Patent GB-471763-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1936-03-16
Abstract: 471,763. Semi -automatic exchange systems. SIEMENS BROS. & CO., Ltd., and HENSLER, B. A. March 16, 1936, No. 7883. [Class 40 (iv)] Long-distance trunk calls are set up in stages by an operator over first and second trunk selectors at the originating and intermediate exchanges under the control of a registertranslator at each exchange which receives code digits for routing the call to the next stage. The register-translator provides two translations. one or other of which is made effective under the control of circuits which indicate the condition of each trunk group to route the call over the direct route or over an alternative route involving a further intermediate exchange. In the latter case the additional digits necessary to effect routing at the further exchange are inserted by the operator at the originating exchange or automatically at an intermediate exchange. The same trunks may be capable of use for direct and alternative routing. If both direct and alternative routes are unavailable at the originating exchange, the call is directed to storage equipment associated with the required direct trunk group. If similar congestion is met at an intermediate exchange, the call is routed to an operator at that exchange or, if that exchange is in an alternative route, at the preceding exchange in the direct route. The register-translator at the originating exchange, Figs. 1-4 (not shown), is associated with an operator's position and is identical with that described in Specification 471,764. The register-translator at an intermediate exchange, Fig. 6, is associated with an incoming first trunk selector, Fig. 5, and differs mainly from that at the originating exchange in that it is set by impulses and that it supplies additional digits in the case of alternative routing. Both types of registertranslator provide in certain cases for further searching should a trunk selector find no idle outlet. Specifications 443,220 and 465,011 also are referred to. Routing at intermediate exchange. Each trunk has at its outgoing end a relay set for sending A.C. signals of X frequency forward and Y frequency backward. When the trunk is seized an impulse is sent forward to operate relay X (not shown) in A.C. receiving apparatus VFR, Fig. 5. Relay B energizes and brings about the association of a register-translator over the switch SC, whereupon B, Fig. 6, pulls up and connects impulse relay A to wire PU, and the first incoming digit sets the switch 1C, . after which the sequence switch SQ moves from position 1 to position 3 due to the relapse of dialling relay CC. If the digit is 1, indicating that the call is to be completed locally, CT energizes in position 2 of SQ and battery is connected over TS, TT and wires W, X to operate relays which mark outlets to local selectors. After the hunting of the first trunk selector, TS, TT fall back and DS energizes. Relay CO energizes and connects up COS, Fig. 5, which brings about release of the register-translator and switches through. The numerical digits are repeated forward by RY, since contact at is not operated in this case. If the call is not to be completed locally, the second digit sets the switch 2C in position 3 of SQ, a preliminary movement to a subnormal position being made if the first digit is 6-0. In position 4 of SQ, the translating switch CM picks up the joint marking of 1C, 2C, and GC connects relays MB, SY, PY over wipers CM9-11 to the group control wires. If delayed working is in force or if no route is available, MB energizes and brings about routing to an operator. If the direct route is available, PY energizes and connects up CT and hence the marking relays AW-AZ appropriate for setting the first trunk selector. When the latter is set, DS responds, SQ moves to position 6 and GC falls back, operating the marking relays for setting the second trunk selector. In position 8 a marking is applied to cause hunting of the latter and in position 10, CO energizes and connects up COS, Fig. 5, which brings about release of the register-translator and completes the through connection, while the closure of contact at maintains RX, RY. Release takes place in response to a long Y frequency impulse. If the alternative route is available, but not the direct route, SY energizes and causes the translating switch CM to pick up a fresh marking over a different pair of wipers of 1C, 2C. Relay CT energizes and the trunk selectors are set as before. SQ advances from position 10 to position 15 under the control of pulsing relay Y, and PY energizes in position 11 and causes CM to pick up the direct route marking again. Wipers CM12, 13 in positions 16, 17 of SQ mark terminals of a sending switch SW to provide the two additional digits required for routing at the next exchange. Relay SS energizes in position 15 and a preliminary train of 11 impulses is sent over wires W, X by relay Y under the control of the sending switch SW, after which the two routing digits are sent. The register-translator is released in position 18 of SQ. At an exchange in an alternative route, the train of 11 impulses advances 1C to a subnormal position in which AR operates, connecting up ARS, Fig. 5, and substituting FB for MB for a purpose described below. Busy conditions. If the first trunk selector finds no idle local selector, battery on wire Y in position 3 of SQ operates MB which connects high resistance earth to wire T to operate MBS, Fig. 5, to route the call to an operator. If no idle second trunk selector is found, battery on wire Y in position 5 of SQ operates RL which opens the marking wires and connects up RLS, Fig. 5, and RM. The latter brings about a further search as described in Specification 471,764 when SQ has stepped round again to position 4, and if congestion still exists and the exchange is in the direct route, MB energizes in position 5 and routes the call to an operator. If, however, the exchange is in an alternative route, FB energizes in place of MB and connects direct earth to wire T to operate FBS, Fig. 5, to return a Y frequency signal over the incoming trunk. At the preceding exchange in the direct route, this operates FC (since ARS is back), which connects up COS, MBS to release the trunk and route the call to an operator at that exchange. If the second trunk selector finds no idle outlet, MB or FB energizes in position 9 of SQ.