Measure how much of a fiber plant is lit: strands in use, wavelengths per pair, spare capacity and dark-fiber headroom.
Fiber has two independent dimensions of headroom: unlit strands and unused wavelengths on the strands already lit. Adding channels to an existing pair is a transponder purchase, while lighting new strands is a much larger optical-line-system project. Knowing which kind of headroom you have decides whether the next 400G service is a card order or a capital project — and whether the route needs new fiber at all.
Fiber Utilization
strand utilisation = lit strands ÷ total strands; capacity = lit pairs × channels in service × per-channel rate.
strand utilisation = lit strands ÷ total strands; capacity = lit pairs × channels in service × per-channel rate. Fiber has two independent dimensions of headroom: unlit strands and unused wavelengths on the strands already lit. Adding channels to an existing pair is a transponder purchase, while lighting new strands is a much larger optical-line-system project.
Knowing which kind of headroom you have decides whether the next 400G service is a card order or a capital project — and whether the route needs new fiber at all.
This calculator takes 5 inputs: Fiber strands in the cable, Strands currently lit, DWDM channels per fiber pair, Channels in service per lit pair, Capacity per channel. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.