Patent GB-1134499-A (GB)
Title: Automatic telecommunication exchange system
IPC: H04Q3/54
Filed: 1965-12-01
Abstract: 1,134,499. Automatic exchange systems. CIT-COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS. 1 Dec., 1965 [2 Dec., 1964; 15 Dec., 1964; 15 March, 1965], No. 51070/65. Heading H4K. An exchange has line switching network frames each serving a group of subscribers and each being linked to a group selector network, each inlet to the line switching network being available both for call originations using links to the originating side of the group selector network and for call terminations using links to the terminating side of the group selecting network, the linking between the line network and the group selecting network being such that it is necessary to prohibit the use of homologously related switches on each side of the group selecting network when a connection is being set up between subscribers from the same group. If homologous switches were employed the path over the group selecting network would be looped to the same inlet of the line switching network and the feed bridge located in the group selector would be short circuited. Cross-bar switches are employed for the networks. The group selecting network comprises a number of parallel acting switch frames each having an originating stage linked by way of feed-bridges to a terminating stage. The marking system extends potential from the calling and wanted subscribers' appearances in the line switching network to obtain at a first step the identity of a group selector switch frame that is accessible to the subscribers on both sides. Having determined such a frame, the marking network is employed to obtain the identity of free originating and terminating switch inlets providing a path across the frame. As shown in Fig. 8, marking wires corresponding to links from subscribers' groups GA1- GA20 to each of the originating and terminating switches of a group selector frame are commoned at points CG and CS, respectively. Each originating switch has a saturable core TI, a winding of which is connected between the common CG and the common CS of its homologously related switch, and also has a core TA, a winding of which is connected between the common CG and the commons CS of all terminating switches other than the homologously related one. Each terminating switch is similarly, provided with saturable cores TI, TA, except that the connections of the marking wires to commons CG is dependant upon contacts CX associated with each terminating switch. If the inlet of an originating switch is busy, a corresponding contact Ml disconnects the associated marking wire; contacts M2 similarly indicating the busy condition of inlets of the terminating switches. Marking current from the line switching network turns over cores TI, TA, of the originating switches if they have free inlets giving access to the wanted subscriber's group. A control circuit associated with the group selector switch frame detects which cores turn over to catalogue available switches. By closing the contacts CX it can be seen by the turning over of cores TI, TA of the terminating switches which of such switches have a free inlet suitable to complete a path across the group selector frame. If the calling and wanted subscribers belong to the same group, the switch frame control circuit energizes bias windings ei on the cores TI so that they cannot be turned over and consequently blocks all routes that might involve homologously related switches in the originating and terminating stages. Each subscriber's group line switching frame is served by its own group of registers.