We have a Nortel PBX connected to an Adtran 916. We are experiencing intermittent call drops of incoming calls. Callers report that they call our main number, the call is answered in 2 rings (as programmed), there is a couple seconds of silence and then they here a dial tone. This can be replicated when calling from an inside line to our main number. What should happen after 2 rings is that the caller hears our auto attendant.
When viewing the call monitor in the GUI, I can see the calls coming in and terminating. During one call "no battery" showed next to both lines under status.
Any suggestions on cause or troubleshooting?