A switching system of some sort is needed to enable any terminal (e.g. a telephone, a teleprinter, a facsimile unit) to pass information to any other terminal, as selected by the calling customer.

If the network is small, direct links, (Fig. 38.1) can be provided between each possible pair of terminals and a simple selecting switch installed at each terminal. If there are five terminals, each must be able to access four links, so if there are N terminals there must be a total of ½N (N–1) links.

A slightly different approach would be to have one link permanently connected to each terminal, always used for calls to that particular terminal (Fig. 38.2). Again, each terminal would need a selection switch to choose the ...

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