Re: A general (learning) query

[Dan Williams <dcbw redhat com>]

On Wed, 2012-06-13 at 00:11 +0530, Ajay Garg wrote:
> Hi Experts :)
> 
> I am trying to connect via a 3G USB modem (via wvdial), and get the
> following error ::
> 
> ############################################################################
> -bash-4.1#  wvdial
> --> WvDial: Internet dialer version 1.61
> --> Cannot get information for serial port.
> --> Initializing modem.
> --> Sending: ATZ
> ATZ
> OK
> --> Sending: ATQ0 V1 E1 S0=0 &C1 &D2
> ATQ0 V1 E1 S0=0 &C1 &D2
> OK
> --> Modem initialized.
> --> Sending: ATDT*99#
> --> Waiting for carrier.
> ATDT*99#
> ERROR
> --> Invalid dial command.
> --> Disconnecting at Tue Jun 12 15:35:16 2012
> ############################################################################
> 
> 
> I have googled, and found quite a posts.
> However, all these points discuss about implementation details, and I
> am feeling overwhelmed.
> 
> I will be grateful if someone could please point me to some
> literature, that states the entire lifecylce of USB modem connection
> In particular, I don't quite understand how some particular AT
> commands are linked to the USB-model/ISP/APN.

It's a bit off-topic for this list since it doesn't involve ModemManager
or NetworkManager.  But here's your problem.  To connect packet data
(ie, GPRS or UMTS or whatever) you need an "APN".  It's simply an
identifier to the gateway on their network that handles your packet
data.  You must tell the modem your APN before the data connection can
start.  For GPRS/UMTS modems, you do this through the AT+CGDCONT
command.  It's usually automatic (well, pre-programmed) for CDMA/EVDO
devices and thus doesn't need an AT command.

You can have multiple "profiles" stored in your phone, each one for a
specific APN.  When you connect with ATDT you need to tell the phone
which profile (and thus which APN) to use.  You do that by telling the
phone the profile number as returned from "AT+CGDCONT?".  Then you dial
with that number:

ATD*99***<number>#

You can, of course, also get errors when dialing if your subscription is
not set up right, if the APN is wrong, if the signal is not strong
enough, etc.

Dan