Patent GB-759682-A (GB)
Title: Improvements in and relating to telecommunication systems embodying automatic exchanges
Inventor: CHUBB ALEXANDER ALBERT
IPC: H04Q11/04
Filed: 1950-09-22
Abstract: 759,682. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd. Aug. 31, 1951 [Sept. 22, 1950], No. 23341/50. Class 40 (4). A calling subscriber's line circuit obtains access to a link through the exchange and also to a register which in response to dialling signals seizes the called subscriber's line circuit and transmits to it signals indicative of the identity of the seized link, which signals are utilized to effect connection between the link and the called subscriber's line circuit, thereby completing the connection. The invention is described with reference to a system in which the speech channels through the exchange are pulse multiplex channels 17, 18, Fig. 1, fed from the high-frequency pulse source 14. Separate multiplex channels 19, 20 are also provided for metering and busy signalling. Each channel is terminated at the incoming end by a " calling unit " 15, and a " called unit " 16 is capable of being connected to the outgoing ends of any of the channels. A calling subscriber's line circuit 12 obtains access to a calling unit 15 which seizes a register 23 which thereupon receives the dialled digits. A signal indicating the speech channel to which the calling unit 15 belongs is also passed to the register. The register with the aid of the router 22 then seizes the wanted subscriber's line circuit which thereupon seizes an idle called unit. The identity of the speech channel to be used is signalled from the calling unit via the register, router and called subscriber's line circuit to the called unit which is thereby set to receive signals from the channel. The identities of the wanted line and of the selected speech channel are signalled by pulses of a pulse cycle produced by the low-frequency pulse generator 21. The pulse cycle consists of 70 pulses, the first four groups of ten being used to represent the thousands (M), hundreds (C), tens (D) and units (U) digits respectively of the wanted subscriber, and the next 2 groups to represent the tens (d<1>) and units (u<1>) digits of the number representing the speech channels within the exchange. Of the last ten pulse positions only position 66 is used, to provide a resetting pulse for a translation device associated with the called unit. Detailed description. Seizure of calling unit, register and registration of digits. Each subscriber's line circuit, Fig. 2, is provided with a uniselector, the first half of whose outlets are connected to calling units and the second half to called units. A calling subscriber's loop operates L to initiate hunting for a free calling unit, Fig. 3, and when one is found K operates to switch through and release L in the usual manner. In the calling unit line relay A and release relay B come up, the resulting earth on AL causing an allotter, Fig. 4 (not shown), to seize a register, Fig. 5, whose finder CUF then hunts for the calling unit. When the calling unit is found E in the calling unit and KF in the register both operate, the latter stopping the finder and the former releasing the allotter. Relay E operates hold relay H in the register over lead HO. Relay E also fires the thyratron V2 to bring up F which connects up dial tone. Relay A repeats the dialled digits to AA in the register to set the digit switches M, C, D, U. When the last digit has been received PQ operates to earth leads MM, PP. Seizure of called subscriber's line circuit. Earth on MM causes the finder RF of the router, Fig. 6, to hunt for the register and when it is found RR operates to stop the switch and connect up terminal RO, to feed a series of M, C, D, U, d<1>, u<1>, pulses to the subsequent gate circuits. The M, C, D, U pulses are derived from banks M1 . . . U1 of the digit switches in the register which are connected to the appropriate pulse sources. Pulses d<1>, u<1> indicative of the link associated with the calling unit, are connected at Td<1>0, Tu<1>0 to the calling unit, the pulses then passing over the lead Rd<1>u<1> and bank CUF2 to the terminal RO. The pulses then pass to gates MGO, MG1 (in a 2000 line system) which are also fed by pulses M0, M1 One of the gates (say MG1) is opened by the M pulse to pass the succeeding C, D, U, d<1>, u<1> pulses. The C pulse then opens similarly one of the gates CG0 . . . 9 (say CG4) and a D pulse opens one of the gates DG0 . . . 9 (say DG6) to pass the remaining U, d<1>, u<1> pulses to lead RT13. This lead is connected to the lead RT of all 10 subscribers of the group thus selected (1461 . . . 0). Each terminal UP in the subscriber's line circuits is connected to one of the U pulse sources and in one of these belonging to the selected group this pulse will coincide with the U pulse received over lead RT to fire valve V1, thereby energizing relay Z. Seizure and setting of called unit. Relay Z brings up L which initiates hunting by the uniselector S which is prevented from seizing a calling unit by earth connected by Z to the arc BC2 swept by wiper S5. When the first free called unit is found K operates to stop the switch and de-energizes Z and L. In the seized called unit, Fig. 8, RQ operates over lead PI2 and enables valves V28, V29. The d<1>, u<1> pulses fed over RT and bank CS are fed to the translater 25, Fig. 1, which is also fed by all the d<1> and u<1> pulses from the low-frequency pulse source. The translator, Fig. 9 (not shown), comprises a series of coincidence circuits each fed by the pulses received over CS and also with one of the d<1> or u<1> pulses and applies potential to one bank terminal of each of banks ZRD1, ZRU1 corresponding to the time positions of the d<1> and u<1> pulses respectively received over the CS terminal. The uniselectors ZRD, ZRU then hunt for these markings, being stopped by relays DA, UA respectively which are operated by the firing of the thyratrons V28, V29 by the markings received over ZBU1, ZBD1. Banks ZRU3, ZRD3 apply corresponding d and u pulses from the high-frequency pulse generator to a coincidence circuit R40, W20, whose output consists of a pulse corresponding to the time position of the seized channel in the speech multiplex. When the uniselectors ZRD, ZRU have both stopped, CD releases to connect the channel pulse to gates V24, V25. Completion of connection. Channel pulses from V25 are fed to V26 to cause the operation of RB which connects up ringing current. When the called subscriber replies ring trip relay F operates followed by back bridge relay RD which connects the channel pulses to the metering multiplex over ASP1. These are received over ASP01 in the calling unit where they are gated in by channel pulses present at point GP these pulses being derived by combination of the appropriate d and u pulses fed in at T0, Tud1. The pulses thus enable valve V6 to operate D which applies a metering pulse over PO1 during the release time of relay J. The GO speech signals then pass via the hybrid transformer HY1 in the calling unit whence they are gated to the GO multiplex by valve V4 fed by channel pulses from the point GP. In the called unit the pulses are gated in by valve V25 and applied to a pulse lengthener circuit associated with the transformer XF2. The pulses are then demodulated by the filter FIL2 and fed to line via the hybrid transformer HY2. The " Return " speech passes from the hybrid HY2 and the gating valve V24 to the " Return " multiplex at terminal RSP2 and is admitted over terminal RSPO1 of the calling unit to the gating valve V5 whence after pulse lengthening and demodulating it is applied to the calling line via the hybrid transformer HY1. Called subscriber busy. In this case with K operated in the called subscriber's line circuit d<1> and u<1> pulses received over RT are fed to a "'busy" junction over BJ1 and thence to terminal BJO of the register, Fig. 5, where they are gated in by the d<1> and u<1> pulses received over bank CUF2 to fire V7 and V8 in succession. Relay BR is thereupon operated to bring up G in the calling unit whereby busy tone is reverted to the calling subscriber. Release. The release of the line and hold relays A and B in the calling unit release that unit and the register which is thereupon restored to normal. Relay B also disconnects the channel pulses at point GP from the GO channel gating valve V4. The consequent cessation of the pulses arriving at terminal GSPO1 in the called unit releases RB. Relays F, RD, UA, DA follow the last two homing the switches ZRU, ZRD. Alternative arrangements are described in which the short d<1> and u<1> pulses having separate pulse positions after the M, C, D, and U pulses for identifying the speech channels are omitted and long d<11> and u<11> pulses are used, each u pulse occupying an interval equal to that occupied by all the M, C, D, U pulses and each d pulse occupying the whole period covered by 10u pulses. The M, C, D and U pulses are then only present during recurring periods determined by the coincidence of a d<11> and u<11> pulse, the time position of this period identifying the exchange link to be used. Current supply equipment. High-frequency pulse generator, Fig. 12. Voltage from the oscillator OS1 is applied to the tuned amplifier V59 whose output passes via diodes V60, V63, respectively, to valves V61, V64. V61 conducts on positive half-cycles and cuts off on negative half-cycles. V64 operates similarly but in antiphase with V61. Their outputs feed cathode followers V62, V65, respectively, to produce output pulses on terminals TA, TB, respectively, the TA pulses occurring half-way between the TB pulses. The output of V65 is also differentiated and applied to an inverter V66 to produce an output at terminal TC. The output of TC synchronizes a 5: 1 frequency dividing multivibrator V69, V70 whose output is fed via the cathode follower V71 to the output terminal TD. The output of V71 also synchronizes a further 2: 1 frequency dividing multivibrator V75, V76 whose output is applied to terminal TE via a cathode follower V<1>73.