# Optical ports of an FIU board

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An FIU board has a total of seven optical ports.
The IN/OUT optical port is used to receive and transmit line optical signals.
The RC/TC optical port is used to receive and transmit optical signals of the main optical channel.
The RM/TM optical port is used to receive and transmit optical signals of the supervisory channel.
The MON optical port is used to output optical signals to the spectrum analyzer board for online optical performance monitoring.

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Functions of each port on the FIU board
An FIU board 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.

FIU ports available for connection to the OSC board
An OSC board can be connected to the TM or RM port of an FIU board.

Split ratio of the MON port on the FIU board
For TN11FIU, TN12FIU, TN13FIU01, TN14FIU, and TN21FIU boards, the split ratio between the MON port and OUT port is 1:99. In other words, the optical power of the MON port is 20 dB lower than that of the OUT port, which can be calculated using the following formula: Optical power (dBm) of the OUT port �?Optical power (dBm) of the MON port = 10 x lg(99/1) = 20 dB. For the TN13FIU02 board, the split ratio between the MON port and OUT port is 0.1:99.9. In other words, the optical power of the MON port is 30 dB lower than that of the OUT port, which can be calculated using the following formula: Optical power (dBm) of the OUT port �?Optical power (dBm) of the MON port = 10 x lg(99.9/0.1) = 30 dB.

Whether an FIU board on an OSN 1800 supports optical power detection
A TNF2FIU board on OSN 1800 V100R005C00SPC200 supports optical power detection.

Optical ports of the OTU board
The OTU board provides two groups of optical ports: IN/OUT and Rx/Tx. The IN and OUT ports correspond to WDM-side input and output, and the Rx and Tx ports correspond to SDH-side input and output. The WDM side is also called the line side; the SDH side is also called the client side. In the alarm parameters, 1 indicates the WDM-side transceiver optical port, and 2 indicates the SDH-side transceiver optical port. In some documents, the optical ports of the OTU board are classified into system-side and line-side ports. In the early period, the system side is also called the client side.

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