外文翻译--基于哈希模式的负载均衡性能研究Word文档下载推荐.docx
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外文翻译--基于哈希模式的负载均衡性能研究Word文档下载推荐.docx
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毕业设计外文翻译
专 业 网络工程
班 级
学生姓名 xx
学 号 xx
指导教师
PerformanceofHashing-BasedSchemesforInternetLoadBalancing
ZhiruoCao,ZhengWang,EllenZegura
CollegeofComputingGeorgiaInstituteofTechnology
Atlanta,GA30332-0280BellLabs
LucentTechnologiesHolmdel,NJ07733
Abstract—LoadbalancingisakeytechniqueforimprovingInternetperformance.
Effectiveuseofloadbalancingrequiresgoodtrafficdistributionschemes.Westudytheperformanceofseveralhashingschemesfordistributingtrafficovermultiplelinkswhilepreservingtheorderofpacketswithinaflow.Althoughhashing-basedloadbalancingschemeshavebeenproposedinthepast,thisisthefirstcomprehensivestudyoftheirperformanceusingrealtraffictraces.
Weevaluatefivedirecthashingmethodsandonetable-basedhashingmethod.
Wefindthathashingusinga16-bitCRCovertheFivetuplegivesexcellentloadbalancingperformance.Further,load-adaptivetable-basedhashingusingtheexclusiveORofthesourceanddestinationIPaddressesachievescomparableperformancetothe16-bitCRC.Table-basedhashingcanalsodistributetrafficloadaccordingtounequalweights.Wealsoreportonfourotherschemeswithpoortomoderateperformance.
Keywords—Loadsharing,hashing.
I.INTRODUCTION
Loadbalancing(alsoknownasloadsharing)isakeytechniqueforimprovingtheperformanceandscalabilityoftheInternet.Forexample,manylargeenterprisenetworksareconnectedtomultipleInternetServiceProviders(ISPs)toachieveredundantconnectivityandtodistributetrafficloading.InsidetheInternet,thebackbonesareoftenengineeredtohavemultipleparalleltrunksbetweenmajorPointsofPresencetoensurehighavailability.Typically,theseparalleltrunksareconfiguredasequal-costpathsandallowloadbalancingoverthem.
TheparalleltrunksmaybecomeevenmoreubiquitouswhenthepromisingDenseWavelengthDivisionMultiplexing(DWDM)technologyisdeployedinthefutureInternetback-bone.DWDMexpandsthecapacityofcommunicationtrunksbyallowingagreaternumberofchannelstobecarriedonasingleopticalfiber.WithpotentiallytensorevenhundredsofDWDMchannelsbetweenmajorpoints,loadbalancingisessentialinbestutilizingthemultipleparallelchannels.
ParallelarchitectureshavebeenusedforpacketprocessingforcopingwithexponentialgrowthinInternettraffic,Insteadofoneprocessingengine,packetsaredispatchedtomultipleparallelenginesinsidearoutertoincreasetheoverallprocessingthroughput.Thesametechniqueisalsousedinscalingwebservers.
PopularwebserversoftenoperateafarmofmachinesandtheroutersconnectedtothemsplittheHTTPrequeststodifferentmachines.
Foralloftheseexamples,effectiveuseofloadbalancingrequiresgoodschemesforsplittingtrafficovermultiplelinks.Inaddition,sincethemajorityofthetrafficontheInternetisTCP-based[1],trafficsplittingschemesneedtoavoidpacketmisorderingwithinaTCPflow,whichcanfalselytriggercongestioncontrolmechanismsandcauseunnecessarythroughputdegradation[2],[3].
Inthispaper,weproposeandevaluateaclassofhashingbasedtrafficsplittingalgorithmswhichpreserveper-flowpacketordering.Weconsiderfivehashfunctionsthatare“direct,”meaningthatthehashfunctionproducesavalueintherangeof0...N-1,whereNisthenumberofoutgoinglinks.Wealsoconsideratable-basedgeneralizationthatinvolveshashingtoMbins,thenassigningtheMbinstotheNoutgoinglinks.Tablebasedhashingrequiresmorestatethandirecthashing,buthastheflexibilitytosupportunequalloaddistributionanddynamicadaptation.
Ourresultsareobtainedbysimulatingtheperformanceofatrafficsplitter,usingpackettracestakenfromtwotrunksofamajorInternetbackboneprovider.WefindthatdirecthashingwiththedestinationIPaddresscausessignificantimbalanceacrosstwolinks.UsingtheInternetchecksumortheexclusiveORofboththesourceIPaddressanddestinationIPaddressimprovestheperformanceconsiderably,thoughmoderateimbalancepersists.Themorecomputationallycomplex16-bitCRCofthefive-tuple(sourceaddress,destinationaddress,sourceport,destinationportand
protocolid)givesexcellentloadbalancingperformance,keepingtheloadandqueuelengthsverysimilarontwolinks.Equallygoodloadbalancingcanbeachievedusingtable-basedhashingwithadaptation,whichrequireslesscomputationthantheCRCbutnecessitatesmonitoringthelinkloadsandstoring(andadjusting)themappingfromtablebinstolinks.
Table-basedhashinghastheadditionaladvantagethatitcandistributetheloadaccordingtounequalweights.Further,anindex-basedversionofthisschemecanaltertheweightdistributionwithminimaldisruptiontoexistingflows.Ourresultsconfirmthattheindex-based
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