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Asterisk / chan_capi - DTMF detection issue

Issue:

In certain scenarios DTMF digits may not be properly recognized because the DTMF tones are too short.

By default, Asterisk issues DTMF listen commands with a 80 ms Minimum Tone Time and 80 ms Minimum Gap Time.

During sending and receiving chan_capi uses the same hard coded values.

chan_capi.h, #define CAPI_DTMF_DURATION 0x50

Note: 50 hex = 80 decimal

Solution/Workaround:

This following describes how the DTMF duration can be modified in order to address such issues.

 The fastest way to achieve the desired changes would be to modify the chan_capi sources as follows:

cd /usr/lib/opendiva/divas/src/src
mkdir chancapi
tar -zxvf chancapi.tgz -C chancapi
cd chancapi

 Now open the file chan_capi.c and search for "Setting up DTMF detector". Immediately below the values can be adjusted. Here you can configure new values according to your needs.

e.g.

#define CAPI_DTMF_MIN_TONE_DURATION 60
#define CAPI_DTMF_MIN_GAP_DURATION 80

error = capi_sendf(i, 0, CAPI_FACILITY_REQ, i->PLCI, get_capi_MessageNumber(),
"w(www()())",
((i->channeltype != CAPI_CHANNELTYPE_NULL) || (i->line_plci != 0)) ? FACILITYSELECTOR_DTMF : PRIV_SELECTOR_DTMF_ONDATA,
(flag == 1) ? 1:2, /* start/stop DTMF listen */
CAPI_DTMF_MIN_TONE_DURATION,
CAPI_DTMF_MIN_GAP_DURATION
);

In general the settings in this example should be sufficient. There are only rare cases where different settings are needed.