Re: ttyACM0, ttyUSB0, usb0 ???

[Dan Williams <dcbw redhat com>]

On Mon, 2010-02-01 at 10:11 -0200, José Queiroz wrote:
> Hi,
> 
> I used to use a 3g usb dongle (Sony MD300). The first time I plugged
> it, it created a device called "ttyACM0", in a way that I could use
> wvdial and use pppd to conect it.
> 
> But after some updates on NetworkManager, it started to show up as
> "usb0", and the pppd process was hidden in some way that wvdial could
> no more work.

The Sony Ericsson MD300/MD400, F3507g, and F3607gw don't normally use
PPP.  Instead, they provide a ttyACM0 control channel and a cdc-ether
usb0 network device.  The control channel is used to set up the
connection, and then DHCP is used on the usb0 network device.

Keep in mind that PPP is entirely pointless on 3G networks; the PPP is
solely between your computer and the dongle, and it actually slows
connections down to the point where you cannot achieve 3.6Mbps or
7.2Mbps HSDPA transfer rates.

> Now I have another dongle (Onda MSA405HS), from another ISP, and when
> I plug it, it shows up as "ttyUSB2". I can easily connect using
> wvdial, but NetworkManager doesn't works.

The ONDA/ZTE device does use PPP since it does not have the capability
to bypass PPP and use a network device.

> My questions:
> 
> 1) Why did the MD300 changed from "ttyACM0" to "usb0"? Will this be a
> rule, in all 3g connections?

Not all cards support bypassing PPP.  Only Ericsson and Option cards
support it at this time.

> 2) Why didn't "ttyUSB2" turned into "usb0", also?

Because the ZTE/ONDA device's firmware does not have the capability to
bypass PPP.

> 3) The MSA405HS have 2 other devices, "ttyUSB0" and "ttyUSB1". Why do
> NM chooses to work with "ttyUSB2"?

ModemManager automatically detects the modem ports that a device
provides, but sometimes the device only handles PPP on one of its ports.
Unfortunately we can't always automatically detect that, so ModemManager
needs a little help.

You may need to update your version of ModemManager to get a new version
of the /lib/udev/rules.d/77-mm-zte-port-types.rules file.  If you don't
see your device's USB IDs in that file, please tell me:

1) what the USB IDs of your device are
2) what port works for PPP (ie, what you can use with wvdial)

and I'll update that file which will make ModemManager use the correct
port.

> 4) How can I configure NM to give me more information, said, activate
> debug messages right from boot?

Run it with --no-daemon.  Or just look in /var/log/messages
or /var/log/daemon.log, depending on your distribution.

> 5) I created a connection called "Claro3G" to use with the MD300, and
> another one called "TimWeb" to use with the MSA405HS. How can I assure
> that "Claro3G" will use the "usb0" device, and "TimWeb" will use
> "ttyUSB2"?

At this point it's not possible, but will be in the future.  We need to
find a unqiue identifier to "lock" a connection to a specific device;
that can't be the USB ID because often many different devices will have
the same USB ID (Huawei) or there are of course locked and unlocked
versions of the same device.  So this will probably end up being based
on your IMSI or (for CDMA) the ESN.

Dan