CoAP Observer loses connection after RRC idle

RE: CoAP Observer loses connection after RRC idle

Achim Kraus — Fri, 04 Apr 2025 15:46:07 GMT

The NAT timeout isn't an issue of CoAP. Using UDP will not prevent to send the empty messages.

I don't know, why you need the server to initiate sending data to the device, in other cases it's OK to do this as response, when the device initiates the communication.

Anyway, if you really need the server to initiate the communication, then eDRX and a VPN to your M(V)NO will be your friend (if both is supported).

RE: CoAP Observer loses connection after RRC idle

siliconwitch — Fri, 04 Apr 2025 15:37:10 GMT

Indeed I discovered two issues: The first one was on my server side code. I had to enable a keep-alive option in order to prevent the CoAP library from terminating the socket.

After that, the timeout would then happen at ~120 seconds. I suppose that's the MNO NAT timeout.

I had some success sending empty UDP packets periodically to keep the socket open, but over many devices the cost of doing this would be quite expensive.

So, rather than using CoAP observer, we've now just opened a UDP listener on the device side so that the server can send messages directly. This actually turned out to be a cleaner solution on both sides.

RE: CoAP Observer loses connection after RRC idle

Achim Kraus — Fri, 04 Apr 2025 14:57:54 GMT

In many case it will be either a NAT (Network Address Translator) at your cloud server or at the MNO public internet break out.

What is the interval your server sends notifications to the device? 10s will be very fast for the idea with the NAT, but may be it's rather 60s than 10s.

RE: CoAP Observer loses connection after RRC idle

Øyvind — Wed, 02 Apr 2025 13:07:33 GMT

Hello

Are you able to share more information about your setup? There isn't much information from the provided logs. Does your device actually loose network connection, or does the device stop responding to logging as well?

Are you using your application or a sample from us? Will need some more information in order to understand what is going on with your device. Could you provide a modem trace as well?

Kind regards,
Øyvind