3Com 3C16630A, User Manual

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Counters E - 7
DUA1663-0BAA03
Counters
Counters are the MIB objects which hold and update the number of
occurrences of a particular event through a port, module, repeater or
on the network. The management facility reads the counters it needs
for the output, processes the information and displays the result. The
counter may be associated with a port, or a module, or a repeater, or
even a chassis. It can be counting any recurring event: typical examples
are traffic, collisions, and FCS errors.
W hen a port is disabled, some of the statistics counters associated with
it may no longer be updated.
When using the counters, it is better to employ differences between
values rather than spot values. By using values at fixed time intervals
the rates of change of the counters can be derived. The time intervals
can be as short or as long as you find convenient. These rates will be
more meaningful than spot values and may be compared to provide
more useful data.
There is a sound reason for using differences. The counters cannot be
infinite. They will roll-over (return to zero) when they reach their limit.
Thus a low value may or may not be truly representing the situation. A
negative difference indicates that roll-over has occurred. You can be
more sure of what has occurred by changing (either shortening or
lengthening) the time interval and comparing the results.
Counters and RMON Alarms
The Module s upports the RMON alarm. Alarms can be assigned by
Transcend or any SNMP network manager to monitor any counter.
Consult the manual of the application you use for details of how to set
up the possible 1024 alarms.
Each alarm monitors its assigned counter, by calculating the differences
over a preset time interval. It remembers the high and low tide marks
and it can take actions when the value of the counter has crossed
preset thresholds.