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Definition

Communicationprotocolreferstotherulesandconventionsthatthetwoentitiesmustfollowtocompletethecommunicationorservice.Theprotocoldefinestheformatusedbythedataunit,theinformationandmeaningthattheinformationunitshouldcontain,theconnectionmethod,andthetimingofinformationsendingandreceiving,soastoensurethatthedatainthenetworkissmoothlytransmittedtoacertainplace.

Incomputercommunication,thecommunicationprotocolisusedtorealizethestandardbetweenthecomputerandthenetwork.Ifthenetworkdoesnothaveaunifiedcommunicationprotocol,theinformationtransferbetweencomputerscannotberecognized.Thecommunicationprotocolreferstothecommunicationrulesagreedbythepartiesinadvance,whichcanbesimplyunderstoodasthecommonlanguageusedbycomputersformutualconversation.Thecommunicationprotocolthattwocomputersmustusewhencommunicating.

Threeelements

Thecommunicationprotocolismainlycomposedofthefollowingthreeelements:

Syntax:Howtocommunicate,includingdataformat,codingandsignallevel(electricalLevelheight)andsoon.

Semantics:thecontentofcommunication,includingdatacontent,meaning,andcontrolinformation.

Timingrules(sequence):Whentocommunicate,theorderofcommunication,ratematchingandsortingareclearlydefined.

Features

Thecommunicationprotocolishierarchical,reliableandeffective.

Architecture

Thebasicconceptsofthehierarchicalcommunicationarchitectureareasfollows:

  1. Thecommunicationfunctionisdividedintoseverallevels,eachThelevelcompletesapartofthefunction,andeachlevelcooperateswitheachothertocompletethecommunicationfunction.

  2. Eachlayeronlydealswiththetwodirectlyadjacentlayers.Itusesthefunctionsprovidedbythenextlayertoprovidethehigherlayerwithservicesthatcanbecompletedbythislayer.

  3. Eachlayerisindependent,thecompartmentscanbeimplementedwiththemostsuitabletechnology,andeachlayercanbedevelopedandtestedseparately.Whenthetechnologicalprogressofacertainlayerchanges,aslongastheinterfacerelationshipremainsunchanged,theotherlayersarenotaffected.

Theschematicdiagramofthehierarchicalstructureisshowninthefigure.Eachlayerrealizesrelativelyindependentfunctions,thelowerlayerprovidesservicestotheupperlayer,andtheupperlayeristheuserofthelowerlayer.Eachlayercooperateswitheachothertocompletethecommunicationfunction.

Thelayeringofthenetworksystemistodecomposethecomplexcommunicationnetworkcoordinationproblems,andthendealwiththemseparatelytosimplifythecomplexproblemssoastofacilitatetheunderstandingofthenetworkandthedesignandimplementationofeachpart.

Theprotocolisonlyforacertainlayerandisformulatedforcommunicationbetweenthesameentities.Itiseasytoimplementandmaintain,hasgoodflexibility,andisstructurallyseparable.

Commonlyusedprotocols

CommunicationprotocolscommonlyusedinlocalareanetworksmainlyincludeTCP/IP,NETBEUIandIPX/SPX,eachofwhichhasitsapplicableapplicationenvironment.

TCP/IP

ThehistoryofTCP/IP(TransportControlProtocol/InternetProtocol,TransmissionControlProtocol/InternetProtocol)shouldbetracedbacktothepredecessoroftheInternet-ARPAnetera.Inordertorealizetheinterconnectionbetweendifferentnetworks,theUSDepartmentofDefensedevelopedtheTCP/IParchitectureandprotocolfrom1977to1979.TCP/IPiscomposedofagroupofmultiplesub-protocolsforprofessionalpurposes.Thesesub-protocolsincludeTCP,IP,UDP,ARP,ICMP,etc.TCP/IPhasdevelopedrapidlybyvirtueofitslowimplementationcost,safeandreliablecommunicationamongmultipleplatforms,androutableadvantages,andhasbecomeastandardprotocolintheInternet.Inthe1990s,TCP/IPhasbecomethepreferredprotocolinlocalareanetworks.Inthelatestoperatingsystems(suchasWindows7,WindowsXP,WindowsServer2003,etc.),TCP/IPhasbeenusedasthedefaultcommunicationprotocol.

NetBEUIprotocol

NetBEUI(NetBIOSEnhancedUserInterface)protocolisdevelopedandperfectedbyNetBIOS(NetworkBasicInputOutputSystem).TheprotocolonlyrequiressimpleconfigurationandlessNetworkresourceconsumption,andcanprovideverygooderrorcorrectionfunction,isafastandeffectiveprotocol.However,duetoitslimitednetworknodesupport(upto254nodes)andnon-routing,itisonlysuitableforsmalllocalareanetworksbasedontheWindowsoperatingsystem.

IPX/SPXprotocol

IPX/SPX(InternetPacketExchange/SerialPacketExchange)protocolismainlyusedinNovellLANbasedonNetWareoperatingsystem,andLANbasedonotheroperatingsystems(SuchasWindowsServer2003)cancommunicatewithNovellnetworkthroughIPX/SPXprotocol.InWindows2000/XP/2003systems,IPX/SPXprotocolandNetBEUIprotocolarecollectivelyreferredtoasNWLink.

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