Tones from IVR stop inbound audio stream

I’ve narrowed down a strange problem I’ve been having today. I have been working with my provider to solve a problem when calling companies with an IVR that subsequently transfer a call to an ACD queue for a live agent. After the IVR to ACD handoff there is only silence until the call just drops. The provider could not replicate.

During a test call today I had a network capture running and later played the RTP stream with Wireshark. The inbound audio stream was intact. The call did go to the ACD queue, music did start, and agent did answer, and after a few greetings, hung up.

When the IVR hands off to the ACD it injects 4 tones into the RTP stream. None on these tones are forwarded to the extension, nor any audio after them. It appears that the outbound audio stream may still be active, but I can’t verify that it this time.

So, the obvious… anybody ever see this?.. anybody know how to make it stop?.. any suggestions to track down specifically what is causing it, because something has obviously been triggered by a tone?

This is on the latest FreePBX distro, running Asterisk


Looking closer at the trace I have received RFC 2833 RTP Events apparently as a result of the tones. I have received Event ID DTMF * (0x0a) followed by Event ID DTMF 8 (0x08).

So, apparently the tones from the IVR were picked up and RFC 2833 events were sent. My server apparently is responding to those events.

Should inbound RFC 2833 events trigger feature codes?

And, for what its worth, dtmfmode=inband

The current problem seems to have been solved by changing dtmfmode=auto. Provider clearly supports RFC 2833 as evidenced by the RFC 2833 RTP Events. The inband tones from the IVR was breaking the inbound audio stream.