There is no CSU. I have been in programming. The T1 is configured for B8ZS. I cantacted the carrier when the T went down. They did some testing and said that everything looked fine. I monitored the system all day yesterday and didn't get any alarms. I'm thinking that maybe it went down for just a moment and had trouble syncing back up. The ringing was not the vm alarm. The ringing was coming in on the line keys. It was displaying 500 on the display. I do understand that this could be a hard issue to track down. It may have just been a fluke thing. I will continue to monitor the system and see if it happens again. Thanks for your help