[core] Retransmission of non-confirmable response message upon receiving request message retranmission?

[Christer Holmberg <[e-mail]>]

Hi,

A couple of questions for clarification.


Assume a CoAP server receives a confirmable request message.

According to Section 4.5. of RFC 7252, the server SHOULD retransmit the associated ACK whenever it receives a retransmission of the request message. So far, so good.

Then, assume that the sever sends a non-confirmable response message to the request. AFAIK, that is allowed.

---

Q1:

Perhaps I have missed it, I can’t find any text saying that the server would retransmit the response message if it receives a retransmission of the request. Section 4.3 does say that a server may choose to transmit multiple copies of a non-confirmable message, but there is no text saying that such transmits would be triggered by a retransmission of the request.

Section 4.5. does say:

     “A server might relax the requirement to answer all retransmissions
      of an idempotent request with the same response (Section 4.2),”

Where does Section 4.2 talk about answering retransmissions of an idempotent request (or any request, for that matter) with the same response?

---

Q2:

Related to Q1, Section 4.5 says:

      ”For example, an implementation might want to process duplicate
      transmissions of a GET, PUT, or DELETE request as separate
      requests if the effort incurred by duplicate processing is less
      expensive than keeping track of previous responses would be.”


Maybe I misunderstand this “process as separate requests” thing, but:

First, it means that each response could be different from the previous one, and the sender of the request would have to process each of them.

Second, does this mean that, if the responses are confirmable, the server should expect an ACK for each response? “Process as separate requests” makes it sound like that.

---

Regards,

Christer