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FAQ - How to calculate the total fiber line loss

Issue Description
Q- How to calculate the total fiber line loss?
1- In the DWDM system, the power loss introduced by line fiber, optical modules, and optical components is needed to be compensated for by the optical amplifier (Erbium-doped fiber amplifier or Raman amplifier).
2- The method of counting fiber attenuation greatly affects system design. The following defines six rules of counting fiber attenuation, based on bidding documents.
3- If the margin is no less than 3 dB, neglect FIU insertion loss during power calculation.

Alarm Information
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Handling Process
user provides the accurate factual loss of each line during the planning of network, we can directly add the system engineering margin to the actually measured value. Usually, the system engineering margin is 3dB in the budget. If the optical supervisory channel (OSC) is adopted, it is needed to consider the extra power of fiber line units. Usually the extra power is considered as 3dB (the insertion loss of the FIUs at the two ends) in the budget. If the electric supervisory channel (ESC) is used, this extra power can be ignored while making the budget.
Root Cause
A - There are 6 conditions to calculate the line loss :
1-  If specific formula to calculate the fiber loss is provided, we use the following formula to calculate the fiber loss:Line loss = f(x) + FIU insertion loss and We consider FIU insertion loss = 0.9dB
2-  If only line loss X is provided, we use following procedure to find the attenuation:Line loss = X + Margin + FIU insertion loss and Default Margin = 3dB.but If Margin≥3dB, neglect FIU insertion loss.
3-  If the maximum loss of the fiber at the end of life is provided:Line loss = Max. loss + FIU insertion loss
4-  If the distance and the attenuation coefficient with margin are provided:Line loss = Length x Coefficient + FIU insertion loss and Coefficient provided by customer.
5-  If only the actual distance is provided:Line loss = Length x Default Attenuation Coefficient + Margin
+ Flange loss + FIU insertion loss  and Default Attenuation Coefficient = 0.22dB/km, Default Margin = 3dB, Flange loss = 0.5dB/two flanges
6-  If the actual distance less than 40km:Line loss = Length x Default Attenuation Coefficient + Margin
+ Flange loss + FIU insertion loss  and Default Margin = 1.5dB

Suggestions

If the bidding documents do not describe the fiber attenuation coefficient, just provide design parameters according to common fiber parameters, Huawei provides the following defaults for project evaluation:
1- Fiber insertion loss: 0.22 dB/km
2- Fiber aging margin: 3 dB

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