Patent GB-642455-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1948-02-27
Abstract: 642,455. Automatic exchange systems. WESTERN ELECTRIC CO., Inc. Feb. 27, 1948, No. 6072. Convention date, Sept. 15, 1939. [Class 40 (iv)] An automatic telephone exchange employing crossbar switches is characterized by a multifrequency system which signals to a control device the location of an incoming line and a desired outgoing line whereby the two may be connected. Calls to a toll exchange are registered on an incoming sender which seizes a marker to control the routing of the call to a group of outgoing trunks. The frames, to which the incoming call and the outgoing trunks are connected, receive characteristic multi-frequency signals from a generating circuit, and in turn transmit these signals to the marker which then effects a connection between them. General arrangement. A toll exchange is shown diagrammatically in Figs. 1-8. Calls may be from various sources, Fig. 1, tandem calls originating in the exchange area, as an example, being handled in tandem switchboards 112, 115 and routed over toll crossbar switches (upper part of Figs. 2 and 3) to outgoing intertoll trunks to go to other toll exchanges 401, 403 or 405. Distant toll exchanges 120, 124, 128 may send calls to intertoll trunks 121, 125, 129 which may be of via, terminating or combined type, i.e. the intertoll trunk may be connected to the toll train of crossbar switches, the terminating train (lower part of Figs. 2 and 3) or to both. Tributary exchanges may be reached over either train. Selection of sender. General. An incoming calling signal energizes apparatus in an incoming intertoll trunk which automatically starts the operation of a link such as 500 or 535, comprising a small train of cross-bar switches, for associating the incoming trunk, either directly with an idle incoming sender of a group such as 518 or 522, or with an idle cordless operator's position such as 531, 532, 533, associated respectively with senders 528, 529, 530, the type of sender selected depending on the type of incoming call. Selection. of sender. Details. Each incoming trunk is connected to a primary crossbar switch such as 501 and to a start relay in the control relay unit, which actuates an idle link connector such as 506 to seize an idle link control circuit such as 507. The link control circuit controls the primary and secondary cross-bar switches of the link to connect an automatic incoming trunk to an idle sender or a manual incoming trunk to an idle cordless operator's position, after which the control relay unit, connector and link control circuit are released, the link switches being held by the sender or the cordless operator's position. Automatic calls, through link 500, record on registers in the sender the type of incoming trunk and the designation of exchange or subscriber to which the call shall be routed. Manual calls reach a cordless operator's position through link 535, the distant operator transmitting the desired connection which is set up by the cordless operator on an associated sender. The senders are associated through connectors 543-545 with markers 624, 625, 640. The registrations in the sender control the marker to route the call by one or more route relays to an idle one of a group of outgoing trunks extending to a particular toll exchange or to a local office. Signalling to marker the location of incoming and outgoing trunk switches. A multi-frequency signalling system transmits signals to the marker to give the location of the switches connected to the incoming and outgoing trunks selected for the connection and whether they are on odd or even numbered frames. A plurality of transformers such as 800-801 are fed by three of a group of different frequency generators 840-844 through amplifying circuits, the secondary windings of the transformers being connected to the select magnets on one frame of incoming primary or outgoing secondary switches, each frame receiving a different set of frequencies. A combination of three frequencies is thus transmitted through a select magnet such as 201 of the incoming trunk primary cross-bar switch, over the incoming trunk, link 500 or 535, the selected sender and connector to transformer 617 in the selected marker. The secondary of the transformer feeds several filters 600- 604, which, respectively, pass the frequencies generated by the corresponding generators 840-844, so that the combination of three frequencies energizes corresponding tubes in a series 608 to 610 and corresponding relays in a series 611 to 613, which operate corresponding relays in a series 614 to 616. A relay such as 633 corresponding to the frame number of the incoming primary switch thus operates in a circuit which also indicates whether the frame number is odd or even, connecting the marker to the odd or even link 209 or 210 accordingly. The trunk group and number are also signalled to the marker to identify the primary incoming switch positively. Outgoing trunks are connected to terminal assignment frames or to patching jacks on the toll trunk assignment frames, Fig. 7, the patching jacks providing flexibility in re-arranging trunk grouping. When an idle outgoing trunk to the desired exchange or local office has been found, relays 619, 620 and outgoing frame cut-in relay 631 operate, whereupon in a manner similar to that already described, the marker ascertains the frame number of the outgoing secondary switch, whether this number is odd or even and also the identity of the trunk group and number. Selection of junctor between incoming and outgoing switches. According to the registrations thus transmitted to the marker, the marker is guided to select frame connections. such as 209, 210, 309, 310 in the via toll train or 229, 230, 339, 340 in the terminating train, to reach frames having switches to be used in the connection of the call. On a first trial to complete the connection, a home channel is seized, that is, if the incoming trunk is on an even-numbered frame, an even-numbered connector such as 210 is energized to establish a connection between the marker and the incoming cross-bar switches. In the event of a second trial being necessary, a mate channel is seized, that is if the incoming trunk is even, an odd-numbered connector such as 209 is energized. A similar arrangement exists for the outgoing connectors 309, 310. The connector circuits, in combination with the marker, control the selection of secondary incoming switches such as 202 and primary outgoing switches such as 300 and a set of junctors connecting them through a cross-connecting frame 217, the connection being tested before completion. All the channels are associated with a like number of channels in the marker, the busy channels are eliminated and one idle channel selected by a sequence circuit. Both halves of the junctor link are tested for continuity and double connections before the hold magnets of the incoming secondary and outgoing primary switches operate to complete the connection, a ringing relay and supervisory lamps operating in the usual manner to indicate satisfactory working. Overflow arrangements. A group of outgoing trunks can be enlarged temporarily by taking into use an additional group on some other frame. If the marker finds all the trunks in the regular group extending to a particular exchange or office busy, it tests the additional group. Jack 721 of the last trunk in a regular group is connected by a patching cord 748 with the added or jump hunt group of trunks 727, which applies earth from all idle trunks to energize relay 724 which applies earth through relay 723 to the sleeve of jack 722. In a similar manner, the regular group, whenever it includes an idle trunk, applies earth to a relay 725 to apply earth to all the sleeve conductors of the patching jacks of the regular group and so will not let relay 723 operate, so indicating to the marker that there are idle trunks in the regular group. When all regular trunks are busy, relay 723 pulls up to make the jump hunt group available, a multifrequency signal through -transformer 730, relay 726, the last jack 722 and transformer 617 operating a set of three relays in the group 614 to 616 to energize the jump-hunt cut-in relay 632 and releasing the outgoing trunk cutin relay 631. The operation of relay 726 applies a second combination of frequencies to the marker to operate a particular route relay for reaching the jump-hunt group of trunks. Use of outgoing senders. If an outgoing sender is required for a call, a link such as 500 is seized by the outgoing trunk circuit to connect a sender of appropriate type to the outgoing trunk. The outgoing sender is set by the incoming sender over the link 500, the train of switches in Figs. 2 and 3 and the same or another link 500. The pulses are then transmitted directly over the outgoing trunks to the distant exchange or terminating office, Fig. 4. Failure to complete connection. If the marker is unable to complete the connection between the incoming and desired outgoing trunks, a timing circuit functions to release the connector, such as 543, and seize another connector which seizes an idle marker, usually not the same, a pair of relays in the marker operating to indicate that this is a second trial whereby the mate and not the home channels are used, that is if the call is on an evennumbered frame, an odd-numbered connector such as 209 is used between the marker and the incoming cross-bar switches. If the marker fails again, a timing circuit releases both the marker and the sender. Overflow indication. A group of overflow trunks are separated from the other trunks in a group and are taken into use only when all the others are busy, lighting a supervisory lamp. If all the overflow trunks are busy, the lamp flashes at a different rate to call attention to the condition. Multi-frequency check circuit. If less than three frequencies are transmitted, no circuit is made through the contacts