Specifications

Quality of Service Overview
May 09, 2011 Page 3 of 38
Class of Service (CoS)
YouimplementQoSfeaturesinaClassofService(CoS).Therearefourhardwareresource
componentsthatcanbeconfiguredaspartofaCoS.
• TransmitQueues(TxQ)‐representthequeuinghardwareresourcesforeachportthatare
usedinschedulingpacketsforegressingthedevice,aswellasrate
shapingoftrafficbased
uponoutboundbuffering.
• InboundRateLimiters(IRL)‐allowyoutoconfigureathresholdabovewhichaportwillnot
processtraffic.
• OutboundRateLimiters(ORL)‐allowyoutoconfigureathresholdabovewhichaportwill
nottransmittraffic.
• FloodControl‐configuresathreshold
abovewhichaportwillnotreceiveunknown‐unicast,
multicast,orbroadcastpackets.
TheCoSconfigurationofeachqueue orporthardwareresourceisoptional.TxQshavethree
configurablequeueoptions:queuemapping,queuerateshapingandqueuescheduling.IRL,ORL,
andfloodcontroleachhaveasingleconfigurableratelimiting
porthardwareresourceoption.
CoSconfigurationisappliedtotheingressingpacketbaseduponthepacket’s802.1priority,port,
andpolicysettings.
Howthefirmwaretreatsapacketasittransitsthelinkdependsuponthepriorityandforwarding
treatmentsconfiguredintheCoSassignedtothepacket.Upto256
uniqueCoSentriescanbe
configured.CoSentries0–7areconfiguredbydefaultwithan802.1ppriorityassignedanddefault
forwardingtreatment.CoSentries0–7cannotberemoved.CoSentries0–7arereservedfor
mappingan802.1pprioritytoaCoSindex.CoSentries8‐255canbeconfiguredandused
bypolicy
forthefollowingservices:
• 802.1ppriority
•IPTypeofService(ToS)marking
•PriorityTransmitQueue(TxQ)withconfigurableforward ingbehavior
•In‐bound(IRL)and/oroutbound(ORL)ratelimiter
• Outboundrateshaperpertransmitqueue
• Floodcontrol
ThereareuptofourareasofCoSconfigurationdependingonwhattypeof hardware
resourceyou
wanttoconfigure.TheterminologyassociatedwithCoSconfigurationisintroducedinTable 1.
Table 1 CoS Configuration Terminology
Term Description
CoS Setting Maps configured resources to a CoS index. When a packet is received, the
packet is mapped to a CoS index based on the packet 802.1 priority, port,
and policy role, if a policy role is present. The CoS index translates into
available hardware resources through indirect mappings to TxQ, IRL, ORL,
or the administrative state of flood control. An optional drop precedence can
be configured.
CoS Reference Provides a means of mapping a CoS setting to a specific hardware resource,
such as a TxQ, IRL, or ORL.