Networking Terms Glossary _ Definitions of Network Technology

5/3/2015 NetworkingTermsGlossary|DefinitionsofNetworkTechnology
http://www.wildpackets.com/resources/compendium/glossary_of_networking_terms/printable 1/64
GlossaryofNetworkingTermsA|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|XZ
10Base2
10MbpsbasebandEthernetspecificationusing50ohmthincoaxialcable.10Base2,whichispartoftheIEEE802.3specification,hasadistancelimitof185meterspersegment.
10Base5
10MbpsbasebandEthernetspecificationusingstandard(thick)50ohmbasebandcoaxialcable.10Base5,whichispartoftheIEEE802.3basebandphysicallayerspecification,hasadistancelimitof500meterspersegment.
10BaseF
10MbpsbasebandEthernetspecificationthatreferstothe10BaseFB,10BaseFL,and10BaseFPstandardsforEthernetoverfiberopticcabling.
10BaseFB
10MbpsbasebandEthernetspecificationusingfiberopticcabling.10BaseFBispartoftheIEEE10BaseFspecification.Itisnotusedtoconnectuserstations,butinsteadprovidesasynchronoussignalingbackbonethatallowsadditionalsegmentsandrepeaterstobeconnectedtothenetwork.10BaseFBsegmentscanbeupto2,000meterslong.
10BaseFL
10MbpsbasebandEthernetspecificationusingfiberopticcabling.10BaseFLispartoftheIEEE10BaseFspecificationand,whileabletointeroperatewithFOIRL,isdesignedtoreplacetheFOIRLspecification.10BaseFLsegmentscanbeupto1,000meterslongifusedwithFOIRL,andupto2,000metersif10BaseFLisusedexclusively.
10BaseFP
10MbpsfiberpassivebasebandEthernetspecificationusingfiberopticcabling.10BaseFPispartoftheIEEE10BaseFspecification.Itorganizesanumberofcomputersintoastartopologywithouttheuseofrepeaters.10BaseFPsegmentscanbeupto500meterslong.
10BaseT
AspecificationoftheIEEE802.3committeefortheimplementationof10MbitEthernetonunshieldedtwistedpairwiring.
10Broad36
10MbpsbroadbandEthernetspecificationusingbroadbandcoaxialcable.10Broad36,whichispartoftheIEEE802.3specification,hasadistancelimitof3,600meterspersegment.
100BaseFX
100MbpsbasebandFastEthernetspecificationusingtwostrandsofmultimodefiberopticcableperlink.Toguaranteepropersignaltiming,a100BaseFXlinkexceed400metersinlength.BasedontheIEEE802.3standard.
100BaseT
A100MBEthernetspecificationusingLevel5UTP.
100BaseT4
100MbpsbasebandFastEthernetspecificationusingfourpairsofCategory3,4,or5UTPwiring.Toguaranteepropersignaltiming,a100BaseT4segmentcannotexceed100metersinlength.BasedontheIEEE802.3standard.
100BaseTX
100MbpsbasebandFastEthernetspecificationusingtwopairsofeitherUTPorSTPwiring.Thefirstpairofwiresisusedtoreceivedata,thesecondisusedtotransmit.Toguaranteepropersignaltiminga100BaseTXsegmentcannotexceed100metersinlength.BasedontheIEEE802.3standard.
100BaseX
100MbpsbasebandFastEthernetspecificationthatreferstothe100BaseFXand100BaseTXstandardsforFastEthernetoverfiberopticcabling.BasedontheIEEE802.3standard.
100VGAnyLAN
100MbpsFastEthernetandTokenRingmediatechnologyusingfourpairsofCategory3,4,or5UTPcabling.Thishighspeedtransporttechnology,developedbyHewlettPackard,canbemadetooperateonexisting10BaseTEthernetnetworks.BasedontheIEEE802.12standard.
4B/5Blocalfiber
4byte/5byteloc100Mbpsovermultimodefiber.SeealsoTAXI4B/5B.
08/10Blocalfiber
8byte/10bytelocalfiber.Fiberchannelphysicalmediathatsupportsspeedsupto149.76Mbpsovermultimodefiber.
A&Bbitsignaling
ProcedureusedinT1transmissionfacilitiesinwhicheachofthe24T1subchannelsdevotesonebitofeverysixthframetothecarryingofsupervisorysignalinginformation.Alsocalled24thchannelsignaling.
Home>Resources>NetworkingGlossary>

AAL
ATMadaptationlayer.Servicedependentsublayerofthedatalinklayer.TheAALacceptsdatafromdifferentapplicationsandpresentsittotheATMlayerintheformof48byteATMpayloadsegments.AALsconsistoftwosublayers,CSandSAR,AALsdifferonthebasisofthesourcedestinationtimingused,whethertheyuseDBRorVBR,andwhethertheyareusedforconnectionorientedorconnectionlessmodedatatransfer.Atpresent,thefourtypesofAALrecommendedbytheITUTareAAL1,AAL2,AAL3/4,andAAL5.
AAL1
ATMadaptationlayer1.OneoffourAALsrecommendedbytheITUT.AAL1isusedforconnectionoriented,delaysensitiveservicesrequiringconstantbitrates,suchasuncompressedvideoandotherisochronoustraffic.
AAL2
ATMadaptationlayer2.OneoffourAALsrecommendedbytheITUT.AAL2isusedforconnectionorientedservicesthatsupportavariablebitrate,suchassomeisochronousvideoandvoicetraffic.
AAL3/4
ATMadaptationlayer3/4.OneoffourAALs(mergerfromtwoinitiallydistinctadaptationlayers)recommendedbytheITUT.AAL3/4supportsbothconnectionlessandconnectionorientedlinks,butisprimarilyusedforthetransmissionofSMDSpacketsoverATMnetworks.
AAL5
ATMadaptationlayer5.OneoffourAALsrecommendedbytheITUT.AAL5supportsconnectionoriented,VBRservices,andisusedpredominantlyforthetransferofclassicIPoverATMandLANEtraffic.AAL5usesSEALandistheleastcomplexofthecurrentAALrecommendations.Itofferslowbandwidthoverheadandsimplerprocessingrequirementsinexchangeforreducedbandwidthcapacityanderrorrecoverycapability.
AARP
AppleTalkAddressResolutionProtocol.ProtocolintheAppleTalkprotocolstackthatmapsadatalinkaddresstoanetworkaddress.
AARPprobepackets
PacketstransmittedbyAARPthatdeterminewhetherarandomlyselectednodeIDisbeingusedbyanothernodeinanonextendedAppleTalknetwork.IfthenodeIDisnotbeingused,thesendingnodeusesthatnodeID.IfthenodeIDisbeingused,thesendingnodechoosesadifferentIDandsendsmoreAARPprobepackets.
ABM
AsynchronousBalancedMode.AnHDLC(andderivativeprotocol)communicationmodesupportingpeeroriented,pointtopointcommunicationsbetweentwostations,whereeitherstationcaninitiatetransmission.
ABR
1.availablebitrate.QOSclassdefinedbytheATMForumforATMnetworks.ABRisusedforconnectionsthatdonotrequiretimingrelationshipsbetweensourceanddestination.ABRprovidesnoguaranteesintermsofcelllossordelays,providingonlybesteffortservice.Trafficsourcesadjusttheirtransmissionrateinresponsetoinformationtheyreceivedescribingthestatueofthenetworkanditscapabilitytosuccessfullydeliverdata.ComparewithCBR,UBR,andVBR.2.areaborderrouter.RouterlocatedontheborderofoneormoreOSPFareasthatconnectsthoseareastothebackbonenetwork.ABRsareconsideredmembersofboththeOSPFbackboneandtheattachedareas.Theythereforemaintainroutingtablesdescribingboththebackbonetopologyandthetopologyoftheotherareas.
AC
AlternatingCurrent.Anelectricalpowertransmissionsysteminwhichthedirectionofcurrentflowalternatesonaperiodicbasis.
Accelerator
Ahardwareadditiontoanexistingcomputingdevicethatincreasesthecomputer'sprocessingspeedandcapabilities.
Access
Referringtotheabilityofacomputingdevicetousedataorresourcesbeyonditsnativecapabilities.
AccessList
Listkeptbyrouterstocontrolaccesstoorfromtherouterforanumberofservices.Forexample,thelistcanpreventpacketswithacertainIPaddressfromleavingaparticularinterfaceontherouter.
AccessMethod
ThetypeofMediaAccessControlmethodthatanodeusestogaincontrolofanetwork.
Accounting
OneoffivecategoriesofnetworkmanagementdefinedbyISOfor
Management
managementofOSInetworks.Accountingmanagementsubsystemsareresponsibleforcollectingnetworkdatarelatingtoresourceusage.Seealsoconfigurationmanagement,faultmanagement,performancemanagement,andsecuritymanagement.
Accuracy
Referringtohowcloselyatestinstrument'smeasurementscomparetoastandardvalue,usuallyexpressedasapercentageofthevaluemeasured.
ACF
AdvancedCommunicationsFunction.AgroupofSNAproductsthatprovidesdistributedprocessingandresourcesharing.

ACF/NCP
AdvancedCommunicationsFunction/NetworkControlProgram.TheprimarySNANCP.ACF/NCPresidesinthecommunicationscontrollerandinterfaceswiththeSNAaccessmethodinthehostprocessortocontrolnetworkcommunications.
Acknowledgment
Notificationsentfromonenetworkdevicetoanothertoacknowledgethatsomeevent(forexample,receiptofamessage)hasoccurred.SometimesabbreviatedACK.
ACR
Allowscellrate.ParameterdefinedbytheATMForumforATMtrafficmanagement.ACRvariesbetweentheMCRandthePCR,andisdynamicallycontrolledusingcongestioncontrolmechanisms.
ACSE
Associationcontrolserviceelement.AnOSIconventionusedtoestablish,maintainorterminateaconnectionbetweentwoapplications.
ActiveHub
MultiporteddevicethatamplifiesLANtransmissionsignals.
ActiveMonitor
DeviceresponsibleformanagingaTokenRing.AnetworknodeisselectedtobetheactivemonitorifithasthehighestMACaddressonthering.Theactivemonitorisresponsibleformanagementtaskssuchasensuringthattokensarenotlostorthatframesdonotcirculateindefinitely.
Adapter
Hardwarethatallowsacomputingdevicephysicalaccesstoanetwork.
AdaptiveRouting
Seedynamicrouting.
ADCCP
AdvancedDataCommunicationsControlProtocol.
Address
Anumericaldesignationthatuniquelyreferstoaspecificcommunicationentity.
AddressedCall
Modethatpermitscontrolsignalsandcommandsto
Mode
establishandterminatecallsinV.25bis.
AddressMapping
Techniquethatallowsdifferentprotocolstointeroperatebytranslatingaddressesfromoneformattoanother.Forexample,whenroutingIPoverX.25,theIPaddressesmustbemappedtotheX.25addressessothattheIPpacketscanbetransmittedbytheX.25network.Seealsoaddressresolution.
AddressMask
Bitcombinationusedtodescribewhichportionofanaddressreferstothenetworkorsubnetandwhichpartreferstothehost.Sometimesreferredtosimplyasmask.alsosubnetmask.
AddressResolution
Whentwoaddressingsystemsrefertothesameentity,theprocessoftranslatingorexpressingtheaddressofanentityononesystemtotheequivalentaddressofthesameentityinthesecondsystem.Forinstance,translatinganIPaddresstoitsgivenDNSname.
AddressResolution
SeeARP
Protocol
AddressSpace
Therangeofpossibleuniqueaddressesallowedbyanaddressingscheme.
Adjacency
Relationshipformedbetweenselectedneighboringroutersandendnodesfortheproposeofexchangingroutinginformation.Adjacencyisbasedupontheuseofacommonmediasegment.
AdjacentNodes
1.InSNA,nodesthatareconnectedtoagivennodewithnointerveningnodes.2.InDECnetandOSI,nodesthatshareacommonnetworksegment(inEthernet,FDDI,orTokenRingnetworks).
AdministrativeDistance
Arateofthetrustworthinessofaroutinginformationsource.Thehigherthevalue,thelowerthetrustworthinessrating.
AdmissionControl

Seetrafficpolicing.
ADPCM
Adaptivedifferentialpulsecodemodulation.Processbywhichanalogvoicesamplesareencodedintohighqualitydigitalsignals.
ADSU
ATMDSU.TerminaladapterusedtoaccessanATMnetworkviaanHSSIcompatibledevice.SeealsoDSU.
Advertising
Routerprocessinwhichroutingorserviceupdatesaresentatspecifiedintervalssothatotherroutersonthenetworkcanmaintainlistsofusableroutes.
AEP
AppleTalkEchoProtocol.UsedtotestconnectivitybetweentwoAppleTalknodes.Onenodesendsapackettoanothernodeandreceivesaduplicate,orecho,ofthatpacket.
AFP
AppleTalkFilingProtocol.TheAppleproprietaryspecificationforanetworkfilesystem.
Agent
1.Anactiveprocessinacomputerthatisresponsibleforacertaintypeofactivitywhendemandedbyanoutsideentity.2.InSNMP,theactiveprocessinacomputingdevicethatisresponsiblefordeterminingtheparametersdefinedintheMIB(ManagementInformationBase)andreportingthemondemandtoaConsole.
AIS
Alarmindicationsignal.InaT1transmission,anallonessignaltransmittedinlieuofthenormalsignaltomaintaintransmissioncontinuityandtoindicatetothereceivingterminalthatthereisatransmissionfaultthatislocatedeitherat,orupstreamfrom,thetransmittingterminal.
AIX
IBM'simplementationofUnix.
Alarm
Messagenotifyinganoperatororadministratorofanetworkproblem.Seealsoeventandtrap.
AlarmIndicationSignal
SeeAIS.
Alaw
TheITUTcompandingstandardusedintheconversionbetweenanaloganddigitalsignalsinPCMsystems.AlawisusedprimarilyinEuropeantelephonenetworksandissimilartotheNorthAmericanmulawstandard.Seealsocompandingandmulaw.
Algorithm
Asetofrulesanddecisionstructuresforactionsinaspecificallydefinedsetofcircumstances.
Alias
Afilewhosesolepurposeistorepresentanotherfile.
AlignmentError
InIEEE802.3networks,anerrorthatoccurswhenthetotalnumberofbitsofareceivedframeisnotdivisiblebyeight.Alignmenterrorsareusuallycausedbyframedamageduetocollisions.
AllringsExplorerPacket
Seeallroutesexplorerpacket.
AllroutesExplorerExplorerPacket
packetthattraversesanentireSRBnetwork,followingallpossiblepathstoaspecificdestination.Sometimescalledallringsexplorerpacket,Seealsoexplorerpacket,localexplorerpacket,andspanningexplorerpacket.
ALOE
Archaic.AppleTalkLowOverheadEncapsulation.AvendordevelopedalternativetoAURP,ALOEprovidesamechanismtotunnelAppleTalkprotocolsinsideIPpackets,typicallyinWANlinks.
Alphanumeric
Referringtoagroupofprintablecharactersthatincludesthelettersofthealphabetinbothupperandlowercase,thenumeralsplusalimitedgroupofadditionalsymbolsandpunctuationmarks.
AM
AmplitudeModulation.Modulationtechniquewherebyinformationisconveyedthroughtheamplitudeofthecarriersignal.ComparewithFMandPAM.Seealsomodulation.
Ambient
Referringtoasetofconditionsthatexistindependentlyofthesystemofinterest.
AMI

Alternatemarkinversion.LinecodetypeusedonT1andE1circuits.InAMI,zerosarerepresentedby01duringeachbitcell,andonesarerepresentedby11or00,alternately,duringeachbitcell.AMIrequiresthatthesendingdevicemaintainonesdensity.Onesdensityisnotmaintainedindependentofthedatastream.Sometimescalledbinarycodedalternatemarkinversion.Seealsoonesdensity.
Amp
Ampere.Astandardunitofmeasurementforelectricalcurrentflow.
Amplitude
Intheterminologyofwavemotion,theheightofthewave.Amplitudeisusuallymeasuredfromareferencepointof0.Inelectricalwaves,amplitudeistypicallyexpressedinvolts.
Analog
Referringtoasystemorcomponentthatusesasystemofmeasurement,responseorstorageinwhichvaluesareexpressedasamagnitudeusingacontinuousscaleofmeasurement.
AnalogTransmission
Signaltransmissionoverwiresorthroughtheairinwhichinformationisconveyedthroughvariationofsomecombinationofsignalamplitude,frequency,andphase.
Anomaly
Anunusualinstanceorcircumstance.
ANSI
AmericanNationalStandardsInstitute.TheprinciplegroupintheUS.fordefiningstandards.
AOCE
AppleOpenCollaborationEnvironment.Asystemofhigherlevelprotocolsusedforthetransmissionofdataandauthenticationbetweenapplications.
APaRT
Automatedpacketrecognition/translation.TechnologythatallowsaservertobeattachedtoCDDIorFDDIwithoutrequiringthereconfigurationofapplicationsornetworkprotocols.APaRTrecognizesspecificdatalinklayerencapsulationpackettypesand,whenthesepackettypesaretransferredfromonemediumtoanother,translatesthemintothenativeformatofthedestinationdevice.
API
ApplicationProgrammingInterface.Asetoftoolsandproceduresprovidedbytheprogrammerofanapplicationsothatotherprogrammerscancontrol,exchangedatawith,orextendthefunctionalityofanapplication.
ApolloDomain
ProprietarynetworkprotocolsuitedevelopedbyApolloComputerforcommunicationonproprietaryApollonetworks.
APPC
AdvancedProgramtoProgramCommunication.IBMSNAsystemsoftwarethatallowshighspeedcommunicationbetweenprogramsondifferentcomputersinadistributedcomputingenvironment.APPCestablishesandtearsdownconnectionsbetweencommunicatingprograms,andconsistsoftwointerfaces,aprogramminginterfaceandadataexchangeinterface.Theformerrepliestorequestsfromprogramsrequiringcommunicationthelatterestablishessessionsbetweenprograms.APPCrunsonLU6.2devices.SeealsoLU6.2.
AppleEvent
Apple'sprimarymechanismforinterprocesscommunication.
AppleScript
AprogramminglanguagethatcancalltaskswithinMacintoshapplications.
AppleShare
AnapplicationpublishedbyApplethatallowsaMacintoshtobeafileserverusingtheAFPprotocol.
AppleTalk
1.Apple'sproprietarynetworkarchitecture.2.Theprotocols,applications,networksandservicesincludedinApple'snetworkarchitecture.
Application
Anindependentlyexecutablesetofalgorithmsanddatastructuresthatperformaspecificsetoffunctions.
ApplicationLayer
Layer7oftheOSIreferencemodel.Thislayerprovidesservicestoapplicationprocesses(suchaselectronicmail,filetransfer,andterminalemulation)thatareoutsideoftheOSImodel.Theapplicationlayeridentifiesandestablishestheavailabilityofintendedcommunicationpartners(andtheresourcesrequiredtoconnectwiththem),synchronizescooperatingapplications,andagreementonproceduresforerrorrecoveryandcontrolofdataintegrity.CorrespondsroughlywiththetransactionserviceslayerintheSNAmodel.Seealsodatalinklayer,networklayer,physicallayer,presentationlayer,sessionlayer,andtransportlayer.
APPN
AdvancedPeertoPeerNetworking.EnhancementtotheoriginalIBMSNAarchitecture.APPNhandlessessionestablishmentbetweenpeernodes,dynamictransparentroutecalculation,andtrafficprioritizationforAPPCtraffic.ComparewithAPPN+.SeealsoAPPC.

APPN+
NextgenerationAPPNthatreplacesthelabelswappingroutingalgorithmwithsourcerouting.Alsocalledhighperformancerouting.SeealsoAPPN.
ARA
AppleTalkRemoteAccess.ProtocolthatprovidesMacintoshusersdirectaccesstoinformationandresourcesataremoteAppleTalksite.
Architecture
Thesumtotalofallofthespecifications,protocolsandimplementationsthatdefineaparticularnetworkingsystem.
Archive
Astorageofinfrequentlyusedorhistoricaldata.
ARCnet
AttachedResourceComputerNetwork.A2.5MbpstokenbusLANdevelopedinthelate1970sandearly1980sbyDatapointCorporation.
Area
Logicalsetofnetworksegments(eitherCLNS,DECnet,OSPFbased)andtheirattacheddevices.Areasareusuallyconnectedtootherareasviarouters,makingupasingleautonomoussystem.Seealsoautonomoussystem.
ARM
Asynchronousresponsemode,HDLCcommunicationmodeinvolvingoneprimarystationandatleastonesecondarystation,whereeithertheprimaryoroneofthesecondarystationscaninitiatetransmissions.Seealsoprimarystationandsecondarystation.
ARP
AddressResolutionProtocol.TheprotocolformappingIPaddressestophysicaladdressessuchasEthernetorTokenRing.
ARPA
AdvancedResearchProjectsAgency,ResearchanddevelopmentorganizationthatispartofDoD.ARPAisresponsiblefornumeroustechnologicaladvancesincommunicationsandnetworking.ARPAevolvedinDARPA,andthenbackintoARPAagain(in1994).SeealsoDARPA.
ARPANET
AdvancedResearchProjectsAgencyNetwork.Landmarkpacketswitchingnetworkestablishedin1969.ARPANETwasdevelopedinthe1970sbyBBNandfundedbyARPA(andlaterDARPA).IteventuallyevolvedintotheInternet.ThetermARPANETwasofficiallyretiredin1990.
ARQ
Automaticrepeatrequest.Communicationtechniqueinwhichthereceivingdevicedetectserrorsandrequestsretransmission.
AS
Seeautonomoussystem.
ASBR
Autonomoussystemboundaryrouter.ABRlocatedbetweenanOSPFautonomoussystemandanonOSPFnetwork.ASBRsrunbothOSPFandanotherroutingprotocol,suchasRIP,ASBRsmustresideonanonstubOSPFarea.
ASCII
Referringtoastandard7bitcharactersystemthatincludesthealphanumericcharactersandprintercontrolcodes.
ASDSP
AppleTalkSecureDataStreamProtocol.AnencryptedversionofADSPusedbyAOCE.
ASIC
ApplicationSpecificIntegratedCircuit.Acustomchipforaspecificapplication.
ASLM
AppleSharedLibraryManager.
ASN.1
AbstractSyntaxNotationOne.InSNMP,thelanguageusedtodescribedatamanagedbytheMIB.
AssociativeMemory
Memorythatisaccessedbasedonitscontents,notonitsmemoryaddress.Sometimescalledcontentaddressablememory(CAM).
AST
Automaticspanningtree.FunctionthatsupportstheautomaticresolutionofspanningtreesinSRBnetworks,providingasinglepathforspanningexplorerframestotraversefromagivennodeinthenetworktoanother.ASTisbasedontheIEEE802.1standard.
ASTA
AdvancedSoftwareTechnologyandAlgorithms.ComponentoftheHPCCprogramintendedtodevelopsoftwareand

algorithmsforimplementationonhighperformancecomputerandcommunicationssystems.SeealsoHPCC.
Asymmetry
Innetworking,asysteminwhichtherelationshipbetweentwoentitiesisinherentlyunequal,witheachentityrestrictedtoasetofoperationsandprerogativesdefinedbyitsroleintherelationship.
Asynchronous
Asystemofcommunicationinwhicheachdiscreetdeliveryofinformationestablishesitsowntimingimpulseratherthanhavingtoconformtothetimingimpulseofpreviousdeliveries.
Asynchronous
Termdescribingdigitalsignalsthataretransmittedwithoutpreciseclocking.Suchsignalsgenerallyhavedifferentfrequenciesandphaserelationships.Asynchronoustransmissionsusuallyencapsulateindividualcharactersincontrolbits(calledstartandstopbits)thatdesignatethebeginningandendofeachcharacter.ComparewithIsochronoustransmission,plesiochronoustransmission,andsynchronoustransmission.
ATcommandsTransmission
Asetofcommandsthatcontrolamodemoralteritscharacteristics.
ATDM
Asynchronoustimedivisionmultiplexing.MethodofsendinginformationthatresemblesnormalTDM,exceptthattimeslotsareallocatedasneededratherthanpreassignedtospecifictransmitters.ComparewithFDM,Statisticalmultiplexing,andTDM.
ATM
AsynchronousTransferMode.Abroadbandtransmissionsystemusing53octetpacketsoveracellswitchednetworkatspeedsupto2.2GBPS.
ATP
AppleTalkTransactionProtocol.Transportlevelprotocolthatallowsreliablerequestresponseexchangesbetweentwosocketclients.
Attenuation
Alossintheamplitudeorstrengthofasignalduetoaninteractionwiththesignal'smedia.Generallyexpressedindecibels.
Attribute
Configurationdatathatdefinesthecharacteristicsofdatabaseobjectssuchasthechassis,cards,ports,orvirtualcircuitsofaparticulardevice.Attributesmightbepresetoruserconfigurable.OnaLightStream2020ATMswitch,attributesaresetusingtheconfigurationprogramorCLIcommands.
AUI
Attachmentunitinterface.IEEE802.3interfacebetweenanMAUandaNIC(networkinterfacecard).Alsocalledtransceivercable.
AURP
AppleTalkUpdateBasedRoutingProtocol.Apple'sWANprotocol.
AURPTunnel
ConnectioncreatedinanAURPWANthatfunctionsasasingle,virtualdatalinkbetweenAppleTalkinternetworksphysicallyseparatedbyaforeignnetwork(aTCP/IPnetwork,forexample).
AuthorityZone
AssociatedwithDNS,anauthorityzoneisasectionofthedomainnametreeforwhichonenameserveristheauthority.
AutomaticCallReconnect
Featurepermittingautomaticcallreroutingawayfromafailedtrunkline.
AutonomousConfederation
Groupofautonomoussystemsthatrelyontheirownnetworkreachabilityandroutinginformationmorethantheyrelyonthatreceivedfromotherautonomoussystemsorconfederations.
AutonomousSystem
Collectionofnetworksunderacommonadministrationsharingacommonroutingstrategy.Autonomoussystemsaresubdividedbyareas.Anautonomoussystemmustbeassignedaunique16bitnumberbytheIANA.SometimesabbreviatedAS.
Autoreconfiguration
ProcessperformedbynodeswithinthefailuredomainofaTokenRingnetwork.Nodesautomaticallyperformdiagnosticsinanattempttoreconfigurethenetworkaroundthefailedareas.
AverageRate
Theaveragerate,inkilobitspersecond(kbps),atwhichagivenvirtualcircuitwilltransmit.
B8ZS
Binary8zerosubstitution.Linecodetype,usedonT1andE1circuits,inwhichaspecialcodeissubstitutedwhenever8consecutivezerosaresentthroughthelink.Thiscodeistheninterpretedattheremoteendoftheconnection.Thistechniqueguaranteesonesdensityindependentofthedatastream.Sometimescalledbipolar8zerosubstitution.ComparewithAMI.Seealsoonesdensity.

BackEnd
Nodeorsoftwareprogramthatprovidesservicestoafrontend.Seealsoclient,frontend,andserver.
BackEndProcessor
Acomputerrunninganapplicationthatsuppliesdatatoothercomputersondemand,buthasnouserinterface.
BackPressure
Propagationofnetworkcongestioninformationupstreamthroughaninternetwork.
Backbone
Referringtotheinternet,acentralnetworkthatprovidesapathwayforothernetworkstocommunicate.
BackgroundTask
Acomputingtaskthatisexecutingwhileanothertaskorapplicationisdisplayingitsuserinterface.
Backoff
The(usuallyrandom)retransmissiondelayenforcedbycontentiousMACprotocolsafteranetworknodewithdatatotransmitdeterminesthatthephysicalmediumisalreadyinuse.
Backplane
Thecommunicationchannelsofasingledevice'sarchitecture,suchasinahuborconcentrator.
Backup
Acopyofasetoffilesmadeforreplacementpurposesincasetheoriginalsetisdamagedorlost.
BackwardCompatible
Anupgradedcomponentofacomputingsystemthatcanbeusedinterchangeablywithitspreviousversion.
BackwardLearning
Algorithmicprocessusedforroutingtrafficthatsurmisesinformationbyassumingsymmetricalnetworkconditions.Forexample,ifnodeAreceivesapacketfromnodeBthroughintermediatenodeC,thebackwardlearningroutingalgorithmwillassumethatAcanoptimallyreachBthroughC.
BalancedConfiguration
InHDLC,apointtopointnetworkconfigurationwithtwocombinedstations.
Balun
Balanced/Unbalanced.Adevicethatlinkstogetherdissimilarwiretypesandattemptstominimizeanynegativeeffectstothesignalthatwouldnormallyresultfromthedissimilarity.
Band
Inanalogcommunications,therangeoffrequenciesoverwhichacommunicationsystemoperates.
Bandwidth
Inanalogcommunications,thedifferencebetweenthehighestandlowestfrequenciesavailableintheband.Indigitalcommunications,bandwidthislooselyusedtorefertotheinformationcarryingcapacityofanetworkorcomponentofanetwork.
BandwidthAllocation
SeeBandwidthreservation.
BandwidthReservation
Processofassigningbandwidthtousersandapplicationsservedbyanetwork.Involvesassigningprioritytodifferentflowsoftrafficbasedonhowcriticalanddelaysensitivetheyare.Thismakesthebestuseofavailablebandwidth,andifthenetworkbecomescongested,lowerprioritytrafficcanbedropped.Sometimescalledbandwidthallocation.Seealsocallpriority.
BARRNet
BayAreaRegionalResearchNetwork.RegionalnetworkservingtheSanFranciscoBayArea.TheBARRNetbackboneiscomposedoffourUniversityofCaliforniacampuses(Berkeley,Davis,SantaCruz,andSanFrancisco),StanfordUniversity,LawrenceLivermoreNationalLaboratory,andNASAAmesResearchCenter.BARRNETisnowpartofBBNPlanet.
Baseaddress
Thelowestaddressavailableinanaddressrange.
Baseband
Acommunicationsysteminwhichonlyonesignaliscarriedatanyonetime.
Baud
Unitofsignalingspeedequaltothenumberofdiscretesignalelementstransmittedpersecond.Baudissynonymouswithbitspersecond(bps),ifeachsignalelementrepresentsexactly1bit.
BaudRate
Thenumberofvoltageorfrequencytransitionspersecond.
BBN

Bolt,Beranek,andNewman,Inc.HightechnologycompanylocatedinMassachusettsthatdevelopedandmaintainedtheARPANETandlater,theInternet,coregatewaysystem.
BBNPlanet
SubsidiarycompanyofBBNthatoperatesanationwideInternetaccessnetworkcomposedinpartoftheformerregionalnetworksBARRNET,NEARNET,andSURAnet.
Bc
CommittedBurst.NegotiatedtariffmetricinFrameRelayinternetworks.Themaximumamountofdata(inbits)thataFrameRelayinternetworkiscommittedtoacceptandtransmitattheCIR.
BChannel
Bearerchannel.InISDN,afullduplex,64kbpschannelusedtosenduserdata.ComparetoDchannel,Echannel,andHchannel.
Be
ExcessBurst.NegotiatedtariffmetricinFrameRelayinternetworks.ThenumberofbitsthataFrameRelayinternetworkwillattempttotransmitafterBcisaccommodated.Bedatais,ingeneral,deliveredwithalowerprobabilitythanBcdatabecauseBedatacanbemarkedasDEbythenetwork.
Beacon
FramefromaTokenRingorFDDIdeviceindicatingaseriousproblemwiththering,suchasabrokencable.Abeaconframecontainstheaddressofthestationassumedtobedown.
BECN
Backwardexplicitcongestionnotification.BitsetbyaFrameRelaynetworkinframestravelingintheoppositedirectionofframesencounteringacongestedpath.DTEreceivingframeswiththeBECNbitsetcanrequestthathigherlevelprotocolstakeflowcontrolactionasappropriate.ComparewithFECN.
Bellcore
BellCommunicationsResearch.OrganizationthatperformsresearchanddevelopmentonbehalfoftheRBOCs.
BellmanFordRoutingAlgorithm
Seedistancevectorroutingalgorithm.
Benchmark
Atestperformedtcompareacomputerprocessinonesetofcircumstancestoanother.
BER
1.Biterrorrate.Theratioofreceivedbitsthatcontainerrors.2.Basicencodingrules.RulesforencodingdataunitsdescribedintheISOASN.1standard.
BGP
BorderGatewayProtocol.InterdomainroutingprotocolthatreplacesEGP.BGPexchangesreachabilityinformationwithotherBGPsystems.ItisdefinedbyRFC1163.
BGP4
BGPVersion4.Version4ofthepredominantinterdomainroutingprotocolusedontheInternet.BGP4supportsCIDRandusesrouteaggregationmechanismstoreducethesizeofroutingtables.
BIGA
BusInterfaceGateArray.TechnologythatallowstheCatalyst5000toreceiveandtransmitframesfromitspacketswitchingmemorytoitsMAClocalbuffermemorywithouttheinterventionofthehostprocessor.
Bigendian
Methodofstoringortransmittingdatainwhichthemostsignificantbitorbyteispresentedfirst.Comparewithlittleendian.
Binary
1.Anumericalsystemusing"2"asitsbase.2.Datathatisencodedorpresentedinmachinereadableform(1's&0's).
BIND
BerkeleyInternetNameDomain.ThestandardTCP/IPnamingservicethatlinksnetworknameswithIPaddresses.
BiphaseCoding
BipolarcodingschemeoriginallydevelopedforuseinEthernet.Clockinginformationisembeddedintoandrecoveredfromthesynchronousdatastreamwithouttheneedforseparateclockingleads.Thebiphasesignalcontainsnodirectcurrentenergy.
Bipolar
Electricalcharacteristicdenotingacircuitwithbothnegativeandpositivepolarity.Contrastwithunipolar.
BISDN
BroadbandISDN.ITUTcommunicationstandardsdesignedtohandlehighbandwidthapplicationssuchasvideo.BISDNcurrentlyusesATMtechnologyoverSONETbasedtransmissioncircuitstoprovidedataratesfrom155to622Mbpsandbeyond.
Bit
Thebasicunitofdatarepresentationindigitalcomputers.amemorylocationthatcanhaveoneoftwovalues.

BITNET
"BecauseIt'sTime"NetworkingServices.Lowcost,lowspeedacademicnetworkconsistingprimarilyofIBMmainframesand9600bpsleasedlines.BITNETisnowapartofCREN.SeealsoCREN.
BITNETIII
DialupserviceprovidingconnectivityformembersofCREN.
BitorientedProtocol
Classofdatalinklayercommunicationprotocolsthatcantransmitframesregardlessofframecontent.Comparedwithbyteorientedprotocols,bitorientedprotocolsprovidefullduplexoperationandaremoreefficientandreliable.Comparewithbyteorientedprotocol.
Bitpattern
Asequenceofbitsthathasaspecificpurposeormeaning.
Bitrate
Therateatwhichbitsaretransmittedorreceivedduringcommunication,expressedasthenumberbitsinagivenamountoftime,usuallyonesecond.
Bitmap
Adatastructurethatusesbitstorepresenttheattributesofanobjectthatisnotcharacterbased.
BlackBox
Adevicethatperformsafunctionusingmechanismsthatareunimportantorimpossibletounderstand.
BlackHole
Routingtermforanareaoftheinternetworkwherepacketsenter,butdonotemerge,duetoadverseconditionsorpoorsystemconfigurationwithinaportionofthenetwork.
Block
Thebasicunitofstorageonacomputerdisk.
Blocking
Inaswitchingsystem,aconditioninwhichnopathsareavailabletocompleteacircuit.Thetermisalsousedtodescribeasituationinwhichoneactivitycannotbeginuntilanotherhasbeencompleted.
BlockMultiplexerIChannel
BMstylechannelthatimplementstheFIPS60channel,AUS.Channelstandard.ThischannelisalsoreferredtoasOEMIchanneland370blockmuxchannel.
BNC
Bayonet"N"Connector.1.Thelockingconnectortypeusedin10Base2(ThinEthernet).2.Anyconnectorsimilartothetypeusedby10Base2forCATV,andotherelectronicuses.
BNN
Boundarynetworknode.InSNAterminology,asubareanodethatprovidesboundaryfunctionsupportforadjacentperipheralnodes.Thissupportincludessequencing,pacing,andaddresstranslation.
Board
Aprintedcircuitandthesubstrateonwhichitlies.
BOC
Belloperatingcompany.SeeRBOC.
Boot
Acomputer'sstartupoperation.
BootDrive
Thediskthatcontainsacomputers'startupinstructions.
BOOTP
BootstrapProtocol.AnIPprotocolusedbydisklessworkstationstoreceivebootinformationfromabootserver.
BootPROM
Bootprogrammablereadonlymemory.Chipmountedonaprintedcircuitboardusedtoprovideexecutablebootinstructiontoacomputerdevice.
BorderGateway
Routerthatcommunicateswithroutersinotherautonomoussystems.
BoundaryFunction
CapabilityofSNAsubareanodestoprovideprotocolsupportforattachedperipheralnodes.TypicallyfoundinIBM3745devices.
BPDU
Bridgeprotocoldataunit.SpanningTreeProtocolhellopacketthatissentoutatconfigurableintervalstoexchange

informationamongbridgesinthenetwork.
BPS
BitsPerSecond.Acommonlyusedmeasureoftherateofdatatransmissionthatspecifiesthenumberofbitsthataretransmittedinonesecond.MaybeprefixedwithmultiplierssuchasK,M,andGwhichindicateratesofthousands,millionsandbillionsofbitspersecond.
BRI
BasicRateInterface.anISDNservicewithtwobearerchannelsat64KBPSplusa"DataLink"orcontrolchannelat16KBPS.
Bridge
ADataLinkLayerdevicethatlimitstrafficbetweentwonetworksegmentsbyfilteringthedatabetweenthembasedonhardwareaddresses.
BridgeForwarding
ProcessthatusesentriesinafilteringdatabasetodeterminewhetherframeswithagivenMACdestinationaddresscanbeforwardedtoagivenportorports.DescribedintheIEEE802.1standard.SeealsoIEEE802.1.
BridgeNumber
NumberthatidentifieseachbridgeinanSRBLAN.Parallelbridgesmusthavedifferentbridgenumbers.
BridgeStaticFiltering
Processinwhichabridgemaintainsafilteringdatabaseconsistingofstaticentries.EachstaticentryequatesaMACdestinationaddresswithaportthatcanreceiveframeswiththisMACdestinationaddressandasetofportsonwhichtheframescanbetransmitted.DefinedintheIEEE802.1standard.
Broadband
Atransmissionsystemcapableofcarryingmanychannelsofcommunicationsimultaneouslybymodulatingthemononeofseveralcarrierfrequencies.
Broadcast
Aninformationtransmissionthatisintendedtobeinterpretedbyallentitiescapableofreceivingit.
BroadcastAddress
Specialaddressreservedforsendingamessagetoallstations.Generally,abroadcastaddressisaMACdestinationaddressofallones.Comparewithmulticastaddressandunicastaddress.
BroadcastDomain
Thesetofalldevicesthatwillreceivebroadcastframesoriginatingfromanydevicewithintheset.Broadcastdomainsaretypicallyboundedbyroutersbecauseroutersdonotforwardbroadcastframes.
BroadcastSearch
Propagationofasearchrequesttoallnetworknodesifthelocationofaresourceisunknowntotherequester.
BroadcastStorm
Undesirablenetworkeventinwhichmanybroadcastsaresentsimultaneouslyacrossallnetworksegments.Abroadcaststormusessubstantialnetworkbandwidthand,typically,causesnetworktimeouts.
Brouter
Adevicethatincorporatesthefunctionalityofabridgeandarouterinasingleunit.
BSC
Binarysynchronouscommunication.Characterorienteddatalinklayerprotocolforhalfduplexapplications.Oftenreferredtosimplyasbisync.
BSD
BerkeleySoftwareDistribution.UCBerkeley'sdistributionoftheUnixoperatingsystem.
BT
Bursttolerance.ParameterdefinedbytheATMForumforATMtrafficmanagement.ForVBRconnections,BTdeterminesthesizeofthemaximumburstofcontiguouscellsthatcanbetransmitted.
Buffer
Atemporarymemorystorageareaforinformation.
Bug
Aflawinasoftwareprogram.
Bundled
Referstothepracticeofautomaticallyincludinganadditionalapplicationorcapabilityinthesaleordeliveryofacomputingcomponentthatisnotordinarilyassociatedwiththatcomponent.
BUS
Broadcastandunknownserver.MulticastserverusedinELANsthatisusedtofloodtrafficaddressedtoanunknowndestination,andtoforwardmulticastandbroadcasttraffictotheappropriateclients.
Bus

Atypeofnetworktopologyinwhichnodesareconnectedalongacontinuouspaththatisnotaclosedcircuit.AlsoreferstoacommunicationschannelusedbyasinglecomputersuchasNubus,SCSI,etc.
BusandTagChannel
IBMchannel,developedinthe1960s,incorporatingcoppermultiwiretechnology.ReplacedbytheEXCONchannel.SeealsoESCONchannelandparallelchannel.
BusTopology
LinearLANarchitectureinwhichtransmissionsfromnetworkstationspropagatethelengthofthemediumandarereceivedbyallotherstations.Comparewithringtopology,startopology,andtreetopology.
BypassMode
OperatingmodeonFDDIandTokenRingnetworksinwhichaninterfacehasbeenremovedfromthering.
BypassRelay
AllowsaparticularTokenRinginterfacetobeshutdownandthuseffectivelyremovedfromthering.
Byte
Agroupof8bits.
ByteorientedProtocol
Classofdatalinkcommunicationsprotocolsthatuseaspecificcharacterfromtheusercharactersettodelimitframes.Theseprotocolshavelargelybeenreplacedbybitorientedprotocols.Comparewithbitorientedprotocol.
ByteReversal
Processofstoringnumericdatawiththeleastsignificantbytefirst.UsedforintegersandaddressesondeviceswithIntelmicroprocessors.
Byte
Agroupof8bits.
Cable
Thetransmissionmediaofanetwork.
CableRange
RangeofnetworknumbersthatisvalidforusebynodesonanextendedAppleTalknetwork.Thecablerangevaluecanbeasinglenetworknumberoracontiguoussequenceofseveralnetworknumbers.Nodeaddressesareassignedbasedonthecablerangevalue.
Cache
Agroupofmemorylocationssetasidefortemporarystorageofdata,especiallyfrequentlyuseddataordataneedinghighspeedretrievalbytheCPU.
CallAdmissionControl
TrafficmanagementmechanismusedinATMnetworksthatdetermineswhetherthenetworkcanofferapathwithsufficientbandwidthforarequestedVCC.
CallPriority
Priorityassignedtoeachoriginationportincircuitswitchedsystems.Thisprioritydefinestheorderinwhichcallsarereconnected.Callpriorityalsodefineswhichcallscanorcannotbeplacedduringabandwidthreservation.
CallSetupTime
ThetimerequiredtoestablishaswitchedcallbetweenDTEdevices.
CAM
Contentaddressablememory.Seeassociativememory.
Card
Acircuitboardthatplugsintoacomputer'sbustoextendthecomputer'scapability.
Carrier
Electromagneticwaveoralternatingcurrentofasinglefrequency,suitableformodulationbyanother,databearingsignal.
CaseInsensitive
Referringtoasysteminwhichuppercaselettersarenotdifferentiatedfromtheirlowercaseform.
CaseSensitive
Referringtoasysteminwhichuppercaselettersaredifferentiatedfromtheirlowercaseform.
Category1Cabling
OneoffivegradesofUTPcablingdescribedintheEIA/TIA586standard.Category1cablingisusedfortelephonecommunicationsandisnotsuitablefortransmittingdata.ComparewithCategory2cabling,Category3cabling,Category4cabling,andCategory5cabling.SeealsoEIA/TIA586andUTP.
Category2Cabling
OneoffivegradesofUTPcablingdescribedintheEIA/TIA586standard.Category2cablingiscapableoftransmittingdataatspeedsupto4Mbps.ComparewithCategory1cabling,Category3cabling,Category4cabling,andCategory5cabling.

SeealsoEIA/TIA586andUTP.
Category3cabling
OneoffivegradesofUTPcablingdescribedintheEIA/TIA586standard.Category3cablingisusedin10BaseTnetworksandcantransmitdataatspeedsupto10Mbps.ComparewithCategory1cabling,Category2cabling,Category4cabling,andCategory5cabling.SeealsoEIA/TIA586andUTP.
Category4cabling
OneoffivegradesofUTPcablingdescribedintheEIA/TIA586standard.Category4cablingisusedinTokenRingnetworksandcantransmitdataatspeedsupto16Mbps.ComparewithCategory1cabling,Category2cabling,Category3cabling,andCategory5cabling.SeealsoEIA/TIA586andUTP.
Category5cabling
OneoffivegradesofUTPcablingdescribedintheEIA/TIA586standard.Category5cablingisusedforrunningCDDIandcantransmitdataatspeedsupto100MbpsComparewithCategory1cabling,Category2cabling,Category3cabling,andCategory4cabling.SeealsoEIA/TIA586andUTP.
Catenet
Networkinwhichhostsareconnectedtodiversenetworks,whichthemselvesareconnectedwithrouters.TheInternetisaprominentexampleofacatenet.
CATV
Cabletelevision.Communicationsystemwheremultiplechannelsofprogrammingmaterialaretransmittedtohomesusingbroadbandcoaxialcable.FormerlycalledCommunityAntennaTelevision.
CBDS
ConnectionlessBroadbandDataService.Europeanhighspeed,packetswitched,datagrambasedWANnetworkingtechnology.SimilartoSMDS.
CBR
Constantbitrate.QOSclassdefinedbytheATMForumforATMnetworks.CBRisusedforconnectionsthatdependonpreciseclockingtoensureundistorteddelivery.
CCITT
ConsultativeCommitteeforInternationalTelegraphandTelevisionandTelephone.Internationalorganizationresponsibleforthedevelopmentofcommunicationsstandards.NowcalledtheITUT.
CCS
CommonChannelSignaling.Signalingsystemusedintelephonenetworksthatseparatessignalinginformationfromuserdata.Aspecifiedchannelisexclusivelydesignatedtocarrysignalinginformationforallotherchannelsinthesystem.
CD
CarrierDetect.Signalthatindicateswhetheraninterfaceisactive.Also,asignalgeneratedbyamodemindicatingthatacallhasbeenconnected.
CDDI
CopperDistributedDataInterface.ImplementationofFDDIprotocolsoverSTPandUTPcabling.CDDItransmitsoverrelativelyshortdistance(about100meters),providingdataratesof100Mbpsusingadualringarchitecturetoprovideredundancy.BasedontheANSITwistedPairPhysicalMediumDependent(TPPMD)standard.
CDEV
ThedesignationofaControlPanelDeviceinMacintoshSystem6andearlier(obsolete).
CDPD
CellularDigitalPacketData.Openstandardfortwowaywirelessdatacommunicationoverhighfrequencycellulartelephonechannels.AllowsdatatransmissionsbetweenaremotecellularlinkandaNAP.Operatesat19.2Kbps.
CDVT
Celldelayvariationtolerance.ParameterdefinedbytheATMForumforATMtrafficmanagement.InCBRtransmissions,determinesthelevelofjitterthatistolerableforthedatasamplestakenbythePCR.
CEDI
CaymanEncapsulatedDDPinIP.AnAppleTalktunnelingprotocoldevelopedbyCayman.
Cell
ThebasicunitforATMSwitchingandmultiplexing.Cellscontainidentifiersthatspecifythedatastreamtowhichtheybelong.Eachcellconsistsofa5byteheaderand48bytesofpayload.Seealsocellrelay.
CellLossPriority
SeeCLP.
CellRelay
Networktechnologybasedontheuseofsmall,fixedsizepackets,orcells.Becausecellsarefixedlength,theycanbeprocessedandswitchedinhardwareathighspeeds.CellrelayisthebasisformanyhighspeednetworkprotocolsincludingATM,IEEE802.6,andSMDS.
CellsPerSecond
Abbreviatedcps.

CellularRadio
Technologythatusesradiotransmissionstoaccesstelephonecompanynetworks.Serviceisprovidedinaparticularareabyalowpowertransmitter.
Centrex
AT&TPBXthatprovidesdirectinwarddialingandautomaticnumberingidentificationofthecallingPBX.
CEPT
ConfrenceEuropennedesPostesetdesTlcommunications.Associationofthe26EuropeanPTTsthatrecommendscommunicationspecificationstotheITUT.
CERTnet
CaliforniaEducationandResearchFederationNetwork.TCP/IPnetwork,basedinSouthernCalifornia,thatconnectshundredsofhighereducationcentersinternationallywhilealsoprovidingInternetaccesstosubscribers.CERFnetwasfoundedin1988bytheSanDiegoSupercomputerCenterandGeneralAutomicsandisfundedbytheNSF.
Chaining
SNAconceptinwhichRUsaregroupedtogetherfortheproposeoferrorrecovery.
Channel
1.Acommunicationpath.Multiplechannelscanbemultiplexedoverasinglecableincertainenvironments.2.InIBM,thespecificpathbetweenlargecomputers(suchasmainframes)andattachedperipheraldevices.
Channelattached
Pertainingtoattachmentofdevicesdirectlybydatachannels(input/outputchannels)toacomputer.
ChannelizedE1
Accesslinkoperatingat2.048Mbpsthatissubdividedinto30Bchannelsand1Dchannel,SupportsDDR,FrameRelay,andX.25.ComparewithchannelizedT1.
ChannelizedT1
Accesslinkoperatingat1.544Mbpsthatissubdividedinto24channels(23Bchannelsand1Dchannel)of64Kbpseach.Theindividualchannelsorgroupsofchannelsconnecttodifferentdestinations.SupportsDDR,FrameRelay,andX.25.AlsoreferredtoasfractionalT1.ComparewithchannelizedE1.
ChannelServiceUnit
SeeCSU.
CHAP
ChallengeHandshakeAuthenticationProtocol.SecurityfeaturesupportedonlinesusingPPPencapsulationthatpreventsunauthorizedaccess.CHAPdoesnotitselfpreventunauthorizedaccess,itmerelyidentifiestheremoteend.Therouteroraccessserverthandetermineswhetherthatuserisallowedaccess.ComparetoPAP.
Character
1.Asymbolsuchasaletter,numberorpunctuationmarkthatcanbearrangedtorepresenthigherunitsofmeaning,suchaswordsandsentences.2.Thegroupofbitsthatrepresentssuchasymbol.
ChatScript
Stringoftextthatdefinesthelogin"conversation"thatoccursbetweentwosystems.Consistofexpectsendpairsthatdefinethestringthatthelocalsystemexpectstoreceivefromtheremotesystemandwhatthelocalsystemshouldsendasareply.
Cheapernet
IndustrytermusedtorefertotheIEEE802.310Base2standardorthecablespecifiedinthatstandard.ComparewithThinnet.Seealso10Base2,Ethernet,andIEEE802.3.
Checksum
Theresultofamathematicaloperationthatusesthebinaryrepresentationofagroupofdataasitsbasis,usuallytochecktheintegrityofthedata.
ChokePacket
Packetsenttoatransmittertotellitthatcongestionexistsandthatitshouldreduceitssendingrate.
CIA
SeeclassicIPoverATM.
CICNet
Regionalnetworkthatconnectsacademic,reserach,nonprofit,andcommercialorganizationsintheMidwesternUnitedStates.Foundedin1988,CICNetwasapartoftheNSFNETandwasfundedbytheNSFuntiltheNSFNETdissolvedin1995.SeealsoNSFNET.
CICS
CustomerInformationControlSystem.IBMapplicationsubsystemallowingtransactionsenteredatremoteterminalstobeprocessedconcurrentlybyuserapplications.
CIDR
Classlessinterdomainrouting.TechniquesupportedbyBGP4andbasedonrouteaggregation.CIDRallowsrouterstogrouproutestogetherinordertocutdownonthequantityofroutinginformationcarriedbythecorerouters.WithCIDR,severalIPnetworksappeartonetworksoutsidethegroupasasingle,largerentity.

CIR
Committedinformationrate.TherateatwhichaFrameRelaynetworkagreestotransferinformationundernormalconditions,averagedoveraminimumincrementoftime.CIR,measuredinbitspersecond,isoneofthekeynegotiatedtariffmetrics.
Circuit
1.Anyelectricalpathway.2.Anarrangementofelectricalandelectronicdevicesandtheconductivepathsbetweenthem.
CircuitGroup
Groupingofassociatedseriallinesthatlinktwobridges.Ifoneoftheseriallinksinacircuitgroupisinthespanningtreeforanetwork,anyoftheseriallinksinthecircuitgroupcanbeusedforloadbalancing.Thisloadbalancingstrategyavoidsdataorderingproblemsbyassigningeachdestinationaddresstoaparticularseriallink.
CircuitSwitching
Switchingsysteminwhichadedicatedphysicalcircuitpathmustexistbetweensenderandreceiverforthedurationofthe"call."Usedheavilyinthetelephonecompanynetwork.Circuitswitchingcanbecontrastedwithcontentionandtokenpassingasachannelaccessmethod,andwithmessageswitchingandpacketswitchingasaswitchingtechnique.
ClassicIPOverATM
SpecificationforrunningIPoverATMinamannerthattakesfulladvantageofthefeaturesofATM.DefinedinRFC1577.SometimescalledCIA.
CLAW
CommonLinkAccessforWorkstations.DatalinklayerprotocolusedbychannelattachedRISCSystem/6000seriessystemsandbyIBM3172devicesrunningTCP/IPoffload.CLAWimprovesefficiencyofchanneluseandallowstheCIPtoprovidethefunctionalityofa3172inTCP/IPenvironmentsandsupportdirectchannelattachment.TheoutputfromTCP/IPmainframeprocessingisaseriesofIPdatagramsthattheroutercanswitchwithoutmodifications.
ClearToSend
SeeCTS.
Client
Nodeorsoftwareprogram(frontenddevice)thatrequestsservicesfromaserver.Seealsobackend,frontendandserver.
Client/Server
Atypeofrelationshipbetweentwocomputerswherethetwohavedifferentrolesintherelationship.Typically,theclientcomputerdrivestherelationshipandusesaresourceoftheservercomputer.
CLNP
ConnectionlessNetworkProtocol.OSInetworklayerprotocolthatdoesnotrequireacircuittobeestablishedbeforedataistransmitted.SeealsoCLNS.
CLNS
ConnectionlessNetworkService.OSInetworklayerservicethatdoesnotrequireacircuittobeestablishedbeforedataistransmitted.CLNSroutesmessagestotheirdestinationsindependentlyofanyothermessages.SeealsoCLNP.
CLP
Celllosspriority.FieldintheATMcellheaderthatdeterminestheprobabilityofacellbeingdroppedifthenetworkbecomescongested.CellwithCLP=0areinsuredtraffic,whichisunlikelytobedropped.CellswithCLP=1arebestefforttraffic,whichmightbedroppedincongestedconditionsinordertofreeupresourcestohandleinsuredtraffic.
Clock
1.Acomponentinacomputerthatprovidesatimingpulseforothercomponents.2.Thetimingpulseofanetworktransmission.
Clustercontroller
1.Generally,anintelligentdevicethatprovidestheconnectionsforaclusterofterminalstobedatalink.2.InSNA,aprogrammabledevicethatcontrolstheinput/outputoperationsofattacheddevices.Typically,anIBM3174or3274device.
CMI
Codedmarkinversion.ITUTlinecodingtechniquespecifiedforSTS3ctransmissions.AlsousedinDS1systems.
CMIP
CommonManagementInformationProtocol.
CMIS
CommonManagementInformationServices.OSInetworkmanagementserviceinterfacecreatedandstandardizedbyISOforthemonitoringandcontrolofheterogeneousnetworks.SeealsoCMIP.
CMNS
ConnectionModeNetworkService.ExtendslocalX.25switchingtoavarietyofmedia(Ethernet,FDDI,TokenRing).Seealso.
CMT
Connectionmanagement.FDDIprocessthathandlesthetransitionoftheringthroughitsvariousstates(off,active,connect,andsoon),asdefinedbytheANSIX3T9.5specification.
CO

Centraloffice.Localtelephonecompanyofficetowhichalllocalloopsinagivenareaconnectandinwhichcircuitswitchingofsubscriberlinesoccurs.
Coaxialcable
Anelectricalcableinwhichtheconductorsshareacommonaxis.
CODEC
Coderdecoder.DevicethattypicallyusesPCMtotransformanalogsignalsintoadigitalbitstreamanddigitalsignalsbackintoanalog.
Coding
Electricaltechniquesusedtoconveybinarysignals.
CollapsedBackbone
Nondistributedbackboneinwhichallnetworksegmentsareinterconnectedbywayofaninternetworkingdevice.Acollapsedbackbonemightbeavirtualnetworksegmentexistinginadevicesuchasahub,arouter,oraswitch.
Collision
InEthernet,theresultoftwonodestransmittingsimultaneously.Theframesfromeachdeviceimpactandaredamagedwhentheymeetonthephysicalmedia.SeealsoCollisiondomain.
CollisionAvoidance
AMediaAccessControl(MAC)methodinwhichanynodemaytakecontrolofthenetworkaftertakingcertainstepstoinsurethatthecableisnotinuseorabouttobeusedbyanothernode.
CollisionDetection
AMACmethodinwhichanynodemaytakecontrolofthenetworkwhenitisnotinusebyanothernode.Whiletransmitting,stationscontinuetolistenforincomingsignals(collisions)andemitajammingsignaltonotifyallotherstationsofthecollision.
CollisionDomain
InEthernet,thenetworkareawithinwhichframesthathavecollidedarepropagated.RepeatersandhubspropagatecollisionsLANswitches,bridgesandroutersdonot.Seealsocollision.
CommonCarrier
Licensed,privateutilitycompanythatsuppliescommunicationservicestothepublicatregulatedprices.
Communication
Transmissionofinformation.
CommunicationController
InSNA,asubareanode(suchasanIBM3745device)thatcontainsanNCP.
CommunicationServer
CommunicationsprocessorthatconnectsasynchronousdevicestoaLANorWANthroughnetworkandterminalemulationsoftware.PerformsonlyasynchronousroutingofIPandIPX.Comparewithaccessserver.
CommunicationsLine
Thephysicallink(suchaswireoratelephonecircuit)thatconnectsoneormoredevicestooneormoreotherdevices.
Community
InSNMP,alogicalgroupofmanageddevicesandNMSsinthesameadministrativedomain.
CommunityString
TextstringthatactsasapasswordandisusedtoauthenticatemessagessentbetweenamanagementstationandaroutercontainingaSNMPagent.Thecommunitystringissentineverypacketbetweenthemanagerandtheagent.
Companding
Contractionderivedfromtheoppositeprocessesofcompressionandexpansion.PartofthePCMprocesswherebyanalogsignalvaluesarelogicallyroundedtodiscretescalestepvaluesonanonlinearscale.Thedecimalstepnumberisthencodedinitsbinaryequivalentpriortotransmission.Theprocessisreversedatthereceivingterminalusingthesamenonlinearscale.Comparewithcompressionandexpansion.Seealsoalawandmulaw.
Component
Anindivisibleunitoffunctionality,usuallyembodiedinhardware.
Compression
Analterationperformedonaunitofinformationintendedtoincreaseitdensityduringstorageoftransmission.
Concentrator
Asynonymforamultiportrepeaterthatmayalsoperformbridgingandroutingfunctions.
Conductor
Thecurrentcarryingcomponentofatransmissioncable,typicallyacopperwire.
ConfigurationManagement
OneoffivecategoriesofnetworkmanagementofOSInetworks.Configurationmanagementsubsysemsareresponsiblefor

detectinganddeterminingthestateofanetwork.Seealsoaccountmanagement,faultmanagement,performancemanagement,andsecuritymanagement.
Congestion
Trafficinexcessofnetworkcapacity.
ConnectionOriented
Indatanetworks,atypeofcomputerrelationshipinwhichthenetworkequipmentconstructsacircuitbetweenthetwodevicesforthedurationoftheirrelationship.Oncethecircuitisestablished,thedevicespassinformationbackandforththroughthecircuitwithoutregardtotheirphysicaladdresses.Thecircuitmaybephysicalorvirtual.
Connectionless
Atypeofrelationshipbetweentwodeviceswhereeachinformationpacketmustcontaintheaddressofthepartnerdevice.Connectionlesscommunicationallowsamessagetobesentfromoneendpointtoanotherwithoutpriorarrangement,andhasverylowoverhead,butcannotguaranteethattherewillbenoloss,errorinsertion,misdelivery,duplication,oroutofsequencedeliveryofthepackets.
Connectivity
Atermreferringtotheabilityofadevicetotradedataandshareresourceswithotherdevicesofasimilaranddissimilartypethroughelectronicmeansincludingserialandparallelconnections,networkingandtelecommunications.
Connector
Adevicethatestablishesaphysicalconnectionbetweenoneconductororcircuitandanother.
CONP
ConnectionOrientedNetworkProtocol,OSIprotocolprovidingconnectionorientedoperationtoupperlayerprotocols.
Console
InSNMP(SimpleNetworkManagementProtocol),asoftwareprogramthathasthecapabilityofinteractingwithanagent,includingexaminingorchangingthevaluesofthedataobjectsintheagent'sManagementInformationBase(MIB).
Contention
Anetworkaccessmethodwhereallthedevicesonthenetworkhaveequalchangesofgainingcontrolofthenetworkatanytime.Includesavoidance(CSMA/CA)accessmethods.
ControlPanel
IntheMacintosh,asoftwareapplicationthathastheabilitytocontrolanaspectofsystemconfiguration,suchasthepixeldepthofthemonitor(Monitors),thechoiceofnetworktype(Network),etc.
Convergence
Thespeedandabilityofagroupofinternetworkingdevicesrunningaspecificroutingprotocoltoagreeonthetopologyofaninternetworkafterachangeinthattopology.
ConvergenceSublayer
SeeCS.
Conversation
InSNA,anLU6.2sessionbetweentwotransactionprograms.
CopperDistributedDataInterface
SeeCDDI.
CoreGateway
TheprimaryroutersintheInternet.
CoreRouter
Inapacketswitchedstartopology,arouterthatispartofthebackboneandthatservesasthesinglepipethroughwhichalltrafficfromperipheralnetworksmustpassonitswaytootherperipheralnetworks.
COS
1.Classofservice.Indicationofhowanupperlayerprotocolrequiresthatalowerlayerprotocoltreatitsmessages.InSNAsubarearouting,COSdefinitionsareusedbysubareanodestodeterminetheoptimalroutetoestablishtogivensession.ACOSdefinitioncomprisesavirtualroutenumberandatransmissionpriorityfield.AlsocalledTOS(typeofservice).2.CorporationforOpenSystems.OrganizationthatpromulgatestheuseofOSIprotocolsthroughconformancetesting,certification,andrelatedactivities.
COSINE
CooperationforOpenSystemsInterconnectionNetworkinginEurope.EuropeanprojectfinancedbytheEuropeanCommunity(EC)tobuildacommunicationnetworkbetweenscientificandindustrialentitiesinEurope.Theprojectendedin1994.
Cost
Arbitraryvalue,typicallybasedonhopcount,mediabandwidth,orothermeasures,thatisassignedbyanetworkadministratorandusedtocomparevariouspathsthroughaninternetworkenvironment.Costvaluesareusedbyroutingprotocolstodeterminethemostfavorablepathtoaparticulardestination:thelowerthecost,thebetterthepath.Sometimescalledpathcost.Seealsoroutingmetric.
CounttoInfinity
Problemthatcanoccurinroutingalgorithmsthatareslowtoconverge,inwhichrouterscontinuouslyincrementthehop

counttoparticularnetworks.Typically,somearbitraryhopcountlimitisimposedtopreventthisproblem.
CP
Controlpoint.InSNAnetworks,elementthatidentifiestheAPPNnetworkingcomponentsofaPU2.1node,managesdevicerresources,andcanprovideservicestootherdevices.InAPPN,CPsareabletocommunicatewithlogicallyadjacentCPsbywayofCPtoCPsessions.SeealsoENandNN.
CPCS
Commonpartconvergencesublayer.OneofthetwosublayersofanyAAL.TheCPCSisserviceindependentandisfurtherdividedintotheCSandtheSARsublayers.TheCPCSisresponsibleforpreparingdatafortransportacrosstheATMnetwork,includingthecreationofthe48bytepayloadcellsthatarepassedtotheATMlayer.SeealsoAAL,ATMlayer,CS,SAR,andSSCS.
CPE
Customerpremisesequipment.Terminatingequipment,suchasterminals,telephones,andmodems,suppliedbythetelephonecompany,installedatcustomersites,andconnectedtothetelephonecompanynetwork.
CPIC
CommonProgrammingInterfaceforCommunications.PlatformindependentAPIdevelopedbyIBMandusedtoprovideportabilityinAPPCapplications.SeealsoAPPC.
CPS
Cellspersecond.
CPU
CentralProcessingUnit.Themainprocessorinthecomputer'sconfigurationthathandlesprocessingtasksordirectsauxiliaryprocessors(coprocessors)toperformthem.
CPUbound
AcomputingactivityornetworkinteractionwhosespeedislimitedbythespeedatwhichtheCPUcanperformthenecessarycomputingtasks.
Crash
Anabruptterminationorcomputingactivitycausedbyanerror.Inmanyinstances,thecomputerbecomescompletelyunusableandmustberestartedbeforeactivitycanresume.
CRC
CyclicRedundancyCheck.Amethodofinsuringdataintegritywhereacalculationisperformedusingthebinaryrepresentationofthedataitselfasthebasisofthecalculation.TheCRCisthenumericalresultofthiscalculationandisheldseparatelyfromthedata.TheintegrityofthedataischeckedbycalculatinganewCRC.IfthetwoCRC'smatch,thenthereisahighdegreeofconfidencethatthedatahasnotchanged.
CREN
CorporationforResearchandEducationalNetworking.TheresultofamergerofBITNETandCSNET.CRENisdevotedtoprovidingInternetconnectivitytoitsmembers,whichincludethealumni,students,faculty,andotheraffiliatesofparticipatingeducationalandresearchinstitutions,viaBITNETIII.SeealsoBITNET,BITNETIII,andCSNET.
Crosstalk
Inelectronicsignaling,anerrorconditioncausedwhenthesignalfromonecircuitcausesadisturbancetothesignalofthenearbycircuit..
CS
Convergencesublayer.OneofthetwosublayersoftheAALCPCS,responsibleforpaddinganderrorchecking.PDUspassedfromtheSSCSandappendedwitha8bytetrailer(forerrorcheckingandothercontrolinformation)andpadded,ifnecessary,sothatthelengthoftheresultingPDUisdivisibleby48.ThesePDUsarethenpassedtotheSARsublayeroftheCPCSforfurtherprocessing.SeealsoAAL,CPCS,SAR,andSSCS.
CSA
CanadianStandardsAssociation.AgencywithinCanadathatcertifiesproductsthatconformtoCanadiannationalsafetystandards.
CSLIP
CompressedSerialLinkInternetProtocol.ExtensionofSLIPthat,whenappropriate,allowsjustheaderinformationtobesentacrossaSLIPconnection,reducingoverheadandincreasingpacketthroughputonSLIPlines.SeealsoSLIP.
CSMA/CD
Carriersensemultipleaccesscollisiondetect.Mediaaccessmechanismwhereindevicesreadytotransmitdatafirstcheckthechannelforacarrier.Ifnocarrierissensedforaspecificperiodoftime,adevicecantransmit.Iftwodevicestransmitatonce,acollisionoccursandisdetectedbyallcollidingdevices.Thiscollisionsubsequentlydelaysretransmissionsfromthosedevicesforsomerandomlengthoftime.CSMA/CDaccessisusedbyEthernetandIEEE802.3.
CSNET
ComputerScienceNetwork.Largeinternetworkconsistingprimarilyofuniversities,researchinstitutions,andcommercialconcerns.CSNETmergedwithBITNETtoformCREN.
CSNP
CompletesequencenumberPDU.PDUsentbythedesignatedrouterinanOSPFnetworktomaintaindatabasesynchronization.
CSU

Channelserviceunit.Digitalinterfacedevicethatconnectsenduserequipmenttothelocaldigitaltelephoneloop.OftenreferredtotogetherwithDSU,asCSU/DSU.SeealsoDSU.
CTS
1.ClearToSend.CircuitintheEIA/TIA232specificationthatisactivatedwhenDCEisreadytoacceptdatafromDTE.2.Commontransportsemantic.CornerstoneoftheIBMstrategytoreducethenumberofprotocolsonnetworks.CTSprovidesasingleAPIfordevelopersofnetworksoftwareandenablesapplicationstorunoverAPPN,OSI,orTCP/IP.
CUT
ControlUnitTerminal.
CutthroughPacketSwitching
Packetswitchingapproachthatstreamsdatathroughaswitchsothattheleadingedgeofapacketexitstheswitchattheoutputportbeforethepacketfinishesenteringtheinputport.Adeviceusingcutthroughpacketswitchingreads,processes,andforwardspacketsassoonasthedestinationaddressislookedup,andtheoutgoingportdetermined.Alsoknownasontheflypacketswitching.Contrastwithstoreandforwardpacketswitching.
DAC
Dualattachedconcentrator.FDDIorCDDIconcentratorcapableofattachingtobothringsofanFDDIorCDDInetwork.ItcanalsobedualhomedfromthemasterportsofotherFDDIorCDDiconcentrators.
Daemon
IntheUNIXoperatingsystem,acomputingprocessthat,oncestarted,isnotunderusercontrol,butcontinuestoruninthebackground.Daemonsusuallyperformaparticularpurposeondemand,suchassupplyinginformationtoanotherprocessor.AnexampleinAppleTalknetworkingistheatalkaddaemon,whichsuppliesAppleTalktunnelinginformationtoroutersonrequest.
DaisyChain
InLocalTalk,adaisychainismadebylinkingLocalTalkconnectorstogetherwithpatchcord.Intelephony,adaisychainreferstothemethodoflinkingaseriesofwalloutletstogetherwithtwistedpaircablingratherthanthenormalpracticeofconnectingthewalloutletstoacentrallocation(homerun).Intelephony,"daisychaining"isequivalenttothe"backbone"methodofLocalTalkconstruction.
DAL
DataAccessLanguage.AdatabasemetalanguagedesignedbyApple.AsupersetofSQL.
DARPA
DefenseAdvancedResearchProjectsAgency.US.governmentagencythatfundedresearchforandexperimentationwiththeInternet.EvolvedfromARPA,andthen,from1994,backtoARPA.
DARPAInternet
ObsoletetermreferringtotheInternet.SeeInternet.
DAS
Dualattachmentstation.DeviceattachedtoboththeprimaryandthesecondaryFDDIrings.DualattachmentprovidesredundancyfortheFDDIringiftheprimaryringfails,thestationcanwraptheprimaryringtothesecondaryring,isolatingthefailureandretainingringintegrity.AlsoknownasaClassAstation.
DAT
DigitalAudioTape.Atypeofstoragemediausedforthebackupofcomputingdata.
Data
Informationrepresentedinaformatreadablebyacomputer.
DataBase
AcollectionofdatathatcanbeselectivelyretrievedbyatypeofapplicationknowsasaDataBaseManagementSystem.
DataFlowControlLayer
Layer5oftheSNAarchitecturalmodel.Thislayerdeterminesandmanagesinteractionsbetweensessionpartners,particularlydataflow.CorrespondstothesessionlayeroftheOSImodel.Seealsodatalinkcontrollayer,pathcontrollayer,physicalcontrolllayer,presentationserviceslayer,transactionserviceslayer,andtransmissioncontrollayer.
Datagram
Logicalgroupingofinformationsentasanetworklayerunitoveratransmissionmediumwithoutpriorestablishmentofavirtualcircuit.IPdatagramsaretheprimaryinformationunitsintheInternet.Thetermsframe,message,packet,andsegmentarealsousedtodescribelogicalinformationgroupingatvariouslayersoftheOSIreferencemodelandinvarioustechnologycircles.
DataLink
ThephysicalconnectionbetweentwodevicessuchasEthernet,LocalTalkorTokenRingthatiscapableofcarryinginformationintheserviceornetworkingprotocolssuchasAppleTalk,TCP/IPorXNS.
DataLinkLayer
Layer2oftheOSIreferencemodel.Thislayerprovidesreliabletransitofdataacrossaphysicallink.Thedatalinklayerisconcernedwithphysicaladdressing,networktopology,linediscipline,errornotification,ordereddeliveryofframes,andflowcontrol.TheIEEEhasdividedthislayerintotwosublayers:TheMACsublayerandtheLLCsublayer.Sometimessimplycalledlinklayer.RoughlycorrespondstothedatalinkcontrollayeroftheSNAmodel.Seealsoapplicationlayer,LLC,MAC,networklayer,physicallayer,presentationlayer,sessionlayer,andtransportlayer.
DataLinkProtocol

Theprotocolthatcontrolsthenetworksignalingandreceivinghardware,performingdataintegritychecksandformattinginformationaccordingtotherulesofthedatalink.
DataSink
Networkequipmentthatacceptsdatatransmissions.
DataStream
Alldatatransmittedthroughacommunicationslineinasinglereadorwriteoperation.
dB
Decibels.
DBConnector
Databasebusconnector.Typeofconnectorusedtoconnectserialandparallelcablestoadatabus.DBconnectornamesareoftheformatDBx,wherexrepresentsthenumberof(wires)withintheconnector.Eachlineisconnectedtoapinontheconnector,butinmanycases,notallpinsareassignedafunction.DBconnectorsaredefinedbyvariousEIA/TIAstandards.
DCA
DefenseCommunicationsAgency.US.governmentorganizationresponsibleforDDNnetworkssuchasMILNET.NowcalledDISA.
DCC
DataCountryCode.OneoftwoATMAddressformatsdevelopedbytheATMForumforusebyprivatenetworks.AdaptedfromthesubnetworkmodelofaddressinginwhichtheATMlayerisresponsibleformappingnetworklayeraddressestoATMAddresses.SeealsoICD.
DCE
DistributedComputingEnvironment.
DChannel
1.Datachannel.Fullduplex,16kbps(BRI)or64kbps(PRI)ISDNchannel.ComparetoBchannel,Echannel,andHchannel.2.InSNA,adevicethatconnectsaprocessorandmainstoragewithperipherals.
DDM
DistributedDataManagement.SoftwareinanIBMSNAenvironmentthatprovidespeertopeercommunicationandfilesharing.OneofthreeSNAtransactionservices.SeealsoDIAandSNADS.
DDN
DefenseDataNetwork.US.militarynetworkcomposedofanunclassifiednetwork(MILNET)andvarioussecretandtopsecretnetworks.DDNisoperatedandmaintainedbyDISA.SeealsoDISAandMILNET.
DDP
DatagramDeliveryProtocol.AppleComputernetworklayerprotocolthatisresponsibleforthesockettosocketdeliveryofdatagramsoveranAppleTalkinternetwork.
DDR
Dialondemandrouting.TechniquewherebyaCiscoroutercanautomaticallyinitiateandcloseacircuitswitchedsessionastransmittingstationsdemand.Therouterspoofskeepalivessothatendstationstreatthesessionasactive.DDRpermitsroutingoverISDNortelephonelinesusinganexternalISDNterminaladapterormodem.
DE
Discardeligible.Seetaggedtraffic.
Deadlock
1.Unresolvedcontentionfortheuseofaresource.2.InAPPN,whentwoelementsofaprocesseachwaitforactionbyoraresponsefromtheotherbeforetheyresumetheprocess.
Decay
Alossintheclarityorreadabilityofanelectronicsignalcausedbytheinteractionofthesignalwithitscarrierandelectricalenvironment.
Decibel
Ameasurementthatreferstotheratioofthestrengthofonesignaltoanother.Decibelsarecommonlyusedtoexpresssignallossortherelationshipofthesignalstrengthtoambientnoise.
DECnet
Groupofcommunicationsproducts(includingaprotocolsuite)developedandsupportedbyDigitalEquipmentCorporation.DECnet/OSI(alsocalledDECnetPhaseV)isthemostrecentiterationandsupportsbothOSIprotocolsandproprietaryDigitalprotocols.PhaseIVPrimesupportsinherentMACaddressesthatallowDECnetnodestocoexistwithsystemsrunningotherthathaveMACaddressrestrictions.SeealsoDNA.
DECnetRouting
ProprietaryroutingschemeintroducedbyDigitalEquipmentCorporationinDECnetPhaseIII.InDECnetPhaseV,DECnetcompleteditstransitiontoOSIroutingprotocols(ESISandISIS).
Decryption
Thereverseapplicationofanencryptionalgorithmtoencrypteddata,therebyrestoringthatdatatoitsoriginal,unencryptedstate.Seealsoencryption.

DedicatedLAN
Networksegmentallocatedtoasingledevice.UsedinLANswitchednetworktopologies.
DedicatedLine
Communicationslinethatisindefinitelyreservedfortransmissions,ratherthanswitchedastransmissionisrequired.Seealsoleasedline.
DeFactoStandard
Standardthatexistsbynatureofitswidespreaduse.Comparewithdejurestandard.Seealsostandard.
DefaultRoute
Routingtableentrythatisusedtodirectframesforwhichanexthopisnotexplicitlylistedintheroutingtable.
DeJureStandard
Standardthatexistbecauseofitsapprovalbyanofficialstandardsbody.Comparewithdefactostandard.Seealsostandard.
Delay
Thetimebetweentheinitiationofatransactionbyasenderandthefirstresponsereceivedbythesender.Also,thetimerequiredtomoveapacketfromsourcetodestinationoveragivenpath.
DemandPriority
Mediaaccessmethodusedin100VGAnyLANthatusesahubthatcanhandlemultipletransmissionrequestsandcanprocesstrafficaccordingtopriority,makingitusefulforservicingtimesensitivetrafficsuchasmultimediaandvideo.Demandpriorityeliminatestheoverheadofpacketcollisions,collisionrecovery,andbroadcasttraffictypicalinEthernetnetworks.Seealso100VGAnyLAN.
Demarc
DemarcationpointbetweencarrierequipmentandCPE.
Demodulation
Processofreturningamodulatedsignaltoitsoriginalform.Modemsperformdemodulationbytakingananalogsignalandreturningittoitsoriginal(digital)form.Seealsomodulation.
Demultiplexing
Theseparatingofmultipleinputstreamsthathavebeenmultiplexedintoacommonphysicalsignalbackintomultipleoutputstreams.Seealsomultiplexing.
DenseModePIM
SeePIMdensemode.
DES
DataEncryptionStandard.StandardcryptographicalgorithmdevelopedbytheUS.
DesignatedBridge
Thebridgethatincursthelowestpathcostwhenforwardingaframefromasegmenttotheroutebridge.
DesignatedRouter
OSPFrouterthatgeneratesLSAsforamultiaccessnetworkandhasotherspecialresponsibilitiesinrunningOSPF.EachmultiaccessOSPFnetworkthathasatleasttwoattachedroutershasadesignatedrouterthatiselectedbytheOSPFHelloprotocol.Thedesignatedrouterenablesareductioninthenumberofadjacenciesrequiredonamultiaccessnetwork,whichinturnreducestheamountorroutingprotocoltrafficandthesizeofthetopologicaldatabase.
Desktop
IntheMacintoshuserinterface,thebackgroundimageoftheFinderonwhichtheiconsforapplications,directoriesanddatafilesaredisplayed.
DestinationAddress
Addressofanetworkdevicethatisreceivingdata.Seealsosourceaddress.
DeterministicLoadDistribution
Techniquefordistributingtrafficbetweentwobridgesacrossacircuitgroup.Guaranteespacketorderingbetweensourcedestinationpairsandalwaysforwardstrafficforasourcedestinationpaironthesamesegmentinacircuitgroupforagivencircuitgroupconfiguration.
Device
Seenode.
DeviceDriver
SoftwarethatactsasanintermediarybetweenaCPUandaperipheraldevice.TheCPUsendsacommandtothedevicedriver,whichtranslatesthatcommandintoacommandmeaningfultotheperipheraldevice.
DFT
DistributedFunctionTerminal.
DIA
DocumentInterchangeArchitecture.Definestheprotocolsanddataformatsneededforthetransparentinterchangeof

documentsinanSNAnetwork.OneofthreeSNAtransactionservices.SeealsoDDMandSNADS.
Diagnostic
Atestorthedatafromatestwhichindicatestheconditionofthestateofacomputerornetwork'shealth.
DialupLine
Communicationscircuitthatisestablishedbyaswitchedcircuitconnectionusingthetelephonecompanynetwork.
DifferentialEncoding
Digitalencodingtechniquewherebyabinaryvalueisdenotedbyasignalchangeratherthanaparticularsignallevel.
DifferentialManchesterEncoding
Digitalcodingschemewhereamidbittimetransitionisusedforclocking,andatransitionatthebeginningofeachbittimedenotesazero.ThecodingschemeusedbyIEEE802.5andTokenRingnetworks.
Dijkstra'salgorithm
SeeSPF.
DIN
DeutscheIndustrieNorm.Germannationalstandardsorganization.
DINConnector
DeutscheIndustrieNormconnector.MultipinconnectorusedinsomeMacintoshandIBMPCcompatiblecomputers,andonsomenetworkprocessorpanels.
DirectedSearch
Searchrequestsenttoaspecificnodeknowntocontainaresource.Adirectedsearchisusedtodeterminethecontinuedexistenceoftheresourceandtoobtainroutinginformationspecifictothenode.Seealsobroadcastsearch.
DirectMemoryAccess
SeeDMA.
DirectoryServices
Servicesthathelpnetworkdeviceslocateserviceproviders.
DISA
DefenseInformationSystemsAgency.US.militaryorganizationresponsibleforimplementingandoperatingmilitaryinformationsystems,includingtheDDN.SeealsoDDN.
DiscoveryArchitecture
APPNsoftwarethatenablesamachineconfiguredasanAPPNENtoautomaticallyfineprimaryandbackupNNswhenthemachineisbroughtontoanAPPNnetwork.
DiscoveryMode
MethodbywhichanAppleTalkinterfaceacquiresinformationaboutanattachednetworkfromanoperationalnodeandthenusesthisinformationtoconfigureitself.Alsocalleddynamicconfiguration.
DistanceVectorRoutingAlgorithm
Classofroutingalgorithmsthatiterateonthenumberofhopsinaroutetofindashortestpathspanningtree.Distancevectorroutingalgorithmscallforeachroutertosenditsentireroutingtableineachupdate,butonlytoitsneighbors.Distancevectorroutingalgorithmscanbepronetoroutingloops,butarecomputationallysimplerthanlinkstateroutingalgorithms.AlsocalledBellmanFordroutingalgorithm.SeealsolinkstateroutingalgorithmandSPF.
Distortion
Achangeinaelectronicsignalthatoccurswhendifferentfrequencycomponentsofthesignaldecayatdifferentrates.Inasignalmadeupofmanyfrequencycomponents(suchasasquarewave),thehigherfrequencycomponentsofasignaltypicallydecayfasterthanthelowerfrequencycomponents.
DistortionDelay
Problemwithacommunicationsignalresultingfromnonuniformtransmissionspeedsofthecomponentsofasignalthroughatransmissionmedium.Alsocalledgroupdelay.
DLCI
Datalinkconnectionidentifier.ValuethatspecifiesaPVCorSVCinaFrameRelaynetwork.InthebasicFrameRelayspecification,DLCIsarelocallysignificant(connecteddevicesmightusedifferentvaluestospecifythesameconnection).IntheLMIextendedspecification,DLCIsaregloballysignificant(DLCIsspecifyindividualenddevices).SeealsoLMI.
DLL
DynamicallyLinkedLibraries.AcomponentofMicrosoft'sOLE.
DLSw
Datalinkswitching.Interoperabilitystandard,describedinRFC1434,thatprovidesamethodforforwardingSNAandNetBIOStrafficoverTCP/IPnetworksusingdatalinklayerswitchingandencapsulation.DLSwusesSSP(SwitchtoSwitchProtocol)insteadofSRB,eliminatingthemajorlimitationsofSRB,includinghopcountlimits,broadcastandunnecessarytraffic,timeouts,lackofflowcontrol,andlackofprioritizationschemes.SeealsoSRB,andSSP(SwitchtoSwitchProtocol).
DLU
DependentLU.AnLUthatdependsontheSSCPtoprovideservicesforestablishingsessionwithotherLUs.SeealsoLU

andSSCP.
DLUR
DependentLURequester.TheclienthalfoftheDependentLURequester/ServerenhancementtoAPPN.TheDLURcomponentresidesinAPPNENsandNNsthatsupportadjacentDLUsbysecuringservicesfromtheDLUS.SeealsoAPPN,DLU,andDLUS.
DLURNode
InAPPNnetworks,anENorNNthatimplementstheDLURcomponent.SeealsoDLUR.
DLUS
DependentLUServer.TheserverhalfoftheDependentLURequester/ServerenhancementtoAPPN.TheDLUScomponentprovidesSSCPservicestoDLURnodesoveranAPPNnetwork.SeealsoAPPN,DLU,AndDLUR.
DLUSNode
InAPPNnetworks,anNNthatimplementstheDLUScomponent.SeealsoDLUS.
DMA
Directmemoryaccess.Thetransferofdatafromaperipheraldevice,suchasaharddiskdrive,intomemorywithoutthatdatapassingthroughthemicroprocessor.DMAtransfersdataintomemoryathighspeedswithnoprocessoroverhead.
DMAC
DestinationMAC.TheMACaddressspecifiedintheDestinationAddressfieldofapacket.ComparewithSMAC.SeealsoMACaddress.
DNA
DigitalNetworkArchitecture.NetworkarchitecturedevelopedbyDigitalEquipmentCorporation.TheproductsthatembodyDNA(includingcommunicationsprotocols)arecollectivelyreferredtoasDECnet.SeealsoDECnet.
DNIC
DataNetworkIdentificationCode.PartofanX.121address.DNICsaredividedintotwoparts:thefirstspecifyingthecountryinwhichtheaddressedPSNislocatedandthesecondspecifyingthePSNitself.SeealsoX.121.
DNS
DomainNameService
DNSIX
DepartmentofDefenseIntelligenceInformationSystemNetworkSecurityforInformationExchange.CollectionofsecurityrequirementsfornetworkingdefinedbytheUS.DefenseIntelligenceAgency.
DoD
DepartmentofDefense.US.governmentorganizationthatisresponsiblefornationaldefense.TheDoDhasfrequentlyfundedcommunicationprotocoldevelopment.
domain
1.IntheInternet,aportionofthespanninghierarchytreethatreferstogeneralgroupingsofnetworksbasedonorganizationtypeorgeography.2.InSNA,anSSCPandtheresourcesitcontrols.3.InISIS,alogicalsetofnetworks.
Domain
NetworkingsystemdevelopedbyApolloComputer(nowpartofHewlettPackard)foruseinitsengineeringworkstations.
DOS
TheoperatingsystemofIBMcompatiblepersonalcomputers.
DotAddress
ReferstothecommonnotationforIPaddressesintheformwhereeachnumbernrepresents,indecimal,1byteofthe4byteIPaddress.Alsocalleddottednotationorfourpartdottednotation.
DottedNotation
Seedotaddress.
DownlinkStation
Seegroundstation.
Download
Thetransferofafilefromaremotecomputertoalocalcomputer.
Downsizing
Thetransferofcomputingtaskspreviouslyperformedbymainframeorminicomputerstopersonalcomputers.
Downtime
1.Atemporaryinterruptionintheusabilityofacomputersystem.2.Aworkstoppagecausedbythetemporarylackofusabilityofacomputersystem.
DQDB
DistributedQueueDualBus.Datalinklayercommunicationprotocol,specifiedintheIEEE802.6standard,designedforuseinMANs.DQDB,whichpermitsmultiplesystemstointerconnectusingtwounidirectionallogicalbuses,isanopenstandard

thatisdesignedforcompatibilitywithcarriertransmissionstandardsandisalignedwithemergingstandardsforBISDN.SIP(SMDSInterfaceProtocol)isbasedonDQDB.SeealsoMAN.
DRAM
Dynamicrandomaccessmemory.RAMthatstoresinformationincapacitorsthatmustbeperiodicallyrefreshed.DelayscanoccurbecauseDRAMsareinaccessibletotheprocessorwhenrefreshingtheircontents.However,DRAMsarelesscomplexandhavegreatercapacitythanSRAMs.SeealsoSRAM.
Drive
Adatastoragedevice.
Drop
Pointonamultipointchannelwhereaconnectiontoanetworkeddeviceismade.
DropCable
Generally,acablethatconnectsanetworkdevice(suchasacomputer)toaphysicalmedium.AtypeofAUI.SeealsoAUI.
DS0
Digitalsignallevel0.Framingspecificationusedintransmittingdigitalsignalsoverasinglechannelat64kbpsonaT1facility.ComparewithDS1andDS3.
DS1
Digitalsignallevel1.Framingspecificationusedintransmittingdigitalsignalsat1.544MbpsonaT1facility(intheUnitedStates)orat2.108MbpsonanE1facility(inEurope).ComparewithDS0andDS3.
DS1/DTI
DS1domestictrunkinterface.InterfacecircuitusedforDS1applicationswith24trunks.
DS3
Digitalsignallevel3.Framingspecificationusedfortransmittingdigitalsignalsat44.736MbpsonaT3facility.ComparewithDS0andDS1.SeealsoE3andT3.
DSAP
Destinationserviceaccesspoint.TheSAPofthenetworknodedesignatedintheDestinationfieldofapacket.ComparetoSSAP.SeealsoSAP(serviceaccesspoint).
DSP
Domainspecificpart.ThepartofaCLNSaddressthatcontainsanareaidentifier,astationidentifier,andaselectorbyte.
DSPU
Downstreamphysicalunit.InSNA,aPUthatislocateddownstreamfromthehost.
DSPUConcentration
SeeDSPUandPU.
DSR
Datasetready.EIA/TIA232interfacecircuitthatisactivatedwhenDCEispoweredupandreadyforuse.
DSU
Dataserviceunit.DeviceusedindigitaltransmissionthatadaptsthephysicalinterfaceonaDTEdevicetoatransmissionfacilitysuchasT1orE1.TheDSUisalsoresponsibleforfunctionssuchassignaltiming.OftenreferredtotogetherwithCSU,asCSU/DSU.SeealsoCSU.
DSX1
CrossconnectionpointforDS1signals.
DTE
DataTerminalEquipment.TheX.25termforanendnode.Deviceattheuserendofausernetworkinterfacethatservesasadatasource,destination,orboth.DTEconnectstoadatanetworkthroughaDCEdevice(forexample,amodem)andtypicallyusesclockingsignalsgeneratedbytheDCE.CTEincludesdevicessuchascomputers,protocoltranslators,andmultiplexers.ComparewithDCE.
DTMF
Dualtonemultifrequency.Useoftwosimultaneousvoicebandtonesfordialing(suchastouchtone).
DTR
Dataterminalready.EIA/TIA232circuitthatisactivatedtolettheDCEknowwhentheDTEisreadytosendandreceivedata.
DTS
DistributedTimeService.
DUAL
DiffusingUpdateAlgorithm.ConvergencealgorithmusedinEnhancedIGRPthatprovidesloopfreeoperationateveryinstantthroughoutaroutecomputation.Allowsroutersinvolvedinatopologychangetosynchronizeatthesametime,whilenotinvolvingroutersthatareunaffectedbythechange.SeealsoEnhancedIGRP.
DualCounterrotationRing

Networktopologyinwhichtwosignalpaths,whosedirectionsareoppositeoneanother,existinatokenpassingnetwork.FDDIandCDDIarebasedonthisconcept.
DualhomedStation
DeviceattachedtomultipleFDDIringstoprovideredundancy.
DualHoming
Networktopologyinwhichadeviceisconnectedtothenetworkbywayoftwoindependentaccesspoints(pointsofattachment).Oneaccesspointistheprimaryconnection,andtheotherisastandbyconnectionthatisactivatedintheeventofafailureoftheprimaryconnection.
DualISIS
SeeIntegratedISIS.
DVMRP
DistanceVectorMulticastRoutingProtocol.Internetworkgatewayprotocol,largelybasedonRIP,thatimplementsatypicaldensemodeIPmulticastscheme.DVMRPusesIGMPtoexchangeroutingdatagramswithitsneighbors.SeealsoIGMP.
DXI
DataExchangeInterface.ATMForumspecification,describedinRFC1483,thatdefineshowanetworkdevicesuchasabridge,router,orhubcaneffectivelyactasanFEPtoanATMnetworkbyinterfacingwithaspecialDSUthatperformspacketsegmentationandreassembly.
DynamicAddressResolution
Useofanaddressresolutionprotocoltodetermineandstoreaddressinformationondemand.
DynamicAddressing
Asystemofaddressinginwhichthecomputerselectsitsownaddresswithouttheuser'sintervention.
DynamicConfiguration
Seediscoverymode.
DynamicRouting
Routingthatadjustsautomaticallytonetworktopologyortrafficchanges.Alsocalledadaptiverouting.
E1
WideareadigitaltransmissionschemeusedpredominantlyinEuropethatcarriesdataatarateof2.048Mbps.E1linescanbeleasedforprivateusefromcommoncarriers.ComparewithT1.SeealsoDS1.
E.164
ITUTrecommendationforinternationaltelecommunicationnumbering,especiallyinISDN,BISDN,andSMDS.Anevolutionofstationtelephonenumbers.
E3
Wideareadigitaltransmissionscheme,usedpredominantlyinEurope,thatcarriesdataatarateof34.368Mbps.E3linescanbeleasedforprivateusefromcommoncarrier.ComparewithT3.SeealsoDS3.
Email
ElectronicMail.Anetworkapplicationthatcandelivermessagesfromonecomputerusertoanother.
EarlyTokenRelease
TechniqueusedinTokenRingnetworksthatallowsastationtoreleaseanewtokenontotheringimmediatelyaftertransmitting,insteadofwaitingforthefirstframetoreturn.Thisfeaturecanincreasethetotalbandwidthonthering.SeealsoTokenRing.
EARN
EuropeanAcademicResearchNetwork.Europeannetworkconnectinguniversitiesandresearchinstitutes.EARNmergedwithRAREtoformTERENA.SeealsoRAREandTERENA.
EBCDIC
Extendedbinarycodedecimalinterchangecode.AnyofanumberofcodedcharactersetsdevelopedbyIBMconsistingof8bitcodedcharacters.ThischaractercodeisusedbyolderIBMsystemsandtelexmachines.ComparewithASCII.
EChannel
Echochannel.64KbpsISDNcircuitswitchingcontrolchannel.TheEchannelwasdefinedinthe1984ITUTISDNspecification,butwasdroppedinthe1988specification.ComparewithBchannel,Dchannel,andHchannel.
Echo
1.Inelectronicsignaling,thereflectionofasignalcausedbyasuddenchangeintheimpedanceofthecarrier.2.Anetworkcontinuitytestwherepacketsaresenttoadistantnodethatisobligatedtoimmediatelysendthepacketsback.
EchoChannel
SeeEchannel.
Echoplex
Modeinwhichkeyboardcharactersareechoedonaterminalscreenuponreturnofasignalfromtheotherendofthelineindicatingthatthecharacterswerereceivedcorrectly.

EchoProtocol
IntheAppleTalkprotocolfamily,aprotocolthatallowsacomputertoreturntestpackets.ThepurposeofEchoProtocolisttestthedeliveryconditionstoaremotenode,includingreachability,reliabilityandroundtriptime.
EchoTest
Adiagnostictestinwhichpacketsaresentbyonenodetoanothernode,whichimmediatelyreturnsthemtotheoriginalnode.Thedatarecordedbytheechotestincludesthesuccessrateofthereturnaswellasthetimeneededtocompletetheroundtrip.
ECMA
EuropeanComputerManufacturersAssociation.GroupofEuropeancomputervendorswhohavedonesubstantialOSIstandardizationwork.
EDI
ElectronicDocument(orData)Interchange.ThetermEDIusuallyconnotesasystemwhereauthenticationandsecuritymethodsguaranteetheintegrityandoriginoftheinformation.
EDIFACT
ElectronicDataInterchangeforAdministration,Commerce,andTransport.DataexchangestandardadministeredbytheUnitedNationstobeamultiindustryEDIstandard.
EEPROM
Electricallyerasableprogrammablereadonlymemory.EPROMthatcanbeerasedusingelectricalsignalsappliedtospecificpins.SeealsoEPROM.
EGP
ExteriorGatewayProtocol.Internetprotocolforexchangingroutinginformationbetweenautonomoussystems.DocumentedinRFC904.Nottobeconfusedwiththegeneraltermexteriorgatewayprotocol.EGPisanobsoleteprotocolthathasbeenreplacedbyBGP.SeealsoBGP.
EIA
ElectronicIndustriesAssociation.Groupthatspecifieselectricaltransmissionstandards.TheEIAandTIAhavedevelopednumerouswellknowncommunicationsstandards,includingEIA/TIA232andEIA/TIA449.SeealsoTIA.
EIA530
ReferstotwoelectricalimplementationsofEIA/TIA449:RS422(forbalancedtransmission)andRS423(forunbalancedtransmission).Seealso422,RS423,andEIA/TIA449.
EIA/TIA232
CommonphysicallayerinterfacestandarddevelopedbyEIAandTIA,thatsupportsunbalancedcircuitsatsignalspeedsofupto64kbps.CloselyresemblestheV.24specification.FormerlyknownasRS232.
EIA/TIA449
PopularphysicallayerinterfacedevelopedbyEIAandTIA.Essentially,afaster(upto2Mbps)versionofEIA/TIA232capableoflongercableruns.FormerlycalledRS449.SeealsoEIA530.
EIA/TIA586
StandardthatdescribesthecharacteristicsandapplicationsforvariousgradesofU

Networking Terms Glossary _ Definitions of Network Technology

Documents

Glossary of Marketing Definitions

Glossary of ZIMS Terms and Definitions -...

Glossary of Terms and Definitions - Stakeholdermap.com ·.....

20B Definitions and glossary · Definitions and glossary...

Cancer Glossary Definitions

Autonomic Networking – Definitions and Design Goals ·...

GLOSSARY OF INTELLIGENCE TERMS AND DEFINITIONS

IEEE standard glossary of computer networking terminology...

Home NetworkingHome Networking Glossary Below is a list of.....

Glossary of Stock Market Terms and Definitions

Bible Glossary & Definitions - Life More Abundant...

FSA Handbook: Guidance on the Glossary of definitions...

GLOSSARY OF MARKETING DEFINITIONS -...

A Glossary of Basic Terms and Definitions

Computer Networking Definitions

Computer Networking Glossary