全国大学生创新创业会材料.ppt

1 5 IntroductiontoNetworking 中医免费资料 2 References HeldG InternetworkingLANsandWANs Concepts TechniquesandMethods Wiley 2ndEd 1998Comment GoodatconceptsStallingsW DataandComputerCommunications PrenticeHall 7thEd 2004Comment Goodatconceptsandveryup to dateForouzanB A DataCommunicationsandNetworking McGraw Hill 2ndEd 2000Comment ManygoodrevisionquestionsatendsofchaptersRedmondW MCSETrainingKit NetworkingEssentialsPlus MicrosoftPress 2000Comment Practicaloriented 3 WhatisaNetwork Anetworkconsistsof2ormorecomputersconnectedtogether andtheycancommunicateandshareresources e g information 4 WhyNetworking Sharinginformation i e datacommunication Doyoupreferthese Orthis 5 Sharinghardwareorsoftware Centralizeadministrationandsupport E g printdocument E g Internet based soeveryonecanaccessthesameadministrativeorsupportapplicationfromtheirPCs 6 HowmanykindsofNetworks Dependingonone sperspective wecanclassifynetworksindifferentways Basedontransmissionmedia Wired UTP coaxialcables fiber opticcables andWirelessBasedonnetworksize LANandWAN andMAN Basedonmanagementmethod Peer to peerandClient ServerBasedontopology connectivity Bus Star Ring 7 Twomaincategories Guided wires cablesUnguided wirelesstransmission e g radio microwave infrared sound sonarWewillconcentrateonguidedmediahere Twisted Paircables UnshieldedTwisted Pair UTP cablesShieldedTwisted Pair STP cablesCoaxialcablesFiber opticcables TransmissionMedia 8 Ifthepairofwiresarenottwisted electromagneticnoisesfrom e g motors willaffectthecloserwiremorethanthefurtherone therebycausingerrors Twisted PairCables 9 UnshieldedTwisted Pair UTP Typicallywrappedinsideaplasticcover formechanicalprotection AsampleUTPcablewith5unshieldedtwistedpairsofwires 10 ShieldedTwisted Pair STP STPcablesaresimilartoUTPcables exceptthereisametalfoilorbraided metal meshcoverthatencaseseachpairofinsulatedwires 11 CategoriesofUTPCablesEIAclassifiesUTPcablesaccordingtothequality Category1 thelowestquality onlygoodforvoice mainlyfoundinveryoldbuildings notrecommendednowCategory2 goodforvoiceandlowdatarates upto4Mbpsforlow speedtokenringnetworks Category3 atleast3twistsperfoot forupto10Mbps commoninphonenetworksinresidentialbuildings Category4 upto16Mbps mainlyfortokenrings Category5 or5e upto100Mbps commonfornetworkstargetedforhigh speeddatacommunications Category6 moretwiststhanCat5 upto1Gbps 12 CoaxialCablesIngeneral coaxialcables orcoax carrysignalsofhigherfreq 100KHz 500MHz thanUTPcablesOutermetallicwrappingservesbothasashieldagainstnoiseandasthesecondconductorthatcompletesthecircuit 13 Fiber OpticCablesLighttravelsat3 108ms 1infreespaceandisthefastestpossiblespeedintheUniverseLightslowsdownindensermedia e g glassRefractionoccursatinterface withlightbendingawayfromthenormalwhenitentersalessdensemediumBeyondthecriticalangle totalinternalreflection 14 Anopticalfiberconsistsofacore densermaterial andacladding lessdensematerial Simplestoneisamultimodestep indexopticalfiberMultimode multiplepaths whereasstep index refractiveindexfollowsastep functionprofile i e anabruptchangeofrefractiveindexbetweenthecoreandthecladding LightbouncesbackandforthalongthecoreCommonlightsources LEDsandlasers 15 AdvantagesandDisadvantagesNoiseresistance externallightisblockedbyouterjacketLesssignalattenuation asignalcanrunformileswithoutregeneration currently thelowestmeasuredlossisabout 4 or0 16dBperkm Higherbandwidth currently limitsondataratescomefromthesignalgeneration receptiontechnology notthefiberitselfCost OpticalfibersareexpensiveInstallation maintenance anycrackinthecorewilldegradethesignal andallconnectionsmustbeperfectlyaligned 16 LANandWAN LocalAreaNetwork LAN Smallnetwork shortdistanceAroom afloor abuildingLimitedbyno ofcomputersanddistancecoveredUsuallyonekindoftechnologythroughouttheLANServeadepartmentwithinanorganizationExamples NetworkinsidetheStudentComputerRoomNetworkinsideCF502Networkinsideyourhome 17 WideAreaNetwork WAN Anetworkthatuseslong rangetelecommunicationlinkstoconnect2ormoreLANs computershousedindifferentplacesfarapart Towns states countriesExamples NetworkofourCampusInternet WAN StudentComputerCentre Yourhome USA 18 ExampleWANtechnologies ISDN IntegratedServiceDigitalNetworkBasicrate 192KbpsPrimaryrate 1 544MbpsT Carriers basicallydigitalphonelinesT1 1 544MbpsT3 28 T1FramerelayEachlinkoffers1 544MbpsorevenhigherATM AsynchronousTransferModeSupportB ISDN 155Mbpsor622MbpsorhigherSONET SynchronousOpticalNetworkBasicrateOC1 51 84MbpsSupportOC12anduptoOC192 9953 28Mbps orevenhigherinthefuture 19 ExampleofWAN BroadbandCableNetwork CableTVserviceshavebeenextensivelydevelopedinmostmoderncitiesCableTVcompaniestrytomakeuseoftheircoaxialcableinstalled thataresupposedtocarryTVsignals todeliverbroadbanddataservicesManycablenetworkwiringhasbeenreplacedwithhybridfiber coax HFC i e useoffiber opticcabletoconnecttothesubscribers buildings andthentheoriginalcoaxialcabletoconnecttoeachhousehold 20 Theconnectionissharedbyanumberofsubscribers hencemayraiseperformanceandsecurityproblems Fiber opticcable Cablecompany CoaxialCable TV PC CableDrop 21 CableisanasymmetricaltechnologyDownstream max36MbpsUpstream max10MbpsMaybereducedto3 10Mbpsdownstreamand2Mbpsupstream dependingonno ofsubscribersNeedaspecialcablemodem EthernetlinktoPC CoaxiallinkfromcableTVsocket TeryonCableModem 22 Peer to PeerNetworks Peer to peernetworkisalsocalledworkgroupNohierarchyamongcomputers allareequalNoadministratorresponsibleforthenetwork Peer to peer 23 Advantagesofpeer to peernetworks LowcostSimpletoconfigureUserhasfullaccessibilityofthecomputer Disadvantagesofpeer to peernetworks MayhaveduplicationinresourcesDifficulttoupholdsecuritypolicyDifficulttohandleunevenloading Wherepeer to peernetworkisappropriate 10orlessusersNospecializedservicesrequiredSecurityisnotanissueOnlylimitedgrowthintheforeseeablefuture 24 ClientsandServers NetworkClients Workstation ComputersthatrequestnetworkresourcesorservicesNetworkServersComputersthatmanageandprovidenetworkresourcesandservicestoclientsUsuallyhavemoreprocessingpower memoryandharddiskspacethanclientsRunNetworkOperatingSystemthatcanmanagenotonlydata butalsousers groups security andapplicationsonthenetworkServersoftenhaveamorestringentrequirementonitsperformanceandreliability 25 Advantagesofclient servernetworksFacilitateresourcesharing centrallyadministrateandcontrolFacilitatesystembackupandimprovefaulttoleranceEnhancesecurity onlyadministratorcanhaveaccesstoServerSupportmoreusers difficulttoachievewithpeer to peernetworks Disadvantagesofclient servernetworksHighcostforServersNeedexperttoconfigurethenetworkIntroduceasinglepointoffailuretothesystem 26 Topology 3basictypes Howsomanycomputersareconnectedtogether BusTopologyRingTopolog