This is Unity 4.2.1 with PIMG on Nortel M1.
We have 4 ports configured for MWI only on one of the PIMG units.
Occasionally the bottom PIMG port will go into "TDM out of service" condition for up to 10-15 minutes and then reset itself and come back up.
This is not related to a particular PIMG unit or port (we have moved the MWI ports around). Also we have moved the extension on the M1 side to different card - no change.
The problem is that Unity does not recognize the port being out of service, and keeps pushing out MWI requests to the same port causing MWI failures.
This is frustrating due to the PIMG not putting the port SIP state into busy.
Also Unity does not do round-robin MWI port usage which would minmize the problem it would simply complete the next request on another port.
I believe the constant hammering of MWI requests on this port while in a down state is making the problem worse. I have had other ports do this on PIMG units (call answer only) but they only go out of service for a few seconds and recover.
PIMG code is 5.0.64 - does the latest firmware do anything for this?