DTLS minimum handshake timeout

[samuel4]

Hi

It seems that the default minium DTLS handshake timeout is about 1 second. That means, there is a retransmission if a response isn't received within this timeout. In NB-IoT/LTE-M this leads to many unnecessary retransmission:

The server is configured to a higher timeout, but how can I configure the nRF9151 to be more patient during handshake? Since NB-IoT has latencies up to 10 seconds, retransmitting every second does barely make sense.

I have tried a lot of socket options so far, but none seem to work. Zephyr itself offers TLS_DTLS_HANDSHAKE_TIMEOUT_MIN, but this one is not supported on offloaded sockets. Am I missing something? It would be a pitty if I have to switch to mbedTLS, because of a missing handshake timeout.

NCS version: v3.0.2

Best regards
Samuel

[Øyvind]

Hi Samuel, 

Could you please provide more information on the DTLS solution that you are using? You are not using mbedTLS? What modem FW are you running on your device?

Looking through our documentation, there should be a socket option called SO_KEEPOPEN that will keep DTLS CID enabled sessions during network outages, i.e. from nrfxlib/nrf_modem/include/nrf_socket.h: Keep socket open when its PDN connection is lost.

Does this provide any solution to your issue?

Kind regards,
Øyvind