OpenWRT Sierra EM7455 drops connection while driving

[Peter Krause]

Yeah, I had to change a lot of things up.
When moving, the Sierra modem may switch bands, change IP addresses, go through dead zones, or through tower handoffs.  The Sierra stays up -- if you use minicom or some other comm port read/writer on the AT port (/dev/ttyUSB2 for me), you can do:
at!gstatus? ---to see the connection statusat+cgcontrdp -- to see the IP addresses 

There are two sides to the LTE session, the Sierra -> Carrier and the Sierra -> OpenWRT/Linux.  Using those AT commands, you can see the Sierra recovers from each of the above events.  However, the Sierra -> Openwrt network session usually does not recover.  It may have the old IP or gateway in the wwan interface, or even if it keeps the same IP, sometimes the link just breaks and needs to be reestablished depending on the size of the dead zone you went through.
Aleksander said earlier in this thread that MM doesn't handle the reconnect of the Sierra->Openwrt side yet.
So, I ended up moving off of MM, checking connection status with AT commands, then setting up the IP link with a script.  Once you get the IP/Gateway with 'uqmi --get-current-settings', you can use:ip addr -- delete the old IPip addr -- add the new iproute del default gw old.old.old.oldroute add default gw xx.xx.xx.xx 
You may or may not need to do an ifup wwan, and you have to make sure that /sys/class/net/wwan0/qmi/raw_ip is set to Y, or no data will go through.
It's really tricky, I've been banging my head on it for a couple weeks, but I'm almost stable now.  I just have some issues with Sierra AT command settings for different carriers to deal with.



      From: Nick <mips171 at icloud.com>
 To: Peter Krause <peter at uringme.com> 
Cc: ModemManager <modemmanager-devel at lists.freedesktop.org>
 Sent: Sunday, January 13, 2019 10:44 PM
 Subject: Re: OpenWRT Sierra EM7455 drops connection while driving
   
Hey Peter,

Did you ever make any progress on this?  I think I am seeing the same thing over here.

Best,
Nicholas

   
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/modemmanager-devel/attachments/20190114/67a72af9/attachment.html>