The value of tApsMcApsCtlLinkState indicates the current state of
the 7x50 Multi-Chassis (MC) APS Group Control Link.
Note that for a Single-Chassis APS group the state is always up.
The state 'up' indicates that the 7x50 MC-APS controller has received a
valid control message from its neighboring router within the last
tApsMcHoldTime interval, and the MC-APS control link is considered as
operational.
The state 'dnSignalingFailure' indicates that the 7x50 MC-APS
controller hasn't received any control message from its neighboring
router or vice-versa within the last tApsMcHoldTime interval.The MC-APS
control link is considered as operationally down.
The state 'dnIncompatibleNbr' indicates that the 7x50 MC-APS controller
has received a control message from a neighboring router within the
last tApsMcHoldTime interval, but the member circuit type
(i.e. working/protection) of the neighboring router is not compatible
with that of the local router. The MC-APS control link is considered as
operationally down.