计算机网络教程课件ch1-Introduction.ppt

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1、1IntroductionTwoAdvancesinTechnologyDevelopmentofPowerfulMicroprocessorsMoore’sLaw:Theperformanceofsemiconductorswasgrowingexponentiallyandwouldcontinueto.In1975,Moorestatedthatthenumberoftransistorsdoubledaboutevery18months.GordonBell’sLaw(1975)SystemPrice=

2、5x3x.04xMemorySize/1.26(t-1972)K$5x:Memoryis20%ofcost3x:DECmarkup.04x:$perbyteHigh-speedcomputernetworksHigh-speedLANSandWANsDistributedsystemDistributedsystemAcollectionofindependentcomputersappearstoitsusersasasinglecoherentsystemAsinglemodelorparadigmthat

3、itpresentstotheusersAlayerofsoftwareontopoftheoperatingsystem,calledmiddleware,isresponsibleforimplementingthismodelComputerNetworksComputerNetworksAcollectionofautonomouscomputersinterconnectedbyasingletechnologyUsersareexposedtotheactualmachinesIfthemachin

4、eshavedifferenthardwareanddifferentoperatingsystems,thatisfullyvisibletotheusers1.2NetworkHardwareTransmissiontechnologyandscaleTransmissiontechnologyBroadcastnetworksSendingapackettoalldestinations,eachmachinecheckstheaddressfieldIfthepacketisintendedforthe

5、receivingmachine,thatmachineprocessesthepacketIfthepacketisintendedforsomeothermachine,itisjustignored.UnicastingBroadcastingMulticasting(subscribe)Point-to-pointnetworksTogofromthesourcetothedestination,apacketmayvisitoneormoreintermediatemachines(Oftenmult

6、ipleroutesarepossible,findinggoodonesisimportant)ClassificationbyscaleLocalAreaNetworksTopologyTwobroadcastnetworks(a)Bus(b)RingChannelallocationStatic&DynamicAtypicalstaticallocationDividetimeintodiscreteintervalsandusearound-robinalgorithm,allowingeachmach

7、inetobroadcastonlywhenitstimeslotcomesupDynamicallocationmethodsCentralizedDecentralizedMANandWANMetropolitanAreaNetworksAmetropolitanareanetworkbasedoncableTV.Topology:subnet,LAN,hostRelationbetweenhostsonLANsandthesubnetCommunicationsubnetTransmissionlines

8、Switchingelements(Router)Store-and-forward(packet-switched)Routingdecisions:RoutingalgorithmMessagePathSingle-pathvs.Multi-pathBestroutemustbeusedRoutingdecisionsaremadelocallyInternetworksInter