I know this is an old thread but thought my information may be useful for anyone else out there that is still using the RB411U + Sierra Wireless miniPCI-E 3G card combo.
I have 110 units in field running 24/7/365. I have several models of the Sierra Wireless miniPCI-Ecards in use and none of them are perfectly stable. My units are spread over a geographical area larger than 7.5 million square kilometres with just myself and another tech responsible for keeping them online. Apart from the expected issues with reception signal strength, rare component failure (had some faulty pigtail cables) and Telco stuff ups, I still get regular issues with the router boards where the board loses its port settings and therefore the 3G connection fails. I also occasionally get the resetting link loop mentioned in this thread.
Powering the router off and on, sometimes several times with increasingly longer power off intervals will recover most routers but sometimes you must attend the router and log in locally via ethernet to fix the interface.
Roughly it would break down like this:-
110 units
A normal to bad day might see around 9 units lose connectivity.. 5 of those would eventually auto-recover
The remaining 4 units will need to be powered off and on to recover... 3 of those will recover at the first attempt
That last unit will recover after multiple power off/on... 70% of the time under 3 cycles, 20% of the time more than 3 cycles, 10% physical attendance required.
I don't have technical staff at our sites so I rely on non-technical staff (not directly responsible to me) who are willing to turn the power switches on and off a few times for me. When Physical attendance is required a tech is sent. It's expensive and frustrating!
Sierra wireless cards I use are listed below:-
8775 - Revision 2_0_6_0 or greater - I originally had mostly this card but ended up replacing all the lower revisions entirely. In reality I won't be buying anymore because of there over 30% rate of being problematic.
8780 - I only have 8 of these so statistically difficult to rate the model individually - they seem stable.
8795 - Only 10 in total sprinkled through the fleet again difficult to say but only have one that seems temperamental.
8781 - I have 78 of these and they are the most stable card I could find for the right per unit cost but they still fail to remain stable at a rate of around 5%.
So the search for that elusive dead stable combination continues.
For those interested.. What possible solutions do I have? Well we are developing a small piece of electronics, that will "plug and play" to the router units.. monitor internet connectivity and when necessary properly switch the router power off to recover the 3G connection... sort of an external 3rd party watchdog that actually does a proper "hard" reboot of the router instead of the "soft" reboot performed by the ROS software watchdog. It's a bit of a hack but I really need to improve stability.. especially since the plan is to provision several hundred more sites, that we already have, with the same remote telemetry systems as this first 110.
Thanks for listening