3CX not delivering RTP stream to the phone/extension despite receiving it, and only for some numbers

[NEO WEB]

Since a month or so I have noticed that my 3CX on-premise (behind a router with the SIP and RTP ports already natted) does not deliver the audio to the phones/extensions, i am trunked to my ISP via a proxy (of the ISP itself).

Inspecting the audio capture i can see the media streaming from the proxy to my 3CX server, i can hear the audio by playing it, but the 3CX is not delivering the RTP stream to my extension.

Tried with a softphone, physical phone, and android app both inside and outside the LAN to no avail.

I have noticed this behavior only on some remote numbers, which can be consistently reproduced (calling said numbers again the problem always happens, calling other numbers it works just fine).

Attached the activity logs in trace mode of one test call, i have modified my user (DummyUser1), my number (0101010101), the number i called (020202020), and my public IP (5.5.5.5), do anyone have any idea why this would happen?

My 3CX version is the latest (16.0.8.9), i wonder if there's a bug on this specific version (?)

Thank you very much for your help in advance

 

[JohnS_3CX]

Hi,

Firstly ensure that you have forwarded your entire RTP range on the firewall https://www.3cx.com/docs/ports/
Note: The 3CX firewall checker only tests the first and last ports, not the entire range. If these are not confirmed first, do not proceed with anything else.

What codec does your provider support? I noticed the phone and provider codecs and phone codecs are not perfectly matched and this could potentially cause a problem. Blindly, I would suggest you use PCMA (G.711 A) on both the phone provisioning settings, and the trunk settings - just to get this possibility out of the way.
Ask your provider to confirm their supported codecs and priority list just to be sure.

Also consider using the below settings on the trunk as you see here: