GB634706A - Arrangement in automatic telephone networks for connecting waiting calls to subscribers' lines - Google Patents

Abstract

634,706. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON. March 13, 1946, No. 7892. Convention date, March 15, 1945. [Class 40 (iv)] In an automatic exchange system having a manual board for establishing calls waiting for a busy subscriber, the board comprises a number of indicators each set according to an awaited subscriber's number when the operator's connecting link is set on that subscriber's line, and if the number registered on any of the indicators is that set up in a register controller by a fresh caller, the latter is given a distinctive tone or else switched through to the manual board. The arrangements may be such that the register setting is compared with the indicator settings for every incoming call, or if the system is such that the final selector reverts a busy signal to the register-controller the comparison may take place only when a busy subscriber is called. The digit switches in the registers REG have additional arcs Re1 ... 4, all of whose outlets are commoned to all the banks Re11 ... 14 of the indicator equipment M. Comparison is effected by means of a single common equipment K taken into use by the register on operation of the contact-set G. Gas-lamp GL glows, its drop in impedance busying the equipment K, and RR1 operates, followed by GR1. As the. sequence switch V steps to positions 2 ... 5, relays RM1 ... RM3 in the indicator circuits and GR4 ... GR6 in the control circuit test in succession whether there is correspondence between the settings of banks Re1 ... 3 and Re11 ... 13, each test circuit being made over a contact of a preceding RM relay so that at any stage the pair of test relays can only operate if the same settings exist on all the switches so far tested in an indicator and in the register. If at any stage one of the relays GR4 ... 6 fails to operate, RR2 is operated in the register, thereby releasing the control circuit K. Correspondence of the final digits is tested by RM4 and if this relay does not operate, RR2 operates to release the control circuit. If RM4 operates, RM5 and GR3 follow, the latter opening the circuit for RR2. When V reaches position 6, GR2 operates to stop the switch. Relay GR3 operates RR3 in the register, which can then send back a special tone to the caller, but in the embodiment described the first group selector is thereby caused to seize a switch TLV which hunts for the indicator circuit in question, whereupon RM6 connects the caller to the operator and lights the calling lamp KL. Relay RM6 releases GR3, whereupon RR2 operates to disconnect and restore the control circuit. The switch V may be replaced by a relay chain.