Patent GB-378585-A (GB)
Title: Improvements relating to automatic and semi-automatic telephone systems and the like
IPC: H04Q3/00
Filed: 1931-06-13
Abstract: 378,585. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, PATTERSON, W. G., 68, Eltham Road, Lee, CHRISTIAN, D. A., Morven, Charlton Road, Charlton, all in London, and GRINSTED, W. H., Under the Plane, London Lane, Bromley, Kent. June 13, 1931, No. 17232. [Class 40 (iv).] The trunking scheme of an exchange or network of exchanges is such that at some or all of the selecting stages other than the final stage numerically-separated calls are merged in a common group of trunks and are reseparated at the next selecting stage in accordance with a discriminating signal received thereat. The signal may cause the preliminary movement of the selector to a subnormal position or the selection of one of a number of wiper sets. At the first selector the discriminating signal may take the form of a preliminary impulse train. Fig. 1 shows the layout for a 20000 line exchange. Although bi-directional selectors are shown for convenience, the selectors may be of the single-motion type. The first digit 1 or 2 determines the lower or upper five levels of the first selector I, and the trunks from each level are common to a pair of second digits, a signal discriminating between the pair being sent to the second selector II to route the call over the lower or upper five levels. In the same way the trunks from each level of the second selector are common to a pair of third digits, and a discriminating signal is sent to the final selector FS to effect wiper selection thereat. In an extension of this scheme for a 40000 line exchange, the second selectors also have two wiper sets, and a four-way discrimination determines the set of wipers to be used and the lower or upper five levels. Fig. 3 shows a layout for five exchanges A .. E as regards calls initiated at A, which accommodates 10000 lines having the first digit 2. Local calls are routed over the lower five levels of the first selector AI to a second selector AIII and final selector AFS as in the scheme of Fig. 1. B and C accommodate 1000 and 2000 lines respectively and are reached over the 6th level of AI and the second and first levels respectively of a second selector AII. The incoming selector BIII has only five levels, the trunks from each being common to a pair of third digits. The trunks from the 6th level of AI are common to the initial digits 3, 4, and the remaining levels of All may give access to other exchanges like B and C. D is a 10000 line exchange without special trunking arrangements and is reached directly over the 8th level of AI. E is a 19000 line exchange reached directly over the 7th level of AI in response to the initial digit 5 or 6. A heavily-loaded thousands group, e.g. that denoted by the digits 55, may have a particular level of the incoming selector EII allotted to it exclusively. The 8th level of AI may give access directly to other exchanges like D and E or via second selectors to other exchanges like B and C. The setting up of a call from exchange A to exchange E is described in detail. Selectors of the single-motion type are employed in which the wiper-shaft is rotated by a pair of magnets DM1, DM2 which operate alternately as long as a sprag magnet SM is energized and control a rotary armature. First selector, Figs. 4 and 5. The associating relay K(I) operates upon seizure, and line relay A energizes and connects up release relay B(I) and dialling relay C(I). Relay K(II) locks in series with relay H(I), while relay JB energizes and opens the initial circuits of the relays such as K in all the selectors of the group. The subscriber receives dialling tone, and impulses are repeated at contact a1 to the magnet DSM and dialling relay C(II) to step the switch DS. Assuming first that the digit 2 which denotes a local call is received, when relay C falls back, relay PP(I) energizes over wiper DS3, locks and connects up the sprag magnet SM, whereupon the selector is advanced until the dotted line wipers engage their first terminals, when relay T operates and cuts the drive. Meanwhile the magnet DSM automatically steps the switch DS to the 12th or subnormal position, in which relay E energizes. over wiper DS8 and dialling relay C(I) reoperates, releasing relay PP by means of its opposing winding PP(II). The switch DS now advances in accordance with the second digit, and when relay C falls back the trunks of the wanted group are marked over wiper DS2 and test relay T. The selector advances again and relay T (which includes a rectifier R in its circuit) energizes over the test and marking wipers when an idle trunk is found and connects up relay TT which locks. Switching relay H(I) operates and holds over H(II) when earth is returned over the test wiper. If the second digit is odd, relay SL(II) energizes over wiper DS3 and connects earth to the negative wire to effect discrimination at the second selector. Also if the second digit is 7-0, wiper-switching relay WS energizes over wiper DS4. The first digit 1 is not used, and should it be dialled, relay E energizes and causes rotation of the selector to its last position, in which a tone is transmitted as described below. In the case of any other first digit, relay E energizes over wiper DS3 and the selector searches at once in the group marked over wiper DS2. If the digit is 3 or 5, relay SL(II) energizes in series with relay E to transmit a discriminating signal as above, while if it is 7, 8 or 0, wiper-switching relay WS energizes. If no idle trunk is found in the marked group, the selector rotates to its last position in which relays T, LC operate in series and a busy signal is sent from wire BT, an overflow meter OM being actuated over wiper DS6. In the case of a " dead " group, however, relay SL(I) operates over wiper DS6 and substitutes NU tone for the busy signal. If no impulses are received, relays S(I), SL(I) operate under the control of time pulses, and the switch DS takes a single step. Relay E energizes and the selector makes connection to an idle one of a number of special circuits marked over wiper DS2. The control circuit is released and an alarm is given. Should all the special circuits be in use, the selector rotates to its last position and NU tone is sent. The selector multiple may be divided into two parts each served by a sub-group of selectors, in which case pairs of banks DS4, 5 and DS6, 7 are provided for the two sub-groups. Repeater, Fig. 6. Upon seizure of the junction, line relay A energizes, followed by relays BD, HA, the latter completing the junction loop over which relay I operates. A local short-circuit is removed from relay P(I), which energizes and locks over P(II), unless it is still short-circuited by the signal earth on the negative wire, in which case earth is connected to the positive wire of the junction to repeat the signal. Release relay B energizes and holds relay BD. Impulses are repeated at contact a2, and dialling relay C energizes at the first impulse, closing a low-impedance loop, while relay P(II) operates if not already operated and removes the signal earth. When the called subscriber responds, shunt-field relay D responds, disconnecting relay BD and connecting up reversing relay DD. Metering relay J which was energized by relay B now falls back and applies a metering impulse to the c wire during its release period. If busy flash is applied at a subsequent selector, the first relapse and re-operation relay I releases relay BD and connects up relay BR(I), which holds over BR(II) and applies a busy signal over wire BT. Release relay B falls back and disconnects relay HA to release the subsequent selectors. When release is initiated by the calling party, relays C, BD re-operate momentarily to delay the freeing of the junction. Incoming selector, Fig. 7, with individual marking relays. Incoming c and d wires are provided since the selector may in some instances be preceded by the feed bridge shown in Fig. 8. Line relay A energizes over the junction, followed by dialling relay C(I) and release relay B. If the positive wire of the junction is not connected to the signal earth, wiper-switching relay WS(I) energizes and locks over WS(II). Relay P(I) energizes at the first impulse break, while relay Q(I) energizes at the succeeding make. At the second impulse break a circuit is closed through relays P(II), Q(II), whereupon relay P falls back due to differential action, while relay Q(II) falls back at the succeeding make. Thus both relays P, Q are operated after each odd impulse, while dialling relay C(II) is held throughout the train. The terminals of the marking wiper are connected in the manner shown, terminals 1, 22, 43 in the earlier row and 12, 32 in the later row being stopping points at the beginning of each group of trunks. After the first impulse, the sprag magnet SM operates and the selector advances to the first stopping point, when relay T energizes and cuts the drive. At the third and each subsequent odd impulse, relay T is disconnected momentarily and the selector advances to the next stopping point. When relay C(II) falls back, a circuit is made for the sprag magnet SM: for stepping the selector over the selected group, test relay T (in series with a rectifier R) energizing when an idle trunk is found followed by switching relay H(I). If the received digit is odd, relays P, Q are operated and earth is connected to the negative wire. The last test terminals of the groups are cross-connected as required. to terminals N, BP, NP, B to control the application of a busy signal or of NU tone, the choice being dependent where necessary on the condition of relay P, i.e. on whether the digit is odd or even. Pre-final selector, Figs. 9 and 10. Apart from the marking arrangements, the circuits are generally similar to those of the first selector, Figs. 4 and 5. Relay P energizes in series with line relay A unless the signal earth is connected to the negative wire and connects up relay PP(I), which closes an