GB1432775A - Telephone exchange apparatus - Google Patents

Abstract

1432775 Automatic exchange systems GENERAL ELECTRIC CO Ltd 6 July 1973 [26 July 1972] 35042/72 Heading H4K In a telephone exchange comprising a plurality of cascade-connected switching stages the subscribers of the exchange are connected to one side of a plurality of first stage units and incoming and outgoing junctions are connected to one side of a plurality of final stage units and the exchange is adapted to effect a connection between an incoming and an outgoing junction by the operation of only two crosspoint switches, these switches being situated in the final stage units. Cross-bar switches are preferably employed but reed relays may be substituted therefor. The exchange is a PABX and the incoming/ outgoing junctions 14, 15 are tie lines. In normal operation a calling extension is connected through to a register 10 via an A stage, a B stage and a C stage, C3 or C4. On receipt of the dialled digits a common control in known manner completes a connection either to a further extension using a C1 or C2 stage in place of the C3 or C4 stage or to an external outgoing line 13. An incoming external call on line 14 is connected to an operator who by dialling the appropriate digits completes a connection to the required extension. Alternatively the extension may be obtained by. direct inward dialling. However it is also possible for the operator to complete a connection to an outgoing line 13 by dialling appropriate digits. The common control then operates two crosspoints in the appropriate C3 or C4 stage. Where the stage C3 or C4 employ cross-bar switches this is achieved by operating two select magnets and one bridge magnet. In a modification to the trunking shown some of the paths between the B and C3, C4 stages may be multipled to both the latter switch units and the external lines may not be multipled to both these switch units as shown. A connection between two external lines then involves one cross-point in each of two C stages.