Patent GB-759686-A (GB)
Title: Improvements in and relating to calling line identification systems for automatic telephone exchanges
Inventor: LEVY MAURICE MOIESE
IPC: H04M15/08
Filed: 1950-09-22
Abstract: 759,686. Automatic exchange systems- GENERAL ELECTRIC CO., Ltd. Sept. 20, 1951 [Sept. 22, 1950], No. 23345/50. Class 40 (4). In a calling line identification system a switch passes in turn voltages characteristic of each subscriber (or group of subscribers) to a plurality of gating devices, associated respectively with the subscriber's line circuits (or groups thereof), one of which gates is conditioned by the calling line circuit to pass the corresponding characteristic voltage whereby the switch is locked in a position indicative of the calling subscriber's number (or a digit thereof). As described, the voltages take the form of pulses whose position in a pulse cycle characterize the calling subscriber's number (or a digit thereof). In the following embodiment the pulse cycle comprises 40 pulse positions, 10 pulse positions for each possible digit of a 4-digit number. The respective sets of pulses will hereinafter be referred to as the M, C, D and U pulses. As shown, Fig. 3, one of the calling subscribers 1-10,000 obtains access to the operator's position 11 through the automatic exchange 10. Operation of switch 13 completes a control circuit 14 for switches provided with indicators M, C, D, U. The pulse source 17 feeds the inlets to the switches and also the set of gates 18. The inlets of the switches M, C, D, U are fed with pulses characteristic of the digits to which the switches are set. The M, C and D switch home positions also are respectively fed with every M, C or D pulse. The set of gates 18 is divided into four groups, there being 10 M gates, 100 C gates, 1,000 D gates and 10,000 U gates, the outlet of each gate feeding 10 succeeding gates, Fig. 4. Each gate is connected to receive a characteristic M, C, D or U pulse direct from the pulse generator and is opened when this pulse coincides with a pulse received over the M, C, D or U switches. The gate then passes all succeeding pulses until closed by a switching operation as described later. In operation, pulses received over the M, C and D switches in their home positions open in turn all the M, C and D gates. The U switch is set hunting and pulses received over its wiper successively open all the U gates in all the tens groups until the line connected to the operator's position is reached. The output pulse is then transmitted (preferably over the P-wire) to the operator's position where it effects a switching operation which stops the U switch, closes all the gates and sets the switch D hunting. As before, all the M and C gates open and the D gates are opened in turn by pulses from the switch D to pass the succeeding U pulse determined by the setting of the U switch to the corresponding U gate in the successive tens groups. When a pulse is returned to the operator's position the D switch is stopped, the gates are reclosed and the C switch started hunting. The C and M switches are then set similarly. In order that a number of switch units 15 may be provided in common to the equipment 18, it may be arranged that successive whole groups of M, C, D, U pulses are provided in turn to the different switch units in a recurring cycle. In a further modification, Figs. 8, 9 (not shown), two groups of switch units 15 feed two separate sets of M, C, D gates, these gates feeding a common set of U gates the M, C, D, U pulses for the two sets being staggered so that the M, C, D pulses of one set occur during the interval used for the U pulses of the other set and vice versa. Identification of a subscriber at remote exchange. The identification equipment M, C, D, U switches at the remote exchange may be provided with an extra wiper each which connects up frequencies characteristic of the digits for transmission to the central exchange. Specifications 759,682 and 759,684 are referred to.