Physicallayer
Thefirstlayeristhephysicallayer(thatis,thefirstandlowestlayerintheOSImodel)
Itisoftenoverlookedinclassof.Itseemsverysimple.However,certainaspectsofthislayersometimesrequirespecialattention.Thephysicallayerisactuallywiring,opticalfibers,networkcardsandotherthingsusedtoconnecttwonetworkcommunicationdevicestogether.Evenacarrierpigeoncanbeconsideredalayer1device.Networktroubleshootingofteninvolveslayer1issues.Wecan'tforgetthelegendarystoryofconnectingtheentirefloorwithafive-categoryline.Becauseofficechairsareoftenpressedoverthecables,thenetworkconnectionappearsintermittent.Unfortunately,suchfailuresareverycommon,andittakesalongtimetotroubleshootsuchfailures.
Datalinklayer
Thesecondlayeristhedatalinklayer
RunEthernetandotherprotocols.Remember,wewanttomakethisproblemsimpler.Themostimportantthinginlayer2isthatyoushouldunderstandwhatabridgeis.Theswitchcanberegardedasanetworkbridge,andpeoplecallitthatway.Thebridgesallworkatlayer2,focusingonlyontheMACaddressontheEthernet.IfyouaretalkingaboutMACaddresses,switchesornetworkcardsanddrivers,youareinthelayer2category.Hubsbelongtothefirstlayerofthedomain,becausetheyarejustelectronicdevices,withouttheknowledgeofthesecondlayer.Thesecond-levelrelatedissueshavetheirownpartinthiswebinar,soIwon’tdiscussthedetailsofthisissueindetail.Youonlyneedtoknowthatlayer2convertsthedataframeintobinarybitsforlayer1processing.
Networklayer
Thethirdlayeristhenetworklayer
Theremaybemanydatalinksbetweentwocomputerscommunicatinginacomputernetwork.Itmayalsopassthroughmanycommunicationsubnets.Thetaskofthenetworklayeristoselectappropriateroutingandswitchingnodesbetweennetworkstoensuretimelydatatransmission.Thenetworklayercomposestheframesprovidedbythedatalinklayerintodatapackets,andthepacketisencapsulatedwithanetworklayerheader,whichcontainslogicaladdressinformation-thenetworkaddressesofthesourcesiteandthedestinationsiteaddress.
IfyouaretalkingaboutanIPaddress,thenyouaredealingwithalayer3problem,whichisa"packet"problem,notalayer2"frame".IPispartofthelayer3problem,inadditiontosomeroutingprotocolsandaddressresolutionprotocol(ARP).Everythingaboutroutingishandledatlayer3.AddressresolutionandroutingareimportantpurposesofLayer3.
Informationtransportlayer
Thefourthlayeristhetransportlayerforprocessinginformation.
Thedataunitsoflayer4arealsocalledpackets.However,whenyoutalkaboutspecificprotocolssuchasTCP,therearespecialnames.ThedataunitsofTCParecalledsegmentsandthedataunitsofUDPprotocolarecalled"datagrams."Thislayerisresponsibleforobtainingallinformation.Therefore,itmustkeeptrackofdataunitfragments,out-of-sequencedatapacketsandotherhazardsthatmayoccurduringtransmission.Anotherwaytounderstandlayer4isthatlayer4providesend-to-endcommunicationmanagement.SomeprotocolslikeTCPareverygoodatensuringthereliabilityofcommunication.Someprotocolsdonotcarewhethersomedatapacketsarelost.UDPprotocolisaprimeexample.
Thefifthlayeristhesessionlayer
Thislayercanalsobecalledthemeetinglayerorthedialoguelayer.Inthehighlevelofthesessionlayerandabove,theunitofdatatransmissionisnolongerseparateNaming,collectivelyreferredtoasmessages.Thesessionlayerdoesnotparticipateinspecifictransmissions.Itprovidesmechanismsforestablishingandmaintainingcommunicationbetweenapplications,includingaccessverificationandsessionmanagement.Iftheserververifiestheuserloginiscompletedbythesessionlayer.
Thesixthlayeristhepresentationlayer
Thislayermainlysolvestheproblemofgrammaticalrepresentationofuserinformation.ItconvertsthedatatobeexchangedfromanabstractsyntaxsuitableforacertainusertoatransfersyntaxsuitableforinternaluseintheOSIsystem.Thatistoprovideformattedrepresentationandconversiondataservices.Thepresentationlayerisresponsiblefordatacompressionanddecompression,encryptionanddecryption.
Theseventhlayeris"everything".Layer7isalsocalledthe"applicationlayer".
isdedicatedtoapplications.Theapplicationlayerdeterminesthenatureofthecommunicationbetweenprocessestomeetuserneedsandprovideinterfaceservicesbetweenthenetworkanduserapplicationsoftware.Ifyourprogramrequiresdatainaspecificformat,youcaninventsomethingyouwanttobeabletosendthedatatothedestinationFormat,andcreatealayer7protocol.SMTP,DNSandFTParealllayer7protocols.
Correspondence
However,OSI/RMisanidealnetworkmodel.Inreality,theTCP/IPreferencemodeloccupiesmostofthenetwork.Thebriefdescriptionisasfollows:
TCP/IPreferencemodelisdividedintofourlayers
1.Applicationlayer(applicationlayer)
2.Transportlayer(transportlayer)
3.Internetlayer
4.Host-to-networklayer
TCP/IPreferenceCorrespondencebetweenthemodelandtheOSIinterconnectreferencemodel
Host-NetworkLayer
Thelowestlayerofthereferencemodel,responsibleforsendingandreceivingIPdatagramsthroughthenetwork;
Allowthehosttouseavarietyofready-madeandpopularprotocolswhenconnectingtothenetwork,suchasLANEthernet,tokennetwork,packetswitchingnetworkX.25,framerelay,ATMprotocol,etc.;
WhenaphysicalnetworkisusedasachannelfortransmittingIPdatapackets,itcanbeconsideredasthecontentofthislayer;
ItfullyreflectsthecompatibilityandadaptabilityoftheTCP/IPprotocol,anditisalsoTCPThesuccessof/IPlaidthefoundation.
Interconnectionlayer
EquivalenttoOSIreferencemodelnetworklayerconnectionlessnetworkservice;
Handleinterconnectionrouting,flowcontrolandcongestionissues;
p>TheIPprotocolisaconnectionlessnetworklayerprotocolthatprovides"besteffort"services.
Transportlayer
Themainfunctionistoestablishanend-to-endconnectionforconversationbetweenthepeerentitiesofthesourcehostandthedestinationhostintheInternet;
TransportThecontrolprotocolTCPisareliableconnection-orientedprotocol;
UserDatagramProtocolUDPisanunreliableconnectionlessprotocol.
Applicationlayer
Applicationlayerprotocolsmainlyinclude:
NetworkterminalprotocolTelnet
FiletransferprotocolFTP
SimpleMailTransferProtocolSMTP
DomainNameSystemDNS
SimpleNetworkManagementProtocolSNMP
HypertextTransferProtocolHTTP