In an OA system, the lower threshold of the receive optical power of a line...

In an OA (Optical Amplifier) system, the lower threshold of the receive optical power for a line board with a PIN receiver or the WDM side of an OTU board is typically the optical module’s receiver sensitivity plus 3 dB, not 5 dB. Adding 3 dB accounts for margin to ensure reliable reception without unnecessary overdesign. The 5 dB margin usually applies when an APD receiver is used, which is more sensitive but also more susceptible to noise. Thus, for PIN receivers, HCIP-Transmission guidelines specify the lower threshold as sensitivity plus 3 dB to maintain signal quality while preventing false alarms or unnecessary protection switching.