> I am helping manage a freeSWITCH server with IVR, and we have had an intermittent issue with receiving tones from some callers. To try and control for this issue, I have currently set up a FS 1.10 instance running on Debian 10 (Buster) running minimal test scripts to send or receive calls and capture tones.
>
> At first FS was not recognizing any tones on any test calls. I eventually determined that I had to send at least some audio on the line before tone receipt would appear in the FS debug log. Most endpoints appeared to work correctly at this point.
>
> However, at least one endpoint is sending DTMF packets that FS still does not appear to process at all; tested with the same script, FS does not even include a RECEIVED DTMF event in the debug log. However, Wireshark examination indicates that RTP EVENT packets with tone payloads are reaching our server in all cases, including calls where FS does not process them, on the same ports were audio is being successfully recorded.
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> Our near carrier is Flowroute; their page states that they support RFC2833 and RFC4733. Our gateway file specifies <param name="dtmf-type" value="rfc2833"/>.
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> The only suspicion I have is that on the calls that don't register, the Volume field of the DTMF payload is listed as 0, where it is values like 10 or 13 on other calls. But research has not definitively identified that as a problem.
>
> To recap:
>
> * We are receiving RFC2833 tone payloads on expected ports for all calls tested.
> * FreeSWITCH is processing events for these tones in most cases but not all.
> * The same scripts and origination dialstrings are being used for all callers.
> * Is volume of zero a significant issue?
> * What else might we need to correct?