一个在线拍卖系统的性能研究外文翻译可编辑Word文档格式.docx

一个在线拍卖系统的性能研究外文翻译可编辑Word文档格式.docx

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外文翻译

PerformanceInvestigationofanOn-LineAuctionSystemMaterialSource:

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42.9402Author:

JaneHillston,LeilaKloulAbstract:

Thestandarddesignofon-lineauctionsystemsplacesmostofthecomputationalloadontheserveranditsadjacentlinks,resultinginabottleneckinthesystem.Inthispaper,weinvestigatetheimpact,intermsoftheperformanceoftheserveranditsadjacentlinks,ofintroducingactivenodesintothenetwork.TheperformancestudyofthesystemisdoneusingthestochasticprocessalgebraformalismPEPA.

1IntroductionInthispaperweinvestigatetheinterplayoftwoemergingtechnologies:

activenetworksandsoftwareagentstosupportelectroniccommerce.

Activenetworksareacompellingnewinitiativeinnetworking.Anactivenetworkextendsaconventionalonewiththeabilityfornetworkswitchestoprocessdataasitisbeingtransmitted.Theprocessingwhichistobeperformedcanbecustomisedbythenetworkuseronaper-applicationorevenper-messagebasis.Thisinnovationisadramaticdeparturefromtraditionalnetworkdesignwheretheemphasisisonthe

avoidanceofexaminationormodificationofdata.Activenetworksaresupportedbyavarietyofsoftwaretechnologies,executionenvironmentsandnodeoperatingsystemsSomerecentworkhasfocusedontheperformancegainsthatactivenetworktechnologymaybringtodistributedapplications.Examplesincludeactivereliable-multicastandcacherouting.Inon-lineauctionsaresuggestedasapplicationswhichmightbenefitfromprocessingatactivenodeswithinthenetworkTheInternetoffersexcitingnewprospectsforelectroniccommerce,butitcannotalwaysdelivertheperformancenecessarytomakethemviable.Theelectronictransactionstakeavarietyofformsbutincreasinglythereisamovetowardsagent-basedsystemsinwhichpersonalizedsemi-autonomoussoftwareagent’sactonbehalfofconsumersorbusinesses.Inmanycasessuchsystemsrelyontheexchangeofinformationandnegotiation.Iftheintegrityofsuchtransactionsistobemaintained,thereisaclearneedfortimelybehaviouroftheunderlyinginfrastructureSeveralon-lineauctionsystemshavebeendevelopedexperimentally,suchastheAuctionBotsystemfromtheUniversityofMichigan,theFishmarketProjectortheeAuctionHousewhichsupportscombinatorialauctionsandwhichisfromtheUniversityofWashington.Insuchsystems,competitivebehaviouronthepartofthebidderreliesonarapidresponsetosubmittedbids.Howeverthismaybejeopardizedbynetworklatencyand/orserveroverload.Assuggested,butnot

investigatedin,thein-networkprocessingcapabilitiesprovidedbyanactivenetworkappearstoprovideasolutiontothisproblem.AsfarasweareawarenothoroughperformanceanalysisofsuchascenariohasbeencarriedoutInthispaper,weinvestigatetheperformanceissuessurroundingsuchasituation.Theideawedevelopinvolvesreplacingstandard,basicintermediarynodesofthenetworkbyactivenodes,thegoalbeingtotransfersometasksfromtheservertothesenodes.Thisshouldresultinasignificantbenefitintermsofbothsystemthroughputandsystemlatency.TheresultingsystemisthenanalysesusingthestochasticprocessalgebramodelingformalismPEPAThepaperisorganizedasfollows.InSection2,wedescribetheon-lineauctionsystemweinvestigate,andthemotivationfortheapproachthatwetake.Then,inSection3,afterabriefintroductiontothemodelingformalismweuse,PEPA,wepresentthedetailsofourmodel.OursolutiontechniqueisoutlinedinSection4,togetherwiththeexperimentsweconductedandthenumericalresultswehaveobtained.Someconclusionsofthiswork,togetherwiththepossibleextensions,arediscussedinSection5.

2TheOn-lineAuctionSystemInanon-lineauctionsystem,aserverreceivesandprocessesbidsfromremotesoftwareagentsrepresentinginterestedconsumers.Thesesemi-autonomousagentssubmitbidsaccordingtoapredeterminedstrategytogetherwiththeinformationthattheycanascertainfromtheserver.Theserverprocessesbids,eitheraccepting

themorrejectingthem,dependingontheirvalue.InsomesystemsadditionalattributesmaybeconsideredwhencomparingbidsofthesameorclosevalueInadditiontobids,bidderagentsmayalsosubmitpricenotificationrequests,askingtheservertotellthemthelatestbiddingprice.Notethatthebidderagentscanneverbecertainthattheyhaveanaccuraterepresentationofthecurrentpriceduetonetworklatency.Theycan,however,becertainthattheircurrentrepresentationisoutofdatewhenasubmittedbid,whichishigherthantheirideaofthe'

current'

price,isrejectedTheeffectivenessofthebidderagentswilldependontheproportionoftimethattheirpriceinformationisaccurate.Maintainingsuchaccurateinformationplacesstringentperformancerequirementsontheunderlyinginfrastructure.Moreoverthescalabilityofsuchsystems,intermsofthenumberofbidderagentsthatcanbesatisfactorilyaccommodated,couldbeseverelylimitedbytheperformanceofthenetwork.Fromthepointofviewofaccessibilityitisimportantthatsuchauctionsystemsuseexistinginfrastructure,i.e.theInternet,andsotheabilitytodirectlyaddressperformanceproblemsmaybelimited.However,inthispaperweconsiderhowsuchperformancelimitationsmaybecircumvented,byincorporatingactivenodeswithinthenetworkThestandarddesignofanon-lineauctionsystemnecessarilyplacesmostofthecomputationalloadontheserveranditsadjacentlinks,formingabottleneckinthesystem.Weinvestigatetheadvantagesofintroducing

bidcachesatintermediarynodeswithinthenetworkbetweentheserverandsomebidders.Suchnodesare"

active"

inthesensethat,inadditiontorouting,theyexaminethecontentsofbidandpricerequestmessagesandformcaches,storingrecentbidandpriceinformation.Thesecachesdonothavetheabilitytoacceptbidsbutmayactasfilters,byrejectingbidswhichareknowntobetoolow.Thisreducestheloadonboththeserveranditsadjacentnetworkelements.Weassumethatthecache'

spriceinformationisgleanedfromthebidswhichithandlestogetherwiththeirrespectiveresponses,butalsofromaperiodicupdatemessagesentfromtheserver.Forbidswhicharepassedtotheserverthelatencyduetoprocessingwithinthenetworkisincreased;

howevertheintentionisthatthiswillbemorethancompensatedbythereducedtrafficreachingthebottleneckofthesystemInordertoquantifytheadvantagesofintroducinganactivenodetoactasacachefortheon-lineauctionsystem,wecomputeandcomparetheperformanceoftwosuchsystems:

onesystemdeployedonasimplenetworkwithoutactivenodesandanotheronthesamenetworkinwhichonenodebecomesactive.TheapproachwetaketodevelopperformancemeasuresisbasedonthestochasticprocessalgebraPEPAPerformanceEvaluationProcessAlgebra.PEPAservesasahigh-levelnotationforMarkovmodeling:

itispossibletoautomaticallygenerateacontinuous-timeMarkovprocessdirectlyfromthePEPAmodelwhichfaithfullyencodesthebehavioralandtemporalaspectsofthemodeled

system.Detailsofthismappingcanbefoundelsewhere.Otherhigh-levelnotationsforMarkovprocesses,suchasGSPNorSANcouldequallyhavebeenusedbutthecompositionalstructureofPEPAseemedwell-suitedtothestructureoftheauctionsystem.Usingaformalmodel,suchasprocessalgebra,allowsustoadditionallyverifythefunctionalcorrectnessoftheproposedsystem.Moreover,PEPAsupportsanautomaticaggregationtechniquewhichallowsthestatespaceofthemodeltobereducedwithoutlossofinformation,transparentlytotheuserOurstudyisdecomposedintotwoparts.Inthefirstpart,weconsiderthesystemwithonlytraditionalnodesasgivenbyFigure1.Wemodelthatsystemandcomputeitsperformanceintermsofthroughput.Inthesecondpartofthestudy,wereplaceoneofthetraditionalnodesbyanactiveone.Inthemodelsweadoptanumberofassumptionsandconventions.

Allbidderagentsinthesystemadoptthesamestrategy.Accordingtothisstrategy,wheneverabidisrejectedthebiddersubmitsapricenotificationrequesttogetanupdatedpriceestimatebeforesubmittinganymorebids

Intheserver,aservingagentisspawnedtocorrespondwitheachbidderagent.Thisagentisresponsibleformaintainingthecurrentstateofinteractionswiththecorrespondingbidder.

Inthemodelalldatadependentbehaviourisabstracted.Thismeansthatwedonotrepresentthecurrentprice,orthevalueofabid.Nor

dowerepresentdetailsofanybiddingstrategy,orselectionstrategyforchoosingbetweenbidsofcomparablevalue.Insteadweuseprobabilitiestorepresenttherelativefrequencywithwhichbidsaresuccessful.

Sincebidswhicharesubjecttolongerlatenciesaremorelikelytobeunsuccessful,weadjusttheacceptanceprobabilitiesaccordingtotheroutesbywhichbidswillarriveattheserver,orthecache.

Wemakeadistinctionbetweenthenodesofthesystem.Thisdistinctionreflectsthepositionofthenodeinthesystemandthustheelementstowhichitisconnected.However,notethattheessentialbehaviourandtimingcharacteristicsofthenodeswithoutcachearethesameineachcaseOurmodelisstochastic,meaningthatalltimesarerepresentedasrandomvariables.SincewewilluseMonroviananalysistocalculateperformancemeasures,allrandomvariablesareassumedtobeexponentiallydistributed.Performancemeasuresarederivedfromequilibrium,orsteadystate,behaviourInthefollowingsectionwebrieflyintroducethePEPAformalism,beforepresentingthemodels