Calculating the Fiber-Optic Cable Power Budget for a QFX Series Device

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 (`PB`) for the link:

1. Determine values for the link's minimum transmitter power (`PT`) and minimum receiver sensitivity (`PR`). For example, here, (`PT`) and (`PR`) are measured in decibels, and decibels are referenced to 1 milliwatt (dBm):

`PT` = –15 dBm

`PR` = –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 (`PB`) by subtracting (`PR`) from (`PT`):

–15 dBm – (–28 dBm) = 13 dBm