Specifications

Why Would I Use It in My Network?
May 09, 2011 Page 2 of 38
TheS‐SeriesFlex‐Edgefeature,supportedonlyonS‐Seriesswitches,providestheunique
capabilitytoclassifyandprioritizetrafficasitenterstheswitch,assertflowcontrol,andensure
thathigherprioritytrafficreceivedbytheswitchisforwardedtothepacketprocessoraheadof
lowerprioritytraffic.A
separatefeatureguideexistsfortheS‐SeriesFlex‐Edgefeatureandcanbe
foundathttps://extranet.enterasys.com/downloads.
Why Would I Use It in My Network?
WithoutQoS,allpacketsaretreatedasthoughthedeliveryrequirementsandcharacteristicsof
anygivenpacketareequaltoanyotherpacket.Inotherwords,non‐QoSpacketdeliveryisnot
abletotakeintoaccountapplicationsensitivitytopacketdelay,jitter,amountofbandwidth
required,packetloss,oravailability
requirementsoftheflow.QoSprovidesmanagement
mechanismsfortheseflowcharacteristics.
How Can I Implement Quality of Service?
QoSdetermineshowaflowwillbetreatedasittransitsthelink.Todeterminehowaflowshould
betreated,youmustfirstunderstandthecharacteristicsoftheflowsonyournetwork,and
secondly,youmustidentifytheseflowsinawaythatQoScanrecognize.Inthissense,QoS
isthe
thirdstepinathreestepprocess.Thethree‐stepsEnterasysrecommendsforconfiguringQoSare:
• UnderstandyournetworkflowsusingNetFlow
• AssociatetheflowsonyournetworkwithawelldefinedroleusingEnterasyspolicy
• Configuretheappropriatelinkbehaviorforthatrolebyassociatingtherolewitha
QoS
configuration
Quality of Service Overview
QoSisallaboutmanagingthebandwidthinamannerthatalignsthedeliveryrequirementsofa
givenflowwiththeavailableportresources.InaQoScontext,aflowisastreamofpacketsthatare
classifiedwiththesameclassofserviceasthepacketstransittheinterface.QoS
manages
bandwidthforeachflowby:
• Assigningdifferentprioritylevelstodifferentpacketflows.
•Markingorre‐markingthepacketpriorityatportingresswithaTypeofService(ToS).
• Sortingflowsbytransitqueue.Higherpriorityqueuesgetpreferentialaccesstobandwidth
duringpacketforwarding.
• Limitingtheamountofbandwidthavailable
toagivenflowbyeitherdropping(ratelimiting)
orbuffering(rateshaping)packetsinexcessofconfiguredlimits.
TheseQoSabilitiescollectivelymakeupaClassofService(CoS).Theremainderofthissection
willdescribeCoSanditscomponents.
Note: The following overview and configuration discussion will take place in an S-Series context.
See Feature Differences by Platform on page 28 for a listing of CoS feature differences.