3.13    Circuit group supervision message type

           8  7  6  5  4  3  2  1
        1  H  G  F  E  D  C  B  A

The following codes are used in the circuit group supervision message type parameter field:
        bits
        BA      Circuit group supervision message type indicator
0 0     maintenance oriented
0 1     hardware failure oriented
1 0     reserved for national use (used in 1984 version)
1 1     spare
        bits H-C        Spare