GB759687A - Improvements in and relating to automatic exchanges - Google Patents

Abstract

759,687. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd. Nov. 23, 1951 [Nov. 23, 1950], No. 28703/50. Class 40 (4). An automatic exchange system comprises a series of low-grade channels equal in number to the number of subscribers and a smaller number of high-grade channels for speech transmission, a calling subscriber's line circuit seizing a highgrade channel and also in response to the dialled digits a low-grade channel in which is transmitted a signal indicative of the high-grade channel seized. This signal is fed to the called subscriber's line circuit for which it serves as a seizing signal and effects the connection thereof with the highgrade channel to complete the connection. As shown, Fig. 1, calling subscriber's line circuit 12 seizes a calling unit 15 permanently associated with one end of a highgrade channel which comprises a go and a return path of the multiplex speech junctions 17, 18. Pulses for determining the time position of the channel in the multiplex system are obtained by combining a " d " and a " u " pulse from the high-frequency pulse generator 14. The calling unit 15 also seizes a register 23 which is then set by the dialled digits and selects a set of MCDU pulses from the generator 26 which are then combined to produce a single 100Á sec. pulse which recurs at intervals of one second, the time position of this pulse in the cycle denoting the wanted subscriber's number. This pulse position constitutes a lowgrade channel in the signalling junction 25 and to this channel a pair of d<1> and u<1> pulses from the low-frequency pulse generator 21 designating the calling unit (and hence the highgrade channel) are fed from the calling unit via the register. Each subscriber's line circuit 13 is provided by the MCDU pulse generator 26 with a pulse coincident with that determining the corresponding low-grade channel in junction 25 and this pulse is used to gate in the d<1> and u<1> pulses received from the signalling junction. The called subscriber's line circuit is seized thereby, whereupon it seizes a free called unit 16 and feeds the d<1> and u<1> pulses thereto. These pulses are used to set a " translator " which then selects a pair of d and u pulses from the high-frequency generator 14 which are combined to produce a gating pulse for connecting the called unit to the selected highgrade junction. With the exception that some of the gating circuits are modified to cater for the slightly different signalling arrangements between the register 23 and the called subscriber's line circuits 13, the circuits are substantially identical with those described in Specification 759,682. Busy signalling, release and metering arrangements are also identical in the two cases. Pulse supplies. The high-frequency pulse generator 14 is identical with that described in Specification 759,682. The low-frequency generator 21 may comprise an oscillator followed by a differentiating circuit feeding a frequency divider whose output feeds the first of a succession of " flip-flops " each of which on restoring triggers the next. The d<1> and u<1> pulses are obtained from the outputs of these " flip-flops," Fig. 14 (not shown). The output from the above-mentioned frequency divider is also fed to a further frequency divider (¸10) which then feeds a further series of " flip-flops " to generate the U pulses. Further stages of frequency dividers and " flip-flops " generate the D, C and M pulses, Fig. 16 (not shown). Specifications 759,683 and 759,684 also are referred to.