Solved 3CX PBX not able to sending DTMF outbound

[Chris_P]

We have a problem with being able to send DTMF tones via our 3CX PBX if we enable PBX Delivers Audio on the SIP trunks. If PBX Delivers Audio is disable then DTMF works fine, but then we have issues with our incoming callers who call into our Digital Reception. The inbound caller loses the ability to hear the recorded message and when transferred through to an agent, the agent can't hear the caller.

From the wire-shark trace you can see that the PBX is recongising the DTMF tone, but it seems to not be accepted by the SIP provider (TPG in Australia).

Anyone got any suggestions on how to overcome this problem?

 

[JohnS_3CX]

Hi Chris,

Before moving forward, can you show a screenshot of your SIP trunk Options tab?

Also tell us if this is a SIP trunk or it is based on a gateway by your provider

 

[Chris_P]

Hi John

Please find attached the screenshots for the Trunk options.

This is a SIP trunk. I'm not sure what you mean by "based on a gateway by your provider"? we authenticate with our SIP provider via username and password, instead of IP address if that is was you mean.

 

[cobaltit]

He's asking if the trunk goes over the internet or if the provider has a gateway local to the PBX (like a eMTA) that you register to.

 

[Chris_P]

Over the internet, its public SIP.

 

[JohnS_3CX]

Hi Chris,

I think you need to review the settings on the Options tab in this case to solve the audio issue first. Try to match the below and tell us if this fixes the problem with the audio before we proceed to the DTMF:

 

[Chris_P]

Hi John

Thank you for your prompt response. So that I can understand the technical side better, can you explain how un-ticking "Supports Re-Invite" and moving the order in the codecs to have G.711 U-Law to the top of the order will effect the audio?

 

[JohnS_3CX]

Hi Chris,

I have not seen a capture of your system to be certain of the issue, so I'm suggesting some base settings.

Re-invites are not necessarily problematic, we use them on the deskphones internally for example. But on the trunk they can cause the audio issue since we don't know how the untested provider or the other side will handle it. If it is avoided altogether then we reduce the chances of a problem happening, generally speaking.

PBX Delivers Audio potentially does not send the DTMF through from your phone to the other side because the provider likely does not reply to support RFC2833 in the SDP so the PBX does not forward it as it is not considered to be accepted. Your screenshot was from device to PBX I'm guessing (i saw all local IPs), so you were looking at the wrong leg of the call. You want to see the one between the provider and the PBX to establish whether your PBX sends it.

Codec order will not really affect things in this case, so we can ignore that for now.

 

[Chris_P]

Hi John

Thanks for your help. I made the recommended changes and it seems to have fixed our issue.

 

[JohnS_3CX]

Glad to hear!