PPP issues with SIM7100

Geert Lens g.lens at livetech-systems.com
Thu Apr 22 12:09:02 UTC 2021

Hi all,

We are using a SIMCOM SIM7100A modem and are experiencing some issues when
trying to connect via PPP.

When we use ModemManager and NetworkManager to set up the modem and
connected it to the network, it fails when pppd is trying to request IP and
DNS configuration of the network. We are getting the error "Modem hangup"
from pppd.

The strange thing is that when we disable ModemManager and use the provided
ppp-create.sh to connect via pppd, the modem connects without any issue.
After we manually use the ppp-create.sh script, we are also able to connect
the modem via the ModemManager and NetworkManager combo, which didn't work
before that. Even after a power cycle it still works.

We are puzzled about how this can be.

We have tried adding the pppd options that are used in the ppp-create.sh
when using NetworkManager to connect, as we thought the issue might have to
do with data compression that was not allowed.
But this didn't have any effect.

Can anyone give us a lead on this issue? Or has seen a similar issue? We
are currently stuck as we have no idea how to debug this issue further.

I have added the ModemManager and NetworkManager logs as well as the script
we used to manually set up the connection.

Best regards,
Geert Lens
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