ZTE MF622 USB Modem Under Linux

I recently bought a 3G wireless card to use with my laptop, a ZTE, model MF622.

Since the first time I tried linux, also the first time I encountered this kind of problems with my usb ADSL modem, and this being an usb modem also, I knew I was going to have troubles.

At first I tried USB ModeSwitch which has experimental support for ZTE's MF620 model with no luck. I then followed the instructions on the site to snoop the usb comunication under M$ Win to get the messages being sent to the device so I could mimic that under linux. Still, no luck.

I then tried to code a python script which used the libusb so that I could make the device switch to the modem configuration. Still, no luck.

I spent a lot of time on this subject and then one time I removed the usb_storage module while hal was waiting for the device to settle down and guess what!? After a few seconds, the device changed itself to the modem configuration. All I needed now was to automate this procedure.

Here's the udev script that does the job:

ACTION!="add", GOTO="ZTE_End"

# Is this the ZeroCD device?
SUBSYSTEM=="usb", SYSFS{idProduct}=="2000",
SYSFS{idVendor}=="19d2", GOTO="ZTE_ZeroCD"

# Is this the actual modem?
SUBSYSTEM=="usb", SYSFS{idProduct}=="0001",
SYSFS{idVendor}=="19d2", GOTO="ZTE_Modem"

LABEL="ZTE_ZeroCD"
# This is the ZeroCD part of the card, remove
# the usb_storage kernel module so
# it does not get treated like a storage device
RUN+="/sbin/rmmod usb_storage"

LABEL="ZTE_Modem"
# This is the Modem part of the card, let's
# load usbserial with the correct vendor
# and product ID's so we get our usb serial devices
RUN+="/sbin/modprobe usbserial vendor=0x19d2 product=0x0001",
# Make users belonging to the dialout group
# able to use the usb serial devices.
MODE="660", GROUP="dialout"

LABEL="ZTE_End" 

Save this file as /etc/udev.d/15-zte-mf622.rules for example(this path is a good one under (K)Ubuntu).

The next time you plug-in the modem, at first, the usb_storage module get's removed. After a few seconds, since the modem is not being handled like a storage device, it'll switch to the modem configuration. At this stage we tell udev to load the usbserial kernel module with the vendor and product id's and you'll get 3 ttyUSB devices. The /dev/ttyUSB0 will be the one you should use to make a connection.

You can now point ppp or wvdial to that device a start the connection, or, you might also want to check UMTSmon, this is an application suited for these kind of modems.