Observing Resources in the Constrained Application Protocol (CoAP)
RFC 7641

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Internet Engineering Task Force (IETF)                         K. Hartke
Request for Comments: 7641                       Universitaet Bremen TZI
Category: Standards Track                                 September 2015
ISSN: 2070-1721

   Observing Resources in the Constrained Application Protocol (CoAP)

Abstract

   The Constrained Application Protocol (CoAP) is a RESTful application
   protocol for constrained nodes and networks.  The state of a resource
   on a CoAP server can change over time.  This document specifies a
   simple protocol extension for CoAP that enables CoAP clients to
   "observe" resources, i.e., to retrieve a representation of a resource
   and keep this representation updated by the server over a period of
   time.  The protocol follows a best-effort approach for sending new
   representations to clients and provides eventual consistency between
   the state observed by each client and the actual resource state at
   the server.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7641.

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RFC 7641               Observing Resources in CoAP        September 2015

Copyright Notice

   Copyright (c) 2015 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.

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RFC 7641               Observing Resources in CoAP        September 2015

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Background  . . . . . . . . . . . . . . . . . . . . . . .  4
     1.2.  Protocol Overview . . . . . . . . . . . . . . . . . . . .  4
     1.3.  Consistency Model . . . . . . . . . . . . . . . . . . . .  6
     1.4.  Observable Resources  . . . . . . . . . . . . . . . . . .  7
     1.5.  Requirements Notation . . . . . . . . . . . . . . . . . .  8
   2.  The Observe Option  . . . . . . . . . . . . . . . . . . . . .  9
   3.  Client-Side Requirements  . . . . . . . . . . . . . . . . . . 10
     3.1.  Request . . . . . . . . . . . . . . . . . . . . . . . . . 10
     3.2.  Notifications . . . . . . . . . . . . . . . . . . . . . . 10
     3.3.  Caching . . . . . . . . . . . . . . . . . . . . . . . . . 11
     3.4.  Reordering  . . . . . . . . . . . . . . . . . . . . . . . 12
     3.5.  Transmission  . . . . . . . . . . . . . . . . . . . . . . 13
     3.6.  Cancellation  . . . . . . . . . . . . . . . . . . . . . . 13
   4.  Server-Side Requirements  . . . . . . . . . . . . . . . . . . 14
     4.1.  Request . . . . . . . . . . . . . . . . . . . . . . . . . 14
     4.2.  Notifications . . . . . . . . . . . . . . . . . . . . . . 14
     4.3.  Caching . . . . . . . . . . . . . . . . . . . . . . . . . 15
     4.4.  Reordering  . . . . . . . . . . . . . . . . . . . . . . . 16
     4.5.  Transmission  . . . . . . . . . . . . . . . . . . . . . . 17
   5.  Intermediaries  . . . . . . . . . . . . . . . . . . . . . . . 20
   6.  Web Linking . . . . . . . . . . . . . . . . . . . . . . . . . 20
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . 21
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . 22
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . 22
     9.2.  Informative References  . . . . . . . . . . . . . . . . . 22
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . . 24
     A.1.  Client/Server Examples  . . . . . . . . . . . . . . . . . 24
     A.2.  Proxy Examples  . . . . . . . . . . . . . . . . . . . . . 28
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . . 30
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . 30

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