Re: new problems with connecting with an LTE modem

[Dan Williams <dcbw redhat com>]

On Fri, 2016-05-20 at 16:10 +0200, Bhima wrote:
> Hi Guys!
>
> I'm having problems with a Sierra MC7710 LTE modem, running in a
> Soekris 
> Net6501, after a recent update to Ubuntu 16.04 to the 4.4.0-22-
> generic 
> kernel.  For the past few years I've been using the qmi-network
> helper 
> script to connect cdc-wdm0, which in turn created a wwan0 port.  Now 
> that's all gone pear shaped and I've gone around in circles trying 
> figure out what's gone wrong.
>
> looking in dmesg, I see that wwan0 is actually getting renamed to 
> wwp2s2f3u3i8, which is confirmed by status returned by "mmcli -m 0" 
> (ports: 'ttyUSB0 (qcdm), ttyUSB2 (at), cdc-wdm0 (qmi), wwp2s2f3u3i8 
> (net)').  I can get a dhcp address on 'wwp2s2f3u3i8' but the
> throughput 
> on the resulting channel is severely constrained.
>
> So now I'm wondering what exactly the proper way to configure and
> use 
> this modem from the command line these days.

Probably the same way you always have; as you've found the interface is
now named something different, which is happening because of udev's
interface renaming policy in the updated Ubuntu release.  But it's
still the same interface as before and should work the same way as
before.

How much of a drop in throughput have you've found?  Any throughput
drop will likely be related to kernel driver changes in qmi_wwan and
the kernel USB layer, as opposed to something in ModemManager itself or
the qmi-network script.  When the througput is bad, what is the signal
strength of LTE connection?

Dan