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Supporting Real-Time Applications with Better QoS Guarantees in 802.11

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SupportingReal-TimeApplicationswithBetterQoS

Guaranteesin802.11

KiranDiwakarSridharIyer

[kiran,sri]@it.iitb.ac.in

SchoolofInformationTechnology

IITBombay

Abstract—TheproliferationofIEEE802.11basedwirelessLANshasledtoalotofinterestinprovidingQualityofService(QoS)guaranteesinsuchnetworks.802.11eistheQoSvariantofthe802.11familyofprotocols.Itsuggestsaflow-basedsolutionbasedonpriorityqueuesatthenode,forprovidingQoSguarantees.Weproposeadifferentapproach,usingavariantofTDMA,calledDynamicTime-divisionMultipleAccess(DTMA).Itisbasedontheobservationthattheratioofdatatransmissiontimetocontrolpacket(polloracknowledgement)transmissiontimeistypically6:1,anddropsdownalmostto2:1whenthedatapacketsizebecomessmallerthan600bytes.DTMAfocussesonreducingcontrolinformationandtherebyincreasingtimeavailablefordatatransmission.Moretimeavailablefordatatransmissionimpliesincreasedthroughput.WeexpungetheoverheadofcontrolpacketsinHCFbyusingcummulativeacknowledgementsandpiggybacking.Takingadvantageof802.11’sinherentlimitedrange,DTMA,amodifiedTDMAisusedfordatatransferinHCF,withoutencounteringtheproblemofdistributedtimesynchronization.Inthispaper,wedotheanalysisof802.11eandDTMAusingprobabilitymodelsandalsopresentsimulationresultstosupportthesemodels.Thus,aidedbysimulationsandanalyticalmethods,weprovethatDTMAhasstricterandlesserdelayboundsthan802.11e,forreal-timeandQoSsensitiveapplications.WealsoshowthatDTMAenhancestheoverallthroughputbyalmost20%,therebyimplyingbetterQoSguaranteesinthe802.11domain.

I.INTRODUCTION

Wirelesslocalareanetworks(WLANs)arenowexpectedto

supportrealtimemultimediaapplicationslikevideoconferenc-

ing,streamingservers,whichrequirefinitedelayguarantees.

The802.11eGroup,formedtoenhanceandimprovethecur-

rent802.11MAC,hassuggestedmodificationstothelegacy

802.11toprovidetherequiredQoSguarantees[1].

The802.11eEnhancedDistributedCo-ordinationFunc-

tion(EDCF)isbasedonInterFrameSpace(IFS)andCon-

tentionWindow(CW)priorities,providingasmanyas8

serviceclasses.EachserviceclasshasadifferentIFSand

alsodifferentCW.Thesetwoparametershelptodistinguish

betweendifferentserviceclasses.TheHybridCo-ordination

Function(HCF)isanextensiontothePCFmode.TheHybrid

Coordinator(HC)controlsthechannelaccessandensuresQoS

guaranteesforprioritizedflowsbygrantingexplicitaccessto

thehighprioritynodesintheContentionPeriod(CP).

InDTMAwekeepalltheexplicitcontrolmessagestothe

minimum.WeusethedynamicallyslottedTDMAapproach

wherein,theprivilegednodesdonotrequiretobepolledorbe

sentacknowledgementsimmediatelyafterdatatransmission.Weusepiggybackinganddeferredcummulativeacknowl-

edgementstoovercomethetransmissionofexplicitcontrol

messages.Theprivilegednodesagaincontendforchannel

accessintheCP,withalowerCWandalsoalowerIFS,

ensuringbetterchancefortransmission.

Thispaperisorganizedasfollows.SectionIIdescribes

the802.11eextensiontosupportQoSinWLANs.Sections

IIIgivesthemotivationforanewscheme.SectionIVgives

thedescriptionofDTMAforprovidingbetterQoSguarantees

followedbysectionVconsistingoftheanalysisof802.11e.

SectionVIprovidestheanalysisofDTMA,followedby

simulationresultsinthenextsection.

II.802.11E-THEQOSEXTENSION

Legacy802.11isnotsuitableforQoSguaranteesbecause

thereisnoprioritizationamongnodesorflows.TheMAC

lackstheabilitytodifferentiatebetweentrafficstreams.Hence

theneedof802.11etosupportQoSinthewirelessnetworks.

802.11e[1]hasthefollowingmodesofoperation:

1)EnhancedDistributedCoordinationFunction

2)HybridCoordinationFunction

Thesemodesmakeuseoftheconceptofpriorityclassescalled

TrafficCategories(TCs).

A.EnhancedDistributedCoordinationFunction

EnhancedDistributedCoordinationFunction(EDCF)is

DCFwithsomeelementsoftheMACmodified.EDCFis

aflowbasedapproachthatclassifiesflowsintodifferent

TCs.ThereisaqueueforeachoftheTCs.Theminimum

ContentionWindow(CW)foreachTCisdifferentandthis

isthebasisforgivingpriorities.AlsoanaddedIFSisused

forservicedifferentiation,calledArbitrationInterFrame

Space(AIFS).AIFSisthetimethenodehastocheckthe

channeltobeidlebeforetransmission.TheAIFSvalueis

dependentontheparticularTC.

EDCFovercomestheflatnatureof802.11DCF,allowing

prioritizationfortherequiredQoS.ThequeuesforeachTC

actasvirtualstationswithinthatnode.Thedifferentbackoff

intervalsandAIFSdecidethetimeforschedulingaparticular

queueandthusdecidetheflowfortransmission.

B.HybridCoordinationFunction

HybridCoordinationFunctionisanextensiontothePCF

ideaofthe802.11.ItcomprisesofalternatingContentionFreePeriod(CFP)andtheContentionPeriod(CP).ThePoint

Coordinatorinthelegacy802.11PCFisreplacedbyaHybrid

Coordinator(HC).TheHCgovernsthedecisionofchannel

access.InagivenCFP,thetheHCpollstheprivilegedstations.

AstationrespondstoapollinSIFSamountoftime,failing

todoso,theHCtakescontrolofthechannelagain.TheHC

theneitherpollsthenextstationorsendsCFEndifthereis

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Fast Handoff for 802.11 Wireless Network

Fast Handoff for 802.11 Wireless Network

Fast Handoff for 802.11 Wireless Network

Obay H. Sabrie;Hasan S. Hasan;Rosli Salleh

【期刊名称】《通讯与网络（英文）》

【年(卷),期】2011(3)4

【摘 要】Whenever the mobile station moves from the range of one access

point and comes to the range of another access point a handoff process is

occurred. This process takes a long time when using the IEEE 802.11

standard handoff and this delay affect the real time and multimedia

applications. This paper provides a layer 2 handoff process for the IEEE

802.11 that is able to eliminate the scanning delay and reduce the total

handoff delay.

【总页数】7页(P250-256)

【关键词】Handoff;Delay;IEEE;802.11;Layer;2;Handoff;WLAN

【作 者】Obay H. Sabrie;Hasan S. Hasan;Rosli Salleh

【作者单位】不详

【正文语种】中 文

【中图分类】TN92

【相关文献】

1.Pre-scan based fast handoff scheme for enterprise IEEE 802.11 networks

[J], Zhang Biao;Wen Xiangming;Lu Zhaoming;Lei Tao 2.Smart Proactive Caching Scheme for Fast Authenticated Handoff in

802.11 beacon帧结构

802.11 beacon帧结构

Packet Info

Packet Number: 1

Flags: 0x00000000

Status: 0x00000000

Packet Length: 254

Timestamp: 16:05:15.346494000 10/10/2012

Data Rate: 2

1.0 Mbps

Channel: 1

2412MHz 802.11b

Signal Level: 100%

Signal dBm: -29

Signal dBm1: -29

Signal dBm2: -33

Signal dBm3: -99

Noise Level: 10%

Noise dBm: -5

Noise dBm1: 0

Noise dBm2: 0

Noise dBm3: 0 802.11 MAC Header

Version: 0

Type: %00

Management

Subtype: %1000

Beacon

Frame Control Flags: %00000000

0... .... Non-strict order

.0.. .... Non-Protected Frame

..0. .... No More Data

...0 .... Power Management - active mode

.... 0... This is not a Re-Transmission

.... .0.. Last or Unfragmented Frame

.... ..0. Not an Exit from the Distribution System

.... ...0 Not to the Distribution System

Duration: 0

Microseconds

Destination: FF:FF:FF:FF:FF:FF

Ethernet Broadcast

01-11 WLAN QoS配置

01-11 WLAN QoS配置

11

WLAN QoS配置

11.1 WLAN QoS介绍

11.2 WLAN QoS原理描述

11.3 WLAN QoS应用场景

11.4 WLAN QoS配置任务概览

11.5 WLAN QoS配置注意事项

11.6 WLAN QoS缺省配置

11.7 配置WLAN QoS

11.8 WLAN QoS配置举例

11.1 WLAN QoS介绍

定义

WLAN QoS（Quality of Service）是为了满足无线用户的不同网络流量需求而提供的

一种差分服务的能力。在WLAN网络中使用QoS技术，可以实现：

1.无线信道资源的高效利用：通过Wi-Fi多媒体标准WMM（Wi-Fi Multimedia），

让高优先级的数据优先竞争无线信道。

2.网络带宽的有效利用：通过优先级映射，让高优先级数据优先进行传输。

3.网络拥塞的降低：通过流量监管，限制用户的发送速率，有效避免因为网络拥塞

导致的数据丢包。

4.无线信道的公平占用：通过Airtime调度，同一射频下的多个用户可以在时间上相

对公平的占用无线信道。

5.不同类型业务的差分服务：通过将报文信息与ACL规则进行匹配，识别同类报

文。为同类报文提供相同的QoS服务，实现对不同类型业务的差分服务。

目的

不同的应用需求对于网络的要求是不同的，原始的WLAN网络由于速率较低，更多的

应用在普通的数据传输。随着WLAN技术的快速发展和广泛应用，WLAN技术逐渐地

应用到媒体、金融、教育机构以及企业网络中，WLAN网络中的流量除了普通的数S12700, S12700E 系列敏捷交换机

配置指南-WLAN-AC11 WLAN QoS配置

文档版本 02 (2021-03-17)版权所有 © 华为技术有限公司485据，还包括延时性要求较高的多媒体数据，例如语音、视频等。通过WLAN QoS，网

络管理者根据各种业务的特点来对网络资源进行合理的规划和分配，从而为不同的应

用提供不同质量的接入服务，以满足用户需求，同时提高网络资源的利用率。