Patent GB-364740-A (GB)
Title: Improvements in automatic telephone exchange systems provided with means for establishing long distance telephone connections
IPC: H04Q3/42
Filed: 1930-11-05
Abstract: 364,740. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON, 33, Kungsgatan, Stockholm. Nov. 5, 1930, No. 33288. Convention date, Nov. 6, 1929. [Class 40 (iv).] In systems in which long-distance calls are normally set up over the same switches as are used for local calls, a special trunk offering switch is automatically brought into use and set on the wanted line when this line is found busy, and is used to bring about the release of the local connection, after which the local switch automatically makes connection with the wanted line. In the system shown, calls between subscribers LAI, LA2, LA3 are set up over links SL by switches W1, W2, W3 of which the calling subscriber's switch hunts for a free link and the called subscriber's switch, selected by a register marker, hunts for the link seized by the calling line. The links may comprise two groups each having access to a register REG1 or REG2, either of which may be associated over switch GO with a marking set GRG. Long-distance calls may be set up directly by the distant operator or through a local operator represented by jack IT. The operator's switch IW hunts for a local link and, if the wanted line is idle, the marked one of switches W1, W2, W3 completes the connection. If the line is busy, the marking is transferred to terminals of a special switch TW which completes the connection and, after the operator has released the local connection, the local switch is again automatically marked and completes the call. Call between subscribers L366, L363. Line relay LA completes the circuit for magnet D366 of switch W over interrupter 2 and, when an idle link SL is found, LP (upper) operates in series with SP, locks and connects up positive busy potential over its lower winding, and connects impulse relay RI to the b wire. RV1 pulls up and connects dialling tone from 8 to secondary of TR over a wiper of RS. Relay R1 repeats the first digit to register R100, RV2 being operated during the train to complete the circuit of back-stroke magnet of RS. At the end of the train RV2 relapses and RS takes a step so that the second digit is registered on R10, the third digit being sent to R1 in a similar manner. RS moves to position 4 in which RG1 operates and switch GO is stepped until GR pulls up in series with RG2 which operates relays of the marking sets NH, NT and connects GP to the selected marking wire 16 which operates relays LR, LA of subscriber L363. This subscriber's switch W steps in the same manner as switch W of the calling party but tests over its fourth wiper, the driving circuit being opened when test relay LP operates in series with GR1 (in the marker) which operates ST which locks up and releases SP. The register is released and speaking current is fed over SB, LA. Wanted line busy The marking circuit is open at a contact of the test relay, so that GP remains inert and RB pulls up, locks and connects busy tone to transformer TR. Relays RG1, RG2 fall back and disconnect the marker from the register. Long-distance call Switch IW hunts for an idle line in the same manner as the switches W, but an impulse relay RII specially adapted for longdistance working is connected to the b wire and repeats impulses to RI. If the wanted party is idle, the connection is set up as previously described, the b wire of the long-distance line being connected to the local b multiple over a contact of ST. If the wanted party is busy, RB cannot operate since its circuit has been opened by RII, and the register and marker therefore remain in circuit. Relay TA (otherwise short-circuited by RB) pulls up and TR, TWE follow in turn so that magnet TWM drives switch TW until TWP operates over the marking wire and locks in parallel with TS which operates TGT to open the circuit of TS. TR locks up before TA releases on operation of GP in the marking circuit, and RGT pulls up to release RG1, RG2 and the marker. During the transient operation of TS, tone is connected over transformer TTR to the operator and the parties in the local call, the long-distance line being connected up over leads GL. The operator breaks down the local connection by dialling digit 1 to operate TG which releases RGT so that the marker is again brought into circuit, and operates TT which by connecting positive potential to the a wire of the wanted party, releases his relays LA, LP. Relay LA reoperates in series with LR and GP in the marker, and TT falls back to disconnect the breakdown potential. Switch W of the wanted party now hunts for the line seized by IW and the connection is completed as in a local call. The switch TW and associated relays are released when RV1 falls back.