NRF9160: Any way to persist DTLS Connection-ID (CID)/Session across e.g. socket closing/modem flight mode?

RE: NRF9160: Any way to persist DTLS Connection-ID (CID)/Session across e.g. socket closing/modem flight mode?

Achim Kraus — Thu, 26 Oct 2023 14:04:16 GMT

Your welcome.

RE: NRF9160: Any way to persist DTLS Connection-ID (CID)/Session across e.g. socket closing/modem flight mode?

HFled — Thu, 26 Oct 2023 11:47:06 GMT

I played around with CONN_LOAD/SAVE but without success. The documentation also still explicitly states that context is lost on socket close, so I suppose that's to be expected.

I'm aware that PSM would solve my issue, but I'm explicitly interested in the non-psm case. Moving the DTLS context out of the modem/into app-space seems to be the obvious/proper solution for that. Though I'll still need to investigate the Blog post linked by Charlie above.

PS: Just randomly want to say thanks for all the work and support you're doing around here and generally speaking in the DTLS/Coap realm. "So I stumbled across this post/answer/project" by Achim has become a bit of a running gag among me and my colleagues (in a positive way ofc. ;) ).

RE: NRF9160: Any way to persist DTLS Connection-ID (CID)/Session across e.g. socket closing/modem flight mode?

Achim Kraus — Wed, 25 Oct 2023 18:05:00 GMT

Hi Henning,

using PSM there is no need to "turn off" the modem. So you don't need to close the socket.

AFAIK, there is also a possibility to save (TLS_DTLS_CONN_SAVE) and load (TLS_DTLS_CONN_LOAD) the connection. So in cases, where the modem lose the network and closes the socket on its own, that may help. I didn't test that.

I'm using my own implementation (https://github.com/boaks/zephyr-coaps-client), where tinydtls is used and is outside of the socket and so more resilient against "TCP style implementations", which drops sockets, when the network is temporary lost. That also needs to close and open the UDP socket (that's caused by the modem), but the DTLS context is not affected.

RE: NRF9160: Any way to persist DTLS Connection-ID (CID)/Session across e.g. socket closing/modem flight mode?

Charlie — Wed, 25 Oct 2023 12:26:47 GMT

Hi Henning,

You can refer to (+) Extend your battery life with nRF Cloud's CoAP interface - Blogs - Nordic Blog - Nordic DevZone (nordicsemi.com) for the usage of DTLS 1.2 Connection ID (CID) extension (RFC 9146) in CoAP.

It needs support from both the client and server side. nRF9160 MFW from v1.3.5 and the current nRF Cloud CoAP API support this extension.

Best regards,

Charlie