Question about Gobiserial Vs qmi_wwan

Aleksander Morgado aleksander at
Fri Aug 15 12:09:05 PDT 2014

On Fri, Aug 15, 2014 at 8:30 PM, Gopakumar Choorakkot Edakkunni
<gopakumar.c.e at> wrote:
> Thanks for the response, great blog post ! Even for the Gobinet driver, for
> some devices like Pantech UML295, I dont even see them putting a linux gobi
> driver for that in their webpage .. Looks like other than netgear (ie old
> sierra wireless), no one seems to be really putting the vendor specific
> version of GobiNet driver on their website !!
> Now in this whole scheme of things, where does the sierra_net.c stand ? I
> see that netgear  packages sierra.c (serial) and sierra_net.c (direct ip) as
> their drivers for some of their models, and GobiNet as their driver for some
> other models. So is sierra.c and sierra_net.c the driver which was created
> before GobiNet and then later GobiNet became the standard vendor provided
> driver which provides the same functionality as sierra.c and sierra_net.c ?
> Also I see that the sierra_net.c is still used along with qmmi/cdc modules -
> I guess the sierra_net.c is used for the ethernet/data portion and qmmi/cdc
> is purely for management/control ?

Sierra has been developing their own modem control protocol and data
interfaces for a while...

 In old modems they exposed only AT and HIP/CnS capable TTYs. AT is
the good old AT command set, plus Sierra specific extensions. HIP/CnS
is a binary protocol developed entirely by Sierra, running through
serial ports. Data connection in both these cases would be done via
ATD call plus PPP in the TTY. Newer modems usually also have these
kind of ports, but its use is no longer suggested (especially the PPP

Newer Sierra modems ended up avoiding the TTY for the data connection;
i.e. no more PPP. Instead, you would get a WWAN port managed by the
sierra_net kernel driver. This would be the Direct IP mode. Management
and control can still be done via TTY using AT or CnS.

And lately, Sierra has ended up providing 2 more different control
protocols: QMI (from Qualcomm) and MBIM (standard from the USB-IF,
a.k.a. "windows 8 mode" by different vendors). The same device,
therefore could be managed using either DirectIP, QMI or MBIM modes.
Switching between modes could be a matter of issuing some special AT
command or switching USB configurations.

Of all these 3 latest ways to manage the modem, GobiNet and qmi_wwan
are only applicable to the QMI part. If you don't want ot use QMI (so
no GobiNet and no qmi_wwan) you can still use the modem using DirectIP
mode (via the sierra_net driver and e.g. ModemManager) or MBIM (via
the cdc_mbim driver, and e.g. libmbim/mbimcli or ModemManager).

Probably missing something, but that's more or less the overall
picture of Sierra modems lately.


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