Introduction
Networkcodingwasfirstproposedinthepaper"NetworkInformationFlow"publishedbyAhlswedeetal.onIEEETransactionsonInformationTheoryin2000.Networkcodingismainlyusedinmulticastnetworks,wherenodesarecodedtoincreasetheinformationtransmissionrate.Accordingtothetraditionalscheme,thenodeisgenerallyarouterthatusesa"store-and-forward"mechanism.Asthetraditionalviewbelievesthat"processingdataonanintermediatenodewillnotbringbenefits",therouterdoesnotprocesstheinformationitself.Networkcodingprocessesthedataonthenodes,therebyincreasingtheinformationtransmissionrate.
Thetraditionalwayofdatatransmissionincommunicationnetworksisstoreandforward,thatis,nodesotherthanthesendingnodeandreceivingnodeofthedataareonlyresponsibleforrouting,anddonotdoanyprocessingonthedatacontent.Theintermediatenodeactsasarepeater.Role.Foralongtime,ithasbeengenerallybelievedthatprocessingthetransmitteddataontheintermediatenodewillnotproduceanybenefits.However,thenetworkcodingtheoryproposedbyRAhlswedeetal.[1]in2000completelyoverturnedthistraditionalview.
Networkcodingisaninformationexchangetechnologythatcombinesroutingandcoding.Itscoreideaistoprocesstheinformationreceivedoneachchanneloneachnodeinthenetworklinearlyornon-linearly.,Andthenforwardedtothedownstreamnode,theintermediatenodeplaystheroleofencoderorsignalprocessor.Accordingtothemaximumflow-mincuttheoremingraphtheory[2],themaximumrateofcommunicationbetweenthesenderandthereceiverofdatacannotexceedthemaximumflowvalue(orminimumcutvalue)betweenthetwoparties,ifthetraditionalmulticastroutingmethodisused,Generallycannotreachtheupperbound.RAhlswedeetal.tookthestudyofbutterflynetworkasanexample,andpointedoutthatthroughnetworkcoding,themaximumflowofmulticastroutingtransmissioncanbereached,andthetransmissionefficiencyofinformationhasbeenimproved,thusestablishingtheimportantpositionofnetworkcodinginthefieldofmodernnetworkcommunicationresearch.
Sincethebirthofnetworkcodingtechnologysevenyearsago,itcanbesaidthatitisbasicallyhiddeninuniversitiesandlaboratoriesandislittleknown.Thisisacodingalgorithm,supportersclaimthatitcandoubletheexistingnetworkthroughput,whilealsoimprovingthereliabilityofthenetworkandtheabilitytopreventattacks.Themostenthusiasticsupportersofnetworkcodingtechnologysaythatthetechnologywillleadtothenextrevolutioninthenetwork;othersbelievethatnetworkcodingtechnologyismorelikelytosubtlychangetherouting-basednetworkarchitecture.
Workingprinciple
Theworkingprincipleofnetworkcodingistoconvertdifferentinformationinto"trace"withsmallerbits,andthendeductivelyrestoreitatthetargetnode,sothatthereisnoneedtorepeatedlytransmitOrcopyalltheinformation.Tracescanberepeatedlypassedonmultiplepathsbetweenmultipleintermediatenodes,andthensenttothefinaldestinationendpoint.Itdoesnotrequireadditionalcapacityandrouting—justconvertthetracesofinformationintoabitstream,andthisconversioncanbesupportedbytheexistingnetworkinfrastructure.
Securityissues
Researchersadmitthatthecombinationofeavesdroppingmethodsandtheconceptofxorbitstreamsmayraisesecurityconcerns.
ButMedardoftheMassachusettsInstituteofTechnologybelievesthatnetworkcodingdisguisedataduringexecutionandcaneffectivelycarrydata,soitactuallyenhancesthesecurityofinformation,whichisbetterthantransmittingonthenetwork.Traditionalencryptiontechniquesforundecipherablealgorithmstreamsaremoresecure.
"Whenyoudothiskindofdatapacketmixing,ithastheperformanceofdatahidingitself."Medardsaid."Forexample,therearetwobitgroupsAandB,andthexoroperationisperformedonthetwobitgroups.Youcan'tseewhichbitgroupdataisobtainedfromtheresult.Youmayknowthevalueofsomeofthebits,butyouItisimpossibletorestorethedataoftheAbitgroupunlessyoufullyknowthedataoftheBbitgroup."
Shesaidthatnetworkcodingtechnologycanalsodetectmalicious"pollution"attacksinP2Ptransmissionandcorrectthem.mistake.
Ofcourse,alotofworkneedstobedonetodeterminetheimpactofnetworkcodingonsecurity.AsforwhethernetworkcodingcaneventuallyreplaceroutersinasharedinfrastructuresuchastheInternet,therearealsomanyproblemsthatneedtoberesolved.Forexample,customersmustknowhowtoimplementnetworkcodingwheninformationcannotbemixedinasharednetwork;theyalsoneedtopayattentiontothenuancesofnetworkcodinginwiredandwirelessinfrastructure;andtheindustrymustbeabletoidentifysomekindofMethod,whentheoperatormixesthedifferenttrafficofdifferentcustomerswitheachother,howshouldcustomerspay?
Medardsaidthatsheandotherresearchersareconsideringwaystosolvetheseproblemsandcontinuetoexplorevariouswaystoimprovethenetworkinordertomakethenetworkanindispensablepartofhumansociety.
Researchprogress
Networkcodingallowsnetworknodestoparticipateindataprocessingonthebasisoftraditionaldataforwarding,andhasbecomeaneffectivemethodtoimprovenetworkthroughput,robustnessandsecurity.Onthebasisofintroducingthebasicprinciplesofnetworkcoding,itcomparestheadvantagesanddisadvantagesofcentralizedanddistributednetworkcodingconstructionmethods,andreviewsthesynchronization,errorcorrection,codecspeedandotherissuesinvolvedinpracticalnetworkcodingdesign;further,Thelatestapplicationsofnetworkcodinginwirelessnetworks,P2Psystems,distributedfilestorageandnetworksecurityaresummarized;finally,thedevelopmenttrendofnetworkcodingtheoryandapplicationresearchisanalyzedandprospected.Designingasimpleandefficientimplementationmechanism,andcombiningitwithotherfieldsoftechnologysuchaschannelcodingandmodulation,routingalgorithms,queuescheduling,andstreamingmediatechnology,willbeanimportanttrendinthedevelopmentofnetworkcoding.