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Home Telephone Exchange Service and Systems Step-by-Step Dial Equipment
 
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Step-by-Step Dial Equipment

Step-by-step central-office equipment4,18,19 consists of three fundamental units: (1) line switches or line finder switches, (2) selector switches, and (3) connector switches, all of which may function in establishing a connection between two lines. (In a very small exchange the selector switches are not required as will be shown later.)

When a subscriber lifts the handset or the receiver, the line switch or line finder switch connects the calling line to a selector switch (or connector switch in a small installation), thereby closing a circuit from the subscriber line to the central-office equipment. When the dial is operated, this circuit is interrupted at regular intervals (depending upon the digit dialed), and the central-office switches are operated to connect the calling line to the called line.

Because much of the step-by-step apparatus is based on a two-motion switch invented by Strowger in about 1887, this switch will be described before proceeding with the operation of the step-by-step system.


Home Telephone Exchange Service and Systems Step-by-Step Dial Equipment

Last Update: 2011-05-30