Juniper EX4600, Руководство по оборудованию, Страница: 94 / 230

of component attenuation, power penalties (including those from dispersion), and a
safety margin for unexpected losses.
Related
Documentation
Calculating the EX Series Switch Fiber-Optic Cable Power Budget on page 76
•
•
Calculating the EX Series Switch Fiber-Optic Cable Power Margin on page 76
Calculating the EX Series Switch Fiber-Optic Cable Power Budget
Calculate the link's power budget when planning fiber-optic cable layout and distances
to ensure that fiber-optic connections have sufficient power for correct operation. 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, even though
all the parts of an actual system do not operate at the worst-case levels.
To calculate the worst-case estimate for fiber-optic cable power budget ( P
B
) for the
link:
1.
Determine values for the link's minimum transmitter power ( P
T
) and minimum receiver
sensitivity ( P
R
). For example, here, ( P
T
) and ( P
R
) are measured in decibels, and
decibels are referred to one milliwatt (dBm).
P
T
= –15 dBm
P
R
= –28 dBm
NOTE: See the specifications for your transmitter and receiver to find the
minimum transmitter power and minimum receiver sensitivity.
2.
Calculate the power budget ( P
B
) by subtracting ( P
R
) from ( P
T
):
–15 dBm – (–28 dBm) = 13 dBm
Related
Documentation
Calculating the EX Series Switch Fiber-Optic Cable Power Margin on page 76
•
•
Understanding EX Series Switches Fiber-Optic Cable Signal Loss, Attenuation, and
Dispersion on page 74
•
Pluggable Transceivers Supported on EX Series Switches
Calculating the EX Series Switch Fiber-Optic Cable Power Margin
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 (
P
M
) is the amount of power available after
attenuation or link loss ( LL ) has been subtracted 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 all the parts of an actual system do not operate at worst-case
Copyright © 2014, Juniper Networks, Inc. 76
EX4600 Switch Hardware Guide