FDDI Protocol Elements
As is the case on a Token Ring, stations on an FDDI ring pass a token around. The holder of the token has the right to transmit data for a period of time. The token then is passed to the next station.
FDDI allocates bandwidth to each station in a different manner than the Token Ring protocol. Each station is guaranteed a reserved time quota and is permitted to transmit frames for that time period when it receives the token. Use of the reserved time is called synchronous transmission.
There also is an extra amount of time that is loosely shared by the stations. During ring initialization, the stations agree on a Target Token Rotation Timeout (TTRT). This is the average time that any station expects to wait before it ...