Re: Modem-/NetworkManager support for modems not using PPP

[Dan Williams <dcbw redhat com>]

On Sat, 2011-04-16 at 14:57 +0200, Marius Kotsbak wrote:
> Hi!
> 
> There seems to be now quite a bit of modems appearing now that does not
> support the old method of using PPP protocol on the same tty device as
> the AT commands are sent, or it is not recommended for higher HSPA+ and
> LTE modems because of performance limitations of the PPP/tty layer.
> Those devices typically accept AT commands at one interface and use
> another interface for the network traffic (including first a DHCP query).
> 
> One example is the Samsung GT-B3730 I'm currently developing drivers for:
> 
> https://github.com/mkotsbak/Samsung-GT-B3730-linux-driver
> 
> It seems to be the same case for LG VL600 4G (LTE):
> 
> http://ubuntuforums.org/showpost.php?p=10589647&postcount=17
> 
> https://github.com/balrog-kun/LG-VL600-utils
> 
> The Ericsson Mobile Broadband Modules (I have an F5521gw based modem)
> seems to offer both the old ACM ports and support USB WCM / CDC NCM /
> CDC Ethernet protocols for higher performance:
> 
> http://www.thinkwiki.org/wiki/Ericsson_F3507g_Mobile_Broadband_Module#Connecting_to_the_net_via_CDC_Ethernet_interface
> 
> http://sourceforge.net/apps/mediawiki/mbm/index.php?title=MBM#Prerequisites
> 
> http://cateee.net/lkddb/web-lkddb/USB_NET_CDC_NCM.html
> 
> I wonder if support for this has been implemented or thought about in
> Modem-/NetworkManager. We probably need a flag for a modem manager
> module to tell that it does not use PPP and require to get IP address
> using DHCP instead.
> 
> Else those devices benefit from the code in modem manager (and should be
> classified as such to the user as well), like the PIN unlocking, signal
> strength (typically found on the same device as dialling happened, since
> network traffic flow on a separate interface)  etc. The configuration
> tab for PPP could be hidden for those devices. For devices offering
> multiple ways to connect, the modem manager module should probably find
> the best performing according to the available kernel modules and use
> that method.

It all depends on whether the modem gets detected correctly; there's
some udev files for mapping the various IDs to a specific driver, and
that driver determines whether to use PPP or the net interface.
Unfortunately there's no standard for using the net interface so we have
to use custom code for each device.

ModemManager handles modem configuration, but the clients of MM (like
NetworkManager) handle all the IP configuration, mainly because upper
level clients like NM already need to handle ethernet and PPP for other
devices, so why duplicate that code in ModemManager...  So that's the
level split, think of it as L2 = MM, L3 = NM.

Dan