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 65.
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 29 on page 66 (here, the link is 2 km long and multimode, and
the (P
B
) is 13 dBm).
Table 29: Estimated Values for Factors Causing Link Loss
Sample Link Loss (LL) Calculation ValuesEstimated Link Loss ValueLink-Loss Factor
0.5 dBmMultimode—0.5 dBmHigher-order mode losses
0 dBmSingle-mode—None
0 dBmMultimode—None, if product of
bandwidth and distance is less
than 500 MHz/km
Modal and chromatic
dispersion
0 dBmSingle-mode—None
This example assumes five connectors. Loss for five
connectors: 5 (0.5 dBm) = 2.5 dBm.
0.5 dBmConnector
This example assumes twosplices. Lossfor twosplices:
2 (0.5 dBm) = 1 dBm.
0.5 dBmSplice
This example assumes the link is 2 km long. Fiber
attenuation for 2 km: 2 km (1 dBm/km) = 2 dBm.
Multimode—1 dBm/kmFiber 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 dBm1 dBmClock 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 © 2017, Juniper Networks, Inc.66
QFX3500 Device Hardware Documentation
To Next Page
Loading...
