[Asterisk-Users] DTMF information?

[Steve Underwood]

Chris Lee wrote:

> I am looking at building an IVR product with a few interesting 
> features and need some more information about how asterisk and VoIP 
> work and what I can get from them.
>
> As far as I can tell when I use ISDN/GSM telephone networks the DTMF 
> information travels as data representing 'start tone' and 'stop tone' 
> for each button pressed, it is then generated at the other end if an 
> audio representation is required.
> I am interested to know if I can get access to these events 'start 
> tone' and 'stop tone' through the dialplan or an AGI or by acting as a 
> VoIP device. Or of course if I am completely off track and should give 
> up now.
>
> I am looking to get the length of time a button was held down rather 
> than that it was pressed.
>
> Thanks for any help

ISDN never does this. GSM only does this between the handset and the 
base-station. You only see DTMF tones from outside the GSM network 
itself. For fancy IVRs, beware that the timing of DTMF from a GSM 
handset has nothing to do with the timing of the user's keypresses. 
Because the base-station generates the tones, it controls their timing, 
and always generates rather long slow pulses of DTMF tones.

Regards,
Steve