Network Working Group A. Keranen
Internet-Draft Ericsson
Intended status: Standards Track M. Mohajer
Expires: September 6, 2018 u-blox UK
March 5, 2018
Media Types for FETCH & PATCH with Sensor Measurement Lists (SenML)
draft-keranen-core-senml-fetch-00
Abstract
The Sensor Measurement Lists (SenML) media type and data model can be
used to send collections of resources, such as batches of sensor data
or configuration parameters. The CoAP PATCH and FETCH methods enable
accessing and updating parts of a resource or multiple resources with
one request. This document defines two new media types that can be
used with the CoAP PATCH and FETCH methods for resources represented
with the SenML data model.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Media Type Definitions . . . . . . . . . . . . . . . . . . . 3
3.1. SenML FETCH Media Type . . . . . . . . . . . . . . . . . 3
3.1.1. Wild Card Selectors . . . . . . . . . . . . . . . . . 4
3.2. SenML PATCH Media Type . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. CoAP Content-Format Registration . . . . . . . . . . . . 6
5.2. senml-fetch+json Media Type . . . . . . . . . . . . . . . 6
5.3. senml-patch+json Media Type . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The Sensor Measurement Lists (SenML) media type [I-D.ietf-core-senml]
and data model can be used to transmit collections of resources, such
as batches of sensor data or configuration parameters.
Example of a SenML collection is shown below:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850", "vb":true},
{"n":"5851", "v":42},
{"n":"5750", "vs":"Ceiling light"}
]
Here three resources "3306/0/5850", "3306/0/5851", and "3306/0/5750",
of an IPSO dimmable light smart object [IPSO] are represented using a
single SenML Pack with three SenML Records. All resources share the
same base name "2001:db8::2/3306/0/", hence full names for resources
are "2001:db8::2/3306/0/5850", etc.
The CoAP [RFC7252] PATCH and FETCH methods [RFC8132] enable accessing
and updating parts of a resource or multiple resources with one
request.
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This document defines two new media types that can be used with the
CoAP PATCH and FETCH methods with resources represented with the
SenML data model.
2. Terminology
The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT',
'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'MAY', and 'OPTIONAL' in this
specification are to be interpreted as described in [RFC2119].
Readers should also be familiar with the terms and concepts discussed
in [RFC8132] and [I-D.ietf-core-senml]. Also the following terms are
used in this document:
FETCH Record: One set of parameters that is used to match SenML
Record(s). Presented using the SenML data model with extensions
defined in this document.
FETCH Pack: One or more FETCH Records in an array structure.
PATCH Record: One set of parameters similar to FETCH Record but
contains also instructions on how to change existing SenML
Pack(s).
PATCH Pack: One or more PATCH Records in an array structure.
3. Media Type Definitions
The FETCH and PATCH media types for SenML are both modeled as
extensions to the SenML media type to enable re-use of existing SenML
parsers and generators, in particular on constrained devices. Unless
mentioned otherwise, FETCH and PATCH Packs are constructed with the
same rules and constraints as SenML Packs.
3.1. SenML FETCH Media Type
The FETCH media type is used to select and return parts of one or
more SenML Packs. The SenML records are selected by giving the
name(s) of the resources using the SenML "name" and/or "base name"
Fields. The same rules for concatenating the name and base name
Fields apply as for SenML Packs.
For example, to select resources "5850" and "5851" from the example
in Section 1, the following FETCH Pack can be used:
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[
{"bn":"2001:db8::2/3306/0/", "n":"5850"},
{"n":"5851"}
]
The result to a FETCH request with the example above would be:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850", "vb":true},
{"n":"5851", "v":42},
]
When SenML records contain also time values, a name may no longer
uniquely identify a single record. When no time is given in a FETCH
Record, all SenML Records with the given name are be matched. When
time is given in the FETCH Record, only a SenML Record (if any) with
equal time value is matched.
3.1.1. Wild Card Selectors
Multiple SenML Records can be chosen simply by listing all names, and
potentially times, in separate FETCH Records. However, for
efficiency, also wild card operations for selecting multiple SenML
records with a single FETCH Record MAY be supported.
Implementations that do not support wild card operations MUST return
4.00 "Bad Request" when receiving a request with wild cards.
TBD: better response code than 400?
The format for SenML wild card operations is for further study. This
section proposes one possible format for discussion.
SenML names are often split to multiple segments using the "/" and/or
":" characters. For example, "3306/0/5850" contains three segments:
"3306", "0", and "5850".
A new SenML Field, FETCH filter ("ff"), is defined for use with wild
card operations. The filter expression is concatenated to the base
name like the name field. The filter can contain asterisk ("*")
characters that are used to match any set of characters within a
SenML name until the next segment separator ("/" or ":").
TBD: more formal specification of matching rules
For example, the filter expression "3306/0/*" together with the base
name "2001:db8::2/" would match all three Records in the example
SenML Pack from Section 1.
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Note that the "*" character is not a valid character in SenML names.
The "n" and "ff" Fields MUST NOT be used together.
Example of using the filter expression "3306/0/*" in a FETCH Pack is
shown below:
[
{"bn":"2001:db8::2/", "ff":"3306/0/*"}
]
Similarly, when used with the same base name, the filter expression
"*/0/*" would match all the three Records and the filter expression
"*/0/5850" would match only the Record with name "5850".
3.2. SenML PATCH Media Type
The PATCH media type is used to change the values of SenML Records.
The names and times of the Records are given in same way as for the
FETCH media type but PATCH Packs can include also new values and
other SenML Fields for the Records.
For example, the following document could be given as PATCH payload
to change/set values of two SenML Records for the example in
Section 1:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850", "vb":false},
{"n":"5851", "v":10}
]
If the request is successful, the resulting representation of the
example SenML Pack would be as follows:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850", "vb":false},
{"n":"5851", "v":10},
{"n":"5750", "vs":"Ceiling light"}
]
4. Security Considerations
TBD
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5. IANA Considerations
This document registers two new media types, one for the FETCH and
one for the PATCH use, and CoAP Content-Format IDs for both media
types.
5.1. CoAP Content-Format Registration
IANA is requested to assign CoAP Content-Format IDs for the SenML
PATCH and FETCH media types in the "CoAP Content-Formats" sub-
registry, within the "CoRE Parameters" registry [RFC7252]. All IDs
are assigned from the "Expert Review" (0-255) range. The assigned
IDs are show in Table 1.
+------------------------------+-----+
| Media type | ID |
+------------------------------+-----+
| application/senml-patch+json | TBD |
| | |
| application/senml-fetch+json | TBD |
+------------------------------+-----+
Table 1: CoAP Content-Format IDs
5.2. senml-fetch+json Media Type
Type name: application
Subtype name: senml-fetch+json
Required parameters: none
Optional parameters: none
Encoding considerations: Must be encoded as using a subset of the
encoding allowed in [RFC8259]. See RFC-AAAA for details. This
simplifies implementation of very simple system and does not impose
any significant limitations as all this data is meant for machine to
machine communications and is not meant to be human readable.
Security considerations: See Section 4 of RFC-AAAA.
Interoperability considerations: TBD
Published specification: RFC-AAAA
Applications that use this media type: Applications that use the
SenML media type for resource representation.
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Fragment identifier considerations: TBD
Additional information:
Magic number(s): none
File extension(s): senml-fetch-json
Windows Clipboard Name: "SenML fetch format"
Macintosh file type code(s): none
Macintosh Universal Type Identifier code: org.ietf.senml-fetch-json
conforms to public.text
Person & email address to contact for further information: Ari
Keranen ari.keranen@ericsson.com
Intended usage: COMMON
Restrictions on usage: None
Author: Ari Keranen ari.keranen@ericsson.com
Change controller: IESG
5.3. senml-patch+json Media Type
TBD (similar to senml-fetch)
6. Acknowledgements
TBD
7. References
7.1. Normative References
[I-D.ietf-core-senml]
Jennings, C., Shelby, Z., Arkko, J., Keranen, A., and C.
Bormann, "Media Types for Sensor Measurement Lists
(SenML)", draft-ietf-core-senml-13 (work in progress),
March 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997, <https://www.rfc-editor.org/info/
rfc2119>.
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[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, DOI 10.17487/
RFC7252, June 2014, <https://www.rfc-editor.org/info/
rfc7252>.
[RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and
FETCH Methods for the Constrained Application Protocol
(CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017,
<https://www.rfc-editor.org/info/rfc8132>.
[RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259, DOI 10.17487/
RFC8259, December 2017, <https://www.rfc-editor.org/info/
rfc8259>.
7.2. Informative References
[IPSO] IPSO, "IP for Smart Objects - IPSO Objects", 2018,
<https://github.com/IPSO-Alliance/pub>.
Authors' Addresses
Ari Keranen
Ericsson
Email: ari.keranen@ericsson.com
Mojan Mohajer
u-blox UK
Email: Mojan.Mohajer@u-blox.com
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