Patent GB-826933-A (GB)
Title: Signalling on telephone systems
IPC: H04Q1/44
Filed: 1954-10-25
Abstract: 826,933. Automatic exchange systems; voice-frequency signalling. ROBINSON, W. L., and PERKINS, G. H. Jan. 25, 1956 [Oct. 25, 1954], No. 30664/54. Class 40 (4). Signals other than calling, clearing, and dialling are transmitted between a parent exchange and an unattended satellite exchange by voice frequencies over the speech path while the telephones at the ends are disconnected from that path. In the embodiment described the satellite is a unit automatic exchange of the type known as a U.A.X.13, suitably modified, and signals and speech are conveyed between the exchanges on a multi-channel carrier link. Calling, dialling, and clearing signals are transmitted by steady state changes in carrier level, which cannot be simulated by speech currents, and other signals are sent by voice-frequency tones over the speech path. General operation. Low-level carrier is normally transmitted in both directions over the carrier link. When an ordinary satellite subscriber dials " 0," a relay group at the satellite seizes a junction and locks high-level carrier on it, lighting an operator's calling lamp at the parent exchange. If the calling subscriber is at a coin-box substation, the operation is the same except that a tone " Y " is applied to the carrier channel, causing a tuned relay at the parent exchange to respond and light the calling lamp allotted to coin-box substations. If a satellite subscriber dials " 9," a carrier channel is established and a different tone " X " is applied to it, the calling subscriber's line being momentarily disconnected. At the parent exchange a tuned relay connects the carrier channel to the automatic equipment which responds to dialling in the normal way when the calling line is reconnected. The usual manual hold and trunk offering facilities are provided. Carrier link terminal, Fig. 8. Each exchange has such a terminal, with outgoing and incoming lines L1 and L2 respectively. In idle conditions, low-level carrier is transmitted in both directions. A change to high-level carrier gives a calling signal (forward) or a supervisory signal (backward), and a subsequent reversion to lowlevel carrier gives the clearing signal, dial impulses being transmitted as interruptions of the carrier. Outgoing speech from the exchange is received at terminals HYB1, HYB2 and sent through modulator M to line L1 (with added carrier). The carrier with speech sidebands from the other exchange arrives on line L2, and the speech is demodulated at DM and passed through amplifier RA to a winding of the hybrid coil HYB. The received signal is applied also to signal receiver SR controlling a relay HY. An outgoing call is extended through the line finder and group selector to the carrier equipment, operating relays AA and SZ to raise the level of the transmitted carrier by cutting out an attenuator pad R1, R2 and to increase the gain of amplifier RA so that the operators may converse on the low-level carrier on line L2. At the receiving end, the high-level carrier operates relay HY which then repeats to the selectors the dialling impulses transmitted, as interruptions of the carrier, by relay AA at the calling exchange. When the called subscriber answers, the usual reversal of potential brings up relay AA at the called exchange and high-level carrier is returned to the calling exchange to operate relay HY there. This sends a supervisory signal to the exchange equipment and also releases relay SZ to reduce the gain of amplifier RA. The conversation may then take place over the established carrier channel. When the parties hang up, the relays AA are released and the carrier reverts to its lower level, releasing the relays HY. Fig. 9 shows the relationship of the other Figures to each other and to exchange equipment not shown therein. Relay operations at satellite UAX13, Figs. 1-5. (i) Ordinary satellite subscriber dials " 0 " to call operator at parent exchange. Battery is extended from the group selector over a 2000 ohms resistance to terminal MGS1, which is connected to the M-wires of all the selector levels except 1, 2, 3 and 9. Relay WS operates, but the current is not sufficient to operate CB. The calling loop extended from the group selector to terminals GS1, GS2 brings up relay A which energizes relay B (Fig. 3). This earths terminal GSP connected to the group selector P-wire and also brings up relays WA (Fig. 1) and BD (Fig. 4). Relay WA keeps the calling line disconnected from the speech path, terminating hybrid coil HYB on resistor YR, while relay BD starts the ringing generator and operates relay HJ (Fig. 3) followed by DD (which connects ringing tone), SK (which earths the outgoing P-wire) (both in Fig. 4), DB (Fig. 3), and AA and SZ (Figs. 4 and 8) which call the parent exchange by the application of high-level carrier as described above. The sluggish relays HJ and SK contribute to the junction guard period, and SK also delays the connection of supervisory relay DZ (Fig. 5) to prevent metering if the circuit is seized from both ends simultaneously. When the operator at the parent exchange answers, high-level carrier is returned on line L2 to operate relay HY (Figs. 4 and 8) as described above. This energizes relay HZ (Fig. 4) to release SZ and bring up DZ which releases DD, removing the shunt from relay J (Fig. 3) which operates to trip the ringing and energize relay JB (Fig. 4) which extends the calling line to the carrier equipment. Relay DD re-operates, followed by relays JA (Fig. 3), D (Fig. 4), DC (Fig. 2), and DE (Fig. 2) which reverses the potentials of the incoming speech wires from the group selector and also brings up relay DF (Fig. 1). Relay DC, which maintained A operated during the operating time of DE, now falls back slowly, and the speech connections are complete. (ii) " 0 " level call from coin-box substation. This is similar to the ordinary call described in (i) above, except that battery from the group selector is extended to terminal MGS1 over a resistance sufficiently small to permit relay CB to operate after WS, so that WR (Fig. 1) operates after B and SY (Fig. 4) after HJ, connecting " Y " tone to the carrier channel. The operation continues as in (i), SY releasing to disconnect the " Y " tone following the operation of HZ when the operator answers. (iii) Satellite subscriber dials " 9 " to obtain access to automatic equipment at parent exchange. In this case the M-wire of the group selector outlet is connected to terminal MGS2. If the call is from an ordinary subscriber his earthed meter is connected to the M-wire. In the case of a coin-box call, battery is connected over a low resistance in order to operate relay CB, which sends signals to the auxiliary equipment for multi-metering and route discriminating AEMR, whereas an interdialling exchange extends positive battery to over-ride route-barring arrangements in AEMR. Relay A operates to the calling loop, and relays B, BD, HJ, DD, SK, AA, and SZ operate as for an " 0 " level call described in (i) above, but WS, WA, and DB remain inoperative so that the operation of HJ brings up relay SX (Fig. 4) to apply " X " tone to the carrier channel and disconnect the calling loop from it. When the calling subscriber dials the wanted number, relays A and AA repeat the impulses over lead PU to the equipment AEMR and over line L1 as breaks in the carrier to the parent exchange. The first relapse of A brings up relays C (Fig. 3), CC (Fig. 4), CA (Fig. 2), CZ (Fig. 4), BB (Fig. 2), and MD (Fig. 2), and relay SX falls back to disconnect the " X " tone. Relay CZ bridges condensers QA, QB and resistors YQ, YP across the line and terminates the hybrid transformer HYB on resistor YN. Relay MD prepares a circuit for busy and N.U. tones from the equipment AEMR over lead TN. Between impulse trains relays C, CC, CA, and CZ are released, relay CC sending signals over lead C to AEMR. Ringing tone is received from the parent exchange and the called subscriber is rung. When he answers, high-level carrier is returned on line L2, relays HY, HZ and DZ operate and SZ falls back as in (i) above. Relay D is energized to release MD and complete the " S " pulse circuit of relay DA (Fig. 3), and relays DC, DE, and DF interact as before. The first " S " meter pulse operates DA which locks, completes the " Z " pulse circuit for relay DB (Fig. 3), and prepares the metering lead to M in AEMR. This metering circuit is completed at the next " Z " pulse by the operation of DB, which also breaks the " S " pulse and locking circuits of DA and the lead PU to AEMR and brings up relay J followed by JB which connects the calling line to the carrier equipment. At the end of the " Z " pulse DA releases to trip the ringing and disconnect the metering lead from AEMR. (iv) Forced release is effected by the operation of relays TM and PR (Fig. 3) by means of the usual time pulse equipment if the calling subscriber fails to dial further after dialling " 9 " or if he fails to clear after the called party has cleared. (v) Incoming call. Relays HY and HZ respond to high-level carrier received from the parent exchange. If the satellite is not completely released from an outgoing call, relay SK may be still operated. In this case HZ brings up relay BR (Fig. 5), which operates relay L (Fig. 5) and also initiates release of any relays still operated from the previous call before finally releasing itself following the relapse of SK. Normally, however, relay L is operated directly by HZ. Relay BA (Fig. 3) operates, energizing relays CC (Fig. 4), which busies the group selector outlet at GSP, and BC (Fig. 4) which prepares a circuit for relay JA (Fig. 3) in case of premature dialling and connects relays HA and HB (Fig. 5) to linefinder control sets (LFC) Nos. 1 and 2 respectively. If LFC No. 1 is free and is the first choice (or is the second choice and the first is busy), HA operates, joins leads ST and STR to start the linefinder control circuit, ma