Specifications

B.8 Ring Operation
FDDI Overview B–17
B.8.5 Steady State
In the steady state, the token circulates around the ring. The time for a token to circle
once around the ring without being used by anyone is known as the token latency.
Stations that wish to transmit must capture the token, and can transmit as long as
allowed by the token holding rules.
All stations keep a timer called the valid transmission timer (TVX) which they use
for timing valid activity on the ring. If, for any reason, a token gets lost, the TVX
timer expires and all stations enter the claim process to elect a new token.
During the Steady State, all stations in the ring exchange frames that report their
adjacent stations. This information is communicated via Station Management (SMT)
frames, that are sent at a rate of approximately 1 every 10 to 30 seconds.
Using these frames, all stations on the ring determine their upstream and downstream
neighbors. For example, Station 2 is said to be downstream of Station 1 if Station 2
receives the token after it was received by Station 1.