Patent GB-765926-A (GB)
Title: Improvements in or relating to telecommunication systems
Inventor: DAVISON ALAN
IPC: H04Q3/52
Filed: 1952-05-13
Abstract: 765,926. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. May 11, 1953 [May' 13, 1952], No. 12063/52. Class 40 (4). In a 10,000 line system using gas discharge tubes as described in Specification 765,925, voice-frequency supervisory signalling (e.g. ringing, metering, holding and releasing) is carried out on a time division basis. A connection is held by tubes controlled by voicefrequencies from the two parties. When voicefrequency is cut off there is a delay of 150 millisecs. before the corresponding tube is extinguished so that either of the two voicefrequencies can be interrupted, as for dialling, without releasing the connection. Signalling between originating and terminating trunk connecting circuits may be carried out for 50 millisecs. in each direction alternately. Three of the five 10-millisec. periods in one direction may be used for holding and two periods in the other direction may be used for metering, the spare periods being available for other signals. But, in the embodiment described, the holding signal takes all the five periods in one direction and the metering signal only two periods in the other direction. Ringing, metering, holding and release signals are gated under the control of common equipment. Ringing and metering signals are also transmitted from the outgoing trunk connecting circuit to line equipment on a time division basis over a common circuit. The trunking arrangements, Figs. 1, 2, are the same as in the previous Specification. Figs. 3 to 7, when placed side by side, show as much of a single connection as is necessary to understand the invention. When a line SL is in calling condition, tube VK4 is biased so as to strike and to conduct only temporarily when scanned by one of a series of testing pulses transmitted through condenser C1 in a control circuit LF/FS.CC. Tube VK5, biased over R1, strikes and remains conductive. Tubes VK15 in all links (see Fig. 4) available to the line are primed over lead SU2 from the control circuit which then selects the first free originating trunk connecting circuit OTCC available to the calling line and operates VK15 over SU3 to make the connection to the trunk connecting circuit. In the speech circuit, tubes VK12, VK13 follow VK15 directly and VK6, VK7 follow VK9 which strikes when VN6, VK11 follow VK15. With the line loop on SL closed, a rectifier gate MR passes voice frequency from a source VF1 over lead P1, tubes VN5, VK9, VN6, VK15, lead P2 and transformer TR3 to a tube VT1 which repeats dialled impulses over lead CL2 to circuit CON and register REG. The voice frequency from VT1 is also rectified at RVD1 to make VT2 contact and to extinguish VK19 which is normally conductive. A delay circuit ensures that VK19 cannot strike for 150 millisecs. after stoppage of the voice frequency. Tubes VK19, VK20 are used in the release of the connection later. Over lead SU4, tubes VK25 are primed and tubes VN9 are struck in all group selector links available to the originating trunk connecting circuit. Tubes VK27, VK28 follow VN9 and prime VK31 in all such links. The common equipment GSCC now marks the equipment LF/FS.CC, serving the called line over leads SU6, SU7, SU8, tube VN2 strikes in the called line circuit, VK5 follows and the line finder/final selector operates as for a calling line except that all idle terminating trunk connecting circuits are now marked. The first free terminating circuit available to both the selected originating circuit and the called line is selected by a hunting operation, and a pulse is applied to tube VK43 in the selected terminating circuit. A pulse on lead SU5 from the control circuit GSCC strikes VK31 which is followed by VK29, VK30, VN11, VK26, VK25, VK24, VK23 to complete the connection. Tube VK27 is backed off to mark the link busy. Ringing. Tube VK42 is primed by VK43 and is struck by the next ringing control pulse on lead RF4. A pulse transmitted over lead DC1, Figs. 7, 4, strikes VK14. Tube VK8 follows and a pulse is applied to both tubes VK2, VK3 in the called line circuit but only VK2 strikes as there are ringing control pulses at this time in leads RF1, RF2, RF3, RF4 but no control pulses on MF1, MF2. The pulse on RF3 is 2.5 millisecs. after the pulse on RF4. The pulses on RF1 &c. control bursts of ringing, lead RF1 being connected to a source of interrupted ringing current. H.T. is supplied on RF2 for only one second in three. When the call is answered, voice-frequency is transmitted from VF1 in the final selector to lead P2 in the terminating trunk connecting circuit TTCC where it makes tube VT7 conductive and extinguishes VT6. Tube VK35 strikes and is followed by VK34, VK44. Tube VT9 becomes conductive but with no effect at this stage. When VK44 strikes, VK43 extinguishes and VK42 stops the ringing pulses on DC1. The ringing pulses on leads RF2, RF4 fall within 30 millisec. periods in the 50 millisec. periods used for signalling right to left. A signalling circuit between the originating and terminating trunk connecting circuits OTCC, TTCC is conditioned for transmission for 50 millisecs. in one direction and for 50 millisecs. in the opposite direction alternately under the control of periodic biasing potentials on leads VFG1, VFG2. With VK20 extinguished and a biasing potential on VFG1, voice-frequency from VF2 is gated by rectifier MR3 and is transmitted over lead P3, tubes VK25, VN8, VN11, VK31, lead P4, rectifier gate MR8 to transformer TR9. Similarly with VK32 extinguished, voice-frequency from VF3 is transmitted through rectifier gates MR7, MR4 leads P4, P3 to transformer TR6. Holding. To hold the connection VK38 is backed off by pulses on P4 controlled by the calling party and VK36 is maintained conductive by the voice-frequency from the called party. Metering. When tube VK34 strikes as described on reply, tubes VK32, VK33 follow during a metering pulse on leads MF3, MF4 to transmit a voice-frequency signal to the originating terminating trunk circuit where VT4, VT3, VK18, VK17 respond to strike VK14 over lead DC1. Tubes VK8, VK3 follow, the latter being primed over MF1, MF2, and the meter MTR is operated. Tube VK33 extinguishes VK34 and is itself extinguished almost immediately by capacitor C12 so that a second metering pulse cannot be transmitted. The simultaneous metering pulses on leads MF2 to MF4 take 20 millisecs. of each right to left 50 millisecs. period whilst the pulses on MF1 last 300 millisecs. each. . Release. If the calling party hangs up first, the voice-frequency from VF1 is cut off and both tubes VK19, VK20 strike at the next reset pulse on RSF1, RSF2. Rectifier gate MR3 is closed to stop the transmission of voice-frequency from VF2. The connection from the calling line to the first group selector is released when tube VK20 strikes and is followed by VK16, VK21, VK22. Tubes VK6, VK7, VK9 are extinguished by VK10 which follows VK14 and VK16 during a reset pulse on RSF5. Tube VK21 follows VK20 and extinguishes VK15. A control potential applied to both way amplifier BWA causes a tube to strike therein to extinguish VK12, VK13, VK23, VK24. Tube VK25 is extinguished by VK22. In the terminating trunk connecting circuit TTCC, tube VK38 is backed off during a connection by the voice-frequency from VF2. When the voice-frequency is stopped, VK38 strikes during the next reset pulse on RSF3 and is followed by VK45 in the sequence control circuit, VK44 now being extinguished. The circuit remains in this condition until the called party hangs up. Voice-frequency on P2 then ceases, VK35 extinguishes and VT9 is cut off. The positive pulse from the anode of VT9 strikes VT46 in the sequence control circuit, being extinguished. Tube VK40 is primed by VK46 and strikes at the next reset pulse in RSF4 being followed by VK36, VK37, VK41, VK48. Tube VK36 extinguishes tubes VK29, VK30, VK31 in the group selector. Tube VK37 extinguishes VK12, VK13, VK15 in the final selection. Tube VK41 causes a pulse to be transmitted over lead DC1 to strike VK14 and to complete the release of the final selector as previously described for the line finder. Tube VK48 restores the sequence control circuit to normal and extinguishes itself. If the called party hangs up first, the extinction of VT9 strikes VK47 in the sequence control circuit, VK47 being primed by VK44 which conducts during conversation. Both tubes VK38, VK39 are primed by VK47 but neither strikes till the calling party hangs up. A voltage is developed across R14 as VK39 strikes and the release of the connection then proceeds as before.