775,252. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Bell Telephone Manufacturing Co., Soc. Anon.). Aug. 12, 1955, No. 23288/55. Class 40(4). In an automatic exchange system in which all the conversational switches are small capacity (e.g. 10 or 20 outlets) cross-bar switches which are marker controlled the extension of a locally originated connection to a both-way junction circuit is initiated by a single line marker common to all subscribers' lines, which is released after controlling such an extension, but which, prior to its release, signals the identity of the calling line to storage equipment, and in which discriminating equipment common to the bothway junction circuits and to local link circuits responds to the dialled digits, determines whether the call is local or outgoing, and if it is local causes the line marker to be again seized (when free) and co-operates with the marker to control the extension of a connection over a local link circuit, the connection initially extended to the both-way junction circuit being released. A separate P.B.X. marker controls connections to lines other than the first of P.B.X. groups. General description. The exchange has a capacity for 1000 subscribers' lines which are sub-divided into 100-line groups, the lines of each group being multipled to four line finders LF1-LF4 (Fig. 3) each consisting of a 10 x 10 crossbar switch. The subscribers' lines are arranged vertically in line-finders LF1, LF2, and horizontally in LF3, LF4, as described in Specification 657,657. The ten subscriber links (one per bridge) from each line finder LF1-LF4 are terminated on an intermediate finder IF which is a 10 x 10 crossbar switch similar to the LF switches but which is arranged for double group working, the ninth and tenth select magnets controlling connection to intermediate links to local group selectors, or to intermediate links to junction group selectors respectively. Each finder 1F has eight outlets to local group selectors and eight to junction group selectors; the former being multipled to form a single group of outlets, and the latter from 1F1, 1F2 and 1F3, 1F4 being separately multipled to form two subgroups 1-8 and 9-16 (Fig. 3), respectively. Each of the ten junction group selectors consists of two primary (8 X 10) switches connected in cascade with one secondary (10 x 10) switch arranged for double group working. The intermediate links from the ten groups of subscribers are terminated on corresponding ones of the ten contacts per bridge of the primary switches, links 1-8 being associated with bridges 1-8 of the first primary switch, and links 9-16 with bridges 1-8 of the second primary switch. The eight outlets of each primary switch are wired to the secondary switch, the auxiliary select magnets of which select either links 1-8 or links 9-16. The ten outlets from the secondary switch lead to bothway junction circuits (seven) and local link circuits (three). Each of the ten local group selectors consists of a primary (8 x 10) switch and a secondary (5 x 8) switch. The intermediate links from the ten groups of subscribers are terminated on the contacts of the primary switch and the eight outlets of that switch on the contacts of the secondary switch. The latter switch does not exist as a separate switch but consists of spare bridges on other switches. Thus in each group selector the primary switches are in fact 10 x 10 switches of which only eight bridges are used so that there are four spare bridges in each junction group selector and two in each local group selector; five of these six bridges form the local group selector secondary switch. Each local group selector has access to five local link circuits. The exchange includes ten control circuits, an allotted one of which can be connected to any junction or any local link via a single control connecting circuit; two group selector markers either of which can be associated with any group selector; two subscriber markers common to the 1000 subscribers; one subscriber group starting circuit; one hundreds marker for detecting the group of a calling subscriber; one main starting circuit; one junction starting circuit for controlling the seizure of free junction circuits or local link circuits; and an allotter. Originating call. The subscriber marker, the hundreds marker, the main starting circuit and the subscriber group starting circuit are seized and the identity of the calling line is recorded in the first two. A free junction circuit is seized, a free control circuit is connected to it and the identity of the calling line is transferred to the control circuit. The caller is then connected via a junction group selector to the junction circuit under the control of the subscriber marker, the hundreds marker and the group selector marker, whereupon the markers and the main starting circuit are released. The caller dials the wanted number which is stored in the control circuit and is also repeated over the junction. Local call. If the call is local, the junction is released and the control circuit is connected by a circuit by-passing the control connecting circuit to a free local link circuit. The main starting circuit and the subscriber and hundreds markers are again seized, and the identity of the calling line is transferred to the markers which control the connection of the calling line to the local link circuit via a junction group selector. The markers, the main starting circuit and the junction circuit are released. The main starting circuit and the subscriber and hundreds markers are again seized by the control circuit which transfers the number of the called line to the markers, whereupon the markers control the connection of the called line to the same local link circuit via a local group selector. The main starting circuit and the markers are again released. If the called line is free the local link circuit switches through; if not, the local link circuit is disconnected from the caller who receives busy tone from his own line circuit. Outgoing call. The control circuit and markers are released and selection takes place in the distant exchange. If all junctions are busy, the caller may make local calls only. Incoming call. A free junction is seized from the distant exchange, a free control circuit is connected via the control connecting circuit to the junction and the identity of the wanted line is stored in the control circuit which seizes the main starting circuit, subscriber marker and hundreds marker and transfers to the markers the identity of the wanted line. The called line, if free, is then connected to the junction. Calls to P.B.X. lines. A separate P.B.X. marker is provided for testing the lines of P.B.X. groups, for determining the identity of the first free line, other than the first, of a group and for transferring this identity to the subscriber and hundreds markers to control connection to that line. The Specification describes the exchange with reference to detailed circuit drawings. This Specification, however, has reference only to the block diagram (Fig. 1), in which the number of equipments of each type provided is indicated by the numbers in brackets, and the trunking diagram of Fig. 3 (above). Originating call. On the initiation of a call, operation of the caller's line relay causes the extension of ground to the main starting circuit which in turn extends ground to the allotter circuit. The main starting circuit also extends ground via the subscriber's line circuit to the subscriber group starting circuit to operate a relay therein indicative of the hundreds group to which the calling line belongs. The subscriber marker allotted by the allotter is seized and that one of ten horizontal magnets (of a crossbar switch) which corresponds to the hundreds group is operated, followed by all ten vertical magnets of the switch. Operation of this switch connects the subscriber marker to the required hundreds group of line circuits. The subscriber group starting circuit operates the relays in the hundreds marker relevant to the calling hundred line group. The main starting circuit initiates search for free junction circuits via the junction starting circuit. In the junction starting circuit a relay is provided for each of the ten junction sub-groups, and those relays corresponding to sub-groups having free junctions operate. The allotter gives preference to the junctions in one sub-group and if they include a free junction the corresponding relay locks up and releases the other relays. If all junctions in the chosen sub-group are busy the relay corresponding to the next sub-group having a free junction locks up with similar results. If no junctions are free, a slowoperating relay in the junction starting circuit pulls up and the relays then test for free local link circuits. Assuming that there are free junction circuits available in the allotted subgroup a relay is operated in each of those free junction circuits by ground extended from the main starting circuit via front contacts of the operated junction sub-group relay in the junction starting circuit, the windings of the relays in the free junction circuits and front contacts of the operated junction sub-group relay to battery, lock-out circuits ensuring that the relay of only one junction circuit locks to effect seizure of that one junction circuit. In the subscriber marker the tens and units relays corresponding to the tens and units digits of the calling line operate in series over the relevant tens and units leads which extend to the calling subscriber's line circuit and which are connected together therein consequent upon operation of the line relay. The auxiliary select (horizontal) magnet corresponding to outlets to junction group selectors operates in the intermediate link finders to ground extended from the subscriber marker; and the horizontal magnet in the group selector marker switch correspond