Patent GB-781561-A (GB)
Title: Improvements in or relating to electronic telephone exchange systems
Inventor: HARRIS LIONEL ROY FRANK
IPC: H04Q11/04
Filed: 1952-01-01
Abstract: 781,561. Automatic exchange systems. POSTMASTER GENERAL. Dec. 17, 1952 [Jan. 1, 1952], No. 105/52. Class 40 (4). In a telephone exchange system in which communication is established between two audio circuits over one or more pulse multiplex channels, a comparison is effected between all pulse trains which can be used and those which are already in use, to indicate all the free pulse positions one of which is then selected and fed to the modulators associated with each of the audio circuits. In the case where two or more multiplex paths are involved a gate or gates interconnecting the paths are also pulsed with the selected pulse train. General description. A calling subscriber 1 belonging to a group 2 obtains access to group common leads 10, 11 via a go modulator 5 and a return channel gate 6 and demodulator 7. Such a combination is hereinafter referred to as a terminating modulator set 4. The group common leads obtain access to further group common leads over gate pairs such as 12 or 13 hereinafter referred to as intermediate modulators. For each set of modulators, e.g. all the terminating modulators 4 of a group, a number of pulse circulating devices (e.g. a mercury delay line or some form of magnetic or cathode-ray tube store) is provided, a different combination of two of these, e.g. 63, 64, being associated with each modulator, in which is effective that pulse train defined by the coincidence of the pulse outputs from the two circulating devices. In setting up a connection between two subscribers in different groups a pulse train is chosen which is free in both groups, and applied to the appropriate terminating modulators and also to intermediate modulators connecting the two pairs of group common leads. Connection of a calling subscriber to a register during the setting up of the call is achieved in a similar manner, a further set of common leads 14, 15 being provided for the registers, with intermediate modulators 16 for connecting the register common leads with the group common leads 10, 11 and terminating modulators 18 for connecting the register common leads to the registers. Detailed description. Connection to register. A calling subscriber 1 belonging to a group 2 applies through his line circuit 3 a D.C. calling potential to the pulse generator 37 common to the group. This pulse generator produces one of a set of time-spaced pulse trains indicative of the identity of the calling line. This train passes via gate 38, which suppresses the pulses of busy lines or calling lines in the process of establishing a connection, to a pulse lengthener 43 whose D.C. output enables the suppression gate 44. The latter is fed by pulses from a course 9 having time positions indicative of all possible channels in the group common leads 10, 11. Such of these as are already in use are suppressed in the gate 44 by pulses over the lead 45, and those which are already in use in the register common leads 14, 15 are suppressed in the gate 48 by pulses received over lead 47. The remainder feed a pulse lengthener 49 whose D.C. output indicates that the group 2 contains a calling line, and that there is at least one pulse train free both in the group and in the register common lead. The selecting device 50 is fed by a pulse lengtheners 49 for every group, and if more than one group has a calling line it selects one and indicates it by applying D.C. to a pair of leads 164, 165 out of a plurality of such leads. These are combined in a gate 162 to indicate the group by D.C. on a single lead, which is applied to enable the gate 40 to pass pulse trains indicative of calling lines in group 2 to a selecting device 41 individual to the group. If more than one incoming line 1 of the group is calling the device 41 selects pulse train appropriate to one of them and feeds it to a pulse circulating device 56 wherein it is subsequently maintained through coincidence between the circulating pulses and the pulses from the generator 37. The circulating device 56 stores the pulses appropriate to all the busy lines of the group whether they are busy as calling or, as will be seen below, as called lines, and applies the pulses to the suppression gate 38 as described above. The device 41 indicates the chosen calling subscriber by applying D.C. to a combination of two leads 59, 60 out of a plurality of such leads thereby opening the gates 61, 62. Each lead is associated with a delay device such as 63, 64 whose outputs control the terminating modulator 4. The D.C. placed on the group indicating lead by the selector 50 permits gate 52 to pass the pulse trains from 48 to the common selection device 53 which selects one of the pulse trains and injects it into the circulating devices 63, 64 associated with the calling subscriber via gates 61, 62. The D.C. output of the selecting device 50 on the pair of leads 164, 165 indicative of the group is applied to open gates 71, 72 associated with the circulating systems 69, 70, which control the register intermediate modulator 16, connecting the group common leads 10, 11 to the register common leads 14, 15. The pulse train selected by the device 53 is injected via the gates 71, 72 to the circulation systems 69, 70. This pulse train is also injected into the circulating systems 74; 75 associated with the terminating modulator 18 for a free register 17 pre-selected by the device 73. The seized register causes the modulator 18 to transmit the pulse train in use over the register common and group common leads 15, 11 to the terminating modulator 4 whose pulse demodulator 7 provides a further D.C. signal for maintaining the pulse circulation in the storage device 56. The pulse circulation in the devices 63, 64 is maintained by the coincidence in e.g. the gate 67 of the circulation pulse with pulses received from the group common leads 10, 11 via gate 65. Similar maintenance arrangements are provided for the other circulation devices. The register emits a D.C. signal which is gated on to common lead 87, by pulses from the circulating systems 74, 75 and thence as pulse trains on leads 90 individual to the calling group by pulses from the circulating systems 69, 70. The pulses on lead 90 are pulse lengthened at 91 to provide a D.C. marking on lead 92 associated with the group containing the calling line. When the register is thus connected up the pulse train emitted on lead 15 coincides with the pulse train emitted by the selector 53 and this coincidence may be used to provide a releasing signal for the selectors 73, 50, 53 and to all the calling circuit selectors 41. Completion of connection between subscribers in different groups. When the register has received sufficient information, e.g. as dialled digits, it seizes a marker 77 which applies D.C. marking to a lead 78 thereby causing the generators 79 in one or more groups to generate pulses indicative of the called lines. The pulse trains generated in generator 79 are coincident with those of generator 37 in the corresponding group. Thus supposing the line 1 is called then generator 79 produces a pulse train indicative thereof and if this line is not busy this pulse train passes through the suppression gate 81 to the pulse lengthener 82 whose D.C. output (indicating that the group has a free but wanted line), enables the gate 83 to pass the pulse trains from the source 9 indicative of all possible channels except those which are suppressed by busy pulse trains received over lead 45. The pulses of free trains then pass to the gate 97 except in the case where a wanted line is in the same group as the calling line, in which case they are suppressed in gate 95. In the calling group all busy pulse trains, indicated over lead 45, are passed via gate 93 (opened by D.C. on 92) to a common lead 94 whence they pass to suppress any corresponding pulses in 'gate 97, whose output thus consists of pulse trains free in both groups. The output of gate 97 passes to pulse lengthener 100 whose D.C. output indicates that its associated group has a free wanted line to which the connection can be completed. If more than one such group exists the selection device 101 chooses one such group which it indicates by D.C. over one of a number of leads such as 102 which opens the gate 103 to pass the permissible pulse trains to the selection device 104. The latter selects one such train and passes it to lead 105. The D.C. output from 101 opens the gate 107 of the selected group to pass the pulse trains from 79 indicative of all free called circuits in the chosen group to the selecting device 108 which selects one of these circuits which it indicates in two ways, the first being as a pulse train over lead 150 for injection into the busy indicating circulation system 56, and the second being as a D.C. combination on two leads 109, 110 out of a number of such leads. These open the gates 111, 112 to admit the selected pulse train, present on lead 105, to the circulation systems 63, 64 which control the called line's terminating modulator. For injection of the selected pulse train into the calling subscriber's pair of circulating systems, the appropriate pair are identified by comparing their circulating pulses with the pulses on lead 90 which are coincident with those used for setting up the connection to the register. Comparison takes place in a gate such as 114 whose output is pulse lengthened to provide D.C. to open a gate 116 for injection of the selected pulse train from lead 105. The leads 92, 117 are marked by D.C. to indicate the calling and called groups, and when applied together open a gate 118 to admit the selected pulse train to the circulating systems associated with the intermediate modulators 12 connecting the two pairs of group common leads together. The call having thus been set up the circulating arrangements are maintained as described in the case of the connection to the register. When connection to the called subscriber is comp