specified for the type of link in the Telcordia Technologies document GR-253-CORE (Section 4.3) and
International Telecommunications Union (ITU) document G.957.
When chromatic dispersion is at the maximum allowed, its effect can be considered as a power penalty in
the power budget. The optical power budget must allow for the sum of component attenuation, power
penalties (including those from dispersion), and a safety margin for unexpected losses.
Calculating the Fiber-Optic Cable Power Budget for an MX10008 Router
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 the 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 referenced to 1 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
SEE ALSO
Understanding Fiber-Optic Cable Signal Loss, Attenuation, and Dispersion
Calculating the Fiber-Optic Cable Power Margin for an MX10008 Router | 123
122
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