PPP protocol over serial port

Question

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,

Answer 1

You'll find the original PPP RFC documents listed at the bottom of this Wikipedia writeup on PPP.

I would start by reading Section 3 in RFC 1661.

LWIP is one of the better documented/supported lightweight implementations of PPP. (actually full TCP) However, the source is still several thousands of lines and in my opinion daunting to a newcomer.

This is the smallest working implementation of PPP that I know of. It's easy to get to work on mbed-supported boards AFTER following the instructions on how to set up PPP networking on Windows. (Did not test it on a Linux box)

Depending on your application, it might indeed be simpler to define your own protocol to transfer data between your WIFI SOC and a Linux box.

For example, this lab is a good guide on how to use node.js to move embedded data to the internet via a serial port and a PC.

Answer 2

I'm not sure if you have already resolved your problem, if yes, we could have your courtesy for sharing the solution.

if not,you need to make sure your SOC is listed in your linux as a tty/serial device and that you are able to execute AT commands on it like you would do with any serial modem.

If the above is happening, you need to make sure you have someone to dial to, like a server with a similar setup to answer "the call".

You need to read the "PPP Howto" and setup PPP in both ends and it will work as an old 56k dial up connection.