I have a 228. I get Blue alarms periodically.
"Blue Alarm
A blue alarm signal is an unframed all ones signal. It is transmitted by a remote device (usually a CSU) and when received,
indicates a transmission failure upstream of that device toward the local end. The AIS alarm signal is also
known as the “keep alive” signal. In that sense, it prevents the T1 (or ISDN PRI) circuit repeaters from malfunctioning
when transmit from the remote end is lost."
I don't really understand this. Is that saying that the CSU is having problems transmitting to the CO and that it sees this and is sending all 1's to the T1 card in the IDS so that the connection between the IDS and the Adtran stays up?

I believe that when a CSU recieves a yellow alarm from upstream it sends a blue the other way (Downstream to you) the failure is at least one step upstream from the CSU in this case. Probably a down T-1 and the Network interface is sending yellow to your csu.

No, a piece of equipment that puts out alarm code will put out a yellow if it receives an all one's also known as a blue or red alarm. If a piece of equipment receives a yellow it doesn't put out anything, unless of course it's the cause of the incoming yellow.

Your "Blue Alarm" is a failure coming into you.