Patent GB-299033-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/58
Filed: 1928-07-31
Abstract: 299,033. Associated Telephone & Telegraph Co., (Assignees of Ruggles. L. la F.). Oct. 21, 1927, [Convention date]. Semi-automatic exchange systems; party-line systems.-In a system in which operators at an operating centre control the selectors at a number of small exchanges, the same junctions which are temporarily used for controlling the setting up of a call internal to a small exchange ara used as conversation junctions in calls that pass through the operating centre, e.g. in calls from one small exchange to another and in toll calls. A calling subscriber A, Fig. 1, is connected by switches LS, SS to a junction 314, 315 terminating at the operating centre in the equipment shown in Fig. 3 and at the exchange in a selector S which serves for incoming calls. The operator at board LB answers the call and extends it to another exchange, or if an internal connection is wanted she dials back over the junction to set a selector SL and connector C, the junction being released as soon as the operator unplugs it. If a toll connection is wanted the operator at LB tells the subscriber to hang up and passes the call to a toll operator at TB, who has access to the same junctions, and who in due course recalls the subscriber over selector S and connector C. The operators' calling and supervising signals are controlled by reversals of potential on the junction. At the toll board standard loop supervision is provided, at the board LB "dark-shelf" supervision. the difference being brought about bv a relay 303 which is energized from jack J2 but not from J1. The lines at the exchange shown are tenparty, ringing current of different frequencies being applied to one or other leg by a switch PS set by an extra digit. For reverting calls, the operator dials a number 1xx to seize a ring- back switch RBS, Fig. 5, and to set it to a position denoting the party-line numbers of both the calling and wanted parties, and as soon as the operator has released the junction and the calling subscriber has hung up, ringing currents characteristic of the calling and wanted parties are alternately sent back to the calling line. When a false call is received from a faulty line, the operator dials the digit 3 to connect the line to a trunk TC2, which marks it out-of-order to connectors. Internal call. When a call is extended by a line switch LS to selector SL, relay 121 sets the switch SS into action to find a junction 314, 315. Relay 406 switches the junction to relay 122, which is reversely connected in comparison with line relay 407 of selector S, so that relay 301 is energized and lights lamp CL. The operator plugs into J<2>, energizing relay 302 which lights a busy lamp BL and bridges a polarized relay 306 across the, junction. Having ascertained the wanted number the operator plugs a dialling- cord DC into DJ2 and dials. Relay 310 connects the junction to the dialling circuit and relay 313 is energized when the dial is off-normal to remove a short from this circuit. Selector SL and connector C. Relay 122 is energized for the first time when the operator plugs in her dialling-cord (the junction resistance having previously been too high) and energizes 123, which short-circuits the calling line to prevent clicking noises during dialling and to keep 121 energized after the switching relay 126 has disconnected it from the calling line. Selector SL operates in the usual manner to find a connector C, and relay 203 is energized over the calling line and energizes 204. The second digit is repeated by relay 122 over a fourth wiper 129 to vertical magnet 215 and the third digit to rotary magnet 216. Busy test. If the line is busy, relay 207 is energized from 212, locks itself, opens the impulse circuit 147, and sends back busy tone from BT. Party-line ringing. If the line is idle, relay 209 is energized from 212, locks itself, and extends the impulse circuit 147 to switch PS, which is operated bv the final digit. On the relapse of relay 208 at the conclusion of the digit, relay 207 is energized from an off-normal contact of PS, closes a ringing tone circuit RBT, and connects wipers 211, 214, to 221, 222. According to the setting of PS, ringing current of a particular frequency is connected intermittently to one or other leg of the called line and the other leg is connected to relay 206. When the subscriber answers, relay 206 is energised, locks itself, disconnects PS, and switches through, and the line, is fed from the reversing relay 201. Release of junction. The operator unplugs the junction as soon as she has finished dialling. Relays 122, 123, 121, 401 thereupon fall back, and the junction is freed. Reverting call. The operator dials a number 1xx of which the first digit causes the selector SL to engage a ring-back switch RBS, Fig. 5. Relays 503, 504, 502 are energized, and the second digit is repeated over 129, 143 to vertical magnet 518. The relapse of the parallel relay 506 unlocks 502, so that the final digit is repeated to rotary magnet 519. Relay 505 is energized and locks itself. When the operator takes down her plugs, relays 122, 123, 121 fall back and a, bridge that was closed across the calling line through a first-level shaft contact 119 is opened. This enables relay 503 to fall back when the calling subscriber hangs up, and also enables hang-up tone from HUT to reach the calling subscriber, who hangs up. Relay 503 falls back and energizes 501, which keeps 504 energized and switches the wires 141, 144 to ringing circuits, which send back alternately ringing currents appropriate to the calling and wanted substations. Relay 502, which determines to which wire, 141 or 144, ringing current shall be sent, is steadily energized or de-energized or is alternately energized and deenergized by interrupter 11 according to the wiring of the terminal engaged by wiper 510, and relay 509 is similarly controlled over wiper 511 to select, in conjunction with wipers 512, 513, the appropriate frequency or frequencies of ringing current. For example, if the switch RBS has been set on terminals 514 - - 517, relays 502, 509 are both intermittently energized and ringing current of 50 cycles is sent back over 141, 101 alternately with ringing current of 66 cycles over 144, 102. When either subscriber lifts his receiver and bridges the line, relay 508 energizes 507, which locks itself, opens the ring- ing circuit, de-energizes 501, and energizes magnet 520 to restore the switch RBS. Relays 503, 502 are again energized. When both subscribers hang up, 503, 504 fall back and the selector SL is released. Toll call. A subscriber A desiring a longdistance connection is connected as before to an operator at the board LB, Fig. 3, who fills up a ticket and passes it to a toll operator at TB and tells the subscriber to hang up. In due course the toll operator plugs into the jacks J1, DJ1 of an idle junction and dials the calling number all except the final digit. Connection is made to the calling line by the incoming selector S and connector C (which in this case is set by impulses in the loop 145, 148 and not in the circuit 147). Assuming that the line is found idle, the operator then unplugs the dialling jack DJ1 while she gets connection with the wanted distant number (If, during this interval, another subscriber on the calling line lifts his receiver, an auxiliary back-bridge relay 202 is energized, closing a local circuit for line relay 203 while opening the line 145, 148. This deenergizes the polarized relay 306 to give the operator a signal, in the same way as though the line current had been reversed, but without the risk that reversal would involve of momentarily de-energizing relay 203 and generating a false impulse, which at this stage would take effect on the switch PS. The operator throws her speaking key and instructs the intruding subscriber to hang up). After getting the wanted number the toll operator again plugs into DJ1, dials the final (party-line) digit of the calling number, and unplugs DJ1. The digit sets the switch PS and the calling subscriber is selectively rung. When he replies, relays 206, 201 are energized and the reversal of current in the circuit 145, 148 de-energizes relay 306, which bridges the cord through relay 308 to give answered supervision. Release depends on unplugging of the jack J1, the junction being opened when relay 302 falls back. Call from a near-by exchange. The operator at the board LB plugs into J2, DJ2 and dials the wanted number, the connection being set up by the incoming selector S and connector C and the subscriber selectively rung by the switch PS. Relays 302, 303 are energized when J2 is plugged. and 308 is bridged across the cord and locks itself. When DJ2 is plugged, relays 304, 305, 310 are energized and 308 is unlocked. When DJ2 is unplugged 304, 310 fall back, 306 is energized over the junction, and the cord is bridged through an inductance 307. When the subscriber answers, polarized relay 306 falls back, and the cord is again bridged through 308 instead of 307. When the subscriber hangs up, relay 306 is energized again and opens the bridge through relay 308, but this relay remains locked bv its upper winding so that the bridge through 307 is not now closed. In this way "darkshelf" supervision is given, the cord lamp being extinguished (by closure of the circuit through 307) when the operator withdraws her dialling plug, irrespective of the called subscriber'; reply, and lighting again when the called subscriber disconnects himself. In the case of a toll call, described above, relays 303, 304 do not come into action, there is no circuit through 307 and no locking circuit for 308, and supervision is of the standard loop type, the cord lamp not being extinguished until the subscriber replies. Line out of order. An operator getting a call due to a faulty line dials the digit 3 to connect the line to an out-of-order trunk TC2, which grounds the circuits 150, 128, 111, 104