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

For an OA system, the lower threshold of receive optical power of a line board with an APD receiver or the WDM side of an OTU board is the optical module’s receiver sensitivity plus 3 dB, not 5 dB. The 5 dB margin applies mainly to PIN receivers. This distinction is critical because APDs have higher sensitivity and thus require a smaller margin to avoid false alarms or unnecessary protection switching. HCIP-Transmission clearly differentiates these thresholds to ensure proper optical power management and alarm settings in the network.