Question

Which CoAP message transfers response from the server within the acknowledgment message?
1.Separate
2.Confirmable 3.Non-confirmable
4.Piggyback

Answer 1

The answer is Option 4.

The piggyback CoAP message transfers response from the server within the acknowledge message.  This type of messaging mode is used in direct client-server communication. The server sends a response immediately as soon as it receives the message.  This response is sent within the acknowledge message.