3Com 4007, Руководство по внедрению, Страница: 638 / 684

638 C
HAPTER
23: D
EVICE
M
ONITORING
Counters are useful when you compare their values at specific time
intervals to determine rates of change. The time intervals can be short or
long, depending on what you measure.
Occasionally, counters can produce misleading results. Because counters
are finite, they are useful for comparing rates. When counters reach a
predetermined limit, they
roll over (that is, return to 0). A single low
counter value may accurately represent a condition on the network. On
the other hand, the same value may simply indicate a rollover.
When you disable a port, the application may not update some of its
associated statistics counters.
An alarm calculates the difference in counter values over a set time
interval and remembers the high and low values. When the value of a
counter exceeds a preset threshold, the alarm reports this occurrence.
Using Transcend Network Control Services or any other SNMP network
management application, you can assign alarms to monitor any counter,
gauge, timetick, or integer. See the documentation for your management
application for details about setting up alarms.
Setting Alarm Thresholds Thresholds determine when an alarm
reports that a counter has exceeded a certain value. You can set alarm
thresholds manually through the network, choosing any value for them
that is appropriate for your application. The network management
software monitors the counters and thresholds continually during normal
operations to provide data for later calibration.