This reports the total received optical power at the OTS (optical line/section) level -- the combined power of every wavelength multiplexed onto this fiber, not just one channel. Because this reading comes from the still-filling, live 15-minute bin for this wavelength/line, this line-wide aggregation is what makes the value move when an amplifier, a whole fiber span, or a large group of channels is affected, which is how you distinguish a line-wide problem from a single-wavelength one. For example, a total OTS receive power that drops several dB while individual OCh readings on this line stay proportionally similar points to an EDFA or fiber-span issue upstream of the whole multiplex, not one transponder, so far within this still-open 15-minute interval.