計(jì)算機(jī)網(wǎng)絡(luò)主要知識點(diǎn)

主要知識點(diǎn)2013年6月第一章概述網(wǎng)絡(luò)概念及分類協(xié)議分層基本概念：協(xié)議，服務(wù)ISOOSI/RMTCP/IP/RM傳輸時延，傳播時延Protocol,Service,InterfaceProtocolServicePrimitivesServicePrimitivesServiceUserServiceService

providerLayernLayern+1ServiceUserSAPSAPInterfaceInterfaceSAP--ServiceAccessPointRelationshipofServicestoProtocolsRecap:Service–sayswhatalayerdoesInterface–sayshowtoaccesstheserviceProtocol–sayshowistheserviceimplemented.：AsetofrulesandformatsthatgovernthecommunicationbetweentwopeersAlayerprovidesaservicetotheoneabove [vertical]Alayertalkstoitspeerusingaprotocol [horizontal]ISOOSI/RM與TCP/IP/RM計(jì)算機(jī)網(wǎng)絡(luò)的主要性能指標(biāo)帶寬(bandwidth)時延(timedelay,latency)時延帶寬積(BDP:Bandwidth-delayproduct)和往返時延(RTT：Round-TripTime)1.帶寬(bandwidth)信號的帶寬信號具有的頻率寬度，單位為HZ、KHZ、MHZ線路的帶寬模擬線路:通信線路允許通過的頻帶范圍,單位HZ數(shù)字線路:用數(shù)據(jù)率(傳送數(shù)字信號的速率)作為線路帶寬單位為bps，kbps，Mbps，Gbps，Tp/s吞吐量

指每秒實(shí)際發(fā)送的比特?cái)?shù);對數(shù)字線路,帶寬也表示吞吐量隨著帶寬的增大，數(shù)字信號在時間軸上的帶寬就越窄2.時延(timedelay,latency)發(fā)送時延：發(fā)送數(shù)據(jù)時使數(shù)據(jù)塊從結(jié)點(diǎn)進(jìn)入到傳輸介質(zhì)所需的時間發(fā)送時延＝數(shù)據(jù)塊長度/信道帶寬(傳輸速率)

傳播時延：電磁波在信道中需要傳播一定的距離而花費(fèi)的時間

傳播時延＝信道長度/電磁波在信道上的傳播速度處理時延：數(shù)據(jù)在交換結(jié)點(diǎn)進(jìn)行存儲轉(zhuǎn)發(fā)所花費(fèi)的時間一般可用排隊(duì)時延作為處理時延總時延＝發(fā)送時延＋傳播時延＋處理時延傳輸速率(發(fā)送速率)和傳播速率不同傳輸速率是指某個端口或某個點(diǎn)上的發(fā)送速率，單位為b/s；傳播速率是指傳輸線路上比特的傳播速率，單位為km/s.三種時延產(chǎn)生的地方2.時延(續(xù))3.時延帶寬積和往返時延時延帶寬積=傳播時延X帶寬

時延帶寬積表示鏈路可以容納多少比特，又稱為以比特為單位的鏈路長度。往返時延(Round-TripTime)：

從發(fā)送端發(fā)送數(shù)據(jù)開始，到發(fā)送端收到來自接收端的確認(rèn)，總共經(jīng)歷的時延。往返時延帶寬積=往返時延X帶寬

表示當(dāng)發(fā)送端發(fā)送數(shù)據(jù)時，在收到對方的確認(rèn)之前，發(fā)送到鏈路上的比特?cái)?shù)。第二章物理層四個特性奈奎斯特定理信道復(fù)用技術(shù)傳輸介質(zhì)電路交換，包交換FromSignalstoPackets001011100010100010101011100101010101011101110000001111010101110101010101101Header/BodyHeader/BodyHeader/BodyReceiverSenderApplicationPresentationSessionTransportNetworkDatalinkPhysicalFourcharacteristicsMechanicalcharacteristics:mechanicalspecificationofelectricalconnectorsandcables,forexamplemaximumcablelengthElectricalcharacteristics:electricalspecificationoftransmissionlinesignallevelandimpedanceFunctionalcharacteristics:thefunctionlogicofelectricsignalsgeneratedoncertainwiresinthephysicalmediaProceduralcharacteristics:theproceduresofprotocolsthatcontrolthesequenceofeventsMaximumDataRateofaChannelNyquist’stheoremrelatesthedataratetothebandwidth(B)andnumberofsignallevels(V):Shannon'stheoremrelatesthedataratetothebandwidth(B)andsignalstrength(S)relativetothenoise(N):

Oftenexpressedindecibels(db)::=10log10(S/N)Max.datarate=2Blog2Vbits/secMax.datarate=Blog2(1+S/N)bits/secHowfastsignalcanchangeHowmanylevelscanbeseenMultiplexingTechniquesmultiplexingschemesshareachannelamongusers.FrequencyDivisionMultiplexingTimeDivisionMultiplexingWavelengthDivisionMultiplexingCodeDivisionMultipleAccessTransmissionMedia

GuidedTransmissionMedia

Realitycheck：Storagemedia

Wires:Twistedpairs，Coaxialcable，Powerlines

Fibercables

WirelessTransmission

CommunicationSatellitesSwitchingcircuitswitched

networksvs.packet-switchednetworksDatagramPacketSwitchingvs.Virtual-CircuitPacketSwitching第三章數(shù)據(jù)鏈路層零比特插入——解決透明傳輸問題CRC校驗(yàn)碼計(jì)算停止等待協(xié)議滑動窗口連續(xù)AQR，gobacknHDLC（High-LevelDataLinkControl）PPP（Point-to-PointProtocol）ARQ:AutomaticRepeatreQuestPAR:PositiveAcknowledgementwithRetransmissionAone-bitSlidingProtocol:Stop-and-WaitProtocolContinualARQProtocol:Go-Back-NSelectiveARQ(2)SlidingWindowProtocolbeusedtodescribeandimplementtheARQsProtocolifWT=1,WR=1thenSlidingWindowProtocol=one-bitStop-and-WaitProtocolifWT>1,WR=1thenSlidingWindowProtocol

=ContinualARQifWT>1,WR>1thenSlidingWindowProtocol=SelectiveARQ

SlidingWindowProtocolandARQs第四章MACALOHA，CSMA，CSMA/CD，CSMA/CA，RTS/CTS隱蔽站，暴露站IEEE802體系結(jié)構(gòu)MACAddressEthernetMACFrame，最短幀長，幀突發(fā)技術(shù)互連設(shè)備，網(wǎng)橋/交換機(jī)的工作原理 VLAN802.11WLAN（不同幀間隔）MultipleaccessprotocolsFDMATDMACDMAControlled-accessprotocolStaticmodelDynamicmodelWDMAswitchingRandomAccessProtocolMultiplexingallowsseveraltransmissionsourcestosharealargertransmissioncapacity.Oftenusedinhierarchicalstructures.Multipleaccess:twoormoresimultaneoustransmissionsshareabroadcastchannel.OftenusedinaccessnetworksMultipleAccessProtocolLimited-ContentionProtocolOne-bitmapBinaryCountdownTreewalkIfthetwonodesinvolvedinacollisionarethemaximumdistanceapart,thesignalfromthefirsttakestimetoreachthesecond,andtheeffectofthecollisiontakesanothertime

toreachthefirst.Sotherequirementisthatthefirstnodemuststillbetransmittingafter2.MinimumFrameSizeisnecessaryinCSMA/CDMinimumFrameSize=2×Ts(transmissionrate)

Repeaters,Hubs,Bridges,Switches,Routers&GatewaysVLAN：VirtualLANPort-basedVLANMAC-basedVLANProtocol-basedVLANIPAddress-basedVLANDifferentIFSDifferentIFSs(differentinterframespaces)havedifferentpriorityrightstoacquirethechannel

SFIS<PIFS<DIFS<EIFS(SFIS<AIFS1<DIFS<AIFS2<EIFS,AIFs:Arbitraryinter-framespace,IEEE802.11e,QoS)SIFS(ShortestInterFrameSpace),28μshighestpriority,forACK,RTS,CTS,pollingresponseetc.PIFS(PCFIFS)(DCF->PCF)(PCFInterFrameSpacing),28+50=78μsmediumpriority,fortime-boundedserviceusingPCFDIFS(DCFIFS)(DCFInterFrameSpacing),78+50=128μslowestpriority,forasynchronousdata

serviceEIFS:ExtendedInterFrameSpacing第五章網(wǎng)絡(luò)層面向連接和無連接路由算法：DV，LS路由器IP協(xié)議（頭部字段及含義、分片）分類地址、子網(wǎng)劃分、超網(wǎng)、CIDR（地址聚集，路由最長匹配）、網(wǎng)絡(luò)地址規(guī)劃IP報(bào)文轉(zhuǎn)發(fā)過程擁塞控制、QoS組播移動IPNATIPv6（了解）ICMP，ARPRIP，OSPFBGP（了解）MPLS（了解）PositionofIPv4inTCP/IPprotocolsuite29CollegeofComputerScience

10000000000010110000001100011111100000000000101100000011000111111128

11331DotteddecimalnotationRoutingtablesIPdeliverybasingonipandsubnetEachrouterandeachhostkeepsaroutingtablewhichtellstherouterhowtoprocessanoutgoingpacketMaincolumns:Destinationaddress:whereistheIPdatagramgoingto?SubnetMasksNexthoporinterface:howtosendtheIPdatagram?RoutingtablesaresetsothatadatagramgetsclosertotheitsdestinationRoutingtableofahostorrouterIPdatagramscanbedirectlydelivered(“direct”)oraresenttoanexthoprouter(“R2”)DestinationnetworkaddressSubnetmaskNexthop282828Interface0Interface1R231CollegeofComputerScienceIPAddresses:CIDRAddressesareallocatedinblockscalledprefixesPrefixisdeterminedbythenetworkportionHas2Laddressesalignedon2LboundaryWrittenaddress/length,e.g.,/2432CollegeofComputerScienceIPAddresses–CIDRAggregationAggregationjoinsmultipleIPprefixesintoasinglelargerprefixtoreduceroutingtablesizeISPcustomershavedifferentprefixesISPadvertisesasingleprefixClasslessInter-DomainRouting33CollegeofComputerScienceIPAddress

andPhysicalAddress

TCPmessageIPDatagramMACFrameDataofApplicationLayerHeaderHeaderTailHeaderLinklayerandthefollowingusingthePhysicaladdressPhysicalAddressNetworklayerandaboveusingtheIPaddress

IPAddressPhysicalAddressHardwareAddressMACAddress34CollegeofComputerScience35CollegeofComputerScienceIPAddresses(3)–CIDRAggregationAggregationjoinsmultipleIPprefixesintoasinglelargerprefixtoreduceroutingtablesizeISPcustomershavedifferentprefixesISPadvertisesasingleprefixClasslessInter-DomainRoutingAS,IGPandEGPIGPEGPPopularroutingprotocols(OpenShortestPathFirst)--LinkStateRouting(RoutingInformationProtocol)--DistanceVectorRouting(BorderGatewayProtocol)112131FEDCBA51612151314141611151net

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1112131416112A22A314162CupdateFinally,routingtableofallroutersupdated.FEDCBA11213142B52E63B1122A32A43A5162F12E22D33C42C516113B23B32B4152F61net

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412A2132A43A5162F12A22A314153C62COSPF:ConceptofLinkStateRoutingExampleofformationofShortestPathTreeCalculatingofRoutingTablefromShortestPathTreeTable14.1RoutingtablefornodeA47CollegeofComputerScienceNATNAT(NetworkAddressTranslation)boxmapsoneexternalIPaddresstomanyinternalIPaddressesUsesTCP/UDPporttotellconnectionsapartViolateslayering;verycommoninhomes,etc.第六章運(yùn)輸層端口UDP，偽首部TCP，連接建立三次握手，連接釋放四次握手，可靠傳輸，流控機(jī)制，MSS擁塞控制：慢啟動，擁塞避免，快恢復(fù)客戶/服務(wù)器Thenetworklayerisresponsibleforthe

deliveryofindividualpacketsfromthesourcehosttothedestinationhost.ThetransportlayerisresponsibleforthedeliveryofamessagefromoneprocesstoanotherTransportlayer