Defineclassification
Inbroadterms
Computernetworkisalsocalledcomputercommunicationnetwork.Thesimplestdefinitionofacomputernetworkis:acollectionofautonomouscomputersthatareconnectedtoeachotherforthepurposeofsharingresources.Accordingtothisdefinition,theearlyterminal-orientednetworkscannotberegardedascomputernetworks,butcanonlybecalledonlinesystems(becausemanyterminalsatthattimecannotberegardedasautonomouscomputers).However,withthedeclineinhardwareprices,manyterminalshaveacertaindegreeofintelligence,so"terminals"and"autonomouscomputers"graduallylosetheirstrictboundaries.Ifamicrocomputerisusedasaterminal,accordingtotheabovedefinition,theearlyterminal-orientednetworkcanalsobecalledacomputernetwork.
Inaddition,fromtheperspectiveoflogicalfunction,acomputernetworkisacollectionofcomputersystemsthatconnectmultiplecomputerswithcommunicationlinesforthebasicpurposeoftransmittinginformation.Acomputernetworkconsistsoftransmissionmediaandcommunicationequipment..
Fromtheperspectiveofusers,computernetworksaredefinedasfollows:Thereisanetworkoperatingsystemthatcanbeautomaticallymanagedforusers.Itcallsandcompletestheresourcescalledbytheuser,andtheentirenetwork,likealargecomputersystem,istransparenttotheuser.
Amoregeneraldefinitionis:theuseofcommunicationlinestoconnectgeographicallydispersedcomputersystemsandcommunicationequipmentwithindependentfunctionsindifferentforms,andrealizeresourcesharingwithcompletenetworksoftwareandprotocolsAndinformationtransmissionsystem.
Onthewhole,acomputernetworkisalarge-scaleandpowerfulsystemthatconnectscomputersdistributedindifferentgeographicalareaswithspecializedexternalequipmentusingcommunicationlines,sothatmanycomputerscaneasilycommunicatewitheachother.Transferinformationandshareresourcessuchashardware,software,dataandinformation.Simplyput,acomputernetworkisacollectionofmanyautonomouslyworkingcomputersconnectedtoeachotherbycommunicationlines.
Thesimplestcomputernetworkhasonlytwocomputersandonelinkconnectingthem,thatis,twonodesandonelink.
Connectbyconnection
Computernetworkisacollectionofautonomouscomputersinterconnectedbywires.Tobeprecise,itisacollectionofcomputerswithindependentworkingabilitydistributedindifferentgeographicallocations.Theterminalanditsancillaryequipmentareconnectedwithcommunicationequipmentandcommunicationlines,andnetworksoftwareisconfiguredtorealizeasystemofcomputerresourcesharing.
Ondemand
Computernetworkiscomposedofalargenumberofindependentbutinterconnectedcomputerstocompletecomputertaskstogether.Thesesystemsarecalledcomputernetworks.
DevelopmentHistory
Sincetheemergenceofcomputernetworks,thespeedofitsdevelopmentandtheextentofitsapplicationshavebeenamazing.Lookingatthedevelopmentofcomputernetworks,ithasroughlygonethroughthefollowingfourstages:
Birthstage
Thefirstgenerationofcomputernetworksbeforethemid-1960swascenteredonasinglecomputerThetypicalapplicationoftheremoteonlinesystemisanairplaneticketbookingsystemconsistingofacomputerandmorethan2,000terminalsacrosstheUnitedStates.Theterminalisacomputerperipheraldevice,includingamonitorandakeyboard,withoutCPUandmemory.Withtheincreaseofremoteterminals,afrontendmachine(FEP)isaddedinfrontofthehost.Atthattime,peopledefinedacomputernetworkas"asystemthatisconnectedforthepurposeoftransmittinginformationtorealizeremoteinformationprocessingorfurtherachieveresourcesharing."Suchacommunicationsystemhastheembryonicformofanetwork.
Formationstage
Thesecond-generationcomputernetworkfromthemid-1960stothe1970swasinterconnectedbymultiplehoststhroughcommunicationlinestoprovideservicesforusers.Itemergedinthe1960sInthelaterperiod,thetypicalrepresentativewasARPANETdevelopedwiththeassistanceoftheAdvancedResearchProjectsAgencyoftheUSDepartmentofDefense.Thehostsarenotdirectlyconnectedbylines,butareinterconnectedafterbeingtransferredbytheInterfaceMessageProcessor(IMP).IMPandtheirinterconnectedcommunicationlinesareresponsibleforthecommunicationtasksbetweenhosts,formingacommunicationsubnet.Thehostsconnectedbythecommunicationsubnetareresponsibleforrunningprograms,providingresourcesharing,andformingaresourcesubnet.Duringthisperiod,thenetworkconceptwas"acollectionofcomputerswithindependentfunctionsinterconnectedforthepurposeofbeingabletoshareresourceswitheachother",formingthebasicconceptofcomputernetworks.
Interconnectionstage
Thethird-generationcomputernetworkfromthelate1970stothe1990swasanopenandstandardizednetworkwithaunifiednetworkarchitectureandcompliancewithinternationalstandards.AftertheriseofARPANET,computernetworkshavedevelopedrapidly,andmajorcomputercompanieshavesuccessivelyintroducedtheirownnetworkarchitecturesandsoftwareandhardwareproductsthatimplementthesestructures.Becausethereisnounifiedstandard,itisdifficulttointerconnectproductsofdifferentmanufacturers.Peopleurgentlyneedanopen,standardizedandpracticalnetworkenvironment.Thishasledtotheemergenceoftwomostimportantinternationalarchitectures,namelytheTCP/IPsystem.StructureandtheOSIsystemstructureoftheInternationalOrganizationforStandardization.
High-speednetworktechnologystage
Thefourth-generationcomputernetworkfromthe1990stothepresent,duetothematuredevelopmentoflocalareanetworktechnology,theemergenceofopticalfiberandhigh-speednetworktechnology,theentirenetworkislikeauserThelargetransparentcomputersystemdevelopedintotheInternetrepresentedbytheInternet.
Composition
Theclassificationofcomputernetworksisthesameasthegeneralclassificationofthings,whichcanbeclassifiedaccordingtothedifferentnatureandcharacteristicsofthings(thatis,theattributesofthings).Generallyspeaking,acomputernetworkiscomposedofmultiplecomputers(orothercomputernetworkdevices)thatarephysically(orlogically)connectedthroughtransmissionmediaandsoftware.Generallyspeaking,thecompositionofacomputernetworkbasicallyincludesfourparts:acomputer,anetworkoperatingsystem,atransmissionmedium(itcanbetangibleorintangible,suchasthetransmissionmediumofawirelessnetworkisspace)andcorrespondingapplicationsoftware.
Function
Datacommunication
Datacommunicationisoneofthemostimportantfunctionsofcomputernetworks.Datacommunicationisacommunicationmethodandcommunicationservicethatusesdatatransmissiontechnologytotransferdatainformationbetweentwoterminalsinaccordancewithacertaincommunicationprotocol.Itcanrealizethetransferofdataandinformationbetweencomputersandcomputers,computersandterminals,andterminalsandterminals.Itisthethirdlargestcommunicationserviceaftertelegraphandtelephoneservices.Theinformationtransmittedindatacommunicationisexpressedintheformofbinarydata.Anotherfeatureofdatacommunicationisthatitisalwaysconnectedwithremoteinformationprocessing,whichisabroadinformationprocessingincludingscientificcalculation,processcontrol,informationretrieval,andsoon.
Resourcesharing
Resourcesharingisoneofthemainpurposesforpeopletobuildcomputernetworks.Computerresourcesincludehardwareresources,softwareresourcesanddataresources.Thesharingofhardwareresourcescanimprovetheutilizationofequipmentandavoidrepeatedinvestmentinequipment,suchasusingcomputernetworkstobuildnetworkprinters;thesharingofsoftwareresourcesanddataresourcescanmakefulluseofexistinginformationresources,reducelaborinthesoftwaredevelopmentprocess,andavoidRepetitiveconstructionoflargedatabases.
Centralizedmanagement
Thedevelopmentandapplicationofcomputernetworktechnologyhascausedchangesinmodernofficemethodsandmanagement.Atpresent,therearemanymanagementinformationsystems,officeautomationsystems,etc.,throughwhichcentralizedmanagementofdailyworkcanberealized,workefficiencycanbeimproved,andeconomicbenefitscanbeincreased.
Realizedistributedprocessing
Thedevelopmentofnetworktechnologymakesdistributedcomputingpossible.Forlarge-scaletopics,itcanbedividedintomanysmalltopics,whicharecompletedbydifferentcomputers,andthenconcentratedtosolvetheproblem.
Loadbalancing
Loadbalancingmeansthatworkisevenlydistributedtoeachcomputersystemonthenetwork.Thenetworkcontrolcenterisresponsiblefordistributionanddetection.Whenacomputerisoverloaded,thesystemwillautomaticallytransfertheloadtoalightercomputersystemforprocessing.
Itcanbeseenthatcomputernetworkscangreatlyexpandthefunctionsofcomputersystems,expandtheirapplicationscope,improvereliability,andprovideconvenienceforusers,whilealsoreducingcostsandimprovingperformance-priceratios.
Classification
Althoughtherearevariousstandardsfortheclassificationofnetworktypes,theclassificationofgeographicalareasisauniversalnetworkclassificationstandardthateveryonerecognizes.Accordingtothisstandard,variousnetworktypescanbedividedintofourtypes:localareanetwork,metropolitanareanetwork,wideareanetworkandInternet.Generallyspeaking,alocalareanetworkcanonlybeinasmallarea.Ametropolitanareanetworkisanetworkinterconnectionbetweendifferentareas.However,onepointtobeexplainedhereisthatthenetworkdivisionheredoesnothaveastrictgeographicaldistinction,butcanonlybeaqualitativeone.theconceptof.Thefollowingbrieflyintroducesthesekindsofcomputernetworks.
LocalAreaNetwork
(LocalAreaNetwork;LAN)Usuallyourcommon"LAN"referstothelocalareanetwork,whichisourmostcommonandwidelyusednetwork.Withthedevelopmentandimprovementoftheentirecomputernetworktechnology,thelocalareanetworkhasbeenfullyappliedandpopularized.Almosteveryunithasitsownlocalareanetwork,andsomeevenhavetheirownsmalllocalareanetworkinthefamily.Obviously,theso-calledlocalareanetworkisanetworkwithinalocalarea,anditcoversarelativelysmallarea.Therearenottoomanyrestrictionsonthenumberofcomputersinthelocalareanetwork.Generallyspeaking,intheenterpriseLAN,thenumberofworkstationsisabouttenstotwohundred.Generallyspeaking,thegeographicdistanceinvolvedinthenetworkcanbewithinafewmetersto10kilometers.Thelocalareanetworkisgenerallylocatedinabuildingoraunit,thereisnopathfindingproblem,anddoesnotincludetheapplicationofthenetworklayer.
Charakteristikami této sítě jsou: úzký rozsah připojení, malý počet uživatelů, snadná konfigurace a vysoká rychlost připojení. V současné době je nejrychlejší rychlost LAN 10GEthernet. Standardní výbor IEEE 802 definuje různé velké sítě LAN: Ethernet, DDI TokenDitributNetwork, Fi twork (ATM) a nejnovější bezdrátová LAN (WLAN). Tyto budou podrobně popsány později.
MetropolitanAreaNetwork
(MetropolitanAreaNetwork;MAN)Thiskindofnetworkisgenerallyconnectedtocomputersinacitybutnotinthesamegeographicarea.Theconnectiondistanceofthiskindofnetworkcanbe10~100kilometers,itadoptsIEEE802.6standard.ComparedwithLAN,MANhasalongerextensiondistanceandalargernumberofconnectedcomputers,whichcanbesaidtobeanextensionofLANnetworkintermsofgeographicscope.Inalargecityormetropolitanarea,aMANnetworkisusuallyconnectedtomultipleLANnetworks.SuchastheLANthatconnectsgovernmentagencies,theLANofhospitals,theLANoftelecommunications,theLANofcompaniesandenterprises,andsoon.Duetotheintroductionofopticalfiberconnection,high-speedLANinterconnectioninMANbecomespossible.
ManymetropolitanareanetworksuseATMtechnologyasthebackbonenetwork.ATMisahigh-speednetworktransmissionmethodfordata,voice,video,andmultimediaapplications.ATMincludesaninterfaceandaprotocol,whichcanswitchbetweentheconstantandvaryingtrafficvolumeofthebitrateonaconventionaltransmissionchannel.ATMalsoincludeshardware,software,andmediaconsistentwithATMprotocolstandards.ATMprovidesascalablebackboneinfrastructuretobeabletoadapttonetworksofdifferentsizes,speeds,andaddressingtechnologies.ThebiggestdisadvantageofATMisitshighcost,soitisgenerallyusedingovernmentmetropolitanareanetworks,suchaspostalservices,banks,andhospitals.
WideAreaNetwork
(WideAreaNetwork,WAN)Thistypeofnetworkisalsocalledalong-distancenetwork,anditcoversawiderareathanametropolitanareanetwork(MAN).TheLANorMANnetworkinterconnectionbetweencities,thegeographicalrangecanbefromhundredsofkilometerstothousandsofkilometers.Becausethedistanceisfar,theinformationattenuationismoreserious,sothiskindofnetworkgenerallyneedstoleaseadedicatedline,whichisconnectedthroughtheIMP(InterfaceInformationProcessing)protocolandthelinetoformameshstructuretosolvetheproblemofrouting.Thiskindofmetropolitanareanetworkisconnectedtomanyusersandthetotalexportbandwidthislimited,sotheuserterminalconnectionrateisgenerallylow,usually9.6Kbps-45Mbps,suchas:CHINANET,CHINAPAC,andCHINADDNoftheMinistryofPostsandTelecommunications.
Theabovementionedseveralclassificationsofnetworks.Infact,inreallife,theonewereallyencountermostisthelocalareanetwork,becauseitcanbelargeorsmall,anditisrelativelyeasytoimplementinboththeworkunitandthefamily.,Theapplicationisalsothemostextensivekindofnetwork,soweneedtomakeafurtherunderstandingofthelocalareanetworkandtheaccessequipmentinthelocalareanetworkbelow.
Wirelessnetwork
WiththeincreasingpopularityanddevelopmentofportablecomputerssuchasnotebookcomputersandPersonalDigitalAssistants(PDAs),peopleoftenhavetobeontheroadAnswercalls,sendfaxesande-mails,readonlineinformation,andlogintoremotemachines.However,itisimpossibletoconnecttotheunit'snetworkthroughawiredmediuminacaroranairplane.Atthistime,youmaybeinterestedinawirelessnetwork.Althoughwirelessnetworksandmobilecommunicationsareoftenlinkedtogether,thetwoconceptsarenotexactlythesame.Forexample,whenaportablecomputerisconnectedtoatelephonejackviaaPCMCIAcard,itbecomesapartofthewirednetwork.Ontheotherhand,thelocationofsomecomputersconnectedviaawirelessnetworkmaybefixed.Forexample,betweenbuildingsthatareinconvenienttoconnectviaawiredcable,thecomputersintwobuildingscanbeconnectedviaawirelessnetwork.
Wirelessnetworks,especiallywirelesslocalareanetworks,havemanyadvantages,suchaseasyinstallationanduse.However,wirelesslocalareanetworksalsohavemanyshortcomings:forexample,itsdatatransmissionrateisgenerallylower,muchlowerthanthatofwiredlocalareanetworks;inaddition,thebiterrorrateofwirelesslocalareanetworksisalsorelativelyhigh,andmutualinterferencebetweensitesisrelativelysevere.Therearedifferentwaystorealizetheuser'swirelessnetwork.Someuniversitiesabroadhaveinstalledmanyantennasontheircampuses,allowingstudentstositunderatreeandviewlibrarymaterials.Thissituationisachievedthroughdigitalcommunicationbetweentwocomputersdirectlythroughawirelesslocalareanetwork.Anotherpossiblewayistouseatraditionalanalogmodemtocommunicatethroughacellularphonesystem.Manycitiesabroadhavebeenabletoprovidecellulardigitalpacketdata(CellularDigitalPacketData,CDPD)services,soawirelesslocalareanetworkcanbeestablisheddirectlythroughtheCDPDsystem.Wirelessnetworkisthecurrentresearchhotspotathomeandabroad,andtheresearchofwirelessnetworkisdrivenbyhugemarketdemand.Thecharacteristicofthewirelessnetworkisthattheusercanaccessthecomputernetworkatanytimeandanyplace,andthischaracteristicmakesithaveastrongapplicationprospect.Manywirelessnetwork-basedproductshaveemerged,suchasPersonalCommunicationSystem(PCS)phones,wirelessdataterminals,portablevideophones,andpersonaldigitalassistants(PDAs).Thedevelopmentofwirelessnetworksdependsonthesupportofwirelesscommunicationtechnology.Wirelesscommunicationsystemsmainlyinclude:low-powercordlesstelephonesystems,analogcellularsystems,digitalcellularsystems,mobilesatellitesystems,wirelessLANandwirelessWAN,etc.
Performance
Theperformanceofacomputernetworkgenerallyreferstoseveralimportantperformanceindicators.Butinadditiontotheseimportantperformanceindicators,therearesomenon-performancefeatures,whichalsohaveagreatimpactontheperformanceofcomputernetworks.
1.Ukazatele výkonu počítačových sítí
Performanceindicatorsmeasuretheperformanceofcomputernetworksfromdifferentaspects.
(1) Sazba
Thesignalssentbythecomputerareindigitalform.Bitistheunitofdatavolumeincomputers,anditisalsotheunitofinformationvolumeusedininformationtheory.TheEnglishwordbitcomesfrombinarydigit,whichmeansa"binarydigit",soabitisa1or0inabinarydigit.Therateinnetworktechnologyreferstotherateatwhichahostconnectedtoacomputernetworktransmitsdataonadigitalchannel.Itisalsocalleddatarateorbitrate.Speedisoneofthemostimportantperformanceindicatorsincomputernetworks.Theunitofrateisbit/s(bitpersecond)(iebitpersecond).
(2)Šířka pásma
„Šířka pásma“ má následující dva různé významy.
①Bandwidthoriginallyreferstothebandwidthofacertainsignal.Thebandwidthofasignalreferstothefrequencyrangeoccupiedbythevariousfrequencycomponentscontainedinthesignal.Forexample,thestandardbandwidthofatelephonesignaltransmittedonatraditionalcommunicationlineis3.1kHz(from300Hzto3.4kHz,thatis,thefrequencyrangeofthemaincomponentofvoice).Theunitofbandwidthinthissenseishertz(orkilohertz,megahertz,gigahertz,etc.).
②Inacomputernetwork,bandwidthisusedtoindicatetheabilityofthenetwork'scommunicationlinestotransmitdata.Therefore,thenetworkbandwidthindicatestheamountoftimethatcanbepassedfromonepointtoanotherpointinthenetworkinaunitoftime.Highestdatarate".The"bandwidth"generallymentionedherereferstothis.Theunitofbandwidthinthissenseis"bitspersecond",whichisrecordedasbit/s.
(3)Propustnost
Throughputmeanstheamountofdatapassingthroughacertainnetwork(orchannelorinterface)inaunittime.Throughputismoreoftenusedasameasureofthenetworkintherealworldinordertoknowhowmuchdataactuallycanpassthroughthenetwork.Obviously,throughputislimitedbythebandwidthofthenetworkortheratedrateofthenetwork.Forexample,fora100Mbit/sEthernet,itsratedrateis100Mbit/s,thenthisvalueisalsotheabsoluteupperlimitoftheEthernetthroughput.Therefore,for100Mbit/sEthernet,itstypicalthroughputmaybeonly70Mbit/s.Sometimesthroughputcanalsobeexpressedbythenumberofbytesorframestransmittedpersecond.
(4)Zpoždění
Latencyreferstothedata(amessageorpacket,orevenabit)requiredtobetransmittedfromoneendofthenetwork(orlink)totheotherendtime.Latencyisaveryimportantperformanceindicator,itissometimescalleddelayordelay.Thedelayinthenetworkiscomposedofthefollowingdifferentparts.
①Zpoždění odesílání.
Senddelayisthetimerequiredforthehostorroutertosendadataframe,thatis,thetimefromwhenthefirstbitofthedataframeissenttotheendofthelastbitoftheframe.
Sosendingdelayisalsocalledtransmissiondelay.Thecalculationformulaforsendingdelayis:
Zpoždění odesílání=délka datového rámce (bit/s)/šířka pásma kanálu (bit/s)
Itcanbeseenthatforacertainnetwork,Thetransmissiondelayisnotfixed,butisproportionaltothetransmittedframelength(inbits)andinverselyproportionaltothechannelbandwidth.
②Zpoždění šíření.
Propagationdelayisthetimeittakesforelectromagneticwavestotravelacertaindistanceinthechannel.Thecalculationformulaofpropagationdelayis:
Zpoždění šíření=délka kanálu (m)/rychlost šíření elektromagnetické vlny na kanálu (m/s)
PropagationofelectromagneticwaveinfreespaceThespeedisthespeedoflight,whichis300000km/s.Thepropagationrateofelectromagneticwavesinnetworktransmissionmediaisslightlylowerthaninfreespace.
③Prodleva zpracování.
Whenthehostorrouterreceivesthepacket,ittakesacertainamountoftimetoprocess,suchasanalyzingtheheaderofthepacket,extractingthedatapartfromthepacket,performingerrorcheckingorfindinganappropriateroute,etc.,whichproducesProcessingtimedelay.
④Zpoždění řazení.
Whenthepacketistransmittedthroughthenetwork,ithastopassthroughmanyrouters.However,afterthepacketenterstherouter,itmustbequeuedintheinputqueueforprocessing.Aftertherouterdeterminestheforwardinginterface,italsoqueuesupintheoutputqueueforforwarding.Thiscreatesqueuingdelay.
Inthisway,thetotaldelayexperiencedbythedatainthenetworkisthesumoftheabovefourkindsofdelays:
Totaldelay=transmissiondelay+propagationdelay+processingdelay+queuingdelay
(5)Produkt zpožděné šířky pásma
Multiplythetwomeasuresofnetworkperformancediscussedabove—propagationdelayandbandwidth,andgetanotherusefulMetric:Propagationdelaybandwidthproduct,immediatedelaybandwidthproduct=propagationdelay×bandwidth.
(6)Zpáteční (RTT)
Incomputernetworks,theround-triptimeisalsoanimportantperformanceindicator,whichmeansthatthedataissentfromthesendertothesenderreceivesThetotalelapsedtimefortheconfirmationfromthereceiver(thereceiversendstheconfirmationimmediatelyafterreceivingthedata).
Při použití satelitní komunikace je doba oběhu (RTT) relativně dlouhá.
(7) Míra využití
Therearetwotypesofutilizationrate:channelutilizationrateandnetworkutilizationrate.Thechannelutilizationratereferstoafewpercentofthetimethatachannelisused(thereisdatapassing),andtheutilizationrateofacompletelyidlechanneliszero.Thenetworkutilizationistheweightedaverageofthechannelutilizationoftheentirenetwork.
2.Nevýkonnostní charakteristiky počítačových sítí
Thesenon-performancecharacteristicshaveagreatrelationshipwiththeperformanceindicatorsintroducedabove.
(1)Cena
Thepriceofthenetwork(includingthecostofdesignandimplementation).Theperformanceofthenetworkiscloselyrelatedtoitsprice.Generallyspeaking,thehigherthenetworkspeed,thehighertheprice.
(2)Kvalita
Thequalityofthenetworkdependsonthequalityofallthecomponentsinthenetworkandhowthesecomponentsmakeupthenetwork.Thequalityofthenetworkaffectsmanyaspects,suchasthereliabilityofthenetwork,theeaseofnetworkmanagement,andsomeoftheperformanceofthenetwork.However,theperformanceofthenetworkisnotthesameasthequalityofthenetwork.Forexample,somenetworkswithacceptableperformancewillfailafterrunningforaperiodoftimeandbecomeunabletocontinueworking,indicatingthattheirqualityisnotgood.High-qualitynetworkstendtobemoreexpensive.
(3)Standardizace
Thedesignofnetworkhardwareandsoftwarecaneitherfollowgeneralinternationalstandardsorfollowspecificdedicatednetworkstandards.Itisbesttoadopttheinternationalstandarddesign,sothatyoucangetbetterinteroperability,easiertoupgradeandrepair,andeasiertogettechnicalsupport.
(4) Spolehlivost
Reliabilityiscloselyrelatedtothequalityandperformanceofthenetwork.Networkswithhigherspeedsarenotnecessarilylessreliable.However,itisoftenmoredifficultforahigher-speednetworktooperatereliably,andatthesametime,thecostwillbehigher.
(5) Škálovatelnost a upgradovatelnost
Whenconstructingthenetwork,itshouldbeconsideredthatitmayneedtobeexpandedinthefuture(thatis,scaleexpansion)andupgrade(thatis,theperformanceandversionoftheimprove).Thehighertheperformanceofthenetwork,thehigheritsexpansioncostisoften,andthedifficultywillincreaseaccordingly.
(6)Snadná správa a údržba
Ifthenetworkisnotwellmanagedandmaintained,itisdifficulttoachieveandmaintainthedesignedperformance.
Relatedapplications
Inthe21stcentury,mankindwillfullyentertheinformationage.Theimportantcharacteristicsoftheinformationagearedigitization,networkingandinformationization.Torealizeinformatization,wemustrelyonacompletenetwork,becausethenetworkcantransmitinformationveryquickly.Therefore,thenetworkhasnowbecomethelifebloodoftheinformationsocietyandanimportantfoundationforthedevelopmentoftheknowledgeeconomy.TheInternethasexertedanimmeasurableinfluenceonmanyaspectsofsociallifeandonthedevelopmentofsocialeconomy.
Thenetworkmentionedherereferstothe"threenetworks",thatis,telecommunicationnetwork,cableTVnetworkandcomputernetwork.Thesethreetypesofnetworksprovidedifferentservicestousers.Usersoftelecommunicationsnetworkscangetservicessuchastelephone,telegraph,andfax;usersofcableTVnetworkscanwatchvariousTVprograms;computernetworkscanenableuserstoquicklytransmitdatafiles,andfindandobtainvarioususefulinformationfromthenetwork.Includingimageandvideofiles.Thesethreekindsofnetworksallplayaveryimportantroleintheprocessofinformatization,butthefastestgrowingandcoreroleisthecomputernetwork.Withthedevelopmentoftechnology,telecommunicationsnetworksandcabletelevisionnetworkshavegraduallymergedintothetechnologyofmoderncomputernetworks(alsoknownascomputercommunicationnetworks),whichgaverisetotheconceptof"networkintegration".
Sincethe1990s,thecomputernetworkrepresentedbytheInternethasdevelopedrapidly.Ithasgraduallydevelopedfromtheinitialeducationandscientificresearchnetworktoacommercialnetwork,andhasbecomesecondonlytotheglobalThesecondlargesttelephonenetworkintheworld.TheInternetischangingallaspectsofourworkandlife.Ithasbroughthugebenefitstomanycountriesandacceleratedtheprocessoftheglobalinformationrevolution.TheInternetisthebiggestchangeincommunicationsincetheinventionofprinting.Now,people'slife,work,studyandcommunicationareallinseparablefromtheInternet.
Therearetwomostimportantfunctionsprovidedbycomputernetworkstousers,namely,connectivityandsharing.
Themainreasonwhysomanycomputernetworksareestablishedisthattheuseofcomputernetworksisfavoredbyindividualsandcompanies.
Za prvé, komerční aplikace.
1.Themainpurposeistorealizeresourcesharingandfinallybreakthetyrannyofgeography,andmainlyusetheclient-servermodel.
2. Poskytněte výkonné komunikační médium. Například: e-mail (e-mail), videokonference.
3.Činnosti elektronického obchodování.Například různí dodavatelé nakupují podsystémy a poté tyto součásti sestavují.
4.Provádějte různé transakce se zákazníky prostřednictvím internetu.Například:knihkupectví,audiovizuální nákupy zboží nebo služeb doma.
2. Rodinné použití
1.Získejte přístup k informacím na dálku.Například:procházením webových stránek získáte informace o umění, podnikání, vaření, vládě, zdraví, historii, zálibách, zábavě, vědě, sportu, cestování atd.
2.Komunikace mezi jednotlivci.Jako:používání rychlých zpráv (okamžitých zpráv), chatovací místnosti, komunikace typu peer-to-komunikace (komunikace typu peer-to-).
3.Interaktivní zábava.Jako:videona vyžádání,okamžitý komentář a účast na činnostech,online hry.
4. Elektronický obchod v širokém smyslu. Například: selektivní placení účtů, správa bankovních účtů a zpracování investic.
3. Uživatelé mobilních zařízení
Besedonwirelessnetworks.
1. Vyjímatelné počítače: notebooky, PDA, 3G mobilní telefony.
2.Vojna:Awar se při komunikaci nemůže spoléhat na vybavení LAN.
3.Aplikace, jako jsou zasažené flotily, taxíky a expresní vozidla.
Čtyři.Sociální problémy
ThewidespreaduseoftheInternethasledtonewsocial,ethicalandpoliticalissues.