大一计算机导论第九章

ComputingEssentials2008Chapter9:CommunicationsandNetworksChapterOutlinePage1of14Communications(242)oTheprocessofsharingdata,programs,andinformationbetweentwoormorecomputers.oConnectivity-usingcomputernetworkstolinkpeopleandresources.oTheWirelessRevolution-thewidespreaduseofmobileorwirelesstelephones.ThesinglemostdramaticchangeinconnectivityandcommunicationsinthepastfiveyearsoCommunicationssystems(243)-electronicsystemsthattransmitdatafromonelocationtoanotherSendingandreceivingdevices-originate(send)aswellasaccept(receive)messagesintheformofdata,information,and/orinstructionsCommunicationchannel–transmissionmediumthatcarriesthemessage.Connectiondevices-convertoutgoingmessagesintopacketsthatcantravelacrossthecommunicationchannelandreversetheprocessforincomingmessages.Datatransmissionspecifications-rulesandproceduresthatcoordinatethesendingandreceivingdevicesCommunicationsChannels(244)oActuallycarrythedatafromonecomputertoanotheroPhysical(wired)-asolidmediumtoconnectsendingandreceivingdevices.Twistedpair-hundredsofcopperwires.Coaxialcable-ahigh-frequencytransmissioncableFiber-opticcable-transmitsdataaspulsesoflightthroughtinytubesofglass.oWireless(245)Infrared-usesinfraredlightwavestocommunicateovershortdistances(line-of-sight)Broadcastradio-usesspecialsendingandreceivingtowerscalledtransceivers,whichsendandreceiveradiosignalsfromwirelessdevicesMicrowave-communicationthroughhigh-frequencyradiowavesandprovidesline-of-sightcommunicationbutovershortdistances.BluetoothisaformofmicrowavetransmissionSatellite-amplifiedmicrowavesthatusepoint-to-pointcommunicationtorelaydevices(satellites)orbitingtheearth.Communicationinterferencescanoccurinbadweather.ConnectionDevices(247)oModems-connectioncomputersoveranalogphonelines.Theconvertthecomputer’sdigitalsignaltoananalogtransmissiontosendoverthephoneline(modulation)andthenre-convertittodigitalwhenreceivinginformationfromthephonelines(demodulation).Transferrateisinbits-per-second.Fourtypes:Internal,external,PCcard,andWirelessoConnectionservice(248)Digitalsubscriberline(DSL)-usesexistingtelephonelinestoprovidehigh-speedconnections.(≈30mbps)ComputingEssentials2008Chapter9:CommunicationsandNetworksChapterOutlinePage2of14Cablemodems-useexistingtelevisioncablestoprovidehigh-speedconnections.(≈40mbps)Satellite/airconnection(249)-usesatellitesandtheairtodownload(downlink)orsenddatatousers.(≈900kbps)Cellularservices-analternativeformobiledevicesandlaptops,using3Gcellularnetworks,devicessuchascellphonesandappropriatelyequippedlaptopcomputers,usecellulartowerstoupload(≈50kbps)ordownload(≈550kbps)data.Datatransmission(249)oBandwidth-ameasurementofthewidthorcapacityofthecommunicationchannel.Basically,howmuchinformationcanmoveacrossthecommunicationchannelinagivenamountoftime.Voiceband(250)-usedforstandardtelephonecommunicationMediumband-usedinspecialleasedlinesBroadband-usedforhigh-capacitytransmissions.oProtocols-asetofcommunicationrulesfortheexchangeofinformation.oTCP/IP–TransmissionControlProtocol/InternetProtocolIdentification:EverycomputerontheInternethasauniquenumericaddresscalledanIPaddress(InternetProtocoladdress).Reformatting:Beforeamessageissent,itisreformattedorbrokendownintosmallpartscalledpackets.Networks(251)oAcomputernetworkisacommunicationsystemthatconnectstwoormorecomputerssothattheycanexchangeinformationandshareresources.oNode—anydevicethatisconnectedtoanetwork.oClient—anodethatrequestsandusesresourcesavailablefromothernodes.oServer—anodethatsharesresourceswithothernodes.oHub—thecenterorcentralnodeforothernodes.oNetworkinterfacecards(NIC)—expansioncardslocatedwithinthesystemunitthatconnectthecomputertoanetworkoNetworkoperatingsystems(NOS)—controlandcoordinatetheactivitiesofallcomputersandotherdevicesonanetwork.oDistributedprocessing—asysteminwhichcomputingpowerislocatedandsharedatdifferentlocations.oHostcomputer—alargecentralizedcomputeroNetworkmanager—acomputerspecialistresponsibleforefficientnetworkoperationsandimplementationofnewnetworks.NetworkTypes(253)oLocalAreaNetworks-NetworkswithnodesthatareinclosephysicalproximityoHomeNetworks(254)–networksbeingusedbyindividualsintheirhomesandapartments.oMetropolitanAreaNetworks-spandistancesupto100miles.linksbetweenofficebuildingsthatarelocatedthroughoutacity.oWideAreaNetworks-countrywideandworldwidenetworks.NetworkArchitecture(255)oHowanetworkisarrangedandhowresourcesarecoordinatedandshared.oTopologyComputingEssentials2008Chapter9:CommunicationsandNetworksChapterOutlinePage3of14Star-anumberofsmallcomputersorperipheraldevicesarelinkedtoacentralunit.Bus(258)-eachdeviceinthenetworkhandlesitsowncommunicationscontrol.Thereisnohostcomputer.Ring-eachdeviceisconnectedtotwootherdevices,formingaring.Thereisnocentralfileserver.Hierarchical—network—consistsofseveralcomputerslinkedtoacentralhostcomputer.However,theseothercomputersarealsohoststoother,smallercomputersortoperipheraldevices.MakingitWorkForYou(256)oHomeNetworkingsetupandconfigurationInstallationusingWindowsXPUsingthenetwork–filesharing,pr