"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."
in the Bell System
A Step by Step System is an outdated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