Patent GB-815281-A (GB)
Title: Improvements relating to automatic exchange systems
Inventor: FLOOD JOHN EDWARD
IPC: H04Q11/04
Filed: 1954-06-11
Abstract: 815,281. Automatic exchange systems. SIEMENS EDISON SWAN Ltd. Sept. 9,1955 [June 11, 1954], No. 34614/53. Class 40 (4). In an electronic selector switch with a number of inlets and 99 outlets one channel of a 99 channel time - division - multiplex system is allotted to each outlet and an inlet is connected to it by selection of the appropriate channel. Rectifier gates are used. Signals for controlling ringing, metering and identification of the calling line are transmitted in channels in a separate pulse highway common to all the connections through the switch but separate from the speech highway or highways. Arrangements are described for controlling ringing, metering and calling line identification in a party line system. In a cycle of 59 millisecs ringing signals and metering signals are transmitted to a line circuit in separate periods of 25 millisecs. The 59 millisec cycle may include 19 millisecs each for ringing and metering and 9 millisecs for calling line identification. In a party line circuit serving four parties, each party is allotted one second for signalling in a cycle of four seconds. General arrangement, Figs. 1 A, 1B.-An exchange system comprises primary selectors PS, incoming secondary selectors ISS and outgoing secondary selectors OSS, all of similar construction. In a primary selector, 99 line circuits LC and a number of trunks are interconnected in one direction by pulse highways 13, 14 and in the other by highways 15, 16. The line circuits and trunks are linked to the highways by pulse modulators BMD, SMD and demodulators BDM, SDM. Each trunk has a slave selector SS which, in known manner, selects the desired channel and outlet under the control of a master selector (not shown). Control pulses each of 1 microsec. recur in cycles of 9, 11 and 25 microsecs. The 99 line circuits LC are each identified by a combination of a P/9 pulse and a P/11 pulse controlling a modulator BMD and a demodulator BDM. P/N indicates one pulse in a cycle of N microsec. and Pn/N indicates the nth pulse of a cycle of N microsec. A metering or ringing signal on wire 23 in the trunk produces 100 microsec. pulses repeated at intervals of 2475 (9x11x25) microsecs. on wire 18 individual to the line circuit to which the slave selector SS is set. Gate GS controlled by the slave selector SS transmits 1 microsec. P/99 pulses characteristic of the called line. Gate GM controlled by P/25 pulses transmits only 1 microsec P/2475 pulses. These pulses are accepted by only the one of 9 gates GP/9 that is marked by the P/9 pulse characteristic of the called line. The pulse is lengthened by TP/9 to 100 microsecs. and is applied to a number of gates GB individual to line circuits identified in part by the P/9 marking on the associated GP/9 gate. These gates GB are also marked by pulses from counters CH, CHA which each produce eleven 225 microsec pulses in a period of 2475 microsecs., the pulses being applied in succession to the leads SP/11 and SPA/11. The counter CH consists of a chain of discharge tubes which are stepped by 20 microsec. P/2475 pulses from a gate GQ and a pulse lengthener TQ. The count is started afresh by each 20 microsec. P/225 pulse from a gate GP and a pulse lengthener TP. Gates GP, GQ are controlled by one-microsec. pulses P1/9, P1/11 and P/25. The counter CHA is controlled by pulses P9/9, P5/11 and P/25, the pulses on leads SPA/11 being delayed 126 microsecs with respect to the pulses on the corresponding leads SP/11. Triodes are used for amplification. Supervisory link circuits SLCA, SLCB, Figs. 1B, 2.-When a circuit is free, this forward holding wire 21X is grounded, triode V1 conducts and, in consequence, triode V2 is cut off and cold cathode gas-filled tubes CT1, CT2, CT3 are non-conductive. When a negative holding condition appears on 21X, V1 is cut off, V2 conducts and a negative holding condition is applied from the junction of anode resistors R9, R10 to both the backward and forward holding wires 22X, 22Y. When V1 is cut off, tubes CT1, CT4 strike and the potential of the junction of cathode resistors R16, R17 rises to ground to enable 25 millisec. ringing timing pulses, Fig. 3, on terminal 53 to be transmitted over control wire 23Y. During ringing an intermittent holding condition ( -10v) is returned from the called line circuit over wire 21Y and triode V3 transmits a positive pulse to tube CT2 which, being primed by CT1, strikes and opens rectifier gate MR2 to pass ringing tone from generator RT to the calling line over speech wires 20X. Reply is signalled by a steady holding condition. Triode V3 is cut off and capacitor C7 charges sufficiently to strike CT3 which extinguishes CT2 by means of the common anode resistor R6 and cuts off ringing tone. Tube CT3 also strikes a tube CT5 to extinguish CT4 and thereby to stop transmission of ringing pulses on 23Y. A condenser C9 and a resistance R24 make CT5 self-extinguishing but the delay is long enough to enable operation of the meter in the line circuit by pulses on wire 23X controlled by metering pulses, Fig. 3, on terminal 54. When the calling line clears, the holding condition is removed from wire 21X and after a delay of 200 microsecs. produced by condenser C4 and resistor R5, triode V1 conducts again, the circuit returns to normal and the holding condition is removed from wires 22X, 22Y. Line circuit LC, Fig. 8. A discharge tube CT17 is triggered by a 100 microsec. signal on wire 18 but the discharge is maintained only so long as there is a 150 v. ringing timing pulse or a metering timing pulse on terminal 71A or 72A in phase with the pulses shown in Fig. 3. The timing pulses on terminals 71A, 72A fix the 25 millisec. periods of a 59 millisec. cycle during which ringing and metering signals are transmitted. Terminals 71, 72 (not shown) control the transmission of the signals from gate YT, Fig. 1B. When CT17 strikes in response to 100 microsec. ringing pulses on wire 18, pulses are transmitted through transformer TRL to the line wires 86, 87 to produce in effect 17 c/s. ringing. The pulses also produce an intermittent holding condition on wire 17. The meter M is energized in response to the 100 microsec. metering pulses on wire 18 and is held operated between successive pulses by rectifier MR24. The ringing and metering circuits are decoupled by rectifiers MR21, MR23. Calling line identification, Figs. 3, 9.-In the cycle of 59 millisecs. 9 millisecs. are used for identification. During the 9 millisecs., the terminal 96 is raised to 150 v. and in response to an identification signal on terminal 88 (from wire 18) a pulse is passed through transformer TRC to wires 92 to 95. These wires are common to the whole exchange and mark the units, tens, hundreds and thousands digits of the line. Party line working, Fig.10.-One second is allotted to each of four parties in a four-second cycle. During one second, discriminating pulses for metering, ringing and identification are applied in 59 millisec. cycles to terminals 71AY, 72AY, 96Y of one line. In response to a ringing pulse on terminal 88 (from wire 18), relay RR controls code ringing. During the same second, metering and identification pulses are effective as before. Reference has been directed by the Comptroller to Specification 718,833.