Patent GB-814099-A (GB)
Title: System of electronic telephonic switching by pulses
IPC: H04Q11/04
Filed: 1956-05-04
Abstract: 814,099. Automatic exchange systems. DAYONNET, F. J. D., and GLOES, P. F. M. May 4, 1956 [May 4, 1955], No. 13789/56. Class 40 (4). In a multiplex switching system, each multiplex cycle comprises a number of minor cycles, at least equal to the number of possible simultaneous connections, each subscriber being permanently allotted a position in each minor cycle. Fig. 1 illustrates two multiplex cycles for an exchange having 10 subscribers and three possible simultaneous connections. The minor cycles a, b, c are used for dealing with incoming speech and minor cycles a<SP>1</SP> (= b), b<SP>1</SP> (= c), c<SP>1</SP> (= d) are used for dealing with outgoing speech. Cycles d and d<SP>1</SP> (= a) are used for control purposes. In each minor cycle the instants t 1  ... t 10 are allotted to subscribers and t o  to a busy tone generator. Fig. 4 illustrates the principle of operation. Subscribers III and V are connected via hybrids 36 3 , 36 5  to transmit and receive multiplex highways 32, 33. The subscribers' modulators 22 3 , 22 5  are fed by control circuit 27 with both pulses a 3 , a 5 (Fig. 1), but since 22 3  is also pulsed by i 3  and 22 5  is pulsed by i 5  only pulses a 3  are effective in 22 3   and only pulses a 5  are effective in 22 5 . The modulators thus pass speech-modulated pulses A 3 , A 5  on to the highway 32. These pulses pass to a "repeater-remodeller " which during the subsequent minor cycle produces the waveform A<SP>1</SP> 3 - 5  which consists of a pulse whose amplitude is A 3  + A 5  except at instants i 3  and i when the amplitudes are A 6  and A 3  respectively. The signal A<SP>1</SP> 3 -5 is fed via the receive highway 33 to the demodulators 24 3 , 24 5  (inter alia), these two being fed from the control circuit 27 by the a 3 , a 5  pulses delayed by delay line 28 by one minor cycle, to positions a<SP>1</SP> 3 , a<SP>1</SP> 5 . Demodulator 24 5 , pulsed at instant i 5 , thus accepts a signal of amplitude A 3  at position a<SP>1</SP> 5  for demodulation and transmission to subscriber V: and demodulator 24 3  pulsed at instant i 3  accepts a signal of amplitude A 5  at position a 3  for demodulation and transmission to subscriber III. Detailed description. Line finder action. When a calling subscriber III, Fig. 7, lifts his receiver the resulting rise in potential over resistance 59 enables the valve 60. The control circuit, Fig. 11, comprises a " short " memory device 120 of the closed circulating type having a delay line 121 whose delay equals the period of one minor cycle. In the normal state trigger R is operated and gate 123 is open and further delay lines 124, 125 each of delay equal to one pulse period are introduced into the circulating system. An initial pulse is introduced into the system from the multivibrator 141 which is thereafter inhibited by the output from the delay line 121. This pulse in circulating shifts its position on each circulation. The delay line output is fed through gate 143 which permits only "d" pulses to pass to terminal 37 and these pulses therefore in due course pass through all possible " d " positions. When this pulse coincides with i 3 , valve 60 in the calling subscriber's circuit passes a pulse to terminal 40. Terminal 40 may also carry " d " pulses of other subscribers already engaged in conversation. Such subscribers have a, b or c versions of their pulses in the " long " memory device 110 which comprises four delay lines 111 3  ... 111 4  each of delay equal to a minor cycle. " d " Versions of these pulses must be present on one or other of the terminals 117, 118, 119 and these feed an inhibiting lead of gate 144 whose output therefore contains " d " pulses of calling subscribers only. The first of these operates trigger N, and is also inserted in the long memory device 110. With N operated R is restored via gate 146 at the next instant b o . The calling subscriber now receives his "d 3 " pulses from the long memory 110 via gate 147. During this period the pulse existing in the short memory is deleted by gate 123 and an i o  pulse is inserted via gate 149 and continues to circulate via gates 128, 130 in that time position. The repeater-modeller, Fig. 8, feeds dial tone during the d periods via a minor cycle delay line 97 to terminal 42 which thus receives dial tone during the d<SP>1</SP> periods. The d 3  pulse in the long memory device 110 is also taken out by gate 148 during the d<SP>1</SP> period to terminal 38. The valve 67 in the subscriber's line circuit, Fig. 7, thus passes dial tone modulated pulses, which are demodulated at 70 to provide dial tone to the calling subscriber via amplifier 68 and hybrid 36 3 . Selector action. When the subscriber dials, the "d 3 " pulses received over lead 40 are correspondingly broken up and a dialling circuit 132 is caused to emit a pulse at time t 11  for each dialled impulse. Each t 11  pulse operates the trigger 129 which closes gate 130 and opens 131 so inflicting a delay of one pulse period on the circulating pulse by diverting it through delay line 125. As the pulse passes through gate 131 it restores trigger 129 to normal. Thus the total delay inflicted on the circulating pulse is determined by the number of pulses dialled. Thus if the called subscriber is number tV the circulating pulse now has position t 5 . One second after the receipt of the first impulse a timer 150 operates and at time d 12  restores N and operates trigger T. T remains operated until the following d 11  instant. The circulating system of the short memory is maintained via gate 122. During this time this pulse is compared with busy pulses from the long memory in gate 153 and if a coincidence occurs trigger B operates to inhibit gate 122 to erase the pulse in the short memory and replace it by a to pulse fed through gate 149 for feeding busy tone as described later. Whether or not B operates the calling subscriber's pulse is fed into the short memory via gate 155 during the d period and the corresponding d pulse is eliminated at gate 113 from the long memory device. The short memory now contains the calling party's pulse and either the called party's pulse or a to pulse. Trigger M is operated (and B released if necessary) when T is restored. From terminal 119 (three quarters of the way round the long memory loop) the conditions of the channels a, b, c are observed during periods d, a, b by trigger 156 which is set whenever it receives a busy pulse and is reset at the end of each minor cycle. At the end of each period (except c) gate 157 is opened and if the channel is free as indicated by the unset condition of trigger 156, triggers E and S are set and M restored. Thus supposing channel a is observed to be free (as tested during the dperiod) then E is operated during the a period to cause the two pulses present in the short memory to pass to the long memory in channel a, via gate 158. These pulses are then fed continuously in channel a via gate 154 to terminal 37 and in channel a<SP>1</SP> via gate 148 to terminal 38. The pulses are maintained in the short memory by the gate 122 sufficiently long for the called subscriber's pulse to be emitted in the d<SP>1</SP> position via gate 160 to terminal 38. Trigger S is then restored and R re-operated. Ringing called subscriber. In the called subscriber's line circuit the corresponding d<SP>1</SP> pulse is gated in by valve 67 enabled by the appropriate i pulse and a d<SP>1</SP> pulse from the repeater modeller (see below). The pulse then passes a gate 74 opened by a d<SP>1</SP> pulse to fire tube 75, which connects ringing current to the called subscriber's line via transformer 79. In order to prevent the ringing current affecting the valve 60 sufficiently to simulate a called-partyanswer signal the voltages at its grid derived over resistance 59, and from condensers 54, 55 and the hybrid coil 36 3  are arranged to be in opposition. Any residual unbalance modulates the calling party's pulses which pass to terminal 40 thereby providing "ring-back tone." When the called subscriber answers valve 60 is enabled to pass pulses on terminal 37 to its anode circuit transformer 77 which thereupon supplies oscillations of sufficient amplitude to extinguish tube 75. If the calling party hangs up before the called party answers the pulses on terminal 38 from the control circuit disappear as described below thus causing a cessation of the pulse output from valve 67. These pulses are detected and integrated at 82, 84 to provide a continuous D.C. signal. The termination of this signal when the caller hangs up produces a negative pulse in transformer 78 to extinguish the thyratron 75. Connection to called subscriber or to busy tone generator. The calling and called subscriber's speech modulate their appropriate pulses in the selected channel in valves 60 whose outputs A 3 , As, Fig. 9A, feed lead 40 of the input to the "repeater-remodeller," Fig. 8. These are combined with d 0  pulses modulated with dial tone. The combined output is fed to an integrating circuit 88 feeding condenser 89 which is discharged at the end of each minor cycle by pulses C on 81. The charge B on the condenser reaches an amplitude A 3  + A5 during the a period. The discharge current D of the condenser slightly delayed at 92 feeds an integrator circuit 93 charging a condenser 94 which is discharged at the end of each cycle by a pulse on terminal 81, to produce the waveform F. The waveform A with t 0  pulses deleted is also fed to a delay line 97 of period equal to one minor cycle and thence to a polarity inverter 98 to produce an output G. These are combined in circuit 99 to produce at terminal 42 an output H which in channel a<SP>1</SP> consists of A 3  + A 5  except at positions a<SP>1</SP> 3 , a<SP>1</SP> 5  where the outputs are A 5  and A 3  respectively; and in channel d<SP>1</SP> a pulse modulated with dial tone. The pulses A<SP>1</SP> 3  and A<SP>1</SP> 5  are gated in the line