2-Unit1 A Brief history of communications

EnglishonTelecommunicationsWUYUNewwordsandphrases•signal•auditory•visual•symbol•message•invent•telegraph•impulse•character•sequence•transmit•code•medium•convert•vary•voltage•connection•switchboard•device•processNewwordsandphrases•transistor•route•transfer•magnetic•transport•store•transmitter•receiver•antenna•optical•fiber•coaxialPASSAGEABriefHistoryofCommunicationsPASSAGE•Thefieldofcommunicationsiscertainlynotnew:Peoplehavebeencommunicatingsinceearlyhumansgruntedandscratchedpicturesoncavewalls.Forthousandsofyearspeoplecommunicatedusinglittlemorethanwords,parchments,stonetablets,andsmokesignals.Theprimaryformsofsendinginformationwerebasedontheauditoryandvisualsenses.Youeitherheardsomeonespeakingorsawthelettersandsymbolsthatdefinedamessage.PASSAGE•Communicationschangeddrasticallyin1837,whenSamuelMorseinventedthetelegraph.Thisinventionmadeitpossibletosendinformationusingelectricalimpulsesoveracopperwire.Thecharactersinamessagewerefirsttranslatedintoasequenceoflongorshortelectricalimpulses(orinlesstechnicalterms,dotsanddashes),andthen,themessagewastransmitted.PASSAGE•ThisassociationofcharacterswithelectricalimpulseswascalledtheMorsecode.Theabilitytosendinformationwithnoobviousverbalorvisualmediumbeganasequenceofeventsthatforeverchangedthewaypeoplecommunicate.PASSAGE•In1876AlexanderGrahamBelltookthetelegraphonestepfurther.Ratherthanconvertingamessageintoasequenceofdotsanddashes,heshowedthatavoicecouldbeconverteddirectlytoelectricalenergyandtransmittedoverawireusingcontinuouslyvaryingvoltages.Atthewire’sotherendtheelectricalsignalswereconvertedbacktosound.PASSAGE•Theresultwasthataperson’svoicecouldbetransmittedelectronicallybetweentwopointsaslongasaphysicalconnectionexistedbetweenthem.Tomostpeoplewhoseliveswerebasedononlywhattheycouldseeandhear,thisinventionwasabsolutelyincredibleandseemedmagical.PASSAGE•Theearliesttelephonesrequiredadifferentpairofwiresforeachphonetowhichyouwishedtoconnect.Toplaceacall,apersonhadtofirstconnectthetelephonetothecorrectwiresandthenhopethepersonontheotherendwasthere,listening.Therewerenobellsorsignalingdevicestointerrupthisorherdinner.PASSAGE•Thatchangedwiththeinventionoftheswitchboard,aswitchingdevicethatconnectedlinesbetweentwotelephones.Callerssimplepickedupthephoneandrecitedthenumberofthepersontheywishedtocall.Establishingconnectionswasvoice-activated.Thatis,anoperatorheardthenumberandthenusedaswitchboardtoconnectoneperson’sphonelineswithanotherperson’slines.PASSAGE•Duringthenext70yearsthetelephonesystemgrewtothepointwherethetelephonebecameacommondeviceinahome.Mostofusdonoteventhinkabouthowthetelephonesystemworks.Weknowwecandialanumberandbeconnectedtojustaboutanywhereintheworld.PASSAGE•Anothereventimportanttocommunicationsoccurredin1945withtheinventionofthefirstelectroniccomputer,ENIAC(ElectronicNumericalIntegratorandCalculator).DesignedforcomputingballisticstablesforWorldWarII,itwasthefirstdevicethatcouldactuallyprocessinformationelectronically.AlthoughENIACplayednodirectroleindataorcomputercommunications,itdidshowthatcalculationsanddecision-makingcouldbedoneelectronically,animportantabilityintoday’scommunicationssystems.PASSAGE•Therelationbetweencomputersandcommunicationsbegantoemergeaftertheinventionofthetransistorin1947allowedsmallerandcheapercomputerstobebuilt.Thenewgenerationofcomputersthatemergedduringthe1960smadenewapplicationssuchasprocessingandroutingtelephonecallseconomicallyfeasible.Inaddition,morebusinesseswerebuyingcomputersanddevelopingapplications,andtheneedtotransferinformationbetweenthembegantogrow.PASSAGE•Thefirstcommunicationsystembetweencomputerswassimple.Basically,itinvolvedwritinginformationfromonecomputerontoamagnetictape,throwingthetapeintothebackofthecar,andthentransportingthetapetoanothercomputer.Oncethere,theothercomputercouldreadtheinformationonthetape.Thiswasaveryreliableformofcommunication,assumingthepersondrivingthecardidn’tgetintoanaccident(PeopletodaystilldothesamethingalthoughthetapehasbeenreplacedbydisksandCD-ROMs).PASSAGE•Anothermilestoneinelectroniccommunicationsoccurredwiththedevelopmentofthepersonalcomputer(PC).Theabilitytohavecomputingpoweronadeskgeneratedanentirelynewwayofstoringandretrievinginformation.The1980ssawtheinfusionofmillionsofPCsintovirtuallyeverybusiness,company,school,andorganizationandintomanyhomesaswell.Thefactthatsomanypeoplehadcomputersgeneratedtheneedtomakeinformationevenmoreeasilyaccessible.PASSAGE•Satellitecommunicationsystembeganin1962.Today,manycommunicationssatellitestransmittelevisionsignals.Atransmitterinonepartoftheworldsendsasignaltoanorbitingsatellite,whichrelaysthesignaltoreceiversonotherparts.SignalsfromthereceiveraresenttobroadcastingtowersandaretransmittedlocallyusingafrequencyapprovedbytheFederalCommunicationsCommission(FCC).Anantennareceivesthesignalsandrelaysthemtothetelevisionsetinyourhome.PASSAGE•Televisionantennasarenottheonlywaytoreceivesignals.Manyhomessubscribetoacabletelevisionservicethatbringssignalsintothehomeusingopticalfibersandcoaxialcable.Inaddition,manypeoplepurchasetheirownreceivingdishes