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.
Cable modems use the DOCSIS standard. On the downstream to everyone’s house, everyone’s data packets are combined by a CMTS into electrical signals using various modulation techniques. Modems extract the data addressed to that home and convert it to ethernet. For the upstream, modem’s are given specific time slots to broadcast (time division multiplex) so their signals do not collide with other modems.
It is more complex than that covering both MAC-PHY (layer 2 and 1), but over that it’s just IPs. If you want to know more, I would start looking for introductory material on DOCSIS.