best regards
Mark
----- Original Message -----
From: "Marcel Holtmann" <mar...@holtmann.org>
To: "Dan Williams" <d...@redhat.com>
Cc: <networkmanager-list@gnome.org>
Sent: Wednesday, November 18, 2009 9:12 AM
Subject: Re: Does NetworkManager support blocking non-home networks
(UMTS/3g)
> Hi Dan,
>
>> > > > > > I can't seem to find it in the GUI or in the documentation.
>> > > > > >
>> > > > > > Can NetworkManager be configured to only connect to home
>> > > > > > networks? Say I
>> > > > > > am on Vodafone and get free data usage, but then move to an
>> > > > > > area with
>> > > > > > poor signal for Vodafone, can I prevent switching to
>> > > > > > T-Mobile
>> > > > > > which
>> > > > > > costs me money?
>> > > > > >
>> > > > > > If yes, can this be determined automatically, or is this
>> > > > > > done
>> > > > > > with a
>> > > > > > string match?
>> > > > >
>> > > > > For cards where we actually know the commands for controlling
>> > > > > roaming,
>> > > > > yes we can do this, otherwise NM will need to send the
>> > > > > specific
>> > > > > MCC/MNC
>> > > > > of your operator to the modem, which has its own problems.
>> > > > > This
>> > > > > is
>> > > > > definitely going to be fixed in the near future, but there's
>> > > > > no
>> > > > > facility
>> > > > > for doing so now other than entering the MCC/MNC of your
>> > > > > operator
>> > > > > into
>> > > > > teh Network entry in the connection editor.
>> > > >
>> > > > what do you mean by this. It makes no sense. Which card can be
>> > > > controlled to roam or not via its firmware. Normally this is all
>> > > > host
>> > > > stack stuff.
>> > >
>> > > Yeah, seems that's mostly CDMA cards right now. My bad.
>> >
>> > so with CDMA cards you can actually tell them to allow roaming or
>> > not?
>> > If so, do you get notifications when it does.
>> >
>> > > > You get the current MCC/MNC from the network notifications and
>> > > > your
>> > > > home
>> > > > network is part of the IMSI. Only trick part with the IMSI is
>> > > > that
>> > > > you
>> > > > have to check first if the MNC is two or three digits long. That
>> > > > value
>> > > > is stored somewhere in the SIM card.
>> > >
>> > > Does that mean talking directly to the SIM to find out the MNC
>> > > length?
>> > > There's boatloads of networks with 3-digit MNC (americas and India
>> > > mostly) so it would completely suck if you couldn't tell just from
>> > > the
>> > > MNC.
>> >
>> > Actually you really can't tell it by just looking at the IMSI. In
>> > oFono
>> > we have to do some heavy lifting to get this information out of the
>> > SIM
>> > card. And it is the only way to find the home network that actually
>> > issued your SIM card (at least to me knowledge).
>>
>> So when you say stack-side, you mean that the modem controller has to
>> detach the PDP context (or otherwise terminate the data connection)
>> when
>> it gets an unsolicited update that the modem has roamed to a cell that
>> doesn't have the home MCC/MNC?
>
> for the data connections you have to use CGREG and it will tell you
> when
> you are roaming. GSM does support seamless handover between home and
> roaming networks.
>
> However remember that your voice network can be still your home network
> while your data network is already roaming and vice versa. Will not
> happen that often, but potentially possible.
>
>> If that's the case, that sucks. Because often networks will have
>> quite
>> a few MCC/MNCs that the device can roam to (including most US and
>> Indian
>> carriers). I assume all the "home" MCC/MNCs are stored somewhere on
>> the
>> SIM then? Couldn't that lead to the at least a Kb or so of roaming
>> traffic before the stack notices the update and terminates the
>> connection?
>
> I think you misunderstood me here. With CGREG you always get the
> current
> network. However when you are roaming and you wanna know what is your
> home network (for the device setup for example), then you have to get
> the MCC/MNC of your home network from the IMSI. And to know if the MNC
> is 2 or 3 digits you need to read bits and pieces from the SIM card.
>
> There is no list of home MCC/MNC stored anyway. What you are talking
> about is a preferred list of roaming partners. And that is really not
> important since in the end the modem does this all by itself.
>
> However you are right, potentially there could be some kb of roaming
> data before you can cut the connection. I have never played with that
> since normally I arrive by airplane and put the device into flight mode
> during the time when crossing borders.
>
> Regards
>
> Marcel
>
>
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