Patent GB-582786-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1944-07-17
Abstract: 582,786. Automatic and semi-automatic exchange systems. SIEMENS BROS. & CO., Ltd., and HENSLER, B. A. July 17, 1944, No. 13599. [Class 40(iv)] In a trunking system employing voice frequency currents for impulsing and supervision, all supervisory signals consist of pulses which are repeated until acknowledged by a pulse in the opposite direction and different single frequencies are used for the signals in the two directions. In the system described below, the one-way trunks are accessible both from trunk selectors and from a manual board and terminate in incoming selectors although they may be switched to a manual board. Provision is made for recall between operators by means of signals which comprise the frequencies allocated to supervisory signals in the opposite direction. Another system is described in which the trunks do not appear on manual boards. Specification 499,820 is referred to in the Provisional Specification. Outgoing end, Figs. 3, 3A. Seizure over trunk selector. Relay GS energizes in the test circuit and connects up release relay B, and a seizing pulse is sent by relays TN, SP during the operating time of relay GT which locks in series with relay CB. Relay B locks and connects up Z. Numerical impulses of X frequency pass over the trunk from the selector and control the setting up of the call to the wanted party or to a distant operator. In response to the reply signal consisting of Y frequency pulses, relays ZR, G energize and Z falls back slowly and connects up splitting relay SP. Relay ZR falls back in turn and connects up AR, AK, and at the end of the pulse the relapse of G connects TN in series with SP to send an acknowledgment pulse during the release period of AK. At the same time, AS (previously short-circuited) pulls up in series with AR and reverses the battery connections on the calling side. The clear back signal which is similar to the reply signal is received and acknowledged in the same way, but in this case the left-hand windings of AR, AS are energized, with the result that AR is released by differential action and AS falls back at the end of the acknowledgment pulse and restores the original battery connections. Upon release of GS from the trunk selector, SP operates and TN is controlled over pulse wire EP to send the clear forward signal consisting of 1050-1200 ms. pulses of X frequency at intervals of 600-700 ms. until an acknowledgment pulse of 600 ms. is received during an interval, this pulse being long enough to release B by short-circuiting after ZR has fallen back. Relay GT is shunted down by a final release pulse and CB falls back at the end of the pulse and removes the busy marking. On a tandem call, relay TT is energized and prevents the operation of SP; AR, AS, AK by the reply and clear back signals. The signal acknowledging the clear forward signal short-circuits B, which shunts down TT at the end of the signal thereby releasing GS from the trunk selector, and the final release signal releases GT, CB as before. Seizure from manual board. When the operator plugs in, sleeve relays M, MM connect up SD, GS, whereupon the seizing pulse is sent and B, GT, Z energize as described above. Actuation of the dialling key operates RF over the tip, whereupon DT pulls up and connects the jack to a battery loop through AA. Relay RF goes back and connects TN, SP in series with DT, so that dialled impulses are repeated by AA as X frequency pulses. On the return of the dialling key, LR operates over the sleeve and disconnects DT, TN, SP, AA. The supervisory lamp is controlled by AR in response to the reply and clear back signals. When the operator unplugs, LR, GS fall back and the release operations take place as described above, battery being maintained on the sleeve by CB until the final release signal takes effect. If the operator actuates her dialling key again without unplugging, RF now locks, since LR is up, energizes SP and connects pulse wire EPR to TN to send a recall signal consisting of Y frequency pulses. The acknowledgment pulse operates K which disconnects RF and restores the circuit to the condition before reply. A recall signal from the distant operator consisting of X frequency pulses operates RB which connects up AK to send an acknowledgment pulse and flashes the supervisory lamp by means of interrupting relay LF. Relay SD responds during a dark period when the speaking key is thrown and disconnects RB. Incoming end, Figs. 4, 4A. Call extended over incoming selector. The seizing pulse energizes relays XA, ZR and release relay B, and at the end of the pulse relay A operates and seizes the incoming selector, while Z pulls up in place of ZR. Splitting relay SP is operative during the pulse. Numerical impulses are repeated by A, and the relapse of dialling relay C connects up switching relays AX, AY. Relay D responds upon reply, connecting up SP, and TN is controlled over pulse wire EP to send Y frequency pulses until it is disconnected by G when the acknowledgment pulse is received. The relapse of ZR after that of Z connects up AR which cuts out the attenuation pad AP, and on the re-operation of Z at the end of the pulse AS energizes in series with AR and SP falls back. When the called party hangs up, the clear back signal is sent and acknowledged in the same way, but now the right-hand windings of AR, AS are energized, AR releasing by differential action and replacing the pad AP, and AS falling back at the end of the acknowledgment pulse and restoring the conditions before reply. If the called party reconnects himself at this time, a fresh reply signal is sent. The clear forward signal brings about the release of B after Z, ZR have fallen back and the operation of AK, AL, GA, and at the end of the signal when G falls back a long acknowledgment pulse is sent during the release time of AK, AL, the selector being hold by AL meanwhile. Relay AK reoperates momentarily to release GA and send a final release pulse. On a tandem call, relay TT is energized from the outgoing trunk circuit, releases B, operates GA, AK, holds A, AX, AY and disables the signalling contact x. When release is to take place. TT is short-circuited as described with reference to Figs. 3, 3A and GA is disconnected in the selector, whereupon a final release signal is sent back during the release time of AK. Call extended by operator. The trunk is switched over to the jack J by relay MB when the incoming selector is set on certain outlets, and the calling lamp is lit. Sleeve relays S, SS operate when the operator plugs in. Relay D is connected to the ring and controls the sending of supervisory signals when the called party replies and hangs up, and release takes place in response to the clear forward signal as described above. The receipt from the outgoing operator of a recall signal consisting of Y frequency pulses energizes RF which connects up AK to send an acknowledgment pulse and flashes the supervisory lamp by means of interrupting relay LF until SD is operated by the speaking key. If, however, the incoming operator has already cleared, RF releases SS and thus relights the calling lamp and SD operates when she again plugs in. To retain the trunk, the incoming operator actuates her ringing key to energize RR momentarily over the tip, whereupon RB operates and connects pulse wire EP to TN to send a recall signal of X frequency pulses. If a signal is already being sent at this time, SP holds RR and delays the operation of RB. Relay RB is disconnected by the response of K to the acknowledgment pulse.