Calculating Power Budget For Fiber-Optic Cable For M Series, Mx Series, And T Series Routers; Calculating Power Margin For Fiber-Optic Cable For M Series, Mx Series, And T Series Routers - Juniper T320 Hardware Manual

T320 Core Router Hardware Guide

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

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

254
To ensure that fiber-optic connections have sufficient power for correct operation, you
must calculate the link's optical power budget, which is the maximum amount of optical
power it can transmit. When you calculate the optical power budget, you use a worst-case
analysis to provide a margin of error, even though all the parts of an actual system do
not operate at the worst-case levels. To calculate the worst-case estimate of optical
power budget ( P ), you assume minimum transmitter power (
B
sensitivity ( ):
P
R
P = P – P
B T R
The following hypothetical optical 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
T320 Fiber-Optic and Network Cable Specifications on page 251
T320 Attenuation and Dispersion in Fiber-Optic Cable on page 252
Calculating Power Margin for Fiber-Optic Cable for M Series, MX Series, and T Series
Routers on page 254
T320 Signal Loss in Multimode and Single-Mode Fiber-Optic Cable on page 251
After calculating a link's optical power budget you can calculate the optical power margin
( P ), which represents the amount of power available after subtracting attenuation or
M
link loss ( ) from the optical power budget (
LL
maximum :
LL
P = P – LL
M B
A P greater than zero indicates that the optical power budget is sufficient to operate
M
the receiver.
Factors that can cause link loss include higher-order mode losses, modal and chromatic
dispersion, connectors, splices, and fiber attenuation. Table 31 on page 255 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.
P ) and minimum receiver
T
). A worst-case estimate of
P
B
Copyright © 2010, Juniper Networks, Inc.
assumes
P
M