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
Multiple phone lines. In the old days (90’s and before), they’d actually pull bundles of cables instead of a single pair for a single phone line. Each pair would be connected to a modem. There would be banks of modems in racks to do just that. The modems would be connected to a network router that connected to the internet via a T1 or similar. The phone number is just what’s assigned at the phone company. It has a switch that routes calls to a single phone number to the next open line in the bundle that they send to the customer.
But yes, at it’s core, the phone copper goes from the customer house all the way to the ISP’s modem. It went through several switches that physically connect one set of copper wires to another. A modem is just a device that converts an analog signal to a digital signal. Once at the ISP’s modem, the digital signal goes through the ISP’s router to the internet.
Source: I was a sysadmin at an ISP in the early 2000’s.
Latest Answers