Patent GB-946263-A (GB)
Title: Selection system for circuits or electric equipment
IPC: H03K3/284
Filed: 1962-02-23
Abstract: 946,263. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Feb. 23, 1962 [March 3, 1961], No. 7065/62. Heading H4K. In a system for interconnecting circuits of a first set and circuits of a second set via a connecting network, means are provided for marking points, which correspond to particular circuits it is desired to interconnect, at either end of a route selection network which simulates said connecting network, whereby electrical signals when applied to one of said marked points pass via all paths through the selecting network which correspond to free routes in the connecting network and further means are provided for blocking the paths in a certain sequence until only one path remains available, whence the identity of this path is signalled to the connecting network in order that the connection between the said particular circuits may be completed. The invention is applied to the connection of telephone subscribers via a number of stages of cross-bar multi-switches in which the availability of the switches and the condition of the line circuits &c. is determined using electronic scanners. Each terminal multi-switch (final selector) comprises eight sections arranged as shown in Fig. 4 and each subscriber is connected to a certain level in each of two different vertical sections and so has access to eight sections in a tertiary switching stage (ET, Fig. 1) since each vertical bar (hereinafter referred to as a selector) 1-16 is connected to a different section of the tertiary stage. The tertiary, secondary and primary multi-switches each comprise only two sections, but these sections have between 16 and 22 selectors in each and all such selectors have access to a different section in the preceding stage. General description (Fig. 1).-Looping of his line circuit by a calling subscriber AB, say, brings up line relay ra so that when an electronic line scanner EXL (represented as a uniselector for simplicity) reaches the position corresponding to lead #11, pulses from a logic circuit LG will pass via marking wire mga and amplifiers ATM, AT, AS, AP, which are associated with multiswitches ETM, ET, ES and EP, to " piloting " wires mqj leading to a marker MJ. In the latter all contacts rt11 corresponding to idle feed bridges are closed as soon as LG " discovers " a calling subscriber and the pulses on wires mqj will thus be returned to LG indicating that at least one free path exists between the line circuit and a feed bridge. Each amplifier ATM (Fig. 8) comprises a number of gates which are associated one with each section of a multiswitch and the selectors in each section have associated therewith contacts dtm which are closed if the corresponding selector is free. Each subscriber's marking wire mqa is multipled on to at least two sections of the terminal switch ETM so that marking pulses will pass through at least two gates in amplifier ATM. In order to select one free path therefore, step-by-step scanner EXTM (again representation as a uniselector is purely symbolic) blocks several of these gates (say half of them) and if the pulses continue it blocks several of the as yet unblocked gates and so on until only one gate is left open. If at any step the pulses cease, then it indicates that the free paths occur in the blocked gates and consequently some of these will be unblocked in a similar manner until a single free path is obtained. Thus if there are 128 sections in the terminal switch, it is only necessary to effect seven blocking operations in order to obtain a unique path through the gates of this stage. A similar procedure is adopted for scanners EXT, EXS, EXP, EXJ until a single path between JAB and a free feed bridge has been selected. Control circuits CTM-CP are then " energized " to cause operation of the corresponding switches to complete the speech path. Setting up a local call.-A scanner EXL, which comprises a number of stages of multivibrators, continually scans the subscriber's line circuits JAB and when it finds one in a calling condition (ra operated) it stops thereon, seizes the marker MJ via a route translator TRR and allows pulses from a logic circuit LG to be extended to the subscriber's marking wire mqa. These pulses of - 48 volt amplitude when applied to the gates of amplifier ATM cause a transistor trl (Fig. 9) to saturate whereby the changes of collector potential cause via isolating circuit circuit CD (Figs. 11 and 12, not shown) the production of +48v pulses on leads f127 leading to the gates of amplifier AT (Figs. 8 and 10). Consequently transistor tr2 is blocked and transistor tr3 saturates if (as is normal) a potential of -12v is present on lead f113. The changes of collector voltage again cause +48v pulses to be produced via an isolating circuit CD and these pulses are applied to similar amplifiers AS, AP (Figs. 8 and 10). In the marker MJ (which is used to mark free incoming and outgoing junction circuits in addition to free feed bridges) (Fig. 13), each contact dp associated with selectors of the same rank in the various sections of the primary switch is multipled on to transistor tr4, with the contacts rt11 of the routing relays which characterize the directions accessible to the particular selectors being in series therewith. These contacts rt11 associated with free feed bridges are closed when LG seizes the marker. The amplifier AF (Fig. 8) is shown in detail in Fig. 13 and comprises essentially transistor (r5. Application of the aforesaid +48v pulses to the marker blocks tr4 and so saturates tr5, thus causing 24v pulses to be transmitted to the logic circuit and thereby indicating that at least one free path exists in the selection chain. In order to locate this path, a potential of + 1 volt is applied from scanner EXTM over either or both leads #11,#112 (Fig. 9), whereby a portion of the transistors tr1 are blocked and in the continued presence of pulses through the selection chain, further batches of transistors tr1 are blocked until only one remains through which pulses can be maintained. Similar tests are performed over leads f114 from scanners EXT-EXP and over #115 from EXJ so that eventually only one path remains unblocked. The " positions " of the scanners are now supplied to control circuits CTM-CP and LG signals over wires #13-#16 that the connection should be completed. The select and connecting magnets are then operated in conventional manner, Figs. 14 and 15 (not shown), the connecting magnets being held by remanence. A transistor circuit for increasing the speed of operation of the magnets is described (Figs. 16 and 17, not shown) and in addition a contact rz7, Figs. 9, 10, is operated so as to temporarily busy the amplifiers ATM &c. during the switching operation so that contact bounce and a possible attempt to set up another call using the same switch sections will not inadvertently release the call under consideration. A signal is then passed over the C-wire (private wire) of this connection from control circuit CP and the identities of the selectors used therein are recorded in transistorized identification units ITM-IP, the subscriber's class of service as assessed from the position of his line circuit on the banks of terminal stage ETM being stored in IA. These identities are compared with those in the corresponding control circuits and if they agree the feed bridge connects the caller to a register and the marker is released, otherwise the connection is broken down and a new path is selected. The identification procedure is discused with reference to Figs. 18 and 19. With the connection properly set-up, dial tone is reverted and the dialled digits are recorded in the register. The latter seizes LG over wire #125 and as a result of this, the route translator TRR causes the contacts rt11 on the called subscriber's side of the feed bridge to be closed. The bridge signals its identity, i.e. its position on the banks of switch EP, over the c-wire to identifier IP and the latter via the control circuit orientates scanners EXP and EXJ into the appropriate positions. Additionally, the registered number is signalled to " translator " TRA, which comprises a number of relays corresponding to each subscriber and a " translation field " for converting directory numbers of subscribers into their real positions on the banks of switch ETM, and pulses over f153 are applied through this field to the called subscriber's marking wire mqa provided that he is free, i.e. ra and rc back. The completion and checking of the connection then takes place as described above. Release.-When one party hangs up, LG is seized over wire f19 from the feed bridge and signals are applied first over the c-wire of the selecting switches used on the calling side and the identity of the selectors used in the call are recorded in the identifiers. The latter pass this information to the control circuits which then orientate the scanners on to the appropriate positions. The selectors are now restored by passing a releasing current through the magnets in a direction opposite to that of the operating current. Pulses are passed over a wire f124 to check that the selectors have released, i.e. contacts dtm, dt, &c., have restored, and in case of a fault, the latter's location may be ascertained by means of pulses over wires f130 (Fig. 10). The called side of the connection is similarly released. Junction call.-In this case the register informs the route translator and the logic circuit that such a call is to be set up and LG causes the selection of a free path to an idle junction, the original path to the feed bridge being released in favour of this new one. The control circuits at the exchanges involved in the call are linked so that they can synchronously scan the junctions between them and so select an idle one. The operation and release of the selectors at each exchange is otherwise the same as above. However, an alternative form of marker may be employ