Patent GB-522273-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1938-12-05
Abstract: 522,273. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and HENSLER, B. A. Dec. 5, 1938, No. 35369. [Class 40 (iv)] A trunk having automatic access to other circuits of differing types as regards signalling arrangements has terminal equipment which ir addition to transmitting and responding tc signals over the trunk, transmits and responds to signals appropriate to the circuit tc which it has obtained access. As described a voice - frequency trunk, in response to ar incoming digit has access over a bi-directional switch to local switches, "ring down' trunks and voice - frequency trunks, and moreover, when the switch is set to a particular level, the trunk is switched directly to a manual board. The local switches require D.C. impulse: and loop supervision, the signalling arrangements at a ring-down trunk terminal require leg signalling between that terminal and the voice - frequency trunk terminal, the manual board employs leg signalling, and when the trunk is connected to another voice-frequency trunk straight through signalling is used wher the connection has been made but the terinina' responds to a long release pulse and to a D.C re-routing signal from the switch. The signal translating circuits at the terminal are controlled by signals reverted from the switch. Calls may be set up in both directions over the trunk: Fourwire working and pad control in accordance with losses in the connected trunks as described in Specification 499,832 may be employed. Call incoming over the trunk. Receiver VF in response to a short pulse of frequency X operates x whereupon B, BR, BS, CB, BA, C and Z operate. Relay C loops the wires (top left-hand set in Fig. 2) to the selector over which both local and outgoing calls are set up and BA grounds the holding wire PW thereof. On termination of the pulse, A pulls up to close a contact in the loop and C falls back but the loop is now maintained over relay D, Fig. 1, polarized by rectifiers. AX, AY pull up to complete the speech circuit to the selector, which is isolated as regards DC by condensers CO, the normal trunk termination network YO being replaced by YN. On receipt of the first impulse train repeated by A over the loop, C re-operates to make a low impedance loop and AX, AY relapse, the condition of the speech circuit being restored by these relays on termination of the digit. The circuits of the selector .are described in a subsequent paragraph. Local call. Further digits transmitted in similar manner set the switches, and on reply of the called party D pulls up and locks over D (ii) in series with SP which together with TN operated over pulse wire EP, connects pulses of frequency Y to one wire of the trunk, XY being a common return lead from the other wire. An acknowledgment pulse of frequency Y received from the distant end of the' trunk operates contacts y whereupon G pulls up to disconnect TN and cut off the backward signal, and AR pulls up on the slow release of Z to disconnect the locking circuit of D and open the pulse wire EP. At the end of the pulse, Z pulls up again and G relapses, SP being released to restore the circuit to the conversational condition. When the called party replaces his receiver, D falls back, TN and SP are re-connected to the pulse wire EP and backward Y pulses are transmitted as before. When the distant end of the trunk is cleared, a long Y pulse operates G, ZR and releases Z which initiates the release of ZR, relays AT and FL being operated in parallel and SP held over its middle winding. As ZR releases before the end of the pulse, relay B falls back followed by BR and BS so that A, AX, AY relapse and release the local switch train. When the release signal ceases G, FL and AT fall back and release BA but during their release period RR (ii) pulls up, locks, continues to hold CB but releases AR. The release of BA removes ground from the hold wire of the selector. When BR released, TN and and SP were operated and then held by RR to send a Y pulse back over the trunk and when the outgoing selector reaches normal ground returned over wire NW shunts RR to terminate the pulse and release CB which removes the busy marking from the incoming selector multiple and jack OLJ. Call extended over a ring- down trunk. In response to the first digit, the selector returns ground over wire SAW .to operate SA which - connects ground over relay D to' one leg of the trunk, disconnects C and connects XA to contact x so that XA operates when the operator sends forward a " ringing " pulse of frequency X. Relay Z now falls back and connects battery to the forward -ve wire as a result of which a relay at the ring-down trunk causes the forward transmission of ringing current and backward connection of battery to the +ve wire. A ring-down trunk terminal is described in a subsequent paragraph. Relay D responds, and the transmission of answering Y pulses, establishment of conversational condition and eventually release takes place as previously described. The originating operator may recall over the ring-down trunk during the backward release signal (Y pulses) by sending a pulse of X frequency to operate XA. Call extended over a voicefrequency trunk. The selector operates SA as for a ring- down trunk but in addition connects wire TTW over a wiper to a relay simliar to TT (ii) so that TT (iii) pulls up and locks over (i). Relay TT prevents the operation of XA by the X frequency signals which in this case pass through to the distant equipment, the answering Y pulses being passed without any effective operations at the trunk terminal shown. There is no circuit for answering' relay D but the Y pulses cause the operation of G and release of Z, SP being prevented from operating so that the trunk is not opened and the X and Y frequency leads are not connected up. Clearing is initiated by a long Y pulse from the originating end. This has results similar to the long Y pulse in a local call but the effective operation is the release of Z to release B while G is still operated by the pulse. When the pulse ceases, G releases followed by BR and the operation of RR. Relay BS falls back and since TT is operated removes 'holding ground from the selector, and a Y pulse is reverted by the operation of TN and SP. Relay BA eventually release and the circuit is restored to normal. All voice-frequency trunks busy. The selector grounds wire REW to operate RE whereupon TN and SP pull up to revert a re-routing signal which is of X frequency. Call to manual board. The selector in response to the digit steps. into the level and returns ground to operate MB which locks up. (All calls may be directed to the. board by strapping a ground contact of B to MB (ii)). Holding ground is thereby removed from the selector which releases, the trunk is connected jack ILJ and the balance pair of wires (see later) is connected to jack BJ. Calling lamp relay CL operates and when the operator responds, sleeve relay S operates in series with one winding DS and connects up a second differential winding. SA (ii) pulls up and connects ground over relay D and battery to the line wires to the jack. The connection is set up, D responds to the reply signal and voice frequency signalling over the trunk takes place as previously described, clearing being initiated on the release of D by the called party, the operator receiving the usual signal. If the operator leaves the plug in the balance jack BJ, FW maintains BA operated so that RR is held and the back release signal previously described is maintained. Re-calling the operator. A long X pulse from the originating operator energizes XA followed by the release of Z and operation of RC (ii) which locks up over (i) and connects flash lead IE to relay LF. The supervisory lamp is thereby flashed, differential relay DS being simultaneously maintained in balance. When the operator replies DS operates during a release of LF and releases RC. If the operator has withdrawn before the re-call, SA is released by XA when Z releases and calling relay CL operates. Call outgoing over the trunk from another voice-frequency trunk. The selector tests in over wire PM of the right hand group at the top of Fig. 2 whereupon GS (i) pulls up, connects GS (ii) and RR (ii) in parallel to the grounded winding of slow operating relay GT, and operates CB. Relay TT also pulls up and disables the circuits of contacts x, y, so that voicefrequency signals from the distant end of the trunk are ineffective. Relay RR operates TN and SP which send a calling X pulse over the trunk and GT which has now operated releases RR to terminate the pulse, completes a circuit in which DM steps itself to contact 9, and operates HB and SA followed by BA. All supervisory signals pass through without effective response therein although Z operated by HB is released by a Y pulse, and the circuits remain in this condition until the selector is released from the calling end. When this occurs, GS falls back. and connects pulse lead TP to magnet DM which slowly steps the switch. Prior to the release of the selector, the clearing signal had been transmitted over the trunk and the backward Y pulse should be received before DM reaches contacts 11. This pulse releases Z and GT whereupon DM steps to normal over wiper 3 by self-interruption 'and SA, BA fall back. When the pulse ceases, HB held by the pulse falls back and releases CB. Irregular release conditions. If the backward Y pulse is not received before DM reaches contacts 11, GT (lower) is held over wiper 4 in series with RR (ii) which pulls up and operates TN and SP to send forward a Y pulse while DM is stepping to 23 to provide time for receiving the backward Y pulse in response thereto. If the pulse is still absent, GT is released in position 24. Calls other than from a similar trunk. These are dealt with by an operator over jack OLJ. Relay M operates over the sleeve followed by MM which connects flicker le