Patent GB-777933-A (GB)
Title: Improvements in or relating to time-division multiplex communication systems
Inventor: HARRIS LIONEL ROY FRANK
IPC: H04J3/00
Filed: 1952-11-19
Abstract: 777,933. Automatic exchange systems. POSTMASTER GENERAL. Nov. 6, 1953 [Nov. 19, 1952], No. 29267/52. Class 40 (4). [Also in Group XL (c)] Each of three or more time division multiplex transmission paths is connected by pulse gate circuits to at least two of the other paths, communication between a multiplex channel of one path and a synchronous multiplex channel of another path being effected by applying to the gate circuit interconnecting the paths pulses coincident with the channels. In a switch, Fig. 3, for connecting a calling incoming circuit CT1 ... CT3, e.g. a subscriber's line or a junction to a free outgoing circuit CT4 ... CT6, the incoming and outgoing circuits are formed in groups GRP1 ... GRP3, GRP4 ... GRP6, respectively, which are each connected to an individual time division multiplex transmission circuit having go and return paths such as GT1, GR1. The multiplex channels of the common paths are equal in number and coincident. Each common path of an incoming group is connected by gates such as M1 with the common paths of all outgoing groups. Each incoming or outgoing circuit has a terminating set comprising a transmit modulator TM1, a receiving gate RM1 and a demodulator and amplifier DA1. A connection is effected between an incoming circuit, say CT1, and an outgoing circuit, say CT4, by applying the same pulse train over leads PDL1, PDL7 to the associated terminating sets and over lead PDL13 to the interconnecting gates M1, M4. In switches having equal numbers of incoming and outgoing circuits, each incoming circuit or alternatively each outgoing circuit may be permanently allotted a particular channel, but in a switch having fewer outgoing than incoming circuits it is desirable that all circuits should be able to make use of any channel. Such a switch is shown in Fig. 5. When a seizing potential is applied over lead H1 of an incoming circuit CT1 of group GRPI through a suppression circuit PSG1 to a pulse generator MX1 associated with the incoming circuits of group GRP1, a pulse train is produced on a common lead PIL1 in a time position indicating the calling circuit CT1. A selecting device SEL1 as described in Specification 722,179 responds to one pulse train at a time and when the pulse train corresponding to the calling circuit CT1 is selected the selecting device biases a combination of leads DCIL1, DCIL2 characteristic of the calling circuit to open gates PG6, PG7 and a lead DCIL7 to open gate PG1 which passes the pulse trains corresponding to free channels of the common transmission paths GT1, GR1 of group GRF1 to gate PCG3. In an outgoing group GRP4, suppression circuits PSG2 associated with outgoing circuits CT4 having no busy potential on the go and return path test leads H2, H3 pass a potential from a lead DCL4 to a pulse generator MX2 which produces pulse trains indicating the free outgoing circuits of the group on a common lead PIL2. A selecting device SEL2 responds to one of these trains and biases a combination of leads DCIL3, DCIL4 corresponding to, say, the outgoing circuit CT4 and opens gates PG11, PG12. Since a free outgoing circuit exists in group GRP4, the selecting device SEL2 opens a gate PG2 which passes pulse trains coinciding with all free channels of the transmission paths GR4, GT4 of the group GRP4 to a lead PIL3. Similarly, pulse trains coinciding with the free channels of other outgoing groups are applied to the lead PIL3 which is connected to the gate PCG3 of each incoming group. If at the gate PCG3 of the incoming group GRP1 one of the pulse trains corresponding to free channels of GRP1 coincides with one of the pulse trains on the lead PIL3, this pulse train passes to a pulse lengthener PLM2 which produces a bias causing a pulse generator MX3 to apply to a selecting device SEL3 common to the incoming groups a pulse train indicating that a calling circuit exists in incoming group GRP1 and can be connected. When the selecting device SEL3 responds to the pulse train it biases a lead DCIL9 characteristic of the incoming group GRP1 to open gate PG3 which passes pulse trains coinciding with the free channels of group GRP1 over lead PIL4 to gates PCG2 each associated with an outgoing group and each supplied from a gate PG2 with the pulse trains corresponding to the free channels of the associated outgoing group. Coincident pulses are passed by gates PCG2 to gates PG4 and to pulse lengtheners PLM3 which bias a pulse generator MX4 to feed pulse trains characterizing the outgoing groups which are available to the calling circuit CT1 to a selecting device SEL4. Supposing the selecting device SEL4 chooses the outgoing group GRP4, it biases the combination of leads DCIL5, DCIL6 characteristic thereof to open gates PG8, PG9, and by means of a coincidence circuit PCG1 to bias DCIL10 to open gates PG4 and PG10. Gate PG4 passes pulse trains coinciding with the channels available for connecting the calling circuit CT to the chosen outgoing circuit CT4 to a selector SEL5 which feeds one pulse train over lead PIL5 through gate PG10 to the pulse supply lead PL2 of the outgoing group GRP4 and through the gate PGS opened by the selecting device SEL3 to the pulse supply lead PL1 of the incoming group GRP1. The pulse train on lead PL1 passes through gates PG6, PG7 opened by the selecting device SEL1 and regenerating circuits TD1, TD2, e.g. of the delay line circulating type, to a pair of leads PDL1, PDL2, whereupon the coincident pulses on this pair of leads operate the terminating set TMP1 to connect the incoming line CT1 to the chosen channel. Similarly the pulse train on lead PL1 passes through gates PG8, PG9 and regenerators TD5, TD6 to operate the gates MP1 connecting the common transmission paths of groups GRP1, GRP4. The coincident pulse train on the supply lead PL2 passes through the gates PG11, PG12, opened by the selecting device SEL2, to regenerators TD3, TD4 which operate the terminating set TMP4 to complete the connection to the outgoing circuit CT4. The outputs of the regenerators TD2, TD3 are fed to pulse suppression gates PSG2, PSG3 which prevent the corresponding pulse trains reaching leads PFL1, PFL3 and so guards the chosen channel from seizure by any other circuits in groups GRP1, GRP4. Pulses on the common transmission paths are tapped through decouplers DM2, DM3 and applied over leads PHL1, PHL2 to the regenerators. At the end of a call the disappearance of these pulses stops the regenerators producing pulses corresponding to the freed channel. The pulse trains on leads PDL1, PDL2 of the calling circuit CT1 are passed by a coincidence gate PCG1 to a pulse lengthener PLM1 which biases the suppression circuit PSG1 to remove the calling condition from the pulse generator MX1. Thus the selecting devices SEL1, SEL3, SEL5 are released. The application of busy potential. to the leads H2, H3 of the outgoing circuit CT4 also operates suppression circuit PSG2 so that the selecting devices SEL2, SEL4 are similarly released. Alternatively the selecting devices may be released a fixed time after responding to a pulse train. Instead of the common transmission paths of incoming groups being connected directly to the common transmission paths of outgoing groups, intermediate common paths with gates at each end may be made available to a plurality of common transmission paths. Specifications 707,384, [Group XL (c)], 718,262 and 718,269, [Group XL (c)], also are referred to.