Networking Terms Glossary _ Definitions of Network Technology

5/3/2015 NetworkingTermsGlossary|DefinitionsofNetworkTechnology

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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.

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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

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