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:
Thecommunicationfunctionisdividedintoseverallevels,eachThelevelcompletesapartofthefunction,andeachlevelcooperateswitheachothertocompletethecommunicationfunction.
Eachlayeronlydealswiththetwodirectlyadjacentlayers.Itusesthefunctionsprovidedbythenextlayertoprovidethehigherlayerwithservicesthatcanbecompletedbythislayer.
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.