Хъб

Въведение

Hub(Hub)referstoadevicethatconnectsmultipleEthernettwistedpairsoropticalfiberstogetherunderthesamephysicalmedium.ThehubisthephysicallayeroperatingintheOSImodel.Itcanberegardedasamulti-portrepeater,ifitdetectsacollision,itwillsubmitablockingsignal.

ThehubusuallycomeswithaBNCand/orAUIadaptertoconnecttoatraditional10BASE2or10BASE5network.

Becausethehubwillregenerateoramplifyanydigitalsignalreceived,andthensubmititfromallportsofthehub,thiswillcauseagreatchanceofcollisionbetweensignals,andthesignalmayalsobetapped.Andthismeansthatalldevicesconnectedtothehubbelongtothesamecollisiondomainnameandbroadcastdomainname,somosthubshavebeenreplacedbyswitches.

Принцип

Принцип на препращане на сигнала

ThehubworksatthephysicallayeroftheOSI/RMreferencemodelandtheMAC(MediaAccessControl)sublayerofthedatalinklayer.Thephysicallayerdefineselectricalsignals,symbols,linestatusandclockrequirements,connectorsfordataencodinganddatatransmission.Becausethehubonlyreshapesandamplifiesthesignalandthenretransmitsitwithoutcoding,itisaphysicallayerdevice.The10Mhubhas4standardinterfacesavailableatthephysicallayer,namely:10BASE-5,10BASE-2,10BASE-T,and10BASE-F.The10BASE-5(AUI)portofthe10Mhubisusedtoconnectlayer1andlayer2.

ThehubusestheCSMA/CD(CarrierFrameListeningMultipleAccess/ConflictDetection)protocol.CSMA/CDistheMAClayerprotocol,sothehubalsocontainsthecontentofthedatalinklayer.

Asaspecialmulti-portrepeater,the10Mhubmustfollowthe5-4-3ruleinthenetworkrelayexpansion,thatis:anetworksegmentcanonlybedividedinto5sub-networksegmentsatmost;Anetworksegmentcanonlyhave4repeatersatmost;anetworksegmentcanonlyhaveatmostthreesubnetsegmentscontainingPCs,asshowninFigure19,subnetsegment2andsubnetsegment4areusedtoextendthedistance.

Theworkingprocessofthehubisverysimple.Itcanbedescribedsimplyasfollows:First,thenodesendsasignaltotheline,andthehubreceivesthesignal.Becausethesignalisattenuatedduringcabletransmission,thehubwillTheattenuatedsignalisshapedandamplified,andfinallythehubbroadcastsandforwardstheamplifiedsignaltoallotherports.

Класификация

Обработка

HUBcanbedividedintopassiveHUB,activeHUB,smartHUBandotherHUBsaccordingtothewaytheinputsignalisprocessed.

PassiveHUB

Itistheworst-qualityone,doesnotdoanyprocessingonthesignal,doesnotextendthetransmissiondistanceofthemedium,andisThesignalhasacertaininfluence.EachcomputerconnectedtothisHUBcanreceivesignalsfromallothercomputersonthesameHUB;

ActiveHUB

ThedifferencebetweenanactiveHUBandapassiveHUBisthatitcanamplifyorregeneratethesignal,sothatitextendstheeffectivetransmissiondistancebetweenthetwohosts;

SmartHUB

Whenyouhearthisword,youknowthatthisguymustbebetterthanthosetwo!InadditiontoallthefunctionsofanactiveHUB,theintelligentHUBalsohasnetworkmanagementandroutingfunctions.InthesmartHUBnetwork,noteverymachinecanreceivethesignal,onlythecomputerwiththesameaddressasthesignaldestinationaddresscanreceiveit.SomesmartHUBscanchoosethebestpathbythemselves,whichhasagoodmanagementofthenetwork!

други

Според други методи има много типове, като 10M, 100M, 10/100Madaptive HUB и т.н., които няма да бъдат представени тук. Накратко, пазарната цена не е толкова скъпа, така че опитайте да купите по-добра.

Структураfunction

Accordingtothestructureandfunctionclassification,hubscanbedividedintothreetypes:unmanagedhubs,stackedhubsandchassishubs.

(1) Неуправляван хъб

ThesimplesthubprovidesacentralnetworkconnectionthroughanEthernetbus,whichisconnectedintheformofastar.Thisiscalledanunmanagedhubandisonlyusedinverysmallnetworksofupto12nodes(inafewcases,morecanbeused).Unmanagedhubsdonothavemanagementsoftwareorprotocolstoprovidenetworkmanagementfunctions.Suchhubscanbepassiveoractive.Activehubsareusedmoreoften.

(2) Подредени главини

Stackedhubsareslightlymorecomplicatedhubs.Themostnotablefeatureofastackinghubisthat8transponderscanbedirectlyconnectedtoeachother.Inthisway,thenetworkcanbeexpandedbysimplyaddingahubandconnectingittoanalreadyinstalledhub.Thismethodisnotonlylowincost,butalsosimpleandeasytoimplement.

(3) Шаси

Chassishubisamodulardevice,andmultipletypesofmodulescanbeinsertedonitsbackplanecircuitboard.Somehubshaveredundantbackplanesandpowersupplies.Atthesametime,somemodulesallowuserstoreplacethosefailedmoduleswithoutshuttingdowntheentirehub.Thebackplaneofthehubpreparesmultiplebusesforplug-inmodules.Theseplug-inmodulescanadapttodifferentsegments,suchasEthernet,FastEthernet,FiberDistributedDataInterface(FDDl)andAsynchronousTransferMode(AsynchronousTransferMode).,ATM).Somehubsalsoincludebridges,routers,orswitchingmodules.Activechassishubsmayalsohaveretimingmodulestoassociatewithamplifieddatasignals.

Природата

Ahub(HUB)isabasicdeviceinadatacommunicationsystemandhasatrafficmonitoringfunction.Itisakindofhardwaredevicethatdoesnotrequireanysoftwaresupportorrequiresverylittlemanagementsoftwaremanagement,justlikethetransmissionmediumsuchastwistedpaircable.Itiswidelyusedin

различни центрове (18 снимки)

invariousoccasions.Thehubworksinalocalareanetwork(LAN)environmentandiscalledaphysicallayerdevice.Thehubuseselectricalinterconnection.WhentheLANmaintenanceenvironmentisalogicalbusorringstructure,thehubcanbeusedtoestablishaphysicalstarortreenetworkstructure.Inthisrespect,thehubfunctionsasamulti-portrepeater.Infact,ahubisactuallyakindofrepeater.Thedifferenceisonlythatthehubcanprovidemoreportservices,sothehubisalsocalledamulti-portrepeater.

Therearethreeshortcomingsinthewayofsendingdatabybroadcastofthiskindofequipment:(1)Userdatapacketsaresenttoallnodes,whichislikelytobringinsecurefactorsindatacommunication.Somepeoplewithulteriormotivescaneasilyinterceptotherpeople’sdataillegally.Bag.(2)Sincealldatapacketsaresenttoallnodesatthesametime,coupledwithitssharedbandwidthmethod(iftwodevicessharea10Mhub,theneachdevicehasonly5Mbandwidth),itismorelikelytocausenetworktrafficjams.Itfurtherreducestheefficiencyofnetworkexecution.(3)Non-duplextransmission,lownetworkcommunicationefficiency.Atthesametime,eachportofthehubcanonlycarryoutdatacommunicationinonedirection,andcannotcarryouttwo-wayduplextransmissionlikeaswitch.Thenetworkexecutionefficiencyislow,anditcannotmeetthecommunicationneedsoflargernetworks.

Структура

Theexternalboardstructureoftheordinaryhubisverysimple.Forexample,D-Link'ssimplest10BASE~TEthernetHubhubisarectangularparallelepiped,withACpowersocketsandswitches,anAUIinterfaceandaBNCinterfaceontheback,andarowof17RJ-45interfacesonmostofthefront.Ontherightsideofthefront,thereareLEDinterfaceindicatorsandLEDstatusindicatorscorrespondingtoeachRJ-45interface.High-endhubsarenotmuchdifferentfrommodernroutersorswitchingroutersfromtheoutside.Inparticular,moderndual-speedadaptiveEthernethubsgenerallyhavebuilt-inswitchingmodulesthatcancommunicatewitheachotherbetweeninternal10Mb/sand100Mb/snetworksegments,sothatthistypeofhubcanbeusedinthenetworksegmentwiththehubasthenode.,Torealizethecommunicationexchangebetweenvariousnodes,andsometimespeoplesimplycallthistypeofswitchinghubaswitch,whichmakesitdifficultforuserswhousethehubforthefirsttimetodistinguishthemcorrectly.Butitisarelativelysimplemethodtodistinguishthehubbasedonthetypeofbackplaneinterface.

Предназначение

AccordingtotheIEEE802.3protocol,thehubfunctionistorandomlyselectaportdevice,andletitmonopolizetheentirebandwidth,andthehub'suplinkdevices(switches,switches,Routerorserver,etc.)tocommunicate.Itcanbeseenfromthisthatthehubhasthefollowingtwocharacteristicsatwork.

Firstofall,theHubisjustamulti-portsignalamplifyingdevice.Whenaportreceivesadatasignalduringwork,becausethesignalhasbeenattenuatedduringthetransmissionfromthesourceporttotheHub,theHubisThesignalisreshapedandamplified,sothattheattenuatedsignalisregenerated(recovered)tothestatewhenitwassent,andthenforwardedtoallotherportsintheworkingstate.ItcanbeseenfromtheworkingmodeofHubthatitonlyplaystheroleofsignalamplificationandretransmissioninthenetwork.Itspurposeistoexpandthetransmissionrangeofthenetworkwithouttheabilitytotransmitsignals.Itisastandardshareddevice.Sosomepeoplecallhubs"sillyHub"or"dumbHub".

However,withthedevelopmentoftechnologyandchangesindemand,manyHubshaveexpandedtheirfunctionsandarenolongeraffectedbythisworkingmechanism.ThenetworkcomposedofHubisasharednetwork,andHubcanonlyworkinhalf-duplex.

Hubismainlyusedfortheestablishmentofsharednetworks,anditisthemosteconomicalsolutionfromtheservertothedesktop.Inaswitchednetwork,theHubisdirectlyconnectedtotheswitch,andthedataontheswitchportissenttothedesktop.TheHubisflexibleinnetworking.Itislocatedatastar-shapednodeinthenetwork,andcentrallymanagestheworkstationsconnectedtothenode,sothattheworkstationsthathaveproblemswillnotaffectthenormaloperationoftheentirenetwork,andusersarealsofreetojoinandexit.

Разделяне на локална мрежа

Fromtheperspectiveoflocalareanetwork,hubscanbedividedintofivedifferenttypes.

(1) Единичен мрежов сегментен хъб

ThesimplesthubisatypeofhubusedinthesimplesttrunkLANnetworksegment,andstackableEthernetHubortokenringnetworkmulti-stationaccessunit(MAU),etc.aresimilar.

(2)Многосегментна главина

Itisdirectlyderivedfromasingle-relaynetworksegmenthubandusesahubbackplane.Thistypeofhubhasmultiplerelaynetworksegments.Itsmainadvantageisthatuserscanbedistributedonmultiplerelaynetworksegmentstoreducetheinformationtrafficloadofeachnetworksegment.Informationtrafficbetweennetworksegmentsgenerallyrequiresindependentbridgesorrouters.

(3) Хъб за превключване на портове

Thisintegratorisbasedonamulti-segmenthub,whichautomatestheconnectionprocessbetweenuserportsandmultiplebackplanenetworksegments,Andbyincreasingtheportswitchmatrix(PSM)toachievethehub.PSMcanprovideanautomatictoolforconnectinganyexternaluserporttoanytrunknetworksegmentonthehubbackplane.Themainadvantageoftheportswitchinghubisthatitcanrealizetheautomaticfeaturesofmovement,additionandmodification.

(4) Хъб за свързване на мрежата

Portswitchinghubsfocusonportswitching,whilenetworkinterconnectionhubscanprovidesometypesofintegratedconnectionsbetweenmultiplenetworksegmentsonthebackplane.Thisfunctionisaccomplishedthroughanintegratedbridge,routerorLANswitch.Thistypeofhubusuallyadoptstheformofachassis.

(5) Превключващ хъб

Theboundarybetweenhubandswitchhasbecomeblurred.Theswitchinghubhasacoreswitchingbackplane,whichusesapureswitchingsystemtoreplacethetraditionalsharedmediarelaynetworksegment.Suchproductsarealreadyonthemarket,andhybrid(relay/switching)hubsarelikelytocontrolthismarketinthenextfewyears.Itshouldbenotedthatthereisalmostnodifferenceinthecharacteristicsbetweenthistypeofhubandswitch.

Withthedevelopmentoftechnology,inlocalareanetworks,especiallyinsomelargeandmedium-sizedlocalareanetworks,hubshavegraduallywithdrawnfromapplicationandreplacedbyswitches.Hubsaremainlyusedintheedgeofsomesmallandmedium-sizednetworksorlargeandmedium-sizednetworks.Thefollowingfeaturestheapplicationofsmallandmedium-sizedlocalareanetworks,andintroducesitsselectionmethod.

Скорост

Thechoiceofhubspeedismainlydeterminedbythefollowingthreefactors.

(1) Широчина на честотната лента на устройството за връзка нагоре

Iftheuplinkdeviceallows100Mbit/s,youcannaturallypurchasea100Mbit/shub;otherwise,a10Mbit/shubshouldbeanidealchoice,becauseForanetworkwithasmallnumberofnetworkconnecteddevicesandasmallcommunicationflow,a10Mbit/shubcanmeetapplicationneeds.

(2) Брой предоставени портове за връзка

Sinceallstationsconnectedtothehubcompeteforthesameuplinkbus,themorethenumberofportsconnected,theeasieritistocauseconflict.Atthesametime,datasenttoanyportofthehubwillbesenttoallportsconnectedtothehub.Toomanyportswillreducetheeffectiveutilizationoftheequipment.Accordingtopracticalexperience,thenumberofcomputersmanagedbya10Mbit/shubshouldnotexceed15,andthatof100Mbit/sshouldnotexceed25.Ifitexceeds,aswitchshouldbeusedinsteadofahub.

(3) Изисквания за кандидатстване

Thecontenttobetransmitteddoesnotinvolvevoiceorimage.Whenthetransmissionvolumeisrelativelysmall,select10Mbit/s.Ifthetransmissionvolumeislargeandmultimediaapplicationsmaybeinvolved(notethatthehubisnotsuitablefortransmittingtime-sensitivesignals,suchasvoicesignals),a100Mbit/sor10/100Mbit/sadaptivehubshouldbeselected.Thepriceof10/100Mbit/sadaptivehubisgenerallyhigherthanthatof100Mbit/s.

Ретранслатор

Ahubisaspecialrepeaterthatcanbeusedasaswitchingdeviceformultiplenetworksegments,becauseseveralhubscanbecascaded.Theintelligenthubcanalsointegratenetworkfunctionssuchasnetworkmanagementandpathselection.Thehubisthesmallestunitofthemanagementnetworkandthestarconnectionpointofthelocalareanetwork.Itcentrallymanagestheworkstationsandpreventstheproblematicsectionfromaffectingthenormaloperationoftheentirenetwork.Hubisthemostwidelyusedconnectiondeviceinthelocalareanetwork.Accordingtotheconfigurationform,itcanbedividedintothreetypes:independenthub,modularhubandstackedhub.Itsfunctioncanbesimplyunderstoodasconnectingsomemachinestoformalocalareanetwork.

Themainspecificationsare8,16,24porthubs.

Forthemostcommonandmostcommonlyusedstartopology,thehub(HUB)istheheartpart.Onceithasaproblem,theentirenetworkcannotwork.Thenetworkisveryimportant.

Операционен метод

Метод на подреждане

Inordertomakethehubmeettherequirementsofthenumberofportsinthelargenetwork,thestackingorlevelofthehubisgenerallyusedinthelargernetwork.Thewaytosolvetheproblem.However,themainapplicationscenariosofthetwomethodsaredifferent,andthestackingmethodwillbeintroducedfirst.

Thestackingmethodreferstoconnectingseveralhubswithcablesthroughstackingportstoachievetheexpansionofthenumberofportsofasinglehub.Itshouldbenotedthatonlystackablehubshavethiskindofport,onestackableHubsgenerallyhaveboth"UP"and"DOWN"stackingports,seeFigure9.

Thehubstackisconnecteddirectlyfromthe"UP"stackportofonetothe"DOWN"stackportofanotherhubthroughadedicatedconnectioncableprovidedbythemanufacturer.Allthehubsinthestackcanberegardedasawholehubformanagement,thatis,allthehubsinthestackcanberegardedasonehubfromthetopologicalstructure.Figure20showsthestackconnectiondiagramofa3ComSuperStackIIPSHub40/50stackinghub,andFigure21showsthestackconnectiondiagramoftheCiscoFastHub300/400stackinghub.Theconnectionbetweensuchhubsusuallydoesnotoccupytheoriginalordinaryportsonthehub,andthestackporthasintelligentidentificationperformance,sothestackedhubscanbetreatedasahubforunifiedmanagement.Thehubstackingtechnologyusesadedicatedmanagementmoduleandstackconnectioncables,whichcanestablishawiderbroadbandlinkbetweenhubs,sothatthebandwidthofeachactualusermaybewider(onlywhennotallportsareUsecase).

Theportexpansionmethodofastackedhubislimitedbythetypeandspacingofthehub.Thefirstconditionisthatthestackedhubmustbestackable;anothertypeofstackconnectionisgenerallyveryclosetoeachother.Theconnectionbetweenthehubs(thestackconnectioncableprovidedbythemanufacturerisgenerally1m),sothiskindofhubportexpansionconnectionmethodistoolimitedbythedistance.

Инсталационни точки

Forspecificconstructionmethods,pleaserefertotheNationalBuildingStandardDesignAtlas"SmartHomeControlSystemConstructionAtlas03X602"andtheinternationalstandardspecification"EIA/TIA569CommercialBuildingCommunicationChannelandSpacestandard".

Отстраняване на неизправности

Thehub(HUB)orswitch(Switch)isthemostpopulardeviceinthelocalareanetwork.Undernormalcircumstances,theyprovideconvenienceforuserstofindnetworkfaults.Forexample,byobservingwhethertheindicatorlightoftheportconnectedtotheHUB(orSwitch)ison,itcanbejudgedwhetherthenetworkconnectionisnormal.For10/100Mb/sadaptiveHUB(orSwitch),youcanalsojudgewhethertheconnectedcomputerisworkingunder10Mb/sor100Mb/sthroughthedifferentcolorsoftheconnectionportindicator.Therefore,inmostapplications,theuseofHUB(orSwitch)isbeneficialtonetworkmaintenance.However,becauseofimproperuseofHUB(orSwitch)oritsowndamage,itwillbringproblemstothenetworkconnection.

[Отстраняване на неизправности]

След надграждане на мрежата от 10Mb/до 100Mb/s, мрежата не може да работи нормално.

[Анализ и обработка на грешки]

Inalocalareanetwork,whenthenetworkconnectionrangeislarge,thetransmissiondistanceofthenetworkcanbeexpandedthroughthecascadeconnectionbetweenHUBs.Uptofourlevelscanbecascadedina10Mb/snetwork,sothatthemaximumtransmissiondistanceofthenetworkcanreach600m.Butwhenthenetworkisupgradedfrom10Mb/sto100Mb/soranew100Mb/slocalareanetworkiscreated,ifthenormalmethodisusedtoconnect100MHUB,thelocalareanetworkwillnotworknormally.Asweallknow,onlytwo100Mb/sHUBsareallowedtobecascadedina100Mb/snetwork,andtheconnectiondistancebetweentwo100Mb/sHUBscannotbegreaterthan5m,sothemaximumdistanceof100Mb/sLANwhenusingHUBis205m.Iftheactualconnectiondistancedoesnotmeettheaboverequirements,thenetworkwillnotbeabletoconnect.Enoughattentionshouldbepaidtothispoint,otherwiseitiseasytocauseseriouserrorswhenusersplanthenetwork.

[Отстраняване на неизправности]

Aunitbuiltalocalareanetworkonitsown,usingtwo16-port(andacascadeport)10Msharedhub,allcomputersthroughtheHUBandConnecttotheHUBintheswitchboardroom.Amongthem,HUBAisconnectedtothe16thportofHUBBthroughthecascadeport,HUBBisconnectedtotheHUBinthemaincomputerroomthroughthecascadeport,andtheotherportsarerespectivelyconnectedtotheworkstation.TheentireworkstationusesastaticIPaddress,thevalues​​ofwhichare192.168.0.2,192.168.0.3...andsoon,192.168.0.1isallocatedtotheNTserver,andeachcomputer(includingtheserver)’Ssubnetmasksareall255.255.255.0.Beforetheserverisformallyconnectedtoeachworkstation,thePingcommandisusedtotesteachworkstation.Theresultsareallconnected,andalltheworkstationsconnectedtoHUBAcanalsousethePingcommandtocommunicatewiththeworkstationsconnectedtoHUBB.However,afterconnectingtotheserver,onlytheworkstationconnectedtoHUBBcanlogintotheserver,buttheworkstationconnectedtoHUBAcannotlogin.

[Отстраняване на неизправности]

ByobservingtheindicatorlightsofthecomputernetworkcardandtheindicatorsofeachportonthetwoHUBs,exceptforthediscoveryofthe16thportofHUBBandHUBATheindicatorlightcorrespondingtothecascadeportoftheHUBAisnoton,andtheindicatorsofallthenetworkcardsandotherportsareevenlylit,indicatingthattheconnectionbetweenthecomputerandtheHUBisnormal.Therefore,theproblemismostlikelycausedbythecascadeportoftheHUBAandtheHUB.Onthe16thportofHUBB.Accordingtothissituation,itissuspectedthatatleastoneofthecascadeportsofHUBAandthe16thportofHUBBisbroken.Inordertofurtherconfirmthattheportisbroken,thepositionsofthetwoHUBscanbeexchanged,buttheresultisstillthesame.Next,Itriedtoplugthetwisted-paircableconnectedtothecascadeportofHUBAtoanordinaryportelsewhereonHUBB.Asaresult,theproblemwassolved.Allworkstationsinthenetworkcancommunicatewiththeserver,andthetwoHUBsareconnected.Allworkstationscanrespondtoeachother.ItcanbeseenthatthecascadeportofsomeHUBsandaportnexttoitarenottwoindependentports,butshouldbelongtothesameport(althoughtherearetwoindependentphysicalports).ManypreviousHUBsusedatoggleswitchtoselectthecascadeportbetweenthetwoports,butthisswitchisomittedinthesubsequentproducts,butifoneoftheportsisusedasacascadeport,theotherOneportwillbeinvalid.

[Отстраняване на неизправности]

AHUBconnectingtwobuildingsoftenburnsout,sometimesthreeorfourtimesamonth.

[Анализ и лечение на грешки]

Aftertesting,thepowersystemofBuildingAhasbeenaging,theabsolutevoltageoftheneutralwireis30V,theabsolutevoltageofthelivewireis250V,andthemultimeterisusedtomeasurethevoltage.220V;UBtoBbuildingHUB,thetwoHUBshavetowithstanda30Vpotentialdifference,whichislikelytobedamaged.Thesolutionisverysimple,justconnectagroundwireintheswitchroomofBuildingA.

Weknowthatthereisonlyonephysicalsignaltransmissionchannelinaringnetwork,allofwhicharetransmittedthroughonetransmissionmedium.Inthisway,thereisacontradictionbetweeneachnodecompetingforthechannel,andthetransmissionefficiencyislow.Aftertheintroductionofthehub,anetworkconcentratingdevice,eachstationisconnectedtothehubwithitsowndedicatedtransmissionmedium.Thereisnolongeronlyonetransmissionchannelbetweeneachnode.Thesignalsentbackbyeachnodeisconcentratedthroughthehub,andthehubthentransmitsthesignalAfterbeingreshapedandamplified,itissenttoallnodessothatatleasttherewillbenocollisionsontheuplinkchannel.However,thehub-basednetworkisstillalocalareanetworkwithsharedmedia.The"sharing"hereisactuallytheinternalbusofthehub,sotherewillstillbesignalcollisionswhentheuplinkchannelandthedownlinkchannelsenddataatthesametime.Whenthehubdetectsacollisionfromitsinternalport,itgeneratesacollisionenhancementsignal(Jam)andtransmitsittothetargetportconnectedtothehub.Atthistime,alldatawillnotbeabletobesentsuccessfully,resultingina"bigtrafficjam"onthenetwork.

Theemergenceofthiskindofnetworkphenomenoncanbeillustratedbyavividreality,thatis,carscomingintwodirectionsonasinglelaneatthesametime.

Weknowthatasingle-lanelaneusuallyonlyallowscarsinonedirectiontopass,butinsmalltowns,thereareusuallynosuchregulationswhenconditionsarelimited,andasingle-lanelaneislikelytoallowcarsintwodirectionstopass.,Butitmustbeadifferenttime.Thesameistrueinthehub.Althoughtheconnectionbetweeneachnodeandthehubhasitsownindependentchannel,thereisonlyonecommonchannelinsidethehub.Uplinkanddownlinkdatamustbesentandreceivedthroughthissharedchannel.ThismaybelikeLikeasinglelane,trafficjamsmayoccurwhentherearedatatransmissionsontheupanddownchannelsatthesametime.Isiteasytounderstand?

Becauseoftheshortcomingsofthehub,itcannotbeusedinalargernetworkalone(usuallysharingasmallpartofthenetworkcommunicationloadwithswitchesandotherequipment),justlikeinthecenterofabigcityTherecannotbeasinglelane,becausethelargerthenetwork,thegreaterthechanceofnetworkcollision.Becauseofthis,thedatatransmissionefficiencyofthehubisrelativelylow,becauseitcanonlytransmitdatainonedirectionatthesametime,whichistheso-called"simple"method.Ifahubistobeusedasasinglehubdeviceinthenetwork,thenetworksizeshouldbelessthan10,andthehubbandwidthshouldbemorethan10/100Mbps.

Inadditiontotheshortcomingsofthehubsharingbandwidth,thereisanotheraspectthatmustbeconsideredwhenchoosingahub,andthatisitsbroadcastingmethod.Becausethehubisapurehardwarenetworkbottomdevice,basicallyitdoesnothavethe"intelligentmemory"ability,letalonethe"learning"ability.ItalsodoesnothavetheMACaddresstablethattheswitchhas,asshowninFigure2.

Thisbroadcastdatatransmissionmethodhastwoshortcomings:Inaddition,thesharedbandwidthmethodintroducedaboveismorelikelytocausenetworktrafficjamsandfurtherreducetheefficiencyofnetworkexecution.

Afterunderstandingtheworkingprincipleofthehub,let’stakealookattheinstallationandconnectionmethodofthehubinthelocalareanetwork.

Themostimportantthingaboutanaccessdeviceisitsinterfacetechnology.Differentinterfacesareusedindifferentapplicationenvironments,anddifferentapplicationscorrespondtocorrespondinginterfaces,notonlyhubs,butalsoswitchesthatwillbediscussedlater.,Routers,etc.arethesame.Theinterfaceofthehubisrelativelythesimplest.Inordertoenableyoutomasterthevariousapplicationconnectionsofthehub,itisnecessaryforustounderstandsomeofthemaininterfacesofthehub.

Hubsusuallyprovidethreetypesofports,namelyRJ-45ports,BNCports,andAUIports,whicharesuitableforconnectingdifferenttypesofcablestobuildnetworks.Somehigh-endhubsalsoprovidefiberportsandothertypesofports.

(1) RJ-45 интерфейс

TheRJ-45interfacecanbeusedtoconnecttotheRJ-45connector,whichissuitablefornetworksconstructedbytwistedpaircables.Thiskindofportisthemostcommon,Generallyspeaking,Ethernethubswillprovidethiskindofport.ThenumberofhubsweusuallytalkaboutreferstothenumberofRJ-45ports.AsshowninFigure3.

TheRJ-45portofthehubcanbedirectlyconnectedtoterminaldevicessuchascomputersandnetworkprinters,andcanalsobeconnectedtootherswitches,hubsandotherhubdevicesandrouters.Itshouldbenotedthatwhenconnectingtodifferentdevices,thejumpermethodofthetwistedpaircableusedisdifferent.Fordetails,pleaserefertotheintroductionofthenetworkcableproductionsectionintroducedabove.

(2)BNCпорт

TheBNCportistheinterfaceusedtoconnecttothethincoaxialcable.ItisgenerallyconnectedthroughaBNCT-typeconnector,asshowninFigure4.ItisaschematicdiagramoftheBNCportofahubconnectedthroughaBNCtypeconnector.

Most10Mbit/shubshaveaBNCport.WhenthehubhasbothBNCandRJ-45ports,itcanbeconnectedtoatwisted-pairnetworkthroughtheRJ-45portandathincablenetworkthroughaBNCinterface.Therefore,twistedpairandthincoaxialcablescanberealizedTheconnectionbetweentwonetworksthatusedifferentcommunicationtransmissionmedia.Thisdual-interfacefeaturecanbeusedtobecompatiblewiththeoriginalthincoaxialcablenetwork(10Base-2),andcanrealizethegradualtransitiontothemainstreamtwistedpairnetwork(10Base-T),andofcourse,itcanalsorealizethesameastheremoteTheconnectionbetweentheshaftcablenetwork(lessthan185meters),thefollowingfigure5showsaschematicdiagramofthenetworkconnectionoftwodifferenttransmissionmedianetworksthroughtheBNCinterfaceofthehubandthetwistedpairRJ-45interface.

Similarly,ifthedistancebetweenthetwonetworksisgreaterthan100meters,andtheconnectionbetweenthetwonetworkscannotberealizedbyusingtwisted-paircables,youcanalsousethethincoaxialcablethroughtheBNCportofthehubTransmissionconnectstwotransmissionnetworks,andbothnetworkscanstillusetwisted-pair,acheapandcommontransmissionmedium,asshowninFigure6.However,itshouldbenotedthatthedistancebetweenthesetwonetworksstillcannotbegreaterthan185m.

(3) AUI порт

TheAUIportcanbeusedtoconnecttheAUIconnectorofthethickcoaxialcable,sothisinterfaceisusedtoconnecttothethickcoaxialcablenetwork,itsschematicdiagramAsshowninFigure7,therearerelativelyfewhubswiththiskindofinterface,mainlyinsomebackbone-levelhubs.

Becauseofthehighcostofnetworksusingthickcoaxialcablesasthetransmissionmedium,andthedifficultyofwiring,itisveryrarethatthickcoaxialcablesareactuallyusedforwiringinpractice.However,sincethetransmissiondistancesupportedbyasinglesectionofthickcoaxialcable(10Base-5)isupto500meters,thickcoaxialcablecanbeusedasacommunicationcableforconnectionbetweenlonger-distancenetworks.Therefore,itcanalsobeusedasacheapremoteconnectionsolution.Fortheconnectiondiagram,refertoFigure6above.Theconnectionmediumusedhereisathickcoaxialcable.

Withtheaidofthetransceiver,theAUIportcanalsobeconnectedtotheRJ-45interface,BNCinterface,andevenopticalfiberinterface.Figure8belowshowsfromlefttoright:AUItoRJ-45transceiver(usedtoconnectAUIportandRJ-45interface),AUItoBNCtransceiver(usedtorealizeAUIportandBNCinterfaceConnection),AUItoSTtransceiver(usedtorealizetheconnectionbetweentheAUIportandtheopticalfiberinterface).Ofcourse,therearemanytypesofsuchtransceivers,suchasRJ-45toRS-232,RJ-45toBNCandsoon.Butdon’tunderestimatethislittlegadget.Guessitsprice.Ithinkinmostcases,youwilllookdownonit.Icouldn’tfigureoutthepricewhenIfirstboughtit,butIasked.Afteralotofhomes(reallyhardtofind),IrealizedthatIhadtoaccepttheprice.Generallyspeaking,thiskindofproductcostsabout130yuanforagenuineproduct.Isitoutofyourexpectation?Themainbrandsofthiskindofinterfacetransceiverare:D-Link,HP,etc.Thisproductactsasaninterfacetypeconversion(ofcourse,itisnotassimpleasacableconnection,whichneedstobecompletedthroughacertaincircuit),soitisusuallycalledan"adapter".

(4)Hubstackingport

Ofcourse,thiskindofportisonlyavailableforstackablehubs,anditsfunctionisjustlikeitsname,itisusedtoconnecttwoStackablehub.Generallyspeaking,astackablehubhastwoportswithsimilarappearance:oneismarkedas"UP"andtheotherismarkedas"DOWN".Whenconnecting,acableisusedtoconnectfromthe"UP"portofonehubtotheother.Onthe"DOWN"portofastackablehub,thereareall"female"headers,sothecableendsmustbe"male",butthiskindofcableisprovidedbythemanufacturerwhenyoupurchaseastackablehubIfitisdamagedorlost,youcanalsomakeonedirectlyinthecomputercity,aslongasyouexplainthepurposetothemerchant,theportdiagramisshowninFigure9below.

Theinstallationofthehubisrelativelysimple,especiallythefoolhub,aslongasitisfixedinthewiringcabinetandpluggedinthepowercord.Whichtwistedpairneedstobeconnected,justinserttheRJ-45headofwhichtwistedpairintothehubport.Althoughthesmarthubisfixedandreadyforuse,ifyouwanttorealizeremotemanagement,youmustperformthenecessaryconfigurationandspecifytheIPaddressinformationforthehub.Inaddition,rack-mountedhubsaregenerallyusedinsomelargenetworks,whichinvolvesrackinstallationofthehub.

Therearetwotypesofhubsintermsofstructure:racktypeanddesktoptype.Thehubusedingeneraldepartmentsisdesktoptype;enterprisecomputerroomsusuallyuseracktype.Rack-mountedhubsareeasytofixinafixedplace,usuallywithotherhubs,switches,andsomewithserversinacabinet.Thisisthesameforeasynetworkconnectionandmanagement,andalsosavesonequipmentThespaceoccupied.Ifyouchoosearack-mountedhubwhenpurchasing,youcanchooseahubrack(generallyprovidedbythemanufacturer).Let'stakealookattheinstallationofrackhubs.

Rack-typehubsaregenerallyinstalledincabinetstogetherwithotherequipment.Ofcourse,thesecabinetshavecorrespondingstructuralstandardsintheindustry,especiallyintermsofsize(suchaswidth,1U(unit)height,etc.),sothatalldevicescanbeinstalledtogetherconvenientlyandbeautifully.Thisiswhythehubisemptybutmustbemadethesamesize.Ofcourse,alargechassishasanotheradvantage.Thatisbetterheatdissipation.

Intermsofwidth,internationalstandardcabinetscanberoughlydividedintothreetypes:19inches,23inchesand24inches,whicharemainlydeterminedaccordingtotherequirementsofservercabinets.Dependingonthenumberofinstalleddevices,cabinetsofdifferentheightscanalsobeselected.Theheightofthecabinetisusually"U"astheunit."U"actuallymeans"Unit",whichmeans"oneunit"inChinese,and1U=1.75inches.Theinstallationofthiskindofcabinetisusuallycarriedoutmainlyinthefollowingsteps.

Стъпка 1: Фиксирайте монтажната скоба

Beforeinstallingthehubtothecabinet,youshouldinstallthefixingbracketonthespecifiedpositionofthehub(thisshouldbedoneaccordingtotheoperationmanual).Prepareforinstallingthehubontherackinthefuture.Differenthubshavebigdifferencesinthebracketsinstalled,buttheinstallationprinciplesarebasicallythesame.Figure10showsamountingbracketprovidedbytheCiscohub.

ThesizeofCisco'snetworkequipmentismostly19inches(because19inchesisthemostpopularcabinetstandardintheworld).Wheninstallinga19-inchnetworkdeviceintoa19-inchcabinet,howtofixthemountingbracketAsshowninFigure11.Whenthesizeofthecabinetis23or24inches,thenetworkequipmentneedstobeinstalledinthe23or24inchescabinet,andthefixingmethodofthemountingbracketisshowninFigure12.

Стъпка 2: Поправете устройството

Afterthemountingbracketisfixed,thenextthingtodoistoputthehubdevicewiththebracketinstalledinthecorrespondingpositionofthecabinetandfixitinthecabinetNS.Infact,thisinstallationmethodisveryeasy.Infact,itonlyneedstofixafewscrews.RefertoFigure13fortheinstallationmethod.

Стъпка 3: Поправете ръководството за кабела

Afterthehubisinstalledinthecabinet,itisnecessarytoconnectthenetworkcable.Generallyspeaking,thereareseveralnetworkdevicesonthegroundinacabinet.Inthisway,therearemanynetworkcablesconcentratedinthiscabinet.Ifthesecablesarenotclear,itwillbringgreatinconveniencetonetworkmanagement.Forthisreason,weneedtobundleandinstallthenetworkcables.Atthistime,itisgenerallynecessarytoinstallawireguideforthenetworkcable,sothatthebundlednetworkcablebecomesneatandbeautiful,andeasytomanage.TheinstallationmethodofthethreadguideisshowninFigure14.

Aboveweintroducedthemethodofinstallingrack-mountedhubsincabinets.Thisisgenerallysuitableforlargernetworks.Forsmalloffices,thereareusuallynocabinets,andthehubscanonlybeinstalledonthedesktoporonthewall.

Toinstallthehubonthedesktop,youcanfirstfixthemountingbracketonthedesktop.Thisinstallationmethodshouldpayattentiontotwodifferentinstallationdirections:oneisthehorizontalinstallationmethodthatallowsthehubtobeplacedhorizontally.Figure15showsthehorizontalfixingmethod;theotheristoplacethehubvertically,anditsbracketfixingmethodisshowninFigure16.

Therearealsotwowaystoinstallthehubonthewall:oneistofixthehubhorizontallyonthewall,youcanusetheinstallationmethodshowninFigure17;theotheristoinstallthehubWhenitisinstalledverticallyonthewall,itshouldbeinstalledasshowninFigure18.

Althoughtheconnectionofthehubissimpleandbasicallydoesnotrequireanyconfiguration,theunderstandingofitsconnectionprinciplecanmakebetteruseofthehubtomeettheneedsofsmallandmedium-sizednetworkapplications.Beforeformallyintroducingtheconnectionmethodofthehub,let'sfirstunderstandthesignalforwardingprincipleofthehub.

Авариен метод

Whenahubprovidesinsufficientports,therearegenerallythefollowingtwomethodstoexpandthenumberofusers.

(1) Подреждане

Stackingisawaytosolvetheproblemofinsufficientportsofasinglehub,butbecausemultiplehubsstackedtogetherstillworkinthesameenvironment,stackingThenumberoflayerscannotbetoomany.However,manyhubsonthemarkethavemorestackinglayersthanotherbrandsasasellingpoint.Ifyouencounterthissituation,youmusttreatthemdifferently:ontheonehand,themorestackablelayers,thehigherthestabilityofthehub;Ontheonehand,themorelayersthatcanbestacked,thesmallerthebandwidththateachusercanactuallyenjoy.

(2) Каскадна връзка

Cascadeconnectionisanotherwaytoincreasethenumberofusersinthenetwork,buttheuseofthisfunctionisgenerallyconditional,thatis,theHubmustProvideacascadableport.Thisportisoftenmarkedas"Uplink"or"MDI".UsethisporttocascadewithotherHubs.Ifnodedicatedportisprovidedandcascadingisnecessary,thetwistedpairconnectingthetwohubsmustbemiswiredduringproduction.

TheearlyHubisalow-endproductandcannotbemanaged.Withthedevelopmentoftechnology,somehubshaveintroducedthefunctionofaswitchintechnology,andthesimplemanagement(SNMP)ofthehubcanberealizedbyaddinganetworkmanagementmoduletofacilitatetheuse.ButitneedstobepointedoutthatalthoughthesameprovidessupportforSNMP,modulesofdifferentmanufacturerscannotbemixed,andthemodulesofdifferentproductsofthesamemanufacturerarealsodifferent.HubsthatprovideSNMPfunctionshavehigherprices.Forexample,D-Link'sDEl824non-intelligent24-port10Base-Tisabout1,000yuancheaperthantheDEl8241withanetworkmanagementmodule.

Ifthenetworksystemisrelativelysimple,thereisnointegratedwiringbetweenbuildings,andtherearefewerusersinthenetwork,suchasafamily,oneorseveraladjacentoffices,thereisnoneedtoconsidertheappearanceoftheHubsize.Butsometimesthisisnotthecase.Forexample,inordertofacilitatethecentralizedmanagementofmultipleHubs,youhavepurchasedacabinetbeforepurchasingtheHub.Atthistime,youmustconsideritsdimensionswhenpurchasingtheHub,otherwisetheHubcannotbeinstalledintherack.superior.Thecabinetsonthemarketgenerallyfollowthe19-inchindustrialspecificationwhendesigning,anditcaninstallmostofthe5-port,8-port,16-portand24-portHubs.However,inordertopreventaccidents,youmustpayattentiontowhetheritmeetsthe19-inchworkingspecificationwhenpurchasing,sothatitcanbemanagedsafelyandcentrallyinthecabinet.

Likenetworkcards,theHubsonthemarketarebasicallydominatedbyAmericanbrandsandTaiwanesebrands,andseveralmainlandcompanieshavealsolaunchedhubproducts.Amongthem,high-endHubsaremainlyoccupiedbyAmericanbrands,suchas3COM,Intel,Bay,etc.Theyareuniqueindesign,usuallyseveralorevenoneprocessorperport,ofcourse,thepriceisalsohigher.D-LinkandAcctoninmycountry'sTaiwanregionaccountedforthemainshareofthelow-endHub.MainlandcompaniessuchasLenovo,Shida,TPLinkandothercompanieshavelaunchedtheirownproductstothemarketwithstrongstrength.Thesemiddleandlow-endproductsallusesingle-processortechnology,andthedesignideasoftheirperipheralcircuitsaresimilar.Theweldingprocessmethodstorealizetheseideasarebasicallythesame,andthepricesaresimilar.Mainlandproductsarerelativelycheaperandareincreasinglyoccupyingalargermarketshare.Withtheever-decreasingpriceofswitchproducts,themarketforhubsisshrinking.However,oncertainoccasions,hubscanbringhigherefficiencywithlowerinvestmentduetotheirlowlatency.Theswitchcannotcompletelyreplacethehub.