[Asterisk-Users] DTMF information?

[Chris Lee]

Steve Underwood wrote:
> 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
> 
Thanks for the info, I will have to re-think my plans.

With GSM the tone lasts until the user releases the key, this I have 
tested GSM to GSM and GSM to Land Line (pots).

I assume then that the ISDN carries DTMF as audio and this must be 
decoded by something? hardware or software depending on the card in the PC.
I have noticed with analogue modems that the hardware decoders provide a 
'DTMF tone received' indicator and then ignore the length of the tone,

Does any one know if tone length is acquired by any of the asterisk 
drivers? and retained/passed on within asterisk?

It seems like throwing away information, which could be useful, if the 
length of the key press is ignored and only the fact it was pressed is 
retained.
I dont know what the standards say but I have noticed that all phones I 
have tested (except DECT phones) send a continuous tone until the button 
is released.

Chris.