Patent GB-856732-A (GB)
Title: Improvements in automatic electric switching systems such as automatic telephone exchanges
Inventor: WARD PETER WILLIAM
IPC: H04Q11/04
Filed: 1956-03-10
Abstract: 856,732. Automatic exchange systems. GENERAL ELECTRIC CO. Ltd. Feb. 28, 1957 [March 10, 1956], No. 7573/56. Class 40 (4). In a pulse multiplex automatic exchange system, in which subscribers are divided into groups, means associated with the called group emits pulses free in the called group, and these are compared with pulses busy in the calling group, to obtain a pulse free in the calling group and having a preassigned difference of phase with a free pulse in the called group. The two pulses thus defined are then fed to the calling and called subscribers' line circuits respectively for modulation. The preassigned phase difference may be zero, or may be a definite fixed quantity preferably equal to half the channel pulse repetition period. In each embodiment subscribers are divided into groups of 500, each served by a multiplex consisting of two highways, (1) a speech output highway (SOH) which carries pulses modulated by the speech output of the associated subscriber, and (2) a speech input highway (SIH) which carries pulses modulated by the speech the associated subscriber will receive. In the first embodiment the pulses on the two highways for the same call are synchronous, provided that the two subscribers are in different groups and a single pulse train is fed to each subscriber's line circuit for gating the signals on and off the highways. If the subscribers are in the same group two pulse trains 50 channels apart are used, and a phase changer -(consisting of a pair of demodulator/modulator links) interconnecting the input and output highways is taken into use. In the second embodiment the pulses on the two highways are always separated by 50 channels irrespective of whether the calls are between subscribers of the same or different groups. In this ease two pulse trains are fed to each subscriber's line circuit the trains being separated by 50 channels. Pulse supplies, Figs. 2, 3. Pulses C, D and U are required to identify a subscriber within his 500 group. Pulses CO ... C4 indicate the hundreds digit and are of 233 Á-sec. duration. Pulses DO - . D4 of 466 Á-sec. in combination with D5 or D6 pulses of 233 Á-sec. indicate the tens digit. Pulses U0 . . . U4 of 466 Á-sec. in combination with U5 or U6 pulses of 233 Á-sec. indicate the units digit. The CO ... C4, DO ... D4 and U0 ... U4 pulses have repetition periods of 7 x, 11 X and 13 x 233 Á-sec. respectively, so that a whole cycle of identities takes 7 x 11 X 13 X 233 Á-sec.=0.233 sees. approx. Pulses P and Q lying wholly within the first or second halves respectively of any 233 Á-sec. period are also provided. 233 Á-sec. pulses X, Y, and Z are also provided as subsequently described. The 1 Mc/s. generator 100 (2) produces an output sine wave a (3) on terminal S and feeds a squarer 103 to produce output pulses c (3) which gate an initial pulse from starter circuit 123 into a closed circulating system comprising a 120 Á-sec. delay line 107 and a 113 Á-sec. delay line 115. A 111 Á-sec. tapping 110 of the delay line provides pulses c (3) for operating counting circuits for producing the C, D and U pulses. 9 Á-sec. later a pulse on output 108 of the delay line operates a bi-stable circuit 120 to produce the leading edge of a P pulse. 102 Á-sec. later the output from a tapping 121 of delay line 115 restores the circuit 120 to terminate the P pulse. 11 Á-sec. later the output from delay line 115 operates a bi-stable circuit 111 to produce the leading edge of a Q pulse. 102 Á-sec. later circuit 111 is restored over the tapping 109 of the delay line to terminate the Q pulse. This occurs 9 Á-sec. before the appearance of a pulse c (3) on tapping 110. The pulses on lead 110 feed a three-stage binary counter 130 ... 132, feeding gate circuits GCO ... GC4 so that during the intervals when the counter registers 1 ... 5 they emit pulses CO ... C4 respectively. When the counter registers 7, gate GC5 is opened to pass a Q pulse to lead 140, which resets the counter, the cycle then being repeated. The D pulses are produced by a four-stage binary counter 145, 151 . . . 153, the last three stages controlling gates GDO ... GD4 so that they emit 466 Á-sec. pulses DO ... D4 during the periods when the counter registers 1, 2 ; 3, 4; ... 9, 10. Gate GD5 opens during the eleventh pulse to restore the counter. 233 Á-sec. D5, D6 pulses are derived from the first stage 145. The U0 . . . U4, U5, U6 pulses are similarly derived from counter 167, 174 ... 176 which is, however, not restored until 13 pulses are received. In addition a gate GW is opened to provide a pulse when the U-counter is in its 11th or 12th position at the same time as a D5 and a D0 pulse coincide. This output feeds a three-gate GX which produces a 233 Á-sec. output pulse X every time this coincides with a U5 and a C0 pulse. This pulse occurs once in each identification cycle of 0.233 sees. Coincidence of the GW pulse with U6 and C3 causes gate GY to emit a pulse Y of similar duration and repetition frequency but delayed 66 X 0.233 Á-sec. after X. Coincidence of the GW pulse with U5 and C3 causes GZ to emit a pulse Z of similar duration and repetition frequency but delayed 77 X 0.233 Á-sec. from Y. These pulses do not correspond to any CDU combination since the U counter is either at its 11th or 12th position. Furthermore the 233 Á-sec. periods immediately preceding and succeeding these pulses do not correspond to CDU combinations. First embodiment. Allocation of pulse train for connection of calling subscriber to register. Each section control unit is associated with a different combination of C and D pulses which are fed to terminals 345 (4), 346 respectively. Each section control unit, e.g. A/2 (4) carries a free pulse ready for allocation to a calling subscriber of its associated group in the 100 Á-sec. circulating system 355. If no pulse exists in this system then during the C/D period (C0/D0 in the case of A/2) gate 363 operates the bi-stable trigger 357 to enable gate 369, so that during the next Q-period it emits a stream of clock pulses (provided they are not present in the busy channel store 303) to lead 404 as a demand to gate 408 (5) in the register control and channel pulse store K7 (5). At the beginning of each Q pulse, trigger 419 is operated to enable gate 408 to pass to lead 405 such pulses as are received over lead 404 which are not in use in the registers (i.e. are not present in stores RDI . . . RD8) and are not present on the register highway RH. The first emitted pulse (or the trailing edge of the Q-pulse if no pulse is emitted) restores trigger 419 to close gate 408. The first pulse so received over lead 405 is admitted by gate 348 (4) to the circulating system 355 and the trailing edge of this pulse also restores trigger 357 to close the gate 348, so that no further pulses are admitted to the circulating system. Subsequently although C0/DO pulses may operate trigger 357 it is restored by the pulses in 355 before gate 369 can be opened by a subsequent Q-pulse to issure a further demand. If during another C/D period another section control circuit issues a demand, it may be allocated the pulse already circulating in store 355 of A/2. This pulse being received on leads 405 for all section control circuits is admitted by gate 349 of A/2 (since trigger 357 is unoperated in this C/D period) and thence fed to the inhibiting lead of gate 353 to suppress the pulse in store 355. This section then makes another demand for a free pulse in the next C0/D0 period. Operation of " converter " (10). In its normal state when not co-operating with a register, the converter supplies scanning potentials for calling lines, the potentials being provided on different combinations of three out of 16 leads T1 . . . T16, each subscriber in a 500-group being allotted a different combination. The marking of the specific combinations takes place as follows :-In the normal state composite gates 621, 630, 638 are open to pass C0 . . . C4, D0 . . . D6 and U0 . . . U6 pulses received from the master generator. During an interval in which a U5 and a D5 pulse coincide (a U5/D5 interval) gate 747 is open and gates 750, 751 are closed so that composite gates 712, 642 and 734 are open and gates 742, 724 and 673 are closed. Closure of 742 ensures that gates 656, 657, 697, 698 are also closed. In these circumstances any of the pulses C0 . . . C4 is emitted on a corresponding one of leads T1 ... T5, any of the pulses D0 . . . D4 is emitted on a corresponding one of T6... T10 and any of the pulses U0 ... U4 is emitted on a corresponding one of T 11 . . . T15. In a D5/U6 interval, none of gates 747, 750, 751 are open, gates 742, 642, 734 are open and 712, 724, 673 are closed. With 742 open then if a U0 pulse is present 656 is open and a C pulse, e.g. C1, not only passes straight through to terminal T2, but also passes via gate 656 to T3. Likewise if a U1 pulse is present, the C1 pulse passes directly to T2 and also via gate 657 to T4. Thus the presence of a U0 or a U1 pulse results in a pair of terminals, different for U0 and U1, being energized from a C source. Gates 697, 698 perform similar functions for the D pulses if pulses U2, U3 are present. Thus for a U0 or U1 pulse two terminals of T1 ... T5 and one terminal of T6 ... T10 are energized whilst for a U2 or U3 pulse one terminal out of T1 ... T5 and two terminals out of T6 ... T10 are energized. In a D6/U5 interval, gate 750 is open to provide the same conditions as previously, except that 673 is now open and 734 closed. The output potentials are therefore the same except that terminals T11 ... T15 are energized instead of T6 ... T10. In a D6/U6 interval gate 751 is open so that conditions on gates 642, 724; 673, 734 are reversed as compared with the previous case. As a result the C-potentials originally on T1 ... T5 are diverted to T11 ... T15 and the D-potentials appear on T6 ... T10, there being two wires of the former set or two wires