1Computer Networks and Communication 计算机网络与通信（双语）Professor Chunsheng Li 主讲：李春生 教授 Department of Computer Engineering2Course Overview0.1 What is Computer networks?（什么是计算机网络） 0.2 What is this course about?(本课程是干什么的） 0.3 A top-down approach（一种从上到下的方法） 0.4 Contents of this course（本课程的内容）30.1 What is Computer Networks?1Computer network is a communication system to connect at least two computers together for sharing hardware, software, and information resources.(计算机网络：用于共享硬件资源、软件资源和信息资源 的连接两台或更多台计算机进行通信的系统。)2Categories of Computer NetworksrAccording to the communicating distance：WAN (Wide Area Networks 广域网), MAN (Municipal Area Networks 城域网), LAN (Local Area Networks 局域网)rAccording to the topology：Star(星型), Tree(树型), Ring (环型), Bus(总线型结构)。 40.2 What is this course about?Introductory (first) course in computer networkingqlearn principles of computer networkingqlearn practice of computer networkingqInternet architecture/protocols as case study Goals:qlearn a lot (not just factoids, but principles and practice)qhave fun (well, it should be interesting, at least) prerequisites:valgorithms, Operating Systems, programming skills50.3 A top-down approach:This course will cover networking top-downqend-system applications, end-end transportqnetwork core: routing, hooking nets togetherqlink-level protocols, e.g., Ethernetqother stuff: security, mobility, management60.4 Contents of this Course:Part 1: Introduction (3 classes, text: Chapter 1) qwhat is the Internet, What is a protocol? qnetwork edge, network coreqnetwork access, physical media qInternet backbones, NAPs and ISPs qdelay, loss in packet-switched networks qprotocol layers, service models (Application, Transport, Network, Link, Physical Layers) qbrief history of networking, Internet7Contents of this Course (Cont.):Part 2: Application Layer (3 classes, text: Ch. 2) qprinciples of application-layer protocols qWorld Wide Web: HTTP qfile transfer: FTP qelectronic mail in the Internet qthe Internets directory service: DNS qsocket programming with TCP 8Contents of this Course (Cont.):Part 3: Transport Layer (6 classes, text Ch. 3) qTransport-layer services and principles qMultiplexing and demultiplexing applications qConnectionless transport: UDP qPrinciples of reliable of data transfer qConnection-Oriented Transport: TCP qPrinciples of congestion control qTCP congestion control 9Contents of this Course (Cont.):Part 4: Network Layer (6 classes, text: Ch. 4) qintroduction and network service model qwhats inside a router?qrouting principles (algorithms)qhierarchical routing qIP: the Internet Protocol qInternet routing: RIP, OSPF, BGP10Contents of this Course (Cont.):Part 5: Link Layer, LANs (3 classes, text: Ch. 5) qintroduction, services qerror detection, correction qmultiple access protocols, LANs qLAN addresses, ARP qEthernet qInterconnection: Hubs and Switches11Chapter 1: IntroductionOur goal: rget “feel” and terminologyrmore depth, detail later in courserapproach:muse Internet as exampleOverview:rwhats the Internetrwhats a protocol?rnetwork edgernetwork coreraccess net, physical mediarInternet/ISP structurerperformance: loss, delayrprotocol layers, service models12Chapter 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/server (Two kinds of definitions in P9 )rpeer-peer model:m minimal (or no) use of dedicated serversme.g. Skype, BitTorrent, KaZaA231.2 Network edge: 2. connection-oriented service (two types of services of Internet) Goal: data transfer between end systemsrhandshaking: setup (prepare for) data transfer ahead of timemHello, hello back human protocolmset up “state” in two communicating hostsrTCP - Transmission Control Protocol mInternets connection- oriented serviceTCP services RFC 793rreliable, in-order byte- stream data transfermloss: acknowledgements and retransmissionsrflow control: msender wont overwhelm receiverrcongestion control: msenders “slow down sending rate” when network congested241.2 Network edge: 3. connectionless serviceGoal: data transfer between end systemsmsame as before!rUDP - User Datagram Protocol RFC 768: mconnectionless munreliable data transfermno flow controlmno congestion controlApps using TCP: rHTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email)Apps using UDP:rstreaming media, teleconferencing, DNS, Internet telephony25Chapter 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 & loss in packet-switched networks 1.7 Protocol layers, service models 1.8 History261.3 The Network CorerMeaning of the network core: mesh of routers that interconnect the Internets end systems.rThere are two ways to construct the network core:mcircuit switching: dedicated circuit per call: telephone netmpacket-switching: data sent thru net in discrete “chunks”