Re: How to debug 3G USB modem problems?

On Thu, 2011-05-05 at 01:15 +0300, Uwe Geuder wrote:
> I understand that this a upstream list and most readers are interested
> in the bleeding edge. However, I have to support some systems for
> "naive" users and I prefer to use a plain vanilla distribution as long
> as possible. So please bear with my question regarding versions
> straight from the museum...
> On Ubuntu 10.04 (long time support) they have nm version 0.8-0ubuntu3

So what you want to do here is also grab modem-manager logs as described

under the "Debugging NetworkManager 0.8.x 3G connections" section.

> The USB modem in use is a Nokia CS-17. (I know that if you search for
> trouble, you select a 3G USB modem. Unfortunately this variant is
> really by orders of magnitude cheaper in this case than anything more
> reliable.)

Huh, because they are $120 on eBay which isn't cheap at all :)
Otherwise I'd buy one.

> The good news is that the CS-17 works even with that old software.
> The bad news is that it's completely unreliable. Some 30%-50% of the
> connection attempts just fail. Unfortunately the failures seem to come
> in waves. If it fails the first time, it will also fail the 2nd, 3rd
> etc. Removing the modem does not help. But 1 or 2 hours later it might
> just work again. Alternatively if I want to repeat the problem, I can
> make 15 connections in a row without any failure. 

So in this case, more logs from NetworkManager's PPP debugging would
help, as would the ModemManager logs as described above.

> The other problem is that while the connection typically stays open
> for hours during normal web browsing, it will disconnect with quite
> high probability when downloading bigger files. Today I needed 4 attempts
> to download a 20 MB file.

What does the PPP debugging say when this happens?  NM wont' terminate
the connection unless PPP says it's down.


> I would exclude network-side problems or weak signal, because I use 3G
> data on the same network nearly all day long on my smartphone without
> such problems. Additionlly, when the USB modem fails to connect I can use
> my phone as the modem using the data cable and everything works. 
> So how could I debug this? Is it a Linux-side problem or a firmware problem
> in the CS-17? (Haven't had a chance to test it with M$ yet)
> From searching in the mailing list archives I found 2 debugging hints:
> 1. starting nm from command line as
> # NM_SERIAL_DEBUG=1 NM_PPP_DEBUG=1 NetworkManager --no-daemon | tee log.txt
> That works nicely. When the connection attempt fails I see how PPP
> negotiation starts, but it doesn't seem to get any reply. 
> sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x5c8b3860> <pcomp> <accomp>]
> After 5 repetitions pppd seems to give up and nm complains that the
> connection failed.
> (Not sure whether NM_SERIAL_DEBUG has any effect, I don't think I see that
> variable in the source code of my version)
> The problem is that using the command line (and root) is OK for me on
> my test machine, but not for the user in question on the real target
> machine. So I'd like to configure the "real" service such that logging is
> always on.
> I tried to do so by adding the 2 environment variables to
> /etc/init/network-manager.conf (Ubuntu uses upstart)
> env NM_PPP_DEBUG=1
> exec NetworkManager
> Unfortunately that seems to have no effect to the pppd logging. The
> pppd stuff that I can see when running with --no-daemon does just not
> appear in syslog, neither in successful nor in failing cases. (I have
> checked from /proc/nnn/environ that the environment variables really
> end up in the network-manager process)
> Also the debug parameter appears on the pppd command line as shown in syslog.
> How can I get pppd logging when running as a daemon?
> 2. The other hint I found in the mailing archive was a config file entry
> [logging]
> level=WARN
> I changed that to level=DEBUG, but I don't think it made a
> difference. Could not find such parameter in my source code. Has it
> possibly been added only in a later version?
> Yesterday I read in some forum that killing modem-manager after a
> failed connection attempt helps. Today I had only very few failed
> attempts in my testing and killing modem-manager helped each time. Not
> yet sure whether this is really a reliable work-around. If yes, I
> could of course script it.
> Does the problem description ring any bells? If you remember specific fixes
> that solve these issues, I might try to backport them to my
> version. Or just install a newer version manually.
> Regards,
> Uwe
> P.S. Yes, I am aware of the modeswitching. I left that out from the
> description above, I'm sure that the modem was always in the right
> mode.
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> networkmanager-list gnome org

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