Juniper QFX5220, Hardware Manual

Page: 94 / 247

Table 33: Estimated Values for Factors Causing Link Loss (continued)
Estimated Link-Loss Value Link-Loss Factor
0.5 dB Connector
0.5 dB Splice
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 33 on page 96 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 33 on page 96 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.
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