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

["Mark Haack" <Mark Haack werk55 de>]

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.

<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.

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.

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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