Description: This indicates the current state of the Topology Change state machine. This object will hold the value 'inactive' when the Topology Change state machine is in the INACTIVE state, the value 'learning' when the state machine is in the LEARNING state, the value 'active' when the state machine is in the ACTIVE state, the value 'detected' when the state machine is in the DETECTED state, the value 'notifiedtcn' when the state machine is in the NOTIFIED_TCN state, the value 'notifiedtc' when the state machine is in the NOTIFIED_TC state, the value 'propagating' state when the state machine is in the PROPAGATING state and the value 'acknowledged' when the state machine is in the ACKNOWLEDGED state.