Put a loop back in the network side of the CSU.
If the network stays up, the problem is on your side, also put the loopback into the pbx and see if it stays in sync.
I had similar problems and everybody denied it was on their side. I had a vendor meet and the BOC tech said everything was fine, I asked him to check the programming of the card in the smartjack. Low and behold the smartjack card had the wrong formatting and line coding. Once he reprogrammed it the T-1 came up.
Point being - don't trust what the network side guys say!
