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1Chapter5Communication2•5.1AShortHistoryofCommunication•5.2WirelessCommunicationTechnology•5.3OpticalFiberCommunication•5.4BasicNetworkingConceptsforComputerNetwork3TEXT5.1AShortHistoryofCommunication•1.Originaltechnologiesofcommunication•2.Communicationatthespeedofelectricity4•convergencen.集中,收敛,融合•couriern.送快信的人,旅行从仆•circuitswitching电路交换•cyberterrorismn.网络•dot-comsn.网络企业•ecommercen.电子商务•heliographn.日光仪5•InterfaceMessageProcessors•n.接口信息处理机•messageswitching报文交换•monopolyn.垄断semaphoren..信号灯•shacklevt.束缚•skepticsn.怀疑学派•sabbaticaln.学术假期•Telenetn.远程通信网•Telecopiern.远程复印机•6•Nomatterwhatcareeryouenter,you’llneedtocommunicatewithpeople.Webelievethatcultural,social,andpersonalexperienceimprovesthroughmoreeffectiveunderstandingandpracticeofcommunication.CommunicationStudiesseektounderstandcommunicationandtoimproveitspracticeinavarietyofrelationships.7•Wefocusontwopersonandfamilycommunication,communicationinsmallgroupsandinlargeorganizations,communicationacrosscommunities,thenatureoflanguageandsymbols,andthenatureofargumentandpersuasioninpoliticalsettingsandinsocialmovements.8•Thehistoryofcommunicationcangobacktothousandsofyears.•However,thetechnologiesthatsomanyofusareaddictedtotoday-mobilephones,theinternet,satelliteTV-arebuiltonourachievements.9•Eachnewdevelopmenthastransformedtheworldwelivein.•Anunderstandingofthejourneywehavetakentogetwherewearenowshowsthattoday'stechniquesarerefinementsofwhatcamebefore.•Reallybigrevolutionsmaybestilltocome.101.Originaltechnologiesofcommunication•Communicationbeginswiththefirstconversationsbetweenpeople.•Fireandthesmokeitproducesmayalsohavebeenusedforsimplecommunicationbetweenseparatedgroups.11•TheinventionoftheprintingpressinChinasometimeafter300ADmeantthatthesamemessagecouldbedeliveredtomanypeoplecheaplyandmorequicklythancopyingoutthemessagemanytimesbyhand.122.Communicationatthespeedofelectricity•Withthediscoveryofelectricitythespeedandrangeofcommunicationonceagainbegantoincrease.13•TheinventionoftechniquessuchasMorsecodeallowedcomplexmessagestobetransferredatveryhighspeedsoverthisnewmedium.Thesehadhugerepercussionsformanyaspectsofhumanlife,forexample,transportcouldbebettercoordinated,governmentcouldtransmitdecisionstodistantofficesalmostinstantaneously,andbusinessescouldworkwithmorebusinessesoverlargerdistances.14•Thefirstamplitudemodulation(AM)radiostationbeganoperatinginSpringfield,Mass.,shortlyafterWorldWarI,andthefirstfrequencymodulation(FM)stationwasauthorizedtooperatebytheFederalCommunicationsCommission(FCC)in1940.15•ThefirsttelevisionstationwasauthorizedbytheFCCin1941andthefirstCATVstationsystembeganseveralyearslater.16•SeeTable5-1Electricalcommunicationhistory17•Atthesametimeasthesedevelopmentsinsound,peoplewereworkinghardoncapturingimages.Forhundredsofyearsartistsandscientistshadknownthatasmallholeinthewallofadarkenedroomwouldprojectanimageoftheoutsideworldontheoppositewall.18•In1814JosephNicéphoreNiépceusedthisprincipletoprojectanimageoftheworldontochemicallytreatedpaperinabox,sothefirstphotographhadbeentaken.Imagesfromonepartoftheworldcouldbebroughttoanother.19•ThisallowedpeopleinTanzaniatoseewhataLondonStreetlookedlike,andpeopleinLondontomarvelatMaasaiwarriorsdressedintheirfinery.In1877,EadweardMuybridgedevelopedacamerawhichcouldtakeaseriesofphotographsinrapidsuccession.20•Hedidthisinordertowinabetonwhetherallahorseshoovesleftthegroundwhenitran.Helostthebet,butinventedthemoviecamera.By1927thishadbeencombinedwithrecordedsound,allowingpeopletosharerealisticexperiencesaroundtheworld.21Thetechnologiesthatwehavediscussedhaveallhelpedusstoreandtransmitcommunication.Allthesetechnologiesarejoiningtogetherintheformofcomputersandtheinternet.225.2WirelessCommunicationTechnology•1Introduction•2.Wirelesscommunicationtechnology23•In1895,Guglielmo-Marconiopenedthewayformodernwirelesscommunicationsbytransmittingthethree-dotMorsecodefortheletter‘S’overadistanceofthreekilometersbyelectromagneticwaves.241.IntroductionTherearetwofundamentalaspectsofwirelesscommunicationthatmaketheproblemchallengingandinteresting.25Firstisphenomenonoffading:thetimevariationofthechannelstrengthsduetothesmall-scaleeffectofmultipathfadingandshadowingbyobstacles.Second,wirelessuserscommunicateovertheairandthereissignificantinterferencebetweenthem.26•Theinterferencecanbebetweentransmitterscommunicatingwithacommonreceiver,betweensignalsfromasingletransmittertomultiplereceivers,orbetweendifferenttransmitter-receiverpairs.27Howtodealwithfadingandinterferenceiscentraltothedesignofwirelesscommunication.28Therearemanywirelesscommunicationstechnologiesthatcanbedifferentiatedbyfrequency,bandwidth,range,andapplications.29Thesecategoriesrangefromwirelesswideareanetworks(WWANs)whichcoverthewidestgeographicarea,towirelesspersonalareanetworks(WPANs)whichcoverlessthan10meters.302.WirelesscommunicationtechnologyWPAN•AWPANisapersonalareanetwork,anetworkforinterconnectingdevicescenteredaroundanindividualperson'sworkspace,inwhichtheconnectionsarewireless.31•communicationwithinabout10metersusedmainlyascablereplacementtechnolo