Calculating The Fiber-Optic Cable Power Margin For Ex Series Devices - Juniper EX4300 Series Hardware Manual

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

Before calculating the power margin, calculate the power budget (see
Power Budget for EX Series 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 loss 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 you subtract attenuation or link loss (
( P ).
B
When you calculate the power margin, you use a worst-case analysis to provide a margin of error, even
though not all parts of an actual system operate at worst-case levels. A power margin (
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 that the link will work. A (
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 58: Estimated Values for Factors Causing Link Loss
Link-Loss Factor
Higher-order mode losses
(HOL)
Modal and chromatic
dispersion
Connector
).
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
0.5 dBm
Calculating the Fiber-Optic Cable
LL ) from the power budget
P
) that is zero or negative
M
P ) for the link:
M
Table 58 on page 149
Sample (LL) Calculation Values
•
0.5 dBm
•
0 dBm
•
0 dBm
•
0 dBm
This example assumes 5 connectors.
Loss for 5 connectors:
(5) * (0.5 dBm) = 2.5 dBm
149
P
)
M
P
) greater than
M