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My 4G device is on an automobile that travels around 500 kms in a night. The network disconnects sometimes. And this is the log I see in the Syslog. Can someone help me understand what is going on? And what solution could help?

The connection takes 8 steps to be successful. When the disconnection happens, This is the first message I see in Syslog

Feb 10 04:20:45 busnet1-desktop ModemManager[3820]: <info>  Modem /org/freedesktop/ModemManager1/Modem/0: 3GPP Registration state changed (roaming -> registering)
Feb 10 04:20:45 busnet1-desktop ModemManager[3820]: <info>  Modem /org/freedesktop/ModemManager1/Modem/0: 3GPP Registration state changed (registering -> home)
Feb 10 04:21:03 busnet1-desktop ModemManager[3820]: <info>  Modem /org/freedesktop/ModemManager1/Modem/0: 3GPP Registration state changed (home -> registering)
Feb 10 04:21:03 busnet1-desktop ModemManager[3820]: <info>  Modem /org/freedesktop/ModemManager1/Modem/0: 3GPP Registration state changed (registering -> roaming)

The OS keeps trying to reestablish connection every 5 minutes. The last step doesn't go through every time. The following is the log when the connection fails.

Feb 10 04:51:48 busnet1-desktop ModemManager[3820]: <info>  Simple connect state (7/8): Connect
Feb 10 04:51:48 busnet1-desktop ModemManager[3820]: <info>  Modem /org/freedesktop/ModemManager1/Modem/0: state changed (registered -> connecting)
Feb 10 04:51:48 busnet1-desktop ModemManager[3820]: <info>  Modem /org/freedesktop/ModemManager1/Modem/0: state changed (connecting -> registered)
Feb 10 04:51:48 busnet1-desktop NetworkManager[4261]: <info>  [1581290508.1122] modem["ttyUSB0"]: modem state changed, 'registered' --> 'connecting' (reason: user-requested)
Feb 10 04:51:48 busnet1-desktop NetworkManager[4261]: <info>  [1581290508.1126] modem["ttyUSB0"]: modem state changed, 'connecting' --> 'registered' (reason: user-requested)
Feb 10 04:51:48 busnet1-desktop NetworkManager[4261]: <warn>  [1581290508.1127] modem-broadband[ttyUSB0]: failed to connect modem: Couldn't connect: this bearer is already connected
Feb 10 04:51:48 busnet1-desktop NetworkManager[4261]: <info>  [1581290508.1128] device (ttyUSB0): state change: prepare -> failed (reason 'unknown', sys-iface-state: 'managed')
Feb 10 04:51:48 busnet1-desktop NetworkManager[4261]: <info>  [1581290508.1136] manager: NetworkManager state is now DISCONNECTED
Feb 10 04:51:48 busnet1-desktop NetworkManager[4261]: <warn>  [1581290508.1149] device (ttyUSB0): Activation: failed for connection 'Airtel Default'
Feb 10 04:51:48 busnet1-desktop NetworkManager[4261]: <info>  [1581290508.1166] device (ttyUSB0): state change: failed -> disconnected (reason 'none', sys-iface-state: 'managed')

We have a cron restarting the machine every hour. So when the device reboots, the connection gets established in the first try. How do we re-establish connection without having to reboot?

This is the Syslog entry when the connection is successful

Feb 10 05:00:42 busnet1-desktop ModemManager[3997]: <info>  Modem /org/freedesktop/ModemManager1/Modem/0: 3GPP Registration state changed (unknown -> registering)
Feb 10 05:00:42 busnet1-desktop ModemManager[3997]: <info>  Simple connect state (6/8): Bearer
Feb 10 05:00:42 busnet1-desktop ModemManager[3997]: <info>  Simple connect state (7/8): Connect
Feb 10 05:00:42 busnet1-desktop ModemManager[3997]: <info>  Modem /org/freedesktop/ModemManager1/Modem/0: state changed (enabled -> connecting)
Feb 10 05:00:42 busnet1-desktop NetworkManager[4073]: <info>  [1581291042.6598] modem["ttyUSB0"]: modem state changed, 'enabled' --> 'connecting' (reason: user-requested)
Feb 10 05:00:42 busnet1-desktop ModemManager[3997]: <info>  Modem /org/freedesktop/ModemManager1/Modem/0: 3GPP Registration state changed (registering -> home)
Feb 10 05:00:43 busnet1-desktop ModemManager[3997]: <info>  Modem /org/freedesktop/ModemManager1/Modem/0: state changed (connecting -> connected)
Feb 10 05:00:43 busnet1-desktop ModemManager[3997]: <info>  Simple connect state (8/8): All done
Feb 10 05:00:43 busnet1-desktop NetworkManager[4073]: <info>  [1581291043.2063] modem["ttyUSB0"]: modem state changed, 'connecting' --> 'connected' (reason: user-requested)
Feb 10 05:00:43 busnet1-desktop NetworkManager[4073]: <warn>  [1581291043.2150] device (ttyUSB0): ip-ifname: set ifname 'ttyUSB1', unknown ifindex
Feb 10 05:00:43 busnet1-desktop NetworkManager[4073]: <info>  [1581291043.2155] device (ttyUSB0): state change: prepare -> config (reason 'none', sys-iface-state: 'managed')
Feb 10 05:00:43 busnet1-desktop NetworkManager[4073]: <info>  [1581291043.2163] device (ttyUSB0): state change: config -> ip-config (reason 'none', sys-iface-state: 'managed')
Feb 10 05:00:43 busnet1-desktop NetworkManager[4073]: <warn>  [1581291043.2168] device (ttyUSB0): interface ttyUSB1 not up for IP configuration
Feb 10 05:00:43 busnet1-desktop NetworkManager[4073]: <info>  [1581291043.2168] modem["ttyUSB0"]: using modem-specified IP timeout: 20 seconds
Feb 10 05:00:43 busnet1-desktop NetworkManager[4073]: <info>  [1581291043.2223] loaded PPP plugin /usr/lib/aarch64-linux-gnu/NetworkManager/libnm-ppp-plugin.so
Feb 10 05:00:43 busnet1-desktop NetworkManager[4073]: <info>  [1581291043.2238] ppp-manager: starting PPP connection
Feb 10 05:00:43 busnet1-desktop NetworkManager[4073]: <info>  [1581291043.2341] ppp-manager: pppd started with pid 6073
Feb 10 05:00:43 busnet1-desktop NetworkManager[4073]: <info>  [1581291043.2343] modem["ttyUSB0"]: IPv6 configuration disabled

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