Specifications

Quality of Service Overview
May 09, 2011 Page 10 of 38
accesstoitspercentageoftimeslicessolongastherearepacketsinthequeue.Thenqueue2has
accesstoitspercentageoftimeslices,andsoonroundrobin.Weightedfairqueuingassuresthat
eachqueuewillgetatleasttheconfiguredpercentageofbandwidthtimeslices.The
valueof
weightedfairqueuingisinitsassurancethatnoqueueisstarvedforbandwidth.Thedownsideof
weightedfairqueuingisthatpacketsinahighpriorityqueue,withlowtolerancefordelay,will
waituntilallotherqueueshaveusedthetimeslicesava ilabletothembefore
forwarding.So
weightedfairqueuingwouldnotbeappropriateforapplicationswithhighsensitivitytodelayor
jitter,suchasVoIP .
Figure 3 Weighted Fair Queuing Packet Behavior
Hybrid Queuing
Hybridqueuingcombinesthepropertiesofbothstrictpriorityandweightedfairqueuing.
Figure 4onpage 11,depictshybridqueuing.Theconfigurationisforstrictpriorityqueuingon
queue3andweightedfairqueuingfortheremainingqueues,withqueue2receiving50percentof
theremainingtimeslices,andtheother
queuesreceiving25percenteach.Thebenefitofhybrid
queuingisthatqueuesconfiguredasstrictwillreceiveallthebandwidththatisavailableinthe
orderoftheirpriorityuntilempty.Remainingbandwidthwillbeusedbytheweightedfairqueues
baseduponthetimeslicepercentagesconfigured.The
downsideremainsthatanytimestrict
priorityqueuingisused,shouldthestrictpriorityqueuesneverfullyempty,remainingqueues
willbestarvedofbandwidth.