ubuntu-phone team mailing list archive

[Jacob Nielsen <snobel@xxxxxxxxxxx>]

On 2015-12-10 08:35, Alfonso Sanchez-Beato wrote:
> On Wed, Dec 9, 2015 at 8:18 PM, sturmflut <sturmflut@xxxxxxxxxxxxxx 
> <mailto: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.

Thanks for looking into this. I haven't been able to find hard evidence 
that Telenor/Telia are using EPLMN, but according to this comment...

https://newz.dk/forbedret-3g-netvaerk-i-danmark-grundet-sammenlaegning#21

...from back when the TT network went active, they do:

"Telia and Telenor common network utilizes the new 66 code in areas 
where 3G is shared to support older 3G mobiles. Both operators have 
started to send this code in their EPLMN list which tells the phone that 
66 should be interpreted on an equal footing with their unique code (02 
for Telenor and 20 for Telia)"

Regards,
Jacob Nielsen

>     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