Processors and processing in telephone exchanges

Exchanges are controlled by processors which comprise logical switching and memory apparatus. The total processing is divided, for economy, between groups of processors, each associated with a transmission circuit or trunk in the exchange. The processors necessary for the control of a connection thus become associated as the connection is built up. Further economy results from the time sharing of a smaller number of processors among the circuit processors of a group by parallel connection, when required, through an interface switch. Electronic devices add time-division time sharing to space-division time sharing and stored-program logic to wired-logic techniques that are already well established in telephone-exchange control systems. Processors and processing in general, and the principles of division for series operation and for time-shared parallel operation, with special reference to the new conditions created by electronic devices, are analysed and defined. Wired and stored-program logic processors are compared, with the conclusion that wired logic should continue as the basis for exchange control systems, but with a backing of stored-program processors for operations that do not greatly affect the economics of exchanges, and for which the flexibility of stored-program logic is an advantage. The conclusions are the basis for exchange systems described in other papers.