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