The reason why APS switch happened. When the working line on one end fails, its other end is told to do an APS switch. The following options in the increasing order of priority indicate what type of switch request it is. slSonetApsRevertive : Switch back to working line after the Wait-to-Restore interval is over, and failures are cleared. It is the lowest priority. slSonetApsManual : Manual switch causes APS switch unless a request of equal or higher priority is in effect. slSonetApsSignalDefectLow : Switch happened because threshold for 'slSonetApsSigFaultBER' was exceeded. slSonetApsSignalDefectHigh : Same as above, but higher priority. slSonetApsSignalFailureLow : Switch happened because threshold for 'slSonetApsSigDegradeBER' was exceeded. slSonetApsSignalFailureHigh : Same as above, but higher priority. slSonetApsForceSwitch : Forced switch forces hardware to switch the active line even if the other line (could be working line or protection line) is in alarm. slSonetApsLockOut : This is the highest priority switch. This will override all other requests. slSonetApsRemoteRequest : indicates that the local switchover was in response to a remote request to switch. slSonetApsLockOut : indicates that the last switchover to the working occurred because of protection lockout.