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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

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outlines

Introduction Proposed MAC (DCF/SC) Simulation environments Simulation results Conclusions

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Introduction (1/2) Diffserv is expected to be wisely implemted in futur

e internet equipment. IEEE 802.1D brings the Qos to local area networks b

ut a proper mapping to Diffserv is still wanting. Qos ,to be provided by the PCF doesn’t map to IEE

E802.1D or Diffserv architecture.

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Introduction (2/2) DCF use CSMA/CA but under hi

gh 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.

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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.

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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

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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.

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Proposed MAC

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Proposed MAC Flow diagram

Intelligent station (ISTA): the ISTA set its status to active or freezing acc

ording 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

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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

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Simulation environments The 802.11 TG-E considers two stati

c loading models as a testbed for MAC enhancement test of IEEE 802.11a :

• Home and Enterprise Each model consists of several kind

s of traffic sources as : voice , MPx , MPEG2 and bulk data

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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

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Simulation results

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Conclusions The combination of the DCF/SC and DCF makes the service di

fferentiation 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.