Re: Augmenting mobile-broadband-provider-info

[Denis Kenzior <denkenz gmail com>]

Hi Dan,

On Wed, Jan 20, 2010 at 3:10 PM, Dan Williams <dcbw redhat com> wrote:
>
> On Mon, 2009-11-23 at 17:15 +0100, Marcel Holtmann wrote:
> > Hi Antti,
> >
> > > > you can't trust the network name string returned by AT+COPS since there
> > > > are so many factors coming into play here. So first of all you have the
> > > > names stored in the modem itself, then the names stored on the SIM card
> > > > and then the potential updates over the network. Every hardware does
> > > > different things to present the result of AT+COPS.
> > >
> > > AFAIK if there's a name stored in the SIM card it will have precedence
> > > over the ones stored inside the modem. And the ones that network sends
> > > are probably most reliable. I have to look though the specs if there's
> > > any information on this.
> > >
> > > Anyway the point is that in most situations we should have a correct
> > > alphabetical name for the provider, right?
> >
> > I have seen different hardware with the same SIM card give different
> > names. And I also have seen different SIM card with the same hardware
> > result in different results.
> >
> > Also you have the problem that names change over time and some hardware
> > and SIM card combination returns still the old one, while newer pieces
> > would give you the new name.
>
> T-Mobile USA hasn't been Voicestream Wireless since 2002, but my ZTE
> MF627 (a quite recent device sold by 3UK) returns:
>
> +COPS: (2,"AT&T@","AT&TD","310410",0),(3,"Voicestream Wireless Corporation","VSTREAM","31026",0),
>
> The SIM is a T-Mobile US SIM that is known to return "T-Mobile" in most
> other cases.  And what's up with the "AT&T@" and "AT&TD" anyway?
>
> Basically, we simply can't trust that the COPS results are going to be
> in any way accurate...
>

Fully agreed, the COPS name is junk, and on properly implemented
hardware the COPS name can actually
change once the network performs a NITZ update.  Unfortunately there's
no standard way of knowing what
name the hardware is reporting, the one burned into firmware or taken
from NITZ.  I've seen this happen on
the Freerunner.  Immediately after registering COPS returns
"Cingular", 5 minutes later it will return "AT&T".

Any such database has to account for the PCS digit for North American
carriers.  For instance, T-Mobile
SIMs are provisioned with 3 digit MNC, 260.  Yet most (all?) T-Mobile
cells will actually report a 2 digit
MNC, 26.  Whether the 3rd MNC digit is reported is completely up to
the network cell tower.  Refer to
table 10.5.3 in 3GPP 24.008.

Ultimately the SIM is the one to trust here, not COPS or any other
combination of COPS/CREG, etc.
Much of the COPS/CREG information can be ultimately overridden by the
contents of the SIM
elementary files like EFspn, EFspdi, EFehplmn, EFehplmnpi, EFpnn,
EFopl, etc.  Of course various
stacks / modems get this right in varying degrees of correctness.

Regards,
-Denis