Cabletron Systems 7C03, 7C04-R manual How Rising and Falling Thresholds Work

Basic Alarm Configuration

Before you decided whether or not to assign an action to a rising or falling alarm, it is

TIP important to understand something about the hysteresis function built in to the RMON alarm functionality. See How Rising and Falling Thresholds Work, below, for more information.

The remainder of the window fields provide the means for configuring alarms for each available interface. Note that the information provided in this screen is static

once it is displayed; for updated information, click on . Adding or modifying an alarm automatically updates the list.

How Rising and Falling Thresholds Work

Rising and falling thresholds are intended to be used in pairs, and can be used to provide notification of spikes or drops in a monitored value — either of which can indicate a network problem. To make the best use of this powerful feature, pairs of thresholds should not be set too far apart, or the alarm notification process may be defeated: a built-in hysteresis function designed to limit the generation of events specifies that, once a configured 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 3-2illustrates such a configuration.

Event

Rising Threshold

Falling Threshold

Event

Event

Rising Threshold

Falling Threshold

Event

Figure 3-2. Sample Rising and Falling Threshold Pairs

The current version of the Basic Alarm application only allows you to configure a single

TIP pair of thresholds for each alarm variable on each interface; be sure to keep this hysteresis function in mind when configuring those threshold values.

3-6 Viewing Alarm Status