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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 24, 2019 5 Expires: January 25, 2020 7 Additional Units for SenML 8 draft-bormann-senml-more-units-01 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 derived units that 16 cannot be in SenML's main registry. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at https://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on January 25, 2020. 35 Copyright Notice 37 Copyright (c) 2019 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (https://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 2. New Units . . . . . . . . . . . . . . . . . . . . . . . . . . 2 54 3. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 4. New Registry . . . . . . . . . . . . . . . . . . . . . . . . 4 56 5. Security Considerations . . . . . . . . . . . . . . . . . . . 5 57 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 58 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 5 59 8. Normative References . . . . . . . . . . . . . . . . . . . . 5 60 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 62 1. Introduction 64 The Sensor Measurement Lists (SenML, [RFC8428]) media type supports 65 the indication of a unit, using the SenML field "u", for the quantity 66 given as a data value in a SenML record. For this purpose, SenML 67 defines an IANA registry of defined Unit names and their meanings. 69 This short document registers a number of additional units in the 70 IANA registry for Units in SenML that appear to be necessary for 71 further adopting SenML in other Standards Development Organizations 72 (SDOs). 74 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 75 "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and 76 "OPTIONAL" in this document are to be interpreted as described in 77 BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all 78 capitals, as shown here. 80 2. New Units 82 IANA is requested to assign new units in the "SenML Units" 83 subregistry of the SenML registry [IANA.senml] (as defined in 84 [RFC8428]): 86 +--------+--------------------------------------+-------+-----------+ 87 | Symbol | Description | Type | Reference | 88 +--------+--------------------------------------+-------+-----------+ 89 | B | Byte (information content) | float | RFCthis | 90 | | | | | 91 | VA | volt-ampere (Apparent Power) | float | RFCthis | 92 | | | | | 93 | var | volt-ampere reactive (Reactive | float | RFCthis | 94 | | Power) | | | 95 | | | | | 96 | J/m | joule per meter (Energy per | float | RFCthis | 97 | | distance) | | | 98 | | | | | 99 | deg | degrees (angle)* | float | RFCthis | 100 +--------+--------------------------------------+-------+-----------+ 102 Table 1: New units registered for SenML 104 3. Rationale 106 SenML [RFC8428] takes the position that unscaled SI units should 107 always be used. However, SenML makes one exception: The degree 108 Celsius (as Cel) is allowed as an alternative to the K (Kelvin). 110 This document takes the position that the same should apply to a 111 small number of alternative units in wide use: 113 o The Byte. [IEC-80000-13] defines both the bit (item 13-9.b) and 114 the byte (item 13-9.c, also called octet) as alternative names for 115 the coherent unit one for the purpose of giving storage capacity 116 and related quantities. While the name octet is associated with 117 the symbol o, this is in wide use only in French-speaking 118 countries. Globally more wide-spread is the symbol B for byte, 119 even though B is already taken in SI for bel. [RFC8428] therefore 120 registers dB as the SenML unit for logarithmic relative power, 121 leaving B free for the usage proposed here. While this is 122 potentially confusing, the situation is widely understood in 123 engineering circles and is unlikely to cause actual problems. 125 o The Volt-Ampere. [IEC-80000-6]} item 6-57.a defines the VA (volt 126 ampere) as a unit for apparent power; items 6-59.a, 6-60.a and 127 6-61.a also use the unit for complex, reactive, and non-active 128 power. 130 o The Volt-Ampere-reactive. [IEC-80000-6] item 6-60.b defines the 131 var (volt ampere reactive) as an alternative (and fully 132 equivalent) unit to VA specifically for reactive power (with the 133 primary unit VA). It is not presently known to this author how 134 the upcoming revision of IEC 80000-6 will update this, but it has 135 became clear since that there is strong interest in using this 136 unit specifically for the imaginary content of complex power, 137 reactive power [IEEE-1459]. 139 The unit "degrees" is unit in wide use in practice for plane angle 140 (as in heading, bearing, etc.). It is marked with an asterisk 141 because the preferred coherent SI unit is radian ("rad"). 143 The Joule per meter is not a traditional electromagnetic unit. It 144 and its scaled derivatives (in particular Wh/km) are used to describe 145 the energy expended for achieving motion over a given distance, e.g. 146 as an equivalent for electrical cars of the inverse of "mileage". 148 4. New Registry 150 IANA is requested to create a "scaled units" subregistry in the SenML 151 registry [IANA.senml] defined in [RFC8428]. 153 The registry has four columns: 155 o scaled unit: a newly registered name allocated within the same 156 namespace as SenML units 158 o SenML unit: an existing SenML unit from the SenML units registry 160 o scale, offset: two rational numbers, expressed in decimal or as a 161 fraction divided by a "/" character. 163 Quantities expressed in the derived unit can be converted into the 164 SenML unit by first multiplying their value with the scale number and 165 then adding the offset, yielding the value in the given SenML unit. 167 +-------------+------------+--------+--------+ 168 | scaled unit | SenML unit | scale | offset | 169 +-------------+------------+--------+--------+ 170 | ms | s | 1/1000 | 0 | 171 | | | | | 172 | km | m | 1000 | 0 | 173 | | | | | 174 | dBm | dBW | 1 | -30 | 175 +-------------+------------+--------+--------+ 177 Example: the value of a quantity given as 100 ms is first multiplied 178 by 1/1000, yielding the number 0.1, and then the offset 0 is added, 179 yielding the number 0.1 again, leading to a quantity of 0.1 s. 181 New entries can be added to the registration by Expert Review as 182 defined in [RFC8126]. Experts should exercise their own good 183 judgment, with the same guidelines as used for SenML units 184 (Section 12.1 of [RFC8428]), but without applying the rules 4 and 5. 186 SenML packs MAY, but SHOULD NOT use scaled units in place of SenML 187 units, except in the context of specific data models that are based 188 on these scaled units. 190 [So does this spec update RFC 8428?] 192 5. Security Considerations 194 The security considerations of [RFC8428] apply. The introduction of 195 new measurement units poses no additional security considerations 196 except from a possible potential for additional confusion about the 197 proper unit to use. 199 6. IANA Considerations 201 See Section 2 and Section 4. 203 Acknowledgements 205 Ari Keranen pointed out the need for additional units in SenML. 207 8. Normative References 209 [IANA.senml] 210 IANA, "Sensor Measurement Lists (SenML)", 211 . 213 [IEC-80000-13] 214 "Quantities and units - Part 13: Information science and 215 technology", IEC 80000-13, Edition 1.0, March 2008. 217 [IEC-80000-6] 218 "Quantities and units - Part 6: Electromagnetism", 219 IEC 80000-6, Edition 1.0, March 2008. 221 [IEEE-1459] 222 "IEEE Standard Definitions for the Measurement of Electric 223 Power Quantities Under Sinusoidal, Nonsinusoidal, 224 Balanced, or Unbalanced Conditions", IEEE Std 1459-2010, 225 March 2010. 227 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 228 Requirement Levels", BCP 14, RFC 2119, 229 DOI 10.17487/RFC2119, March 1997, 230 . 232 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 233 Writing an IANA Considerations Section in RFCs", BCP 26, 234 RFC 8126, DOI 10.17487/RFC8126, June 2017, 235 . 237 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 238 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 239 May 2017, . 241 [RFC8428] Jennings, C., Shelby, Z., Arkko, J., Keranen, A., and C. 242 Bormann, "Sensor Measurement Lists (SenML)", RFC 8428, 243 DOI 10.17487/RFC8428, August 2018, 244 . 246 Author's Address 248 Carsten Bormann 249 Universitaet Bremen TZI 250 Postfach 330440 251 Bremen D-28359 252 Germany 254 Phone: +49-421-218-63921 255 Email: cabo@tzi.org