# Monitoring signaling bits

Once battery is enabled, the DSP can monitor signaling bits. This topic describes how to:

- Start signal detection

- Stop signal detection

## Starting signal detection

To start on-board monitoring of the signaling bits for a station, invoke cdiStartSignalDetector. In the invocation, pass a pointer to the CDI_SIGNALDETECTOR_PARMS structure.

If monitoring is started successfully, cdiStartSignalDetector returns SUCCESS, and signal monitoring events are enabled. Subsequent events indicate bit state changes.

## Stopping signal detection

If enhanced mode is enabled, the DSP automatically stops detecting signaling from a station when the station goes on-hook (CDIEVN_ON_HOOK is returned). If enhanced mode is disabled, the application can invoke cdiStopSignalDetector to stop detection.

If the station is on-hook, and cdiStopSignalDetector is invoked, CTAERR_FUNCTION_NOT_ACTIVE is returned.