# QSIG Callback (Call Completion)

Users can request a Callback when they reach a busy or unanswered station.

Callback with service retention is supported for the following Call Completion (CC) Supplementary Services:

- Completion of Calls to Busy Subscribers (SS-CCBS): users can set a Callback against a busy station.

- Completion of Calls on No Reply (SS-CCNR): users can set a Callback against a station that doesn't answer.

NOTE: Service retention is the capability to continue with a CC Request after the CC Call failed.

Related Topics

- QSIG Description

- QSIG Conditions

- QSIG Operation

- QSIG Programming