Some years ago I configured some raspberrys with a 3g dongle modem (usb) to work in headless mode. Due to the instability of the 3g connection (or the modem itself) I ended up making a rather complex script to recover the connection in case of losing it. If the connection could not recover it I had to put a relay to cut the power to the modem.
My doubt, as 3 or more years have passed since this, is if there is any way to manage the interface wwan0 or ppp0 from the operating system itself, so that the operating system controls the reconnections.
Somebody with personal experience with USB modem and headless system to tell me your experience?