I have a FreePBX installation, with a TDM400P card containing 2 x FXO modules and 1 x FXS module. I installed and configured this a couple of months ago, with a single FXO set up as a trunk (a BT line in the UK). All was working perfectly.
For some reason, about a month ago, outbound calls via the BT line stopped working properly. The destination phone would ring, but on answer there would be no audio at all. There would be no “ringing” sound on the calling party either. When the called party hangs up, the calling line gets a “all circuits are busy now” announcement.
I ran a Wireshark trace for the SIP messages, and noticed that immediately after the INVITE, there is a “401 Unauthorized” response, immediately followed by an ACK. This is immediately followed by another INVITE and a “100 Trying”, but no RINGING is received. Nothing else happens until I end the call.
Inbound calls are working fine (via an IVR), and calls to other SIP extensions are also fine (though I did notice the same “401 Unauthorized” when calling another extension, even though it connected fine).
I’m not sure of this is a SIP problem or a DAHDI problem. Even more curious is the fact that it worked fine, then suddenly stopped.
Has anyone come across this before?