[asterisk-dev] Can Asterisk detect A,B,C,D DTMF signals

[John Todd]

On Jun 28, 2009, at 6:07 AM, Nir Simionovich wrote:

> Hi All,
>
> I've been asked by a prospect if Asterisk can handle the additional  
> DTMF signals that
> may be produced by some emergency systems. According to the DTMF  
> standard,
> there are 4 additional tones that can be generated, however, these  
> are not used in most
> phones.
>
> Can these be intercepted by Asterisk?
>
> Nir Simionovich



Yes, they are recognized by Asterisk.  They are sometimes called "4th  
column tones".  My familiarity with them dates back to 4A switch test  
sequence & AUTOVON, but best not to go into those ancient days in too  
much detail.

The matching on these keys in Asterisk of course illustrates the  
difficulty in how we would handle instant messages, or SIP names, or  
anything else as part of exensions.  The keypad digit "a" also would  
match "a" in a text string.  How do you differentiate between text and  
4th column tone designators?  It's a head-scratcher.

JT

---
John Todd                       email:jtodd at digium.com
Digium, Inc. | Asterisk Open Source Community Director
445 Jan Davis Drive NW -  Huntsville AL 35806  -   USA
direct: +1-256-428-6083         http://www.digium.com/