Beaconing
The first station turned on in a Token Ring network becomes the active monitor.
It ensures that the network continues to function by periodically sending a packet around the ring to ensure ring integrity.
Any Token Ring NIC can detect a failure on the ring. If a NIC does detect a failure, it starts beaconing. Beaconing means that the NIC sends frames to all other NICs on the wire.
A computer can remove itself from the network to run self-diagnostics. If the diagnostics pass, the NIC will reinsert itself on the wire; otherwise, it will remain disconnected from the ring.
Once the failure point is detected, the ring is automatically reconfigured around the failed computer.