Calculating Power Budget For Fiber-Optic Cable; Calculating Power Margin For Fiber-Optic Cable; Transceiver And Cable Specifications; Table 42: Estimated Values For Factors Causing Link Loss - Juniper MX2020 Hardware Manual

Calculating Power Budget for Fiber-Optic Cable

Calculating Power Margin for Fiber-Optic Cable

Copyright © 2015, Juniper Networks, Inc.
To calculate the power budget and power margin, perform the following tasks:
Calculating Power Budget for Fiber-Optic Cable on page 129
1.
Calculating Power Margin for Fiber-Optic Cable on page 129
2.
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
you assume minimum transmitter power (P
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
After calculating a link's power budget, you can calculate the power margin (P
represents the amount of power available after subtracting attenuation or link loss (LL)
from the power budget (P
P = P – LL
M B
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.
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 42: Estimated Values for Factors Causing Link Loss

Link-Loss Factor
Higher-order mode losses
Modal and chromatic dispersion
Chapter 11: Transceiver and Cable Specifications
) and minimum receiver sensitivity (P
T
). A worst-case estimate of P
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
), which
M
assumes maximum LL:
M
Table 42 on page 129 lists an
),
B
):
R
129