Specifications

Quality of Service Overview
May 09, 2011 Page 12 of 38
Figure 5 Rate Limiting Clipping Behavior
Flood Control
CoS‐basedfloodcontrol,isaformofratelimitingthatpreventsconfiguredportsfrombeing
disruptedbyatrafficstorm,byratelimitingspecifictypesofpacketsthroughthoseports.When
floodcontrolisenabledonaport,incomingtrafficismonitoredoveronesecondintervals.During
aninterval,the
incomingtrafficrateforeachconfiguredtraffictype(unknown‐unicast,broadcast,
ormulticast)iscomparedwiththeconfiguredtrafficfloodcontrolrate,specifiedinpacketsper
second.If,duringaonesecondinterval,theincomingtrafficofaconfiguredtypereachesthe
trafficfloodcontrolrateconfiguredontheport,
CoS‐basedfloodcontroldropsthetrafficuntilthe
intervalends.Packetsarethenallowedtoflowagainuntilthelimitisagainreached.
Rate Shaping
RateShapingthrottlestherateatwhichaporttransmits(outbound)queuedpackets.RateShaping
bufferspacketsreceivedabovetheconfiguredrateonaperCoSbasis,ratherthandroppingthem.
Onlywhenbuffercapacityisexceededarepacketsdropped.Rateshapingmay beconfiguredfora
CoSonaport,
foran802.1ppriorityonaport,orforallClassesofServiceonaport.
Figure 6onpage 13illustrateshowburstytrafficissmoothedoutwhenitburstsabovethe
assignedthresholdwithrateshapingapplied.