This chapter provides information about alarms supported for SONET and SDH, and their maintenance.
Alarms are triggered when a component fails or does not perform as expected. Alarms are triggered by the chassis.
Alarms can be defined using the following two terms:
Alarm State—It is the state the chassis enters when a certain event occurs. For example, the state of the chassis when the
ambient temperature is beyond the specified limits.
Alarm Indication—It is a visual signal to indicate the alarm state. For example, the TEMP LED glows red if the ambient temperature
is beyond the specified limits, and it turns green if the ambient temperature is within specified limits.
Typically, a failure condition detected by a chassis results in one or more error conditions sent both upstream and downstream
on the network.
Alarm Indication Signal (AIS)—AIS alarms are reported downstream from a detecting device, and to prevent consequential downstream
failures or alarms from being raised.
Remote Defect Indicator (RDI)—RDI alarms are always reported upstream from the detecting device.
Even when the controller is in the down state with alarms, the cross connection between the controllers is up.