[lwip-users] lwip with 4G modem

[Giuseppe Modugno]

I have an embedded project where lwip is used in a microcontroller 
(Cortex-M3 by LPC). The network interface is a standard Ethernet. The 
MCU features a MMI interface with an external Ethernet PHY.

It works well, I'm able to open a MQTTs connection with a broker, enable 
NTP request, download some file from HTTP server.

Now I'd like to use this project as a base for a new project, where the 
network interface will be replaced by a 4G modem that is controlled by 
standard AT commands.

My question is: what should I change in my project to replace Ethernet 
with 4G modem? I think I have to use ppp over a serial line to open a 4G 
data connection and it seems ppp is supported by lwip distribution.

Another question (I don't know if it is OT), will I be able to make 
voice calls at the same time the data connection is open and active? The 
serial channel for ppp/data and AT commands is single, so how can I 
multiplex them? Should I use CMUX?

Last question. If I have 4G modem and Ethernet PHY, is lwip able to 
manage two network interface at the same time?