n a long fibre cable there may be many splices which join the individual lengths of fibre together. In a Local Area Network there will be many connectors because of the number of subscribers to the system. At each connector and/or splice some light will be reflected back along the fibre in the opposite direction. This will happen even for the most perfect splice or connector. Light reflected backwards does not leave the fibre but is no longer usefully available for the rest of the fibre, i.e. it is no longer part of the ongoing light.