Alarm status of the shelf.An implementation may not support all the values. possible values are : clear (1) : shelf is not in alarm minor (2) : Indicates that a non-service affecting condition has occurred and that corrective action should be taken in order to prevent a more serious fault. major (3) : Indicates that a service affecting condition has occurred and urgent corrective action is required. critical (4) : Indicates that a service affecting condition has occurred and immediate corrective action is required. The definition for minor(2),major(3),critical(4) are taken from Bell Core document : GR-1248-CORE.