Specifications

CoS Hardware Resource Configuration
May 09, 2011 Page 13 of 38
Figure 6 Rate Shaping Smoothing Behavior
Rateshapingretainsexcesspacketsinaqueueandthenschedulesthesepacketsforlater
transmissionovertime.Therefore,thepacketoutputrateissmoothedandburstsintransmission
arenotpropagatedasseenwithratelimiting.
Rateshapingcanbeimplementedformultiplereasons,suchascontrollingbandwidth,to
offer
differinglevelsofservice,ortoavoidtrafficcongestiononotherlinksinthenetworkbyremoving
theburstinesspropertyoftrafficthatcanleadtodiscardedpackets.Rateshapingisimportantfor
real‐timetraffic,wherepacketlossisextremelydetrimentaltotheseapplications.Insteadof
discardingtrafficimposed
byratelimiting,delaysareinducedintoitstransmissionbyretaining
thedataforfuturetransmission.However,thedelaysmustalsobeboundedtothedegreethatthe
trafficissensitivetodelays.
CoS Hardware Resource Configuration
ThissectionprovidesaconfigurationexampleforeachCoShardwareresource.
TxQ Scheduling Configuration
Transmitqueues(TxQ)representthehardwareresourcesforeachportthatareusedinscheduling
packetsforegressingthedevice.TheS‐SeriesschedulerrunsinaLow‐Latencymodewhichallows
thecustomertoconfigureahybridofstrictpriorityandweightedfairqueuing.
Forthedeviceinthisexample,
eachporthas11transmitqueues.Queues0,9and10arelow
latencyqueues(LLQ).YoucannotconfigureanLLQ.Queues1‐8arenon‐LLQsandcanbe
configured.Thehardwareschedulerwillserviceallpacketsonqueue10andthenqueue9.Once
thereareno
morepackets,theavailablebandwidthwillbeusedtoservicequeues1‐8basedonthe
configured(strictorweightedfairqueue)ordefaultmode(strict).Ifthereisanyavailable
bandwidthafterservicingthesequeues,thentheremainderofthebandwidthwillbeusedto
processqueue0.
Bydefault,
non‐LLQsruninstrictprioritymodebutcanbeconfiguredforweightedfairqueue
mode.ThroughCoSreferencemappings,youcanmaptheTxQreferencetoaTxQhardware
queueandfurtherconfigureCoStomeetyourrequirements.
TheremainderofthissectiondetailsaTxQconfigurationthat:
•Createsa
newportgroup