Stronger competition together with the development of new technologies have forced the Telecom Service Providers (TSP's) in the Netherlands to look for sophisticated optimisation methods to reduce the costs of their communication services especially for new areas such as the application of fibre technology. Fibre is being considered as the transmission medium of the future because fibre deadens the signals much less than the traditional media such as copper and coax, a lot of data can be transmitted at the same time and there are only a few failures. Another advantage is that fibre cables are thin and light so that they can be put into the ground rather easily. This article describes optimisation models with the objective to minimise the costs of constructing and managing a fibre network. The optimisation models have been developed to support decisions about the design and use of a fibre network and are based on the practical situation at Enertel being one of the new TSP’s. For Enertel a national backbone was already realised. The main problem to be solved concerned the optimisation of the access to the fibre network.