SIST EN 301 709 V8.0.1:2003

• Abstract:

  Upgrade to R99

• 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 301 709 V8.0.1 (2000-10) - Digital cellular telecommunications system (Phase 2+) (GSM); Link Adaptation (GSM 05.09 version 8.0.1 Release 1999)

Overview

SIST EN 301 709 V8.0.1:2003 is a European standard developed for the digital cellular telecommunications system (GSM Phase 2+), specifically focusing on link adaptation for the Adaptive Multi-Rate (AMR) speech codec. This standard aligns with the 1999 Release (R99) of GSM specifications and outlines mandatory link adaptation procedures for both Mobile Stations (MS) and Base Station Systems (BSS) that support AMR speech traffic channels.

The adoption of effective link adaptation is essential for maximizing spectral efficiency and voice quality in GSM networks, especially under variable radio transmission conditions. This standard provides the framework and detailed protocols needed to dynamically adjust speech and channel codec modes, contributing to more resilient and efficient mobile communications.

Key Topics

• Link Adaptation: Describes procedures for real-time selection of the optimal speech and channel codec mode based on current channel conditions, as measured by the MS or BSS.
• Adaptive Multi-Rate (AMR) Codec: Defines how the AMR codec's configuration and adaptation mechanisms are handled during calls, including codec mode changes and signaling.
• In-band Signaling: Specifies two types of in-band signaling for AMR adaptation:
  • Frequent signaling for codec mode indications and requests.
  • Robust, less frequent signaling for AMR configuration changes (RATSCCH protocol).
• Codec Mode Adaptation: Details how quality indicators derived from radio link measurements are used to determine whether to upgrade or downgrade the codec mode (to balance voice quality and network robustness).
• Tandem Free Operation (TFO): Covers specific procedures for maintaining or adjusting codec modes when TFO is active, allowing efficient end-to-end digital speech transmission.
• Handover Scenarios: Provides guidance on managing codec mode adaptation and synchronization during cell handover, ensuring uninterrupted voice quality.

Applications

This standard is of critical practical importance for:

• Mobile Network Operators: Ensuring interoperable deployment of AMR speech services across network infrastructure from multiple vendors.
• Telecommunications Equipment Manufacturers: Implementing standardized link adaptation features in MS and BSS hardware and software to comply with GSM R99.
• System Integrators and Testers: Verifying compliance with link adaptation protocols to guarantee optimal speech quality and spectrum efficiency.
• Field Engineers and Network Designers: Using the guidance in this standard to tune configuration thresholds for codec adaptation based on real-world network conditions.

Practical benefits enabled by compliance include:

• Improved voice quality for subscribers by dynamically matching codec robustness to channel conditions.
• Increased network capacity and spectral efficiency through optimal use of available radio resources.
• Enhanced resilience to interference, fading, and network congestion during voice calls.

Related Standards

SIST EN 301 709 V8.0.1:2003 is part of a comprehensive suite of GSM standards. Key related documents include:

• GSM 05.09: Core specification for link adaptation in GSM Phase 2+.
• GSM 04.08: Mobile radio interface layer 3 specification.
• GSM 05.03: Channel coding for digital cellular telecommunications.
• GSM 05.05: Transmission and reception technical requirements.
• GSM 08.08: Interface specifications for MSC–BSS communication.
• GSM 08.62: Tandem Free Operation (TFO) protocols and requirements.

These companion standards collectively support interoperable GSM mobile communications, ensuring coordinated adaptation, coding, and signaling processes.

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Keywords: GSM standard, link adaptation, Adaptive Multi-Rate (AMR), in-band signaling, codec mode adaptation, mobile station, base station system, R99, digital cellular telecommunications, speech quality, mobile communication standards, SIST EN 301 709

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digital cellular telecommunications system (Phase 2+) (GSM); Link Adaptation (GSM 05.09 version 8.0.1 Release 1999)33.070.50Globalni sistem za mobilno telekomunikacijo (GSM)Global System for Mobile Communication (GSM)ICS:Ta slovenski standard je istoveten z:EN 301 709 Version 8.0.1SIST EN 301 709 V8.0.1:2003en01-december-2003SIST EN 301 709 V8.0.1:2003SLOVENSKI
STANDARD
ETSIEN301709V8.0.1(2000-10)EuropeanStandard(Telecommunicationsseries)Digitalcellulartelecommunicationssystem(Phase2+);LinkAdaptation(GSM05.09version8.0.1Release1999)GLOBALSYSTEMFORMOBILECOMMUNICATIONSRSIST EN 301 709 V8.0.1:2003

ETSIETSIEN301709V8.0.1(2000-10)2(GSM05.09version8.0.1Release1999)ReferenceREN/SMG-020509Q8KeywordsDigitalcellulartelecommunicationssystem,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 301 709 V8.0.1:2003

ETSIETSIEN301709V8.0.1(2000-10)3(GSM05.09version8.0.1Release1999)ContentsIntellectualPropertyRights.4Foreword.41Scope.51.1References.51.2Abbreviations.52General.63AdaptiveMulti-Rateinbandcontrolandlinkadaptation.63.1Generaloperation.63.1.1OperationwithoutTandemFreeOperation.63.1.2OperationwithongoingTandemFreeOperation.73.1.3OperationathandoverwithongoingTandemFreeOperation.73.2InbandSignalling.73.2.1FrequentinbandsignallingforAMRcodecmodeadaptation.83.2.1.1Generalaspects.83.2.1.2OperationwithDTXenabled.83.2.1.3Transmitter/ReceiverSynchronisation.83.2.2RobustinbandsignallingforAMRconfigurationmodification.83.2.2.1Generalaspects.83.2.2.2RATSCCHprotocol.93.2.2.3RATSCCHmessages.103.2.2.3.1ACK_OKmessage.103.2.2.3.2ACK_ERRmessage.103.2.2.3.3ACK_UNKNOWNmessage.103.2.2.3.4CMI_PHASE_REQmessage.103.2.2.3.5AMR_CONFIG_REQmessage.113.2.2.3.6THRESH_REQmessage.123.3Codecmodeadaptation.123.3.1Channelqualitymeasure.123.3.2GenerationofCodecModeCommandsandRequests.133.3.3Performancerequirements.133.3.3.1MSresponsetotheCodecModeCommand.133.3.3.2BTSresponsetotheCodecModeRequest.133.3.3.3PerformanceoftheCodecModeRequestGeneration.133.4Setupprocedures.143.4.1DefinitionoftheAMRActiveCodecSet.143.4.2DefinitionofCodecModeCommand/Requestdecisionthresholds.143.4.3InitialCodecModeSelectionatCallSetupandHandover.15AnnexA(informative):ExampleSolutionforLinkqualityestimation.16AnnexB(informative):ExampleDefinitionofModeCommand/Requestdecisionthresholds.17AnnexC(informative):PrinciplesforAMRcodecmodeadaptationwithTFO.18C.1Downgrading.18C.1.1Uplinkdowngrading.18C.1.2Downlinkdowngrading.19C.2Upgrading.20C.2.1Downlinkupgrading.20C.2.2Uplinkupgrading.21AnnexD(informative):Changecontrolhistory.22History.23SIST EN 301 709 V8.0.1:2003

ETSIETSIEN301709V8.0.1(2000-10)4(GSM05.09version8.0.1Release1999)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).ThepresentdocumentspecifiestherelevantproceduresforlinkadaptationimplementedintheMobileStation(MS)andBaseStationSystem(BSS)ofthedigitalmobilecellularandpersonalcommunicationsystemsoperatinginthe900MHz,1800MHzand1900MHzband(GSM900,DCS1800andPCS1900).ThecontentsofthepresentdocumentaresubjecttocontinuingworkwithinSMGandmaychangefollowingformalSMGapproval.ShouldSMGmodifythecontentsofthepresentdocumentitwillthenberepublishedbyETSIwithanidentifyingchangeofreleasedateandanincreaseinversionnumberasfollows:Version8.x.ywhere:8indicatesrelease1999ofGSMPhase2+.xtheseconddigitisincrementedforallchangesofsubstance,i.e.technicalenhancements,corrections,updates,etc.ythethirddigitisincrementedwheneditorialonlychangeshavebeenincorporatedinthespecification.NationaltranspositiondatesDateofadoptionofthisEN:1September2000DateoflatestannouncementofthisEN(doa):31December2000DateoflatestpublicationofnewNationalStandardorendorsementofthisEN(dop/e):30June2001DateofwithdrawalofanyconflictingNationalStandard(dow):30June2001SIST EN 301 709 V8.0.1:2003

ETSIETSIEN301709V8.0.1(2000-10)5(GSM05.09version8.0.1Release1999)1ScopeTherequirementsdescribedinthepresentdocumentaremandatoryforimplementationinallGSMMSsandBSSscapableofsupportingtheAdaptiveMulti-Ratespeechtrafficchannel,unlessotherwisestated.Unlessotherwisespecified,referencestoGSMincludeGSMatanyfrequencyband.1.1ReferencesThefollowingdocumentscontainprovisionswhich,throughreferenceinthistext,constituteprovisionsofthepresentdocument.• Referencesareeitherspecific(identifiedbydateofpublication,editionnumber,versionnumber,etc.)ornon-specific.• Foraspecificreference,subsequentrevisionsdonotapply.• Foranon-specificreference,thelatestversionapplies.• Anon-specificreferencetoanETSshallalsobetakentorefertolaterversionspublishedasanENwiththesamenumber.• ForthisRelease1999document,referencestoGSMdocumentsareforRelease1999versions(version8.x.y).[1]GSM01.04:"Digitalcellulartelecommunicationssystem(Phase2+);Abbreviationsandacronyms".[2]GSM04.08:"Digitalcellulartelecommunicationssystem(Phase2+);Mobileradiointerfacelayer3specification".[3]GSM05.02:"Digitalcellulartelecommunicationssystem(Phase2+);Multiplexingandmultipleaccessontheradiopath".[4]GSM05.03:"Digitalcellulartelecommunicationssystem(Phase2+);ChannelCoding".[5]GSM05.05:"Digitalcellulartelecommunicationssystem(Phase2+);Radiotransmissionandreception".[6]GSM08.08:"Digitalcellulartelecommunicationssystem(Phase2+);Mobile-servicesSwitchingCentre-BaseStationSystem(MSC-BSS)interface,Layer3specification".[7]GSM08.62:"Digitalcellulartelecommunicationssystem;InbandTandemFreeOperation(TFO)ofSpeechCodecs".1.2AbbreviationsForthepurposesofthepresentdocument,thefollowingabbreviationsapply.FurtherGSMrelatedabbreviationsarelistedinGSM01.04.AMRAdaptiveMulti-RateACSActiveCodecSetCMCCodecModeCommandCMICodecModeIndicationCMRCodecModeRequestICMInitialCodecModeRATSCCHRobustAMRTrafficSynchronizedControlChannelSIST EN 301 709 V8.0.1:2003

ETSIETSIEN301709V8.0.1(2000-10)6(GSM05.09version8.0.1Release1999)2GeneralThepresentdocumentgivesthedetailedrequirementsforthecorrectoperationofincallservicespecificlinkadaptationandcontrolforGSMservicesimplementedinGSMMobileStations(MS)sandBaseStationSystems(BSS)s.FortheAdaptiveMulti-Rate(AMR)speechservice,thedetaileddescriptionandrequirementsfortheassociatedinbandsignaling,AMRcodecmodeadaptation,andAMRcodecconfigurationaregiven.AninbandsignalingchannelisdefinedforAMRwhichenablestheMSandtheBTStoexchangemessagesonappliedorrequestedspeechandchannelcodecmodes.CodecmodeadaptationforAMRisbasedonreceivedchannelqualityestimationinbothMSandBTS,followedbyadecisiononthemostappropriatespeechandchannelcodecmodetoapplyatagiventime.TheoveralloperationofAMR,intermsofusedcodecmodesaswellasgeneraladaptationbehaviouriscontrolledbythenetwork.3AdaptiveMulti-Rateinbandcontrolandlinkadaptation3.1Generaloperation3.1.1OperationwithoutTandemFreeOperationAhigh-levelblockdiagramofthecompleteAMRsystemisdepictedinfigure1.ThesystemconsistsofthemajorcomponentsTRAUandBTSonthenetworksideandtheMS.Onthenetworkside,speechencoder(SPE)andchannelencoder(CHE)aswellaschanneldecoder(CHD)andspeechdecoder(SPD)areconnectedviatheserialA-bisinterface.Foreachlink,qualityinformationisderivedbyestimatingthecurrentchannelstate.Basedonthechannelstate,andalsotakingintoconsiderationpossibleconstraintsfromnetworkcontrol,thecodecmodecontrol,whichislocatedonthenetworkside,selectsthecodecmodestobeapplied.Thechannelmodetouse(TCH/AFSorTCH/AHS)iscontrolledbythenetwork.Uplinkanddownlinkalwaysapplythesamechannelmode.Forcodecmodeadaptationthereceivingsideperformslinkqualitymeasurementsoftheincominglink.ThemeasurementsareprocessedyieldingaQualityIndicator.Foruplinkadaptation,theQualityIndicatorisdirectlyfedintotheULmodecontrolunit.ThisunitcomparestheQualityIndicatorwithcertainthresholdsandgenerates,alsoconsideringpossibleconstraintsfromnetworkcontrol,aCodecModeCommandindicatingthecodecmodetobeusedontheuplink.TheCodecModeCommandisthentransmittedinbandtothemobilesidewheretheincomingspeechsignalisencodedinthecorrespondingcodecmode.Fordownlinkadaptation,theDLModeRequestGeneratorwithinthemobilecomparestheDLQualityindicatorwithcertainthresholdsandgeneratesaCodecModeRequestindicatingthepreferredcodecmodeforthedownlink.TheCodecModeRequestistransmittedinbandtothenetworksidewhereitisfedintotheDLModeControlunit.Thisunitgenerallygrantstherequestedmode.However,consideringpossibleconstraintsfromnetworkcontrol,itmayalsooverridetherequest.Theresultingcodecmodeisthenappliedforencodingoftheincomingspeechsignalindownlinkdirection.Bothforuplinkanddownlink,thepresentlyappliedcodecmodeistransmittedinbandasCodecModeIndicationtogetherwiththecodedspeechdata.Atthedecoder,theCodecModeIndicationisdecodedandappliedfordecodingofthereceivedspeechdata.SIST EN 301 709 V8.0.1:2003

ETSIETSIEN301709V8.0.1(2000-10)7(GSM05.09version8.0.1Release1999)MSBTSTRAUULcodecmode(received)UL-ModeCtrlUL-Meas.SPESPECHECHDSPDCHDCHESPDDL-Meas.DL-ModeCtrlDLcodecmodeULModeCommandULQualityIndicatorULModeCommand(received)DLModeRequest(received)speechdataspeechdataDLcodecmode(received)networkcontrolDL-Req.GenDLQualityIndicatorDLModeRequestFigure1:HighlevelAMRblockdiagramCodecmodeselectionisdonefromasetofcodecmodes(ACS,ActiveCodecSet),whichmayinclude1to4AMRcodecmodes.Associatedwiththissetisalistof1to3switchingthresholdsandhysteresisesusedbytheDLModeRequestGeneratorandtheULmodecontrolunittogeneratetheCodecModeRequestsandCodecModeCommands.Theseconfigurationparameters(ACS,thresholds,hysteresises)aredefinedatcallsetupandcanbemodifiedathandoverorduringacall.3.1.2OperationwithongoingTandemFreeOperationIftandemfreeoperationisongoing(seeGSM08.62)thenthespeechsignalhastobetransmittedovertworadiolinks,firstuplink(MS1toBTS1)andthendownlink(BTS2toMS2),respectivelysymmetricallyinthereversedirection.TheoptimalCodecModeindirectionMS1toMS2shallbederivedfromtheCodecModeRequestforthefirstuplink(CMC1,withinBTS1)andtheCodecModeRequestderivedfortheseconddownlink(CMR2withinMS2)inthefollowingway:MS2shallsendtheCMR2backtoBTS2intheusualway.BTS2shalleitheracceptthisCMR2(default)ormaymodifyitaccordingtonetworkcontrolneeds:CMR2´.ThenBTS2shallsendtheCMR2´furtheruplinktoitsTRAU2,toTRAU1anddownlinktoBTS1(seeGSM08.62onhowthistransmissionshallbehandledonAbisandAinterfaces).BTS1combinesthereceivedCMR2´withitsownderivedCMC1bytakingtheminimumofbothvalues.Ifneeded,BTS1maymodifythisminimumvalueaccordingtoownnetworkcontrol(-->CMC1´´)andshallsenditfinallydownlinktoMS1asCMC.Theidenticalprocedureshallbeperformedinthereversedirection.AnnexCgivesaninformativedescription.3.1.3OperationathandoverwithongoingTandemFreeOperationBeforeandduringanhandoveratoneorbothsidesoftheMS-to-MSconnection,itmaybeneededtofreezethecodecmodeadaptationforashortwhile,e.g.tooptimisethecommonActiveCodecSet,ortoallowfast(re-)synchronisationbetweenBTSandTRAUortooptimisetheCMIPhaseindownlink.BothBTSsmaythereforeenableordisablethecodecmodeadaptation(seeGSM08.62).Aslongasthecodecmodeadaptationisfrozentoaspecificcodecmode,thenthiscodecmodeshallbeusedinbothdirectionsaslongastandemfreeoperationisongoing,ortandemfreeoperationshallbediscontinued.TheCodecModeRequestsfromtheMSsmaybetakenintoaccounttodecidewhethertocontinueTFOornot,butnotforcodecmodeadaptation.3.2InbandSignallingTheAMRinbandsignallingconsistsoftwoparts:-Frequentsignalling,usedforCodecModeIndicationandCodecModeCommand/Request.-Robust,lessfrequentsignalling,basedonframestealing,usedforchangingtheAMRconfiguration(RATSCCH).SIST EN 301 709 V8.0.1:2003

ETSIETSIEN301709V8.0.1(2000-10)8(GSM05.09version8.0.1Release1999)3.2.1FrequentinbandsignallingforAMRcodecmodeadaptation3.2.1.1GeneralaspectsThecodecmodeinformation,whichhastobetransmittedoneachlink,consistsofCodecModeIndicationsandCodecModeCommandsinthedownlink,respectivelyCodecModeIndicationsandCodecModeRequestsintheuplink.CodecModeIndicationsinformthereceiveraboutthecurrentlyappliedcodecmode.CodecModeCommandsinformtheotherendaboutthecodecmodetobeappliedontheotherlink.CodecModeRequestsinformtheotherendaboutthepreferredcodecmodeontheotherlink.Codecmodeinformationistransmittedinbandinthespeechtrafficchannel,usingapartofitstransmissioncapacity.Thecodingofcodecmodesintheinbandsignallingisgiveninsubclause3.4.1.ChannelcodingofcodecmodeinformationisspecifiedinGSM05.03[4]forallframetypes.Codecmodesareconstrainedtochangeonlyeverysecondspeechframe.CodecModeCommands/RequestsandCodecModeIndicationsaresub-sampledsuchthattheyoccuronlyeverysecondframe.CodecModeIndicationsandCodecModeCommands/Requestsshallbetransmittedalternatingwithinconsecutivespeechframes.Both,CodecModeIndicationandCodecModeCommand/Request,shallbetransmittedtogetherwithineveryRATSCCHframe.3.2.1.2OperationwithDTXenabledForSID_FIRSTframes,theCodecModeIndicationorCodecModeCommand/Requestinphasewiththealternatingtransmissionshallbetransmitted(samephaseasinspeechframes).Both,CodecModeIndicationandCodecModeCommand/Request,shallbetransmittedtogetherineverySID_UPDATEframe(asinRATSCCHframes).ForONSETframestheCodecModeIndicationforthesubsequentspeechframeshallbetransmitted,regardlessofthephaseoftheinbandsignalling.Thegeneralphaseoftheinbandsignallingshallnotbechangedbythat.3.2.1.3Transmitter/ReceiverSynchronisationThealternatingtransmissionofthecodecmodeinformationrequiressynchronisationoftransmittingandreceivingends,suchthatCodecModeIndicationsandCodecModeCommands/Requestsaredecodedincorrectorder.Toensurepropersynchronisation,thecodecmodeinformationshallbetransmittedalignedtothe(SACCH)multi-framestructureoftheGSMsystem.ForTCH/AFS,thedefaulttransmissionphaseshallbesuchthatCodecModeIndicationsaresentalignedwithTDMAframe0intheuplinkandwithTDMAframe4inthedownlinkasdefinedinGSM05.02[3].ForTCH/AHS,thedefaulttransmissionphaseshallbesuchthatModeIndicationsaresentalignedwithTDMAframe0or1dependingonthesubchannelintheuplinkandwithTDMAframe4or5dependingonthesubchannel,inthedownlink,asdefinedinGSM05.02[3].ThisdefaultphaseoftheCodecModeIndicationindownlinkdirectioniscalled"odd",thealternativephase,onespeechframeshifted,iscalled"even".Thephaseinuplinkisalwaysthesameandisneverchanged.Atcallsetupandaftereveryhandoverthedefaultphase(odd)shallbeusedindownlinkdirection.Duringacall,thephaseofCodecModeIndicationmaybechangedindownlinkbyusingaRATSCCHmessage.IncaseofhandoverfailureandfallbacktotheBTSbeforethehandoverattempt,thephasebeforethehandoverattemptshallbeusedagain.3.2.2RobustinbandsignallingforAMRconfigurationmodification3.2.2.1GeneralaspectsTheRATSCCHmechanismmaybeusedincaseofTandemFreeOperationtomodifytheAMRConfigurationontheradiointerfacewithoutinterruptionofthespeechtransmission.ItsapplicationforTFOisdescribedinGSM08.62.ThisrecommendationdefinestheRATSCCHprotocolandtheRATSCCHmessages.ThechannelcodingisdefinedinGSM05.03andthereceiverperformanceinGSM05.05.RATSCCHhandlingismandatoryforMSandoptionalforBTS.SIST EN 301 709 V8.0.1:2003

ETSIETSIEN301709V8.0.1(2000-10)9(GSM05.09version8.0.1Release1999)RATSCCHisbasedonframestealing.OnTCH/AFS,onespeechframeisstolenforeachRATSCCHmessage,andonTCH/AHStwospeechframesarestolen.InTCH/AHSRATSCCHismappedontotwoconsecutivespeechframes,theRATSCCH_MARKERandtheRATSCCH_DATA.Bothshallbesentalwaysasonepair.FACCHframeshavehigherprioritythanRATSCCHframes.IfFACCHandRATSCCHarescheduledfortransmissionforthesamespeechframe,thentheFACCHshallbesentfirst,followedbytheRATSCCH.IftheRATSCCHisdelayedduetoFACCH,thentheappropriatecounters(see3.2.2.2)shallalsobestartedone(TCH/AFS)respectivelytwo(TCH/AHS)frameslater.IfinthecaseofTCH/AHS,FACCHstealsthesecondframeofoneRATSCCHmessage(RATSCCH_DATA),thecompleteRATSCCHmessage(RATSCCH_MARKERandRATSCCH_DATA)shallbesentfollowingtheFACCHframe.3.2.2.2RATSCCHprotocolTheRATSCCHprotocolelementsconsistofanumberofREQuestMessagesandthreeACKnowledgementMessages.OneinformationexchangeconsiststypicallyofoneREQ-ACKcyclebetweenthe"Initiator"andthe"Addressee".WhiletheInitiatoriswaitingforanACK,itshallnotsendanynewREQmessage,i.e.transmissionandacknowledgementofoneREQ-ACKcycleshallbecompletedbeforethenextcycleisstarted.ACKmessages,asreactiontoreceivedREQmessages,shallalwaysbesentbackassoonaspossible,andlatestwithin3speechframes.BothsidesshallcontinuouslymonitortheradioreceptionfortheRATSCCHpatternanddecodetheRATSCCHmessage.ThetypicalREQ-ACKcycleisdefinedas:1)Ifoneside("Initiator")wantstoinitiatetheinformationexchange,itshallsendthedesiredREQmessage.AtthesametimetheInitiatorshallstarttwocounters:ACK_Timeoutthatshallcounttheelapsedspeechframes(afterREQ)inreceivedirectionandREQ_ActivationthatshallcounttheelapsedspeechframesafterREQinsenddirection.2)IftheREQmessagewasdecodederror-free(byCRCcheck,seeGSM05.03[4])andisdefined(seesubclause3.2.2.3)atreceiverside("Addressee"),thentheAddresseeshallsendanACK_OKmessageback.AtthesametimetheAddresseeshallstart(orrestart)twoowncounters:REQ_ActivationthatshallcounttheelapsedspeechframesafterREQinreceivedirectionandACK_ActivationthatshallcounttheelapsedspeechframesafterACKinsenddirection.3)IftheInitiatorreceivesanACK_OK,thenitshallignoreitsACK_TimeoutcounterandshallstartanACK_ActivationcounterinsteadthatshallcounttheelapsedspeechframesafterACK_OKinreceivedirection.4)ThecontentsoftheREQmessagesshallbecomevalidinthedirectionfromInitiatortoAddresseeexactlyinthatframe,wheretheREQ_Activationcountersreachthevalue12andforallfollowingframes.ThecontentsoftheREQmessageshallbecomevalidinthedirectionfromAddresseetoInitiatorexactlyinthatframe,wheretheACK_Activationcountersreachthevalue12andforthefollowingframes.NOTE:DuetothetransmissiondelayandthereactiontimewithintheAddressee(REQtoACK)theactivationtakesplaceingeneralatfourdifferentpointsintime,butexactlysynchronisedanddefinedinbothdirections.ErrorHandling:1)IftheREQmessagewasdecodederror-free(noCRCerror),butthemessageisnotdefinedattheAddresseeside,thentheAddresseeshallsendanACK_UNKNOWNmessageback.Nocountersareneededinthiscase.TheInitiator,whenreceivingthisACK_UNKNOWNmessageshallterminatetheexchangeforthistypeofREQmessage.2)IftheRATSCCHmessagewasdetected,butcouldnotbedecodedcorrectly(CRCfailure),oritscontentswasnotconsistent,thentheAddresseeshallsendanACK_ERRmessageback.Nocountersare
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