Juniper SRX5400, Hardware Manual

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Calculating Power Budget for Fiber-Optic Cable for the SRX5400 Services Gateway
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 (
P
B
),
you assume minimum transmitter power ( P
T
) and minimum receiver sensitivity ( P
R
):
P
B
= P
T
– P
R
The following hypothetical power budget equation uses values measured in decibels
(dB) and decibels referred to one milliwatt (dBm):
P
B
= P
T
– P
R
P
B
= –15 dBm – (–28 dBm)
P
B
= 13 dB
Related
Documentation
Signal Loss in Multimode and Single-Mode Fiber-Optic Cable for the SRX5400 Services
Gateway on page 124
•
•
Attenuation and Dispersion in Fiber-Optic Cable for the SRX5400 Services Gateway
on page 125
•
Calculating Power Margin for Fiber-Optic Cable for the SRX5400 Services Gateway
on page 126
Calculating Power Margin for Fiber-Optic Cable for the SRX5400 Services Gateway
After calculating a link's power budget, you can calculate the power margin ( P
M
), which
represents the amount of power available after subtracting attenuation or link loss ( LL )
from the power budget ( P
B
). A worst-case estimate of P
M
assumes maximum LL :
P
M
= P
B
– LL
A P
M
greater than zero indicates that the power budget is sufficient to operate the receiver.
Factors that can cause link loss include higher-order mode losses, modal and chromatic
dispersion, connectors, splices, and fiber attenuation.
Table 49 on page 127 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, see your vendor documentation.
Copyright © 2017, Juniper Networks, Inc. 126
SRX5400 Services Gateway Hardware Guide