Calculating Power Margin For Fiber-Optic Cable For M Series, Mx Series, And T Series Routers; Table 25: Estimated Values For Factors Causing Link Loss - Juniper M7I Hardware Manual

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Calculating Power Margin for Fiber-Optic Cable for M Series, MX Series, and T Series Routers

Copyright © 2010, Juniper Networks, Inc.
Appendix E: Cable and Wire Guidelines and Specifications for the M7i Router
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 M7i Router on page 174
Signal Loss in Multimode and Single-Mode Fiber-Optic Cable for the M7i Router on
page 175
Attenuation and Dispersion in Fiber-Optic Cable on M Series, MX Series, and T Series
Routers on page 175
Calculating Power Margin for Fiber-Optic Cable for M Series, MX Series, and T Series
Routers on page 177
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
P = P – LL
M B
A greater than zero indicates that the power budget is sufficient to operate the receiver.
P
M
Factors that can cause link loss include higher-order mode losses (HOL), modal and
chromatic dispersion, connectors, splices, and fiber attenuation. Table 25 on page 177
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 25: 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
B
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
P ), which
M
P assumes maximum LL :
M
)
LL
177