Definition
1.ThecommunicationsubnetisanindependentcommunicationsystemcomposedofthenodecomputerNCusedforinformationexchangeandcommunicationlines.Itisresponsibleforthedatatransmission,switching,andCommunicationprocessingworksuchasprocessingandexchange.Amongthem:
Subnet:usuallyonlymeaningfulwhentalkingaboutWAN,itreferstothecollectionofroutersandcommunicationlinesownedbynetworkoperators.
2.Thefunctionofthecommunicationsubnetistotransmitinformationfromonehosttoanother;theresourcesubnetisacollectionofvariousnetworkresources(hardware,software,datainformation).
3,thecommunicationsubnet,thepositionintheOSIsystemisthelowerthreelayers.
Function
(1)Networkhardwareequipmentmainlyincludes:networkadapters,repeaters,hubs,bridges,routers,serversandtransmissioncables.
Mainlygrasptheroleofrelatedinterconnectionequipment,whichlevelofthenetworkarchitecturemodelworks.
1.Networkadapter(networkcard):workingatthephysicallayer;
2.Repeater:adeviceworkingatthephysicallayer,usedforsimplenetworkexpansion,Itisanelectronicdevicethatreceivesasinglesignalandbroadcastsittomultipleports.
3.Hub:amulti-portrepeater.Typesinclude:passivehubs,activehubs,smarthubs.
⑴Itisusedforsimplenetworkexpansion,increasingthetransmissiondistanceofthelocalareanetwork,andperformingsignalregenerationandamplification,butithasnofilteringfunction.
⑵Sharebandwidth;therefore,themoredevicesconnected,thelessbandwidtheachdevicegets.
⑶WorkinthephysicallayerofOSI.
4,bridge(Bridge):thetypeofbridge:transparentbridge,sourceroutingbridge.
⑴ItisabridgetoestablishaconnectionbetweentwoLANs,usedtoexpandtheLANandcommunicationmeans;
⑵CanconnecttwodifferenttypesofLANs;suchasEthernet,tokenRingnetwork;
⑶candividealargenetworkintomultiplesmallsubnets;itcanalsoselectivelysendsignalswithaddressesfromonetransmissionmediumtoanothertransmissionmedium.Thiscanbalancetheloadofeachnetworksegment,reducetheamountofinformationinthenetworksegment,andimprovenetworkperformance;
⑷canprovidefilteringfunctions,andcaneffectivelylimittheinsignificantcommunicationinthetwomediasystemstopreventTransmitthepacketsofacertainLANsegmentthroughthenetworksegmentsthatarenotrelatedtothem,reducetheamountofnetworkinformationandimproveperformance;
⑸WorkatthedatalinklayerofOSI.
[Question1]Whatisanetworkbridge,andwhydoIneedanetworkbridge?
Anetworkbridgeisanetworkdevicethatconnectsmultiplenetworksegments,andisabridgebetweenlocalareanetworks.
⑴Differentdepartmentsofalargeunithavedifferentnatureofwork,sodifferentlocalareanetworksareused.Suchas802.3and802.4,buttheyneedtobeexchangedsoonerorlater.
⑵Thegeographicallydispersedunitsplantobuildalocalareanetwork,andthenconnectthemwithabridgetoreducecosts.
(3)DivideasinglelogicalLANintomultipleLANs,adjusttheload,andenhancethereliabilityofthenetwork.
⑷Thephysicaldistanceofthenetworkcanbeincreasedbyusingabridge.
⑸Settingupanetworkbridgecanseparatethenetworktopreventinformationfrombeingstolen,interceptimportantinformation,andenhancenetworksecurity.
[Question2]Howthebridgeworks.ThehostgroupingplusLLCheadergroupingplus802.3headergroupingisuploadedtotheMAClayerinthebridgetoremovetheMACheader
Note:IfyouconnectKbridgeswithdifferentLANs,thereareKdifferentMACsublayersandPhysicallayer.
[Question3]describeshowbridgescanbeusedtoreducenetworktrafficproblems.
Theuseofbridgescanseparatethetrafficbetweentwonetworks,andcanalsobeusedtodividenetworksegmentstoreducedata"trafficbottlenecks",adjustnetworkload,andreducenetworktrafficproblems.
5.Router:Itisusedtoconnectmultiplelogicallyseparatednetworkdevices,andhasthefunctionsofrealizingprotocolconversion,judgingnetworkaddressesandpathselection.Itcanestablishflexibleconnectionsinamulti-networkinterconnectionenvironment,andcanconnectvarioussubnetswithcompletelydifferentdatapacketsandmediaaccessmethods.Generallyspeaking,aroutershouldbeusedfortheinterconnectionofheterogeneousnetworksortheinterconnectionofmultiplesubnets.Workatthenetworklayer.
Note:Gateway:Itisarouterusedforprotocolconversionanddatareorganizationbetweenheterogeneousnetworks,andthegatewaytotheInternet.Inacomputernetwork,whenconnectingdifferenttypesofnetworkswithlargeprotocoldifferences,gatewayequipmentshouldbeused.Thefunctionofthegatewayreflectsthehigh-leveloftheOSImodel.Itconvertstheprotocolandregroupsdatatocommunicatebetweentwodifferenttypesofnetworksystems.Workatthenetworklayer.
3.Thenetworktransmissionmediuminthecommunicationsubnet
Thetransmissionmediumdeterminesthenetworkdatatransmissionrate,themaximumlengthofthenetworksegment,thereliabilityofthetransmissionandthecomplexityofthenetworkadapter.
Technology
LocalAreaNetwork
1.Ethernet:TheIEEE802.3standardprotocolsuiteisaconflictingprotocol,CSMA/CDcoretechnology,andEthernetTheconnectiondistancehasacertaindegreeoflimitation.
2,FastEthernet:adoptsIEEE802.3ustandardprotocol
3,Token-Ring:isaringnetwork,adoptsIEEE802.5standardprotocolItisaconflict-freeagreement.
4.FDDI(FiberDistributedDataInterface):adoptstheIEEE802.8standardprotocol(duallooptopology),whichiscompletelybasedontheIEEE802.5protocolasatemplate(aconflict-freeprotocol);
5.Coreswitch
6.SwitchandVLANtechnology
[Question1]WhatisVLAN?
VLANisactuallyalocation-independentlocalareanetworkconnectedtoalargeswitch;itbelongstothesecondlayerofOSItechnology.
[Question2]WhydividethenetworkintoVLANs?
Inatraditionallocalareanetwork,channelconflictsandbroadcaststormscausedbythesharingoftransmissionchannelsbysitesareimportantfactorsthataffectnetworkperformance(usuallyanIPsubnetorIPXsubnetlayerisinabroadcastdomain.Accordingtothephysicalnetwork),inordertoavoidbroadcaststormsonthenetworkconnectedtothelargeswitch,thenetworkneedstobedividedintomultipleVLANs.
[Question3]WhatarethebenefitsofdividingthenetworkintoVLANs?
⑴Simplifynetworkdesignandnetworkmanagement,reduceconstructioncosts,andreducenetworkmanagementoverhead.
⑵Reducenetworktrafficandavoidbroadcaststorms.BydividingtheLANintoseveralVLANs,itisactuallyarestrictiononthebroadcastdomain;
3Isolatesubnetcommunicationandimprovenetworksecurity.RouterscanbeusedbetweendifferentVLANstoconnectandfilterbroadcastinformation.
[Question4]HowtodivideanetworkintoVLAN?
⑴VLANcanbedividedbasedonmultiplesecuritystrategies.Forexample,itisdividedbasedonapplicationtype,accessauthorityequalstosecuritypolicy.
⑵Therearemainlyfourmethodsofdivision:VLANbasedonport,VLANbasedonMACaddress,VLANbasedonlayer3andVLANbasedonstrategy.
[Question5]WhatisthemaindifferencebetweenVLANandLAN?
⑴VLANcoverageisnotlimited,
⑵VLANisbuiltonthebasisofswitches,belongstothesecondlayer,isfast,easytomanage,
⑶VLANsecurity,ItisnotaccessiblebetweendifferentVLANs.
7.ISDNintegratedservicedigitalnetwork
⑴ISDN:isanetworkdevelopedbythecombinationoftelephonenetworkanddigitalnetwork,whichprovidesend-to-enddigitalconnection,usedtocarryMultipleservicesincludingvoiceandnon-voice.Suchasdigitaltelephone,fax,videotext,andvideoservices.
⑵ThreecharacteristicsofISDN:end-to-enddigitalconnection,integratedservices,andstandardmulti-purposenetworkaccessinterface.
ThetechnicalcoreofISDN:dividethebandwidthintoseveralchannels,includingBandDchannels.
Bchannelisakindofloadchannel,usedforvoiceordigital,thechanneliswide,thespeedisfast,andthetransmissionrateisupto64kb/s.
Dchannelisakindofout-of-bandsignaling,itonlycarriesinformationabouttheloadchannel,andthetransmissionrateisonly16kb/s.
Note:Generallyspeaking,thebandwidthofISDNchannelis128kb/s,becausetheDchannelisnotopened;whatisthebasicrateofISDN?Itshouldbe2B+D,thatis,therateis144kb/s.
8.ATMtechnology
Wideareanetwork
x.25publicpacketswitchingnetwork,DDNdigitaldatanetwork,PSTNpublictelephonenetwork,ISDNintegratedservicedigitalnetwork,Framerelay,ATMasynchronoustransmissionmode.
DataCommunication
AdvantagesandDisadvantages
Analogcommunicationmethod:Itisthecommunicationmethodinwhichinformationtransmitsanalogsignalsonanalogchannels.Advantages:⑴Therearealargenumberofcommunicationchannels;
⑵Itcantransmitinformationoverlongdistances,andthosedigitalsignalsrepresentedbycodescanbemodulatedbyhighfrequency.
Long-distancetransmission(belongingtobroadbandtransmission)onthechanneloropticalchannel.
Disadvantages:Long-distancetransmissionwillbesubjecttoaseriesof
Digitalcommunicationmethods:Itisthecommunicationmethodthatinformationtransmitsdigitalsignalsondigitalchannels.Advantages:⑴Thesignaldoesnotneedtobemodulated,butdirectlycomposedof0and1binarycodesfortransmission(belongingtobasebandtransmission);
⑵Thetransmissiondistortionissmall,thebiterrorrateislow,andthedatatransmissionspeedishigh.Communicationhopesso.
Disadvantages:short-rangecommunication
Bandwidthandcapacity
Bandwidth:therangeoffrequenciesthatcanbetransmittedinthephysicalchannelsatbothendsofthechannel,thatis,thetransmissionofbitsignalsThemaximumtransmissionrate,inHertzHz.Ifasignalrangeis3000HZ~4000HZ,thebandwidthis4000HZ-3000HZ=1000HZ,whichmeansthatthemaximumtransmissionrateofthechannelis1000timespersecond.Thewiderthebandwidthofachannel,thegreatertheamountofinformationthatcanbetransmittedperunittime.Thecarryis1000carry.
Capacity:Themaximumnumberofbitsthatcanbetransmittedonthechannelperunittime,inbps(bits)/second.Thecarryis1024carry.
Relationship:Shannon'stheorem:C=Wlog2(1+S/N).Amongthem:C:capacity,W:bandwidth,S:signalpower,N:noisepower.
Signalunit
⑴Baud:Itisameasurementunitusedtoexpressthenumberoftimestheanalogsignalchangespersecond.
⑵Baudrate:Thenumberofbaudsthatcanbetransmittedpersecond.
⑶bit(bit):isthebasicunitofmeasurementusedtorepresent(digitalsignal)binaryinformation.
⑷Bitrate:Thenumberofbitsthatcanbetransmittedpersecond,alsoknownastherateofadigitalchannel.
Note1:Therateofthesignaltransmittedbyab-baudlineisnotnecessarilybbitspersecond,andeachsignalcancarryseveralbits.
ThisismainlybasedonThesignalvaluedependsonthevoltage.Whenthevoltagevaluetakesthe8valuesof0,1,2,3,4,5,6,and7,wedividethesignallevelintoVlevels,soaccordingtotheNyquisttheorem,themaximumtransmissionTherateis:D=2Wlog2V(bps)orb/s,suchas:
WhenthelevelisV=2,aunitpulsesignalcancarry1Bit,namely0,1,thenbaudrate=bitrate.
WhenthelevelisV=4,aunitpulsesignalcancarry2bits,namely00,01,10,11.
WhenthelevelisV=8,aunitpulsesignalcancarry3bits,namely000,001,010,011,100,101,110,111.
Note2:Bytesareusuallyusedtodescribethestoragecapacityofnumbers:1byteByte=8bits,1kB=1024Byte,1MB=1024kB,1GB=1024MB.
Thecommunicationrateofdataisexplainedinbitspersecond:1Kbps=1000bits,1Mbps=1000Kbps,1Gbps=1000Mbps.
Codingmethod
Manchestercoding:thefirstT/2ofthebitrepresentingthe1signalishigh,andthelastT/2islow;the0signalisjusttheopposite.
DifferentialManchesterencoding:Whenthebitis1,thelevelofthefirstT/2bitisthesameasthelevelofthelastT/2bitofthepreviousbit;whenthebitis0,thepreviousTheleveloftheT/2bitisoppositetothelevelofthelastT/2bitofthepreviousbit.
Relateddifferences
(1)Resourcesubnet:Resourcesubnetreferstotheuserendsystem(intra-officedispatchingautomationnetwork,MISnetworkandsubstationlocalareanetwork),includinguserapplicationresources,Suchasservers,faultcollectioncomputers,peripherals,systemsoftwareandapplicationsoftware.Theresourcesubnetconsistsofcomputersystems,terminals,terminalcontrollers,networkedperipherals,varioussoftwareresourcesandinformationresources.Theresourcesubnetisresponsibleforthedataprocessingoftheentirenetworkandtheprovisionofresourcesandnetworkservicestonetworkusers,includingnetworkdataprocessingresourcesanddatastorageresources.
(2)Communicationsubnet:Communicationsubnet(communicationsubnet,orsubnetforshort)referstothecollectionofequipmentandsoftwarethatrealizethenetworkcommunicationfunctioninthenetwork,communicationequipment,networkcommunicationprotocol,communicationControlsoftware,etc.belongtothecommunicationsubnet,whichistheinnerlayerofthenetworkandisresponsibleforthetransmissionofinformation.Mainlyprovideuserswithdatatransmission,switching,processing,conversion,etc.Thetaskofthecommunicationsubnetistotransmitmessagesbetweenendnodes,whichismainlycomposedoftransfernodesandcommunicationlinks.IntheARPAnetwork,thetransferpointiscommonlyreferredtoastheinterfaceprocessor(IMP).Thecommunicationsubnetmainlyincludeshardwaredevicessuchasrepeaters,hubs,bridges,routers,andgateways.