The 802.4 IEEE standard defines the Token Bus protocol
for a token-passing access method on a bus topology.
In a token-passing access method, a special packet called
a token is passed from station to station and only the
token holder is permitted to transmit packets onto the LAN.
Thus, no collisions can occur with this protocol.
When a station is done transmitting its packets,
it passes the token to the "next" station.
The next station does not need to be physically closest
to this one on the bus, just the next logical station.
A station can hold the token for only a certain amount of time
before it must pass it on -even if it has not completed
transmitting all of its data.
This assures access to all stations on the bus within a specified
period of time.
Copyright © 1999 by SAS Institute Inc., Cary, NC, USA. All rights reserved.