This invention relates in general to time space time (TST) telecommunication system switches, and, in particular, to TST switches for interconnecting digital Time Division Multiplex (TDM) communication lines, using two basic modules, a plurality of time switching modules and a plurality of space switching modules. A time folded TST switch concept is taught and claimed in co-pending application, Ser. No. 497,214, filed Aug. 14, 1974 with two of the co-inventors here being common co-inventors with another inventor thereof. Time Space Time (TST) switches are a particularly useful configuration of switching elements providing both time and space translation between channels of Time Division Multiplexed (TDM) telecommunications transmission lines. A TST switch interconnects digital bi-directional TDM communication lines with TDM communication involving the sharing of single transmission paths, individually, in time to provide multiple channels in a single transmission medium. This is a fundamental system improvement in telephone communications that should prove helpful in reducing cost of ordinary telephone service, and in enhancing the ability to provide many new kinds of service in meeting expanded communications needs. Electromechanical crossbar and relay switching systems, as generally used today in telecommunications switching have, for practical purposes, reached the limit of their capabilities. Extensive, continued adherence to these older technologies severely restricts capability, and greatly increases costs of telecommunication systems; and, particularly so with the expansion to systems of great size and complexity. While many advances have been made in capability and efficiency in the transmission area, with microwave, satellite, and high-capacity cable, and with both analog and digital repeaters and terminals being used, the exchange plant, including switching equipment in central offices and branch exchanges, remain in essence the same as in the very early days. Recent advances in solid state technology make the use of all digital switching and transmission techniques more attractive today than ever before. The advent of digital multiplex transmission systems gives rise to many possibilities, particularly with TDM multiplex terminals beginning to look like switches. Message signals in these terminals appear in "time slots," and transfer of signals between time slots is accomplished by a "time slot interchange," with time-division switches connected directly to multiplex transmission lines. Another important saving is accomplished through elimination of digital-to-analog, and analog-to-digital, conversions at every switch. The existing local exchange area plant represents the major part of telephone plant investment, and the least efficient portion of the system--with large quantities of scarce materials required. Further, physical congestion problems are encountered with entrance cables as they approach the central office, and, many times, there are difficult growth problems in central office main distribution frames. Present central office switching includes bulky electromechanical switching stages located in large, costly, building space. Costs for new construction and maintenance of such traditional exchange area plants are constantly increasing, particularly with large cable networks employed when cable pair utilization is inherently very low with a dedicated physical wire pair used to connect each subscriber station to its central office. Thus, system improvements attainable with time division transmission and switching techniques are very significant. It is therefore a principal object of this invention to provide a time space time (TST) switch system achieving significant improvements in operation and in minimized equipment costs, in using two basic modules, a time switching module and a space switching module, in selectively interconnecting digital bi-directional Time Division Multiplexed (TDM)...
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