A large Tier-1 Carrier in Europe, BT, identified a problematic link on their new converged backbone network. The BT Operation team could not add new 10GbE traffic on the link of 140kms located in the center of England. They suspected that the OSNR could be lower than their design requirement.

After months of debate, BT Design team decided to call on mdi’s eyeD expert team to carry out tests in the field to trouble-shoot the cause of the problem and get an independent opinion. They decided to work with them because of mdi’s unique capability to measure multiple impairments on a link in-service.

The eyeD expert service engineer first created a library module at the carrier labs by taking a sample of ten 10G NRZ signals with the eyeD 360 monitor and its calibration kit. mdi had previously worked on the same system vendor equipment but for a different format.

On Day 1 of the field engagement, the eyeD 360 was connected to a tap port on the DWDM terminal. Right away, mdi’s expert was able to identify on the GUI that the received signals had significant noise (low OSNR) and unusually high chromatic dispersion (very high CD). The measurements confirmed the results and it was clear that the link was not correctly compensated. This came as a surprise and a relief. BT and mdi worked together to find the root cause of the problem and a remedy.

With the critical measurement results BT identified an incorrect Dispersion Compensation Module (DCM). They asked mdi’s service engineer to try a new DCM by inserting it in front of the monitor. The signal cleared on the GUI of the eyeD 360 and the correct value for compensation was confirmed. BT could now order the right part and start the process to fix the link. 

Within 3 days the eyeD expert team was able to calibrate for the new signal type, and identify the incorrect CD compensation without requiring taking traffic down.  Now that the link can be fixed, the Carrier will be able to deploy new 10GbE traffic on this critical route.  BT was also impressed with mdi’s ability to measure true OSNR where the embedded channel analyzer on the DWDM equipment reported higher OSNR values.

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