Dispersion topology affects system performance.
Symptom
The AB network uses the OptiX BWS 1600G 80-channel system, the system OSNR satisfies the requirement for transmitting 10G services. However, BEFFEC_EXC alarms are reported for some wavelengths, indicating that the pre-FEC BER exceeds the permitted range. In addition, the multi-channel spectrum analyzer (MCA) scanning result shows that the OSNRs for some wavelengths are low.
The OSNRs for all wavelengths transmitted from site B to site A are low, and BEFFEC_EXC alarms are reported for some wavelengths.
The following figure shows the network topology.
Cause Analysis
The inherent dispersion of G.655 fibers is near 0 ps/nm.km. Therefore, the signal transmission performance is likely affected by non-linear effects during long-haul transmission of wavelengths over G.655 fibers. The non-linear effects lead to a wider spectrum. A wider spectrum results in a higher noise base than the actual noise base and lower scanned OSNRs than the actual OSNRs.
Dispersion and non-linearity affect one other. The dispersion topology in the direction from site A to site B has a relatively good quality and minimizes the impact of non-linear effects on the optical spectrum. Therefore, the scanned OSNRs in this direction are close to the actual OSNRs. The dispersion topology in the direction from site B to site A has a relatively poor quality and fails to effectively suppress the impact of non-linear effects on the optical spectrum. Therefore, the scanned OSNRs in this direction are lower than the actual OSNRs.
The impact of non-linear effects on the system performance can be minimized by optimizing the dispersion topology in the direction from site B to site A. By doing this, the scanned OSNRs will be closer to the actual OSNRs.
Procedure
- Collect data from the live network. The network conditions satisfy the requirements for commissioning line optical power.
- Verify that the flatness of each wavelength. The flatness of each wavelength is within the permitted range using the MCA.
- Calculate the residual network dispersion according to the design documents. The residual dispersion is within the range defined in 10G OTU board specifications.
- Optimize the dispersion topology in the direction from site B to site A to minimize the impact of non-linear effects on the system performance. The scanned OSNRs are closer to the actual OSNRs. The problem is resolved.
Reference Information
Optical fibers (such as LEAF and G.653 fibers) with smaller dispersion coefficients cause more intensive non-linear effects than optical fibers (such as SMF fibers) with larger dispersion coefficients. To improve the receive-end system performance, you can optimize the dispersion topology.
MORE BLOG:
No comments:
Post a Comment