Patent GB-754654-A (GB)
Title: Improvements relating to equipment for interconnecting electrical circuits such as telephone exchange circuits
IPC: H04Q3/00
Filed: 1950-01-16
Abstract: 754,654. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Hertog, M. den, and Zeeuw, C. de). Jan. 12, 1951 [Jan. 16, 1950], No. 1098/50. Class 40 (4). Exploring means associated with each circuit of a first set of similar electrical circuits is caused to explore the circuits of a second set of similar circuits under control of electrical conditions occurring in a repetitive cycle of time positions in such a manner that in each time position a number of circuits from the second set is individually and selectively offered to an equal number of circuits from the first set, a different selection of circuit offerings occurring in each successive time position. Similar offering in the reverse direction is also provided. The invention is applied to the interconnection of register-controllers and call detectors in a telephone. exchange. General description. The system employs relayless line circuits associated with call detectors, one per hundred lines, and the exchange lay-out is a variation of that described in Specifications 737,865 and 737,866. Instead of the call detectors being provided with forward hunting equipment for selecting link circuits or register-controllers, each registercontroller is provided with a static scanning equipment which continuously hunts for an operated call detector, and on one being found the register-controller connects itself via a link chooser to a link circuit. In a 10,000-line exchange the line-finders of the link circuits are second line-finders. The Specification discusses the requirements of line-finders, link circuits, link choosers, and register-controllers to equip such an exchange having a high busy hour traffic rate and requiring 21 linefinders per one hundred lines. The scanners, by means of which the register-controllers detect the calling condition of a call detector are arranged so that all register-controllers are available to all call detectors. For the purpose of making decimal selections, use is made of a number of impulse sources which in principle provide a cycle of one hundred time units (one each for one hundred outlets) and of a number of approximately ten sources one for each of the groups of outlets. Ideally, sources are used with an impulse length equal to the time unit on which the system is based, but this requires that the different groups of impulse sources each comprise a prime number of sources in order to obtain a number of combinations equal to the product of the numbers of sources in the groups. However, a cycle of 100 time units could not be produced in this way. Rather than have a cycle of 105 time units with three groups of 3, 5 and 7 sources respectively, it is preferred to use three groups (a, b, c) of 5, 5 and 4, the second group having an impulse length of 5 time units, since this allows the switch outlets to be arranged in four groups of 25. To designate the numerical groups of outlets of a switch a further group (d) of 11 sources is used, and another group (e) of 3 sources serves in conjunction therewith to provide 33 routing indications as described in Specification 744,291. The switches employed are multi-switches as described in the Specification mentioned above. Call originated. A scanning circuit by which 96 register-controllers scan 100 call detectors is described (Figs. 3, 4, not shown), part of which is shown in the upper portion of Fig. 5. A relatively positive potential is transmitted from call detector in the calling condition and reaches each register-controller at a different time determined by the combination of sources Pc, Pd and Pe connected up in each. A free register-controller responds, provided that it has access to one free link circuit in the sub-group giving access to the calling line and that this link circuit has access to at least one free linefinder giving access to the calling line, and causes the tube at the right-hand bottom part of Fig. 5 to produce a positive impulse which is applied to a scanner by which the call detectors scan the register-controllers. The pulse sources connected up at the call detectors are so chosen that this impulse is returned to the particular call detector which caused the register-controller to respond, and there causes the cancellation of the calling condition. The response of the register-controller occurs in a time unit which for that particular register-controller is characteristic of the call detector, and which is recorded by cold cathode tubes controlled by pulse sources similar to those used in the scanner. There are groups of tubes for the Pd, Pc and Pe cycles, the Pd tube which fires indicating immediately the group of link circuits to which the register-controller should seek access; and the combination of Pc and Pe tubes which fires, the wanted first linefinder group to which the second line-finder of the link circuit is to be connected. To reduce the scanning times for finding a free link circuit and a free first line-finder, only those outlets which correspond to the wanted group are connected up in each case. Operation on response of register-controller. As soon as a record has been made of the call detector calling, the register-controller operates the ESBO (electronic selection and multiswitch cross-bar operation) connectors associated with it, which provide direct access to the group of second line-finders and the group of first line-finders via which the call is to be completed. Certain operations at the second line-finder ESBO circuit and at the first linefinder and final selector ESBO circuit may then be carried out simultaneously. The registercontroller is connected, via the first line-finder and final selector ESBO circuit of the group of 100 lines to which the calling line belongs, to the corresponding call detector at a point where it delivers impulses characteristic of the identity of the calling line, and immediately records this identity and proceeds with the operation of the corresponding vertical bar at the first line-finder ESBO circuit. It may also determine the class of the calling line. At the same time, scanning by the second line-finder ESBO circuit takes place for the first line-finder group recorded on the Pc and Pe tubes. As there is only one call detector per hundred lines, only one register-controller at a time can be connected to an ESBO circuit for first line-finders and final selectors for the purpose of connecting to a calling line, but the same ESBO circuit may be used simultaneously by other register-controllers for extending calls to called lines over the final selectors. Detailed description, Figs. 10-24. The subscriber's line circuit (Fig. 10), which is similar to that of Specification 682,985, results in an impulse being produced on the common wire CW in a time position characteristic of a calling line. Call detector. The cathode follower CT1 (Fig. 11A), repeats these impulses to lead I leading to the 1st line-finder and final selector ESBO circuit, and via rectifier RC1 to comparator tube VT1, The grid of VT1 is connected to source d2 which produces short negative trigger pulses towards the end of each of the impulses employed in Fig. 10 and coincidence of an impulse from the cathode of CT1 and one from d2 cuts off VT1. This proceeds a positive impulse at its anode which changes over the triggered pair FT1, FT2 so that the cathode of CT2 (Fig. 11B) goes positive, thus closing the gate RC3 and allowing impulses to pass from the scanner to tube VT2. Seizure of free register-controller. A relay Gfr (Fig. 18), is provided per group of link circuits and is operated as long as any link circuit of the group associated with a particular sub-group of register-controllers is free. Each register-controller includes a contact of this relay, e.g. Gf1-6 so that whenever there is a free link circuit in the group, the Rd source allotted will produce positive impulses at the grid of tube TP (Fig. 18), at times at which the register-controller may be tested to serve calls originated in the groups of lines served by the link group concerned. The impulses are retransmitted from the cathode circuit over a front contact rf (Fig. 17) of relay Rfr (Fig. 24), which is operated as long as the registercontroller is free, to the scanning circuit of Fig. 11B. On reception of an impulse from the free register-controller, tube VT2 (Fig. 11B) responds at a time controlled by trigger impulse d3, which provides a short impulse at the end of each time unit of the scanning cycle, causing a negative impulse to be transmitted to the grid of cathode follower CT3 (Fig. 11A), which changes over the flip-flop circuit FT3, FT4. Tube CT3 also drives its own cathode negative so that the gate RC4 (Fig. 11A) is opened and the triggered pair FT1, FT2 is returned to its normal condition. The grid of CT2 goes negative, the gate RC3 is opened and further impulses arriving from free register-controllers are absorbed. When CT2 conducts, following the calling condition, a relatively positive potential is applied to charge capacitor CP2 (Fig. 11A), connected to the anode circuit of tube FT5, and when CT2 reverts to normal the negative impulse applied to CP2 passes through rectifier RC6 and capacitor CP3 to the grid of FT6 and changes over the flip-flop circuit FT5, FT6. In order to make the length of the impulse repeated by this circuit to the grids of CT4, CT5 (Fig. 11B), independent of circuit constants FT5, FT6, are restored by a short positive pulse d3 applied through CP5 and RC7 (Fig. 11A) to the anode of FT5. RC7 is normally non-conductive and will not pass the d3 pulse, but as soon as the leading edge of the regenerated impulse appears at the cathodes of CT4, CT5 it is transmitted via CP6 to charge CP5 and unbias RC7, so that the next pulse d3 restores the flip-flop circuit, thus producing a 200 microsecond impulse which is sent to all register-controllers. In the register-controller this impulse is repeated by tube IT