Patent GB-181118-A (GB)
Abstract: 181,118. Relay Automatic Telephone Co., Ltd., and Johnson, B. B. March 7, 1921. Automatic and semi-automatic exchange systems.-In systems of the type in which the selection of and connection to wanted lines is effected over different paths, the capacity of an exchange is increased, without increasing either the number of switching stages for any of the lines or the numerical capacity of the connecting switches, by increasing the capacity of the apparatus used for setting up the selective path only. The invention is described as applied to a system, normally arranged for 1000 lines, of the type in which a calling subscriber on removing his receiver is connected to an idle impulse responder, which in response to dialling impulses marks a hundreds wire H, a tens wire T, and a units wire U, leading to a " marker," Fig. 4, which completes a marking circuit individual to the wanted subscriber, who is then connected to the calling subscriber over non-numerical connecting apparatus. The " marker " operates in the following manner. Each hundreds wire H is connected to a hundreds marking relay HDM, which, when energized in a selective circuit completed by the impulse recorder over a wire H, prepares the circuits of ten tens marking relays TNM<1> - - TNM<0>. A tens marking relay TNM energizes, corresponding to the particular tens wire T marked by the recorder, and prepares the marking circuits of a group of tens subscribers, only the marking circuit individual to the called subscriber, however, being completed over the selected units wire U. The capacity of the exchange is increased by using an impulse responder, as described in Specification 181,119, normally operative by three digits but capable of being set to four digits when the first digit is a predetermined one, 8. In a system described, the capacity of the system for local exchange working is decreased by three hundred owing to the hundreds digits 0, 1, and 9 being used for distant exchange calls, the corresponding hundreds wires being disconnected from hundreds marking relays. This loss of capacity is counterbalanced by further suppressing the digit 8 as a hundreds digit and forming a new numerical group 8100-8499. The second digits following the predetermined one 8, in the manner described in the before mentioned Specification, close circuits over auxiliary hundreds marking wires 81 - - 84, Fig. 6, leading to the hundreds marking relays HDM81 - - HDM84, which would normally be associated with hundreds wires corresponding to the suppressed hundreds digits. The capacity is thus restored to 1000 local lines numbered 200-799 and 8100-8499. According to a modification in which the capacitv of an exchange is increased to over 1000 lines, none of the hundreds digits except the discriminating digit 8 are suppressed, but additional digits are interposed between the first digit 8 and the tens digits, to close circuits over auxiliary hundreds wires 81-85, Fig. 7, associated with additional hundreds relays HDM81 - - HDM85, the necessary tens marking relays TNM also being added. In this case the exchange has a capacity of 1400 lines numbered 0-799, 900-999 and 8100-8599. The 'Provisional Specification describes a method of increasing the capacity of an exchange in which a temporary selective path is established over a mechanical two-coordinate group selector and a mechanical single-coordinate connector. The contacts in certain levels of the group selector are led to two-coordinate connectors, the lines terminating in which are available by dialling a predetermined first digit and an additional digit. Specifications 19553/11, 410/12, and 142,265 also are referred to.