What are the functions of each port on the FIU board?

Huawei OSN6800 OSN8800 fiber interface board FIU multiplexes and demultiplexes signals the main optical path and OSC signals. The RC port of the FIU board receives signals from the main optical path and the RM port receives signals from the OSC. 

The two types of signals are then multiplexed into one signal using the multiplexer module and are output from the OUT port. The IN port receives signals from the line and then sends the signals to the demultiplexer module. The demultiplexing module splits the signals into main optical path signals and OSC signals, which are then output through the TC and TM ports respectively.