Patent GB-264164-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1927-01-05
Abstract: 264,164. Siemens &. Halske Akt.-Ges. Jan. 5, 1926, [Convention date]. Automatic exchange systems. - In a system in Which calls from a first exchange VStI to a second exchange VStII are extended via a third exchange VStIII when all direct trunks VL1 are busy, the trunks VL2 from exchange VStI to exchange VStIII are used in common for normal calls to exchange VStIII and for overflow calls to exchange VStII and discrimination between the two classes of call is determined by the level DK2 or DK3 of the first group selector IGWI over which the trunk VL2 has been seized. The incoming ends of the trunks VL2 have associated therewith local group selectors IIGW3 and hunting switches MW for selecting an idle trunk VL3 to the exchange VStII; the routing of an overflow call via exchange VStIII does not therefore involve the introduction of any additional numerical selection at the latter exchange. In the arrangement shown in Fig. 1, the routing of overflow calls through the exchange VStIII is effected by the intervention of an attendant who substitutes a jumper 1, 3 for the jumper 1, 2 when it has been ascertained that all trunks VL1 are busy. Fig. 2 shows an arrangement in which overflow-routing is automatically effected, the first five terminals of the second level DK2 of the group selector IGW1 being connected to trunks VL2 whilst the second five terminals are multipled to the first five terminals of the third level DK3 and have access to trunks VL2. In the arrangement shown in Fig. 5 and described in detail in the next paragraph, the trunk VL2 comprises two conductors only. In an alternative arrangement with a three-conductor trunk, discrimination between the two classes of call is effected by means of two relays connected in series to the third conductor at its incoming end and so arranged that when the trunk is seized over the second level of switch IGW1, only one of these relays operates over a high resistance connected to the conductor at its outgoing end, whilst when seized over the third level both relays operate and the second immediately short-circuits the first. The two relays control respectively the operation of the switch MW and the preparation of the group selector IIGW3 to receive impulses. In another arrangement, the trunk VL2 contains two test conductors over which the discriminating. relays at the incoming end are respectively controlled. In a further modification, the non-numerical and numerical functions of the switches MW, IIGW3 are combined in one switch by providing the group selector with an additional level below the first level. In the case of calls for the exchange VStIII the selector operates in the usual way, but for overflow calls to the exchange VStII the rotary magnet circuit is immediately completed and the selector hunts over its additional level for an idle trunk VL3. In other modifications, the group selectors IIGW3 and the trunks VL3 may be associated with the trunks VL2 over two sets of call-finders provided with discriminating arrangements controlling the respective starting circuits, and additional forward-hunting non- numerical switches may also be employed in series with the call-finders. Arrangement, Fig. 5, employing two-wire trunks VL2. When the trunk VL2 is seized over the third level 53 - - 55, relay C7 operates, disconnecting relay C8 and switching through the lower talking conductor. Impulses of the next digit are repeated by relay A1 to the vertical magnet H1 and during impulsing relays B1, C9 are energized. At the end of the digit, relay B1 releases and completes a circuit for the rotary magnet D2 and when an idle trunk is found the last relay P4 operates in the usual manner. At the end of conversation, relays P3, C7 release and relays F, B1 operate in series over conductors 67 and complete a circuit for relay A1. Relays A1, B1 jointly short-circuit relay C9, the release of which disconnects relav P4 and connects up the release magnet M1. When the trunk VL2 is seized over the second level 100, 101, 91, relay C8 operates, completing a circuit for relay C7. Before the latter can operate, however, a circuit is completed over contacts 104, 93, 105 for relay C10 which locks up, connects conductors 60, 67 to conductors 110, 111, and completes a circuit for the stepping magnet D3 of the hunting switch MW. When an idle trunk VL3 to exchange VStII has been found, relay P5 operates and switches through. At the end of the conversation, relays F, B2 operate in series and relays A2, B2 jointly short-circuit relay C10.