[asterisk-dev] DTMF detection and generation code

[Chris Lee]

Steve Underwood wrote:
> Vahan Yerkanian wrote:
> 
>> Steve Underwood wrote:
>>
>>> With most cellular base stations each press of the buttons on the 
>>> phone produces a fixed length DTMF pulse, with a fixed silence 
>>> following it. If you press keys in quick succession, they are 
>>> buffered up, and played out as tones at the pace the base station 
>>> sees fit. Typically they make the tones very long, for some reason. 
>>> 0.5 seconds in many cases. I think your application sounds broken by 
>>> design. I've been through this before, trying to build things which 
>>> require rhythmic input. It just doesn't work, unless your application 
>>> is limited to plain old analogue land line phones.
>>
>>
>> DTMF buffer is another useful thing - currently digits sent too fast 
>> are guaranteed to be skipped. Ironically, I never get a double or 
>> skipped digits from cellular networks - these send DTMFs with loooong 
>> durations as the developers have accounted for lossy nature of the 
>> cellular technology.
> 
> The lossy nature of cellular networks has no impact on DTMF. The phones 
> do not generate DTMF. The base stations do. The phones merely send 
> messages saying "user pressed one", "user pressed five", etc. and they 
> don't tell the base station how long it was pressed for. The base 
> station generates the DTMF tone in a non-lossy environment.
> 
> Steve
Steve,
I would be happy to call you from my cellular phone and hold down keys
to show you that the DTMF is generated for the duration of the hold down.
I don't know if the UK networks are special but they (all of them tested
except for 3) do provide a tone from minimum length (variable length 150
to 500 ms) to duration of key held down.
This works for all Nokia SonyEricson Siemens and LG phones so they are
sending key down and key up information.

Chris.
> 
> _______________________________________________
> --Bandwidth and Colocation provided by Easynews.com --
> 
> asterisk-dev mailing list
> To UNSUBSCRIBE or update options visit:
>   http://lists.digium.com/mailman/listinfo/asterisk-dev
> 
>