The current status of the APS group.
Bit 0 - Extra Traffic. Indicates that extra traffic is
currently being accepted on the protection line.
Bit 1 - Protection Switching Byte Defect. Indicates that either
an inconsistent APS byte or an invalid code has been detected.
Bit 2 - Channel Mismatch. Indicates that a mismatch between the
transmitted K1 channel and the received K2 channel has been
detected.
Bit 3 - APS Mode Mismatch. Indicates a conflict between the
current local mode and the received K2 mode information. Modes
other than 1+1 unidirectional monitor protection line: K2 bit 5
indicates the architecture; K2 bits 6-8 indicate if the mode is
unidirectional or bidirectional.
Bit 4 - Far-End Protection-Line Defect. Indicates the LTE
received an SF code for the protection line, which means that
the far-end LTE is no longer receiving its request, or (in
bidirectional operation) the far-end LTE considers the near-end
LTE's request to be invalid.