+CREG vs. +CGREG

[lgnom]

Michael 'Mickey' Lauer wrote:
> 
> I want to add a GPRS availability signal to ogsmd. We have some 
> Calypso-specific ways of doing that, but I'd rather implement it only
> using 
> GSM 07.07 standard commands.
> 
> Does anyone know whether +CGREG and +CREG really refer to different
> services 
> (data vs. circuit) when a mobile station supports both?
> 

I think there is no 07.07 standard command available just to monitor GPRS
availibility. +CGREG can be used only to monitor GPRS registration state of
the mobile (attached, not attached, trying to attach, ...). So, as soon as
you have initated the GPRS attach, you can use the +CGREG command/indicator
to check GPRS availibility. But depending on your operator you will be
charged already just for the plain attach!

Your terminal equipment may support vendor specific commands/indicators to
check for GPRS coverage, e.g. for most of the Cinterion modules you can use
AT^SMONG.

Regarding the relation between +CREG and +CGREG: I think the +CREG command
can be used to check the network registration state of your mobile. It is
independent from +CGREG state. But +CGREG state depends on +CREG state. You
will never attach without being network registered first. But there are
similarities: if your network registration state is "registered roaming"
(+CREG:5) and then you attach to GPRS, then your GPRS registration state on
success will be "GPRS registered roaming" (+CGREG:5). Also both
commands/indicators will show you the same <lac> and <ci> in registered
state.

BR
Peter

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