Patent GB-653002-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1948-02-20
Abstract: 653,002. Automatic exchange systems. WESTERN ELECTRIC CO., Inc. Feb. 20, 1948, No. 5088. Convention date, Sept. 15, 1939. [Class 40 (iv)] Automatic telephone switching apparatus comprises means in incoming and outgoing trunk circuits for transmitting signals to a link circuit which associates an idle link control circuit therewith to select different types of equipment according to the signals, the link control circuit operating primary and secondary link switches to associate the different types of equipment with the signalling trunk. The invention is described with reference to a cross-bar exchange in which calls are received from a distant exchange 2501 for transmission either to a local subscriber or to a further distant exchange 2508. An incoming trunk 2502 has access to an incoming sender 2515 while an outgoing trunk 2507 has access to either an outgoing sender 2518 or a voice-amplifying repeater 2519 through the switches of a link circuit 2510.  General description. The system is shown schematically in Fig. 25. (1) Use of incoming sender. A call from a distant exchange 2501 energizes the apparatus of an incoming intertoll trunk circuit 2502 to select a link 2510 and a link control circuit 2540 for associating an incoming sender such as 2515 with the incoming trunk through the primary and secondary switches of the link. Impulses from the distant exchange set either the code or both the code and numerical registers in.the incoming sender. The sender 2515 seizes a marker 2516 and transfers the code registrations to the marker, which causes the selection of an outgoing trunk 2507 to the desired distant exchange 2508 and also operates switches 2503- 2506 to connect the incoming and outgoing trunks. (2) Use of outgoing sender. For calls requiring transmission of numerical digits, the outgoing trunk energizes a circuit through a link and link control circuit to seize an outgoing sender such as 2518. The numerical digits are then transferred from the incoming sender 2515 through the link switches 2510, the incoming trunk circuit 2502, the line switches 2503-2506, the outgoing trunk circuit 2507 and the link switches 2510 to the registers of the outgoing sender 2518, which subsequently transmits the numerical digits to the distant exchange 2508 over the link switches and the outgoing trunk conductors. (3) Use of voice-amplifying repeater. For long incoming and outgoing trunks, a repeater is required. The class of trunk, signalled by the incoming trunk, and the required exchange are registered in the marker which sends a signal through the incoming sender, the link switches, the incoming trunk and the line switches to the outgoing trunk to energize a repeater selecting relay in the outgoing trunk, which is automatically locked to await the selection of an outgoing sender before indicating that a repeater is required. Choice of link control circuits. For the detailed description, reference is had to those figures not enclosed in square brackets in Fig. 26. A two-way trunk, Figs. 1, 7, is used in the example as an incoming trunk, a call from a distant toll exchange 100 on conductor 113 operating relays 704, 719. Relay 704 marks leads 112, 121 to prevent the distant exchange sending impulses until an incoming sender has been seized. 719 operates 706 if an inter-toll and not a terminating trunk is required, and also 107, 716, the last marking the incoming trunk busy to any marker trying to use it as an outgoing trunk. Link start relay 1311 then operates to energize an idle connector circuit (Fig. 12, not shown) which tests for and selects an idle link control circuit in known manner. Choice of sender or repeater. A class signal is sent to the link control circuit to operate 1330, 1331 or 1332 according as to whether an incoming or outgoing sender or a repeater is required. Relays 2201, 2203, 2205 are each associated with a different switch combination comprising a vertical on both the primary and secondary link switches (Fig. 8, not shown). All the idle senders or repeaters are connected to sets of relays 2202, 2204, 2206, respectively, each set being arranged in a chain circuit so that one idle sender or repeater is selected. According to the switch and to the level on the switch on which the idle sender or repeater is found, so a relay 1805, 1809 or 1810 (Fig. 18, not shown) and one of 1320-1324 operate. A secondary test of the sender or repeater is then made. If the sender or repeater is idle, a relay such as 918 (not shown), in the case of an incoming sender, is normal and the sender or repeater applies battery to a tube 2410 through relays 2403, 2405. If no other control circuit is attempting to seize this sender or repeater, the plate resistance of the tube drops immediately and relays 2403, 2405 operate. If 2405 operates, 2402 pulls up and locks the related relay in the chain 2202, 2204, 2206. If two control circuits attempt to seize the same sender or repeater, the tube 2410 in the later control circuit cannot fire and the next sender or repeater represented in the chain 2202, 2204, 2206 is selected and tested. If two control circuits seize the sender or repeater at exactly the same moment, neither tube can energize and an alarm circuit (Fig. 19, not shown) operates after a time interval. If the test is successful, the selected sender or repeater is busied and seized. Relay 2402 energizes the select magnet associated with the level connected to the sender or repeater, and also causes the release of the relay 1330, 1331 or 1332 to restore the chain of relays 2202, 2204, 2206 other than that corresponding to the selected sender or repeater. The link control circuit then completes the circuit through the primary and secondary link switches in known manner to connect the sender or repeater to the incoming or outgoing trunk. Incoming sender and marker. After an incoming sender has been connected to the incoming trunk through a link circuit, the sender registers code and numerical digits received from the distant exchange, after which a marked connector is actuated and an idle marker is selected for finding an idle out going trunk and for setting the switches between the incoming and the selected outgoing trunks, in the manner described in Specification 642,455. According to whether 706 is operated or not, i.e. according to the destination of the call, a toll marker or a local marker is employed. Conditions for use of repeater. Uni-directional voice-amplifying repeaters 1411, 1412 are provided for the channels of a 4-wire transmission system. The channels may be connected to a twowire toll line extending to a distant exchange directly or through hybrid coils. Repeaters are inserted in each transmission channel of the outgoing trunk under control of the marker when a long incoming trunk is connected to a long outgoing trunk. The system can be adapted to a two-wire system. A long incoming trunk applies ground to contact 9 of splitting relay 104 to energize the long incoming trunk relay 520 (not shown) in the incoming sender, to cause the operation of a long incoming trunk relay 600 in the marker after the marker has been selected and seized. In establishing the desired connection, the marker energizes a route relay, such as 602, and according as to whether the selected route relay is concerned with long or short outgoing trunks, so 606 energizes or remains normal. In the latter case, repeater selection does not take place. If 606 energizes, .however, as soon as an idle outgoing trunk is found and busied, relay 605 pulls up to energize both windings of 608 in a circuit extending in parallel over conductors 620, 621, the incoming sender, the incoming and outgoing trunks and the upper and lower windings of retard coil 307, one branch going also through the lower winding of relay 322. Relay 322 does not operate because of the high resistance of the lower winding of 608. Operation of 608, however, operates 607, which releases the lower winding of 608 to permit the operation of repeater relay 322 in the outgoing trunk circuit. Outgoing sender. In the manner already described, the outgoing trunk circuit seizes an idle link control circuit to obtain access to an outgoing sender. The class of outgoing trunk is indicated over the contacts of 306 and 1500 (not shown) to marginal pulsing relays 2006- 2013 (Fig. 20, not shown), to operate one of the class of service relays 2000-2005, after which 306 operates to disconnect the class information leads and establish pulsing circuits from the incoming sender to the outgoing sender over the link circuit, incoming trunk, line switches, outgoing trunk and another link circuit, the registrations being transferred under the control of steering relays in known manner. Outward pulses to distant exchange. When the incoming sender has finished transmitting the registration pulses, it sends a special pulse of low resistance ground and high resistance battery to release the incoming sender and cause the operation of a start relay 1520 (not shown) for sending pulses from the outgoing sender over the link switches and the trunk conductors to the distant exchange 330. When the pulses for the last digit have been transmitted, a special pulse is generated to cause the release of the outgoing sender and the release of the outgoing trunk relay 306. This is a signal to the outgoing trunk to effect talking connection, or when a repeater is required, to cause the selection of a repeater to be inserted in the talking conductors. Selection and operation of repeater. Relay 319 was operated when the outgoing trunk was selected, relays 320, 306, 305 were operated by the outgoing sender, and relay 322 by the marker. Release of 306 now energizes 321 and link start relay 1311 to associate a link control circuit therewith for the selection of an idle repeater. With 320 operated, class leads 334, 332 are connected and energization of connector relay 1314 by 1311 eff