Table of Contents
Advertisement
Calculating Power Margin for Fiber-Optic Cable
Table 58: Estimated Values for Factors Causing Link Loss
Link-Loss Factor
Higher-order mode losses
Modal and chromatic dispersion
Connector
Splice
Fiber attenuation
Copyright © 2018, Juniper Networks, Inc.
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.
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
The following sample calculation for a 2-km-long multimode link with a power budget
(P
) of 13 dB uses the estimated values from
B
(LL) as the sum of fiber attenuation (2 km @ 1 dB/km, or 2 dB) and loss for five connectors
(0.5 dB per connector, or 2.5 dB) and two splices (0.5 dB per splice, or 1 dB) as well as
higher-order mode losses (0.5 dB). The power margin (P
Chapter 12: Network Cable and Transceiver Planning
). A worst-case estimate of P
B
Table 58 on page 103
), which
M
assumes maximum LL:
M
Table 58 on page 103
lists an
to calculate link loss
) is calculated as follows:
M
103
Advertisement
Table of Contents
Troubleshooting
