The technology behind telecommunication.

Today everything happens inside your router, fast and silent. My father was a telecommunications engineer. When I was a amall boy (late 1980s) he once took me to his workplace (it was in the evening and he was supposed to troubleshoot). What today fits onto a few silicone chips inside a router took much more space back them.

I was in a room that was filled with several wardsobe-sized cabinets. Inside there were hundreds of electro-mechanical relays that were in motion, spinning and clicking, each time someone in the city dialed a number (back then rotary phones were quite common). It was quite loud. There also was a phone receptor inside one of the cabinets where one could tap into an established connection, listening into the conversation two strage people had (it was for checking if a connectiion works).

I still remeber the distinct "electrical" smell of that room (probably hazardous vapors from long forbidden cable insulation and other electrical components).

So when you dialed a number at one place with your rotary phone, you were able to move some electro-mechanical parts at another place that could be located somewhere else around the globe (hence long distance calls).