1.20Integrated Services Digital Network (ISDN) Service Features
1.20.1.10Completion of Calls to Busy Subscriber (CCBS)
Description
If the called party is busy and the call has been made using an ISDN line, an extension user can set to receive callback ringing when the called party becomes free. When the user answers the callback ringing, that party’s number is automatically dialled.
This feature complies with the following European Telecommunication Standard (ETS) specifications: ETS 300 359 Completion of Calls to Busy Subscriber (CCBS) supplementary service.
Conditions
•This feature is available under the following conditions:
a)The caller’s PBX is capable of using CCBS and the service is provided by the network.
b)The called party’s PBX is capable of accepting CCBS.
•To receive and send CCBS, receiving and sending CCBS must be enabled individually on an ISDN port basis through system programming.
•An extension user can set only one CCBS. The last setting is effective.
•The CCBS setting is cancelled if there is no callback ringing within 60 minutes or callback ringing is not answered within 10 seconds.
•If an extension user makes a call using the CCBS feature, the preassigned CLIP number for the extension will be used even though the extension has set CLIR or the extension has used the CLIP for the incoming call distribution group by pressing the ICD Group button when the CCBS has set. ( 
1.20.1.2 Calling/Connected Line Identification Presentation (CLIP/COLP))
•After using the CCBS feature, using Last Number Redial will not retrieve the number dialled by CCBS. ( 
1.6.1.4 Last Number Redial)
•An extension user that has set the CCBS feature cannot receive callback ringing while the extension is holding a call.
User Manual References
User Manual
1.2.4 When the Dialled Line is Busy or There is No Answer
