The optical-power budget

Do not use fiber cable with a light loss that exceeds 3.75dB/Km with Madge Ringnodes.

The optical-power budget is the sum of the losses of light that occur over a particular fiber-optic link. Some light is always lost during communication over fiber-optic cable. It is lost both along the cable itself, and at each connection on the link.

The draft standard allows for a signal loss of 13dB from the link between your Ringnode and a concentrator. Each connection on your link typically entails a loss of 1dB, and you need to anticipate a further loss of 3dB to allow for the effects of temperature, wear to your connector, possible splices of broken cable, and other future causes of light-loss.