Patent GB-1102864-A (GB)
Title: Improvements in or relating to automatic telephone exchanges
Inventor: ALLUM ROBIN DEVENISH
IPC: H04Q3/00
Filed: 1964-11-10
Abstract: 1,102,864. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. and H. M. POSTMASTER GENERAL. 4 Nov., 1965 [10 Nov., 1964], No. 45697/64. Heading H4K. Group selectors comprising primary and secondary cross-point arrays have outlets divided into basic groups; a group, to which the selector is directed in search of an idle outlet by means of a digit from a registertranslator, comprising one or more of the basic groups; and where more than one basic group is indicated by a digit the search over the outlets being conducted serially over the basic groups. As described, an array of 8 AS switches of 12 inlets and 20 outlets each, and an array of 20 BS switches of 8 inlets and 10 outlets each, comprises a group selector giving connection from any one of 96 access circuits to selected groups formed from the 200 outlets of the BS switches. The links from a particular AS switch go to the horizontals, one in each BS switch, having a position in the BS switches corresponding to the position of the AS switch in its array. Corresponding outlets of the BS switches are grouped to form so-called levels; there are thus 10 levels of 20 outlets each. In each level, LEV1 to LEVO, the outlets 1 to 10 and the outlets 11 to 20 each form a basic group. Each inlet to the AS switches has an access circuit AC which may be seized from a register-translator (not described). When seized an access circuit AC operates a line relay contacts of which identify the AS switch involved by means of a lock-out circuit 1 LOC and identifies the particular inlet of that switch by means of a lock-out circuit 2 LOC. The AS switch calling for service is indicated by the operated one of relays (LA to LH) and its contacts are employed to gate the line relays of the calling switch to the lock-out circuit 2 LOC, to mark all cross-points in the BS array to which the AS switch has access, and to connect the calling access circuit AC to a register REG-A, or a register REG-B, depending on which one is marked available for use. These registers may be used alternately for successive calls or for successive prescribed time intervals, or one may be held in reserve as a substitute should the active partner encounter a fault. When connected, a register transmits a proceed-to-send signal comprising fixed voltages on the speech wires backwards to the register-translator. This signal elicits a digit held by the register-translator which digit is sent as a choice out of four voltages on the negative speech wire and a choice out of three voltages on the positive speech wire. Reception of the digit in the register removes the proceed-to-send voltages and feeds a decoder which operates one out of the ten digit relays (1R to 0R) in a digit register DR common to both registers. Each digit, which is to say each relay (1R to OR), indicates a group of outlets comprising one to four basic outlet groups. Each outlet group has a group busy circuit GBC to which application is made before the group may be searched for an outlet. Corresponding group busy circuits in three other group selectors having access to the same outlet groups are interconnected to deny access to the group so long as it is being searched by any one group selector. Supposing the wanted group is available for search, then the busy circuit GBC extends priming potential to a number (from 1 to 4) of transistors in an interrogation circuit INT each of which transistors can extend voltage to a set of ten links representing a basic group of ten outlets of the BS switching array. Each of these links has a diode pair to allow a lead to the outlet to hold the link at earth if the outlet is busy. Each busy circuit GBC primes its basic group representing transistors in INT and at the same time sends a start signal to a four-state counter MC which switches on the primed transistors in INT one by one thereby allowing the circuit INT to look for a free route in the basic groups one after the other. Where a link in INT is not marked busy from an outlet in a group indicated by a switched transistor it primes one of a set of 20 transistors (T0BS) indicating that BS switch giving access to that outlet of the group. Circuit INT also contains a set of 8 transistors (TAS) a conducting one of which indicates the calling AS switch and marks a set of 20 links each provided with diode pairs held to earth by leads to the corresponding links between the calling AS switch and the BS switches if any such link is busy. Where the INT links indicate free links they prime corresponding transistors (TIBS) in a set of twenty representing the BS switch available to the calling AS switch. The transistors (TOBS and TIBS) associated with the same BS switch are interconnected and when both are primed, one by backward marking and the other by forward marking, as explained above, they both conduct to indicate a free outlet of the basic group. Where more than one outlet is free in a basic group a one-out-of-ten preference circuit SC selects the lowest denomination outlet and locks out all others. The circuit SC indicates the selected outlet of the group by energizing one of the ten relays in a set (QA to ZA). As soon as a free outlet is found the counter MC is halted and the energized one of the four relays (GA to GD) indicates which basic group is involved. If the counter MC steps over all the basic groups without finding a free outlet, a busy condition is returned. Given three operated relays, one from each of the sets (1R to 0R), (QA to ZA), and (GA to GD) a marker OM is applied to and one out of 50 relays is energized to operate four contacts in its marking field, only one of these four contacts being switched to operating potential to bring up the selected A and B cross-points, operating coils for which are connected in the H-wire. The register and marker may now retire. The group busy circuits GBC, described above, allow the group selectors to look for free outlets provided they are each concerned with different groups. The circuits can be simplified if, among the four group selectors, only one is allowed to search for an outlet of any sort at any one time. The outlets may be divided into two major groups of 100 outlets each, one such group being accessible to the circuits AC when these are approached from one inlet and the other such group being accessible to the circuits AC when these are approached from a second inlet; such an arrangement forming the subjectmatter of Specification 1,102,865.