The difference, in dB, between the equipment power budget (transmitter output minus receiver sensitivity) and the actual link loss. Designers hold back about 3 dB of margin for repairs, connector wear, aging and temperature. Too little margin means the next splice after a backhoe cut can take the link down; on short links with powerful optics, the received power can instead sit above the receiver's overload limit, which calls for an attenuator.
We'll only have 1.5 dB of margin after the extra splice, so put the higher-power optic on that end.
Also heard as
- system margin
- power margin
- headroom
Related terms
Loss budget
The calculated total loss a fiber link should have, built from fiber length, connectors and splices.
dBm
Optical power in decibels relative to one milliwatt, the unit of power meters and transceiver specs.
Light levels
The transmit and receive optical power readings on a transceiver, read from a meter or the switch's optic diagnostics.
Insertion loss
The optical power lost when a component or a whole link is placed in the light path, measured in dB.