ISDN communication failed, is it the line or my hardware?

Question

My ISDN TA lights an alert and the line is busy, is it the terminal hardware or the line at fault.

Answer 1

Yes, it is one or the other. What have to tried to see if you can clear it?
Reset the modem, just unplug it wait a minute, reconnect it.
If the problem clears you just fixed it.
If you have the ability to check the line that would be step two.
If not you will probably need your providers help.