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4-8
Setting Up the Hub
Target Token Rotation Time (T-Req)
The FDDI ring is initialized every time a station joins or leaves the ring. During
the initialization process, all stations on the ring agree on a "token rotation
time." This is the maximum amount of time that any station has to wait for a
token to arrive, and it establishes the minimum level of service on the ring.
(Level of service relates to how often a station requires access to the token.)
The Target Token Rotation Time (TTRT) is the service level required by an
individual station. During the initialization process, each station makes a
request for a level of service that is identical to its local TTRT. This service
level request is called T-Req.
T-Req is stored in nonvolatile RAM and can be set using the set treq command.
The factory-set default is 165 milliseconds. Changes to T-Req take effect only
when the system is reset.
To display the current value of the Target Token Rotation Time parameter, enter
the show treq command. This display appears:
Current T-Req = 165000 microseconds
Initialize T-Req as = 160000 microseconds
Link Error Rate (LER)
The Link Error Monitor (LEM) examines the Link Error Rate (LER) per active
port as part of its responsibility for keeping link quality at an acceptable level.
The LEM uses a threshold test to compare the current LER cutoff threshold to
the LER alarm threshold.
NOTE: You must always keep the LER_Alarm parameter larger than the value
entered for the LER_Cutoff parameter.
These two thresholds are explained below:
LER_Alarm. This threshold is the LER at which a link connection exceeds the
present threshold and will generate an alarm. The factory-set default is 10.E-08
-8
(10
). This error rate is equivalent to about one error per second.
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