The Constrained Application Protocol (CoAP)
RFC 7252
| Document | Type |
RFC - Proposed Standard
(June 2014; Errata)
Was draft-ietf-core-coap (core WG)
|
|
|---|---|---|---|
| Last updated | 2018-12-20 | ||
| Replaces | draft-shelby-core-coap | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Reviews | |||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Andrew McGregor | ||
| Shepherd write-up | Show (last changed 2013-03-13) | ||
| IESG | IESG state | RFC 7252 (Proposed Standard) | |
| Consensus Boilerplate | Yes | ||
| Telechat date | |||
| Responsible AD | Barry Leiba | ||
| Send notices to | (None) | ||
| IANA | IANA review state | IANA OK - Actions Needed | |
| IANA action state | RFC-Ed-Ack | ||
Internet Engineering Task Force (IETF) Z. Shelby
Request for Comments: 7252 ARM
Category: Standards Track K. Hartke
ISSN: 2070-1721 C. Bormann
Universitaet Bremen TZI
June 2014
The Constrained Application Protocol (CoAP)
Abstract
The Constrained Application Protocol (CoAP) is a specialized web
transfer protocol for use with constrained nodes and constrained
(e.g., low-power, lossy) networks. The nodes often have 8-bit
microcontrollers with small amounts of ROM and RAM, while constrained
networks such as IPv6 over Low-Power Wireless Personal Area Networks
(6LoWPANs) often have high packet error rates and a typical
throughput of 10s of kbit/s. The protocol is designed for machine-
to-machine (M2M) applications such as smart energy and building
automation.
CoAP provides a request/response interaction model between
application endpoints, supports built-in discovery of services and
resources, and includes key concepts of the Web such as URIs and
Internet media types. CoAP is designed to easily interface with 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
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/rfc7252.
Shelby, et al. Standards Track [Page 1]
RFC 7252 The Constrained Application Protocol (CoAP) June 2014
Copyright Notice
Copyright (c) 2014 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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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
1.1. Features . . . . . . . . . . . . . . . . . . . . . . . . 5
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
2. Constrained Application Protocol . . . . . . . . . . . . . . 10
2.1. Messaging Model . . . . . . . . . . . . . . . . . . . . . 11
2.2. Request/Response Model . . . . . . . . . . . . . . . . . 12
2.3. Intermediaries and Caching . . . . . . . . . . . . . . . 15
2.4. Resource Discovery . . . . . . . . . . . . . . . . . . . 15
3. Message Format . . . . . . . . . . . . . . . . . . . . . . . 15
3.1. Option Format . . . . . . . . . . . . . . . . . . . . . . 17
3.2. Option Value Formats . . . . . . . . . . . . . . . . . . 19
4. Message Transmission . . . . . . . . . . . . . . . . . . . . 20
4.1. Messages and Endpoints . . . . . . . . . . . . . . . . . 20
4.2. Messages Transmitted Reliably . . . . . . . . . . . . . . 21
4.3. Messages Transmitted without Reliability . . . . . . . . 23
4.4. Message Correlation . . . . . . . . . . . . . . . . . . . 24
4.5. Message Deduplication . . . . . . . . . . . . . . . . . . 24
4.6. Message Size . . . . . . . . . . . . . . . . . . . . . . 25
4.7. Congestion Control . . . . . . . . . . . . . . . . . . . 26
4.8. Transmission Parameters . . . . . . . . . . . . . . . . . 27
4.8.1. Changing the Parameters . . . . . . . . . . . . . . . 27
4.8.2. Time Values Derived from Transmission Parameters . . 28
5. Request/Response Semantics . . . . . . . . . . . . . . . . . 31
5.1. Requests . . . . . . . . . . . . . . . . . . . . . . . . 31
5.2. Responses . . . . . . . . . . . . . . . . . . . . . . . . 31
5.2.1. Piggybacked . . . . . . . . . . . . . . . . . . . . . 33
5.2.2. Separate . . . . . . . . . . . . . . . . . . . . . . 33
5.2.3. Non-confirmable . . . . . . . . . . . . . . . . . . . 34
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