Patent GB-744121-A (GB)
Title: Improvements in or relating to telecommunication systems
Inventor: MERCER RICHARD
IPC: H04Q3/00
Filed: 1950-05-31
Abstract: 744,121. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. May 29, 1951 [May 31, 1950], No. 13534/50. Class 40 (4). In a system using route selection as in Specification 656,559, a calling line has access to a called line over a number of different paths through different finder-selector links. A finder-selector link has access through singleaccess relay selectors to all the lines of the exchange but has access through finders to only a hundred lines. There is only one switching path by which a pair of lines can be connected through a particular link. The switches available to a number of finder-selector links (one link for each 100-group of lines) are multipled to make available a single path from any calling line to any called line. Such switches are described as a single route. Cycles of mechanically generated pulses are used to mark switches busy as described in Specification 652,881. Different cycles of pulses are also used to control switches as described in Specification 665,129. At the'start of a call, the first free finder-selector link and an associated responder are seized. The wanted number is stored and the responder tests -for a free route and completes the connection in that route. The equipment available to a group of 100 lines is shown in Fig. 1. A hundred lines with line equipments such as CLCO1, CLCO4, CLCOA, &c., are multipled to three finder-finals, PXFF, QPFF, XQFF, each comprising ten switches if A is 10. The groups have access respectively to routes identified by prefixes Pp-Px, Qp-Qx, Xp-Xx and each line, being multipled to all these finder-finals, has access to all the routes. Each route has access to only one finder-final but each finder-final has access to all the lines. The routes are identified by the battery-feed equipments PpBF &c., which are, in effect, links between the linefinders and the numerical selectors of the routes. Finder-final PXFF is a finder for the P routes and a final for the X routes, XQFF is a finder for the X routes and a final for the Q routes and so on. If Pp is the first available route, a call from CLCO1 is extended through a finder-final in PXFF, and a second finder Pp2F to a battery-feed circuit PpBF, which provides busy tone when necessary, and to an impulse responder IR. The wanted number is registered in five digit responders EDR (exchange digit), 1DR ... 4DR the first four being in tandem and the last (4DR) being permanently associated with the route-finding equipment of IR. Busy numerical switches such as Pp1D, Pp2D, Pp3D, &c., in the groups selected by the digit registers in all the routes are marked by pulses on a common test lead CTL over leads TL1D . . . TL3D and TLJ. The busy pulses are in time-positions denoting the routes to which the switches belong. The calling finderfinal is also busy-marked for other calls by pulses on leads TLFD, TLFF but the busy-markings for the routes Pp ... Px with which it is associated as a finder are cancelled as the route selection takes place so that the route Pp over which the responder IR was seized may be used in the final connection if otherwise available. Individual lines in a finder-final are busy-marked on BTFF which is independent of CTL. If the wanted line is idle, a route is selected by detecting the first time-position in which no busy-marking appears on CTL. The conversation switches are then operated to complete the connection. If the wanted line is busy, no conversational switches are operated and busy tone is transmitted from PpBF. If the selected route is not Pp, finder Pp2F and sometimes PXFF are released with the responder. If the call is to another exchange, it is routed from the exchange digit selector PpED to a switch PpJ which hunts for a free junction as described in Specification 744,124. All the digits are stored as in a local call and the numerical digits are repeated by a dial repeater as described in Specification 458,095. An incoming call over a junction is handled by a junction-finder PpJF, a responder JIR (Fig. 3) and other responders like those used for local calls. Fig. 3 illustrates how corresponding outlets of exchange digits selectors PpED in different 100-groups 1111-11AA, to 1A11- 1AA are commoned to the inlet of a first numerical digit selector Pp1D Similarly, corresponding outlets from the selector Pp1D of different 1000-groups 1111-1AAA, to A111-A1AA are commoned to the inlet of a second digit selector Pp2D. Figs. 4 to 15 when arranged as shown in Fig. 22 illustrate in detail how a local call may be set up. Four series of pulses are generated by cams as shown in Fig. 21. Cams FF control the finder-finals. Cams HS control hunting circuits. Cams 2F control second finder switches and cams 1RF control responder circuits. The pulses may be either battery pulses or ground pulses denoted by the reference B or E. A terminal supplied with pulses has a reference such as PpE which indicates the cam position (Pp) of the pulses and the kind (E) of pulse. Line circuit and finders, Figs. 4, 5. When line relay L11 operates at the start of a call from X (No. 2xx11) to Y (No. 2AAAA) the connection is extended at instant 1 of the FF cycle by a cut-off relay CO11 and a connect relay P11 in a free finder-final PXFF, the lower windings being energized in series with relay P1L. The line is marked busy by pulses IE on conductor BTFF. The second stage finder Pp2F is seized by operation of relays PpL, Pp1 in series with cut-off relay P1CO and the connection is held by ground on the holding lead HLPp at PpL. Line relays L 11, P1L are cut off and busy relay P1B extends the operating leads OL1, HL1 to the next finder QPFF for further calls. Registration of wanted number, Figs. 10 to 15. Relay PpL connects battery to an operating lead OL 1R and at instant Pp in the responder cycle seizes.a responder IRA associated with the route Pp by operating relays Ppa, PpCo in series. Relay PpL falls back and Ppa locks in series with Pa which connects pulses PpE, P9E, PxE to mark the finder find PXFF busy to all the routes Pp, Pq, Px during route selection. The speaking leads are extended over contacts of Ppa to relay Aa in the responder. A busy relay Ba follows, connects backward and forward holding ground to leads HLa, HL1RPp and connects operating leads OL1R, HL1R to the next responder IRb in readiness for the next call. Dial tone is transmitted in known manner through the windings of Aa. Dialled impulses are repeated on conductor ILa. A dialling relay Ca responds to the digits and controls counting relays ISE, IS1-IS4 which operate in turn at the end of the respective digits to distribute the impulses over leads ILE, IL1-IL4 to digit responders EDR, 1DR-4DR. The impulses of the exchange digit are counted by chain relays ERI ...ERA, relay ER2 being operated by the digit 2. Each counting relay is a two-step relay which operates partially when the lower winding is energized at the beginning of an impulse and operates fully through the upper winding at the end of an impulse. Relay ER2 prepares circuits over operating lead OLE and test lead TL1D for operating relay E2 at instant Pp and for applying a busy-marking PpE to the common test lead CTL. When relay ISE operates at the end of the exchange digit, a selector 1DRH is connected over contacts of ER2, ISE and a test lead TL1DR to a number, n, of first digit responders and hunts for a free one IDRn, the free responders being marked by earth at instants a ... n respectively. If the nth responder is selected, E2n operates and locks in series with relay 1DCO and extends the impulsing lead ILI, the holding lead HLa and other leads to the selected responder 1DRn which responds to the first numerical digit in the same manner as the exchange digit responder responded to the exchange digit. The first second and third numerical digits are stored in relay groups 1DR1-1DRA, 2DR1-2DRA, 3DR1-3DRA, the first two of these storing operations being followed by a hunting action to find a free digit responder in the next stage. The operated relays in the digit responders IDRn ... 3DRn connect selector relays 1DA ... 3DA to the common operating lead STL over leads OLID ... OL3D and prepares circuits for connecting busy pulses to the leads IL1 ... IL2 over leads TL2D ... TL3D when the selector relays operate. The fourth digit A is stored on chain relays 4DR1 ... 4DRA, Fig. 11, in which 4DRA operates. If the wanted line is busy when the fourth digit is counted by IS4 relay BR operates at instant A in a circuit from AB on a contact of 4DRA to AE on test lead BTFF. Relay IRT, which controls selection of an idle route, is disabled and at instant (A+ 1) in the 2F cycle, breakdown relay BDa operates in series with relay DIR. The breakdown relay releases Ba to remove holding ground from the connection and DIR connects a busy tone generator BTG and a temporary holding ground at PpBR, relay PpB having operated with PpL and having been held by PpCO. The calling finder-final PXFF is identified in the responder by operation of relay FR1 in a finder 2FR. Over leads TLFD, TLFF pulses PpE ... PxE are applied to CTL to make the routes available to PXFF. Selection of route, Figs. 10, 11, &c. If the called line is free, relay IRT operates instead of BR and connects battery to one-terminal of start relay STa. The other terminal of STa is continuously supplied with selecting pulses PpE ... XxE through windings of relays Ppa ... Xxa and of the cut-off relays PpCO ... XxCO in the finders 2F of all the routes. Relay STa is short-circuited at any instant in which a busy pulse appears on the common test lead CTL. Relays FFO, BFO are cyclically operated by pulses PpE, PqE, PxE and by PpE respectively to cancel the busy markings of the calling finder-final PXFF and of the battery feed equipment PpBF which are busied by the same call and are available to complete the call if the route Pp is not otherwise busy. If no busy marking pulse PpE is fo