that is triggered as soon as a network component detects the loss of the input signal. This applies equally to electrical and optical signals. The Loss of Signal error message is reported by the corresponding station to the network management system.
In ATM networks, the Loss of Signal (LoS) signal is used as a maintenance signal. The LOS signal is used to indicate that the receiving station has lost the received signal. This signal is used to monitor the performance of the physical layer in ATM networks.