How did old dial phones figure out where the call is going without having a computer inside? What is the mechanism behind the dial?
In: Technology
Phones don’t decide where calls are going. The only thing any phone does is send and receive signals to its network. Even when you make a cell phone call, all it’s doing is sending a phone number to its tower, and it’s the machinery behind the tower that does the work of connecting a call.
Originally, you didn’t even dial numbers. When you picked up the phone, you waited for an operator to notice (you might have a way to ring a bell to draw their attention). Then you’d tell them who you wanted to connect to, and they’d manually make the connection. They sat at a machine called a “switchboard”, and they were a “switchboard operator”, which is why we called them “an operator” for short.
Phones still work that way, but we’ve mostly replaced operators with machines.
The phone is connected to machines that can receive those signals. When you use a touch-tone phone, the machine is listening for those specific sounds and it uses the series of numbers to talk with other machines to connect the call, just like the operator did. When you use a rotary phone, the spinning part of the phone generates electrical pulses at a specific speed. Dialing 9 makes 9 pulses, dialing 1 makes 1 pulse, etc. The machines at the phone company count the pulses, figure out the number, then do the same thing they’d do for a touch-tone call.
In a way, it’s a very simple version of how we used to get internet over plain old phone lines! A modem is just a device that can send signals over a phone wire. Some people say it plays sounds over a phone, but sound is just an electrical signal on the wire to the phone. So it would “pick up” the line, send the signals for the number to an ISP, then start sending signals to the ISP’s machines that, while we could hear the noise if we picked up the phone, these signals were meant to efficiently transmit data about internet traffic, not sound pleasant!
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