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

[Dan Williams <dcbw redhat com>]

On Wed, 2009-11-18 at 10:30 +0100, Mark Haack wrote:
> Hi Dan
> 
> if you dont want to fiddle with SIM card file system the pragmatic solution 
> is to just use a shadow list for the MNC length. In this case you are 
> independant from
> vendors firmware implementations of the generic and/or restricted sim 
> access.
> In gsm-world USA and India are the most common 3 digits MNC countries.
> Maybe its a good idea to use 2 digits as default and add USA and India as 
> exceptions.

We have such a list which I try to update pretty frequently:

http://git.gnome.org/cgit/mobile-broadband-provider-info/

any additional information greatly appreciated :)

> <MCCLengthInfo>
> 
>  <MCCInfoSet>
>    <MCC>310</MCC>
>    <MNCLength>3</MNCLength>
>  </MCCInfoSet>
> ...
>   <MCCInfoSet>
>    <MCC>302</MCC>
>    <MNCLength>3</MNCLength>
>   </MCCInfoSet>
> ...
>  <MCCInfoSet>
>    <MCC>262</MCC>
>    <MNCLength>2</MNCLength>
>   </MCCInfoSet>
>  </MCCLengthInfo>
> 
> 
> To control our network just use the PLMN AT Command from 3GPP "+cops".
> 
> (a) "+cops?" returns the current network
> (b) "+cops=?" return the result of broadcast gsm networks wqith status
> (c) "+cops=mode,PLMN" enables you to select a manual network etc.

That's currently what ModemManager and NM will do when you plug the
specific MCC/MNC into the "Network:" box in the connection editor.  They
will use COPS to lock the card to a specific MCC/MNC as you point out.

> The implementation of the command slightly differs among implementation of 
> major device vendors.
> In conjuction with 3GPPs "+creg" you can easly build a abstract "gsm network 
> mode" proxy which reflects the network state of the device, which also 
> allows the adjustment of the actual roaming partner.

Yeah, NM/MM do most of that already.  But the problem here is that you
can't just tell the card to terminate the PDP context when it detects
roaming (when the unsolicited registration status reports 5) so we may
have a bit of a roaming data window.

DAn

> best regards
> Mark
> 
> ----- Original Message ----- 
> From: "Marcel Holtmann" <marcel holtmann org>
> To: "Dan Williams" <dcbw 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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