Abbreviated as SxS.
"An automatic switching system in which a call is extended progressively step-by-step to the desired terminal under direct control of pulses from a customer's dial or from a sender."
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Engineering and
Operations in the
Bell System, 1977
A Step by Step System is an
outdated type of
telephone routing. As of 1977, about 34% of all telephone lines in the US were served by this type of switching. Since then, the percentage has dropped closer to zero. This is largely due to the fact that Step by Step switching works only with
pulse dialing and does not handle things like
tone dialing, which are basic requirements these days.
Step by Step switching is a direct progressive control system. This means that the dialing pulses generated by a
telephone directly control the stepping switches, and each successive
signal affects the
route through the system. A Step by Step switch is an
electromechanical device, meaning that connections are made using
rotary stepping motors and
contact brushes. This makes them cheap to
manufacture and easy to
expand, but very hard to
upgrade for new functions.