"Connected" state after losing signal

[Dan Williams]

On Mon, 2019-06-10 at 07:03 +1000, Nick wrote:
> Hey,
> 
> A couple of other testers and myself are seeing a minor issue with
> ModemManager (on OpenWrt).  The simplest way to describe it is if the
> modem loses signal or connectivity, the wwan interface still shows as
> connected.  I have seen this myself, and wrote a hot plug script[1]
> to work around the issue, and I think I have seen it mentioned in the
> mailing list before.  There is also one report of it in the OpenWrt
> forum thread[2] for modem manager. 
> 
> It’s fairly easy to reproduce in most cases, just remove the
> antennas, or if needed put attenuators on and observe.  If the modem
> did not change base stations it usually can reconnect, but not
> always.
> 
> Is there any more information on this out there about why this
> happens?  Any ideas for what we can do about it?

If you can get debug logs from ModemManager we may be able to identify
a signal from the modem that connectivity has been lost.

However, it's not uncommon for devices to continue saying they are
"connected" when they actually cannot pass traffic to the base station,
like when you're going through a tunnel and they'll reconnect on the
other side.

But if the modem does report some state that MM can use to identify
that it really is disconnected then we can fix that in MM.

Dan

> [1] 
> https://gitlab.freedesktop.org/mips171/modem-manager-keepalive/blob/master/13-keepalive_modemmanager
> [2] Forum 
> https://forum.openwrt.org/t/new-luci-protocol-luci-proto-modemmanager-testing/23696/38
> 
> All the best,
> Nicholas
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