Calculating The Power Budget For Fiber-Optic Cable For The Srx1400 Services Gateway; Calculating The Power Margin For Fiber-Optic Cable For The Srx1400 Services Gateway - Juniper SRX1400 Hardware Manual

SRX1400 Services Gateway Hardware Guide

Calculating the Power Budget for Fiber-Optic Cable for the SRX1400 Services Gateway

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Calculating the Power Margin for Fiber-Optic Cable for the SRX1400 Services Gateway

196
To ensure that fiber-optic connections have sufficient power for correct operation, you
need to calculate the link's power budget, which is the maximum amount of power it
can transmit. When you calculate the 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 power budget (
you assume minimum transmitter power (
P = P – P
B T R
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
SRX1400 Services Gateway Electrical Wiring Guidelines on page 193
Signal Loss in Multimode and Single-Mode Fiber-Optic Cable for the SRX1400 Services
Gateway on page 194
Attenuation and Dispersion in Fiber-Optic Cable for the SRX1400 Services Gateway
on page 195
Calculating the Power Margin for Fiber-Optic Cable for the SRX1400 Services Gateway
on page 196
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 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. Table 50 on page 197 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.
) and minimum receiver sensitivity (
P
T
). A worst-case estimate of
B
P
P
P ), which
M
P assumes maximum LL :
M
Copyright © 2011, Juniper Networks, Inc.
),
B
):
R
)
LL