Constrained Application Protocol (CoAP)
draft-ietf-core-coap-09

CoRE Working Group                                             Z. Shelby
Internet-Draft                                                 Sensinode
Intended status: Standards Track                               K. Hartke
Expires: September 13, 2012                                   C. Bormann
                                                 Universitaet Bremen TZI
                                                                B. Frank
                                                              SkyFoundry
                                                          March 12, 2012

                Constrained Application Protocol (CoAP)
                        draft-ietf-core-coap-09

Abstract

   This document specifies the Constrained Application Protocol (CoAP),
   a specialized web transfer protocol for use with constrained networks
   and nodes for machine-to-machine applications such as smart energy
   and building automation.  These constrained nodes often have 8-bit
   microcontrollers with small amounts of ROM and RAM, while networks
   such as 6LoWPAN often have high packet error rates and a typical
   throughput of 10s of kbit/s.  CoAP provides a method/response
   interaction model between application end-points, supports built-in
   resource discovery, and includes key web concepts such as URIs and
   content-types.  CoAP easily translates to HTTP for integration with
   the web while meeting specialized requirements such as multicast
   support, very low overhead and simplicity for constrained
   environments.

Status of this Memo

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   This Internet-Draft will expire on September 13, 2012.

Copyright Notice

Shelby, et al.         Expires September 13, 2012               [Page 1]
Internet-Draft   Constrained Application Protocol (CoAP)      March 2012

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.1.  Features . . . . . . . . . . . . . . . . . . . . . . . . .  5
     1.2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . .  6
   2.  Constrained Application Protocol . . . . . . . . . . . . . . .  8
     2.1.  Messaging Model  . . . . . . . . . . . . . . . . . . . . .  8
     2.2.  Request/Response Model . . . . . . . . . . . . . . . . . . 10
     2.3.  Intermediaries and Caching . . . . . . . . . . . . . . . . 12
     2.4.  Resource Discovery . . . . . . . . . . . . . . . . . . . . 12
   3.  Message Syntax . . . . . . . . . . . . . . . . . . . . . . . . 12
     3.1.  Message Format . . . . . . . . . . . . . . . . . . . . . . 13
       3.1.1.   Message Size Implementation Considerations  . . . . . 14
     3.2.  Option Format  . . . . . . . . . . . . . . . . . . . . . . 15
   4.  Message Semantics  . . . . . . . . . . . . . . . . . . . . . . 16
     4.1.  Reliable Messages  . . . . . . . . . . . . . . . . . . . . 17
     4.2.  Unreliable Messages  . . . . . . . . . . . . . . . . . . . 19
     4.3.  Message Matching Rules . . . . . . . . . . . . . . . . . . 19
     4.4.  Message Types  . . . . . . . . . . . . . . . . . . . . . . 19
       4.4.1.   Confirmable (CON) . . . . . . . . . . . . . . . . . . 20
       4.4.2.   Non-Confirmable (NON) . . . . . . . . . . . . . . . . 20
       4.4.3.   Acknowledgement (ACK) . . . . . . . . . . . . . . . . 20
       4.4.4.   Reset (RST) . . . . . . . . . . . . . . . . . . . . . 20
     4.5.  Multicast  . . . . . . . . . . . . . . . . . . . . . . . . 21
     4.6.  Congestion Control . . . . . . . . . . . . . . . . . . . . 22
   5.  Request/Response Semantics . . . . . . . . . . . . . . . . . . 22