< draft-ietf-core-coap-tcp-tls-06.txt   draft-ietf-core-coap-tcp-tls-07.txt >
CORE C. Bormann CORE C. Bormann
Internet-Draft Universitaet Bremen TZI Internet-Draft Universitaet Bremen TZI
Updates: 7641 (if approved) S. Lemay Updates: 7641 (if approved) S. Lemay
Intended status: Standards Track Zebra Technologies Intended status: Standards Track Zebra Technologies
Expires: August 18, 2017 H. Tschofenig Expires: September 7, 2017 H. Tschofenig
ARM Ltd. ARM Ltd.
K. Hartke K. Hartke
Universitaet Bremen TZI Universitaet Bremen TZI
B. Silverajan B. Silverajan
Tampere University of Technology Tampere University of Technology
B. Raymor, Ed. B. Raymor, Ed.
Microsoft Microsoft
February 14, 2017 March 06, 2017
CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets CoAP (Constrained Application Protocol) over TCP, TLS, and WebSockets
draft-ietf-core-coap-tcp-tls-06 draft-ietf-core-coap-tcp-tls-07
Abstract Abstract
The Constrained Application Protocol (CoAP), although inspired by The Constrained Application Protocol (CoAP), although inspired by
HTTP, was designed to use UDP instead of TCP. The message layer of HTTP, was designed to use UDP instead of TCP. The message layer of
the CoAP over UDP protocol includes support for reliable delivery, the CoAP over UDP protocol includes support for reliable delivery,
simple congestion control, and flow control. simple congestion control, and flow control.
Some environments benefit from the availability of CoAP carried over Some environments benefit from the availability of CoAP carried over
reliable transports such as TCP or TLS. This document outlines the reliable transports such as TCP or TLS. This document outlines the
skipping to change at page 1, line 48 skipping to change at page 1, line 48
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 18, 2017. This Internet-Draft will expire on September 7, 2017.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Conventions and Terminology . . . . . . . . . . . . . . . 5 2. Conventions and Terminology . . . . . . . . . . . . . . . . . 5
2. CoAP over TCP . . . . . . . . . . . . . . . . . . . . . . . . 6 3. CoAP over TCP . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Messaging Model . . . . . . . . . . . . . . . . . . . . . 6 3.1. Messaging Model . . . . . . . . . . . . . . . . . . . . . 6
2.2. Message Format . . . . . . . . . . . . . . . . . . . . . 7 3.2. Message Format . . . . . . . . . . . . . . . . . . . . . 7
2.3. Message Transmission . . . . . . . . . . . . . . . . . . 10 3.3. Message Transmission . . . . . . . . . . . . . . . . . . 10
2.4. Connection Health . . . . . . . . . . . . . . . . . . . . 11 3.4. Connection Health . . . . . . . . . . . . . . . . . . . . 11
3. CoAP over WebSockets . . . . . . . . . . . . . . . . . . . . 11 4. CoAP over WebSockets . . . . . . . . . . . . . . . . . . . . 11
3.1. Opening Handshake . . . . . . . . . . . . . . . . . . . . 13 4.1. Opening Handshake . . . . . . . . . . . . . . . . . . . . 13
3.2. Message Format . . . . . . . . . . . . . . . . . . . . . 14 4.2. Message Format . . . . . . . . . . . . . . . . . . . . . 14
3.3. Message Transmission . . . . . . . . . . . . . . . . . . 15 4.3. Message Transmission . . . . . . . . . . . . . . . . . . 15
3.4. Connection Health . . . . . . . . . . . . . . . . . . . . 15 4.4. Connection Health . . . . . . . . . . . . . . . . . . . . 15
4. Signaling . . . . . . . . . . . . . . . . . . . . . . . . . . 15 5. Signaling . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.1. Signaling Codes . . . . . . . . . . . . . . . . . . . . . 16 5.1. Signaling Codes . . . . . . . . . . . . . . . . . . . . . 16
4.2. Signaling Option Numbers . . . . . . . . . . . . . . . . 16 5.2. Signaling Option Numbers . . . . . . . . . . . . . . . . 16
4.3. Capabilities and Settings Messages (CSM) . . . . . . . . 16 5.3. Capabilities and Settings Messages (CSM) . . . . . . . . 16
4.4. Ping and Pong Messages . . . . . . . . . . . . . . . . . 18 5.4. Ping and Pong Messages . . . . . . . . . . . . . . . . . 18
4.5. Release Messages . . . . . . . . . . . . . . . . . . . . 19 5.5. Release Messages . . . . . . . . . . . . . . . . . . . . 19
4.6. Abort Messages . . . . . . . . . . . . . . . . . . . . . 20 5.6. Abort Messages . . . . . . . . . . . . . . . . . . . . . 20
4.7. Signaling examples . . . . . . . . . . . . . . . . . . . 21 5.7. Signaling examples . . . . . . . . . . . . . . . . . . . 21
5. Block-wise Transfer and Reliable Transports . . . . . . . . . 22 6. Block-wise Transfer and Reliable Transports . . . . . . . . . 22
5.1. Example: GET with BERT Blocks . . . . . . . . . . . . . . 23 6.1. Example: GET with BERT Blocks . . . . . . . . . . . . . . 23
5.2. Example: PUT with BERT Blocks . . . . . . . . . . . . . . 24 6.2. Example: PUT with BERT Blocks . . . . . . . . . . . . . . 24
6. CoAP over Reliable Transport URIs . . . . . . . . . . . . . . 24 7. CoAP over Reliable Transport URIs . . . . . . . . . . . . . . 24
6.1. coap+tcp URI scheme . . . . . . . . . . . . . . . . . . . 25 7.1. coap+tcp URI scheme . . . . . . . . . . . . . . . . . . . 25
6.2. coaps+tcp URI scheme . . . . . . . . . . . . . . . . . . 25 7.2. coaps+tcp URI scheme . . . . . . . . . . . . . . . . . . 25
6.3. coap+ws URI scheme . . . . . . . . . . . . . . . . . . . 26 7.3. coap+ws URI scheme . . . . . . . . . . . . . . . . . . . 26
6.4. coaps+ws URI scheme . . . . . . . . . . . . . . . . . . . 27 7.4. coaps+ws URI scheme . . . . . . . . . . . . . . . . . . . 27
6.5. Uri-Host and Uri-Port Options . . . . . . . . . . . . . . 28 7.5. Uri-Host and Uri-Port Options . . . . . . . . . . . . . . 28
6.6. Decomposing URIs into Options . . . . . . . . . . . . . . 28 7.6. Decomposing URIs into Options . . . . . . . . . . . . . . 28
6.7. Composing URIs from Options . . . . . . . . . . . . . . . 29 7.7. Composing URIs from Options . . . . . . . . . . . . . . . 29
7. Securing CoAP . . . . . . . . . . . . . . . . . . . . . . . . 29 8. Securing CoAP . . . . . . . . . . . . . . . . . . . . . . . . 29
7.1. TLS binding for CoAP over TCP . . . . . . . . . . . . . . 29 8.1. TLS binding for CoAP over TCP . . . . . . . . . . . . . . 30
7.2. TLS usage for CoAP over WebSockets . . . . . . . . . . . 30 8.2. TLS usage for CoAP over WebSockets . . . . . . . . . . . 30
8. Security Considerations . . . . . . . . . . . . . . . . . . . 30 9. Security Considerations . . . . . . . . . . . . . . . . . . . 31
8.1. Signaling Messages . . . . . . . . . . . . . . . . . . . 31 9.1. Signaling Messages . . . . . . . . . . . . . . . . . . . 31
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
9.1. Signaling Codes . . . . . . . . . . . . . . . . . . . . . 31 10.1. Signaling Codes . . . . . . . . . . . . . . . . . . . . 31
9.2. CoAP Signaling Option Numbers Registry . . . . . . . . . 31 10.2. CoAP Signaling Option Numbers Registry . . . . . . . . . 32
9.3. Service Name and Port Number Registration . . . . . . . . 32 10.3. Service Name and Port Number Registration . . . . . . . 33
9.4. Secure Service Name and Port Number Registration . . . . 33 10.4. Secure Service Name and Port Number Registration . . . . 34
9.5. URI Scheme Registration . . . . . . . . . . . . . . . . . 34 10.5. URI Scheme Registration . . . . . . . . . . . . . . . . 34
9.6. Well-Known URI Suffix Registration . . . . . . . . . . . 36 10.6. Well-Known URI Suffix Registration . . . . . . . . . . . 37
9.7. ALPN Protocol Identifier . . . . . . . . . . . . . . . . 36 10.7. ALPN Protocol Identifier . . . . . . . . . . . . . . . . 37
9.8. WebSocket Subprotocol Registration . . . . . . . . . . . 36 10.8. WebSocket Subprotocol Registration . . . . . . . . . . . 37
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 37 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
10.1. Normative References . . . . . . . . . . . . . . . . . . 37 11.1. Normative References . . . . . . . . . . . . . . . . . . 38
10.2. Informative References . . . . . . . . . . . . . . . . . 38 11.2. Informative References . . . . . . . . . . . . . . . . . 39
Appendix A. Updates to RFC7641 Observing Resources in the Appendix A. Updates to RFC 7641 Observing Resources in the
Constrained Application Protocol (CoAP) . . . . . . 40 Constrained Application Protocol (CoAP) . . . . . . 40
A.1. Notifications and Reordering . . . . . . . . . . . . . . 40 A.1. Notifications and Reordering . . . . . . . . . . . . . . 40
A.2. Transmission and Acknowledgements . . . . . . . . . . . . 40 A.2. Transmission and Acknowledgements . . . . . . . . . . . . 41
A.3. Freshness . . . . . . . . . . . . . . . . . . . . . . . . 40 A.3. Freshness . . . . . . . . . . . . . . . . . . . . . . . . 41
A.4. Cancellation . . . . . . . . . . . . . . . . . . . . . . 41 A.4. Cancellation . . . . . . . . . . . . . . . . . . . . . . 41
Appendix B. CoAP over WebSocket Examples . . . . . . . . . . . . 41 Appendix B. CoAP over WebSocket Examples . . . . . . . . . . . . 42
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 44 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 45
C.1. Since draft-core-coap-tcp-tls-02 . . . . . . . . . . . . 44 C.1. Since draft-ietf-core-coap-tcp-tls-02 . . . . . . . . . . 45
C.2. Since draft-core-coap-tcp-tls-03 . . . . . . . . . . . . 44 C.2. Since draft-ietf-core-coap-tcp-tls-03 . . . . . . . . . . 45
C.3. Since draft-core-coap-tcp-tls-04 . . . . . . . . . . . . 44 C.3. Since draft-ietf-core-coap-tcp-tls-04 . . . . . . . . . . 45
C.4. Since draft-core-coap-tcp-tls-05 . . . . . . . . . . . . 44 C.4. Since draft-ietf-core-coap-tcp-tls-05 . . . . . . . . . . 45
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 45 C.5. Since draft-ietf-core-coap-tcp-tls-06 . . . . . . . . . . 46
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 45 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 45 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46
1. Introduction 1. Introduction
The Constrained Application Protocol (CoAP) [RFC7252] was designed The Constrained Application Protocol (CoAP) [RFC7252] was designed
for Internet of Things (IoT) deployments, assuming that UDP [RFC0768] for Internet of Things (IoT) deployments, assuming that UDP [RFC0768]
or DTLS [RFC6347] over UDP can be used unimpeded. UDP is a good or DTLS [RFC6347] over UDP can be used unimpeded. UDP is a good
choice for transferring small amounts of data across networks that choice for transferring small amounts of data across networks that
follow the IP architecture. follow the IP architecture.
Some CoAP deployments need to integrate well with existing enterprise Some CoAP deployments need to integrate well with existing enterprise
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then CoAP over TCP between the back-end services. A TCP-to-UDP then CoAP over TCP between the back-end services. A TCP-to-UDP
gateway can be used at the cloud boundary to communicate with the gateway can be used at the cloud boundary to communicate with the
UDP-based IoT device. UDP-based IoT device.
To allow IoT devices to better communicate in these demanding To allow IoT devices to better communicate in these demanding
environments, CoAP needs to support different transport protocols, environments, CoAP needs to support different transport protocols,
namely TCP [RFC0793], in some situations secured by TLS [RFC5246]. namely TCP [RFC0793], in some situations secured by TLS [RFC5246].
In addition, some corporate networks only allow Internet access via a In addition, some corporate networks only allow Internet access via a
HTTP proxy. In this case, the best transport for CoAP might be the HTTP proxy. In this case, the best transport for CoAP might be the
WebSocket Protocol [RFC6455]. The WebSocket protocol provides two- WebSocket protocol [RFC6455]. The WebSocket protocol provides two-
way communication between a WebSocket client and a WebSocket server way communication between a WebSocket client and a WebSocket server
after upgrading an HTTP/1.1 [RFC7230] connection and may be available after upgrading an HTTP/1.1 [RFC7230] connection and may be available
in an environment that blocks CoAP over UDP. Another scenario for in an environment that blocks CoAP over UDP. Another scenario for
CoAP over WebSockets is a CoAP application running inside a web CoAP over WebSockets is a CoAP application running inside a web
browser without access to connectivity other than HTTP and browser without access to connectivity other than HTTP and
WebSockets. WebSockets.
This document specifies how to access resources using CoAP requests This document specifies how to access resources using CoAP requests
and responses over the TCP/TLS and WebSocket protocols. This allows and responses over the TCP, TLS and WebSocket protocols. This allows
connectivity-limited applications to obtain end-to-end CoAP connectivity-limited applications to obtain end-to-end CoAP
connectivity either by communicating CoAP directly with a CoAP server connectivity either by communicating CoAP directly with a CoAP server
accessible over a TCP/TLS or WebSocket connection or via a CoAP accessible over a TCP, TLS or WebSocket connection or via a CoAP
intermediary that proxies CoAP requests and responses between intermediary that proxies CoAP requests and responses between
different transports, such as between WebSockets and UDP. different transports, such as between WebSockets and UDP.
Appendix A updates Observing Resources in the Constrained Application Appendix A updates the "Observing Resources in the Constrained
Protocol [RFC7641] for use with CoAP over reliable transports. Application Protocol" [RFC7641] specification for use with CoAP over
[RFC7641] is an extension to the CoAP core protocol that enables CoAP reliable transports. [RFC7641] is an extension to the CoAP protocol
clients to "observe" a resource on a CoAP server. (The CoAP client that enables CoAP clients to "observe" a resource on a CoAP server.
retrieves a representation of a resource and registers to be notified (The CoAP client retrieves a representation of a resource and
by the CoAP server when the representation is updated.) registers to be notified by the CoAP server when the representation
is updated.)
1.1. Conventions and Terminology 2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
[RFC2119]. [RFC2119].
This document assumes that readers are familiar with the terms and This document assumes that readers are familiar with the terms and
concepts that are used in [RFC6455], [RFC7252], [RFC7641], and concepts that are used in [RFC6455], [RFC7252], [RFC7641], and
[RFC7959]. [RFC7959].
The term "reliable transport" is used only to refer to transport The term "reliable transport" is used only to refer to transport
protocols such as TCP which provide reliable and ordered delivery of protocols, such as TCP, which provide reliable and ordered delivery
a byte-stream. of a byte-stream.
BERT Option: BERT Option:
A Block1 or Block2 option that includes an SZX value of 7. A Block1 or Block2 option that includes an SZX value of 7.
BERT Block: BERT Block:
The payload of a CoAP message that is affected by a BERT Option in The payload of a CoAP message that is affected by a BERT Option in
descriptive usage (Section 2.1 of [RFC7959]). descriptive usage (see Section 2.1 of [RFC7959]).
Connection Initiator: Connection Initiator:
The peer that opens a reliable byte stream connection, i.e., the The peer that opens a reliable byte stream connection, i.e., the
TCP active opener, TLS client, or WebSocket client. TCP active opener, TLS client, or WebSocket client.
Connection Acceptor: Connection Acceptor:
The peer that accepts the reliable byte stream connection opened The peer that accepts the reliable byte stream connection opened
by the other peer, i.e., the TCP passive opener, TLS server, or by the other peer, i.e., the TCP passive opener, TLS server, or
WebSocket server. WebSocket server.
For simplicity, a Payload Marker (0xFF) is shown in all examples for For simplicity, a Payload Marker (0xFF) is shown in all examples for
message formats: message formats:
... ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 1 1 1 1 1| Payload (if any) ... |1 1 1 1 1 1 1 1| Payload (if any) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Payload Marker indicates the start of the optional payload and is The Payload Marker indicates the start of the optional payload and is
absent for zero-length payloads (see section 3 of [RFC7252]). absent for zero-length payloads (see Section 3 of [RFC7252]).
2. CoAP over TCP 3. CoAP over TCP
The request/response interaction model of CoAP over TCP is the same The request/response interaction model of CoAP over TCP is the same
as CoAP over UDP. The primary differences are in the message layer. as CoAP over UDP. The primary differences are in the message layer.
The message layer of CoAP over UDP supports optional reliability by The message layer of CoAP over UDP supports optional reliability by
defining four Types of messages: Confirmable, Non-confirmable, defining four types of messages: Confirmable, Non-confirmable,
Acknowledgement, and Reset. In addition, messages include a Message Acknowledgement, and Reset. In addition, messages include a Message
ID to relate Acknowledgments to Confirmable messages and to detect ID to relate Acknowledgments to Confirmable messages and to detect
duplicate messages. duplicate messages.
2.1. Messaging Model 3.1. Messaging Model
Conceptually, CoAP over TCP replaces most of the message layer of Conceptually, CoAP over TCP replaces most of the message layer of
CoAP over UDP with a framing mechanism on top of the byte-stream CoAP over UDP with a framing mechanism on top of the byte-stream
provided by TCP/TLS, conveying the length information for each provided by TCP/TLS, conveying the length information for each
message that on datagram transports is provided by the UDP/DTLS message that on datagram transports is provided by the UDP/DTLS
datagram layer. datagram layer.
TCP ensures reliable message transmission, so the message layer of TCP ensures reliable message transmission, so the message layer of
CoAP over TCP is not required to support acknowledgements or to CoAP over TCP is not required to support acknowledgements or to
detect duplicate messages. As a result, both the Type and Message ID detect duplicate messages. As a result, both the Type and Message ID
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| "22.5 C" | | "22.5 C" | | "22.5 C" | | "22.5 C" |
|<-------------------+ |<-------------------+ |<-------------------+ |<-------------------+
| | | | | | | |
CoAP over UDP CoAP over reliable CoAP over UDP CoAP over reliable
transport transport
Figure 2: Comparison between CoAP over unreliable and reliable Figure 2: Comparison between CoAP over unreliable and reliable
transport transport
2.2. Message Format 3.2. Message Format
The CoAP message format defined in [RFC7252], as shown in Figure 3, The CoAP message format defined in [RFC7252], as shown in Figure 3,
relies on the datagram transport (UDP, or DTLS over UDP) for keeping relies on the datagram transport (UDP, or DTLS over UDP) for keeping
the individual messages separate and for providing length the individual messages separate and for providing length
information. information.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver| T | TKL | Code | Message ID | |Ver| T | TKL | Code | Message ID |
skipping to change at page 8, line 16 skipping to change at page 8, line 16
deduplication, there is no need for the reliability mechanisms deduplication, there is no need for the reliability mechanisms
provided by CoAP over UDP. The Type (T) and Message ID fields in provided by CoAP over UDP. The Type (T) and Message ID fields in
the CoAP message header are elided. the CoAP message header are elided.
o The Version (Vers) field is elided as well. In contrast to the o The Version (Vers) field is elided as well. In contrast to the
message format of CoAP over UDP, the message format for CoAP over message format of CoAP over UDP, the message format for CoAP over
TCP does not include a version number. CoAP is defined in TCP does not include a version number. CoAP is defined in
[RFC7252] with a version number of 1. At this time, there is no [RFC7252] with a version number of 1. At this time, there is no
known reason to support version numbers different from 1. If known reason to support version numbers different from 1. If
version negotiation needs to be addressed in the future, then version negotiation needs to be addressed in the future, then
Capabilities and Settings Messages (CSM see Section 4.3) have been Capabilities and Settings Messages (CSM see Section 5.3) have been
specifically designed to enable such a potential feature. specifically designed to enable such a potential feature.
o In a stream oriented transport protocol such as TCP, a form of o In a stream oriented transport protocol such as TCP, a form of
message delimitation is needed. For this purpose, CoAP over TCP message delimitation is needed. For this purpose, CoAP over TCP
introduces a length field with variable size. Figure 4 shows the introduces a length field with variable size. Figure 4 shows the
adjusted CoAP message format with a modified structure for the adjusted CoAP message format with a modified structure for the
fixed header (first 4 bytes of the CoAP over UDP header), which fixed header (first 4 bytes of the CoAP over UDP header), which
includes the length information of variable size, shown here as an includes the length information of variable size, shown here as an
8-bit length. 8-bit length.
skipping to change at page 9, line 9 skipping to change at page 9, line 9
13. 13.
14: A 16-bit unsigned integer (Extended Length) in network byte 14: A 16-bit unsigned integer (Extended Length) in network byte
order follows the initial byte and indicates the length of order follows the initial byte and indicates the length of
options/payload minus 269. options/payload minus 269.
15: A 32-bit unsigned integer (Extended Length) in network byte 15: A 32-bit unsigned integer (Extended Length) in network byte
order follows the initial byte and indicates the length of order follows the initial byte and indicates the length of
options/payload minus 65805. options/payload minus 65805.
The encoding of the Length field is modeled on CoAP Options (see The encoding of the Length field is modeled after the Option Length
section 3.1 of [RFC7252]). field of the CoAP Options (see Section 3.1 of [RFC7252]).
The following figures show the message format for the 0-bit, 16-bit, The following figures show the message format for the 0-bit, 16-bit,
and the 32-bit variable length cases. and the 32-bit variable length cases.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Len | TKL | Code | Token (if any, TKL bytes) ... | Len | TKL | Code | Token (if any, TKL bytes) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options (if any) ... | Options (if any) ...
skipping to change at page 10, line 24 skipping to change at page 10, line 24
|1 1 1 1 1 1 1 1| Payload (if any) ... |1 1 1 1 1 1 1 1| Payload (if any) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: CoAP message format with 16-bit Extended Length field Figure 7: CoAP message format with 16-bit Extended Length field
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Len=15 | TKL | Extended Length (32 bits) |Len=15 | TKL | Extended Length (32 bits)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Code | Token (if any, TKL bytes) ... | Code | Token (if any, TKL bytes) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options (if any) ... | Options (if any) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1 1 1 1 1 1 1 1| Payload (if any) ... |1 1 1 1 1 1 1 1| Payload (if any) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: CoAP message format with 32-bit Extended Length field Figure 8: CoAP message format with 32-bit Extended Length field
The semantics of the other CoAP header fields are left unchanged. The semantics of the other CoAP header fields are left unchanged.
2.3. Message Transmission 3.3. Message Transmission
Once a connection is established, both endpoints MUST send a Once a connection is established, both endpoints MUST send a
Capabilities and Settings message (CSM see Section 4.3) as their Capabilities and Settings message (CSM see Section 5.3) as their
first message on the connection. This message establishes the first message on the connection. This message establishes the
initial settings and capabilities for the endpoint such as maximum initial settings and capabilities for the endpoint, such as maximum
message size or support for block-wise transfers. The absence of message size or support for block-wise transfers. The absence of
options in the CSM indicates that base values are assumed. options in the CSM indicates that base values are assumed.
To avoid a deadlock, the Connection Initiator MUST NOT wait for the To avoid a deadlock, the Connection Initiator MUST NOT wait for the
Connection Acceptor to send its initial CSM message before sending Connection Acceptor to send its initial CSM message before sending
its own initial CSM message. Conversely, the Connection Acceptor MAY its own initial CSM message. Conversely, the Connection Acceptor MAY
wait for the Connection Initiator to send its initial CSM message wait for the Connection Initiator to send its initial CSM message
before sending its own initial CSM message. before sending its own initial CSM message.
To avoid unnecessary latency, a Connection Initiator MAY send To avoid unnecessary latency, a Connection Initiator MAY send
additional messages without waiting to receive the Connection additional messages without waiting to receive the Connection
Acceptor's CSM; however, it is important to note that the Connection Acceptor's CSM; however, it is important to note that the Connection
Acceptor's CSM might advertise capabilities that impact how the Acceptor's CSM might advertise capabilities that impact how the
initiator is expected to communicate with the acceptor. For example, initiator is expected to communicate with the acceptor. For example,
the acceptor CSM could advertise a Max-Message-Size option (see the acceptor CSM could advertise a Max-Message-Size option (see
Section 4.3.1) that is smaller than the base value (1152). Section 5.3.1) that is smaller than the base value (1152).
Endpoints MUST treat a missing or invalid CSM as a connection error Endpoints MUST treat a missing or invalid CSM as a connection error
and abort the connection (see Section 4.6). and abort the connection (see Section 5.6).
CoAP requests and responses are exchanged asynchronously over the CoAP requests and responses are exchanged asynchronously over the
TCP/TLS connection. A CoAP client can send multiple requests without TCP/TLS connection. A CoAP client can send multiple requests without
waiting for a response and the CoAP server can return responses in waiting for a response and the CoAP server can return responses in
any order. Responses MUST be returned over the same connection as any order. Responses MUST be returned over the same connection as
the originating request. Concurrent requests are differentiated by the originating request. Concurrent requests are differentiated by
their Token, which is scoped locally to the connection. their Token, which is scoped locally to the connection.
The connection is bi-directional, so requests can be sent both by the The connection is bi-directional, so requests can be sent both by the
entity that established the connection and the remote host. entity that established the connection (Connection Initiator) and the
remote host (Connection Acceptor). If one side does not implement a
CoAP server, an appropriate error response such as 4.04 (Not Found)
or 5.01 (Not Implemented) MUST be returned for all CoAP requests from
the other side.
Retransmission and deduplication of messages is provided by the TCP/ Retransmission and deduplication of messages is provided by the TCP
TLS protocol. protocol.
2.4. Connection Health 3.4. Connection Health
Empty messages (Code 0.00) can always be sent and MUST be ignored by Empty messages (Code 0.00) can always be sent and MUST be ignored by
the recipient. This provides a basic keep-alive function that can the recipient. This provides a basic keep-alive function that can
refresh NAT bindings. refresh NAT bindings.
If a CoAP client does not receive any response for some time after If a CoAP client does not receive any response for some time after
sending a CoAP request (or, similarly, when a client observes a sending a CoAP request (or, similarly, when a client observes a
resource and it does not receive any notification for some time), it resource and it does not receive any notification for some time), it
can send a CoAP Ping Signaling message (Section 4.4) to test the can send a CoAP Ping Signaling message (see Section 5.4) to test the
connection and verify that the CoAP server is responsive. connection and verify that the CoAP server is responsive.
3. CoAP over WebSockets 4. CoAP over WebSockets
CoAP over WebSockets is intentionally similar to CoAP over TCP; CoAP over WebSockets is intentionally similar to CoAP over TCP;
therefore, this section only specifies the differences between the therefore, this section only specifies the differences between the
transports. transports.
CoAP over WebSockets can be used in a number of configurations. The CoAP over WebSockets can be used in a number of configurations. The
most basic configuration is a CoAP client retrieving or updating a most basic configuration is a CoAP client retrieving or updating a
CoAP resource located on a CoAP server that exposes a WebSocket CoAP resource located on a CoAP server that exposes a WebSocket
endpoint (Figure 9). The CoAP client acts as the WebSocket client, endpoint (see Figure 9). The CoAP client acts as the WebSocket
establishes a WebSocket connection, and sends a CoAP request, to client, establishes a WebSocket connection, and sends a CoAP request,
which the CoAP server returns a CoAP response. The WebSocket to which the CoAP server returns a CoAP response. The WebSocket
connection can be used for any number of requests. connection can be used for any number of requests.
___________ ___________ ___________ ___________
| | | | | | | |
| _|___ requests ___|_ | | _|___ requests ___|_ |
| CoAP / \ \ -------------> / / \ CoAP | | CoAP / \ \ -------------> / / \ CoAP |
| Client \__/__/ <------------- \__\__/ Server | | Client \__/__/ <------------- \__\__/ Server |
| | responses | | | | responses | |
|___________| |___________| |___________| |___________|
WebSocket =============> WebSocket WebSocket =============> WebSocket
Client Connection Server Client Connection Server
Figure 9: CoAP Client (WebSocket client) accesses CoAP Server Figure 9: CoAP Client (WebSocket client) accesses CoAP Server
(WebSocket server) (WebSocket server)
The challenge with this configuration is how to identify a resource The challenge with this configuration is how to identify a resource
in the namespace of the CoAP server. When the WebSocket protocol is in the namespace of the CoAP server. When the WebSocket protocol is
used by a dedicated client directly (i.e., not from a web page used by a dedicated client directly (i.e., not from a web page
through a web browser), the client can connect to any WebSocket through a web browser), the client can connect to any WebSocket
endpoint. Section 6.3 and Section 6.4 define new URI schemes that endpoint. Section 7.3 and Section 7.4 define new URI schemes that
enable the client to identify both a WebSocket endpoint and the path enable the client to identify both a WebSocket endpoint and the path
and query of the CoAP resource within that endpoint. When the and query of the CoAP resource within that endpoint.
WebSocket protocol is used from a web page, the choices are more
limited [RFC6454], but the challenge persists.
Another possible configuration is to set up a CoAP forward proxy at Another possible configuration is to set up a CoAP forward proxy at
the WebSocket endpoint. Depending on what transports are available the WebSocket endpoint. Depending on what transports are available
to the proxy, it could forward the request to a CoAP server with a to the proxy, it could forward the request to a CoAP server with a
CoAP UDP endpoint (Figure 10), an SMS endpoint (a.k.a. mobile phone), CoAP UDP endpoint (Figure 10), an SMS endpoint (a.k.a. mobile phone),
or even another WebSocket endpoint. The CoAP client specifies the or even another WebSocket endpoint. The CoAP client specifies the
resource to be updated or retrieved in the Proxy-Uri Option. resource to be updated or retrieved in the Proxy-Uri Option.
___________ ___________ ___________ ___________ ___________ ___________
| | | | | | | | | | | |
skipping to change at page 13, line 6 skipping to change at page 13, line 6
Figure 10: CoAP Client (WebSocket client) accesses CoAP Server (UDP Figure 10: CoAP Client (WebSocket client) accesses CoAP Server (UDP
server) via a CoAP proxy (WebSocket server/UDP client) server) via a CoAP proxy (WebSocket server/UDP client)
A third possible configuration is a CoAP server running inside a web A third possible configuration is a CoAP server running inside a web
browser (Figure 11). The web browser initially connects to a browser (Figure 11). The web browser initially connects to a
WebSocket endpoint and is then reachable through the WebSocket WebSocket endpoint and is then reachable through the WebSocket
server. When no connection exists, the CoAP server is unreachable. server. When no connection exists, the CoAP server is unreachable.
Because the WebSocket server is the only way to reach the CoAP Because the WebSocket server is the only way to reach the CoAP
server, the CoAP proxy should be a Reverse Proxy. server, the CoAP proxy should be a reverse-proxy.
___________ ___________ ___________ ___________ ___________ ___________
| | | | | | | | | | | |
| _|___ ___|_ _|___ ___|_ | | _|___ ___|_ _|___ ___|_ |
| CoAP / \ \ ---> / / \ CoAP / / \ ---> / \ \ CoAP | | CoAP / \ \ ---> / / \ CoAP / / \ ---> / \ \ CoAP |
| Client \__/__/ <--- \__\__/ Proxy \__\__/ <--- \__/__/ Server | | Client \__/__/ <--- \__\__/ Proxy \__\__/ <--- \__/__/ Server |
| | | | | | | | | | | |
|___________| |___________| |___________| |___________| |___________| |___________|
UDP UDP WebSocket <=== WebSocket UDP UDP WebSocket <=== WebSocket
Client Server Server Client Client Server Server Client
Figure 11: CoAP Client (UDP client) accesses CoAP Server (WebSocket Figure 11: CoAP Client (UDP client) accesses CoAP Server (WebSocket
client) via a CoAP proxy (UDP server/WebSocket server) client) via a CoAP proxy (UDP server/WebSocket server)
Further configurations are possible, including those where a Further configurations are possible, including those where a
WebSocket connection is established through an HTTP proxy. WebSocket connection is established through an HTTP proxy.
3.1. Opening Handshake 4.1. Opening Handshake
Before CoAP requests and responses are exchanged, a WebSocket Before CoAP requests and responses are exchanged, a WebSocket
connection is established as defined in Section 4 of [RFC6455]. connection is established as defined in Section 4 of [RFC6455].
Figure 12 shows an example. Figure 12 shows an example.
The WebSocket client MUST include the subprotocol name "coap" in the The WebSocket client MUST include the subprotocol name "coap" in the
list of protocols, which indicates support for the protocol defined list of protocols, which indicates support for the protocol defined
in this document. Any later, incompatible versions of CoAP or CoAP in this document. Any later, incompatible versions of CoAP or CoAP
over WebSockets will use a different subprotocol name. over WebSockets will use a different subprotocol name.
skipping to change at page 14, line 21 skipping to change at page 14, line 21
Sec-WebSocket-Version: 13 Sec-WebSocket-Version: 13
HTTP/1.1 101 Switching Protocols HTTP/1.1 101 Switching Protocols
Upgrade: websocket Upgrade: websocket
Connection: Upgrade Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo= Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
Sec-WebSocket-Protocol: coap Sec-WebSocket-Protocol: coap
Figure 12: Example of an Opening Handshake Figure 12: Example of an Opening Handshake
3.2. Message Format 4.2. Message Format
Once a WebSocket connection is established, CoAP requests and Once a WebSocket connection is established, CoAP requests and
responses can be exchanged as WebSocket messages. Since CoAP uses a responses can be exchanged as WebSocket messages. Since CoAP uses a
binary message format, the messages are transmitted in binary data binary message format, the messages are transmitted in binary data
frames as specified in Sections 5 and 6 of [RFC6455]. frames as specified in Sections 5 and 6 of [RFC6455].
The message format shown in Figure 13 is the same as the CoAP over The message format shown in Figure 13 is the same as the CoAP over
TCP message format (see Section 2.2) with one change. The Length TCP message format (see Section 3.2) with one change. The Length
(Len) field MUST be set to zero because the WebSockets frame contains (Len) field MUST be set to zero because the WebSockets frame contains
the length. the length.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Len=0 | TKL | Code | Token (TKL bytes) ... | Len=0 | TKL | Code | Token (TKL bytes) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options (if any) ... | Options (if any) ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 15, line 10 skipping to change at page 15, line 10
identifier that is negotiated during the opening handshake. identifier that is negotiated during the opening handshake.
Requests and response messages can be fragmented as specified in Requests and response messages can be fragmented as specified in
Section 5.4 of [RFC6455], though typically they are sent unfragmented Section 5.4 of [RFC6455], though typically they are sent unfragmented
as they tend to be small and fully buffered before transmission. The as they tend to be small and fully buffered before transmission. The
WebSocket protocol does not provide means for multiplexing. If it is WebSocket protocol does not provide means for multiplexing. If it is
not desirable for a large message to monopolize the connection, not desirable for a large message to monopolize the connection,
requests and responses can be transferred in a block-wise fashion as requests and responses can be transferred in a block-wise fashion as
defined in [RFC7959]. defined in [RFC7959].
3.3. Message Transmission 4.3. Message Transmission
As with CoAP over TCP, both endpoints MUST send a Capabilities and As with CoAP over TCP, both endpoints MUST send a Capabilities and
Settings message (CSM see Section 4.3) as their first message on the Settings message (CSM see Section 5.3) as their first message on the
WebSocket connection. WebSocket connection.
CoAP requests and responses are exchanged asynchronously over the CoAP requests and responses are exchanged asynchronously over the
WebSocket connection. A CoAP client can send multiple requests WebSocket connection. A CoAP client can send multiple requests
without waiting for a response and the CoAP server can return without waiting for a response and the CoAP server can return
responses in any order. Responses MUST be returned over the same responses in any order. Responses MUST be returned over the same
connection as the originating request. Concurrent requests are connection as the originating request. Concurrent requests are
differentiated by their Token, which is scoped locally to the differentiated by their Token, which is scoped locally to the
connection. connection.
The connection is bi-directional, so requests can be sent both by the The connection is bi-directional, so requests can be sent both by the
entity that established the connection and the remote host. entity that established the connection and the remote host.
As with CoAP over TCP, retransmission and deduplication of messages As with CoAP over TCP, retransmission and deduplication of messages
is provided by the WebSocket protocol. CoAP over WebSockets is provided by the WebSocket protocol. CoAP over WebSockets
therefore does not make a distinction between Confirmable or Non- therefore does not make a distinction between Confirmable or Non-
Confirmable messages, and does not provide Acknowledgement or Reset Confirmable messages, and does not provide Acknowledgement or Reset
messages. messages.
3.4. Connection Health 4.4. Connection Health
As with CoAP over TCP, a CoAP client can test the health of the CoAP As with CoAP over TCP, a CoAP client can test the health of the CoAP
over WebSocket connection by sending a CoAP Ping Signaling message over WebSocket connection by sending a CoAP Ping Signaling message
(Section 4.4). WebSocket Ping and unsolicited Pong frames (Section 5.4). WebSocket Ping and unsolicited Pong frames
(Section 5.5 of [RFC6455]) SHOULD NOT be used to ensure that (Section 5.5 of [RFC6455]) SHOULD NOT be used to ensure that
redundant maintenance traffic is not transmitted. redundant maintenance traffic is not transmitted.
4. Signaling 5. Signaling
Signaling messages are introduced to allow peers to: Signaling messages are introduced to allow peers to:
o Related characteristics such as maximum message size for the o Learn related characteristics, such as maximum message size for
connection the connection
o Shut down the connection in an orderly fashion o Shut down the connection in an orderly fashion
o Provide diagnostic information when terminating a connection in o Provide diagnostic information when terminating a connection in
response to a serious error condition response to a serious error condition
Signaling is a third basic kind of message in CoAP, after requests Signaling is a third basic kind of message in CoAP, after requests
and responses. Signaling messages share a common structure with the and responses. Signaling messages share a common structure with the
existing CoAP messages. There is a code, a token, options, and an existing CoAP messages. There is a code, a token, options, and an
optional payload. optional payload.
(See Section 3 of [RFC7252] for the overall structure, as adapted to (See Section 3 of [RFC7252] for the overall structure of the message
the specific transport.) format, option format, and option value format.)
4.1. Signaling Codes 5.1. Signaling Codes
A code in the 7.00-7.31 range indicates a Signaling message. Values A code in the 7.00-7.31 range indicates a Signaling message. Values
in this range are assigned by the "CoAP Signaling Codes" sub-registry in this range are assigned by the "CoAP Signaling Codes" sub-registry
(see Section 9.1). (see Section 10.1).
For each message, there is a sender and a peer receiving the message. For each message, there is a sender and a peer receiving the message.
Payloads in Signaling messages are diagnostic payloads as defined in Payloads in Signaling messages are diagnostic payloads as defined in
Section 5.5.2 of [RFC7252]), unless otherwise defined by a Signaling Section 5.5.2 of [RFC7252]), unless otherwise defined by a Signaling
message option. message option.
4.2. Signaling Option Numbers 5.2. Signaling Option Numbers
Option numbers for Signaling messages are specific to the message Option numbers for Signaling messages are specific to the message
code. They do not share the number space with CoAP options for code. They do not share the number space with CoAP options for
request/response messages or with Signaling messages using other request/response messages or with Signaling messages using other
codes. codes.
Option numbers are assigned by the "CoAP Signaling Option Numbers" Option numbers are assigned by the "CoAP Signaling Option Numbers"
sub-registry (see Section 9.2). sub-registry (see Section 10.2).
Signaling options are elective or critical as defined in Signaling options are elective or critical as defined in
Section 5.4.1 of [RFC7252]. If a Signaling option is critical and Section 5.4.1 of [RFC7252]. If a Signaling option is critical and
not understood by the receiver, it MUST abort the connection (see not understood by the receiver, it MUST abort the connection (see
Section 4.6). If the option is understood but cannot be processed, Section 5.6). If the option is understood but cannot be processed,
the option documents the behavior. the option documents the behavior.
4.3. Capabilities and Settings Messages (CSM) 5.3. Capabilities and Settings Messages (CSM)
Capabilities and Settings messages (CSM) are used for two purposes: Capabilities and Settings messages (CSM) are used for two purposes:
o Each capability option advertises one capability of the sender to o Each capability option advertises one capability of the sender to
the recipient. the recipient.
o Setting options indicate a setting that will be applied by the o Each setting option indicates a setting that will be applied by
sender. the sender.
One CSM MUST be sent by both endpoints at the start of the One CSM MUST be sent by both endpoints at the start of the
connection. Further CSM MAY be sent at any other time by either connection. Further CSM MAY be sent at any other time by either
endpoint over the lifetime of the connection. endpoint over the lifetime of the connection.
Both capability and setting options are cumulative. A CSM does not Both capability and setting options are cumulative. A CSM does not
invalidate a previously sent capability indication or setting even if invalidate a previously sent capability indication or setting even if
it is not repeated. A capability message without any option is a no- it is not repeated. A capability message without any option is a no-
operation (and can be used as such). An option that is sent might operation (and can be used as such). An option that is sent might
override a previous value for the same option. The option defines override a previous value for the same option. The option defines
how to handle this case if needed. how to handle this case if needed.
Base values are listed below for CSM Options. These are the values Base values are listed below for CSM Options. These are the values
for the capability and setting before any Capabilities and Settings for the capability and setting before any Capabilities and Settings
messages send a modified value. messages send a modified value.
These are not default values for the option as defined in These are not default values for the option, as defined in
Section 5.4.4 in [RFC7252]. A default value would mean that an empty Section 5.4.4 in [RFC7252]. A default value would mean that an empty
Capabilities and Settings message would result in the option being Capabilities and Settings message would result in the option being
set to its default value. set to its default value.
Capabilities and Settings messages are indicated by the 7.01 code Capabilities and Settings messages are indicated by the 7.01 code
(CSM). (CSM).
4.3.1. Max-Message-Size Capability Option 5.3.1. Max-Message-Size Capability Option
The sender can use the elective Max-Message-Size Option to indicate The sender can use the elective Max-Message-Size Option to indicate
the maximum message size in bytes that it can receive. the maximum message size in bytes that it can receive.
+---+---+---+---------+------------------+--------+--------+--------+ +---+---+---+---------+------------------+--------+--------+--------+
| # | C | R | Applies | Name | Format | Length | Base | | # | C | R | Applies | Name | Format | Length | Base |
| | | | to | | | | Value | | | | | to | | | | Value |
+---+---+---+---------+------------------+--------+--------+--------+ +---+---+---+---------+------------------+--------+--------+--------+
| 2 | | | CSM | Max-Message-Size | uint | 0-4 | 1152 | | 2 | | | CSM | Max-Message-Size | uint | 0-4 | 1152 |
+---+---+---+---------+------------------+--------+--------+--------+ +---+---+---+---------+------------------+--------+--------+--------+
C=Critical, R=Repeatable C=Critical, R=Repeatable
As per Section 4.6 of [RFC7252], the base value (and the value used As per Section 4.6 of [RFC7252], the base value (and the value used
when this option is not implemented) is 1152. when this option is not implemented) is 1152.
The active value of the Max-Message-Size Option is replaced each time The active value of the Max-Message-Size Option is replaced each time
the option is sent with a modified value. Its starting value is its the option is sent with a modified value. Its starting value is its
base value. base value.
4.3.2. Block-wise Transfer Capability Option 5.3.2. Block-wise Transfer Capability Option
+---+---+---+---------+-----------------+--------+--------+---------+ +---+---+---+---------+-----------------+--------+--------+---------+
| # | C | R | Applies | Name | Format | Length | Base | | # | C | R | Applies | Name | Format | Length | Base |
| | | | to | | | | Value | | | | | to | | | | Value |
+---+---+---+---------+-----------------+--------+--------+---------+ +---+---+---+---------+-----------------+--------+--------+---------+
| 4 | | | CSM | Block-wise | empty | 0 | (none) | | 4 | | | CSM | Block-wise | empty | 0 | (none) |
| | | | | Transfer | | | | | | | | | Transfer | | | |
+---+---+---+---------+-----------------+--------+--------+---------+ +---+---+---+---------+-----------------+--------+--------+---------+
C=Critical, R=Repeatable C=Critical, R=Repeatable
A sender can use the elective Block-wise Transfer Option to indicate A sender can use the elective Block-wise Transfer Option to indicate
that it supports the block-wise transfer protocol [RFC7959]. that it supports the block-wise transfer protocol [RFC7959].
If the option is not given, the peer has no information about whether If the option is not given, the peer has no information about whether
block-wise transfers are supported by the sender or not. An block-wise transfers are supported by the sender or not. An
implementation that supports block-wise transfers SHOULD indicate the implementation that supports block-wise transfers SHOULD indicate the
Block-wise Transfer Option. If a Max-Message-Size Option is Block-wise Transfer Option. If a Max-Message-Size Option is
indicated with a value that is greater than 1152 (in the same or a indicated with a value that is greater than 1152 (in the same or a
different CSM message), the Block-wise Transfer Option also indicates different CSM message), the Block-wise Transfer Option also indicates
support for BERT (see Section 5). Subsequently, if the Max-Message- support for BERT (see Section 6). Subsequently, if the Max-Message-
Size Option is indicated with a value equal or less than 1152, BERT Size Option is indicated with a value equal to or less than 1152,
support is no longer indicated. BERT support is no longer indicated.
4.4. Ping and Pong Messages 5.4. Ping and Pong Messages
In CoAP over reliable transports, Empty messages (Code 0.00) can In CoAP over reliable transports, Empty messages (Code 0.00) can
always be sent and MUST be ignored by the recipient. This provides a always be sent and MUST be ignored by the recipient. This provides a
basic keep-alive function. In contrast, Ping and Pong messages are a basic keep-alive function. In contrast, Ping and Pong messages are a
bidirectional exchange. bidirectional exchange.
Upon receipt of a Ping message, the receiver MUST return a Pong Upon receipt of a Ping message, the receiver MUST return a Pong
message with an identical token in response. Unless there is an message with an identical token in response. Unless there is an
option with delaying semantics such as the Custody Option, it SHOULD option with delaying semantics such as the Custody Option, it SHOULD
respond as soon as practical. As with all Signaling messages, the respond as soon as practical. As with all Signaling messages, the
recipient of a Ping or Pong message MUST ignore elective options it recipient of a Ping or Pong message MUST ignore elective options it
does not understand. does not understand.
Ping and Pong messages are indicated by the 7.02 code (Ping) and the Ping and Pong messages are indicated by the 7.02 code (Ping) and the
7.03 code (Pong). 7.03 code (Pong).
4.4.1. Custody Option 5.4.1. Custody Option
+---+---+---+----------+----------------+--------+--------+---------+ +---+---+---+----------+----------------+--------+--------+---------+
| # | C | R | Applies | Name | Format | Length | Base | | # | C | R | Applies | Name | Format | Length | Base |
| | | | to | | | | Value | | | | | to | | | | Value |
+---+---+---+----------+----------------+--------+--------+---------+ +---+---+---+----------+----------------+--------+--------+---------+
| 2 | | | Ping, | Custody | empty | 0 | (none) | | 2 | | | Ping, | Custody | empty | 0 | (none) |
| | | | Pong | | | | | | | | | Pong | | | | |
+---+---+---+----------+----------------+--------+--------+---------+ +---+---+---+----------+----------------+--------+--------+---------+
C=Critical, R=Repeatable C=Critical, R=Repeatable
skipping to change at page 19, line 25 skipping to change at page 19, line 25
elective Custody Option in the Pong message. This option indicates elective Custody Option in the Pong message. This option indicates
that the application has processed all the request/response messages that the application has processed all the request/response messages
received prior to the Ping message on the current connection. (Note received prior to the Ping message on the current connection. (Note
that there is no definition of specific application semantics for that there is no definition of specific application semantics for
"processed", but there is an expectation that the receiver of a Pong "processed", but there is an expectation that the receiver of a Pong
Message with a Custody Option should be able to free buffers based on Message with a Custody Option should be able to free buffers based on
this indication.) this indication.)
A sender can also include an elective Custody Option in a Ping A sender can also include an elective Custody Option in a Ping
message to explicitly request the inclusion of an elective Custody message to explicitly request the inclusion of an elective Custody
Option in the corresponding Pong message. The receiver SHOULD delay Option in the corresponding Pong message. In that case, the receiver
its Pong message until it finishes processing all the request/ SHOULD delay its Pong message until it finishes processing all the
response messages received prior to the Ping message on the current request/response messages received prior to the Ping message on the
connection. current connection.
4.5. Release Messages 5.5. Release Messages
A Release message indicates that the sender does not want to continue A Release message indicates that the sender does not want to continue
maintaining the connection and opts for an orderly shutdown. The maintaining the connection and opts for an orderly shutdown. The
details are in the options. A diagnostic payload (see Section 5.5.2 details are in the options. A diagnostic payload (see Section 5.5.2
of [RFC7252]) MAY be included. A peer will normally respond to a of [RFC7252]) MAY be included. A peer will normally respond to a
Release message by closing the TCP/TLS connection. Messages may be Release message by closing the TCP/TLS connection. Messages may be
in flight when the sender decides to send a Release message. The in flight when the sender decides to send a Release message. The
general expectation is that these will still be processed. general expectation is that these will still be processed.
Release messages are indicated by the 7.04 code (Release). Release messages are indicated by the 7.04 code (Release).
skipping to change at page 20, line 21 skipping to change at page 20, line 21
+---+---+---+---------+------------------+--------+--------+--------+ +---+---+---+---------+------------------+--------+--------+--------+
C=Critical, R=Repeatable C=Critical, R=Repeatable
The elective Alternative-Address Option requests the peer to instead The elective Alternative-Address Option requests the peer to instead
open a connection of the same scheme as the present connection to the open a connection of the same scheme as the present connection to the
alternative transport address given. Its value is in the form alternative transport address given. Its value is in the form
"authority" as defined in Section 3.2 of [RFC3986]. "authority" as defined in Section 3.2 of [RFC3986].
The Alternative-Address Option is a repeatable option as defined in The Alternative-Address Option is a repeatable option as defined in
Section 5.4.5 of [RFC7252]. Section 5.4.5 of [RFC7252]. When multiple occurrences of the option
are included, the peer can choose any of the alternative transport
addresses.
+---+---+---+---------+-----------------+--------+--------+---------+ +---+---+---+---------+-----------------+--------+--------+---------+
| # | C | R | Applies | Name | Format | Length | Base | | # | C | R | Applies | Name | Format | Length | Base |
| | | | to | | | | Value | | | | | to | | | | Value |
+---+---+---+---------+-----------------+--------+--------+---------+ +---+---+---+---------+-----------------+--------+--------+---------+
| 4 | | | Release | Hold-Off | uint | 0-3 | (none) | | 4 | | | Release | Hold-Off | uint | 0-3 | (none) |
+---+---+---+---------+-----------------+--------+--------+---------+ +---+---+---+---------+-----------------+--------+--------+---------+
C=Critical, R=Repeatable C=Critical, R=Repeatable
The elective Hold-Off Option indicates that the server is requesting The elective Hold-Off Option indicates that the server is requesting
that the peer not reconnect to it for the number of seconds given in that the peer not reconnect to it for the number of seconds given in
the value. the value.
4.6. Abort Messages 5.6. Abort Messages
An Abort message indicates that the sender is unable to continue An Abort message indicates that the sender is unable to continue
maintaining the connection and cannot even wait for an orderly maintaining the connection and cannot even wait for an orderly
release. The sender shuts down the connection immediately after the release. The sender shuts down the connection immediately after the
abort (and may or may not wait for a Release or Abort message or abort (and may or may not wait for a Release or Abort message or
connection shutdown in the inverse direction). A diagnostic payload connection shutdown in the inverse direction). A diagnostic payload
(see Section 5.5.2 of [RFC7252]) SHOULD be included in the Abort (see Section 5.5.2 of [RFC7252]) SHOULD be included in the Abort
message. Messages may be in flight when the sender decides to send message. Messages may be in flight when the sender decides to send
an Abort message. The general expectation is that these will NOT be an Abort message. The general expectation is that these will NOT be
processed. processed.
skipping to change at page 21, line 21 skipping to change at page 21, line 24
C=Critical, R=Repeatable C=Critical, R=Repeatable
The elective Bad-CSM-Option Option indicates that the sender is The elective Bad-CSM-Option Option indicates that the sender is
unable to process the CSM option identified by its option number, unable to process the CSM option identified by its option number,
e.g. when it is critical and the option number is unknown by the e.g. when it is critical and the option number is unknown by the
sender, or when there is parameter problem with the value of an sender, or when there is parameter problem with the value of an
elective option. More detailed information SHOULD be included as a elective option. More detailed information SHOULD be included as a
diagnostic payload. diagnostic payload.
One reason for an sender to generate an Abort message is a general For CoAP over UDP, messages which contain syntax violations are
syntax error in the byte-stream received. No specific option has processed as message format errors. As described in Sections 4.2 and
been defined for this, as the details of that syntax error are best 4.3 of [RFC7252], such messages are rejected by sending a matching
left to a diagnostic payload. Reset message and otherwise ignoring the message.
4.7. Signaling examples For CoAP over reliable transports, the recipient rejects such
messages by sending an Abort message and otherwise ignoring the
message. No specific option has been defined for the Abort message
in this case, as the details are best left to a diagnostic payload.
5.7. Signaling examples
An encoded example of a Ping message with a non-empty token is shown An encoded example of a Ping message with a non-empty token is shown
in Figure 14. in Figure 14.
0 1 2 0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0x01 | 0xe2 | 0x42 | | 0x01 | 0xe2 | 0x42 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 22, line 18 skipping to change at page 22, line 21
| 0x01 | 0xe3 | 0x42 | | 0x01 | 0xe3 | 0x42 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Len = 0 -------> 0x01 Len = 0 -------> 0x01
TKL = 1 ___/ TKL = 1 ___/
Code = 7.03 Pong --> 0xe3 Code = 7.03 Pong --> 0xe3
Token = 0x42 Token = 0x42
Figure 15: Pong Message Example Figure 15: Pong Message Example
5. Block-wise Transfer and Reliable Transports 6. Block-wise Transfer and Reliable Transports
The message size restrictions defined in Section 4.6 of CoAP The message size restrictions defined in Section 4.6 of CoAP
[RFC7252] to avoid IP fragmentation are not necessary when CoAP is [RFC7252] to avoid IP fragmentation are not necessary when CoAP is
used over a reliable transport. While this suggests that the Block- used over a reliable transport. While this suggests that the Block-
wise transfer protocol [RFC7959] is also no longer needed, it remains wise transfer protocol [RFC7959] is also no longer needed, it remains
applicable for a number of cases: applicable for a number of cases:
o large messages, such as firmware downloads, may cause undesired o large messages, such as firmware downloads, may cause undesired
head-of-line blocking when a single TCP connection is used head-of-line blocking when a single TCP connection is used
skipping to change at page 22, line 50 skipping to change at page 23, line 6
value in [RFC7959]. value in [RFC7959].
In control usage, a BERT option is interpreted in the same way as the In control usage, a BERT option is interpreted in the same way as the
equivalent Option with SZX == 6, except that it also indicates the equivalent Option with SZX == 6, except that it also indicates the
capability to process BERT blocks. As with the basic Block protocol, capability to process BERT blocks. As with the basic Block protocol,
the recipient of a CoAP request with a BERT option in control usage the recipient of a CoAP request with a BERT option in control usage
is allowed to respond with a different SZX value, e.g. to send a non- is allowed to respond with a different SZX value, e.g. to send a non-
BERT block instead. BERT block instead.
In descriptive usage, a BERT Option is interpreted in the same way as In descriptive usage, a BERT Option is interpreted in the same way as
the equivalent Option with SZX == 6, except that the payload is the equivalent Option with SZX == 6, except that the payload is also
allowed to contain a multiple of 1024 bytes (non-final BERT block) or allowed to contain a multiple of 1024 bytes (non-final BERT block) or
more than 1024 bytes (final BERT block). more than 1024 bytes (final BERT block).
The recipient of a non-final BERT block (M=1) conceptually partitions The recipient of a non-final BERT block (M=1) conceptually partitions
the payload into a sequence of 1024-byte blocks and acts exactly as the payload into a sequence of 1024-byte blocks and acts exactly as
if it had received this sequence in conjunction with block numbers if it had received this sequence in conjunction with block numbers
starting at, and sequentially increasing from, the block number given starting at, and sequentially increasing from, the block number given
in the Block Option. In other words, the entire BERT block is in the Block Option. In other words, the entire BERT block is
positioned at the byte position that results from multiplying the positioned at the byte position that results from multiplying the
block number with 1024. The position of further blocks to be block number with 1024. The position of further blocks to be
skipping to change at page 23, line 26 skipping to change at page 23, line 31
As with SZX == 6, the recipient of a final BERT block (M=0) simply As with SZX == 6, the recipient of a final BERT block (M=0) simply
appends the payload at the byte position that is indicated by the appends the payload at the byte position that is indicated by the
block number multiplied with 1024. block number multiplied with 1024.
The following examples illustrate BERT options. A value of SZX == 7 The following examples illustrate BERT options. A value of SZX == 7
is labeled as "BERT" or as "BERT(nnn)" to indicate a payload of size is labeled as "BERT" or as "BERT(nnn)" to indicate a payload of size
nnn. nnn.
In all these examples, a Block Option is decomposed to indicate the In all these examples, a Block Option is decomposed to indicate the
kind of Block Option (1 or 2) followed by a colon, the block number kind of Block Option (1 or 2) followed by a colon, the block number
(NUM), more bit (M), and block size exponent (2**(SZX+4)) separated (NUM), more bit (M), and block size (2**(SZX+4)) separated by
by slashes. E.g., a Block2 Option value of 33 would be shown as slashes. E.g., a Block2 Option value of 33 would be shown as
2:2/0/32), or a Block1 Option value of 59 would be shown as 2:2/0/32), or a Block1 Option value of 59 would be shown as
1:3/1/128. 1:3/1/128.
5.1. Example: GET with BERT Blocks 6.1. Example: GET with BERT Blocks
Figure 16 shows a GET request with a response that is split into Figure 16 shows a GET request with a response that is split into
three BERT blocks. The first response contains 3072 bytes of three BERT blocks. The first response contains 3072 bytes of
payload; the second, 5120; and the third, 4711. Note how the block payload; the second, 5120; and the third, 4711. Note how the block
number increments to move the position inside the response body number increments to move the position inside the response body
forward. forward.
CoAP Client CoAP Server CoAP Client CoAP Server
| | | |
| GET, /status ------> | | GET, /status ------> |
skipping to change at page 24, line 21 skipping to change at page 24, line 21
| GET, /status, 2:3/0/BERT ------> | | GET, /status, 2:3/0/BERT ------> |
| | | |
| <------ 2.05 Content, 2:3/1/BERT(5120) | | <------ 2.05 Content, 2:3/1/BERT(5120) |
| | | |
| GET, /status, 2:8/0/BERT ------> | | GET, /status, 2:8/0/BERT ------> |
| | | |
| <------ 2.05 Content, 2:8/0/BERT(4711) | | <------ 2.05 Content, 2:8/0/BERT(4711) |
Figure 16: GET with BERT blocks Figure 16: GET with BERT blocks
5.2. Example: PUT with BERT Blocks 6.2. Example: PUT with BERT Blocks
Figure 17 demonstrates a PUT exchange with BERT blocks. Figure 17 demonstrates a PUT exchange with BERT blocks.
CoAP Client CoAP Server CoAP Client CoAP Server
| | | |
| PUT, /options, 1:0/1/BERT(8192) ------> | | PUT, /options, 1:0/1/BERT(8192) ------> |
| | | |
| <------ 2.31 Continue, 1:0/1/BERT | | <------ 2.31 Continue, 1:0/1/BERT |
| | | |
| PUT, /options, 1:8/1/BERT(16384) ------> | | PUT, /options, 1:8/1/BERT(16384) ------> |
| | | |
| <------ 2.31 Continue, 1:8/1/BERT | | <------ 2.31 Continue, 1:8/1/BERT |
| | | |
| PUT, /options, 1:24/0/BERT(5683) ------> | | PUT, /options, 1:24/0/BERT(5683) ------> |
| | | |
| <------ 2.04 Changed, 1:24/0/BERT | | <------ 2.04 Changed, 1:24/0/BERT |
| | | |
Figure 17: PUT with BERT blocks Figure 17: PUT with BERT blocks
6. CoAP over Reliable Transport URIs 7. CoAP over Reliable Transport URIs
CoAP over UDP [RFC7252] defines the "coap" and "coaps" URI schemes. CoAP over UDP [RFC7252] defines the "coap" and "coaps" URI schemes.
This document introduces four additional URI schemes for identifying This document introduces four additional URI schemes for identifying
CoAP resources and providing a means of locating the resource: CoAP resources and providing a means of locating the resource:
o the "coap+tcp" URI scheme for CoAP over TCP o the "coap+tcp" URI scheme for CoAP over TCP
o the "coaps+tcp" URI scheme for CoAP over TCP secured by TLS o the "coaps+tcp" URI scheme for CoAP over TCP secured by TLS
o the "coap+ws" URI scheme for CoAP over WebSockets o the "coap+ws" URI scheme for CoAP over WebSockets
o the "coaps+ws" URI scheme for CoAP over WebSockets secured by TLS o the "coaps+ws" URI scheme for CoAP over WebSockets secured by TLS
Resources made available via these schemes have no shared identity Resources made available via these schemes have no shared identity
even if their resource identifiers indicate the same authority (the even if their resource identifiers indicate the same authority (the
same host listening to the same TCP port). They are distinct same host listening to the same TCP port). They are hosted in
namespaces and are considered to be distinct origin servers. distinct namespaces because each URI scheme implies a distinct origin
server.
The syntax for the URI schemes in this section are specified using The syntax for the URI schemes in this section are specified using
Augmented Backus-Naur Form (ABNF) [RFC5234]. The definitions of Augmented Backus-Naur Form (ABNF) [RFC5234]. The definitions of
"host", "port", "path-abempty", and "query" are adopted from "host", "port", "path-abempty", and "query" are adopted from
[RFC3986]. [RFC3986].
Section 8 (Multicast CoAP) in [RFC7252] is not applicable to these Section 8 (Multicast CoAP) in [RFC7252] is not applicable to these
schemes. schemes.
6.1. coap+tcp URI scheme 7.1. coap+tcp URI scheme
The "coap+tcp" URI scheme identifies CoAP resources that are intended The "coap+tcp" URI scheme identifies CoAP resources that are intended
to be accessible using CoAP over TCP. to be accessible using CoAP over TCP.
coap+tcp-URI = coap+tcp-URI =
"coap+tcp:" "//" host [ ":" port ] path-abempty [ "?" query ] "coap+tcp:" "//" host [ ":" port ] path-abempty [ "?" query ]
The syntax defined in Section 6.1 of [RFC7252] applies to this URI The syntax defined in Section 6.1 of [RFC7252] applies to this URI
scheme with the following changes: scheme with the following changes:
skipping to change at page 25, line 41 skipping to change at page 25, line 42
server is located. (If it is empty or not given, then the default server is located. (If it is empty or not given, then the default
port 5683 is assumed, as with UDP.) port 5683 is assumed, as with UDP.)
Encoding considerations: The scheme encoding conforms to the Encoding considerations: The scheme encoding conforms to the
encoding rules established for URIs in [RFC3986]. encoding rules established for URIs in [RFC3986].
Interoperability considerations: None. Interoperability considerations: None.
Security considerations: See Section 11.1 of [RFC7252]. Security considerations: See Section 11.1 of [RFC7252].
6.2. coaps+tcp URI scheme 7.2. coaps+tcp URI scheme
The "coaps+tcp" URI scheme identifies CoAP resources that are The "coaps+tcp" URI scheme identifies CoAP resources that are
intended to be accessible using CoAP over TCP secured with TLS. intended to be accessible using CoAP over TCP secured with TLS.
coaps+tcp-URI = coaps+tcp-URI =
"coaps+tcp:" "//" host [ ":" port ] path-abempty [ "?" query ] "coaps+tcp:" "//" host [ ":" port ] path-abempty [ "?" query ]
The syntax defined in Section 6.2 of [RFC7252] applies to this URI The syntax defined in Section 6.2 of [RFC7252] applies to this URI
scheme, with the following changes: scheme, with the following changes:
skipping to change at page 26, line 19 skipping to change at page 26, line 19
o If a TLS server does not support the Application-Layer Protocol o If a TLS server does not support the Application-Layer Protocol
Negotiation Extension (ALPN) [RFC7301] or wishes to accommodate Negotiation Extension (ALPN) [RFC7301] or wishes to accommodate
TLS clients that do not support ALPN, it MAY offer a coaps+tcp TLS clients that do not support ALPN, it MAY offer a coaps+tcp
endpoint on TCP port 5684. This endpoint MAY also be ALPN endpoint on TCP port 5684. This endpoint MAY also be ALPN
enabled. A TLS server MAY offer coaps+tcp endpoints on ports enabled. A TLS server MAY offer coaps+tcp endpoints on ports
other than TCP port 5684, which MUST be ALPN enabled. other than TCP port 5684, which MUST be ALPN enabled.
o For TCP ports other than port 5684, the TLS client MUST use the o For TCP ports other than port 5684, the TLS client MUST use the
ALPN extension to advertise the "coap" protocol identifier (see ALPN extension to advertise the "coap" protocol identifier (see
Section 9.7) in the list of protocols in its ClientHello. If the Section 10.7) in the list of protocols in its ClientHello. If the
TCP server selects and returns the "coap" protocol identifier TCP server selects and returns the "coap" protocol identifier
using the ALPN extension in its ServerHello, then the connection using the ALPN extension in its ServerHello, then the connection
succeeds. If the TLS server either does not negotiate the ALPN succeeds. If the TLS server either does not negotiate the ALPN
extension or returns a no_application_protocol alert, the TLS extension or returns a no_application_protocol alert, the TLS
client MUST close the connection. client MUST close the connection.
o For TCP port 5684, a TLS client MAY use the ALPN extension to o For TCP port 5684, a TLS client MAY use the ALPN extension to
advertise the "coap" protocol identifier in the list of protocols advertise the "coap" protocol identifier in the list of protocols
in its ClientHello. If the TLS server selects and returns the in its ClientHello. If the TLS server selects and returns the
"coap" protocol identifier using the ALPN extension in its "coap" protocol identifier using the ALPN extension in its
skipping to change at page 26, line 46 skipping to change at page 26, line 46
extension to negotiate the protocol, then coaps+tcp is implicitly extension to negotiate the protocol, then coaps+tcp is implicitly
selected. selected.
Encoding considerations: The scheme encoding conforms to the Encoding considerations: The scheme encoding conforms to the
encoding rules established for URIs in [RFC3986]. encoding rules established for URIs in [RFC3986].
Interoperability considerations: None. Interoperability considerations: None.
Security considerations: See Section 11.1 of [RFC7252]. Security considerations: See Section 11.1 of [RFC7252].
6.3. coap+ws URI scheme 7.3. coap+ws URI scheme
The "coap+ws" URI scheme identifies CoAP resources that are intended The "coap+ws" URI scheme identifies CoAP resources that are intended
to be accessible using CoAP over WebSockets. to be accessible using CoAP over WebSockets.
coap-ws-URI = coap-ws-URI =
"coap+ws:" "//" host [ ":" port ] path-abempty [ "?" query ] "coap+ws:" "//" host [ ":" port ] path-abempty [ "?" query ]
The port component is OPTIONAL. The default is port 80. The port subcomponent is OPTIONAL. The default is port 80.
The WebSocket endpoint is identified by a "ws" URI that is composed The WebSocket endpoint is identified by a "ws" URI that is composed
of the authority part of the "coap+ws" URI and the well-known path of the authority part of the "coap+ws" URI and the well-known path
"/.well-known/coap" [RFC5785]. The path and query parts of a "/.well-known/coap" [RFC5785]. The path and query parts of a
"coap+ws" URI identify a resource within the specified endpoint which "coap+ws" URI identify a resource within the specified endpoint which
can be operated on by the methods defined by CoAP: can be operated on by the methods defined by CoAP:
coap+ws://example.org/sensors/temperature?u=Cel coap+ws://example.org/sensors/temperature?u=Cel
\______ ______/\___________ ___________/ \______ ______/\___________ ___________/
\/ \/ \/ \/
skipping to change at page 27, line 29 skipping to change at page 27, line 29
Figure 18: The "coap+ws" URI Scheme Figure 18: The "coap+ws" URI Scheme
Encoding considerations: The scheme encoding conforms to the Encoding considerations: The scheme encoding conforms to the
encoding rules established for URIs in [RFC3986]. encoding rules established for URIs in [RFC3986].
Interoperability considerations: None. Interoperability considerations: None.
Security considerations: See Section 11.1 of [RFC7252]. Security considerations: See Section 11.1 of [RFC7252].
6.4. coaps+ws URI scheme 7.4. coaps+ws URI scheme
The "coaps+ws" URI scheme identifies CoAP resources that are intended The "coaps+ws" URI scheme identifies CoAP resources that are intended
to be accessible using CoAP over WebSockets secured by TLS. to be accessible using CoAP over WebSockets secured by TLS.
coaps-ws-URI = coaps-ws-URI =
"coaps+ws:" "//" host [ ":" port ] path-abempty [ "?" query ] "coaps+ws:" "//" host [ ":" port ] path-abempty [ "?" query ]
The port component is OPTIONAL. The default is port 443. The port subcomponent is OPTIONAL. The default is port 443.
The WebSocket endpoint is identified by a "wss" URI that is composed The WebSocket endpoint is identified by a "wss" URI that is composed
of the authority part of the "coaps+ws" URI and the well-known path of the authority part of the "coaps+ws" URI and the well-known path
"/.well-known/coap" [RFC5785]. The path and query parts of a "/.well-known/coap" [RFC5785]. The path and query parts of a
"coaps+ws" URI identify a resource within the specified endpoint "coaps+ws" URI identify a resource within the specified endpoint
which can be operated on by the methods defined by CoAP. which can be operated on by the methods defined by CoAP.
coaps+ws://example.org/sensors/temperature?u=Cel coaps+ws://example.org/sensors/temperature?u=Cel
\______ ______/\___________ ___________/ \______ ______/\___________ ___________/
\/ \/ \/ \/
Uri-Path: "sensors" Uri-Path: "sensors"
wss://example.org/.well-known/coap Uri-Path: "temperature" wss://example.org/.well-known/coap Uri-Path: "temperature"
Uri-Query: "u=Cel" Uri-Query: "u=Cel"
Figure 19: The "coaps+ws" URI Scheme Figure 19: The "coaps+ws" URI Scheme
Encoding considerations: The scheme encoding conforms to the Encoding considerations: The scheme encoding conforms to the
encoding rules established for URIs in [RFC3986]. encoding rules established for URIs in [RFC3986].
Interoperability considerations: None. Interoperability considerations: None.
Security considerations: See Section 11.1 of [RFC7252]. Security considerations: See Section 11.1 of [RFC7252].
6.5. Uri-Host and Uri-Port Options 7.5. Uri-Host and Uri-Port Options
CoAP over reliable transports maintains the property from CoAP over reliable transports maintains the property from
Section 5.10.1 of [RFC7252]: Section 5.10.1 of [RFC7252]:
The default values for the Uri-Host and Uri-Port Options are The default values for the Uri-Host and Uri-Port Options are
sufficient for requests to most servers. sufficient for requests to most servers.
Unless otherwise noted, the default value of the Uri-Host Option is Unless otherwise noted, the default value of the Uri-Host Option is
the IP literal representing the destination IP address of the request the IP literal representing the destination IP address of the request
message. The default value of the Uri-Port Option is the destination message. The default value of the Uri-Port Option is the destination
skipping to change at page 28, line 34 skipping to change at page 28, line 34
For CoAP over TLS, these default values are the same unless Server For CoAP over TLS, these default values are the same unless Server
Name Indication (SNI) [RFC6066] is negotiated. In this case, the Name Indication (SNI) [RFC6066] is negotiated. In this case, the
default value of the Uri-Host Option in requests from the TLS client default value of the Uri-Host Option in requests from the TLS client
to the TLS server is the SNI host. to the TLS server is the SNI host.
For CoAP over WebSockets, the default value of the Uri-Host Option in For CoAP over WebSockets, the default value of the Uri-Host Option in
requests from the WebSocket client to the WebSocket server is requests from the WebSocket client to the WebSocket server is
indicated by the Host header field from the WebSocket handshake. indicated by the Host header field from the WebSocket handshake.
6.6. Decomposing URIs into Options 7.6. Decomposing URIs into Options
The steps are the same as specified in Section 6.4 of [RFC7252] with The steps are the same as specified in Section 6.4 of [RFC7252] with
the following changes: minor changes.
This step from [RFC7252]:
3. If |url| does not have a <scheme> component whose value, when 3. If |url| does not have a <scheme> component whose value, when
converted to ASCII lowercase, is "coap" or "coaps", then fail converted to ASCII lowercase, is "coap" or "coaps", then fail
this algorithm. this algorithm.
If |url| does not have a <scheme> component whose value, when is updated to:
converted to ASCII lowercase, is "coap+tcp", "coaps+tcp", "coap+ws",
or "coaps+ws" then fail this algorithm. 3. If |url| does not have a <scheme> component whose value, when
converted to ASCII lowercase, is "coap+tcp", "coaps+tcp",
"coap+ws", or "coaps+ws", then fail this algorithm.
This step from [RFC7252]:
7. If |port| does not equal the request's destination UDP port, 7. If |port| does not equal the request's destination UDP port,
include a Uri-Port Option and let that option's value be |port|. include a Uri-Port Option and let that option's value be |port|.
If |port| does not equal the request's destination TCP port, include is updated to:
a Uri-Port Option and let that option's value be |port|.
6.7. Composing URIs from Options 7. If |port| does not equal the request's destination TCP port,
include a Uri-Port Option and let that option's value be |port|.
7.7. Composing URIs from Options
The steps are the same as specified in Section 6.5 of [RFC7252] with The steps are the same as specified in Section 6.5 of [RFC7252] with
the following changes: minor changes.
This step from [RFC7252]:
1. If the request is secured using DTLS, let |url| be the string 1. If the request is secured using DTLS, let |url| be the string
"coaps://". Otherwise, let |url| be the string "coap://". "coaps://". Otherwise, let |url| be the string "coap://".
For CoAP over TCP, if the request is secured using TLS, let |url| be is updated to:
the string "coaps+tcp://". Otherwise, let |url| be the string
"coap+tcp://". For CoAP over WebSockets, if the request is secured 1. For CoAP over TCP, if the request is secured using TLS, let |url|
using TLS, let |url| be the string "coaps+ws://". Otherwise, be the string "coaps+tcp://". Otherwise, let |url| be the string
let |url| be the string "coap+ws://". "coap+tcp://". For CoAP over WebSockets, if the request is
secured using TLS, let |url| be the string "coaps+ws://".
Otherwise, let |url| be the string "coap+ws://".
This step from [RFC7252]:
4. If the request includes a Uri-Port Option, let |port| be that 4. If the request includes a Uri-Port Option, let |port| be that
option's value. Otherwise, let |port| be the request's option's value. Otherwise, let |port| be the request's
destination UDP port. destination UDP port.
If the request includes a Uri-Port Option, let |port| be that is updated to:
option's value. Otherwise, let |port| be the request's destination
TCP port.
7. Securing CoAP 4. If the request includes a Uri-Port Option, let |port| be that
option's value. Otherwise, let |port| be the request's
destination TCP port.
8. Securing CoAP
Security Challenges for the Internet of Things [SecurityChallenges] Security Challenges for the Internet of Things [SecurityChallenges]
recommends: recommends:
... it is essential that IoT protocol suites specify a mandatory ... it is essential that IoT protocol suites specify a mandatory
to implement but optional to use security solution. This will to implement but optional to use security solution. This will
ensure security is available in all implementations, but ensure security is available in all implementations, but
configurable to use when not necessary (e.g., in closed configurable to use when not necessary (e.g., in closed
environment). ... even if those features stretch the capabilities environment). ... even if those features stretch the capabilities
of such devices. of such devices.
A security solution MUST be implemented to protect CoAP over reliable A security solution MUST be implemented to protect CoAP over reliable
transports and MUST be enabled by default. This document defines the transports and MUST be enabled by default. This document defines the
TLS binding, but alternative solutions at different layers in the TLS binding, but alternative solutions at different layers in the
protocol stack MAY be used to protect CoAP over reliable transports protocol stack MAY be used to protect CoAP over reliable transports
when appropriate. Note that there is ongoing work to support a data when appropriate. Note that there is ongoing work to support a data
object-based security model for CoAP that is independent of transport object-based security model for CoAP that is independent of transport
(see [I-D.ietf-core-object-security]). (see [I-D.ietf-core-object-security]).
7.1. TLS binding for CoAP over TCP 8.1. TLS binding for CoAP over TCP
The TLS usage guidance in [RFC7925] applies. The TLS usage guidance in [RFC7925] applies.
During the provisioning phase, a CoAP device is provided with the During the provisioning phase, a CoAP device is provided with the
security information that it needs, including keying materials, security information that it needs, including keying materials,
access control lists, and authorization servers. At the end of the access control lists, and authorization servers. At the end of the
provisioning phase, the device will be in one of four security modes: provisioning phase, the device will be in one of four security modes:
NoSec: TLS is disabled. NoSec: TLS is disabled.
skipping to change at page 30, line 30 skipping to change at page 30, line 47
scheme and the TCP CoAP default port. The system is secured only by scheme and the TCP CoAP default port. The system is secured only by
keeping attackers from being able to send or receive packets from the keeping attackers from being able to send or receive packets from the
network with the CoAP nodes. network with the CoAP nodes.
"PreSharedKey", "RawPublicKey", or "Certificate" is mandatory-to- "PreSharedKey", "RawPublicKey", or "Certificate" is mandatory-to-
implement for the TLS binding depending on the credential type used implement for the TLS binding depending on the credential type used
with the device. These security modes are achieved using TLS and are with the device. These security modes are achieved using TLS and are
indicated by the "coaps+tcp" scheme and TLS-secured CoAP default indicated by the "coaps+tcp" scheme and TLS-secured CoAP default
port. port.
7.2. TLS usage for CoAP over WebSockets 8.2. TLS usage for CoAP over WebSockets
A CoAP client requesting a resource identified by a "coaps+ws" URI A CoAP client requesting a resource identified by a "coaps+ws" URI
negotiates a secure WebSocket connection to a WebSocket server negotiates a secure WebSocket connection to a WebSocket server
endpoint with a "wss" URI. This is described in Section 6.4. endpoint with a "wss" URI. This is described in Section 7.4.
The client MUST perform a TLS handshake after opening the connection The client MUST perform a TLS handshake after opening the connection
to the server. The guidance in Section 4.1 of [RFC6455] applies. to the server. The guidance in Section 4.1 of [RFC6455] applies.
When a CoAP server exposes resources identified by a "coaps+ws" URI, When a CoAP server exposes resources identified by a "coaps+ws" URI,
the guidance in Section 4.4 of [RFC7925] applies towards mandatory- the guidance in Section 4.4 of [RFC7925] applies towards mandatory-
to-implement TLS functionality for certificates. For the server-side to-implement TLS functionality for certificates. For the server-side
requirements in accepting incoming connections over a HTTPS (HTTP- requirements in accepting incoming connections over a HTTPS (HTTP-
over-TLS) port, the guidance in Section 4.2 of [RFC6455] applies. over-TLS) port, the guidance in Section 4.2 of [RFC6455] applies.
8. Security Considerations 9. Security Considerations
The security considerations of [RFC7252] apply. For CoAP over The security considerations of [RFC7252] apply. For CoAP over
WebSockets and CoAP over TLS-secured WebSockets, the security WebSockets and CoAP over TLS-secured WebSockets, the security
considerations of [RFC6455] also apply. considerations of [RFC6455] also apply.
8.1. Signaling Messages 9.1. Signaling Messages
o The guidance given by an Alternative-Address Option cannot be The guidance given by an Alternative-Address Option cannot be
followed blindly. In particular, a peer MUST NOT assume that a followed blindly. In particular, a peer MUST NOT assume that a
successful connection to the Alternative-Address inherits all the successful connection to the Alternative-Address inherits all the
security properties of the current connection. security properties of the current connection.
9. IANA Considerations 10. IANA Considerations
9.1. Signaling Codes 10.1. Signaling Codes
IANA is requested to create a third sub-registry for values of the IANA is requested to create a third sub-registry for values of the
Code field in the CoAP header (Section 12.1 of [RFC7252]). The name Code field in the CoAP header (Section 12.1 of [RFC7252]). The name
of this sub-registry is "CoAP Signaling Codes". of this sub-registry is "CoAP Signaling Codes".
Each entry in the sub-registry must include the Signaling Code in the Each entry in the sub-registry must include the Signaling Code in the
range 7.00-7.31, its name, and a reference to its documentation. range 7.00-7.31, its name, and a reference to its documentation.
Initial entries in this sub-registry are as follows: Initial entries in this sub-registry are as follows:
skipping to change at page 31, line 46 skipping to change at page 32, line 26
| 7.05 | Abort | [RFCthis] | | 7.05 | Abort | [RFCthis] |
+------+---------+-----------+ +------+---------+-----------+
Table 1: CoAP Signal Codes Table 1: CoAP Signal Codes
All other Signaling Codes are Unassigned. All other Signaling Codes are Unassigned.
The IANA policy for future additions to this sub-registry is "IETF The IANA policy for future additions to this sub-registry is "IETF
Review or IESG Approval" as described in [RFC5226]. Review or IESG Approval" as described in [RFC5226].
9.2. CoAP Signaling Option Numbers Registry 10.2. CoAP Signaling Option Numbers Registry
IANA is requested to create a sub-registry for Options Numbers used IANA is requested to create a sub-registry for Options Numbers used
in CoAP signaling options within the "CoRE Parameters" registry. The in CoAP signaling options within the "CoRE Parameters" registry. The
name of this sub-registry is "CoAP Signaling Option Numbers". name of this sub-registry is "CoAP Signaling Option Numbers".
Each entry in the sub-registry must include one or more of the codes Each entry in the sub-registry must include one or more of the codes
in the Signaling Codes subregistry (Section 9.1), the option number, in the Signaling Codes subregistry (Section 10.1), the option number,
the name of the option, and a reference to the option's the name of the option, and a reference to the option's
documentation. documentation.
Initial entries in this sub-registry are as follows: Initial entries in this sub-registry are as follows:
+------------+--------+---------------------+-----------+ +------------+--------+---------------------+-----------+
| Applies to | Number | Name | Reference | | Applies to | Number | Name | Reference |
+------------+--------+---------------------+-----------+ +------------+--------+---------------------+-----------+
| 7.01 | 2 | Max-Message-Size | [RFCthis] | | 7.01 | 2 | Max-Message-Size | [RFCthis] |
| | | | | | | | | |
skipping to change at page 32, line 47 skipping to change at page 33, line 40
o Whether the option is critical or elective, as determined by the o Whether the option is critical or elective, as determined by the
Option Number. Option Number.
o Whether the option is repeatable. o Whether the option is repeatable.
o The format and length of the option's value. o The format and length of the option's value.
o The base value for the option, if any. o The base value for the option, if any.
9.3. Service Name and Port Number Registration 10.3. Service Name and Port Number Registration
IANA is requested to assign the port number 5683 and the service name IANA is requested to assign the port number 5683 and the service name
"coap+tcp", in accordance with [RFC6335]. "coap+tcp", in accordance with [RFC6335].
Service Name. Service Name.
coap+tcp coap+tcp
Transport Protocol. Transport Protocol.
tcp tcp
Assignee. Assignee.
IESG <iesg@ietf.org> IESG <iesg@ietf.org>
Contact. Contact.
IETF Chair <chair@ietf.org> IETF Chair <chair@ietf.org>
Description. Description.
Constrained Application Protocol (CoAP) Constrained Application Protocol (CoAP)
Reference. Reference.
[RFCthis] [RFCthis]
Port Number. Port Number.
5683 5683
9.4. Secure Service Name and Port Number Registration 10.4. Secure Service Name and Port Number Registration
IANA is requested to assign the port number 5684 and the service name IANA is requested to assign the port number 5684 and the service name
"coaps+tcp", in accordance with [RFC6335]. The port number is "coaps+tcp", in accordance with [RFC6335]. The port number is
requested to address the exceptional case of TLS implementations that requested to address the exceptional case of TLS implementations that
do not support the "Application-Layer Protocol Negotiation Extension" do not support the "Application-Layer Protocol Negotiation Extension"
[RFC7301]. [RFC7301].
Service Name. Service Name.
coaps+tcp coaps+tcp
skipping to change at page 34, line 5 skipping to change at page 34, line 46
Description. Description.
Constrained Application Protocol (CoAP) Constrained Application Protocol (CoAP)
Reference. Reference.
[RFC7301], [RFCthis] [RFC7301], [RFCthis]
Port Number. Port Number.
5684 5684
9.5. URI Scheme Registration 10.5. URI Scheme Registration
URI schemes are registered within the "Uniform Resource Identifier URI schemes are registered within the "Uniform Resource Identifier
(URI) Schemes" registry maintained at (URI) Schemes" registry maintained at
http://www.iana.org/assignments/uri-schemes/uri-schemes.xhtml . http://www.iana.org/assignments/uri-schemes/uri-schemes.xhtml .
9.5.1. coap+tcp 10.5.1. coap+tcp
IANA is requested to register the Uniform Resource Identifier (URI) IANA is requested to register the Uniform Resource Identifier (URI)
scheme "coap+tcp". This registration request complies with scheme "coap+tcp". This registration request complies with
[RFC7595]. [RFC7595].
Scheme name: Scheme name:
coap+tcp coap+tcp
Status: Status:
Permanent Permanent
skipping to change at page 34, line 34 skipping to change at page 35, line 28
The scheme is used by CoAP endpoints to access CoAP resources The scheme is used by CoAP endpoints to access CoAP resources
using TCP. using TCP.
Contact: Contact:
IETF chair <chair@ietf.org> IETF chair <chair@ietf.org>
Change controller: Change controller:
IESG <iesg@ietf.org> IESG <iesg@ietf.org>
Reference: Reference:
Section 6.1 in [RFCthis] Section 7.1 in [RFCthis]
9.5.2. coaps+tcp 10.5.2. coaps+tcp
IANA is requested to register the Uniform Resource Identifier (URI) IANA is requested to register the Uniform Resource Identifier (URI)
scheme "coaps+tcp". This registration request complies with scheme "coaps+tcp". This registration request complies with
[RFC7595]. [RFC7595].
Scheme name: Scheme name:
coaps+tcp coaps+tcp
Status: Status:
Permanent Permanent
skipping to change at page 35, line 4 skipping to change at page 35, line 47
coaps+tcp coaps+tcp
Status: Status:
Permanent Permanent
Applications/protocols that use this scheme name: Applications/protocols that use this scheme name:
The scheme is used by CoAP endpoints to access CoAP resources The scheme is used by CoAP endpoints to access CoAP resources
using TLS. using TLS.
Contact: Contact:
IETF chair <chair@ietf.org> IETF chair <chair@ietf.org>
Change controller: Change controller:
IESG <iesg@ietf.org> IESG <iesg@ietf.org>
Reference: Reference:
Section 6.2 in [RFCthis]
9.5.3. coap+ws Section 7.2 in [RFCthis]
10.5.3. coap+ws
IANA is requested to register the Uniform Resource Identifier (URI) IANA is requested to register the Uniform Resource Identifier (URI)
scheme "coap+ws". This registration request complies with [RFC7595]. scheme "coap+ws". This registration request complies with [RFC7595].
Scheme name: Scheme name:
coap+ws coap+ws
Status: Status:
Permanent Permanent
skipping to change at page 35, line 35 skipping to change at page 36, line 29
The scheme is used by CoAP endpoints to access CoAP resources The scheme is used by CoAP endpoints to access CoAP resources
using the WebSocket protocol. using the WebSocket protocol.
Contact: Contact:
IETF chair <chair@ietf.org> IETF chair <chair@ietf.org>
Change controller: Change controller:
IESG <iesg@ietf.org> IESG <iesg@ietf.org>
Reference: Reference:
Section 6.3 in [RFCthis] Section 7.3 in [RFCthis]
9.5.4. coaps+ws 10.5.4. coaps+ws
IANA is requested to register the Uniform Resource Identifier (URI) IANA is requested to register the Uniform Resource Identifier (URI)
scheme "coaps+ws". This registration request complies with scheme "coaps+ws". This registration request complies with
[RFC7595]. [RFC7595].
Scheme name: Scheme name:
coaps+ws coaps+ws
Status: Status:
Permanent Permanent
skipping to change at page 36, line 12 skipping to change at page 37, line 6
The scheme is used by CoAP endpoints to access CoAP resources The scheme is used by CoAP endpoints to access CoAP resources
using the WebSocket protocol secured with TLS. using the WebSocket protocol secured with TLS.
Contact: Contact:
IETF chair <chair@ietf.org> IETF chair <chair@ietf.org>
Change controller: Change controller:
IESG <iesg@ietf.org> IESG <iesg@ietf.org>
References: References:
Section 6.4 in [RFCthis] Section 7.4 in [RFCthis]
9.6. Well-Known URI Suffix Registration 10.6. Well-Known URI Suffix Registration
IANA is requested to register the 'coap' well-known URI in the "Well- IANA is requested to register the 'coap' well-known URI in the "Well-
Known URIs" registry. This registration request complies with Known URIs" registry. This registration request complies with
[RFC5785]: [RFC5785]:
URI Suffix. URI Suffix.
coap coap
Change controller. Change controller.
IETF IETF
Specification document(s). Specification document(s).
[RFCthis] [RFCthis]
Related information. Related information.
None. None.
9.7. ALPN Protocol Identifier 10.7. ALPN Protocol Identifier
IANA is requested to assign the following value in the registry IANA is requested to assign the following value in the registry
"Application Layer Protocol Negotiation (ALPN) Protocol IDs" created "Application Layer Protocol Negotiation (ALPN) Protocol IDs" created
by [RFC7301]. The "coap" string identifies CoAP when used over TLS. by [RFC7301]. The "coap" string identifies CoAP when used over TLS.
Protocol. Protocol.
CoAP CoAP
Identification Sequence. Identification Sequence.
0x63 0x6f 0x61 0x70 ("coap") 0x63 0x6f 0x61 0x70 ("coap")
Reference. Reference.
[RFCthis] [RFCthis]
9.8. WebSocket Subprotocol Registration 10.8. WebSocket Subprotocol Registration
IANA is requested to register the WebSocket CoAP subprotocol under IANA is requested to register the WebSocket CoAP subprotocol under
the "WebSocket Subprotocol Name Registry": the "WebSocket Subprotocol Name Registry":
Subprotocol Identifier. Subprotocol Identifier.
coap coap
Subprotocol Common Name. Subprotocol Common Name.
Constrained Application Protocol (CoAP) Constrained Application Protocol (CoAP)
Subprotocol Definition. Subprotocol Definition.
[RFCthis] [RFCthis]
10. References 11. References
10.1. Normative References 11.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981, RFC 793, DOI 10.17487/RFC0793, September 1981,
<http://www.rfc-editor.org/info/rfc793>. <http://www.rfc-editor.org/info/rfc793>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>. <http://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 38, line 35 skipping to change at page 39, line 26
Application Protocol (CoAP)", RFC 7641, Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015, DOI 10.17487/RFC7641, September 2015,
<http://www.rfc-editor.org/info/rfc7641>. <http://www.rfc-editor.org/info/rfc7641>.
[RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer [RFC7925] Tschofenig, H., Ed. and T. Fossati, "Transport Layer
Security (TLS) / Datagram Transport Layer Security (DTLS) Security (TLS) / Datagram Transport Layer Security (DTLS)
Profiles for the Internet of Things", RFC 7925, Profiles for the Internet of Things", RFC 7925,
DOI 10.17487/RFC7925, July 2016, DOI 10.17487/RFC7925, July 2016,
<http://www.rfc-editor.org/info/rfc7925>. <http://www.rfc-editor.org/info/rfc7925>.
10.2. Informative References 11.2. Informative References
[HomeGateway] [HomeGateway]
Eggert, L., "An experimental study of home gateway Eggert, L., "An experimental study of home gateway
characteristics", Proceedings of the 10th annual characteristics", Proceedings of the 10th annual
conference on Internet measurement , 2010. conference on Internet measurement , 2010.
[I-D.ietf-core-cocoa] [I-D.ietf-core-cocoa]
Bormann, C., Betzler, A., Gomez, C., and I. Demirkol, Bormann, C., Betzler, A., Gomez, C., and I. Demirkol,
"CoAP Simple Congestion Control/Advanced", draft-ietf- "CoAP Simple Congestion Control/Advanced", draft-ietf-
core-cocoa-00 (work in progress), October 2016. core-cocoa-00 (work in progress), October 2016.
skipping to change at page 39, line 31 skipping to change at page 40, line 21
Cheshire, "Internet Assigned Numbers Authority (IANA) Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165, Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011, RFC 6335, DOI 10.17487/RFC6335, August 2011,
<http://www.rfc-editor.org/info/rfc6335>. <http://www.rfc-editor.org/info/rfc6335>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>. January 2012, <http://www.rfc-editor.org/info/rfc6347>.
[RFC6454] Barth, A., "The Web Origin Concept", RFC 6454,
DOI 10.17487/RFC6454, December 2011,
<http://www.rfc-editor.org/info/rfc6454>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing", Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014, RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>. <http://www.rfc-editor.org/info/rfc7230>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in [RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959, the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016, DOI 10.17487/RFC7959, August 2016,
<http://www.rfc-editor.org/info/rfc7959>. <http://www.rfc-editor.org/info/rfc7959>.
[SecurityChallenges] [SecurityChallenges]
Polk, T. and S. Turner, "Security Challenges for the Polk, T. and S. Turner, "Security Challenges for the
Internet of Things", Interconnecting Smart Objects with Internet of Things", Interconnecting Smart Objects with
the Internet / IAB Workshop , February 2011, the Internet / IAB Workshop , February 2011,
<http://www.iab.org/wp-content/IAB-uploads/2011/03/ <http://www.iab.org/wp-content/IAB-uploads/2011/03/
Turner.pdf>. Turner.pdf>.
Appendix A. Updates to RFC7641 Observing Resources in the Constrained Appendix A. Updates to RFC 7641 Observing Resources in the Constrained
Application Protocol (CoAP) Application Protocol (CoAP)
In this appendix, "client" and "server" refer to the CoAP client and In this appendix, "client" and "server" refer to the CoAP client and
CoAP server. CoAP server.
A.1. Notifications and Reordering A.1. Notifications and Reordering
When using the Observe Option with CoAP over UDP, notifications from When using the Observe Option with CoAP over UDP, notifications from
the server set the option value to an increasing sequence number for the server set the option value to an increasing sequence number for
reordering detection on the client since messages can arrive in a reordering detection on the client since messages can arrive in a
skipping to change at page 40, line 38 skipping to change at page 41, line 23
alive and wishes to receive further notifications. A reset message alive and wishes to receive further notifications. A reset message
indicates that the client does not recognize the token which causes indicates that the client does not recognize the token which causes
the server to remove the associated entry from the list of observers. the server to remove the associated entry from the list of observers.
Since TCP eliminates the need for the message layer to support Since TCP eliminates the need for the message layer to support
reliability, CoAP over reliable transports does not support reliability, CoAP over reliable transports does not support
confirmable or non-confirmable message types. All notifications are confirmable or non-confirmable message types. All notifications are
delivered reliably to the client with positive acknowledgement of delivered reliably to the client with positive acknowledgement of
receipt occurring at the TCP level. If the client does not recognize receipt occurring at the TCP level. If the client does not recognize
the token in a notification, it MAY immediately abort the connection the token in a notification, it MAY immediately abort the connection
(see Section 4.6). (see Section 5.6).
A.3. Freshness A.3. Freshness
For CoAP over UDP, if a client does not receive a notification for For CoAP over UDP, if a client does not receive a notification for
some time, it MAY send a new GET request with the same token as the some time, it MAY send a new GET request with the same token as the
original request to re-register its interest in a resource and verify original request to re-register its interest in a resource and verify
that the server is still responsive. For CoAP over reliable that the server is still responsive. For CoAP over reliable
transports, it is more efficient to check the health of the transports, it is more efficient to check the health of the
connection (and all its active observations) by sending a CoAP Ping connection (and all its active observations) by sending a CoAP Ping
Signaling message (Section 4.4) rather than individual requests to Signaling message (Section 5.4) rather than individual requests to
confirm active observations. confirm active observations.
A.4. Cancellation A.4. Cancellation
For CoAP over UDP, a client that is no longer interested in receiving For CoAP over UDP, a client that is no longer interested in receiving
notifications can "forget" the observation and respond to the next notifications can "forget" the observation and respond to the next
notification from the server with a reset message to cancel the notification from the server with a reset message to cancel the
observation. observation.
For CoAP over reliable transports, a client MUST explicitly For CoAP over reliable transports, a client MUST explicitly
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If the client observes one or more resources over a reliable If the client observes one or more resources over a reliable
transport, then the CoAP server (or intermediary in the role of the transport, then the CoAP server (or intermediary in the role of the
CoAP server) MUST remove all entries associated with the client CoAP server) MUST remove all entries associated with the client
endpoint from the lists of observers when the connection is either endpoint from the lists of observers when the connection is either
closed or times out. closed or times out.
Appendix B. CoAP over WebSocket Examples Appendix B. CoAP over WebSocket Examples
This section gives examples for the first two configurations This section gives examples for the first two configurations
discussed in Section 3. discussed in Section 4.
An example of the process followed by a CoAP client to retrieve the An example of the process followed by a CoAP client to retrieve the
representation of a resource identified by a "coap+ws" URI might be representation of a resource identified by a "coap+ws" URI might be
as follows. Figure 20 below illustrates the WebSocket and CoAP as follows. Figure 20 below illustrates the WebSocket and CoAP
messages exchanged in detail. messages exchanged in detail.
1. The CoAP client obtains the URI <coap+ws://example.org/sensors/ 1. The CoAP client obtains the URI <coap+ws://example.org/sensors/
temperature?u=Cel>, for example, from a resource representation temperature?u=Cel>, for example, from a resource representation
that it retrieved previously. that it retrieved previously.
skipping to change at page 43, line 7 skipping to change at page 44, line 7
+--------->| Close frame (opcode=%x8, FIN=1, MASK=1) +--------->| Close frame (opcode=%x8, FIN=1, MASK=1)
| | | |
|<---------+ Close frame (opcode=%x8, FIN=1, MASK=0) |<---------+ Close frame (opcode=%x8, FIN=1, MASK=0)
| | | |
Figure 20: A CoAP client retrieves the representation of a resource Figure 20: A CoAP client retrieves the representation of a resource
identified by a "coap+ws" URI identified by a "coap+ws" URI
Figure 21 shows how a CoAP client uses a CoAP forward proxy with a Figure 21 shows how a CoAP client uses a CoAP forward proxy with a
WebSocket endpoint to retrieve the representation of the resource WebSocket endpoint to retrieve the representation of the resource
"coap://[2001:DB8::1]/". The use of the forward proxy and the "coap://[2001:db8::1]/". The use of the forward proxy and the
address of the WebSocket endpoint are determined by the client from address of the WebSocket endpoint are determined by the client from
local configuration rules. The request URI is specified in the local configuration rules. The request URI is specified in the
Proxy-Uri Option. Since the request URI uses the "coap" URI scheme, Proxy-Uri Option. Since the request URI uses the "coap" URI scheme,
the proxy fulfills the request by issuing a Confirmable GET request the proxy fulfills the request by issuing a Confirmable GET request
over UDP to the CoAP server and returning the response over the over UDP to the CoAP server and returning the response over the
WebSocket connection to the client. WebSocket connection to the client.
CoAP CoAP CoAP CoAP CoAP CoAP
Client Proxy Server Client Proxy Server
(WebSocket (WebSocket (UDP (WebSocket (WebSocket (UDP
Client) Server) Endpoint) Client) Server) Endpoint)
| | | | | |
+--------->| | Binary frame (opcode=%x2, FIN=1, MASK=1) +--------->| | Binary frame (opcode=%x2, FIN=1, MASK=1)
| | | +------------------------------------+ | | | +------------------------------------+
| | | | GET | | | | | GET |
| | | | Token: 0x7d | | | | | Token: 0x7d |
| | | | Proxy-Uri: "coap://[2001:DB8::1]/" | | | | | Proxy-Uri: "coap://[2001:db8::1]/" |
| | | +------------------------------------+ | | | +------------------------------------+
| | | | | |
| +--------->| CoAP message (Ver=1, T=Con, MID=0x8f54) | +--------->| CoAP message (Ver=1, T=Con, MID=0x8f54)
| | | +------------------------------------+ | | | +------------------------------------+
| | | | GET | | | | | GET |
| | | | Token: 0x0a15 | | | | | Token: 0x0a15 |
| | | +------------------------------------+ | | | +------------------------------------+
| | | | | |
| |<---------+ CoAP message (Ver=1, T=Ack, MID=0x8f54) | |<---------+ CoAP message (Ver=1, T=Ack, MID=0x8f54)
| | | +------------------------------------+ | | | +------------------------------------+
skipping to change at page 44, line 9 skipping to change at page 45, line 9
| | | +------------------------------------+ | | | +------------------------------------+
| | | | | |
Figure 21: A CoAP client retrieves the representation of a resource Figure 21: A CoAP client retrieves the representation of a resource
identified by a "coap" URI via a WebSockets-enabled CoAP proxy identified by a "coap" URI via a WebSockets-enabled CoAP proxy
Appendix C. Change Log Appendix C. Change Log
The RFC Editor is requested to remove this section at publication. The RFC Editor is requested to remove this section at publication.
C.1. Since draft-core-coap-tcp-tls-02 C.1. Since draft-ietf-core-coap-tcp-tls-02
Merged draft-savolainen-core-coap-websockets-07 Merged draft-bormann- Merged draft-savolainen-core-coap-websockets-07 Merged draft-bormann-
core-block-bert-01 Merged draft-bormann-core-coap-sig-02 core-block-bert-01 Merged draft-bormann-core-coap-sig-02
C.2. Since draft-core-coap-tcp-tls-03 C.2. Since draft-ietf-core-coap-tcp-tls-03
Editorial updates Editorial updates
Added mandatory exchange of Capabilities and Settings messages after Added mandatory exchange of Capabilities and Settings messages after
connecting connecting
Added support for coaps+tcp port 5684 and more details on Added support for coaps+tcp port 5684 and more details on
Application-Layer Protocol Negotiation (ALPN) Application-Layer Protocol Negotiation (ALPN)
Added guidance on CoAP Signaling Ping-Pong versus WebSocket Ping-Pong Added guidance on CoAP Signaling Ping-Pong versus WebSocket Ping-Pong
Updated references and requirements for TLS security considerations Updated references and requirements for TLS security considerations
C.3. Since draft-core-coap-tcp-tls-04 C.3. Since draft-ietf-core-coap-tcp-tls-04
Updated references Updated references
Added Appendix: Updates to RFC7641 Observing Resources in the Added Appendix: Updates to RFC7641 Observing Resources in the
Constrained Application Protocol (CoAP) Constrained Application Protocol (CoAP)
Updated Capability and Settings Message (CSM) exchange in the Opening Updated Capability and Settings Message (CSM) exchange in the Opening
Handshake to allow initiator to send messages before receiving Handshake to allow initiator to send messages before receiving
acceptor CSM acceptor CSM
C.4. Since draft-core-coap-tcp-tls-05 C.4. Since draft-ietf-core-coap-tcp-tls-05
Addressed feedback from Working Group Last Call Addressed feedback from Working Group Last Call
Added Securing CoAP section and informative reference to OSCOAP Added Securing CoAP section and informative reference to OSCOAP
Removed the Server-Name and Bad-Server-Name Options Removed the Server-Name and Bad-Server-Name Options
Clarified the Capability and Settings Message (CSM) exchange Clarified the Capability and Settings Message (CSM) exchange
Updated Pong response requirements Updated Pong response requirements
Added Connection Initiator and Connection Acceptor terminology where Added Connection Initiator and Connection Acceptor terminology where
appropriate appropriate
Updated LWM2M 1.0 informative reference Updated LWM2M 1.0 informative reference
C.5. Since draft-ietf-core-coap-tcp-tls-06
Addressed feedback from second Working Group Last Call
Acknowledgements Acknowledgements
We would like to thank Stephen Berard, Geoffrey Cristallo, Olivier We would like to thank Stephen Berard, Geoffrey Cristallo, Olivier
Delaby, Christian Groves, Nadir Javed, Michael Koster, Matthias Delaby, Esko Dijk, Christian Groves, Nadir Javed, Michael Koster,
Kovatsch, Achim Kraus, David Navarro, Szymon Sasin, Goran Selander, Matthias Kovatsch, Achim Kraus, David Navarro, Szymon Sasin, Goran
Zach Shelby, Andrew Summers, Julien Vermillard, and Gengyu Wei for Selander, Zach Shelby, Andrew Summers, Julien Vermillard, and Gengyu
their feedback. Wei for their feedback.
Contributors Contributors
Matthias Kovatsch Matthias Kovatsch
Siemens AG Siemens AG
Otto-Hahn-Ring 6 Otto-Hahn-Ring 6
Munich D-81739 Munich D-81739
Phone: +49-173-5288856 Phone: +49-173-5288856
EMail: matthias.kovatsch@siemens.com EMail: matthias.kovatsch@siemens.com
 End of changes. 137 change blocks. 
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