Calculating The Fiber-Optic Cable Power Margin For Ex Series Devices - Juniper EX9253 Hardware Manual

Calculating the Fiber-Optic Cable Power Margin for EX Series Devices

Before calculating the power margin:
• Calculate the power budget (see
Devices ).
Calculate the link's power margin when planning fiber-optic cable layout and distances to ensure that
fiber-optic connections have sufficient signal power to overcome system losses and still satisfy the
minimum input requirements of the receiver for the required performance level. The power margin (
is the amount of power available after attenuation or link loss (
P
budget ( ).
B
When you calculate the power margin, you use a worst-case analysis to provide a margin of error, even
though all the parts of an actual system do not operate at worst-case levels. A power margin (
greater than zero indicates that the power budget is sufficient to operate the receiver and that it does
not exceed the maximum receiver input power. This means the link will work. A (
negative indicates insufficient power to operate the receiver. See the specification for your receiver to
find the maximum receiver input power.
To calculate the worst-case estimate for the power margin (
1. Determine the maximum value for link loss (
factors—for example, use the sample values for various factors as provided in
(here, the link is 2 km long and multimode, and the (
Table 27: Estimated Values for Factors Causing Link Loss
Link-Loss Factor
Higher-order mode losses
(HOL)
Modal and chromatic
dispersion
Calculating the Fiber-Optic Cable Power Budget for EX Series
LL ) by adding estimated values for applicable link-loss
P
) is 13 dBm):
B
Estimated Link-Loss Value
•
Multimode—0.5 dBm
•
Single mode—None
•
Multimode—None, if product of
bandwidth and distance is less
than 500 MHz/km
•
Single mode—None
LL ) has been subtracted from the power
P
M
P
) for the link:
M
Table 27 on page 65
Sample (LL) Calculation Values
•
0.5 dBm
•
0 dBm
•
0 dBm
•
0 dBm
P
)
M
P )
M
) that is zero or
65