1+1 APS provides revertive and non-revertive modes; non-revertive mode is the default option. In revertive mode, the activity is switched back to the working port after the working line has recovered from a failure (or the manual switch is cleared). In non-revertive mode, a switch to the protection line is maintained even after the working line has recovered from a failure (or the manual switch is cleared).
To prevent frequent automatic switches that result from intermittent failures, a revert-time is defined for revertive switching. The revert-time is configurable from 0 to 60 min in increments of 1 min; the default value is 5 min. In some scenarios, performance issues can occur if the revert-time is set to 0; therefore, it is recommended that the revert-time always be set to a value of 1 or higher. Any change in the revert-time value takes effect upon the next initiation of the wait-to-restore (WTR) timer. The change does not modify the duration of a WTR timer that has already been started. The WTR timer of a non-revertive switch can be assumed to be infinite.
If both working and protection lines fail, the line that has less-severe errors will be active. If there is signal degradation on both ports, the active port that failed last will stay active. If there is signal failure on both ports, the working port will always be active because signal failure on the protection line is a higher priority than on the working line.