Table 25: 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 example uses the estimated values in Table 25 on page 177 to calculate
link loss (
LL
) for a 2-km-long multimode link with a power budget (
P
B
) of 13 dB:
•
Fiber attenuation for 2 km @ 1.0 dB/km= 2 dB
•
Loss for five connectors @ 0.5 dB per connector = 5(0.5 dB) = 2.5 dB
•
Loss for two splices @ 0.5 dB per splice =2(0.5 dB) = 1 dB
•
Higher-order mode loss = 0.5 dB
•
Clock recovery module = 1 dB
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 25 on page 177 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 174
•
•
Signal Loss in Multimode and Single-Mode Fiber-Optic Cable for the M7i Router on
page 175
Copyright © 2010, Juniper Networks, Inc.
178
M7i Multiservice Edge Router Hardware Guide
All manuals and user guides at all-guides.com
