9-30C3 B
 What is the meaning of the "ACB" Inmarsat-C Non-Delivery Notification (NDN) failure code?
A. The terminal received an invalid answer-back from the destination. 
B. Access to the Inmarsat system has been barred. 
C. The Automatic Communications Bit error rate was exceeded.
D. An Inmarsat message channel failure occurred.
