Patent GB-727395-A (GB)
Title: Improvements in or relating to communication switching systems
Inventor: RIDLINGTON ANTHONY DOUGLAS VAU
IPC: H04Q11/04
Filed: 1950-11-15
Abstract: 727,395. Automatic exchange systems. POSTMASTER GENERAL. Nov. 5, 1951 [Nov. 15, 1950], No. 27960/50. Class 40 (4). Common equipment, e.g. a register-controller or metering apparatus, is connected to a calling and a called line or trunk over corresponding channels of separate time-division multiplex switches and the common signal paths of the switches are connected through pulse suppression gates, direct communication between the calling and called lines or trunks being prevented until required by the application of a suppressing pulse train or trains to the gates. Each multiplex switch comprises go and return paths. Trunks are connected over individual modulators and demodulators to the incoming and outgoing ends respectively of the paths, and the modulator and demodulator associated with each trunk is supplied with the same pulse train. A pulse train appears on the common signal path only when a potential is continuously applied to a transmission path of a trunk. Such potentials are hereafter termed backward or forward hold. Signals are transmitted through the switches by modulating the pulse train in amplitude, position or width. Forward hold appearing on an incoming trunk A causes a modulator AP to apply a pulse train pr having a time position characterizing A to the common path FH1, whereupon a control circuit X sets a pulse generator S associated with a free trunk B leading to a register-controller R to feed a demodulator BQ with a pulse train pr1 synchronous with pr. In response to the forward hold received from the demodulator BQ the register-controller R applies backward hold to a modulator BP to which S also feeds pr1 so that the calling trunk A is placed in bothway communication with the register-controller R over the common paths FH1, BH2. The register-controller R connects forward hold to the modulator CP fed by S so that the pulse train pr1 appears on the forward common signal path FH3 of the second multiplex switch. When it has received sufficient information, the register-controller marks a free wanted outlet D of the second switch as described in Specification 722,172 and the generator T pertaining to that outlet is set by a control circuit Y to supply a pulse train pr1 1 synchronous with pr1 to the demodulator DQ. The connection between R and the outlet D is completed when backward hold is applied to the modulator DP for the pulse train to be sent over BH4 to the demodulator CQ fed by S. Terminals J1, J2 are respectively connected to JB, JF so that when the pulse train pr1 is present on the paths BH2, FH3, the pulse suppression gates KF, KB prevent direct communication between the incoming and outgoing trunks A, D respectively. When the register-controller releases, it removes the hold signals whereupon the output of generator S ceases and the gates KF, KB are opened to a pulse train synchronous with pr. Gates G1 . . . G4 restrict the duration of pulses passing therethrough to prevent false connections. The suppressing pulses for the gates K3, KF may be supplied directly from the pulse generator S, or KB may be supplied from terminal J1 and KF from both J1 and J2. The control circuits and pulse generators may be similar to those described in Specification 722,179. Alternatively, the generator may comprise a mercury delay line circuit having a delay equal to the time between successive pulses. Suitable modulators and demodulators are described in Specifications 694,092, 707,379 and 707,384, [both in Group XL (c)]. Specifications 667,370 and 716,171 also are referred to.