A Management System for Load Balancing through Ada

AManagementSystemforLoadBalancingthroughAdaptiveRoutinginMulti-serviceATMNetworksPanosGeorgatsosALPHASystemsS.A.3,Xanthoustr.17778Tavros,Athens,GreeeceTel.:[phone]Fax.:[phone]Email:[e-mail]fComputerScienceFoundationofResearchandTechnollogy/HELLASP.O.Box1`385HeraklionGR710/10,Crete,GreeceTel.:[phone]Fax.:[phone]Email:[e-mail]sesahierarchicalapproachtotheroutingissueinATM-basedbroadbandmulti-servicenetworks.WeshowhowdistributedRouteSelectionAlgorithmsembeddedwithinnetworknodesmaybemanagedbyaTMNsystem,byvirtueofamanagementservicecalledLoadBalancing,toincreasetheiradaptivitytonetworkwideconditionsandthereforetheireffectiveness.Theproposedmanagementserviceinfluencesroutingdecisionsbyconveyingnetwork-wideinformationandcontributestonetworkloadbalancingbydirectingtheroutingalgorithmstoroutetraffictotheleastcongestednetworkareas.WedemonstratehowtheprocessingpoweroftheTMNcanbeusedtoensurethatthenetworkisusedasefficientlyaspossiblewhileatthesametimeensuringthatqualityofserviceisnotcompromised.Theproposedmanagementarchitectureenablestheroutingalgorithmsembeddedinthenetworknodestobeassimpleaspossible,allowingfastdecisionstobemadeatcallset-uptimesbutwithouthavingtoinvolvetheTMNinon-linedecisionsandwithoutimposingacommunicationoverheadbetweenthenetworknodes.ThepaperpresentstheissuesinvolvedandpresentsspecificalgorithmsandaTMNarchitecturefulfillingtheobjectivesoftheproposedLoadBalancingmanagementservice.11.IntroductionTheessentialtargetoffutureB-ISDNnetworksisthecoexistenceofmanydifferentservices,rangingfromthehumbletelephoneservicetointeractivemulti-mediaconferences,onthesamenetworkinfrastructure.ThenotionofATMhasbeenwidelyrecognizedasanidealnetworktechnologyforsupportingsuchserviceintegration.TheintegrationofthevarietyofservicetypesimpliesthatATM-basedB-ISDNnetworksmustbeabletoguaranteetheperformancetargetsoftheservicesatthesametimeasensuringthatnetworkavailabilityorservicecallblockingprobabilityiswithinacceptablelevels.Routingisacriticalnetworkdesignissuewiththeoverallaimofmaximizingnetworkthroughputintermsofservicecalladmissions,whileguaranteeingtheperformanceofthenetworkserviceswithinspecifiedlevels.RoutinginATM-basednetworksisbasedonVirtualPathConnections(VPCs).ArouteisdefinedasasequenceofVPCs,whereeachVPCisdefinedasasequenceoflinksbeingallocatedaspecificportionoflinkcapacity.Multipleroutesforagivensource-destination(s-d)pairandforaparticularservicemaybeavailable(alternativerouting).Alternativeroutingisdesirablesinceitreducesthelikelihoodofblocking,itreducesnetworkvulnerabilityandenhancesroutingadaptivitytotopologicalandtrafficchanges.Experimentalstudieshaveverifiednetworkperformanceimprovementwithalternativerouting[3],[14].Thedefinitionofaroutingpolicyinvolves:•thedefinitionofasuitablenetworkofVPCs,•thedefinitionofaRoutingPlancomprisingasetofadmissibleroutesforeach(s-d)pairandCoS(connectiontype,networkbearerservicetype,makingupthenetworkservices),basedonthedefinednetworkofVPCs,•thedefinitionofapolicyforrouteselectionincaseofalternativerouting.Thedesignofanefficientroutingpolicyisofenormouscomplexity,sinceitdependsonanumberofvariableandsometimesuncertainparameters.Thecomplexityisevengreater,consideringthediversityofbandwidthandperformancerequirementsoftheservicesthatthenetworkmustsupport.Theroutingpolicyshouldthereforebeadaptivetocaterfortrafficandtopologicalchanges.2TheITU-TintroducedtheTelecommunicationsManagementNetwork(TMN)[21],asameansofprovisioningtherequirednetworkmanagementintelligenceandhavedistinguishedbetweenthemanagementandcontrolplanesintheoperationofcommunicationnetworks[18],[19].Followingthisdistinction,theroutingfunctionalityintroducedaboveisspreadoverthecontrolandmanagementplanesasfollows[7]:thedefinitionoftheVPCnetworkandtheRoutingPlanareofconcerntothemanagementplane.Ontheotherhand,routeselectionfunctionalityinvokedatcallrequestepochs,iscontrolplanefunctionalityperformedwithinthenetworkitself.Allpossibleroutesforagiven(s-d)pairandparticularCoSaredownloadedbytheTMNtonetworkswitches(inaccessnodesonlyforsourcenoderouting,orinbothaccessandtransitnodesinthecaseofdistributed-hop-by-hop-routing),wheretheactualroutingdecisionsaretakenatcallset-uptime.RouteselectionisdonebymeansofaRouteSelectionAlgorithm(RSA).Withoutlossofgenerality,itisassumedthatRSAsoperateonthebasisofparameters(routeselectionparameters)associatedwiththeavailableroutes.Followingtheideasonthetaxonomyofroutingalgorithms[11],[12],severaltypesofRSAscanbedistinguishedaccordingtotheselectionmethodtheyemploy,theinformationtheyutilizeandthedegreeofadaptivitytheyoffer.Accordingtotheselectionmethodemployed,aRouteSelectionAlgorithmcanbe:•Deterministic,wherebyrouteselectionismadeaccordingtoapredefinedorder.Inthiscase,apriorityisassignedtoeachalternaterouteandtheroutesofhigherpriorityareselectedfirst.•Random,wherebyrouteselectionismadebasedonprobabilisticcriteria.Eachrouteisassignedaprobabilityorafrequencyandtheselectionsaremadesothattoguaranteethisfrequency.•Lo