Johdanto
Kehitys
Thefirststage:languageisthemainstay,andinformationistransmittedthroughprimitivemeanssuchasmanpower,horsepower,andbeacon.
Nämä toinen vaihe: teksti, viesti. (Lisää tiedonlevityksen keinoja)
Kolmas vaihe: tulostus. (Laajenna tiedonlevityksen alaa)
Neljäs vaihe: lennätin, puhelin, lähetys. (Sähkölaitteiden aikakauteen tulo)
Thefifthstage:Intheinformationage,inadditiontolanguageinformation,therearedataandimagehistory.
Communicationastelecommunicationsisfromthe19thcenturyItstartedinthe1930s.Faradaydiscoveredelectromagneticinductionin1831.Morseinventedthetelegraphin1837.Maxwell'selectromagneticfieldtheoryin1873.Bellinventedthetelephonein1876.Marconiinventedtheradioin1895.Openedupaneweraoftelecommunications.Theelectronictubewasinventedin1906,andanalogcommunicationwasdeveloped.TheNyquistcriterionandsamplingtheoremin1928.Shannon'stheoremin1948.Inthe1950s,semiconductorswereinventedanddigitalcommunicationsweredeveloped.Theintegratedcircuitwasinventedinthe1960s.Theconceptofageostationarysatellitewasputforwardinthe1940s,butitcouldnotberealized.Aerospacetechnologyinthe1950s.Synchronoussatellitecommunicationwasrealizedforthefirsttimein1963.Inthe1960s,thelaserwasinventedandattemptedtobeusedincommunication,butwasunsuccessful.Opticalfiberwasinventedinthe1970s,andopticalfibercommunicationwasdeveloped.
Historiallisia henkilöitä
Bell(1847-1922),brittiläinen,työskenteli Lontoossa1868.Vuonna 1871, hän aloitti työskentelyn Bostonissa.Vuonna 1873 hän toimi professorina Bostonin yliopistossa.Vuonna 1875,multipleksitelegrafi keksittiin.Vuonna 1876, puhelin keksittiin.
Marconi(1874-1937),Italian,experimentedinhisfather'smanorin1894.In1896,hewenttoLondon.In1897,awirelesstelegraphcompanywasestablished.In1899,wirelesscommunicationbetweenBritainandFrancewasrealizedforthefirsttime.In1916,shortwaveradiocommunicationwasrealized.In1929,aworldwidewirelesscommunicationnetworkwasestablished.WontheNobelPrize.ParticipatedintheFascistParty.
Tietoliikenteen historia
Datacommunicationstartedintheearly1950swiththedevelopmentofcomputertelematicsapplications.Earlytelematicssystemsweremostlycenteredononeorseveralcomputers,relyingondatacommunicationmeanstoconnectalargenumberofremoteterminalstoformaterminal-orientedcentralizedprocessingsystem.Inthelate1960s,startingfromthebirthoftheARPAcomputernetworkintheUnitedStates,aheterogeneouscomputercommunicationnetworkwiththepurposeofresourcesharingappeared,thusopeningupanewfieldofcomputertechnology-networkinganddistributedprocessingtechnology.Afterthe1970s,therapiddevelopmentofcomputernetworksanddistributedprocessingtechnologyhasalsopromotedthedevelopmentofdatacommunications.In1976,CCITTformallyannouncedtheX.25recommendation,animportantstandardforpacket-switcheddatanetworks.Afterthat,ithasbeenimprovedandrevisedmanytimes,layingthefoundationforthetechnologicaldevelopmentofpublicandprivatedatanetworks.Inthelate1970s,theInternationalOrganizationforStandardization(ISO)proposedtheOpenSystemInterconnection(OSI)referencemodelinordertopromotetheinterconnectionofsystemsofdifferenttypes,anditwasformallyadoptedin1984asaninternationalstandard.Sincethen,thedevelopmentofcomputernetworktechnologyandapplicationhasproceededinaccordancewiththismodel.
Luokittelu
Luokiteltu tietojen mukaan
Puhelinjärjestelmä
Tietoliikennejärjestelmä
Kaapeli-TV-järjestelmä
p>Modulaatioluokituksen mukaan
Kantataajuinen lähetys
Modulaatiolähetys
Lähetyssignaalin ominaisuuksien mukaan
Analoginen viestintäjärjestelmä
p>Digitaalinen viestintäjärjestelmä
Lähetysvälineet
Kaapeliviestintä
Kierretty pari, koaksiaalikaapeli jne. Paikallispuhelut ja kaukoviestintä. Modulaatiomenetelmä: SSB/FDM. Koaksiaalipohjainen PCM-aikajakomultipleksidigitaalikantakaistalähetystekniikka. Optinen kuitu korvaa vähitellen koaksiaalisen.
Mikroaaltokäyttöinen viestintä
Comparedwithcoaxialcable,itiseasytosetup,smallinvestmentandshortcycle.AnalogtelephonemicrowavecommunicationmainlyadoptsSSB/FM/FDMmodulation,andthecommunicationcapacityis6000channels/channel.DigitalmicrowaveadoptsBPSK,QPSKandQAMmodulationtechnology.Using64QAM,256QAMandothermulti-levelmodulationtechnologiestoincreasethemicrowavecommunicationcapacity,itcantransmit1920to7680PCMdigitaltelephonesina40Mchannel.
Optinen kuituviestintä
Usingthecharacteristicsoflong-distancetransmissionoflaserinopticalfiber,ithasthecharacteristicsoflargecommunicationcapacity,longcommunicationdistanceandstronganti-interference.Itisusedforlocal,long-distance,andtrunktransmission,andgraduallydevelopsuseropticalfibercommunicationnetwork.Basedonlong-wavelasersandsingle-modeopticalfibers,thenumberofcommunicationchannelsperopticalfiberexceeds10,000,andthecommunicationfiberpoweroftheopticalfiberitselfisveryhuge.Overthepastfewdecades,opticalfibercommunicationtechnologyhasdevelopedrapidly,andtherearevariousequipmentapplications,suchasaccessequipment,photoelectricconversionequipment,transmissionequipment,switchingequipment,networkequipment,andsoon.Optinen kuituviestintäequipmentiscomposedoftwoparts:photoelectricconversionunitanddigitalsignalprocessingunit.
Satelliittiviestintä
Thecommunicationdistanceislong,thetransmissioncapacityislarge,thecoverageareaislarge,anditisnotrestrictedbygeographicalareaandhighreliability.Maturetechnologyusesanalogmodulation,frequencydivisionmultiplexingandfrequencydivisionmultipleaccess.Digitalsatellitecommunicationadoptsdigitalmodulation,timedivisionmultiplexingandtimedivisionmultipleaccess.
Matkaviestintä
Matkaviestintäiscommunicationbetweenmovingbodies,orbetweenmovingbodiesandfixedbodies.Themovingbodycanbeaperson,oramovingobjectsuchasacar,train,ship,radio,etc.Themobilecommunicationsystemconsistsoftwoparts:
(1) Avaruusjärjestelmä
(2)Maajärjestelmä:①Satelliittimobiiliradioasema ja antenni;②Yhdyskäytäväasema, tukiasema.
Sinceitsbirthinthe1980s,themobilecommunicationsystemwillgenerallygothroughfivegenerationsofdevelopmentby2020,andwilltransitionfromthethirdgenerationtothefourthgeneration(4G)by2010.By4G,inadditiontocellularphonesystems,broadbandwirelessaccesssystems,millimeterwaveLANs,intelligenttransmissionsystems(ITS)andstratosphericplatform(HAPS)systemswillbeputintouse.Themostobvioustrendoffuturegenerationsofmobilecommunicationsystemsistorequirehighdatarates,highmobilityandseamlessroaming.Realizingtheserequirementswillfacegreatertechnicalchallenges.Inaddition,systemperformance(suchascellsizeandtransmissionrate)willlargelydependonthefrequency.Takingintoaccountthesetechnicalissues,somesystemswillfocusonprovidinghighdatarates,andsomesystemswillfocusonenhancingmobilityorexpandingcoverage.
Käyttäjien näkökulmasta käyttötekniikoihin, joita voidaan käyttää, ovat: matkapuhelinlangattomat järjestelmät, kuten 3G;langattomat järjestelmät, kuten DECT;lyhyen kantaman viestintäjärjestelmät, kuten BluetoothandDECT-tietojärjestelmät;langatonpaikallinen verkkolähetysjärjestelmä;
Viestintäjärjestelmä
Offline-tiedonsiirto
Itsimplyusestelephoneorsimilarlinkstotransmitdata,excludingcomputersystems.Theequipmentusedatbothendsofsuchalinkisnotapartofthecomputer,oratleastdoesnotimmediatelyprovidethedatatothecomputerforprocessing,thatis,thedataisofflinewhenitissentorreceived.Thisdatacommunicationisrelativelycheapandsimple.
Etäeräkäsittely
Thetermappliestosuchamethod:theuseofdatacommunicationtechnologytomaketheinputandoutputofdatageographicallyawayfromthecomputerthatprocessestheminbatchmode.
Online-tiedonkeruu
referstothemethodofusingdatacommunicationtechnologytoprovidethecomputerwiththeinputdatajustgeneratedinrealtime.Thedataisthenstoredinacomputer(suchasonadisk)andprocessedatpredeterminedintervalsorasneeded.
Interaktiivinen järjestelmä
Asthenameimplies,itprovidesuserswiththefunctionofextractinginformationfromthecomputer.Theinquiryfunctionispassive.Inotherwords,itdoesnotmodifythestoredinformation.Thequestioncanbeverysimple,forexample:"Retrievetherecordwiththeemployeenumber1234"oritcanbecomplicated.Suchsystemsmayuseterminalsthatcanproducehardcopiesand/orvisualdisplays.
Reaaliaikainen järjestelmä
isatypeofsysteminwhichthecomputersystemobtainsandprocessesinformationinadynamicsituationsothatthecomputercantakeactionstoaffecttheeventthatisoccurring(suchasProcesscontrolapplications)orcaninfluencepeople(operators)throughaccurateandconstantlyupdatedinformationstoredincomputers,suchasinpre-salessystems.
Perusteoria
Spektri ja kaistanleveys
Thesignalistheelectromagneticcodeofthedata,andthesignalcontainsthedatatobetransmitted.Signalsgenerallytaketimeastheindependentvariable,andacertainparameter(amplitude,frequency,orphase)representingthemessage(ordata)asthedependentvariable.Thesignalcanbedividedintocontinuoussignalanddiscretesignalaccordingtowhetherthevalueoftheindependentvariabletimeiscontinuous;accordingtowhetherthevalueofthedependentvariableiscontinuous,itcanbedividedintoanalogsignalanddigitalsignal.
Thesignalhastwobasicmanifestationsandcharacteristicsintimedomainandfrequencydomain.Thetimedomaincharacteristicreflectsthechangeofthesignalovertime.Thefrequencydomaincharacteristicnotonlycontainsthesameamountofinformationinthetimedomainofthesignal,butalsocanclearlyunderstandthefrequencyspectrumdistributionofthesignalandthebandwidthoccupiedbythesignalspectrumanalysis.Inordertoobtaintherequirementsofthetransmittedsignalonthereceivingequipmentandchannel,itisnotenoughtounderstandthetime-domaincharacteristicsofthesignal.Itisalsonecessarytoknowthefrequencyspectrumdistributionofthesignal.Thetimedomaincharacteristicsofthesignalshowhowthesignalchangesovertime.Sincemostoftheenergyinthesignalisconcentratedinarelativelynarrowfrequencyband,wecallthebandwheremostoftheenergyisconcentratedinthesignalastheeffectivebandwidth,orbandwidthforshort.Anysignalhasbandwidth.Generallyspeaking,thelargerthesignalbandwidth,thehigherthedatatransmissionrateusingthissignal,andthelargerthebandwidthrequiredforthetransmissionmedium.
Belowwewillbrieflyintroducethefrequencyspectrumandbandwidthofcommonsignals.Thefrequencyspectrumofthesoundsignalisroughlyintherangeof20Hzto2000kHz(signalsbelow20Hzareinfrasound,signalsabove2000kHzareultrasound),butamuchnarrowerbandwidthcanproduceacceptablevoicereproductionTherefore,thestandardfrequencyspectrumofthevoicesignalis300Hzto3400Hz,anditsbandwidthis3kHz.ThefrequencyspectrumoftheTVsignalis0to4MHz,soitsbandwidthis4MHz.Asaspecialexample,thebandwidthofamonostablepulsesignalisinfinite.Forbinarysignals,thebandwidthgenerallydependsontheexactshapeofthesignalwaveformandtheorderof0and1.Thegreaterthebandwidthofthesignal,themorefaithfullyitrepresentsthedigitalsequence.
Katkaisutaajuus ja kaistanleveys
AccordingtotheFourierseries,weknowthatifallfrequencycomponentsofasignalcanbetransmittedtothereceivingendthroughthechannelcompletelyunchanged,thenatthereceivingendbyThesignalformedbythesuperpositionofthesefrequencycomponentsisexactlythesameasthesignalatthetransmittingend,thatis,thereceivingendcompletelyrestoresthesignalsentbythetransmittingend.Butintherealworld,nochannelcanpassallfrequencycomponentswithoutloss.IfallFouriercomponentsareattenuatedequally,thesignalreceivedatthereceivingendisattenuatedinamplitude,butthereisnodistortion.However,alltransmissionchannelsandequipmenthavedifferentattenuationlevelsfordifferentfrequencycomponents.Somefrequencycomponentshavealmostnoattenuation,andsomefrequencycomponentsareattenuatedalittle.Thatistosay,thechannelalsohascertainamplitudefrequencycharacteristics,whichleadstoTheoutputsignalisdistorted.Usually,theharmonicsinthefrequencyrangeof0tofcarenotattenuatedduringchanneltransmission(ortheattenuationisaverysmallconstant),andherefcAlltheharmonicsabovethefrequencyareattenuatedgreatlyduringthetransmissionprocess.Weattenuatetheamplitudeofacertaincomponentofthesignalinthechanneltransmissionprocesstotheoriginal0.707(thatis,thepoweroftheoutputsignalisreducedbyhalf).Thatfrequencyiscalledthecut-offfrequencyofthechannel.Thecut-offfrequencyreflectstheinherentphysicalcharacteristicsofthetransmissionmediumitself.Inothercases,itisbecausepeoplehavedeliberatelyinstalledfiltersinthelinetolimitthebandwidthusedbyeachuser.Sometimes,becauseadouble-passfilterisaddedtothechannel,thechannelcorrespondstotwocut-offfrequenciesf1andf2,whicharecalledlowercut-offfrequenciesandUppercutofffrequency.Thedifferencebetweenthesetwocutofffrequenciesf2-f1iscalledthebandwidthofthechannel.Ifthebandwidthoftheinputsignalissmallerthanthebandwidthofthechannel,allfrequencycomponentsoftheinputsignalcanpassthroughthechannel,sotheoutputwaveformobtainedatthechanneloutputwillbeundistorted.However,ifthebandwidthoftheinputsignalisgreaterthanthebandwidthofthechannel,somefrequencycomponentsinthesignalcannotpassthroughthechannel,sotheoutputsignalwillbesomewhatdifferentfromthesignalsentbythetransmitter,thatis,distortionwilloccur.Inordertoensurethecorrectnessofdatatransmission,thebandwidthofthesignalmustbelimited.
2.2.3ThemaximumdatatransmissionrateofthechannelThenumberofbinarydigitsthatcanbetransmittedwithinaunittimeiscalledthedatatransmissionrate.Theincreaseofthedatatransmissionratemeansthatthetimeoccupiedbyeachbitisreduced,thatis,thecycletimeofthebinarydigitalpulsesequencewillbereduced,andofcoursethepulsewidthwillalsobereduced.Wehavealreadyknownintheprevioussectionthatevenifabinarydigitalpulsesignalpassesthroughanidealchannelwithlimitedbandwidth,waveformdistortionwilloccur,andwhenthebandwidthoftheinputsignalisconstant,thesmallerthechannelbandwidth,thegreatertheoutputwaveformdistortion.Toputitanotherway,whenthebandwidthofthechannelisconstant,thelargerthebandwidthoftheinputsignal,thegreaterthedistortionoftheoutputsignal.Therefore,whenthedatatransmissionrateincreasestoacertainextent(thesignalbandwidthincreasestoacertainextent),thechanneloutputThesignalreceiverontheabovesimplycannotrecoverthetransmitteddigitalsequencefromthedistortedoutputsignal.Thismeansthatevenforanidealchannel,thelimitedbandwidthlimitsthechanneldatatransmissionrate.
Asearlyas1924,H.Nyquist(Nyquist)recognizedtheexistenceofthisbasiclimitationandderivedaformulathatexpressedthemaximumdatatransmissionrateofanoise-freelimitedbandwidthchannel.In1948,C.ShannonextendedNyquist'sworkfurthertothesituationwherethechannelisinterferedbyrandomnoise.Herewebrieflydescribetheseresultsthatareregardedasclassicswithoutproof.Nyquistprovedthatafteranycontinuoussignalf(t)passesthroughanoise-freechannelwithbandwidthB,itsoutputsignalisatimecontinuoussignalg(t)withbandwidthB.Ifyouwanttooutputadigitalsignal,youmustalsosampleg(t)atequalintervalsatacertainrate.Samplingspeedhigherthan2Btimespersecondismeaningless,becausethehighfrequencycomponentsinthesignalhigherthanthechannelbandwidthBhavebeenattenuatedbythechannel.Ifg(t)iscomposedofVdiscretizationlevels,thatis,thepossibleresultofeachsamplingisoneofVdiscretizationlevels,thenthemaximumdatatransmissionrateofthechannelisRmaxIs:
Rmax=2Blog2V(bitspersecond)
Forexample,anoise-freebandwidthis3000HzThechannelcannottransmitbinarydigitalsignalswitharateexceeding6000bitspersecond.Earlierweonlyconsideredtheidealchannelwithoutnoise.Fornoisychannels,thesituationwillquicklydeteriorate.Thethermalnoiseinthechannelismeasuredbytheratioofsignalpowertonoisepower,andtheratioofsignalpowertonoisepoweriscalledthesignal-to-noiseratio(Signal-to-NoiseRatio).IfweuseStodenotesignalpowerandNtodenotenoisepower,thesignal-to-noiseratioshouldbeexpressedasS/N.However,peopleusuallydonotusetheabsolutevalueofthesignal-to-noiseratio,butuse10log10S/Ntorepresentit,andtheunitisdecibel(dB).ForachannelwithS/Nequalto10,thesignal-to-noiseratioiscalled10dB;inthesameway,ifthechannel'sS/Nisequalto100,thesignal-to-noiseratioiscalled20dB;andsoon.Shannon’sconclusiononthemaximumdatatransmissionrateofanoisychannelis:ForachannelwithabandwidthofBHzandasignal-to-noiseratioofS/N,themaximumdatatransmissionrateRmaxis:
Rmax=Blog2(1+S/N)(bitspersecond)
Forexample,forabandwidthof3kHz,thesignaltonoiseForachannelwitharatioof30dB,nomatterhowmanyquantizationlevelsareusedorhowfastthesamplingspeedis,thedatatransmissionratecannotbegreaterthan30,000bits/sec.Shannon’sconclusionisderivedfromtheinformationtheoryandhasawiderangeofapplications.Itisalmostimpossibletosurpassthisconclusionlikeinventingaperpetualmotionmachine.ItisworthnotingthatShannon'sconclusiononlygivesatheoreticallimit,andinfact,itisquitedifficulttoapproachthislimit.
Yhteenveto
Asignalisanelectromagneticcodeofamessage(ordata),andthesignalcontainsthemessagetobetransmitted.Accordingtowhetherthevalueofthedependentvariableiscontinuous,thesignalcanbedividedintoanalogsignalanddigitalsignal.Correspondingly,communicationcanalsobedividedintoanalogcommunicationanddigitalcommunication.Fourierhasprovedthatanysignal(whetheritisananalogsignaloradigitalsignal)iscomposedofharmonicsofvariousfrequencies,andanysignalhasacorrespondingbandwidth.Moreover,anychannelwillattenuatethesignalwhenittransmitssignals.Therefore,anychannelhasadatatransmissionratelimitwhentransmittingsignals.ThisistheconclusionthatNyquistandShannon'stheoremwantstotellus.
Transmissionmediaisthemostbasiccomponentofcomputernetworksandcommunications,anditoccupiesalargeproportionofthecostoftheentirecomputernetwork.Inordertoimprovetheutilizationofthetransmissionmedium,wecanusemultiplexingtechnology.Therearethreetypesofmultiplexingtechnologies:frequencydivisionmultiplexing,wavelengthdivisionmultiplexingandtimedivisionmultiplexing,whichareusedindifferentoccasions.Dataswitchingtechnologiesincludecircuitswitching,messageswitchingandpacketswitching,eachofwhichhasadvantagesanddisadvantages.Modemisadeviceusedtotransmitbinarydataofacomputeronananalogtelephonenetwork.Modemmodulationmethodsincludeamplitudemodulation,frequencymodulation,phasemodulationandquadratureamplitudemodulation,andModemalsosupportsdatacompressionanderrorcontrol.
Synkronointimenetelmä
Datacommunicationsynchronizationmainlyincludesbitsynchronizationandcharactersynchronization.
Bitsynchronization:Thepurposeistoenablethereceivertocorrectlyaccepteachbinarybit.Generally,therearetwomethods:self-synchronizationandexternalsynchronization.Theself-synchronizationmethodmeansthatthereceiverdirectlyusesthecharacteristicsofthecommunicationcodetoobtainsynchronizationinformationfromthedatablock,includingusingauniquesignaltoactivatethereceivingaction,orusingthelevelconversioninthedatablocktoadjustthereceivedsamplingpulse.
Theexternalsynchronizationmethodmeansthatthesendersendsaseriesofsynchronousclocksequencestothereceiverbeforesendingdata,andthereceiverlocksthereceivingfrequencyaccordingtotheclockpulsefrequencyandtiming,sothatintheprocessofreceivingdataAlwayskeepinsyncwiththesender.
Charactersynchronizationisalsocalledgroupsynchronization,anditspurposeistoenablethereceivertorecognizethedata(oftenreferringtoacharacter)toformacompletemessage.Obviously,charactersynchronizationisbasedonbitsynchronization,andonlywhentheuniquesynchronizationpatternisrecognized,cantherealdatabereceived.
Aiheeseen liittyviä aikakauslehtiä
"DataCommunication"magazineissponsoredbytheInstituteofDataCommunicationScienceandTechnologyoftheMinistryofInformationIndustry.Wirelesscommunication,networkandinformationsecurity,dataprocessing,datatransmission,testingandmaintenance.
ominaisuudet
Datacommunicationhasmanycharacteristicsdifferentfromtelegraphandtelephonecommunication.Whatitrealizesismainly"human(throughterminal)-machine(computer)"communicationand"machine-machine"communication,butitalsoincludes"human(throughintelligentterminal)-human"communication.Theinformationconveyedindatacommunicationisexpressedintheformofbinarydata.Anotherimportantfeatureofdatacommunicationisthatitisalwaysconnectedwithtelematics.Informationprocessingherereferstoinformationprocessinginabroadsense,includingscientificcomputingandprocesscontrol.Duetothedifferenceininformationprocessingcontentandprocessingmethods,therequirementsfordatacommunicationarealsoverydifferent.Forexample,accordingtothedifferentapplicationsofthesystem,thatis,theinformationprocessingcontentandprocessingmethods,theterminaltype,transmissioncode,transmissionrate,transmissionmethod,systemresponsetime,informationsecurityandaccuracy,systemreliability,etc.Therequirementsarealsodifferent.Therefore,thefactorsinvolvedindatacommunicationarealsomorecomplicated.
Avainteknologia
Tiedonsiirto
Inordertorealizedatacommunication,datatransmissionmustbecarriedout,thatis,datainformationfromadatasourcelocatedinoneplaceistransmittedthroughatransmissionchannelDatareceivingequipmenttoanotherplace.Thechannelusedfordatatransmissioncanbeasolid-linebasebandcircuit,orafrequency-divisionanalogcircuitoratime-divisiondigitalcircuit.Becausethetelephonenetworkhasalonghistoryofdevelopment,largecommunicationcapacity,andwidecoverage,itiseconomicallyandtechnicallyappropriatetouseittoprovidedatatransmissionchannels,anditisacommonway.Butwhenthetelephonecircuitisusedasadatatransmissionchannel,certainmeasuresmustbetakentoadaptittotherequirementsoftransmittingdatasignals.
Inadatacommunicationsystem,onlythetransmissionfunctionofsendingdatageneratedinoneplacetoanotherplaceisoftennotenough.Inordertoimprovethetransmissionquality,reducetheerrorrate,andenablethetransmissionprocesstobecarriedouteffectively,thesystemmustalsohaveadatalinkcontrolprocedure(seedatalink).Inthistypeofregulation,alltransmissioncontrolfunctionsincludingerrorcontrolarespecifiedindetail.Therearedifferenttypesofdatalinkcontrolregulationsforactualdatacommunicationsystemsorcomputernetworks,someofwhichcomplywithinternationalstandards,andsomeareformulatedbythecountryorcompanyitself.
Tiedonvaihto- ja viestintäprotokolla
Inadatacommunicationsystemorcomputernetwork,thetransmissionchannelusedcanbefixedorprovidedbytheexchangenetwork.Therearetwomainwaysofdataexchange:circuitswitchingandpacketswitching,amongwhichpacketswitchingismorecommonlyusedinactualdatanetworks.Inadatanetworkthatusespacketswitching,inadditiontothefunctionsrequiredbythedatatransmissionanddatalinkcontrolproceduresbetweenadjacentswitchingnodes,thestorageandstorageofdatapacketsoneachswitchingnodemustbecompleted.Forwarding;routing,flowcontrol,congestioncontrol,useraccesstothenetwork,andrelatednetworkmaintenanceandmanagement.Correspondingly,certainrelatedfunctionsneedtobeimplementedintheendsystemconnectedtothedataexchangenetwork.Allthesefunctionsrelatedtotheformationofthedataexchangenetworkarespecifiedintheformofcommunicationprotocols,andtheyalsoincludetheinterfaceprotocolbetweentheendsystemandthenetwork.Theso-calledprotocolreferstotherulesandconventionsthatbothpartiesmustfollowinordertocommunicateaccuratelyandeffectively.Theyareofgreatsignificanceindatacommunication,andthedatalinkcontrolprocedurementionedaboveisactuallyadatacommunicationprotocol.
Datacommunicationprotocolscanbedividedintotwocategories.Oneistheprotocolrelatedtothedatacommunicationnetwork(fromtheperspectiveofthecompositionofthecomputernetwork,sometimescalledthecommunicationsubnet),includingtheprotocolbetweennodesandnodesinthenetwork,andbetweenthenetworkandtheendsystem.Theyareprotocolsnecessarytoformadatacommunicationnetworkandrealizedatacommunicationbetweenendsystemsthroughit.Theotheristheagreementbetweentheendsystemandtheendsystem.Theyarebasedonthefunctionsimplementedbytheprevioustypeofagreement,inordertorealizetheintercommunicationbetweentheendsystemsandachievecertainapplicationpurposes,ortobeprecise,inordertoAprotocolnecessaryforcommunicationbetweenapplicationprocessesoftwoendsystems.Allcommunicationfunctionsofadatacommunicationsystemorcomputernetworkaregenerallydividedandorganizedaccordingtoacertainhierarchicalstructure.Datacommunicationprotocolsareactuallyspecificprovisionsforthecontentandimplementationrulesofeachlayer'sfunction,sotheyaregenerallyformulatedbylayer.
Sovellus
Asacommunicationservice,datacommunicationprovidesservicesforrealizingtelematicsinabroadsense.Withtheincreasinguseofcomputersandvariousintelligentdeviceswithprocessingfunctionsinvariousfields,theapplicationscopeofdatacommunicationisalsoexpanding.Itstypicalapplicationsinclude:filetransmission,e-mail,voicemail,visualtext,directorysearch,smartusertelegramandremotecontrol,etc.Foreachspecificapplication,thecommunicationfunctionsrelatedtotheapplicationmustbeimplementedinthetelematicssystemorcomputernetwork,andthesefunctionsarealsospecifiedintheformofalayeredprotocol.
Kehityssuunta
Thedevelopmenttrendofdatacommunicationisconcentratedonthefollowing:
1.Theexpansionofapplicationscopeandapplicationscale,newapplicationservicessuchaselectronicdataexchangeExchange(EDI),multimediacommunications,etc.continuetoemerge.
2.Withtheincreaseintheamountofcommunication,theInternetisincreasinglydevelopinginthedirectionofhigh-speed,broadband,digitaltransmissionandcomprehensiveutilization.Forexample,manynewtechnologiessuchasopticalfiberhigh-speedlocalareanetwork,metropolitanareanetwork,broadbandintegratedservicedigitalnetwork,relay,fastpacketswitching,etc.havedevelopedrapidly,andsomehaveenteredthepracticalstage.
3.Inconjunctionwiththedevelopmentofmobilecommunications,mobiledatacommunicationsaregainingrapiddevelopment.
4.Withthecontinuousexpansionofthescaleofnetworksandsystems,theimportanceoftheinterconnectionofdifferenttypesofnetworksandsystems(includingtheoperationandmanagementoftheinterconnectionnetwork)hasbecomeincreasinglyprominent.
5.Therehasbeenalargeincreaseincommunicationprotocolstandards,andprotocolengineeringtechnologyhasdevelopeddaybyday.
Osallisuus/vaikutus
IncludedbytheGeneralAdministrationofPressandPublication
ThesecondandthirdprizesoftheMinistryofInformationScienceandTechnologyOutstandingJournals