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1、NetworkCoding:TheCaseofMultipleUnicastSessionsZongpengLi,BaochunLiDepartmentofElectricalandComputerEngineeringUniversityofTorontofarcane,blig@eecg.toronto.eduAbstractInthispaper,weinvestigatethebene tofnetworkcodingoverroutingformultipleindependentunicasttransmissions.Wecompa
2、rethemaximumachievablethroughputwithnetworkcodingandthatwithroutingonly.Weshowthattheresultdependscruciallyonthenetworkmodel.Indirectednetworks,orinundi-rectednetworkswithintegralroutingrequirement,networkcodingmayoutperformrouting.Inundirectednetworkswithfractionalrouting,we
3、showthatthepotentialfornetworkcodingtoincreaseachievablethroughputisequivalenttothepotentialofnetworkcodingtoincreasebandwidtheciency,bothofwhichweconjecturetobenon-existent.1IntroductionWestudyinthispaperthedi erencesbetweennetworkcodingandpureroutingformultipleindependentu
4、nicasttransmissionsessions.Theconceptofnetworkcoding[1,2]buildsuponthefundamentalobservationthateveninerror-freecommunicationnetworks,comparedtoroutingonly,applyingcodingoperationsatintermediatenodesaswellasattheterminalnodesintroducesextra
exibilitiesandnewpossibilities,whic
5、hleadtonewunderstandingsinachievinghigh-rate,low-cost,orfault-tolerantdatatransmission.Previousdirectionsinnetworkcodingstudiesinclude,amongothers,characterizingthefeasibilityofcodedtransmissions[1,2],investigationofthesuciencyoflinearcodes[3,4],computationofcoded
owtopology
6、[5,6],codeassignment[7],comparisonwithrouting[8,9],applicationinoverlayandwirelessnetworks[10,11].Inpreviouswork[9],weanalyzedthebene tofnetworkcodinginimprovingthrough-putforsingletransmissionsessions,includingsingleunicast,singlebroadcast,andsinglemulticast.Weprovedthatthei
7、mprovementisalwaysboundedbyaconstantfactor2.However,inthepresenceofmultipleconcurrentsessions,littleisknownregardingthestructureofacodedtransmissionsscheme,thereforethecomparisonwithroutingbe-comesmuchharder.Asaspecialcase,thescenarioofmultiplebroadcastsessionsisstilltractabl
8、e.Multiplebroadcastsessionscanbeviewedasagroupcommunication,andisthe
