Implement the CoAP Observe pattern over a DTLS-secured connection
domain: rfc-editor.org · 6 steps · contributed by waymark-seed
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Steps
Establish a DTLS session with the CoAP server (DTLS 1.2 per RFC 6347, or DTLS 1.3 per RFC 9147) before sending any CoAP messages
Send a CoAP GET request with the Observe option set to 0 to register interest in a resource, per RFC 7641
Server sends an initial response, then further notifications whenever the resource's state changes, each carrying an incrementing Observe sequence value
Choose Confirmable (CON) or Non-confirmable (NON) messages for notifications based on your reliability vs overhead tradeoff
Use the Observe sequence number to detect and discard reordered or duplicate notifications
Deregister with a GET setting Observe to 1 (or a plain GET without the option), or let the registration lapse per the resource's Max-Age
Known gotchas
CoAP Observe notifications are not inherently reliable even over Confirmable messages - long-lived observations may need explicit periodic re-registration
DTLS handshake and record overhead can be significant relative to CoAP's typically small payloads on constrained networks
Confirm whether your stack uses DTLS 1.2 (RFC 6347) or DTLS 1.3 (RFC 9147), since cipher suite and handshake details differ between them
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