[asterisk-dev] DTMF length (Re: [svn-commits] russell: branch 1.4 r61763 - /branches/1.4/main/channel.c)

asterisk at ntplx.net asterisk at ntplx.net
Mon Apr 23 16:21:37 MST 2007

Here is what I found on-line at:


"The values shown are those stated by AT&T in Compatibility Bulletin 105.
For compatibility with ANSI T1.401-1988, the minimum inter-digit interval
shall be 45msec, the minimum pulse duration shall be 50msec, and the minimum
duty cycle for ANSI-compliance shall be 100msec."

Looks like you should also enforce a mimimum interdigit delay. It
seems 100ms is long enough, I remember 75ms being something
that old modems could generate and would work when I was trying
to dial lots of DTMF digits quickly.

I have found many sites that say equipment will detect same digits with
a 40ms tone and 40ms interdigit delay and also different digits with a
0ms (no) interdigit delay....but don't count on it for everything.

So my vote is to drop it to 80ms tone and force a 45ms delay until the next
DTMF digit as part of the total time (if it could be done that way).

Or just ignore me and leave it at 100ms an move on to the next bug.


> Author: russell
> Date: Mon Apr 23 12:57:32 2007
> New Revision: 61763
> URL: http://svn.digium.com/view/asterisk?view=rev&rev=61763
> Log:
> Ensure that digits passing through Asterisk have a reasonable minimum length.
> It is currently 100 ms.  If someone thinks this should be different,  
>  feel free
> to speak up.  (related to issues #8944, #9250, and #9348)

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