[asterisk-dev] DTMF detection and generation code

[Vahan Yerkanian]

Steve Underwood wrote:
> Adding duration to IAX2 DTMF messges is a bad idea. RFC2833 is brain 
> dead for having it (actually RFC2833 is just rather brain dead). The 
> length of DTMF has no relevance, as long as it meet the minimum required 
> length for the DTMF specs. I think the problem in some parts of the 
> system is the minimum is not being enforced.

I think in the general case Asterisk has to forward the same DTMF 
durations that it receives in one format to the other format. Many many 
proprietary weird systems are tuned to accept specific DTMF durations, 
and by Murphy's law, your next project involves such a system. So, it's 
not uncommon for customer raising the question why "this new cool 
system" cuts the tone duration to a defined length while he is still 
keeping his finger on the button.

> Many many things in the telephone network - cellular systems, key 
> systems, many large PBXes with digital telephones - change the length of 
> DTMF so what is sent is completely unrelated to what it pressed. 
> Anything which cares about the length of a DTMF digit, other than 
> meeting the requred minimum, is badly broken.

It is exactly this assumption that has broken havoc on this DTMF opera. 
Ask 10 random people - what they expect - keep hearing a tone until they 
  release the pressed keypad button or a fixed length beep. DTMF has 
been around like 25 years, lets not invent wheels, I mean don't break 
people's habits - there are people that use DTMF to jokingly "spice-up" 
their conversations with morse code :)

Just my 2 cents,
Vahan