Flaky internet connection

[qbrick]

A few days ago my internet connection started to behave flaky, which means that after several minutes of internet use, the browser (Firefox & Chromium) doesn't get any urls resolved. I am using an HUAWEI 3G-USB stick on two computers here, one with another well known distro from 2009 (via NetworkManager) and this one with PCLinuxOS LXDE 2010 and the network control-applet (pppd). When I plug the stick into the former computer, everything works fine as always with no interrupts at all, so I suspect the problem is with the PCLOS box, which worked without problems since I set it up late in April until now.
As I said, the interrupts occur more often, when no data are transmitted for a short while even. Usually I close the connection with the netconfig-applet and reestablish it. After that it works for another while until the same happens again and the connection simply seems to be blocked. 3G reception quality is alway fine (4 of 5 or even 5 of 5).
I searched the log files for any hints, but the only thing that sprang into my eye was this. I'm not sure, if it has anything to do with it:

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Jul  5 17:51:18 localhost pppd[17285]: Could not determine remote IP address: defaulting to x.x.x.x
BTW to transmit my topic I had to reestablish the connection again, because my browser stuck at 'Resolving host...' again.

[Ramchu]

you could try removing your connection and setting it up again as a new connection.

[qbrick]

Already did that several times. To restart the connection is the only way to get it working again, once it stops.
Played with Firefox proxy settings, too.
All the system settings are pretty much unchanged, except of IPv6, which I have deactivated both in the system wide network config and in Firefox for better network performance.