《计算机网络英文课件》由会员分享，可在线阅读，更多相关《计算机网络英文课件（103页珍藏版）》请在金锄头文库上搜索。
1、Chapter 1Computer Networks and the InternetIntroduction and OverviewrThe merging of computers and communications has had a profound influence on the way computer systems are organized. rwe will use the term computer network to mean a collection of autonomous computers interconnected by a single tech
2、nology. mTwo computers are said to be interconnected if they are able to exchange information. mThe connection need not be via a copper wire; fiber optics, microwaves, infrared, and communication satellites can also be used. mNetworks come in many sizes, shapes and forms.Introduction and OverviewUse
3、s of Computer NetworksrBusiness ApplicationsmResource sharing, high reliability, saving moneymPowerful communication medium(electronic mail, videoconference) me-commerce (electronic commerce)rHome ApplicationsmAccess to remote information(surfing, on-line digital library)mPerson-to-person communicat
4、ion(E-mail,instant messaging, chat room,newsgroups,peer-to-peer communication)mInteractive entertainment(video on demand(VOD),game playing)mElectronic commerce(home online shopping, access to financial institutions, electronic flea markets (e-flea)Introduction and OverviewUses of Computer NetworksrM
5、obile UsersmMobile computers, such as notebook computers and personal digital assistants (PDAs), are one of the fastest-growing segments of the computer industry. mmerger of cell phones and PDAs into tiny wireless computers, WAP (Wireless Application Protocol)mportable officemwireless networks on ca
6、mpus mwireless networks on militaryrSocial IssuesmPrivacymFreedom of speechmCopyrightmIntroduction and OverviewTaxonomy of Computer NetworksrThere is no generally accepted taxonomy into which all computer networks fit, but two dimensions stand out as important: transmission technology and scale. Bro
7、adcast networksPoint-to-point networks LAN MAN WAN internetTransmission technologyScaleIntroduction and OverviewTaxonomy of Computer NetworksrBroadcast networks have a single communication channel that is shared by all the machines on the network. mShort messages, called packets in certain contexts,
8、 sent by any machine are received by all the others. mWhen two or more machines want to transmit at the same time, an arbitration mechanism is needed to resolve conflicts.Introduction and OverviewTaxonomy of Computer Networks rPoint-to-point networks consists of many connections between individual p
9、airs of machines. mTo go from the source to the destination, a packet on this type of network may have to first visit one or more intermediate machines. mOften multiple routes, of different lengths, are possible, so finding good ones is important in point-to- point networks. Introduction and Overvie
10、wTaxonomy of Computer NetworksrGenerally, msmaller,geographically localized networks tend to use broadcasting,mwhereas larger networks usually are point-to-point.rSo LANs often use broadcasting and WANs usually use point-to-point.Introduction and OverviewTaxonomy of Computer NetworksrClassification
11、of interconnected processors by scale.Introduction and OverviewTaxonomy of Computer NetworksrA collection of interconnected networks is called an internetwork or internet.minternet vs. InternetrA common form of internet is a collection of LANs connected by a WAN.Chapter 1: Computer Networks and the
12、InternetOur goal: rget context, overview, “feel” of networkingrmore depth, detail later in courserapproach:mdescriptivemuse Internet as exampleOverview:rwhats the Internetrwhats a protocol?rnetwork edgernetwork coreraccess net, physical mediarInternet/ISP structurerperformance: loss, delayrprotocol
13、layers, service modelsrnetwork modelingrhistoryChapter 1: roadmap1.1 What is the Internet? 1.2 Network edge 1.3 Network core 1.4 Network access and physical media 1.5 Internet structure and ISPs 1.6 Delay email client/serverRequestResponser peer-peer model:m host interaction symmetric, minimal (or n
14、o) use of dedicated serversme.g.: BitTorrent, KaZaA, eMuleThe network edge:rThe links, routers and other pieces of the Internet provide the means to transport the messages between the end system applications. RequestResponserBut what are the characteristics of this communication service that is prov
15、ided?mconnection-oriented servicemconnectionless serviceNetwork edge: connection-oriented serviceGoal: data transfer between end sys.rhandshaking: setup (prepare for) data transfer ahead of timemHello, hello back human protocolmset up “state” in two communicating hostsrTCP - Transmission Control Pro
16、tocol mInternets connection- oriented serviceTCP service RFC 793rreliable, in-order byte- stream data transfermloss: acknowledgements and retransmissionsrflow control: msender wont overwhelm receiverrcongestion control: msenders “slow down sending rate” when network congestedNetwork edge: connectionless serviceGoal: data transfer between end systemsmsame as before!rUDP - User Datagram Protocol RFC 768: mconnectionlessmun
