alt Hacker NewsReally, its own internet system before the internet. Massive load of calls. The routing has to be correct. I never understood it before working in telecom, but phones numbers are unique... for routing, like IP-addresses. And it could never go "down". In the 80s it was all digial too (Ericsson switches) and had to be real-time.
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Combination of Ericsson and GEC/Plessey/BT "System X" (see https://en.wikipedia.org/wiki/System_X_(telephony)). Erisson AXE10 was known as "System Y" in the UK and a hedge against buying exclusively System X equipment.
> Really, its own internet system before the internet. ... for routing, like IP-addresses.
There's a great video from Connections Museum (mentioned further up the thread) where they're going through the operation of, I want to say, one of those crossbar switches? And they start using terminology like "routing table", "longest-prefix matching", and "default route", which all sounds well and good, until you realize they're talking about systems that existed decades before the Internet or even ARPANET, all electromechanical... Dope stuff. Cool to see how things rhyme even as they change.
Before modern digital electronics, telephone numbers were literal routes - when the turned dial on your phone ran back to zero, a corresponding 10-pole motorised rotary switch at the exchange turned and connected you to one of 10 lines. This connected you to another such rotary switch for the next digit, until eventually you were connected to the final destination. The ingenious Strowger exchange.