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HiSpeed Switch Troubleshooting Guide
12-2
US7070447-001, Rev 01
Draft Level—Hitachi Confidential
In a normal ring operation, an FDDI station captures a free token and transmits
completely unless the token holding timer (THT) expires. As the frame traverses
the ring, every station examines the frame and checks for errors. When the
destination station receives the frame, it copies the frame into its buffer, sets the
error, AR, and FC indicators and places the frame back onto the ring. Finally, the
frame is returned to the sending station where it is stripped off the ring and the
token is released.
Station Management (SMT) unique to FDDI, detects, isolates, and recovers
network faults on the ring. The HiSpeed switch participates in the ring recovery
process as a function of SMT. Built-in timers are used by all stations to ensure
timely transmission of data across the ring. Beacon frames indicate that a logical
problem has occurred and the fault domain is identified. Given its error detection
and recovery mechanisms, FDDI is considered to be highly reliable and is widely
employed as a backbone for local and campus area networks.
HiSpeed FDDI Uplink
Figure 12-2. FDDI Uplink Module installed in an HS150
LEDs
Optical Bypass
Connector
Port B Port A