Juniper EX9214 - Calculate the Fiber-Optic Cable Power Budget for EX Series Devices; Calculating the Fiber-Optic Cable Power Margin for EX Series Devices

Calculate the Fiber-Opc Cable Power Budget for EX Series Devices
To ensure that ber-opc connecons have sucient power for correct operaon, calculate the link's
power budget when planning ber-opc cable layout and distances. This planning helps you ensure that
ber-opc connecons have sucient power for correct operaon. The power budget is the maximum
amount of power the link can transmit. When you calculate the power budget, you use a worst-case
analysis to provide a margin of error. You use a worst-case analysis even though not all the parts of an
actual system operate at the worst-case levels.
To calculate the worst-case esmate for a ber-opc cable power budget ( P
B
) for the link:
1. Determine values for the link's minimum transmier power ( P
T
) and minimum receiver sensivity
( P
R
). In the following example, we measure both ( P
T
) and ( P
R
) in decibels relave to one milliwa
(dBm).
P
T
= – 15 dBm
P
R
= – 28 dBm
NOTE: See the specicaons for your transmier and receiver to nd the minimum
transmier power and minimum receiver sensivity.
2. Calculate the power budget ( P
B
) by subtracng ( P
R
) from ( P
T
):
– 15 dBm – (–28 dBm) = 13 dBm
Calculang the Fiber-Opc Cable Power Margin for EX Series Devices
Before calculang the power margin, calculate the power budget (see Calculang the Fiber-Opc Cable
Power Budget for EX Series Devices ).
Calculate the link's power margin when planning ber-opc cable layout and distances to ensure that
ber-opc connecons have sucient signal power to overcome system loss and sll sasfy the
minimum input requirements of the receiver for the required performance level. The power margin ( P
M
)
is the amount of power available aer you subtract aenuaon or link loss ( LL ) from the power budget
( 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 (
P
M
) greater than
zero indicates that the power budget is sucient to operate the receiver and that it does not exceed the
maximum receiver input power. This means that the link will work. A ( P
M
) that is zero or negave
140