Description of the problem

The customer signal flow is: (Station B) SF16E --- BA --- RPC01--------------RPC02-PA-DCU-SF16E (Station A) with consistent reverse signaling.

Failure phenomenon: Customer feedback on both sides of the signal tuning through the A station found that the error rate before error correction is 6, there is a pre-correction error code overrun alarm BEFFEC_EXC.

Alarm information

Alarm BEFFEC_EXC is reported on SF16E single board at station A.

Processing

Processing idea:

1. Insufficient dispersion compensation leads to

2. Non-linearity or signal-to-noise ratio problems lead to

Processing:

1. Consider the problem of error code before error correction caused by insufficient dispersion compensation. the transmission distance between stations A and B is 303 kilometers, and the cross-segment attenuation is about 60 db. SF16E single board is used, and according to the product document, the dispersion constrained distance of this single board is 120 kilometers, and the customer has used a two-way 80 kilometers DCU and a one-way 40 kilometers DCU at station A. The compensation distance is 200 kilometers. According to the dispersion calculation formula: dispersion compensation distance = transmission distance - restricted distance +10~30, the dispersion compensation is sufficient, excluding the cause of dispersion.

2. Consider the error code before error correction caused by nonlinearity. Sending end is BA + RPC01 double-stage amplification, receiving end of the receiving light for -33dbm or so, according to the 60db or so of the cross-section attenuation, the sending end of the power of 27dbm or so, the incoming optical power is too strong will cause nonlinearities and thus lead to BER, dealing with nonlinearities, a common idea is to add optical attenuation at the sending end of the optical power of the low incoming fiber, but due to unmanned stations in the B site does not have the conditions.

3. After confirming that the incoming fiber power can be reduced by reducing the forward Raman pump power, first try to reduce 0.5db, found that the BER before error correction becomes 8, the BER before error correction cross-limit alarm disappears, and then reduce 0.5db, found that the BER before error correction is 0.

Suggestion and Summary

1. When dealing with long-distance transmission BERs, if you consider nonlinearities or signal-to-noise ratio caused by BERs, you can solve the problem by adjusting the optical power of the Raman pump source, if it is a signal-to-noise ratio problem you can increase the optical power of the pump source to try, and if it is the cause of the nonlinearities to reduce the pump power, reduce the power of the incoming fiber, to avoid nonlinearities caused by too much optical power. The problem of reducing the power of the hair end, the BER disappeared. From the experience of debugging, in the case of BA into the fiber power is large, forward Raman do not open too large, usually ensure that after the equivalent of forward Raman into the fiber power in the +23dB or so.

2. In the adjustment of the pump source optical power should not be adjusted at once too large, in accordance with the 0.5db step gradually adjust the observation.

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