No. 1 ESS Bus System

The function of the bus system of No. 1 ESS is to provide intramachine data and control communication. The need for large amounts of such communication is a natural outgrowth of the functional unit structure of the over-all system. At the same time the interconnection method must be highly flexible to permit easy growth and to adapt to large variations between different installations. Existing electromechanical switching systems send most of their intramachine data by dc ground-return signaling. Most relays used in telephony are relatively easy to control at a distance because of their limited frequency response and high signal threshold. Semiconductor logic circuits, on the other hand, have a wide frequency response and can be disturbed by relatively small noise signals. It became apparent quite early in the development that conventional interconnection techniques would not be satisfactory. The No. 1 ESS bus system described in this paper has proved to be a successful solution of the interconnection problem. l.i Size Telephone switching systems tend to be relatively large assemblies of equipment consisting of many separate functional units. Compared to 2021