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ITU V.42:2002

ITU V.42:2002 Error-correcting Procedures For Dces Using Asynchronous-to-synchronous Conversion Describes error-correcting protocols for use with V-series duplex DCEs to accept start-stop data from the DTE and transmit in synchronous mode. Contains HDLC-based protocol referred to as the Link Acc

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Table of Contents

FOREWORD
CONTENTS
1Scope
1.1General
1.2Relationshiptootherinternationalstandards
1.3References
2Definitions
3Abbreviations
4Establishinganerror-correctedconnection
5Interchangecircuitsaffectedbyerrorcorrection
6Overviewoferror-correctingDCEoperation
6.1General
6.2Overviewofthecontrolfunction
6.3Overviewoftheerrorcontrolfunction
6.4Communicationbetweenthecontrolfunctionandthe
errorcontrolfunction
7Operationofthecontrolfunction
7.1Physicalhandshake
7.2Phasesoferror-correctingprotocolestablishment
7.2.1Detectionphase
7.2.2Protocolestablishmentphase
7.3Datatransfer
7.3.1FlowcontrolacrosstheDTE/DCEinterface
7.4Transferofbreaksignal
7.5Receiptofbreak
7.6Negotiation/Indicationofparametervaluesand
optionalprocedures
7.7Orderlyreleaseoftheerror-correctedconnection
7.8Loop-backtest
7.9OperationoftheDTE-DCEinterfaceafterfailureto
establisherror-co
7.10Suspensionoferrorcorrectionprocedure
7.10.1ReceptionofL-SUSPENDrequestprimitive
duringthedetectionphase
7.10.2ReceptionofL-SUSPENDrequestprimitive
duringtheprotocolestablishmentphaseor
afteranerror...
7.11Resumptionoferrorcorrectionprocedure
8Operationoftheerrorcontrolfunction:LAPMprocedures
8.1General
8.1.1Framestructureandfields
8.1.2Formatconventions
8.1.3Invalidframes
8.1.4Frameabort
8.1.5Interframetimefill
8.2LAPMelementsofproceduresandfieldformats
8.2.1Addressfieldformat
8.2.2Controlfieldformat
8.2.3Controlfieldparametersandassociatedstate
variables
8.2.4Frametypes
8.2.5Useoftimers
8.3Establishmentoftheerror-correctedconnection
8.3.1General
8.3.2Detailedprocedures
8.4TransferofuserdatafromtheV.24interface
8.4.1TransmittingIframes
8.4.2ReceivingIframes
8.4.3Sendingandreceivingacknowledgements
8.4.4ReceivingREJframes
8.4.5ReceivingSREJframes
8.4.6ReceivingRNRframes
8.4.7Own-receiverbusycondition
8.4.8Waitingacknowledgement
8.4.9Terminationoftheerror-correctedconnection
8.5Exceptionconditionreportingandrecovery
8.5.1N(S)sequenceerror
8.5.2N(R)sequenceerror
8.5.3Timer-recoverycondition
8.5.4Invalid-framecondition
8.5.5Frame-rejectioncondition
8.5.6ReceiptofanFRMRresponseframe
8.5.7Unsolicitedresponseframes
8.6Transferofuser-controlinformation
8.7Orderlyreleaseofanerror-correctedconnection
8.7.1General
8.7.2Releaseprocedure
8.7.3ProcedureonexpiryoftimerT401
8.8Disconnectedstate
8.9Collisionofunnumberedcommandsandresponses
8.9.1Identicaltransmittedandreceivedset-mode
commands
8.9.2Differenttransmittedandreceivedset-mode
commands
8.9.3UnsolicitedDMresponseandSABMEorDISC
command
8.10Negotiation/indicationofparametervaluesand
optionalprocedures
8.10.1General
8.10.2Negotiation/Indicationprocedure
8.10.3ProcedureonexpiryoftimerT401
8.11Loop-backtest
8.12Monitoringfunctions
8.12.1General
8.12.2Supervisionduringtheconnectedstate
8.12.3Connectionverificationprocedures
8.13Transferofbreak
8.13.1General
8.13.2Statevariablesandparameters
8.13.3Breakprocedures
9Systemparameters
9.1Parametersofthecontrolfunction
9.1.1Detectionphasetimer(T400)
9.2Parametersoftheerrorcontrolfunction
9.2.1Acknowledgementtimer(T401)
9.2.2Maximumnumberofretransmissions(N400)
9.2.3Maximumnumberofoctetsinaninformation
field(N401)
9.2.4Windowsize(k)
9.2.5Replydelaytimer(T402)-Optional
9.2.6Inactivitytimer(T403)-Optional
9.2.7DLCIvalues
9.3Otherparameters
10Negotiationofoptionalprocedures
11Controlfunction-to-controlfunctionconnection
12Encodingofinformationfields
12.1InformationfieldsinIframes
12.2InformationfieldsinXIDframes
12.2.1General
12.2.2Encodingfornegotiation/indicationof
parametervaluesandoptionalprocedures
12.3InformationfieldsinUIframes
12.3.1EncodingofBRKmessage
12.3.2EncodingofBRKACKmessage
12.4InformationfieldsinTESTframe
12.5InformationfieldsinSREJframes
AnnexA-Operationoftheerrorcontrolfunction-
Alternativeprocedure
AnnexB-Mappingofcharacterformatsto8-bitformat
AppendixI-Interworkingwithanon-errorcorrectingDCE
I.1Interworkingwithanon-error-correctinganswerer
I.2Interworkingwithanon-error-correctingoriginator
I.3Dispositionofunrecognizedbits
AppendixII-Dataforwardingconditions
AppendixIII-AdditionalinformationforV.42implementers
regardingrobustnessofoperation
III.1Transmissionoftheanswererdetectionpattern
III.2ValueofparameterN400(maximumnumberof
retransmissions)
III.3IncompleteXIDexchange
III.4Selectiveretransmission
III.5Rejectondetectionoferroredframes
III.6Checkpointing
AppendixIV-Factorsfordeterminingtheacknowledgement
timer
AppendixV-PotentialenhancementstoLAPMprotocol
AppendixVI-AdditionalinformationforV.42implementers
regardinganswererdetectionpatterns
VI.1Alternativeanswererdetectionpatterns
VI.2Skippingoforiginator/answererdetectionpatterns

Abstract

Describes error-correcting protocols for use with V-series duplex DCEs to accept start-stop data from the DTE and transmit in synchronous mode. Contains HDLC-based protocol referred to as the Link Access Procedure for Modems (LAPM). Provides addition of the capability for suspension and resumption of error correction in support of the V.92 modem-on-hold feature. Also gives guidance on the use of answerer detection patterns.

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