LTE network shutdown after some time

Lansirinne, Mika mlansirinne at
Tue Jan 15 18:28:44 UTC 2019


I am testing a couple of LTE modems from Sierra (EM7455 and EM7565 specifically), and found some strange behavior: after some time of working, the LTE network seems to drop the connection without having any indication of that happening, other than that the traffic does not flow any more of course. The both models work the same way.

I am currently very unsure on what level this is happening. To my mind the disconnect can perhaps happen at least because the modem itself (hardware or firmware level), in mbim library, by the ISP or because of my SIM card / data plan. Neither of which make any sense since I can't figure out why would one want to disconnect the connection (without reconnecting automatically again) if the device is in use. And if this really is intended behavior, I wonder if I could at least get some event of this happening so that I can act on it as a workaround.

I have connected to the network using the mbimcli commands, with the mbim-proxy running on the background:

# mbimcli -p -d /dev/cdc-wdm0 --query-subscriber-ready-status

# mbimcli -p -d /dev/cdc-wdm0 --query-registration-state

# mbimcli -p -d /dev/cdc-wdm0 --attach-packet-service

# mbimcli -p -d /dev/cdc-wdm0 --register-automatic

# mbimcli -p -d /dev/cdc-wdm0 --connect=apn=internet

After that I fetched the ip parameters and set the ip address manually since these modems do not support the DHCP:

# mbimcli -p -d /dev/cdc-wdm0 --query-ip-configuration

# ip addr...
# ip route...

All of that works perfectly.

I ran a test over a weekend in which I sent one ping packet once in a minute, and if that failed then reconnecting the lte. It turned out that the connection was dropped exactly every 12 hours and four minutes. The query-packet-service-state was showing that "no cells in the location area" in that time. Yet the re-connection was immediately successful so there really were no actual problems with the LTE towers.

# mbimcli -p -d /dev/cdc-wdm0 --query-packet-service-state

[/dev/cdc-wdm0] Packet service status:
                 Network error: 'no-cells-in-location-area'
          Packet service state: 'detached'
        Available data classes: 'unknown'
                  Uplink speed: '0 bps'
                Downlink speed: '0 bps'

Without sending the ping packets, i.e. just letting the modem idle and detecting the outage by the query-packet-service-state command, the disconnection may happen much sooner, even less than an hour but normally not immediately.

Would anyone have any ideas if I am just using it wrongly or is there some real problem which could be fixed on some level?

Best regards,


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