计网计算机网络课件

Chapter1IntroductionComputernetwork-Introduction2/88OpenquestionsWhatiscomputernetwork?Howtosolvethenetworkproblems?HowdoyoufeeltheComputernetwork?Computernetwork-Introduction3/88CourseStaffInstructorsWeifengSun<wfsun.dlut@>,Office40587571607;81648638Teachingassistants:?Computernetwork-Introduction4/88Importantinfo.AboutthisUnitTopassthisunit:FinalExam70%Assignment20~15%Attendance10~15%Don’tfailanycomponent.Computernetwork-Introduction5/88CourseGoalsBecomefamiliarwiththeprinciplesandpracticeofdatanetworking.Routing,transportprotocols,naming,...Learnhowtowritenetworkedapplications:C/SmodelTCP/UDPGetsomeunderstandingaboutnetworkinternalsinahandsonway.TCP-stylecongestioncontrolComputernetwork-Introduction6/88ReferenceComputerNetworking:ATopDownApproachFeaturingtheInternet,

3rdedition.JimKurose,KeithRoss

Addison-Wesley,July2004.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MoreBooks–havepeoplegonetothebookstore?Howmanycopies?Shouldbethere…meterials/cn//~wfsun/cn/cn_wfsun@Computernetwork-Introduction7/88Computernetwork-Introduction8/88ChallengesforNetworksGeographicscopeTheInterne tvs.Andrew,etc.ScaleTheInternetvs.yourhomenetworkApplicationtypesEmailvs.VideoconferencingTrustandAdministrationCorporatenetwork–onenetwork“provider”Internet–17,000networkprovidersSecurityComputernetwork-Introduction9/88“Cool”internetappliances(2006)World’ssmallestwebserver/~shri/iPic.htmlIPpictureframe/Web-enabledtoaster+weatherforecasterInternetphonesComputernetwork-Introduction10/88Howtostudy?Studyvs.learnNovelOurownwayForcomputernetworkorotherlessonsComputernetwork-Introduction11/88HowtoDrawaNetworkNodeLinkNodeComputernetwork-Introduction12/88Buildingblock:TheLinksElectricalquestionsVoltage,frequency,…Wiredorwireless?Link-layerissues:Howtosenddata?Whentotalk–caneveryonetalkatonce?Whattosay–low-levelformat?Staytunedforlecture5Okay…whataboutmorenodes?NodeLinkNodeComputernetwork-Introduction13/88…Butwhatifwewantmorehosts?Scalability?!OnewireWiresforeverybody!Computernetwork-Introduction14/88Multiplexing!NeedtosharenetworkresourcesHow?SwitchednetworkParty“A”getsresourcessometimesParty“B”getsthemsometimesInteriornodesactas“Routers”or“Switches”Whatmechanismscanshareresources?Computernetwork-Introduction15/88PacketSwitching(ouremphasis)Sourcesendsinformationasself-containedpacketsthathaveanaddress.SourcemayhavetobreakupsinglemessageinmultipleEachpackettravelsindependentlytothedestinationhost.RoutersandswitchesusetheaddressinthepackettodeterminehowtoforwardthepacketsAnalogy:aletterinsurfacemail.Computernetwork-Introduction16/88Chapter1:IntroductionOurgoal:

get“feel”andterminologymoredepth,detaillaterincourseapproach:useInternetasexampleOverview:what’stheInternetwhat’saprotocol?networkedgenetworkcoreaccessnet,physicalmediaInternet/ISPstructureperformance:loss,delayprotocollayers,servicemodelsnetworkmodelingComputernetwork-Introduction17/88Chapter1:roadmap1.1WhatistheInternet?1.2Networkedgeendsystems,accessnetworks,links1.3Networkcorecircuitswitching,packetswitching,networkstructure1.4Delay,lossandthroughputinpacket-switchednetworks1.5Protocollayers,servicemodels1.6Networksunderattack:security1.7HistoryComputernetwork-Introduction18/88“TheInternet”Aninter-net:anetworkofnetworks.AsetofnetworksthatareconnectedwitheachotherNetworksareconnectedusingroutersthatsupportcommunicationinahierarchicalfashionOftenneedotherspecialdevicesattheboundariesforsecurity,accounting,..TheInternet:theinterconnectedsetofnetworksoftheInternetServiceProviders(ISPs)providingdatacommunicationsservices.About17,000differentnetworksmakeuptheInternetInordertointer-operate,allparticipatingnetworkshavetofollowacommonsetofrules.Computernetwork-Introduction19/88WhatisComputernetwork?Aserialsofcomputers.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）Computernetwork-Introduction20/88What’stheInternet:“nutsandbolts”viewmillionsofconnectedcomputingdevices:hosts=endsystems

runningnetworkappsHomenetworkInstitutionalnetworkMobilenetworkGlobalISPRegionalISProuterPCserverwirelesslaptopcellularhandheldwiredlinksaccesspointscommunicationlinksfiber,copper,radio,satellitetransmissionrate=bandwidthrouters:forwardpackets(chunksofdata)Computernetwork-Introduction21/88What’stheInternet:“nutsandbolts”viewprotocols

controlsending,receivingofmsgse.g.,TCP,IP,HTTP,Skype,EthernetInternet:“networkofnetworks”looselyhierarchicalpublicInternetversusprivateintranetInternetstandardsRFC:RequestforcommentsIETF:InternetEngineeringTaskForceHomenetworkInstitutionalnetworkMobilenetworkGlobalISPRegionalISPComputernetwork-Introduction22/88What’saprotocol?humanprotocols:“what’sthetime?”“Ihaveaquestion”introductions…specificmsgssent…specificactionstakenwhenmsgsreceived,orothereventsnetworkprotocols:machinesratherthanhumansallcommunicationactivityinInternetgovernedbyprotocolsprotocolsdefineformat,orderofmsgssentandreceivedamongnetworkentities,andactionstakenonmsgtransmission,receipt

Computernetwork-Introduction23/88What’saprotocol?ahumanprotocolandacomputernetworkprotocol:Q:Otherhumanprotocols?HiHiGotthetime?2:00TCPconnectionrequestTCPconnectionresponseGet/kurose-ross<file>timeComputernetwork-Introduction24/88Chapter1:roadmap1.1WhatistheInternet?1.2Networkedgeendsystems,accessnetworks,links1.3Networkcorecircuitswitching,packetswitching,networkstructure1.4Delay,lossandthroughputinpacket-switchednetworks1.5Protocollayers,servicemodels1.6Networksunderattack:security1.7HistoryComputernetwork-Introduction25/88Acloserlookatnetworkstructure:networkedge:applicationsandhostsaccessnetworks,physicalmedia:wired,wirelesscommunicationlinks

networkcore:

interconnectedroutersnetworkofnetworksComputernetwork-Introduction26/88Thenetworkedgeendsystems(hosts):runapplicationprogramse.g.Web,emailat“edgeofnetwork”client/serverpeer-peerclient/servermodelclienthostrequests,receivesservicefromalways-onservere.g.Webbrowser/server;emailclient/serverpeer-peermodel:minimal(orno)useofdedicatedserverse.g.Skype,BitTorrentComputernetwork-Introduction27/88AccessnetworksandphysicalmediaQ:Howtoconnectendsystemstoedgerouter?residentialaccessnetsinstitutionalaccessnetworks(school,company)mobileaccessnetworksKeepinmind:bandwidth(bitspersecond)ofaccessnetwork?sharedordedicated?Computernetwork-Introduction28/88Residential:Howtoaccess?Residentialaccess:pointtopointaccessDialupviamodemDSL:digitalsubscriberlineHFC:hybridfibercoaxnetworkofcableandfiberattacheshomestoISProuterdeployment:availableviacableTVcompanieshomecableheadendcabledistributionnetworkComputernetwork-Introduction29/88Residentialaccess:cablemodemsComputernetwork-Introduction30/88Companyaccess:localareanetworkscompany/univlocalareanetwork(LAN)connectsendsystemtoedgerouterEthernet:

10Mbs,100Mbps,1Gbps,10GbpsEthernetmodernconfiguration:endsystemsconnectintoEthernet

switchLANs:chapter5Computernetwork-Introduction31/88HomenetworksTypicalhomenetworkcomponents:DSLorcablemodemrouter/firewall/NATEthernetwirelessaccesspointwirelessaccesspointwirelesslaptopsrouter/firewallcablemodemto/fromcableheadendEthernetComputernetwork-Introduction32/88Physicalmedia:radiosignalcarriedinelectromagneticspectrumnophysical“wire”bidirectionalpropagationenvironmenteffects:reflectionobstructionbyobjectsinterferenceRadiolinktypes:terrestrialmicrowavee.g.upto45MbpschannelsLAN(e.g.,Wifi)11Mbps,54Mbpswide-area(e.g.,cellular)e.g.3G:hundredsofkbpssatelliteKbpsto45Mbpschannel(ormultiplesmallerchannels)270msecend-enddelaygeosynchronousversuslowaltitudeComputernetwork-Introduction33/88PhysicalMediaBit:propagatesbetween

transmitter/rcvrpairsphysicallink:whatliesbetweentransmitter&receiverguidedmedia:

signalspropagateinsolidmedia:copper,fiber,coaxunguidedmedia:

signalspropagatefreely,e.g.,radioTwistedPair(TP)twoinsulatedcopperwiresCategory3:traditionalphonewires,10MbpsEthernetCategory5:

100MbpsEthernetComputernetwork-Introduction34/88PhysicalMedia:coax,fiberCoaxialcable:twoconcentriccopperconductorsbidirectionalbaseband:singlechanneloncablelegacyEthernetbroadband:multiplechannelsoncableHFCFiberopticcable:glassfibercarryinglightpulses,eachpulseabithigh-speedoperation:high-speedpoint-to-pointtransmission(e.g.,10’s-100’sGps)lowerrorrate:repeatersspacedfarapart;immunetoelectromagneticnoiseComputernetwork-Introduction35/88Networkedge:connection-orientedserviceGoal:datatransferbetweenendsystemshandshaking:setup(preparefor)datatransferaheadoftimeHello,hellobackhumanprotocolsetup“state”intwocommunicatinghostsTCP-TransmissionControlProtocolInternet’sconnection-orientedserviceTCPservice

[RFC793]reliable,in-orderbyte-streamdatatransferloss:acknowledgementsandretransmissionsflowcontrol:

senderwon’toverwhelmreceivercongestioncontrol:

senders“slowdownsendingrate”whennetworkcongestedComputernetwork-Introduction36/88Networkedge:connectionlessserviceGoal:datatransferbetweenendsystemssameasbefore!UDP-UserDatagramProtocol[RFC768]:connectionlessunreliabledatatransfernoflowcontrolnocongestioncontrolApp’susingTCP:

HTTP(Web),FTP(filetransfer),Telnet(remotelogin),SMTP(email)App’susingUDP:streamingmedia,teleconferencing,DNS,InternettelephonyComputernetwork-Introduction37/88Chapter1:roadmap1.1WhatistheInternet?1.2Networkedgeendsystems,accessnetworks,links1.3Networkcorecircuitswitching,packetswitching,networkstructure1.4Delay,lossandthroughputinpacket-switchednetworks1.5Protocollayers,servicemodels1.6Networksunderattack:security1.7HistoryComputernetwork-Introduction38/88TheNetworkCoremeshofinterconnectedroutersthefundamentalquestion:howisdatatransferredthroughnet?circuitswitching:dedicatedcircuitpercall:telephonenetpacket-switching:datasentthrunetindiscrete“chunks”Computernetwork-Introduction39/88NetworkCore:CircuitSwitchingEnd-endresourcesreservedfor“call”linkbandwidth,switchcapacitydedicatedresources:nosharingcircuit-like(guaranteed)performancecallsetuprequiredComputernetwork-Introduction40/88NetworkCore:CircuitSwitchingnetworkresources(e.g.,bandwidth)dividedinto“pieces”piecesallocatedtocallsresourcepieceidleifnotusedbyowningcall(nosharing)dividinglinkbandwidthinto“pieces”frequencydivisiontimedivisionComputernetwork-Introduction41/88CircuitSwitching:FDMandTDMFDMfrequencytimeTDMfrequencytime4usersExample:Computernetwork-Introduction42/88NumericalexampleHowlongdoesittaketosendafileof640,000bitsfromhostAtohostBoveracircuit-switchednetwork?Alllinksare1.536MbpsEachlinkusesTDMwith24slots/sec500msectoestablishend-to-endcircuitLet’sworkitout!Computernetwork-Introduction43/88Switchingnetwork

…

交换机Computernetwork-Introduction44/88NetworkCore:PacketSwitchingeachend-enddatastreamdividedintopacketsuserA,Bpacketssharenetworkresources

eachpacketusesfulllinkbandwidthresourcesusedasneeded

resourcecontention:

aggregateresourcedemandcanexceedamountavailablecongestion:packetsqueue,waitforlinkusestoreandforward:packetsmoveonehopatatimeNodereceivescompletepacketbeforeforwardingBandwidthdivisioninto“pieces”DedicatedallocationResourcereservationComputernetwork-Introduction45/88PacketSwitching:StatisticalMultiplexingSequenceofA&Bpacketsdoesnothavefixedpattern,sharedondemand

statisticalmultiplexing.TDM:eachhostgetssameslotinrevolvingTDMframe.ABC100Mb/sEthernet1.5Mb/sDEstatisticalmultiplexingqueueofpacketswaitingforoutputlinkComputernetwork-Introduction46/88Packet-switching:store-and-forwardTakesL/Rsecondstotransmit(pushout)packetofLbitsontolinkorRbpsEntirepacketmustarriveatrouterbeforeitcanbetransmittedonnextlink:storeandforwarddelay=3L/R(assumingzeropropagationdelay)Example:L=7.5MbitsR=1.5Mbpsdelay=15secRRRLmoreondelayshortly…Computernetwork-Introduction47/88Packetswitchingversuscircuitswitching1Mb/slinkeachuser:100kb/swhen“active”active10%oftimecircuit-switching:

10userspacketswitching:

with35users,probability>10activeatsametimeislessthan.0004Packetswitchingallowsmoreuserstousenetwork!Nusers1MbpslinkQ:howdidwegetvalue0.0004?Computernetwork-Introduction48/88PacketswitchingversuscircuitswitchingGreatforburstydataresourcesharingsimpler,nocallsetupExcessivecongestion:packetdelayandlossprotocolsneededforreliabledatatransfer,congestioncontrolQ:Howtoprovidecircuit-likebehavior?bandwidthguaranteesneededforaudio/videoappsstillanunsolvedproblemIspacketswitchinga“slamdunkwinner?”Q:humananalogiesofreservedresources(circuitswitching)versuson-demandallocation(packet-switching)?Computernetwork-Introduction49/88InternetstructureandISPsComputernetwork-Introduction50/88Internetstructure:networkofnetworks“Tier-2”ISPs:smaller(oftenregional)ISPsConnecttooneormoretier-1ISPs,possiblyothertier-2ISPsTier1ISPTier1ISPTier1ISPNAPTier-2ISPTier-2ISPTier-2ISPTier-2ISPTier-2ISPTier-2ISPpaystier-1ISPforconnectivitytorestofInternettier-2ISPiscustomeroftier-1providerTier-2ISPsalsopeerprivatelywitheachother,interconnectatNAPComputernetwork-Introduction51/88Internetstructure:networkofnetworks“Tier-3”ISPsandlocalISPslasthop(“access”)network(closesttoendsystems)Tier1ISPTier1ISPTier1ISPNAPTier-2ISPTier-2ISPTier-2ISPTier-2ISPTier-2ISPlocalISPlocalISPlocalISPlocalISPlocalISPTier3ISPlocalISPlocalISPlocalISPLocalandtier-3ISPsarecustomersofhighertierISPsconnectingthemtorestofInternetComputernetwork-Introduction52/88Chapter1:roadmap1.1WhatistheInternet?1.2Networkedgeendsystems,accessnetworks,links1.3Networkcorecircuitswitching,packetswitching,networkstructure1.4Delay,lossandthroughputinpacket-switchednetworks1.5Protocollayers,servicemodels1.6Networksunderattack:security1.7HistoryComputernetwork-Introduction53/88Howdolossanddelayoccur?packetsqueueinrouterbuffers

packetarrivalratetolinkexceedsoutputlinkcapacitypacketsqueue,waitforturnABpacketbeingtransmitted(delay)packetsqueueing(delay)free(available)buffers:arrivingpacketsdropped(loss)ifnofreebuffersComputernetwork-Introduction54/88Foursourcesofpacketdelay1.nodalprocessing:

checkbiterrorsdetermineoutputlinkABpropagationtransmissionnodalprocessingqueueing2.queueingtimewaitingatoutputlinkfortransmissiondependsoncongestionlevelofrouterComputernetwork-Introduction55/88Delayinpacket-switchednetworks3.Transmissiondelay:R=linkbandwidth(bps)L=packetlength(bits)timetosendbitsintolink=L/R4.Propagationdelay:d=lengthofphysicallinks=propagationspeedinmedium(~2x108m/sec)propagationdelay=d/sABpropagationtransmissionnodalprocessingqueueingNote:sandRareverydifferentquantities!Computernetwork-Introduction56/88Nodaldelaydproc=processingdelaytypicallyafewmicrosecsorlessdqueue=queuingdelaydependsoncongestiondtrans=transmissiondelay=L/R,significantforlow-speedlinksdprop=propagationdelayafewmicrosecstohundredsofmsecsComputernetwork-Introduction57/88Queueingdelay(revisited)R=linkbandwidth(bps)L=packetlength(bits)a=averagepacketarrivalratetrafficintensity=La/RLa/R~0:averagequeueingdelaysmallLa/R->1:delaysbecomelargeLa/R>1:more“work”arrivingthancanbeserviced,averagedelayinfinite!Computernetwork-Introduction58/88“Real”Internetdelaysandroutes1cs-gw(54)1ms1ms2ms2(45)1ms1ms2ms3(30)6ms5ms5ms4(29)16ms11ms13ms5(36)21ms18ms18ms6()22ms18ms22ms7(6)22ms22ms22ms853(53)104ms109ms106ms9(29)109ms102ms104ms10(0)113ms121ms114ms11(4)112ms114ms112ms12nio-n2.cssi.renater.fr(3)111ms114ms116ms13nice.cssi.renater.fr(02)123ms125ms124ms14r3t2-nice.cssi.renater.fr(10)126ms126ms124ms15(4)135ms128ms133ms165(5)126ms128ms126ms17***18***19fantasia.eurecom.fr(42)132ms128ms136

mstraceroute:towww.eurecom.frThreedelaymeasurementsfromto*meansnoresponse(probelost,routernotreplying)Computernetwork-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Computernetwork-Introduction60/88Packetlossqueue(akabuffer)precedinglinkinbufferhasfinitecapacitypacketarrivingtofullqueuedropped(akalost)lostpacketmayberetransmittedbypreviousnode,bysourceendsystem,ornotatallABpacketbeingtransmittedpacketarrivingtofullbuffer

islostbuffer(waitingarea)Computernetwork-Introduction61/88Chapter1:roadmap1.1WhatistheInternet?1.2Networkedgeendsystems,accessnetworks,links1.3Networkcorecircuitswitching,packetswitching,networkstructure1.4Delay,lossandthroughputinpacket-switchednetworks1.5Protocollayers,servicemodels1.6Networksunderattack:security1.7HistoryComputernetwork-Introduction62/88Protocol“Layers”Networksarecomplex!many“pieces”:hostsrouterslinksofvariousmediaapplicationsprotocolshardware,softwareQuestion:

Isthereanyhopeoforganizingstructureofnetwork?Oratleastourdiscussionofnetworks?Computernetwork-Introduction63/88Organizationofairtravelaseriesofstepsticket(purchase)baggage(check)gates(load)runwaytakeoffairplaneroutingticket(complain)baggage(claim)gates(unload)runwaylandingairplaneroutingairplaneroutingComputernetwork-Introduction64/88ticket(purchase)baggage(check)gates(load)runway(takeoff)airplaneroutingdepartureairportarrivalairportintermediateair-trafficcontrolcentersairplaneroutingairplaneroutingticket(complain)baggage(claimgates(unload)runway(land)airplaneroutingticketbaggagegatetakeoff/landingairplaneroutingLayeringofairlinefunctionalityLayers:eachlayerimplementsaserviceviaitsowninternal-layeractionsrelyingonservicesprovidedbylayerbelowComputernetwork-Introduction65/88Whylayering?Dealingwithcomplexsystems:explicitstructureallowsidentification,relationshipofcomplexsystem’spieceslayeredreferencemodelfordiscussionmodularizationeasesmaintenance,updatingofsystemchangeofimplementationoflayer’sservicetransparenttorestofsysteme.g.,changeingateproceduredoesn’taffectrestofsystemlayeringconsideredharmful?Computernetwork-Introduction66/88Internetprotocolstackapplication:supportingnetworkapplicationsFTP,SMTP,HTTPtransport:process-processdatatransferTCP,UDPnetwork:routingofdatagramsfromsourcetodestinationIP,routingprotocolslink:datatransferbetweenneighboringnetworkelementsPPP,Ethernetphysical:bits“onthewire”applicationtransportnetworklinkphysicalComputernetwork-Introduction67/88ISO/OSIreferencemodelpresentation:allowapplicationstointerpretmeaningofdata,e.g.,encryption,compression,machine-specificconventionssession:synchronization,checkpointing,recoveryofdataexchangeInternetstack“missing”theselayers!theseservices,ifneeded,mustbeimplementedinapplicationneeded?applicationpresentationsessiontransportnetworklinkphysicalComputernetwork-Introduction68/88sourceapplicationtransportnetworklinkphysicalHtHnMsegmentHtdatagramdestinationapplicationtransportnetworklinkphysicalHtHnHlMHtHnMHtMMnetworklinkphysicallinkphysicalHtHnHlMHtHnMHtHnMHtHnHlMrouterswitchEncapsulationmessageMHtMHnframeComputernetwork-Introduction69/88Chapter1:roadmap1.1WhatistheInternet?1.2Networkedgeendsystems,accessnetworks,links1.3Networkcorecircuitswitching,packetswitching,networkstructure1.4Delay,lossandthroughputinpacket-switchednetworks1.5Protocollayers,servicemodels1.6Networksunderattack:security1.7HistoryComputernetwork-Introduction70/88NetworkSecurityThefieldofnetworksecurityisabout:howbadguyscanattackcomputernetworkshowwecandefendnetworksagainstattackshowtodesignarchitecturesthatareimmunetoattacksInternetnotoriginallydesignedwith(much)securityinmindoriginalvision:“agroupofmutuallytrustingusersattachedtoatransparentnetwork”

Internetprotocoldesignersplaying“catch-up”Securityconsiderationsinalllayers!Computernetwork-Introduction71/88BadguyscanputmalwareintohostsviaInternetMalwarecangetinhostfromavirus,worm,ortrojanhorse.

Spywaremalwarecanrecordkeystrokes,websitesvisited,uploadinfotocollectionsite.

Infectedhostcanbeenrolledinabotnet,usedforspamandDDoSattacks.

Malwareisoftenself-replicating:fromaninfectedhost,seeksentryintootherhostsComputernetwork-Introduction72/88More?laterComputernetwork-Introduction73/88Chapter1:roadmap1.1WhatistheInternet?1.2Networkedgeendsystems,accessnetworks,links1.3Networkcorecircuitswitching,packetswitching,networkstructure1.4Delay,lossandthroughputinpacket-switchednetworks1.5Protocollayers,servicemodels1.6Networksunderattack:security1.7HistoryComputernetwork-Introduction74/88InternetHistory1961:Kleinrock-queueingtheoryshowseffectivenessofpacket-switching1964:Baran-packet-switchinginmilitarynets1967:ARPAnetconceivedbyAdvancedResearchProjectsAgency1969:firstARPAnetnodeoperational1972:

ARPAnetpublicdemonstrationNCP(NetworkControlProtocol)firsthost-hostprotocolfirste-mailprogramARPAnethas15nodes1961-1972:Earlypacket-switchingprinciplesComputernetwork-Introduction75/88InternetHistory1970:ALOHAnetsatellitenetworkinHawaii1974:CerfandKahn-architectureforinterconnectingnetworks1976:EthernetatXeroxPARClate70’s:proprietaryarchitectures:DECnet,SNAlate70’s:switchingfixedlengthpackets(ATMprecursor)1979:ARPAnethas200nodesCerfandKahn’sinternetworkingprinciples:minimalism,autonomy-nointernalchangesrequiredtointerconnectnetworksbesteffortservicemodelstatelessroutersdecentralizedcontroldefinetoday’sInternetarchitecture1972-1980:Internetworking,newandproprietarynetsComputernetwork-Introduction76/88InternetHistory1983:deploymentofTCP/IP1982:smtpe-mailprotocoldefined1983:DNSdefinedforname-to