Cabletron Systems 7000 manual How Rising and Falling Thresholds Work

Alarm Configuration

The top portion of the window contains the device information boxes, as well as the event index number and the event description; the log itself includes the following Þelds:

Index	This index number is not the eventÕs index, but a separate
	index that uniquely identiÞes this occurrence of the
	event.
Time	Indicates the date and time of each event occurrence.
Description	Provides a detailed description of the alarm that
	triggered the event: whether it was a rising or falling
	alarm, the alarm index number, the alarm variable name
	and object identiÞer (OID), the alarmSampleType
	(1=absolute value; 2=delta value), the value that
	triggered the alarm, the conÞgured threshold that was
	crossed, and the event description. Use the scroll bar at
	the bottom of the log to view all the information
	provided.

Each log will hold only a Þnite number of entries, which is determined by the resources available on the device; when the log is full, the oldest entries will be replaced by new ones.

How Rising and Falling Thresholds Work

Rising and falling thresholds are intended to be used in pairs, and can be used to provide notiÞcation of spikes or drops in a monitored value Ñ either of which can indicate a network problem. To make the best use of this powerful feature, however, pairs of thresholds should not be set too far apart, or the alarm notiÞcation process may be defeated: a built-in hysteresis function designed to limit the generation of events speciÞes that, once a conÞgured threshold is met or crossed in one direction, no additional events will be generated until the opposite threshold is met or crossed. Therefore, if your threshold pair spans a wide range of values, and network performance is unstable around either threshold, you will only receive one event in response to what may be several dramatic changes in value. To monitor both ends of a wide range of values, set up two pairs of thresholds: one set at the top end of the range, and one at the bottom. Figure 4-8illustrates such a conÞguration.

4-26 How Rising and Falling Thresholds Work