mbim cli - Telit LN920A connection process take more than 5 minutes

[Aleksander Morgado]

Hey Borja!

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> I am reaching out to discuss a critical situation we are facing with the LN920A module fw version M0L.010002 and  mbimcli tool.
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> We have encountered connectivity problems with Telit LN920A module when it is connected to a MNO in Japan. The connection process takes more than 5 minutes, which is significantly longer than expected.
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> Please find enclosed the logs of the tests performed by the customer in their device using mbimcli (Customer-Testmbimb1.22).
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> We have performed tests using a PPP connection in the device of the customer, and the results have shown that the registration process is fast and efficient. We have attached the PPP log files (PPP_logs) for your reference.
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> Additionally, we have conducted tests with Telit Evaluation Kit in different location using mbimcli version 1.24, and the results have been successful. The connection process proceeded smoothly without any delays or issues. This further indicates that the problem may be specific to the customer's network environment or configuration. (Telit-Test-mbim1.24.24.log)
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> We appreciate your assistance in helping us identify the root cause of the prolonged connection time issue and finding a resolution. Please let us know if you require any further information or if there are any specific tests or diagnostics that you would like us to perform.
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Looks like the tool is configuring the PDP context #1 explicitly. This
setting is taken as the initial EPS bearer settings the modem will use
during registration (i.e. attach APN).

0206 000247.019 P27912[Thread3G_0] - SendReceiveATCommand OK
[AT+CGDCONT=1,"IP","mmtmobile.jp"] - [OK]
0206 000247.019 P27912[Thread3G_0] - Thread3G: APN:[mmtmobile.jp]
successfully configured!

And then launching the connection attempt via mbimcli:

0206 000333.774 P27912[Thread3G_0] - CIkusNetApp::ExecExternalProcess:
Executing cdc_dev="/dev/$(ls $(realpath
/sys/class/net/wwan1)/../../usbmisc/)"; mbimcli -d $cdc_dev
--connect=apn='mmtmobile.jp',session-id=0,username='nipponsim at dhacorp',password='dhacorp',auth='CHAP'
--no-close --no-open=4...
error: operation failed: Failure

The settings in the MBIM connection attempt differ from the ones in
the attach settings. The APN is the same, but the MBIM attempt has
user/pass, which were not configured via AT commands. Given that the
settings mismatch, it is very likely that the MBIM connection attempt
is launching a new PDP context activation, instead of reusing the one
performed during the attach. If this takes a very long time to
complete, it could also be because the modem supports only one single
active PDN connection, so when you launch the new MBIM connection
attempt with different settings, the modem may actually be
unregistering from the network and trying to register again with the
new settings (modems without the single PDN connection may not be
affected by this flow).

In order to solve this, you can try several things, the purpose of all
of them is to ensure the attach and connect settings are equal.

1) Not only configure the APN with +CGDCONT, but also the user/pass
with AT#PDPAUTH=1,2,... This should make the settings match when the
MBIM connection is launched.

2) Use MBIM also to configure the lte attach settings, but I've just
realized there is no mbimcli support for this yet, only to query
(--ms-query-lte-attach-configuration). We would need to update mbimcli
to support this. ModemManager does support setting the lte attach
settings via MBIM.

Trying to use AT for some things and MBIM for others, as in this case,
could cause weird things as you're seeing :/

-- 
Aleksander