Calculating Power Margin For Fiber-Optic Cable; Table 55: Estimated Values For Factors Causing Link Loss - Juniper MX104 Hardware Manual

MX104 3D Universal Edge Router Hardware Guide

Calculating Power Margin for Fiber-Optic Cable

Table 55: Estimated Values for Factors Causing Link Loss

Link-Loss Factor
Higher-order mode losses
Modal and chromatic dispersion
Connector
Splice
Fiber attenuation
80
After calculating a link's power budget, you can calculate the power margin (P
represents the amount of power available after subtracting attenuation or link loss (LL)
from the power budget (P
P = P – LL
M B
P greater than zero indicates that the power budget is sufficient to operate the receiver.
M
Factors that can cause link loss include higher-order mode losses, modal and chromatic
dispersion, connectors, splices, and fiber attenuation.
estimated amount of loss for the factors used in the following sample calculations. For
information about the actual amount of signal loss caused by equipment and other
factors, refer to vendor documentation.
Estimated Link-Loss Value
Single-mode—None
Multimode—0.5 dB
Single-mode—None
Multimode—None, if product of bandwidth and distance is less than 500
MHz-km
0.5 dB
0.5 dB
Single-mode—0.5 dB/km
Multimode—1 dB/km
The following sample calculation for a 2-km-long multimode link with a power budget
(P ) of 13 dB uses the estimated values from
B
(LL) as the sum of fiber attenuation (2 km @ 1 dB/km, or 2 dB) and loss for five connectors
(0.5 dB per connector, or 2.5 dB) and two splices (0.5 dB per splice, or 1 dB) as well as
higher-order mode losses (0.5 dB). The power margin (P
P = P – LL
M B
P = 13 dB – 2 km (1 dB/km) – 5 (0.5 dB) – 2 (0.5 dB) – 0.5 dB
M
P = 13 dB – 2 dB – 2.5 dB – 1 dB – 0.5 dB
M
P = 7 dB
M
). A worst-case estimate of P
B
Table 55 on page 80
), which
M
assumes maximum LL:
M
Table 55 on page 80 lists an
to calculate link loss
) is calculated as follows:
M
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