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ITU-T Q.953.3 (06/1997)

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Stage 3 description for call completion supplementary services using DSS 1 : Completion of calls to busy subscribers (CCBS)
This Recommendation specifies the stage three of the Completion of Calls to Busy Subscribers (CCBS) supplementary service for the Integrated Services Digital Network (ISDN) at the T reference point or coincident S and T reference point by means of the Digital Subscriber Signalling System No. 1 (DSS 1) protocol. Stage three identifies the protocol procedures and switching functions needed to support a telecommunication service.The CCBS supplementary service enables a calling user A, encountering a busy destination B, to be notified when the busy destination B becomes not-busy and to have the service provider reinitiate the call to the specified destination B, if user A desires.The CCBS supplementary service is applicable to all circuit-switched basic telecommunication services using one B-channel.
Citation: https://handle.itu.int/11.1002/1000/4064
Series title: Q series: Switching and signalling, and associated measurements and tests
  Q.850-Q.999: Digital subscriber Signalling System No. 1
  Q.950-Q.959: Stage 3 description for supplementary services using DSS1
Approval date: 1997-06-05
Approval process:TAP
Status: In force
Maintenance responsibility: ITU-T Study Group 11
Further details: Patent statement(s)