计算机网络 Computer Networks温武少 wwensysugmail.comIntroduction1-1Introduction1-2Chapter 1 IntroductionAcknowledgement Computer Networking: A Top Down Approach , 4th edition. Jim Kurose, Keith Ross Addison-Wesley, July 2007. EE284 Lecture Note Nick McKeown Professor of Electrical Engineering and Computer Science, Stanford University1-3Some Ground RulesvOne of the most important courses in the IT areavLet me orchestrate the questions.vAsk questions if things not clearvListen to other peoples questions.vBe here.vBe here on time.1-4An Introduction to the mail systemWenChensysuPeking UnivAdminAdmin1-5Characteristics of the mail systemvEach envelope is individually routed.vNo time guarantee for delivery.vNo guarantee of delivery in sequence.vNo guarantee of delivery at all!vThings get lostvHow can we acknowledge delivery?vRetransmissionvHow to determine when to retransmit? Timeout?vNeed local copies of contents of each envelope.vHow long to keep each copy.vWhat if an acknowledgement is lost? 6An Introduction to the mail systemWenChenSYSUPEK UnivAdminAdminApplication LayerTransport LayerNetwork LayerLink Layer1-5An Introduction to the InternetWenChenss.sysu.edu.cncs.pku.edu.cnNetwork LayerLink LayerApplication LayerTransport LayerO.S.O.S.HeaderDataHeaderDataDatagram1-6Characteristics of the InternetvEach packet is individually routed.vNo time guarantee for delivery.vNo guarantee of delivery in sequence.vNo guarantee of delivery at all!vThings get lostvAcknowledgementsvRetransmissionvHow to determine when to retransmit? Timeout?vNeed local copies of contents of each packet.vHow long to keep each copy?vWhat if an acknowledgement is lost? 1-7Characteristics of the Internet (2)vNo guarantee of integrity of data.vPackets can be fragmented.vPackets may be duplicated.1-8Layering in the InternetvTransport LayervProvides reliable, in-sequence delivery of data from end-to-end on behalf of application.vNetwork LayervProvides “best-effort”, but unreliable, delivery of datagrams.vLink LayervCarries data over (usually) point-to-point links between hosts and routers; or between routers and routers.1-9An Introduction to the mail systemWenChenSYSUPeking UnivAdminAdminApplication LayerTransport LayerNetwork LayerLink Layer1-10Some questions about the mail systemvHow many sorting offices are needed and where should they be located?vHow much sorting capacity is needed?vShould we allocate for Spring Festival?vHow can we guarantee timely delivery?vWhat prevents delay guarantees?vOr delay variation guarantees?vHow do we protect against fraudulent mail deliverers, or fraudulent senders?1-11Some questions about the network mail systemvNetworking is similar to the mail systemIntroduction1-12Reading Assignment: Chapter 1Introduction1-15Chapter 1: IntroductionOur goal: qget “feel” and terminologyqmore depth, detail later in courseqapproach:vuse Internet as exampleOverview:qwhats the Internet?qwhats a protocol?qnetwork edge; hosts, access net, physical mediaqnetwork core: packet/circuit switching, Internet structureqperformance: loss, delay, throughputqsecurityqprotocol layers, service modelsqhistoryIntroduction1-16Whats the Internet: “nuts and bolts” viewqmillions of connected computing devices: hosts = end systems v running network appsHome networkInstitutional networkMobile networkGlobal ISPRegional ISProuterPCserverwirelesslaptop cellular handheldwiredlinksaccess pointsqcommunication linksvfiber, copper, radio, satellitevtransmission rate = bandwidthqrouters: forward packets (chunks of data)Introduction1-16“Cool” internet appliancesWorlds smallest web server http:/www-ccs.cs.umass.edu/shri/iPic.htmlIP picture frame http:/www.ceiva.com/Web-enabled toaster + weather forecasterInternet phonesIntroduction1-18Whats the Internet: “nuts and bolts” viewqprotocols control sending, receiving of msgsve.g., TCP, IP, HTTP, Skype, EthernetqInternet: “network of networks”vloosely hierarchicalvpublic Internet versus private intranetqInternet standardsvRFC: Request for commentsvIETF: Internet Engineering Task ForceHome networkInstitutional networkMobile networkGlobal ISPRegional ISPIntroduction1-19Whats a protocol?a human protocol and a computer network protocol:Q: Other human protocols? HiHiGot the time? 2:00TCP connectionrequestTCP connection responseGet http:/www.awl.com/kurose-rosstimeIntroduction1-20Whats the Internet: a service viewqcommunication infrastructure enables distributed applications:vWeb, VoIP, email, games, e-commerce, file sharingqcommunication services provided to apps:vreliable data delivery from source to destinationv“best effort” (unreliable) data deliveryIntroduction1-21Chapter 1: roadmap1.1 What is the Internet? 1.2 Network edgeq end systems, access networks, links 1.3 Network coreq circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet-switched networks 1.5 Protocol layers, service models 1.6 Networks under attack: security 1.7 HistoryIntroduc