通信网络英语课件

IST220-002:

NetworkingandTelecommunications

Chapter1:Introductionto

ComputerNetworks&DataCommunicationDr.LeeGiles

001ThomasBuilding,SchoolofISTPhone8657884Email:giles@1InformationTechnology(IT)CommunicationTechnologyComputerTechnologyTocollect,store,process,search,retrieve,andpresentelectronicinformationtomeettheneedsofvariouskindsofusers,e.g.,computerhardware&software,PDAs,printers,groupware,smartcards….WhatisInformationTechnology(IT)?Todeliver,disseminate,exchange,transmit,andreceiveelectronicinformationinlocal,regionalorglobalcontexts,e.g.,networks,faxmachines,cellphones,email,satellites,GPS,Internet,telephony,….2ComputerSystemsRedefinedComputersystemsusedtobedefinedas:Computersystemsarenowredefinedas:hardwarenetworkssoftwarehardwaresoftware+++3Information&CommunicationGenerationandtransferofinformationiscriticaltotoday’sbusinessesFlowofinformationbothmirrorandshapeorganizationalstructuresNetworksaretheenablingtechnologyforthisprocess4The“Manager’sDilemma”TechnologyisnecessaryforcompetitivenessCostoftechnologyhasdecreasedRelianceontechnologyhasincreasedNumberofchoiceshaveincreasedChoicesarebothmoredifficultandmoreimportant5WhatisDataCommunication?CommunicationofdatabetweensourcesDataformats–analogordigitalorbothDatatravelsbyamediumWiresSpace6EssentialsofDataCommunicationMessageSenderReceiverMediumUnderstandabilityErrordetectionSecurity7TypesofMessages8ProtocolsEnablescommunication–howwecommunicate(conventionusedforestablishingtransmissionrules)WhenWhereHowWhatwithHowmuch9Protocols10ImportantDatesintheHistoryofDataCommunications(1)1837–Inventionofthetelegraph 1876–Inventionofthetelephone 1947–Inventionofthetransistor(replacedvacuumtubes)1948–Firstcommercialcomputerinstalled,theUNIVACI1958–FirstU.S.Communicationssatellitesentintoorbit1959–FCCapprovesprivatemicrowavecommunicationsnetworks1964–PacketswitchingnetworkconceptproposedbytheRandCorporation1966–IBM'sbinarysynchronous(BISYNCorBSC)protocolannounced1969–ARPANET,firstpacketswitchingnetwork(latertobecometheInternet),beginsoperation 11ImportantDatesintheHistoryofDataCommunications(2)1972–Ethernetlocalareanetworkspecificationsformulated1972–IBM'sSynchronousDataLinkControl(SDLC)protocolannounced1974–IBMannouncesitsSystemsNetworkArchitecture(SNA)1975–Personalcomputersintroduced,theAltaire8800replacedterminalsinmanycases1981–IBMPCintroduced1985–Cellularradiotelephonesareintroduced 1990–WorldWideWebisintroduced1993–Websearchenginesintroduced1995–TheInternetgrowstooverfourmillionhostcomputers1999–TheInternetgrowstoovertenmillionhostcomputers12DataCommunicationApplications(1)Batch-bi-directionaltransfersoflargeamountsofdatainconcentratedgroups

DataEntry-Lengthyinputswithshortresponses

Distributed-dataand/orprocessingishandledbymorethanoneprocessingunit

Inquiry/Response-Smallinputsofdatathatmayresultinlargeresponses

13DataCommunicationApplications(2)Interactive-Shortinputsandoutputs.Real-timeresponsewithdirectuserinteraction

Sensor-Based-Inputderivedfromsensorsinsteadofhumanoperators

Combined-Morethanoneoftheaboveapplicationsrunningatthesametime

14WhatisaComputerNetwork?Twoormorecomputersorcommunicationsdevicesconnectedbytransmissionmediaandchannelsandguidedbyasetofrulesforcommunicationpurposesthatallowuserstocommunicatewitheachotherandshareapplicationsanddata.Hardware:ComputerNetworkcardRoutersModem…Media:CableWireMicrowave…Software:NetworkOSUtilities…NetworkDesign:LogicallayoutPhysicallayout…ComponentsofaComputerNetwork15ApplicationsofaComputerNetworkMasstransitInterstatehighways24-hourbankers,grocerystoresCabletelevisionPagersMobiletelephonesMostbusinessesandschoolsRetailoutlets…16TechnologiesEthernetTokenRingTransmissionControlProtocol/InternetProtocol(TCP/IP)WirelessApplicationProtocol(WAP)NetworkOSBusTopologyRingTopologyStarTopologyLocalAreaNetwork(LAN)MetropolitanAreaNetwork(MAN)WideAreaNetwork(WAN)Client/ServerPeer-to-PeerModelsTopologiesTypesNetworkEssentials17NetworkTechnologiesBasedonbustopology;butcanbeusedinstartopology;Higherspeed:firstFastEthernet,thenGigabitEthernet;Mostpopular:inexpensive,easytoinstallandmaintain.EthernetTokenRingTCP/IPWAPBasedonaringtopology;butcanuseastartopology;Token-passingschemetopreventcollisionofdata;Thesecondmostwidely-usedprotocolafterEthernet.Basedonclient/servermodelofnetworkcomputing;Usespacketswitchingtechniquefordatatransmission;CommonlyusedforInternetapplications.Usesclient/servermodelofnetworkcomputing;AllowswirelessdevicestoaccesstheInternetandWWW;MeetsincreasingdemandsforwirelessInternetaccess.18TheWorldofConnectivityWiredorwirelesscommunicationslinksofferseveraloptionsforinformationandcommunications.Source:TheMcGraw-HillCompanies,Inc.,199919ComputerNetworkConfigurations:

ConnectionsbetweenNetworksComputerterminaltomainframecomputerMicrocomputertomainframecomputerMicrocomputertolocalareanetworkMicrocomputertoInternetLocalareanetworktolocalareanetworkLocalareanetworktowideareanetworkSensortolocalareanetworkSatelliteandmicrowaveWirelesstelephone20ComputerNetworkConfigurations:

ComputerTerminaltoMainframeComputerUsedinmanytypesofbusinessesfordataentryanddataretrieval.Usuallyinvolvesalow-speedconnection.2122ComputerNetworkConfigurations:

MicrocomputertoLocalAreaNetworkVerycommonthroughoutbusinessandacademicenvironments.Typicallyamedium-tohigh-speedconnection.2324ComputerNetworkConfigurations:

MicrocomputertoInternetVerypopularwithhomeusers.Typicallyamodemisusedtoconnectuser’smicrocomputertoanInternetServiceProvider.NewertechnologiessuchasDSLandcablemodemsarereplacingmodems.2526ComputerNetworkConfigurations:

LANtoLANConnectionsFoundinbusinessesandschoolsthathavetwoormoreLANsandaneedforthemtointercommunicate.ThebridgeisatypicaldeviceusedtointerconnectLANs.27

DataCommunicationsandComputerNetworks

Chapter1

28ComputerNetworkConfigurations:

LANtoWANConnectionsOneofthebestwaystointerconnectauseronaworkstationtotheInternet(awideareanetwork).ArouteristhetypicaldevicethatperformsLANtoWANconnections.2930ComputerNetworkConfigurations:

SensortoLANConnectionsOftenfoundinindustrialenvironments.Assemblylinesandroboticcontrolsdependheavilyonsensor-basedlocalareanetworks.3132ComputerNetworkConfigurations:

SatelliteandMicrowaveManytypesofapplicationsincludinglongdistancetelephone,television,radio,long-hauldatatransfers,andwirelessdataservices.Typicallyexpensiveservicesbutmanycompaniesoffercompetitiveservicesandrates.3334ComputerNetworkConfigurations:WirelessTelephoneQuicklyexpandingmarketacrosstheU.S.andworld.FirstgenerationanalogservicesandsecondgenerationPCSservicesavailableinmostareasandundermanytypesofplans.ThirdgenerationservicesbeginningtoappearinEuropeandAsia.3536WhyAreNetworksImportant?

BUSINESSENTERPRISETraditionalDataTextImages

InformationGraphicsVoiceVideoMulti-mediaApplicationsFunctionsOrganizationalProcessesPersonalUsersEnterpriseOrganizationDepartmentIndividualNetworkLANsMansWANsInternetWiredWireless37Networks:ProsandConsResourcesharingPrinters,CD-ROMs,computers

DataandinformationsharingCommunicationsReducedCostOn-lineservicesGroupwareSoftwarethatsupportsgroupeffortsoveranetworkElectronicdatainterchangeSecurityrisksincreasewithnetworksComplexityisassociatedwithnetworksInvestmentishighandreturnonitmaynothappenProsCons38KeyIssuesofNetworksAccesstotheInternetNetworkAccessWiredaccessCablemodemDSLWirelessaccessWirelessLANRosettaNet–XMLbasedNetworksecurityGoalsandMeasuresFirewalls39WhyUseaNetwork?Sharingof

Data,messages,graphics…Applications…Devices,e.g.,harddrives,backups,printers,modems,faxmachines…CentralizedadministrationInstallingandupgradingapplicationsoftwareCommunicationandcollaborationTeleconferences,groupdecisionsupportsystems40ClassDiscussionIfyoucoulddesignyourownhome,whatkindsofcomputernetworkordatacommunicationslabor-savingdeviceswouldyouincorporate?Usingalaptopcomputerwithawirelessconnectionintothecompany’slocalareanetwork,youdownloadaWebpagefromtheInternet.Listallthedifferentnetworkconfigurationsinvolvedinthisoperation.41LanguageofComputerNetworksImportanttermsandconcepts.42ComponentsofaNetworkServerAcomputerthatprovidesservicestoothernetworkedcomputersClientAcomputerinaclient/serverrelationship,e.g.,aWebbrowserHardware/SoftwareNetworkcard,router,modem,hub/NToperatingsystems,utilities…MediaThewaytoconnectcomputersonanetworkDataFilesobesharedbynetworkcomputersResourcesPeripherals,e.g.,printers,tobeusedby

networkcomputers43MediaofNetworkingCoaxcableTwistedpaircableFiberopticcableMicrowaveCommunicationssatelliteCellularphones

44NetworkingHardwareWorkstationsServersBridgesRoutersHubsandswitchesNodes45NetworkModels

Microcomputerusers,orclients,shareservicesofacentralizedcomputercalledaserver.Computersshareequallywithoneanotherwithouthavingtorelyonacentralserver.Client/ServerModelPeer-to-PeerModel46Client/Server

Adistinctionexistsbetweencomputersthatmakeavailablenetworkresources(servers)andthosecomputersthatusetheresources(clientsorworkstations).Pros:VerysecureCentralizedserverseasytomanagePhysicallycentralizedSecureOSBetterperformanceCentralizedbackupsReliabilitySimplejobtodoplusbuiltinredundancyCons:RequireprofessionaladministrationMorehardwareintensive47Peer-to-Peer(p2p)Computersonthenetworkcommunicatewitheachothersasequalsandeachcomputerisresponsibleformakingitsownresourcesavailabletoothercomputersonthenetwork.Pros:UseslessexpensivecomputernetworksEasytoadministerNoNOS(networkoperatingsystem)requiredMorebuilt-inredundancySharedresources–somemachinewillhavewhatyouneedCons:IndividualuserperformanceeasilyaffectedNotverysecureTragedyofthecommons–noguaranteeotherswilladministertheirresourcesproperly(almostguaranteedwithover10machines)Hardtobackup.48Client/Servervs.

Peer-to-Peer:

AdvantagesandDisadvantages

Advantages:VerysecureOS.Betterperformance.Centralizedservers,easytomanage.Centralizedbackups.Highreliability.Peer-to-PeerModelClient/ServerModelDisadvantages:Expensiveadministration.Morehardwareintensive.Advantages:Useslessexpensivenetworks.Easytoadminister.Containbothnetworkoperatingsystemandapplicationsoftware.Idealforsmallbusinessandhomeusers.Disadvantages:Individualuserperformanceeasilyaffected.Notverysecure.Hardtobackup.49NetworkingEssentialsComputerNetworks

AhostcomputerconnectedwithcommunicationcircuitsandequipmenttoterminalsTwoormorecomputersconnectedviaacommunicationmedium

IntranetAprivateversionoftheInternetEnterpriseNetwork

TwoormoreLANsconnectedtoeachother,oroneormoreLANsconnectedtoaWANFileServer

AcomputerthatcontainsfilessharedbyPCsonanetwork

50CategorizationofNetworksBysize:WideAreaNetwork(WAN)MetropolitanAreaNetwork(MAN)LocalAreaNetworks(LAN)Bycapability:Client/serverPeer-to-peer51ThreeMajorTypesofNetworks

LocalAreaNetwork(LAN)Servesuserswithinaconfinedgeographicalarea(usuallywithinamile).

MetropolitanAreaNetwork(MAN)Coversageographicareathesizeofacityorsuburb.ThepurposeofaMANisoftentobypasslocaltelephonecompanieswhenaccessinglong-distanceservice.

WideAreaNetwork(WAN)

Coversawidegeographicalarea,suchasastateoracountry.Examples:Tyment,Telenet,Uninet,andAccunet.52Interconnection

between

LANsandWANs53CharacteristicsDifferentiate

OneNetworkfromAnotherTopology:Thegeometricarrangementofdevicesonthenetwork.Forexample,devicescanbearrangedinaringorinabusorinastartopology.Protocols:Therulesandencodingspecificationsforsendingdata.Theprotocolsalsodeterminewhetherthenetworkusesapeer-to-peerorclient/servermodel.Media:Devicescanbeconnectedbytwisted-pairwire,coaxialcables,orfiberopticcables.Wirelessnetworksareconnectedviaradiowaves.MediumAccessControl:Schemetoallowsharingofthemedia.54ComponentsofaTypicalLANSource:TheMcGraw-HillCompanies,Inc.,199955NetworkTypologies:StarThisarrangementconnectsallthenetwork’sdevicestoacentralhostcomputer,throughwhichallcommunicationsmustpass.Source:TheMcGraw-HillCompanies,Inc.,199956NetworkTypologies:RingThisarrangementconnectsthenetwork’sdevicesinaclosedloop.Source:TheMcGraw-HillCompanies,Inc.,199957NetworkTypologies:BusAsinglechannelconnectsallcommunicationsdevices.Source:TheMcGraw-HillCompanies,Inc.,199958NetworkingandTelecommunicationsNetworking-aninterconnectionofcomputersandcomputingequipmentusingeitherwiresorradiowavesoversmallorlargegeographicdistancesTelecommunications-studyoftelephonesandthesystemsthattransmittelephonesignalsNetworkmanagement-design,installation,andsupportofanetworkanditshardwareandsoftware59NetworkingAspectsComputerNetworks

AhostcomputerconnectedwithcommunicationcircuitsandequipmenttoterminalsTwoormorecomputersconnectedviaacommunicationmedium

IntranetAprivateversionoftheInternetEnterpriseNetwork

TwoormoreLANsconnectedtoeachother,oroneormoreLANsconnectedtoaWANFileServer

AcomputerthatcontainsfilessharedbyPCsonanetwork

60NetworkSelectionCriteriaSizeoftheorganizationLevelofrequiredsecurityLevelofavailableadministrativesupportAmountofnetworktrafficNeedsofthenetworkusersBudgetforbuildingthenetwork61RequirementsofaNetworkSystem(1)IdealsystemDoeswhatwewantinstantlywhenwewantitwithnoerrorsorproblemsandonlyweknowaboutit.PerformanceConsistencyFlexibilityAvailabilityReliabilityRecoverySecurity62RequirementsofaNetworkSystem(2)PerformanceResponsetimeTimefortransmissionTimefordataprocessingTransactionRate(throughput)Theamountofworkperformedbyasystemperunitoftime63RequirementsofaNetworkSystem(3)ConsistencySamethingallthetimeResponsetime64RequirementsofaNetworkSystem(4)FlexibilityGrowthandchangeavailablewithminimumimpactonusersLegacysystemsStandardshelp65RequirementsofaNetworkSystem(5)AvailabilityWhenneededWhereavailableHowavailable66RequirementsofaNetworkSystem(6)ReliabilityMeasureofsystemfailureMTBF–meantimebetweenfailureFault-tolerancesolutionDesignDuplication67RequirementsofaNetworkSystem(7)RecoveryAllsystemsfailHowlongbeforestartup?WhatdowegetwhenthesystemstartsupagainSavedinformation68RequirementsofaNetworkSystem(8)SecurityWhohasaccess?Howgoodistheprotection?Privacy69NetworkArchitectureModelsAreferencemodelthatdescribesthelayersofhardwareandsoftwarenecessarytotransmitdatabetweentwopoints.Referencemodelsarenecessarytoincreasethelikelihoodthatdifferentcomponentsfromdifferentmanufacturerswillconverse.Therearetwostandardmodelsthatareimportant:TheOSIModel,andtheInternetModel.70StandardsStandards

arerulesofoperationthatarefollowedbymostorallvendorsStandardsallowhardwareandsoftwarefromdifferentvendorstoworktogetherCompetitionamongvendorsbringslowerpricesandfeature-richproducts71StandardsISO-InternationalStandardsOrganization:Anorganizationthatsetscommunicationstandards,alsoIEEEOSI-OpenSystemsInterconnection:AsevenlayerreferencemodelfordevelopingdatacommunicationsystemsOpenArchitecture-inwhichthenetworkspecificationsareavailabletoanycompany72OSILayersofCommunication73ApplicationLayerWheretheapplicationusingthenetworkresides.Commonnetworkapplicationsincluderemotelogin,filetransfer,e-mail,andwebpagebrowsing.FunctionalitydefinedbyuserApplicationdependent74PresentationLayerPerformsaseriesofmiscellaneousfunctionsnecessaryforpresentingthedatapackageproperlytothesenderorreceiverFormatofthedataEncryptionCompressionScreenformatting75SessionLayerEstablishesconnectionbetweenapplicationsEnforcesrulesOrderPacingReestablishconnection76TransportLayerProvidesanend-to-end,error-freenetworkconnection.Makessurethedataarrivesatthedestinationexactlyasitleftthesource.Makessureallinformationisaccountedfor:MissinginformationDuplicatedinformation77NetworkLayerResponsibleforcreatingmaintainingandendingnetworkconnections.Transfersadatapacketfromnodetonodewithinthenetwork.MessageroutingBillingAccounting78DataLinkLayerResponsiblefortakingthedataandtransformingitintoaframewithheader,controlandaddressinformation.PhysicalpathcommunicationErrordetectionErrorcorrectionResolvecompetingrequests79PhysicalLayerHandlesthetransmissionofbitsoveracommunicationschannel.Includes:VoltagelevelsElectricalconnectionsMediachoicesAdaptersConnectorsModulationtechniques8081LayersinInternetModelvs.OSIModelInterfacelayer-equivalenttotheOSI’sphysicalanddatalinklayers.Networklayer-roughlyequivalenttotheOSI’snetworklayer.Transportlayer-performssamefunctionasOSItransportlayer.Applicationlayer-equivalenttotheOSI’spresentationandapplicationlayers.82TheInternetModelvs.theOSIMode