Patent GB-1115745-A (GB)
Title: Improvements to centrally controlled switching networks
IPC: H04Q3/545
Filed: 1965-06-30
Abstract: 1,115,745. Automatic exchange systems. P. LUCAS, J. DUQUESNE, P. LEGALL, and M. ROUZIER. 30 June, 1965 [30 June, 1964], No. 27734/65. Heading H4K. In a multi-stage switching network in which groups of subscribers' lines are served by associated line network blocks each having access to any one of an array of group selector network blocks each of which serves a group of junctors, some of the terminals on the junctor side of the group selector blocks are linked to terminals on the line network side of other such blocks so that, if a direct path across the network is not available because of congestion, alternative routes by way of the inter-group selector network block links (termed mutual aid links) can be put to use. The network is controlled by a programmed central processor and each network block has its own control register into which commands from the processor are loaded. The network can use crossbar switches or ferreed matrices and each link between switching stages in the line selector blocks, and each link in the group selector blocks, is associated with a two-state device which marks the link idle or busy in a network simulating the switching network. The two-state devices may control ferreed contacts or semi-conductor gates in the simulation network. The links between the line and group selector blocks are represented in the simulation network by AND gates which are tested serially in search of a match between free routes marked on one side through the group selector block simulation network and on the other side through the line switching block simulation network. A further set of AND gates represent the mutual aid links, selective connections being set up between the simulation networks of the two group selector blocks for which a serial inspection of the AND gates is undertaken in search for routes that are free across one group selector block from a junctor to a mutual aid link and free from that link over the other group selector block and a line switching block. As described the network has two-stage line switching blocks and threestage group selecting blocks. Each junctor is identified by digits ABCG where ABC identifies the junctor in the group served by selector block G. Each subscriber's line is identified by numbers KLN where KL identifies the subscriber in the group served by block N. In selecting a direct connection the simulation network is tested with fixed values of BC and successive trial values of the first interstage link parameter D in the group selector block, values of interstage link parameters E and F being implicit in the scan of AND gates which match free paths in the group and line blocks. In selecting a mutual aid route a free mutual aid link to a group block G<SP>1</SP> is found and a free path between this link and the subscriber's line over the block G<SP>1</SP> is searched for in the same manner as is a direct path to a junctor. A matching free path between the required junctor and the mutual aid link is sought by scanning the mutual aid AND gates in the simulation network. If no match is found for one mutual aid link another is tried; this corresponds to successive trial values of B and C in the assistance group selector block G<SP>1</SP>, each set of values of B and C in G<SP>1</SP> determining corresponding values of parameters D and E in the group block G serving the required junctor. If assistance block G<SP>1</SP> proves to have no mutual aid link giving access to the junctor over G, further tests are conducted with another assistance block and so on until a free path is found or until all possibilities have been exhausted. Search for direct paths is confined to the route selection equipment of one group selector block and the central processor can conduct at the same time as many searches for direct connections as there are blocks. Searches for mutual aid paths are conducted by a route selection circuit common to the group selection blocks since pairs of blocks have to be accessed and worked in unison to find a free route. Mutual aid routes are therefore handled by the processor one-at-a-time for the network.