How did dial up ISPs handle multiple concurrent calls?

Question

I’m trying to understand how an ISP could handle multiple concurrent calls on a single phone number? And did they need a physical modem for each connection? How did this scale to medium to large cities with millions of people? How did the call get transferred from copper wiring between the modem at home, to a modem in an exchange somewhere? What was that modem connected to? Did it vary between countries?

My naive understanding is that there is a direct connection (circuit) between the two modems, but I don’t understand how you could support two concurrent calls on one number.

In: 1

Answer 1

https://www.wikiwand.com/en/Dial-up_Internet_access#Media/File:Modem-bank-1.jpg here’s what it might have looked like.