The power margin (P
M
) is calculated as follows:
P
M
= P
B
– LL
P
M
= 13 dB – 2 km (1.0 dB/km) – 5 (0.5 dB) – 2 (0.5 dB) – 0.5 dB [HOL] – 1 dB [CRM]
P
M
= 13 dB – 2 dB – 2.5 dB – 1 dB – 0.5 dB – 1 dB
P
M
= 6 dB
The following sample calculation for an 8-km-long single-mode link with a power budget
(P
B
) of 13 dB uses the estimated values from Table 51 on page 94 to calculate link loss
(LL) as the sum of fiber attenuation (8 km @ 0.5 dB/km, or 4 dB) and loss for seven
connectors (0.5 dB per connector, or 3.5 dB). The power margin (P
M
) is calculated as
follows:
P
M
= P
B
– LL
P
M
= 13 dB – 8 km (0.5 dB/km) – 7(0.5 dB)
P
M
= 13 dB – 4 dB – 3.5 dB
P
M
= 5.5 dB
In both examples, the calculated power margin is greater than zero, indicating that the
link has sufficient power for transmission and does not exceed the maximum receiver
input power.
Related
Documentation
• Fiber-Optic and Network Cable Specifications for the M7i Router on page 91
• Signal Loss in Multimode and Single-Mode Fiber-Optic Cable for the M7i Router on
page 92
• Attenuation and Dispersion in Fiber-Optic Cable on M Series, MX Series, and T Series
Routers on page 91
• Calculating Power Budget for Fiber-Optic Cable for M Series, MX Series, and T Series
Routers on page 93
95Copyright © 2019, Juniper Networks, Inc.
Chapter 12: Network Cable and Transceiver Planning
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