Patent GB-794812-A (GB)
Title: Improvements in or relating to automatic telecommunication exchanges
Inventor: BRAY FREDERICK HARRY
IPC: H04Q3/52
Filed: 1954-10-05
Abstract: 794,812. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Sept. 30, 1955 [Oct. 5, 1954], No. 28635/54. Class 40 (4). In an automatic exchange having subscribers' individual switches for extending connections from subscriber's lines both for outgoing and for incoming calls, a plurality of non-numerical switching stages is provided for interconnecting the outlets of the outgoing and incoming call switches, the initiation of a call causing the caller's individual switch for outgoing calls to seize a free one of its outlets leading to one end of the non-numerical stages, and also giving access to a free register, which in response to the designation of a wanted subscriber causes the wanted line to be marked, thus initiating the operation of that subscriber's switch for incoming calls to seize a free outlet to the other end of the non-numerical stages, control equipment independent of the registers then selecting a free path through the non-numerical stages between the seized outlet from the calling subscriber's outgoing call switch and the seized outlet from the called subscriber's incoming call switch, whereafter that path is set up through the non-numerical stages. General description. The exchange described uses the cold-cathode tube switches of the type employed in Specification 788,592. The subscribers are arranged in 50-line groups and are each connected to an inlet of a terminal connector 1 (Fig. 1) giving access to first links 2 and to final links 3 (Fig. 3). Each line has access to ten first links and ten final links. Each calling line marker 4 (Fig. 1) serves fifty lines having the same tens and units digits so that in a 10,000-line exchange there are two hundred such markers. When a subscriber 5 (Fig. 1) lifts his receiver to initiate a call the appropriate calling line marker is seized (the other calling line markers being locked out) and marks the inlets of all the terminal connectors 1 which are connected to lines associated with that marker which are calling. The terminal connector outlets leading to first links are scanned during the first part of a period allotted for the setting up of a call, by pulses applied cyclically thereto, the coincidence of a pulse and a marking causing the tubes connecting a calling line in the marker's group to the first free first link to ionise. This link circuit seizes a free register 6 via a register connector 7, dial tone is reverted and the digits dialled by the caller are repeated by the link circuit to the register. Providing no other register is controlling a call, the call distributer 8 signals the register to proceed to establish the wanted call. The register then transfers the called number to a called line marker 9 by signals over four leads M, C, D, U, which result in the firing of one tube in each of four groups of tubes indicative of the four digits. The outputs of tubes in the 1000's and 100's groups are combined to give one hundred bus-bars 10, each indicative of a two-digit combination, and the tens and units tubes are similarly connected to one hundred bus-bars 11. Each line circuit 5 has a line mark gate 12 connected to the two bus-bars 10 and 11 relevant to the number of that line. The two bus-bars energized by the storing of the wanted number open the gate 12 of the wanted line and thus mark the relevant inlets of the terminal connector. The terminal connector outlets connected to final links are scanned during that part of the period allocated for that purpose, a free final link to which the called line has access is selected and the line is connected thereto. The seized first link is marked from the register so that an inlet to the " A " frame (Fig. 2) and an outlet from the " C " frame (Fig. 3) are now marked. The " A " and " C " frames are each divided into 50 groups and the B " frame into 30 groups; the first links forming the inlets to each group in the " A " frame are connected to the terminal connector outlets for four groups of fifty subscribers, connections between the " A," " B," and " C " frames being as shown in Figs. 2, 3. A route selector 13 (Figs. 2, 3) common to the exchange, which is also shown in the schematic diagram of Figs. 4, 5, now selects a free path to connect the marked inlet of the A " frame to the marked outlet of the " C frame. The marked " A " frame inlet 2 applies a condition over lead 14 (Fig. 2) to the circuit 15 (Fig. 4), common to all inlets of that " A " frame group, which in turn conditions the gates AG1,AG2 ... each individual to one of the outlets of that group. Each gate corresponding to a free outlet is primed so that those gates corresponding to free outlets from the " A " frame group including the marked inlet will open. In a similar manner the marked " C " frame outlet causes circuit 17 (Fig. 5) to condition gates CG1, CG2 ..., and those gates corresponding to free " C " frame inlets open. The outputs from the open AG and CG gates are applied to master gates MAGI ... and MCG1 ... , respectively, and thence to devices 20 and 21 which control gates G1, G2 .... Thus if outlet No. 1 from the " A " frame and inlet No. 1 to the " C " frame are free, gate G1 is opened and actuates a control device 21A (Fig. 5) to apply a condition to all outlets No. 1 from all groups of the " A " frame over leads such as 22 (Fig. 2). Lock-out circuits ensure that only one device such as 21A can operate. The marked " A " frame inlet is thus connected to the No. 1 outlet of its own group of the " A " frame by ionization of the relevant tubes of the " A " frame selector due to the coincidence of the inlet marking and the outlet condition from device 21A, and marks the corresponding " B " frame inlet. The route selector applies a condition to all " B " frame outlets having access to the required " C " frame group and a connection is established through the " B " frame between the marked inlet and one of the conditional outlets, thus marking the corresponding inlet in the required " C " frame group, whereupon that inlet is connected by the " C " frame switch to the marked " C " frame outlet and the required connection is completed. Detailed operation. On the initiation of a call the line relay L in the caller's line circuit (Figs. 6, 7) pulls up to the loop and extends ground over a back contact of relay K to a calling line marker (Fig. 7). Each such marker is common to fifty lines having the same tens and units digits and either an odd, or an even, hundreds digit, and thus a seized calling line marker can mark only one line in any one numerical group. The ground thus extended raises the trigger potential of tube VI (Fig. 7) so that when its anode potential goes positive at T10 (the tenth time position of the controlling time cycle) this tube fires and continues to discharge until T33 when the anode voltage is restored to normal. The time cycle is of 42 ms. duration, each time position being equal to 1 ms. When VI fires, relay M operates, and the lock-out resistor R2, common to all two hundred tubes such as V1 in the 10,000-line exchange, prevents any other tube V1 from firing and in addition causes the common tube V2 to raise the trigger potentials of all other tubes VI to approximately that of their commoned cathodes to prevent spurious firing between trigger and cathode of those tubes. From T20 to T32 a positive marking is applied over front contacts of M to the fifty line circuits served by the marker, and is extended over front contacts of L, back contact of K, and the centre winding of relay K in the calling line circuit to the ten pairs of talking wire anodes constituting that line's inlet to the terminal connector. The potential so applied is caught at + 70 v. by MR3 (Fig. 7) to prevent premature firing of the terminal connector tubes. The cathodes of the pairs of tubes of the terminal connector giving access to free first link circuits are cyclically pulsed by the free first link circuits (Figs. 9 to 12) constituting the outlets of the terminal connector. These pulses which are negative-going are of ¢ ms. duration, are spaced by ¢ ms. and are applied in turn to the ten first link circuits associated with any group of calling lines during the period T21 to T30. If a first link is busy, MR8 (Fig. 9) of that link is conductive and the pulse is dissipated in R8; but when the first free first link circuit is pulsed the cathodes of the fifty pairs of tubes in the terminal connectors connected to that link circuit are lowered to the pulse potential of - 220 v. The anodes of the ten pairs of tubes marked from the calling line circuit are at +70 v. and that pair of tubes receiving both the marking and the pulse fires, bringing up relays K (Fig. 6), and S (Fig. 9) in the seized first link circuit. Relay S disconnects ground from R9 (Fig. 10), thus allowing the anodes of the tubes RCT of the register connector (Figs. 10 and 29) relevant to the seized first link circuit to be raised to + 80 v. The operation of K (Fig. 6) disconnects the calling line marking lead and short-circuits RR. The conditions are such that the anode-cathode circuits of the fired terminal connector tubes are balanced and each anode passes 10 mA. Thus 20. mA. flows in relay A (Fig. 10) which thereupon operates and opens a point in the circuit of the V.F. generator (Fig. 10). Seizure of free register. Each free register (Figs. 29-35) pulses the cathodes of the tubes RCT of the register connector giving access thereto over back contacts of RS (Fig. 29), each pulse being negative-going of ¢ ms. duration, the pulses being spaced by ¢ ms. and the registers pulsing in time positions T1 to T10, respectively. The cathode potential of RCT is caught at - 225 v. by MR50 (Fig. 29), and the first tube RCT which receives both the + 80 v. marking and the - 225 v. pulse fires and connects the seized first link circuit to a free register. A relatively high current flows in the " register " anode and, with the resulting low