Telit LE910Cx, MBIM vs AT
u.mohr at semex-engcon.com
Thu Dec 2 14:57:09 UTC 2021
I got a Telit LE910C1-EU attached to an embedded device, using
ModemManager 1.19.0 (main branch, 2 commits behind) and libmbim 1.27.3
(main branch, 1 commit behind). Linux Kernel is v5.12.
I was able connect successfully to an LTE network using both PPP (USB
profile 0x1201, 3 AT ports) and MBIM (USB profile 0x1252, MBIM + 2AT
ports). Both configurations seem to work -- I was able to ping a server
using those interfaces.
But there are some inconsistencies that I see:
* While PPP shows a signal quality of 85%, MBIM only shows between 9
and 19 % signal quality. (When I use a AT+CSQ command in MBIM mode,
the result is 20 which is in the middle of the range, so I that
should be more than 20%)
* While PPP does not show any sim lock, MBIM shows a SimPin2 lock
(although we are connected).
So my question are:
* Is it normal / ok to see those inconsistencies?
* Where do these inconsistencies come from?
* Where to start looking to fix those inconsistencies?
* Can I safely ignore the SimPin2 lock?
* What limitations do I get when I use PPP instead MBIM?
I have no experience with MBIM at all, so perhaps I got something wrong
BTW: I also tried RNDIS, but that is ignored by MM completely. Instead,
the AT ports are used for PPP connection. I assume there is no support
for RNDIS within the telit plugin?
Thank you in advanced, any help appreciated .... :-)
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