Patent GB-805328-A (GB)
Title: Improvements relating to automatic telephone exchange systems
Inventor: HOPKINS RONALD SYDNEY
IPC: H04Q3/42
Filed: 1956-01-24
Abstract: 805,328. Automatic exchange systems. SIEMENS EDISON SWAN Ltd. Jan. 24, 1957 [Jan. 24, 1956], No. 2399/56. Class 40 (4). In systems in which the number of code digits for which translation is required is variable, the addresses and corresponding translations are arranged to be read in parallel from a magnetic drum or like storage device, the addresses corresponding to the larger combinations of code digits being encountered before those with smaller combinations, whereby if no translation is obtained for the larger number of code digits a translation is sought for a smaller combination. The invention is applicable to a system in which areas are denoted by one, two, or three code digits and exchanges within an area by a further three digits. For calls to exchanges in other areas which have a direct junction to the calling exchange translation of all the code digits is required. If such a translation is not available or if the route is busy a translation is sought to give access to the switching centre in-the area containing the wanted exchange. Use is made of a magnetic drum of the parallel type as described in one of the embodiments disclosed in Specification 805,326. As described in that Specification, digits A-F are received in a common translator from a register and select appropriate reading heads HA-HF associated with address tracks. The register applies afresh to the translator for each digit of the translation. When an output is received from all six heads, gates Gland G2 open to enable gates GT1-GT5 which pass the first or second choice translation, according to the choice signalled by the register on lead L7 or L8 and the digit required as denoted by which of seven relays RR is energized in two-out-offive code to triggers T1-T5 from which the required translation digit is sent to the register. The output of gate G2 also operates trigger T6 to close gate G2 until the start of the next revolution of the drum when T6 restores. If there is no translation for all six digits a translation is found in respect of the first three digits at a later place on the drum. Modification, Fig. 2. The routing digits may be selected from a translation whereby the translator saves time by ascertaining whether a route is busy or free. The first and second choices of a translation in respect of digits A-F and a third choice in respect of digits A-C only are spaced apart round the drum. The register does not initially ask for any choice of translation but merely for the first trans-, lation digit by opening gate GR1. At the beginning of the next revolution of the drum timing element B1 operates trigger T6, resets. all the other trigger circuits and resets counter CR1. When the address corresponding to digits A-F is read gates G1 and G2<SP>1</SP> open to pulse gates G4, G5, G6, the last-mentioned stepping counter CR1 to position 1. The pulse from GR1 stimulates G4 and G7 whereby the first translation digit is applied to triggers T1-T5 and the basic routing digits to TX1- TX5 and TZ1-TZ5. If the route is free there is no marking on the appropriate " route busy " wire and the first translation digit passes over leads *L10 to the register. At the same time counter CR1 signals over the first lead of L1 1 that the first choice has been taken whereupon the register marks the first choice lead L7 at subsequent applications to the trans. lator. The output of G4 has meanwhile restored T6 so that gate G2<SP>1</SP> is ineffective for the remainder of the drum revolution. If, on the other hand, there had been a mark on the "route busy " wire gate G3 is opened to re-operate T6 and enable a second or third choice translation to be sought, counter CR1 being stepped each time a translation is encountered. If all three translations are in respect of busy routes CR1 steps to fourth position to signal a busy condition to the register. The counter CR1 may comprise a multi-cathode cold cathode discharge tube (Fig. 5, not shown).