DTMF on outbound calls from our SIP phones is unreliable. The problem appears to be specific to certain external numbers, and the symptoms are that after the call connects key-presses on the phone don’t generate any audible tone and are not recognized by the remote application (e.g., an IVR). We have not experienced any other problems with outbound calls.
We are running Trixbox 2.2/Asterisk 1.2.18 with zaptel 1.2.19. The PBX has a TDM400 card which we use for a small number of internal analog phones – none of which exhibit this behavior when calling outbound – and a TE120 which we use for our fractional PRI connection to the external world.
Our SIP phones are a mix of Aastra 9112i’s and 9133i’s, as well as the X-lite client. I have tried increasing “toneduration” in zapata.conf. I have also tried setting “dtmfmode” to “inband” in extensions_additional.conf (via the FreePBX GUI) and disabling out-of-band DTMF on the Aastra phones. None of these measures fixed the problem.
Any ideas? Again, outbound DTMF from the SIP phones generally works, but there are some external numbers for which it does not.