LE910 connection with custom APN on AT&T SIM

[David McCullough]

Hi Bjørn,

Comments below.

Bjørn Mork wrote the following:
> Nate Pleasant <nate.pleasant at accelerated.com> writes:
> 
> > I have a Telit LE910 modem that ModemManager doesn't seem to be able
> > to connect with when using an AT&T SIM card with a custom APN.  See
> > output and debug messages below for reference.  If I connect this same
> > SIM card with a Sierra MC7354 or Sierra MC7455 modem, it's able to
> > connect with ModemManager just fine.  Is there something I'm missing
> > when connecting with this Telit LE910 modem?
> 
> I hope some Telit experts will chime in if I am wrong but the LE910 is
> based on an Intel chipset, isn't it?
> 
> If so, then I think some of the findings wrt the Sierra Wireless EM7345
> are relevant. My memory is foggy at best, but I found this:
> https://lists.freedesktop.org/archives/libmbim-devel/2014-May/000283.html
> 
> There were a few surprises (to me at least) there.  I don't know how
> much of that has been fixed/changed in newer firmware revisions.  But
> some issues to be aware of:
> 
> - the modem might bring up a default bearer using some APN you never
>  configured, based on the SIM/operator.

We have seen this on Sierra modems as well when the AT+CGDCONT list has
APN's but we are connecting through QMI,  sometimes it uses the APN from
the +CGDCONT list.


> - this default bearer can conflict with later attempts to connect other
>   APNs using MBIM and the same IP-type.  Note that in my case I could
>   easily detect this error since I knew the two APNs used different
>   address types (global vs rfc1918)
> 
> - you might be able to work around the issues by explictly configuring
>   contexts before attempting to do an MBIM connect.


We actually do this,  we have a wrapper that ensures before we connect that
the AT command versions and the MBIM versions of all contexts match.

It has saved us on more than one modem.


> My proposal is to play with the AT+CGDCONT list and see if it changes
> the behaviour in any way.


We have learned that the data session is working, we can use the telit
socket commands (at#sd etc) to make a connection to a website and load a web
page,  however,  no traffic seems to pass through the wwan0 interface.

We can however put another SIM in there and have it work fine.  It sure is
confusing.

I would suspect the MBIM driver if it were not for the large number of
working SIM/APN combinations that work.  This particular SIM/custom APN is
the first we have had that does not work,  yet clearly the data connection
is working on the radio side.

Big thanks for any and all ideas :-),

Cheers,
Davidm


-- 
David McCullough,  david.mccullough at accelerated.com,   Ph: 0410 560 763