Calculating Power Margin For Fiber-Optic Cable For M Series, Mx Series, And T Series Routers; Table 31: Estimated Values For Factors Causing Link Loss - Juniper M40E Hardware Manual

M40e Multiservice Edge Router Hardware Guide
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Calculating Power Margin for Fiber-Optic Cable for M Series, MX Series, and T Series Routers

286
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The following hypothetical power budget equation uses values measured in decibels
(dB) and decibels referred to one milliwatt (dBm):
P = P – P
B T R
P = –15 dBm – (–28 dBm)
B
P = 13 dB
B
Fiber-Optic and Network Cable Specifications for the M40e Router on page 283
Signal Loss in Multimode and Single-Mode Fiber-Optic Cable for the M40e Router on
page 284
Attenuation and Dispersion in Fiber-Optic Cable on M Series, MX Series, and T Series
Routers on page 284
Calculating Power Margin for Fiber-Optic Cable for M Series, MX Series, and T Series
Routers on page 286
After calculating a link's power budget you can calculate the power margin (
represents the amount of power available after subtracting attenuation or link loss (
from the power budget ( P
B
P = P – LL
M B
A 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 (HOL), modal and
chromatic dispersion, connectors, splices, and fiber attenuation. Table 31 on page 286 lists
an 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.

Table 31: Estimated Values for Factors Causing Link Loss

Link-Loss Factor
Higher-order mode losses
Modal and chromatic dispersion
Connector
Splice
). A worst-case estimate of
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
), which
P
M
P assumes maximum LL :
M
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LL )