SIST EN 300 938 V6.2.1:2003

• 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 V6.2.1 (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 6.2.1 Release 1997)

Overview

SIST EN 300 938 V6.2.1:2003 specifies the Data Link (DL) layer protocol for the interface between Mobile Stations (MS) and Base Station Systems (BSS) within the Global System for Mobile Communications (GSM) Phase 2+. As an adopted Slovenian standard identical to EN 300 938, it provides essential guidelines for implementing reliable and efficient signaling and information transfer over the air interface in digital cellular networks. This standard is vital for manufacturers, network operators, and solution developers working with GSM technologies, ensuring interoperability and consistent communication between network elements.

Key Topics

• Data Link Layer (DL) Protocol: Defines rules and structures for data exchange at Layer 2 between mobile devices and base stations over the GSM network.
• LAPDm (Link Access Procedure for the Dm Channel): Specifies procedures and frame formats derived from LAPD, adapted for mobile communications to ensure robust peer-to-peer and layer-to-layer communication.
• Frame Structures: Outlines various frame formats (A, B, Bbis, Bter, B4, etc.) suitable for different GSM signaling channels, accommodating both acknowledged and unacknowledged operations.
• Operational Modes:
  • Unacknowledged operation-typically used on broadcast and common control channels.
  • Acknowledged operation-applied to dedicated channels requiring guaranteed delivery.
• Error Handling: Defines mechanisms for detecting and responding to parameter errors in address, control, and length indicator fields within frames.
• Random Access Procedures: Provides normative procedures for random access channel usage, crucial for mobile stations requesting channel access.
• Layer-to-Layer Communication Primitives: Specifies standard requests, responses, indications, and confirm procedures supporting robust multi-layer communication.

Applications

Implementing SIST EN 300 938 V6.2.1:2003 has significant practical value in digital cellular telecommunications:

• Interoperability: Enables equipment from different manufacturers to communicate seamlessly within GSM networks, ensuring reliable mobile service for end-users.
• Network Scalability: Supports efficient signaling for large-scale deployments, allowing operators to expand GSM services without compromising consistency.
• Error Management: By clearly defining error reporting and recovery, the standard minimizes service interruptions and enhances system resilience.
• Optimized Communication: Ensures efficient use of bandwidth and timely delivery of messages, which is critical for both voice and data services in mobile networks.
• Legacy Support: Serves as a foundation for continued maintenance and improvement of existing GSM infrastructure, facilitating smooth transitions to advanced network architectures as needed.
• Compliance and Certification: Assists regulatory bodies and operators in verifying that networks and devices adhere to the defined European telecommunication standards.

Related Standards

For comprehensive GSM network implementation and to ensure full protocol compatibility, SIST EN 300 938 V6.2.1:2003 references and works alongside several key standards:

• GSM 04.01: MS-BSS interface general aspects and principles
• GSM 04.03: Channel structures and access capabilities for MS-BSS interface
• GSM 04.05: General aspects of data link (DL) layer in GSM
• GSM 04.07 & 04.08: Layer 3 general aspects and specifications
• GSM 05.02: Multiplexing and multiple access on the radio path
• GSM 08.56 & 08.58: BSC-BTS interface Layer 2 and Layer 3 specifications

Organizations requiring up-to-date GSM implementation should reference these related standards to maintain compliance and achieve optimal network performance.

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Keywords: GSM Phase 2+, Data Link Layer, LAPDm, MS-BSS Interface, Digital Cellular Telecommunications, Frame Structure, Signaling, Error Handling, Mobile Communications Standard, SIST EN 300 938.

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 6.2.1 Release 1997)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 6.2.1SIST EN 300 938 V6.2.1:2003en01-december-2003SIST EN 300 938 V6.2.1:2003SLOVENSKI
STANDARD
ETSIEN300938V6.2.1(2000-09)EuropeanStandard(Telecommunicationsseries)Digitalcellulartelecommunicationssystem(Phase2+);MobileStation-BaseStationSystem(MS-BSS)interface;DataLink(DL)layerspecification(GSM04.06version6.2.1Release1997)GLOBALSYSTEMFORMOBILECOMMUNICATIONSRSIST EN 300 938 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)2(GSM04.06version6.2.1Release1997)ReferenceREN/SMG-020406Q6R2KeywordsDigitalcellulartelecommunicationssystem,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 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)3(GSM04.06version6.2.1Release1997)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.142.8.3Fieldmappingconvention.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.163.4.1Informationtransferformat-I.163.4.2Supervisoryformat-S.163.4.3Unnumberedformat-U.163.4aShortL2headertype1.173.5Controlfieldparametersandassociatedstatevariables.173.5.1Poll/Finalbit.173.5.2Multipleframeoperation-variablesandsequencenumbers.173.5.2.1Modulus.173.5.2.2SendstatevariableV(S).173.5.2.3AcknowledgestatevariableV(A).173.5.2.4SendsequencenumberN(S).183.5.2.5ReceivestatevariableV(R).183.5.2.6ReceivesequencenumberN(R).183.5.2.7Otherparametersandvariables.183.5.3Unacknowledgedoperationvariablesandparameters.183.6Lengthindicatorfieldformat.183.7Lengthindicatorfieldvariables.193.7.1Lengthindicatorfieldextensionbit(EL).193.7.2Moredatabit(M).193.7.3Lengthindicator(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 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)4(GSM04.06version6.2.1Release1997)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.264.2Primitiveprocedures.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).355.4.2Informationtransfer.365.4.2.1Generalrequirements.365.4.2.2Errorconditions.365.4.2.3Fillframes.375.4.3Suspensionandresumptionofmultipleframeoperation.375.4.3.1General.375.4.3.2Suspension.385.4.3.3Resumption.38SIST EN 300 938 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)5(GSM04.06version6.2.1Release1997)5.4.3.3.1Procedureafterchannelchange.385.4.3.3.2Procedureafterreturningtotheoldchannel(MSonly).395.4.4Terminationofmultipleframeoperation.395.4.4.1General.395.4.4.2Normalreleaseprocedure.395.4.4.3ProcedureonexpiryoftimerT200fornormalrelease.405.4.4.4Localendreleaseprocedure.405.4.5Idlestate.405.4.6Collisionofunnumberedcommandsandresponses.415.4.6.1Identicaltransmittedandreceivedcommands.415.4.6.2Differenttransmittedandreceivedcommands.415.4.6.3UnsolicitedDMresponseandSABMorDISCcommand.415.5Proceduresforinformationtransferinmultipleframeoperation.415.5.1TransmittingIframes.415.5.2ReceivingIframes.425.5.2.1PbitofthereceivedIframesetto"1".425.5.2.2PbitofthereceivedIframesetto"0".425.5.3Receivingacknowledgement.435.5.3.1OnreceiptofavalidIframe.435.5.3.2ReceivingsupervisorycommandframeswiththePbitsetto"1".435.5.4ReceivingREJframes.435.5.4.1ReceiptofavalidREJframe.435.5.4.2Transmittingframes.445.5.5ReceivingRNRframe.445.5.6Datalinklayerownreceiverbusycondition.465.5.7Waitingacknowledgement.465.6Abnormalreleaseandre-establishmentofmultipleframeoperation.475.6.1Criteriaforre-establishment.475.6.2Criteriaforabnormalrelease.475.6.3Proceduresforre-establishment.475.6.4Proceduresforabnormalrelease.475.7Exceptionconditionreportingandrecoveryformultipleframeoperation.485.7.1N(S)sequenceerror.485.7.2Timerrecovery.485.7.3Invalidframecondition.485.7.4N(R)sequenceerror.495.8Listofsystemparameters.495.8.1TimerT200.495.8.1.1ForSAPI=0andSAPI=3.495.8.1.2ForSAPIsotherthan0or3.495.8.2Maximumnumberofretransmissions(N200).505.8.2.1ForSAPI=0and3.505.8.2.2ForSAPIsotherthan0or3.505.8.3MaximumnumberofoctetsinanI,UI,SABMandUAframepartiallyorentirelyavailablefortheinformationfield(N201).505.8.4MaximumnumberofoutstandingIframes(k).505.8.5MaximumnumberofoctetsinaLayer3message.505.9Systemperformancerequirements.516SpecialprotocoloperationonSAPI=0andSAPI=3.52AnnexA(normative):Randomaccessprocedures.53A.1Descriptionoftheprocedure.53A.1.1ProcedureintheMS.53A.1.2ProcedureintheBS.53SIST EN 300 938 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)6(GSM04.06version6.2.1Release1997)A.2Format.53AnnexG(normative):Handlingofframeswithparametererrorsintheaddress,controlandlengthindicatorfields.54G.1General.54G.2Parametererrorsintheaddressfield.54G.2.1UnallocatedSAPI.54G.2.2WrongvalueoftheC/Rbit.54G.2.3EAbitsetto"0".54G.3Parametererrorsinthecontrolfield.55G.3.1Supervisoryframes.55G.3.2Unnumberedframes.55G.4Parametererrorsinthelengthindicatorfield.55G.4.1ELbiterror.55G.4.2Informationframes.55G.4.3Supervisoryframes.56G.4.4DISCandDMframes.56G.4.5SABMUAandUIframes.56AnnexH(informative):ChangeRequestHistory.57History.58SIST EN 300 938 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)7(GSM04.06version6.2.1Release1997)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:Version6.x.ywhere:6indicatesRelease1997ofGSMPhase2+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 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)8(GSM04.06version6.2.1Release1997)0ScopeThepresentdocumentdefinesadatalinklayerprotocoltobeusedforsignalling,andpossiblyalsoforotherapplications,ontheMS-BSinterface.0.1ReferencesThefollowingdocumentscontainprovisionswhich,throughreferenceinthistext,constituteprovisionsofthepresentdocument.• Referencesareeitherspecific(identifiedbydateofpublication,editionnumber,versionnumber,etc.)ornon-specific.• Foraspecificreference,subsequentrevisionsdonotapply.• Foranon-specificreference,thelatestversionapplies.• Anon-specificreferencetoanETSshallalsobetakentorefertolaterversionspublishedasanENwiththesamenumber.• ForthisRelease1997document,referencestoGSMdocumentsareforRelease1997versions(version6.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 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)9(GSM04.06version6.2.1Release1997)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 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)10(GSM04.06version6.2.1Release1997)2Framestructureforpeer-to-peercommunication2.1GeneralAlldatalinklayerpeer-to-peerexchangesareinframesconformingtooneoftheformatsshowninfigure1.Severalformattypesareshowninthefigure:-FormatAisusedonDCCHsforframeswherethereisnoinformationfield.-FormatsB,BterandB4areusedonDCCHsforframescontaininganinformationfield:-formatBterisusedonrequestofhigherlayersifandonlyifshortL2headertype1issupportedandaUIcommandistobetransmittedonSAPI0;-formatB4isusedforUIframestransmittedbythenetworkonSACCH;-formatBisappliedinallothercases.-FormatBbisisusedonlyonBCCH,PCH,NCH,andAGCH.-InadditionthereisaFormatCfortransmissionofrandomaccesssignals.FormatCframesaredescribedinannexA.FormatA,B,Bbis,BterandB4framesaredescribedintheremainderofthisETS.Bit87654321OctetNo1:Addressfield:kControlfieldk+1k+2:Lengthindicatorfield:nn+1:Fillbits:N201+nFormattypeAFigure1/GSM04.06(sheet1of3):GeneralframeformatsSIST EN 300 938 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)11(GSM04.06version6.2.1Release1997)Bit87654321OctetNo1:Addressfield:kControlfieldk+1k+2:Lengthindicatorfield:nn+1:Informationfield:NN+1:Fillbits:N201+nFormattypeBBit87654321OctetNo1:::Informationfield:::N201FormattypeBbisFigure1/GSM04.06(sheet2of3):GeneralframeformatsSIST EN 300 938 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)12(GSM04.06version6.2.1Release1997)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.SIST EN 300 938 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)13(GSM04.06version6.2.1Release1997)Theendoftheusefulpartoftheframe,i.e.theendofthelengthindicatorfieldintypeAframesandtheendoftheinformationfieldintypeBframes,isdeterminedbyalengthindicatorcontainedinthelengthindicatorfield.TheusefulpartofaBbisframestakesallN201octetsofthatframe.TheusefulpartofaBterframetakesallN201octetsofthatframeexceptthosebitsofoctet1whichcontaintheshortL2headertype1.TheusefulpartofaB4frametakesallN201octetsofthatframeexceptthoseoctetswhichcontaintheaddressfieldandthecontrolfield.IfaframecontainsalengthindicatorhasavaluelessthanN201,theframecontainsfillbits.Octetscontainingfillbitsshalltakethebinaryvalue"00101011",whensentbythenetwork.Octetscontainingfillbitsshalltakethevalue"00101011"or"11111111",whensentbythemobilestation.NOTE:Thevalue"00101011"ischosenduetothemodulationandinterleavingschemeusedintheGSMsystem.2.3AddressfieldTheaddressfieldmayconsistofavariablenumberofoctets.However,forapplicationsoncontrolchannelsthefieldconsistsofonlyoneoctet.TheaddressfieldidentifiestheSAPforwhichacommandframeisintendedandtheSAPtransmittingaresponseframe.Theformatoftheaddressfieldisdefinedinsubclause3.2.2.4ControlfieldThecontrolfieldconsistsofoneoctet.Theformatofthecontrolfieldisdefinedinsubclause3.4.2.5LengthindicatorfieldThelengthindicatorfieldmayconsistofavariablenumberofoctets.However,forapplicationsoncontrolchannelsthefieldconsistsofonlyoneoctet.Theformatofthefieldisdefinedinsubclause3.6.2.5aShortL2headertype1TheshortL2headertype1consistsoftwobits.Itscontentsaredefinedinsubclause3.4a.2.6InformationfieldTheinformationfieldofaframe,whenpresent,hasthepositionintheframedefinedinsubclause2.1.Themaximumnumberofoctetsintheinformationfield(N201)isdefinedinsubclause5.8.3.2.7TransparencyBecauseoftheframedelimitationtechniqueused(seesubclause2.2),theframecanincludeanypossiblesequenceofbitswithouttheneedforadditionaltransparencymechanisms.2.8Formatconvention2.8.1NumberingconventionThebasicconventionusedinthisTechnicalSpecificationisillustratedinfigure2.Thebitsaregroupedintooctets.Thebitsofanoctetareshownhorizontallyandarenumberedfrom1to8.Multipleoctetsareshownverticallyandarenumberedfrom1ton.SIST EN 300 938 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)14(GSM04.06version6.2.1Release1997)Bit87654321Octetno12;;nFigure2/GSM04.06:Formatconvention2.8.2OrderofbittransmissionTheorderofbittransmissionisdefinedinGSM04.04.2.8.3FieldmappingconventionWhenafieldiscontainedwithinasingleoctet,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;SIST EN 300 938 V6.2.1:2003

ETSIETSIEN300938V6.2.1(2000-09)15(GSM04.06version6.2.1Release1997)-andtheLinkProtocolDiscriminatorLPD.Theformatoftheaddressfieldforcontrolchannelsisshowninfigure4.Theaddressfieldextensionbit,EA,enablesextensionofthefieldtospanmorethanoneoctet.Thevalue"0"isusedtoindicateanextension,thevalue"1"shallbeusedforthefinaladdressfieldoctet.TheLinkProtocolDiscriminator(LPD)correspondingtotheuseinthisTechnicalSpecificationshalltakethevalue"00",allothervaluesarereserved.NOTE:LPD="01"correspondstothedatalinkprotocolusedforSMSCB(seeGSM04.12).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",andresponsesaresentwithC/Rsetto"0".ThecombinationsfortheBSsideandMSsideareshownintable1.Table1/GSM04.06:C/RfieldbitusageTypeDirectionC/RvalueCommandBSsidetoMSside1MSsidetoBSside0ResponseBSsidetoMSside0MSsidetoBSside13.3.3Serviceaccesspointidentifier(SAPI)Theserviceaccesspointidentifier(SAPI)identifiesapointatwhichdatalinklayerservicesareprovidedbythedatalinklayertoalayer3entity(seeGSM04.05).TheSAPIallows8serviceaccesspointstobespecifiedinitially,wherebit3oftheaddressfieldoctetcontainingtheSAPIistheleastsignificantbinarydigitandbit5isthemostsignificant.TheSAPIvaluesareallocatedasshownintable2.SIST EN 300 938 V6.2.1:2003

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