Garbled description with --nas-get-serving-system

[Paul Gildea]

Great, thanks Daniele.

On Wed 11 Dec 2019, 07:51 Daniele Palmas, <dnlplm at gmail.com> wrote:

> Hi Paul,
>
> Il giorno mar 3 dic 2019 alle ore 15:36 Paul Gildea <gildeap at tcd.ie> ha
> scritto:
> >
> > Hi Daniele,
> >
> > I've tried it with regular carrier and it worked ok. It didn't work for
> two different brand of private networks/EPC's that we tried here.
> >
>
> the issue has been fixed on the firmware side and will be possibly
> available in the next release.
>
> Thanks,
> Daniele
>
> > --
> > Paul
> >
> > On Mon, 2 Dec 2019 at 22:31, Daniele Palmas <dnlplm at gmail.com> wrote:
> >>
> >> Hi all,
> >>
> >> Il giorno lun 2 dic 2019 alle ore 17:27 Aleksander Morgado
> >> <aleksander at aleksander.es> ha scritto:
> >> >
> >> > Hey!
> >> >
> >> > > > Hi, I was wondering had any knowledge of an issue we are seeing.
> We
> >> > > > are
> >> > > > connecting to private networks we are running on two different
> brands
> >> > > > of
> >> > > > EPC. Then, we are using libqmi to query the modem for the network
> >> > > > info via
> >> > > > --nas-get-serving-system
> >> > >
> >> > > 0A:      D4:F2:9C:EE:2C:D3:EF:6F:F9:1A
> >> > > ^length  ^ data
> >> > >
> >> > > So length is 10 bytes, but in ASCII "TestNetwork" is 11 bytes long.
> >> > > Hmm. What do we know packs more than one character into each byte...
> >> > >
> >> > > The string is most likely GSM7 encoded and libqmi is expecting all
> >> > > strings in UTF8, which is what almost everything in QMI is reported
> as.
> >> > >
> >> > > So my best guess is that the Telit modem firmware is not correctly
> >> > > converting the network name to Unicode for us. Every other QMI
> >> > > implementation we've seen does :)
> >> > >
> >> > > ModemManager has some special code to ignore the description when
> it's
> >> > > not UTF-8 safe, and libqmi only does it for printable stuff like
> what
> >> > > qmicli outputs. Perhaps it could work around the Telit firmware
> >> > > somehow.
> >> > >
> >> >
> >> > Other messages, like "Get Home Network" (0x0025), have a special TLV
> >> > indicating the encoding of the network description with the following
> >> > supported values:
> >> > • 0x00 – Octet, unspecified
> >> > • 0x02 – 7-bit ASCII
> >> > • 0x04 – Unicode
> >> > • 0x09 – GSM 7-bit default
> >> >
> >> > I don't know of any such TLV in "Get Serving System", but maybe
> >> > there's a new one we don't know of. There isn't any unknown one in the
> >> > provided message as far as I can see.
> >> >
> >> > As Dan said, ModemManager has UTF-8 validity checks before using the
> >> > strings, but the printable TLV descriptions in libqmi and the qmicli
> >> > output lack that logic.
> >> >
> >> > @Daniele Palmas @Carlo Lobrano do you know if this is a Telit specific
> >> > issue or a more generic one? Is the firmware preferring the GSM-7
> >> > output for this field over Unicode when the characters fit in GSM-7?
> >> >
> >>
> >> let me check this, it will take a few days.
> >>
> >> @Paul, is this happening only with your test network or also with
> >> normal carriers? I'm not seeing the issue in normal usage.
> >>
> >> Regards,
> >> Daniele
> >>
> >> > --
> >> > Aleksander
> >> > https://aleksander.es
>
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