background image
88
Chapter 2
Protocol Attributes
changed into a start-of-frame identifier, no other station on the ring can use
the token to transmit data, thus eliminating collisions.
The altered frame leaves the source station and circles the ring in search
of the destination station. Each station looks at the frame and determines
whether it is the destination host. If a station is the destination, it copies the
frame and then processes it, as necessary. The frame continues to travel
around the ring until it reaches the source host. Once reaching the source, the
frame is removed and a new token is generated and sent out onto the ring.
This way, each station has an equal opportunity to transmit data.
F I G U R E 2 . 2 5
Token passing
Fault Recovery
Token Ring/IEEE 802.5 uses several methods to help prevent and heal net-
work failures quickly and efficiently. An Active Monitor is designated by the
workstations on the ring. The Active Monitor is responsible for token mon-
itoring, token generation when the token seems to have disappeared, purging
recycling frames, and other ring maintenance.
Copyright ©2000 SYBEX , Inc., Alameda, CA
www.sybex.com