Re: Sierra USB 306 - GetSignalQuality() fails when connected: "Could not parse the +CIND response"

[Dan Williams <dcbw redhat com>]

On Fri, 2012-11-23 at 17:33 -0800, Kelsey Sigurdur wrote:
> Hi folks,
> 
> Newb here. As the subject says,  GetSignalQuality() is failing with
> the error "Could not parse the +CIND response" when connected to the
> network. When disconnected but enabled GetSignalQuality() properly
> returns a value.
> 
> I'm just looking to find out if this is a issue with the hardware or
> perhaps a bug in ModemManager.
> 
> I've scoured the archives as far back as January 2011 and the closest
> problem to mine that I've found so far is the following thread, which
> wasn't followed up on:
> 
> "Re: how to get signal strength of EVDO modem"
> https://mail.gnome.org/archives/networkmanager-list/2011-January/msg00073.html

So here's what's going on.

1) you don't appear to have the sierra_net driver on your system, or if
you do, it's not bound to the USB 306.  The USB 306 should expose a
network port as well as a few serial TTYs, and ModemManager should pick
that network port up.  The logs you posted indicate that the kernel
isn't binding sierra_net to the USB 306, so this appears to be a kernel
or modeswitch issue.

2) Because there's no network port, you only get one full-featured AT
command port, which is used for PPP while connected.  The other
AT-capable ports have limited AT command parsers which do not allow the
AT+CIND command, which is why you get that error.  However, there's a
bug in ModemManager where it should just report the signal quality
obtained by +CSQ instead of returning an error.

So, I'd suggest finding out why sierra_net isn't getting used, but I'll
also fix the MM bug too.

Dan