Re: problems with 3g based connections

[Dan Williams <dcbw redhat com>]

On Tue, 2010-06-22 at 15:28 +0200, van Schelve wrote:
> Hi,
> 
> some days ago I have reported a curious issue with modem-manager. 
> My main Problem is that I'm sometimes not able to dialup a modem based 3g
> connection. The connection is not listed in nm-applet in this case and in
> syslog I have entries like this one: 
> 
> ... 
> May 21 10:055:28 nc0631 modem-manager: (tty/ttyUSB0): outstanding support
> task prevents export of /sys/devices/pci0000:00/0000:00:1d.1/usb6/6-1
> ...

This means that some ports of the modem are still being detected and
probed.  The modem cannot be used until all ports have completed
detection.

> @Dan, you asked me to bring more debug but I'm not able to reproduce this
> issue while manually starting nm / mm in debug mode. 
> Therefore: is it possible to run network-manager / modem-manager per
> default in debug mode while starting over upstart?

Possibly, but the debug output doesn't go to syslog, so unless it gets
stored somewhere by upstart it'll get lost.

> A second problem, reported by our testorganisation is that existing
> connections are sometimes terminated. I cannot see the reason for this
> behaviour.

Getting logs from modem-manager and from NetworkManager with
NM_PPP_DEBUG=1 are helpful here:

http://live.gnome.org/NetworkManager/Debugging

I'd guess that PPP is terminating for some reason, but we need to figure
out why that is, and the NM PPP debug logs might help us figure that
out.  There are a ton of reasons why the call might get terminated, and
many of them are network side or handoff-related.  Or the firmware
screws up.  This happens on other platforms too :)

> And maybe there is a third problem. It looks like that it takes a long
> time ~6 seconds from powering up the modem until it can be used with
> network-manager. In the logfiles I see that the different ports are getting
> probed with all the available plugins. Is there any way to optimize this
> behaviour?

What do you mean by "powering up"?  Just plugging the modem in?

You might also be forgetting about modeswitching, which takes a few
seconds (perhaps up to 5 or 7) depending on the device.  Otherwise,
there might be a few things we can do to eliminate delays, but you'll
also find that on other platforms things take a while to initialize too.
That doesn't mean we can't do better than we do right now, but there
will always be some amount of delay as the device is modeswitched,
detected, and initialized.

Getting the ModemManager debug logs help here.

Note that some devices (Airlink 3GU and other Longcheer-based modems)
have kernel driver problems that delay their detection by up to 30 or
more seconds.

Dan