reset to its initial state and the cycle is repeated application_number US 66267076 A description fig1 represents the simplified block diagram of a central control telephone exchange the subscribers 39 lines la are each terminated by a subscriber 39 s line individual equipment or subscriber 39 s junctor ja via its subscriber 39 s junctor ja each line is connected to an outlet of a switching network rc as an example there has been represented a switching network constituted by three stages of crossbar switches the inlets of this network rc are connected to common units of various types according to the requirements among which have been represented junctors jr a junctor jr has two accesses one of which is connected to an inlet of the switching network rc and the other for example to a circuit lr leading towards another exchange it is provided for the establishment of a call between a line such as la and circuit lr through the switching network rc junctor jr supplies on the line and circuit the necessary currents and signals it enables the call supervision and in particular the detection of the call termination the operation of this exchange is controlled by two central units uca and ucb which are stored program electronic computers these central units receive information supplied by the subscribers 39 junctors ja through a line scanner exl and by the common units such as junctors jr through a unit scanner fds each central unit processes the information thus obtained in a way defined by the stored program and deduces the actions to be taken with.