When one node initiates a signal transmission, this signal is transferred over the ring until it comes back to the source that blocks the signal. At this moment of time, no other data should be transmitted over the network. To ensure this condition, there is a timeout of 500 µs provided by TCF-142.
Having done some measurement on the 25-kilometer fiber network we found out that the data is transmitted from one side to the other within 120µs. Moreover, the signal processing delay by TCF-142 equals to 1µs. Hence, in order to provide the timeout of 500~550µs, the maximum fiber ring length should not exceed 100km.
Therefore, if the fiber optic cable between TCF-142 is 20km long, then, in total, 5 devices can be connected into a ring. If the fiber optic cable is 2km long, then 50 devices can be connected in the ring.
