An absolute power unit: 0 dBm equals 1 mW, minus 10 dBm is 100 µW and minus 30 dBm is 1 µW. Transmit power, receive power and receiver sensitivity are quoted in dBm, while losses and gains are plain dB, a ratio. Subtracting a measured receive level from the transmit level gives the link loss in dB.
Transmitting minus 2 dBm and receiving minus 9, so we've got 7 dB of loss on a link that should be 3.
Also heard as
- decibel-milliwatt
Do not mix it up with
- Insertion loss: Loss is a ratio stated in dB; dBm is an absolute power level.
Related terms
Insertion loss
The optical power lost when a component or a whole link is placed in the light path, measured in dB.
Loss budget
The calculated total loss a fiber link should have, built from fiber length, connectors and splices.
Light levels
The transmit and receive optical power readings on a transceiver, read from a meter or the switch's optic diagnostics.
OLTS
Optical Loss Test Set: a light source and power meter used together to measure end-to-end link loss.