"Connected" state after losing signal

[Nick]

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?

[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