Additional Media Descriptors in SDP during INVITE break external calls

[event it AG]

We have a problem with our 3CX system:
Currently it happens with some extensions that they deliver an additional media description line in the SDP part of the INVITE package when connecting to external telephone numbers:
m=video 0 RTP/AVP 31
Format 31 is H.261, so the phone tries to offer a video signal.
This is something that our SIP provider, Vodafone, apparently cannot cope with (statement from technical support).

As a result, the other party rings when making a call, but when the call is answered, the connection is immediately interrupted with the announcement that the call could not be established.
The physical Vodafone NGN gateway, via which our 3CX system registers it's SIP Trunk, reports a "503 Service Unavailable".

The problem only occurs in the iOS and Android App, and only for some extensions.
Unfortunately, I don't know what change has caused this problem, but it has only been known for a few days.

We are also in contact with Vodafone technical support, but we need to fix the issue on our side.

Hopefully someone here knows more
Best regards

 

[OlegR_3CX]

Hi there.

Are you sure this comes from the 3CX applications, as this kind of codec we don't use

INVITE package when connecting to external telephone numbers:
m=video 0 RTP/AVP 31
Format 31 is H.261, so the phone tries to offer a video signal.

3CX mobiles apps uses VP8,9 and H264 for video and not H.261

 

[event it AG]

This is network traffic I have intercepted between 3CX and our external SIP Gateway. These are packets that 3CX generates, so I'm relatively sure.
I have also found no documentation whatsoever for this codec from 3CX which is why I am starting to suspect this to be a faulty installation of some kind.

 

[OlegR_3CX]

From what i can see, you have multiple installs, do you face the same issue from in both of the systems?

 

[event it AG]

We only have one install that's actually productive. We are currently in the proccess of setting up another 3CX install in the hopes that we can upload a backup of the productive install, to see if the problems come from a corrupted VM.

 

[OlegR_3CX]

Let us know how it goes.
Thank you