QoS-aware routing schemes based on hierarchical load-balanci(3)

bethesetofavailablepathsinthenet-Let

work.BydividingitintodifferentsubsetsandorderingthemaccordingtotheStaticCostfunction,weobtainapathas-signmentfromthesourcestothedestinations,achieving,hopefully,abetterexploitationofthenetworkcapacitythanbysimpleMinimum-Hopordering.NoticethatMinimum-Hopor-deringyieldsexactlythesamepathselection,regardlessofitbeingrunonalltraf cclassestogetherorhierarchicallyclassbyclass.

Wedescribeasinglesortingcriteria,althoughmoreheuristicswerestudiedin[8],andobviouslymanymorecanbede ned.Thealgorithmworksincycles:ineverycycle,itassignoneandonlyonepathpersource-destinationpair,ifitexists,startingfromthepathswiththeminimumnumberofhops.

Forthesakeofclaritythealgorithmisdescribedforasin-gletraf cclass,avoidinganadditionalloopontraf cclassesandtheconsequentcomplicationinthenotation.Hierarchically

isre-movingfromoneclasstothenext,thestaticlinkcost

ofhigher-QoS-classessourceswhosesettothestaticload

belongsto.Wechosenottotakeintoac-primarypath

counttheloadduetosecondarypathsfromhigherclasses,sincesecondarypathsarelesslikelytocarrynewlyactivatedcallsthanprimarypaths.

5.;

=EP();6.

;7.

;8.

do9.for

;10.

do11.while

=HF12.

=SLS(13.

14.

15.return;

;

);

;

Fig.1.AlgorithmBalancedPrimaryFirst(BPF)

IV.SIMULATIONSETUP

Theeffectivenessofthealgorithmpresentedintheprevioussectionswasstudiedbymeansofacall-levelsimulationtoolforhigh-speednetworks,calledANCLES[9][10][11],assumingtwotraf cclasses:ahighpriority,guaranteed-QoSclassandalowpriority,best-effortclass.ThenetworktopologyofchoiceisshowninFig.2;itcombinesarathertightmeshwithhundredsofloop-freepathsandalocalizedbottleneck.Thelinkspeed,whichisthesameforalllinks,isequalto500Mb/s.Amixofconstant-andvariable-bitratesources,locatedineverynode,areassumedtogeneratetraf cinthehighestQoSclass:the

Mb/srateconstant-bitratesourcestrytoopencallsat

towardeachother,(callholdingtimesaredeterminedbyi.i.d.exponentialrandomvariablesaveragingat500seconds);the

Mb/swhich,variable-bitratesourcesactivatecallsat

onceactivatedandadmittedtothenetwork,holdforanexponen-tiallydistributedperiod,withaverage1000seconds;variable-bitratecallsexhibitaburstinessdegree(peak-to-meanrateratio)

Mb/s.equalto5,thusresultinginanaveragerate

Thecalladmissioncontrolschemetowhichtheabovecallsaresubjectisrathersimple;foreachlink,newcallsareacceptedif:

(1)

B.Algorithm:BalancedPrimaryFirstBPF()

Thefollowingalgorithmassignsateveryloopasinglepath

(ifitexists)fromthesourcetothedestination,resort-ingtheremainingpathset,inorderto ndthebestpathtoas-signinthenextcycle.Thisisobtainedbyapplying,insequence,theMinHopalgorithmtosetasidealltheshortestpathsforallsource-destinationpairs,thentheEquivalentPathalgorithmtoidentifyallthesubsetswith-equivalentpaths.EachsubsetisprocessedbytheHopFirstalgorithmwhich,inturn,yieldsasub-subsetofshortestpaths.Eventually,theStaticLoadSort-ingalgorithmisusedoverallsub-subsetsidenti edabovetoobtainthe nalorder,asshowninFig.1.Theresultisare-,thereorderedpathssetwhere,foreachtraf crelation

inwhichthe rstoneistermedisanorderedpathssub-set

primaryandalltheothersaretermedsecondary.Theroutingfunctionprobesallthepathsinorderandtheconnectionisre-fusedonlyiftheCACfunctionscannotallocateitonanypaths

,asisdoneintheUncontrolledAlternateofthesub-set

Routing[5].

do1.while

=MH();2.

;3.

do4.while

andarethesetsofconstant-andvariable-bitratewhere

calls,respectively,isthelinkcapacity,andisaprotection

)thatcanbesetsoastoavoidthatthewholecoef cient(

Abstract—This paper presents a load balancing method to improve network utilization when static routing algorithms are employed. Static routing algorithms can generally be reduced to a path assignment problem with the aim of minimizing a cost function: i.

4

1e+00

1e-011e-02

no lbwith lbγ = 0.4γ = 1

1e-03

1e-04

1e-05

1.5

1.61.7

Load

1.81.92

3.Callblockingprobabilitiesasafunctionoftheoverallguaranteed-class

networkloadinGb/s

andingconnectionswithacellratevaluemidwaybetween,accordingtoafactor;thatis:

(2)

AdiscussionoftheCACschemejustdescribedanditsrelationtosomeequivalentbandwidthexpressionscanbefoundin[12].

and(and,forInoursimulations,wechose

,yieldingpeakallocation).someresults,

Forwhatconcernsbest-effort,lower-priorityusers,nodesN1,N8andN12arerequestedtoactivateconnectionswith

(butwealsoreportresultswithapeakrate

)andaverageholdingtimeequalto60seconds.

Eachbest-effortsourceequallydirectsitstraf ctowardnodesN4,N6andN10.Theactualbandwidth,possiblysmallerthanthepeak,exploitedbyusersofthisclassisdeterminedbyamax-minfairnessallocationschemethat,foreachcall,accountsforthenumberofcallsonthebottlenecklinkandfortheresidualcapacityavailabletothebest-effortclass1.NoCACisimple-mentedforbest-effortcalls.

Thenetworktraf cwassplitamongguaranteed(40%oftheoveralltraf c)andbest-effort(60%)calls.Also,callsareroutedaccordingtotheHierarchicalLoadBalancingAlgorithmde-tailedinSubsectionIII-A;notethat,sincethereisnoCACforbest-efforttraf c,allcallsinthisclassareroutedovertheirre-spectiveprimarypaths.

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