ubuntu-phone team mailing list archive

[Alfonso Sanchez-Beato <alfonso.sanchez-beato@xxxxxxxxxxxxx>]

On Wed, Dec 9, 2015 at 8:18 PM, sturmflut <sturmflut@xxxxxxxxxxxxxx> wrote:

> Dear list,
>
> I'm the original reporter of bug 1449990. Today I took the time to read
> the technical stuff (3GPP standards) to find out how National Roaming is
> supposed to be implemented, and then I tried to find out what the
> operators are actually doing and why it just works on Android.
>
> Hope this helps:
>
> Assuming a 3GPP-compliant handset (any smartphone should do) and
> assuming the operators don't want to hand out new SIM cards to
> everybody, the way to go is to use the "Equivalent PLMN" (EPLMN) list
> stored on the SIM card. All mobile networks on this list have to be
> considered equal by the device, so if I put my home network "E-Plus" and
> the "other" network ("O2") on it, the phone has to treat O2 like my home
> network.
>

Historically MVNOs have used EF_SPDI and EF_OPL to define which are their
home networks. We have not seen yet the case of the more modern EF_PLMN
file being used, although that is what would be the right thing to do
according to the standards. I will try to produce a debugging version of
ofono to see if you have that file on your SIM, will contact you later on
irc.

However, note that the modem is the one which decides whether to jump in
into one or another network. The only thing that we do on the Ubuntu side
is to avoid showing the roaming flag in case the network we are registered
to is on one of the lists above, which is a workaround for a modem FW bug,
that is "lying" and telling us it is roaming when it is not. In fact, this
is necessary only for MTK modems, Qualcomm modems handle this nicely.

So taking into account EF_PLMN if present will only solve issues with
roaming status, but will not influence network selection as that is handled
internally by the modem.


>
> The trick is that this list can be automatically updated over the
> network by the home operator, so the process is seamless to the
> subscriber and requires at most a device reboot.
>
>
> http://mobilesociety.typepad.com/mobile_life/2015/06/equivalent-plmns-in-germany-telefonica-o2-and-eplus-network-network-integration.html
> documents that my operators are using this feature.
>
> So I think the question is: Do our Ubuntu phones maybe not honor the
> EPLMN? Is there a way to debug this any further, maybe dump the
> currently used SIM parameters?
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Br,
Alfonso