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1、Chapter 1: Computer Network and Internet计算机网络原理计算机网络原理Computer NetworkChapter 1: Computer Network and Internet课程要求课程要求u了解了解计算机网络的体系结构，计算机网络的体系结构，掌握掌握TCP/IP网络的体系结构网络的体系结构u了解了解计算机网络协议的概念、协议层次及各层次的主要协议计算机网络协议的概念、协议层次及各层次的主要协议u掌握掌握主要的网络传输介质、数据交换的主要类型及基本原理主要的网络传输介质、数据交换的主要类型及基本原理u掌握掌握应用层应用层协议原理及典型的应用层协议编
2、程协议原理及典型的应用层协议编程u掌握掌握传送层传送层主要原理，主要原理，熟练掌握熟练掌握TCP、UDP原理及编程原理及编程u掌握掌握网络层网络层主要原理，主要原理，熟练掌握熟练掌握协议地址、路由原理协议地址、路由原理u掌握掌握链路层链路层及及局域网局域网主要概念、标准、差错控制等原理主要概念、标准、差错控制等原理u了解多媒体网络原理了解多媒体网络原理u了解网络安全的相关问题、主要原理了解网络安全的相关问题、主要原理u了解网络管理的基本问题了解网络管理的基本问题Chapter 1: Computer Network and Internet教学安排教学安排u教学方法：课堂讲授，课后练习，编程及
3、实习教学方法：课堂讲授，课后练习，编程及实习u教学手段：教学课件教学手段：教学课件+多媒体投影多媒体投影u总体学时安排：讲授总体学时安排：讲授48学时，期中考试学时，期中考试2学时，实验学时，实验32学时学时（7个必做实验、个必做实验、1个选做实验）。个选做实验）。u理论课期中、期末考核：闭卷考试理论课期中、期末考核：闭卷考试u实验课单列学分、单独评定成绩。实验课单列学分、单独评定成绩。Chapter 1: Computer Network and Internet教材和参考书：教材和参考书：教教材：材：ComputerNetworkingAtop-downapproachfeaturingt
4、heInternetJamesF.Kurose/KeithW.Ross计算机网络计算机网络自顶向下的方法与自顶向下的方法与Internet特色特色参考书：参考书：1、数据通信与网络技术数据通信与网络技术，清华大学出版社，清华大学出版社，Datacommunicationandnetworking,BehrouzA.Forouzan2、现代通信网络技术现代通信网络技术,西南交通大学出版社西南交通大学出版社,曾华燊著曾华燊著.3、ComputerNetworks,FourthEditionByAndrewS.TanenbaumChapter 1: Computer Network and Inte
5、rnet相关信息相关信息任课教师：于倩任课教师：于倩联系电话：联系电话：13888639373电子邮件：电子邮件：Chapter 1: Computer Network and InternetuMaincontentsIntroducingsomebasicteminologyandconceptsExaminethebasichardwareandsoftwarecomponentsthatmakeupanetworkNetworksedge:endsystemsandnetworkapplicationsNetworkcore:thelinks,theswitches,theaccess
6、networksandphysicalmediaHowthenetworksconnectwitheachotherExaminethedelay,lossandthroughputinacomputernetwork,providingasimplemodelforunderstandingtransmission,propagation,andqueuingdelaysProtocollayingandservicemodelsChapter 1: Computer Network and Internet23 七月 20247（1）Computer NetworklWhat is net
7、work? Human network as an example. Computer Networkthe collection of computers: Computer Networkthe collection of computers:uuConnected Via communication linksConnected Via communication linksuuWith the target to share resourcesWith the target to share resourcesuuResources include: hardware/software
8、/ Resources include: hardware/software/ information (data) and something useful to others information (data) and something useful to otherslWhat is computer network?1.Computer Network definition and structurelIn a computer network, Computer is the element of the set.Chapter 1: Computer Network and I
9、nternet23 七月 20248（2）internet and InternetInternet is one specific internet;Internet is one specific internet;Internet is a world-wide computer network;Internet is a world-wide computer network;lWhat is internet?lWhat is Internet?the the internetinternet is the interconnection of “Computer Network”
10、is the interconnection of “Computer Network”Can be seen as the collection of computer networks, i.e. Can be seen as the collection of computer networks, i.e. Network of networks.Network of networks.lWhat support the internet and Internet to run well:Various communication protocolsVarious communicati
11、on protocols1、Computer Network definition and structurepinternet是指多个网络相互连接构成的网络，并更多地代是指多个网络相互连接构成的网络，并更多地代表网络互连技术；表网络互连技术；pInternet是一个特定的、实际运行的是一个特定的、实际运行的internet，是国际互，是国际互连网的简称。连网的简称。Chapter 1: Computer Network and Internet23 七月 20249lWhats the Internet: “nuts and bolts(具体细节具体细节)” viewumillions of
12、 connected computing devices: hosts, end-systemspcs, workstations, serversPDAs, phones, toasters (烤箱烤箱) running network applicationsucommunication linksfiber, copper, radio, satelliteurouters: forward packets (chunks) of data thru networkuOther net devices, e.g. switches regional ISPcompanynetwork注注
13、1 ISP：Internet service Providerlocal ISP1routerworkstationservermobileHostsChapter 1: Computer Network and Internet23 七月 202410l Whats the Internet: “nuts and bolts” viewuprotocols: control sending, receiving of messagese.g., TCP, IP, HTTP, FTP, PPPuInternet: “network of networks”loosely hierarchica
14、lpublic Internet versus private IntranetuInternet standards RFC: Request for commentsIETF: Internet Engineering Task Force (Internet工程任务组工程任务组)local ISPcompanynetworkregional ISProuterworkstationservermobileHostsChapter 1: Computer Network and Internet23 七月 202411（3）The network edge: Service descrip
15、tionlend systems (hosts):run application programse.g., WWW, emailat “edge of network”lclient/server modelclient host requests, receives service from servere.g., WWW client (browser)/ server; email client/serverlpeer-peer modelminimal (or no) use of dedicated serverse.g.: BT,eMule, Skype1、Computer Ne
16、twork definition and structureChapter 1: Computer Network and Internet(3) Network edge: connection-oriented serviceGoal: data transfer between end systems.uhandshaking: setup (prepare for) data transfer ahead of timeHello, hello back human protocolset up “state” in two communicating hostsuTCP Connec
17、tion:In a very loose mode;Only the end systems is aware(明白的明白的);Virtual Connection: vs. physical connection in circuit switching.TCP service RFC 793uTCP - Transmission Control Protocol Internets connection-oriented serviceureliable, in-order byte-stream data transferloss: acknowledgements and retran
18、smissionsuflow control: sender wont overwhelm receiverucongestion control: senders “slow down sending rate” when network congested23 七月 202412Chapter 1: Computer Network and Internet(3) Network edge: connectionless serviceGoal: data transfer between end systemssame as before!uUDP - User Datagram Pro
19、tocol RFC 768: Internets connectionless service no handshakingno flow controlno congestion controlunreliable data transferApps using TCP: uHTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP (email)Apps using UDP:ustreaming media, teleconferencing, Internet telephony23 七月 202413Chapter 1: C
20、omputer Network and Internet23 七月 202414（4）The Network Coreumesh of interconnected routersuthe fundamental question: how is data transferred through net?circuit switching: a dedicated circuit per call: telephone netpacket-switching: data sent thru net in discrete “chunks”1、Computer Network definitio
21、n and structureChapter 1: Computer Network and Internetu我我们知道，知道，电路交路交换主要主要针对电信网的，特信网的，特别是是电话通通讯网。网。u如果如果让N部部电话两两相两两相连，就需要，就需要N*（N-1）对电线。当。当电话机数量很大机数量很大时，这种种连接方法需要的接方法需要的电线数量就太大了。因数量就太大了。因此此为使使电话之之间能方便地通信，使用了能方便地通信，使用了电话交交换机机。u电路交路交换网中，相互通信的端系网中，相互通信的端系统所需所需资源，在其通信期源，在其通信期间，必必须全部全部预留。留。23 七月 2024软件学
22、院 于倩15（4）The Network Core1、Computer Network definition and structureChapter 1: Computer Network and Internetu中中继线可以同可以同时传送几十或几百路送几十或几百路电话。很多交。很多交换机通机通过中中继线互互联来完成全网的交来完成全网的交换任任务，这样形成了覆盖全球的形成了覆盖全球的电信网。从通信信网。从通信资源分配的角度来看，源分配的角度来看，“交交换”就是按照某种就是按照某种方式方式动态地分配地分配传输路路线的的资源。用源。用户线归电话用用户专用，用，而交而交换机之机之间大量大量话路的
23、中路的中继线则是是许多用多用户共享的，正在共享的，正在通通话的用的用户只占用了其中一个只占用了其中一个话路。路。23 七月 2024软件学院 于倩16（4）The Network Core1、Computer Network definition and structureChapter 1: Computer Network and Internet23 七月 202417（5）Another view of computer NetworkComputer Network =Computer Network = Communication subnet + Resources subnet
24、 Communication subnet + Resources subnet or Communication subnet + User subnet or Communication subnet + User subnet or Network core + Network edge or Network core + Network edge1.Computer Network definition and structureHostHostHostHostHostHostHostCommunication Communication Subnet/network coreSubn
25、et/network coreResources Subnet/network edgeChapter 1: Computer Network and Internet23 七月 2024182、DataswitchingtechnologiesData Switching:Circuit Switching（电路交换）（电路交换）Packet Switching（分组交换）（分组交换）Chapter 1: Computer Network and Internet23 七月 202419Circuit SwitchingHostHostHostHostHostHostHostHostHost
26、HostHostHostSourceSourceDestinationDestination2、DataswitchingtechnologiesChapter 1: Computer Network and Internet补充一些基本概念补充一些基本概念u1）信号）信号带宽是指信号是指信号频谱的的宽度，也就是信号的最度，也就是信号的最高高频率分量与最低率分量与最低频率分量之差。如一方波信号最率分量之差。如一方波信号最低低频率率为2khz，最高，最高频率率为14khz，则该信号的信号的带宽为14-2=12khz。u2）基）基带信号就是将数字信号信号就是将数字信号1或或0直接用两种不直接用两种
27、不同的同的电压来表示，然后送到来表示，然后送到线路上去路上去传输。u3）宽带信号信号则是将基是将基带信号信号调制制为互相不会混淆的互相不会混淆的信号信号进行行传输。家庭家庭宽带信号是模信号是模拟信号。信号。23 七月 2024软件学院 于倩20Chapter 1: Computer Network and Internetu4）宽带信号的信号的传输采用了多路复用技采用了多路复用技术的基本原理的基本原理是：各路信号在是：各路信号在进入同一个有入同一个有线的或无的或无线的的传输媒媒质之前，先采用之前，先采用调制技制技术把它把它们调制制为互相不会混互相不会混淆的已淆的已调制信号，然后制信号，然后进入
28、入传输媒媒质传送到送到对方，方，在在对方再用解方再用解调（反（反调制）技制）技术对这些信号加以区些信号加以区分，并使它分，并使它们恢复成原来的信号，从而达到多路复恢复成原来的信号，从而达到多路复用的目的。用的目的。5）常用的多路复用技）常用的多路复用技术有有频分多路复用技分多路复用技术和和时分分多路复用技多路复用技术。23 七月 2024软件学院 于倩21Chapter 1: Computer Network and Internetu带宽本来是指某个信号具有的本来是指某个信号具有的频带宽度。度。u我我们知道，一个特定的信号往往是由知道，一个特定的信号往往是由许多不同的多不同的频率成分率成分组
29、成的。因此，一个信号的成的。因此，一个信号的带宽是指是指该信号的各种不同信号的各种不同频率成率成分所占据的分所占据的频率范率范围。u例如，在例如，在传统的通信的通信线路上路上传送的送的电话信号的信号的标准准带宽是是3.1kHz（从（从300Hz到到3.4kHz，即，即话音的主要成分的音的主要成分的频率范率范围）。带宽的的单位是赫位是赫兹、千赫、兆赫。因在、千赫、兆赫。因在过去很去很长一段一段时间，通信的主干通信的主干线路都是用来路都是用来传送模送模拟信号（即信号（即连续变化的信号）。化的信号）。23 七月 2024软件学院 于倩22Chapter 1: Computer Network and
30、 Internetu因此，表示通信因此，表示通信线路允路允许通通过的信号的信号频带范范围就称就称为线路的路的带宽。当通信。当通信线路用来路用来传送数字信号送数字信号时，数据率，数据率应当成当成为数数字信道最重要的指字信道最重要的指标。但。但习惯上，人上，人们愿意将愿意将“带宽”作作为数字信道所能数字信道所能传送的送的“最高数据率最高数据率”的同的同义词。数据率指数。数据率指数字信道字信道传送数字信号的速率，也称比特率。因此网送数字信号的速率，也称比特率。因此网络或或链路路的的带宽单位是比特每秒（位是比特每秒（b/s).千比每秒（千比每秒（kb/s）、）、Mb/s、Gb/sTb/s23 七月 2
31、024软件学院 于倩23Chapter 1: Computer Network and Internet23 七月 2024242、Data switching technologiesCircuitSwitchingEnd-endresourcesreservedfor“call”ulinkbandwidth,switchcapacityudedicatedresources:nosharingucircuit-like(guaranteed)performanceucallsetuprequiredChapter 1: Computer Network and Internetu频分多路复
32、用是将各路信号分分多路复用是将各路信号分别调制到不同的制到不同的频段段进行行传输，多用于模，多用于模拟通信。通信。u这样许多用多用户可在同可在同样的的时间占用大家共享的占用大家共享的线路路资源，从源，从频率域来看，它率域来看，它们占用的占用的频率范率范围是各种是各种分开而互不干分开而互不干扰。23 七月 2024软件学院 于倩25Circuit Switching: FDM and TDMChapter 1: Computer Network and Internetu比如一个比如一个标准准话路的路的频率范率范围是是3003400Hz，则信号信号带宽是是3100Hz，因，因话路之路之间应有一些
33、有一些频率率间隔隔，因此国，因此国际标准取准取4kHz为一个一个标准准话路所占用的路所占用的频带宽度。度。u在在频分复用系分复用系统中，中，发送端的各路信号送端的各路信号经各自的各自的低通低通滤波器波器分分别对各路各路载波波进行行调制制,再由各路再由各路带通通滤波器波器滤出相出相应的的边带（载波波电话通常采用通常采用单边带调制），相加后便形成制），相加后便形成频分多路信号分多路信号。u注意注意:频分分时要考要考虑传输媒体能媒体能传输的的电磁波的磁波的带宽。23 七月 2024软件学院 于倩26Circuit Switching: FDM and TDMChapter 1: Computer N
34、etwork and Internetub）时分多路复用技分多路复用技术是利用是利用时间上离散的上离散的脉冲脉冲组成成相互不重叠的多路信号，广泛相互不重叠的多路信号，广泛应用于数字通信。用于数字通信。u把把时间分成周期性的分成周期性的帧，每一，每一帧再分割成若干再分割成若干时隙隙（无（无论帧或或时隙都是隙都是互不重叠的）互不重叠的）.u当网当网络跨越跨越链路路创建一条建一条连接接时，该网网络在每个在每个帧中中为该连接指定一个接指定一个时隙。此隙。此时隙隙为该连接独占使接独占使用，用于用，用于传输该连接的数据。接的数据。23 七月 2024软件学院 于倩27Circuit Switching:
35、FDM and TDMChapter 1: Computer Network and InternetCircuit Switching: FDM and TDMFDMfrequencytimeTDMfrequencytime4 usersExample:23 七月 202428Chapter 1: Computer Network and Internet时分复用可能会造成时分复用可能会造成线路资源的浪费线路资源的浪费 ABCDaabbcdb cattttt4 个时分复用帧#1acbcd时分复用#2#3#4用户23 七月 202429Chapter 1: Computer Network a
36、nd Internet统计时分复用统计时分复用 STDM 用户ABCDabcdttttt3 个 STDM 帧#1acbab bcacd#2#3统计时分复用23 七月 202430Chapter 1: Computer Network and Internet统计时分复用统计时分复用 STDM u统计时分复用使用分复用使用集中器集中器将将4个低速用个低速用户连接起来，然后将它接起来，然后将它们的数据集中起来的数据集中起来通通过高速高速线路路发送送到一个到一个远地地计算机。算机。u每个每个STDM帧中的中的时隙数小于隙数小于连接在集中器上的用接在集中器上的用户数。各用数。各用户有了数据就随有了数据
37、就随时发往集中器的往集中器的输入入缓存，然后集中器按存，然后集中器按顺序依次序依次扫描描输入入缓存，就将存，就将缓存中的存中的输入数据放入入数据放入STDM帧中。中。对没有数据的没有数据的缓存就跳存就跳过去。当一个去。当一个帧的数据放的数据放满了，了，就就发送出去。送出去。u因此因此STDM帧不是固定分配不是固定分配时隙，而是按需隙，而是按需动态地分配地分配时隙。隙。因此，因此，每个每个时隙隙还必必须有用有用户的地址信息的地址信息。23 七月 2024软件学院 于倩31Chapter 1: Computer Network and InternetNumerical exampleuHowlo
38、ngdoesittaketosendafileof640,000bitsfromhostAtohostBoveracircuit-switchednetwork?Alllinksare1.536MbpsEachlinkusesTDMwith24slots/sec500msectoestablishend-to-endcircuitLetsworkitout!23 七月 202432Chapter 1: Computer Network and Internetupackets:thesourcebreakslongmessagesintosmallerchunksofdataknownaspa
39、ckets.uPacketsaretransmittedovereachcommunicationlinkatarateequaltothefulltransmissionrateofthelink.uMostpacketswitchesusestore-and-forwardtransmissionattheinputstothelinks.ustore-and-forwardtransmissionmeansthattheswitchmustreceivetheentirepacketbeforeitcanbegintotransmitthefirstbitofthepacketontot
40、heoutboundlink.Packet Switching2、Dataswitchingtechnologies23 七月 202433Chapter 1: Computer Network and Internet23 七月 2024软件学院 王世普34Packet Switching昆明昆明成都成都西安西安广州广州武汉武汉上海上海北京北京沈阳沈阳HostHostHostHostHostHostHostHost1 12 23 34 41 12 23 34 41 14 42 23 33 34 41 12 21 14 42 21 12 23 34 42、Dataswitchingtechno
41、logiespppppPacketBufferStore-and-forwardpppppppChapter 1: Computer Network and Internet23 七月 2024352、Data switching technologieseachend-enddatastreamdividedintopacketsuuserA,Bpacketssharenetworkresourcesueachpacketusesfulllinkbandwidthuresourcesusedas neededresource contention: uaggregate resource d
42、emand（总资源需求）（总资源需求） can exceed amount availableucongestion: packets queue, wait for link useustore and forward: packets move one hop at a timeNode receives complete packet before forwardingPacket SwitchingChapter 1: Computer Network and Internet23 七月 202436SequenceofA&Bpacketsdoesnothavefixedpattern
43、,sharedondemandstatistical multiplexing.TDM:eachhostgetssameslotinrevolvingTDMframe.ABC10 Mb/sEthernet1.5 Mb/sDEstatistical multiplexingqueue of packetswaiting for outputlink6、Data switching technologiesPacket Switching: Statistical MultiplexingChapter 1: Computer Network and Internet23 七月 202437Pac
44、ket switching versus circuit switchingu1Mb/slinkueachuser:100kb/swhenactive”active10%oftimeucircuit-switching:10usersupacketswitching:Ifthereare35users,probability10ctivelessthan.0004Packetswitchingallowsmoreuserstousenetwork!N users1 Mbps link6、Data switching technologiesChapter 1: Computer Network
45、 and Internet23 七月 202438Network TaxonomyTelecommunicationnetworksCircuit-switchednetworksFDMTDMPacket-switchednetworksNetworkswith VCsDatagramNetworksFDatagram network is not either connection-oriented or connectionless.FInternet provides both connection-oriented (TCP) and connectionless services (
46、UDP) to apps.Chapter 1: Computer Network and InternetHow do loss and delay occur?packetsqueueinrouterbuffersupacketarrivalratetolinkexceedsoutputlinkcapacityupacketsqueue,waitforturnABpacket being transmitted (delay)packets queueing (delay)free (available) buffers: arriving packets dropped (loss) if
47、 no free buffers2、DataswitchingtechnologiesDelay in packet-switched networks分组交换网性能关键参数分组交换网性能关键参数23 七月 202439Chapter 1: Computer Network and InternetFour sources of packet delayu1.nodalprocessing:checkbiterrorsEximinethepacketsheaderanddetermineoutputlinkOntheorderofmicrosecondsorlessABpropagationt
48、ransmissionnodalprocessingqueueingu2.queueingtimewaitingatoutputlinkfortransmissiondependsoncongestionlevelofrouterMicrosecondsormilliseconds23 七月 202440Chapter 1: Computer Network and InternetDelay in packet-switched networks3.Transmissiondelay:uR=linkbandwidth(bps)uL=packetlength(bits)utimetosendb
49、itsintolink=L/R4.Propagationdelay:ud=lengthofphysicallinkus=propagationspeedinmedium(2x108m/sec)upropagationdelay=d/sABpropagationtransmissionnodalprocessingqueueingNote:sandRarevery differentquantities!23 七月 202441Chapter 1: Computer Network and Internet23 七月 202442Delay in packet-switched networks
50、分组交换网性能关键参数分组交换网性能关键参数Transmission delay（传输时延）（传输时延）Processing delay（处理时延）（处理时延）Queuing delay（排队时延）（排队时延）Propagation delay（传播时延）（传播时延）2、Dataswitchingtechnologies处理时延处理时延排队时延排队时延传输时延传输时延分组完分组完全到达全到达分组送到分组送到输出队列输出队列分组第一分组第一位送出位送出分组最后分组最后一位送出一位送出传播时延传播时延分组第一位分组第一位到接收方到接收方时间时间时间时间senderRecv分组最后位分组最后位到接收
51、方到接收方ABpropagationtransmissionnodalprocessing queueingsenderReceiverChapter 1: Computer Network and Internet23 七月 202443通过一个节点的总时延通过一个节点的总时延dnodal=dtrans+ dproc+dqueue+dprop端到端的总时延端到端的总时延 其中即其中即Q是通过的通信链路数，意味着中间结点（路由是通过的通信链路数，意味着中间结点（路由器）的个数是（器）的个数是（Q-1）。）。2、DataswitchingtechnologiesDelay in packet-s
52、witched networksChapter 1: Computer Network and Internet23 七月 202444分组平均到达率分组平均到达率（The average rate of packets arrive to queue) ：单位时间单位时间second内平均到达的分内平均到达的分组数，用组数，用a表示。表示。则：则：称称La/R为为通信强度通信强度（Traffic intensity)。其中：。其中：L是分组长度、是分组长度、R为线路传输速率。为线路传输速率。2、DataswitchingtechnologiesQueuing Delay in packet-
53、switched networksChapter 1: Computer Network and Internet23 七月 202445讨论：讨论：1、如果、如果La/R1，则表明，则表明LaR，即到达的分组超过了能，即到达的分组超过了能够传输的分组。够传输的分组。 随着分组的不断到达，将在随着分组的不断到达，将在Queue中不断积累，中不断积累，将最终使分组的将最终使分组的Queuing delay为为 。 因此，从理论上说，只有因此，从理论上说，只有La/R1时，网络才能时，网络才能实现有效通信。实现有效通信。2、DataswitchingtechnologiesQueuing Dela
54、y in packet-switched networksChapter 1: Computer Network and Internet23 七月 202446讨论：讨论： 到达流量的性质影响排队时延到达流量的性质影响排队时延2、假定分组是定期到达的假定分组是定期到达的，且在，且在L/R时间只到达一个分组，则时间只到达一个分组，则每个到达的分组都将不需要排队即可被立即发送出去，每个到达的分组都将不需要排队即可被立即发送出去， Queuing delay =0； 如果在如果在(L/R)N的时间内有的时间内有N个分组同时到达，则第一个分个分组同时到达，则第一个分组的组的Queuing delay
55、=0，第二个分组的，第二个分组的Queuing delay=L/R秒，第秒，第N个分组个分组Queuing delay=（N-1）L/R秒秒 平均平均Queuing delay为：为： L/R+2L/R+(N-1)L/R/N= 1+2+(N-1) L/R/N= =(S)(S)RN LNN-2) 1(2、Dataswitchingtechnologies= =RLN- 2) 1(SecondsSecondsQueuing Delay in packet-switched networksChapter 1: Computer Network and Internet23 七月 202447讨论：
56、讨论： 3、实际上分组是随机到达的实际上分组是随机到达的，Average Queuing delay与通信强度的关系为：与通信强度的关系为：1 1La/RAverage Queuing delay0 02、DataswitchingtechnologiesQueuing Delay in packet-switched networksChapter 1: Computer Network and Internet“Real” Internet delays and routesuWhatdo“real”Internetdelay&losslooklike?uTracerouteprogram
57、:providesdelaymeasurementfromsourcetorouteralongend-endInternetpathtowardsdestination.Foralli:sendsthreepacketsthatwillreachrouterionpathtowardsdestinationrouteriwillreturnpacketstosendersendertimesintervalbetweentransmissionandreply.3 probes3 probes3 probes23 七月 202448Chapter 1: Computer Network an
58、d Internet“Real” Internet delays and routes1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0- (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0- (204.147.136.136) 21 ms 18 ms 18
59、ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2- (62.40.96.129) 109 ms 102 ms 104 ms10 (62.40.96.50) 113 ms 121 ms 114 ms11 renater- (62.40.103.54) 112 ms 114 ms
60、 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom- (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17
61、 * * *18 * * *19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 mstraceroute: gaia.cs.umass.edu to www.eurecom.frThree delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu * means no response (probe lost, router not replying)trans-oceaniclink23 七月 202449Chapter 1: Computer Network
62、 and Internet23 七月 2024503.Network ProtocolA human protocol and a computer network protocol:HiHiGot thetime?2:00TCP connection req.TCP connectionreply.Get http:/cs.smith.edu/Welcome.htmltimeuProtocols are very important. Learning computer network is focused on learning network protocols, to understa
63、nding the what, why, and how of networking protocols.Chapter 1: Computer Network and Internet23 七月 202451 A protocol defines the format and the order of messages exchanged between two or more communicating entities, as well as the actions taken on the transmission and/or receipt of message or other
64、event. A protocol is a set of rules that govern data communication. It is an agreement between the communication entities. 协议是支配数据通信的规则的集合，是通信实体之间的一种约定。协议是支配数据通信的规则的集合，是通信实体之间的一种约定。 A protocol defines what is communicated , how it is communicated , and when it is communicated. 协议定义通信的种类、如何通信、什么时候通信。
65、协议定义通信的种类、如何通信、什么时候通信。The elements of a protocol are syntax , semantics, and timing. 协议主要包括三个部分：协议主要包括三个部分： 语法、语义、时序语法、语义、时序3. Network ProtocolChapter 1: Computer Network and Internet23 七月 202452 Syntax: Syntax refers to the structure or format of the data, the order in which they are presented. 语法是
66、指数据的格式或结构，也就是数据字段的排列顺序。语法是指数据的格式或结构，也就是数据字段的排列顺序。 Semantics:Semantics refers to the meaning of each section of bits . 语义是指数据包中每个数据字段的含义。语义是指数据包中每个数据字段的含义。 Timing:Timing refers to two characteristics: when data should be send and how fast they can sent . 时序是指数据在什么时候发送、以多快的速度发送。时序是指数据在什么时候发送、以多快的速度发送。
67、3. Network ProtocolChapter 1: Computer Network and InternetProtocol “Layers”Networksarecomplex!umany“pieces”:hostsrouterslinksofvariousmediaapplicationsprotocolshardware,softwareQuestion:Isthereanyhopeoforganizingstructureofnetwork?Oratleastourdiscussionofnetworks?23 七月 202453Chapter 1: Computer Net
68、work and InternetOrganization of air traveluaseriesofstepsticket (purchase)baggage (check)gates (load)runway takeoffairplane routingticket (complain)baggage (claim)gates (unload)runway landingairplane routingairplane routing23 七月 202454Chapter 1: Computer Network and Internet2024/7/2355互联网之父互联网之父TCP
69、/IP发明人发明人2004年图灵奖得主年图灵奖得主VintonG.CelfVintonG.CelfBobKahnBobKahnVinton CerfVinton Cerf先在先在StanfordStanford获得获得数学学士，后在加州理工学院获数学学士，后在加州理工学院获计算机科学硕、博士。毕业后计算机科学硕、博士。毕业后CerfCerf一直在一直在SRISRI从事从事ARPAARPA网的网的研究。研究。19731973年后，年后，CerfCerf与与MITMIT的的数学教授数学教授KahnKahn合作，搞出了一套合作，搞出了一套 19971997年年1212月，克林顿总统向月，克林顿总统向
70、CerfCerf和他的合作者和他的合作者Robert E. Robert E. KahnKahn授予了授予了美国国家技术勋章美国国家技术勋章美国国家技术勋章美国国家技术勋章，以表彰其为互联网的建立和发展以表彰其为互联网的建立和发展所做的贡献。所做的贡献。 用于网络互连软件系统，用于网络互连软件系统，TCP/IPTCP/IP协议就这样诞生了。协议就这样诞生了。Chapter 1: Computer Network and Internetticket (purchase)baggage (check)gates (load)runway (takeoff)airplane routingdepa
71、rtureairportarrivalairportintermediate air-trafficcontrol centersairplane routingairplane routingticket (complain)baggage (claimgates (unload)runway (land)airplane routingticketbaggagegatetakeoff/landingairplane routingLayering of airline functionalityLayers:eachlayerimplementsaserviceviaitsowninter
72、nal-layeractionsrelyingonservicesprovidedbylayerbelow23 七月 202456Chapter 1: Computer Network and InternetWhy layering?Dealingwithcomplexsystems:uexplicitstructureallowsidentification,relationshipofcomplexsystemspieceslayeredreferencemodelfordiscussionumodularizationeasesmaintenance,updatingofsystemc
73、hangeofimplementationoflayersservicetransparenttorestofsysteme.g.,changeingateproceduredoesntaffectrestofsystemulayeringconsideredharmful?23 七月 202457Chapter 1: Computer Network and InternetISO/OSI-7 Layers ModelISO: International Standards OrganizationOSI: Open System Interconnection Reference Mode
74、l23 七月 202458Chapter 1: Computer Network and InternetApplicationProtocolPresentationProtocolSessionProtocolTransportProtocolNetworkProtocolDataLinkProtocolPhysicalProtocol4. ISO/OSI-7 Layers ModelHostAHostBMessageMessageMessageMessagePacketFrameBit7654321ProcessaProcessbPDU：Protocol Data UnitCommuni
75、cationSubnet/RouterChapter 1: Computer Network and Internet7654321ProcessaProcessbMessageP1P2H4H4MMP1P2H4H4H3H3P1P2H4H4H3H3H2H2T2T2MessageP1P2H4H4MMP1P2H4H4H3H3P1P2H4H4H3H3H2H2T2T24. ISO/OSI-Data Transmission 1 10 01 10 0Chapter 1: Computer Network and InternetApplication Layer Services for Processe
76、s(进程进程）:The type of message（报文报文） exchangedThe syntax of the various message typesThe semantics of fieldsRules for determining when and how sends messages and responds to message4. ISO/OSI-Functions of LayersChapter 1: Computer Network and InternetPresentation Layer Presentation of InformationMessag
77、e Compression（报文压缩）（报文压缩）Conversion between character codesConversion of file formatsAlleviate for other incompatible problems4. ISO/OSI-Functions of LayersChapter 1: Computer Network and InternetSession Layer Users Interface into the networkSetting up a session connection with a process in another
78、machine. For Example , log in.management of the sessions Conversion session address to transport addressclose of the session 4. ISO/OSI-Functions of LayersChapter 1: Computer Network and InternetTransport Layer Host-Host messagemessage deliverySource-destination ( end-to-end ) delivery MessagesMessa
79、gesService-point addressingSegmentation and reassemblyConnect managementFlow controlCongest controlError control4. ISO/OSI-Functions of LayersChapter 1: Computer Network and InternetNetwork Layer Host-Host PacketPacket DeliverySource-destination ( end-to-end ) delivery PacketPacketLogical addressing
80、routingError control4. ISO/OSI-Functions of LayersChapter 1: Computer Network and InternetData Link Layer Node-to-Node FrameFrame DeliveryNode-to-Node delivery FrameFrameFraming (成帧，帧的封装成帧，帧的封装)Physical addressingFlow controlError controlAccess control4. ISO/OSI-Functions of LayersChapter 1: Compute
81、r Network and InternetPhysical Layer Transmit a bit streambit streamTransmit a bit streambit stream over a physical mediumRepresentation of bits（Ex. Encoding/Decoding）Data rate ( bits per second , bps)Synchronization of bits ( Sender and receiver )Line configuration (point-to-point , multipoint)Phys
82、ical topology (bus, star, ring, etc.）Transmission mode (simplex, half-duplex, duplex)4. ISO/OSI-Functions of LayersChapter 1: Computer Network and Internet23 七月 202468 TCP/IP ModelSMTPSMTP HTTPHTTP SNMPSNMPDNSDNSRTPRTPFTPFTPTCPTCPUDPUDPIPIPRARPARP4.ApplicationLayer4.ApplicationLayer(Message)(Message
83、)3.TransportLayer3.TransportLayer(Segment(SegmentOrUserDatagram)OrUserDatagram)2.2.NetworkLayerNetworkLayer(Datagram)(Datagram)1.1.LinkLayerLinkLayer(Frameandbit)(Frameandbit)TCP/IPLayerTCP/IPLayerApplicationLayerApplicationLayerPresentationLayerPresentationLayerSessionLayerSessionLayerTransportLaye
84、rTransportLayerNetworkLayerNetworkLayerDatalinkLayerDatalinkLayerPhysicalLayerPhysicalLayerISO/OSILayerISO/OSILayerEthernetADSLATMDDNFRFDDIICMPICMPIGMPIGMPChapter 1: Computer Network and InternetInternet protocol stackuapplication:supportingnetworkapplicationsFTP,SMTP,HTTPutransport:process-processd
85、atatransferTCP,UDPunetwork:routingofdatagramsfromsourcetodestinationIP,routingprotocolsulink:datatransferbetweenneighboringnetworkelementsPPP,Ethernetuphysical:bits“onthewire”applicationtransportnetworklinkphysical23 七月 202469Chapter 1: Computer Network and Internetsourceapplicationtransportnetworkl
86、inkphysicalHtHnMsegmentHtdatagramdestinationapplicationtransportnetworklinkphysicalHtHnHlMHtHnMHtMMnetworklinkphysicallinkphysicalHtHnHlMHtHnMHtHnMHtHnHlMrouterswitchTCP/IP Model EncapsulationmessageMHtMHnframe23 七月 202470Chapter 1: Computer Network and InternetTCP address TCP Port NumberService-poi
87、nt Address - A service number, Logical address of a Service in a hostEx.: ftp at 21、http at 80、SMTP at 25 Service = An applicationapplication that responses for incoming callTCP/IP Model-addressesChapter 1: Computer Network and InternetIP address Internetworking Protocol addressLogical address of a
88、hostEach IPv4 address consists of 4 bytes ( 32bits) Defining 3 fields: class type, netid, and hostidClassClassTypeTypeNetidNetworkIDNetidNetworkIDHostid-HostIDHostid-HostID1-4bits7-28bits2-24bits32bitsTCP/IP Model-addressesChapter 1: Computer Network and InternetIPv4 address class type:0 0NetidNetid
89、HostidHostidClassAClassA1 1 0 0NetidNetidHostidHostidClassBClassB1 1 1 1 0 0NetidNetidHostidHostidClassCClassC1 1 1 1 1 1 0 0MulticastAddressMulticastAddressClassDClassD1 1 1 1 1 1 1 1ReservedAddressReservedAddressClassEClassEByte1Byte1Byte2Byte2Byte3Byte3Byte4Byte4TCP/IP Model-addressesChapter 1: C
90、omputer Network and InternetIPv4 address class type and the value of byte 1 :Byte1Byte1Value(decimal)Value(decimal)0 0x x x x x x xx x x x x x xClassAClassA01270127000000000111111100000000011111111 1 0 0 x x x x x xx x x x x xClassBClassB128191128191100000001011111110000000101111111 1 1 1 0 0 x x x
91、x xx x x x xClassCClassC192223192223110000001101111111000000110111111 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 x x x xx x x xClassDClassD224239224239111000001110111111100000111011111 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 x x x xx x x xClassEClassE24025524025511110000111111111111000011111111Value(Binary)Value(Binary)TC
92、P/IP Model-addressesChapter 1: Computer Network and InternetIPv4 address - Dotted-Decimal Notation:100000011000000100111001001110010100011101000111111000001111000001129.57.71.225TCP/IP Model-addressesChapter 1: Computer Network and Internet用名字表示用名字表示 IP 地址地址uIP地址既地址既难记忆，又很，又很难从从键盘输入。入。u一个事一个事实：人不擅人不
93、擅长于于记忆长串数字，串数字，但但记忆名字却比名字却比较容易。容易。u因此想到把因此想到把IP地址地址变成名字。成名字。u因特网因特网设立立专门的机构管理名字：的机构管理名字：采用分采用分级管理名字的方法。管理名字的方法。每一每一级的名字都是各不相同的。的名字都是各不相同的。Chapter 1: Computer Network and Internet因特网的域名因特网的域名u域名其域名其实就是名字。只是因就是名字。只是因为使用分使用分级管理，因特管理，因特网使用多网使用多级的域，因此就出的域，因此就出现了了“域名域名”这个名个名词。u因特网的域名分因特网的域名分为：顶级域名域名二二级域名域
94、名三三级域名域名四四级域名域名Chapter 1: Computer Network and Internetu中央中央电视台向因特网提供万台向因特网提供万维网服网服务的的计算机的域算机的域名是：名是：因特网的域名举例因特网的域名举例提供万维网服务的计算机名意思是：商业机构中央电视台顶级域名二级域名三级域名三级域名.二级域名.顶级域名Chapter 1: Computer Network and Internetu清清华大学向因特网提供网站服大学向因特网提供网站服务的的计算机的域名算机的域名是：是：因特网的域名举例因特网的域名举例意思是：中国中国 顶级域名教育机构教育机构二级域名二级域名清华大
95、学清华大学三级域名网站服务器的计算机名字网站服务器的计算机名字四级域名四级域名四级域名. .三级域名三级域名. .二级域名二级域名. .顶级域名顶级域名Chapter 1: Computer Network and InternetuURL用来用来标识万万维网上的各种文档。网上的各种文档。u因特网上的每一个文档，在整个因特网的因特网上的每一个文档，在整个因特网的范范围内具有惟一的内具有惟一的标识符符URL。uURL实际上就是文档在因特网中的地址。上就是文档在因特网中的地址。统一资源定位符统一资源定位符URL(UniformResourceLocator)Chapter 1: Computer
96、Network and Internetu举例：例：URL的格式的格式http:/ 的网站服务器在因特网上使用的域名所要浏览的文件名（包含路径）Chapter 1: Computer Network and InternetAccess networks and physical mediaQ: How to connect end systems to edge router?uresidentialaccessnetsuinstitutionalaccessnetworks(school,company)umobileaccessnetworksKeep in mind: ubandwid
97、th(bitspersecond)ofaccessnetwork?usharedordedicated?23 七月 202482Chapter 1: Computer Network and InternetResidential access: point to point accessuDialupviamodemupto56Kbpsdirectaccesstorouter(oftenless)Cantsurfandphoneatsametime:cantbe“alwayson”uDSL:digitalsubscriberlinedeployment:telephonecompany(ty
98、pically)upto1Mbpsupstream(todaytypically256kbps)upto8Mbpsdownstream(todaytypically1Mbps)dedicatedphysicallinetotelephonecentraloffice23 七月 202483Chapter 1: Computer Network and InternetResidential access: cable modemsuHFC:hybridfibercoaxasymmetric:upto30Mbpsdownstream,2Mbpsupstreamunetworkofcableand
99、fiberattacheshomestoISProuterhomesshareaccesstorouterudeployment:availableviacableTVcompanies23 七月 202484Chapter 1: Computer Network and InternetCable Network Architecture: Overviewhomecable headendcable distributionnetwork (simplified)Typically 500 to 5,000 homes23 七月 202485Chapter 1: Computer Netw
100、ork and InternetCable Network Architecture: Overviewhomecable headendcable distributionnetworkserver(s)23 七月 202486Chapter 1: Computer Network and InternetCable Network Architecture: Overviewhomecable headendcable distributionnetwork (simplified)23 七月 202487Chapter 1: Computer Network and InternetCo
101、mpany access: local area networksucompany/univlocalareanetwork(LAN)connectsendsystemtoedgerouteruEthernet:10Mbps,100Mbps,1Gbps,10GbpsEthernetmodernconfiguration:endsystemsconnectintoEthernetswitchuLANs:chapter523 七月 202488Chapter 1: Computer Network and InternetWireless access networksusharedwireles
102、saccessnetworkconnectsendsystemtorouterviabasestationaka“accesspoint”uwirelessLANs:802.11b/g(WiFi):11or54Mbpsuwider-areawirelessaccessprovidedbyTelecommunicationscompanies1Mbpsovercellularsystem(EVDO,HSDPA)nextup(?):WiMAX(10sMbps)overwideareabasestationmobilehostsrouter23 七月 202489Chapter 1: Compute
103、r Network and InternetHome networksTypicalhomenetworkcomponents:uDSLorcablemodemurouter/firewall/NATuEthernetuwirelessaccesspointwirelessaccess pointwirelesslaptopsrouter/firewallcablemodemto/fromcableheadendEthernet23 七月 202490Chapter 1: Computer Network and Internet5. Physical MediauBit:propagates
104、betweentransmitter/rcvrpairsuphysicallink:whatliesbetweentransmitter&receiveruguidedmedia:signalspropagateinsolidmedia:copper,fiber,coaxuunguidedmedia:signalspropagatefreely,e.g.,radioTwistedPair(TP)utwoinsulatedcopperwiresCategory3:traditionalphonewires,10MbpsEthernetCategory5:100MbpsEthernet23 七月
105、202491Chapter 1: Computer Network and InternetPhysical Media: coax, fiberCoaxialcable:utwoconcentriccopperconductorsubidirectionalubaseband:singlechanneloncablelegacyEthernetubroadband:multiplechannelsoncableHFCFiberopticcable:uglassfibercarryinglightpulses,eachpulseabituhigh-speedoperation:high-spe
106、edpoint-to-pointtransmission(e.g.,10s-100sGps)ulowerrorrate:repeatersspacedfarapart;immunetoelectromagneticnoise23 七月 202492Chapter 1: Computer Network and InternetPhysical media: radiousignalcarriedinelectromagneticspectrumunophysical“wire”ubidirectionalupropagationenvironmenteffects:reflectionobst
107、ructionbyobjectsinterferenceRadiolinktypes:uterrestrialmicrowave(地面微波)e.g.upto45MbpschannelsuLAN(e.g.,Wifi)11Mbps,54Mbpsuwide-area(e.g.,cellular)3Gcellular:1MbpsusatelliteKbpsto45Mbpschannel(ormultiplesmallerchannels)270msecend-enddelaygeosynchronousversusLow-altitude23 七月 202493Chapter 1: Computer Network and Internetu作作业：uP93：R12、R17、R23uP96：P5、P14、P24
