Internet DRAFT - draft-lucas-coap-multicast
draft-lucas-coap-multicast
core R. Lucas
Internet Draft Cisco International Limited
Intended status: Standards Track September 13, 2017
Expires: March 17, 2018
CoAP Multicast
draft-lucas-coap-multicast-00.txt
Abstract
Multicast is a preferred approach to send a single message to
multiple recipients but it is typically lossy. CoAP is the choice of
messaging for IoT. If using multicast to transmit CoAP messages
there is a risk they get lost and a further risk that sequences of
messages get disrupted and leave the system in an unknown or
unpleasant state.
In the device world we might want to guarantee that a whole sequence
of commands arrives at the device. For example a sequence to Open,
Report, Do some action, and Close. It is better that all of these
messages arrive or all of them do not arrive rather than have some
of them arrive and to not know which ones failed.
CoAP messages tend to be small due to constrained resources on the
recipient devices. Existing frame sizes though are relatively large
so it is possible to pack these frames with several smaller CoAP
messages and send them as a group.
CoAP Multicast proposes the simplest way to do this. It is a device
independent method and adds no need for encryption channels.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
reference material or to cite them other than as "work in
progress."
This Internet-Draft will expire on April 13th, 2018.
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Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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warranty as described in the Simplified BSD License.
1. Introduction
In the device world we might want to guarantee that a whole sequence
of commands arrives at the device.
For example a sequence to Open, Report, Do some action, and Close.
It is better that all of these messages arrive or all of them do not
arrive.
Existing relatively large frame sizes allow smaller CoAP messages to
be packed together in the same multicast. CoAP Multicast proposes
the simplest way to pack the frames using a device independent
method.
There is no mention or burden added here of encryption or security.
You can further decide of course to close the lossy reliability loop
with a clever mechanism to ACK or complete/confirm a transaction but
that is neither a function of multicast or a task for CoAP multicast
which simply aims to provide an efficiency boost and a reliability
boost in its own right by allowing groups of CoAP messages to be
sent together.
2. Assumptions
The multicast transport layer returns data frames with known
lengths.
The multicast transport layer is not restricted to a maximum data
frame length OR the maximum data frame length is sufficient for the
messages that we wish to send.
3. Summary
Keeping it as simple as possible.
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Each multicast frame contains one or more CoAP messages. Multicast
communication is unreliable so allowing multiple CoAP messages in a
single multicast frame allows for simple atomic delivery of a set of
CoAP messages.
The CoAP multicast frame contains a CBOR array of byte strings.
Each byte string is a CoAP message.
>> Each CoAP message MUST be marked as non-Confirmable.
>> Each CoAP message SHOULD be idempotent (i.e. probably PUT only).
The receiver should simply replay each message in turn. No responses
should be generated because the messages MUST be marked as
non-confirmable, but if any responses are generated then they should
be discarded.
4. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying significance described in RFC 2119.
In this document, the characters ">>" preceding an indented line(s)
indicates a statement using the key words listed above. This
convention aids reviewers in quickly identifying or finding the
portions of this RFC covered by these keywords.
5. Security Considerations
None
6. IANA Considerations
None
7. Conclusions
None
8. References
8.1. Normative References
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
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DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
[RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR), RFC 7049, DOI 10.17487/RFC7049,
October 2013, <http://www.rfc-editor.org/info/rfc7049>
8.2. Informative References
[RFC7390] Rahman, A., Ed., and E. Dijk, Ed., "Group Communication
for the Constrained Application Protocol (CoAP)", RFC 390,
DOI 10.17487/RFC7390, October 2014,
<http://www.rfc-editor.org/info/rfc7390>.
[I-D.dijk-core-groupcomm-misc]
Dijk, E., and A. Rahman, "Miscellaneous CoAP Group
Communication Topics",
draft-dijk-core-groupcomm-misc, June 2014,
https://datatracker.ietf.org/doc/
draft-dijk-core-groupcomm-misc/
https://www.ietf.org/archive/id/
draft-dijk-core-groupcomm-misc-06.txt
9. Acknowledgments
Parts of this document are a byproduct of the "aSSURE" project,
partially funded by Innovate UK. It is provided "as is" and without
any express or implied warranties, including, without limitation,
the implied warranties of fitness for a particular purpose. The
views and conclusion contained herein are those of the authors and
should not be interpreted as necessarily representing the official
policies or endorsements, either expressed or implied, of the aSSURE
project or Innovate UK.
Author's Address
Roger Lucas
c/o Cisco International Limited
10, New Square Park
Bedfont Lakes
Feltham
TW14 8HA
United Kingdom
Email: iot@hiddenengine.co.uk
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