adesmier at sequans.com
Thu Apr 10 07:54:44 PDT 2014
Using DSS we got 2 issues due to VLAN mapping of DSS channels:
1. If your interface come down you can not anymore communicate with
your DSS, but DSS should not be related to wwan intarface status.
2. DSS are not IP based, but as kernel saw them as network interface
it forward ip broadcast and multicast to it. Even when we set VLAN
interface flags to only UP we got some unknown packets forwarded to it
(Wireshark is not able to decode them).
After some discussions with Bjørn Mork to understand how mbim driver is
working for DSS channels we concluded that currently DSS channels are
fully dependent of wwan interface state. It means that even if we switch
to TTY we will get the same behavior except for point 2 that should be
MBIM specification says that we have 2 bulk endpoints for data
communications (IP based and DSS), one is used for TX and the second for
RX. But those endpoints are handled by usbnet driver that don't know
One solution could be to alter usbnet driver to add a new flag
preventing endpoints to be down when wwan interface come down and at
least one DSS channel is up.
Does anyone already encounter this kind of problem?
Windows is handling DSS channels as we could expect, It's a bad news if
Windows can do better than Linux :-)
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