Juniper QFX5110, Руководство по оборудованию

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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 Fiber-Optic Cable Power Budget for
a QFX Series Device” on page 66 .
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 30 on page 67 (here, the link is 2 km long and multimode, and
the (P
B
) is 13 dBm).
Table 30: Estimated Values for Factors Causing Link Loss
Sample Link Loss (LL) Calculation Values Estimated Link Loss Value Link-Loss Factor
0.5 dBm Multimode—0.5 dBm Higher-order mode losses
0 dBm Single-mode—None
0 dBm Multimode—None, if product of
bandwidth and distance is less
than 500 MHz/km Modal and chromatic
dispersion
0 dBm Single-mode—None
This example assumes five connectors. Loss for five
connectors: 5 (0.5 dBm) = 2.5 dBm. 0.5 dBm Connector
This example assumes two 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 dBm/km) = 2 dBm. Multimode—1 dBm/km Fiber attenuation
This example assumes the link is 2 km long. Fiber
attenuation for 2 km: 2 km (0.5 dBm/km) = 1 dBm. Single-mode—0.5 dBm/km
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
):
67 Copyright © 2017, Juniper Networks, Inc.
Chapter 7: Transceiver and Cable Specifications