This flag is set true when the phy is experiencing a far-end receive failure, meaning the remote end has reported it cannot receive properly even though this side's transmit path is intact. Because FERF means the fault lies beyond this phy rather than at it, seeing this flag true while cadpStatLossOfSignal stays false points a technician toward the remote end's optics or the return fiber rather than at this card. FERF true with LOS false on the same phy suggests a one-way fiber cut or a dirty connector on the remote end's receive path, not a fault on this box.