Kanghee Kim; Ahmad, A.; Kiseon Kim; Wireless Communications and Networking, 2003. March 2003

1. A wireless multimedia LAN architecture using DCF with shortened contention window for QoS provisioning Kanghee Kim; Ahmad, A.; Kiseon Kim;Wireless Communications and Networking, 2003. March 2003 演講者:洪英富

2. outlines • Introduction • Proposed MAC (DCF/SC) • Simulation environments • Simulation results • Conclusions

3. Introduction (1/2) • Diffserv is expected to be wisely implemted in future internet equipment. • IEEE 802.1D brings the Qos to local area networks but a proper mapping to Diffserv is still wanting. • Qos ,to be provided by the PCF doesn’t map to IEEE802.1D or Diffserv architecture.

4. Introduction (2/2) • DCF use CSMA/CA but under high load condition, where the DCF starts to break. • PCF use polling. • IEEE 802.11 TG-E enhance MAC capabilities to expand support for applications with Oos requirements.

5. Proposed MAC • DCF and DCF/SC 1.DCF/SC : DCF with shortened contention window. 2.DCF :a good medium-sharing mechanism for best-effort traffic. 3.DCF/SC provide shortened-delay for real-time traffic. 4.the shortened contention-window set of DCF/SC provides higher priority than original DCF, thus helping in services class differentiation.

6. Proposed MAC • MAC architecture and operation 1.super-period:period 1 and period 2. 2.three service class using both DCF/SC and DCF with period restriction. 3.flow diagram

7. Proposed MAC • Period 1: 1.only premium service traffic is allowed to be transmitted with DCF/SC. 2.PIFS is used as basic IFS in period 1. 3.AP declares the end of the period 1 if there is no transmission during DIFS. • Period 2: 1.the premium and assured services are governed by DCF/SC , and the best –effort service is operating with DCF. 2.two fundamental coordination function are operating simultaneously with the same basic IFS of DIFS.

8. Proposed MAC

9. Proposed MAC • Flow diagram • Intelligent station (ISTA): the ISTA set its status to active or freezing according to its expected packet air time including backoff and remaining duration of period •no active stations: if the remained time of the maximum duration of the Period 1 is shorter than the estimated packet air time , including backoff , of the stations with the premium service packets

10. Simulation environments • General simulation consideration • Total simulation time : 4 seconds • Super-period duration : 1ms • Maximum duration of period : 600 us • Physical layer : 54Mbps IEEE 802.11a OFDM PHY • Mac scheme : proposed MAC architecture (DCF/SC , DCF) • Traffic loading model : static loading , 50% total traffic load without handoff

11. Simulation environments • The 802.11 TG-E considers two static loading models as a testbed for MAC enhancement test of IEEE 802.11a : • Home and Enterprise • Each model consists of several kinds of traffic sources as : voice , MPx , MPEG2 and bulk data

12. Simulation results • We compare two MAC schemes under Home and Enterprise environments with respect to the channel utilization , stream throughput , latency and jitter of the premium service • Utilization : the ratio of total successful transmission air time of pure data , excluding preambles and header , to the total simulation time. • Throughput : the ratio of the number of successful transmitted packets to the generated packets of each stream. • latency • jitter

13. Simulation results

14. Conclusions • The combination of the DCF/SC and DCF makes the service differentiation possible at all the time and the performance gains last under the heavy loading case with the need of PCF • The proposed MAC shceme has 25% and 71% channel utilization enhancement under Home and Enviroments. • In the case of the voice traffic , there are 67% and 78% latency reduction under Home and Enviroments. • The changes in MAC layer standard require intensive research and should be tested for the correctness in detail and in depth.