Re: Does NetworkManager support blocking non-home networks (UMTS/3g)

[Dan Williams <dcbw redhat com>]

On Tue, 2009-11-17 at 23:35 +0100, Marcel Holtmann wrote:
> 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?

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?

Dan