Juniper EX4550, Hardware Manual, Page: 112 / 330

This means the link will work. A ( P
M
) that is zero or negative indicates insufficient power
to operate the receiver. See the specification for your receiver to find the maximum
receiver input power.
Before you begin to calculate the power margin:
•
Calculate the power budget. See “Calculating the EX Series Switch Fiber-Optic Cable
Power Budget” on page 89 .
To calculate the worst-case estimate for the power margin ( P
M
) for the link:
1.
Determine the maximum value for link loss ( LL ) by adding estimated values for
applicable link-loss factors—for example, use the sample values for various factors
as provided in
Table 48 on page 90 (here, the link is 2 km long and multimode, and
the ( P
B
) is 13 dBm):
Table 48: Estimated Values for Factors Causing Link Loss
Sample (LL) Calculation Values Estimated Link-Loss Value Link-Loss Factor
• 0.5 dBm
• 0 dBm
• Multimode—0.5 dBm
• Single mode—None
Higher-order mode losses (HOL)
• 0 dBm
•
0 dBm
• Multimode—None, if product of
bandwidth and distance is less than
500 MHz/km
•
Single mode—None
Modal and chromatic dispersion
This example assumes 5 connectors.
Loss for 5 connectors:
(5) * (0.5 dBm) = 2.5 dBm
0.5 dBm Connector
This example assumes 2 splices. Loss for
two splices:
(2) * (0.5 dBm) = 1 dBm
0.5 dBm Splice
This example assumes the link is 2 km
long. Fiber attenuation for 2 km:
•
(2 km) * (1.0 dBm/km) = 2 dBm
• (2 km) * (0.5 dBm/km) = 1 dBm
• Multimode—1 dBm/km
•
Single mode—0.5 dBm/km
Fiber attenuation
1 dBm 1 dBm Clock Recovery Module (CRM)
NOTE: For information about the actual amount of signal loss caused by
equipment and other factors, see your vendor documentation for that
equipment.
2.
Calculate the ( P
M
) by subtracting ( LL ) from ( P
B
):
P
B
– LL = P
M
Copyright © 2015, Juniper Networks, Inc. 90
EX4550 Switch Hardware Guide