Apparently Aron is not the first to experience such problems. See here:

https://freeswitch.org/confluence/display/FREESWITCH/RTP+Issues#RTPIssues-DTMFProblems

Bote

From: freeswitch-users-bounces@lists.freeswitch.org [mailto:freeswitch-users-bounces@lists.freeswitch.org] On Behalf Of Donny Hardyanto
Sent: Friday, 20 March, 2015 08:12
To: FreeSWITCH Users Help
Subject: Re: [Freeswitch-users] DTMF missing digits

I have done integration with sonus. I am sending rfc2833. Usually the dtmf suppression and fax detection setting on the sonus is the problem.

donny

On Friday, March 20, 2015, Stanislav Sinyagin <ssinyagin@gmail.com> wrote:

how do you send DTMF to sonus? info or rfc2833?


On Thu, Mar 19, 2015 at 5:10 PM, Podrigal, Aron
<aronp@guaranteedplus.com> wrote:
> I am experiencing problems with sonus dtmf. I tried setting different
> parameters related to the RTP BUGS listed in switch_types.h but it did not
> seem to fix the problem.
>
> I have freeswitch ----> [carrier(sonus), ...]  -----> freeswitch
>
> freeswitch sends the following digits to our carrier, and is received by the
> other end (also a freeswitch) missing the digits marked in black.
> pcap shows the missing digits as being part of the previous packet, so two
> 1's becomes one 1 with the duration sum of two.
>
>  1   -    1   -    2   -    1   -    1   -    #
>
> What are the relevant parameters I should set?
>
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