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1、AboutModemTelephonelinesweredesignedtocarrythehumanvoice,notelectronicdatafromacomputer.Modemswereinventedtoconvertdigitalcomputersignalsintoaformthatallowsthemtotraveloverthephonelines.Thosearethescratchysoundsyouhearfromamodem'sspeaker.Amodemontheotherendofthelinecanunderstanditandconvertt
2、hesoundsbackintodigitalinformationthatthecomputercanunderstand.Bytheway,thewordmodemstandsforMOdulator/DEModulator. Buyingandusingamodemusedtoberelativelyeasy.Nottoolongago,almostallmodemstransferreddataatarateof2400Bps(bitspersecond).Today,modemsnotonlyrunfaster,theyarealsoloadedwithfeatur
3、eslikeerrorcontrolanddatacompression.So,inadditiontoconvertingandinterpretingsignals,modemsalsoactliketrafficcops,monitoringandregulatingtheflowofinformation.Thatway,onecomputerdoesn'tsendinformationuntilthereceivingcomputerisreadyforit.Eachofthesefeatures,modulation,errorcontrol,anddatacomp
4、ression,requiresaseparatekindofprotocolandthat'swhatsomeofthosetermsyouseelikeV.32,V.32bis,V.42bisandMNP5referto.Ifyourcomputerdidn'tcomewithaninternalmodem,considerbuyinganexternalone,becauseitismucheasiertoinstallandoperate.Forexample,whenyourmodemgetsstuck(notanunusualoccurrence),youneedt
5、oturnitoffandontogetitworkingproperly.Withaninternalmodem,thatmeansrestartingyourcomputer--awasteoftime.Withanexternalmodemit'saseasyasflippingaswitch. Here'satipforyou:inmostareas,ifyouhaveCallWaiting,youcandisableitbyinserting*70infrontofthenumberyoudialtoconnecttotheInternet(oranyonlines
6、ervice).Thiswillpreventanincomingcallfromaccidentallykickingyouofftheline.Thistableillustratestherelativedifferenceindatatransmissionspeedsfordifferenttypesoffiles.Amodem'sspeedismeasuredinbitspersecond(bps).A14.4modemsendsdataat14,400bitspersecond.A28.8modemistwiceasfast,sendingandreceiving
7、dataatarateof28,800bitspersecond.Untilnearlytheendof1995,theconventionalwisdomwasthat28.8Kbpswasaboutthefastestspeedyoucouldsqueezeoutofaregularcoppertelephoneline.Today,youcanbuy33.6Kbpsmodems,andmodemsthatarecapableof56Kbps.Thekeyquestionforyou,i