国家软件资格水平考试 网络工程师 王维轩 Objectives Oncompletionofthischapter youwillbeabletoperformthefollowingtasks DescribehowdatatrafficisexchangedbetweensourceanddestinationdevicesIdentifytherolesandfunctionsofahub switch androuter andwheretheybestfitinthenetworkIdentifytheIPprotocolstack itsprotocollayerfunctions andcommonlyusedIPprotocolsIdentifyIPaddressclasses IPaddresses IPsubnetmasks IPnetworknumbers subnetnumbers andpossiblehostnumbers 网络体系结构 DefiningComponentsoftheNetwork MainOffice BranchOffice HomeOffice MobileUsers Internet Floor2 Floor1 ServerFarm DefiningtheComponentsofaNetwork BranchOffice Telecommuter ISDN Remote Campus NetworkStructureDefinedbyHierarchy DistributionLayer CoreLayer AccessLayer AccessLayerCharacteristics Endstationentrypointtothenetwork AccessLayer DistributionLayercharacteristics AccessLayerAggregationPointRoutestrafficBroadcast MulticastDomainsMediaTranslationSecurityPossiblepointforremoteaccess DistributionLayer CoreLayerCharacteristics FasttransporttoenterpriseservicesNopacketmanipulation CoreLayer OSIModelOverview Application Upper Layers Session Presentation Application OSIModelOverview DataFlowLayers TransportLayer DataLink NetworkLayer Physical RoleofApplicationLayers TelnetFTP UserInterface EXAMPLES Application TelnetFTP ASCIIEBCDICJPEG UserInterface HowdataispresentedSpecialprocessingsuchasencryption EXAMPLES Presentation Application RoleofApplicationLayers TelnetFTP ASCIIEBCDICJPEG Keepingdifferentapplications dataseparate UserInterface HowdataispresentedSpecialprocessingsuchasencryption OperatingSystem ApplicationAccessScheduling EXAMPLES Session Presentation Application RoleofApplicationLayers Keepingdifferentapplications dataseparate UserInterface HowdataispresentedSpecialprocessingsuchasencryption TransportLayer DataLink NetworkLayer Physical EXAMPLES Session Presentation Application RoleofApplicationLayers RoleofDataFlowLayers EIA TIA 232V 35 EXAMPLES Physical MovebitsbetweendevicesSpecifiesvoltage wirespeedandpin outcables 802 3 802 2HDLC EIA TIA 232V 35 EXAMPLES RoleofDataFlowLayers DataLink Physical CombinesbitsintobytesandbytesintoframesAccesstomediausingMACaddressErrordetectionnotcorrection MovebitsbetweendevicesSpecifiesvoltage wirespeedandpin outcables 802 3 802 2HDLC EIA TIA 232V 35 IPIPX EXAMPLES RoleofDataFlowLayers Network DataLink Physical CombinesbitsintobytesandbytesintoframesAccesstomediausingMACaddressErrordetectionnotcorrection MovebitsbetweendevicesSpecifiesvoltage wirespeedandpin outcables Providelogicaladdressingwhichroutersuseforpathdetermination TCPUDPSPX 802 3 802 2HDLC EIA TIA 232V 35 IPIPX EXAMPLES RoleofDataFlowLayers Transport DataLink Physical ReliableorunreliabledeliveryErrorcorrectionbeforeretransmit CombinesbitsintobytesandbytesintoframesAccesstomediausingMACaddressErrordetectionnotcorrection MovebitsbetweendevicesSpecifiesvoltage wirespeedandpin outcables Network Providelogicaladdressingwhichroutersuseforpathdetermination TCPUDPSPX 802 3 802 2HDLC EIA TIA 232V 35 IPIPX Presentation Application Session EXAMPLES RoleofDataFlowLayers ReliableorunreliabledeliveryErrorcorrectionbeforeretransmit CombinesbitsintobytesandbytesintoframesAccesstomediausingMACaddressErrordetectionnotcorrection MovebitsbetweendevicesSpecifiesvoltage wirespeedandpin outcables Transport DataLink Physical Network Providelogicaladdressingwhichroutersuseforpathdetermination EncapsulatingData Transport DataLink Physical Network UpperLayerData UpperLayerData TCPHeader Data IPHeader Data LLCHeader 0101110101001000010 Data MACHeader Presentation Application Session Segment Packet Bits Frame PDU UpperLayerData De encapsulatingData LLCHdr IP TCP UpperLayerData MACHeader IP TCP UpperLayerData LLCHeader TCP UpperLayerData IPHeader UpperLayerData TCPHeader 0101110101001000010 Transport DataLink Physical Network Presentation Application Session Application Presentation Session Transport Network DataLink Physical OSIModel PDU FunctionalResponsibilities Examples WrittenExercise OSIModel PhysicalLayerFunctions DefinesMediatypeConnectortypeSignalingtype Ethernet 802 3 V 35 Physical EIA TIA 232 PhysicalLayer Ethernet 802 3 Hub Hosts Host 10Base2 ThinEthernet10Base5 ThickEthernet 10BaseT TwistedPair HubsOperateatPhysicallayer A B C D Physical AlldevicesinthesamecollisiondomainAlldevicesinthesamebroadcastdomainDevicessharethesamebandwidth Hubs OneCollisionDomain MoreendstationsmeansmorecollisionsCSMA CDisused DataLinklayerFunctions DefinesPhysicalsourceanddestinationaddressesHigherlayerprotocol ServiceAccessPoint associatedwithframeNetworktopologyFramesequencingFlowcontrolConnection orientedorconnectionless DataLink Physical EIA TIA 232v 35 Ethernet FrameRelay HDLC 802 2 802 3 Data Sourceadd FCS Length Destadd Variable 2 6 6 4 0000 0Cxx xxxx Vendorassigned IEEEassigned MACLayer 802 3 DataLinkLayerFunctions cont Preamble EthernetIIuses Type hereanddoesnotuse802 2 MACAddress 8 Bytes EachsegmenthasitsowncollisiondomainAllsegmentsareinthesamebroadcastdomain DataLink SwitchesandBridgesOperateatDataL