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2 Network Working Group C. Jennings
3 Internet-Draft Cisco
4 Intended status: Standards Track Z. Shelby
5 Expires: May 4, 2017 ARM
6 J. Arkko
7 A. Keranen
8 Ericsson
9 C. Bormann
10 Universitaet Bremen TZI
11 October 31, 2016
13 Media Types for Sensor Measurement Lists (SenML)
14 draft-ietf-core-senml-04
16 Abstract
18 This specification defines media types for representing simple sensor
19 measurements and device parameters in the Sensor Measurement Lists
20 (SenML). Representations are defined in JavaScript Object Notation
21 (JSON), Concise Binary Object Representation (CBOR), eXtensible
22 Markup Language (XML), and Efficient XML Interchange (EXI), which
23 share the common SenML data model. A simple sensor, such as a
24 temperature sensor, could use this media type in protocols such as
25 HTTP or CoAP to transport the measurements of the sensor or to be
26 configured.
28 Status of This Memo
30 This Internet-Draft is submitted in full conformance with the
31 provisions of BCP 78 and BCP 79.
33 Internet-Drafts are working documents of the Internet Engineering
34 Task Force (IETF). Note that other groups may also distribute
35 working documents as Internet-Drafts. The list of current Internet-
36 Drafts is at http://datatracker.ietf.org/drafts/current/.
38 Internet-Drafts are draft documents valid for a maximum of six months
39 and may be updated, replaced, or obsoleted by other documents at any
40 time. It is inappropriate to use Internet-Drafts as reference
41 material or to cite them other than as "work in progress."
43 This Internet-Draft will expire on May 4, 2017.
45 Copyright Notice
47 Copyright (c) 2016 IETF Trust and the persons identified as the
48 document authors. All rights reserved.
50 This document is subject to BCP 78 and the IETF Trust's Legal
51 Provisions Relating to IETF Documents
52 (http://trustee.ietf.org/license-info) in effect on the date of
53 publication of this document. Please review these documents
54 carefully, as they describe your rights and restrictions with respect
55 to this document. Code Components extracted from this document must
56 include Simplified BSD License text as described in Section 4.e of
57 the Trust Legal Provisions and are provided without warranty as
58 described in the Simplified BSD License.
60 Table of Contents
62 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
63 2. Requirements and Design Goals . . . . . . . . . . . . . . . . 4
64 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
65 4. SenML Structure and Semantics . . . . . . . . . . . . . . . . 5
66 4.1. Base attributes . . . . . . . . . . . . . . . . . . . . . 6
67 4.2. Regular attributes . . . . . . . . . . . . . . . . . . . 6
68 4.3. Considerations . . . . . . . . . . . . . . . . . . . . . 7
69 4.4. Resolved Records . . . . . . . . . . . . . . . . . . . . 8
70 4.5. Associating Meta-data . . . . . . . . . . . . . . . . . . 8
71 5. JSON Representation (application/senml+json) . . . . . . . . 9
72 5.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 10
73 5.1.1. Single Datapoint . . . . . . . . . . . . . . . . . . 10
74 5.1.2. Multiple Datapoints . . . . . . . . . . . . . . . . . 10
75 5.1.3. Multiple Measurements . . . . . . . . . . . . . . . . 11
76 5.1.4. Resolved Data . . . . . . . . . . . . . . . . . . . . 12
77 5.1.5. Multiple Data Types . . . . . . . . . . . . . . . . . 13
78 5.1.6. Collection of Resources . . . . . . . . . . . . . . . 13
79 5.1.7. Setting an Actuator . . . . . . . . . . . . . . . . . 14
80 6. CBOR Representation (application/senml+cbor) . . . . . . . . 15
81 7. XML Representation (application/senml+xml) . . . . . . . . . 17
82 8. EXI Representation (application/senml+exi) . . . . . . . . . 19
83 9. Usage Considerations . . . . . . . . . . . . . . . . . . . . 22
84 10. CDDL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
85 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
86 11.1. Units Registry . . . . . . . . . . . . . . . . . . . . . 25
87 11.2. SenML Label Registry . . . . . . . . . . . . . . . . . . 28
88 11.3. Media Type Registration . . . . . . . . . . . . . . . . 29
89 11.3.1. senml+json Media Type Registration . . . . . . . . . 29
90 11.3.2. senml+cbor Media Type Registration . . . . . . . . . 31
91 11.3.3. senml+xml Media Type Registration . . . . . . . . . 32
92 11.3.4. senml+exi Media Type Registration . . . . . . . . . 33
94 11.4. XML Namespace Registration . . . . . . . . . . . . . . . 34
95 11.5. CoAP Content-Format Registration . . . . . . . . . . . . 34
96 12. Security Considerations . . . . . . . . . . . . . . . . . . . 35
97 13. Privacy Considerations . . . . . . . . . . . . . . . . . . . 35
98 14. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 35
99 15. References . . . . . . . . . . . . . . . . . . . . . . . . . 35
100 15.1. Normative References . . . . . . . . . . . . . . . . . . 35
101 15.2. Informative References . . . . . . . . . . . . . . . . . 37
102 Appendix A. Links Extension . . . . . . . . . . . . . . . . . . 38
103 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 38
105 1. Overview
107 Connecting sensors to the Internet is not new, and there have been
108 many protocols designed to facilitate it. This specification defines
109 new media types for carrying simple sensor information in a protocol
110 such as HTTP or CoAP. This format was designed so that processors
111 with very limited capabilities could easily encode a sensor
112 measurement into the media type, while at the same time a server
113 parsing the data could relatively efficiently collect a large number
114 of sensor measurements. The markup language can be used for a
115 variety of data flow models, most notably data feeds pushed from a
116 sensor to a collector, and the web resource model where the sensor is
117 requested as a resource representation (e.g., "GET /sensor/
118 temperature").
120 There are many types of more complex measurements and measurements
121 that this media type would not be suitable for. SenML strikes a
122 balance between having some information about the sensor carried with
123 the sensor data so that the data is self describing but it also tries
124 to make that a fairly minimal set of auxiliary information for
125 efficiency reason. Other information about the sensor can be
126 discovered by other methods such as using the CoRE Link Format
127 [RFC6690].
129 SenML is defined by a data model for measurements and simple meta-
130 data about measurements and devices. The data is structured as a
131 single array that contains a series of SenML Records which can each
132 contain attributes such as an unique identifier for the sensor, the
133 time the measurement was made, the unit the measurement is in, and
134 the current value of the sensor. Serializations for this data model
135 are defined for JSON [RFC7159], CBOR [RFC7049], XML, and Efficient
136 XML Interchange (EXI) [W3C.REC-exi-20140211].
138 For example, the following shows a measurement from a temperature
139 gauge encoded in the JSON syntax.
141 [
142 {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","v":23.1}
143 ]
145 In the example above, the array has a single SenML Record with a
146 measurement for a sensor named "urn:dev:ow:10e2073a01080063" with a
147 current value of 23.1 degrees Celsius.
149 2. Requirements and Design Goals
151 The design goal is to be able to send simple sensor measurements in
152 small packets on mesh networks from large numbers of constrained
153 devices. Keeping the total size of payload under 80 bytes makes this
154 easy to use on a wireless mesh network. It is always difficult to
155 define what small code is, but there is a desire to be able to
156 implement this in roughly 1 KB of flash on a 8 bit microprocessor.
157 Experience with Google power meter and large scale deployments has
158 indicated that the solution needs to support allowing multiple
159 measurements to be batched into a single HTTP or CoAP request. This
160 "batch" upload capability allows the server side to efficiently
161 support a large number of devices. It also conveniently supports
162 batch transfers from proxies and storage devices, even in situations
163 where the sensor itself sends just a single data item at a time. The
164 multiple measurements could be from multiple related sensors or from
165 the same sensor but at different times.
167 The basic design is an array with a series of measurements. The
168 following example shows two measurements made at different times.
169 The value of a measurement is in the "v" tag, the time of a
170 measurement is in the "t" tag, the "n" tag has a unique sensor name,
171 and the unit of the measurement is carried in the "u" tag.
173 [
174 {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020076e+09,
175 "v":23.5},
176 {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020091e+09,
177 "v":23.6}
178 ]
180 To keep the messages small, it does not make sense to repeat the "n"
181 tag in each SenML Record so there is a concept of a Base Name which
182 is simply a string that is prepended to the Name field of all
183 elements in that record and any records that follow it. So a more
184 compact form of the example above is the following.
186 [
187 {"bn":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020076e+09,
188 "v":23.5},
189 {"u":"Cel","t":1.276020091e+09,
190 "v":23.6}
191 ]
193 In the above example the Base Name is in the "bn" tag and the "n"
194 tags in each Record are the empty string so they are omitted.
196 Some devices have accurate time while others do not so SenML supports
197 absolute and relative times. Time is represented in floating point
198 as seconds and values greater than zero represent an absolute time
199 relative to the Unix epoch while values of 0 or less represent a
200 relative time in the past from the current time. A simple sensor
201 with no absolute wall clock time might take a measurement every
202 second and batch up 60 of them then send it to a server. It would
203 include the relative time the measurement was made to the time the
204 batch was send in the SenML Pack. The server might have accurate NTP
205 time and use the time it received the data, and the relative offset,
206 to replace the times in the SenML with absolute times before saving
207 the SenML Pack in a document database.
209 3. Terminology
211 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
212 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
213 "OPTIONAL" in this document are to be interpreted as described in
214 [RFC2119].
216 This document also uses the following terms:
218 SenML Record: One measurement or configuration instance in time
219 presented using the SenML data model.
221 SenML Pack: One or more SenML Records in an array structure.
223 4. SenML Structure and Semantics
225 Each SenML Pack carries a single array that represents a set of
226 measurements and/or parameters. This array contains a series of
227 SenML Records with several attributes described below. There are two
228 kind of attributes: base and regular. The base attributes can only
229 be included in the first SenML Record and they apply to the entries
230 in all Records. All base attributes are optional. Regular
231 attributes can be included in any SenML Record and apply only to that
232 Record.
234 4.1. Base attributes
236 Base Name: This is a string that is prepended to the names found in
237 the entries.
239 Base Time: A base time that is added to the time found in an entry.
241 Base Unit: A base unit that is assumed for all entries, unless
242 otherwise indicated. If a record does not contain a Unit value,
243 then the Base Unit is used. Otherwise the value found in the Unit
244 (if any) is used.
246 Base Value: A base value is added to the value found in an entry,
247 similar to Base Time.
249 Base Sum: A base sum is added to the sum found in an entry, similar
250 to Base Time.
252 Version: Version number of media type format. This attribute is an
253 optional positive integer and defaults to 5 if not present. [RFC
254 Editor: change the default value to 10 when this specification is
255 published as an RFC and remove this note]
257 4.2. Regular attributes
259 Name: Name of the sensor or parameter. When appended to the Base
260 Name attribute, this must result in a globally unique identifier
261 for the resource. The name is optional, if the Base Name is
262 present. If the name is missing, Base Name must uniquely identify
263 the resource. This can be used to represent a large array of
264 measurements from the same sensor without having to repeat its
265 identifier on every measurement.
267 Unit: Units for a measurement value. Optional. If the Record has
268 no Unit, the Base Unit is used as the Unit. Having no Unit and no
269 Base Unit is allowed.
271 Value Value of the entry. Optional if a Sum value is present,
272 otherwise required. Values are represented using basic data
273 types. This specification defines floating point numbers ("v"
274 field for "Value"), booleans ("vb" for "Boolean Value"), strings
275 ("vs" for "String Value") and binary data ("vd" for "Data Value").
276 Exactly one value field MUST appear unless there is Sum field in
277 which case it is allowed to have no Value field.
279 Sum: Integrated sum of the values over time. Optional. This
280 attribute is in the units specified in the Unit value multiplied
281 by seconds.
283 Time: Time when value was recorded. Optional.
285 Update Time: An optional time in seconds that represents the maximum
286 time before this sensor will provide an updated reading for a
287 measurement. This can be used to detect the failure of sensors or
288 communications path from the sensor.
290 4.3. Considerations
292 The SenML format can be extended with further custom attributes.
293 Both new base and regular attributes are allowed. See Section 11.2
294 for details. Implementations MUST ignore attributes they don't
295 recognize.
297 Systems reading one of the objects MUST check for the Version
298 attribute. If this value is a version number larger than the version
299 which the system understands, the system SHOULD NOT use this object.
300 This allows the version number to indicate that the object contains
301 mandatory to understand attributes. New version numbers can only be
302 defined in an RFC that updates this specification or it successors.
304 The Name value is concatenated to the Base Name value to get the name
305 of the sensor. The resulting name needs to uniquely identify and
306 differentiate the sensor from all others. If the object is a
307 representation resulting from the request of a URI [RFC3986], then in
308 the absence of the Base Name attribute, this URI is used as the
309 default value of Base Name. Thus in this case the Name field needs
310 to be unique for that URI, for example an index or subresource name
311 of sensors handled by the URI.
313 Alternatively, for objects not related to a URI, a unique name is
314 required. In any case, it is RECOMMENDED that the full names are
315 represented as URIs or URNs [RFC2141]. One way to create a unique
316 name is to include some bit string that has guaranteed uniqueness
317 (such as a 1-wire address) that is assigned to the device. Some of
318 the examples in this draft use the device URN type as specified in
319 [I-D.arkko-core-dev-urn]. UUIDs [RFC4122] are another way to
320 generate a unique name. Note that long-term stable unique
321 identifiers are problematic for privacy reasons [RFC7721] and should
322 be used with care or avoided.
324 The resulting concatenated name MUST consist only of characters out
325 of the set "A" to "Z", "a" to "z", "0" to "9", "-", ":", ".", or "_"
326 and it MUST start with a character out of the set "A" to "Z", "a" to
327 "z", or "0" to "9". This restricted character set was chosen so that
328 these names can be directly used as in other types of URI including
329 segments of an HTTP path with no special encoding and can be directly
330 used in many databases and analytic systems. [RFC5952] contains
331 advice on encoding an IPv6 address in a name.
333 If either the Base Time or Time value is missing, the missing
334 attribute is considered to have a value of zero. The Base Time and
335 Time values are added together to get the time of measurement. A
336 time of zero indicates that the sensor does not know the absolute
337 time and the measurement was made roughly "now". A negative value is
338 used to indicate seconds in the past from roughly "now". A positive
339 value is used to indicate the number of seconds, excluding leap
340 seconds, since the start of the year 1970 in UTC.
342 If only one of the Base Sum or Sum value is present, the missing
343 attribute is considered to have a value of zero. The Base Sum and
344 Sum values are added together to get the sum of measurement. If
345 neither the Base Sum or Sum are present, then the measurement does
346 not have a sum value.
348 Representing the statistical characteristics of measurements, such as
349 accuracy, can be very complex. Future specification may add new
350 attributes to provide better information about the statistical
351 properties of the measurement.
353 4.4. Resolved Records
355 Sometimes it is useful to be able to refer to a defined normalized
356 format for SenML records. This normalized format tends to get used
357 for big data applications and intermediate forms when converting to
358 other formats.
360 A SenML Record is referred to as "resolved" if it does not contain
361 any base values and has no relative times, but the base values of the
362 SenML Pack (if any) are applied to the Record. That is, name and
363 base name are concatenated, base time is added to the time of the
364 Record, if the Record did not contain Unit the Base Unit is applied
365 to the record, etc. In addition the records need to be in
366 chronological order. An example of this is show in Section 5.1.4.
368 Future specification that defines new base attributes need to specify
369 how the attribute is resolved.
371 4.5. Associating Meta-data
373 SenML is designed to carry the minimum dynamic information about
374 measurements, and for efficiency reasons does not carry significant
375 static meta-data about the device, object or sensors. Instead, it is
376 assumed that this meta-data is carried out of band. For web
377 resources using SenML Packs, this meta-data can be made available
378 using the CoRE Link Format [RFC6690]. The most obvious use of this
379 link format is to describe that a resource is available in a SenML
380 format in the first place. The relevant media type indicator is
381 included in the Content-Type (ct=) attribute.
383 5. JSON Representation (application/senml+json)
385 The SenML labels (JSON object member names) shown in Table 1 are used
386 in JSON SenML Record attributes.
388 +---------------+-------+---------+
389 | Name | label | Type |
390 +---------------+-------+---------+
391 | Base Name | bn | String |
392 | Base Time | bt | Number |
393 | Base Unit | bu | String |
394 | Base Value | bv | Number |
395 | Base Sum | bs | Number |
396 | Version | bver | Number |
397 | Name | n | String |
398 | Unit | u | String |
399 | Value | v | Number |
400 | String Value | vs | String |
401 | Boolean Value | vb | Boolean |
402 | Data Value | vd | String |
403 | Value Sum | s | Number |
404 | Time | t | Number |
405 | Update Time | ut | Number |
406 | Link | l | String |
407 +---------------+-------+---------+
409 Table 1: JSON SenML Labels
411 The root content consists of an array with one JSON object for each
412 SenML Record. All the fields in the above table MAY occur in the
413 records with the type specified in the table.
415 Only the UTF-8 form of JSON is allowed. Characters in the String
416 Value are encoded using the escape sequences defined in [RFC7159].
417 Octets in the Data Value are base64 encoded with URL safe alphabet as
418 defined in Section 5 of [RFC4648].
420 Systems receiving measurements MUST be able to process the range of
421 floating point numbers that are representable as an IEEE double
422 precision floating point numbers [IEEE.754.1985]. The number of
423 significant digits in any measurement is not relevant, so a reading
424 of 1.1 has exactly the same semantic meaning as 1.10. If the value
425 has an exponent, the "e" MUST be in lower case. The mantissa SHOULD
426 be less than 19 characters long and the exponent SHOULD be less than
427 5 characters long. This allows time values to have better than micro
428 second precision over the next 100 years.
430 5.1. Examples
432 5.1.1. Single Datapoint
434 The following shows a temperature reading taken approximately "now"
435 by a 1-wire sensor device that was assigned the unique 1-wire address
436 of 10e2073a01080063:
438 [
439 {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","v":23.1}
440 ]
442 5.1.2. Multiple Datapoints
444 The following example shows voltage and current now, i.e., at an
445 unspecified time.
447 [
448 {"bn":"urn:dev:ow:10e2073a01080063;","n":"voltage","u":"V","v":120.1},
449 {"n":"current","u":"A","v":1.2}
450 ]
452 The next example is similar to the above one, but shows current at
453 Tue Jun 8 18:01:16.001 UTC 2010 and at each second for the previous 5
454 seconds.
456 [
457 {"bn":"urn:dev:ow:10e2073a0108006;","bt":1.276020076001e+09,
458 "bu":"A","bver":5,
459 "n":"voltage","u":"V","v":120.1},
460 {"n":"current","t":-5,"v":1.2},
461 {"n":"current","t":-4,"v":1.3},
462 {"n":"current","t":-3,"v":1.4},
463 {"n":"current","t":-2,"v":1.5},
464 {"n":"current","t":-1,"v":1.6},
465 {"n":"current","v":1.7}
466 ]
468 Note that in some usage scenarios of SenML the implementations MAY
469 store or transmit SenML in a stream-like fashion, where data is
470 collected over time and continuously added to the object. This mode
471 of operation is optional, but systems or protocols using SenML in
472 this fashion MUST specify that they are doing this. SenML defines a
473 separate media type to indicate Sensor Streaming Measurement Lists
474 (SensML) for this usage (see Section 11.3.1). In this situation the
475 SensML stream can be sent and received in a partial fashion, i.e., a
476 measurement entry can be read as soon as the SenML Record is received
477 and not have to wait for the full SensML Stream to be complete.
479 For instance, the following stream of measurements may be sent via a
480 long lived HTTP POST from the producer of a SensML to the consumer of
481 that, and each measurement object may be reported at the time it was
482 measured:
484 [
485 {"bn":"urn:dev:ow:10e2073a01080063","bt":1.320067464e+09,
486 "bu":"%RH","v":21.2},
487 {"t":10,"v":21.3},
488 {"t":20,"v":21.4},
489 {"t":30,"v":21.4},
490 {"t":40,"v":21.5},
491 {"t":50,"v":21.5},
492 {"t":60,"v":21.5},
493 {"t":70,"v":21.6},
494 {"t":80,"v":21.7},
495 ...
497 5.1.3. Multiple Measurements
499 The following example shows humidity measurements from a mobile
500 device with a 1-wire address 10e2073a01080063, starting at Mon Oct 31
501 13:24:24 UTC 2011. The device also provides position data, which is
502 provided in the same measurement or parameter array as separate
503 entries. Note time is used to for correlating data that belongs
504 together, e.g., a measurement and a parameter associated with it.
505 Finally, the device also reports extra data about its battery status
506 at a separate time.
508 [
509 {"bn":"urn:dev:ow:10e2073a01080063","bt":1.320067464e+09,
510 "bu":"%RH","v":20},
511 {"u":"lon","v":24.30621},
512 {"u":"lat","v":60.07965},
513 {"t":60,"v":20.3},
514 {"u":"lon","t":60,"v":24.30622},
515 {"u":"lat","t":60,"v":60.07965},
516 {"t":120,"v":20.7},
517 {"u":"lon","t":120,"v":24.30623},
518 {"u":"lat","t":120,"v":60.07966},
519 {"u":"%EL","t":150,"v":98},
520 {"t":180,"v":21.2},
521 {"u":"lon","t":180,"v":24.30628},
522 {"u":"lat","t":180,"v":60.07967}
523 ]
525 The size of this example represented in various forms, as well as
526 that form compressed with gzip is given in the following table.
528 +----------+------+-----------------+
529 | Encoding | Size | Compressed Size |
530 +----------+------+-----------------+
531 | JSON | 573 | 206 |
532 | XML | 649 | 235 |
533 | CBOR | 254 | 196 |
534 | EXI | 174 | 197 |
535 +----------+------+-----------------+
537 Table 2: Size Comparisons
539 Note the EXI sizes are not using the schema guidance so the EXI
540 representation could be a bit smaller.
542 5.1.4. Resolved Data
544 The following shows the example from the previous section show in
545 resolved format.
547 [
548 {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067464e+09,
549 "v":20},
550 {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067464e+09,
551 "v":24.30621},
552 {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067464e+09,
553 "v":60.07965},
554 {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067524e+09,
555 "v":20.3},
556 {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067524e+09,
557 "v":24.30622},
558 {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067524e+09,
559 "v":60.07965},
560 {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067584e+09,
561 "v":20.7},
562 {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067584e+09,
563 "v":24.30623},
564 {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067584e+09,
565 "v":60.07966},
566 {"n":"urn:dev:ow:10e2073a01080063","u":"%EL","t":1.320067614e+09,
567 "v":98},
568 {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067644e+09,
569 "v":21.2},
570 {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067644e+09,
571 "v":24.30628},
572 {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067644e+09,
573 "v":60.07967}
574 ]
576 5.1.5. Multiple Data Types
578 The following example shows a sensor that returns different data
579 types.
581 [
582 {"bn":"urn:dev:ow:10e2073a01080063;","n":"temp","u":"Cel","v":23.1},
583 {"n":"label","vs":"Machine Room"},
584 {"n":"open","vb":false},
585 {"n":"nfv-reader","vd":"aGkgCg=="}
586 ]
588 5.1.6. Collection of Resources
590 The following example shows how to query one device that can provide
591 multiple measurements. The example assumes that a client has fetched
592 information from a device at 2001:db8::2 by performing a GET
593 operation on http://[2001:db8::2] at Mon Oct 31 16:27:09 UTC 2011,
594 and has gotten two separate values as a result, a temperature and
595 humidity measurement.
597 [
598 {"bn":"http://[2001:db8::2]/","bt":1.320078429e+09,
599 "n":"temperature","u":"Cel","v":27.2},
600 {"n":"humidity","u":"%RH","v":80}
601 ]
603 5.1.7. Setting an Actuator
605 The following example show the SenML that could be used to set the
606 current set point of a typical residential thermostat which has a
607 temperature set point, a switch to turn on and off the heat, and a
608 switch to turn on the fan override.
610 [
611 {"bn":"urn:dev:ow:10e2073a01080063;"},
612 {"n":"temp","u":"Cel","v":23.1},
613 {"n":"heat","u":"/","v":1},
614 {"n":"fan","u":"/","v":0}
615 ]
617 In the following example two different lights are turned on. It is
618 assumed that the lights are on a 802.1BA network that can guarantee
619 delivery of the messages to the two lights within 15 ms and uses
620 802.1AS for time synchronization. The controller has set the time of
621 the lights coming on to 20 ms in the future from the current time.
622 This allows both lights to receive the message, wait till that time,
623 then apply the switch command so that both lights come on at the same
624 time.
626 [
627 {"bt":1.320078429e+09,"bu":"/","n":"http://[2001:db8::3]/","v":1},
628 {"n":"http://[2001:db8::4]/","v":1}
629 ]
631 The following shows two lights being turned off using a non
632 deterministic network that has a high odds of delivering a message in
633 less than 100 ms and uses NTP for time synchronization. The current
634 time is 1320078429. The user has just turned off a light switch
635 which is turning off two lights. Both lights are dimmed to 50%
636 brightness immediately to give the user instant feedback that
637 something is changing. However given the network, the lights will
638 probably dim at somewhat different times. Then 100 ms in the future,
639 both lights will go off at the same time. The instant but not
640 synchronized dimming gives the user the sensation of quick responses
641 and the timed off 100 ms in the future gives the perception of both
642 lights going off at the same time.
644 [
645 {"bt":1.320078429e+09,"bu":"/","n":"http://[2001:db8::3]/","v":0.5},
646 {"n":"http://[2001:db8::4]/","v":0.5},
647 {"n":"http://[2001:db8::3]/","t":0.1,"v":0},
648 {"n":"http://[2001:db8::4]/","t":0.1,"v":0}
649 ]
651 6. CBOR Representation (application/senml+cbor)
653 The CBOR [RFC7049] representation is equivalent to the JSON
654 representation, with the following changes:
656 o For JSON Numbers, the CBOR representation can use integers,
657 floating point numbers, or decimal fractions (CBOR Tag 4); however
658 a representation SHOULD be chosen such that when the CBOR value is
659 converted back to an IEEE double precision floating point value,
660 it has exactly the same value as the original Number. For the
661 version number, only an unsigned integer is allowed.
663 o Characters in the String Value are encoded using a definite length
664 text string (type 3). Octets in the Data Value are encoded using
665 a definite length byte string (type 2) .
667 o For compactness, the CBOR representation uses integers for the map
668 keys defined in Table 3. This table is conclusive, i.e., there is
669 no intention to define any additional integer map keys; any
670 extensions will use string map keys. This allows translators
671 converting between CBOR and JSON representations to convert also
672 all future labels without needing to update implementations.
674 +---------------+-------+------------+
675 | Name | Label | CBOR Label |
676 +---------------+-------+------------+
677 | Version | bver | -1 |
678 | Base Name | bn | -2 |
679 | Base Time | bt | -3 |
680 | Base Units | bu | -4 |
681 | Base Value | bv | -5 |
682 | Base Sum | bs | -6 |
683 | Name | n | 0 |
684 | Units | u | 1 |
685 | Value | v | 2 |
686 | String Value | vs | 3 |
687 | Boolean Value | vb | 4 |
688 | Value Sum | s | 5 |
689 | Time | t | 6 |
690 | Update Time | ut | 7 |
691 | Data Value | vd | 8 |
692 | Link | l | 9 |
693 +---------------+-------+------------+
695 Table 3: CBOR representation: integers for map keys
697 o For streaming SensML in CBOR representation, the array containing
698 the records SHOULD be an CBOR indefinite length array while for
699 non streaming SenML, a definite length array MUST be used.
701 The following example shows a dump of the CBOR example for the same
702 sensor measurement as in Section 5.1.2.
704 0000 87 a7 21 78 1b 75 72 6e 3a 64 65 76 3a 6f 77 3a |..!x.urn:dev:ow:|
705 0010 31 30 65 32 30 37 33 61 30 31 30 38 30 30 36 3b |10e2073a0108006;|
706 0020 22 fb 41 d3 03 a1 5b 00 10 62 23 61 41 20 05 00 |".A...[..b#aA ..|
707 0030 67 76 6f 6c 74 61 67 65 01 61 56 02 fb 40 5e 06 |gvoltage.aV..@^.|
708 0040 66 66 66 66 66 a3 00 67 63 75 72 72 65 6e 74 06 |fffff..gcurrent.|
709 0050 24 02 fb 3f f3 33 33 33 33 33 33 a3 00 67 63 75 |$..?.333333..gcu|
710 0060 72 72 65 6e 74 06 23 02 fb 3f f4 cc cc cc cc cc |rrent.#..?......|
711 0070 cd a3 00 67 63 75 72 72 65 6e 74 06 22 02 fb 3f |...gcurrent."..?|
712 0080 f6 66 66 66 66 66 66 a3 00 67 63 75 72 72 65 6e |.ffffff..gcurren|
713 0090 74 06 21 02 f9 3e 00 a3 00 67 63 75 72 72 65 6e |t.!..>...gcurren|
714 00a0 74 06 20 02 fb 3f f9 99 99 99 99 99 9a a3 00 67 |t. ..?.........g|
715 00b0 63 75 72 72 65 6e 74 06 00 02 fb 3f fb 33 33 33 |current....?.333|
716 00c0 33 33 33 |333|
717 00c3
719 7. XML Representation (application/senml+xml)
721 A SenML Pack or Stream can also be represented in XML format as
722 defined in this section.
724 Only the UTF-8 form of XML is allowed. Characters in the String
725 Value are encoded using the escape sequences defined in [RFC7159].
726 Octets in the Data Value are base64 encoded with URL safe alphabet as
727 defined in Section 5 of [RFC4648].
729 The following example shows an XML example for the same sensor
730 measurement as in Section 5.1.2.
732
733
735
736
737
738
739
740
741
743 The SenML Stream is represented as a sensml tag that contains a
744 series of senml tags for each SenML Record. The SenML Fields are
745 represents as XML attributes. The following table shows the mapping
746 of the SenML labels, which are used for the attribute name, to the
747 attribute types used in the XML senml tags.
749 +---------------+-------+---------+
750 | Name | Label | Type |
751 +---------------+-------+---------+
752 | Base Name | bn | string |
753 | Base Time | bt | double |
754 | Base Unit | bu | string |
755 | Base Value | bv | double |
756 | Base Sum | bs | double |
757 | Base Version | bver | int |
758 | Name | n | string |
759 | Unit | u | string |
760 | Value | v | double |
761 | String Value | vs | string |
762 | Data Value | vd | string |
763 | Boolean Value | vb | boolean |
764 | Value Sum | s | double |
765 | Time | t | double |
766 | Update Time | ut | double |
767 | Link | l | string |
768 +---------------+-------+---------+
770 Table 4: XML SenML Labels
772 The RelaxNG schema for the XML is:
774 default namespace = "urn:ietf:params:xml:ns:senml"
775 namespace rng = "http://relaxng.org/ns/structure/1.0"
777 senml = element senml {
778 attribute bn { xsd:string }?,
779 attribute bt { xsd:double }?,
780 attribute bv { xsd:double }?,
781 attribute bs { xsd:double }?,
782 attribute bu { xsd:string }?,
783 attribute bver { xsd:int }?,
785 attribute l { xsd:string }?,
787 attribute n { xsd:string }?,
788 attribute s { xsd:double }?,
789 attribute t { xsd:double }?,
790 attribute u { xsd:string }?,
791 attribute ut { xsd:double }?,
793 attribute v { xsd:double }?,
794 attribute vb { xsd:boolean }?,
795 attribute vs { xsd:string }?,
796 attribute vd { xsd:string }?
797 }
799 sensml =
800 element sensml {
801 senml+
802 }
804 start = sensml
806 8. EXI Representation (application/senml+exi)
808 For efficient transmission of SenML over e.g. a constrained network,
809 Efficient XML Interchange (EXI) can be used. This encodes the XML
810 Schema structure of SenML into binary tags and values rather than
811 ASCII text. An EXI representation of SenML SHOULD be made using the
812 strict schema-mode of EXI. This mode however does not allow tag
813 extensions to the schema, and therefore any extensions will be lost
814 in the encoding. For uses where extensions need to be preserved in
815 EXI, the non-strict schema mode of EXI MAY be used.
817 The EXI header option MUST be included. An EXI schemaID options MUST
818 be set to the value of "a" indicating the scheme provided in this
819 specification. Future revisions to the schema can change this
820 schemaID to allow for backwards compatibility. When the data will be
821 transported over CoAP or HTTP, an EXI Cookie SHOULD NOT be used as it
822 simply makes things larger and is redundant to information provided
823 in the Content-Type header.
825 The following is the XSD Schema to be used for strict schema guided
826 EXI processing. It is generated from the RelaxNG.
828
829
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
862 The following shows a hexdump of the EXI produced from encoding the
863 following XML example. Note this example is the same information as
864 the first example in Section 5.1.2 in JSON format.
866
867
869
870
872 Which compresses with EXI to the following displayed in hexdump:
874 0000 a0 30 3d cd 95 b9 b5 b0 b9 9d 95 b8 b9 e1 cd 90 |.0=.............|
875 0010 80 79 d5 c9 b8 e9 91 95 d8 e9 bd dc e8 c4 c1 94 |.y..............|
876 0020 c8 c0 dc cd 84 c0 c4 c0 e0 c0 c0 d8 cc ed 82 5d |...............]|
877 0030 9b db 1d 18 59 d9 48 0d 58 ac 42 60 18 e1 2c 6e |....Y.H.X.B`..,n|
878 0040 ae 4e 4c ad ce 84 06 82 41 90 0e |.NL.....A..|
879 004b
881 The above example used the bit packed form of EXI but it is also
882 possible to use a byte packed form of EXI which can makes it easier
883 for a simple sensor to produce valid EXI without really implementing
884 EXI. Consider the example of a temperature sensor that produces a
885 value in tenths of degrees Celsius over a range of 0.0 to 55.0. It
886 would produce an XML SenML file such as:
888
889
890
892 The compressed form, using the byte alignment option of EXI, for the
893 above XML is the following:
895 0000 a0 00 48 81 ee 6c ad cd ad 85 cc ec ad c5 cf 0e |..H..l..........|
896 0010 6c 80 01 07 1d 75 72 6e 3a 64 65 76 3a 6f 77 3a |l....urn:dev:ow:|
897 0020 31 30 65 32 30 37 33 61 30 31 30 38 30 30 36 33 |10e2073a01080063|
898 0030 02 05 43 65 6c 01 00 e7 01 01 00 03 01 |..Cel........|
899 003d
901 A small temperature sensor devices that only generates this one EXI
902 file does not really need an full EXI implementation. It can simply
903 hard code the output replacing the 1-wire device ID starting at byte
904 0x20 and going to byte 0x2F with it's device ID, and replacing the
905 value "0xe7 0x01" at location 0x37 and 0x38 with the current
906 temperature. The EXI Specification [W3C.REC-exi-20140211] contains
907 the full information 'on how floating point numbers are represented,
908 but for the purpose of this sensor, the temperature can be converted
909 to an integer in tenths of degrees (231 in this example). EXI stores
910 7 bits of the integer in each byte with the top bit set to one if
911 there are further bytes. So the first bytes at is set to low 7 bits
912 of the integer temperature in tenths of degrees plus 0x80. In this
913 example 231 & 0x7F + 0x80 = 0xE7. The second byte is set to the
914 integer temperature in tenths of degrees right shifted 7 bits. In
915 this example 231 >> 7 = 0x01.
917 9. Usage Considerations
919 The measurements support sending both the current value of a sensor
920 as well as the an integrated sum. For many types of measurements,
921 the sum is more useful than the current value. For example, an
922 electrical meter that measures the energy a given computer uses will
923 typically want to measure the cumulative amount of energy used. This
924 is less prone to error than reporting the power each second and
925 trying to have something on the server side sum together all the
926 power measurements. If the network between the sensor and the meter
927 goes down over some period of time, when it comes back up, the
928 cumulative sum helps reflect what happened while the network was
929 down. A meter like this would typically report a measurement with
930 the units set to watts, but it would put the sum of energy used in
931 the "s" attribute of the measurement. It might optionally include
932 the current power in the "v" attribute.
934 While the benefit of using the integrated sum is fairly clear for
935 measurements like power and energy, it is less obvious for something
936 like temperature. Reporting the sum of the temperature makes it easy
937 to compute averages even when the individual temperature values are
938 not reported frequently enough to compute accurate averages.
939 Implementors are encouraged to report the cumulative sum as well as
940 the raw value of a given sensor.
942 Applications that use the cumulative sum values need to understand
943 they are very loosely defined by this specification, and depending on
944 the particular sensor implementation may behave in unexpected ways.
945 Applications should be able to deal with the following issues:
947 1. Many sensors will allow the cumulative sums to "wrap" back to
948 zero after the value gets sufficiently large.
950 2. Some sensors will reset the cumulative sum back to zero when the
951 device is reset, loses power, or is replaced with a different
952 sensor.
954 3. Applications cannot make assumptions about when the device
955 started accumulating values into the sum.
957 Typically applications can make some assumptions about specific
958 sensors that will allow them to deal with these problems. A common
959 assumption is that for sensors whose measurement values are always
960 positive, the sum should never get smaller; so if the sum does get
961 smaller, the application will know that one of the situations listed
962 above has happened.
964 10. CDDL
966 For reference, the JSON and CBOR representations can be described
967 with the common CDDL [I-D.greevenbosch-appsawg-cbor-cddl]
968 specification in Figure 1.
970 SenML-Pack = [initial-record, * follow-on-record]
972 initial-record = initial-defined .and initial-generic
973 follow-on-record = follow-on-defined .and follow-on-generic
975 ; first do a specification of the labels as defined:
977 initial-defined = {
978 ? bn => tstr, ; Base Name
979 ? bt => numeric, ; Base Time
980 ? bu => tstr, ; Base Units
981 ? bv => numeric, ; Base value
982 ? bver => uint, ; Base Version
983 follow-on-defined-group,
984 + base-key-value-pair
985 }
987 follow-on-defined-group = (
988 ? n => tstr, ; Name
989 ? u => tstr, ; Units
990 ? s => numeric, ; Value Sum
991 ? t => numeric, ; Time
992 ? ut => numeric, ; Update Time
993 * key-value-pair,
994 ? ( v => numeric // ; Numeric Value
995 vs => tstr // ; String Value
996 vb => bool // ; Boolean Value
997 vd => binary-value ) ; Data Value
998 )
999 follow-on-defined = { follow-on-defined-group }
1001 ; now define the generic versions
1003 initial-generic = {
1004 follow-on-generic-group,
1005 * base-key-value-pair,
1006 }
1008 follow-on-generic-group = (
1009 + key-value-pair,
1010 )
1011 follow-on-generic = { follow-on-generic-group }
1013 key-value-pair = ( non-b-label => value )
1015 base-key-value-pair = ( b-label => value )
1017 non-b-label = tstr .regexp "[A-Zac-z0-9][-_:.A-Za-z0-9]*" / uint
1018 b-label = tstr .regexp "b[-_:.A-Za-z0-9]+" / nint
1020 value = tstr / binary-value / numeric / bool
1021 numeric = number / decfrac
1023 Figure 1: Common CDDL specification for CBOR and JSON SenML
1025 For JSON, we use text labels and base64url-encoded binary data
1026 (Figure 2).
1028 bver = "bver" n = "n" s = "s"
1029 bn = "bn" u = "u" t = "t"
1030 bt = "bt" v = "v" ut = "ut"
1031 bu = "bu" vs = "vs" vd = "vd"
1032 bv = "bv" vb = "vb" l = "l"
1034 binary-value = tstr ; base64url encoded
1036 Figure 2: JSON-specific CDDL specification for SenML
1038 For CBOR, we use integer labels and native binary data (Figure 3).
1040 bver = -1 n = 0 s = 5
1041 bn = -2 u = 1 t = 6
1042 bt = -3 v = 2 ut = 7
1043 bu = -4 vs = 3 vd = 8
1044 bv = -5 vb = 4 l = 9
1046 binary-value = bstr
1048 Figure 3: CBOR-specific CDDL specification for SenML
1050 11. IANA Considerations
1052 Note to RFC Editor: Please replace all occurrences of "RFC-AAAA" with
1053 the RFC number of this specification.
1055 11.1. Units Registry
1057 IANA will create a registry of SenML unit symbols. The primary
1058 purpose of this registry is to make sure that symbols uniquely map to
1059 give type of measurement. Definitions for many of these units can be
1060 found in location such as [NIST811] and [BIPM]. Units marked with an
1061 asterisk are NOT RECOMMENDED to be produced by new implementations,
1062 but are in active use and SHOULD be implemented by consumers that can
1063 use the related base units.
1065 +----------+------------------------------------+-------+-----------+
1066 | Symbol | Description | Type | Reference |
1067 +----------+------------------------------------+-------+-----------+
1068 | m | meter | float | RFC-AAAA |
1069 | kg | kilogram | float | RFC-AAAA |
1070 | g | gram* | float | RFC-AAAA |
1071 | s | second | float | RFC-AAAA |
1072 | A | ampere | float | RFC-AAAA |
1073 | K | kelvin | float | RFC-AAAA |
1074 | cd | candela | float | RFC-AAAA |
1075 | mol | mole | float | RFC-AAAA |
1076 | Hz | hertz | float | RFC-AAAA |
1077 | rad | radian | float | RFC-AAAA |
1078 | sr | steradian | float | RFC-AAAA |
1079 | N | newton | float | RFC-AAAA |
1080 | Pa | pascal | float | RFC-AAAA |
1081 | J | joule | float | RFC-AAAA |
1082 | W | watt | float | RFC-AAAA |
1083 | C | coulomb | float | RFC-AAAA |
1084 | V | volt | float | RFC-AAAA |
1085 | F | farad | float | RFC-AAAA |
1086 | Ohm | ohm | float | RFC-AAAA |
1087 | S | siemens | float | RFC-AAAA |
1088 | Wb | weber | float | RFC-AAAA |
1089 | T | tesla | float | RFC-AAAA |
1090 | H | henry | float | RFC-AAAA |
1091 | Cel | degrees Celsius | float | RFC-AAAA |
1092 | lm | lumen | float | RFC-AAAA |
1093 | lx | lux | float | RFC-AAAA |
1094 | Bq | becquerel | float | RFC-AAAA |
1095 | Gy | gray | float | RFC-AAAA |
1096 | Sv | sievert | float | RFC-AAAA |
1097 | kat | katal | float | RFC-AAAA |
1098 | m2 | square meter (area) | float | RFC-AAAA |
1099 | m3 | cubic meter (volume) | float | RFC-AAAA |
1100 | l | liter (volume)* | float | RFC-AAAA |
1101 | m/s | meter per second (velocity) | float | RFC-AAAA |
1102 | m/s2 | meter per square second | float | RFC-AAAA |
1103 | | (acceleration) | | |
1104 | m3/s | cubic meter per second (flow rate) | float | RFC-AAAA |
1105 | l/s | liter per second (flow rate)* | float | RFC-AAAA |
1106 | W/m2 | watt per square meter (irradiance) | float | RFC-AAAA |
1107 | cd/m2 | candela per square meter | float | RFC-AAAA |
1108 | | (luminance) | | |
1109 | bit | bit (information content) | float | RFC-AAAA |
1110 | bit/s | bit per second (data rate) | float | RFC-AAAA |
1111 | lat | degrees latitude (note 2) | float | RFC-AAAA |
1112 | lon | degrees longitude (note 2) | float | RFC-AAAA |
1113 | pH | pH value (acidity; logarithmic | float | RFC-AAAA |
1114 | | quantity) | | |
1115 | dB | decibel (logarithmic quantity) | float | RFC-AAAA |
1116 | Bspl | bel (sound pressure level; | float | RFC-AAAA |
1117 | | logarithmic quantity)* | | |
1118 | count | 1 (counter value) | float | RFC-AAAA |
1119 | / | 1 (Ratio e.g., value of a switch, | float | RFC-AAAA |
1120 | | note 1) | | |
1121 | % | 1 (Ratio e.g., value of a switch, | float | RFC-AAAA |
1122 | | note 1)* | | |
1123 | %RH | Percentage (Relative Humidity) | float | RFC-AAAA |
1124 | %EL | Percentage (remaining battery | float | RFC-AAAA |
1125 | | energy level) | | |
1126 | EL | seconds (remaining battery energy | float | RFC-AAAA |
1127 | | level) | | |
1128 | 1/s | 1 per second (event rate) | float | RFC-AAAA |
1129 | 1/min | 1 per minute (event rate, "rpm")* | float | RFC-AAAA |
1130 | beat/min | 1 per minute (Heart rate in beats | float | RFC-AAAA |
1131 | | per minute)* | | |
1132 | beats | 1 (Cumulative number of heart | float | RFC-AAAA |
1133 | | beats)* | | |
1134 +----------+------------------------------------+-------+-----------+
1136 Table 5
1138 o Note 1: A value of 0.0 indicates the switch is off while 1.0
1139 indicates on and 0.5 would be half on. The preferred name of this
1140 unit is "/". For historical reasons, the name "%" is also
1141 provided for the same unit - but note that while that name
1142 strongly suggests a percentage (0..100) -- it is however NOT a
1143 percentage, but the absolute ratio!
1145 o Note 2: Assumed to be in WGS84 unless another reference frame is
1146 known for the sensor.
1148 New entries can be added to the registration by either Expert Review
1149 or IESG Approval as defined in [RFC5226]. Experts should exercise
1150 their own good judgment but need to consider the following
1151 guidelines:
1153 1. There needs to be a real and compelling use for any new unit to
1154 be added.
1156 2. Units should define the semantic information and be chosen
1157 carefully. Implementors need to remember that the same word may
1158 be used in different real-life contexts. For example, degrees
1159 when measuring latitude have no semantic relation to degrees
1160 when measuring temperature; thus two different units are needed.
1162 3. These measurements are produced by computers for consumption by
1163 computers. The principle is that conversion has to be easily be
1164 done when both reading and writing the media type. The value of
1165 a single canonical representation outweighs the convenience of
1166 easy human representations or loss of precision in a conversion.
1168 4. Use of SI prefixes such as "k" before the unit is not
1169 recommended. Instead one can represent the value using
1170 scientific notation such a 1.2e3. The "kg" unit is exception to
1171 this rule since it is an SI base unit; the "g" unit is provided
1172 for legacy compatibility.
1174 5. For a given type of measurement, there will only be one unit
1175 type defined. So for length, meters are defined and other
1176 lengths such as mile, foot, light year are not allowed. For
1177 most cases, the SI unit is preferred.
1179 6. Symbol names that could be easily confused with existing common
1180 units or units combined with prefixes should be avoided. For
1181 example, selecting a unit name of "mph" to indicate something
1182 that had nothing to do with velocity would be a bad choice, as
1183 "mph" is commonly used to mean miles per hour.
1185 7. The following should not be used because the are common SI
1186 prefixes: Y, Z, E, P, T, G, M, k, h, da, d, c, n, u, p, f, a, z,
1187 y, Ki, Mi, Gi, Ti, Pi, Ei, Zi, Yi.
1189 8. The following units should not be used as they are commonly used
1190 to represent other measurements Ky, Gal, dyn, etg, P, St, Mx, G,
1191 Oe, Gb, sb, Lmb, mph, Ci, R, RAD, REM, gal, bbl, qt, degF, Cal,
1192 BTU, HP, pH, B/s, psi, Torr, atm, at, bar, kWh.
1194 9. The unit names are case sensitive and the correct case needs to
1195 be used, but symbols that differ only in case should not be
1196 allocated.
1198 10. A number after a unit typically indicates the previous unit
1199 raised to that power, and the / indicates that the units that
1200 follow are the reciprocal. A unit should have only one / in the
1201 name.
1203 11. A good list of common units can be found in the Unified Code for
1204 Units of Measure [UCUM].
1206 11.2. SenML Label Registry
1208 IANA will create a new registry for SenML labels. The initial
1209 content of the registry is:
1211 +---------------+-------+------+----------+----+---------+
1212 | Name | Label | CBOR | XML Type | ID | Note |
1213 +---------------+-------+------+----------+----+---------+
1214 | Base Name | bn | -2 | string | a | RFCXXXX |
1215 | Base Sum | bs | -6 | double | a | RFCXXXX |
1216 | Base Time | bt | -3 | double | a | RFCXXXX |
1217 | Base Unit | bu | -4 | string | a | RFCXXXX |
1218 | Base Value | bv | -5 | double | a | RFCXXXX |
1219 | Base Version | bver | -1 | int | a | RFCXXXX |
1220 | Boolean Value | vb | 4 | boolean | a | RFCXXXX |
1221 | Data Value | vd | 8 | string | a | RFCXXXX |
1222 | Name | n | 0 | string | a | RFCXXXX |
1223 | String Value | vs | 3 | string | a | RFCXXXX |
1224 | Time | t | 6 | double | a | RFCXXXX |
1225 | Unit | u | 1 | string | a | RFCXXXX |
1226 | Update Time | ut | 7 | double | a | RFCXXXX |
1227 | Value | v | 2 | double | a | RFCXXXX |
1228 | Value Sum | s | 5 | double | a | RFCXXXX |
1229 | Link | l | 9 | string | a | RFCXXXX |
1230 +---------------+-------+------+----------+----+---------+
1232 Table 6: SenML Labels
1234 Note to RFC Editor. Please replace RFCXXXX with the number for this
1235 RFC.
1237 All new entries must define the Label Name, Label, and XML Type but
1238 the CBOR labels SHOULD be left empty as CBOR will use the string
1239 encoding for any new labels. The ID fields contains the EXI schemaID
1240 of the first Schema which includes this label or is empty if this
1241 label was not intended for use with EXI. The Note field SHOULD
1242 contain information about where to find out more information about
1243 this label.
1245 The JSON, CBOR, and EXI types are derived from the XML type. All XML
1246 numeric types such as double, float, integer and int become a JSON
1247 Number. XML boolean and string become a JSON Boolean and String
1248 respectively. CBOR represents numeric values with a CBOR type that
1249 does not loose any information from the JSON value. EXI uses the XML
1250 types.
1252 New entries can be added to the registration by either Expert Review
1253 or IESG Approval as defined in [RFC5226]. Experts should exercise
1254 their own good judgment but need to consider that shorter labels
1255 should have more strict review.
1257 All new SenML labels that have "base" semantics (see Section 4.1)
1258 MUST start with character 'b'. Regular labels MUST NOT start with
1259 that character.
1261 Extensions that add a label that is intended for use with XML need to
1262 create a new RelaxNG scheme that includes all the labels in the IANA
1263 registry.
1265 Extensions that add a label that is intended for use with EXI need to
1266 create a new XSD Schema that includes all the labels in the IANA
1267 registry then allocate a new EXI schemaID. Moving to the next letter
1268 in the alphabet is the suggested way to create the new EXI schemaID.
1269 Any labels with previously blank ID values SHOULD be updated in the
1270 IANA table to have their ID set to this new schemaID value.
1272 11.3. Media Type Registration
1274 The following registrations are done following the procedure
1275 specified in [RFC6838] and [RFC7303].
1277 Note to RFC Editor - please remove this paragraph. Note that a
1278 request for media type review for senml+json was sent to the media-
1279 types@iana.org on Sept 21, 2010. A second request for all the types
1280 was sent on October 7, 2016.
1282 11.3.1. senml+json Media Type Registration
1284 Type name: application
1286 Subtype name: senml+json and sensml+json
1288 Required parameters: none
1290 Optional parameters: none
1291 Encoding considerations: Must be encoded as using a subset of the
1292 encoding allowed in [RFC7159]. See RFC-AAAA for details. This
1293 simplifies implementation of very simple system and does not impose
1294 any significant limitations as all this data is meant for machine to
1295 machine communications and is not meant to be human readable.
1297 Security considerations: Sensor data can contain a wide range of
1298 information ranging from information that is very public, such the
1299 outside temperature in a given city, to very private information that
1300 requires integrity and confidentiality protection, such as patient
1301 health information. This format does not provide any security and
1302 instead relies on the transport protocol that carries it to provide
1303 security. Given applications need to look at the overall context of
1304 how this media type will be used to decide if the security is
1305 adequate.
1307 Interoperability considerations: Applications should ignore any JSON
1308 key value pairs that they do not understand. This allows backwards
1309 compatibility extensions to this specification. The "bver" field can
1310 be used to ensure the receiver supports a minimal level of
1311 functionality needed by the creator of the JSON object.
1313 Published specification: RFC-AAAA
1315 Applications that use this media type: The type is used by systems
1316 that report e.g., electrical power usage and environmental
1317 information such as temperature and humidity. It can be used for a
1318 wide range of sensor reporting systems.
1320 Additional information:
1322 Magic number(s): none
1324 File extension(s): senml and sensml
1326 Macintosh file type code(s): none
1328 Person & email address to contact for further information: Cullen
1329 Jennings
1331 Intended usage: COMMON
1333 Restrictions on usage: None
1335 Author: Cullen Jennings
1337 Change controller: IESG
1339 11.3.2. senml+cbor Media Type Registration
1341 Type name: application
1343 Subtype name: senml+cbor and sensml+cbor
1345 Required parameters: none
1347 Optional parameters: none
1349 Encoding considerations: Must be encoded as using [RFC7049]. See
1350 RFC-AAAA for details.
1352 Security considerations: Sensor data can contain a wide range of
1353 information ranging from information that is very public, such the
1354 outside temperature in a given city, to very private information that
1355 requires integrity and confidentiality protection, such as patient
1356 health information. This format does not provide any security and
1357 instead relies on the transport protocol that carries it to provide
1358 security. Given applications need to look at the overall context of
1359 how this media type will be used to decide if the security is
1360 adequate.
1362 Interoperability considerations: Applications should ignore any key
1363 value pairs that they do not understand. This allows backwards
1364 compatibility extensions to this specification. The "bver" field can
1365 be used to ensure the receiver supports a minimal level of
1366 functionality needed by the creator of the CBOR object.
1368 Published specification: RFC-AAAA
1370 Applications that use this media type: The type is used by systems
1371 that report e.g., electrical power usage and environmental
1372 information such as temperature and humidity. It can be used for a
1373 wide range of sensor reporting systems.
1375 Additional information:
1377 Magic number(s): none
1379 File extension(s): senmlc and sensmlc
1381 Macintosh file type code(s): none
1383 Person & email address to contact for further information: Cullen
1384 Jennings
1386 Intended usage: COMMON
1387 Restrictions on usage: None
1389 Author: Cullen Jennings
1391 Change controller: IESG
1393 11.3.3. senml+xml Media Type Registration
1395 Type name: application
1397 Subtype name: senml+xml and sensml+xml
1399 Required parameters: none
1401 Optional parameters: none
1403 Encoding considerations: Must be encoded as using
1404 [W3C.REC-xml-20081126]. See RFC-AAAA for details.
1406 Security considerations: Sensor data can contain a wide range of
1407 information ranging from information that is very public, such the
1408 outside temperature in a given city, to very private information that
1409 requires integrity and confidentiality protection, such as patient
1410 health information. This format does not provide any security and
1411 instead relies on the transport protocol that carries it to provide
1412 security. Given applications need to look at the overall context of
1413 how this media type will be used to decide if the security is
1414 adequate.
1416 Interoperability considerations: Applications should ignore any tags
1417 or attributes that they do not understand. This allows backwards
1418 compatibility extensions to this specification. The "bver" attribute
1419 in the senml tag can be used to ensure the receiver supports a
1420 minimal level of functionality needed by the creator of the XML.
1422 Published specification: RFC-AAAA
1424 Applications that use this media type: The type is used by systems
1425 that report e.g., electrical power usage and environmental
1426 information such as temperature and humidity. It can be used for a
1427 wide range of sensor reporting systems.
1429 Additional information:
1431 Magic number(s): none
1433 File extension(s): senmlx and sensmlx
1434 Macintosh file type code(s): none
1436 Person & email address to contact for further information: Cullen
1437 Jennings
1439 Intended usage: COMMON
1441 Restrictions on usage: None
1443 Author: Cullen Jennings
1445 Change controller: IESG
1447 11.3.4. senml+exi Media Type Registration
1449 Type name: application
1451 Subtype name: senml+exi and sensml+exi
1453 Required parameters: none
1455 Optional parameters: none
1457 Encoding considerations: Must be encoded as using
1458 [W3C.REC-exi-20140211]. See RFC-AAAA for details.
1460 Security considerations: Sensor data can contain a wide range of
1461 information ranging from information that is very public, such the
1462 outside temperature in a given city, to very private information that
1463 requires integrity and confidentiality protection, such as patient
1464 health information. This format does not provide any security and
1465 instead relies on the transport protocol that carries it to provide
1466 security. Given applications need to look at the overall context of
1467 how this media type will be used to decide if the security is
1468 adequate.
1470 Interoperability considerations: Applications should ignore any tags
1471 or attributes that they do not understand. This allows backwards
1472 compatibility extensions to this specification. The "bver" attribute
1473 in the senml tag can be used to ensure the receiver supports a
1474 minimal level of functionality needed by the creator of the XML.
1475 Further information on using schemas to guide the EXI can be found in
1476 RFC-AAAA.
1478 Published specification: RFC-AAAA
1480 Applications that use this media type: The type is used by systems
1481 that report e.g., electrical power usage and environmental
1482 information such as temperature and humidity. It can be used for a
1483 wide range of sensor reporting systems.
1485 Additional information:
1487 Magic number(s): none
1489 File extension(s): senmle and sensmle
1491 Macintosh file type code(s): none
1493 Person & email address to contact for further information: Cullen
1494 Jennings
1496 Intended usage: COMMON
1498 Restrictions on usage: None
1500 Author: Cullen Jennings
1502 Change controller: IESG
1504 11.4. XML Namespace Registration
1506 This document registers the following XML namespaces in the IETF XML
1507 registry defined in [RFC3688].
1509 URI: urn:ietf:params:xml:ns:senml
1511 Registrant Contact: The IESG.
1513 XML: N/A, the requested URIs are XML namespaces
1515 11.5. CoAP Content-Format Registration
1517 IANA is requested to assign CoAP Content-Format IDs for the SenML
1518 media types in the "CoAP Content-Formats" sub-registry, within the
1519 "CoRE Parameters" registry [RFC7252]. All IDs are assigned from the
1520 "Expert Review" (0-255) range. The assigned IDs are show in Table 7.
1522 +-------------------------+-----+
1523 | Media type | ID |
1524 +-------------------------+-----+
1525 | application/senml+json | TBD |
1526 | application/sensml+json | TBD |
1527 | application/senml+cbor | TBD |
1528 | application/sensml+cbor | TBD |
1529 | application/senml+xml | TBD |
1530 | application/sensml+xml | TBD |
1531 | application/senml+exi | TBD |
1532 | application/sensml+exi | TBD |
1533 +-------------------------+-----+
1535 Table 7: CoAP Content-Format IDs
1537 12. Security Considerations
1539 See Section 13. Further discussion of security properties can be
1540 found in Section 11.3.
1542 13. Privacy Considerations
1544 Sensor data can range from information with almost no security
1545 considerations, such as the current temperature in a given city, to
1546 highly sensitive medical or location data. This specification
1547 provides no security protection for the data but is meant to be used
1548 inside another container or transport protocol such as S/MIME or HTTP
1549 with TLS that can provide integrity, confidentiality, and
1550 authentication information about the source of the data.
1552 14. Acknowledgement
1554 We would like to thank Alexander Pelov, Andrew McClure, Andrew
1555 Mcgregor, Bjoern Hoehrmann, Christian Amsuess, Christian Groves,
1556 Daniel Peintner, Jan-Piet Mens, Joe Hildebrand, John Klensin, Karl
1557 Palsson, Lennart Duhrsen, Lisa Dusseault, Lyndsay Campbell, Martin
1558 Thomson, Michael Koster, and Stephen Farrell, for their review
1559 comments.
1561 15. References
1563 15.1. Normative References
1565 [BIPM] Bureau International des Poids et Mesures, "The
1566 International System of Units (SI)", 8th edition, 2006.
1568 [IEEE.754.1985]
1569 Institute of Electrical and Electronics Engineers,
1570 "Standard for Binary Floating-Point Arithmetic",
1571 IEEE Standard 754, August 1985.
1573 [NIST811] Thompson, A. and B. Taylor, "Guide for the Use of the
1574 International System of Units (SI)", NIST Special
1575 Publication 811, 2008.
1577 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
1578 Requirement Levels", BCP 14, RFC 2119,
1579 DOI 10.17487/RFC2119, March 1997,
1580 .
1582 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
1583 DOI 10.17487/RFC3688, January 2004,
1584 .
1586 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
1587 Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
1588 .
1590 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
1591 IANA Considerations Section in RFCs", BCP 26, RFC 5226,
1592 DOI 10.17487/RFC5226, May 2008,
1593 .
1595 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
1596 Specifications and Registration Procedures", BCP 13,
1597 RFC 6838, DOI 10.17487/RFC6838, January 2013,
1598 .
1600 [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
1601 Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
1602 October 2013, .
1604 [RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
1605 Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
1606 2014, .
1608 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
1609 Application Protocol (CoAP)", RFC 7252,
1610 DOI 10.17487/RFC7252, June 2014,
1611 .
1613 [RFC7303] Thompson, H. and C. Lilley, "XML Media Types", RFC 7303,
1614 DOI 10.17487/RFC7303, July 2014,
1615 .
1617 [W3C.REC-exi-20140211]
1618 Schneider, J., Kamiya, T., Peintner, D., and R. Kyusakov,
1619 "Efficient XML Interchange (EXI) Format 1.0 (Second
1620 Edition)", World Wide Web Consortium Recommendation REC-
1621 exi-20140211, February 2014,
1622 .
1624 [W3C.REC-xml-20081126]
1625 Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
1626 F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
1627 Edition)", World Wide Web Consortium Recommendation REC-
1628 xml-20081126, November 2008,
1629 .
1631 15.2. Informative References
1633 [I-D.arkko-core-dev-urn]
1634 Arkko, J., Jennings, C., and Z. Shelby, "Uniform Resource
1635 Names for Device Identifiers", draft-arkko-core-dev-urn-03
1636 (work in progress), July 2012.
1638 [I-D.greevenbosch-appsawg-cbor-cddl]
1639 Vigano, C. and H. Birkholz, "CBOR data definition language
1640 (CDDL): a notational convention to express CBOR data
1641 structures", draft-greevenbosch-appsawg-cbor-cddl-09 (work
1642 in progress), September 2016.
1644 [I-D.ietf-core-links-json]
1645 Li, K., Rahman, A., and C. Bormann, "Representing CoRE
1646 Formats in JSON and CBOR", draft-ietf-core-links-json-06
1647 (work in progress), July 2016.
1649 [RFC2141] Moats, R., "URN Syntax", RFC 2141, DOI 10.17487/RFC2141,
1650 May 1997, .
1652 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
1653 Resource Identifier (URI): Generic Syntax", STD 66,
1654 RFC 3986, DOI 10.17487/RFC3986, January 2005,
1655 .
1657 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
1658 Unique IDentifier (UUID) URN Namespace", RFC 4122,
1659 DOI 10.17487/RFC4122, July 2005,
1660 .
1662 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
1663 Address Text Representation", RFC 5952,
1664 DOI 10.17487/RFC5952, August 2010,
1665 .
1667 [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
1668 Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
1669 .
1671 [RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
1672 Considerations for IPv6 Address Generation Mechanisms",
1673 RFC 7721, DOI 10.17487/RFC7721, March 2016,
1674 .
1676 [UCUM] Schadow, G. and C. McDonald, "The Unified Code for Units
1677 of Measure (UCUM)", Regenstrief Institute and Indiana
1678 University School of Informatics, 2013,
1679 .
1681 Appendix A. Links Extension
1683 An attribute to support a link extension for SenML is defined as a
1684 string attribute by this specification. The link extension can be
1685 used for additional information about a SenML Record. The definition
1686 and usage of the contents of this value are specified in
1687 [I-D.ietf-core-links-json].
1689 For JSON and XML the attribute has a label of "l" and a value that is
1690 a string.
1692 The following shows an example of the links extension.
1694 [
1695 {"bn":"urn:dev:ow:10e2073a01080063;","bt":1.320078429e+09,
1696 "l":"[{\"href\":\"humidity\",\"foo\":\"bar1\"}",
1697 "n":"temperature","u":"Cel","v":27.2},
1698 {"n":"humidity","u":"%RH","v":80}
1699 ]
1701 Authors' Addresses
1703 Cullen Jennings
1704 Cisco
1705 400 3rd Avenue SW
1706 Calgary, AB T2P 4H2
1707 Canada
1709 Email: fluffy@iii.ca
1710 Zach Shelby
1711 ARM
1712 150 Rose Orchard
1713 San Jose 95134
1714 USA
1716 Phone: +1-408-203-9434
1717 Email: zach.shelby@arm.com
1719 Jari Arkko
1720 Ericsson
1721 Jorvas 02420
1722 Finland
1724 Email: jari.arkko@piuha.net
1726 Ari Keranen
1727 Ericsson
1728 Jorvas 02420
1729 Finland
1731 Email: ari.keranen@ericsson.com
1733 Carsten Bormann
1734 Universitaet Bremen TZI
1735 Postfach 330440
1736 Bremen D-28359
1737 Germany
1739 Phone: +49-421-218-63921
1740 Email: cabo@tzi.org