Finisar Surveyor - Manual (Page 192)

9-8
Surveyor
User’s Guide
Thresholds and Alarms
Alarm thresholds are set by specifying the values in the Sample Type , Rising Value ,
Falling Value , and Interval fields for each alarm row in the alarm table. The numbers
or percentages set for rising and falling values are referred to as thresholds. The key
to creating a meaningful alarm is to specify these values so you get alerted to the
exact network conditions you want to analyze.
The sample type can be set to either Delta or Absolute . The setting for the Sample
Type field determines how Surveyor will use the threshold values set in the Rising
Value and Falling Value fields.
An absolute sample means that if the Rising Value is exceeded an alarm event
occurs. If a value is specified for the Falling Value , an alarm event occurs when the
value drops below the threshold.
A delta sample type means that if a difference between samples increases (rising) or
decreases (falling) over time is more than the specified threshold, an alarm event
occurs. The
Interval field sets the time period between samples. Samples are actually
taken at least twice as often as the interval. This allows the detection of threshold
crossings that span the sample boundary. For example, if the delta sample is taken
twice per interval, the sum of the latest two samples are compared to the threshold.
For most cases, the default Sample Type of delta is more useful. One exception is
the MAC Layer Alarm for Utilization. Because utilization is expressed in the Rising
Value field as a percentage, the absolute sample type is more useful to catch
utilization that exceeds a certain percentage from a baseline of zero network traffic.
Multi-QoS alarms do not use the Sample Type , Rising Value , Falling Value , and
Interval fields. A simple threshold value is used to trigger the alarm when the
threshold is exceeded.