How to get status of message transmission

RE: How to get status of message transmission

Achim Kraus — Wed, 23 Apr 2025 15:40:34 GMT

[quote userid="117940" url="~/f/nordic-q-a/120767/how-to-get-status-of-message-transmission/532641"]But e.g. I can get buffer overflow, if packets are stuck in buffer for some reason.[/quote]

It's not, that I don't agree, that this functions would be valuable. But 2 years ago there was a ticket Bug report: Non-blocking send fails with EWOULDBLOCK even though poll returned POLLOUT which explains some of the limitations (modem buffers + app buffers), and so I guess, this is still not implemented nor is there a schedule for implementing it.

RE: How to get status of message transmission

Martin Vitek — Wed, 23 Apr 2025 15:00:40 GMT

I have implemented ACK/timeout with retransmission in my protocol. And I agree, that those informations are not important from UDP point of view. But e.g. I can get buffer overflow, if packets are stuck in buffer for some reason.

RE: How to get status of message transmission

Achim Kraus — Fri, 18 Apr 2025 07:12:37 GMT

While that will make it easier to implement a UDP based protocol, it may be also seen as "duplicate", because regardless if the modem has sent the message, it may not reach the destination.

Therefore UDP based protocols use some ACK/timeout mechanisms to cover that. In my experience it's therefore only important to know, when to start the transmission timer. I use "registered + pdn context + rrc active" to start that timer. To make it a little more reliable on "wake up after PSM", it may be considered to add "for 2s" because in rare cases of some gone network registrations, you get "rrc active", while the registration is still from the last "rrc active" and then changes to "searching" short after.

For CoAP/DTLS 1.2 CID that works pretty well. I don't use the current coap-client logic , I've implemented my own timeout/retransmission mechanism.