811,107. Automatic exchange systems. SIEMENS EDISON SWAN Ltd. July 15, 1955 [April 18, 1954], No. 1433/54. Class 40 (4). In a 10,000 line single marker exchange like that described in Specification 759,599, a forward marking is extended from a calling line LC to a free register RG through a free intermediate link circuit ILC. A forward marking is then extended from the register through the link circuit to all the primary selectors PS accessible to the link. The primary selectors PS serve as line finders and as final selectors. On receipt of the dialled digits, the register RG enables the marker MK to back-mark the wanted line and a brief setting signal is returned from the marked primary selector to operate switches to make the desired connection. At each switching stage, groups of high-speed latch magnet selectors with multipled bank contacts have common control circuits in which the identities of the trunks to be interconnected at that stage are stored by means of gas-filled discharge tubes. The marker is released as soon as all the stores are set and the selectors operate in accordance with the stored information. As in the Specification referred to, each selector PS, ISS, IS, OSS has access to 200 trunks on two banks of 100 contacts. The register secondary and tertiary selectors RSS and RTS have access to only 100 bank-side trunks each, the two banks being used respectively for incoming and outgoing signalling. PBX or junction lines can be spread over a number of groups of selectors. General arrangement.-When a line LC assumes a calling condition the common control circuit of the group of primary selectors to which the line is multipled stores the identities of the line and of the first available selector. The selector operates to connect the line and a forward marking is extended over a trunk 102 and a link circuit ILC to a group of register secondary selectors RSS. A free selector is allotted in the group, the identities of the bank and wiper-side trunks concerned are recorded in the common control circuit and the forward marking is extended to a group of register tertiary selectors RTS. Again, a free selector is allotted, the trunk identities are recorded and the forward marking is extended to a register RG. Each allotted selector operates in accordance with the identities recorded. The register applies an engaging earth to the P-wire, reverts dialling tone to the calling line and operates a switching relay H in the link. Upon receiving the dialled digits, the register seizes the marker MK, when it is free, and extends a forward marking over the outgoing section of the operated selectors RTS, RSS and link ILC (H now up) to a group of incoming secondary selectors ISS. The common control of the group of ISS selectors concerned records the identity of the link ILC and extends a forward marking through the common control circuits of selectors IS, OSS and through supervisory circuits SLC to all final selectors PS available to the link ILC. At the same time, the marker MK back-marks the wanted line in the common control circuit of the appropriate group of primary selectors PS. In response to the coincidence of a backward marking and a forward marking the common control of a group of primary selectors serving the calling line reverts a signal to the marker which then applies a brief setting signal to the control circuit, A master selector in the control circuit concerned records the identity of the wanted line and of the first available forward marked selector of the group, signals the marker that the master selector has been set and proceeds to operate the selector PS. The brief setting signal is repeated from the selector PS to the outgoing secondary selector OSS, to the intermediate selector IS and then to the incoming secondary selector ISS. Each selector operates in a similar manner to PS. The marker MK releases without waiting for the selectors to operate, as soon as a master-selector - set signal is received from all the stages. The supervisory link circuit SLC grounds the P- wire to hold the connection (which was previously held from the register), transmits ringing current to the called station and reverts ringing tone to the register. The register releases in response to ringing tone and the relay H falls back. The line circuit LCD, Fig. 2A, is identical with that described in Specification 759,599. Primay selector PS (Figs. 2A, 2B); Line calling.-When the line LC assumes a calling condition, multiplex MXI produces pulses in a channel allotted to the line. If the line is otherwise free, the pulse is transmitted by a gate 15 and the identity of the line is recorded in the incoming bank side store IBS of a master selector, previously prepared by an allotter A1. A master selector includes bank-side and wiperside stores and a coupling switch but only the outgoing master selector (OBS, OWS, CW1- CW6) is shown completely. The corresponding wiper-side store IWS is signalled over lead 37. Over a circuit equivalent to the outgoing circuit of OBS from wire 16, differentiating circuit BC, wiper CW3, multiplex MX2 and pulse lengthener L2, gate G5 is opened at the time position allotted to the selector contact on which CW3 stands and remains open. A multiplex MX6 transmits pulses on a time position allotted to a PS selector so long as lead 130 indicates that a register is availble and so long as gate IB is not closed by a busy condition on the P-wire, a forward marking on OG/FM or, a setting condition on lead 42. The first pulse from multiplex MX6 transmitted by G5 is recorded in store IWS to identify the first free selector available. Latch magnet LMA operates and the coupling switch CW is driven to find the selector marked by lead 35 in the bank corresponding to CW1. A test relay TA stops the switch, relay HA follows and latch magnet LMB of the free selector operates. The selector is driven until test relay TB pulls up when the line marked on wire 49 by IBS is joined by wiper M. A potential detector PD responds only to the characteristic test potential of the master selector, provided by OBS. Wiper choosing relay WS pulls up if necessary. Differentiating element BE operates with element BC to signal the marker over lead 18 that the master selector is set. The master selector is restored to normal when the P-wire is grounded in the register later. Primary selector PS ; Line called.-A called line is marked on lead 10, the marking being extended as a pulse channel by a multiplex MX4. If the line is feee, the pulses are transmitted by gate I6 and control a gate G7 through a pulse lengthener L3. If there is a forward marking on lead OG/FM to be transmitted through multiplex MX5, pulse lengthener L1 and gate 13 to provide a second control for G7, the marker is signalled over wire 24 that " a connection can be made ". Gate 13, however, is closed by G2 if all the master selectors are busy. A setting signal (earth) is returned over wire 48 and an allotter A2 allots a free outgoing master-selector which records the identity of the called line in outgoing store OBS providing that gate G8 is not blocked by pulses marking the line busy on in the course of setting up a call. The wiper-side store OWS is signalled over wire 37 and is set by the first forward marking pulse subsequently received over highway 8. Gate G1 releases pulses from MX5 to highway 8 when store OBS is set and applies a signal to lead 16. Differentiating element BC transmits a brief signal over wiper CW3 and multiplex MX2 to pulselengthener L2 which controls the gate G1. When set, OWS earths output lead 42 to mark the selector identified by the pulse on highway 8 and differentiating element BD extends a brief setting signal over setting wire S. The latch magnet LMA is energized when store OBS is set and the coupling switch operates as before. Gates15, I6 are closed by pulses from MX3 if the line is busy, the P-wire then being grounded. Bank-side stores.-The stores IBS, OBS are identical, OBS being shown in Fig. 5. An allocation signal on lead 39 changes over a trigger pair of discharge tubes V22, V23, the latter tube being normally conductive. The current in triode V24 increases and the volt drop across cathode resistor R57 serves as anode potential for storage tubes V25, with auxiliary gaps which are maintained conductive. The same potential closes gate MR35 and opens a gate between amplifying triodes V3, V4 in the pulse input from highway 17. A pulse, amplified by V3, V4 is repeated to the storage tubes V25 by a blocking oscillator V5. A storage tube V25 with a coincident marking pulse on terminal 186 strikes to record the pulse. Triode V26 then conducts, closes the gate between triodes V3, V4 to prevent further storage and applies a - 20 v. setting signal to lead 37. Appropriate storage tubes are coupled to triode V27 and relay W which controls the wiper choosing relay WS over wire 40. At the same time, pulses from terminal 188 are transmitted over wire 15 in a time position characteristic of the storage tube V25. Terminal 189 is marked with a negative potential of less than 100 volts, characteristic of the master selector. When a storage tube V25 strikes the potential on wire 56 rises from - 100 v. to the characteristic potential. A reset signal on wire 44 restores the trigger pair V22, V23, triode V24 is cut off and the storage circuit returns to normal. One differentiating element BC is shown. Wiper-side stores.-Stores IWS, OWS are identical. In OWS, Fig. 6, the setting signal on lead 37 cuts off pentode V20. The resultant potential across cathode resistor R15 of triode V21 serves as anode potential for storage tubes V16. A pulse on lead 8 identifying a wiper-sidetrunk is repeated by amplifying triodes V17, V18 and a blocking oscillator V19 as in OBS and strikes a storage tube V16 marked by a coincident marking pulse on terminal 179. Lead 42 is grounded to mark the selector on switch bank CW1 (Fig. 2B), triode V7