SIST EN 300 357 V1.2.1:2005

• Abstract:

  Update of the interaction between the CCBS and Call Forwarding No Reply (CFNR) and between the CCBS and Call Forwarding Busy (CFB) supplementary services.

• Status: Published
• Publication Date: 31-Dec-2004
• ICS: 33.080 - Integrated Services Digital Network (ISDN)
• Technical Committee: SPN - Services and Protocols for Networks
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Jan-2005
• Due Date: 01-Jan-2005
• Completion Date: 01-Jan-2005
• Ref Project: ETSI EN 300 357 V1.2.1 (2001-05) - Integrated Services Digital Network (ISDN); Completion of Calls to Busy Subscriber (CCBS) supplementary service; Service description

SIST EN 300 357 V1.2.1:2005 is the Slovenian adoption of ETSI EN 300 357 Version 1.2.1 for Integrated Services Digital Network (ISDN) Completion of Calls to Busy Subscriber (CCBS). It gives the stage one service description, so it explains how the CCBS supplementary service behaves from the user’s point of view and how it is handled by the network.

The standard covers the update of CCBS interaction with Call Forwarding No Reply (CFNR) and Call Forwarding Busy (CFB), together with the service rules that matter for public ISDN operation and interworking.

What does SIST EN 300 357 V1.2.1:2005 specify?

SIST EN 300 357 V1.2.1:2005 specifies stage one of the CCBS supplementary service for the pan-European ISDN. It describes what the service does, who it is for, how it is activated and recalled, and how it behaves with other services.

The document is organized into clauses on scope, references, definitions, description, procedures, intercommunication considerations, and interaction with other supplementary services. It also has two annexes.

Annex	What it covers
Annex A	Determination of the existence of compatible terminals
Annex B	Bibliography

The scope also states what is outside the document: charging principles, interactions with supplementary services not listed in clause 7, and the detailed human interface. The service is intended for users connected through basic access or primary rate access.

What are the key requirements of SIST EN 300 357 V1.2.1:2005?

SIST EN 300 357 V1.2.1:2005 defines how CCBS works when a user calls a busy destination B and asks the network to complete the call later. In practice, this means the network must keep the call state, watch for destination B becoming free, recall user A, and then place the call automatically if user A accepts.

Service provision and subscription

Clause 5.1 says the service is provided after prior arrangement with the service provider or as a general offering. The service may also be withdrawn by the provider or at the subscriber’s request. A subscription option called recall mode can be set to Global or Specific, and this affects which terminal can deactivate requests later.

Activation, queuing, and timers

Clause 5.2.2.1 requires the network to retain call information long enough for activation after a busy indication. It also checks for a compatible terminal at destination B before registering a CCBS request. The document sets limits for the CCBS recall timer, the CCBS service duration timer, the destination idle guard timer, and the retention timer, which matters because these timers control how long the network waits and when it abandons the request.

Limits on outstanding requests

Clause 5.2.2.1 lets user A have only a limited number of CCBS requests outstanding, with the maximum controlled by the network provider. The destination B queue is also limited, and the queue can even be reduced to zero length for individual users. This is important for capacity planning because it affects how many callbacks can be stored and how CCBS interacts with other services.

Deactivation and failure cases

Clause 5.2.2.2 and clause 5.3 describe deactivation by the user and automatic deactivation by the network. Requests can be removed when timers expire, when the recall is not accepted, or when another service conflicts with the request. The network also distinguishes short-term denial from long-term denial, which helps service desks and terminals present the right reason to the user.

Interworking and service interactions

Clauses 6 and 7 define how CCBS behaves across public ISDN, private ISDN, non-ISDN networks, and with other supplementary services. The document gives special rules for Call Forwarding Unconditional, Call Forwarding Busy, Call Forwarding No Reply, call waiting, call hold, freephone, closed user group, multiple subscriber number, subaddressing, terminal portability, three-party, and user-to-user signalling. For implementers, this section is the main guide for avoiding service conflicts and unexpected call routing.

What terms does SIST EN 300 357 V1.2.1:2005 define?

• Completion of Calls to Busy Subscriber (CCBS) - A supplementary service that lets user A ask the network to complete a call to destination B later, after destination B is no longer busy.
• Integrated Services Digital Network (ISDN) - The network type for which this service description is written.
• user A - The user who originated the original call and who receives the CCBS recall.
• destination B - The party addressed in the original call and the user whose busy state triggers CCBS.
• CCBS request - An activated CCBS request held by the network until the completion conditions are met.
• CCBS recall - The network indication to user A that the callback can now be started.
• compatible terminal - A terminal that can support the requested bearer service or teleservice and can accept calls to the relevant ISDN number and subaddress.
• suspended CCBS request - A request that cannot be served until user A is no longer busy or CCBS busy.

Who uses SIST EN 300 357 V1.2.1:2005?

SIST EN 300 357 V1.2.1:2005 is used by ISDN service providers, network operators, switch and signalling engineers, and terminal implementers. It matters to teams that need to design, provision, test, or support CCBS behavior in public ISDN and private ISDN interworking. Quality managers and buyers use it to check that an implementation follows the expected user-visible service behavior.

Which standards are used with SIST EN 300 357 V1.2.1:2005?

The document depends on several referenced ITU-T and ETSI standards:

• ITU-T Recommendation I.130 - defines the stage 1, 2, and 3 service description structure.
• ITU-T Recommendation I.112 - provides ISDN and service vocabulary.
• ITU-T Recommendation I.210 - gives principles for describing ISDN services.
• ITU-T Recommendation E.164 - defines the international numbering plan used for ISDN numbers.
• ITU-T Recommendation Q.9 - gives switching and signalling terms, including access definitions.
• ITU-T Recommendation I.221 - defines common service characteristics such as busy.
• ETSI EN 300 359-1 - gives the stage 3 DSS1 protocol for CCBS.
• ETSI EN 300 356-18 - gives the stage 3 ISUP specification for CCBS.
• ETSI ETS 300 358 - is the stage 2 companion for functional capabilities and information flows.

What does the SIST EN 300 357 V1.2.1:2005 document contain?

The document contains a service description, procedure rules, interworking rules, and service interaction rules for CCBS. Clause 5 sets out provisioning, activation, deactivation, invocation, recall handling, and interrogation. Clause 7 explains how CCBS behaves with other supplementary services, including forwarding, call waiting, and user-to-user signalling.

Annex A gives the rule for deciding whether a compatible terminal exists at destination B, which matters because CCBS depends on a usable terminal at the called side. The document also includes one subscription option table and a bibliography in Annex B.

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.VWRULWHYIntegrated Services Digital Network (ISDN); Completion of Calls to Busy Subscriber (CCBS) supplementary service; Service description33.080Digitalno omrežje z integriranimi storitvami (ISDN)Integrated Services Digital Network (ISDN)ICS:Ta slovenski standard je istoveten z:EN 300 357 Version 1.2.1SIST EN 300 357 V1.2.1:2005en01-januar-2005SIST EN 300 357 V1.2.1:2005SLOVENSKI
STANDARD
ETSIEN300357V1.2.1(2001-05)EuropeanStandard(Telecommunicationsseries)IntegratedServicesDigitalNetwork(ISDN);CompletionofCallstoBusySubscriber(CCBS)supplementaryservice;ServicedescriptionSIST EN 300 357 V1.2.1:2005

ETSIETSIEN300357V1.2.1(2001-05)2ReferenceREN/SPAN-110096KeywordsCCBS,ISDN,stage1,supplementaryserviceETSI650RoutedesLuciolesF-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.©EuropeanTelecommunicationsStandardsInstitute2001.Allrightsreserved.SIST EN 300 357 V1.2.1:2005

ETSIETSIEN300357V1.2.1(2001-05)3ContentsIntellectualPropertyRights.5Foreword.51Scope.62References.63Definitionsandabbreviations.73.1Definitions.73.2Abbreviations.84Description.85Procedures.85.1Provisionandwithdrawal.85.2Normalprocedures.95.2.1Registrationanderasure.95.2.2Activationanddeactivation.95.2.2.1Activation.95.2.2.2Deactivation.105.2.3Invocationandoperation.105.2.4Interrogation.115.3Exceptionalprocedures.115.3.1Registrationanderasure.115.3.2Activationanddeactivation.115.3.2.1Activation.115.3.2.2Deactivation.125.3.3Invocationandoperation.125.3.3.1ExceptionalsituationatdestinationB'sside.125.3.3.2ExceptionalsituationatuserA'sside.135.3.3.3Networkcongestion.135.3.4Interrogation.136Intercommunicationconsiderations.146.1Interworkingwithnon-ISDNs.146.2InterworkingwithprivateISDNs.147Interactionwithothersupplementaryservices.147.1Adviceofchargeservices.147.1.1Charginginformationatcallset-uptime.147.1.2Charginginformationduringthecall.147.1.3Charginginformationattheendofacall.147.2Callwaiting.157.3Callhold.157.4Explicitcalltransfer.157.5Numberidentificationservices.157.5.1Callinglineidentificationpresentation.157.5.2Callinglineidentificationrestriction.157.5.3Connectedlineidentificationpresentation.157.5.4Connectedlineidentificationrestriction.157.6Closedusergroup.157.7Completionofcallstobusysubscriber.167.8Conferenceservices.167.8.1Conferencecall,add-on.167.8.2Meet-meconference.167.9Directdiallingin.167.10Diversionservices.167.10.1Callforwardingunconditional.167.10.2Callforwardingbusy.17SIST EN 300 357 V1.2.1:2005

ETSIETSIEN300357V1.2.1(2001-05)47.10.3Callforwardingnoreply.177.10.4Calldeflection.187.11Freephone.187.12Maliciouscallidentification.187.13Multiplesubscribernumber.187.14Subaddressing.187.15Terminalportability.187.16Threeparty.187.17User-to-usersignalling.19AnnexA(normative):Determinationoftheexistenceofcompatibleterminals.20AnnexB(informative):Bibliography.21History.22SIST EN 300 357 V1.2.1:2005

ETSIETSIEN300357V1.2.1(2001-05)5IntellectualPropertyRightsIPRsessentialorpotentiallyessentialtothepresentdocumentmayhavebeendeclaredtoETSI.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)hasbeenproducedbyETSITechnicalCommitteeServicesandProtocolsforAdvancedNetworks(SPAN).InaccordancewithITU-TRecommendationI.130[1],thefollowingthreelevelstructureisusedtodescribethesupplementarytelecommunicationsservicesasprovidedbyEuropeanpublictelecommunicationsoperatorsunderthepan-EuropeanIntegratedServicesDigitalNetwork(ISDN):-Stage1:isanoverallservicedescription,fromtheuser'sstandpoint;-Stage2:identifiesthefunctionalcapabilitiesandinformationflowsneededtosupporttheservicedescribedinstage1;and-Stage3:definesthesignallingsystemprotocolsandswitchingfunctionsneededtoimplementtheservicedescribedinstage1.Thepresentdocumentdetailsthestage1aspects(overallservicedescription)fortheCompletionofCallstoBusySubscriber(CCBS)supplementaryservice.Thestage2aspectsaredetailedinETS300358(seebibliography)andthestage3aspectsaredetailedinEN300359-1[7]andEN300356-18[8].NationaltranspositiondatesDateofadoptionofthisEN:25May2001DateoflatestannouncementofthisEN(doa):31August2001DateoflatestpublicationofnewNationalStandardorendorsementofthisEN(dop/e):28February2002DateofwithdrawalofanyconflictingNationalStandard(dow):28February2002SIST EN 300 357 V1.2.1:2005

ETSIETSIEN300357V1.2.1(2001-05)61ScopeThepresentdocumentdefinesthestageoneoftheCompletionofCallstoBusySubscriber(CCBS)supplementaryserviceforthepan-EuropeanIntegratedServicesDigitalNetwork(ISDN)asprovidedbyEuropeanpublictelecommunicationsoperators.Stageoneisanoverallservicedescriptionfromtheuser'spointofview(seeITU-TRecommendationI.130[1]),butdoesnotdealwiththedetailsofthehumaninterfaceitself.ThepresentdocumentdefinestheinterworkingrequirementsofprivateISDNswiththepublicISDN.Inaddition,thepresentdocumentspecifiesthebasefunctionalitywheretheserviceisprovidedtotheuserviaaprivateISDN.ThepresentdocumentdoesnotspecifytheadditionalrequirementswheretheserviceisprovidedtotheuserviaatelecommunicationsnetworkthatisnotanISDNbutdoesincludeinterworkingrequirementsofothernetworkswiththepublicISDN.Interactionswithsupplementaryservicesnotlistedinclause7areoutsidethescopeofthepresentdocument.Chargingprinciplesareoutsidethescopeofthepresentdocument.TheCCBSsupplementaryserviceenablesuserA,encounteringabusydestinationB,tohavethecallcompletedwithouthavingtomakeanewcallattemptwhenthedestinationBbecomesnotbusy.TheCCBSsupplementaryserviceisapplicabletoallcircuit-switchedtelecommunicationsserviceswiththefollowingexceptions:a)call2,ofthevideotelephonyteleservice(seeETS300264inbibliography);b)allothercircuit-switchedtelecommunicationsservicesrequiringtheuseofmorethanoneB-channel.ThepresentdocumentisapplicabletothestagetwoandstagethreedocumentsfortheISDNCCBSsupplementaryservice.Theterms"stagetwo"and"stagethree"arealsodefinedinITU-TRecommendationI.130[1].Wherethetextindicatesthestatusofarequirement(i.e.asstrictcommandorprohibition,asauthorizationleavingfreedom,orasacapabilityorpossibility),thisshallbereflectedinthetextoftherelevantstagetwoandstagethreedocuments.Furthermore,conformancetothepresentdocumentismetbyconformingtothestagethreedocumentwiththefieldofapplicationappropriatetotheequipmentbeingimplemented.Therefore,nomethodoftestingisprovidedforthepresentdocument.2ReferencesThefollowingdocumentscontainprovisionswhich,throughreferenceinthistext,constituteprovisionsofthepresentdocument.• Referencesareeitherspecific(identifiedbydateofpublication,editionnumber,versionnumber,etc.)ornon-specific.• Foraspecificreference,subsequentrevisionsdonotapply.• Foranon-specificreference,subsequentrevisionsdoapply.[1]ITU-TRecommendationI.130(1988):"MethodforthecharacterizationoftelecommunicationservicessupportedbyanISDNandnetworkcapabilitiesofanISDN".[2]ITU-TRecommendationI.112(1988):"VocabularyoftermsforISDNs".[3]ITU-TRecommendationI.210(1993):"PrinciplesoftelecommunicationservicessupportedbyanISDNandthemeanstodescribethem".[4]ITU-TRecommendationE.164(1997):"Theinternationalpublictelecommunicationnumberingplan".SIST EN 300 357 V1.2.1:2005

ETSIETSIEN300357V1.2.1(2001-05)7[5]ITU-TRecommendationQ.9(1988):"Vocabularyofswitchingandsignallingterms".[6]ITU-TRecommendationI.221(1993):"Commonspecificcharacteristicsofservices".[7]ETSIEN300359-1(V1.3.2):"IntegratedServicesDigitalNetwork(ISDN);CompletionofCallstoBusySubscriber(CCBS)supplementaryservice;DigitalSubscriberSignallingSystemNo.one(DSS1)protocol;Part1:Protocolspecification".[8]ETSIEN300356-18(V3.1.3):"IntegratedServicesDigitalNetwork(ISDN);SignallingSystemNo.7;ISDNUserPart(ISUP)version3fortheinternationalinterface;Part18:CompletionofCallstoBusySubscriber(CCBS)supplementaryservice[ITU-TRecommendationQ.733,clause3(1997),modified]".3Definitionsandabbreviations3.1DefinitionsForthepurposesofthepresentdocument,thefollowingtermsanddefinitionsapply:basicaccess:seeITU-TRecommendationQ.9[5],clause1,definition1551basiccallprocedures:proceduresbywhichacall(asaninstanceofatelecommunicationsservice)isestablishedandterminatedbusy:seeITU-TRecommendationI.221[6],clause3.CCBSbusy:anyoneofthefollowingconditionswillcauseuserAtobeconsideredasCCBSbusy:-maximumnumberofcallsreachedatuserA;-noB-channelsavailableatuserA;-CCBSrecallpendingonuserA.CCBScall:callgeneratedbythenetworkfromuserAtodestinationBresultingfromuserA'sacceptanceofaCCBSrecallCCBSrecall:indicationinforminguserAthatthenetworkisreadytoinitiateaCCBScalltodestinationBandthatthenetworkisawaitingaresponsetothisindicationCCBSrecalltimer:maximumtimethenetworkwillwaitforuserAtorespondtoaCCBSrecall.Thevalueofthistimershallbeaminimumof10secondsandamaximumof20secondsCCBSrequest:instanceofanactivationoftheCCBSsupplementaryservicewhichisheldinaqueuependingthecorrectconditionsfortheCCBSsupplementaryservicetobecompletedCCBSservicedurationtimer:maximumtimetheCCBSsupplementaryservicewillremainactivatedforuserAwithinthenetwork.Thevalueofthistimershallbeaminimumof15minutesandamaximumof45minutescompatibleterminal:terminalwhichcansupportthebearerserviceorteleservicerequestedfortheoriginalcalltodestinationBandwhichcanacceptcallstotheISDNnumberandsubaddressidentifyingthecalleduserintheoriginalcalltodestinationBdestinationB:entityaddressedintheoriginalcalldestinationBidleguardtimer:timethenetworkwillwaitafterdestinationBhasbecomenotbusybeforeinforminguserA.Thevalueofthistimershallbeamaximumof15secondsIntegratedServicesDigitalNetwork(ISDN):seeITU-TRecommendationI.112[2],clause2.3,definition308ISDNnumber:numberconformingtothenumberingplanandstructurespecifiedinITU-TRecommendationE.164[4]primaryrateaccess:seeITU-TRecommendationQ.9[5],clause1,definition1552SIST EN 300 357 V1.2.1:2005

ETSIETSIEN300357V1.2.1(2001-05)8retentiontimer:thistimerspecifiestheamountoftimethatthenetworkretainsalloftheinformationsuppliedbythecallinguserwhenthecallencountersbusy.Thistimerispartofthebasiccallprocedures.Althoughthistimerisoptionalforthebasiccallprocedures,itisneededfortheoperationoftheCCBSsupplementaryservice.Thevalueshallbegreaterthan15secondsservice;telecommunicationsservice:seeITU-TRecommendationI.112[2],clause2.2,definition201subaddress:seeITU-TRecommendationE.164[4],clause11.2supplementaryservice:seeITU-TRecommendationI.210[3],clause2.4suspendedCCBSrequest:CCBSrequestwhichcannotbeservedevenifdestinationBisnotbusy,becauseuserAisbusyorCCBSbusyuserA:userwhooriginatedthecallandtowhomtheCCBSsupplementaryserviceisprovided3.2AbbreviationsForthepurposesofthepresentdocument,thefollowingabbreviationsapply:CCBSCompletionofCallstoBusySubscriberISDNIntegratedServicesDigitalNetwork4DescriptionTheCCBSsupplementaryserviceenablesuserA,encounteringabusydestinationB,tohavethecallcompletedwithouthavingtomakeanewcallattemptwhenthedestinationBbecomesnotbusy.WhenuserArequeststheCCBSsupplementaryservice,thenetworkwillmonitorfordestinationBbecomingnotbusy.WhendestinationBbecomesnotbusy(i.e.accessresources,e.g.atleastoneB-channel,arenotbusy)thenthenetworkwillwaitashorttimeinordertoallowtheresourcestobere-usedfororiginatingacall.Iftheresourcesarenotre-usedbydestinationBwithinthistime,thenthenetworkwillautomaticallyrecalluserA.WhenuserAacceptstheCCBSrecall,thenthenetworkwillautomaticallygenerateaCCBScalltodestinationB.TheCCBSsupplementaryserviceshallbeavailabletouserswhoareconnectedtothenetworkviaabasicaccessoraprimaryrateaccess.NOTE:AsupplementaryserviceprovidedtodestinationBwhichpreventstheregistrationofCCBSrequestsisoutsidethescopeofthepresentdocument.5Procedures5.1ProvisionandwithdrawalTheCCBSsupplementaryserviceshallbeprovidedtouserAafterpriorarrangementwiththeserviceproviderorshallbegenerallyavailable.TheCCBSsupplementaryserviceshallbewithdrawnbytheserviceprovideruponrequestofthesubscriberorforserviceproviderreasons.Asaserviceprovideroption,theCCBSsupplementaryservicecanbeofferedwithasubscriptionoption,whichshallapplytothewholeaccessofuserA.Thesubscriptionoptionisdetailedintable1.SIST EN 300 357 V1.2.1:2005

ETSIETSIEN300357V1.2.1(2001-05)9Table1SubscriptionoptionValuesRecallmode-Global,i.e.CCBSrecallofferedtoallterminals.-Specific,i.e.CCBSrecallofferedtotheterminal,whichactivatedtheCCBSsupplementaryservice.Ifthesubscriptionoptionisnotoffered,oneofthetwovaluesshallbechosenbytheserviceprovider.5.2Normalprocedures5.2.1RegistrationanderasureNotapplicable.5.2.2Activationanddeactivation5.2.2.1ActivationWhenthenetworkencountersabusydestinationB,itshallretainthecallinformationfortheCCBSsupplementaryservicefortheperioddefinedbytheretentiontimer.DuringthistimeuserAcanactivatetheCCBSsupplementaryservice.Thevalueoftheretentiontimershallbeaminimumof15seconds.UponreceiptofarequestfortheactivationoftheCCBSsupplementaryservicethenetworkshallcheckthatacompatibleterminalexistsatdestinationB(seeannexA).WhenithasbeenestablishedthatacompatibleterminalexistsatdestinationB,thenetworkshallregistertheCCBSrequestbasedontheretainedcallinformationanduserAshallbeinformedthattheactivationwassuccessful.MultiplerequestsagainstdestinationBshallbequeued.WhentheactivationoftheCCBSsupplementaryserviceisacceptedtheCCBSservicedurationtimershallbestarted.Thevalueofthistimershallbeaminimumof15minutesandamaximumof45minutes.ThenetworkshallmonitorfordestinationBbecomingnotbusy.UserAcanhavealimitednumberofCCBSrequestsoutstanding.Thislimitshallapplyingeneralforallusersanditsvalueshallbeanetworkprovideroptionwithamaximumvalueof5.Therequestscanbetodifferentdestinations,orcanbetothesamedestinationBwithdifferentservicerequirements(e.g.bearerserviceandteleservicerequirements),orasanetworkoption,thesameservicerequirements.DestinationBcanhavealimitednumberofincomingCCBSrequestsoutstanding.Thislimitshallapplyingeneralforallusersanditsvalueshallbeadestinationnetworkoptionwithamaximumvalueof5.Asafurtherdestinationnetworkoption,thesizeofthedestinationBCCBSqueuecanbereducedforindividualusers.Thereducedsizecanhavezerolength.NOTE1:ReducingthequeuelengthallowsanetworkoperatortobalancetheinteractionbetweentheCCBSsupplementaryserviceandothersupplementaryservices(e.g.thecallwaitingsupplementaryserviceandthefreephonesupplementaryservice).NOTE2:Asaconsequenceofthequeuehavingzerolength,theCCBSsupplementaryservicewillbeunavailabletouserscallingdestinationB.HavingactivatedtheCCBSsupplementaryservice,userAcanoriginatecallsandreceivecallsasnormal.SIST EN 30
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