This is the instantaneous, most-recently-sampled value of the combined received optical power across all optical lanes of this multi-lane coherent port during the current performance-monitoring interval. A live combined-power reading gives an admin the whole-port view right now, complementing the individual lane readings when deciding whether a problem is port-wide or confined to one lane. For example, if inOpticalPowerLaneTotalInstant drops even though both individual lane readings look only mildly reduced, an admin would suspect a shared upstream component, like a port-level connector, rather than either lane individually.