Mr. Jeremy Godfrey:

Long-term deployments of fibre, particularly in rural areas, are quite new, but there is evidence that fibre does degrade over time. It must be able to take the light over very long distances. We are not just talking about a piece of glass but a very carefully constructed piece of glass which must ensure the light is properly constrained within it. As it gradually gets a little cloudier, its capability to transmit light lessens and that loss of power does get greater over time. As Mr. Leavy said, we have assumed a 20-year lifetime. One finds that sometimes things last longer than that and that at other times they do not.