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1、RFoundationsandTrendsinNetworkingVol.2,No.1(2007)1–133c2007C.FragouliandE.SoljaninDOI:10.1561/1300000003NetworkCodingFundamentalsChristinaFragouli1andEminaSoljanin21EcolePolytechniqueF´´ed´eraledeLausanne(EPFL),Switzerland,christina.fragouli@epfl.ch2BellLaboratori
2、es,Alcatel-Lucent,USA,emina@research.bell-labs.comAbstractNetworkcodingisanelegantandnoveltechniqueintroducedattheturnofthemillenniumtoimprovenetworkthroughputandperformance.Itisexpectedtobeacriticaltechnologyfornetworksofthefuture.Thistutorialaddressesthefirstmostn
3、aturalquestionsonewouldaskaboutthisnewtechnique:hownetworkcodingworksandwhatareitsbene-fits,hownetworkcodesaredesignedandhowmuchitcoststodeploynetworksimplementingsuchcodes,andfinally,whethertherearemeth-odstodealwithcyclesanddelaythatarepresentinallrealnetworks.Acom
4、panionissuedealsprimarilywithapplicationsofnetworkcoding.1IntroductionNetworkedsystemsariseinvariouscommunicationcontextssuchasphonenetworks,thepublicInternet,peer-to-peernetworks,ad-hocwirelessnetworks,andsensornetworks.Suchsystemsarebecomingcentraltoourwayoflife.
5、Duringthepasthalfacentury,therehasbeenasignificantbodyofresearcheffortdevotedtotheoperationandmanagementofnetworks.Apivotal,inherentpremisebehindtheoper-ationofallcommunicationnetworkstodayliesinthewayinforma-tionistreated.WhetheritispacketsintheInternet,orsignalsina
6、phonenetwork,iftheyoriginatefromdifferentsources,theyaretrans-portedmuchinthesamemannerascarsonatransportationnetworkofhighways,orfluidsthroughanetworkofpipes.Namely,indepen-dentinformationstreamsarekeptseparate.Today,routing,datastor-age,errorcontrol,andgenerallyall
7、networkfunctionsoperateonthisprinciple.Onlyrecently,withtheadventofnetworkcoding,thesimplebutimportantobservationwasmadethatincommunicationnetworks,wecanallownodestonotonlyforwardbutalsoprocesstheincominginde-pendentinformationflows.Atthenetworklayer,forexample,inte
8、rme-diatenodescanperformbinaryadditionofindependentbitstreams,23whereas,atthephysicallayerofopticalnetworks,intermediatenodescansuperimposeincomi