Google searches have only yielded 5th grade level examples (“the modem talks between your ISP and your home network!”) or articles I would need a degree to understand. Can anyone provide an explanation that’s somewhere in between the two? I understand the fundamentals of how the Internet works, and how LAN works regarding a router and individual devices, but I’m curious to know more about the link between those.
It used to be a lot simpler. The “Modem” received a stream of serial data (UART/RS232 + AT control codes).
The digital stream needed to be “encoded” and converted to electrical signals which could be sent on a physical wire… most often the PSTN network (Public service telephone network)… aka “the phone line”.
The audio/analoge technique used to produce the electrical signals was not as you might expect sending “blips” for 1s and silence for 0s. For way out of scope reasons that isn’t efficient. Techniques like PCM or PWM, Pulse code/width modulation. Beyond the scope. However this gets you the “MODulator”, “DEModulator”. Which is you “MoDem”
Today, these still exist. Most would refer to them as “dial up modems”. Rare. We tend to have “home broadband” technologies today which range from plain old twisted pair phone lines carrying 100s of times more bandwidth than an “analogu phone line”, but over the same wires. We have old “Coax” cable for “Cable TV” carrying high speed internet. We even now have pure optical fibre connections in to the home.
At this point, really, it can be argued there is no modem. Certainly not in the terminology used to previously describe one. What often gets refered to as the “Modem” is usually an ONT or similar ePon/docsis device controlled by an ISP which “converts” or “bridges” the optical (or other broadband signal) to “Ethernet”. Most, not all then additionally handle the authentication and “PPP” Peer to peer protocol used to transmit your data over this “You-ISP network”. In larger enterprise these components can be broken down into individual (or multitudes of) different boxes. ONT, PPPoE client, Router, Firewall, Switch, Wifi Access point. In most homes they will either be a single box provided by the ISP or 2 boxes with one provided by the “Network operator” and the other by your “Internet retailer.”