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Network hub



Introduction

Itiswidelyusedinvariousoccasions.Thehubworksinalocalareanetwork(LAN)environment,likeanetworkcard,appliedtothefirstlayeroftheOSIreferencemodel,soitisalsocalledaphysicallayerdevice.Thehubuseselectricalinterconnection.WhentheLANmaintenanceenvironmentisalogicalbusorringstructure,thehubcanbeusedtoestablishaphysicalstarortreenetworkstructure.Inthisrespect,thehubfunctionsasamulti-portrepeater.Infact,ahubisactuallyakindofrepeater.Thedifferenceisonlythatthehubcanprovidemoreportservices,sothehubisalsocalledamulti-portrepeater.

Details

Themainfunctionofthenetworkhubistoregenerate,reshape,andamplifythereceivedsignaltoexpandthetransmissiondistanceofthenetwork,whileconcentratingallnodesonitasthecenterNode.ItworksonthefirstlayeroftheOSI(OpenSystemInterconnectionReferenceModel)referencemodel,the"physicallayer".Thehubisthesameasthetransmissionmediumsuchasnetworkcardandnetworkcable,whichbelongstothebasicequipmentinthelocalareanetworkandadoptsCSMA/CD(adetectionprotocol)accessmethod.

Thenetworkhubisapurehardwarenetworkbottomdevice,andbasicallydoesnothavethe"intelligentmemory"and"learning"capabilitiessimilartoswitches.ItalsodoesnothavetheMACaddresstablethattheswitchhas,soitisnottargetedwhensendingdata,butissentbybroadcast.Thatistosay,whenitwantstosenddatatoanode,itdoesnotdirectlysendthedatatothedestinationnode,butsendsthedatapackettoallnodesconnectedtothehub.

NetworkhubscanbedividedintopassiveHUB,activeHUB,andsmartHUBaccordingtothewaytheinputsignalisprocessed.PassiveHUB:Itisthemostinferiorone,doesnotdoanyprocessingtothesignal,doesnotextendthetransmissiondistanceofthemedium,andhasacertaininfluenceonthesignal.EachcomputerconnectedtothiskindofHUBcanreceivesignalsfromallothercomputersonthesameHUBhub;

ActiveHUB:ThedifferencebetweenanactiveHUBandapassiveHUBliesinitItcanamplifyorregeneratethesignal,sothatitextendstheeffectivetransmissiondistancebetweentwohosts;

SmartHUB:InadditiontoallthefunctionsofanactiveHUB,thesmartHUBalsohasnetworkmanagementandroutingfunctions..InthesmartHUBnetwork,noteverymachinecanreceivethesignal,onlythecomputerwiththesameaddressasthesignaldestinationaddresscanreceiveit.SomesmartHUBscanchoosethebestpathbythemselves,whichhasagoodmanagementofthenetwork.

Accordingtothestructureandfunctionclassification,HUBhubscanbedividedintothreetypes:unmanagedhubs,stackedhubsandchassishubs.

Fromtheperspectiveoflocalareanetworks,networkhubscanbedividedintofivetypes:single-relaysegmenthubs,multi-segmenthubs,portswitchinghubs,networkinterconnectionhubs,andswitchinghubs.

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