6.3 DTMF Detector

AG boards are capable of detecting DTMF digits. Chapter 5 discussed an interface for collecting digits (DTMFs) in your application. Digit collection assumes that DTMF detection is enabled.

All protocols (including NOCC) default to running the DTMF detector in conversation state. Detection parameters are loaded when the protocol is started. You can later disable, re-enable, or modify the DTMF detection parameters if necessary via the adiStartDTMFDetector and adiStopDTMFDetector functions.

You can modify the DTMF detector's default behavior by specifying the following parameters when invoking adiStartProtocol or adiStartDTMFDetector.

• Column-four Flag: A flag indicating that the fourth column of DTMFs, listed as 'A', 'B', 'C', and 'D', should be detected.

• On Qualification Time: The minimum duration in milliseconds of a recognized DTMF signal before a DTMF-begin event is sent.

• On Qualification Amplitude: The minimum signal level in dBm, recognized as a DTMF signal.

• Off Qualification Time: The minimum duration in milliseconds of absence of a recognized DTMF signal before a DTMF-end event will be sent.

• Off Qualification Amplitude: The minimum signal level in dBm to maintain recognition of a DTMF signal once recognition has started.

Refer to Figure 24 for an illustration of these parameters.

The above parameter information is communicated via the ADIDTMFDETECT parameter structure. For the exact representation of these parameters, refer to Appendix D of the AG Access Function Reference Manual.

The remaining parameters in the structure (specifically, onthreshold and offthreshold) should not be modified. They are parameters to the DSP algorithms and are included in the structure in the case of a field problem for which an NMS engineer may request modification.

The adiStopDTMFDetector function immediately terminates DTMF detection. AG Access generates an ADIEVN_DTMFDETECT_DONE event with the value set to ADI_REASON_STOPPED.

AG Access may also generate the ADIEVN_DTMFDETECT_DONE event with an error code, ADIERR_xxx, if the function is started incorrectly.

Copyright 1996 Natural MicroSystems, Inc. All Rights Reserved.