GPRS support for Ofono

[Rémi Denis-Courmont]

----- Message d'origine -----
> > But there are some more fundamental issues. First, the ISI General Packet
> > Data Service does not provide any location informations (roaming/not
> > roaming, area code, cell ID). And I must say I don't understand why this is
> > part of the GPRS atom. This has nothing to do with packet data.
>
> That is because 3GPP in their infinite wisdom structured the spec this way. 

Just because AT commands group both pieces of unrelated data does not mean it is a good idea. I fail to see why the DBus and driver API should do the same mistake as 3GPP 27.007.

> There are 2 registration states, one reported by CREG and one reported by
> CGREG.  Both report essentially the same information, namely registration
> status, lac, cellid and radio access technology.
>
> The way we know an AT-command based modem is attached is when we start
> receiving these CGREG indications (registered/roaming + lac/ci/rat)

A device cannot attach to GPRS an a different network than the one it is registered with. I do not see the value of tying those in oFono. The caller can use the network registration interface, and in fact, I think it should.

I am not an expert on GPRS internals but I guess the protocol does not provide those values, and this is just a misdesign of AT commands.

> I'm open to suggestions on how to fix this (for instance we can get rid of
> Status, LocationAreaCode, CellId attributes, since they're essentially the
> same as in NetworkRegistration interface), but for now this can be easily
> faked by just re-using the information you're providing to netreg atom.

I could steal that data, but it would be vomitively ugly. Worse, it would be hide a race condition through the DBus interface. There is no way for me to request both atomically. 

> > Second, I couldn't figure how to handle auto-attach. The ISI protocol
> > supports it, but I could not find the driver callback. Thus, I would have
> > to force the device into manual mode. This is going to be an issue as some
> > operators require auto-attach
>
> Is this where the network requests an attach or are you talking about
> something else?

No no, I am not talking about network-initiated context *activation*. I am talking about the requirement from some operator that the device be always *attached* even if it has no active contexts. Note that the battery impact is negligible. Also, this is NOT quite the same as attaching when oFono starts: the device could be outside of the GPRS network; auto-attach will get it attached as soon as possible.

Rémi