Establishing connections to multiple PDPs simultaneously with MBIM

[Bjørn Mork]

Dan Williams <dcbw at redhat.com> writes:

> On Wed, 2015-08-05 at 17:47 +0200, Markus Gothe wrote:
>> Per specification MBIM allows you to have up to 256 simultanous data connections IIRC.
>> 
>> You can use the command line interface for mbimcli or even better modemmanager to allocate simultanous connections. Then you need to do vlan-tagging etc on the "ethernet device".
>> 
>> It is kinda complex but doable.
>
> Bjorn implemented this on the kernel side, so he'd know exactly what has
> to happen.
>
> But I think what you do is create a new VLAN interface on top of the
> ethernet interface that gets created for the device.  Then each VLAN
> interface gets mapped to a specific data session that you've created.
>
> https://www.kernel.org/doc/Documentation/networking/cdc_mbim.txt
>
> I guess this is one area where ModemManager would help, since it would
> create these interfaces for you and just hand you the interface name and
> the IP details (though this isn't all implemented yet).
>
> Otherwise you get to poke the kernel yourself.  Something like:
>
> 1) make sure the device supports multiple sessions using
> "--query-device-caps".  My XMM7160 device only supports 16.

"only"?  How many APNs do you want to connect using a single SIM? :)

Note that my EM7345 (also XMM7160) increased the number from 8 to 16
when the firmware was upgraded, so I believe these numbers are really
arbitrary firmware imposed limits.

> 2) create a kernel VLAN interface on top of the MBIM network interface
> using the session ID you'd like to use; you get to manage the session
> IDs :)
> 3) run the mbimcli connect and send it the session ID you chose
> 4) assign the IP address information that mbimcli returns from the
> connect request to the VLAN interface
> 5) send some packets
>
> But it doesn't actually look like mbimcli supports multiple sessions
> since it always passes '0' to the functions that deal with connect.  So
> we'd need to fix that up and allow passing a specific session ID to
> --connect, --disconnect, and --query-connection-state.  

Yup.  I've had this on my TODO list for a while now, along with some way
to create/manage the associated data interface(s). But it's not like
anything is going to happen soon, given my current coding progress...



Bjørn