Juniper QFX5120 Series Hardware Manual page 78

To calculate the worst-case estimate for the power margin (P
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
the link is 2 km long and multimode, and the power margin (P
Table 31: Estimated Values for Factors Causing Link Loss
Link-Loss Factor
Higher-order mode
losses
Modal and chromatic
dispersion
Connector
Splice
Fiber attenuation
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 ) by subtracting (LL) from (P
M
P – LL = P
B M
13 dBm – 0.5 dBm [HOL] – 5 x (0.5 dBm) – 2 (0.5 dBm) – 2 km (1.0 dBm/km) – 1 dB [CRM] = P
Estimated Link Loss Value
Multimode—0.5 dBm
Single-mode—None
Multimode—None, if the sum of
bandwidth and distance is less
than 500 MHz/km
Single-mode—None
0.5 dBm
0.5 dBm
Multimode—1 dBm/km
Single-mode—0.5 dBm/km
1 dBm
):
B
) for the link:
M
Table 31 on page 80
) is 13 dBm).
M
Sample Link Loss Calculation Values
0.5 dBm
0 dBm
0 dBm
0 dBm
This example assumes five connectors. Loss for five
connectors: (5)x(0.5 dBm) = 2.5 dBm.
This example assumes two splices. Loss for two
splices: 2 (0.5 dBm) = 1 dBm.
This example assumes the link is 2 km long. Fiber
attenuation for 2 km: 2 km (1 dBm/km) = 2 dBm.
This example assumes the link is 2 km long. Fiber
attenuation for 2 km: 2 km (0.5 dBm/km) = 1 dBm.
1 dBm
80
(here,
M