Internet DRAFT - draft-bormann-senml-more-units
draft-bormann-senml-more-units
Network Working Group C. Bormann
Internet-Draft Universitaet Bremen TZI
Intended status: Standards Track August 29, 2019
Expires: March 1, 2020
Additional Units for SenML
draft-bormann-senml-more-units-04
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. It also defines a registry for secondary units that
cannot be in SenML's main registry as they are derived by linear
transformation from units already in that registry.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. New Units . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. New Registry . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
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).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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]):
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+--------+--------------------------------------+-------+-----------+
| 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) | | |
| | | | |
| vars | volt-ampere reactive seconds | float | RFCthis |
| | (Reactive Energy) | | |
| | | | |
| J/m | joule per meter (Energy per | float | RFCthis |
| | distance) | | |
| | | | |
| kg/m3 | kilograms per cubic meter (mass | float | RFCthis |
| | concentration) | | |
| | | | |
| deg | degrees (angle)* | float | RFCthis |
+--------+--------------------------------------+-------+-----------+
Table 1: New units registered for SenML
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
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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 unit "degrees" is unit in wide use in practice for plane angle
(as in heading, bearing, etc.). It is marked with an asterisk
because the preferred coherent SI unit is radian ("rad").
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. New Registry
IANA is requested to create a "secondary units" subregistry in the
SenML registry [IANA.senml] defined in [RFC8428].
The registry has four columns:
o secondary unit: a newly registered name allocated within the same
namespace as SenML units
o SenML unit: an existing SenML unit from the SenML units registry
o scale, offset: two rational numbers, expressed in decimal
(optionally, with a decimal exponent given) or as a fraction
divided by a "/" character.
Quantities expressed in the secondary unit can be converted into the
SenML unit by first multiplying their value with the scale number and
then adding the offset, yielding the value in the given SenML unit.
The initial content of the secondary units registry is:
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+----------------+------------+-----------+--------+-----------+
| secondary unit | SenML unit | scale | offset | Reference |
+----------------+------------+-----------+--------+-----------+
| ms | s | 1/1000 | 0 | RFCthis |
| | | | | |
| min | s | 60 | 0 | RFCthis |
| | | | | |
| h | s | 3600 | 0 | RFCthis |
| | | | | |
| kW | W | 1000 | 0 | RFCthis |
| | | | | |
| kVA | VA | 1000 | 0 | RFCthis |
| | | | | |
| kvar | var | 1000 | 0 | RFCthis |
| | | | | |
| Ah | C | 3600 | 0 | RFCthis |
| | | | | |
| Wh | J | 3600 | 0 | RFCthis |
| | | | | |
| kWh | J | 3600000 | 0 | RFCthis |
| | | | | |
| kvar | var | 1000 | 0 | RFCthis |
| | | | | |
| varh | vars | 3600 | 0 | RFCthis |
| | | | | |
| Wh/km | J/m | 3.6 | 0 | RFCthis |
| | | | | |
| KiB | B | 1024 | 0 | RFCthis |
| | | | | |
| mV | V | 1/1000 | 0 | RFCthis |
| | | | | |
| mA | A | 1/1000 | 0 | RFCthis |
| | | | | |
| dBm | dBW | 1 | -30 | RFCthis |
| | | | | |
| ug/m3 | kg/m3 | 1e-9 | 0 | RFCthis |
| | | | | |
| mm/h | m/s | 1/3600000 | 0 | RFCthis |
| | | | | |
| ppm | / | 1e-6 | 0 | RFCthis |
| | | | | |
| hPa | Pa | 100 | 0 | RFCthis |
| | | | | |
| mm | m | 1/1000 | 0 | RFCthis |
+----------------+------------+-----------+--------+-----------+
Example: the value of a quantity given as 100 ms is first multiplied
by 1/1000, yielding the number 0.1, and then the offset 0 is added,
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yielding the number 0.1 again, leading to a quantity of 0.1 s. The
value of a quantity given as 10 dBm is first multiplied by 1,
yielding the number 10, and then the offset -30 is added, yielding
the number -20, leading to a quantity of -20 dBW.
New entries can be added to the registration by Expert Review as
defined in [RFC8126]. Experts should exercise their own good
judgment, with the same guidelines as used for SenML units
(Section 12.1 of [RFC8428]), but without applying the rules 4 and 5.
Guidelines to the difference between units (which can go into the
registry) and quantities are widely available, see for instance [RS].
SenML packs MAY, but SHOULD NOT use secondary units in place of SenML
units, where the exception of the "SHOULD NOT" lies in the context of
specific existing data models that are based on these secondary
units.
[So does this spec update RFC 8428?]
5. 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.
6. IANA Considerations
See Section 2 and Section 4.
Acknowledgements
Ari Keranen pointed out the need for additional units in SenML.
8. References
8.1. 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.
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[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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
8.2. Informative References
[RS] Rohde&Schwarz, "Standard-compliant usage of quantities,
units and equations", version 4.0, November 2016,
<https://karriere.rohde-schwarz.de/fileadmin/user_upload/
Standard-compliant_usage_of_quantities_units_and_equations
_bro_en_5214-5061-62_v0400_96dpi.pdf>.
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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