The token ring receiver portion of the station expects to see continuous signal transitions on the input. This counter is incremented if the station fails to see a transition for 5 half bit times. To prevent this error being recorded on subsequent stations the detecting station transmits idle after failing to detect a transition after 4 half bit times.

GENERAL: Soft Errors

The token ring architecture includes an inherent error monitoring protocol. Each station records local errors. These errors are generically referred to as 'soft errors'. Soft errors represent intermittent faults that temporarily disrupt normal operation of the ring. Stations periodically transmit their soft error counters onto the ring where they can be received by any stations which have the ring error monitor functional address active.

There are two categories of soft error. Isolating errors and Non-isolating errors. An isolating error will be reported by exactly one station on the ring and the error is known to have occurred between that station and it's upstream neighbour. The second category are non-isolating. That is, errors of this nature may be seen and reported by more than one ring station. With these errors it is not possible to resolve the source of the error.