Outlines of a t.d.m. two-wire telephone switching system and its control

Abstract

The application of certain basic principles of switching and logic system design in electronic telephone switching systems is illustrated in an outline description of a fully-solid-state switching system for exchanges having some 10 000 lines and 1000 junctions. Speech transmissionis ensured on a one-wire time-multiplex p.a.m. basis using the principle of resonant transfer between modem circuits.A particular arrangement of the highway interconnecting network reduces the total number of cross-points to less than 1.2 per line and 2.5 per junction for speech and signalling. Although unbalanced multiplex highways are used throughout, the problem of inter-highway crosstalk can be mastered without particular difficulties, while the overall transmission losses can be reduced to 1.7 dB.Central control has been conceived as a separate data-processing system using ferrite stores and semiconductor logic at relatively low speeds, determined mainly by the real-time requirements of dial-pulse detection and supervision.Outstanding flexibility and design facility has been achieved by the large-scale use of semi-permanent information stores for translation, hunting and programme-controlled logic.