Initially I'd like to investigate this topic without considering the
protocol (AT, MBIM, QMI), and only the modem's capabilities, although this
note from the above mentioned discussion is really appealing

MBIM modems can multiplex IP sessions over a single data port.

​and as Dan said, QMI should not support this with a single data port.​

Also this note caught my attention

There's an issue here; the port needs to be a NET port, because that
> is what the Bearer should export in the interface. This is, if you
> have 2 bearers, they should both expose "wwan0", and not
> "/dev/cdc-wdm...". NetworkManager needs to know which is the NET port
> where the IP config
> is to be applied.

does this mean that the required changes will touch other actors (like
NetworkManager and/or the driver)?

On 19 September 2016 at 16:55, Dan Williams <> wrote:

> On Mon, 2016-09-19 at 12:38 +0200, Aleksander Morgado wrote:
> > On Mon, Sep 19, 2016 at 11:20 AM, Carlo Lobrano <>
> > wrote:
> > >
> > >
> > > I have a question about the maximum number of bearers that can be
> > > created.
> > >
> > > My understanding is that this number is bind to the number of data
> > > ports and
> > > these have to be of NET type (like wwan). Is that correct?
> > I think it depends on what the modem supports. I've seen at least one
> > case where you can setup multiple bearers in a single WWAN, just by
> > issuing different connection requests to different APNs where you get
> > different IPs that should be set on the same WWAN. No plugin supports
> > that yet in MM, but it should be totally doable. Maybe, I don't
> > recall, there is a limit hardcoded in the generic code base that
> > limits the number of bearers to the number of wwans, but we should
> > likely let the plugins decide that limit.
> I believe some (many?) devices can do a second bearer with PPP over
> serial ports at the same time as they do a first bearer over the
> WWAN/net port.
> On the QMI side I think there's a 1:1 mapping between net port and
> bearer, and aren't there some Sierra devices that either have non-
> functional or semi-functional QMI ports too?
> In any case, this is going to be highly specific to the modem itself,
> so the plugins are going to have to decide what their hardware supports
> and how to expose it.  But that will also require some logic changes in
> MM itself.
> Dan
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