Patent GB-399866-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1932-04-14
Abstract: 399,866. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, and DIXON, R. G., 162, Westmount Road, Eltham Park, both in London. April 14, 1932, No. 10743. [Class 40 (iv).] Junction lines terminate at a private branch exchange in two linked two-directional switches JS<1>, JS<2>, Fig. 6, the first of which on an incoming call hunts for an idle "operating extension," i.e. one of a number of extensions capable of both establishing and answering mainexchange calls, whilst the second switch JS<2> may be controlled by the answering extension to set up a local connection to a third party to whom if desired the main-exchange call may then be transferred. For outgoing calls, the switch JS<1> acts as a finder, an idle junction being taken into use in response to the dialling of the digit 9 to the connector of a local link, Figs. 2, 3. Certain extensions are not per mitted to establish outgoing calls directly owing to the absence of multipling between the local finder fourth-wire banks PCW and the corresponding banks of the junction switches but may call an operating extension for this purpose by dialling the digit 0. Ordinary extensions have standard sets and initiate the establishment of a third-party enquiry connection by transmitting a single impulse, and in order that the junction apparatus may distinguish between such a control impulse and ordinary selecting impulses transmitted over the junction when the main exchange is automatic, the control impulse is only effective after a definite time-interval. Operating extensions, however, are permitted to establish enquiry connections immediately and for this purpose their sets are provided with earthing keys KO. After an enquiry connection has been established, it may be released and the original connection restored by the transmission of a further impulse or alternatively the main-exchange call may be transferred to the third party by the original extension hanging up. If the third party is busy in a local call, this may be interrupted, also by the transmission of a single impulse. Further transfers may take place in a similar manner, the switches JS<1>, JS<2> being used alternately for this purpose. In a local enquiry call, a feed is included in the junction apparatus but for main-exchange connections the extensions are connected metallically to the junction. Local call. The operation is similar to that described in Specification 389,623. Outgoing call from restricted subscriber. The dialling of the digit 0 causes the operation of relay LM over bank CB. LM connects relay TR to rotary interrupter' contacts rc1 and completes a circuit over contacts tr7 for rotary magnet RC so that hunting occurs over the tenth level for an idle operating extension. When one is found, relay H operates, releasing LM, and ringing current is supplied ove TR. When the extension replies, both parties hang up and the call is set up by the operating extension and then transferred to the originallycalling party in the manner described in subsequent paragraphs. Outgoing call set up by operating extension. The dialling of digit 9 causes the operation over bank CB of relay F which marks the calling line and level in the banks of junction switches JS<1> and operates start relay JST, Fig. 8. Relay JCI interacts, if necessary, with magnet JDM to select an idle junction, relays JT, TA then operating. Relay BJ, Fig. 7, of the selected junction energizes over wiper JAS8, completing a circuit over wipers JAS1, JAS3, for vertical magnet VJ<1> which interacts with relay JG(i). When the marked level is reached, relay JG(ii) is held energized over wiper JAS5 and banks JB, Fig. 7, and FB, Fig. 2, in series with relay JRD. Rotary stepping then takes place in a similar manner and when the calling line is reached, relay JHC operates over wipers JAS7, PC1, Fig. 6, PC, Fig. 2, and bank CA, Fig. 3, in series with relay CO which releases the local connection. Relay JHC closes a circuit over wiper JAS2 for relay FA which switches through the calling line to the junction over relays JA, JD, and the connection is completed over the junction in known manner. Third-party enquiry connection by ordinary extension. A thermostat TTH after an interval of 20 seconds operates relay Y(i) so that the transmission of a single impulse after this interval energizes relay JP(i) which at the end of the impulse locks in series with JQ(i). Relay JQ closes a holding bridge across the junction and connects the calling line to relay AJ which in turn operates relays BA, CA. The tens digit of the third party's number is repeated to magnet VJ<2> of switch JS<2> and at the end of the digit relay CA relapses and relays E, EA, EB operate, re-energizing CA over rotary offnormal contacts nr<1> of JS<1> and rotary normal contacts nr<2> of JS<2>. The units digit is repeated to rotary magnet RJ<2> and when CA again relapses relay HB operates between the relapses of EA, EB. When EB does fall back ringing current is connected over relay JTR and when the third party replies relay JTR operates and connects up relay DJ. If the third party is busy in a junction call relay E remains locked over ground on wiper PC<2> and tone NUT is connected up. If the third party is busy in a local call, relay E releases but EA remains locked over wiper P<2> and busy tone BT is supplied. The calling party may break in on such a connection by dialling a single impulse causing the operation of BI and, at the end of the impulse, HB. JTR also operates to cut. off ringing. In any case the calling party may return to the junction call by dialling a further impulse which at its commencement energizes the differential winding (ii) of relay JP to release this relay, and at the end releases also JQ. Release magnet ZJ<2> of switch JS2 is now energized in series with winding (ii) of relay BA and the enquiry connection is released. Transferring junction call to third party. If the original calling party hangs up, relay AJ releases, transmitting an impulse which by energizing winding (ii) of JP releases this relay. Relay BA then releases followed by JQ, and relay EB energizes to complete the circuit of release magnet ZJ<1> of switch JS<1>. When release is complete, the release of off-normal relay ON energizes relay FB which releases FA. The third party is now connected over relays JA, JD to the junction and further enquiry or transfer connections may be effected in a similar manner if desired. Enquiry or transfer connection by operating extension. This may be effected immediately, independently of thermostat TTH and relay Y, by the operation of key KO, causing the release of JA whilst JD is held and thus transmitting an impulse to the relay group JP, JQ. Incoming call. Ringing current over the junction energizes relay IJRD. Relay ST operates and (1) energizes start relay JST, Fig. 8, (2) switches over from bank JB, Fig. 7, to bank JA so that the first level, in which all the operating extensions appear, is selected, and (3) connects ground to a multiple lead JPO, Fig. 6, which ground is extended to conductors 21 of all other idle junction circuits so that the assigner will connect to the actual junction in use. When the first idle operating-extension is found, relay FA operates and ringing-current is connected up over relay JTR. The call may be transferred as desired in the manner already described. Night service. The operation of key NSK energizes relay NS which grounds wiper P over 11th-step contacts SI so that the switch JS<1> will hunt automatically to its 11th contacts to which a special night service line NSL is connected. Faults. A thermostatic device TH, Fig. 5, after a predetermined interval short-circuits relay S and releases relay'RC so that a new link is assigned. In the junction-assigner, Fig. 8, two thermostats TH<1>, TH<2>, are employed alternately under the control of a pair of relays P, Q.