libqmi, LTE RAT link dropout, reconnect, surveillance etc.

[Christian Melki]

On 4/14/22 15:32, Peter Naulls wrote:
> On 4/14/22 09:04, Christian Melki wrote:
>> Hi.
>>
>> Trying to understand how to deal with various network errors that result in some 
>> sort of disconnection.
>> I've seen situations where the networks seems to drop a client when it's crowded 
>> or some other errors occur.
>>
>> How does one deal with situations like these? Detection? Fallback? Reconnections 
>> etc?
>>
>> Does libqmi provide any detection mechanism or reconnection mechanism that 
>> discovers network errors (not just automatic connect on powerup?).
> 
> Not really. There are some conditions that libqmi/ModemManager know about but
> plenty more they don't. There are numerous network loss conditions that they 
> just don't know about/detect.  In any case, they don't really monitor traffic so
> much, this isn't entirely surprising.  Connection monitoring is left up to the
> system - e.g, NetworkManager in Ubuntu.
> 
> For my uses in OpenWrt I've had to develop an extensive connection monitoring
> system that relies upon not only the status from ModemManager, but also traffic
> monitoring and other conditions. It's never going to be perfect, since it's an
> overlay, but it does seem to cope well enough with most conditions.
> 
> Suffice to say I've discovered numerous instabilities - I've found corner cases
> that cause crashes in libqmi, dnsmasq, qmi-proxy, ModemManager and elsewhere.
> These are all slowly being improved, but it's a long road.
> 
> 

Hi Peter.

Suspected it would be a bit of a minefield. Do you have pointers to code
or scripts that deal with different aspects of this?

I guess I'll have to develop some sort of link monitoring for my uses
aswell.

Thanks.