Optical fibre has replaced copper on point-to-point long distance line
s on a one-for-one basis, with system and network designs scaled direc
tly from our copper experience. However, fibre has introduced radical
changes in almost every system parameter including repeater spacings,
power feed requirements, electro-magnetic compatibility, human interdi
ction, multiplex equipment, corrosion induced failures, and so on. Est
ablished reliability models seldom reflect these radical improvements
or afford sufficient importance to the novel and beneficial features o
f this new technology. These aspects are examined and results and argu
ments are presented that have been derived from new models developed t
o reflect specifically the key aspects of systems and network technolo
gies that will have most impact on our future network thinking and pla
nning.