SIST EN 300 953 V7.0.1:2003
(Main)Digital cellular telecommunications system (Phase 2+) (GSM); Call Waiting (CW) and Call Hold (HOLD) supplementary services; Stage 3 (GSM 04.83 version 7.0.1 Release 1998)
- Abstract
Upgrade from Phase 2+ to Release 1998
- Status
- Published
- Publication Date
- 30-Nov-2003
- Current Stage
- 6060 - National Implementation/Publication (Adopted Project)
- Start Date
- 01-Dec-2003
- Due Date
- 01-Dec-2003
- Completion Date
- 01-Dec-2003
SIST EN 300 953 V7.0.1:2003 is the Slovenian adoption of ETSI EN 300 953 Version 7.0.1 for the GSM Phase 2+ digital cellular system. It specifies Stage 3 radio-interface procedures for the Call Waiting (CW) and Call Hold (HOLD) supplementary services in GSM Release 1998, so it is the document to use when implementing or checking the signalling between a mobile station and the network.
What does SIST EN 300 953 V7.0.1:2003 specify?
SIST EN 300 953 V7.0.1:2003 specifies the procedures used at the radio interface, at reference point Um, for normal operation, registration, erasure, activation, deactivation, invocation and interrogation of call completion supplementary services. It is focused on two services: Call Waiting (CW) and Call Hold (HOLD).
Provision and withdrawal of the supplementary services are treated as administrative matters between the subscriber and the service provider, and they cause no signalling on the radio interface. The document is organized into clause 1 for Call Waiting, clause 2 for Call Hold, and Annex A for change request history.
| Part | What it covers |
|---|---|
| Clause 1 | Call Waiting (CW) procedures |
| Clause 2 | Call Hold (HOLD) procedures |
| Annex A | Change Request History |
What are the key requirements of SIST EN 300 953 V7.0.1:2003?
SIST EN 300 953 V7.0.1:2003 defines how the network and mobile station behave when a waiting call arrives, when the user accepts or clears it, and when the service is activated, deactivated or interrogated. It also defines how a held call is put on hold, retrieved, alternated, and released. In practice, this tells implementers which messages, transaction identifiers, timers and causes to use.
Call Waiting (CW) behaviour
Clause 1 requires the network to signal a waiting call to the served mobile station when CW is active and the B-subscriber is in the relevant call states. The standard uses the transaction identifier of the waiting call, and the existing call keeps its own transaction identifier, so the two calls stay distinct.
When the network confirms the waiting call, the CALL CONFIRMED message carries cause #17 “user busy”. If the network receives ALERTING, it starts timer T2, or timer T3 if Call Forwarding on no reply applies. This matters because the network must then either complete the waiting call, forward it, or clear it within the timer rules.
The standard also defines notification to the calling mobile user when the network has a non-zero SS Screening indicator. The notification is sent with ALERTING/FACILITY and a NotifySS operation indicating that the call is waiting. If the indicator is not present, no such notification is sent.
Accepting, rejecting and timing out a waiting call
Clause 1 gives three successful or unsuccessful outcomes: accept the waiting call and release the existing call, accept the waiting call while putting the existing call on hold, or release the waiting call. If timer T2 expires, the network releases the waiting call with cause #102 “recovery on timer expiry”. If Call Forwarding on no reply is active and the no-reply timer expires, the waiting call is forwarded according to GSM04.82.
CW activation, deactivation and interrogation
Clause 1 says CW is activated and deactivated by the subscriber using Facility messages with ActivateSS or DeactivateSS. If no BasicServiceCode is given, the action applies to all applicable basic services. Interrogation with InterrogateSS returns the active basic service groups, or an SS-Status showing “deactivated” if the service is supported but not active for any group. Invocation causes no radio signalling, and registration and erasure are not applicable.
Call Hold (HOLD) behaviour
Clause 2 defines HOLD as operating on the same MM-connection as the active call. The hold request moves the call into the Call held auxiliary state, disconnects the user information path, and returns HOLDACKNOWLEDGE if successful. A HOLDREJECT returns the call to its prior condition and carries an appropriate cause such as “Facility rejected”, “Requested facility not subscribed” or “Requested facility not implemented”.
Retrieve works in the opposite direction: RETRIEVE reconnects the call, and RETRIEVEACKNOWLEDGE confirms success. Clause 2 also defines alternating between one active call and one held call by sending HOLD for the active call and RETRIEVE for the held call.
What terms does SIST EN 300 953 V7.0.1:2003 define?
- Call Waiting (CW) - The supplementary service that alerts the served user to an incoming call while another call is already in progress.
- Call Hold (HOLD) - The supplementary service that places an active call on hold so the user can keep the connection without keeping the user information path open.
- BasicServiceCode - The code used to scope activation, deactivation or interrogation to one basic service group, or to all applicable basic services if omitted.
- SS Screening indicator - A network check used to decide whether to notify the other party that a call is waiting or has been held/retrieved.
- Transaction identifier - The identifier that keeps the existing call and the waiting or held call separate in signalling.
- MM-connection - The mobility management connection that HOLD and RETRIEVE use for the same call path.
Who uses SIST EN 300 953 V7.0.1:2003?
SIST EN 300 953 V7.0.1:2003 is used by GSM network engineers, mobile station implementers, and protocol test labs that need to build or verify Call Waiting and Call Hold behaviour. It is also relevant to quality managers and buyers checking whether GSM equipment supports the required supplementary-service signalling on the radio interface.
What changed in SIST EN 300 953 V7.0.1:2003 from the previous edition?
SIST EN 300 953 V7.0.1:2003 is the Release 1998 version of GSM 04.83, published as version 7.0.1. The history notes an upgrade to Release 1998 and a publication-style update for version 7.0.1.
Which standards are used with SIST EN 300 953 V7.0.1:2003?
The standard relies on related GSM specifications for abbreviations, service descriptions, stage 2 procedures, radio-interface signalling and coding. The most directly relevant references are:
- GSM01.04 - abbreviations and acronyms used in the document.
- GSM02.04 - general supplementary-service principles.
- GSM02.83 - Stage 1 description of Call Waiting and Call Hold.
- GSM03.11 and GSM03.83 - technical realization and Stage 2 aspects for call completion supplementary services.
- GSM04.02, GSM04.07, GSM04.08, GSM04.10 and GSM04.80 - radio reference configuration, signalling layer 3, layer 3 procedures and coding used for the messages.
- GSM04.82 - the Call Forwarding specification used when CW interacts with forwarding on no reply.
What does the SIST EN 300 953 V7.0.1:2003 document contain?
The document contains signalling flows, message exchanges and state handling for CW and HOLD, with figures showing the setup, confirmation, notification and release sequences. It also includes the hold, retrieve and alternate procedures, together with the auxiliary-state model for hold and retrieve.
For CW, the figures show how SETUP, CALL CONFIRMED, ALERTING, CONNECT and Facility-related messages are used. For HOLD, the document shows how HOLD, HOLDACKNOWLEDGE, HOLDREJECT, RETRIEVE and RETRIEVEACKNOWLEDGE are sequenced, and how notifications are sent to the remote party when screening allows it. Annex A provides the change request history for the specification.
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Frequently Asked Questions
SIST EN 300 953 V7.0.1:2003 is a standard published by the Slovenian Institute for Standardization (SIST). Its full title is "Digital cellular telecommunications system (Phase 2+) (GSM); Call Waiting (CW) and Call Hold (HOLD) supplementary services; Stage 3 (GSM 04.83 version 7.0.1 Release 1998)". This standard covers: Upgrade from Phase 2+ to Release 1998
Upgrade from Phase 2+ to Release 1998
SIST EN 300 953 V7.0.1:2003 is classified under the following ICS (International Classification for Standards) categories: 33.070.50 - Global System for Mobile Communication (GSM). The ICS classification helps identify the subject area and facilitates finding related standards.
SIST EN 300 953 V7.0.1:2003 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digital cellular telecommunications system (Phase 2+) (GSM); Call Waiting (CW) and Call Hold (HOLD) supplementary services; Stage 3 (GSM 04.83 version 7.0.1 Release 1998)33.070.50Globalni sistem za mobilno telekomunikacijo (GSM)Global System for Mobile Communication (GSM)ICS:Ta slovenski standard je istoveten z:EN 300 953 Version 7.0.1SIST EN 300 953 V7.0.1:2003en01-december-2003SIST EN 300 953 V7.0.1:2003SLOVENSKI
STANDARD
ETSIEN300953V7.0.1(2000-01)EuropeanStandard(Telecommunicationsseries)Digitalcellulartelecommunicationssystem(Phase2+);CallWaiting(CW)andCallHold(HOLD)supplementaryservices;Stage3(GSM04.83version7.0.1Release1998)GLOBALSYSTEMFORMOBILECOMMUNICATIONSRSIST EN 300 953 V7.0.1:2003
ETSIETSIEN300953V7.0.1(2000-01)2(GSM04.83version7.0.1Release1998)ReferenceREN/SMG-030483Q7KeywordsDigitalcellulartelecommunicationssystem,GlobalSystemforMobilecommunications(GSM)ETSIPostaladdressF-06921SophiaAntipolisCedex-FRANCEOfficeaddress650RoutedesLucioles-SophiaAntipolisValbonne-FRANCETel.:+33492944200Fax:+33493654716SiretN°34862356200017-NAF742CAssociationàbutnonlucratifenregistréeàlaSous-PréfecturedeGrasse(06)N°7803/88Internetsecretariat@etsi.frIndividualcopiesofthisETSIdeliverablecanbedownloadedfromhttp://www.etsi.orgIfyoufinderrorsinthepresentdocument,sendyourcommentto:editor@etsi.frImportantnoticeThisETSIdeliverablemaybemadeavailableinmorethanoneelectronicversionorinprint.Inanycaseofexistingorperceiveddifferenceincontentsbetweensuchversions,thereferenceversionisthePortableDocumentFormat(PDF).Incaseofdispute,thereferenceshallbetheprintingonETSIprintersofthePDFversionkeptonaspecificnetworkdrivewithinETSISecretariat.CopyrightNotificationNopartmaybereproducedexceptasauthorizedbywrittenpermission.Thecopyrightandtheforegoingrestrictionextendtoreproductioninallmedia.©EuropeanTelecommunicationsStandardsInstitute2000.Allrightsreserved.SIST EN 300 953 V7.0.1:2003
ETSIETSIEN300953V7.0.1(2000-01)3(GSM04.83version7.0.1Release1998)ContentsIntellectualPropertyRights.4Foreword.40Scope.50.1References.50.2Abbreviations.71CallWaiting(CW).71.1Waitingcallindicationandconfirmation.71.2Normaloperationwithsuccessfuloutcome.81.2.1Waitingcallaccepted;existingcallreleased.81.2.2Waitingcallaccepted;existingcallonhold.81.2.3ExistingcallreleasedbyuserA;waitingcallaccepted.91.3Normaloperationwithunsuccessfuloutcome.91.3.1WaitingcallreleasedbysubscriberB.91.3.2WaitingcallreleasedbycallinguserC.91.3.3Waitingcalltimesout.91.3.4Noreplyconditiontimerexpires.91.4Activation.91.5Deactivation.101.6Interrogation.111.7Invocation.111.8Registrationanderasure.112CallHold(HOLD).122.1Normaloperation.122.1.1Holdandretrievefunctions.122.1.2Holdinvocation.122.1.3Retrieveprocedure.132.1.4Alternatefromonecalltotheother.142.1.5Auxiliarystatesforholdandretrieve.152.1.6Anexampleofdimensionedstatespace.162.2Activationanddeactivation.162.3Registration,erasureandinterrogation.16AnnexA(informative):ChangeRequestHistory.17History.18SIST EN 300 953 V7.0.1:2003
ETSIETSIEN300953V7.0.1(2000-01)4(GSM04.83version7.0.1Release1998)IntellectualPropertyRightsIPRsessentialorpotentiallyessentialtothepresentdocumentmayhavebeendeclaredtoETSI.TheinformationpertainingtotheseessentialIPRs,ifany,ispubliclyavailableforETSImembersandnon-members,andcanbefoundinSR000314:"IntellectualPropertyRights(IPRs);Essential,orpotentiallyEssential,IPRsnotifiedtoETSIinrespectofETSIstandards",whichisavailablefromtheETSISecretariat.LatestupdatesareavailableontheETSIWebserver(http://www.etsi.org/ipr).PursuanttotheETSIIPRPolicy,noinvestigation,includingIPRsearches,hasbeencarriedoutbyETSI.NoguaranteecanbegivenastotheexistenceofotherIPRsnotreferencedinSR000314(ortheupdatesontheETSIWebserver)whichare,ormaybe,ormaybecome,essentialtothepresentdocument.ForewordThisEuropeanStandard(Telecommunicationsseries)hasbeenproducedbytheSpecialMobileGroup(SMG).Thepresentdocumentspecifiestheproceduresusedattheradiointerfacefornormaloperation,registration,erasure,activation,deactivation,invocationandinterrogationofcallcompletionsupplementaryserviceswithinthedigitalcellulartelecommunicationssystem.ThespecificationfromwhichthepresentdocumenthasbeenderivedwasoriginallybasedonCEPTdocumentation,hencethepresentationofthepresentdocumentmaynotbeentirelyinaccordancewiththeETSI/PNErules.ThecontentsofthepresentdocumentissubjecttocontinuingworkwithinSMGandmaychangefollowingformalSMGapproval.ShouldSMGmodifythecontentsofthepresentdocumentitwillbere-releasedwithanidentifyingchangeofreleasedateandanincreaseinversionnumberasfollows:Version7.x.ywhere:7indicatesRelease1998ofGSMPhase2+.xtheseconddigitisincrementedforallchangesofsubstance,i.e.technicalenhancements,corrections,updates,etc.ythethirddigitisincrementedwheneditorialonlychangeshavebeenincorporatedinthespecification.NationaltranspositiondatesDateofadoptionofthisEN:31December1999DateoflatestannouncementofthisEN(doa):31March2000DateoflatestpublicationofnewNationalStandardorendorsementofthisEN(dop/e):30September2000DateofwithdrawalofanyconflictingNationalStandard(dow):30September2000SIST EN 300 953 V7.0.1:2003
ETSIETSIEN300953V7.0.1(2000-01)5(GSM04.83version7.0.1Release1998)0ScopeThepresentdocumentspecifiestheproceduresusedattheradiointerface(ReferencepointUmasdefinedinGSM04.02)fornormaloperation,registration,erasure,activation,deactivation,invocationandinterrogationofcallcompletionsupplementaryservices.Provisionandwithdrawalofsupplementaryservicesisanadministrativematterbetweenthemobilesubscriberandtheserviceproviderandcausenosignallingontheradiointerface.InGSM04.10thegeneralaspectsofthespecificationofsupplementaryservicesatthelayer3radiointerfacearegiven.GSM04.80specifiestheformatsandcodingforthesupplementaryservices.DefinitionsanddescriptionsofsupplementaryservicesaregiveninGSM02.04andGSM02.8xandGSM02.9x-series.GSM02.83isrelatedspeciallytocallcompletionsupplementaryservices.TechnicalrealizationofsupplementaryservicesisdescribedinGSM03.11andGSM03.8xandGSM03.9x-series.GSM03.83isrelatedspeciallytocallcompletionsupplementaryservices.TheproceduresforCallControl,MobilityManagementandRadioResourcemanagementatthelayer3radiointerfacearedefinedinGSM04.07andGSM04.08.Thefollowingsupplementaryservicesbelongtothecallcompletionsupplementaryservicesandaredescribedinthepresentdocument:-Callwaiting(CW)(clause1);-Callhold(HOLD)(clause2).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]GSM02.04:"Digitalcellulartelecommunicationssystem(Phase2+);Generalonsupplementaryservices".[3]GSM02.81:"Digitalcellulartelecommunicationssystem(Phase2+);Lineidentificationsupplementaryservices-Stage1".[4]GSM02.82:"Digitalcellulartelecommunicationssystem(Phase2+);CallForwarding(CF)supplementaryservices-Stage1".[5]GSM02.83:"Digitalcellulartelecommunicationssystem(Phase2+);CallWaiting(CW)andCallHold(HOLD)supplementaryservices-Stage1".[6]GSM02.84:"Digitalcellulartelecommunicationssystem(Phase2+);MultiParty(MPTY)supplementaryservices-Stage1".SIST EN 300 953 V7.0.1:2003
ETSIETSIEN300953V7.0.1(2000-01)6(GSM04.83version7.0.1Release1998)[7]GSM02.85:"Digitalcellulartelecommunicationssystem(Phase2+);ClosedUserGroup(CUG)supplementaryservices-Stage1".[8]GSM02.86:"Digitalcellulartelecommunicationssystem(Phase2+);Adviceofcharge(AoC)supplementaryservices-Stage1".[9]GSM02.88:"Digitalcellulartelecommunicationssystem(Phase2+);CallBarring(CB)supplementaryservices-Stage1".[10]GSM02.90:"Digitalcellulartelecommunicationssystem(Phase2+);UnstructuredSupplementaryServicesData(USSD)-Stage1".[11]GSM02.91:"Digitalcellulartelecommunicationssystem(Phase2+);ECTsupplementaryservicesoperation-Stage1".[12]GSM03.11:"Digitalcellulartelecommunicationssystem(Phase2+);Technicalrealizationofsupplementaryservices".[13]GSM03.81:"Digitalcellulartelecommunicationssystem(Phase2+);Lineidentificationsupplementaryservices-Stage2".[14]GSM03.82:"Digitalcellulartelecommunicationssystem(Phase2+);CallForwarding(CF)supplementaryservices-Stage2".[15]GSM03.83:"Digitalcellulartelecommunicationssystem(Phase2+);CallWaiting(CW)andCallHold(HOLD)supplementaryservices-Stage2".[16]GSM03.84:"Digitalcellulartelecommunicationssystem(Phase2+);MultiParty(MPTY)supplementaryservices-Stage2".[17]GSM03.85:"Digitalcellulartelecommunicationssystem(Phase2+);ClosedUserGroup(CUG)supplementaryservices-Stage2".[18]GSM03.86:"Digitalcellulartelecommunicationssystem(Phase2+);AdviceofCharge(AoC)supplementaryservices-Stage2".[19]GSM03.88:"Digitalcellulartelecommunicationssystem(Phase2+);CallBarring(CB)supplementaryservices-Stage2".[20]GSM03.90:"Digitalcellulartelecommunicationssystem(Phase2+);Unstructuredsupplementaryservicesoperation-Stage2".[21]GSM03.91:"Digitalcellulartelecommunicationssystem(Phase2+);ExplicitCallTransfer(ECT)supplementaryservice-Stage2".[22]GSM04.02:"Digitalcellulartelecommunicationssystem(Phase2+);GSMPublicLandMobileNetwork(PLMN)accessreferenceconfiguration".[23]GSM04.07:"Digitalcellulartelecommunicationssystem(Phase2+);Mobileradiointerfacesignallinglayer3;Generalaspects".[24]GSM04.08:"Digitalcellulartelecommunicationssystem(Phase2+);Mobileradiointerfacelayer3specification".[25]GSM04.10:"Digitalcellulartelecommunicationssystem(Phase2+);Mobileradiointerfacelayer3;Supplementaryservicesspecification;Generalaspects".[26]GSM04.80:"Digitalcellulartelecommunicationssystem(Phase2+);Mobileradiointerfacelayer3supplementaryservicesspecification;Formatsandcoding".[27]GSM04.82:"Digitalcellulartelecommunicationssystem(Phase2+);CallForwarding(CF)supplementaryservices-Stage3".SIST EN 300 953 V7.0.1:2003
ETSIETSIEN300953V7.0.1(2000-01)7(GSM04.83version7.0.1Release1998)0.2AbbreviationsAbbreviationsusedinthepresentdocumentarelistedinGSM01.04.1CallWaiting(CW)1.1WaitingcallindicationandconfirmationWhenthisserviceisactivatedforthecontrollingsubscriberBandtheB-subscriberhascallsonlyinstatesU10(Active)orU26(MOModify)asdefinedinGSM04.08,thearrivalofanincomingcallfromsubscriberCshall,ifnoothercalliswaitingbesignalledtothemobilestationBbyanormalcallindication.InthatcasethenetworkandthemobilestationshallactinaccordancewithGSM04.08.Thetransactionidentifiershallbethetransactionidentifier(C-B)allocatedtothewaitingcallandmustnotbethesameasthetransactionidentifier(A-B)forthealreadyexistingcall(seefigure1.1).IntheCALLCONFIRMEDmessagesenttothenetworktheCauseinformationelementshallbeincludedwithcause#17"userbusy"(seefigure1.1).WhentheALERTINGmessageisreceivedbythenetworkthecallwaitingtimerT2shallbestartedorifcallforwardingonnoreplyisactivatedfortheB-subscriberthenoreplyconditiontimerT3shallbestarted.Ifthenetworkreceivedanon-zeroSSScreeningindicatorfromthecallingusersmobilestationtheALERTING/FACILITYmessagesenttoacallingmobileusershallincludetheFacilityinformationelementwithaninvokeoftheNotificationoperationindicatingthatthecalliswaiting(seefigure1.2).Ifthenetworkdidnotreceiveanon-zeroSSScreeningindicatorfromthecallingusersmobilestationitshallnotsendanotification,i.e.eithertheALERTINGmessagedoesnotincludetheNotificationoperationortheFACILITYmessageisomitted.MSNetworkSETUP<------------------------------------------------------------------------------------------------------------------------.Transactionidentifier(C-B).CALLCONFIRMED------------------------------------------------------------------------------------------------------------------------>.Transactionidentifier(C-B).Cause#17(userbusy).ALERTING------------------------------------------------------------------------------------------------------------------------>.Transactionidentifier(C-B).startT2/T3NOTE:TheSETUPmessageshallincludea"SignalInformation"elementwithvalue#7(callwaitingtoneon).ThisshallbeusedbytheMStogenerateanappropriatecallwaitingindication.Figure1.1:CallindicationtothemobilestationonarrivalofanincomingcallandcallconfirmationfromthemobilestationMSNetworkSETUP------------------------------------------------------------------------------------------------------------------------>CALLPROCEEDING<------------------------------------------------------------------------------------------------------------------------ALERTING/FACILITY<------------------------------------------------------------------------------------------------------------------------Facility(Invoke=NotifySS(CW,CallIsWaiting-Indicator))NOTE:Ifpossible,theALERTINGmessageshallbeusedasthecarriermessagefortheCallWaitingnotification.OtherwisetheFACILITYmessageshallbeused.Figure1.2:NotificationtoacallingmobilestationthatthecallisinthewaitingstateSIST EN 300 953 V7.0.1:2003
ETSIETSIEN300953V7.0.1(2000-01)8(GSM04.83version7.0.1Release1998)1.2Normaloperationwithsuccessfuloutcome1.2.1Waitingcallaccepted;existingcallreleasedIfthemobileuserBbeforeexpiryoftimerT2determinestoacceptthewaitingcallandreleasetheexistingcallthemobilestationshallreleasetheexistingcallfirstlyandacceptthewaitingcallsecondly.ForthereleaseoftheexistingcallthemobilestationandthenetworkshallactinaccordancewithGSM04.08.Thetransactionidentifiershallbethetransactionidentifier(A-B)ofthealreadyexistingcall.TheCauseinformationelementinthefirstclearingmessageshallindicatecause#16"normalclearing".FortheacceptanceofthewaitingcallthemobilestationandthenetworkshallactinaccordancewithGSM04.08.Thetransactionidentifiershallbethetransactionidentifier(C-B)ofthewaitingcall.WhenthenetworkreceivestheCONNECTmessagethetimerT2orifapplicablethetimerT3shallbestopped.1.2.2Waitingcallaccepted;existingcallonholdIfthemobileuserBbeforeexpiryoftimerT2orifapplicabletimerT3determinestoacceptthewaitingcallandputtheexistingcallonholdthemobilestationshallputtheexistingcallonholdfirstlyandacceptthewaitingcallsecondly.Incasethereisoneactivecall(A-B)andanothercall(D-B)onholdandcall(C-B)waiting,andthemobileuserBwantstoacceptthewaitingcall(C-B)andputtheactivecall(A-B)onhold,theheldcall(D-B)hastobereleasedfirst,eitherbyuserBoruserD,inaccordancewithGSM04.08.Toputtheexistingcallonholdthemobilestationandthenetworkshallactinaccordancewithclause2.Theholdfunctionshallbeinitiatedbythemobilestationandthetransactionidentifiershallbethetransactionidentifier(A-B)oftheexistingcall(seefigure1.3).FortheacceptanceofthewaitingcallthemobilestationandthenetworkshallactinaccordancewithGSM04.08.Thetransactionidentifiershallbethetransactionidentifier(C-B)ofthewaitingcall(seefigure1.3).WhenthenetworkreceivestheCONNECTmessagethetimerT2orifa
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