Patent GB-794818-A (GB)
Title: Improvements in or relating to automatic telecommunication exchanges
Inventor: BRAY FREDERICK HARRY
IPC: H04Q3/00
Filed: 1956-07-13
Abstract: 794,818. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. July 13, 1956, No. 21802/56. Addition to 794,820. Class 40 (4). In an automatic exchange an odd number of stages of cross-bar switches are provided interconnecting a set of inlets to the cross-bar switches and a set of outlets therefrom, each cross-bar switch of any stage other than the last having its outlets extending one to each of a corresponding number of different switches of the next stage, and each switch of any stage other than the first having its inlets arriving one from each of a corresponding number of different switches of the preceding stage so that the arrangement is symmetrical about the central stage, and, when an inlet to a switch of the first stage is to be connected to an outlet from a switch of the last stage, possible paths are tested by test equipment separate from and common to the stages of cross-bar switches, and, after a free path has been found, that path is set up via the stages of cross-bar switches. In the embodiment described the trunking arrangements and general mode of operation are similar to those described in the parent Specification. Detailed description: Seizure of a register. Looping of a caller's line causes the junction of resistors R2 and R3 in his line circuit (Fig. 3) to go positive. The rectifiers MRA are commoned into sets of 500, each set being connected to a terminal LM individual to the identification circuit (Fig. 4) of the relevant 500-line group. The twenty terminals LM in the 10,000-line exchange are pulsed singly and successively by the pulses LM1 to LM20 (Fig. 2) and when the LM pulse for the identification circuit serving the caller occurs, a positive pulse is extended via MRD and MRE (Fig. 3) of the calling line circuit to terminals LA and LB and thence to the identification circuit (Fig. 4) to give one of twenty-five TL tubes and one of twenty TG tubes, the combination of tubes fired, and of H and G anode relays consequently operated, being individual to the calling line. The crossbar switches employed as talking circuit switches each have fifty outlets, an outlet being selected by the operation of one of twenty-five horizontal magnets and one of two servomagnets whereby one of 25 horizontal bars is operated in the appropriate one of two ways, whereafter operation of a vertical magnet completes the connection to the outlet, the horizontal and servo-magnets then being released. Access to and from the line circuits is had over a combined line finder/final selector stage termed a terminal connector stage, and the operated H and G anode relays (Fig. 4) operate the magnets relevant to the calling line circuit in the terminal connector switch (Fig. 5). Assuming that TLB and TGB (Fig. 4) fire, anode relay HB grounds lead HM2 (Fig. 5) common to all the terminal connector switches serving the 500-line group, and GB applies battery to servo-magnet L (Fig. 5), individual to the switch serving the calling line, and to all the horizontal magnets of that switch. The pair of magnets, L and H2, identifying the calling line circuit, are thus operated and their off-normal contacts ground terminal TCN (Fig. 5). Relay GB also extends a positive marking via GP (Fig. 4) to all links accessible via the terminal connector concerned. A positive pulse is thus applied via GP (Fig. 6) of all accessible first links to C1 and thence to the trigger of TFR. The first links are tested by a pulse FRP (Fig. 2) applied to FRP (Fig. 6), whereupon a tube TFR of a free link which also receives the GP pulse, fires, and relay FR pulls up. The ground on TCN (Figs. 5, 6) then operates vertical magnet V and the caller is extended to the seized first link. Relays A and B operate in that link, and, in the line circuit, relay K pulls up, disconnecting R1 and R2 from the loop, and the line from the called line marker. In the link circuit the operation of FR extends ground to terminal FR during the operate time of B to bring up TR (Fig. 4) which releases the identification circuit and the operated horizontal and servo-magnets (Fig. 5). With B up, TR releases and the identification circuit is again available for use. Tube TT (Fig. 6) fires and its anode relay T operates. The operation of FR also applies positive potential over terminals RFR and GFRA (Figs. 6, 7) to the register connector (Fig. 7) serving all first links. There is a GFR lead for the first links connected to each A frame switch, i.e. fifty GFR leads, so that the tube of TZA-TZN (Fig. 7) appropriate to the A frame switch is fired (in this case TZA) and its anode relay (ZA) applies battery to all thirty horizontal magnets of the appropriate register-hunter cross-bar switch. The potential applied to RFR is extended to the triggers of a set of tubes TXA-TXN (Fig. 7) each in a different accessible register, and, the contacts rb1 being closed in free registers, one tube corresponding to a free register fires. Assuming the first register to be free, TXA fires, and HXA operates and grounds all correspondingly numbered horizontal magnets in the register-hunter, whereupon that in the marked switch operates and grounds lead RH (Figs. 7, 6). The consequent operation of VR (Fig. 6) connects the first link to the register, its off-normal contacts extinguishing TT and releasing T and FR, and grounding RR (Figs. 6, 7) to bring up RTR which douses the fired TX and TZ tubes. Operation of a relay RB (not shown) in the seized register busies that register and, when FR releases RTR (Fig. 7) follows and the register connector is again available for use. The register, which may be similar to that of the parent Specification, reverts dial tone over lead DT (Fig. 6) and relay A to the caller. Marking wanted line. The dialled impulses are repeated by relay A over lead IMP (Fig. 6) to the register (not shown), which stores them as in the parent Specification. Provided the A frame switch to which the first link is connected is not in use HD (Fig. 6) is unoperated and applies a positive potential over lead AF to the register, and when all the digits have been received a common call distributer (similar to that of the parent Specification) gives the register a " go ahead " signal and that register is the only one which can control the setting up of a connection during the following time period (covered by Fig. 2) of 50 ms. The wanted number is transferred to the called line marker as in the parent Specification by pulses DT1 to DT10 (Fig. 2) and a positive marking is applied to terminal CLM (Fig. 3) of the wanted line circuit. If the line is free (K down) this is extended to LA and LB and operation of the identification circuit takes place as for a calling line, positive potential being thus applied via terminal GP to the triggers of tubes TFL (Fig. 11) of final links having access to the wanted line. When the final link test pulse FLP (Fig. 2) occurs, the tube TFL of a free one of these final links fires and relays FL (individual to the link) and GF (common to all links accessible via the same C frame switch) operate. The energization of GP (Fig. 4) for a calling or a called line occurs at different times in the period (Fig. 2), the finder and final link test pulses occurring at similar times, respectively, so that connection of a calling line to a final link, or of a called line to a first link, is avoided. Relay GF is released as soon as FL has completed its operation, and thus momentarily applies positive potential to the junction of MRR and MRS (Fig. 11) to provide the pulse RGA (Fig. 2). This pulse is applied via MRR to the registers to indicate to the register in use that a free final link has been seized, and via MRS to the route selector (Fig. 9). In response to pulse RGA the. register grounds lead MK (Fig. 6), to operate H in the seized first link, and then releases. Choosing a free path through the A, B and C frames. The common test equipment is constituted by the route selector (Fig. 9) which includes a set of gas tubes TAA-TAN equal in number to the outlets from an A frame switch (the A frame outlet store) and a set TCA-TON equal in number to the inlets to a C frame switch (the C frame inlet store). The pulse RGA is applied via MRS (Fig. 11) to a connection per inlet of the C frame switch having access to the seized final link and in the case of idle inlets is extended over off-normal contacts VN3 (Fig. 10) to the route selector. The connections HO and HOM (Fig. 10) are common to all nth C frame inlets and each connection HOM is connected to the trigger of the appropriate tube TCA-TCN, so that a number of these tubes, each of which identifies a free inlet to the relevant C frame switch, are fired. The operation of H (Fig. 6) in the seized first link connects positive potential via HDM (Fig. 6) to all second links to which the relevant A frame switch has access and in the case of idle second links this is extended via off-normal contacts VN3 (Fig. 8) of the B frame switch to terminals HDM in the route selector. Tubes TAATAN (Fig. 9) corresponding to free outlets of the relevant A frame switch are thus fired. If free paths exist then for each such path correspondingly numbered ones of the tubes TAA-TAN and TCA-TON will be fired, the gate connected to their cathodes gives an output, and the corresponding tube of set TMA-TMN is primed. One of these tubes, say TMA, fires and its anode relay, TA, operates to record the identity of the chosen free path. Setting up the chosen path. When H (Fig. 6) operated it extended battery via VL to terminal SLN, and also operated relay HD, which disabled the free outlet signalling path to the route selector, disconnected positive from AF, whereupon the register and called line marker were released, and connected it to terminal HD (Fig. 6) which extends to all second links accessible from the A frame switch. The operation of TA (Fig. 9) now grounds a terminal HD (Fig. 9) connected to all first A frame outlets,