the three flows July 1, 2003

16. AEDCF: Flows Throughput Good multimedia flow performance in medium and high load cases Also, Background flows have better throughput than in EDCF case Throughput (in B/s) Throughput (in B/s) Time (in sec) Time (in sec) Throughput with AEDCF in 11 nodes topology Throughput with AEDCF in 15 nodes topology July 1, 2003

17. AEDCF: Total Throughput Our scheme also provides highest Total Throughput in high load case Total Throughput (in B/s) 3.5 Mbytes/s Total sending rate Total Throughput in 15 nodes topology Time (in sec) With our AEDCF scheme, the T.T is higher about 55 % more than with EDCF and 10 % more than DCF in this high load topology July 1, 2003

18. Our approach: Adaptive DCF (1) Extends DCF by our adapted fast backoff approach Throughput with DCF Throughput with FCR Throughput (in B/s) Throughput (in B/s) Time (in sec) Time (in sec) ADCF provides best medium utilisation in this medium load case Throughput (in B/s) Throughput with ADCF July 1, 2003 Time (in sec)

19. ADCF (2): High load Throughput with DCF Throughput with FCR Throughput (in B/s) Throughput (in B/s) Time (in sec) Time (in sec) Throughput with ADCF We still need service differentiation to maintain a stable multimedia flows quality in high load Throughput (in B/s) Time (in sec) July 1, 2003

20. ADCF (3): Total Throughput In medium and high load cases, ADCF provides the highest Total Throughput 2.75 Mbytes/s Total sending rate Total Throughput (in B/s) Total Throughput (in B/s) 3.5 Mbytes/s Total sending rate Total Throughput in 11 nodes topology Total Throughput in 15 nodes topology Time (in sec) Time (in sec) In this medium load case, DCF is better than FCR FCR is better than DCF only in high load case July 1, 2003

21. Conclusions and Future Work • QoS support in IEEE 802.11 and 802.11e WLANs is not good enough • We propose an extension to the proposed 802.11e EDCF: Adaptive EDCF • Uses adaptive fast backoff mechanism • Provides more transmission opportunity to multimedia applications and higher total throughput during high load situations • we propose an extension to the standard 802.11 DCF: Adaptive DCF • Uses adaptive fast backoff mechanism • Provides better medium utilisation and higher total throughput in medium and high load cases • It is not good enough for multimedia applications in high load state • In this case, it is better to use AEDCF • Future work: Analytic modeling & Real Experimentation July 1, 2003

22. Q & A Thank you Mohammad.Malli@sophia.inria.fr July 1, 2003