Calculating Power Margin For Fiber-Optic Cable; Table 67: Estimated Values For Factors Causing Link Loss - Juniper M320 Hardware Manual

Calculating Power Margin for Fiber-Optic Cable

Copyright © 2015, Juniper Networks, Inc.
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
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 (HOL), modal and
chromatic dispersion, connectors, splices, and fiber attenuation.
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 67: Estimated Values for Factors Causing Link Loss

Link-Loss Factor
Higher-order mode losses
Modal and chromatic dispersion
Connector
Splice
Fiber attenuation
Chapter 12: Network Cable and Transceiver Planning
) 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
0.5 dB
0.5 dB
Single-mode—0.5 dB/km
Multimode—1 dB/km
B
R
), which
M
assumes maximum LL:
M
Table 67 on page 113
),
):
113