SIST EN 300 938 V7.1.2:2003

• Abstract:

  CR SMG#31

• Status: Published
• Publication Date: 30-Nov-2003
• ICS: 33.070.50 - Global System for Mobile Communication (GSM)
• Technical Committee: SS EIT - Technical Board for the electrotechnical, information technology and telecommunications fields
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Dec-2003
• Due Date: 01-Dec-2003
• Completion Date: 01-Dec-2003
• Ref Project: ETSI EN 300 938 V7.1.2 (2000-09) - Digital cellular telecommunications system (Phase 2+) (GSM); Mobile Station - Base Station System (MS - BSS) interface; Data Link (DL) layer specification (GSM 04.06 version 7.1.2 Release 1998)

Overview

SIST EN 300 938 V7.1.2:2003 specifies the Data Link (DL) layer protocol for the Mobile Station - Base Station System (MS - BSS) interface within the Global System for Mobile Communications (GSM) Phase 2+. Developed in alignment with ETSI EN 300 938 (GSM 04.06 version 7.1.2, Release 1998), this standard defines the rules and structures necessary for effective digital cellular communication between mobile devices (MS) and base stations (BSS). It establishes a reliable foundation for signaling and data transfer by standardizing peer-to-peer and layer-to-layer communication protocols at the data link layer (Layer 2) of the GSM radio interface.

The document is essential for organizations and professionals designing, implementing, or maintaining GSM networks, ensuring system compatibility and interoperability at an international level. It covers the LAPDm (Link Access Procedure on the Dm channel) protocol, its frame structures, operational modes, and procedures for error handling and protocol efficiency.

Key Topics

• Data Link Layer Protocol: The standard outlines the protocol for Layer 2 (L2) communications, primarily for signaling over the MS - BSS interface in GSM networks.
• LAPDm Specification: It details the structure and operation of the LAPDm protocol, including supported modes:
  • Unacknowledged mode (UI frames)
  • Acknowledged mode (multiple frame procedure)
• Frame Structures: Various frame formats are defined for different channel types and operational scenarios, ensuring precise data encapsulation and parsing.
• Procedures and Field Formats: The standard specifies elements such as address fields, control fields, length indicators, and operational parameters necessary for both peer-to-peer and layer-to-layer interactions.
• Error Handling: Clear procedures for identifying and responding to parameter errors in protocol fields help safeguard communication reliability.
• Options and Extensions: Support for short L2 headers, optional for both mobile stations and the network, enhances implementation flexibility.
• Channel Specifics: Protocol applicability across different control channels (BCCH, CCCH, DCCH, SACCH, etc.) is addressed, aligning with needs for both signaling and data on the radio interface.

Applications

SIST EN 300 938 V7.1.2:2003 serves as a fundamental reference for the following applications:

• Telecommunication Equipment Design: Ensuring that mobile stations and base stations comply with GSM network requirements at the data link layer.
• Network Implementation and Maintenance: Supporting system integrators and operators in establishing, troubleshooting, and upgrading GSM infrastructures.
• Interoperability Assurance: Facilitating multi-vendor compatibility and smooth handovers between equipment from different manufacturers.
• Compliance Auditing: Assisting regulatory bodies and certification organizations to verify conformance with GSM international standards.
• Testing and Validation: Providing a basis for the development of test tools, simulators, and validation frameworks for the MS - BSS interface.

By enforcing a rigorous standard for signaling and information transfer procedures, the document enhances network stability and optimizes the user experience across GSM services.

Related Standards

SIST EN 300 938 V7.1.2:2003 is used together with several other GSM and telecommunication standards to ensure complete system conformance. Notable related standards include:

• GSM 04.01: General aspects and principles of the MS-BSS interface.
• GSM 04.03: Channel structures and access capabilities for the MS-BSS interface.
• GSM 04.05: General aspects of the Data Link layer.
• GSM 04.07/04.08: Layer 3 specifications covering signaling for GSM radio interfaces.
• GSM 05.02: Multiplexing and multiple access on the radio path.
• GSM 08.56/08.58: Specifications for the Base Station Controller - Base Transceiver Station (BSC-BTS) interfaces.

These standards collectively underpin global GSM network interoperability and reliability in digital cellular communications.

Keywords: GSM, Mobile Station, Base Station System, MS-BSS interface, Data Link layer, LAPDm, signaling, digital cellular telecommunications, protocol standard, telecommunication networks.

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digital cellular telecommunications system (Phase 2+) (GSM); Mobile Station - Base Station System (MS - BSS) interface; Data Link (DL) layer specification (GSM 04.06 version 7.1.2 Release 1998)33.070.50Globalni sistem za mobilno telekomunikacijo (GSM)Global System for Mobile Communication (GSM)ICS:Ta slovenski standard je istoveten z:EN 300 938 Version 7.1.2SIST EN 300 938 V7.1.2:2003en01-december-2003SIST EN 300 938 V7.1.2:2003SLOVENSKI
STANDARD
ETSIEN300938V7.1.2(2000-09)EuropeanStandard(Telecommunicationsseries)Digitalcellulartelecommunicationssystem(Phase2+);MobileStation-BaseStationSystem(MS-BSS)interface;DataLink(DL)layerspecification(GSM04.06version7.1.2Release1998)GLOBALSYSTEMFORMOBILECOMMUNICATIONSRSIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)2(GSM04.06version7.1.2Release1998)ReferenceREN/SMG-020406Q7R1KeywordsDigitalcellulartelecommunicationssystem,GlobalSystemforMobilecommunications(GSM)ETSI650RoutedesLuciolesF-06921SophiaAntipolisCedex-FRANCETel.:[phone]Fax:[phone]SiretN°34862356200017-NAF742CAssociationàbutnonlucratifenregistréeàlaSous-PréfecturedeGrasse(06)N°7803/88ImportantnoticeIndividualcopiesofthepresentdocumentcanbedownloadedfrom:http://www.etsi.orgThepresentdocumentmaybemadeavailableinmorethanoneelectronicversionorinprint.Inanycaseofexistingorperceiveddifferenceincontentsbetweensuchversions,thereferenceversionisthePortableDocumentFormat(PDF).Incaseofdispute,thereferenceshallbetheprintingonETSIprintersofthePDFversionkeptonaspecificnetworkdrivewithinETSISecretariat.Usersofthepresentdocumentshouldbeawarethatthedocumentmaybesubjecttorevisionorchangeofstatus.InformationonthecurrentstatusofthisandotherETSIdocumentsisavailableathttp://www.etsi.org/tb/status/Ifyoufinderrorsinthepresentdocument,sendyourcommentto:[e-mail]opartmaybereproducedexceptasauthorizedbywrittenpermission.Thecopyrightandtheforegoingrestrictionextendtoreproductioninallmedia.©EuropeanTelecommunicationsStandardsInstitute2000.Allrightsreserved.SIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)3(GSM04.06version7.1.2Release1998)ContentsIntellectualPropertyRights.7Foreword.70Scope.80.1References.80.2Abbreviations.81General.91.1Options.92Framestructureforpeer-to-peercommunication.102.1General.102.2Framedelimitationandfillbits.122.3Addressfield.132.4Controlfield.132.5Lengthindicatorfield.132.5aShortL2headertype1.132.6Informationfield.132.7Transparency.132.8Formatconvention.132.8.1Numberingconvention.132.8.2Orderofbittransmission.132.8.3Fieldmappingconvention.143ElementsofproceduresandformatsoffieldsforDataLinkLayerpeer-to-peercommunication.143.1General.143.2Addressfieldformat.143.3Addressfieldvariables.153.3.1Addressfieldextensionbit(EA).153.3.2Command/responsefieldbit(C/R).153.3.3Serviceaccesspointidentifier(SAPI).153.4Controlfieldformats.153.4.1Informationtransferformat-I.163.4.2Supervisoryformat-S.163.4.3Unnumberedformat-U.163.4aShortL2headertype1.163.5Controlfieldparametersandassociatedstatevariables.163.5.1Poll/Finalbit.173.5.2Multipleframeoperation-variablesandsequencenumbers.173.5.2.1Modulus.173.5.2.2SendstatevariableV(S).173.5.2.3AcknowledgestatevariableV(A).173.5.2.4SendsequencenumberN(S).173.5.2.5ReceivestatevariableV(R).183.5.2.6ReceivesequencenumberN(R).183.5.2.7Otherparametersandvariables.183.5.3Unacknowledgedoperationvariablesandparameters.183.6Lengthindicatorfieldformat.183.7Lengthindicatorfieldvariables.183.7.1Lengthindicatorfieldextensionbit(EL).183.7.2Moredatabit(M).183.7.3Lengthindicator(L).193.8Commandsandresponses.193.8.1Information(I)commands.193.8.2Setasynchronousbalancedmode(SABM)command.203.8.3Disconnect(DISC)command.203.8.4Unnumberedinformation(UI)command.213.8.5Receiveready(RR)command/response.21SIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)4(GSM04.06version7.1.2Release1998)3.8.6Reject(REJ)command/response.213.8.7Receivenotready(RNR)command/response.213.8.8Unnumberedacknowledgement(UA)response.223.8.9Disconnectedmode(DM)response.224Elementsforlayer-to-layercommunication.224.1Definitionofprimitivesandparameters.224.1.1Genericnames.224.1.1.1DL-ESTABLISH.224.1.1.2DL-RELEASE.234.1.1.3DL-DATA.234.1.1.4DL-UNITDATA.234.1.1.5DL-SUSPEND.234.1.1.6DL-RESUME.234.1.1.7DL-RECONNECT.234.1.1.8DL-RANDOMACCESS.234.1.1.9MDL-RELEASE.234.1.1.10MDL-ERROR.234.1.1.11PH-DATA.234.1.1.12PH-RANDOMACCESS.244.1.1.13PH-CONNECT.244.1.1.14PH-READY-TO-SEND.244.1.1.15PH-EMPTY-FRAME.244.1.2Primitivestypes.244.1.2.1REQUEST.244.1.2.2INDICATION.244.1.2.3RESPONSE.244.1.2.4CONFIRM.244.1.3Parameterdefinition.254.1.3.1Messageunit.254.1.3.2Channeltype.254.1.3.3ServiceAccessPoint.254.1.3.4Releasemode.264.1.3.5Errorcause.264.1.3.6Establishmode.264.1.3.7L2headertype.264.1.3.8Priority.274.2Primitiveprocedures.305Definitionofthepeer-to-peerprotocolLAPDm.305.1General.305.2GeneralProtocolProcedures.315.2.1Unacknowledgedinformationtransfer.315.2.2Acknowledgedmultipleframeinformationtransfer.325.3Proceduresforunacknowledgedinformationtransfer.325.3.1General.325.3.2Transmissionofunacknowledgedinformation.325.3.3Receiptofunacknowledgedinformation.325.4Proceduresforestablishmentandreleaseofmultipleframeoperation.325.4.1Establishmentofmultipleframeoperation.325.4.1.1General.325.4.1.2Normalestablishmentprocedures.335.4.1.3ProcedureonexpiryoftimerT200:Normalestablishment.345.4.1.4Contentionresolutionestablishmentprocedure.345.4.1.5ProcedureonexpiryoftimerT200:contentionresolution(MSonly).365.4.2Informationtransfer.365.4.2.1Generalrequirements.365.4.2.2Errorconditions.365.4.2.3Fillframes.375.4.3Suspensionandresumptionofmultipleframeoperation.385.4.3.1General.385.4.3.2Suspension.38SIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)5(GSM04.06version7.1.2Release1998)5.4.3.3Resumption.395.4.3.3.1Procedureafterchannelchange.395.4.3.3.2Procedureafterreturningtotheoldchannel(MSonly).395.4.4Terminationofmultipleframeoperation.405.4.4.1General.405.4.4.2Normalreleaseprocedure.405.4.4.3ProcedureonexpiryoftimerT200fornormalrelease.405.4.4.4Localendreleaseprocedure.415.4.5Idlestate.415.4.6Collisionofunnumberedcommandsandresponses.415.4.6.1Identicaltransmittedandreceivedcommands.415.4.6.2Differenttransmittedandreceivedcommands.425.4.6.3UnsolicitedDMresponseandSABMorDISCcommand.425.5Proceduresforinformationtransferinmultipleframeoperation.425.5.1TransmittingIframes.425.5.2ReceivingIframes.435.5.2.1PbitofthereceivedIframesetto"1".435.5.2.2PbitofthereceivedIframesetto"0".435.5.3Receivingacknowledgement.445.5.3.1OnreceiptofavalidIframe.445.5.3.2ReceivingsupervisorycommandframeswiththePbitsetto"1".445.5.4ReceivingREJframes.445.5.4.1ReceiptofavalidREJframe.445.5.4.2Transmittingframes.455.5.5ReceivingRNRframe.455.5.6Datalinklayerownreceiverbusycondition.465.5.7Waitingacknowledgement.475.5.8Preemption.475.5.8.1SenderRequirements.485.5.8.2ReceiverRequirements.485.6Abnormalreleaseandre-establishmentofmultipleframeoperation.485.6.1Criteriaforre-establishment.485.6.2Criteriaforabnormalrelease.485.6.3Proceduresforre-establishment.495.6.4Proceduresforabnormalrelease.495.7Exceptionconditionreportingandrecoveryformultipleframeoperation.495.7.1N(S)sequenceerror.495.7.2Timerrecovery.505.7.3Invalidframecondition.505.7.4N(R)sequenceerror.505.8Listofsystemparameters.505.8.1TimerT200.515.8.1.1ForSAPI=0andSAPI=3.515.8.1.2ForSAPIsotherthan0or3.515.8.2Maximumnumberofretransmissions(N200).515.8.2.1ForSAPI=0and3.515.8.2.2ForSAPIsotherthan0or3.515.8.3MaximumnumberofoctetsinanI,UI,SABMandUAframepartiallyorentirelyavailablefortheinformationfield(N201).515.8.4MaximumnumberofoutstandingIframes(k).525.8.5MaximumnumberofoctetsinaLayer3message.525.9Systemperformancerequirements.526SpecialprotocoloperationonSAPI=0andSAPI=3.53AnnexA(normative):Randomaccessprocedures.54A.1Descriptionoftheprocedure.54A.1.1ProcedureintheMS.54A.1.2ProcedureintheBS.54SIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)6(GSM04.06version7.1.2Release1998)A.2Format.54AnnexG(normative):Handlingofframeswithparametererrorsintheaddress,controlandlengthindicatorfields.55G.1General.55G.2Parametererrorsintheaddressfield.55G.2.1UnallocatedSAPI.55G.2.2WrongvalueoftheC/Rbit.55G.2.3EAbitsetto"0".55G.3Parametererrorsinthecontrolfield.56G.3.1Supervisoryframes.56G.3.2Unnumberedframes.56G.4Parametererrorsinthelengthindicatorfield.56G.4.1ELbiterror.56G.4.2Informationframes.56G.4.3Supervisoryframes.57G.4.4DISCandDMframes.57G.4.5SABMUAandUIframes.57AnnexH(informative):ChangeRequestHistory.58History.59SIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)7(GSM04.06version7.1.2Release1998)IntellectualPropertyRightsIPRsessentialorpotentiallyessentialtothepresentdocumentmayhavebeendeclaredtoETSI.TheinformationpertainingtotheseessentialIPRs,ifany,ispubliclyavailableforETSImembersandnon-members,andcanbefoundinETSISR000314:"IntellectualPropertyRights(IPRs);Essential,orpotentiallyEssential,IPRsnotifiedtoETSIinrespectofETSIstandards",whichisavailablefromtheETSISecretariat.LatestupdatesareavailableontheETSIWebserver(http://www.etsi.org/ipr).PursuanttotheETSIIPRPolicy,noinvestigation,includingIPRsearches,hasbeencarriedoutbyETSI.NoguaranteecanbegivenastotheexistenceofotherIPRsnotreferencedinETSISR000314(ortheupdatesontheETSIWebserver)whichare,ormaybe,ormaybecome,essentialtothepresentdocument.ForewordThisEuropeanStandard(Telecommunicationsseries)hasbeenproducedbyETSITechnicalCommitteeSpecialMobileGroup(SMG).ThepresentdocumentdefinesthedatalinklayerprotocoloftheMobileStation-BaseStationSystem(MS-BSS)interfacewithinthedigitalcellulartelecommunicationssystem.ThecontentsofthepresentdocumentissubjecttocontinuingworkwithinSMGandmaychangefollowingformalSMGapproval.ShouldSMGmodifythecontentsofthepresentdocument,itwillbere-releasedwithanidentifyingchangeofreleasedateandanincreaseinversionnumberasfollows:Version7.x.ywhere:7indicatesRelease1998ofGSMPhase2+xtheseconddigitisincrementedforallchangesofsubstance,i.e.technicalenhancements,corrections,updates,etc.ythethirddigitisincrementedwheneditorialonlychangeshavebeenincorporatedinthespecification.ThespecificationfromwhichthepresentdocumenthasbeenderivedwasoriginallybasedonCEPTdocumentation,hencethepresentationofthepresentdocumentmaynotbeentirelyinaccordancewiththeETSIdraftingrules.AnnexesBtoFweredeletedfromtheoriginalspecification,however,forreferencingpurposestheannexnumberinghasbeenmaintained.NationaltranspositiondatesDateofadoptionofthisEN:25August2000DateoflatestannouncementofthisEN(doa):30November2000DateoflatestpublicationofnewNationalStandardorendorsementofthisEN(dop/e):31May2001DateofwithdrawalofanyconflictingNationalStandard(dow):31May2001SIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)8(GSM04.06version7.1.2Release1998)0ScopeThepresentdocumentdefinesadatalinklayerprotocoltobeusedforsignalling,andpossiblyalsoforotherapplications,ontheMS-BSinterface.0.1ReferencesThefollowingdocumentscontainprovisionswhich,throughreferenceinthistext,constituteprovisionsofthepresentdocument.• Referencesareeitherspecific(identifiedbydateofpublication,editionnumber,versionnumber,etc.)ornon-specific.• Foraspecificreference,subsequentrevisionsdonotapply.• Foranon-specificreference,thelatestversionapplies.• Anon-specificreferencetoanETSshallalsobetakentorefertolaterversionspublishedasanENwiththesamenumber.• ForthisRelease1998document,referencestoGSMdocumentsareforRelease1998versions(version7.x.y).[1]GSM01.04:"Digitalcellulartelecommunicationssystem(Phase2+);Abbreviationsandacronyms".[2]GSM04.01:"Digitalcellulartelecommunicationssystem;MobileStation-BaseStationSystem(MS-BSS)interface;Generalaspectsandprinciples".[3]GSM04.03:"Digitalcellulartelecommunicationssystem(Phase2+);MobileStation-BaseStationSystem(MS-BSS)interfaceChannelstructuresandaccesscapabilities".[4]GSM04.04:"Digitalcellulartelecommunicationssystem;Layer1Generalrequirements".[5]GSM04.05:"Digitalcellulartelecommunicationssystem;DataLink(DL)layerGeneralaspects".[6]GSM04.07:"Digitalcellulartelecommunicationssystem(Phase2+);Mobileradiointerfacesignallinglayer3;Generalaspects".[7]GSM04.08:"Digitalcellulartelecommunicationssystem(Phase2+);Mobileradiointerfacelayer3specification".[8]GSM04.10:"Digitalcellulartelecommunicationssystem;Mobileradiointerfacelayer3Supplementaryservicesspecification;Generalaspects".[9]GSM04.12:"Digitalcellulartelecommunicationssystem(Phase2+);ShortMessageServiceCellBroadcast(SMSCB)supportonthemobileradiointerface".[10]GSM05.02:"Digitalcellulartelecommunicationssystem(Phase2+);Multiplexingandmultipleaccessontheradiopath".[11]GSM08.56:"Digitalcellulartelecommunicationssystem;BaseStationController-BaseTransceiverStation(BSC-BTS)interface;Layer2specification".[12]GSM08.58:"Digitalcellulartelecommunicationssystem(Phase2+);BaseStationController-BaseTransceiverStation(BSC-BTS)interface;Layer3specification".[13]CCITTRecommendationZ.100:"Specificationanddescriptionlanguage(SDL)".0.2AbbreviationsAbbreviationsusedinthepresentdocumentarelistedinGSM01.04.SIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)9(GSM04.06version7.1.2Release1998)1GeneralThepresentdocumentdescribestheframestructure,elementsofprocedure,formatoffieldsandproceduresfortheproperoperationoftheLinkAccessProcedureontheDmchannel,LAPDm.NOTE1:ThetermDmchannelisusedforconveniencetodesignatethecollectionofallthevarioussignallingchannelsrequiredintheGSMsystem.SeealsoGSM04.03.Theconcepts,terminology,overviewdescriptionofLAPDmfunctionsandprocedures,andtherelationshipwithotherTechnicalSpecificationsaredescribedingeneraltermsinGSM04.05.TheframeformatsdefinedforLAPDmarebasedonthosedefinedforLAPD.However,thereareimportantdifferencesbetweenLAPDmandLAPD,inparticularwithregardtoframedelimitationmethodsandtransparencymechanisms.Thesedifferencesarenecessaryforoperationwithintheconstraintssetbytheradiopath.LAPDmsupportstwomodesofoperation:-unacknowledgedoperationusingUIframes;-acknowledgedoperationusingthemultipleframeprocedure.Asachoiceofimplementation,thetwomodesofoperationmaybeimplementedindependentlyofeachother.Thisispossiblesincethereisnointeractionsbetweenthetwomodes,otherthanqueuingatthetransmitter,evenwhentheycoexistonthesamephysicalchannel.ForBCCHsandCCCHsonlytheunacknowledgedmodeofoperationneedstobeimplemented.LAPDmisusedforinformationsentonthecontrolchannelsBCCH,AGCH,NCH,PCH,FACCH,SACCHandSDCCHasdefinedinGSM04.03.NOTE2:AGCH,NCHandPCHaresometimesreferredtobythecollectivenameCCCHandFACCH,SACCHandSDCCHare,similarly,referredtobythecollectivenameDCCH.LAPDmmayalsobeusedonothertypesofchannel.NOTE3:AsstatedinGSM04.05,theterm"datalinklayer"isusedinthemaintextofthisTechnicalSpecification.However,mainlyinfiguresandtables,theterms"layer2"and"L2"areusedasabbreviations.Furthermore,inaccordancewithGSM04.07andGSM04.08,theterm"layer3"isusedtoindicatethelayerabovethedatalinklayer.ThisTechnicalSpecificationisorganizedasfollows.Theframestructureforpeer-to-peercommunicationisgiveninclause2.Theelementsofprocedureandformatsoffieldsaregiveninclause3.Theelementsoflayer-to-layercommunicationarecontainedinclause4.Thedetailsofthepeer-to-peerproceduresaregiveninclause5.Section6summarizesthespecialprotocoloperationsusedmandatorilywithSAPI=0andSAP=3.ThespecificationfortherandomaccesschanneliscontainedinannexA,eventhoughitisnotaLAPDmfunction.Thepresentdocumentisdescriptiveanddoesnotconstraintheimplementationoftherandomaccessfunction.TheprocedureisusedforCHANNELREQUESTontheRACHandHANDOVERACCESSonthemainDCCH.(AnnexesBtoFaredeleted).AnnexGgivesanoverviewofactionstakenonframescontainingparametererrors.1.1OptionsSupportofshortL2headertype1isanoptioninboththemobilestationandthenetwork;undercertainconditionsthesupportismandatory,asspecifiedinotherSpecifications.Alayer2protocolentitynotimplementingshortL2headertype1shalldiagnoseanE/AbiterrorandproceedasdefinedinannexG.2.3.SIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)10(GSM04.06version7.1.2Release1998)2Framestructureforpeer-to-peercommunication2.1GeneralAlldatalinklayerpeer-to-peerexchangesareinframesconformingtooneoftheformatsshowninfigure1.Severalformattypesareshowninthefigure:-FormatAisusedonDCCHsforframeswherethereisnoinformationfield.-FormatsB,BterandB4areusedonDCCHsforframescontaininganinformationfield:-formatBterisusedonrequestofhigherlayersifandonlyifshortL2headertype1issupportedandaUIcommandistobetransmittedonSAPI0;-formatB4isusedforUIframestransmittedbythenetworkonSACCH;-formatBisappliedinallothercases.-FormatBbisisusedonlyonBCCH,PCH,NCH,andAGCH.-InadditionthereisaFormatCfortransmissionofrandomaccesssignals.FormatCframesaredescribedinannexA.FormatA,B,Bbis,BterandB4framesaredescribedintheremainderofthepresentdocument.Bit87654321OctetNo1:Addressfield:kControlfieldk+1k+2:Lengthindicatorfield:nn+1:Fillbits:N201+nFormattypeAFigure1/GSM04.06(sheet1of3):GeneralframeformatsSIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)11(GSM04.06version7.1.2Release1998)Bit87654321OctetNo1:Addressfield:kControlfieldk+1k+2:Lengthindicatorfield:nn+1:Informationfield:NN+1:Fillbits:N201+nFormattypeBBit87654321OctetNo1:::Informationfield:::N201FormattypeBbisFigure1/GSM04.06(sheet2of3):GeneralframeformatsSIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)12(GSM04.06version7.1.2Release1998)Bit87654321OctetNo1:Addressfield:kControlfieldk+1k+2:Informationfield:N201+k+1FormattypeB4Bit87654321OctetNoshortL2headertype112:Informationfield:::N201FormattypeBterFigure1/GSM04.06(sheet3of3):GeneralframeformatsTheparameterN201isthemaximumnumberofoctetswhicharepartiallyorentirelyavailablefortheinformationfieldofaframe.Itdependsonthetypeofchannelandtheformat,seesubclause5.8.3.2.2FramedelimitationandfillbitsFramedelimitationisprovidedbythephysicallayer:-informattypeA,BandB4framesatthebeginningoftheframefordeterminingthestartofthefirstoctetintheaddressfield,informattypeBterframesfordeterminingthestartoftheoctetcontainingtheshortL2headertype1(whichisalsothefirstoctetusedfortheinformationfield),andinformattypeBbisframesfordeterminingthestartofthefirstoctetfortheinformationfield;-attheendoftheframefordeterminingthelastbitoftheframe.Theendoftheusefulpartoftheframe,i.e.theendofthelengthindicatorfieldintypeAframesandtheendoftheinformationfieldintypeBframes,isdeterminedbyalengthindicatorcontainedinthelengthindicatorfield.TheusefulpartofaBbisframestakesallN201octetsofthatframe.TheusefulpartofaBterframetakesallN201octetsofthatframeexceptthosebitsofoctet1whichcontaintheshortL2headertype1.TheusefulpartofaB4frametakesallN201octetsofthatframeexceptthoseoctetswhichcontaintheaddressfieldandthecontrolfield.IfaframecontainsalengthindicatorhasavaluelessthanN201,theframecontainsfillbits.Octetscontainingfillbitsshalltakethebinaryvalue"00101011",whensentbythenetwork.Octetscontainingfillbitsshalltakethevalue"00101011"or"11111111",whensentbythemobilestation.NOTE:Thevalue"00101011"ischosenduetothemodulationandinterleavingschemeusedintheGSMsystem.SIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)13(GSM04.06version7.1.2Release1998)2.3AddressfieldTheaddressfieldmayconsistofavariablenumberofoctets.However,forapplicationsoncontrolchannelsthefieldconsistsofonlyoneoctet.TheaddressfieldidentifiestheSAPforwhichacommandframeisintendedandtheSAPtransmittingaresponseframe.Theformatoftheaddressfieldisdefinedinsubclause3.2.2.4ControlfieldThecontrolfieldconsistsofoneoctet.Theformatofthecontrolfieldisdefinedinsubclause3.4.2.5LengthindicatorfieldThelengthindicatorfieldmayconsistofavariablenumberofoctets.However,forapplicationsoncontrolchannelsthefieldconsistsofonlyoneoctet.Theformatofthefieldisdefinedinsubclause3.6.2.5aShortL2headertype1TheshortL2headertype1consistsoftwobits.Itscontentsaredefinedinsubclause3.4a.2.6InformationfieldTheinformationfieldofaframe,whenpresent,hasthepositionintheframedefinedin2.1.Themaximumnumberofoctetsintheinformationfield(N201)isdefinedinsubclause5.8.3.2.7TransparencyBecauseoftheframedelimitationtechniqueused(seesubclause2.2),theframecanincludeanypossiblesequenceofbitswithouttheneedforadditionaltransparencymechanisms.2.8Formatconvention2.8.1NumberingconventionThebasicconventionusedinthisTechnicalSpecificationisillustratedinfigure2.Thebitsaregroupedintooctets.Thebitsofanoctetareshownhorizontallyandarenumberedfrom1to8.Multipleoctetsareshownverticallyandarenumberedfrom1ton.Bit87654321Octetno12;;nFigure2/GSM04.06:Formatconvention2.8.2OrderofbittransmissionTheorderofbittransmissionisdefinedinGSM04.04.SIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)14(GSM04.06version7.1.2Release1998)2.8.3FieldmappingconventionWhenafieldiscontainedwithinasingleoctet,thelowestbitnumberofthefieldrepresentsthelowestordervalue.Whenafieldspansmorethanoneoctet,theorderofbitvalueswithineachoctetprogressivelydecreasesastheoctetnumberincreases.Inthatpartofthefieldcontainedinagivenoctetthelowestbitnumberrepresentsthelowestordervalue.Forexample,abitnumbercanbeidentifiedasacouple(o,b)whereoistheoctetnumberandbistherelativebitnumberwithintheoctet.Figure3illustratesafieldthatspansfrombit(1,3)tobit(2,7).Thehighorderbitofthefieldismappedonbit(1,3)andtheloworderbitismappedonbit(2,7).Bit876543214321stoctetfield222102ndoctetfield22Figure3/GSM04.06:Fieldmappingconvention3ElementsofproceduresandformatsoffieldsforDataLinkLayerpeer-to-peercommunication3.1GeneralTheelementsofproceduresdefinethecommandsandresponsesthatareusedonthedatalinkconnectionscarriedontheDmchannel.Proceduresarederivedfromtheseelementsofproceduresandaredescribedinclause5.Ifabitpositionismarkedas"spare",itshallbecodedas"0".Forfuturecompatibilityreasons,anentityreceivingframes,wheresparebitpositionsarecodedotherwise,shallignorethosevalueswithoutnotificationofanyerror.3.2AddressfieldformatThefieldconsistsof:-theaddressfieldextensionbitEA;-thecommand/responsebitC/R;-theSAPI;-andtheLinkProtocolDiscriminatorLPD.Theformatoftheaddressfieldforcontrolchannelsisshowninfigure4.Theaddressfieldextensionbit,EA,enablesextensionofthefieldtospanmorethanoneoctet.Thevalue"0"isusedtoindicateanextension,thevalue"1"shallbeusedforthefinaladdressfieldoctet.TheLinkProtocolDiscriminator(LPD)correspondingtotheuseinthisTechnicalSpecificationshalltakethevalue"00",allothervaluesarereserved.NOTE:LPD="01"correspondstothedatalinkprotocolusedforSMSCB(seeGSM04.12).SIST EN 300 938 V7.1.2:2003

ETSIETSIEN300938V7.1.2(2000-09)15(GSM04.06version7.1.2Release1998)Bit87654321SpareLPDSAPIC/REA=1Figure4/GSM04.06:Addressfieldformat3.3Addressfieldvariables3.3.1Addressfieldextensionbit(EA)Theaddressfieldrangeisextendedbyreservingthefirsttransmittedbitoftheaddressfieldoctetstoindicatethefinaloctetoftheaddressfield.Thepresenceofa"1"inthefirstbitofanaddressfieldoctetsignalsthatitisthefinaloctetoftheaddressfield.Figure4showsthecasewherethefieldconsistsofoneoctet.3.3.2Command/responsefieldbit(C/R)TheC/Rbitidentifiesaframeaseitheracommandoraresponse.TheMSsideshallsendcommandswiththeC/Rbitsetto"0",andresponseswiththeC/Rbitsetto"1".TheBSsideshalldotheopposite;thatiscommandsaresentwithC/Rsetto"1",an
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