How to recover a nRF9160 from sporadic ENETDOWN

Question

Using a Thingy!91 (v1.0.0 and v1.4.0, firmware 1.2.3, 1.2.7) I get sometimes (every couple of days) a ENETDOWN when sending data out. Before that ENETDOWN, the device was usually able to exchange 100 and more UDP messages. 
 Currently I do a "sys_reboot(SYS_REBOOT_COLD)", but I'm wondering, if there are less massive ways to recover. 
 I found other questions, but I'm still struggling to see an "useful" answer. e.g. 
 https://devzone.nordicsemi.com/f/nordic-q-a/57642/nrf9160-lte-modem-documentation 
 but the link at the end, ends in "NOT FOUND". 
 So, what is the recommended way to recover from ENETDOWN?

Albrecht Markus Schellenberger · Accepted Answer

Hello Achim, 
 Achim Kraus said: What happens, if the modem lose the network? 
 The modem will perform a new connection attempt according to 3GPP rules. 
 Achim Kraus said: What happens, if the modem gets connected again? 
 The modem will report this to the application (if configured), and wait for further instructions. Depending on network, modem might enter PSM. 
 Achim Kraus said: Is it right, that sockets are not longer usable, if that happens? 
 Yes, if the socket connection can not be kept, the modem will send a socket close request. 
 Achim Kraus said: Is reopening the socket the right thing to do? 
 Since the socket has been closed, it must be re-opened again, yes. 
 Achim Kraus said: Are the cases, that after a network reconnect, more than just reopen the socket is required. 
 That depends on each individual case and on how the implemented application is handling them. 
 Achim Kraus said: Would it be possible, that the developers of these components check their implementation about that? 
 When initialising and starting the modem, it will act according to requests from the application and 3GPP rules. Hence, there should be no need to verify its functionality as it is certified from our side towards all major network operators. But then of course, no software is perfect and you are always welcome to report unexpected behaviour to us :-) Regards, 
 Markus

How to recover a nRF9160 from sporadic ENETDOWN

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