[Asterisk-Users] Problem with DTFM and complex international setup

[Rob Scott]

We have some guys working in the US who can't always dial back to our
company in Europe easily (lots of clients require authorization to make
international calls), so I set up the following:

   - ipkall.com number links to a FWD number
   - office Asterisk box registers with FWD

Then I programmed Asterisk to accept office extension number using DTFM
tones.
This works OK.

Then I programmed Asterisk so that it is possible, using a PIN code, to
dial out from Asterisk onto the local PSTN.

This also works occasionally.
Looking at the message from the Asterisk box it is clear that sometimes
numbers are missed or repeated in the dial string. This I suspect is
because Asterisk is listening to the DTMF tones but the signal is
dropped; sometimes the drop means that a whole digit is dropped and
sometimes is means that a digit is repeated.

Does anyone know how I can fix this to make it more reliable
(out-of-band DTMF?) or a better way to achieve a reliable setup?