This is the received optical power measured on the OSC supervisory channel. An operator monitors this to ensure the low-rate management signal from a neighboring site is still arriving with enough power to be reliably decoded, since the OSC often uses a much lower power budget than the main traffic channels. A drop in OSC Rx power that coincides with intermittent loss of remote management access points directly at a degrading supervisory link rather than the traffic-bearing wavelengths.