Loss of Frame: A condition at the receiver or a maintenance signal transmitted in the PHY overhead indicating that the receiving equipment has lost frame delineation This is used to monitor the performance of the PHY layer
In a TL1 message, LOF typically refers to a loss of frame event - the event whereby the system is unable to detect a framing indication on the optics signal (data) The framing indication is a specific pattern of bits that varies depending on traffic This alarm condition corresponds to an information loss greater than 2 seconds See also OOF