Problem Description

The customer signal flow is: ( Station B) OSN3500 SSN1SF16E --- BA ---RPC01--------------RPC02-PA-SSN2DCU-SSN1SF16E (Station A ), with consistent reverse signaling.

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

Alarm information

Alarm BEFFEC_EXC is reported on SSN1SF16E 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. the single board of SF16E is used, and according to the product document, the dispersion limited distance of the single board is 120 kilometers, and the customer uses a two-way 80-kilometerDCU and a one-way 40-kilometerDCU at station A, and 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 lowering the forward Raman pump power, first try to reduce 0.5db, and found that the BER before error correction becomes 8, and the BER overrun alarm disappears before error correction, and then reduce 0.5db, and find that the BER before error correction is 0.

Suggestions and Summary

1. When dealing with long-distance transmission BER, if you consider the BER caused by nonlinearity or signal-to-noise ratio, you can solve the problem by adjusting the optical power of Raman pump source, if it is a signal-to-noise ratio problem, you can increase the optical power of the pump source to try, if it is a nonlinear reason 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.