Subject: [core] #177: Response suppression for multicast not defined

From: "core issue tracker" <[email-masked]>
Date: Sun, 06 Nov 2011 16:38:51 -0000

#177: Response suppression for multicast not defined

 Matthieu Vial reports:

 In section 4.1 multicast of coap 03 there is a proposition to eliminate
 responses with an error code

 This text has been removed in 07 and the text "SHOULD be a Non-confirmable
 request" is now a "MUST be Non-confirmable request".
 But as I understand coap 07 it is possible to send a response with an
 error code to a NON request as a NON response.
 So I think the text in coap 03 is now missing to avoid response floods.

 Carsten Bormann replies:

 indeed, as we fixed the layering here, we lost this functionality.

 So what the text in 07 says is that multicast needs to be NON, not CON.
 This is at the reliability layer.

 The error code becomes visible at the request/response layer.
 Independent of whether the request is a NON or a CON, if it does arrive,
 the server normally will send a response.
 1) It is up to the server to decide whether the response is sent in a CON,
 piggy-backed in an ACK (only applicable to CON requests, which we just
 excluded), or in a NON.
 2) We need to describe what the expectations are when a server does not
 send a response at all.  I think the server should always send a response
 for a request that arrived via a CON.  However, for a NON-request, it
 might as well pretend it never got the request.  This is a bit of a layer
 violation, as the reliability layer would indicate to the request/response
 layer wether the request was a NON and whether it came in by multicast.

 So yes, I think there should be new text in 4.4 that says the reliability
 layer does indicate to the r/r layer that this was a multicast.  There
 also should be text, probably in 5.2.3, that restores some form of silent
 behavior for requests that are "not applicable".  This needs to be defined
 a bit better, I think (even an empty 2.04 might qualify for a "not
 applicable" here, say in a link-format request with a query.  Note that
 section 4.1 of draft-ietf-core-link-format-07.txt also has something to
 say about multicast.

-- 
--------------------------------+------------------------------------
 Reporter:  cabo@…              |      Owner:  draft-ietf-core-coap@…
     Type:  protocol defect     |     Status:  new
 Priority:  major               |  Milestone:
Component:  coap                |    Version:
 Severity:  Active WG Document  |   Keywords:
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Ticket URL: <http://trac.tools.ietf.org/wg/core/trac/ticket/177>
core <http://tools.ietf.org/core/>