信息通信網(wǎng)絡(luò)概論：第5章 分組交換網(wǎng)-數(shù)據(jù)報網(wǎng)絡(luò)-LAN

2022/11/2NCRL1第5章分組交換網(wǎng)——數(shù)據(jù)報網(wǎng)絡(luò)PacketSwitching分割用戶報文——Packet加上分組控制信息Store-and-ForwardConnectionless——DatagramConnectionOriented——VirtualCircuit2022/11/2NCRL2第5章分組交換網(wǎng)與數(shù)據(jù)報網(wǎng)絡(luò)5.1計算機局域網(wǎng)(LAN)5.2局域網(wǎng)的擴展5.3廣域網(wǎng)與網(wǎng)絡(luò)互聯(lián)5.4TCP/IP技術(shù)與Internet2022/11/2NCRL35.1LocalAreaNetworks5.1.1OverviewofLAN5.1.2ArchitectureofLAN5.1.3IEEE802.3Ethernet5.1.4IEEE802.5

TokenRing5.1.5IEEE802.4TokenBus5.1.6Comparisonof3typeofLANs2022/11/2NCRL45.1.1OverviewofLANLimitedcoverage,limitedamountofTerminalHighertransmissionspeedLowerdelayandlowerBERSimpleprotocolCapableofbroadcastandmulticast2022/11/2NCRL55.1.1OverviewofLANMediumTwistedpair,Coaxialcable,Fiber,Wireless

TopologyStar,Bus,Ring,TreeMACtechnologyCSMATokenRingTokenBusFDDI2022/11/2NCRL62022/11/2NCRL75.1.2ArchitectureofLANIEEE

LANReferenceModelLayeringfunctionaldescriptionIEEE802SerialStandardsMACaddressandSAPaddressServicesprovidedbyLLC2022/11/2NCRL8IEEE

LANReferenceModelDatalinklayerMediumAccessControlLogicallinkcontrolHigherlayerNetworklayerPhysicallayerOSIIEEE802physicallayers()()()SAP2022/11/2NCRL9LayeringfunctionaldescriptionPhysicallayercodinganddecodingaddandremovepreambleforsyncbitsyncandastransceiver除此之外，還有對OSI/RM物理層以下的媒體進行說明傳輸媒體的規(guī)范說明拓撲結(jié)構(gòu)的規(guī)范說明2022/11/2NCRL10LayeringfunctionaldescriptionMediumAccessControlSub-layer

與傳輸媒質(zhì)有關(guān)CoordinateaccesstomediumConnectionlessframetransferserviceMachinesidentifiedbyMAC/physicaladdressBroadcastframeswithMACaddresses2022/11/2NCRL11LayeringfunctionaldescriptionLogicLinkControl

與媒體接入無關(guān)logicallinkestablishingandreleasingdatatransfermonitoring(errorcontrolandflowcontrolforpointtopointtransfer)

BetweenNetworklayer&MACsub-layer2022/11/2NCRL12Layeringfunctionaldescription將數(shù)據(jù)鏈路層分成兩個子層的根本目的：使LLC子層及其上面看不到具體的局域網(wǎng)（總線網(wǎng)、令牌總線網(wǎng)或令牌環(huán)形網(wǎng)）。只有下到MAC子層才可看見所連接的是采用什么標準的局域網(wǎng)。

2022/11/2NCRL13LayeringfunctionaldescriptionLLCPDU

andMACPDU

2022/11/2NCRL14IEEE802SerialStandardsIEEE802委員會有13個分委員會，分別負責下述方面的標準的研究與制定：●802.1--概述、體系結(jié)構(gòu)和網(wǎng)絡(luò)互連，以及網(wǎng)絡(luò)管理和性能測量?！?02.2--邏輯鏈路控制。這是高層協(xié)議與任何一種局域網(wǎng)MAC子層的接口?！?02.3--CSMA／CD。定義CSMA／CD總線網(wǎng)的MAC子層和物理層的規(guī)約。●802.4--令牌總線網(wǎng)。定義令牌傳遞總線網(wǎng)的MAC子層和物理層的規(guī)約?！?02.5--令牌環(huán)形網(wǎng)。定義令牌傳遞環(huán)形網(wǎng)的MAC子層和物理層的規(guī)約?！?02.6--城域網(wǎng)MAN。定義城域網(wǎng)的MAC子層和物理層的規(guī)約?！?02.7--寬帶技術(shù)?！?02.8--光纖技術(shù)?！?02.9--綜合話音數(shù)據(jù)局域網(wǎng)。

●802.10--可互操作的局域網(wǎng)的安全。●802.11--無線局域網(wǎng)。●802.12--優(yōu)先級高速局域網(wǎng)(100Mb／s)。●802.14--電纜電視(Cable-TV)。●802.15--無線個域網(wǎng)●802.16--寬帶無線接入網(wǎng)●802.20--移動無線寬帶接入網(wǎng)（MBWA）●802.21--異構(gòu)網(wǎng)絡(luò)的切換和互操作●802.22--無線區(qū)域網(wǎng)（WRAN）2022/11/2NCRL15IEEE802SerialStandards802.10Security802.1

Architecture802.1Manage802.3CSMA/CD802.4TokenBus802.5TokenRing802.6MAN802.11WLAN802.15WPAN802.16WBA802.3PL802.4PL802.5PL802.6PL802.11PL802.15PL802.16PLPHY802.2LLC802.1BridgeMACLLC網(wǎng)際互連2022/11/2NCRL16MACaddressandSAPaddressTwotypesofaddressindatalinklayerofLANsMAC

address:PhysicaladdressofDTE，transmittedinMACframeSAPaddress:LogicaladdressofprocessinoneDTE,transmittedinLLCframeTwostepsofaddressingStep1.OneDTEgettheMACframebyMACaddressStep2.OneprocessgetpacketfromLLCbySAPaddressConcludeAworkstationhasasingleMACphysicaladdressCanhandleseverallogicalconnections,distinguishedbytheirSAP(serviceaccesspoints).2022/11/2NCRL17MACaddressandSAPaddress（2）（1）（1）

（3）DTEADTEBDTECLANprocessxyabcmSAPLLCLLCLLCMACMACMACPHYPHYPHY（1）（2）18LogicalLinkControlServicesType1:UnacknowledgedconnectionlessserviceUnnumberedframemodeofHDLCType2:Reliableconnection-orientedserviceAsynchronousbalancedmodeofHDLCType3:Acknowledgedconnectionlessservice19LLCPDUStructure1SourceSAPAddressInformation1Control1or2bytesDestinationSAPAddressSourceSAPAddressI/G7bits1C/R7bits1I/G=IndividualorgroupaddressC/R=CommandorresponseframeDestinationSAPAddress1byteExamplesofSAPAddresses:06 IPpacketE0 NovellIPXFE OSIpacketAA SubNetworkAccessprotocol(SNAP)20EncapsulationofMACframesIPLLCHeaderDataMACHeaderFCSLLCPDUIPPacket2022/11/2NCRL215.1.3IEEE802.3CSMA/CD22Abitofhistory…1970ALOHAnetradionetworkdeployedinHawaiianislands1975EthernetI(2.94Mbps)byXerox(施樂)1979DIXEthernetIIStandard

(DEC,Intel,Xerox)1985IEEE802.3LANStandard(10Mbps)1990/1993,EthernetSwitch/full-duplexbyKalpana1995FastEthernet(100Mbps)1998GigabitEthernet200210GigabitEthernetEthernetisthedominantLANstandard23IEEE802.3MAC:EthernetMACProtocol:CSMA/CDSlotTimeisthecriticalsystemparameterTruncatedbinaryexponentialbackoffforretransmissionn:0=<r<2k-1,wherek=min(n,10)Giveupafter16retransmissionsBsenddatato

DCDAE匹配電阻（用來吸收總線上傳播的信號）匹配電阻NoNoNoAcceptB24CSMA/CDcollisiondetectionStationscantransmitjammingsignalswhencollisionbedetected25ThebinaryexponentialbackoffalgorithmAfteracollision,thestationwaitsforarandomtimeandtryagain.Howtherandomizationisdone

?Timeisdividedintodiscreteslotswhoselengthisequaltotheworstcaseroundtrippropagationtime(2).Afterthefirstcollision,eachstationwaitseither0or1slottimeatrandom.Afterthesecondcollision,eachstationwaitseither0,1,2,or3slottimesatrandom.Aftericollisions,arandomnumberbetween0and2i

–1ischosen,andthatnumberofslotsisskipped.After10collisionshavebeenreached,therandomizationintervalisfrozenat1023slots.After16collisions,thecontrollergivesupandreportsfailure.

26EthernetPerformanceEfficiencyofEthernetat10Mbpswith512-bitslottimes.27IEEE802.3OriginalParametersTransmissionRate:10MbpsMinFrame:512bits=64bytesWhy?Slottime:512bits/10Mbps=51.2μsec51.2μsecx2x105km/sec=10.24km,1way5.12kmroundtripdistanceMaxLength:2500meters+4repeaters

Eachx10increaseinbitrate,mustbeaccompaniedbyx10decreaseindistanceLmin/R=2*S/(0.7*C)+2*Tphy+n*Tr

28IEEE802.3OriginalParametersMaxFrame:1500bytesWhy?為避免單一主機占用信道時間過長，以及鏈路傳輸效率。IFG(Inter-frameGap)=96bit(9.6μs)why?讓物理信道恢復平穩(wěn)讓接收者有時間對接收的幀作必要的處理；

29IEEE802.3OriginalParameters30IEEE802.3MACFramePreambleSDDestinationaddressSourceaddressLengthInformationPadFCS71662464-1518bytesSynchStartframe802.3MACFrameEveryframetransmissionbegins“fromscratch”Preamblehelpsreceiverssynchronizetheirclockstotransmitterclock7bytesof10101010generateasquarewaveStartframebytechangesto10101011

Receiverslookforchangein10pattern31IEEE802.3MACFramePreambleSDDestinationaddressSourceaddressLengthInformationPadFCS71662464-1518bytesSynchStartframe0Singleaddress1GroupaddressDestinationaddresssingleaddressgroupaddressbroadcast=111...111AddresseslocalorglobalGlobaladdressesfirst24bitsassignedtomanufacturer;next24bitsassignedbymanufacturerCisco00-00-0C3COM02-60-8C0Localaddress1Globaladdress802.3MACFrame32IEEE802.3MACFramePreambleSDDestinationaddressSourceaddressLengthInformationPadFCS71662464-1518bytesSynchStartframe802.3MACFrameLength:#bytesininformationfieldMaxframe1518bytes,excludingpreamble&SDMaxinformation1500bytes:05DCPad:ensuresminframeof64bytesFCS:CCITT-32CRC,coversaddresses,length,information,padfieldsNICdiscardsframeswithimproperlengthsorfailedCRC33DIXEthernetIIFrameStructurePreambleSDDestinationaddressSourceaddressTypeInformationPadFCS71662464-1518bytesSynchStartframeEthernetIIMACFrameDIX:Digital,Intel,XeroxjointEthernetspecificationTypeField:toidentifyprotocolofPDUininformationfield,e.g.IP,ARP（＞0600H）Framing:Howdoesreceiverknowframelength?physicallayersignal34IEEE802.3PhysicalLayer(a)transceivers(b)10base510base210baseT10baseFXMediumThickcoaxThincoaxTwistedpairOpticalfiberMax.SegmentLength500m200m100m2kmTopologyBusBusStarPoint-to-pointlinkTable6.2IEEE802.310MbpsmediumalternativesThickCoax:Stiff,hardtoworkwithTconnectorsflakyHubs&Switches!Threeparameters:bitrate,transmissiontechnique,max.segmentlength.35PhysicalLayer(Cont.)ManchesterEncodingusedin802.3Naming10Base510Base210BaseT001010110ClockManchester36PhysicalLayer(Cont.)37EthernetHubs&Switches(a)Singlecollisiondomain(b)High-SpeedbackplaneorinterconnectionfabricTwistedPairCheapEasytoworkwithReliablePhysicallyStar-topologyCSMA-CD(Logicallystillbus–topology)Nocollisionsunlessmultiplestationssharesameinputline38FastEthernet100baseT4100baseT100baseFXMediumTwistedpaircategory3UTP4pairsTwistedpaircategory5UTPtwopairsOpticalfibermultimodeTwostrandsMax.SegmentLength100m100m2kmTopologyStarStarStarTableIEEE802.3100MbpsEthernetmediumalternativesTopreservecompatibilitywith10MbpsEthernet:Sameframeformat,sameinterfaces,sameprotocolsHubtopologyonlywithtwistedpair&fiberBustopology&coaxialcableabandonedCategory3twistedpair(ordinarytelephonegrade)requires4pairsCategory5twistedpairrequires2pairs(mostpopular)MostprevalentLANtoday39GigabitEthernetTable6.4IEEE802.31GbpsFastEthernetmediumalternatives1000baseSX1000baseLX1000baseCX1000baseTMediumOpticalfibermultimodeTwostrandsOpticalfibersinglemodeTwostrandsShieldedcoppercableTwistedpaircategory6UTPMax.SegmentLength550m5km25m100mTopologyStarStarStarStarSlottimeincreasedto512bytes(ratherthan64bytes)Smallframesneedtobeextendedto512BFrameburstingtoallowstationstotransmitburstofshortframesFramestructurepreservedbutCSMA-CDessentiallyabandonedExtensivedeploymentinbackboneofenterprisedatanetworksandinserverfarms40GigabitEthernetTable6.5IEEE802.310GbpsEthernetmediumalternatives10GbaseSR10GBaseLR10GbaseEW10GbaseLX4MediumTwoopticalfibersMultimodeat850nm64B66BcodeTwoopticalfibersSingle-modeat1310nm64B66BTwoopticalfibersSingle-modeat1550nmSONETcompatibilityTwoopticalfibersmultimode/single-modewithfourwavelengthsat1310nmband8B10BcodeMax.SegmentLength300m10km40km300m–10kmFramestructurepreservedCSMA-CDprotocolofficiallyabandonedLANPHYforlocalnetworkapplicationsWANPHYforwideareainterconnectionusingSONETOC-192cExtensivedeploymentinmetronetworksanticipated41Server100Mbpslinks10MbpslinksServerServerServer100Mbpslinks10MbpslinksServer100Mbpslinks10MbpslinksServerGigabitEthernetlinksGigabitEthernetlinksServerfarmDepartmentADepartmentBDepartmentCHubHubHubEthernetswitchEthernetswitchEthernetswitchSwitch/routerSwitch/routerTypicalEthernetDeployment2022/11/2NCRL425.1.4IEEE802.5TokenRing43IEEE802.5RingLANUnidirectionalringnetwork4Mbpsand16MbpsontwistedpairDifferentialManchesterlinecodingTokenpassingprotocolprovidesaccessFairnessAccessprioritiesBreaksinringbringentirenetworkdownReliabilitybyusingstartopology44StarTopologyRingLANStationsconnectedinstarfashiontowiringclosetUseexistingtelephonewiringRingimplementedinsideequipmentboxRelayscanbypassfailedlinksorstations2022/11/2NCRL455.1.5IEEE802.4TokenBus總線局域網(wǎng)的爭用總線策略使得它不很適用于工廠的一些對時間有嚴格要求的實時控制系統(tǒng)。令牌環(huán)形網(wǎng)中的令牌繞網(wǎng)一周的時間雖有一個上限值，但它在輕載時的性能不太好，并且還采用了許多的干線耦合器（這里面使用了有源器件）連接成環(huán)路的，其可靠性要比無源的總線要差些。在這種情況下，綜合這兩種局域網(wǎng)的優(yōu)點的令牌總線局域網(wǎng)就產(chǎn)生了。這就是802.4標準。

2022/11/2NCRL465.1.5IEEE802.4TokenBus令牌總線局域網(wǎng)兩個主要特點：在物理上是一個總線網(wǎng)（實際可為星型網(wǎng)），而在邏輯上卻是一個令牌網(wǎng)。令牌傳遞的順序與站的物理位置無關(guān)。

下圖中（x，y，z）表示x是z的前導節(jié)點，y是z的后續(xù)節(jié)點。可以看出來，圖中令牌的傳遞順序為D→A→C→B→E→D…的順序傳遞。2022/11/2NCRL475.1.5IEEE802.4TokenBus令牌總線局域網(wǎng)具有的優(yōu)點既有總線網(wǎng)的“接入方便”和“可靠性較高”的優(yōu)點又有令牌環(huán)形網(wǎng)的“無沖突”和“發(fā)送時延有確定的上限值”的優(yōu)點。

2022/11/2NCRL485.2ExtensionofLAN

由局域網(wǎng)的定義可知它從設(shè)計之初就限制了最大傳輸距離，這主要是由于它采用的技術(shù)決定的。因此擴展局域網(wǎng)必須解決信道共享和信號衰減兩個問題。使用中繼器擴展局域網(wǎng)使用網(wǎng)橋擴展局域網(wǎng)用網(wǎng)橋擴展不同種局域網(wǎng)49Hubs,Bridges&RoutersInterconnectingofLANs

Repeater:interconnectedatphysicallayerSignalregenerationAlltrafficappearsinbothLANsChannelsaturations…Securityandrobustnessproblem

Bridge:interconnectedatMACorDataLinkLayerMACaddressfilteringLocaltrafficstaysinownLAN

Routers:interconnectedatnetworklayer

Gateway:interconnectedathigherlayerthannetworklayerBridgeS1S2S4S3S5S6LAN1LAN250Hubs,Bridges&RoutersHub:ActivecentralelementinastartopologyTwistedPair:inexpensive,easytoinsallSimplerepeaterinEthernetLANs“Intelligenthub”:faultisolation,netconfiguration,statisticsRequirementsthatarise:HubStationStationStationTwoTwistedPairsHubStationStationStationTwoTwistedPairs?Hub51Operationatdatalinklevelimpliescapabilitytoworkwithmultiplenetworktypes(irrelevanttonetworklayer)However,mustdealwithDifferenceinMACformatsDifferenceindatarates,buffering,timersDifferenceinmaximumframelengthsPHYMACLLCNetworkNetworkPHYMACLLC802.3802.3802.5802.5802.3802.3802.3802.5802.5802.5CSMA/CDTokenRingGeneralBridgeIssues52BridgeNetworkPhysicalNetworkLLCPhysicalPhysicalPhysicalLLCMACMACMACMACBridgesofSameTypeCommoncaseinvolvesLANsofsametypeBridgingisdoneatMAClevel53InterconnectionofIEEELANswithcompletetransparencyUsetablelookup,anddiscardframe,ifsource&destinationinsameLANforwardframe,ifsource&destinationindifferentLANuseflooding,ifdestinationunknownUsebackwardlearni