Re: [PATCH] [RFC] [Modem Manager] Fix for CDMA modems not able to connect if SID=0

[Jerone Young <jerone young canonical com>]

Thanks Dan,
	I'll try and get those changes packaged up so users in the bug we have
can test them out and see how they work.

			Thanks,
				Jerone

On Tue, 2010-03-30 at 12:12 -0700, Dan Williams wrote:
> On Wed, 2010-03-24 at 20:54 -0500, Jerone Young wrote:
> > Apparently in some countries, such as India, some providers have an SID
> > ID of 0. 
> 
> This isn't actually the right way to solve the problem.  The problem is
> that we're using SID as a proxy of registration state on devices which
> don't have extended AT commands for registration state.  Unfortunately,
> SID is not a perfect proxy.  The SID should not be 0, and in fact that's
> not really legal.  Every network must have a SID, otherwise roaming and
> other stuff simply doesn't work.  The SID is like the MNC of a GSM
> device.
> 
> SID is also only valid for 1x registration state, since EVDO does not
> use the SID (instead it uses "subnet codes").
> 
> So the problems we've observed are:
> 
> 1) if the device can't find a 1x signal, but has an EVDO signal, then
> the SID isn't necessarily known.  This happens for some providers in
> Russia and India that are EVDO-only, and the modems for those providers
> (AnyDATA and ZTE specifically) often don't have extended AT commands for
> determining registration state.  In the US there really aren't any
> EVDO-only providers, and so the modems always have a 1X registration and
> thus the SID is always known.
> 
> 2) On some devices where there *are* extended AT commands, the SID isn't
> necessarily reported; this was seen on Sierra CDMA modems in some cases.
> 
> The real solution is to use qcdm to determine the actual registration
> state of the device, instead of depending on AT commands that may or may
> not represent registration state.  I've implemented that recently in
> ModemManager git (e7d1e4adb9bf984736ae2bfadbdd616ebc6ade80 and
> 39326f249105b7d71c63125f29e3bee2143a82d2) and am waiting for some
> feedback on that from testers.
> 
> The problem that occurs if you only look for SID 99999 is that if the
> modem *isn't* registered, the connection will immediately fail instead
> of waiting for the device to register.  This was a problem last summer,
> and the +CSS check was introduced during registration as a fix for that
> problem.  It was most visible with connections that were supposed to
> autoconnect the 3G.
> 
> That patch is essentially equivalent to ignoring the GSM +CREG state and
> blindly trying to connect the modem not matter whether it's registered
> or not.
> 
> Dan
> 
> > According to this spec this is the case (page 11):
> > http://www.tiaonline.org/standards/technology/cdma2000/documents/TIA-EIA-IS-707-A-2.pdf
> > 
> > The simple patch to fix this can be found here:
> > https://bugs.launchpad.net/ubuntu/+source/modemmanager/+bug/461096/comments/14
> > 
> > You can see from the bug this patch fixes issue for CDMA users who's
> > providers are following this:
> > https://bugs.launchpad.net/ubuntu/+source/modemmanager/+bug/461096
> > 
> > 
> > 			Thanks,
> > 				Jerone
> > 
> > 
> > 
> > 
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>