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. Lucas Expires March 17, 2018 [Page 1] Internet-Draft CoAP Multicast September 2017 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 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without 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. Lucas Expires March 17, 2018 [Page 2] Internet-Draft CoAP Multicast September 2017 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, Lucas Expires March 17, 2018 [Page 3] Internet-Draft CoAP Multicast September 2017 DOI 10.17487/RFC7252, June 2014, . [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR), RFC 7049, DOI 10.17487/RFC7049, October 2013, 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, . [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 Lucas Expires March 17, 2018 [Page 4]