ElI5 How do telephone wires carry multiple messages at once? How do messages not interrupt each other?
In: Technology
Once upon a time in the Stone Age, there were huge bundled cables packed with wire strands distributed all over the country, and each wire strand carried a single call signal, typically one frequency was used for “upstream” and another frequency for “downstream”. However, there were two wires in your phone jack where the final signal was sent/received by the telephone itself while indoors, and this was handled by the junction box down the street. Switching stations along the call route determined which wire was used (any not already in use) — in the old days, this was done manually, but after WW2 there was increasing interest in mechanical methods of directing call signals, which is why old rotary phone had clicks when dialing a number. Click dialing was eventually rendered obsolete by “touch tone” keypads, and around this time there was a slow increase in digital switching and signalling, and today everything is simply multiplexed.
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