Juniper MX480, Руководство по оборудованию

Страница: 164 / 420

Table 88: Estimated Values for Factors Causing Link Loss (continued)
Estimated Link-Loss Value Link-Loss Factor
Single-mode—0.5 dB/km
Multimode—1 dB/km
Fiber attenuation
The following sample calculation for a 2-km-long multimode link with a power budget
(P
B
) of 13 dB uses the estimated values from Table 88 on page 163 to calculate link loss
(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
M
) is calculated as follows:
P
M
= P
B
– LL
P
M
= 13 dB – 2 km (1 dB/km) – 5 (0.5 dB) – 2 (0.5 dB) – 0.5 dB
P
M
= 13 dB – 2 dB – 2.5 dB – 1 dB – 0.5 dB
P
M
= 7 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 88 on page 163 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.
Understanding Fiber-Optic Cable Signal Loss, Attenuation, and Dispersion
To determine the power budget and power margin needed for fiber-optic connections,
you need to understand how signal loss, attenuation, and dispersion affect transmission.
The MX10008 router uses various types of network cables, including multimode and
single-mode fiber-optic cables.
• Signal Loss in Multimode and Single-Mode Fiber-Optic Cables on page 165
• Attenuation and Dispersion in Fiber-Optic Cable on page 165
Copyright © 2019, Juniper Networks, Inc. 164
MX480 Universal Routing Platform Hardware Guide