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Customer Optical Transport Network spans across West Europe including backbone, aggregate and access/customer layers utilizing OptiX OSN 8800 and OptiX OSN 1800 devices. Within the network somewhere in Madrid, Spain there is a link between SITE A and SITE B where the optical power budget is highly out of product specifications and unbalanced. In particular the EDFA amplifiers have reached maximum output power levels reporting relative alarms and as a result the capacity of the link has been dramatically decreased from 24 OCH End-Of-Life to only 7 OCH. This creates major discrepancy due to all upcoming expansions involving specific link are blocked
The fault rectification process is comprised of the following steps:
1. Acquire Network Data:
2. Process Network Data:
3. Root Cause Analysis:
4. Solution/Workaround Proposal
Major root cause was the mis-design of the link in the various network phases:
As a result the existing EDFA amplifiers were had to be tuned in very high output power levels in order for the transmitted channels to be received at the far ends above the lower sensitivity thresholds. Root Cause Analysis was reviewed by customer 3rd Line O&M and approved
Due to high urgency a Workaround was initially proposed as a temporal remedy in order to reduce the high output power levels of the EDFA amplifiers and allow small-scale expansions in the near future. As a final Solution it had been proposed the redesign of the link with the addition of EDFA amplifiers also in the receive direction to cope with the excessive attenuation values
The basic goals and limitations of the proposed Workaround were:
The basic corrections of the proposed Workaround were:
Proposed Workaround was reviewed by customer 3rd Line O&M and approved. Implementation was done during maintenance window (low traffic hours) and all goals were successfully met
Such major fault can be prevented with correct design from the initial deployment. When designing a DWDM link a number of factors needs to be properly considered e.g. EOL link capacity. In addition during capacity expansions it needs to be verified that each added channel can effectively traverse the existing hardware components (suffering insertion losses) but keeping its optical power levels within product specifications or regeneration needs to be introduced