ModemManager and ppp

[Aleksander Morgado]

On Fri, Mar 10, 2017 at 5:24 PM, Tom Hayward <tom at harbortronics.com> wrote:
> I'm a new user of ModemManager and trying to understand the scope of
> the software.
>
> I've used ModemManager successfully with a cdc-wdm modem. It created a
> wwan0 interface where I could use a dhcp client and then route
> packets.
>
> Now I have a cdc-acm modem that requires running pppd on /dev/ttyACM0.
> I have a pppd and chatscript config to initialize it, a ppp0 interface
> is created, and I can route packets over it. Can I do any of this with
> ModemManager? I've found that I can use --simple-connect="apn=xxxx" to
> get the modem state to change to "connected", but it does not create a
> ppp0 interface on which to route packets.
>
> Is this a matter of configuration, lack of support, or simply outside
> the scope of ModemManager? Is there a way to use ModemManager to
> initiate the ppp connection?

Initiating a ppp session is currently out of scope of MM. MM will put
the TTY in connected mode; then you need to (externally, another app)
launch pppd on the TTY that MM reported as "connected".

The whole MM sequence is the same for TTY-only and QMI/MBIM+wwan
devices; just launch --simple-connect, if successful it creates a
bearer object that is in connected state. The bearer object will
report which is the data interface to use (which could be a wwan, or a
TTY) and also which method to use (ppp over the tty, or DHCP or Static
IP config over the wwan). An application that wants to use MM as modem
management and handle multiple modem types needs to handle all 3
methods and use explicitly the one reported by MM (e.g. some modems
won't be able to use DHCP over a wwan and in that case static IP
setting needs to be performed).


-- 
Aleksander
https://aleksander.es