Alarms are serious conditions that require attention. Excessive errors can trigger alarms, as can hardware problems and signal disruption. The alarms are coded as colors. As with performance events, different vendors define alarms differently, and finding detailed descriptions of them can be challenging. RFC 1232 also describes most alarms, though again, they are described for use in SNMP, and the descriptions are not intended as a standard for hardware implementation.
A red alarm is defined in RFC 1232 as follows:
A Red Alarm is declared because of an incoming Loss of Signal, Loss of Framing, Alarm Indication Signal. After a Red Alarm is declared, the device sends a Yellow Signal to the far-end. The far-end, when it receives the Yellow Signal, declares a Yellow Alarm.
A red alarm is triggered when a local failure has been detected, or continuous OOF errors have been detected for more than x seconds (vendor-specific). The alarm is cleared after a specific amount of time has elapsed with no OOF errors detected (the amount of time varies by hardware).
When a device has a local red alarm, it sends out a yellow alarm.
Figure 21-6 shows a sample red alarm. Something has failed on Telecom Switch C. The switch triggers a local red alarm, and sends out the yellow alarm signal to alert its neighbors of the problem.
Figure 21-6. Red alarm
Figure 21-7 shows another red-alarm scenario. ...