This flag is set true when this specific phy of a redundant dual-PHY card is currently experiencing loss of signal from its connected port, and false otherwise. Because the dual-PHY card keeps two physical links, such as a working and a protect fiber, and automatically fails over between them, this object is what identifies exactly which of the two physical links has actually lost signal, the information needed to judge whether a failover was warranted or whether the standby link is now dead too. If the active phy shows LOS true while the standby phy shows LOS false, the card should automatically switch traffic to the standby.