计算机英语课件Unit 8 Computer Network.ppt

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1、Unit8ComputerNetworkSectionANetworkFundamentalsTheneedtoshareinformationandresourcesamongdifferentcomputershasledtolinkedcomputersystems,callednetworks,inwhichcomputersareconnectedsothatdatacanbetransferredfrommachinetomachine.Inthesenetworks,computeruserscanexchangemessagesandshareres

2、ources—suchasprintingcapabilities,softwarepackages,anddatastoragefacilities-thatarescatteredthroughoutthesystem.Theunderlyingsoftwarerequiredtosupportsuchapplicationshasgrownfromsimpleutilitypackagesintoanexpandingsystemofnetworksoftwarethatprovidesasophisticatednetworkwideinfrastructu

3、re.Inasense,networksoftwareisevolvingintoanetworkwideoperatingsystem.NetworkClassificationsAcomputernetworkisoftenclassifiedasbeingeitheralocalareanetwork(LAN),ametropolitanareanetwork(MAN),orawideareanetwork(WAN).ALANnormallyconsistsofacollectionofcomputersinasinglebuildingorbuildingc

4、omplex.Forexample,thecomputersonauniversitycampusorthoseinamanufacturingplantmightbeconnectedbyaLAN.AMANisanetworkofintermediatesize,suchasonespanningalocalcommunity.AWANlinksmachinesoveragreaterdistance-perhapsinneighboringcitiesoronoppositesidesoftheworld.Anothermeansofclassifyingnet

5、worksisbasedonwhetherthenetwork’sinternaloperationisbasedondesignsthatareinthepublicdomainoroninnovationsownedandcontrolledbyaparticularentitysuchasanindividualoracorporation.Anetworkoftheformertypeiscalledanopennetwork;anetworkofthelattertypeiscalledaclosed,orsometimesaproprietary,net

6、work.TheInternetisanopensystem.Inparticular,communicationthroughouttheInternetisgovernedbyanopencollectionofstandardsknownastheTCP/IPprotocolsuite.Anyoneisfreetousethesestandardswithoutpayingfeesorsigninglicenseagreements.Incontrast,acompanysuchasNovellInc.mightdevelopsystemsforwhichit

7、choosestomaintainownershiprights,allowingthecompanytodrawincomefromsellingorleasingtheseproducts.Networksbasedonsuchsystemsareexamplesofclosednetworks.Stillanotherwayofclassifyingnetworksisbasedonthetopologyofthenetwork,whichreferstothepatterninwhichthemachinesareconnected.Thebustopo