Principles of 7E rotary telephone switching system

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The system is one in which the switching apparatus and the subscribers' line circuit are electronically controlled, the actual connections being made by 100-point power-driven rotary switches. Single-motion selector switches are controlled by the register so that they hunt for particular potentials on the test leads of the outlets, these being compared electronically with the reference potentials stored in the register. The equipment is described in some detail, with notes on its various aspects, such as toll switching, call tracing and indicating, and its working with other systems.