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Network Working Group                                         C. Bormann
Internet-Draft                                    Universität Bremen TZI
Intended status: Informational                                J. Jiménez
Expires: 1 October 2020                                         Ericsson
                                                           30 March 2020

                     CoRE Working Group -- Overview


   The IETF "Constrained RESTful Environments" (CoRE) Working Group
   standardizes application layer protocols that can be used by
   resource-constrained devices, as can be found in the Internet of
   Things (IoT).  It is part of a cluster of about a dozen IETF WGs
   defining specifications for these environments.

   This short document provides an overview of the activities of the
   CoRE WG as of end of March, 2020.

About This Document

   This document is not intended for publication as an RFC.  It provides
   a snapshot of the current status of the WG, from the personal view of
   the authors.  The intention is to keep it updated, roughly once per
   physical IETF meeting (or its digital replacement).

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 https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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 1 October 2020.

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Copyright Notice

   Copyright (c) 2020 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
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Main Specification  . . . . . . . . . . . . . . . . . . . . .   2
   3.  Security  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Operations and Management . . . . . . . . . . . . . . . . . .   3
   5.  Data Formats  . . . . . . . . . . . . . . . . . . . . . . . .   4
   6.  Further Information . . . . . . . . . . . . . . . . . . . . .   4
   7.  Informative References  . . . . . . . . . . . . . . . . . . .   4
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   The IETF "Constrained RESTful Environments" (CoRE) Working Group
   standardizes application layer protocols that can be used by
   resource-constrained devices, as can be found in the Internet of
   Things (IoT).  It is part of a cluster of about a dozen IETF WGs that
   define networking (e.g., 6Lo), routing (e.g., ROLL), and security
   (e.g., ACE, LAKE, SUIT) for these environments.  This cluster has
   been growing since 2005; ten years ago, on 2010-03-09, CoRE was added
   to it.

2.  Main Specification

   The main specification of CoRE is the Constrained Application
   Protocol (CoAP) [RFC7252].  CoAP is for applications including
   constrained devices what HTTP is for general purpose applications.
   By using UDP as the transport protocol as opposed to HTTP's use of
   TCP, and by removing much of the baggage of of HTTP, CoAP can be run
   on quite simple platforms and with very little power use.  Both
   protocols share the Representational State Transfer (REST)
   architecture, the same set of verbs (GET, PUT, POST, DELETE), and
   quite similar semantics.

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   Since CoAP's approval in 2013, further specifications have been added
   to support the Observe pattern of change notifications from a server
   (low-complexity server-push) [RFC7641], to support larger transfers
   [RFC7959], to add verbs (FETCH, PATCH, and idempotent iPATCH
   [RFC8132]), and to enable the use of CoAP over TCP [RFC8323].
   [RFC8768] recently added a way to detect and mitigate loops in a
   proxy configuration, motivated by the requirements of the Distributed
   Denial-of-Service Open Threat Signaling (DOTS
   [I-D.ietf-dots-signal-channel]) specification.

   Two further extensions are now in completion: reducing the need for
   per-request state in clients and proxies [I-D.ietf-core-stateless]
   (in IETF last call) and improving the security between multiple
   active requests [I-D.ietf-core-echo-request-tag], further reducing
   CoAP's exploitability in denial of service attacks (completed
   working-group last call).

3.  Security

   Security has always been a critical enabler for IoT.  Similar to the
   way the HTTP web uses TLS, CoAP was kicked off with a security
   architecture based on Datagram TLS (DTLS), which provides high levels
   of security, but does not support end-to-end security in a
   configuration that includes proxies.  Object Security for CoRE
   (OSCORE) now provides end-to-end security over proxy paths that may
   include both CoAP and HTTP [RFC8613].

   One interesting aspect of OSCORE is that it also supports group
   communication, as it occurs in multicasting requests to collect
   responses from a group of nodes.  CoAP has supported multicast
   requests from the outset, and [RFC7390], Group Communication on top
   of IP multicast, provides additional specification for this.  As DTLS
   only supports unicast, without a security architecture RFC 7390 was
   published an experimental RFC.  Work is now underway to revise this
   RFC [I-D.ietf-core-groupcomm-bis], which includes making use of the
   capabilities provided by OSCORE for group communication
   [I-D.ietf-core-oscore-groupcomm].  Work is now under way in the CoRE,
   ACE, and LAKE working groups to complement this basis with additional
   specifications making use of OSCORE and CoAP group communication.

4.  Operations and Management

   IoT systems need to support a large number of nodes, which need to be
   configured and integrated into an IoT system.  A discovery and self-
   description architecture based on web links has been the first
   product of the WG [RFC6690], which is now being complemented by a
   registration and discovery function (CoRE Resource Directory
   [I-D.ietf-core-resource-directory], in IESG processing).

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   Constrained nodes also need management functions.  While many IoT
   SDOs are integrating these right into their IoT data format
   specifications, the IETF has its own architecture for describing
   management information, YANG [RFC7950].  The "CORECONF"
   specifications that are in Working Group Last Call (including YANG-
   CBOR [I-D.ietf-core-yang-cbor]) make this widely used approach of
   providing management interfaces available in a highly efficient way
   that is applicable to constrained environments, as our complement to
   the established YANG protocols NETCONF and RESTCONF.

5.  Data Formats

   While CoAP can be used with many different data formats, a simple
   CoRE format for sensor and actuator data, Sensor Measurement Lists
   (SenML), was defined in [RFC8428].  Recently, a number of
   specifications have been readied in support of SenML that are now
   undergoing final processing by the RFC editor: Support for the RFC
   8132 verbs [I-D.ietf-core-senml-etch], and modifications to the SenML
   units registry [I-D.ietf-core-senml-more-units] that make it more
   accessible as a basis for data format standards of other Standards
   Development Organizations (SDOs).  A foundation for further data
   format specification that combines the web-linking approach of RFC
   6690 with more modern data representation techniques is now being
   worked on under the name CoRAL [I-D.ietf-core-coral]
   [I-D.ietf-core-href]; application specifications such as CoAP pubsub
   [I-D.ietf-core-coap-pubsub] are expected to pivot to this basis.

6.  Further Information

   To follow and contribute to CoRE's work, please refer to the core
   status page (https://tools.ietf.org/wg/core/
   (https://tools.ietf.org/wg/core/)) and join the core mailing list:
   _core@ietf.org_ via https://www.ietf.org/mailman/listinfo/core

7.  Informative References

              Koster, M., Keranen, A., and J. Jimenez, "Publish-
              Subscribe Broker for the Constrained Application Protocol
              (CoAP)", Work in Progress, Internet-Draft, draft-ietf-
              core-coap-pubsub-09, 30 September 2019,

              Hartke, K., "The Constrained RESTful Application Language
              (CoRAL)", Work in Progress, Internet-Draft, draft-ietf-

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              core-coral-03, 9 March 2020, <http://www.ietf.org/

              Amsuess, C., Mattsson, J., and G. Selander, "CoAP: Echo,
              Request-Tag, and Token Processing", Work in Progress,
              Internet-Draft, draft-ietf-core-echo-request-tag-09, 9
              March 2020, <http://www.ietf.org/internet-drafts/draft-

              Dijk, E., Wang, C., and M. Tiloca, "Group Communication
              for the Constrained Application Protocol (CoAP)", Work in
              Progress, Internet-Draft, draft-ietf-core-groupcomm-bis-
              00, 30 March 2020, <https://www.ietf.org/internet-drafts/

              Hartke, K., "Constrained Resource Identifiers", Work in
              Progress, Internet-Draft, draft-ietf-core-href-03, 9 March
              2020, <http://www.ietf.org/internet-drafts/draft-ietf-

              Tiloca, M., Selander, G., Palombini, F., and J. Park,
              "Group OSCORE - Secure Group Communication for CoAP", Work
              in Progress, Internet-Draft, draft-ietf-core-oscore-
              groupcomm-07, 9 March 2020, <http://www.ietf.org/internet-

              Shelby, Z., Koster, M., Bormann, C., Stok, P., and C.
              Amsuess, "CoRE Resource Directory", Work in Progress,
              Internet-Draft, draft-ietf-core-resource-directory-24, 9
              March 2020, <http://www.ietf.org/internet-drafts/draft-

              Keranen, A. and M. Mohajer, "FETCH & PATCH with Sensor
              Measurement Lists (SenML)", Work in Progress, Internet-
              Draft, draft-ietf-core-senml-etch-07, 9 March 2020,

              Bormann, C., "Additional Units for SenML", Work in
              Progress, Internet-Draft, draft-ietf-core-senml-more-

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              units-06, 19 March 2020, <http://www.ietf.org/internet-

              Hartke, K., "Extended Tokens and Stateless Clients in the
              Constrained Application Protocol (CoAP)", Work in
              Progress, Internet-Draft, draft-ietf-core-stateless-05, 12
              March 2020, <http://www.ietf.org/internet-drafts/draft-

              Veillette, M., Petrov, I., and A. Pelov, "CBOR Encoding of
              Data Modeled with YANG", Work in Progress, Internet-Draft,
              draft-ietf-core-yang-cbor-12, 9 March 2020,

              Reddy.K, T., Boucadair, M., Patil, P., Mortensen, A., and
              N. Teague, "Distributed Denial-of-Service Open Threat
              Signaling (DOTS) Signal Channel Specification", Work in
              Progress, Internet-Draft, draft-ietf-dots-signal-channel-
              41, 6 January 2020, <http://www.ietf.org/internet-drafts/

   [RFC6690]  Shelby, Z., "Constrained RESTful Environments (CoRE) Link
              Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,

   [RFC7252]  Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
              Application Protocol (CoAP)", RFC 7252,
              DOI 10.17487/RFC7252, June 2014,

   [RFC7390]  Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for
              the Constrained Application Protocol (CoAP)", RFC 7390,
              DOI 10.17487/RFC7390, October 2014,

   [RFC7641]  Hartke, K., "Observing Resources in the Constrained
              Application Protocol (CoAP)", RFC 7641,
              DOI 10.17487/RFC7641, September 2015,

   [RFC7950]  Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
              RFC 7950, DOI 10.17487/RFC7950, August 2016,

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   [RFC7959]  Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
              the Constrained Application Protocol (CoAP)", RFC 7959,
              DOI 10.17487/RFC7959, August 2016,

   [RFC8132]  van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and
              FETCH Methods for the Constrained Application Protocol
              (CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017,

   [RFC8323]  Bormann, C., Lemay, S., Tschofenig, H., Hartke, K.,
              Silverajan, B., and B. Raymor, Ed., "CoAP (Constrained
              Application Protocol) over TCP, TLS, and WebSockets",
              RFC 8323, DOI 10.17487/RFC8323, February 2018,

   [RFC8428]  Jennings, C., Shelby, Z., Arkko, J., Keranen, A., and C.
              Bormann, "Sensor Measurement Lists (SenML)", RFC 8428,
              DOI 10.17487/RFC8428, August 2018,

   [RFC8613]  Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
              "Object Security for Constrained RESTful Environments
              (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,

   [RFC8768]  Boucadair, M., Reddy.K, T., and J. Shallow, "Constrained
              Application Protocol (CoAP) Hop-Limit Option", RFC 8768,
              DOI 10.17487/RFC8768, March 2020,


   Marco Tiloca provided comments on a draft of this document.

Authors' Addresses

   Carsten Bormann
   Universität Bremen TZI
   Postfach 330440
   D-28359 Bremen

   Phone: +49-421-218-63921
   Email: cabo@tzi.org

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   Jaime Jiménez

   Phone: +358-442-992-827
   Email: jaime@iki.fi

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