計算機網(wǎng)絡(luò)英文版課件：slide 01 Introduction

ComputerNetworksContentsIntroduction:networkapplication,networkarchitecture,networkprotocolandreferencemodelThePhysicalLayerTheDataLinkLayerTheMediumAccessControl(MAC)SublayerTheNetworkLayerTheTransportLayerTheApplicationLayerNetworkSecurity,andLatestDevelopmentofComputerNetworkGoalsUnderstandtheprinciplesofnetworkarchitecture,referencemodelandnetworkprotocolsUnderstandthefunctionsofthephysicallayer,datalinklayer,MACsublayer,networklayer,transportlayerandapplicationlayerprotocolsUnderstandthemechanismandalgorithmsofnetworkprotocolsReferencesAndrewS.Tanenbaum,ComputerNetworks,4thEd.,PearsonEducationAsiaLimitedandTsinghuaUniversityPress,2004J.F.Kurose,K.W.Ross,ComputerNetworking:ATop-DownApproachFeaturingtheInternet,Addison-WesleyPressandTsinghuaUniversityPress,2001GradingPolicies閉卷：總成績=課堂成績×80%+實驗成績×20%，其中：課堂成績=平時成績×10%+期中成績×15%+期末成績×75%IntroductionUsesofComputerNetworksNetworkHardwareNetworkSoftwareReferenceModelsExampleNetworksNetworkStandardizationBasicConceptComputerNetwork:acollectionofautonomouscomputersinterconnectedbyasingletechnologyInterconnected:beabletoexchangeinformation,theconnectioncouldbeviacopperwire,fiberoptics,microwaves,infrared,andcommunicationsatellitesSingletechnology:InternetisnotasinglenetworkbutanetworkofnetworksWorldWideWebisadistributedsystemthatrunsontopoftheInternetUsesofComputerNetworksBusinessApplicationsHomeApplicationsMobileUsersSocialIssuesBusinessApplicationsofNetworksResourceSharingCommunicationmediumamongpeopleDoingbusinesselectronicallywithothercompaniesE-Commerce(electroniccommerce)BusinessApplicationsofNetworksResourceSharingSharingprogramsSharingequipment,e.g.printer,scanner,CDburnersEspecially,sharinginformation

Anetworkwithtwoclientsandoneserver.BusinessApplicationsofNetworksTheclient-servermodelinvolvesrequestsandreplies.BusinessApplicationsofNetworksCommunicationmediumamongpeople,e.g.e-mail,videoconference/config/mail?.intl=us//messenger/overview/software.phpBusinessApplicationsofNetworksDoingbusinesselectronicallywithothercompanies:placeorderselectronicallyusingcomputernetworksE-Commerce(electroniccommerce):doingbusinesswithconsumersovertheInternet.HomeNetworkApplicationsAccesstoremoteinformationPerson-to-personcommunicationInteractiveentertainmentElectroniccommerceHomeNetworkApplicationsAccesstoremoteinformationSurfingtheWorldWideWebPerson-to-personcommunicationEmailInstantmessaging,chatroomPeer-to-PeercommunicationHomeNetworkApplications(2)Inpeer-to-peersystemtherearenofixedclientsandservers.P2P:centralizeddirectoryoriginal“Napster”design1)whenpeerconnects,itinformscentralserver:IPaddresscontent2)Alicequeriesfor“HeyJude”3)AlicerequestsfilefromBobcentralizeddirectoryserverpeersAliceBob111123ExtractedfromslidesofComputerNetworkingcourseofProf.J.Kurose

HomeNetworkApplicationsInteractiveentertainment//ElectroniccommerceHomeshppping:/OnlineBanking:/index.jspHomeNetworkApplications(3)Someformsofe-commerce.UMassCampusNetworkExtractedfromslidesofComputerNetworkingcourseofProf.J.Kurose

Thenetworkedge:endsystems(hosts):runapplicationprogramse.g.Web,emailat“edgeofnetwork”client/servermodelclienthostrequests,receivesservicefromalways-onservere.g.Webbrowser/server;emailclient/serverExtractedfromslidesofComputerNetworkingcourseofProf.J.Kurose

TheNetworkCoremeshofinterconnectedroutersthefundamentalquestion:howisdatatransferredthroughnet?circuitswitching:dedicatedcircuitpercall:telephonenetpacket-switching:datasentthrunetindiscrete“chunks”ExtractedfromslidesofComputerNetworkingcourseofProf.J.Kurose

Internetstructure:networkofnetworksTier1ISPTier1ISPTier1ISPNAPTier-2ISPTier-2ISPTier-2ISPTier-2ISPTier-2ISPlocalISPlocalISPlocalISPlocalISPlocalISPTier3ISPlocalISPlocalISPlocalISPExtractedfromslidesofComputerNetworkingcourseofProf.J.Kurose

Tier-1ISP:e.g.,SprintSprintUSbackbonenetworkSeattleAtlantaChicagoRoachdaleStocktonSanJoseAnaheimFortWorthOrlandoKansasCityCheyenneNewYorkPennsaukenRelayWash.DCTacomaDS3(45Mbps)OC3(155Mbps)OC12(622Mbps)OC48(2.4Gbps)…to/fromcustomerspeeringto/frombackbone….………POP:point-of-presenceInternetstructure:networkofnetworksapacketpassesthroughmanynetworks!Tier1ISPTier1ISPTier1ISPNAPTier-2ISPTier-2ISPTier-2ISPTier-2ISPTier-2ISPlocalISPlocalISPlocalISPlocalISPlocalISPTier3ISPlocalISPlocalISPlocalISPCERNETTopology徐聞長春哈爾濱烏魯木齊拉薩西寧蘭州銀川呼和浩特臺北沈陽南昌西安徐州武漢合肥鄭州石家莊北京南寧廣州福州杭州上海南京天津貴陽?？谌齺喺拷瓱o錫大連太原濟南煙臺成都長沙重慶黃梅九江昆明青島汕頭唐山漢中宜昌珠海深圳惠州柳州百色廈門BackboneRegionalGigaPopPop桂林深圳MobileNetworkUsersCombinationsofwirelessnetworksandmobilecomputing.SocialIssuesDifferentcountrieshavedifferentandconflictinglaws,thusdebateragesPeople’sprivacyElectronicjunkmail(spam)VirusesIdentitytheftNetworkHardwareLocalAreaNetworksMetropolitanAreaNetworksWideAreaNetworksWirelessNetworksHomeNetworksInternetworksNetworkHardwareClassificationofcomputernetworks:BytransmissiontechnologyBroadcastlinks:Broadcastnetworks:broadcasting,multicastingPoint-to-pointlinks:Point-to-pointnetworks,unicastingByscalePersonalareanetworkLocalareanetworkMetropolitanareanetworkWideareanetworkTheInternetClassificationofinterconnectedprocessorsbyscaleLocalAreaNetworks(LANs)LANsaredistinguishedfromotherkindsofnetworksbythreecharacterisitcs:1)theirsize,2)theirtransmissiontechnology,and3)theirtopologyTwobroadcastnetworks:(a)Bus;(b)RingMetropolitanAreaNetworksAmetropolitanareanetworkbasedoncableTV.IEEE802.16:WideAreaNetworks(WANs)WAN:spansalargegeographicalarea,oftenacountryorcontinent.Communicationsubnet,subnet:consistsoftwodistinctcomponents:transmissionlinesandswitchingelementsHostsRelationbetweenhostsonLANsandthesubnetWideAreaNetworks(2)Astreamofpacketsfromsendertoreceiver.Store-and-forwardorpacket-switchedRouting:routingalgorithmWirelessNetworksCategoriesofwirelessnetworks:Systeminterconnection:BluetoothWirelessLANsIEEE802.11WirelessWANsRadionetworksusedforCellulartelephones:1st,2nd,3rdgenerationIEEE802.16:WirelessNetworks(2)(a)Bluetoothconfiguration(b)WirelessLANWirelessNetworks(3)(a)Individualmobilecomputers(b)AflyingLANHomeNetworksDevicescapableofbeingconnected:Computers(desktopPC,PDA,sharedperipheralsEntertainment(TV,DVD,VCR,camera,stereo,MP3)Telecomm(telephone,cellphone,intercom,fax)Appliances(microwave,fridge,clock,furnace,airco)Telemetry(utilitymeter,burglaralarm,babycam).HomeNetworksDifferentpropertiesofhomenetworkingthanothernetworktypes:TobeeasytoinstallTobefoolproofinoperationLowpriceNeedsbetterperformance,asatlowpricesandinvolvingmultimediaToremainstableSecurityandreliabilitywillbeveryimportantNetworkSoftwareProtocolHierarchiesDesignIssuesfortheLayersConnection-OrientedandConnectionlessServicesServicePrimitivesTheRelationshipofServicestoProtocolsProtocolHierarchiesLayers,protocols,andinterfaces.ProtocolHierarchiesToreducetheirdesigncomplexity,mostnetworksareorganizedasastackoflayersorlevels,eachonebuiltupontheonebelowit.Layernononemachinecarriesonaconversationwithlayernonanothermachine.TherulesandconventionsusedinthisconversationarecollectivelyknownasthelayernprotocolBasically,aprotocolisanagreementbetweenthecommunicatingpartiesonhowcommunicationistoproceedProtocolHierarchiesTheentitiescomprisingthecorrespondinglayersondifferentmachinesarecalledpeers.Betweeneachpairofadjacentlayersisaninterface.Asetoflayersandprotocolsiscalledanetworkarchitecture.Alistofprotocolsusedbyacertainsystem,oneprotocolperlayer,iscalledaprotocolstack.ProtocolHierarchiesThephilosopher-translator-secretaryarchitecture.ProtocolHierarchiesExampleinformationflowsupportingvirtualcommunicationinlayer5.DesignIssuesfortheLayersSomeofthekeydesignissuesthatoccurincomputernetworks:

AddressingErrorControlFlowControlMultiplexingRoutingLayerscanoffertwodifferenttypesofservicestothelayersabovethem:

Connection-orientedservice:Modeledafterthetelephonesystemtouseaconnection-orientednetworkservice,theserviceuserfirstestablishesaconnection,usestheconnection,andthenreleasetheconnection

Connectionlessservice:ModeledafterthepostalsystemEachmessagecarriesthefulldestinationaddress,andeachoneisroutedthroughthesystemindependentofalltheothers.Connection-OrientedandConnectionlessServicesConnection-OrientedandConnectionlessServicesSixdifferenttypesofservice.ServicePrimitivesAserviceisformallyspecifiedbyasetofprimitives(operations)availabletoauserprocesstoaccesstheservice.Thesetofprimitivesavailabledependsonthenatureoftheservicebeingprovided.Fiveserviceprimitivesforimplementingasimpleconnection-orientedserviceServicePrimitives(2)Packetssentinasimpleclient-serverinteractiononaconnection-orientednetwork.ServicestoProtocolsRelationshipTherelationshipbetweenaserviceandaprotocol.ReferenceModelsTheOSIReferenceModelTheTCP/IPReferenceModelAComparisonofOSIandTCP/IPACritiqueoftheOSIModelandProtocolsACritiqueoftheTCP/IPReferenceModelTheOSIreferencemodel.TheOSIReferenceModelThephysicallayer:concernedwithtransmittingrawbitsoveracommunicationchannel.Thedatalinklayer:Mainlytotransformarawtransmissionfacilityintoalinethatappearsfreeofundetectedtransmissionerrorstothenetworklayer.MediumaccesscontrolsublayerThenetworklayer:AkeydesignissueisdetermininghowpacketsareroutedfromsourcetodestinationCongestioncontrolTheOSIReferenceModelThetransportlayer:Thebasicfunctionistoacceptdatafromabove,splititupintosmallerunitsifneedbe,passtothenetworklayer,andensurethatthepiecesallarrivecorrectlyattheotherend.Thetransportlayerisatrueend-to-endlayer,allthewayfromthesourcetothedestination.Thesessionlayer:Toestablishsession:fordialogcontrol,tokenmanagement,andsynchronizationThepresentationlayer:IsconcernedwiththesyntaxandsemanticsoftheinformationtransmittedTheapplicationlayer:ContainsavarietyofprotocolsthatarecommonlyneededbyusersTheTCP/IPreferencemodelProtocolsandnetworksintheTCP/IPmodelinitially.ProtocolsandnetworksintheTCP/IPmodelinitially.TheTCP/IPReferenceModelTheInternetlayer:Topermithoststoinjectpacketsintoanynetworkandhavethemtravelindependentlytothedestination(potentiallyonadifferentnetwork).TheinternetlayerdefinesanofficialpacketformatandprotocolcalledIP(InternetProtocol).Thetransportlayer:isdesignedtoallowpeerentitiesonthesourceanddestinationhoststocarryonaconversation,justasintheOSItransportlayer.Twoend-to-endtransportprotocolshavebeendefined:TCP(TransmissionControlProtocol),andUDP(UserDatagramProtocol)TheTCP/IPReferenceModelTheapplicationlayer:Telnet,FTP,SMTP,DNSTheHost-to-Networklayer:TheTCP/IPreferencemodeldoesnotreallysaymuchaboutwhathappensbelowtheinternetlayer.ComparingOSIandTCP/IPModelsTheOSImodelmadethedistinctionbetweenservices,interfaces,andprotocolsexplicit,whiletheTCP/IPmodeldidnotoriginallyclearlydistinguishbetweenthesethreeconcepts.TheOSIreferencemodelwasdevisedbeforethecorrespondingprotocolswereinvented.WithTCP/IPthereversewastrue.ACritiqueoftheOSIModelandProtocolsWhyOSIdidnottakeovertheworldBadtimingBadtechnologyBadimplementationsBadpoliticsTheapocalypseofthetwoelephants.ACritiqueoftheTCP/IPReferenceModelProblems:Service,interface,andprotocolnotdistinguishedNotageneralmodelHost-to-network“l(fā)ayer”notreallyalayerNomentionofphysicalanddatalinklayersMinorprotocolsdeeplyentrenched,hardtoreplaceHybridModelThehybridreferencemodeltobeusedinthisbook.ExampleNetworksTheInternetConnection-OrientedNetworks:

X.25,FrameRelay,andATMEthernetWirelessLANs:802:11TheARPANET(a)Structureofthetelephonesystem.(b)Baran’sproposeddistributedswitchingsystem.TheARPANET(2)TheoriginalARPANETdesign.TheARPANET(3)GrowthoftheARPANET:

(a)December1969.(b)July1970.(c)March1971.(d)April1972.(e)September1972.NSFNETTheNSFNETbackbonein1988.InternetUsageTraditionalapplications(1970–1990)E-mailNewsRemoteloginFiletransferWWW(WorldWideWeb)ArchitectureoftheInternetOverviewoftheInternetConnection-OrientedNetworks:X.25,FrameRelay,andATMTelephoneSystem:QualityofServiceBillingX.25ConnectionnumberDataPacketFrameRelay:aconnection-orientednetworkwithnoerrorcontrolandnoflowcontrolATM(AsynchronousTransferMode):connection-oriented:virtualcircuitsEachconnection(virtualcircuit),temporaryorpermanent,hasauniqueconnectionidentifier.ATMVirtualCircuitsAvirtualcircuit.ATMVirtualCircuits(2)AnATMcell.ThebasicideabehindATMistotransmitallinformationinsmall,fixed-sizepacketscalledcells.easytobuildhardwarerouterstohandleshort,fixed-lengthcellssmallcellsdonotblockanylineforverylong,whichmakesguaranteeingqualityofserviceeasierTheATMReferenceModelTheATMReferenceModel(2)TheATMlayersandsublayersandtheirfunctions.EthernetArchitectureoftheoriginalEthernet.WirelessLANs:IEEE802.11IEEE802.11hadtoworkintwomodes:Inthepresenceofabasestation:allcommunicationwastogothroughthebasestation,calledanaccesspointin802.11terminologyIntheabsenceofabasestation:thecomputerswouldjustsendtooneanotherdirectly.Thismodeisnowsometimescalledadhocnetworking

(a)Wirelessnetworkingwithabasestation.(b)Adhocnetworking.WirelessLANs:IEEE802.11Someofthemanychallengesthathadtobemetwere:findingasuitablefrequencybandthatwasavailable,preferablyworldwide;dealingwiththefactthatradiosignalshaveafiniterange;ensuringthatusers'privacywasmaintained;takinglimitedbatterylifeintoaccount;worryingabouthumansafety(doradiowavescausecancer?);understandingtheimplicationsofcomputermobility;andfinally,buildingasystemwithenoughbandwidthtobeeconomicallyviable.WirelessLANsTherangeofasingleradiomaynotcovertheentiresystem.WirelessLANsAmulticell802.11network.NetworkStandardizationNetworkstandardsallowdifferentcomputerstocommunicateincreasethemarketforproductsadheringtothestandardStandardsfallintotwocategories:defactostandards:arethosethathavejusthappened,withoutanyformalplandejurestandards:areformal,legalstandardsadoptedbysomeauthorizedstandardizationbodyNetworkStandardizationOrganizationsintheTelecommunicationsWorldITU(InternationalTelecommunicationUnion):,anagencyoftheUnitedNationshasthreemainsectors:1)RadiocommunicationsSector(ITU-R),2)TelecommunicationsStandardizationSector(ITU-T),and3)DevelopmentSector(ITU-D).ITU-Thasfourclassesofmembers:1)Nationalgovernments;2)Sectormembers:includingtelephoneoperators,equipmentmanufacturers,computervendors,chipmanufacturers,IFIP,etc.3)Associatemembers;4)RegulatoryagenciesItshouldbenotedthatITU-Trecommendationsaretechnicallyonlysuggestionsthatgove