Importance

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Abstract

An automatic exchange of a telephone system comprises a PCM switching network with a plurality of cascaded stages for establishing temporal and spatial connections between incoming channels on input lines of the first stage and outgoing channels on output lines of the last stage in response to commands from external controllers dialoguing with internal controllers of the network. Pairs of switching matrices forming part of nonadjacent stages are combined into modular switching units each provided with its own internal controller. Routing instructions are transmitted from an external controller to a first internal controller which selects a signal path through the matrices of its own switching unit and informs a second internal controller of that selection whereupon the latter extends the path through an adjoining switching unit, and so on until the connection is completed. With digital message words such as speech bytes traveling in a forward direction from the input side to the output side of the network, the instruction words pertaining thereto move in the opposite direction over the same interstage links; the two paths are mutually conjugate within each switching unit, their matrices being bypassed by the routing instructions.

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First Claim