Patent GB-212682-A (GB)
Abstract: 212,682. Relay Automatic Telephone Co., Ltd., and Mordin, R. Jan. 5, 1923. Automatic exchange systems.-In a district office system in which local calls are made without tieing up the main office trunks, when a local call is made apparatus at the distant end of the seized main office trunk sends back an impulse to the local exchange apparatus, causing it to release the main office trunk and take into use local apparatus to complete the connection. The invention is described as applied to a relay system in which connections are set up over relay connecting apparatus controlled by temporarily used impulse responding devices. A local exchange having a possible capacity of 10,000 lines is diagrammatically represented in Fig. 1, in which of the four 1000-line groups SE1 - - SE4 shown, only the connecting apparatus of one group SE1 is indicated. The main exchange or local exchange to which a subscriber belongs is represented in his designation bv one or two letters prefixed before the numerical portion of his number. For example, subscribers on the main exchange ME may be designated B****, whilst subscribers on the local exchange SE may be designated BX****. Subscribers terminating in other local exchanges belonging to the main exchange may be alllotted different second letters, such as BM****, whilst subscribers on other main exchanges accessible from the main exchange ME will be given different first letters, such as M****. In addition to the trunks OJ which extend from the group SE1 to the main exchange ME, groups of direct trunks T are provided leading to each of the other local 1000-line groups SE2, SE3, &c. These groups SE2, SE3, &c. may all be situated at one office or they may be in separate offices comprising the local exchange SE. Immediately a subscriber in the group SE1 removes his receiver the calling line SL is extended to a main exchange impulse recorder IRM, over a feed relay group ABF and a relay connecting group FSC at the local exchange, a main exchange trunk OJ, and a repeater REP and recorder connector RC at the main exchange. The recorder IRM receives the first one or two series of impulses corresponding to the letter portion of the wanted subscriber's designation, and determines whether the call is for a line accessible from the main exchange or for a line in the local exchange to which the calling line belongs. In the former case the recorder IRM " marks out " a junction leading in the required direction, whilst in the latter case it causes an impulse to be sent back to the feed relay group ABF, where the main exchange trunk OJ is released and a local recorder FER is temporarily associated with the calling line. The next series of impulses is received by this recorder FER, which marks out a junction T to the wanted 1000-line group, where (assuming the wanted line is in the. group SE1) a temporarilyused recorder F2R responds to the remaining digits and marks out the wanted line. Calls from the main exchange ME to the local exchange SE come in on junctions IJ, a temporarily associated recorder IJR responding to a series of impulses and marking a junction to the wanted 1000-line group, in which the connection is completed as in the case of a local call. Local calls. Upon a subscriber lifting his receiver his line is extended in known manner to a feed relay group, Fig. 2, the relays I, G, GX, and BB of which energize in the order named over circuits 2, 3, 4 and 5. The guard relay GX closes a circuit 6 for a relay MX1 which completes circuits 7 and 8 for an outgoing trunk marking relay OTM, Fig. 3, and a main exchange trunk group relay JM, Fig. 3<a>. Relay OTM energizes a link marking relay OLM1 corresponding to the first idle outgoing link, and a circuit 10 is closed for a group relay GS, Fig. 3<a>, which locks up and closes a circuit 11 for a relay SS which causes the energization of a marking relay OJM associated with the first idle main exchange trunk OJI, to which the calling line is extended by connecting relays OJC, OLC, Fig. 3, which energize in a circuit 13. A holding circuit 14 is now completed, over which the connecting relays OJC, OLC are held, and the relay MX2, Fig. 2, and the link- and trunk-busy relays OLB, Fig. 3, OJB, Fig. 3a, are energized. The relay MX2 initiates the relapse in turn of relays MX1, OTM, JM, GS, and SS. At the main exchange end of the trunk OJ1, the repeater impulse relay I, Fig. 4, responds in a circuit 15 and closes circuit 16 for the guard relay G, which completes a circuit 17 for the starting relay FI, Fig. 5, of a recorder connector, which in known manner takes into use an idle recorder, the preparing relay P of which is energized. The impulses corresponding to the first letter B of the wanted subscriber's number are repeated by the impulse relays I, Figs. 2 and 4, and in known manner cause the energization of a relay ST, Fig. 5, whilst the next impulse series corresponding to the second letter X energizes a marking relay THD9, which prepares a circuit 31 which is completed on the response of the marking control relav MC at the end of the second impulse series, and energizes a relay JR to initiate the release of the main exchange trunk OJ1. The relay JR removes battery from the B wire, thereby unbalancing the repeater relay IS, Fig. 4, and energizing the relay ICO which removes battery from the A and B wires at the feed relay group, Fig. 2. Before the main exchange recorder, Fig. 5, is released by the relapse of the slow-release relay RSR1, a circuit 33 is closed for a relay S1, Fig. 4, which energizes a relay RS1, which in turn energizes a relay RS2 and earths the A wire over circuit 35. Relay RS2 closes a holding circuit 34<1> for relay RS1. The A wire is now earthed, and the B wire disconnected at contact RSC, thereby unbalancing the relay IS, Fig. 2, and causing the energization of the relay ICO which locks up, closes circuit 37 for relay S1, and de-energizes the relay BB,. which, however, does not relapse until a relay RR has responded in a circuit 38. A trunk release relay JR1 is now energized in a circuit 39 and energizes a relay JR2, which locks up and breaks the holding circuit 14, thereby releasing the main exchange connection. Relay JR1 also de-energizes relays RR, ICO, the former of which interrupts the circuit of relay JR1, whilst the latter re-energizes the relays I, BB, and causes the relapse of relay IS. The relay JR2 also closes a starting circuit 41 for the relay FI, Fig. 6, of a local exchange recorder connector, which selects an idle local recorder of well-known construction. The third series of impulses energizes a marking relay, say THM2, the response of which closes a circuit 60 to energize a marking relay JML, Fig. 3b, associated with a group of junctions leading to the wanted thousand section or the wanted office of the local exchange. An idle junction t is selected in known manner and connected to the calling line in a manner similar to that described with reference to the connection to the main exchange trunk OJ1. On the response of the busy relay ISB, Fig. 3<b>, a circuit 70 is closed and initiates the selection of a final three-digit recorder F2R, Fig. 1, which responds to the last three digits of the wanted number and brings about the completion of the connection in known manner. Calls to the main exchange ME. The dialling of the letter B energizes the relay ST, Fig. 5, of the main exchange recorder as before, whilst the transmission of the thousands digit energizes a marking relay, such as THD2. which completes a oircuit 50 for a junction marking relay, similar to JML, Fig. 3<b>, which causes the calling line to be extended to an idle junction leading to the wanted thousands group in the main exchange, where a temporarily-used three-digit recorder is set by the three remaining digits and causes the completion of the connection. Calls to other local exchanges belonging to the main exchange ME. The dialling of the first two letters BM energizes a marking relay, say THD8, Fig. 5, which completes a circuit for a marking relay, similar to JM, Fig. 3<a>, which causes the calling line to be extended to an idle junction leading to the wanted local exchange. Calls to other main exchanges. The dialling of the first letter, say M, causes the energization of a marking relay, such as MX3, Fig. 5, which completes a circuit 51 for a trunk marking relay, similar to JM, Fig. 3a, which causes the calling line to be connected to an idle trunk terminating at the wanted exchange in a repeater, similar to that shown in Fig. 4, which picks up an idle recorder which in response to the first digit it receives marks out a junction to the wanted thousand-line group in the main exchange M or to an associated local exchange. The marking wires can be jumpered to the marking relays MX in any desired manner.