Patent GB-606596-A (GB)
Title: Improvements in or relating to telecommunication exchange systems
IPC: H04Q1/446
Filed: 1946-01-16
Abstract: 606,596. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd., and REYNOLDS, W. J. Jan. 16, 1946, No. 1496. [Class 40 (iv)] In a system employing voice-frequency currents for signals and dialling impulses, all signals (including each impulse train) commence with an XY prefix pulse, thus allowing dialling to be commenced without awaiting dial tone from a distant exchange and conversation to be commenced independent of " end of selection " or " called party answer signals, the speech channel being normally existent, and interrupted only during transmission or reception of V.F. signal pulses. As shown, in the idle' condition of the terminating circuit relays RB, RD and Z are energized, the last relay over wipers sa1, sb1. A voice-frequency receiver connected to terminals V1, V2 (Fig. 1) responds to incoming X and Y pulses operating contacts rx and ry (Fig. 3A) respectively. Incoming call. On receipt of the prefix signal (XY for 270 m/secs.) rx and ry are operated and RG pulls up in series with RB, RD; followed by R, RF and RC, so that the outgoing circuit is busied and RB and RD fall away. At the end of the signal RE comes up and all the operated relays release, whereupon RB and RD re-operate over their original circuits. Meanwhile, when RC comes up, X operates in parallel with it, and on the release of RB brings up L, IC, BG and SL, so that at the end of the prefix the release of X extends a loop to the incoming selector, whereupon positive placed on ICSP brings up SY which causes switch SA to advance one step, releasing Z and bringing up IR, CR and CXY. A compound pulse is thus transmitted, while condenser QA charges over RS3 sufficiently for the cold cathode tube CTB to ionize, CT then pulling up followed by PC which releases CT and CXY to terminate the pulse. The release of CXY also short-circuits pendulum relay IR which then delivers an impulse to operate CY, so that a Y pulse is transmitted, and step the switch SB to the same position as SA. The tube CTA then ionizes, and ZZ, MH and ZR pull up preventing re-operation of SB and IR, while CR and SY fall away and RB, RD reoperate. Condenser QA charges over RS1 and RS2 in parallel, CTB ionizes and CT operates momentarily, releasing PC, followed by ZZ, CC and ZR, and bringing up Z. The signal thus' transmitted (XY-Y) constitutes the " proceed to dial" signal. Each incoming digit comprises a compound prefix, to which the relay group RB, RD ... responds as before, followed by X frequency pulses which relay X repeats to the incoming selector. Relays RB and RD re-operate at the end of the train connecting the channel through to the incoming selector so that conversation. may commence immediately after dialling independently of the transmission of a called party answer signal. However, on the reply of the called party DB pulls up followed by WA and S and the answer' signal comprising the prefix signal followed by an X pulse (SY back) is transmitted repeatedly until acknowledged. Receipt of the acknowledgement signal which consists of the prefix followed by a Y pulse, brings up LL which disconnects S and ensures that when Y falls away, at the end of the signal, WA follows it. If the called party clears first, the relapse of DB brings up SY to transmit a clearing signal (XY-Y) which is repeated as long as DB is back until the calling party clears, when the incoming clearing signal results in the release of L, which, in the absence of " operator hold," releases the selector train and relay MH. Relay CY therefore locks up to the next Y pulse, transmits a long release pulse and releases BG, SL, LL and IC. The operation of Z when CTA flashes releases CY. If "operator hold" is provided, the release of L gives a supervisory signal to the operator who controls release of the selector train. If the calling party clears first, relay Y responds to the clearing signal and releases L at once. Outgoing call. Relay A pulls up to the seizing loop and is followed by B, BR and BG, whereupon Z falls away and brings up CXY to transmit a prefix signal timed by the condenser QA and tube CTB. The release of CXY brings up OG so that when Y responds to the acknowledge signal LL comes up and CTB flashes immediately, the operation of CT being followed by that of Z and SF so that OG relapses. If the acknowledge signal is not received, QA charges over RS4 and when CTB flashes, SF operates before LL and releases OG, busy tone being reverted to the calling subscriber and SA being prevented from receiving dialling pulses. Normally, when the calling party dials, the digit is repeated by relay A to the switch SA, relays C and CC holding up until the end of the digit when they release connecting +130 volts to the condenser connected to the contact on which SA has come to rest. As soon as SA steps, Z is released and a compound prefix is transmitted followed by X pulses while SB follows up SA, CTA flashing to the condenser previously charged by SA, and ZZ and ZR pulling up so that QA charges over RS1 to give an inter-digital pause of about 700 m/secs. After all the digits have been transmitted, sa1 and sb1 will be in line and Z will hold. On the reply of the called party the receipt of the answer signal (XY-X) results in the operation of DA, L, SL and SY and an acknowledge signal (XY-Y) is transmitted, MH pulling up to release SY and prevent repetition of the signal. The receipt of the clearing signal, when the called party clears, results in the release of L and DA, giving supervisory signals if the calling party is an operator. When the calling party clears A, B and BR fall away and the outgoing selector train is released, while SY comes up, on the release of MH, to transmit a clearing signal. If the system is equipped with " operator hold," the strap str is inserted to hold the switch train after the relapse of B until a clearing signal is received from the distant end when the operator releases the connection.