Where can I find some low level information about old days PPP protocol modems, over serial line? I have a embedded WiFi SOC that I want to use from linux as a modem, so "connect" via AT commands, configure, etc, then relay all TCP packets transparently.

I know it can be done since a lot of GSM modems perform this (via AT) but I cannot find a useful start how to implement in SOC (a lot of garbage from google). I mean what will be the logical flow so linux drivers can see a standard modem.

I also presume that I can skip the PPP part and redirect somehow (make a virtual adapter in linux side) that will exchange packets over serial line in a proprietary format, eventually helped by flow control and or other GPIOs tied to my SOC but I feel that I am re-inventing the wheel.

Thanks for suggestions,