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1、IEEETRANSACTIONSONPARALLELANDDISTRIBUTEDSYSTEMS,VOL.19,NO.12,DECEMBER20081683AnalysisofTTL-BasedConsistencyinUnstructuredPeer-to-PeerNetworksXueyanTang,Member,IEEE,JianliangXu,SeniorMember,IEEE,andWang-ChienLee,Member,IEEEAbstract—Consistencymaintenanceis
2、importanttothesharingofdynamiccontentsinpeer-to-peer(P2P)networks.TheTTL-basedmechanismisanaturalchoiceformaintainingfreshnessinP2Pcontentsharing.ThispaperinvestigatesTTL-basedconsistencymaintenanceinunstructuredP2Pnetworks.Inthisapproach,eachreplicaisass
3、ignedanexpirationtimebeyondwhichthereplicastopsservingnewrequestsunlessitisvalidated.WhileTTL-basedconsistencyiswidelyexploredinmanyclient-serverapplications,therehasbeennostudyonTTL-basedconsistencyinP2Pnetworks.Ourmaincontributionisananalyticalmodelthat
4、studiesthesearchperformanceandthefreshnessofP2PcontentsharingunderTTL-basedconsistency.Duetotherandomnatureofrequestrouting,P2PnetworksarefundamentallydifferentfrommostexistingTTL-basedsystemsinthateverynodewithavalidreplicahasthepotentialtoserveanyothern
5、ode.WeidentifyanddiscussthefactorsthataffecttheperformanceofP2PcontentsharingunderTTL-basedconsistency.Ourresultsindicateatradeoffbetweensearchperformanceandfreshness:thesearchcostdecreasessublinearlywithdecreasingfreshnessofP2Pcontentsharing.Wealsocompar
6、etwotypesofunstructuredP2PnetworksandfindthatclusteredP2PnetworksimprovethefreshnessofcontentsharingoverflatP2PnetworksunderTTL-basedconsistency.IndexTerms—UnstructuredP2Pnetwork,TTL-basedconsistency,replication,consistencymaintenance,contentdistribution.
7、Ç1INTRODUCTIONEER-TO-PEER(P2P)networksareoneofthemostprevalentexpires,areplicaisnotallowedtoservenewrequestsPapplicationsintoday’sInternet.Thesenetworksinter-unlessitisvalidated.TTL-basedconsistencyissuitableforconnectmillionsofnodestoformanadhocoverlayne
8、tworkP2Pnetworksduetoanumberofreasons.First,TTL-basedandsharecontentsthroughsearchingandreplication.WithconsistencydoesnotrequirethecontentownertokeeptheproliferationofnewP2Papplicationsthatsharedynamictrackoftherep