Trunking and traffic aspects of a sectionalised telephone exchange system

Sectionalisation is a principle of exchange design which requires the switching network to be divided into a number of sections, each with its own supervisory and selection apparatus. Each call has access to some or all sections and connection is completed by means of either intersectional or intrasectional links. A central control equipment determines which section is best able to deal with each call. It is shown that this enables a sectionalised exchange to use fewer crosspoints than the equivalent unsectionalised switching network. The paper describes the trunking of an electronically controlled reed-relay exchange system designed on these principles and gives details of the statistical studies conducted in the course of its development. Typical congestion formulas for different types of call are given. Traffic simulations with a digital computer confirmed that the theory is sufficiently accurate to serve as a basis for exchange design.