chord a scalable peer-to-peer lookup service for internet

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1、Chord:AScalablePeer-to-peerLookupServiceforInternetApplicationsIonStoica,RobertMorris,DavidKarger,M.FransKaashoek,HariBalakrishnanyMITLaboratoryforComputerSciencechord@lcs.mit.eduhttp://pdos.lcs.mit.edu/chord/Abstractandinvolvesrelativelylittlemovementofke

2、yswhennodesjoinandleavethesystem.Afundamentalproblemthatconfrontspeer-to-peerapplicationsisPreviousworkonconsistenthashingassumedthatnodesweretoefficientlylocatethenodethatstoresaparticulardataitem.Thisawareofmostothernodesinthesystem,makingitimpracticaltopa

3、perpresentsChord,adistributedlookupprotocolthataddressesscaletolargenumberofnodes.Incontrast,eachChordnodeneedsthisproblem.Chordprovidessupportforjustoneoperation:given“routing”informationaboutonlyafewothernodes.Becausetheakey,itmapsthekeyontoanode.Dataloca

4、tioncanbeeasilyroutingtableisdistributed,anoderesolvesthehashfunctionbyimplementedontopofChordbyassociatingakeywitheachdatacommunicatingwithafewothernodes.Inthesteadystate,initem,andstoringthekey/dataitempairatthenodetowhichthean-nodesystem,eachnodemaintai

5、nsinformationonlyaboutkeymaps.Chordadaptsefficientlyasnodesjoinandleavethesystem,andcananswerqueriesevenifthesystemiscontinuously(log)othernodes,andresolvesalllookupsvia(log)mes-sagestoothernodes.Chordmaintainsitsroutinginformationaschanging.Resultsfromt

6、heoreticalanalysis,simulations,andex-nodesjoinandleavethesystem;withhighprobabilityeachsuchperimentsshowthatChordisscalable,withcommunicationcost2andthestatemaintainedbyeachnodescalinglogarithmicallywitheventresultsinnomorethan(log)messages.Threefeaturest

7、hatdistinguishChordfrommanyotherpeer-to-thenumberofChordnodes.peerlookupprotocolsareitssimplicity,provablecorrectness,andprovableperformance.Chordissimple,routingakeythroughase-1.Introductionquenceof(log)othernodestowardthedestination.AChordPeer-to-peersy

8、stemsandapplicationsaredistributedsystemsnoderequiresinformationaboutwithoutanycentralizedcontrolorhierarchicalorganization,where(log)othernodesforefficientrouting,butperformancedegradesgracefullywhen