Patent GB-401394-A (GB)
Title: Improvements relating to telephone systems
IPC: H04M3/523
Filed: 1932-06-07
Abstract: 401,394. Exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, London, GRINSTED, W. H., Under the Plane, London Lane, Bromley, Kent, PETERS, C. L., 53, Penberth Road, Catford, and CHRISTIAN, D. A., Merven, Charlton Road, Charlton, both in London. June 7, 1932, No. 16097. [Class 40 (iv).] In a toll or trunk office in which calls are normally extended directly by demand operators, a call for a busy group of junctions is extended to a storage circuit and a signal is transmitted to the connecting circuit when a junction becomes available, the operator then causing rotary release of the unsuccessful group selector which hunts again. The existence of congestion on a junction group is indicated to all the operators and the number of calls stored is indicated to the delay supervisor. When the maximum number of calls is stored a further signal, which is nullified when the number is reduced by a predetermined amount, is given to the operators to indicate that no more calls are to be directed to the group in question. This signal can, under control of the delay supervisor, be made to operate when a smaller number of calls is stored. While this signal is displayed the demand operators make out tickets for the calls and only attempt to establish them under instructions from the supervisor. Signalling between the connecting circuit and the junction or outgoing selector circuit is effected over a fourth wire with the aid of differential relays associated with each end. The storage circuit comprises a switch with a differential test relay one winding of which receives current over the fourth wires in parallel from all the outgoing selectors holding waiting calls. The other winding receives different currents over the switch wipers and the switch hunts until balance is achieved. After the storage circuit is full a second differential relay is connected to the fourth wire and remains energized until a predetermined number of waiting group selectors have moved away. Operators can hold incoming connections after release by the calling party and can ring his line. In the system described, the demand operators have cordless connecting circuits, Fig. 3, which can be reached from a main office in the same building as the trunk office over the circuit shown in Fig. 1, and from a nearby satellite or main office over the circuit shown in Fig. 10. Calls from more distant offices over the both-way junction circuit shown in Fig. 9 are dealt with by incoming operators having similar connecting circuits. Calls are established with the aid of a key sender, a first selector, Fig. 5, giving access to junctions to automatic and manual offices (Figs. 6 and 7 respectively) and also to second selectors, Fig. 8, which give access to the both-way junctions, Fig. 9, and to the storage circuits, Fig. 11. The sender can be used also to control a connection over the answering end of the connecting circuit with the aid of a group selector, Fig. 12, with the same outlets as that shown in Fig. 5. Calls with which a demand operator cannot deal can be transferred to concentration positions. There are also separate long-distance positions for dealing with calls over the both-way junctions shown in Fig. 13. These positions, in addition to the regular connecting circuits, have connecting circuits with speech amplifiers, Fig. 14. These circuits are provided on each side with selectors, Fig. 15, for selecting a particular outlet, each such selector comprising two permanently associated switches. Distribution of calls to demand and incoming operators. When a call comes in on the circuit JC, Fig. 1, from the local main office or on the circuit JC, Fig. 10, from a nearby office, L, B pull up, a tone signal RS is connected to the talking circuit and, in the circuit of Fig. 1, holding ground and ringing tone are connected to the third wire. At the same time driving and test circuits are made for a distributer IDA which hunts under control of relay T. Assuming there are no waiting calls, the switch stops on its seventh terminals, the first seven terminals in bank 7 being connected to the leads 1 .. 7, Fig. 2, and A pulls up in series with T, connects the next relay B to wire 6 and lights the lamps 1 at the demand positions via a night alarm circuit if desired. An operator then assigns a connecting circuit, Fig. 3, by throwing its speak key SP and the position key CA, Fig. 4, energizing SK, SL, Fig. 3, and ST, Fig. 2. ST disconnects A to release the test relay and allow the distributer to advance and temporarily holds any of the relays B .. F that may have been operated by subsequent calls. On the relapse of A, however, ST falls reconnecting A and releasing the other relays so that the waiting distributers in succession move one step. IDA hunts for the circuit marked over CC4 in its banks 5 and 7 or 6 and 8. If it runs to its last terminals, CO is operated and the hunt is taken up by IDB. If this too is unsuccessful CO is released by the energization of its reverse winding (iii) in series with the test relay, this circuit being at once broken at co3, IDB moves to normal and IDA hunts for a lamp circuit. When the connecting circuit is reached, T energizes S over bank 5 or 6 and wire CC4 and S switches through and energizes SS which cuts off T. In the circuit shown in Fig. 1, SS holds the preceding switches independently of B, and in that shown in Fig. 10 prepares a circuit over the junction for holding the preceding switches if the calling party clears. In the case of a call incoming over the both-way circuit, shown in Fig. 9, the distant operator applies ringing current to the junction and L which is associated with rectifiers responds and starts the distributer which hunts for a lamp circuit displaying before the incoming operators under control of T. T energizes S to busy the junction to the group selectors. When a connecting circuit is assigned T releases S and IDA (and if necessary IDB) hunts for it. Distribution of calls to long-distance operators. Each long distance junction has a calling lamp CL and a busy lamp CE at each of the two long distance positions LDP1, LDP2, Fig. 13. Ringing current on the junction energizes L which energizes Z to light the calling lamps and busy the junction. One of the operators then throws the answering key AK1, AK2 energizing AN with or without AM and assigns a connecting circuit. AN maintains the busy marking after the relapse of Z. The calling lamps are extinguished and the distributer hunts over bank 3 or 4 according to the condition of AM. When the connecting circuit is found, T energizes S which switches through and energizes SS which cuts off T, releases AN and lights the busy lamps. After the relapse of AN the junction is busied by S. Transfer of calls to concentration operator ; night working. If the demand operator cannot deal with a call she throws key XFR to connect battery to the lower talking wire to energize TF in the junction circuit, Fig. 9. TF lights the calling lamp CL at the concentration position. The operator there assigns a connecting circuit and throws key ANK of the junction to operate AN, release S, SS and so make the distributer hunt over its wipers 7, 8 instead of wipers 5, 6. The distributer is driven through normal if necessary by the relapse of TF when the springs ONA change over. The disconnection of S by AN lights the answering lamp in front of the demand operator. At night the key NSK, Fig. 9, is operated to cause an incoming call to energize Z and light the calling lamp CL. The concentration operator then deals with the call in the manner just described. Extension of call by operator. When the distributer finds the connecting circuit B, Fig. 3, pulls up and lights the busy lamp CE. On learning the wanted number, the operator throws SCK, Fig. 4, which makes driving and test circuits for SFS which hunts for an idle sender. The test terminals of busy senders are connected to battery over a high inductive resistance which prevents the operation of TB. When an idle sender (which is characterized by battery over a low non-inductive resistance is reached, TB stops the switch and connects SX in parallel with itself. SX locks to the test circuit, cuts off TB, energizes S, locks SC independently of the key SCK and extends the digit key circuits to the sender. S lights SSL and energizes SD in the connecting circuit. SCK is now released, the wanted office code with or without the number is keyed up and the start sending key STK is operated. ST now extends the sending loop over 19, 20 to the first selector, Fig. 5. When the sender has completed its operation it releases SX which is followed by SC, S, SP and lamp SSL goes out. The operator now communicates with the distant operator or subscriber and then restores SP releasing SK which completes the talking circuit and releases SL. To set up a connection over the answering end of the connecting circuit the operator throws SP, SAK. Driving and test circuits are thus made for switch SF which hunts for an idle selector, Fig. 12, T, TA pulling up when one is found. At the same time a sender is seized owing to the operation of SA. SC being energized, the sending loop is connected to the answering side of the circuit. First selector, Fig. 5, and reverting selector, Fig. 12. Line, release and dialling relays A, B, C pull upon the extension of the sender loop and the first digit is repeated to magnet V. On the relapse of C at the end of the digit magnet R moves the wipers and if the line is busy energizes G over the test wiper. G releases the magnet and falls back and interaction continues until an idle trunk is found, whereupon H switches through, releasing A. Second selector, Fig. 8. A, B, C pull up when the switch is seized and the second digit steps the vertical magnet. On the relapse of C at the end of the digit E pulls up to direct the third digit to the rotary magnet. At the end of this digit C, E fall back in succession