Question about Gobiserial Vs qmi_wwan

Gopakumar Choorakkot Edakkunni gopakumar.c.e at
Fri Aug 15 15:50:59 PDT 2014

Thanks again for the info. I was reading through the "AirCard / AirPrime
USB Driver Developer’s Guide" from Sierra, this explanation put together
with that makes things a lil bit more clearer now ! So if I summarise what
I understand

1. sierra_net.c imlpemented direct-ip where there was one channel on which
the AT/CnS commands were used for control, and the direct-ip channel was
used for sending IP data to the modem (over a wwan0 interface created by
sierra_net.c). The modem probably ran its own pppd server and then sent
these packets over ppp anyways.

2. With QMI, the usbnet.c driver creates a wwan0 interface. The cdc_ether.c
+ qmi_wwan.c + libqmi alltogether implements the QMI control protocol. And
if I understand correctly from the sierra pdf document, the IP data and QMI
control are sent on the same USB channel, so I guess even data has some
kind of qmi encaps which distinguishes data Vs qmi control.


On Fri, Aug 15, 2014 at 12:13 PM, Markus Gothe <nietzsche at>

> sierra_net.c uses “DirectIP” which basically is a Sierra Wireless protocol
> built on-top of their proprietary CnS-proctol suite.
> What one will realise is that DirectIP is just an encapsulation of the PPP
> backhaul as used in 3G. I think they “invented” this driver and technology
> to accelerate slow MCUs/CPUs running Linux (read: embedded systems) and
> letting the modems firmware handle the PPP-connection without the need of
> pppd (and no need to involve Qualcomm because of QMI).
> One big drawback is that like PPP you cannot do ethernet-bridging (dev->net->flags
> |= IFF_NOARP; which is true for PPP). If you look at older modems you
> will see that sierra_net.c implemented a DHCP-server using CnS/HIP (both
> proprietary protocols of Sierra) to give out the IP-addreses received from
> the GGSN.  Your default route using “DirectIP” will be your IP hence the
> assumption that it is PPP.
> Another driver with pretty much the same behaviour is ‘hso.c’.
> sierra.c was used instead of option.c/qcserial.c once, I don’t really see
> any point in still using it.
> //M
> On 15 Aug 2014, at 20:30 , 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 ?
> Rgds,
> Gopa.
> On Fri, Aug 15, 2014 at 9:31 AM, Aleksander Morgado <
> aleksander at> wrote:
>> On Fri, Aug 15, 2014 at 3:52 PM, Gopakumar Choorakkot Edakkunni
>> <gopakumar.c.e at> wrote:
>> >
>> >>>> No, I Sierra Wireless do definitely test their Linux drivers.  And
>> they
>> >>>> do provide support for them (in the embedded market).  So the
>> >>>> GobiSerial/GobiNet drivers *might* be the correct choice for some
>> users,
>> >
>> > So does the Gobinet driver that I get for example from the Netgear
>> AC340U
>> > product page - does that work for ALL classes of Sierra devices or does
>> > Netgear or other vendors (huawei etc..) put in their own fixes on top
>> and
>> > repackage it and put it on their website ? Or is there some other place
>> > where qualcomm maintains a gobinet driver which is the latest and
>> greatest
>> > and supports netgear and huawei and pantech and etc.. etc.. ?
>> More or less on-topic, I wrote a blogpost about this not long ago:
>> There is a 'qualcomm' GobiNet, in the CodeAurora project page, but
>> every vendor keeps its own. E.g. Sierra will modify the stock GobiNet
>> at least to add their specific VID/PID matches as well as their unique
>> USB interface layouts. I guess others do this as well. Sierra actually
>> also decided to port a fix that Bjørn did in the upstream qmi_wwan
>> driver, but don't know if others did that as well.
>> From my POV, there are reasons to use GobiNet instead of qmi_wwan
>> (e.g. if you're looking for the vendor-provided product support), or
>> other things which we currently don't support yet (like firmware
>> loading)... apart from those, I'd really suggest to use qmi_wwan and
>> libqmi (with qmicli and/or ModemManager :) ).
>> --
>> Aleksander
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> //Markus - The panama-hat hacker
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