TELECOM Re: Are any of the #5 Crossbar offices still in service?

The 'Directorized' SxS systems were not that common, and of course

> they did not scale nearly as well as the 'real' common control > switches, but they did exist and they did work quite well. > The 'director' equipment (IIRC) sat between the linefinder and > first incoming selectors and recorded the dial pulses or DTMF > tones (yes, 712-366 had Touch Tone on step) and then either drove > the selectors for an intra-office call or handled the trunk > selection and outpulsing for an inter-office call.

Over here in the U.K. director SxS systems were employed in the six largest urban areas: London, Birmingham, Edinburgh, Glasgow, Liverpool, and Manchester. The directors were indeed between the linefinder and first selector, although they dropped out after the call was cut through so as to be available for other calls.

The directors could translate the 3-digit prefix into a string of routing digits to go into the local switching train or to select the appropriate outgoing trunk and then dial the necessary routing code(s) into that trunk. I forget the precise number now, but a prefix could be translated into anything up to a dozen or so digits if necessary. A store-and-forward register in the director then just repeated the last

4 digits of the number after it had finished its routing translation.

The first selector (which was controlled not directly by the susbcriber's dial but by the director) had the levels arranged to make the most efficient use depending upon local traffic patterns. Commonly used outgoing trunks could be connected directly from the first selector so that the director only had to pulse out a single digit to select them. Less commonly used trunks would be placed on second, or even third selectors.


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Paul Coxwell
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