D-Link DWS-4026 [329/741] Section 6 configuring quality of service

ConfiguringQualityofService

D-Link UnifiedWiredandWirelessAccessSystem

November2011 Page329

D‐LinkUWSUserManual

Section6:ConfiguringQualityofService

ThissectiongivesanoverviewofQualityofService(QoS)andexplainstheQoSfeaturesavailablefromthe

QualityofServicenavigationtreemenu,whichincludethefollowing:

• “ConfiguringClassofService”

• “ConfiguringDiffer entiatedServices”

• “ConfiguringAutoVoIP”

Inatypicalswitch,eachphysicalportconsistsofoneormorequeuesfortr

ansmittingpacketsontheat tached

network.Multiplequeuesperportareoftenprovidedtogivepreferencetocertainpacketsoverothersbased

onuser‐definedcriteria.Whenapacketisqueuedfortransmissioninaport,therateatwhichitisserviced

dependsonhowthequeueisconfiguredan

dpossiblytheamountoftrafficpresentintheotherqueuesofthe

port.Ifadelayisnecessary,packetsgetheldinthequeueuntiltheschedulerauthorizesthequeuefor

transmission.Asqueuesbecomefull,pack etshavenoplacetobeheldfortransmissionandgetdroppedbythe

itch.

QoSisameansofprovidingconsistent,predictabledatadeliverybydistinguishingbetweenpacketsthathave

stricttimingrequirementsfromthosethataremoretolerantofdelay.Packetswithstricttimingrequirements

aregiven“specialtreatment”inaQoScapablenetwork.Withthisinmind,allelementsofthenetworkmus

t

beQoS‐capable.ThepresenceofatleastonenodewhichisnotQoS‐capablecreate sadeficiencyinthe

networkpathandtheperformanceoftheentirepacketflowiscompromised.

ConfiguringClassofService

TheClassofService(CoS)queueingfeatureletsyoudirectlyconfigurecertainaspectsofswitchqueueing.This

providesthedesiredQoSbehaviorfordifferenttypesofnetworktrafficwhenthecomplexitiesofDiffServare

notrequired.Thepriorityofapack etarrivingataninterfacecanbeusedtosteerthepa

ckettotheappropriate

outboundCoSqueuethroughamappingtable.CoSqueuecharacteristicsthataffectqueuemapping,suchas

minimumguaranteedbandwidth,transmissionrateshaping,etc.,areuser‐configurableatthequeue(orport)

level.Thesystemsupportseight(0to7)queuesperport.

Mapping802.1pPriority

TheIEEE802.1pfeatureallowstrafficprioritizationattheMAClevel.Theswitchcanprioritizetrafficbasedon

the802.1ptagattachedtotheL2frame.Eachportontheswitchhasmultiplequeuestogivepreferenceto

certainpacketsoverothersbasedontheclassofservice(CoS)criteriayouspecify

.Whenapacketisqueued

fortransmissioninaport,therateatwhichitisserviceddependsonhowthequeueisconfiguredandpossibly

theamountoftrafficpresentintheotherqueuesoftheport.Ifadelayisnecessary,packetsgetheldinthe

queueuntilthesche

dulerauthorizesthequeuefortransmission.

Usethe802.1pPriorityMappingpageintheClassofServicefoldertoassign802.1ppriorityvaluestovarious

trafficclassesononeormoreinterfaces.