# Connection of the MON port of the OBU board

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The MON port of the OBU board connects to the input optical port of an optical spectrum analyzer board.

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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.

Fiber connections of the OBU board on an OSN 6800
Fiber connections of the OBU board on an OSN 6800 are as follows: The TC port of the FIU board is connected to the VI port of the OBU board. The VO and IN ports of the OBU board are connected. The OUT port of the OBU board is connected to the IN port of the D40 board.

Split ratio calculation for the MON port of the OAU board on OSN 6800
The split ratio between the MON port and the 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 is calculated using the following formula: Pout (dBm) �?Pmon (dBm) = 10 x lg(99/1) = 20 dB.

Whether the VI port on the OBU board can report a LOS alarm
No, the VI port on the OBU board cannot report a LOS alarm. When logical fibers are created on the NMS, if no FIU board is configured at the local site and the multiplexed-wavelength optical signals of the peer site need to be connected to the OBU board at the local site, you are advised to connect the logical fiber to the IN port of the OBU board. In this way, the corresponding logical fiber will turn red in case of a fiber cut.

Optical power difference between the IN port of the D40 board and the OUT/MON port of the M40 board
The MON port of M40 board has 10 dB lower optical power than the IN port of the D40 board and the OUT port of the M40V board. The split ratio between the MON port and OUT port and that between the MON port and IN port are both 10:90. In other words, the optical power of the MON port is 10 dB lower than that of the IN port. The calculation formula is as follows: Optical power (dBm) of the IN port �?Optical power (dBm) of the MON port = 10 x lg(90/10) = 10 dB.

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