Patent GB-1017768-A (GB)
Title: Improvements in telephone switching systems
IPC: H04Q3/00
Filed: 1963-11-22
Abstract: 1,017,768. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Nov. 22, 1963 [Nov. 28, 1962], No. 46213/63. Heading H4K. In a system comprising a plurality of stages of cross-point matrices and a route selection network comprising a plurality of so-called " nodes " of which there is one per matrix, an inlet and outlet of the network are marked whereby all free " nodes " corresponding to available paths through the system are marked in turn starting from the inlet whereafter one " node " in each stage is selected in turn, starting from the outlet whereby a unique path through the network and hence through the system is obtained. A node (Fig. 1b) comprises a plurality of AND gates each of which corresponds to an inlet of the associated cross-point matrix, i.e. E ei  is the gate equivalent to the first inlet of the first matrix in stage A. Each gate has an inlet d connected to a link availability circuit whereby if the link in the switching system corresponding to the centre inlet of the gate is free an actuating potential appears on d and an inlet f connected to a pulse distributer circuit whereby any one gate in each node may be selected. The outlets of the gates in each node are commoned and then linked to inlets of nodes in the succeeding stage in the same manner as the trunking between stages of the switching network. The latter may comprise cross-bar, cross-coil, reed-relay, cold cathode or transistor switches. Selecting a free path (Fig. 2).-The selected inlet Ei and outlet Sj of the selecting network are marked, the link availability circuit 9 marks the d wire of all free links and a selector 14 marks the gates such as 8 and 16 of the inlet and outlet nodes 2 and 4 respectively. Consequently, bi-stable circuit 5 in node 2 operates and applies a marking to all the nodes such as 3 in stage B to which it is linked. A distributer 10 successively pulses the AND gates of each node so that eventually a gate such as 11 in node 3 conducts and sets bistable circuit 6. Similarly, bi-stable circuit 7 in node 4 is set and at the same time a pulse or more usually a series of pulses, is passed to identifier 15 whereby the initial marking process is terminated. The time positions of the pulses produced by distributer 10 each correspond to a particular gate in the nodes. Consequently gate 16 passes a pulse for each free gate in node 4 and the time position of these pulses indicates which gate has transmitted it. One gate is selected by identifier 15 which then causes selector 14 to mark the node in the preceding stage to which the chosen gate has access. This marking is effected over lead 19. Again a number of pulses are transmitted from distributer 10 via gates such as 11 and gate 20 to the identifier. (In the case of B stage of course only one gate, e.g. gate 11, can be simultaneously marked on all three inlets). When a complete path is selected in this manner a marker is operated in order to set up the corresponding path through the switching network. Overflow arrangements.-A trunking diagram wherein some later stages are connected via overflow matrices in earlier stages is depicted in Fig. 4 (not shown). In order to prevent setting-up a path via the overflow network when in fact shorter direct paths exist each node (Fig. 5, not shown) is provided with a delay line having a fixed delay time whereby marking is automatically stopped after pulses corresponding to direct paths are received, i.e. before pulses generated, as a result of free nodes being marked in the overflow network have time to reach the identifier. A node in the penultimate stage is then selected and the bistable devices in all preceding stages are reset, whereafter a new marking process using the selected penultimate node as the outlet of the network is then initiated. This process is repeated back through the network to the first stage whereby the shortest path is chosen. Group or PBX final selector.-If any one of a group of outlets of the switching network may be selected (Fig. 7, not shown), the route selector is provided with an additional node having input gates corresponding to each of the outlets (Fig. 8, not shown). The identifier can then select any one of the outlets in the manner described above. Reference has been directed by the Comptroller to Specification 897,676.