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.