This is the instantaneous, most-recently-sampled value of the actual optical carrier frequency measured at this port's input during the current performance-monitoring interval, expressed in MHz. A live frequency reading lets an admin confirm right now that the receiver is actually locked onto the wavelength the network was designed to deliver to this port. For example, immediately after a ROADM reconfiguration, an admin would check inOpticalFrequencyInstant to confirm the receiver relocked onto the correct grid frequency rather than an adjacent channel.