Having issues with DTMF on external IVRs and ONLY from phones that connect IAX to our asterisk server. Specifically, the IAX connected phones have no internal DTMF issues either. When the phone connects to external IVR systems the CLI (DTMF Debug) shows all the DTMF tones registering however not all get passed to the external IVR, some do and others are omitted. It is also not specific to a particular tone/key.

SIP phones on the same server function flawlessly.

I can only surmise at this point that it is an issue when iax gets converted/translated to sip (in asterisk) to pass to our external carrier. I have looked through the forum and online but can find nothing specific about the iax to sip process in asterisk nor ways to test, adjust, etc.

Our server is running latest CentOS with Sangoma AFT A108D card and Asterisk 1.4.26. As a note, the server is brand new HP ML150 replacing an older Asterisk 1.2 box where this issue did not exist. No phones, codecs, etc. have changed.

Any help or advice on this would be greatly appreciated.