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2 Network Working Group C. Jennings
3 Internet-Draft Cisco
4 Intended status: Standards Track Z. Shelby
5 Expires: October 4, 2018 ARM
6 J. Arkko
7 A. Keranen
8 Ericsson
9 C. Bormann
10 Universitaet Bremen TZI
11 April 2, 2018
13 Media Types for Sensor Measurement Lists (SenML)
14 draft-ietf-core-senml-14
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 one of these media types in protocols
25 such as HTTP or CoAP to transport the measurements of the sensor or
26 to be 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 October 4, 2018.
45 Copyright Notice
47 Copyright (c) 2018 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 . . . . . . . . . . . . . . . . 6
66 4.1. Base Fields . . . . . . . . . . . . . . . . . . . . . . . 6
67 4.2. Regular Fields . . . . . . . . . . . . . . . . . . . . . 7
68 4.3. SenML Labels . . . . . . . . . . . . . . . . . . . . . . 7
69 4.4. Considerations . . . . . . . . . . . . . . . . . . . . . 8
70 4.5. Resolved Records . . . . . . . . . . . . . . . . . . . . 10
71 4.6. Associating Meta-data . . . . . . . . . . . . . . . . . . 10
72 4.7. Configuration and Actuation usage . . . . . . . . . . . . 11
73 5. JSON Representation (application/senml+json) . . . . . . . . 11
74 5.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 12
75 5.1.1. Single Datapoint . . . . . . . . . . . . . . . . . . 12
76 5.1.2. Multiple Datapoints . . . . . . . . . . . . . . . . . 12
77 5.1.3. Multiple Measurements . . . . . . . . . . . . . . . . 13
78 5.1.4. Resolved Data . . . . . . . . . . . . . . . . . . . . 14
79 5.1.5. Multiple Data Types . . . . . . . . . . . . . . . . . 15
80 5.1.6. Collection of Resources . . . . . . . . . . . . . . . 15
81 5.1.7. Setting an Actuator . . . . . . . . . . . . . . . . . 16
82 6. CBOR Representation (application/senml+cbor) . . . . . . . . 17
83 7. XML Representation (application/senml+xml) . . . . . . . . . 19
84 8. EXI Representation (application/senml-exi) . . . . . . . . . 21
85 9. Fragment Identification Methods . . . . . . . . . . . . . . . 24
86 9.1. Fragment Identification Examples . . . . . . . . . . . . 24
87 10. Usage Considerations . . . . . . . . . . . . . . . . . . . . 25
88 11. CDDL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
89 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
90 12.1. Units Registry . . . . . . . . . . . . . . . . . . . . . 27
91 12.2. SenML Label Registry . . . . . . . . . . . . . . . . . . 31
92 12.3. Media Type Registrations . . . . . . . . . . . . . . . . 32
93 12.3.1. senml+json Media Type Registration . . . . . . . . . 33
94 12.3.2. sensml+json Media Type Registration . . . . . . . . 34
95 12.3.3. senml+cbor Media Type Registration . . . . . . . . . 35
96 12.3.4. sensml+cbor Media Type Registration . . . . . . . . 36
97 12.3.5. senml+xml Media Type Registration . . . . . . . . . 37
98 12.3.6. sensml+xml Media Type Registration . . . . . . . . . 39
99 12.3.7. senml-exi Media Type Registration . . . . . . . . . 40
100 12.3.8. sensml-exi Media Type Registration . . . . . . . . . 41
101 12.4. XML Namespace Registration . . . . . . . . . . . . . . . 42
102 12.5. CoAP Content-Format Registration . . . . . . . . . . . . 42
103 13. Security Considerations . . . . . . . . . . . . . . . . . . . 43
104 14. Privacy Considerations . . . . . . . . . . . . . . . . . . . 43
105 15. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 44
106 16. References . . . . . . . . . . . . . . . . . . . . . . . . . 44
107 16.1. Normative References . . . . . . . . . . . . . . . . . . 44
108 16.2. Informative References . . . . . . . . . . . . . . . . . 46
109 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48
111 1. Overview
113 Connecting sensors to the Internet is not new, and there have been
114 many protocols designed to facilitate it. This specification defines
115 new media types for carrying simple sensor information in a protocol
116 such as HTTP [RFC7230] or CoAP [RFC7252]. This format was designed
117 so that processors with very limited capabilities could easily encode
118 a sensor measurement into the media type, while at the same time a
119 server parsing the data could relatively efficiently collect a large
120 number of sensor measurements. SenML can be used for a variety of
121 data flow models, most notably data feeds pushed from a sensor to a
122 collector, and the web resource model where the sensor is requested
123 as a resource representation (e.g., "GET /sensor/temperature").
125 There are many types of more complex measurements and measurements
126 that this media type would not be suitable for. SenML strikes a
127 balance between having some information about the sensor carried with
128 the sensor data so that the data is self describing but it also tries
129 to make that a fairly minimal set of auxiliary information for
130 efficiency reason. Other information about the sensor can be
131 discovered by other methods such as using the CoRE Link Format
132 [RFC6690].
134 SenML is defined by a data model for measurements and simple meta-
135 data about measurements and devices. The data is structured as a
136 single array that contains a series of SenML Records which can each
137 contain fields such as an unique identifier for the sensor, the time
138 the measurement was made, the unit the measurement is in, and the
139 current value of the sensor. Serializations for this data model are
140 defined for JSON [RFC8259], CBOR [RFC7049], XML
142 [W3C.REC-xml-20081126], and Efficient XML Interchange (EXI)
143 [W3C.REC-exi-20140211].
145 For example, the following shows a measurement from a temperature
146 gauge encoded in the JSON syntax.
148 [
149 {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","v":23.1}
150 ]
152 In the example above, the array has a single SenML Record with a
153 measurement for a sensor named "urn:dev:ow:10e2073a01080063" with a
154 current value of 23.1 degrees Celsius.
156 2. Requirements and Design Goals
158 The design goal is to be able to send simple sensor measurements in
159 small packets from large numbers of constrained devices. Keeping the
160 total size of payload small makes it easy to use SenML also in
161 constrained networks, e.g., in a 6LoWPAN [RFC4944]. It is always
162 difficult to define what small code is, but there is a desire to be
163 able to implement this in roughly 1 KB of flash on a 8 bit
164 microprocessor. Experience with power meters and other large scale
165 deployments has indicated that the solution needs to support allowing
166 multiple measurements to be batched into a single HTTP or CoAP
167 request. This "batch" upload capability allows the server side to
168 efficiently support a large number of devices. It also conveniently
169 supports batch transfers from proxies and storage devices, even in
170 situations where the sensor itself sends just a single data item at a
171 time. The multiple measurements could be from multiple related
172 sensors or from the same sensor but at different times.
174 The basic design is an array with a series of measurements. The
175 following example shows two measurements made at different times.
176 The value of a measurement is given by the "v" field, the time of a
177 measurement is in the "t" field, the "n" field has a unique sensor
178 name, and the unit of the measurement is carried in the "u" field.
180 [
181 {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020076e+09,
182 "v":23.5},
183 {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020091e+09,
184 "v":23.6}
185 ]
187 To keep the messages small, it does not make sense to repeat the "n"
188 field in each SenML Record so there is a concept of a Base Name which
189 is simply a string that is prepended to the Name field of all
190 elements in that record and any records that follow it. So a more
191 compact form of the example above is the following.
193 [
194 {"bn":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020076e+09,
195 "v":23.5},
196 {"u":"Cel","t":1.276020091e+09,
197 "v":23.6}
198 ]
200 In the above example the Base Name is in the "bn" field and the "n"
201 fields in each Record are the empty string so they are omitted.
203 Some devices have accurate time while others do not so SenML supports
204 absolute and relative times. Time is represented in floating point
205 as seconds. Values greater than zero represent an absolute time
206 relative to the Unix epoch (1970-01-01T00:00Z in UTC time) and the
207 time is counted same way as the Portable Operating System Interface
208 (POSIX) "seconds since the epoch" [TIME_T]. Values of 0 or less
209 represent a relative time in the past from the current time. A
210 simple sensor with no absolute wall clock time might take a
211 measurement every second, batch up 60 of them, and then send the
212 batch to a server. It would include the relative time each
213 measurement was made compared to the time the batch was sent in each
214 SenML Record. The server might have accurate NTP time and use the
215 time it received the data, and the relative offset, to replace the
216 times in the SenML with absolute times before saving the SenML Pack
217 in a document database.
219 3. Terminology
221 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
222 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
223 "OPTIONAL" in this document are to be interpreted as described in BCP
224 14 [RFC2119] [RFC8174] when, and only when, they appear in all
225 capitals, as shown here.
227 This document also uses the following terms:
229 SenML Record: One measurement or configuration instance in time
230 presented using the SenML data model.
232 SenML Pack: One or more SenML Records in an array structure.
234 SenML Label: A short name used in SenML Records to denote different
235 SenML fields (e.g., "v" for "value").
237 SenML Field: A component of a record that associates a value to a
238 SenML Label for this record.
240 This document uses the terms "attribute" and "tag" where they occur
241 with the underlying technologies (XML, CBOR [RFC7049], and Link
242 Format [RFC6690]), not for SenML concepts per se. Note that
243 "attribute" has been widely used previously as a synonym for SenML
244 "field", though.
246 4. SenML Structure and Semantics
248 Each SenML Pack carries a single array that represents a set of
249 measurements and/or parameters. This array contains a series of
250 SenML Records with several fields described below. There are two
251 kinds of fields: base and regular. The base fields can be included
252 in any SenML Record and they apply to the entries in the Record.
253 Each base field also applies to all Records after it up to, but not
254 including, the next Record that has that same base field. All base
255 fields are optional. Regular fields can be included in any SenML
256 Record and apply only to that Record.
258 4.1. Base Fields
260 Base Name: This is a string that is prepended to the names found in
261 the entries.
263 Base Time: A base time that is added to the time found in an entry.
265 Base Unit: A base unit that is assumed for all entries, unless
266 otherwise indicated. If a record does not contain a Unit value,
267 then the Base Unit is used. Otherwise the value found in the Unit
268 (if any) is used.
270 Base Value: A base value is added to the value found in an entry,
271 similar to Base Time.
273 Base Sum: A base sum is added to the sum found in an entry, similar
274 to Base Time.
276 Version: Version number of media type format. This field is an
277 optional positive integer and defaults to 5 if not present. [RFC
278 Editor: change the default value to 10 when this specification is
279 published as an RFC and remove this note]
281 4.2. Regular Fields
283 Name: Name of the sensor or parameter. When appended to the Base
284 Name field, this must result in a globally unique identifier for
285 the resource. The name is optional, if the Base Name is present.
286 If the name is missing, Base Name must uniquely identify the
287 resource. This can be used to represent a large array of
288 measurements from the same sensor without having to repeat its
289 identifier on every measurement.
291 Unit: Unit for a measurement value. Optional.
293 Value: Value of the entry. Optional if a Sum value is present,
294 otherwise required. Values are represented using basic data
295 types. This specification defines floating point numbers ("v"
296 field for "Value"), booleans ("vb" for "Boolean Value"), strings
297 ("vs" for "String Value") and binary data ("vd" for "Data Value").
298 Exactly one value field MUST appear unless there is Sum field in
299 which case it is allowed to have no Value field.
301 Sum: Integrated sum of the values over time. Optional. This field
302 is in the unit specified in the Unit value multiplied by seconds.
304 Time: Time when value was recorded. Optional.
306 Update Time: Period of time in seconds that represents the maximum
307 time before this sensor will provide an updated reading for a
308 measurement. Optional. This can be used to detect the failure of
309 sensors or communications path from the sensor.
311 4.3. SenML Labels
313 Table 1 provides an overview of all SenML fields defined by this
314 document with their respective labels and data types.
316 +---------------+-------+------------+------------+------------+
317 | Name | Label | CBOR Label | JSON Type | XML Type |
318 +---------------+-------+------------+------------+------------+
319 | Base Name | bn | -2 | String | string |
320 | Base Time | bt | -3 | Number | double |
321 | Base Unit | bu | -4 | String | string |
322 | Base Value | bv | -5 | Number | double |
323 | Base Sum | bs | -6 | Number | double |
324 | Version | bver | -1 | Number | int |
325 | Name | n | 0 | String | string |
326 | Unit | u | 1 | String | string |
327 | Value | v | 2 | Number | double |
328 | String Value | vs | 3 | String | string |
329 | Boolean Value | vb | 4 | Boolean | boolean |
330 | Data Value | vd | 8 | String (*) | string (*) |
331 | Value Sum | s | 5 | Number | double |
332 | Time | t | 6 | Number | double |
333 | Update Time | ut | 7 | Number | double |
334 +---------------+-------+------------+------------+------------+
336 Table 1: SenML Labels
338 Data Value is base64 encoded string with URL safe alphabet as defined
339 in Section 5 of [RFC4648], with padding omitted.
341 For details of the JSON representation see Section 5, for the CBOR
342 Section 6, and for the XML Section 7.
344 4.4. Considerations
346 The SenML format can be extended with further custom fields. Both
347 new base and regular fields are allowed. See Section 12.2 for
348 details. Implementations MUST ignore fields they don't recognize
349 unless that field has a label name that ends with the '_' character
350 in which case an error MUST be generated.
352 All SenML Records in a Pack MUST have the same version number. This
353 is typically done by adding a Base Version field to only the first
354 Record in the Pack.
356 Systems reading one of the objects MUST check for the Version field.
357 If this value is a version number larger than the version which the
358 system understands, the system SHOULD NOT use this object. This
359 allows the version number to indicate that the object contains
360 structure or semantics that is different from what is defined in the
361 present document beyond just making use of the extension points
362 provided here. New version numbers can only be defined in an RFC
363 that updates this specification or it successors.
365 The Name value is concatenated to the Base Name value to yield the
366 name of the sensor. The resulting concatenated name needs to
367 uniquely identify and differentiate the sensor from all others. The
368 concatenated name MUST consist only of characters out of the set "A"
369 to "Z", "a" to "z", "0" to "9", "-", ":", ".", "/", and "_";
370 furthermore, it MUST start with a character out of the set "A" to
371 "Z", "a" to "z", or "0" to "9". This restricted character set was
372 chosen so that concatenated names can be used directly within various
373 URI schemes (including segments of an HTTP path with no special
374 encoding) and can be used directly in many databases and analytic
375 systems. [RFC5952] contains advice on encoding an IPv6 address in a
376 name. See Section 14 for privacy considerations that apply to the
377 use of long-term stable unique identifiers.
379 Although it is RECOMMENDED that concatenated names are represented as
380 URIs [RFC3986] or URNs [RFC8141], the restricted character set
381 specified above puts strict limits on the URI schemes and URN
382 namespaces that can be used. As a result, implementers need to take
383 care in choosing the naming scheme for concatenated names, because
384 such names both need to be unique and need to conform to the
385 restricted character set. One approach is to include a bit string
386 that has guaranteed uniqueness (such as a 1-wire address). Some of
387 the examples within this document use the device URN namespace as
388 specified in [I-D.ietf-core-dev-urn]. UUIDs [RFC4122] are another
389 way to generate a unique name. However, the restricted character set
390 does not allow the use of many URI schemes, such as the 'tag' scheme
391 [RFC4151] and the 'ni' scheme [RFC6920], in names as such. The use
392 of URIs with characters incompatible with this set, and possible
393 mapping rules between the two, are outside of the scope of the
394 present document.
396 If the Record has no Unit, the Base Unit is used as the Unit. Having
397 no Unit and no Base Unit is allowed.
399 If either the Base Time or Time value is missing, the missing field
400 is considered to have a value of zero. The Base Time and Time values
401 are added together to get the time of measurement. A time of zero
402 indicates that the sensor does not know the absolute time and the
403 measurement was made roughly "now". A negative value is used to
404 indicate seconds in the past from roughly "now". A positive value is
405 used to indicate the number of seconds, excluding leap seconds, since
406 the start of the year 1970 in UTC.
408 If only one of the Base Sum or Sum value is present, the missing
409 field is considered to have a value of zero. The Base Sum and Sum
410 values are added together to get the sum of measurement. If neither
411 the Base Sum or Sum are present, then the measurement does not have a
412 sum value.
414 If the Base Value or Value is not present, the missing field(s) are
415 considered to have a value of zero. The Base Value and Value are
416 added together to get the value of the measurement.
418 Representing the statistical characteristics of measurements, such as
419 accuracy, can be very complex. Future specification may add new
420 fields to provide better information about the statistical properties
421 of the measurement.
423 In summary, the structure of a SenML record is laid out to support a
424 single measurement per record. If multiple data values are measured
425 at the same time (e.g., air pressure and altitude), they are best
426 kept as separate records linked through their Time value; this is
427 even true where one of the data values is more "meta" than others
428 (e.g., describes a condition that influences other measurements at
429 the same time).
431 4.5. Resolved Records
433 Sometimes it is useful to be able to refer to a defined normalized
434 format for SenML records. This normalized format tends to get used
435 for big data applications and intermediate forms when converting to
436 other formats.
438 A SenML Record is referred to as "resolved" if it does not contain
439 any base values, i.e., labels starting with the character 'b', except
440 for Version fields (see below), and has no relative times. To
441 resolve the records, the base values of the SenML Pack (if any) are
442 applied to the Record. That is, name and base name are concatenated,
443 base time is added to the time of the Record, if the Record did not
444 contain Unit the Base Unit is applied to the record, etc. In
445 addition the records need to be in chronological order. An example
446 of this is show in Section 5.1.4.
448 The Version field MUST NOT be present in resolved records if the
449 SenML version defined in this document is used and MUST be present
450 otherwise in all the resolved SenML Records.
452 Future specification that defines new base fields need to specify how
453 the field is resolved.
455 4.6. Associating Meta-data
457 SenML is designed to carry the minimum dynamic information about
458 measurements, and for efficiency reasons does not carry significant
459 static meta-data about the device, object or sensors. Instead, it is
460 assumed that this meta-data is carried out of band. For web
461 resources using SenML Packs, this meta-data can be made available
462 using the CoRE Link Format [RFC6690]. The most obvious use of this
463 link format is to describe that a resource is available in a SenML
464 format in the first place. The relevant media type indicator is
465 included in the Content-Type (ct=) link attribute (which is defined
466 for the Link Format in Section 7.2.1 of [RFC7252]).
468 4.7. Configuration and Actuation usage
470 SenML can also be used for configuring parameters and controlling
471 actuators. When a SenML Pack is sent (e.g., using a HTTP/CoAP POST
472 or PUT method) and the semantics of the target are such that SenML is
473 interpreted as configuration/actuation, SenML Records are interpreted
474 as a request to change the values of given (sub)resources (given as
475 names) to given values at the given time(s). The semantics of the
476 target resource supporting this usage can be described, e.g., using
477 [I-D.ietf-core-interfaces]. Examples of actuation usage are shown in
478 Section 5.1.7.
480 5. JSON Representation (application/senml+json)
482 For the SenML fields shown in Table 2, the SenML labels are used as
483 the JSON object member names within JSON objects representing the
484 JSON SenML Records.
486 +---------------+-------+---------+
487 | Name | label | Type |
488 +---------------+-------+---------+
489 | Base Name | bn | String |
490 | Base Time | bt | Number |
491 | Base Unit | bu | String |
492 | Base Value | bv | Number |
493 | Base Sum | bs | Number |
494 | Version | bver | Number |
495 | Name | n | String |
496 | Unit | u | String |
497 | Value | v | Number |
498 | String Value | vs | String |
499 | Boolean Value | vb | Boolean |
500 | Data Value | vd | String |
501 | Value Sum | s | Number |
502 | Time | t | Number |
503 | Update Time | ut | Number |
504 +---------------+-------+---------+
506 Table 2: JSON SenML Labels
508 The root JSON value consists of an array with one JSON object for
509 each SenML Record. All the fields in the above table MAY occur in
510 the records with member values of the type specified in the table.
512 Only the UTF-8 [RFC3629] form of JSON is allowed. Characters in the
513 String Value are encoded using the escape sequences defined in
514 [RFC8259]. Octets in the Data Value are base64 encoded with URL safe
515 alphabet as defined in Section 5 of [RFC4648], with padding omitted.
517 Systems receiving measurements MUST be able to process the range of
518 floating point numbers that are representable as an IEEE double
519 precision floating point numbers [IEEE.754.1985]. This allows time
520 values to have better than microsecond precision over the next 100
521 years. The number of significant digits in any measurement is not
522 relevant, so a reading of 1.1 has exactly the same semantic meaning
523 as 1.10. If the value has an exponent, the "e" MUST be in lower
524 case. In the interest of avoiding unnecessary verbosity and speeding
525 up processing, the mantissa SHOULD be less than 19 characters long
526 and the exponent SHOULD be less than 5 characters long.
528 5.1. Examples
530 5.1.1. Single Datapoint
532 The following shows a temperature reading taken approximately "now"
533 by a 1-wire sensor device that was assigned the unique 1-wire address
534 of 10e2073a01080063:
536 [
537 {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","v":23.1}
538 ]
540 5.1.2. Multiple Datapoints
542 The following example shows voltage and current now, i.e., at an
543 unspecified time.
545 [
546 {"bn":"urn:dev:ow:10e2073a01080063:","n":"voltage","u":"V","v":120.1},
547 {"n":"current","u":"A","v":1.2}
548 ]
550 The next example is similar to the above one, but shows current at
551 Tue Jun 8 18:01:16.001 UTC 2010 and at each second for the previous 5
552 seconds.
554 [
555 {"bn":"urn:dev:ow:10e2073a0108006:","bt":1.276020076001e+09,
556 "bu":"A","bver":5,
557 "n":"voltage","u":"V","v":120.1},
558 {"n":"current","t":-5,"v":1.2},
559 {"n":"current","t":-4,"v":1.3},
560 {"n":"current","t":-3,"v":1.4},
561 {"n":"current","t":-2,"v":1.5},
562 {"n":"current","t":-1,"v":1.6},
563 {"n":"current","v":1.7}
564 ]
566 Note that in some usage scenarios of SenML the implementations MAY
567 store or transmit SenML in a stream-like fashion, where data is
568 collected over time and continuously added to the object. This mode
569 of operation is optional, but systems or protocols using SenML in
570 this fashion MUST specify that they are doing this. SenML defines
571 separate media types to indicate Sensor Streaming Measurement Lists
572 (SensML) for this usage (see Section 12.3.2). In this situation the
573 SensML stream can be sent and received in a partial fashion, i.e., a
574 measurement entry can be read as soon as the SenML Record is received
575 and not have to wait for the full SensML Stream to be complete.
577 For instance, the following stream of measurements may be sent via a
578 long lived HTTP POST from the producer of a SensML to the consumer of
579 that, and each measurement object may be reported at the time it was
580 measured:
582 [
583 {"bn":"urn:dev:ow:10e2073a01080063","bt":1.320067464e+09,
584 "bu":"%RH","v":21.2},
585 {"t":10,"v":21.3},
586 {"t":20,"v":21.4},
587 {"t":30,"v":21.4},
588 {"t":40,"v":21.5},
589 {"t":50,"v":21.5},
590 {"t":60,"v":21.5},
591 {"t":70,"v":21.6},
592 {"t":80,"v":21.7},
593 ...
595 5.1.3. Multiple Measurements
597 The following example shows humidity measurements from a mobile
598 device with a 1-wire address 10e2073a01080063, starting at Mon Oct 31
599 13:24:24 UTC 2011. The device also provides position data, which is
600 provided in the same measurement or parameter array as separate
601 entries. Note time is used to for correlating data that belongs
602 together, e.g., a measurement and a parameter associated with it.
603 Finally, the device also reports extra data about its battery status
604 at a separate time.
606 [
607 {"bn":"urn:dev:ow:10e2073a01080063","bt":1.320067464e+09,
608 "bu":"%RH","v":20},
609 {"u":"lon","v":24.30621},
610 {"u":"lat","v":60.07965},
611 {"t":60,"v":20.3},
612 {"u":"lon","t":60,"v":24.30622},
613 {"u":"lat","t":60,"v":60.07965},
614 {"t":120,"v":20.7},
615 {"u":"lon","t":120,"v":24.30623},
616 {"u":"lat","t":120,"v":60.07966},
617 {"u":"%EL","t":150,"v":98},
618 {"t":180,"v":21.2},
619 {"u":"lon","t":180,"v":24.30628},
620 {"u":"lat","t":180,"v":60.07967}
621 ]
623 The size of this example represented in various forms, as well as
624 that form compressed with gzip is given in the following table.
626 +----------+------+-----------------+
627 | Encoding | Size | Compressed Size |
628 +----------+------+-----------------+
629 | JSON | 573 | 206 |
630 | XML | 649 | 235 |
631 | CBOR | 254 | 196 |
632 | EXI | 161 | 184 |
633 +----------+------+-----------------+
635 Table 3: Size Comparisons
637 5.1.4. Resolved Data
639 The following shows the example from the previous section show in
640 resolved format.
642 [
643 {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067464e+09,
644 "v":20},
645 {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067464e+09,
646 "v":24.30621},
647 {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067464e+09,
648 "v":60.07965},
649 {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067524e+09,
650 "v":20.3},
651 {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067524e+09,
652 "v":24.30622},
653 {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067524e+09,
654 "v":60.07965},
655 {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067584e+09,
656 "v":20.7},
657 {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067584e+09,
658 "v":24.30623},
659 {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067584e+09,
660 "v":60.07966},
661 {"n":"urn:dev:ow:10e2073a01080063","u":"%EL","t":1.320067614e+09,
662 "v":98},
663 {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067644e+09,
664 "v":21.2},
665 {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067644e+09,
666 "v":24.30628},
667 {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067644e+09,
668 "v":60.07967}
669 ]
671 5.1.5. Multiple Data Types
673 The following example shows a sensor that returns different data
674 types.
676 [
677 {"bn":"urn:dev:ow:10e2073a01080063:","n":"temp","u":"Cel","v":23.1},
678 {"n":"label","vs":"Machine Room"},
679 {"n":"open","vb":false},
680 {"n":"nfv-reader","vd":"aGkgCg"}
681 ]
683 5.1.6. Collection of Resources
685 The following example shows the results from a query to one device
686 that aggregates multiple measurements from other devices. The
687 example assumes that a client has fetched information from a device
688 at 2001:db8::2 by performing a GET operation on http://[2001:db8::2]
689 at Mon Oct 31 16:27:09 UTC 2011, and has gotten two separate values
690 as a result, a temperature and humidity measurement as well as the
691 results from another device at http://[2001:db8::1] that also had a
692 temperature and humidity. Note that the last record would use the
693 Base Name from the 3rd record but the Base Time from the first
694 record.
696 [
697 {"bn":"2001:db8::2/","bt":1.320078429e+09,
698 "n":"temperature","u":"Cel","v":25.2},
699 {"n":"humidity","u":"%RH","v":30},
700 {"bn":"2001:db8::1/","n":"temperature","u":"Cel","v":12.3},
701 {"n":"humidity","u":"%RH","v":67}
702 ]
704 5.1.7. Setting an Actuator
706 The following example show the SenML that could be used to set the
707 current set point of a typical residential thermostat which has a
708 temperature set point, a switch to turn on and off the heat, and a
709 switch to turn on the fan override.
711 [
712 {"bn":"urn:dev:ow:10e2073a01080063:"},
713 {"n":"temp","u":"Cel","v":23.1},
714 {"n":"heat","u":"/","v":1},
715 {"n":"fan","u":"/","v":0}
716 ]
718 In the following example two different lights are turned on. It is
719 assumed that the lights are on a network that can guarantee delivery
720 of the messages to the two lights within 15 ms (e.g. a network using
721 802.1BA [IEEE802.1ba-2011] and 802.1AS [IEEE802.1as-2011] for time
722 synchronization). The controller has set the time of the lights
723 coming on to 20 ms in the future from the current time. This allows
724 both lights to receive the message, wait till that time, then apply
725 the switch command so that both lights come on at the same time.
727 [
728 {"bt":1.320078429e+09,"bu":"/","n":"2001:db8::3","v":1},
729 {"n":"2001:db8::4","v":1}
730 ]
732 The following shows two lights being turned off using a non
733 deterministic network that has a high odds of delivering a message in
734 less than 100 ms and uses NTP for time synchronization. The current
735 time is 1320078429. The user has just turned off a light switch
736 which is turning off two lights. Both lights are dimmed to 50%
737 brightness immediately to give the user instant feedback that
738 something is changing. However given the network, the lights will
739 probably dim at somewhat different times. Then 100 ms in the future,
740 both lights will go off at the same time. The instant but not
741 synchronized dimming gives the user the sensation of quick responses
742 and the timed off 100 ms in the future gives the perception of both
743 lights going off at the same time.
745 [
746 {"bt":1.320078429e+09,"bu":"/","n":"2001:db8::3","v":0.5},
747 {"n":"2001:db8::4","v":0.5},
748 {"n":"2001:db8::3","t":0.1,"v":0},
749 {"n":"2001:db8::4","t":0.1,"v":0}
750 ]
752 6. CBOR Representation (application/senml+cbor)
754 The CBOR [RFC7049] representation is equivalent to the JSON
755 representation, with the following changes:
757 o For JSON Numbers, the CBOR representation can use integers,
758 floating point numbers, or decimal fractions (CBOR Tag 4); however
759 a representation SHOULD be chosen such that when the CBOR value is
760 converted back to an IEEE double precision floating point value,
761 it has exactly the same value as the original Number. For the
762 version number, only an unsigned integer is allowed.
764 o Characters in the String Value are encoded using a definite length
765 text string (type 3). Octets in the Data Value are encoded using
766 a definite length byte string (type 2).
768 o For compactness, the CBOR representation uses integers for the
769 labels, as defined in Table 4. This table is conclusive, i.e.,
770 there is no intention to define any additional integer map keys;
771 any extensions will use string map keys. This allows translators
772 converting between CBOR and JSON representations to convert also
773 all future labels without needing to update implementations.
775 +---------------+-------+------------+
776 | Name | Label | CBOR Label |
777 +---------------+-------+------------+
778 | Version | bver | -1 |
779 | Base Name | bn | -2 |
780 | Base Time | bt | -3 |
781 | Base Unit | bu | -4 |
782 | Base Value | bv | -5 |
783 | Base Sum | bs | -6 |
784 | Name | n | 0 |
785 | Unit | u | 1 |
786 | Value | v | 2 |
787 | String Value | vs | 3 |
788 | Boolean Value | vb | 4 |
789 | Value Sum | s | 5 |
790 | Time | t | 6 |
791 | Update Time | ut | 7 |
792 | Data Value | vd | 8 |
793 +---------------+-------+------------+
795 Table 4: CBOR representation: integers for map keys
797 o For streaming SensML in CBOR representation, the array containing
798 the records SHOULD be a CBOR indefinite length array while for
799 non-streaming SenML, a definite length array MUST be used.
801 The following example shows a dump of the CBOR example for the same
802 sensor measurement as in Section 5.1.2.
804 0000 87 a7 21 78 1b 75 72 6e 3a 64 65 76 3a 6f 77 3a |..!x.urn:dev:ow:|
805 0010 31 30 65 32 30 37 33 61 30 31 30 38 30 30 36 3a |10e2073a0108006:|
806 0020 22 fb 41 d3 03 a1 5b 00 10 62 23 61 41 20 05 00 |".A...[..b#aA ..|
807 0030 67 76 6f 6c 74 61 67 65 01 61 56 02 fb 40 5e 06 |gvoltage.aV..@^.|
808 0040 66 66 66 66 66 a3 00 67 63 75 72 72 65 6e 74 06 |fffff..gcurrent.|
809 0050 24 02 fb 3f f3 33 33 33 33 33 33 a3 00 67 63 75 |$..?.333333..gcu|
810 0060 72 72 65 6e 74 06 23 02 fb 3f f4 cc cc cc cc cc |rrent.#..?......|
811 0070 cd a3 00 67 63 75 72 72 65 6e 74 06 22 02 fb 3f |...gcurrent."..?|
812 0080 f6 66 66 66 66 66 66 a3 00 67 63 75 72 72 65 6e |.ffffff..gcurren|
813 0090 74 06 21 02 f9 3e 00 a3 00 67 63 75 72 72 65 6e |t.!..>...gcurren|
814 00a0 74 06 20 02 fb 3f f9 99 99 99 99 99 9a a3 00 67 |t. ..?.........g|
815 00b0 63 75 72 72 65 6e 74 06 00 02 fb 3f fb 33 33 33 |current....?.333|
816 00c0 33 33 33 |333|
817 00c3
818 In CBOR diagnostic notation (Section 6 of [RFC7049]), this is:
820 [{-2: "urn:dev:ow:10e2073a0108006:",
821 -3: 1276020076.001, -4: "A", -1: 5, 0: "voltage", 1: "V", 2: 120.1},
822 {0: "current", 6: -5, 2: 1.2}, {0: "current", 6: -4, 2: 1.3},
823 {0: "current", 6: -3, 2: 1.4}, {0: "current", 6: -2, 2: 1.5},
824 {0: "current", 6: -1, 2: 1.6}, {0: "current", 6: 0, 2: 1.7}]
826 7. XML Representation (application/senml+xml)
828 A SenML Pack or Stream can also be represented in XML format as
829 defined in this section.
831 Only the UTF-8 form of XML is allowed. Characters in the String
832 Value are encoded using the escape sequences defined in [RFC8259].
833 Octets in the Data Value are base64 encoded with URL safe alphabet as
834 defined in Section 5 of [RFC4648].
836 The following example shows an XML example for the same sensor
837 measurement as in Section 5.1.2.
839
840
842
843
844
845
846
847
848
850 The SenML Stream is represented as a sensml element that contains a
851 series of senml elements for each SenML Record. The SenML fields are
852 represented as XML attributes. For each field defined in this
853 document, the following table shows the SenML labels, which are used
854 for the XML attribute name, as well as the according restrictions on
855 the XML attribute values ("type") as used in the XML senml elements.
857 +---------------+-------+---------+
858 | Name | Label | Type |
859 +---------------+-------+---------+
860 | Base Name | bn | string |
861 | Base Time | bt | double |
862 | Base Unit | bu | string |
863 | Base Value | bv | double |
864 | Base Sum | bs | double |
865 | Base Version | bver | int |
866 | Name | n | string |
867 | Unit | u | string |
868 | Value | v | double |
869 | String Value | vs | string |
870 | Data Value | vd | string |
871 | Boolean Value | vb | boolean |
872 | Value Sum | s | double |
873 | Time | t | double |
874 | Update Time | ut | double |
875 +---------------+-------+---------+
877 Table 5: XML SenML Labels
879 The RelaxNG [RNC] schema for the XML is:
881 default namespace = "urn:ietf:params:xml:ns:senml"
882 namespace rng = "http://relaxng.org/ns/structure/1.0"
884 senml = element senml {
885 attribute bn { xsd:string }?,
886 attribute bt { xsd:double }?,
887 attribute bv { xsd:double }?,
888 attribute bs { xsd:double }?,
889 attribute bu { xsd:string }?,
890 attribute bver { xsd:int }?,
892 attribute n { xsd:string }?,
893 attribute s { xsd:double }?,
894 attribute t { xsd:double }?,
895 attribute u { xsd:string }?,
896 attribute ut { xsd:double }?,
898 attribute v { xsd:double }?,
899 attribute vb { xsd:boolean }?,
900 attribute vs { xsd:string }?,
901 attribute vd { xsd:string }?
902 }
904 sensml =
905 element sensml {
906 senml+
907 }
909 start = sensml
911 8. EXI Representation (application/senml-exi)
913 For efficient transmission of SenML over e.g. a constrained network,
914 Efficient XML Interchange (EXI) can be used. This encodes the XML
915 Schema [W3C.REC-xmlschema-1-20041028] structure of SenML into binary
916 tags and values rather than ASCII text. An EXI representation of
917 SenML SHOULD be made using the strict schema-mode of EXI. This mode
918 however does not allow tag extensions to the schema, and therefore
919 any extensions will be lost in the encoding. For uses where
920 extensions need to be preserved in EXI, the non-strict schema mode of
921 EXI MAY be used.
923 The EXI header MUST include an "EXI Options", as defined in
924 [W3C.REC-exi-20140211], with an schemaId set to the value of "a"
925 indicating the schema provided in this specification. Future
926 revisions to the schema can change the value of the schemaId to allow
927 for backwards compatibility. When the data will be transported over
928 CoAP or HTTP, an EXI Cookie SHOULD NOT be used as it simply makes
929 things larger and is redundant to information provided in the
930 Content-Type header.
932 The following is the XSD Schema to be used for strict schema guided
933 EXI processing. It is generated from the RelaxNG.
935
936
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
968 The following shows a hexdump of the EXI produced from encoding the
969 following XML example. Note this example is the same information as
970 the first example in Section 5.1.2 in JSON format.
972
973
975
976
977 Which compresses with EXI to the following displayed in hexdump:
979 0000 a0 30 0d 84 80 f3 ab 93 71 d3 23 2b b1 d3 7b b9 |.0......q.#+..{.|
980 0010 d1 89 83 29 91 81 b9 9b 09 81 89 81 c1 81 81 b1 |...)............|
981 0020 99 d2 84 bb 37 b6 3a 30 b3 b2 90 1a b1 58 84 c0 |....7.:0.....X..|
982 0030 33 04 b1 ba b9 39 32 b7 3a 10 1a 09 06 40 38 |3....92.:....@8|
983 003f
985 The above example used the bit packed form of EXI but it is also
986 possible to use a byte packed form of EXI which can makes it easier
987 for a simple sensor to produce valid EXI without really implementing
988 EXI. Consider the example of a temperature sensor that produces a
989 value in tenths of degrees Celsius over a range of 0.0 to 55.0. It
990 would produce an XML SenML file such as:
992
993
994
996 The compressed form, using the byte alignment option of EXI, for the
997 above XML is the following:
999 0000 a0 00 48 80 6c 20 01 06 1d 75 72 6e 3a 64 65 76 |..H.l ...urn:dev|
1000 0010 3a 6f 77 3a 31 30 65 32 30 37 33 61 30 31 30 38 |:ow:10e2073a0108|
1001 0020 30 30 36 33 02 05 43 65 6c 01 00 e7 01 01 00 03 |0063..Cel.......|
1002 0030 01 |.|
1003 0031
1005 A small temperature sensor device that only generates this one EXI
1006 file does not really need a full EXI implementation. It can simply
1007 hard code the output replacing the 1-wire device ID starting at byte
1008 0x14 and going to byte 0x23 with its device ID, and replacing the
1009 value "0xe7 0x01" at location 0x31 and 0x32 with the current
1010 temperature. The EXI Specification [W3C.REC-exi-20140211] contains
1011 the full information on how floating point numbers are represented,
1012 but for the purpose of this sensor, the temperature can be converted
1013 to an integer in tenths of degrees (231 in this example). EXI stores
1014 7 bits of the integer in each byte with the top bit set to one if
1015 there are further bytes. So the first bytes at is set to low 7 bits
1016 of the integer temperature in tenths of degrees plus 0x80. In this
1017 example 231 & 0x7F + 0x80 = 0xE7. The second byte is set to the
1018 integer temperature in tenths of degrees right shifted 7 bits. In
1019 this example 231 >> 7 = 0x01.
1021 9. Fragment Identification Methods
1023 A SenML Pack typically consists of multiple SenML Records and for
1024 some applications it may be useful to be able to refer with a
1025 Fragment Identifier to a single record, or a set of records, in a
1026 Pack. The fragment identifier is only interpreted by a client and
1027 does not impact retrieval of a representation. The SenML Fragment
1028 Identification is modeled after CSV Fragment Identifiers [RFC7111].
1030 To select a single SenML Record, the "rec" scheme followed by a
1031 single number is used. For the purpose of numbering records, the
1032 first record is at position 1. A range of records can be selected by
1033 giving the first and the last record number separated by a '-'
1034 character. Instead of the second number, the '*' character can be
1035 used to indicate the last SenML Record in the Pack. A set of records
1036 can also be selected using a comma separated list of record positions
1037 or ranges.
1039 (We use the term "selecting a record" for identifying it as part of
1040 the fragment, not in the sense of isolating it from the Pack -- the
1041 record still needs to be interpreted as part of the Pack, e.g., using
1042 the base values defined in earlier records)
1044 9.1. Fragment Identification Examples
1046 The 3rd SenML Record from "coap://example.com/temp" resource can be
1047 selected with:
1049 coap://example.com/temp#rec=3
1051 Records from 3rd to 6th can be selected with:
1053 coap://example.com/temp#rec=3-6
1055 Records from 19th to the last can be selected with:
1057 coap://example.com/temp#rec=19-*
1059 The 3rd and 5th record can be selected with:
1061 coap://example.com/temp#rec=3,5
1063 To select the Records from third to fifth, the 10th record, and all
1064 from 19th to the last:
1066 coap://example.com/temp#rec=3-5,10,19-*
1068 10. Usage Considerations
1070 The measurements support sending both the current value of a sensor
1071 as well as the an integrated sum. For many types of measurements,
1072 the sum is more useful than the current value. For example, an
1073 electrical meter that measures the energy a given computer uses will
1074 typically want to measure the cumulative amount of energy used. This
1075 is less prone to error than reporting the power each second and
1076 trying to have something on the server side sum together all the
1077 power measurements. If the network between the sensor and the meter
1078 goes down over some period of time, when it comes back up, the
1079 cumulative sum helps reflect what happened while the network was
1080 down. A meter like this would typically report a measurement with
1081 the unit set to watts, but it would put the sum of energy used in the
1082 "s" field of the measurement. It might optionally include the
1083 current power in the "v" field.
1085 While the benefit of using the integrated sum is fairly clear for
1086 measurements like power and energy, it is less obvious for something
1087 like temperature. Reporting the sum of the temperature makes it easy
1088 to compute averages even when the individual temperature values are
1089 not reported frequently enough to compute accurate averages.
1090 Implementers are encouraged to report the cumulative sum as well as
1091 the raw value of a given sensor.
1093 Applications that use the cumulative sum values need to understand
1094 they are very loosely defined by this specification, and depending on
1095 the particular sensor implementation may behave in unexpected ways.
1096 Applications should be able to deal with the following issues:
1098 1. Many sensors will allow the cumulative sums to "wrap" back to
1099 zero after the value gets sufficiently large.
1101 2. Some sensors will reset the cumulative sum back to zero when the
1102 device is reset, loses power, or is replaced with a different
1103 sensor.
1105 3. Applications cannot make assumptions about when the device
1106 started accumulating values into the sum.
1108 Typically applications can make some assumptions about specific
1109 sensors that will allow them to deal with these problems. A common
1110 assumption is that for sensors whose measurement values are always
1111 positive, the sum should never get smaller; so if the sum does get
1112 smaller, the application will know that one of the situations listed
1113 above has happened.
1115 11. CDDL
1117 As a convenient reference, the JSON and CBOR representations can be
1118 described with the common CDDL [I-D.ietf-cbor-cddl] specification in
1119 Figure 1 (informative).
1121 SenML-Pack = [1* record]
1123 record = {
1124 ? bn => tstr, ; Base Name
1125 ? bt => numeric, ; Base Time
1126 ? bu => tstr, ; Base Units
1127 ? bv => numeric, ; Base Value
1128 ? bs => numeric, ; Base Sum
1129 ? bver => uint, ; Base Version
1130 ? n => tstr, ; Name
1131 ? u => tstr, ; Units
1132 ? s => numeric, ; Value Sum
1133 ? t => numeric, ; Time
1134 ? ut => numeric, ; Update Time
1135 ? ( v => numeric // ; Numeric Value
1136 vs => tstr // ; String Value
1137 vb => bool // ; Boolean Value
1138 vd => binary-value ) ; Data Value
1139 * key-value-pair
1140 }
1142 ; now define the generic versions
1143 key-value-pair = ( label => value )
1145 label = non-b-label / b-label
1146 non-b-label = tstr .regexp "[A-Zac-z0-9][-_:.A-Za-z0-9]*" / uint
1147 b-label = tstr .regexp "b[-_:.A-Za-z0-9]+" / nint
1149 value = tstr / binary-value / numeric / bool
1150 numeric = number / decfrac
1152 Figure 1: Common CDDL specification for CBOR and JSON SenML
1154 For JSON, we use text labels and base64url-encoded binary data
1155 (Figure 2).
1157 bver = "bver" n = "n" s = "s"
1158 bn = "bn" u = "u" t = "t"
1159 bt = "bt" v = "v" ut = "ut"
1160 bu = "bu" vs = "vs" vd = "vd"
1161 bv = "bv" vb = "vb"
1162 bs = "bs"
1164 binary-value = tstr ; base64url encoded
1166 Figure 2: JSON-specific CDDL specification for SenML
1168 For CBOR, we use integer labels and native binary data (Figure 3).
1170 bver = -1 n = 0 s = 5
1171 bn = -2 u = 1 t = 6
1172 bt = -3 v = 2 ut = 7
1173 bu = -4 vs = 3 vd = 8
1174 bv = -5 vb = 4
1175 bs = -6
1177 binary-value = bstr
1179 Figure 3: CBOR-specific CDDL specification for SenML
1181 12. IANA Considerations
1183 Note to RFC Editor: Please replace all occurrences of "RFC-AAAA" with
1184 the RFC number of this specification.
1186 IANA will create a new registry for "Sensor Measurement Lists (SenML)
1187 Parameters". The sub-registries defined in Section 12.1 and
1188 Section 12.2 will be created inside this registry.
1190 12.1. Units Registry
1192 IANA will create a registry of SenML unit symbols. The primary
1193 purpose of this registry is to make sure that symbols uniquely map to
1194 give type of measurement. Definitions for many of these units can be
1195 found in location such as [NIST811] and [BIPM]. Units marked with an
1196 asterisk are NOT RECOMMENDED to be produced by new implementations,
1197 but are in active use and SHOULD be implemented by consumers that can
1198 use the related base units.
1200 +----------+------------------------------------+-------+-----------+
1201 | Symbol | Description | Type | Reference |
1202 +----------+------------------------------------+-------+-----------+
1203 | m | meter | float | RFC-AAAA |
1204 | kg | kilogram | float | RFC-AAAA |
1205 | g | gram* | float | RFC-AAAA |
1206 | s | second | float | RFC-AAAA |
1207 | A | ampere | float | RFC-AAAA |
1208 | K | kelvin | float | RFC-AAAA |
1209 | cd | candela | float | RFC-AAAA |
1210 | mol | mole | float | RFC-AAAA |
1211 | Hz | hertz | float | RFC-AAAA |
1212 | rad | radian | float | RFC-AAAA |
1213 | sr | steradian | float | RFC-AAAA |
1214 | N | newton | float | RFC-AAAA |
1215 | Pa | pascal | float | RFC-AAAA |
1216 | J | joule | float | RFC-AAAA |
1217 | W | watt | float | RFC-AAAA |
1218 | C | coulomb | float | RFC-AAAA |
1219 | V | volt | float | RFC-AAAA |
1220 | F | farad | float | RFC-AAAA |
1221 | Ohm | ohm | float | RFC-AAAA |
1222 | S | siemens | float | RFC-AAAA |
1223 | Wb | weber | float | RFC-AAAA |
1224 | T | tesla | float | RFC-AAAA |
1225 | H | henry | float | RFC-AAAA |
1226 | Cel | degrees Celsius | float | RFC-AAAA |
1227 | lm | lumen | float | RFC-AAAA |
1228 | lx | lux | float | RFC-AAAA |
1229 | Bq | becquerel | float | RFC-AAAA |
1230 | Gy | gray | float | RFC-AAAA |
1231 | Sv | sievert | float | RFC-AAAA |
1232 | kat | katal | float | RFC-AAAA |
1233 | m2 | square meter (area) | float | RFC-AAAA |
1234 | m3 | cubic meter (volume) | float | RFC-AAAA |
1235 | l | liter (volume)* | float | RFC-AAAA |
1236 | m/s | meter per second (velocity) | float | RFC-AAAA |
1237 | m/s2 | meter per square second | float | RFC-AAAA |
1238 | | (acceleration) | | |
1239 | m3/s | cubic meter per second (flow rate) | float | RFC-AAAA |
1240 | l/s | liter per second (flow rate)* | float | RFC-AAAA |
1241 | W/m2 | watt per square meter (irradiance) | float | RFC-AAAA |
1242 | cd/m2 | candela per square meter | float | RFC-AAAA |
1243 | | (luminance) | | |
1244 | bit | bit (information content) | float | RFC-AAAA |
1245 | bit/s | bit per second (data rate) | float | RFC-AAAA |
1246 | lat | degrees latitude (note 1) | float | RFC-AAAA |
1247 | lon | degrees longitude (note 1) | float | RFC-AAAA |
1248 | pH | pH value (acidity; logarithmic | float | RFC-AAAA |
1249 | | quantity) | | |
1250 | dB | decibel (logarithmic quantity) | float | RFC-AAAA |
1251 | dBW | decibel relative to 1 W (power | float | RFC-AAAA |
1252 | | level) | | |
1253 | Bspl | bel (sound pressure level; | float | RFC-AAAA |
1254 | | logarithmic quantity)* | | |
1255 | count | 1 (counter value) | float | RFC-AAAA |
1256 | / | 1 (Ratio e.g., value of a switch, | float | RFC-AAAA |
1257 | | note 2) | | |
1258 | % | 1 (Ratio e.g., value of a switch, | float | RFC-AAAA |
1259 | | note 2)* | | |
1260 | %RH | Percentage (Relative Humidity) | float | RFC-AAAA |
1261 | %EL | Percentage (remaining battery | float | RFC-AAAA |
1262 | | energy level) | | |
1263 | EL | seconds (remaining battery energy | float | RFC-AAAA |
1264 | | level) | | |
1265 | 1/s | 1 per second (event rate) | float | RFC-AAAA |
1266 | 1/min | 1 per minute (event rate, "rpm")* | float | RFC-AAAA |
1267 | beat/min | 1 per minute (Heart rate in beats | float | RFC-AAAA |
1268 | | per minute)* | | |
1269 | beats | 1 (Cumulative number of heart | float | RFC-AAAA |
1270 | | beats)* | | |
1271 | S/m | Siemens per meter (conductivity) | float | RFC-AAAA |
1272 +----------+------------------------------------+-------+-----------+
1274 Table 6
1276 o Note 1: Assumed to be in WGS84 unless another reference frame is
1277 known for the sensor.
1279 o Note 2: A value of 0.0 indicates the switch is off while 1.0
1280 indicates on and 0.5 would be half on. The preferred name of this
1281 unit is "/". For historical reasons, the name "%" is also
1282 provided for the same unit - but note that while that name
1283 strongly suggests a percentage (0..100) -- it is however NOT a
1284 percentage, but the absolute ratio!
1286 New entries can be added to the registration by Expert Review as
1287 defined in [RFC8126]. Experts should exercise their own good
1288 judgment but need to consider the following guidelines:
1290 1. There needs to be a real and compelling use for any new unit to
1291 be added.
1293 2. Each unit should define the semantic information and be chosen
1294 carefully. Implementers need to remember that the same word may
1295 be used in different real-life contexts. For example, degrees
1296 when measuring latitude have no semantic relation to degrees
1297 when measuring temperature; thus two different units are needed.
1299 3. These measurements are produced by computers for consumption by
1300 computers. The principle is that conversion has to be easily be
1301 done when both reading and writing the media type. The value of
1302 a single canonical representation outweighs the convenience of
1303 easy human representations or loss of precision in a conversion.
1305 4. Use of SI prefixes such as "k" before the unit is not
1306 recommended. Instead one can represent the value using
1307 scientific notation such a 1.2e3. The "kg" unit is exception to
1308 this rule since it is an SI base unit; the "g" unit is provided
1309 for legacy compatibility.
1311 5. For a given type of measurement, there will only be one unit
1312 type defined. So for length, meters are defined and other
1313 lengths such as mile, foot, light year are not allowed. For
1314 most cases, the SI unit is preferred.
1316 (Note that some amount of judgment will be required here, as
1317 even SI itself is not entirely consistent in this respect. For
1318 instance, for temperature [ISO-80000-5] defines a quantity, item
1319 5-1 (thermodynamic temperature), and a corresponding unit 5-1.a
1320 (Kelvin), and then goes ahead to define another quantity right
1321 besides that, item 5-2 ("Celsius temperature"), and the
1322 corresponding unit 5-2.a (degree Celsius). The latter quantity
1323 is defined such that it gives the thermodynamic temperature as a
1324 delta from T0 = 275.15 K. ISO 80000-5 is defining both units
1325 side by side, and not really expressing a preference. This
1326 level of recognition of the alternative unit degree Celsius is
1327 the reason why Celsius temperatures exceptionally seem
1328 acceptable in the SenML units list alongside Kelvin.)
1330 6. Symbol names that could be easily confused with existing common
1331 units or units combined with prefixes should be avoided. For
1332 example, selecting a unit name of "mph" to indicate something
1333 that had nothing to do with velocity would be a bad choice, as
1334 "mph" is commonly used to mean miles per hour.
1336 7. The following should not be used because the are common SI
1337 prefixes: Y, Z, E, P, T, G, M, k, h, da, d, c, n, u, p, f, a, z,
1338 y, Ki, Mi, Gi, Ti, Pi, Ei, Zi, Yi.
1340 8. The following units should not be used as they are commonly used
1341 to represent other measurements Ky, Gal, dyn, etg, P, St, Mx, G,
1342 Oe, Gb, sb, Lmb, mph, Ci, R, RAD, REM, gal, bbl, qt, degF, Cal,
1343 BTU, HP, pH, B/s, psi, Torr, atm, at, bar, kWh.
1345 9. The unit names are case sensitive and the correct case needs to
1346 be used, but symbols that differ only in case should not be
1347 allocated.
1349 10. A number after a unit typically indicates the previous unit
1350 raised to that power, and the / indicates that the units that
1351 follow are the reciprocal. A unit should have only one / in the
1352 name.
1354 11. A good list of common units can be found in the Unified Code for
1355 Units of Measure [UCUM].
1357 12.2. SenML Label Registry
1359 IANA will create a new registry for SenML labels. The initial
1360 content of the registry is:
1362 +--------------+-------+----+-----------+----------+----+-----------+
1363 | Name | Label | CL | JSON Type | XML Type | EI | Reference |
1364 +--------------+-------+----+-----------+----------+----+-----------+
1365 | Base Name | bn | -2 | String | string | a | RFCXXXX |
1366 | Base Time | bt | -3 | Number | double | a | RFCXXXX |
1367 | Base Unit | bu | -4 | String | string | a | RFCXXXX |
1368 | Base Value | bv | -5 | Number | double | a | RFCXXXX |
1369 | Base Sum | bs | -6 | Number | double | a | RFCXXXX |
1370 | Base Version | bver | -1 | Number | int | a | RFCXXXX |
1371 | Name | n | 0 | String | string | a | RFCXXXX |
1372 | Unit | u | 1 | String | string | a | RFCXXXX |
1373 | Value | v | 2 | Number | double | a | RFCXXXX |
1374 | String Value | vs | 3 | String | string | a | RFCXXXX |
1375 | Boolean | vb | 4 | Boolean | boolean | a | RFCXXXX |
1376 | Value | | | | | | |
1377 | Data Value | vd | 8 | String | string | a | RFCXXXX |
1378 | Value Sum | s | 5 | Number | double | a | RFCXXXX |
1379 | Time | t | 6 | Number | double | a | RFCXXXX |
1380 | Update Time | ut | 7 | Number | double | a | RFCXXXX |
1381 +--------------+-------+----+-----------+----------+----+-----------+
1383 Table 7: IANA Registry for SenML Labels, CL = CBOR Label, EI = EXI ID
1385 This is the same table as Table 1, with notes removed, and with
1386 columns added for the information that is all the same for this
1387 initial set of registrations, but will need to be supplied with a
1388 different value for new registrations.
1390 Note to RFC Editor. Please replace RFCXXXX with the number for this
1391 RFC.
1393 All new entries must define the Label Name, Label, and XML Type but
1394 the CBOR labels SHOULD be left empty as CBOR will use the string
1395 encoding for any new labels. The EI column contains the EXI schemaId
1396 value of the first Schema which includes this label or is empty if
1397 this label was not intended for use with EXI. The Note field SHOULD
1398 contain information about where to find out more information about
1399 this label.
1401 The JSON, CBOR, and EXI types are derived from the XML type. All XML
1402 numeric types such as double, float, integer and int become a JSON
1403 Number. XML boolean and string become a JSON Boolean and String
1404 respectively. CBOR represents numeric values with a CBOR type that
1405 does not lose any information from the JSON value. EXI uses the XML
1406 types.
1408 New entries can be added to the registration by Expert Review as
1409 defined in [RFC8126]. Experts should exercise their own good
1410 judgment but need to consider that shorter labels should have more
1411 strict review. New entries should not be made that counteract the
1412 advice at the end of Section 4.4.
1414 All new SenML labels that have "base" semantics (see Section 4.1)
1415 MUST start with the character 'b'. Regular labels MUST NOT start
1416 with that character. All new SenML labels with Value semantics (see
1417 Section 4.2) MUST have "Value" in their (long form) name.
1419 Extensions that add a label that is intended for use with XML need to
1420 create a new RelaxNG scheme that includes all the labels in the IANA
1421 registry.
1423 Extensions that add a label that is intended for use with EXI need to
1424 create a new XSD Schema that includes all the labels in the IANA
1425 registry and then allocate a new EXI schemaId value. Moving to the
1426 next letter in the alphabet is the suggested way to create the new
1427 value for the EXI schemaId. Any labels with previously blank ID
1428 values SHOULD be updated in the IANA table to have their ID set to
1429 this new schemaId value.
1431 Extensions that are mandatory to understand to correctly process the
1432 Pack MUST have a label name that ends with the '_' character.
1434 12.3. Media Type Registrations
1436 The following registrations are done following the procedure
1437 specified in [RFC6838] and [RFC7303]. This document registers media
1438 types for each serialization format of SenML (JSON, CBOR, and EXI)
1439 and also media types for the same formats of the streaming use
1440 (SensML). Clipboard formats are defined for the JSON and XML form of
1441 lists but do not make sense for streams or other formats.
1443 Note to RFC Editor - please remove this paragraph. Note that a
1444 request for media type review for senml+json was sent to the media-
1445 types@iana.org on Sept 21, 2010. A second request for all the types
1446 was sent on October 31, 2016. Please change all instances of RFC-
1447 AAAA with the RFC number of this document.
1449 12.3.1. senml+json Media Type Registration
1451 Type name: application
1453 Subtype name: senml+json
1455 Required parameters: none
1457 Optional parameters: none
1459 Encoding considerations: Must be encoded as using a subset of the
1460 encoding allowed in [RFC8259]. See RFC-AAAA for details. This
1461 simplifies implementation of very simple system and does not impose
1462 any significant limitations as all this data is meant for machine to
1463 machine communications and is not meant to be human readable.
1465 Security considerations: See Section 13 of RFC-AAAA.
1467 Interoperability considerations: Applications MUST ignore any JSON
1468 key value pairs that they do not understand unless the key ends with
1469 the '_' character in which case an error MUST be generated. This
1470 allows backwards compatible extensions to this specification. The
1471 "bver" field can be used to ensure the receiver supports a minimal
1472 level of functionality needed by the creator of the JSON object.
1474 Published specification: RFC-AAAA
1476 Applications that use this media type: The type is used by systems
1477 that report e.g., electrical power usage and environmental
1478 information such as temperature and humidity. It can be used for a
1479 wide range of sensor reporting systems.
1481 Fragment identifier considerations: Fragment identification for
1482 application/senml+json is supported by using fragment identifiers as
1483 specified by RFC-AAAA.
1485 Additional information:
1487 Magic number(s): none
1489 File extension(s): senml
1491 Windows Clipboard Name: "JSON Sensor Measurement List"
1492 Macintosh file type code(s): none
1494 Macintosh Universal Type Identifier code: org.ietf.senml-json
1495 conforms to public.text
1497 Person & email address to contact for further information: Cullen
1498 Jennings
1500 Intended usage: COMMON
1502 Restrictions on usage: None
1504 Author: Cullen Jennings
1506 Change controller: IESG
1508 12.3.2. sensml+json Media Type Registration
1510 Type name: application
1512 Subtype name: sensml+json
1514 Required parameters: none
1516 Optional parameters: none
1518 Encoding considerations: Must be encoded as using a subset of the
1519 encoding allowed in [RFC8259]. See RFC-AAAA for details. This
1520 simplifies implementation of very simple system and does not impose
1521 any significant limitations as all this data is meant for machine to
1522 machine communications and is not meant to be human readable.
1524 Security considerations: See Section 13 of RFC-AAAA.
1526 Interoperability considerations: Applications MUST ignore any JSON
1527 key value pairs that they do not understand unless the key ends with
1528 the '_' character in which case an error MUST be generated. This
1529 allows backwards compatible extensions to this specification. The
1530 "bver" field can be used to ensure the receiver supports a minimal
1531 level of functionality needed by the creator of the JSON object.
1533 Published specification: RFC-AAAA
1535 Applications that use this media type: The type is used by systems
1536 that report e.g., electrical power usage and environmental
1537 information such as temperature and humidity. It can be used for a
1538 wide range of sensor reporting systems.
1540 Fragment identifier considerations: Fragment identification for
1541 application/sensml+json is supported by using fragment identifiers as
1542 specified by RFC-AAAA.
1544 Additional information:
1546 Magic number(s): none
1548 File extension(s): sensml
1550 Macintosh file type code(s): none
1552 Person & email address to contact for further information: Cullen
1553 Jennings
1555 Intended usage: COMMON
1557 Restrictions on usage: None
1559 Author: Cullen Jennings
1561 Change controller: IESG
1563 12.3.3. senml+cbor Media Type Registration
1565 Type name: application
1567 Subtype name: senml+cbor
1569 Required parameters: none
1571 Optional parameters: none
1573 Encoding considerations: Must be encoded as using [RFC7049]. See
1574 RFC-AAAA for details.
1576 Security considerations: See Section 13 of RFC-AAAA.
1578 Interoperability considerations: Applications MUST ignore any key
1579 value pairs that they do not understand unless the key ends with the
1580 '_' character in which case an error MUST be generated. This allows
1581 backwards compatible extensions to this specification. The "bver"
1582 field can be used to ensure the receiver supports a minimal level of
1583 functionality needed by the creator of the CBOR object.
1585 Published specification: RFC-AAAA
1586 Applications that use this media type: The type is used by systems
1587 that report e.g., electrical power usage and environmental
1588 information such as temperature and humidity. It can be used for a
1589 wide range of sensor reporting systems.
1591 Fragment identifier considerations: Fragment identification for
1592 application/senml+cbor is supported by using fragment identifiers as
1593 specified by RFC-AAAA.
1595 Additional information:
1597 Magic number(s): none
1599 File extension(s): senmlc
1601 Macintosh file type code(s): none
1603 Macintosh Universal Type Identifier code: org.ietf.senml-cbor
1604 conforms to public.data
1606 Person & email address to contact for further information: Cullen
1607 Jennings
1609 Intended usage: COMMON
1611 Restrictions on usage: None
1613 Author: Cullen Jennings
1615 Change controller: IESG
1617 12.3.4. sensml+cbor Media Type Registration
1619 Type name: application
1621 Subtype name: sensml+cbor
1623 Required parameters: none
1625 Optional parameters: none
1627 Encoding considerations: Must be encoded as using [RFC7049]. See
1628 RFC-AAAA for details.
1630 Security considerations: See Section 13 of RFC-AAAA.
1632 Interoperability considerations: Applications MUST ignore any key
1633 value pairs that they do not understand unless the key ends with the
1634 '_' character in which case an error MUST be generated. This allows
1635 backwards compatible extensions to this specification. The "bver"
1636 field can be used to ensure the receiver supports a minimal level of
1637 functionality needed by the creator of the CBOR object.
1639 Published specification: RFC-AAAA
1641 Applications that use this media type: The type is used by systems
1642 that report e.g., electrical power usage and environmental
1643 information such as temperature and humidity. It can be used for a
1644 wide range of sensor reporting systems.
1646 Fragment identifier considerations: Fragment identification for
1647 application/sensml+cbor is supported by using fragment identifiers as
1648 specified by RFC-AAAA.
1650 Additional information:
1652 Magic number(s): none
1654 File extension(s): sensmlc
1656 Macintosh file type code(s): none
1658 Person & email address to contact for further information: Cullen
1659 Jennings
1661 Intended usage: COMMON
1663 Restrictions on usage: None
1665 Author: Cullen Jennings
1667 Change controller: IESG
1669 12.3.5. senml+xml Media Type Registration
1671 Type name: application
1673 Subtype name: senml+xml
1675 Required parameters: none
1677 Optional parameters: none
1679 Encoding considerations: Must be encoded as using
1680 [W3C.REC-xml-20081126]. See RFC-AAAA for details.
1682 Security considerations: See Section 13 of RFC-AAAA.
1684 Interoperability considerations: Applications MUST ignore any XML
1685 tags or attributes that they do not understand unless the attribute
1686 name ends with the '_' character in which case an error MUST be
1687 generated. This allows backwards compatible extensions to this
1688 specification. The "bver" attribute in the senml XML tag can be used
1689 to ensure the receiver supports a minimal level of functionality
1690 needed by the creator of the XML SenML Pack.
1692 Published specification: RFC-AAAA
1694 Applications that use this media type: The type is used by systems
1695 that report e.g., electrical power usage and environmental
1696 information such as temperature and humidity. It can be used for a
1697 wide range of sensor reporting systems.
1699 Fragment identifier considerations: Fragment identification for
1700 application/senml+xml is supported by using fragment identifiers as
1701 specified by RFC-AAAA.
1703 Additional information:
1705 Magic number(s): none
1707 File extension(s): senmlx
1709 Windows Clipboard Name: "XML Sensor Measurement List"
1711 Macintosh file type code(s): none
1713 Macintosh Universal Type Identifier code: org.ietf.senml-xml conforms
1714 to public.xml
1716 Person & email address to contact for further information: Cullen
1717 Jennings
1719 Intended usage: COMMON
1721 Restrictions on usage: None
1723 Author: Cullen Jennings
1725 Change controller: IESG
1727 12.3.6. sensml+xml Media Type Registration
1729 Type name: application
1731 Subtype name: sensml+xml
1733 Required parameters: none
1735 Optional parameters: none
1737 Encoding considerations: Must be encoded as using
1738 [W3C.REC-xml-20081126]. See RFC-AAAA for details.
1740 Security considerations: See Section 13 of RFC-AAAA.
1742 Interoperability considerations: Applications MUST ignore any XML
1743 tags or attributes that they do not understand unless the attribute
1744 name ends with the '_' character in which case an error MUST be
1745 generated. This allows backwards compatible extensions to this
1746 specification. The "bver" attribute in the senml XML tag can be used
1747 to ensure the receiver supports a minimal level of functionality
1748 needed by the creator of the XML SenML Pack.
1750 Published specification: RFC-AAAA
1752 Applications that use this media type: The type is used by systems
1753 that report e.g., electrical power usage and environmental
1754 information such as temperature and humidity. It can be used for a
1755 wide range of sensor reporting systems.
1757 Fragment identifier considerations: Fragment identification for
1758 application/sensml+xml is supported by using fragment identifiers as
1759 specified by RFC-AAAA.
1761 Additional information:
1763 Magic number(s): none
1765 File extension(s): sensmlx
1767 Macintosh file type code(s): none
1769 Person & email address to contact for further information: Cullen
1770 Jennings
1772 Intended usage: COMMON
1774 Restrictions on usage: None
1775 Author: Cullen Jennings
1777 Change controller: IESG
1779 12.3.7. senml-exi Media Type Registration
1781 Type name: application
1783 Subtype name: senml-exi
1785 Required parameters: none
1787 Optional parameters: none
1789 Encoding considerations: Must be encoded as using
1790 [W3C.REC-exi-20140211]. See RFC-AAAA for details.
1792 Security considerations: See Section 13 of RFC-AAAA.
1794 Interoperability considerations: Applications MUST ignore any XML
1795 tags or attributes that they do not understand unless the attribute
1796 name ends with the '_' character in which case an error MUST be
1797 generated. This allows backwards compatible extensions to this
1798 specification. The "bver" attribute in the senml XML tag can be used
1799 to ensure the receiver supports a minimal level of functionality
1800 needed by the creator of the XML SenML Pack. Further information on
1801 using schemas to guide the EXI can be found in RFC-AAAA.
1803 Published specification: RFC-AAAA
1805 Applications that use this media type: The type is used by systems
1806 that report e.g., electrical power usage and environmental
1807 information such as temperature and humidity. It can be used for a
1808 wide range of sensor reporting systems.
1810 Fragment identifier considerations: Fragment identification for
1811 application/senml-exi is supported by using fragment identifiers as
1812 specified by RFC-AAAA.
1814 Additional information:
1816 Magic number(s): none
1818 File extension(s): senmle
1820 Macintosh file type code(s): none
1821 Macintosh Universal Type Identifier code: org.ietf.senml-exi conforms
1822 to public.data
1824 Person & email address to contact for further information: Cullen
1825 Jennings
1827 Intended usage: COMMON
1829 Restrictions on usage: None
1831 Author: Cullen Jennings
1833 Change controller: IESG
1835 12.3.8. sensml-exi Media Type Registration
1837 Type name: application
1839 Subtype name: sensml-exi
1841 Required parameters: none
1843 Optional parameters: none
1845 Encoding considerations: Must be encoded as using
1846 [W3C.REC-exi-20140211]. See RFC-AAAA for details.
1848 Security considerations: See Section 13 of RFC-AAAA.
1850 Interoperability considerations: Applications MUST ignore any XML
1851 tags or attributes that they do not understand unless the attribute
1852 name ends with the '_' character in which case an error MUST be
1853 generated. This allows backwards compatible extensions to this
1854 specification. The "bver" attribute in the senml XML tag can be used
1855 to ensure the receiver supports a minimal level of functionality
1856 needed by the creator of the XML SenML Pack. Further information on
1857 using schemas to guide the EXI can be found in RFC-AAAA.
1859 Published specification: RFC-AAAA
1861 Applications that use this media type: The type is used by systems
1862 that report e.g., electrical power usage and environmental
1863 information such as temperature and humidity. It can be used for a
1864 wide range of sensor reporting systems.
1866 Fragment identifier considerations: Fragment identification for
1867 application/sensml-exi is supported by using fragment identifiers as
1868 specified by RFC-AAAA.
1870 Additional information:
1872 Magic number(s): none
1874 File extension(s): sensmle
1876 Macintosh file type code(s): none
1878 Person & email address to contact for further information: Cullen
1879 Jennings
1881 Intended usage: COMMON
1883 Restrictions on usage: None
1885 Author: Cullen Jennings
1887 Change controller: IESG
1889 12.4. XML Namespace Registration
1891 This document registers the following XML namespaces in the IETF XML
1892 registry defined in [RFC3688].
1894 URI: urn:ietf:params:xml:ns:senml
1896 Registrant Contact: The IESG.
1898 XML: N/A, the requested URIs are XML namespaces
1900 12.5. CoAP Content-Format Registration
1902 IANA is requested to assign CoAP Content-Format IDs for the SenML
1903 media types in the "CoAP Content-Formats" sub-registry, within the
1904 "CoRE Parameters" registry [RFC7252]. IDs for the JSON, CBOR, and
1905 EXI Content-Formats are assigned from the "Expert Review" (0-255)
1906 range and for the XML Content-Format from the "IETF Review or IESG
1907 Approval" range. The assigned IDs are shown in Table 8.
1909 +-------------------------+-----+
1910 | Media type | ID |
1911 +-------------------------+-----+
1912 | application/senml+json | TBD |
1913 | application/sensml+json | TBD |
1914 | application/senml+cbor | TBD |
1915 | application/sensml+cbor | TBD |
1916 | application/senml-exi | TBD |
1917 | application/sensml-exi | TBD |
1918 | application/senml+xml | TBD |
1919 | application/sensml+xml | TBD |
1920 +-------------------------+-----+
1922 Table 8: CoAP Content-Format IDs
1924 13. Security Considerations
1926 Sensor data can contain a wide range of information ranging from
1927 information that is very public, such as the outside temperature in a
1928 given city, to very private information that requires integrity and
1929 confidentiality protection, such as patient health information. The
1930 SenML formats do not provide any security and instead rely on the
1931 protocol that carries them to provide security. Applications using
1932 SenML need to look at the overall context of how these media types
1933 will be used to decide if the security is adequate. The SenML
1934 formats defined by this specification do not contain any executable
1935 content. However, future extensions could potentially embed
1936 application specific executable content in the data.
1938 See also Section 14.
1940 14. Privacy Considerations
1942 Sensor data can range from information with almost no security
1943 considerations, such as the current temperature in a given city, to
1944 highly sensitive medical or location data. This specification
1945 provides no security protection for the data but is meant to be used
1946 inside another container or transport protocol such as S/MIME
1947 [RFC5751] or HTTP with TLS [RFC5246] that can provide integrity,
1948 confidentiality, and authentication information about the source of
1949 the data.
1951 The name fields need to uniquely identify the sources or destinations
1952 of the values in a SenML Pack. However, the use of long-term stable
1953 unique identifiers can be problematic for privacy reasons [RFC6973],
1954 depending on the application and the potential of these identifiers
1955 to be used in correlation with other information. They should be
1956 used with care or avoided as for example described for IPv6 addresses
1957 in [RFC7721].
1959 15. Acknowledgement
1961 We would like to thank Alexander Pelov, Alexey Melnikov, Andrew
1962 McClure, Andrew McGregor, Bjoern Hoehrmann, Christian Amsuess,
1963 Christian Groves, Daniel Peintner, Jan-Piet Mens, Jim Schaad, Joe
1964 Hildebrand, John Klensin, Karl Palsson, Lennart Duhrsen, Lisa
1965 Dusseault, Lyndsay Campbell, Martin Thomson, Michael Koster, Peter
1966 Saint-Andre, Roni Even, and Stephen Farrell, for their review
1967 comments.
1969 16. References
1971 16.1. Normative References
1973 [BIPM] Bureau International des Poids et Mesures, "The
1974 International System of Units (SI)", 8th edition, 2006.
1976 [IEEE.754.1985]
1977 Institute of Electrical and Electronics Engineers,
1978 "Standard for Binary Floating-Point Arithmetic", IEEE
1979 Standard 754, August 1985.
1981 [NIST811] Thompson, A. and B. Taylor, "Guide for the Use of the
1982 International System of Units (SI)", NIST Special
1983 Publication 811, 2008.
1985 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
1986 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
1987 RFC2119, March 1997, .
1990 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
1991 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
1992 2003, .
1994 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
1995 DOI 10.17487/RFC3688, January 2004, .
1998 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
1999 Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
2000 .
2002 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
2003 Specifications and Registration Procedures", BCP 13, RFC
2004 6838, DOI 10.17487/RFC6838, January 2013,
2005 .
2007 [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object
2008 Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049,
2009 October 2013, .
2011 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
2012 Application Protocol (CoAP)", RFC 7252, DOI 10.17487/
2013 RFC7252, June 2014, .
2016 [RFC7303] Thompson, H. and C. Lilley, "XML Media Types", RFC 7303,
2017 DOI 10.17487/RFC7303, July 2014, .
2020 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
2021 Writing an IANA Considerations Section in RFCs", BCP 26,
2022 RFC 8126, DOI 10.17487/RFC8126, June 2017,
2023 .
2025 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2026 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
2027 May 2017, .
2029 [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
2030 Interchange Format", STD 90, RFC 8259, DOI 10.17487/
2031 RFC8259, December 2017, .
2034 [RNC] ISO/IEC, "Information technology -- Document Schema
2035 Definition Language (DSDL) -- Part 2: Regular-grammar-
2036 based validation -- RELAX NG", ISO/IEC 19757-2, Annex C:
2037 RELAX NG Compact syntax, December 2008.
2039 [TIME_T] The Open Group Base Specifications, "Vol. 1: Base
2040 Definitions, Issue 7", Section 4.15 'Seconds Since the
2041 Epoch', IEEE Std 1003.1, 2013 Edition, 2013,
2042 .
2045 [W3C.REC-exi-20140211]
2046 Schneider, J., Kamiya, T., Peintner, D., and R. Kyusakov,
2047 "Efficient XML Interchange (EXI) Format 1.0 (Second
2048 Edition)", World Wide Web Consortium Recommendation REC-
2049 exi-20140211, February 2014,
2050 .
2052 [W3C.REC-xml-20081126]
2053 Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
2054 F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
2055 Edition)", World Wide Web Consortium Recommendation REC-
2056 xml-20081126, November 2008,
2057 .
2059 [W3C.REC-xmlschema-1-20041028]
2060 Thompson, H., Beech, D., Maloney, M., and N. Mendelsohn,
2061 "XML Schema Part 1: Structures Second Edition", World Wide
2062 Web Consortium Recommendation REC-xmlschema-1-20041028,
2063 October 2004,
2064 .
2066 16.2. Informative References
2068 [I-D.ietf-cbor-cddl]
2069 Birkholz, H., Vigano, C., and C. Bormann, "Concise data
2070 definition language (CDDL): a notational convention to
2071 express CBOR data structures", draft-ietf-cbor-cddl-02
2072 (work in progress), February 2018.
2074 [I-D.ietf-core-dev-urn]
2075 Arkko, J., Jennings, C., and Z. Shelby, "Uniform Resource
2076 Names for Device Identifiers", draft-ietf-core-dev-urn-01
2077 (work in progress), March 2018.
2079 [I-D.ietf-core-interfaces]
2080 Shelby, Z., Vial, M., Koster, M., Groves, C., Zhu, J., and
2081 B. Silverajan, "Reusable Interface Definitions for
2082 Constrained RESTful Environments", draft-ietf-core-
2083 interfaces-11 (work in progress), March 2018.
2085 [IEEE802.1as-2011]
2086 IEEE, "IEEE Standard for Local and Metropolitan Area
2087 Networks - Timing and Synchronization for Time-Sensitive
2088 Applications in Bridged Local Area Networks", 2011.
2090 [IEEE802.1ba-2011]
2091 IEEE, "IEEE Standard for Local and metropolitan area
2092 networks--Audio Video Bridging (AVB) Systems", 2011.
2094 [ISO-80000-5]
2095 "Quantities and units - Part 5: Thermodynamics", ISO
2096 80000-5, Edition 1.0, May 2007.
2098 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
2099 Resource Identifier (URI): Generic Syntax", STD 66, RFC
2100 3986, DOI 10.17487/RFC3986, January 2005,
2101 .
2103 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
2104 Unique IDentifier (UUID) URN Namespace", RFC 4122, DOI
2105 10.17487/RFC4122, July 2005, .
2108 [RFC4151] Kindberg, T. and S. Hawke, "The 'tag' URI Scheme", RFC
2109 4151, DOI 10.17487/RFC4151, October 2005,
2110 .
2112 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
2113 "Transmission of IPv6 Packets over IEEE 802.15.4
2114 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
2115 .
2117 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
2118 (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/
2119 RFC5246, August 2008, .
2122 [RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
2123 Mail Extensions (S/MIME) Version 3.2 Message
2124 Specification", RFC 5751, DOI 10.17487/RFC5751, January
2125 2010, .
2127 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
2128 Address Text Representation", RFC 5952, DOI 10.17487/
2129 RFC5952, August 2010, .
2132 [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
2133 Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
2134 .
2136 [RFC6920] Farrell, S., Kutscher, D., Dannewitz, C., Ohlman, B.,
2137 Keranen, A., and P. Hallam-Baker, "Naming Things with
2138 Hashes", RFC 6920, DOI 10.17487/RFC6920, April 2013,
2139 .
2141 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
2142 Morris, J., Hansen, M., and R. Smith, "Privacy
2143 Considerations for Internet Protocols", RFC 6973, DOI
2144 10.17487/RFC6973, July 2013, .
2147 [RFC7111] Hausenblas, M., Wilde, E., and J. Tennison, "URI Fragment
2148 Identifiers for the text/csv Media Type", RFC 7111, DOI
2149 10.17487/RFC7111, January 2014, .
2152 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
2153 Protocol (HTTP/1.1): Message Syntax and Routing", RFC
2154 7230, DOI 10.17487/RFC7230, June 2014, .
2157 [RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy
2158 Considerations for IPv6 Address Generation Mechanisms",
2159 RFC 7721, DOI 10.17487/RFC7721, March 2016,
2160 .
2162 [RFC8141] Saint-Andre, P. and J. Klensin, "Uniform Resource Names
2163 (URNs)", RFC 8141, DOI 10.17487/RFC8141, April 2017,
2164 .
2166 [UCUM] Schadow, G. and C. McDonald, "The Unified Code for Units
2167 of Measure (UCUM)", Regenstrief Institute and Indiana
2168 University School of Informatics, 2013,
2169 .
2171 Authors' Addresses
2173 Cullen Jennings
2174 Cisco
2175 400 3rd Avenue SW
2176 Calgary, AB T2P 4H2
2177 Canada
2179 Email: fluffy@iii.ca
2180 Zach Shelby
2181 ARM
2182 150 Rose Orchard
2183 San Jose 95134
2184 USA
2186 Phone: +1-408-203-9434
2187 Email: zach.shelby@arm.com
2189 Jari Arkko
2190 Ericsson
2191 Jorvas 02420
2192 Finland
2194 Email: jari.arkko@piuha.net
2196 Ari Keranen
2197 Ericsson
2198 Jorvas 02420
2199 Finland
2201 Email: ari.keranen@ericsson.com
2203 Carsten Bormann
2204 Universitaet Bremen TZI
2205 Postfach 330440
2206 Bremen D-28359
2207 Germany
2209 Phone: +49-421-218-63921
2210 Email: cabo@tzi.org