Patent GB-391445-A (GB)
Title: Improvements in or relating to automatic telephone exchanges
IPC: H04Q3/58
Filed: 1931-10-26
Abstract: 391,445. Automatic exchange systems. TELEFONAKTIEBOLAGET L. M. ERICSSON, 33, Kunsgatan, Stockholm. Oct. 26, 1931, No. 29693. Convention date, Oct. 27, 1930. [Class 40 (iv).] In a system in which a talking connection is set up over hunting switches under the control of a register-marker, a calling'line is connected non-numerically over a link SL1 comprising tandem switches AS, SV to a feed circuit FL having access to a register-marker MRE, a second link SL2 selected numerically by' the marker hunts for the feed circuit FL and for a free intermediate trunk GL2, and the connection is completed over a third link SL3 which hunts for the marked wanted line and for the intermediate trunk GL2 selected by the switch SG. Connection to and operation of registermarker. The calling subscriber's combined line and cut-off relay LR operates partially to mark the line calling, in series with common .relay LG which operates relays IA in each idle link SL1. Stepping magnets ASM are thus operated and when the calling line is found relay IT1 operates transferring the driving circuit to magnet SVM of switch SV. When an idle feed circuit FL associated with an idle register-marker is found relay IT2 operates in series with relay ST, which connects up.the register-marker. Relays RA, RH1, RH2 operate and dialling tone is supplied from source DS. The-three dialled digits are repeated by relay RA to magnets REM1. REM2, REM3 respectively, relay RV causing the sequence switch SO to advance one step at the end of each digit. In position 4 of SO, relay RG operates completing a circuit 25 for marking-relays LH41... LH44 of the selected hundreds group, circuit 26 for tens-marking relay LT2 and circuit 27 for marking the wanted line B. Completion of talking connection. If the wanted line is free, relay RL energizes over circuit 27, and a circuit 31 is completed for start relay US of the first idle link SL3 of the group giving access to the wanted line. Magnet LVM is thus operated and when the marked line is found relay UT1 operates to connect up magnet SSM. In the meantime hundreds relay LH44 has energized start relay GS of the first idle link SL2 causing magnet SFM of switch SF to operate. When the feed circuit FL is found, relay GT1 operates over circuit 37 connecting up magnet SGM and when an idle: intermediate trunk GL2 is found relay GT2 operates. Switch SS then hunts for the selected trunk GL2 which is marked over the circuit 44, and when it is reached relays UT2, SBR- operate and connect up ringing-current from source PW. When the called subscriber replies, relay STR energizes to cut -off the ringing- current and feed relay SB operates over the loop. Relay SBR also completes circuit 47. for relay SHA which extends the calling loop to feed relay SA, releasing relays ST, RA, RH1, RH2, and thereby restoring the registermarker to normal. Busy test. In position 4 of switch SO, when relay RG operates a stepping circuit 28 is closed for advancing the switch slowly,:to position 10. If the wanted line is idle the operation of relay RL breaks circuit 28 but if this relay has not operated by the time position' 10 is reached, relay RV operates to connect up a busy tone BS. This method of making the busy test forms the subject-matter of Specification 391,446. All links busy. If all the links SL2 or SL3 are busy, circuits 35, 31 are extended over conductor 58 to relay RU, which gives a busy tone. Inter-exchange working. The outgoing ends of junctions to a main exchange or to a P.B.X. may be connected directly to the wipers of switches SS instead of to the banks of switches LV. Similarly their incoming ends may be connected directly to the wipers of switches SV.