Problem Description

A customer's network uses two sets of OSN 3500 to expand two2.5G optical boards, and two SSN3SL16 single boards to open a 2.5G channel, the model number and version of this 2.5G optical board are as follows: 03030EPY -OptiX OSN 3500,SSN3SL1603,STM-16 Optical Interface Board(V-16.2Je,LC);

The software version of the single board is 5.12 and the logic version is: 110;

The software version of this single board matches the version of the main control board. After the engineering supervisor installs these two single boards in 2 sets of OSN 3500 equipment, the optical power reception is qualified, both are around -18dbm, but it is found that both 2.5G optical boards receive regenerative segment error codes.

Alert message

No alarm information, the single board reports regenerative segment error code at 15 minutes current performance during performance query.

Processing

1. At that time, it was suspected that there was a problem with the fiber optic cable, and after the customer switched the cable, the problem remained;

2, the actual distance of the fiber optic cable is 110km, while the single board nominal support 140km, the distance is within a reasonable range, while the optical power is normal.

3、Both sides of the N3SL1603 board plus 20db light failure self-loop, without any error code reported;

4、Replace the N3SL1603 optical board on one side with N1SL1603 V-16.2Je, the regeneration segment error code of N3SL1603 on the opposite side disappears, but there is still regeneration segment error code of N1SL1603 on this side;

5. Replace N1SL1603V-16.2Je with N3SL1603 optical board at the opposite end, and the regeneration segment error code of this end disappears.

6, after R & D positioning, judged to be a single board version of the problem: single board logic version of 130 and below the SSN3SL16 V-16.2Je single board due to the optical module scrambling signal design reasons lead to long-distance transmission may produce a small amount of BER, affecting the transmission performance.

7. Upgrade the FPGA of SSN3SL16 V-16.2Je to 200, and at the same time, upgrade the software of single board, the BER will disappear.

Root Cause

SSN3SL16 V-16.2Je single board with single board logic version 130 and below will generate a small amount of BER during long-distance transmission due to the design of perturbation signal of optical module. on SSN3SL16 single board, FPGA will send the perturbation signal to the optical module, which has already suppressed the nonlinear effect to a certain extent, and external perturbation is equivalent to excessive suppression, and the eye diagram will become poorer. The eye diagram will become worse, thus generating BERs.

Recommendations and Summary

OGN3500 SSN3SL16 V-16.2Je single boards with single board logic version 130 and below may generate a small amount of BERs during long distance transmission due to the design of the scrambling signal of the optical module, which may affect the transmission performance.