The connection between the subscriber and local telephone exchange consists of a pair of wires in a telephone cable. Since a large telephone exchange may have 10000 or more subscribers, the local line network can be quite complicated, particularly because provision must be made for fluctuating demand. The local line network is provided on the basis of forecasts made of the future demand for telephone service, the object being to provide service on demand and as economically as possible.

Since the demand fluctuates considerably there is the problem of forecasting requirements and deciding how much plant should be provided initially and how much at future dates. No matter how carefully the forecasting is carried out, ...

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