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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Possible downref: Non-RFC (?) normative reference: ref. 'IEC-80000-13' -- Possible downref: Non-RFC (?) normative reference: ref. 'IEC-80000-6' -- Possible downref: Non-RFC (?) normative reference: ref. 'IEEE-1459' Summary: 0 errors (**), 0 flaws (~~), 1 warning (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group C. Bormann 3 Internet-Draft Universitaet Bremen TZI 4 Intended status: Standards Track July 25, 2019 5 Expires: January 26, 2020 7 Additional Units for SenML 8 draft-bormann-senml-more-units-03 10 Abstract 12 The Sensor Measurement Lists (SenML) media type supports the 13 indication of units for a quantity represented. This short document 14 registers a number of additional unit names in the IANA registry for 15 Units in SenML. It also defines a registry for secondary units that 16 cannot be in SenML's main registry as they are derived by linear 17 transformation from units already in that registry. 19 Status of This Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at https://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on January 26, 2020. 36 Copyright Notice 38 Copyright (c) 2019 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (https://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 54 2. New Units . . . . . . . . . . . . . . . . . . . . . . . . . . 2 55 3. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 3 56 4. New Registry . . . . . . . . . . . . . . . . . . . . . . . . 4 57 5. Security Considerations . . . . . . . . . . . . . . . . . . . 6 58 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 59 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6 60 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 61 8.1. Normative References . . . . . . . . . . . . . . . . . . 6 62 8.2. Informative References . . . . . . . . . . . . . . . . . 7 63 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 65 1. Introduction 67 The Sensor Measurement Lists (SenML, [RFC8428]) media type supports 68 the indication of a unit, using the SenML field "u", for the quantity 69 given as a data value in a SenML record. For this purpose, SenML 70 defines an IANA registry of defined Unit names and their meanings. 72 This short document registers a number of additional units in the 73 IANA registry for Units in SenML that appear to be necessary for 74 further adopting SenML in other Standards Development Organizations 75 (SDOs). 77 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 78 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 79 "OPTIONAL" in this document are to be interpreted as described in 80 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 81 capitals, as shown here. 83 2. New Units 85 IANA is requested to assign new units in the "SenML Units" 86 subregistry of the SenML registry [IANA.senml] (as defined in 87 [RFC8428]): 89 +--------+--------------------------------------+-------+-----------+ 90 | Symbol | Description | Type | Reference | 91 +--------+--------------------------------------+-------+-----------+ 92 | B | Byte (information content) | float | RFCthis | 93 | | | | | 94 | VA | volt-ampere (Apparent Power) | float | RFCthis | 95 | | | | | 96 | var | volt-ampere reactive (Reactive | float | RFCthis | 97 | | Power) | | | 98 | | | | | 99 | vars | volt-ampere reactive seconds | float | RFCthis | 100 | | (Reactive Energy) | | | 101 | | | | | 102 | J/m | joule per meter (Energy per | float | RFCthis | 103 | | distance) | | | 104 | | | | | 105 | deg | degrees (angle)* | float | RFCthis | 106 +--------+--------------------------------------+-------+-----------+ 108 Table 1: New units registered for SenML 110 3. Rationale 112 SenML [RFC8428] takes the position that unscaled SI units should 113 always be used. However, SenML makes one exception: The degree 114 Celsius (as Cel) is allowed as an alternative to the K (Kelvin). 116 This document takes the position that the same should apply to a 117 small number of alternative units in wide use: 119 o The Byte. [IEC-80000-13] defines both the bit (item 13-9.b) and 120 the byte (item 13-9.c, also called octet) as alternative names for 121 the coherent unit one for the purpose of giving storage capacity 122 and related quantities. While the name octet is associated with 123 the symbol o, this is in wide use only in French-speaking 124 countries. Globally more wide-spread is the symbol B for byte, 125 even though B is already taken in SI for bel. [RFC8428] therefore 126 registers dB as the SenML unit for logarithmic relative power, 127 leaving B free for the usage proposed here. While this is 128 potentially confusing, the situation is widely understood in 129 engineering circles and is unlikely to cause actual problems. 131 o The Volt-Ampere. [IEC-80000-6]} item 6-57.a defines the VA (volt 132 ampere) as a unit for apparent power; items 6-59.a, 6-60.a and 133 6-61.a also use the unit for complex, reactive, and non-active 134 power. 136 o The Volt-Ampere-reactive. [IEC-80000-6] item 6-60.b defines the 137 var (volt ampere reactive) as an alternative (and fully 138 equivalent) unit to VA specifically for reactive power (with the 139 primary unit VA). It is not presently known to this author how 140 the upcoming revision of IEC 80000-6 will update this, but it has 141 became clear since that there is strong interest in using this 142 unit specifically for the imaginary content of complex power, 143 reactive power [IEEE-1459]. 145 The unit "degrees" is unit in wide use in practice for plane angle 146 (as in heading, bearing, etc.). It is marked with an asterisk 147 because the preferred coherent SI unit is radian ("rad"). 149 The Joule per meter is not a traditional electromagnetic unit. It 150 and its scaled derivatives (in particular Wh/km) are used to describe 151 the energy expended for achieving motion over a given distance, e.g., 152 as an equivalent for electrical cars of the inverse of "mileage". 154 4. New Registry 156 IANA is requested to create a "secondary units" subregistry in the 157 SenML registry [IANA.senml] defined in [RFC8428]. 159 The registry has four columns: 161 o secondary unit: a newly registered name allocated within the same 162 namespace as SenML units 164 o SenML unit: an existing SenML unit from the SenML units registry 166 o scale, offset: two rational numbers, expressed in decimal or as a 167 fraction divided by a "/" character. 169 Quantities expressed in the secondary unit can be converted into the 170 SenML unit by first multiplying their value with the scale number and 171 then adding the offset, yielding the value in the given SenML unit. 173 The initial content of the secondary units registry is: 175 +----------------+------------+---------+--------+-----------+ 176 | secondary unit | SenML unit | scale | offset | Reference | 177 +----------------+------------+---------+--------+-----------+ 178 | ms | s | 1/1000 | 0 | RFCthis | 179 | | | | | | 180 | min | s | 60 | 0 | RFCthis | 181 | | | | | | 182 | h | s | 3600 | 0 | RFCthis | 183 | | | | | | 184 | kW | W | 1000 | 0 | RFCthis | 185 | | | | | | 186 | kVA | VA | 1000 | 0 | RFCthis | 187 | | | | | | 188 | kvar | var | 1000 | 0 | RFCthis | 189 | | | | | | 190 | Ah | C | 3600 | 0 | RFCthis | 191 | | | | | | 192 | Wh | J | 3600 | 0 | RFCthis | 193 | | | | | | 194 | kWh | J | 3600000 | 0 | RFCthis | 195 | | | | | | 196 | kvar | var | 1000 | 0 | RFCthis | 197 | | | | | | 198 | varh | vars | 3600 | 0 | RFCthis | 199 | | | | | | 200 | Wh/km | J/m | 3.6 | 0 | RFCthis | 201 | | | | | | 202 | KiB | B | 1024 | 0 | RFCthis | 203 | | | | | | 204 | mV | V | 1/1000 | 0 | RFCthis | 205 | | | | | | 206 | mA | A | 1/1000 | 0 | RFCthis | 207 | | | | | | 208 | dBm | dBW | 1 | -30 | RFCthis | 209 +----------------+------------+---------+--------+-----------+ 211 Example: the value of a quantity given as 100 ms is first multiplied 212 by 1/1000, yielding the number 0.1, and then the offset 0 is added, 213 yielding the number 0.1 again, leading to a quantity of 0.1 s. The 214 value of a quantity given as 10 dBm is first multiplied by 1, 215 yielding the number 10, and then the offset -30 is added, yielding 216 the number -20, leading to a quantity of -20 dBW. 218 New entries can be added to the registration by Expert Review as 219 defined in [RFC8126]. Experts should exercise their own good 220 judgment, with the same guidelines as used for SenML units 221 (Section 12.1 of [RFC8428]), but without applying the rules 4 and 5. 223 Guidelines to the difference between units (which can go into the 224 registry) and quantities are widely available, see for instance [RS]. 226 SenML packs MAY, but SHOULD NOT use secondary units in place of SenML 227 units, where the exception of the "SHOULD NOT" lies in the context of 228 specific existing data models that are based on these secondary 229 units. 231 [So does this spec update RFC 8428?] 233 5. Security Considerations 235 The security considerations of [RFC8428] apply. The introduction of 236 new measurement units poses no additional security considerations 237 except from a possible potential for additional confusion about the 238 proper unit to use. 240 6. IANA Considerations 242 See Section 2 and Section 4. 244 Acknowledgements 246 Ari Keranen pointed out the need for additional units in SenML. 248 8. References 250 8.1. Normative References 252 [IANA.senml] 253 IANA, "Sensor Measurement Lists (SenML)", 254 . 256 [IEC-80000-13] 257 "Quantities and units - Part 13: Information science and 258 technology", IEC 80000-13, Edition 1.0, March 2008. 260 [IEC-80000-6] 261 "Quantities and units - Part 6: Electromagnetism", 262 IEC 80000-6, Edition 1.0, March 2008. 264 [IEEE-1459] 265 "IEEE Standard Definitions for the Measurement of Electric 266 Power Quantities Under Sinusoidal, Nonsinusoidal, 267 Balanced, or Unbalanced Conditions", IEEE Std 1459-2010, 268 March 2010. 270 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 271 Requirement Levels", BCP 14, RFC 2119, 272 DOI 10.17487/RFC2119, March 1997, 273 . 275 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 276 Writing an IANA Considerations Section in RFCs", BCP 26, 277 RFC 8126, DOI 10.17487/RFC8126, June 2017, 278 . 280 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 281 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 282 May 2017, . 284 [RFC8428] Jennings, C., Shelby, Z., Arkko, J., Keranen, A., and C. 285 Bormann, "Sensor Measurement Lists (SenML)", RFC 8428, 286 DOI 10.17487/RFC8428, August 2018, 287 . 289 8.2. Informative References 291 [RS] Rohde&Schwarz, "Standard-compliant usage of quantities, 292 units and equations", version 4.0, November 2016, 293 . 297 Author's Address 299 Carsten Bormann 300 Universitaet Bremen TZI 301 Postfach 330440 302 Bremen D-28359 303 Germany 305 Phone: +49-421-218-63921 306 Email: cabo@tzi.org