Mapping of CCM Defects to APS Events

The continuity check message (CCM) engine marks the status of working and protected transport entities as either Down, Degraded, or Up.

Down—The monitored path is declared down if any of the following Multiple End Point (MEP) defects occur:

• Interface down

• CCM expiry

• RDI indicating signal failure

Degraded—The monitored path is declared degraded if any of the following MEP defects occur:

• FRR on

• FRR-ACK on

Up—The monitored path is declared up in the absence of any of the above events.

Figure 1: Understanding APS Events

As show in Figure 1, the APS event generator generates the following APS events based on the status of the working and protection paths:

• SF—Signal failure on working path

• RSF—Working path recovers from signal failure

• SF-P—Signal failure on protection path

• RSF-P—Protection path recovers from signal failure