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.
Paikallisten verkkojen näkökulmasta verkkokeskittimet voidaan jakaa viiteen tyyppiin: yhden relesegmentin keskittimet, usean segmentin keskittimet, porttikytkentäkeskittimet, verkkojen yhteenliittämiskeskittimet ja kytkentäkeskittimet.