I've got a B400P, with two of the four spans in use, connected to BT ISDN2e lines. Intermittently (approx 1/3 of the calls) an outbound call will happen with one way audio, where the remote party hears silence (i..e the audio being sent out through the ISDN line is disappearing)
I'm seeing it on both of the connected spans, and it seemed to start all of a sudden, with no changes to the software configuration.
Using dahdi_monitor I can see both parts of the audio (that coming in from the ISDN line and what is supposed to be going out to it), and I've verified that it's not a SIP issue etc.
The carrier has run their fault diagnostics which claim the lines are working fine - I don't have a spare card at the moment (though I'm going to get hold of one) to try swapping it out, so I was wondering if anybody has seen anything like this before or has any suggestions of further debugging I can do?