Calculating Power Margin For Fiber-Optic Cable For The Srx5400 Firewall - Juniper SRX5400 Hardware Manual

PB = 13 dB

Calculating Power Margin for Fiber-Optic Cable for the SRX5400 Firewall

After calculating a link's power budget, you can calculate the power margin (
amount of power available after subtracting attenuation or link loss (
PM assumes maximum LL :
worst-case estimate of
PM = PB – LL
PM greater than zero indicates that the power budget is sufficient to operate the receiver.
A
Factors that can cause link loss include higher-order mode losses, modal and chromatic dispersion,
connectors, splices, and fiber attenuation.
factors used in the following sample calculations. For information about the actual amount of signal loss
caused by equipment and other factors, see your vendor documentation.
Table 42: Estimated Values for Factors That Cause Link Loss
Link-Loss Factor
Higher-order mode losses
Modal and chromatic dispersion
Connector
Splice
Fiber attenuation
The following example uses the estimated values in
2 km-long multimode link with a power budget (
Table 42 on page 159
Estimated Link-Loss Value
Single-mode—None
Multimode—0.5 dB
Single-mode—None
Multimode—None, if product of bandwidth and distance is less than 500
MHz–km
0.5 dB
0.5 dB
Single-mode—0.5 dB/km
Multimode—1 dB/km
Table 42 on page 159
PB ) of 13 dB:
PM ), which represents the
LL ) from the power budget ( PB ). A
lists an estimated amount of loss for the
to calculate link loss (
159
LL ) for a