Whether a board with FEC disabled can be interconnected with an OTU board that does not support FEC

Question:
When the 73TRC board with FEC disabled is interconnected with the TWC board, the R_LOF alarm is reported at the receive end and services are unavailable, and even the R_LOS alarm is reported in some cases.
Answer:
1. Functioning as a regeneration board of 73LWC, 73TRC also has the FEC function and has the same rate (2.66G) as 73LWC. After the FEC function is disabled on a board, FEC will not be performed at the receive end of the board; the signals transmitted at the transmit end, however, still contain FEC code. In other words, the board rate remains 2.66G.
2. You can use any of the following three methods to disable the FEC function of a board:
Use the following command (applicable to NEs on the 5.0 platform): :cfg-set-fec: bid, port, path, enable/disable
Use S3 DIP switches.
S3.1 specifies the board type.
0: LWC
1: TRC
S3.2 specifies whether FEC is configured.
0: with FEC
1: without FEC
Use the :ptp,bid,f1,0; command. (The last byte 0 indicates that FEC is configured but 1 indicates that FEC is not configured.)
For the 72LWC board, you can use only the PTP command because the board does not have S3 DIP switches.
Use the :ptp:bid,b4,1; command. (The last byte 0 indicates that FEC is not configured but 1 indicates that FEC is configured.)
Note: The meaning of the last byte in the command for the 71LWC board is opposite to that for the 72LWC board.
The FEC setting and cancellation commands for the 71TRC board are the same as those for the 71LWC board, but the parameters are different.
Command for setting the FEC mode: Ptp:slot ID,f1,2 (like S3.2 DIP switch setting to 0)
Command for canceling the FEC mode: Ptp:slot ID,f1,3 (like S3.2 DIP switch setting to 1)
3. The regeneration boards as follows:
The regeneration board of the TWC board is TWC, at a rate of 2.48G.
The regeneration board of the 71LWC board is 71TRC, at a rate of 2.66G.
The regeneration board of the 72LWC board is 72TRC, at a rate of 2.66G.
The regeneration board of the 73LWC board is 73TRC, at a rate of 2.66G.
Suggestion and conclusion:
Assume that site A and site B are interconnected using an LWC board separately.
LWC (A) ----- LWC (B)
If you disable the FEC function of the LWC board at site A, the signals transmitted at the WDM side of the LWC board at site A remain unchanged, and the signal structure is still marked with FEC redundancy code and the rate is still 2.66G. However, the receive end on the WDM side of the LWC board at site A does not perform error correction. In this case, if the signals received by site A from site B contain bit errors, site A still transparently transmits the signals containing bit errors to the downstream site.
Disabling the FEC function aims at testing the FEC coding gain of the board, rather than interconnecting with the boards that do not have the FEC function. The rate of 2.5G boards without the FEC function is 2.48G, whereas the rate of 2.5G boards with the FEC function is 2.66G. Therefore, the boards cannot be interconnected. Note that the FEC enabling status must be restored after the test.

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