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'XPointerFramework' == Outdated reference: A later version (-08) exists of draft-ietf-cbor-cddl-02 == Outdated reference: A later version (-11) exists of draft-ietf-core-dev-urn-01 == Outdated reference: A later version (-14) exists of draft-ietf-core-interfaces-11 -- Obsolete informational reference (is this intentional?): RFC 2818 (Obsoleted by RFC 9110) -- Obsolete informational reference (is this intentional?): RFC 5751 (Obsoleted by RFC 8551) -- Obsolete informational reference (is this intentional?): RFC 7230 (Obsoleted by RFC 9110, RFC 9112) Summary: 1 error (**), 0 flaws (~~), 5 warnings (==), 10 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Jennings 3 Internet-Draft Cisco 4 Intended status: Standards Track Z. Shelby 5 Expires: November 19, 2018 ARM 6 J. Arkko 7 A. Keranen 8 Ericsson 9 C. Bormann 10 Universitaet Bremen TZI 11 May 18, 2018 13 Sensor Measurement Lists (SenML) 14 draft-ietf-core-senml-16 16 Abstract 18 This specification defines a format 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 https://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 November 19, 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 (https://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 . . . . . . . . . . . . . . . . . . . . . . 8 69 4.4. Extensibility . . . . . . . . . . . . . . . . . . . . . . 8 70 4.5. Records and Their Fields . . . . . . . . . . . . . . . . 9 71 4.5.1. Names . . . . . . . . . . . . . . . . . . . . . . . . 9 72 4.5.2. Units . . . . . . . . . . . . . . . . . . . . . . . . 9 73 4.5.3. Time . . . . . . . . . . . . . . . . . . . . . . . . 10 74 4.5.4. Values . . . . . . . . . . . . . . . . . . . . . . . 11 75 4.6. Resolved Records . . . . . . . . . . . . . . . . . . . . 11 76 4.7. Associating Meta-data . . . . . . . . . . . . . . . . . . 12 77 4.8. Sensor Streaming Measurement Lists (SensML) . . . . . . . 12 78 4.9. Configuration and Actuation usage . . . . . . . . . . . . 12 79 5. JSON Representation (application/senml+json) . . . . . . . . 13 80 5.1. Examples . . . . . . . . . . . . . . . . . . . . . . . . 14 81 5.1.1. Single Datapoint . . . . . . . . . . . . . . . . . . 14 82 5.1.2. Multiple Datapoints . . . . . . . . . . . . . . . . . 14 83 5.1.3. Multiple Measurements . . . . . . . . . . . . . . . . 15 84 5.1.4. Resolved Data . . . . . . . . . . . . . . . . . . . . 16 85 5.1.5. Multiple Data Types . . . . . . . . . . . . . . . . . 17 86 5.1.6. Collection of Resources . . . . . . . . . . . . . . . 17 87 5.1.7. Setting an Actuator . . . . . . . . . . . . . . . . . 17 88 6. CBOR Representation (application/senml+cbor) . . . . . . . . 18 89 7. XML Representation (application/senml+xml) . . . . . . . . . 20 90 8. EXI Representation (application/senml-exi) . . . . . . . . . 22 91 9. Fragment Identification Methods . . . . . . . . . . . . . . . 25 92 9.1. Fragment Identification Examples . . . . . . . . . . . . 25 93 9.2. Fragment Identification for the XML and EXI Formats . . . 26 94 10. Usage Considerations . . . . . . . . . . . . . . . . . . . . 26 95 11. CDDL . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 96 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 97 12.1. Units Registry . . . . . . . . . . . . . . . . . . . . . 29 98 12.2. SenML Label Registry . . . . . . . . . . . . . . . . . . 33 99 12.3. Media Type Registrations . . . . . . . . . . . . . . . . 34 100 12.3.1. senml+json Media Type Registration . . . . . . . . . 35 101 12.3.2. sensml+json Media Type Registration . . . . . . . . 36 102 12.3.3. senml+cbor Media Type Registration . . . . . . . . . 37 103 12.3.4. sensml+cbor Media Type Registration . . . . . . . . 38 104 12.3.5. senml+xml Media Type Registration . . . . . . . . . 39 105 12.3.6. sensml+xml Media Type Registration . . . . . . . . . 41 106 12.3.7. senml-exi Media Type Registration . . . . . . . . . 42 107 12.3.8. sensml-exi Media Type Registration . . . . . . . . . 43 108 12.4. XML Namespace Registration . . . . . . . . . . . . . . . 44 109 12.5. CoAP Content-Format Registration . . . . . . . . . . . . 44 110 13. Security Considerations . . . . . . . . . . . . . . . . . . . 45 111 14. Privacy Considerations . . . . . . . . . . . . . . . . . . . 46 112 15. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 46 113 16. References . . . . . . . . . . . . . . . . . . . . . . . . . 46 114 16.1. Normative References . . . . . . . . . . . . . . . . . . 46 115 16.2. Informative References . . . . . . . . . . . . . . . . . 49 116 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51 118 1. Overview 120 Connecting sensors to the Internet is not new, and there have been 121 many protocols designed to facilitate it. This specification defines 122 a format and media types for carrying simple sensor information in a 123 protocol such as HTTP [RFC7230] or CoAP [RFC7252]. The SenML format 124 is designed so that processors with very limited capabilities could 125 easily encode a sensor measurement into the media type, while at the 126 same time a server parsing the data could relatively efficiently 127 collect a large number of sensor measurements. SenML can be used for 128 a variety of data flow models, most notably data feeds pushed from a 129 sensor to a collector, and the web resource model where the sensor is 130 requested as a resource representation (e.g., "GET /sensor/ 131 temperature"). 133 There are many types of more complex measurements and measurements 134 that this media type would not be suitable for. SenML strikes a 135 balance between having some information about the sensor carried with 136 the sensor data so that the data is self describing but it also tries 137 to make that a fairly minimal set of auxiliary information for 138 efficiency reason. Other information about the sensor can be 139 discovered by other methods such as using the CoRE Link Format 140 [RFC6690]. 142 SenML is defined by a data model for measurements and simple meta- 143 data about measurements and devices. The data is structured as a 144 single array that contains a series of SenML Records which can each 145 contain fields such as an unique identifier for the sensor, the time 146 the measurement was made, the unit the measurement is in, and the 147 current value of the sensor. Serializations for this data model are 148 defined for JSON [RFC8259], CBOR [RFC7049], XML 149 [W3C.REC-xml-20081126], and Efficient XML Interchange (EXI) 150 [W3C.REC-exi-20140211]. 152 For example, the following shows a measurement from a temperature 153 gauge encoded in the JSON syntax. 155 [ 156 {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","v":23.1} 157 ] 159 In the example above, the array has a single SenML Record with a 160 measurement for a sensor named "urn:dev:ow:10e2073a01080063" with a 161 current value of 23.1 degrees Celsius. 163 2. Requirements and Design Goals 165 The design goal is to be able to send simple sensor measurements in 166 small packets from large numbers of constrained devices. Keeping the 167 total size of payload small makes it easy to use SenML also in 168 constrained networks, e.g., in a 6LoWPAN [RFC4944]. It is always 169 difficult to define what small code is, but there is a desire to be 170 able to implement this in roughly 1 KB of flash on a 8 bit 171 microprocessor. Experience with power meters and other large scale 172 deployments has indicated that the solution needs to support allowing 173 multiple measurements to be batched into a single HTTP or CoAP 174 request. This "batch" upload capability allows the server side to 175 efficiently support a large number of devices. It also conveniently 176 supports batch transfers from proxies and storage devices, even in 177 situations where the sensor itself sends just a single data item at a 178 time. The multiple measurements could be from multiple related 179 sensors or from the same sensor but at different times. 181 The basic design is an array with a series of measurements. The 182 following example shows two measurements made at different times. 183 The value of a measurement is given by the "v" field, the time of a 184 measurement is in the "t" field, the "n" field has a unique sensor 185 name, and the unit of the measurement is carried in the "u" field. 187 [ 188 {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020076e+09, 189 "v":23.5}, 190 {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020091e+09, 191 "v":23.6} 192 ] 194 To keep the messages small, it does not make sense to repeat the "n" 195 field in each SenML Record so there is a concept of a Base Name which 196 is simply a string that is prepended to the Name field of all 197 elements in that record and any records that follow it. So a more 198 compact form of the example above is the following. 200 [ 201 {"bn":"urn:dev:ow:10e2073a01080063","u":"Cel","t":1.276020076e+09, 202 "v":23.5}, 203 {"u":"Cel","t":1.276020091e+09, 204 "v":23.6} 205 ] 207 In the above example the Base Name is in the "bn" field and the "n" 208 fields in each Record are the empty string so they are omitted. 210 Some devices have accurate time while others do not so SenML supports 211 absolute and relative times. Time is represented in floating point 212 as seconds. Values greater than or equal to 2**28 represent an 213 absolute time relative to the Unix epoch. Values less than 2**28 214 represent time relative to the current time. 216 A simple sensor with no absolute wall clock time might take a 217 measurement every second, batch up 60 of them, and then send the 218 batch to a server. It would include the relative time each 219 measurement was made compared to the time the batch was sent in each 220 SenML Record. The server might have accurate NTP time and use the 221 time it received the data, and the relative offset, to replace the 222 times in the SenML with absolute times before saving the SenML 223 information in a document database. 225 3. Terminology 227 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 228 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 229 "OPTIONAL" in this document are to be interpreted as described in BCP 230 14 [RFC2119] [RFC8174] when, and only when, they appear in all 231 capitals, as shown here. 233 This document also uses the following terms: 235 SenML Record: One measurement or configuration instance in time 236 presented using the SenML data model. 238 SenML Pack: One or more SenML Records in an array structure. 240 SenML Label: A short name used in SenML Records to denote different 241 SenML fields (e.g., "v" for "value"). 243 SenML Field: A component of a record that associates a value to a 244 SenML Label for this record. 246 SensML: Sensor Streaming Measurement List (see Section 4.8). 248 SensML Stream: One or more SenML Records to be processed as a 249 stream. 251 This document uses the terms "attribute" and "tag" where they occur 252 with the underlying technologies (XML, CBOR [RFC7049], and Link 253 Format [RFC6690]), not for SenML concepts per se. Note that 254 "attribute" has been widely used previously as a synonym for SenML 255 "field", though. 257 All comparisons of text strings are performed byte-by-byte (and 258 therefore necessarily case-sensitive). 260 Where arithmetic is used, this specification uses the notation 261 familiar from the programming language C, except that the operator 262 "**" stands for exponentiation. 264 4. SenML Structure and Semantics 266 Each SenML Pack carries a single array that represents a set of 267 measurements and/or parameters. This array contains a series of 268 SenML Records with several fields described below. There are two 269 kinds of fields: base and regular. Both the base fields and the 270 regular fields can be included in any SenML Record. The base fields 271 apply to the entries in the Record and also to all Records after it 272 up to, but not including, the next Record that has that same base 273 field. All base fields are optional. Regular fields can be included 274 in any SenML Record and apply only to that Record. 276 4.1. Base Fields 278 Base Name: This is a string that is prepended to the names found in 279 the entries. 281 Base Time: A base time that is added to the time found in an entry. 283 Base Unit: A base unit that is assumed for all entries, unless 284 otherwise indicated. If a record does not contain a Unit value, 285 then the Base Unit is used. Otherwise the value found in the Unit 286 (if any) is used. 288 Base Value: A base value is added to the value found in an entry, 289 similar to Base Time. 291 Base Sum: A base sum is added to the sum found in an entry, similar 292 to Base Time. 294 Version: Version number of media type format. This field is an 295 optional positive integer and defaults to 5 if not present. [RFC 296 Editor: change the default value to 10 when this specification is 297 published as an RFC and remove this note] 299 4.2. Regular Fields 301 Name: Name of the sensor or parameter. When appended to the Base 302 Name field, this must result in a globally unique identifier for 303 the resource. The name is optional, if the Base Name is present. 304 If the name is missing, Base Name must uniquely identify the 305 resource. This can be used to represent a large array of 306 measurements from the same sensor without having to repeat its 307 identifier on every measurement. 309 Unit: Unit for a measurement value. Optional. 311 Value: Value of the entry. Optional if a Sum value is present, 312 otherwise required. Values are represented using basic data 313 types. This specification defines floating point numbers ("v" 314 field for "Value"), booleans ("vb" for "Boolean Value"), strings 315 ("vs" for "String Value") and binary data ("vd" for "Data Value"). 316 Exactly one value field MUST appear unless there is Sum field in 317 which case it is allowed to have no Value field. 319 Sum: Integrated sum of the values over time. Optional. This field 320 is in the unit specified in the Unit value multiplied by seconds. 321 For historical reason it is named sum instead of integral. 323 Time: Time when value was recorded. Optional. 325 Update Time: Period of time in seconds that represents the maximum 326 time before this sensor will provide an updated reading for a 327 measurement. Optional. This can be used to detect the failure of 328 sensors or communications path from the sensor. 330 4.3. SenML Labels 332 Table 1 provides an overview of all SenML fields defined by this 333 document with their respective labels and data types. 335 +---------------+-------+------------+------------+------------+ 336 | Name | Label | CBOR Label | JSON Type | XML Type | 337 +---------------+-------+------------+------------+------------+ 338 | Base Name | bn | -2 | String | string | 339 | Base Time | bt | -3 | Number | double | 340 | Base Unit | bu | -4 | String | string | 341 | Base Value | bv | -5 | Number | double | 342 | Base Sum | bs | -6 | Number | double | 343 | Version | bver | -1 | Number | int | 344 | Name | n | 0 | String | string | 345 | Unit | u | 1 | String | string | 346 | Value | v | 2 | Number | double | 347 | String Value | vs | 3 | String | string | 348 | Boolean Value | vb | 4 | Boolean | boolean | 349 | Data Value | vd | 8 | String (*) | string (*) | 350 | Value Sum | s | 5 | Number | double | 351 | Time | t | 6 | Number | double | 352 | Update Time | ut | 7 | Number | double | 353 +---------------+-------+------------+------------+------------+ 355 Table 1: SenML Labels 357 (*) Data Value is base64 encoded string with URL safe alphabet as 358 defined in Section 5 of [RFC4648], with padding omitted. 360 For details of the JSON representation see Section 5, for the CBOR 361 Section 6, and for the XML Section 7. 363 4.4. Extensibility 365 The SenML format can be extended with further custom fields. Both 366 new base and regular fields are allowed. See Section 12.2 for 367 details. Implementations MUST ignore fields they don't recognize 368 unless that field has a label name that ends with the '_' character 369 in which case an error MUST be generated. 371 All SenML Records in a Pack MUST have the same version number. This 372 is typically done by adding a Base Version field to only the first 373 Record in the Pack, or by using the default value. 375 Systems reading one of the objects MUST check for the Version field. 376 If this value is a version number larger than the version which the 377 system understands, the system MUST NOT use this object. This allows 378 the version number to indicate that the object contains structure or 379 semantics that is different from what is defined in the present 380 document beyond just making use of the extension points provided 381 here. New version numbers can only be defined in an RFC that updates 382 this specification or it successors. 384 4.5. Records and Their Fields 386 4.5.1. Names 388 The Name value is concatenated to the Base Name value to yield the 389 name of the sensor. The resulting concatenated name needs to 390 uniquely identify and differentiate the sensor from all others. The 391 concatenated name MUST consist only of characters out of the set "A" 392 to "Z", "a" to "z", "0" to "9", "-", ":", ".", "/", and "_"; 393 furthermore, it MUST start with a character out of the set "A" to 394 "Z", "a" to "z", or "0" to "9". This restricted character set was 395 chosen so that concatenated names can be used directly within various 396 URI schemes (including segments of an HTTP path with no special 397 encoding; note that a name that contains "/" characters maps into 398 multiple URI path segments) and can be used directly in many 399 databases and analytic systems. [RFC5952] contains advice on 400 encoding an IPv6 address in a name. See Section 14 for privacy 401 considerations that apply to the use of long-term stable unique 402 identifiers. 404 Although it is RECOMMENDED that concatenated names are represented as 405 URIs [RFC3986] or URNs [RFC8141], the restricted character set 406 specified above puts strict limits on the URI schemes and URN 407 namespaces that can be used. As a result, implementers need to take 408 care in choosing the naming scheme for concatenated names, because 409 such names both need to be unique and need to conform to the 410 restricted character set. One approach is to include a bit string 411 that has guaranteed uniqueness (such as a 1-wire address [AN1796]). 412 Some of the examples within this document use the device URN 413 namespace as specified in [I-D.ietf-core-dev-urn]. UUIDs [RFC4122] 414 are another way to generate a unique name. However, the restricted 415 character set does not allow the use of many URI schemes, such as the 416 'tag' scheme [RFC4151] and the 'ni' scheme [RFC6920], in names as 417 such. The use of URIs with characters incompatible with this set, 418 and possible mapping rules between the two, are outside of the scope 419 of the present document. 421 4.5.2. Units 423 If the Record has no Unit, the Base Unit is used as the Unit. Having 424 no Unit and no Base Unit is allowed; any information that may be 425 required about units applicable to the value then needs to be 426 provided by the application context. 428 4.5.3. Time 430 If either the Base Time or Time value is missing, the missing field 431 is considered to have a value of zero. The Base Time and Time values 432 are added together to get the time of measurement. 434 Values less than 268,435,456 (2**28) represent time relative to the 435 current time. That is, a time of zero indicates that the sensor does 436 not know the absolute time and the measurement was made roughly 437 "now". A negative value indicates seconds in the past from roughly 438 "now". Positive values up to 2**28 indicate seconds in the future 439 from "now". Positive values can be used, e.g., for actuation use 440 when the desired change should happen in the future but the sender or 441 the receiver does not have accurate time available. 443 Values greater than or equal to 2**28 represent an absolute time 444 relative to the Unix epoch (1970-01-01T00:00Z in UTC time) and the 445 time is counted same way as the Portable Operating System Interface 446 (POSIX) "seconds since the epoch" [TIME_T]. Therefore the smallest 447 absolute time value that can be expressed (2**28) is 1978-07-04 448 21:24:16 UTC. 450 Because time values up to 2**28 are used for presenting time relative 451 to "now" and Time and Base Time are added together, care must be 452 taken to ensure that the sum does not inadvertently reach 2**28 453 (i.e., absolute time) when relative time was intended to be used. 455 Obviously, "now"-referenced SenML records are only useful within a 456 specific communication context (e.g., based on information on when 457 the SenML pack, or a specific record in a SensML stream, was sent) or 458 together with some other context information that can be used for 459 deriving a meaning of "now"; the expectation for any archival use is 460 that they will be processed into UTC-referenced records before that 461 context would cease to be available. This specification deliberately 462 leaves the accuracy of "now" very vague as it is determined by the 463 overall systems that use SenML. In a system where a sensor without 464 wall-clock time sends a SenML record with a "now"-referenced time 465 over a high speed RS 485 link to an embedded system with accurate 466 time that resolves "now" based on the time of reception, the 467 resulting time uncertainty could be within 1 ms. At the other 468 extreme, a deployment that sends SenML wind speed readings over a LEO 469 satellite link from a mountain valley might have resulting reception 470 time values that are easily a dozen minutes off the actual time of 471 the sensor reading, with the time uncertainty depending on satellite 472 locations and conditions. 474 4.5.4. Values 476 If only one of the Base Sum or Sum value is present, the missing 477 field is considered to have a value of zero. The Base Sum and Sum 478 values are added together to get the sum of measurement. If neither 479 the Base Sum or Sum are present, then the measurement does not have a 480 sum value. 482 If the Base Value or Value is not present, the missing field(s) are 483 considered to have a value of zero. The Base Value and Value are 484 added together to get the value of the measurement. 486 Representing the statistical characteristics of measurements, such as 487 accuracy, can be very complex. Future specification may add new 488 fields to provide better information about the statistical properties 489 of the measurement. 491 In summary, the structure of a SenML record is laid out to support a 492 single measurement per record. If multiple data values are measured 493 at the same time (e.g., air pressure and altitude), they are best 494 kept as separate records linked through their Time value; this is 495 even true where one of the data values is more "meta" than others 496 (e.g., describes a condition that influences other measurements at 497 the same time). 499 4.6. Resolved Records 501 Sometimes it is useful to be able to refer to a defined normalized 502 format for SenML records. This normalized format tends to get used 503 for big data applications and intermediate forms when converting to 504 other formats. Also, if SenML Records are used outside of a SenML 505 Pack, they need to be resolved first to ensure applicable base values 506 are applied. 508 A SenML Record is referred to as "resolved" if it does not contain 509 any base values, i.e., labels starting with the character 'b', except 510 for Version fields (see below), and has no relative times. To 511 resolve the Records, the applicable base values of the SenML Pack (if 512 any) are applied to the Record. That is, for the base values in the 513 Record or before the Record in the Pack, name and base name are 514 concatenated, base time is added to the time of the Record, if the 515 Record did not contain Unit the Base Unit is applied to the record, 516 etc. In addition the records need to be in chronological order in 517 the Pack. An example of this is shown in Section 5.1.4. 519 The Version field MUST NOT be present in resolved records if the 520 SenML version defined in this document is used and MUST be present 521 otherwise in all the resolved SenML Records. 523 Future specification that defines new base fields need to specify how 524 the field is resolved. 526 4.7. Associating Meta-data 528 SenML is designed to carry the minimum dynamic information about 529 measurements, and for efficiency reasons does not carry significant 530 static meta-data about the device, object or sensors. Instead, it is 531 assumed that this meta-data is carried out of band. For web 532 resources using SenML Packs, this meta-data can be made available 533 using the CoRE Link Format [RFC6690]. The most obvious use of this 534 link format is to describe that a resource is available in a SenML 535 format in the first place. The relevant media type indicator is 536 included in the Content-Type (ct=) link attribute (which is defined 537 for the Link Format in Section 7.2.1 of [RFC7252]). 539 4.8. Sensor Streaming Measurement Lists (SensML) 541 In some usage scenarios of SenML, the implementations store or 542 transmit SenML in a stream-like fashion, where data is collected over 543 time and continuously added to the object. This mode of operation is 544 optional, but systems or protocols using SenML in this fashion MUST 545 specify that they are doing this. SenML defines separate media types 546 to indicate Sensor Streaming Measurement Lists (SensML) for this 547 usage (see Section 12.3.2). In this situation, the SensML stream can 548 be sent and received in a partial fashion, i.e., a measurement entry 549 can be read as soon as the SenML Record is received and does not have 550 to wait for the full SensML Stream to be complete. 552 If times relative to "now" (see Section 4.5.3) are used in SenML 553 Records of a SensML stream, their interpretation of "now" is based on 554 the time when the specific Record is sent in the stream. 556 4.9. Configuration and Actuation usage 558 SenML can also be used for configuring parameters and controlling 559 actuators. When a SenML Pack is sent (e.g., using a HTTP/CoAP POST 560 or PUT method) and the semantics of the target are such that SenML is 561 interpreted as configuration/actuation, SenML Records are interpreted 562 as a request to change the values of given (sub)resources (given as 563 names) to given values at the given time(s). The semantics of the 564 target resource supporting this usage can be described, e.g., using 565 [I-D.ietf-core-interfaces]. Examples of actuation usage are shown in 566 Section 5.1.7. 568 5. JSON Representation (application/senml+json) 570 For the SenML fields shown in Table 2, the SenML labels are used as 571 the JSON object member names within JSON objects representing the 572 JSON SenML Records. 574 +---------------+-------+---------+ 575 | Name | label | Type | 576 +---------------+-------+---------+ 577 | Base Name | bn | String | 578 | Base Time | bt | Number | 579 | Base Unit | bu | String | 580 | Base Value | bv | Number | 581 | Base Sum | bs | Number | 582 | Version | bver | Number | 583 | Name | n | String | 584 | Unit | u | String | 585 | Value | v | Number | 586 | String Value | vs | String | 587 | Boolean Value | vb | Boolean | 588 | Data Value | vd | String | 589 | Value Sum | s | Number | 590 | Time | t | Number | 591 | Update Time | ut | Number | 592 +---------------+-------+---------+ 594 Table 2: JSON SenML Labels 596 The root JSON value consists of an array with one JSON object for 597 each SenML Record. All the fields in the above table MAY occur in 598 the records with member values of the type specified in the table. 600 Only the UTF-8 [RFC3629] form of JSON is allowed. Characters in the 601 String Value are encoded using the escape sequences defined in 602 [RFC8259]. Octets in the Data Value are base64 encoded with URL safe 603 alphabet as defined in Section 5 of [RFC4648], with padding omitted. 605 Systems receiving measurements MUST be able to process the range of 606 floating point numbers that are representable as an IEEE double 607 precision floating point numbers [IEEE.754.1985]. This allows time 608 values to have better than microsecond precision over the next 100 609 years. The number of significant digits in any measurement is not 610 relevant, so a reading of 1.1 has exactly the same semantic meaning 611 as 1.10. If the value has an exponent, the "e" MUST be in lower 612 case. In the interest of avoiding unnecessary verbosity and speeding 613 up processing, the mantissa SHOULD be less than 19 characters long 614 and the exponent SHOULD be less than 5 characters long. 616 5.1. Examples 618 5.1.1. Single Datapoint 620 The following shows a temperature reading taken approximately "now" 621 by a 1-wire sensor device that was assigned the unique 1-wire address 622 of 10e2073a01080063: 624 [ 625 {"n":"urn:dev:ow:10e2073a01080063","u":"Cel","v":23.1} 626 ] 628 5.1.2. Multiple Datapoints 630 The following example shows voltage and current now, i.e., at an 631 unspecified time. 633 [ 634 {"bn":"urn:dev:ow:10e2073a01080063:","n":"voltage","u":"V","v":120.1}, 635 {"n":"current","u":"A","v":1.2} 636 ] 638 The next example is similar to the above one, but shows current at 639 Tue Jun 8 18:01:16.001 UTC 2010 and at each second for the previous 5 640 seconds. 642 [ 643 {"bn":"urn:dev:ow:10e2073a0108006:","bt":1.276020076001e+09, 644 "bu":"A","bver":5, 645 "n":"voltage","u":"V","v":120.1}, 646 {"n":"current","t":-5,"v":1.2}, 647 {"n":"current","t":-4,"v":1.3}, 648 {"n":"current","t":-3,"v":1.4}, 649 {"n":"current","t":-2,"v":1.5}, 650 {"n":"current","t":-1,"v":1.6}, 651 {"n":"current","v":1.7} 652 ] 654 As an example of Sensor Streaming Measurement Lists (SensML), the 655 following stream of measurements may be sent via a long lived HTTP 656 POST from the producer of the stream to its consumer, and each 657 measurement object may be reported at the time it was measured: 659 [ 660 {"bn":"urn:dev:ow:10e2073a01080063","bt":1.320067464e+09, 661 "bu":"%RH","v":21.2}, 662 {"t":10,"v":21.3}, 663 {"t":20,"v":21.4}, 664 {"t":30,"v":21.4}, 665 {"t":40,"v":21.5}, 666 {"t":50,"v":21.5}, 667 {"t":60,"v":21.5}, 668 {"t":70,"v":21.6}, 669 {"t":80,"v":21.7}, 670 ... 672 5.1.3. Multiple Measurements 674 The following example shows humidity measurements from a mobile 675 device with a 1-wire address 10e2073a01080063, starting at Mon Oct 31 676 13:24:24 UTC 2011. The device also provides position data, which is 677 provided in the same measurement or parameter array as separate 678 entries. Note time is used to for correlating data that belongs 679 together, e.g., a measurement and a parameter associated with it. 680 Finally, the device also reports extra data about its battery status 681 at a separate time. 683 [ 684 {"bn":"urn:dev:ow:10e2073a01080063","bt":1.320067464e+09, 685 "bu":"%RH","v":20}, 686 {"u":"lon","v":24.30621}, 687 {"u":"lat","v":60.07965}, 688 {"t":60,"v":20.3}, 689 {"u":"lon","t":60,"v":24.30622}, 690 {"u":"lat","t":60,"v":60.07965}, 691 {"t":120,"v":20.7}, 692 {"u":"lon","t":120,"v":24.30623}, 693 {"u":"lat","t":120,"v":60.07966}, 694 {"u":"%EL","t":150,"v":98}, 695 {"t":180,"v":21.2}, 696 {"u":"lon","t":180,"v":24.30628}, 697 {"u":"lat","t":180,"v":60.07967} 698 ] 700 The size of this example represented in various forms, as well as 701 that form compressed with gzip is given in the following table. 703 +----------+------+-----------------+ 704 | Encoding | Size | Compressed Size | 705 +----------+------+-----------------+ 706 | JSON | 573 | 206 | 707 | XML | 649 | 235 | 708 | CBOR | 254 | 196 | 709 | EXI | 161 | 184 | 710 +----------+------+-----------------+ 712 Table 3: Size Comparisons 714 5.1.4. Resolved Data 716 The following shows the example from the previous section show in 717 resolved format. 719 [ 720 {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067464e+09, 721 "v":20}, 722 {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067464e+09, 723 "v":24.30621}, 724 {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067464e+09, 725 "v":60.07965}, 726 {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067524e+09, 727 "v":20.3}, 728 {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067524e+09, 729 "v":24.30622}, 730 {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067524e+09, 731 "v":60.07965}, 732 {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067584e+09, 733 "v":20.7}, 734 {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067584e+09, 735 "v":24.30623}, 736 {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067584e+09, 737 "v":60.07966}, 738 {"n":"urn:dev:ow:10e2073a01080063","u":"%EL","t":1.320067614e+09, 739 "v":98}, 740 {"n":"urn:dev:ow:10e2073a01080063","u":"%RH","t":1.320067644e+09, 741 "v":21.2}, 742 {"n":"urn:dev:ow:10e2073a01080063","u":"lon","t":1.320067644e+09, 743 "v":24.30628}, 744 {"n":"urn:dev:ow:10e2073a01080063","u":"lat","t":1.320067644e+09, 745 "v":60.07967} 746 ] 748 5.1.5. Multiple Data Types 750 The following example shows a sensor that returns different data 751 types. 753 [ 754 {"bn":"urn:dev:ow:10e2073a01080063:","n":"temp","u":"Cel","v":23.1}, 755 {"n":"label","vs":"Machine Room"}, 756 {"n":"open","vb":false}, 757 {"n":"nfv-reader","vd":"aGkgCg"} 758 ] 760 5.1.6. Collection of Resources 762 The following example shows the results from a query to one device 763 that aggregates multiple measurements from other devices. The 764 example assumes that a client has fetched information from a device 765 at 2001:db8::2 by performing a GET operation on http://[2001:db8::2] 766 at Mon Oct 31 16:27:09 UTC 2011, and has gotten two separate values 767 as a result, a temperature and humidity measurement as well as the 768 results from another device at http://[2001:db8::1] that also had a 769 temperature and humidity. Note that the last record would use the 770 Base Name from the 3rd record but the Base Time from the first 771 record. 773 [ 774 {"bn":"2001:db8::2/","bt":1.320078429e+09, 775 "n":"temperature","u":"Cel","v":25.2}, 776 {"n":"humidity","u":"%RH","v":30}, 777 {"bn":"2001:db8::1/","n":"temperature","u":"Cel","v":12.3}, 778 {"n":"humidity","u":"%RH","v":67} 779 ] 781 5.1.7. Setting an Actuator 783 The following example show the SenML that could be used to set the 784 current set point of a typical residential thermostat which has a 785 temperature set point, a switch to turn on and off the heat, and a 786 switch to turn on the fan override. 788 [ 789 {"bn":"urn:dev:ow:10e2073a01080063:"}, 790 {"n":"temp","u":"Cel","v":23.1}, 791 {"n":"heat","u":"/","v":1}, 792 {"n":"fan","u":"/","v":0} 793 ] 794 In the following example two different lights are turned on. It is 795 assumed that the lights are on a network that can guarantee delivery 796 of the messages to the two lights within 15 ms (e.g. a network using 797 802.1BA [IEEE802.1ba-2011] and 802.1AS [IEEE802.1as-2011] for time 798 synchronization). The controller has set the time of the lights 799 coming on to 20 ms in the future from the current time. This allows 800 both lights to receive the message, wait till that time, then apply 801 the switch command so that both lights come on at the same time. 803 [ 804 {"bt":1.320078429e+09,"bu":"/","n":"2001:db8::3","v":1}, 805 {"n":"2001:db8::4","v":1} 806 ] 808 The following shows two lights being turned off using a non 809 deterministic network that has a high odds of delivering a message in 810 less than 100 ms and uses NTP for time synchronization. The current 811 time is 1320078429. The user has just turned off a light switch 812 which is turning off two lights. Both lights are dimmed to 50% 813 brightness immediately to give the user instant feedback that 814 something is changing. However given the network, the lights will 815 probably dim at somewhat different times. Then 100 ms in the future, 816 both lights will go off at the same time. The instant but not 817 synchronized dimming gives the user the sensation of quick responses 818 and the timed off 100 ms in the future gives the perception of both 819 lights going off at the same time. 821 [ 822 {"bt":1.320078429e+09,"bu":"/","n":"2001:db8::3","v":0.5}, 823 {"n":"2001:db8::4","v":0.5}, 824 {"n":"2001:db8::3","t":0.1,"v":0}, 825 {"n":"2001:db8::4","t":0.1,"v":0} 826 ] 828 6. CBOR Representation (application/senml+cbor) 830 The CBOR [RFC7049] representation is equivalent to the JSON 831 representation, with the following changes: 833 o For JSON Numbers, the CBOR representation can use integers, 834 floating point numbers, or decimal fractions (CBOR Tag 4); however 835 a representation SHOULD be chosen such that when the CBOR value is 836 converted back to an IEEE double precision floating point value, 837 it has exactly the same value as the original Number. For the 838 version number, only an unsigned integer is allowed. 840 o Characters in the String Value are encoded using a definite length 841 text string (type 3). Octets in the Data Value are encoded using 842 a definite length byte string (type 2). 844 o For compactness, the CBOR representation uses integers for the 845 labels, as defined in Table 4. This table is conclusive, i.e., 846 there is no intention to define any additional integer map keys; 847 any extensions will use string map keys. This allows translators 848 converting between CBOR and JSON representations to convert also 849 all future labels without needing to update implementations. The 850 base values are given negative CBOR labels and others non-negative 851 labels. 853 +---------------+-------+------------+ 854 | Name | Label | CBOR Label | 855 +---------------+-------+------------+ 856 | Version | bver | -1 | 857 | Base Name | bn | -2 | 858 | Base Time | bt | -3 | 859 | Base Unit | bu | -4 | 860 | Base Value | bv | -5 | 861 | Base Sum | bs | -6 | 862 | Name | n | 0 | 863 | Unit | u | 1 | 864 | Value | v | 2 | 865 | String Value | vs | 3 | 866 | Boolean Value | vb | 4 | 867 | Value Sum | s | 5 | 868 | Time | t | 6 | 869 | Update Time | ut | 7 | 870 | Data Value | vd | 8 | 871 +---------------+-------+------------+ 873 Table 4: CBOR representation: integers for map keys 875 o For streaming SensML in CBOR representation, the array containing 876 the records SHOULD be a CBOR indefinite length array while for 877 non-streaming SenML, a definite length array MUST be used. 879 The following example shows a dump of the CBOR example for the same 880 sensor measurement as in Section 5.1.2. 882 0000 87 a7 21 78 1b 75 72 6e 3a 64 65 76 3a 6f 77 3a |..!x.urn:dev:ow:| 883 0010 31 30 65 32 30 37 33 61 30 31 30 38 30 30 36 3a |10e2073a0108006:| 884 0020 22 fb 41 d3 03 a1 5b 00 10 62 23 61 41 20 05 00 |".A...[..b#aA ..| 885 0030 67 76 6f 6c 74 61 67 65 01 61 56 02 fb 40 5e 06 |gvoltage.aV..@^.| 886 0040 66 66 66 66 66 a3 00 67 63 75 72 72 65 6e 74 06 |fffff..gcurrent.| 887 0050 24 02 fb 3f f3 33 33 33 33 33 33 a3 00 67 63 75 |$..?.333333..gcu| 888 0060 72 72 65 6e 74 06 23 02 fb 3f f4 cc cc cc cc cc |rrent.#..?......| 889 0070 cd a3 00 67 63 75 72 72 65 6e 74 06 22 02 fb 3f |...gcurrent."..?| 890 0080 f6 66 66 66 66 66 66 a3 00 67 63 75 72 72 65 6e |.ffffff..gcurren| 891 0090 74 06 21 02 f9 3e 00 a3 00 67 63 75 72 72 65 6e |t.!..>...gcurren| 892 00a0 74 06 20 02 fb 3f f9 99 99 99 99 99 9a a3 00 67 |t. ..?.........g| 893 00b0 63 75 72 72 65 6e 74 06 00 02 fb 3f fb 33 33 33 |current....?.333| 894 00c0 33 33 33 |333| 895 00c3 897 In CBOR diagnostic notation (Section 6 of [RFC7049]), this is: 899 [{-2: "urn:dev:ow:10e2073a0108006:", 900 -3: 1276020076.001, -4: "A", -1: 5, 0: "voltage", 1: "V", 2: 120.1}, 901 {0: "current", 6: -5, 2: 1.2}, {0: "current", 6: -4, 2: 1.3}, 902 {0: "current", 6: -3, 2: 1.4}, {0: "current", 6: -2, 2: 1.5}, 903 {0: "current", 6: -1, 2: 1.6}, {0: "current", 6: 0, 2: 1.7}] 905 7. XML Representation (application/senml+xml) 907 A SenML Pack or Stream can also be represented in XML format as 908 defined in this section. 910 Only the UTF-8 form of XML is allowed. Characters in the String 911 Value are encoded using the escape sequences defined in [RFC8259]. 912 Octets in the Data Value are base64 encoded with URL safe alphabet as 913 defined in Section 5 of [RFC4648]. 915 The following example shows an XML example for the same sensor 916 measurement as in Section 5.1.2. 918 919 921 922 923 924 925 926 927 928 The SenML Stream is represented as a sensml element that contains a 929 series of senml elements for each SenML Record. The SenML fields are 930 represented as XML attributes. For each field defined in this 931 document, the following table shows the SenML labels, which are used 932 for the XML attribute name, as well as the according restrictions on 933 the XML attribute values ("type") as used in the XML senml elements. 935 +---------------+-------+---------+ 936 | Name | Label | Type | 937 +---------------+-------+---------+ 938 | Base Name | bn | string | 939 | Base Time | bt | double | 940 | Base Unit | bu | string | 941 | Base Value | bv | double | 942 | Base Sum | bs | double | 943 | Base Version | bver | int | 944 | Name | n | string | 945 | Unit | u | string | 946 | Value | v | double | 947 | String Value | vs | string | 948 | Data Value | vd | string | 949 | Boolean Value | vb | boolean | 950 | Value Sum | s | double | 951 | Time | t | double | 952 | Update Time | ut | double | 953 +---------------+-------+---------+ 955 Table 5: XML SenML Labels 957 The RelaxNG [RNC] schema for the XML is: 959 default namespace = "urn:ietf:params:xml:ns:senml" 960 namespace rng = "http://relaxng.org/ns/structure/1.0" 962 senml = element senml { 963 attribute bn { xsd:string }?, 964 attribute bt { xsd:double }?, 965 attribute bv { xsd:double }?, 966 attribute bs { xsd:double }?, 967 attribute bu { xsd:string }?, 968 attribute bver { xsd:int }?, 970 attribute n { xsd:string }?, 971 attribute s { xsd:double }?, 972 attribute t { xsd:double }?, 973 attribute u { xsd:string }?, 974 attribute ut { xsd:double }?, 976 attribute v { xsd:double }?, 977 attribute vb { xsd:boolean }?, 978 attribute vs { xsd:string }?, 979 attribute vd { xsd:string }? 980 } 982 sensml = 983 element sensml { 984 senml+ 985 } 987 start = sensml 989 8. EXI Representation (application/senml-exi) 991 For efficient transmission of SenML over e.g. a constrained network, 992 Efficient XML Interchange (EXI) can be used. This encodes the XML 993 Schema [W3C.REC-xmlschema-1-20041028] structure of SenML into binary 994 tags and values rather than ASCII text. An EXI representation of 995 SenML SHOULD be made using the strict schema-mode of EXI. This mode 996 however does not allow tag extensions to the schema, and therefore 997 any extensions will be lost in the encoding. For uses where 998 extensions need to be preserved in EXI, the non-strict schema mode of 999 EXI MAY be used. 1001 The EXI header MUST include an "EXI Options", as defined in 1002 [W3C.REC-exi-20140211], with an schemaId set to the value of "a" 1003 indicating the schema provided in this specification. Future 1004 revisions to the schema can change the value of the schemaId to allow 1005 for backwards compatibility. When the data will be transported over 1006 CoAP or HTTP, an EXI Cookie SHOULD NOT be used as it simply makes 1007 things larger and is redundant to information provided in the 1008 Content-Type header. 1010 The following is the XSD Schema to be used for strict schema guided 1011 EXI processing. It is generated from the RelaxNG. 1013 1014 1018 1019 1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039 1040 1041 1042 1043 1044 1046 The following shows a hexdump of the EXI produced from encoding the 1047 following XML example. Note this example is the same information as 1048 the first example in Section 5.1.2 in JSON format. 1050 1051 1053 1054 1055 Which compresses with EXI to the following displayed in hexdump: 1057 0000 a0 30 0d 84 80 f3 ab 93 71 d3 23 2b b1 d3 7b b9 |.0......q.#+..{.| 1058 0010 d1 89 83 29 91 81 b9 9b 09 81 89 81 c1 81 81 b1 |...)............| 1059 0020 99 d2 84 bb 37 b6 3a 30 b3 b2 90 1a b1 58 84 c0 |....7.:0.....X..| 1060 0030 33 04 b1 ba b9 39 32 b7 3a 10 1a 09 06 40 38 |3....92.:....@8| 1061 003f 1063 The above example used the bit packed form of EXI but it is also 1064 possible to use a byte packed form of EXI which can makes it easier 1065 for a simple sensor to produce valid EXI without really implementing 1066 EXI. Consider the example of a temperature sensor that produces a 1067 value in tenths of degrees Celsius over a range of 0.0 to 55.0. It 1068 would produce an XML SenML file such as: 1070 1071 1072 1074 The compressed form, using the byte alignment option of EXI, for the 1075 above XML is the following: 1077 0000 a0 00 48 80 6c 20 01 06 1d 75 72 6e 3a 64 65 76 |..H.l ...urn:dev| 1078 0010 3a 6f 77 3a 31 30 65 32 30 37 33 61 30 31 30 38 |:ow:10e2073a0108| 1079 0020 30 30 36 33 02 05 43 65 6c 01 00 e7 01 01 00 03 |0063..Cel.......| 1080 0030 01 |.| 1081 0031 1083 A small temperature sensor device that only generates this one EXI 1084 file does not really need a full EXI implementation. It can simply 1085 hard code the output replacing the 1-wire device ID starting at byte 1086 0x14 and going to byte 0x23 with its device ID, and replacing the 1087 value "0xe7 0x01" at location 0x31 and 0x32 with the current 1088 temperature. The EXI Specification [W3C.REC-exi-20140211] contains 1089 the full information on how floating point numbers are represented, 1090 but for the purpose of this sensor, the temperature can be converted 1091 to an integer in tenths of degrees (231 in this example). EXI stores 1092 7 bits of the integer in each byte with the top bit set to one if 1093 there are further bytes. So the first bytes at is set to low 7 bits 1094 of the integer temperature in tenths of degrees plus 0x80. In this 1095 example 231 & 0x7F + 0x80 = 0xE7. The second byte is set to the 1096 integer temperature in tenths of degrees right shifted 7 bits. In 1097 this example 231 >> 7 = 0x01. 1099 9. Fragment Identification Methods 1101 A SenML Pack typically consists of multiple SenML Records and for 1102 some applications it may be useful to be able to refer with a 1103 Fragment Identifier to a single record, or a set of records, in a 1104 Pack. The fragment identifier is only interpreted by a client and 1105 does not impact retrieval of a representation. The SenML Fragment 1106 Identification is modeled after CSV Fragment Identifiers [RFC7111]. 1108 To select a single SenML Record, the "rec" scheme followed by a 1109 single number is used. For the purpose of numbering records, the 1110 first record is at position 1. A range of records can be selected by 1111 giving the first and the last record number separated by a '-' 1112 character. Instead of the second number, the '*' character can be 1113 used to indicate the last SenML Record in the Pack. A set of records 1114 can also be selected using a comma separated list of record positions 1115 or ranges. 1117 (We use the term "selecting a record" for identifying it as part of 1118 the fragment, not in the sense of isolating it from the Pack -- the 1119 record still needs to be interpreted as part of the Pack, e.g., using 1120 the base values defined in earlier records) 1122 9.1. Fragment Identification Examples 1124 The 3rd SenML Record from "coap://example.com/temp" resource can be 1125 selected with: 1127 coap://example.com/temp#rec=3 1129 Records from 3rd to 6th can be selected with: 1131 coap://example.com/temp#rec=3-6 1133 Records from 19th to the last can be selected with: 1135 coap://example.com/temp#rec=19-* 1137 The 3rd and 5th record can be selected with: 1139 coap://example.com/temp#rec=3,5 1141 To select the Records from third to fifth, the 10th record, and all 1142 from 19th to the last: 1144 coap://example.com/temp#rec=3-5,10,19-* 1146 9.2. Fragment Identification for the XML and EXI Formats 1148 In addition to the SenML Fragment Identifiers described above, with 1149 the XML and EXI SenML formats also the syntax defined in the XPointer 1150 element() Scheme [XPointerElement] of the XPointer Framework 1151 [XPointerFramework] can be used. (This is required by [RFC7303] for 1152 media types using the "+xml" structured syntax suffix. SenML allows 1153 this for the EXI formats as well for consistency.) 1155 Note that fragment identifiers are available to the client side only; 1156 they are not provided in transfer protocols such as CoAP or HTTP. 1157 Thus, they cannot be used by the server in deciding which media type 1158 to send. Where a server has multiple representations available for a 1159 resource identified by a URI, it might send a JSON or CBOR 1160 representation when the client was directed to use an XML/EXI 1161 fragment identifier with this. Clients can prevent running into this 1162 problem by explicitly requesting an XML or EXI media type (e.g., 1163 using the CoAP Accept option) when XML/EXI-only fragment identifier 1164 syntax is in use in the URI. 1166 10. Usage Considerations 1168 The measurements support sending both the current value of a sensor 1169 as well as an integrated sum. For many types of measurements, the 1170 sum is more useful than the current value. For historical reasons, 1171 this field is called "sum" instead of "integral" which would more 1172 accurately describe its function. For example, an electrical meter 1173 that measures the energy a given computer uses will typically want to 1174 measure the cumulative amount of energy used. This is less prone to 1175 error than reporting the power each second and trying to have 1176 something on the server side sum together all the power measurements. 1177 If the network between the sensor and the meter goes down over some 1178 period of time, when it comes back up, the cumulative sum helps 1179 reflect what happened while the network was down. A meter like this 1180 would typically report a measurement with the unit set to watts, but 1181 it would put the sum of energy used in the "s" field of the 1182 measurement. It might optionally include the current power in the 1183 "v" field. 1185 While the benefit of using the integrated sum is fairly clear for 1186 measurements like power and energy, it is less obvious for something 1187 like temperature. Reporting the sum of the temperature makes it easy 1188 to compute averages even when the individual temperature values are 1189 not reported frequently enough to compute accurate averages. 1190 Implementers are encouraged to report the cumulative sum as well as 1191 the raw value of a given sensor. 1193 Applications that use the cumulative sum values need to understand 1194 they are very loosely defined by this specification, and depending on 1195 the particular sensor implementation may behave in unexpected ways. 1196 Applications should be able to deal with the following issues: 1198 1. Many sensors will allow the cumulative sums to "wrap" back to 1199 zero after the value gets sufficiently large. 1201 2. Some sensors will reset the cumulative sum back to zero when the 1202 device is reset, loses power, or is replaced with a different 1203 sensor. 1205 3. Applications cannot make assumptions about when the device 1206 started accumulating values into the sum. 1208 Typically applications can make some assumptions about specific 1209 sensors that will allow them to deal with these problems. A common 1210 assumption is that for sensors whose measurement values are always 1211 positive, the sum should never get smaller; so if the sum does get 1212 smaller, the application will know that one of the situations listed 1213 above has happened. 1215 Despite the name sum, the sum field is not useful for applications 1216 that maintain a running count of the number of times that an event 1217 happened or keeping track of a counter such as the total number of 1218 bytes sent on an interface. Data like that can be sent directly in 1219 the value field. 1221 11. CDDL 1223 As a convenient reference, the JSON and CBOR representations can be 1224 described with the common CDDL [I-D.ietf-cbor-cddl] specification in 1225 Figure 1 (informative). 1227 SenML-Pack = [1* record] 1229 record = { 1230 ? bn => tstr, ; Base Name 1231 ? bt => numeric, ; Base Time 1232 ? bu => tstr, ; Base Units 1233 ? bv => numeric, ; Base Value 1234 ? bs => numeric, ; Base Sum 1235 ? bver => uint, ; Base Version 1236 ? n => tstr, ; Name 1237 ? u => tstr, ; Units 1238 ? s => numeric, ; Value Sum 1239 ? t => numeric, ; Time 1240 ? ut => numeric, ; Update Time 1241 ? ( v => numeric // ; Numeric Value 1242 vs => tstr // ; String Value 1243 vb => bool // ; Boolean Value 1244 vd => binary-value ) ; Data Value 1245 * key-value-pair 1246 } 1248 ; now define the generic versions 1249 key-value-pair = ( label => value ) 1251 label = non-b-label / b-label 1252 non-b-label = tstr .regexp "[A-Zac-z0-9][-_:.A-Za-z0-9]*" / uint 1253 b-label = tstr .regexp "b[-_:.A-Za-z0-9]+" / nint 1255 value = tstr / binary-value / numeric / bool 1256 numeric = number / decfrac 1258 Figure 1: Common CDDL specification for CBOR and JSON SenML 1260 For JSON, we use text labels and base64url-encoded binary data 1261 (Figure 2). 1263 bver = "bver" n = "n" s = "s" 1264 bn = "bn" u = "u" t = "t" 1265 bt = "bt" v = "v" ut = "ut" 1266 bu = "bu" vs = "vs" vd = "vd" 1267 bv = "bv" vb = "vb" 1268 bs = "bs" 1270 binary-value = tstr ; base64url encoded 1272 Figure 2: JSON-specific CDDL specification for SenML 1274 For CBOR, we use integer labels and native binary data (Figure 3). 1276 bver = -1 n = 0 s = 5 1277 bn = -2 u = 1 t = 6 1278 bt = -3 v = 2 ut = 7 1279 bu = -4 vs = 3 vd = 8 1280 bv = -5 vb = 4 1281 bs = -6 1283 binary-value = bstr 1285 Figure 3: CBOR-specific CDDL specification for SenML 1287 12. IANA Considerations 1289 Note to RFC Editor: Please replace all occurrences of "RFC-AAAA" with 1290 the RFC number of this specification. 1292 IANA will create a new registry for "Sensor Measurement Lists (SenML) 1293 Parameters". The sub-registries defined in Section 12.1 and 1294 Section 12.2 will be created inside this registry. 1296 12.1. Units Registry 1298 IANA will create a registry of SenML unit symbols. The primary 1299 purpose of this registry is to make sure that symbols uniquely map to 1300 give type of measurement. Definitions for many of these units can be 1301 found in location such as [NIST811] and [BIPM]. Units marked with an 1302 asterisk are NOT RECOMMENDED to be produced by new implementations, 1303 but are in active use and SHOULD be implemented by consumers that can 1304 use the related base units. 1306 +----------+------------------------------------+-------+-----------+ 1307 | Symbol | Description | Type | Reference | 1308 +----------+------------------------------------+-------+-----------+ 1309 | m | meter | float | RFC-AAAA | 1310 | kg | kilogram | float | RFC-AAAA | 1311 | g | gram* | float | RFC-AAAA | 1312 | s | second | float | RFC-AAAA | 1313 | A | ampere | float | RFC-AAAA | 1314 | K | kelvin | float | RFC-AAAA | 1315 | cd | candela | float | RFC-AAAA | 1316 | mol | mole | float | RFC-AAAA | 1317 | Hz | hertz | float | RFC-AAAA | 1318 | rad | radian | float | RFC-AAAA | 1319 | sr | steradian | float | RFC-AAAA | 1320 | N | newton | float | RFC-AAAA | 1321 | Pa | pascal | float | RFC-AAAA | 1322 | J | joule | float | RFC-AAAA | 1323 | W | watt | float | RFC-AAAA | 1324 | C | coulomb | float | RFC-AAAA | 1325 | V | volt | float | RFC-AAAA | 1326 | F | farad | float | RFC-AAAA | 1327 | Ohm | ohm | float | RFC-AAAA | 1328 | S | siemens | float | RFC-AAAA | 1329 | Wb | weber | float | RFC-AAAA | 1330 | T | tesla | float | RFC-AAAA | 1331 | H | henry | float | RFC-AAAA | 1332 | Cel | degrees Celsius | float | RFC-AAAA | 1333 | lm | lumen | float | RFC-AAAA | 1334 | lx | lux | float | RFC-AAAA | 1335 | Bq | becquerel | float | RFC-AAAA | 1336 | Gy | gray | float | RFC-AAAA | 1337 | Sv | sievert | float | RFC-AAAA | 1338 | kat | katal | float | RFC-AAAA | 1339 | m2 | square meter (area) | float | RFC-AAAA | 1340 | m3 | cubic meter (volume) | float | RFC-AAAA | 1341 | l | liter (volume)* | float | RFC-AAAA | 1342 | m/s | meter per second (velocity) | float | RFC-AAAA | 1343 | m/s2 | meter per square second | float | RFC-AAAA | 1344 | | (acceleration) | | | 1345 | m3/s | cubic meter per second (flow rate) | float | RFC-AAAA | 1346 | l/s | liter per second (flow rate)* | float | RFC-AAAA | 1347 | W/m2 | watt per square meter (irradiance) | float | RFC-AAAA | 1348 | cd/m2 | candela per square meter | float | RFC-AAAA | 1349 | | (luminance) | | | 1350 | bit | bit (information content) | float | RFC-AAAA | 1351 | bit/s | bit per second (data rate) | float | RFC-AAAA | 1352 | lat | degrees latitude (note 1) | float | RFC-AAAA | 1353 | lon | degrees longitude (note 1) | float | RFC-AAAA | 1354 | pH | pH value (acidity; logarithmic | float | RFC-AAAA | 1355 | | quantity) | | | 1356 | dB | decibel (logarithmic quantity) | float | RFC-AAAA | 1357 | dBW | decibel relative to 1 W (power | float | RFC-AAAA | 1358 | | level) | | | 1359 | Bspl | bel (sound pressure level; | float | RFC-AAAA | 1360 | | logarithmic quantity)* | | | 1361 | count | 1 (counter value) | float | RFC-AAAA | 1362 | / | 1 (Ratio e.g., value of a switch, | float | RFC-AAAA | 1363 | | note 2) | | | 1364 | % | 1 (Ratio e.g., value of a switch, | float | RFC-AAAA | 1365 | | note 2)* | | | 1366 | %RH | Percentage (Relative Humidity) | float | RFC-AAAA | 1367 | %EL | Percentage (remaining battery | float | RFC-AAAA | 1368 | | energy level) | | | 1369 | EL | seconds (remaining battery energy | float | RFC-AAAA | 1370 | | level) | | | 1371 | 1/s | 1 per second (event rate) | float | RFC-AAAA | 1372 | 1/min | 1 per minute (event rate, "rpm")* | float | RFC-AAAA | 1373 | beat/min | 1 per minute (Heart rate in beats | float | RFC-AAAA | 1374 | | per minute)* | | | 1375 | beats | 1 (Cumulative number of heart | float | RFC-AAAA | 1376 | | beats)* | | | 1377 | S/m | Siemens per meter (conductivity) | float | RFC-AAAA | 1378 +----------+------------------------------------+-------+-----------+ 1380 Table 6 1382 o Note 1: Assumed to be in WGS84 unless another reference frame is 1383 known for the sensor. 1385 o Note 2: A value of 0.0 indicates the switch is off while 1.0 1386 indicates on and 0.5 would be half on. The preferred name of this 1387 unit is "/". For historical reasons, the name "%" is also 1388 provided for the same unit - but note that while that name 1389 strongly suggests a percentage (0..100) -- it is however NOT a 1390 percentage, but the absolute ratio! 1392 New entries can be added to the registration by Expert Review as 1393 defined in [RFC8126]. Experts should exercise their own good 1394 judgment but need to consider the following guidelines: 1396 1. There needs to be a real and compelling use for any new unit to 1397 be added. 1399 2. Each unit should define the semantic information and be chosen 1400 carefully. Implementers need to remember that the same word may 1401 be used in different real-life contexts. For example, degrees 1402 when measuring latitude have no semantic relation to degrees 1403 when measuring temperature; thus two different units are needed. 1405 3. These measurements are produced by computers for consumption by 1406 computers. The principle is that conversion has to be easily be 1407 done when both reading and writing the media type. The value of 1408 a single canonical representation outweighs the convenience of 1409 easy human representations or loss of precision in a conversion. 1411 4. Use of SI prefixes such as "k" before the unit is not 1412 recommended. Instead one can represent the value using 1413 scientific notation such a 1.2e3. The "kg" unit is exception to 1414 this rule since it is an SI base unit; the "g" unit is provided 1415 for legacy compatibility. 1417 5. For a given type of measurement, there will only be one unit 1418 type defined. So for length, meters are defined and other 1419 lengths such as mile, foot, light year are not allowed. For 1420 most cases, the SI unit is preferred. 1422 (Note that some amount of judgment will be required here, as 1423 even SI itself is not entirely consistent in this respect. For 1424 instance, for temperature [ISO-80000-5] defines a quantity, item 1425 5-1 (thermodynamic temperature), and a corresponding unit 5-1.a 1426 (Kelvin), and then goes ahead to define another quantity right 1427 besides that, item 5-2 ("Celsius temperature"), and the 1428 corresponding unit 5-2.a (degree Celsius). The latter quantity 1429 is defined such that it gives the thermodynamic temperature as a 1430 delta from T0 = 275.15 K. ISO 80000-5 is defining both units 1431 side by side, and not really expressing a preference. This 1432 level of recognition of the alternative unit degree Celsius is 1433 the reason why Celsius temperatures exceptionally seem 1434 acceptable in the SenML units list alongside Kelvin.) 1436 6. Symbol names that could be easily confused with existing common 1437 units or units combined with prefixes should be avoided. For 1438 example, selecting a unit name of "mph" to indicate something 1439 that had nothing to do with velocity would be a bad choice, as 1440 "mph" is commonly used to mean miles per hour. 1442 7. The following should not be used because the are common SI 1443 prefixes: Y, Z, E, P, T, G, M, k, h, da, d, c, n, u, p, f, a, z, 1444 y, Ki, Mi, Gi, Ti, Pi, Ei, Zi, Yi. 1446 8. The following units should not be used as they are commonly used 1447 to represent other measurements Ky, Gal, dyn, etg, P, St, Mx, G, 1448 Oe, Gb, sb, Lmb, mph, Ci, R, RAD, REM, gal, bbl, qt, degF, Cal, 1449 BTU, HP, pH, B/s, psi, Torr, atm, at, bar, kWh. 1451 9. The unit names are case sensitive and the correct case needs to 1452 be used, but symbols that differ only in case should not be 1453 allocated. 1455 10. A number after a unit typically indicates the previous unit 1456 raised to that power, and the / indicates that the units that 1457 follow are the reciprocal. A unit should have only one / in the 1458 name. 1460 11. A good list of common units can be found in the Unified Code for 1461 Units of Measure [UCUM]. 1463 12.2. SenML Label Registry 1465 IANA will create a new registry for SenML labels. The initial 1466 content of the registry is: 1468 +--------------+-------+----+-----------+----------+----+-----------+ 1469 | Name | Label | CL | JSON Type | XML Type | EI | Reference | 1470 +--------------+-------+----+-----------+----------+----+-----------+ 1471 | Base Name | bn | -2 | String | string | a | RFC-AAAA | 1472 | Base Time | bt | -3 | Number | double | a | RFC-AAAA | 1473 | Base Unit | bu | -4 | String | string | a | RFC-AAAA | 1474 | Base Value | bv | -5 | Number | double | a | RFC-AAAA | 1475 | Base Sum | bs | -6 | Number | double | a | RFC-AAAA | 1476 | Base Version | bver | -1 | Number | int | a | RFC-AAAA | 1477 | Name | n | 0 | String | string | a | RFC-AAAA | 1478 | Unit | u | 1 | String | string | a | RFC-AAAA | 1479 | Value | v | 2 | Number | double | a | RFC-AAAA | 1480 | String Value | vs | 3 | String | string | a | RFC-AAAA | 1481 | Boolean | vb | 4 | Boolean | boolean | a | RFC-AAAA | 1482 | Value | | | | | | | 1483 | Data Value | vd | 8 | String | string | a | RFC-AAAA | 1484 | Value Sum | s | 5 | Number | double | a | RFC-AAAA | 1485 | Time | t | 6 | Number | double | a | RFC-AAAA | 1486 | Update Time | ut | 7 | Number | double | a | RFC-AAAA | 1487 +--------------+-------+----+-----------+----------+----+-----------+ 1489 Table 7: IANA Registry for SenML Labels, CL = CBOR Label, EI = EXI ID 1491 This is the same table as Table 1, with notes removed, and with 1492 columns added for the information that is all the same for this 1493 initial set of registrations, but will need to be supplied with a 1494 different value for new registrations. 1496 All new entries must define the Label Name, Label, and XML Type but 1497 the CBOR labels SHOULD be left empty as CBOR will use the string 1498 encoding for any new labels. The EI column contains the EXI schemaId 1499 value of the first Schema which includes this label or is empty if 1500 this label was not intended for use with EXI. The Note field SHOULD 1501 contain information about where to find out more information about 1502 this label. 1504 The JSON, CBOR, and EXI types are derived from the XML type. All XML 1505 numeric types such as double, float, integer and int become a JSON 1506 Number. XML boolean and string become a JSON Boolean and String 1507 respectively. CBOR represents numeric values with a CBOR type that 1508 does not lose any information from the JSON value. EXI uses the XML 1509 types. 1511 New entries can be added to the registration by Expert Review as 1512 defined in [RFC8126]. Experts should exercise their own good 1513 judgment but need to consider that shorter labels should have more 1514 strict review. New entries should not be made that counteract the 1515 advice at the end of Section 4.5.4. 1517 All new SenML labels that have "base" semantics (see Section 4.1) 1518 MUST start with the character 'b'. Regular labels MUST NOT start 1519 with that character. All new SenML labels with Value semantics (see 1520 Section 4.2) MUST have "Value" in their (long form) name. 1522 Extensions that add a label that is intended for use with XML need to 1523 create a new RelaxNG scheme that includes all the labels in the IANA 1524 registry. 1526 Extensions that add a label that is intended for use with EXI need to 1527 create a new XSD Schema that includes all the labels in the IANA 1528 registry and then allocate a new EXI schemaId value. Moving to the 1529 next letter in the alphabet is the suggested way to create the new 1530 value for the EXI schemaId. Any labels with previously blank ID 1531 values SHOULD be updated in the IANA table to have their ID set to 1532 this new schemaId value. 1534 Extensions that are mandatory to understand to correctly process the 1535 Pack MUST have a label name that ends with the '_' character. 1537 12.3. Media Type Registrations 1539 The following registrations are done following the procedure 1540 specified in [RFC6838] and [RFC7303]. This document registers media 1541 types for each serialization format of SenML (JSON, CBOR, XML, and 1542 EXI) and also a corresponding set of media types for the streaming 1543 use (SensML, see Section 4.8). Clipboard formats are defined for the 1544 JSON and XML forms of SenML but not for streams or non-textual 1545 formats. 1547 The reason there are both SenML and the streaming SensML formats is 1548 that they are not the same data formats and they require separate 1549 negotiation to understand if they are supported and which one is 1550 being used. The non streaming format is required to have some sort 1551 of end of pack syntax which indicates there will be no more records. 1552 Many implementations that receive SenML wait for this end of pack 1553 marker before processing any of the records. On the other hand, with 1554 the streaming formats, it is explicitly not required to wait for this 1555 end of pack marker. Many implementations that produce streaming 1556 SensML will never send this end of pack marker so implementations 1557 that receive streaming SensML can not wait for the end of pack marker 1558 before they start processing the records. Given the SenML and 1559 streaming SenML are different data formats, and the requirement for 1560 separate negotiation, a media type for each one is needed. 1562 Note to RFC Editor - please remove this paragraph. Note that a 1563 request for media type review for senml+json was sent to the media- 1564 types@iana.org on Sept 21, 2010. A second request for all the types 1565 was sent on October 31, 2016. Please change all instances of RFC- 1566 AAAA with the RFC number of this document. 1568 12.3.1. senml+json Media Type Registration 1570 Type name: application 1572 Subtype name: senml+json 1574 Required parameters: none 1576 Optional parameters: none 1578 Encoding considerations: Must be encoded as using a subset of the 1579 encoding allowed in [RFC8259]. See RFC-AAAA for details. This 1580 simplifies implementation of very simple system and does not impose 1581 any significant limitations as all this data is meant for machine to 1582 machine communications and is not meant to be human readable. 1584 Security considerations: See Section 13 of RFC-AAAA. 1586 Interoperability considerations: Applications MUST ignore any JSON 1587 key value pairs that they do not understand unless the key ends with 1588 the '_' character in which case an error MUST be generated. This 1589 allows backwards compatible extensions to this specification. The 1590 "bver" field can be used to ensure the receiver supports a minimal 1591 level of functionality needed by the creator of the JSON object. 1593 Published specification: RFC-AAAA 1595 Applications that use this media type: The type is used by systems 1596 that report e.g., electrical power usage and environmental 1597 information such as temperature and humidity. It can be used for a 1598 wide range of sensor reporting systems. 1600 Fragment identifier considerations: Fragment identification for 1601 application/senml+json is supported by using fragment identifiers as 1602 specified by RFC-AAAA. 1604 Additional information: 1606 Magic number(s): none 1607 File extension(s): senml 1609 Windows Clipboard Name: "JSON Sensor Measurement List" 1611 Macintosh file type code(s): none 1613 Macintosh Universal Type Identifier code: org.ietf.senml-json 1614 conforms to public.text 1616 Person & email address to contact for further information: Cullen 1617 Jennings 1619 Intended usage: COMMON 1621 Restrictions on usage: None 1623 Author: Cullen Jennings 1625 Change controller: IESG 1627 12.3.2. sensml+json Media Type Registration 1629 Type name: application 1631 Subtype name: sensml+json 1633 Required parameters: none 1635 Optional parameters: none 1637 Encoding considerations: Must be encoded as using a subset of the 1638 encoding allowed in [RFC8259]. See RFC-AAAA for details. This 1639 simplifies implementation of very simple system and does not impose 1640 any significant limitations as all this data is meant for machine to 1641 machine communications and is not meant to be human readable. 1643 Security considerations: See Section 13 of RFC-AAAA. 1645 Interoperability considerations: Applications MUST ignore any JSON 1646 key value pairs that they do not understand unless the key ends with 1647 the '_' character in which case an error MUST be generated. This 1648 allows backwards compatible extensions to this specification. The 1649 "bver" field can be used to ensure the receiver supports a minimal 1650 level of functionality needed by the creator of the JSON object. 1652 Published specification: RFC-AAAA 1653 Applications that use this media type: The type is used by systems 1654 that report e.g., electrical power usage and environmental 1655 information such as temperature and humidity. It can be used for a 1656 wide range of sensor reporting systems. 1658 Fragment identifier considerations: Fragment identification for 1659 application/sensml+json is supported by using fragment identifiers as 1660 specified by RFC-AAAA. 1662 Additional information: 1664 Magic number(s): none 1666 File extension(s): sensml 1668 Macintosh file type code(s): none 1670 Person & email address to contact for further information: Cullen 1671 Jennings 1673 Intended usage: COMMON 1675 Restrictions on usage: None 1677 Author: Cullen Jennings 1679 Change controller: IESG 1681 12.3.3. senml+cbor Media Type Registration 1683 Type name: application 1685 Subtype name: senml+cbor 1687 Required parameters: none 1689 Optional parameters: none 1691 Encoding considerations: Must be encoded as using [RFC7049]. See 1692 RFC-AAAA for details. 1694 Security considerations: See Section 13 of RFC-AAAA. 1696 Interoperability considerations: Applications MUST ignore any key 1697 value pairs that they do not understand unless the key ends with the 1698 '_' character in which case an error MUST be generated. This allows 1699 backwards compatible extensions to this specification. The "bver" 1700 field can be used to ensure the receiver supports a minimal level of 1701 functionality needed by the creator of the CBOR object. 1703 Published specification: RFC-AAAA 1705 Applications that use this media type: The type is used by systems 1706 that report e.g., electrical power usage and environmental 1707 information such as temperature and humidity. It can be used for a 1708 wide range of sensor reporting systems. 1710 Fragment identifier considerations: Fragment identification for 1711 application/senml+cbor is supported by using fragment identifiers as 1712 specified by RFC-AAAA. 1714 Additional information: 1716 Magic number(s): none 1718 File extension(s): senmlc 1720 Macintosh file type code(s): none 1722 Macintosh Universal Type Identifier code: org.ietf.senml-cbor 1723 conforms to public.data 1725 Person & email address to contact for further information: Cullen 1726 Jennings 1728 Intended usage: COMMON 1730 Restrictions on usage: None 1732 Author: Cullen Jennings 1734 Change controller: IESG 1736 12.3.4. sensml+cbor Media Type Registration 1738 Type name: application 1740 Subtype name: sensml+cbor 1742 Required parameters: none 1744 Optional parameters: none 1746 Encoding considerations: Must be encoded as using [RFC7049]. See 1747 RFC-AAAA for details. 1749 Security considerations: See Section 13 of RFC-AAAA. 1751 Interoperability considerations: Applications MUST ignore any key 1752 value pairs that they do not understand unless the key ends with the 1753 '_' character in which case an error MUST be generated. This allows 1754 backwards compatible extensions to this specification. The "bver" 1755 field can be used to ensure the receiver supports a minimal level of 1756 functionality needed by the creator of the CBOR object. 1758 Published specification: RFC-AAAA 1760 Applications that use this media type: The type is used by systems 1761 that report e.g., electrical power usage and environmental 1762 information such as temperature and humidity. It can be used for a 1763 wide range of sensor reporting systems. 1765 Fragment identifier considerations: Fragment identification for 1766 application/sensml+cbor is supported by using fragment identifiers as 1767 specified by RFC-AAAA. 1769 Additional information: 1771 Magic number(s): none 1773 File extension(s): sensmlc 1775 Macintosh file type code(s): none 1777 Person & email address to contact for further information: Cullen 1778 Jennings 1780 Intended usage: COMMON 1782 Restrictions on usage: None 1784 Author: Cullen Jennings 1786 Change controller: IESG 1788 12.3.5. senml+xml Media Type Registration 1790 Type name: application 1792 Subtype name: senml+xml 1794 Required parameters: none 1796 Optional parameters: none 1797 Encoding considerations: Must be encoded as using 1798 [W3C.REC-xml-20081126]. See RFC-AAAA for details. 1800 Security considerations: See Section 13 of RFC-AAAA. 1802 Interoperability considerations: Applications MUST ignore any XML 1803 tags or attributes that they do not understand unless the attribute 1804 name ends with the '_' character in which case an error MUST be 1805 generated. This allows backwards compatible extensions to this 1806 specification. The "bver" attribute in the senml XML tag can be used 1807 to ensure the receiver supports a minimal level of functionality 1808 needed by the creator of the XML SenML Pack. 1810 Published specification: RFC-AAAA 1812 Applications that use this media type: The type is used by systems 1813 that report e.g., electrical power usage and environmental 1814 information such as temperature and humidity. It can be used for a 1815 wide range of sensor reporting systems. 1817 Fragment identifier considerations: Fragment identification for 1818 application/senml+xml is supported by using fragment identifiers as 1819 specified by RFC-AAAA. 1821 Additional information: 1823 Magic number(s): none 1825 File extension(s): senmlx 1827 Windows Clipboard Name: "XML Sensor Measurement List" 1829 Macintosh file type code(s): none 1831 Macintosh Universal Type Identifier code: org.ietf.senml-xml conforms 1832 to public.xml 1834 Person & email address to contact for further information: Cullen 1835 Jennings 1837 Intended usage: COMMON 1839 Restrictions on usage: None 1841 Author: Cullen Jennings 1843 Change controller: IESG 1845 12.3.6. sensml+xml Media Type Registration 1847 Type name: application 1849 Subtype name: sensml+xml 1851 Required parameters: none 1853 Optional parameters: none 1855 Encoding considerations: Must be encoded as using 1856 [W3C.REC-xml-20081126]. See RFC-AAAA for details. 1858 Security considerations: See Section 13 of RFC-AAAA. 1860 Interoperability considerations: Applications MUST ignore any XML 1861 tags or attributes that they do not understand unless the attribute 1862 name ends with the '_' character in which case an error MUST be 1863 generated. This allows backwards compatible extensions to this 1864 specification. The "bver" attribute in the senml XML tag can be used 1865 to ensure the receiver supports a minimal level of functionality 1866 needed by the creator of the XML SenML Pack. 1868 Published specification: RFC-AAAA 1870 Applications that use this media type: The type is used by systems 1871 that report e.g., electrical power usage and environmental 1872 information such as temperature and humidity. It can be used for a 1873 wide range of sensor reporting systems. 1875 Fragment identifier considerations: Fragment identification for 1876 application/sensml+xml is supported by using fragment identifiers as 1877 specified by RFC-AAAA. 1879 Additional information: 1881 Magic number(s): none 1883 File extension(s): sensmlx 1885 Macintosh file type code(s): none 1887 Person & email address to contact for further information: Cullen 1888 Jennings 1890 Intended usage: COMMON 1892 Restrictions on usage: None 1893 Author: Cullen Jennings 1895 Change controller: IESG 1897 12.3.7. senml-exi Media Type Registration 1899 Type name: application 1901 Subtype name: senml-exi 1903 Required parameters: none 1905 Optional parameters: none 1907 Encoding considerations: Must be encoded as using 1908 [W3C.REC-exi-20140211]. See RFC-AAAA for details. 1910 Security considerations: See Section 13 of RFC-AAAA. 1912 Interoperability considerations: Applications MUST ignore any XML 1913 tags or attributes that they do not understand unless the attribute 1914 name ends with the '_' character in which case an error MUST be 1915 generated. This allows backwards compatible extensions to this 1916 specification. The "bver" attribute in the senml XML tag can be used 1917 to ensure the receiver supports a minimal level of functionality 1918 needed by the creator of the XML SenML Pack. Further information on 1919 using schemas to guide the EXI can be found in RFC-AAAA. 1921 Published specification: RFC-AAAA 1923 Applications that use this media type: The type is used by systems 1924 that report e.g., electrical power usage and environmental 1925 information such as temperature and humidity. It can be used for a 1926 wide range of sensor reporting systems. 1928 Fragment identifier considerations: Fragment identification for 1929 application/senml-exi is supported by using fragment identifiers as 1930 specified by RFC-AAAA. 1932 Additional information: 1934 Magic number(s): none 1936 File extension(s): senmle 1938 Macintosh file type code(s): none 1939 Macintosh Universal Type Identifier code: org.ietf.senml-exi conforms 1940 to public.data 1942 Person & email address to contact for further information: Cullen 1943 Jennings 1945 Intended usage: COMMON 1947 Restrictions on usage: None 1949 Author: Cullen Jennings 1951 Change controller: IESG 1953 12.3.8. sensml-exi Media Type Registration 1955 Type name: application 1957 Subtype name: sensml-exi 1959 Required parameters: none 1961 Optional parameters: none 1963 Encoding considerations: Must be encoded as using 1964 [W3C.REC-exi-20140211]. See RFC-AAAA for details. 1966 Security considerations: See Section 13 of RFC-AAAA. 1968 Interoperability considerations: Applications MUST ignore any XML 1969 tags or attributes that they do not understand unless the attribute 1970 name ends with the '_' character in which case an error MUST be 1971 generated. This allows backwards compatible extensions to this 1972 specification. The "bver" attribute in the senml XML tag can be used 1973 to ensure the receiver supports a minimal level of functionality 1974 needed by the creator of the XML SenML Pack. Further information on 1975 using schemas to guide the EXI can be found in RFC-AAAA. 1977 Published specification: RFC-AAAA 1979 Applications that use this media type: The type is used by systems 1980 that report e.g., electrical power usage and environmental 1981 information such as temperature and humidity. It can be used for a 1982 wide range of sensor reporting systems. 1984 Fragment identifier considerations: Fragment identification for 1985 application/sensml-exi is supported by using fragment identifiers as 1986 specified by RFC-AAAA. 1988 Additional information: 1990 Magic number(s): none 1992 File extension(s): sensmle 1994 Macintosh file type code(s): none 1996 Person & email address to contact for further information: Cullen 1997 Jennings 1999 Intended usage: COMMON 2001 Restrictions on usage: None 2003 Author: Cullen Jennings 2005 Change controller: IESG 2007 12.4. XML Namespace Registration 2009 This document registers the following XML namespaces in the IETF XML 2010 registry defined in [RFC3688]. 2012 URI: urn:ietf:params:xml:ns:senml 2014 Registrant Contact: The IESG. 2016 XML: N/A, the requested URIs are XML namespaces 2018 12.5. CoAP Content-Format Registration 2020 IANA is requested to assign CoAP Content-Format IDs for the SenML 2021 media types in the "CoAP Content-Formats" sub-registry, within the 2022 "CoRE Parameters" registry [RFC7252]. IDs for the JSON, CBOR, and 2023 EXI Content-Formats are assigned from the "Expert Review" (0-255) 2024 range and for the XML Content-Format from the "IETF Review or IESG 2025 Approval" range. The assigned IDs are shown in Table 8. 2027 +-------------------------+----------+---------+-----------+ 2028 | Media type | Encoding | ID | Reference | 2029 +-------------------------+----------+---------+-----------+ 2030 | application/senml+json | - | TBD:110 | RFC-AAAA | 2031 | application/sensml+json | - | TBD:111 | RFC-AAAA | 2032 | application/senml+cbor | - | TBD:112 | RFC-AAAA | 2033 | application/sensml+cbor | - | TBD:113 | RFC-AAAA | 2034 | application/senml-exi | - | TBD:114 | RFC-AAAA | 2035 | application/sensml-exi | - | TBD:115 | RFC-AAAA | 2036 | application/senml+xml | - | TBD:310 | RFC-AAAA | 2037 | application/sensml+xml | - | TBD:311 | RFC-AAAA | 2038 +-------------------------+----------+---------+-----------+ 2040 Table 8: CoAP Content-Format IDs 2042 13. Security Considerations 2044 Sensor data presented with SenML can contain a wide range of 2045 information ranging from information that is very public, such as the 2046 outside temperature in a given city, to very private information that 2047 requires integrity and confidentiality protection, such as patient 2048 health information. When SenML is used for configuration or 2049 actuation, it can be used to change the state of systems and also 2050 impact the physical world, e.g., by turning off a heater or opening a 2051 lock. 2053 The SenML formats alone do not provide any security and instead rely 2054 on the protocol that carries them to provide security. Applications 2055 using SenML need to look at the overall context of how these formats 2056 will be used to decide if the security is adequate. In particular 2057 for sensitive sensor data and actuation use it is important to ensure 2058 that proper security mechanisms are used to provide, e.g., 2059 confidentiality, data integrity, and authentication as appropriate 2060 for the usage. 2062 The SenML formats defined by this specification do not contain any 2063 executable content. However, future extensions could potentially 2064 embed application specific executable content in the data. 2066 SenML Records are intended to be interpreted in the context of any 2067 applicable base values. If records become separated from the record 2068 that establishes the base values, the data will be useless or, worse, 2069 wrong. Care needs to be taken in keeping the integrity of a Pack 2070 that contains unresolved SenML Records (see Section 4.6). 2072 See also Section 14. 2074 14. Privacy Considerations 2076 Sensor data can range from information with almost no privacy 2077 considerations, such as the current temperature in a given city, to 2078 highly sensitive medical or location data. This specification 2079 provides no security protection for the data but is meant to be used 2080 inside another container or transfer protocol such as S/MIME 2081 [RFC5751] or HTTP with TLS [RFC2818] that can provide integrity, 2082 confidentiality, and authentication information about the source of 2083 the data. 2085 The name fields need to uniquely identify the sources or destinations 2086 of the values in a SenML Pack. However, the use of long-term stable 2087 unique identifiers can be problematic for privacy reasons [RFC6973], 2088 depending on the application and the potential of these identifiers 2089 to be used in correlation with other information. They should be 2090 used with care or avoided as for example described for IPv6 addresses 2091 in [RFC7721]. 2093 15. Acknowledgement 2095 We would like to thank Alexander Pelov, Alexey Melnikov, Andrew 2096 McClure, Andrew McGregor, Bjoern Hoehrmann, Christian Amsuess, 2097 Christian Groves, Daniel Peintner, Jan-Piet Mens, Jim Schaad, Joe 2098 Hildebrand, John Klensin, Karl Palsson, Lennart Duhrsen, Lisa 2099 Dusseault, Lyndsay Campbell, Martin Thomson, Michael Koster, Peter 2100 Saint-Andre, Roni Even, and Stephen Farrell, for their review 2101 comments. 2103 16. References 2105 16.1. Normative References 2107 [BIPM] Bureau International des Poids et Mesures, "The 2108 International System of Units (SI)", 8th edition, 2006. 2110 [IEEE.754.1985] 2111 Institute of Electrical and Electronics Engineers, 2112 "Standard for Binary Floating-Point Arithmetic", 2113 IEEE Standard 754, August 1985. 2115 [NIST811] Thompson, A. and B. Taylor, "Guide for the Use of the 2116 International System of Units (SI)", NIST Special 2117 Publication 811, 2008. 2119 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 2120 Requirement Levels", BCP 14, RFC 2119, 2121 DOI 10.17487/RFC2119, March 1997, 2122 . 2124 [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 2125 10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November 2126 2003, . 2128 [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, 2129 DOI 10.17487/RFC3688, January 2004, 2130 . 2132 [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data 2133 Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, 2134 . 2136 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 2137 Specifications and Registration Procedures", BCP 13, 2138 RFC 6838, DOI 10.17487/RFC6838, January 2013, 2139 . 2141 [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object 2142 Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, 2143 October 2013, . 2145 [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained 2146 Application Protocol (CoAP)", RFC 7252, 2147 DOI 10.17487/RFC7252, June 2014, 2148 . 2150 [RFC7303] Thompson, H. and C. Lilley, "XML Media Types", RFC 7303, 2151 DOI 10.17487/RFC7303, July 2014, 2152 . 2154 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 2155 Writing an IANA Considerations Section in RFCs", BCP 26, 2156 RFC 8126, DOI 10.17487/RFC8126, June 2017, 2157 . 2159 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2160 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2161 May 2017, . 2163 [RFC8259] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data 2164 Interchange Format", STD 90, RFC 8259, 2165 DOI 10.17487/RFC8259, December 2017, 2166 . 2168 [RNC] ISO/IEC, "Information technology -- Document Schema 2169 Definition Language (DSDL) -- Part 2: Regular-grammar- 2170 based validation -- RELAX NG", ISO/IEC 19757-2, Annex 2171 C: RELAX NG Compact syntax, December 2008. 2173 [TIME_T] The Open Group Base Specifications, "Vol. 1: Base 2174 Definitions, Issue 7", Section 4.15 'Seconds Since the 2175 Epoch', IEEE Std 1003.1, 2013 Edition, 2013, 2176 . 2179 [W3C.REC-exi-20140211] 2180 Schneider, J., Kamiya, T., Peintner, D., and R. Kyusakov, 2181 "Efficient XML Interchange (EXI) Format 1.0 (Second 2182 Edition)", World Wide Web Consortium Recommendation REC- 2183 exi-20140211, February 2014, 2184 . 2186 [W3C.REC-xml-20081126] 2187 Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and 2188 F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth 2189 Edition)", World Wide Web Consortium Recommendation REC- 2190 xml-20081126, November 2008, 2191 . 2193 [W3C.REC-xmlschema-1-20041028] 2194 Thompson, H., Beech, D., Maloney, M., and N. Mendelsohn, 2195 "XML Schema Part 1: Structures Second Edition", World Wide 2196 Web Consortium Recommendation REC-xmlschema-1-20041028, 2197 October 2004, 2198 . 2200 [XPointerElement] 2201 Grosso, P., Maler, E., Marsh, J., and N. Walsh, "XPointer 2202 element() Scheme", W3C Recommendation REC-xptr-element, 2203 March 2003, 2204 . 2206 [XPointerFramework] 2207 Grosso, P., Maler, E., Marsh, J., and N. Walsh, "XPointer 2208 Framework", W3C Recommendation REC-XPointer-Framework, 2209 March 2003, 2210 . 2212 16.2. Informative References 2214 [AN1796] Linke, B., "Overview of 1-Wire Technology and Its Use", 2215 June 2008, 2216 . 2218 [I-D.ietf-cbor-cddl] 2219 Birkholz, H., Vigano, C., and C. Bormann, "Concise data 2220 definition language (CDDL): a notational convention to 2221 express CBOR data structures", draft-ietf-cbor-cddl-02 2222 (work in progress), February 2018. 2224 [I-D.ietf-core-dev-urn] 2225 Arkko, J., Jennings, C., and Z. Shelby, "Uniform Resource 2226 Names for Device Identifiers", draft-ietf-core-dev-urn-01 2227 (work in progress), March 2018. 2229 [I-D.ietf-core-interfaces] 2230 Shelby, Z., Vial, M., Koster, M., Groves, C., Zhu, J., and 2231 B. Silverajan, "Reusable Interface Definitions for 2232 Constrained RESTful Environments", draft-ietf-core- 2233 interfaces-11 (work in progress), March 2018. 2235 [IEEE802.1as-2011] 2236 IEEE, "IEEE Standard for Local and Metropolitan Area 2237 Networks - Timing and Synchronization for Time-Sensitive 2238 Applications in Bridged Local Area Networks", 2011. 2240 [IEEE802.1ba-2011] 2241 IEEE, "IEEE Standard for Local and metropolitan area 2242 networks--Audio Video Bridging (AVB) Systems", 2011. 2244 [ISO-80000-5] 2245 "Quantities and units - Part 5: Thermodynamics", 2246 ISO 80000-5, Edition 1.0, May 2007. 2248 [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, 2249 DOI 10.17487/RFC2818, May 2000, 2250 . 2252 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform 2253 Resource Identifier (URI): Generic Syntax", STD 66, 2254 RFC 3986, DOI 10.17487/RFC3986, January 2005, 2255 . 2257 [RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally 2258 Unique IDentifier (UUID) URN Namespace", RFC 4122, 2259 DOI 10.17487/RFC4122, July 2005, 2260 . 2262 [RFC4151] Kindberg, T. and S. Hawke, "The 'tag' URI Scheme", 2263 RFC 4151, DOI 10.17487/RFC4151, October 2005, 2264 . 2266 [RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler, 2267 "Transmission of IPv6 Packets over IEEE 802.15.4 2268 Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007, 2269 . 2271 [RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet 2272 Mail Extensions (S/MIME) Version 3.2 Message 2273 Specification", RFC 5751, DOI 10.17487/RFC5751, January 2274 2010, . 2276 [RFC5952] Kawamura, S. and M. Kawashima, "A Recommendation for IPv6 2277 Address Text Representation", RFC 5952, 2278 DOI 10.17487/RFC5952, August 2010, 2279 . 2281 [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link 2282 Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, 2283 . 2285 [RFC6920] Farrell, S., Kutscher, D., Dannewitz, C., Ohlman, B., 2286 Keranen, A., and P. Hallam-Baker, "Naming Things with 2287 Hashes", RFC 6920, DOI 10.17487/RFC6920, April 2013, 2288 . 2290 [RFC6973] Cooper, A., Tschofenig, H., Aboba, B., Peterson, J., 2291 Morris, J., Hansen, M., and R. Smith, "Privacy 2292 Considerations for Internet Protocols", RFC 6973, 2293 DOI 10.17487/RFC6973, July 2013, 2294 . 2296 [RFC7111] Hausenblas, M., Wilde, E., and J. Tennison, "URI Fragment 2297 Identifiers for the text/csv Media Type", RFC 7111, 2298 DOI 10.17487/RFC7111, January 2014, 2299 . 2301 [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer 2302 Protocol (HTTP/1.1): Message Syntax and Routing", 2303 RFC 7230, DOI 10.17487/RFC7230, June 2014, 2304 . 2306 [RFC7721] Cooper, A., Gont, F., and D. Thaler, "Security and Privacy 2307 Considerations for IPv6 Address Generation Mechanisms", 2308 RFC 7721, DOI 10.17487/RFC7721, March 2016, 2309 . 2311 [RFC8141] Saint-Andre, P. and J. Klensin, "Uniform Resource Names 2312 (URNs)", RFC 8141, DOI 10.17487/RFC8141, April 2017, 2313 . 2315 [UCUM] Schadow, G. and C. McDonald, "The Unified Code for Units 2316 of Measure (UCUM)", Regenstrief Institute and Indiana 2317 University School of Informatics, 2013, 2318 . 2320 Authors' Addresses 2322 Cullen Jennings 2323 Cisco 2324 400 3rd Avenue SW 2325 Calgary, AB T2P 4H2 2326 Canada 2328 Email: fluffy@iii.ca 2330 Zach Shelby 2331 ARM 2332 150 Rose Orchard 2333 San Jose 95134 2334 USA 2336 Phone: +1-408-203-9434 2337 Email: zach.shelby@arm.com 2339 Jari Arkko 2340 Ericsson 2341 Jorvas 02420 2342 Finland 2344 Email: jari.arkko@piuha.net 2345 Ari Keranen 2346 Ericsson 2347 Jorvas 02420 2348 Finland 2350 Email: ari.keranen@ericsson.com 2352 Carsten Bormann 2353 Universitaet Bremen TZI 2354 Postfach 330440 2355 Bremen D-28359 2356 Germany 2358 Phone: +49-421-218-63921 2359 Email: cabo@tzi.org