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1、Lecture on Computer NetworkFor 09Spring 2011Chapter 1 IntroductionChapter 1 IntroductionIntroduct by Weifeng SunComputer network-Introduction2/88Open questionsWhat is computer network?How to solve the network problems?How do you feel the Computer network?Introduct by Weifeng SunComputer network-Intr
2、oduction3/88Course StaffInstructorsWeifeng Sun , Office 40587571607; 81648638Teaching assistants:?Introduct by Weifeng SunComputer network-Introduction4/88Important info. About this UnitTo pass this unit:oFinal Exam 70%oAssignment 2015%oAttendance 1015%Dont fail any component.Introduct by Weifeng Su
3、nComputer network-Introduction5/88Course GoalsBecome familiar with the principles and practice of data networking.Routing, transport protocols, naming, .Learn how to write networked applications:C/S modelTCP/UDPGet some understanding about network internals in a hands on way.TCP-style congestion con
4、trolIntroduct by Weifeng SunComputer network-Introduction6/88ReferenceComputer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith RossAddison-Wesley, July 2004.计算机网络（第 4 版）电子工业出版社,潘爱民译TCP/IP详解（卷1）数据通信与网络TCP/IP协议族More Books have people gone to the bookstore? How ma
5、ny copies? Should be thereIntroduct by Weifeng Sunmeterialshttp:/ network-Introduction7/88Introduct by Weifeng SunComputer network-Introduction8/88Challenges for NetworksGeographic scopeThe Internet vs. Andrew, etc.ScaleThe Internet vs. your home networkApplication typesEmail vs. VideoconferencingTr
6、ust and AdministrationCorporate network one network “provider”Internet 17,000 network providersSecurityIntroduct by Weifeng SunComputer network-Introduction9/88“Cool” internet appliances(2006)Worlds smallest web serverhttp:/www-ccs.cs.umass.edu/shri/iPic.htmlIP picture framehttp:/ toaster +weather f
7、orecasterInternet phonesIntroduct by Weifeng SunComputer network-Introduction10/88How to study?Study vs. learnNovelOur own wayFor computer network or other lessonsIntroduct by Weifeng SunComputer network-Introduction11/88How to Draw a NetworkNodeLinkNodeIntroduct by Weifeng SunComputer network-Intro
8、duction12/88Building block: The LinksElectrical questionsVoltage, frequency, Wired or wireless?Link-layer issues: How to send data? When to talk can everyone talk at once?What to say low-level format?Stay tuned for lecture 5Okay what about more nodes?NodeLinkNodeIntroduct by Weifeng SunComputer netw
9、ork-Introduction13/88 But what if we want more hosts?Scalability?!One wireWires for everybody!Introduct by Weifeng SunComputer network-Introduction14/88Multiplexing!Need to share network resourcesHow? Switched networkParty “A” gets resources sometimesParty “B” gets them sometimesInterior nodes act a
10、s “Routers” or “Switches”What mechanisms can share resources?Introduct by Weifeng SunComputer network-Introduction15/88Packet Switching (our emphasis)Source sends information as self-contained packets that have an address.Source may have to break up single message in multipleEach packet travels inde
11、pendently to the destination host.Routers and switches use the address in the packet to determine how to forward the packetsAnalogy: a letter in surface mail.Introduct by Weifeng SunComputer network-Introduction16/88Chapter 1: IntroductionOur goal: get “feel” and terminologymore depth, detail later
12、in courseapproach:use Internet as exampleOverview:whats the Internetwhats a protocol?network edgenetwork coreaccess net, physical mediaInternet/ISP structureperformance: loss, delayprotocol layers, service modelsnetwork modelingIntroduct by Weifeng SunComputer network-Introduction17/88Chapter 1: roa
13、dmap1.1 What is the Internet?1.2 Network edgeq end systems, access networks, links1.3 Network coreq circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 HistoryIntrodu
14、ct by Weifeng SunComputer network-Introduction18/88“The Internet”An inter-net: a network of networks.A set of networks that are connected with each otherNetworks are connected using routers that support communication in a hierarchical fashionOften need other special devices at the boundaries for sec
15、urity, accounting, .The Internet: the interconnected set of networks of the Internet Service Providers (ISPs) providing data communications services.About 17,000 different networks make up the InternetIn order to inter-operate, all participating networks have to follow a common set of rules.Introduc
16、t by Weifeng SunComputer network-Introduction19/88What is Computer network?A serials of computers.大公司地区 ISP网络接入点NAP（对等点）公司校园网主干服务提供者校园网校园网校园网校园网本地 ISP地区 ISP地区 ISP地区 ISP本地 ISP本地 ISP大公司大公司网络接入点NAP（对等点）Introduct by Weifeng SunComputer network-Introduction20/88Whats the Internet: “nuts and bolts” viewmi
17、llions of connected computing devices: hosts = end systems running network appsHome networkInstitutional networkMobile networkGlobal ISPRegional ISProuterPCserverwirelesslaptopcellular handheldwiredlinksaccess pointscommunication linksfiber, copper, radio, satellitetransmission rate = bandwidthroute
18、rs: forward packets (chunks of data)Introduct by Weifeng SunComputer network-Introduction21/88Whats the Internet: “nuts and bolts” viewprotocols control sending, receiving of msgse.g., TCP, IP, HTTP, Skype, EthernetInternet: “network of networks”loosely hierarchicalpublic Internet versus private int
19、ranetInternet standardsRFC: Request for commentsIETF: Internet Engineering Task ForceHome networkInstitutional networkMobile networkGlobal ISPRegional ISPIntroduct by Weifeng SunComputer network-Introduction22/88Whats a protocol?human protocols:“whats the time?”“I have a question”introductions speci
20、fic msgs sent specific actions taken when msgs received, or other eventsnetwork protocols:machines rather than humansall communication activity in Internet governed by protocolsprotocols define format, order of msgs sent and received among network entities, and actions taken on msg transmission, rec
21、eipt Introduct by Weifeng SunComputer network-Introduction23/88Whats a protocol?a human protocol and a computer network protocol:Q: Other human protocols? HiHiGot thetime?2:00TCP connection requestTCP connectionresponseGet http:/ by Weifeng SunComputer network-Introduction24/88Chapter 1: roadmap1.1
22、What is the Internet?1.2 Network edgeq end systems, access networks, links1.3 Network coreq circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 HistoryIntroduct by We
23、ifeng SunComputer network-Introduction25/88A closer look at network structure:network edge: applications and hostsaccess networks, physical media: wired, wireless communication links network core: interconnected routersnetwork of networksIntroduct by Weifeng SunComputer network-Introduction26/88The
24、network edgeend systems (hosts):run application programse.g. Web, emailat “edge of network”client/serverpeer-peerclient/server modelclient host requests, receives service from always-on servere.g. Web browser/server; email client/serverpeer-peer model: minimal (or no) use of dedicated serverse.g. Sk
25、ype, BitTorrentIntroduct by Weifeng SunComputer network-Introduction27/88Access networks and physical mediaQ: How to connect end systems to edge router?residential access netsinstitutional access networks (school, company)mobile access networksKeep in mind: bandwidth (bits per second) of access netw
26、ork?shared or dedicated?Introduct by Weifeng SunComputer network-Introduction28/88Residential : How to access?Residential access: point to point accessDialup via modemDSL: digital subscriber lineHFC: hybrid fiber coaxnetwork of cable and fiber attaches homes to ISP routerdeployment: available via ca
27、ble TV companieshomecable headendcable distributionnetworkIntroduct by Weifeng SunComputer network-Introduction29/88Residential access: cable modemsIntroduct by Weifeng SunComputer network-Introduction30/88Company access: local area networkscompany/univ local area network (LAN) connects end system t
28、o edge routerEthernet: 10 Mbs, 100Mbps, 1Gbps, 10Gbps Ethernetmodern configuration: end systems connect into Ethernet switchLANs: chapter 5Introduct by Weifeng SunComputer network-Introduction31/88Home networksTypical home network components: DSL or cable modemrouter/firewall/NATEthernetwireless acc
29、ess pointwirelessaccess pointwirelesslaptopsrouter/firewallcablemodemto/fromcableheadendEthernetIntroduct by Weifeng SunComputer network-Introduction32/88Physical media: radiosignal carried in electromagnetic spectrumno physical “wire”bidirectionalpropagation environment effects:reflection obstructi
30、on by objectsinterferenceRadio link types:terrestrial microwavee.g. up to 45 Mbps channelsLAN (e.g., Wifi)11Mbps, 54 Mbpswide-area (e.g., cellular)e.g. 3G: hundreds of kbpssatelliteKbps to 45Mbps channel (or multiple smaller channels)270 msec end-end delaygeosynchronous versus low altitudeIntroduct
31、by Weifeng SunComputer network-Introduction33/88Physical MediaBit: propagates betweentransmitter/rcvr pairsphysical link: what lies between transmitter & receiverguided media: signals propagate in solid media: copper, fiber, coaxunguided media: signals propagate freely, e.g., radioTwisted Pair (TP)t
32、wo insulated copper wiresCategory 3: traditional phone wires, 10 Mbps EthernetCategory 5: 100Mbps EthernetIntroduct by Weifeng SunComputer network-Introduction34/88Physical Media: coax, fiberCoaxial cable:two concentric copper conductorsbidirectionalbaseband:single channel on cablelegacy Ethernetbro
33、adband: multiple channels on cable HFCFiber optic cable:glass fiber carrying light pulses, each pulse a bithigh-speed operation:high-speed point-to-point transmission (e.g., 10s-100s Gps)low error rate: repeaters spaced far apart ; immune to electromagnetic noiseIntroduct by Weifeng SunComputer netw
34、ork-Introduction35/88Network edge: connection-oriented serviceGoal: data transfer between end systemshandshaking: setup (prepare for) data transfer ahead of timeHello, hello back human protocolset up “state” in two communicating hostsTCP - Transmission Control Protocol Internets connection-oriented
35、serviceTCP service RFC 793reliable, in-order byte-stream data transferloss: acknowledgements and retransmissionsflow control: sender wont overwhelm receivercongestion control: senders “slow down sending rate” when network congestedIntroduct by Weifeng SunComputer network-Introduction36/88Network edg
36、e: connectionless serviceGoal: data transfer between end systemssame as before!UDP - User Datagram Protocol RFC 768: connectionless unreliable data transferno flow controlno congestion controlApps using TCP: HTTP (Web), FTP (file transfer), Telnet (remote login), SMTP (email)Apps using UDP:streaming
37、 media, teleconferencing, DNS, Internet telephonyIntroduct by Weifeng SunComputer network-Introduction37/88Chapter 1: roadmap1.1 What is the Internet?1.2 Network edgeq end systems, access networks, links1.3 Network coreq circuit switching, packet switching, network structure1.4 Delay, loss and throu
38、ghput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 HistoryIntroduct by Weifeng SunComputer network-Introduction38/88The Network Coremesh of interconnected routersthe fundamental question: how is data transferred through net?circuit switching: d
39、edicated circuit per call: telephone netpacket-switching: data sent thru net in discrete “chunks”Introduct by Weifeng SunComputer network-Introduction39/88Network Core: Circuit SwitchingEnd-end resources reserved for “call”link bandwidth, switch capacitydedicated resources: no sharingcircuit-like (g
40、uaranteed) performancecall setup requiredIntroduct by Weifeng SunComputer network-Introduction40/88Network Core: Circuit Switchingnetwork resources (e.g., bandwidth) divided into “pieces”pieces allocated to callsresource piece idle if not used by owning call (no sharing)dividing link bandwidth into
41、“pieces”frequency divisiontime divisionIntroduct by Weifeng SunComputer network-Introduction41/88Circuit Switching: FDM and TDMFDMfrequencytimeTDMfrequencytime4 usersExample:Introduct by Weifeng SunComputer network-Introduction42/88Numerical exampleHow long does it take to send a file of 640,000 bit
42、s from host A to host B over a circuit-switched network?All links are 1.536 MbpsEach link uses TDM with 24 slots/sec500 msec to establish end-to-end circuitLets work it out!Introduct by Weifeng SunComputer network-Introduction43/88Switching network 交换机Introduct by Weifeng SunComputer network-Introdu
43、ction44/88Network Core: Packet Switchingeach end-end data stream divided into packetsuser A, B packets share network resources each packet uses full link bandwidth resources used as needed resource contention: aggregate resource demand can exceed amount availablecongestion: packets queue, wait for l
44、ink usestore and forward: packets move one hop at a timeNode receives complete packet before forwardingBandwidth division into “pieces”Dedicated allocationResource reservationIntroduct by Weifeng SunComputer network-Introduction45/88Packet Switching: Statistical MultiplexingSequence of A & B packets
45、 does not have fixed pattern, shared on demand statistical multiplexing.TDM: each host gets same slot in revolving TDM frame.ABC100 Mb/sEthernet1.5 Mb/sDEstatistical multiplexingqueue of packetswaiting for outputlinkIntroduct by Weifeng SunComputer network-Introduction46/88Packet-switching: store-an
46、d-forwardTakes L/R seconds to transmit (push out) packet of L bits on to link or R bpsEntire packet must arrive at router before it can be transmitted on next link: store and forwarddelay = 3L/R (assuming zero propagation delay)Example:L = 7.5 MbitsR = 1.5 Mbpsdelay = 15 secRRRLmore on delay shortly
47、 Introduct by Weifeng SunComputer network-Introduction47/88Packet switching versus circuit switching1 Mb/s linkeach user: 100 kb/s when “active”active 10% of timecircuit-switching: 10 userspacket switching: with 35 users, probability 10 active at same time is less than .0004Packet switching allows m
48、ore users to use network!N users1 Mbps linkQ: how did we get value 0.0004?Introduct by Weifeng SunComputer network-Introduction48/88Packet switching versus circuit switchingGreat for bursty dataresource sharingsimpler, no call setupExcessive congestion: packet delay and lossprotocols needed for reli
49、able data transfer, congestion controlQ: How to provide circuit-like behavior?bandwidth guarantees needed for audio/video appsstill an unsolved problemIs packet switching a “slam dunk winner?”Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)?
50、Introduct by Weifeng SunComputer network-Introduction49/88Internet structure and ISPsIntroduct by Weifeng SunComputer network-Introduction50/88Internet structure: network of networks“Tier-2” ISPs: smaller (often regional) ISPsConnect to one or more tier-1 ISPs, possibly other tier-2 ISPsTier 1 ISPTi
51、er 1 ISPTier 1 ISPNAPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISP pays tier-1 ISP for connectivity to rest of Internetq tier-2 ISP is customer oftier-1 providerTier-2 ISPs also peer privately with each other, interconnect at NAPIntroduct by Weifeng SunComputer network-Introduction51/
52、88Internet structure: network of networks“Tier-3” ISPs and local ISPs last hop (“access”) network (closest to end systems)Tier 1 ISPTier 1 ISPTier 1 ISPNAPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPTier-2 ISPlocalISPlocalISPlocalISPlocalISPlocalISPTier 3ISPlocalISPlocalISPlocalISPLocal and tier- 3 ISPs
53、 are customers ofhigher tier ISPsconnecting them to rest of InternetIntroduct by Weifeng SunComputer network-Introduction52/88Chapter 1: roadmap1.1 What is the Internet?1.2 Network edgeq end systems, access networks, links1.3 Network coreq circuit switching, packet switching, network structure1.4 De
54、lay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 HistoryIntroduct by Weifeng SunComputer network-Introduction53/88How do loss and delay occur?packets queue in router buffers packet arrival rate to link exceeds output link c
55、apacitypackets queue, wait for turnABpacket being transmitted (delay)packets queueing (delay)free (available) buffers: arriving packets dropped (loss) if no free buffersIntroduct by Weifeng SunComputer network-Introduction54/88Four sources of packet delay1. nodal processing: check bit errorsdetermin
56、e output linkABpropagationtransmissionnodalprocessingqueueing2. queueingtime waiting at output link for transmission depends on congestion level of routerIntroduct by Weifeng SunComputer network-Introduction55/88Delay in packet-switched networks3. Transmission delay:R=link bandwidth (bps)L=packet le
57、ngth (bits)time to send bits into link = L/R4. Propagation delay:d = length of physical links = propagation speed in medium (2x108 m/sec)propagation delay = d/sABpropagationtransmissionnodalprocessingqueueingNote: s and R are very different quantities!Introduct by Weifeng SunComputer network-Introdu
58、ction56/88Nodal delaydproc = processing delaytypically a few microsecs or lessdqueue = queuing delaydepends on congestiondtrans = transmission delay= L/R, significant for low-speed linksdprop = propagation delaya few microsecs to hundreds of msecsIntroduct by Weifeng SunComputer network-Introduction
59、57/88Queueing delay (revisited)R=link bandwidth (bps)L=packet length (bits)a=average packet arrival ratetraffic intensity = La/RLa/R 0: average queueing delay smallLa/R - 1: delays become largeLa/R 1: more “work” arriving than can be serviced, average delay infinite!Introduct by Weifeng SunComputer
60、network-Introduction58/88“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)
61、21 ms 18 ms 18 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
62、) 112 ms 114 ms 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
63、128 ms 126 ms17 * * *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)Introduct by Weifeng SunComputer network-
64、Introduction59/88练 习 题在用百兆网卡连接的两台计算机之间发送大小为67M的rm文件，距离为2km，计算从第一个数据成功发送到最后一个数据成功接收的时间考虑到传输介质影响，假定传输速率为光速的2/3; 忽略处理时延；误码率为0用10M网卡呢？减少了哪一部分时延？总时延 = 发送时延 + 传播时延 + 处理时延Introduct by Weifeng SunComputer network-Introduction60/88Packet lossqueue (aka buffer) preceding link in buffer has finite capacitypack
65、et arriving to full queue dropped (aka lost)lost packet may be retransmitted by previous node, by source end system, or not at allABpacket being transmittedpacket arriving tofull buffer is lostbuffer (waiting area)Introduct by Weifeng SunComputer network-Introduction61/88Chapter 1: roadmap1.1 What i
66、s the Internet?1.2 Network edgeq end systems, access networks, links1.3 Network coreq circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 HistoryIntroduct by Weifeng
67、SunComputer network-Introduction62/88Protocol “Layers”Networks are complex! many “pieces”:hostsrouterslinks of various mediaapplicationsprotocolshardware, softwareQuestion: Is there any hope of organizing structure of network?Or at least our discussion of networks?Introduct by Weifeng SunComputer ne
68、twork-Introduction63/88Organization of air travela series of stepsticket (purchase)baggage (check)gates (load)runway takeoffairplane routingticket (complain)baggage (claim)gates (unload)runway landingairplane routingairplane routingIntroduct by Weifeng SunComputer network-Introduction64/88ticket (pu
69、rchase)baggage (check)gates (load)runway (takeoff)airplane routingdepartureairportarrivalairportintermediate air-trafficcontrol centersairplane routingairplane routingticket (complain)baggage (claimgates (unload)runway (land)airplane routingticketbaggagegatetakeoff/landingairplane routingLayering of
70、 airline functionalityLayers: each layer implements a servicevia its own internal-layer actionsrelying on services provided by layer belowIntroduct by Weifeng SunComputer network-Introduction65/88Why layering?Dealing with complex systems:explicit structure allows identification, relationship of comp
71、lex systems pieceslayered reference model for discussionmodularization eases maintenance, updating of systemchange of implementation of layers service transparent to rest of systeme.g., change in gate procedure doesnt affect rest of systemlayering considered harmful?Introduct by Weifeng SunComputer
72、network-Introduction66/88Internet protocol stackapplication: supporting network applicationsFTP, SMTP, HTTPtransport: process-process data transferTCP, UDPnetwork: routing of datagrams from source to destinationIP, routing protocolslink: data transfer between neighboring network elementsPPP, Etherne
73、tphysical: bits “on the wire”applicationtransportnetworklinkphysicalIntroduct by Weifeng SunComputer network-Introduction67/88ISO/OSI reference modelpresentation: allow applications to interpret meaning of data, e.g., encryption, compression, machine-specific conventionssession: synchronization, che
74、ckpointing, recovery of data exchangeInternet stack “missing” these layers!these services, if needed, must be implemented in applicationneeded?applicationpresentationsessiontransportnetworklinkphysicalIntroduct by Weifeng SunComputer network-Introduction68/88sourceapplicationtransportnetworklinkphys
75、icalHtHnMsegmentHtdatagramdestinationapplicationtransportnetworklinkphysicalHtHnHlMHtHnMHtMMnetworklinkphysicallinkphysicalHtHnHlMHtHnMHtHnMHtHnHlMrouterswitchEncapsulationmessageMHtMHnframeIntroduct by Weifeng SunComputer network-Introduction69/88Chapter 1: roadmap1.1 What is the Internet?1.2 Netwo
76、rk edgeq end systems, access networks, links1.3 Network coreq circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched networks1.5 Protocol layers, service models1.6 Networks under attack: security1.7 HistoryIntroduct by Weifeng SunComputer network-Intr
77、oduction70/88Network SecurityThe field of network security is about:how bad guys can attack computer networkshow we can defend networks against attackshow to design architectures that are immune to attacksInternet not originally designed with (much) security in mindoriginal vision: “a group of mutua
78、lly trusting users attached to a transparent network” Internet protocol designers playing “catch-up”Security considerations in all layers!Introduct by Weifeng SunComputer network-Introduction71/88Bad guys can put malware into hosts via InternetMalware can get in host from a virus, worm, or trojan ho
79、rse.Spyware malware can record keystrokes, web sites visited, upload info to collection site.Infected host can be enrolled in a botnet, used for spam and DDoS attacks.Malware is often self-replicating: from an infected host, seeks entry into other hostsIntroduct by Weifeng SunComputer network-Introd
80、uction72/88More?laterIntroduct by Weifeng SunComputer network-Introduction73/88Chapter 1: roadmap1.1 What is the Internet?1.2 Network edgeq end systems, access networks, links1.3 Network coreq circuit switching, packet switching, network structure1.4 Delay, loss and throughput in packet-switched net
81、works1.5 Protocol layers, service models1.6 Networks under attack: security1.7 HistoryIntroduct by Weifeng SunComputer network-Introduction74/88Internet History1961: Kleinrock - queueing theory shows effectiveness of packet-switching1964: Baran - packet-switching in military nets1967: ARPAnet concei
82、ved by Advanced Research Projects Agency1969: first ARPAnet node operational1972: ARPAnet public demonstrationNCP (Network Control Protocol) first host-host protocol first e-mail programARPAnet has 15 nodes1961-1972: Early packet-switching principlesIntroduct by Weifeng SunComputer network-Introduct
83、ion75/88Internet History1970: ALOHAnet satellite network in Hawaii1974: Cerf and Kahn - architecture for interconnecting networks1976: Ethernet at Xerox PARClate70s: proprietary architectures: DECnet, SNAlate 70s: switching fixed length packets (ATM precursor)1979: ARPAnet has 200 nodesCerf and Kahn
84、s internetworking principles:minimalism, autonomy - no internal changes required to interconnect networksbest effort service modelstateless routersdecentralized controldefine todays Internet architecture1972-1980: Internetworking, new and proprietary netsIntroduct by Weifeng SunComputer network-Intr
85、oduction76/88Internet History1983: deployment of TCP/IP1982: smtp e-mail protocol defined 1983: DNS defined for name-to-IP-address translation1985: ftp protocol defined1988: TCP congestion controlnew national networks: Csnet, BITnet, NSFnet100,000 hosts connected to confederation of networks1980-199
86、0: new protocols, a proliferation of networksIntroduct by Weifeng SunComputer network-Introduction77/88Internet HistoryEarly 1990s: ARPAnet decommissioned1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995)early 1990s: Webhypertext Bush 1945, Nelson 1960sHTML, HTTP: Berner
87、s-Lee1994: Mosaic, later Netscapelate 1990s: commercialization of the WebLate 1990s 2000s:more killer apps: instant messaging, P2P file sharingnetwork security to forefrontest. 50 million host, 100 million+ usersbackbone links running at Gbps1990, 2000s: commercialization, the Web, new appsIntroduct
88、 by Weifeng SunComputer network-Introduction78/88Introduction: SummaryCovered a “ton” of material!Internet overviewwhats a protocol?network edge, core, access networkpacket-switching versus circuit-switchingInternet/ISP structureperformance: loss, delaylayering and service modelshistoryYou now have:
89、 context, overview, “feel” of networkingmore depth, detail to follow!Introduct by Weifeng SunComputer network-Introduction79/88messagePrinciple of Packet switching Too long to transfer 1101000110101010110101011100010011010010Divided to piecesIntroduct by Weifeng SunComputer network-Introduction80/88
90、DataDataDatamessagePrinciple of Packet switchingAnd Header to the Date piecesheaderheaderheaderpacke1packe 2packe 3Introduct by Weifeng SunComputer network-Introduction81/88Principle of Packet switchingReceiver receive the packetsDataheader分组 1Dataheader分组 2Dataheader分组 3Introduct by Weifeng SunComp
91、uter network-Introduction82/88Principle of Packet switchingDataheader分组 1Dataheader分组 2Dataheader分组 3Received dataIntroduct by Weifeng SunComputer network-Introduction83/88DataDataDataPrinciple of Packet switchingGet the original message Assume no packet loss and error in the transmittingmessage1101
92、000110101010110101011100010011010010Introduct by Weifeng SunComputer network-Introduction84/88An exampleH1AnetworkBDECH5H6H4H2H3H1 to H5H2 to H6switchhostIntroduct by Weifeng SunComputer network-Introduction85/88An exampleH1AnetworkBDECH5H6H4H2H3H1 to H5结点交换机主机在结点交换机 A 暂存查找转发表找到转发的端口在结点交换机 C 暂存查找转发表
93、找到转发的端口Store and find the routing tableTo H5Introduct by Weifeng SunComputer network-Introduction86/88SwitchABCDEH1H5H2H4H3H6linkswitch123412341 2 3 41 2 3 41 2 3 4Introduct by Weifeng SunComputer network-Introduction87/88P1P2P3P4P1P2P3P4P3P4报文报文报文A B C D A B C DA B C D报文交换电路交换分组交换t报文P2P1Introduct by Weifeng SunComputer network-Introduction88/88computerhosthostnetwork
