Hi …
I’ve been around with a E156 some time ago, on PC Engines WRAP. At that time ROS 3.16. Today is 3.21.
I don’t know if E156 is closer to E220 or E169 but E156 have those built-in virtual CDROM (which carries win drivers) and a Mini-SD card adaptor.
Anyway, when connected E156 (may be others) creates two USB ports: in my case USB1 = modem data port and USB2 = serial data port (telemetry, AT comands, etc). This ports does not show up as separated ones at Winbox system => resources => USB tab. There will be a single Huawei 3G etc etc.
To make this guy stable (and connected all the time) I needed to disable in “system\console” the serial0 VT102 terminal. Since then, modem connected all the time. But this was 3.16.
From 3.17 afterwards, it was not necessary disable this VT102 anymore.
My initialization string is just … ATZ … because the usual [modem-init=""AT+CGDCONT=1,“ip” …] normally is stored at the modem flash. I set WCDMA only / 2100MHz using windows GUI first. Then installed the modem on Wrap (I used to know the AT command for that … long time ago).
My mobile providor uses only PAP so I disabled all the rest (CHAP/MSCHAP 1 & 2). When all enabled modem tries to conect endless.
On hardware side … 3G modems sinks a lot of current (0.5A). WRAP does provide only 0.1A so I needed to build a power injector to deliver 5V @ 1A max to this particular USB port. With marginal current there was some unstable behaviour.
(my private “home WISP” pix = http://py.qsl.br/wrap_img.htm … I use this to provide WLAN around my home at countryside)
Regards