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Network Working Group                                         C. Bormann
Internet-Draft                                   Universitaet Bremen TZI
Intended status: Standards Track                       February 27, 2019
Expires: August 31, 2019


                       Additional Units for SenML
                   draft-bormann-senml-more-units-00

Abstract

   The Sensor Measurement Lists (SenML) media type supports the
   indication of units for a quantity represented.  This short document
   registers a number of additional unit names in the IANA registry for
   Units in SenML.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  New Units . . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Rationale . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   4
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   The Sensor Measurement Lists (SenML, [RFC8428]) media type supports
   the indication of a unit, using the SenML field "u", for the quantity
   given as a data value in a SenML record.  For this purpose, SenML
   defines an IANA registry of defined Unit names and their meanings.

   This short document registers a number of additional units in the
   IANA registry for Units in SenML that appear to be necessary for
   further adopting SenML in other Standards Development Organizations
   (SDOs).

2.  New Units

   IANA is requested to assign new units in the "SenML Units"
   subregistry of the SenML registry [IANA.senml] (as defined in
   [RFC8428]):

   +--------+--------------------------------------+-------+-----------+
   | Symbol | Description                          | Type  | Reference |
   +--------+--------------------------------------+-------+-----------+
   | B      | Byte (information content)           | float | RFCthis   |
   |        |                                      |       |           |
   | VA     | volt-ampere (Apparent Power)         | float | RFCthis   |
   |        |                                      |       |           |
   | var    | volt-ampere reactive (Reactive       | float | RFCthis   |
   |        | Power)                               |       |           |
   |        |                                      |       |           |
   | J/m    | joule per meter (Energy per          | float | RFCthis   |
   |        | distance)                            |       |           |
   +--------+--------------------------------------+-------+-----------+

                  Table 1: New units registered for SenML







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3.  Rationale

   SenML [RFC8428] takes the position that unscaled SI units should
   always be used.  However, SenML makes one exception: The degree
   Celsius (as Cel) is allowed as an alternative to the K (Kelvin).

   This document takes the position that the same should apply to a
   small number of alternative units in wide use:

   o  The Byte.  [IEC-80000-13] defines both the bit (item 13-9.b) and
      the byte (item 13-9.c, also called octet) as alternative names for
      the coherent unit one for the purpose of giving storage capacity
      and related quantities.  While the name octet is associated with
      the symbol o, this is in wide use only in French-speaking
      countries.  Globally more wide-spread is the symbol B for byte,
      even though B is already taken in SI for bel.  [RFC8428] therefore
      registers dB as the SenML unit for logarithmic relative power,
      leaving B free for the usage proposed here.  While this is
      potentially confusing, the situation is widely understood in
      engineering circles and is unlikely to cause actual problems.

   o  The Volt-Ampere.  [IEC-80000-6]} item 6-57.a defines the VA (volt
      ampere) as a unit for apparent power; items 6-59.a, 6-60.a and
      6-61.a also use the unit for complex, reactive, and non-active
      power.

   o  The Volt-Ampere-reactive.  [IEC-80000-6] item 6-60.b defines the
      var (volt ampere reactive) as an alternative (and fully
      equivalent) unit to VA specifically for reactive power (with the
      primary unit VA).  It is not presently known to this author how
      the upcoming revision of IEC 80000-6 will update this, but it has
      became clear since that there is strong interest in using this
      unit specifically for the imaginary content of complex power,
      reactive power [IEEE-1459].

   The Joule per meter is not a traditional electromagnetic unit.  It
   and its scaled derivatives (in particular Wh/km) are used to describe
   the energy expended for achieving motion over a given distance, e.g.
   as an equivalent for electrical cars of the inverse of "mileage".

4.  Security Considerations

   The security considerations of [RFC8428] apply.  The introduction of
   new measurement units poses no additional security considerations
   except from a possible potential for additional confusion about the
   proper unit to use.





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5.  IANA Considerations

   See Section 2.

Acknowledgements

   Ari Keranen pointed out the need for additional units in SenML.

7.  Normative References

   [IANA.senml]
              IANA, "Sensor Measurement Lists (SenML)",
              <http://www.iana.org/assignments/senml>.

   [IEC-80000-13]
              "Quantities and units - Part 13: Information science and
              technology", IEC 80000-13, Edition 1.0, March 2008.

   [IEC-80000-6]
              "Quantities and units - Part 6: Electromagnetism",
              IEC 80000-6, Edition 1.0, March 2008.

   [IEEE-1459]
              "IEEE Standard Definitions for the Measurement of Electric
              Power Quantities Under Sinusoidal, Nonsinusoidal,
              Balanced, or Unbalanced Conditions", IEEE Std 1459-2010,
              March 2010.

   [RFC8428]  Jennings, C., Shelby, Z., Arkko, J., Keranen, A., and C.
              Bormann, "Sensor Measurement Lists (SenML)", RFC 8428,
              DOI 10.17487/RFC8428, August 2018,
              <https://www.rfc-editor.org/info/rfc8428>.

Author's Address

   Carsten Bormann
   Universitaet Bremen TZI
   Postfach 330440
   Bremen  D-28359
   Germany

   Phone: +49-421-218-63921
   Email: cabo@tzi.org








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