计算机网络主要知识点

主要知识点2013年6月第一章概述网络概念及分类协议分层基本概念：协议，服务ISOOSI/RMTCP/IP/RM传输时延，传播时延Protocol,Service,InterfaceProtocolServicePrimitivesServicePrimitivesServiceUserServiceService

providerLayernLayern+1ServiceUserSAPSAPInterfaceInterfaceSAP--ServiceAccessPointRelationshipofServicestoProtocolsRecap:Service–sayswhatalayerdoesInterface–sayshowtoaccesstheserviceProtocol–sayshowistheserviceimplemented.：AsetofrulesandformatsthatgovernthecommunicationbetweentwopeersAlayerprovidesaservicetotheoneabove [vertical]Alayertalkstoitspeerusingaprotocol [horizontal]ISOOSI/RM与TCP/IP/RM计算机网络的主要性能指标带宽(bandwidth)时延(timedelay,latency)时延带宽积(BDP:Bandwidth-delayproduct)和往返时延(RTT：Round-TripTime)1.带宽(bandwidth)信号的带宽信号具有的频率宽度，单位为HZ、KHZ、MHZ线路的带宽模拟线路:通信线路允许通过的频带范围,单位HZ数字线路:用数据率(传送数字信号的速率)作为线路带宽单位为bps，kbps，Mbps，Gbps，Tp/s吞吐量

指每秒实际发送的比特数;对数字线路,带宽也表示吞吐量随着带宽的增大，数字信号在时间轴上的带宽就越窄2.时延(timedelay,latency)发送时延：发送数据时使数据块从结点进入到传输介质所需的时间发送时延＝数据块长度/信道带宽(传输速率)

传播时延：电磁波在信道中需要传播一定的距离而花费的时间

传播时延＝信道长度/电磁波在信道上的传播速度处理时延：数据在交换结点进行存储转发所花费的时间一般可用排队时延作为处理时延总时延＝发送时延＋传播时延＋处理时延传输速率(发送速率)和传播速率不同传输速率是指某个端口或某个点上的发送速率，单位为b/s；传播速率是指传输线路上比特的传播速率，单位为km/s.三种时延产生的地方2.时延(续)3.时延带宽积和往返时延时延带宽积=传播时延X带宽

时延带宽积表示链路可以容纳多少比特，又称为以比特为单位的链路长度。往返时延(Round-TripTime)：

从发送端发送数据开始，到发送端收到来自接收端的确认，总共经历的时延。往返时延带宽积=往返时延X带宽

表示当发送端发送数据时，在收到对方的确认之前，发送到链路上的比特数。第二章物理层四个特性奈奎斯特定理信道复用技术传输介质电路交换，包交换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第三章数据链路层零比特插入——解决透明传输问题CRC校验码计算停止等待协议滑动窗口连续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隐蔽站，暴露站IEEE802体系结构MACAddressEthernetMACFrame，最短帧长，帧突发技术互连设备，网桥/交换机的工作原理 VLAN802.11WLAN（不同帧间隔）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第五章网络层面向连接和无连接路由算法：DV，LS路由器IP协议（头部字段及含义、分片）分类地址、子网划分、超网、CIDR（地址聚集，路由最长匹配）、网络地址规划IP报文转发过程拥塞控制、QoS组播移动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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412A2132A43A5162F12A22A314153C62COSPF:ConceptofLinkStateRoutingExampleofformationofShortestPathTreeCalculatingofRoutingTablefromShortestPathTreeTable14.1RoutingtablefornodeA47CollegeofComputerScienceNATNAT(NetworkAddressTranslation)boxmapsoneexternalIPaddresstomanyinternalIPaddressesUsesTCP/UDPporttotellconnectionsapartViolateslayering;verycommoninhomes,etc.第六章运输层端口UDP，伪首部TCP，连接建立三次握手，连接释放四次握手，可靠传输，流控机制，MSS拥塞控制：慢启动，拥塞避免，快恢复客户/服务器Thenetworklayerisresponsibleforthe

deliveryofindividualpacketsfromthesourcehosttothedestinationhost.ThetransportlayerisresponsibleforthedeliveryofamessagefromoneprocesstoanotherTransportlayer