Sierra Wireless MC7354: Why all the interfaces?

Einar Jón tolvupostur at
Mon Oct 23 08:33:45 UTC 2017


We are in the process of testing Sierra Wireless MC7354.. It has 3
wwan<N> interfaces (wwan0, wwan1, wwan2), with the corresponding
/dev/cdc-wdm<N> devices.

We are using ModemManager 1.6 with libQMI 1.16.0 and a custom python
script that hooks into D-Bus messages to do the needful.
The modem usually connects on wwan1, but has also connected on wwan0.
The connection seems fine and stable.
We have a lot of script that expect the modem connection to be on wwan0.

So some basic questions:
1) Why multiple interfaces? What do they mean? Are they different
bands (3G/LTE/etc)? Where can I read up on this?
2) Can I limit the number of interfaces to one? Otherwise I need to
change a lot of things from a "static wwan0" interface to a dynamic
one that checks wwan0, wwan1 and wwan2.
3) It seems to work fine with qmi_wwan+cdc_wdm kernel modules (and
friends). Would cdc-mbim (and libMBIM) add anything of value?

Einar Jón

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