One document matched: draft-ietf-core-senml-00.xml
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<rfc ipr="trust200902" docName="draft-ietf-core-senml-00" category="std">
<front>
<title abbrev="Sensor Markup">Media Types for Sensor Markup Language (SenML)</title>
<author initials="C." surname="Jennings" fullname="Cullen Jennings">
<organization>Cisco</organization>
<address>
<postal>
<street>400 3rd Avenue SW</street>
<city>Calgary</city>
<region>AB</region>
<code>T2P 4H2</code>
<country>Canada</country>
</postal>
<phone>+1 408 421-9990</phone>
<email>fluffy@cisco.com</email>
</address>
</author>
<author initials="Z." surname="Shelby" fullname="Zach Shelby">
<organization>ARM</organization>
<address>
<postal>
<street>150 Rose Orchard</street>
<city>San Jose</city>
<code>95134</code>
<country>USA</country>
</postal>
<phone>+1-408-203-9434</phone>
<email>zach.shelby@arm.com</email>
</address>
</author>
<author initials="J." surname="Arkko" fullname="Jari Arkko">
<organization>Ericsson</organization>
<address>
<postal>
<street></street>
<city>Jorvas</city>
<code>02420</code>
<country>Finland</country>
</postal>
<email>jari.arkko@piuha.net</email>
</address>
</author>
<author initials="A." surname="Keranen" fullname="Ari Keranen">
<organization>Ericsson</organization>
<address>
<postal>
<street></street>
<city>Jorvas</city>
<code>02420</code>
<country>Finland</country>
</postal>
<email>ari.keranen@ericsson.com</email>
</address>
</author>
<date year="2016" month="April"/>
<area>ART</area>
<abstract>
<t>This specification defines media types for representing simple sensor
measurements and device parameters in the Sensor Markup Language
(SenML). Representations are defined in JavaScript Object Notation (JSON),
Concise Binary Object Representation (CBOR), eXtensible Markup Language (XML),
and Efficient XML Interchange (EXI), which share the common SenML data model. A
simple sensor, such as a temperature sensor, could use this media type in
protocols such as HTTP or CoAP to transport the measurements of the sensor or to
be configured.</t>
</abstract>
</front>
<middle>
<section anchor="overview" title="Overview">
<t>Connecting sensors to the internet is not new, and there have been many
protocols designed to facilitate it. This specification defines new media types
for carrying simple sensor information in a protocol such as HTTP or CoAP called
the Sensor Markup Language (SenML). This format was designed so that processors
with very limited capabilities could easily encode a sensor measurement into the
media type, while at the same time a server parsing the data could relatively
efficiently collect a large number of sensor measurements. The markup language
can be used for a variety of data flow models, most notably data feeds pushed
from a sensor to a collector, and the web resource model where the sensor is
requested as a resource representation (e.g., “GET /sensor/temperature”).</t>
<t>There are many types of more complex measurements and measurements that this
media type would not be suitable for. SenML strikes a balance between having
some information about the sensor carried with the sensor data so that the data
is self describing but it also tries to make that a fairly minimal set of
auxiliary information for efficiency reason. Other information about the sensor
can be discovered by other methods such as using the CoRE Link Format
<xref target="RFC6690"/>.</t>
<t>SenML is defined by a data model for measurements and simple meta-data about
measurements and devices. The data is structured as a single array that contains
a series of SenML Records which can each contain attributes such as an unique
identifier for the sensor, the time the measurement was made, the unit the
measurement is in, and the current value of the sensor. Serializations for this
data model are defined for JSON <xref target="RFC7159"/>, CBOR <xref target="RFC7049"/>, XML, and
Efficient XML Interchange (EXI) <xref target="W3C.REC-exi-20110310"/>.</t>
<t>For example, the following shows a measurement from a temperature
gauge encoded in the JSON syntax.</t>
<figure><artwork><![CDATA[
[{ "n": "urn:dev:ow:10e2073a01080063", "v":23.1, "u":"Cel" }]
]]></artwork></figure>
<t>In the example above, the array has a single SenML Record with a measurement for
a sensor named “urn:dev:ow:10e2073a01080063” with a current value of 23.5
degrees Celsius.</t>
</section>
<section anchor="requirements-and-design-goals" title="Requirements and Design Goals">
<t>The design goal is to be able to send simple sensor measurements in small
packets on mesh networks from large numbers of constrained devices. Keeping the
total size of payload under 80 bytes makes this easy to use on a wireless mesh
network. It is always difficult to define what small code is, but there is a
desire to be able to implement this in roughly 1 KB of flash on a 8 bit
microprocessor. Experience with Google power meter and large scale deployments
has indicated that the solution needs to support allowing multiple measurements
to be batched into a single HTTP or CoAP request. This “batch” upload capability
allows the server side to efficiently support a large number of devices. It also
conveniently supports batch transfers from proxies and storage devices, even in
situations where the sensor itself sends just a single data item at a time. The
multiple measurements could be from multiple related sensors or from the same
sensor but at different times.</t>
<t>The basic design is an array with a series of measurements. The following
example shows two measurements made at different times. The value of a
measurement is in the “v” tag, the time of a measurement is in the “t” tag,
the “n” tag has a unique sensor name, and the unit of the measurement is carried
in the “u” tag.</t>
<figure><artwork><![CDATA[
[
{ "n": "urn:dev:ow:10e2073a01080063",
"t": 1276020076, "v":23.5, "u":"Cel" },
{ "n": "urn:dev:ow:10e2073a01080063",
"t": 1276020091, "v":23.6, "u":"Cel" }
]
]]></artwork></figure>
<t>To keep the messages small, it does not make sense to repeat the “n” tag in each SenML
Record so there is a concept of a Base Name which is simply a string that is
prepended to the Name field of all elements in that record and any records that
follow it. So a more compact form of the example above is the following.</t>
<figure><artwork><![CDATA[
[
{ "bn": "urn:dev:ow:10e2073a01080063",
"t": 1276020076, "v":23.5, "u":"Cel" },
{ "t": 1276020091, "v":23.6, "u":"Cel" }
]
]]></artwork></figure>
<t>In the above example the Base Name is in the “bn” tag and the “n” tags in each
Record are the empty string so they are omitted. The Base Name also could be put
in a separate Record such as in the following example.</t>
<figure><artwork><![CDATA[
[
{ "bn": "urn:dev:ow:10e2073a01080063" },
{ "t": 1276020076, "v":23.5, "u":"Cel" },
{ "t": 1276020091, "v":23.6, "u":"Cel" }
]
]]></artwork></figure>
<t>Some devices have accurate time while others do not so SenML supports absolute
and relative times. Time is represented in floating point as seconds and values
greater than zero represent an absolute time relative to the unix epoch while
values of 0 or less represent a relative time in the past from the current
time. A simple sensor with no absolute wall clock time might take a measurement
every second and batch up 60 of them then send it to a server. It would include
the relative time the measurement was made to the time the batch was send in the
SenML Pack. The server might have accurate NTP time and use the time it received the
data, and the relative offset, to replace the times in the SenML with absolute
times before saving the SenML Pack in a document database.</t>
</section>
<section anchor="terminology" title="Terminology">
<t>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 <xref target="RFC2119"/>.</t>
<t>This document also uses the following terms:</t>
<t><list style="hanging">
<t hangText='SenML Record:'>
One measurement or configuration instance in time presented
using the SenML data model.</t>
<t hangText='SenML Pack:'>
One or more SenML Records in an array structure.</t>
</list></t>
</section>
<section anchor="semant" title="Semantics">
<t>Each SenML Pack carries a single array that represents a set of
measurements and/or parameters. This array contains a series of objects with
several optional attributes described below:</t>
<t><list style="hanging">
<t hangText='Base Name:'>
This is a string that is prepended to the names found in the entries. This
attribute is optional. This applies to the entries in all Records. A Base Name can
only be included in the first Record of the array.</t>
<t hangText='Base Time:'>
A base time that is added to the time found in an entry. This attribute is
optional. This applies to the entries in all Records. A Base Time can
only be included in the first Record of the array.</t>
<t hangText='Base Unit:'>
A base unit that is assumed for all entries, unless otherwise indicated. This
attribute is optional. If a record does not contain a unit value, then the base unit
is used otherwise the value of found in the Unit is used.
This applies to the entries in all Records. A Base Unit can
only be included in the first object of the array.</t>
<t hangText='Base Value:'>
A base value is added to the value found in an entry, similar to Base Time.
This attribute is optional. This applies to the entries in all Records.
A Base Value can only be included in the first Record of the array.</t>
<t hangText='Version:'>
Version number of media type format. This attribute is optional positive
integer and defaults to 5 if not present. A Version can
only be included in the first object of the array.</t>
<t hangText='Name:'>
Name of the sensor or parameter. When appended to the Base Name attribute,
this must result in a globally unique identifier for the resource. The name is
optional, if the Base Name is present. If the name is missing, Base Name must
uniquely identify the resource. This can be used to represent a large array of
measurements from the same sensor without having to repeat its identifier on
every measurement.</t>
<t hangText='Unit:'>
Units for a measurement value. Optional. If the Record has not Unit, the Base
Unit is used as the Unit. Having no Unit and no Base Unit is allowed.</t>
<t hangText='Value'>
Value of the entry. Optional if a Sum value is present, otherwise
required. Values are represented using three basic data types, Floating point
numbers (“v” field for “Value”), Booleans (“vb” for “Boolean Value”),
Strings (“vs” for “String Value”) and Data (“vd” for “Binary Data Value”) .
Exactly one of these three fields MUST
appear unless there is Sum field in which case it is allowed to have no Value
field or to have “v” field.</t>
<t hangText='Sum:'>
Integrated sum of the values over time. Optional. This attribute is in the
units specified in the Unit value multiplied by seconds.</t>
<t hangText='Time:'>
Time when value was recorded. Optional.</t>
<t hangText='Update Time:'>
An optional time in seconds that represents the maximum time before this sensor will
provide an updated reading for a measurement. This can be used to detect the
failure of sensors or communications path from the sensor.</t>
</list></t>
<t>The SenML format can be extended with further custom attributes. TODO - describe
what extensions are possible and how to do them.</t>
<t>Systems reading one of the objects MUST check for the Version attribute. If this
value is a version number larger than the version which the system understands,
the system SHOULD NOT use this object. This allows the version number to
indicate that the object contains mandatory to understand attributes. New
version numbers can only be defined in an RFC that updates this specification or
it successors.</t>
<t>The Name value is concatenated to the Base Name value to get the name of the
sensor. The resulting name needs to uniquely identify and differentiate the
sensor from all others. If the object is a representation resulting from the
request of a URI <xref target="RFC3986"/>, then in the absence of the Base Name attribute,
this URI is used as the default value of Base Name. Thus in this case the Name
field needs to be unique for that URI, for example an index or subresource name
of sensors handled by the URI.</t>
<t>Alternatively, for objects not related to a URI, a unique name is required. In
any case, it is RECOMMENDED that the full names are represented as URIs or URNs
<xref target="RFC2141"/>. One way to create a unique name is to include some bit string that has guaranteed
uniqueness (such as a 1-wire address) that is assigned to the device. Some of
the examples in this draft use the device URN type as specified in
<xref target="I-D.arkko-core-dev-urn"/>. UUIDs <xref target="RFC4122"/> are another way to generate a
unique name. Note that long-term stable unique identifiers are problematic for privacy
reasons <xref target="RFC7721"/> and should be used with care or avoided.</t>
<t>The resulting concatenated name MUST consist only of characters out of the set
“A” to “Z”, “a” to “z”, “0” to “9”, “-“, “:”, “.”, or “_” and it MUST start with
a character out of the set “A” to “Z”, “a” to “z”, or “0” to “9”. This
restricted character set was chosen so that these names can be directly used as
in other types of URI including segments of an HTTP path with no special
encoding and can be directly used in many databases and analytic
systems. <xref target="RFC5952"/> contains advice on encoding an IPv6 address in a name.</t>
<t>If either the Base Time or Time value is missing, the missing attribute is
considered to have a value of zero. The Base Time and Time values are added
together to get the time of measurement. A time of zero indicates that the
sensor does not know the absolute time and the measurement was made roughly
“now”. A negative value is used to indicate seconds in the past from roughly
“now”. A positive value is used to indicate the number of seconds, excluding
leap seconds, since the start of the year 1970 in UTC.</t>
<t>Representing the statistical characteristics of measurements, such as accuracy,
can be very complex. Future specification may add new attributes to provide
better information about the statistical properties of the measurement.</t>
</section>
<section anchor="associating-meta-data" title="Associating Meta-data">
<t>SenML is designed to carry the minimum dynamic information about measurements,
and for efficiency reasons does not carry significant static meta-data about the
device, object or sensors. Instead, it is assumed that this meta-data is carried
out of band. For web resources using SenML Packs, this meta-data can
be made available using the CoRE Link Format <xref target="RFC6690"/>. The most obvious use
of this link format is to describe that a resource is available in a SenML
format in the first place. The relevant media type indicator is included in the
Content-Type (ct=) attribute.</t>
</section>
<section anchor="json-representation-applicationsenmljson" title="JSON Representation (application/senml+json)">
<t>Record atributes:</t>
<texttable>
<ttcol align='right'>SenML</ttcol>
<ttcol align='left'>JSON</ttcol>
<ttcol align='left'>Type</ttcol>
<c>Base Name</c>
<c>bn</c>
<c>String</c>
<c>Base Time</c>
<c>bt</c>
<c>Number</c>
<c>Base Unit</c>
<c>bu</c>
<c>String</c>
<c>Base Value</c>
<c>bv</c>
<c>Number</c>
<c>Version</c>
<c>bver</c>
<c>Number</c>
<c>Name</c>
<c>n</c>
<c>String</c>
<c>Unit</c>
<c>u</c>
<c>String</c>
<c>Value</c>
<c>v</c>
<c>Number</c>
<c>String Value</c>
<c>vs</c>
<c>String</c>
<c>Boolean Value</c>
<c>vb</c>
<c>Boolean</c>
<c>Data Value</c>
<c>vd</c>
<c>String</c>
<c>Value Sum</c>
<c>s</c>
<c>Number</c>
<c>Time</c>
<c>t</c>
<c>Number</c>
<c>Update Time</c>
<c>ut</c>
<c>Number</c>
</texttable>
<t>The root content consists of an array with JSON objects for each SenML
Record. All the fields in the above table MAY occur in the records with the type
specified in the table.</t>
<t>Only the UTF-8 form of JSON is allowed. Characters in the String Value are
encoded using the escape sequences defined in <xref target="RFC4627"/>. Characters in the Data
Value are base64 encoded with URL safe alphabet as defined in Section 5 of
<xref target="RFC4648"/>.</t>
<t>Systems receiving measurements MUST be able to process the range of floating
point numbers that are representable as an IEEE double-precision floating-point
numbers <xref target="IEEE.754.1985"/>. The number of significant digits in any measurement
is not relevant, so a reading of 1.1 has exactly the same semantic meaning
as 1.10. If the value has an exponent, the “e” MUST be in lower case. The
mantissa SHOULD be less than 19 characters long and the exponent SHOULD be less
than 5 characters long. This allows time values to have better than micro second
precision over the next 100 years.</t>
<section anchor="examples" title="Examples">
<t>TODO - Add example with string, data, boolean, and base value</t>
<section anchor="single-datapoint" title="Single Datapoint">
<t>The following shows a temperature reading taken approximately “now” by a 1-wire
sensor device that was assigned the unique 1-wire address of 10e2073a01080063:</t>
<figure><artwork><![CDATA[
[{ "n": "urn:dev:ow:10e2073a01080063", "v":23.1, "u":"Cel" }]
]]></artwork></figure>
</section>
<section anchor="co-ex" title="Multiple Datapoints">
<t>The following example shows voltage and current now, i.e., at an unspecified
time.</t>
<figure><artwork><![CDATA[
[{"bn": "urn:dev:ow:10e2073a01080063/"},
{ "n": "voltage", "t": 0, "u": "V", "v": 120.1 },
{ "n": "current", "t": 0, "u": "A", "v": 1.2 }
]
]]></artwork></figure>
<t>The next example is similar to the above one, but shows current at Tue Jun 8
18:01:16 UTC 2010 and at each second for the previous 5 seconds.</t>
<figure><artwork><![CDATA[
[{"bn": "urn:dev:ow:10e2073a01080063/",
"bt": 1276020076.001,
"bu": "A",
"bver": 5},
{ "n": "voltage", "u": "V", "v": 120.1 },
{ "n": "current", "t": -5, "v": 1.2 },
{ "n": "current", "t": -4, "v": 1.30 },
{ "n": "current", "t": -3, "v": 0.14e1 },
{ "n": "current", "t": -2, "v": 1.5 },
{ "n": "current", "t": -1, "v": 1.6 },
{ "n": "current", "t": 0, "v": 1.7 }
]
]]></artwork></figure>
<t>Note that in some usage scenarios of SenML the implementations MAY store or
transmit SenML in a stream-like fashion, where data is collected over time and
continuously added to the object. This mode of operation is optional, but
systems or protocols using SenML in this fashion MUST specify that they are
doing this. SenML defines a separate mime type (TODO) to indicate Sensor
Streaming Markup Language (SensML) for this usage. In this situation the SensML
stream can be sent and received in a partial fashion, i.e., a measurement entry
can be read as soon as the SenML Record is received and not have to wait for the
full SensML Stream to be complete.</t>
<t>For instance, the following stream of measurements may be sent via a long lived
HTTP POST from the producer of a SensML to the consumer of that, and each
measurement object may be reported at the time it measured:</t>
<figure><artwork><![CDATA[
[ {"bn": "urn:dev:ow:10e2073a01080063",
"bt": 1320067464,
"bu": "%RH"},
{ "v": 21.2, "t": 0 },
{ "v": 21.3, "t": 10 },
{ "v": 21.4, "t": 20 },
{ "v": 21.4, "t": 30 },
{ "v": 21.5, "t": 40 },
{ "v": 21.5, "t": 50 },
{ "v": 21.5, "t": 60 },
{ "v": 21.6, "t": 70 },
{ "v": 21.7, "t": 80 },
{ "v": 21.5, "t": 90 },
...
]]></artwork></figure>
</section>
<section anchor="an-co-ex" title="Multiple Measurements">
<t>The following example shows humidity measurements from a mobile
device with an IPv6 address 2001:db8::1, starting at Mon Oct 31
13:24:24 UTC 2011. The device also provides position data, which is
provided in the same measurement or parameter array as separate
entries. Note time is used to for correlating data that belongs
together, e.g., a measurement and a parameter associated with it.
Finally, the device also reports extra data about its battery status
at a separate time.</t>
<figure><artwork><![CDATA[
[{"bn": "urn:dev:ow:10e2073a01080063",
"bt": 1320067464,
"bu": "%RH"},
{ "v": 20.0, "t": 0 },
{ "v": 24.30621, "u": "lon", "t": 0 },
{ "v": 60.07965, "u": "lat", "t": 0 },
{ "v": 20.3, "t": 60 },
{ "v": 24.30622, "u": "lon", "t": 60 },
{ "v": 60.07965, "u": "lat", "t": 60 },
{ "v": 20.7, "t": 120 },
{ "v": 24.30623, "u": "lon", "t": 120 },
{ "v": 60.07966, "u": "lat", "t": 120 },
{ "v": 98.0, "u": "%EL", "t": 150 },
{ "v": 21.2, "t": 180 },
{ "v": 24.30628, "u": "lon", "t": 180 },
{ "v": 60.07967, "u": "lat", "t": 180 }
]
]]></artwork></figure>
<t>The size of this example represented in various forms, as well as that form
compressed with gzip is given in the following table.</t>
<texttable title="Size Comparisons" anchor="tbl-sizes">
<ttcol align='left'>Encoding</ttcol>
<ttcol align='right'>Size</ttcol>
<ttcol align='right'>Compressed Size</ttcol>
<c>JSON</c>
<c>567</c>
<c>200</c>
<c>XML</c>
<c>656</c>
<c>232</c>
<c>CBOR</c>
<c>292</c>
<c>192</c>
<c>EXI</c>
<c>160</c>
<c>183</c>
</texttable>
<t>Note the CBOR and EXI sizes are not using the schema guidance so the could be a bit
smaller.</t>
</section>
<section anchor="rest-ex" title="Collection of Resources">
<t>The following example shows how to query one device that can
provide multiple measurements. The example assumes that a client has
fetched information from a device at 2001:db8::2 by performing a GET
operation on http://[2001:db8::2] at Mon Oct 31 16:27:09 UTC 2011,
and has gotten two separate values as a result, a temperature and
humidity measurement.</t>
<figure><artwork><![CDATA[
[{"bn": "urn:dev:ow:10e2073a01080063/",
"bt": 1320078429,
"bver": 5
},
{ "n": "temperature", "v": 27.2, "u": "Cel" },
{ "n": "humidity", "v": 80, "u": "%RH" }
]
]]></artwork></figure>
</section>
</section>
</section>
<section anchor="sec-cbor" title="CBOR Representation (application/senml+cbor)">
<t>The CBOR <xref target="RFC7049"/> representation is equivalent to the JSON representation,
with the following changes:</t>
<t><list style="symbols">
<t>For compactness, the CBOR representation uses integers for the map keys
defined in <xref target="tbl-cbor-labels"/>. This table is conclusive, i.e., there is no
intention to define any additional integer map keys; any extensions will use
string map keys.</t>
<t>For JSON Numbers, the CBOR representation can use integers, floating point
numbers, or decimal fractions (CBOR Tag 4); the common limitations of JSON
implementations are not relevant for these. For the version number, however,
only an unsigned integer is allowed.</t>
</list></t>
<texttable title="CBOR representation: integers for map keys" anchor="tbl-cbor-labels">
<ttcol align='right'>Name</ttcol>
<ttcol align='left'>JSON label</ttcol>
<ttcol align='right'>CBOR label</ttcol>
<c>Version</c>
<c>bver</c>
<c>-1</c>
<c>Base Name</c>
<c>bn</c>
<c>-2</c>
<c>Base Time</c>
<c>bt</c>
<c>-3</c>
<c>Base Units</c>
<c>bu</c>
<c>-4</c>
<c>Base Value</c>
<c>bv</c>
<c>-5</c>
<c>Name</c>
<c>n</c>
<c>0</c>
<c>Units</c>
<c>u</c>
<c>1</c>
<c>Value</c>
<c>v</c>
<c>2</c>
<c>String Value</c>
<c>vs</c>
<c>3</c>
<c>Boolean Value</c>
<c>vb</c>
<c>4</c>
<c>Value Sum</c>
<c>s</c>
<c>5</c>
<c>Time</c>
<c>t</c>
<c>6</c>
<c>Update Time</c>
<c>ut</c>
<c>7</c>
<c>Data Value</c>
<c>vd</c>
<c>8</c>
</texttable>
<t>The following example shows an hexdump of the CBOR example for the same sensor
measurement as in <xref target="co-ex"/>.</t>
<figure><artwork><![CDATA[
0000 88 a4 62 62 6e 78 1c 75 72 6e 3a 64 65 76 3a 6f |..bbnx.urn:dev:o|
0010 77 3a 31 30 65 32 30 37 33 61 30 31 30 38 30 30 |w:10e2073a010800|
0020 36 33 2f 62 62 74 fb 41 d3 03 a1 5b 00 10 62 62 |63/bbt.A...[..bb|
0030 62 75 61 41 64 62 76 65 72 05 a3 61 6e 67 76 6f |buaAdbver..angvo|
0040 6c 74 61 67 65 61 75 61 56 61 76 fb 40 5e 06 66 |ltageauaVav.@^.f|
0050 66 66 66 66 a3 61 6e 67 63 75 72 72 65 6e 74 61 |ffff.angcurrenta|
0060 74 fb c0 14 00 00 00 00 00 00 61 76 fb 3f f3 33 |t.........av.?.3|
0070 33 33 33 33 33 a3 61 6e 67 63 75 72 72 65 6e 74 |33333.angcurrent|
0080 61 74 fb c0 10 00 00 00 00 00 00 61 76 fb 3f f4 |at.........av.?.|
0090 cc cc cc cc cc cd a3 61 6e 67 63 75 72 72 65 6e |.......angcurren|
00a0 74 61 74 fb c0 08 00 00 00 00 00 00 61 76 fb 3f |tat.........av.?|
00b0 f6 66 66 66 66 66 66 a3 61 6e 67 63 75 72 72 65 |.ffffff.angcurre|
00c0 6e 74 61 74 fb c0 00 00 00 00 00 00 00 61 76 fb |ntat.........av.|
00d0 3f f8 00 00 00 00 00 00 a3 61 6e 67 63 75 72 72 |?........angcurr|
00e0 65 6e 74 61 74 fb bf f0 00 00 00 00 00 00 61 76 |entat.........av|
00f0 fb 3f f9 99 99 99 99 99 9a a2 61 6e 67 63 75 72 |.?........angcur|
0100 72 65 6e 74 61 76 fb 3f fb 33 33 33 33 33 33 |rentav.?.333333|
010f
]]></artwork></figure>
</section>
<section anchor="sec-xml-example" title="XML Representation (application/senml+xml)">
<t>A SenML Stream can also be represented in XML format as defined in this
section. The following example shows an XML example for the same sensor
measurement as in <xref target="co-ex"/>.</t>
<figure><artwork><![CDATA[
<sensml xmlns="urn:ietf:params:xml:ns:senml">
<senml bn="urn:dev:ow:10e2073a01080063/" bt="1.276020076001e+09"
bu="A" bver="5"></senml>
<senml n="voltage" u="V" v="120.1"></senml>
<senml n="current" t="-5" v="1.2"></senml>
<senml n="current" t="-4" v="1.3"></senml>
<senml n="current" t="-3" v="1.4"></senml>
<senml n="current" t="-2" v="1.5"></senml>
<senml n="current" t="-1" v="1.6"></senml>
<senml n="current" v="1.7"></senml>
</sensml>
]]></artwork></figure>
<t>The SenML Stream is represented as a sensml tag that contains a series of
senml tags for each SenML Record. The SenML Fields are represents as XML
attributes. The following table shows the mapping the SenML Field names to the
attribute used in the XML senml tag.</t>
<texttable>
<ttcol align='right'>SenML Field</ttcol>
<ttcol align='left'>XML</ttcol>
<ttcol align='left'>Type</ttcol>
<c>Base Name</c>
<c>bn</c>
<c>string</c>
<c>Base Time</c>
<c>bt</c>
<c>double</c>
<c>Base Unit</c>
<c>bu</c>
<c>string</c>
<c>Base Value</c>
<c>bv</c>
<c>double</c>
<c>Base Version</c>
<c>bver</c>
<c>int</c>
<c>Name</c>
<c>n</c>
<c>string</c>
<c>Unit</c>
<c>u</c>
<c>string</c>
<c>Value</c>
<c>v</c>
<c>double</c>
<c>String Value</c>
<c>vs</c>
<c>string</c>
<c>Data Value</c>
<c>vd</c>
<c>string</c>
<c>Boolean Value</c>
<c>vb</c>
<c>boolean</c>
<c>Value Sum</c>
<c>s</c>
<c>double</c>
<c>Time</c>
<c>t</c>
<c>double</c>
<c>Update Time</c>
<c>ut</c>
<c>double</c>
</texttable>
<t>The RelaxNG schema for the XML is:</t>
<figure><artwork><![CDATA[
default namespace = "urn:ietf:params:xml:ns:senml"
namespace rng = "http://relaxng.org/ns/structure/1.0"
link = element l {
attribute * { xsd:string }*
}
senml = element senml {
attribute bn { xsd:string }?,
attribute bt { xsd:double }?,
attribute bv { xsd:double }?,
attribute bu { xsd:string }?,
attribute bver { xsd:int }?,
attribute n { xsd:string }?,
attribute s { xsd:double }?,
attribute t { xsd:double }?,
attribute u { xsd:string }?,
attribute ut { xsd:double }?,
attribute v { xsd:double }?,
attribute vb { xsd:boolean }?,
attribute vs { xsd:string }?,
attribute vd { xsd:string }?,
link*
}
sensml =
element sensml {
senml+
}
start = sensml
]]></artwork></figure>
</section>
<section anchor="exi-representation-applicationsenml-exi" title="EXI Representation (application/senml-exi)">
<t>For efficient transmission of SenML over e.g. a constrained network, Efficient
XML Interchange (EXI) can be used. This encodes the XML Schema structure of
SenML into binary tags and values rather than ASCII text. An EXI representation
of SenML SHOULD be made using the strict schema-mode of EXI. This mode however
does not allow tag extensions to the schema, and therefore any extensions will
be lost in the encoding. For uses where extensions need to be preserved in EXI,
the non-strict schema mode of EXI MAY be used.</t>
<t>The EXI header option MUST be included. An EXI schemaID options MUST be set to
the value of “a” indicating the scheme provided in this specification. Future
revisions to the schema can change this schemaID to allow for backwards
compatibility. When the data will be transported over CoAP or HTTP, an EXI
Cookie SHOULD NOT be used as it simply makes things larger and is redundant to
information provided in the Content-Type header.</t>
<t>TODO - examples probably have the wrong setting the schemaID</t>
<t>The following is the XSD Schema to be used for strict schema guided EXI
processing. It is generated from the RelaxNG.</t>
<figure><artwork><![CDATA[
<?xml version="1.0" encoding="utf-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
elementFormDefault="qualified"
targetNamespace="urn:ietf:params:xml:ns:senml"
xmlns:ns1="urn:ietf:params:xml:ns:senml">
<xs:element name="l">
<xs:complexType>
<xs:anyAttribute processContents="skip" />
</xs:complexType>
</xs:element>
<xs:element name="senml">
<xs:complexType>
<xs:sequence>
<xs:element minOccurs="0" maxOccurs="unbounded"
ref="ns1:l" />
</xs:sequence>
<xs:attribute name="bn" type="xs:string" />
<xs:attribute name="bt" type="xs:double" />
<xs:attribute name="bv" type="xs:double" />
<xs:attribute name="bu" type="xs:string" />
<xs:attribute name="bver" type="xs:int" />
<xs:attribute name="n" type="xs:string" />
<xs:attribute name="s" type="xs:double" />
<xs:attribute name="t" type="xs:double" />
<xs:attribute name="u" type="xs:string" />
<xs:attribute name="ut" type="xs:double" />
<xs:attribute name="v" type="xs:double" />
<xs:attribute name="vb" type="xs:boolean" />
<xs:attribute name="vs" type="xs:string" />
<xs:attribute name="vd" type="xs:string" />
</xs:complexType>
</xs:element>
<xs:element name="sensml">
<xs:complexType>
<xs:sequence>
<xs:element maxOccurs="unbounded" ref="ns1:senml" />
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>
]]></artwork></figure>
<t>The following shows a hexdump of the EXI produced from encoding the
following XML example. Note this example is the same information as the
first example in <xref target="co-ex"/> in JSON format.</t>
<figure><artwork><![CDATA[
<sensml xmlns="urn:ietf:params:xml:ns:senml">
<senml bn="urn:dev:ow:10e2073a01080063/"></senml>
<senml n="voltage" u="V" v="120.1"></senml>
<senml n="current" u="A" v="1.2"></senml>
</sensml>
]]></artwork></figure>
<t>Which compresses with EXI to the following displayed in hexdump:</t>
<figure><artwork><![CDATA[
0000 a0 30 3d cd 95 b9 b5 b0 b9 9d 95 b8 b9 e1 cd 91 |.0=.............|
0010 00 f3 ab 93 71 d3 23 2b b1 d3 7b b9 d1 89 83 29 |....q.#+..{....)|
0020 91 81 b9 9b 09 81 89 81 c1 81 81 b1 99 7f 14 25 |...............%|
0030 d9 bd b1 d1 85 9d 94 80 d5 8a c4 26 01 0a 12 c6 |...........&....|
0040 ea e4 e4 ca dc e8 40 68 24 19 00 90 |......@h$...|
004c
]]></artwork></figure>
<t>The above example used the bit packed form of EXI but it is also possible to use
a byte packed form of EXI which can makes it easier for a simple sensor to
produce valid EXI without really implementing EXI. Consider the example of a
temperature sensor that produces a value in tenths of degrees Celsius over a
range of 0.0 to 55.0. It would produce an XML SenML file such as:</t>
<figure><artwork><![CDATA[
<sensml xmlns="urn:ietf:params:xml:ns:senml">
<senml n="urn:dev:ow:10e2073a01080063" u="Cel" v="23.1"></senml>
</sensml>
]]></artwork></figure>
<t>The compressed form, using the byte alignment option of EXI, for the above XML
is the following:</t>
<figure><artwork><![CDATA[
0000 a0 00 48 81 ee 6c ad cd ad 85 cc ec ad c5 cf 0e |..H..l..........|
0010 6c 80 02 05 1d 75 72 6e 3a 64 65 76 3a 6f 77 3a |l....urn:dev:ow:|
0020 31 30 65 32 30 37 33 61 30 31 30 38 30 30 36 33 |10e2073a01080063|
0030 02 05 43 65 6c 01 00 e7 01 01 00 04 01 |..Cel........|
003d
]]></artwork></figure>
<t>A small temperature sensor devices that only generates this one EXI file does
not really need an full EXI implementation. It can simple hard code the output
replacing the one wire device ID starting at byte 0x16 and going to byte 0x31
with it’s device ID, and replacing the value “0xe7 0x01” at location 0x38 to
0x39 with the current temperature. The EXI Specification
<xref target="W3C.REC-exi-20110310"/> contains the full information ‘on how floating point
numbers are represented, but for the purpose of this sensor, the temperature can
be converted to an integer in tenths of degrees (231 in this example). EXI
stores 7 bits of the integer in each byte with the top bit set to one if there
are further bytes. So the first bytes at is set to low 7 bits of the integer
temperature in tenths of degrees plus 0x80. In this example 231 & 0x7F + 0x80 =
0xE7. The second byte is set to the integer temperature in tenths of degrees
right shifted 7 bits. In this example 231 » 7 = 0x01.</t>
</section>
<section anchor="usage-considerations" title="Usage Considerations">
<t>The measurements support sending both the current value of a sensor as well as
the an integrated sum. For many types of measurements, the sum is more useful
than the current value. For example, an electrical meter that measures the
energy a given computer uses will typically want to measure the cumulative
amount of energy used. This is less prone to error than reporting the power each
second and trying to have something on the server side sum together all the
power measurements. If the network between the sensor and the meter goes down
over some period of time, when it comes back up, the cumulative sum helps
reflect what happened while the network was down. A meter like this would
typically report a measurement with the units set to watts, but it would put the
sum of energy used in the “s” attribute of the measurement. It might optionally
include the current power in the “v” attribute.</t>
<t>While the benefit of using the integrated sum is fairly clear for measurements
like power and energy, it is less obvious for something like
temperature. Reporting the sum of the temperature makes it easy to compute
averages even when the individual temperature values are not reported frequently
enough to compute accurate averages. Implementors are encouraged to report the
cumulative sum as well as the raw value of a given sensor.</t>
<t>Applications that use the cumulative sum values need to understand they are very
loosely defined by this specification, and depending on the particular sensor
implementation may behave in unexpected ways. Applications should be able to
deal with the following issues:</t>
<t><list style="numbers">
<t>Many sensors will allow the cumulative sums to “wrap” back to zero after the
value gets sufficiently large.</t>
<t>Some sensors will reset the cumulative sum back to zero when the device is
reset, loses power, or is replaced with a different sensor.</t>
<t>Applications cannot make assumptions about when the device started
accumulating values into the sum.</t>
</list></t>
<t>Typically applications can make some assumptions about specific sensors that
will allow them to deal with these problems. A common assumption is that for
sensors whose measurement values are always positive, the sum should never get
smaller; so if the sum does get smaller, the application will know that one of
the situations listed above has happened.</t>
</section>
<section anchor="cddl" title="CDDL">
<t>For reference, the CBOR representation can be described with the CDDL
<xref target="I-D.greevenbosch-appsawg-cbor-cddl"/> specification in <xref target="senmlcddl"/>.</t>
<figure title="CDDL specification for CBOR SenML" anchor="senmlcddl"><artwork type="cddl"><![CDATA[
SenML-Pack = [initial-record, * follow-on-record]
initial-record = initial-defined .and initial-generic
follow-on-record = follow-on-defined .and follow-on-generic
; first do a specification of the labels as defined:
initial-defined = {
? bn => tstr, ; Base Name
? bt => numeric, ; Base Time
? bu => tstr, ; Base Units
? bv => numeric, ; Base value
? bver => uint, ; Base Version
follow-on-defined-group,
+ base-key-value-pair
}
follow-on-defined-group = (
? n => tstr, ; Name
? u => tstr, ; Units
? ( v => numeric // ; Numeric Value
vs => tstr // ; String Value
vb => bool // ; Boolean Value
vd => bstr ) ; Data Value
? s => numeric, ; Value Sum
? t => numeric, ; Time
? ut => numeric, ; Update Time
* key-value-pair
)
follow-on-defined = { follow-on-defined-group }
; CBOR version (use the labels)
bver = -1 n = 0 s = 5
bn = -2 u = 1 t = 6
bt = -3 v = 2 ut = 7
bu = -4 vs = 3 vd = 8
bv = -5 vb = 4
; use the label *names* for JSON
; now define the generic versions
initial-generic = {
follow-on-generic-group,
* base-key-value-pair,
}
follow-on-generic-group = (
+ key-value-pair,
)
follow-on-generic = { follow-on-generic-group }
key-value-pair = ( non-b-label => value )
base-key-value-pair = ( b-label => value )
non-b-label = tstr .regexp "[A-Zac-z0-9][-_:.A-Za-z0-9]*" / uint
b-label = tstr .regexp "b[-_:.A-Za-z0-9]+" / nint
value = tstr / bstr / numeric / bool
numeric = number / decfrac
]]></artwork></figure>
<t>TODO - seems to be a problem with CDDL not validating examples</t>
</section>
<section anchor="iana-considerations" title="IANA Considerations">
<t>Note to RFC Editor: Please replace all occurrences of “RFC-AAAA” with the RFC
number of this specification.</t>
<section anchor="sec-units" title="Units Registry">
<t>IANA will create a registry of SenML unit symbols. The primary purpose of this
registry is to make sure that symbols uniquely map to give type of
measurement. Definitions for many of these units can be found in location such
as <xref target="NIST811"/> and <xref target="BIPM"/>.</t>
<texttable anchor="tbl-iana-symbols">
<ttcol align='right'>Symbol</ttcol>
<ttcol align='left'>Description</ttcol>
<ttcol align='left'>Type</ttcol>
<ttcol align='left'>Reference</ttcol>
<c>m</c>
<c>meter</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>g</c>
<c>gram</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>s</c>
<c>second</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>A</c>
<c>ampere</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>K</c>
<c>kelvin</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>cd</c>
<c>candela</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>mol</c>
<c>mole</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>Hz</c>
<c>hertz</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>rad</c>
<c>radian</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>sr</c>
<c>steradian</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>N</c>
<c>newton</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>Pa</c>
<c>pascal</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>J</c>
<c>joule</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>W</c>
<c>watt</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>C</c>
<c>coulomb</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>V</c>
<c>volt</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>F</c>
<c>farad</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>Ohm</c>
<c>ohm</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>S</c>
<c>siemens</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>Wb</c>
<c>weber</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>T</c>
<c>tesla</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>H</c>
<c>henry</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>Cel</c>
<c>degrees Celsius</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>lm</c>
<c>lumen</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>lx</c>
<c>lux</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>Bq</c>
<c>becquerel</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>Gy</c>
<c>gray</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>Sv</c>
<c>sievert</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>kat</c>
<c>katal</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>pH</c>
<c>pH acidity</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>%</c>
<c>Value of a switch (note 1)</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>count</c>
<c>counter value</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>%RH</c>
<c>Relative Humidity</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>m2</c>
<c>area</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>l</c>
<c>volume in liters</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>m/s</c>
<c>velocity</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>m/s2</c>
<c>acceleration</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>l/s</c>
<c>flow rate in liters per second</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>W/m2</c>
<c>irradiance</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>cd/m2</c>
<c>luminance</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>Bspl</c>
<c>bel sound pressure level</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>bit/s</c>
<c>bits per second</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>lat</c>
<c>degrees latitude (note 2)</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>lon</c>
<c>degrees longitude (note 2)</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>%EL</c>
<c>remaining battery energy level in percents</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>EL</c>
<c>remaining battery energy level in seconds</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>beat/m</c>
<c>Heart rate in beats per minute</c>
<c>float</c>
<c>RFC-AAAA</c>
<c>beats</c>
<c>Cumulative number of heart beats</c>
<c>float</c>
<c>RFC-AAAA</c>
</texttable>
<t><list style="symbols">
<t>Note 1: A value of 0.0 indicates the switch is off while 1.0
indicates on and 0.5 would be half on.</t>
<t>Note 2: Assumed to be in WGS84 unless another reference frame is
known for the sensor.</t>
</list></t>
<t>New entries can be added to the registration by either Expert Review or IESG
Approval as defined in <xref target="RFC5226"/>. Experts should exercise their own good
judgment but need to consider the following guidelines:</t>
<t><list style="numbers">
<t>There needs to be a real and compelling use for any new unit to be added.</t>
<t>Units should define the semantic information and be chosen
carefully. Implementors need to remember that the same word may be used in
different real-life contexts. For example, degrees when measuring latitude
have no semantic relation to degrees when measuring temperature; thus two
different units are needed.</t>
<t>These measurements are produced by computers for consumption by
computers. The principle is that conversion has to be easily be done when both
reading and writing the media type. The value of a single canonical
representation outweighs the convenience of easy human representations or loss
of precision in a conversion.</t>
<t>Use of SI prefixes such as “k” before the unit is not allowed. Instead one
can represent the value using scientific notation such a 1.2e3. TODO - Open
Issue. Some people would like to have SI prefixes to improve human
readability.</t>
<t>For a given type of measurement, there will only be one unit type defined. So
for length, meters are defined and other lengths such as mile, foot, light
year are not allowed. For most cases, the SI unit is preferred.</t>
<t>Symbol names that could be easily confused with existing common units or
units combined with prefixes should be avoided. For example, selecting a unit
name of “mph” to indicate something that had nothing to do with velocity would
be a bad choice, as “mph” is commonly used to mean miles per hour.</t>
<t>The following should not be used because the are common SI prefixes: Y, Z, E,
P, T, G, M, k, h, da, d, c, n, u, p, f, a, z, y, Ki, Mi, Gi, Ti, Pi, Ei, Zi,
Yi.</t>
<t>The following units should not be used as they are commonly used to represent
other measurements Ky, Gal, dyn, etg, P, St, Mx, G, Oe, Gb, sb, Lmb, ph, Ci,
R, RAD, REM, gal, bbl, qt, degF, Cal, BTU, HP, pH, B/s, psi, Torr, atm, at,
bar, kWh.</t>
<t>The unit names are case sensitive and the correct case needs to be used, but
symbols that differ only in case should not be allocated.</t>
<t>A number after a unit typically indicates the previous unit raised to that
power, and the / indicates that the units that follow are the reciprocal. A
unit should have only one / in the name.</t>
<t>A good list of common units can be found in the Unified Code for Units of
Measure <xref target="UCUM"/>.</t>
</list></t>
</section>
<section anchor="senml-label-registry" title="SenML label registry">
<t>IANA will create a registry for SenML labels. The initial content of the
registry are shown in TODO.</t>
<t>New entries can be added to the registration by either Expert Review or IESG
Approval as defined in <xref target="RFC5226"/>. Experts should exercise their own good
judgment but need to consider that shorter labels should have more strict review.</t>
</section>
<section anchor="sec-iana-media" title="Media Type Registration">
<t>The following registrations are done following the procedure
specified in <xref target="RFC6838"/> and <xref target="RFC7303"/>.</t>
<section anchor="senmljson-media-type-registration" title="senml+json Media Type Registration">
<t>Type name: application</t>
<t>Subtype name: senml+json and sensml+json</t>
<t>Required parameters: none</t>
<t>Optional parameters: none</t>
<t>Encoding considerations: Must be encoded as using a subset of the encoding
allowed in <xref target="RFC7159"/>. See RFC-AAAA for details. This simplifies implementation
of very simple system and does not impose any significant limitations as all
this data is meant for machine to machine communications and is not meant to be
human readable.</t>
<t>Security considerations: Sensor data can contain a wide range of information
ranging from information that is very public, such the outside temperature in a
given city, to very private information that requires integrity and
confidentiality protection, such as patient health information. This format does
not provide any security and instead relies on the transport protocol that
carries it to provide security. Given applications need to look at the overall
context of how this media type will be used to decide if the security is
adequate.</t>
<t>Interoperability considerations: Applications should ignore any JSON key value
pairs that they do not understand. This allows backwards compatibility
extensions to this specification. The “ver” field can be used to ensure the
receiver supports a minimal level of functionality needed by the creator of the
JSON object.</t>
<t>Published specification: RFC-AAAA</t>
<t>Applications that use this media type: The type is used by systems that report
electrical power usage and environmental information such as temperature and
humidity. It can be used for a wide range of sensor reporting systems.</t>
<t>Additional information:</t>
<t>Magic number(s): none</t>
<t>File extension(s): senml</t>
<t>Macintosh file type code(s): none</t>
<t>Person & email address to contact for further information:
Cullen Jennings <fluffy@iii.ca></t>
<t>Intended usage: COMMON</t>
<t>Restrictions on usage: None</t>
<t>Author: Cullen Jennings <fluffy@iii.ca></t>
<t>Change controller: IESG</t>
</section>
<section anchor="senmlcbor-media-type-registration" title="senml+cbor Media Type Registration">
<t>Type name: application</t>
<t>Subtype name: senml+cbor</t>
<t>Required parameters: none</t>
<t>Optional parameters: none</t>
<t>Encoding considerations: TBD</t>
<t>Security considerations: TBD</t>
<t>Interoperability considerations: TBD</t>
<t>Published specification: RFC-AAAA</t>
<t>Applications that use this media type: The type is used
by systems that report electrical power usage and
environmental information such as temperature and
humidity. It can be used for a wide range of sensor
reporting systems.</t>
<t>Additional information:</t>
<t>Magic number(s): none</t>
<t>File extension(s): senml</t>
<t>Macintosh file type code(s): none</t>
<t>Person & email address to contact for further information:
Cullen Jennings <fluffy@iii.ca></t>
<t>Intended usage: COMMON</t>
<t>Restrictions on usage: None</t>
<t>Author: Cullen Jennings <fluffy@iii.ca></t>
<t>Change controller: IESG</t>
</section>
<section anchor="senmlxml-media-type-registration" title="senml+xml Media Type Registration">
<t>Type name: application</t>
<t>Subtype name: senml+xml and sensml+xml</t>
<t>Required parameters: none</t>
<t>Optional parameters: none</t>
<t>Encoding considerations: TBD</t>
<t>Security considerations: TBD</t>
<t>Interoperability considerations: TBD</t>
<t>Published specification: RFC-AAAA</t>
<t>Applications that use this media type: TBD</t>
<t>Additional information:</t>
<t>Magic number(s): none</t>
<t>File extension(s): senml</t>
<t>Macintosh file type code(s): none</t>
<t>Person & email address to contact for further information:
Cullen Jennings <fluffy@iii.ca></t>
<t>Intended usage: COMMON</t>
<t>Restrictions on usage: None</t>
<t>Author: Cullen Jennings <fluffy@iii.ca></t>
<t>Change controller: IESG</t>
</section>
<section anchor="senml-exi-media-type-registration" title="senml-exi Media Type Registration">
<t>Type name: application</t>
<t>Subtype name: senml-exi</t>
<t>Required parameters: none</t>
<t>Optional parameters: none</t>
<t>Encoding considerations: TBD</t>
<t>Security considerations: TBD</t>
<t>Interoperability considerations: TBD</t>
<t>Published specification: RFC-AAAA</t>
<t>Applications that use this media type: TBD</t>
<t>Additional information:</t>
<t>Magic number(s): none</t>
<t>File extension(s): senml</t>
<t>Macintosh file type code(s): none</t>
<t>Person & email address to contact for further information:
Cullen Jennings <fluffy@iii.ca></t>
<t>Intended usage: COMMON</t>
<t>Restrictions on usage: None</t>
<t>Author: Cullen Jennings <fluffy@iii.ca></t>
<t>Change controller: IESG</t>
</section>
</section>
<section anchor="sec-iana-url" title="XML Namespace Registration">
<t>This document registers the following XML namespaces in the IETF
XML registry defined in <xref target="RFC3688"/>.</t>
<t>URI: urn:ietf:params:xml:ns:senml</t>
<t>Registrant Contact: The IESG.</t>
<t>XML: N/A, the requested URIs are XML namespaces</t>
</section>
<section anchor="coap-content-format-registration" title="CoAP Content-Format Registration">
<t>IANA is requested to assign CoAP Content-Format IDs for the SenML media types in
the “CoAP Content-Formats” sub-registry, within the “CoRE Parameters” registry
<xref target="RFC7252"/>. All IDs are assigned from the “Expert Review” (0-255) range. The
assigned IDs are show in <xref target="tbl-coap-content-formats"/>.</t>
<texttable title="CoAP Content-Format IDs" anchor="tbl-coap-content-formats">
<ttcol align='left'>Media type</ttcol>
<ttcol align='left'>ID</ttcol>
<c>application/senml+json</c>
<c>TBD</c>
<c>application/sensml+json</c>
<c>TBD</c>
<c>application/senml+cbor</c>
<c>TBD</c>
<c>application/senml+xml</c>
<c>TBD</c>
<c>application/sensml+xml</c>
<c>TBD</c>
<c>application/senml-exi</c>
<c>TBD</c>
</texttable>
</section>
</section>
<section anchor="sec-sec" title="Security Considerations">
<t>See <xref target="sec-privacy"/>. Further discussion of security properties can be found in
<xref target="sec-iana-media"/>.</t>
</section>
<section anchor="sec-privacy" title="Privacy Considerations">
<t>Sensor data can range from information with almost no security considerations,
such as the current temperature in a given city, to highly sensitive medical or
location data. This specification provides no security protection for the data
but is meant to be used inside another container or transport protocol such as
S/MIME or HTTP with TLS that can provide integrity, confidentiality, and
authentication information about the source of the data.</t>
</section>
<section anchor="acknowledgement" title="Acknowledgement">
<t>We would like to thank Lisa Dusseault, Joe Hildebrand, Lyndsay Campbell, Martin
Thomson, John Klensin, Bjoern Hoehrmann, Carsten Bormann, and Christian Amsuess
for their review comments.</t>
<t>The CBOR Representation text and CDDL was contributed by Carsten Bormann.</t>
</section>
</middle>
<back>
<references title='Normative References'>
<reference anchor="IEEE.754.1985">
<front>
<title>Standard for Binary Floating-Point Arithmetic</title>
<author>
<organization>Institute of Electrical and Electronics Engineers</organization>
</author>
<date month="August" year="1985" />
</front>
<seriesInfo name="IEEE" value="Standard 754" />
</reference>
<reference anchor='RFC2119' target='http://www.rfc-editor.org/info/rfc2119'>
<front>
<title>Key words for use in RFCs to Indicate Requirement Levels</title>
<author initials='S.' surname='Bradner' fullname='S. Bradner'><organization /></author>
<date year='1997' month='March' />
<abstract><t>In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='14'/>
<seriesInfo name='RFC' value='2119'/>
<seriesInfo name='DOI' value='10.17487/RFC2119'/>
</reference>
<reference anchor='RFC3688' target='http://www.rfc-editor.org/info/rfc3688'>
<front>
<title>The IETF XML Registry</title>
<author initials='M.' surname='Mealling' fullname='M. Mealling'><organization /></author>
<date year='2004' month='January' />
<abstract><t>This document describes an IANA maintained registry for IETF standards which use Extensible Markup Language (XML) related items such as Namespaces, Document Type Declarations (DTDs), Schemas, and Resource Description Framework (RDF) Schemas.</t></abstract>
</front>
<seriesInfo name='BCP' value='81'/>
<seriesInfo name='RFC' value='3688'/>
<seriesInfo name='DOI' value='10.17487/RFC3688'/>
</reference>
<reference anchor='RFC4648' target='http://www.rfc-editor.org/info/rfc4648'>
<front>
<title>The Base16, Base32, and Base64 Data Encodings</title>
<author initials='S.' surname='Josefsson' fullname='S. Josefsson'><organization /></author>
<date year='2006' month='October' />
<abstract><t>This document describes the commonly used base 64, base 32, and base 16 encoding schemes. It also discusses the use of line-feeds in encoded data, use of padding in encoded data, use of non-alphabet characters in encoded data, use of different encoding alphabets, and canonical encodings. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='4648'/>
<seriesInfo name='DOI' value='10.17487/RFC4648'/>
</reference>
<reference anchor='RFC4627' target='http://www.rfc-editor.org/info/rfc4627'>
<front>
<title>The application/json Media Type for JavaScript Object Notation (JSON)</title>
<author initials='D.' surname='Crockford' fullname='D. Crockford'><organization /></author>
<date year='2006' month='July' />
<abstract><t>JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data. This memo provides information for the Internet community.</t></abstract>
</front>
<seriesInfo name='RFC' value='4627'/>
<seriesInfo name='DOI' value='10.17487/RFC4627'/>
</reference>
<reference anchor='RFC5226' target='http://www.rfc-editor.org/info/rfc5226'>
<front>
<title>Guidelines for Writing an IANA Considerations Section in RFCs</title>
<author initials='T.' surname='Narten' fullname='T. Narten'><organization /></author>
<author initials='H.' surname='Alvestrand' fullname='H. Alvestrand'><organization /></author>
<date year='2008' month='May' />
<abstract><t>Many protocols make use of identifiers consisting of constants and other well-known values. Even after a protocol has been defined and deployment has begun, new values may need to be assigned (e.g., for a new option type in DHCP, or a new encryption or authentication transform for IPsec). To ensure that such quantities have consistent values and interpretations across all implementations, their assignment must be administered by a central authority. For IETF protocols, that role is provided by the Internet Assigned Numbers Authority (IANA).</t><t>In order for IANA to manage a given namespace prudently, it needs guidelines describing the conditions under which new values can be assigned or when modifications to existing values can be made. If IANA is expected to play a role in the management of a namespace, IANA must be given clear and concise instructions describing that role. This document discusses issues that should be considered in formulating a policy for assigning values to a namespace and provides guidelines for authors on the specific text that must be included in documents that place demands on IANA.</t><t>This document obsoletes RFC 2434. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t></abstract>
</front>
<seriesInfo name='BCP' value='26'/>
<seriesInfo name='RFC' value='5226'/>
<seriesInfo name='DOI' value='10.17487/RFC5226'/>
</reference>
<reference anchor='RFC6838' target='http://www.rfc-editor.org/info/rfc6838'>
<front>
<title>Media Type Specifications and Registration Procedures</title>
<author initials='N.' surname='Freed' fullname='N. Freed'><organization /></author>
<author initials='J.' surname='Klensin' fullname='J. Klensin'><organization /></author>
<author initials='T.' surname='Hansen' fullname='T. Hansen'><organization /></author>
<date year='2013' month='January' />
<abstract><t>This document defines procedures for the specification and registration of media types for use in HTTP, MIME, and other Internet protocols. This memo documents an Internet Best Current Practice.</t></abstract>
</front>
<seriesInfo name='BCP' value='13'/>
<seriesInfo name='RFC' value='6838'/>
<seriesInfo name='DOI' value='10.17487/RFC6838'/>
</reference>
<reference anchor='RFC7049' target='http://www.rfc-editor.org/info/rfc7049'>
<front>
<title>Concise Binary Object Representation (CBOR)</title>
<author initials='C.' surname='Bormann' fullname='C. Bormann'><organization /></author>
<author initials='P.' surname='Hoffman' fullname='P. Hoffman'><organization /></author>
<date year='2013' month='October' />
<abstract><t>The Concise Binary Object Representation (CBOR) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation. These design goals make it different from earlier binary serializations such as ASN.1 and MessagePack.</t></abstract>
</front>
<seriesInfo name='RFC' value='7049'/>
<seriesInfo name='DOI' value='10.17487/RFC7049'/>
</reference>
<reference anchor='RFC7159' target='http://www.rfc-editor.org/info/rfc7159'>
<front>
<title>The JavaScript Object Notation (JSON) Data Interchange Format</title>
<author initials='T.' surname='Bray' fullname='T. Bray' role='editor'><organization /></author>
<date year='2014' month='March' />
<abstract><t>JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data.</t><t>This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance.</t></abstract>
</front>
<seriesInfo name='RFC' value='7159'/>
<seriesInfo name='DOI' value='10.17487/RFC7159'/>
</reference>
<reference anchor='RFC7252' target='http://www.rfc-editor.org/info/rfc7252'>
<front>
<title>The Constrained Application Protocol (CoAP)</title>
<author initials='Z.' surname='Shelby' fullname='Z. Shelby'><organization /></author>
<author initials='K.' surname='Hartke' fullname='K. Hartke'><organization /></author>
<author initials='C.' surname='Bormann' fullname='C. Bormann'><organization /></author>
<date year='2014' month='June' />
<abstract><t>The Constrained Application Protocol (CoAP) is a specialized web transfer protocol for use with constrained nodes and constrained (e.g., low-power, lossy) networks. The nodes often have 8-bit microcontrollers with small amounts of ROM and RAM, while constrained networks such as IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) often have high packet error rates and a typical throughput of 10s of kbit/s. The protocol is designed for machine- to-machine (M2M) applications such as smart energy and building automation.</t><t>CoAP provides a request/response interaction model between application endpoints, supports built-in discovery of services and resources, and includes key concepts of the Web such as URIs and Internet media types. CoAP is designed to easily interface with HTTP for integration with the Web while meeting specialized requirements such as multicast support, very low overhead, and simplicity for constrained environments.</t></abstract>
</front>
<seriesInfo name='RFC' value='7252'/>
<seriesInfo name='DOI' value='10.17487/RFC7252'/>
</reference>
<reference anchor='RFC7303' target='http://www.rfc-editor.org/info/rfc7303'>
<front>
<title>XML Media Types</title>
<author initials='H.' surname='Thompson' fullname='H. Thompson'><organization /></author>
<author initials='C.' surname='Lilley' fullname='C. Lilley'><organization /></author>
<date year='2014' month='July' />
<abstract><t>This specification standardizes three media types -- application/xml, application/xml-external-parsed-entity, and application/xml-dtd -- for use in exchanging network entities that are related to the Extensible Markup Language (XML) while defining text/xml and text/ xml-external-parsed-entity as aliases for the respective application/ types. This specification also standardizes the '+xml' suffix for naming media types outside of these five types when those media types represent XML MIME entities.</t></abstract>
</front>
<seriesInfo name='RFC' value='7303'/>
<seriesInfo name='DOI' value='10.17487/RFC7303'/>
</reference>
<reference anchor='W3C.REC-exi-20110310'
target='http://www.w3.org/TR/2011/REC-exi-20110310'>
<front>
<title>Efficient XML Interchange (EXI) Format 1.0</title>
<author initials='J.' surname='Schneider' fullname='John Schneider'>
<organization />
</author>
<author initials='T.' surname='Kamiya' fullname='Takuki Kamiya'>
<organization />
</author>
<date month='March' day='10' year='2011' />
</front>
<seriesInfo name='World Wide Web Consortium Recommendation' value='REC-exi-20110310' />
<format type='HTML' target='http://www.w3.org/TR/2011/REC-exi-20110310' />
</reference>
<reference anchor="BIPM" >
<front>
<title>The International System of Units (SI)</title>
<author >
<organization>Bureau International des Poids et Mesures</organization>
</author>
<date year="2006"/>
</front>
<seriesInfo name="8th" value="edition"/>
</reference>
<reference anchor="NIST811" >
<front>
<title>Guide for the Use of the International System of Units (SI)</title>
<author initials="A." surname="Thompson">
<organization></organization>
</author>
<author initials="B." surname="Taylor">
<organization></organization>
</author>
<date year="2008"/>
</front>
<seriesInfo name="NIST" value="Special Publication 811"/>
</reference>
</references>
<references title='Informative References'>
<reference anchor='RFC2141' target='http://www.rfc-editor.org/info/rfc2141'>
<front>
<title>URN Syntax</title>
<author initials='R.' surname='Moats' fullname='R. Moats'><organization /></author>
<date year='1997' month='May' />
<abstract><t>Uniform Resource Names (URNs) are intended to serve as persistent, location-independent, resource identifiers. This document sets forward the canonical syntax for URNs. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='2141'/>
<seriesInfo name='DOI' value='10.17487/RFC2141'/>
</reference>
<reference anchor='RFC3986' target='http://www.rfc-editor.org/info/rfc3986'>
<front>
<title>Uniform Resource Identifier (URI): Generic Syntax</title>
<author initials='T.' surname='Berners-Lee' fullname='T. Berners-Lee'><organization /></author>
<author initials='R.' surname='Fielding' fullname='R. Fielding'><organization /></author>
<author initials='L.' surname='Masinter' fullname='L. Masinter'><organization /></author>
<date year='2005' month='January' />
<abstract><t>A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource. This specification defines the generic URI syntax and a process for resolving URI references that might be in relative form, along with guidelines and security considerations for the use of URIs on the Internet. The URI syntax defines a grammar that is a superset of all valid URIs, allowing an implementation to parse the common components of a URI reference without knowing the scheme-specific requirements of every possible identifier. This specification does not define a generative grammar for URIs; that task is performed by the individual specifications of each URI scheme. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='STD' value='66'/>
<seriesInfo name='RFC' value='3986'/>
<seriesInfo name='DOI' value='10.17487/RFC3986'/>
</reference>
<reference anchor='RFC4122' target='http://www.rfc-editor.org/info/rfc4122'>
<front>
<title>A Universally Unique IDentifier (UUID) URN Namespace</title>
<author initials='P.' surname='Leach' fullname='P. Leach'><organization /></author>
<author initials='M.' surname='Mealling' fullname='M. Mealling'><organization /></author>
<author initials='R.' surname='Salz' fullname='R. Salz'><organization /></author>
<date year='2005' month='July' />
<abstract><t>This specification defines a Uniform Resource Name namespace for UUIDs (Universally Unique IDentifier), also known as GUIDs (Globally Unique IDentifier). A UUID is 128 bits long, and can guarantee uniqueness across space and time. UUIDs were originally used in the Apollo Network Computing System and later in the Open Software Foundation\'s (OSF) Distributed Computing Environment (DCE), and then in Microsoft Windows platforms.</t><t>This specification is derived from the DCE specification with the kind permission of the OSF (now known as The Open Group). Information from earlier versions of the DCE specification have been incorporated into this document. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='4122'/>
<seriesInfo name='DOI' value='10.17487/RFC4122'/>
</reference>
<reference anchor='RFC5952' target='http://www.rfc-editor.org/info/rfc5952'>
<front>
<title>A Recommendation for IPv6 Address Text Representation</title>
<author initials='S.' surname='Kawamura' fullname='S. Kawamura'><organization /></author>
<author initials='M.' surname='Kawashima' fullname='M. Kawashima'><organization /></author>
<date year='2010' month='August' />
<abstract><t>As IPv6 deployment increases, there will be a dramatic increase in the need to use IPv6 addresses in text. While the IPv6 address architecture in Section 2.2 of RFC 4291 describes a flexible model for text representation of an IPv6 address, this flexibility has been causing problems for operators, system engineers, and users. This document defines a canonical textual representation format. It does not define a format for internal storage, such as within an application or database. It is expected that the canonical format will be followed by humans and systems when representing IPv6 addresses as text, but all implementations must accept and be able to handle any legitimate RFC 4291 format. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='5952'/>
<seriesInfo name='DOI' value='10.17487/RFC5952'/>
</reference>
<reference anchor='RFC6690' target='http://www.rfc-editor.org/info/rfc6690'>
<front>
<title>Constrained RESTful Environments (CoRE) Link Format</title>
<author initials='Z.' surname='Shelby' fullname='Z. Shelby'><organization /></author>
<date year='2012' month='August' />
<abstract><t>This specification defines Web Linking using a link format for use by constrained web servers to describe hosted resources, their attributes, and other relationships between links. Based on the HTTP Link Header field defined in RFC 5988, the Constrained RESTful Environments (CoRE) Link Format is carried as a payload and is assigned an Internet media type. "RESTful" refers to the Representational State Transfer (REST) architecture. A well-known URI is defined as a default entry point for requesting the links hosted by a server. [STANDARDS-TRACK]</t></abstract>
</front>
<seriesInfo name='RFC' value='6690'/>
<seriesInfo name='DOI' value='10.17487/RFC6690'/>
</reference>
<reference anchor='RFC7721' target='http://www.rfc-editor.org/info/rfc7721'>
<front>
<title>Security and Privacy Considerations for IPv6 Address Generation Mechanisms</title>
<author initials='A.' surname='Cooper' fullname='A. Cooper'><organization /></author>
<author initials='F.' surname='Gont' fullname='F. Gont'><organization /></author>
<author initials='D.' surname='Thaler' fullname='D. Thaler'><organization /></author>
<date year='2016' month='March' />
<abstract><t>This document discusses privacy and security considerations for several IPv6 address generation mechanisms, both standardized and non-standardized. It evaluates how different mechanisms mitigate different threats and the trade-offs that implementors, developers, and users face in choosing different addresses or address generation mechanisms.</t></abstract>
</front>
<seriesInfo name='RFC' value='7721'/>
<seriesInfo name='DOI' value='10.17487/RFC7721'/>
</reference>
<reference anchor='I-D.arkko-core-dev-urn'>
<front>
<title>Uniform Resource Names for Device Identifiers</title>
<author initials='J' surname='Arkko' fullname='Jari Arkko'>
<organization />
</author>
<author initials='C' surname='Jennings' fullname='Cullen Jennings'>
<organization />
</author>
<author initials='Z' surname='Shelby' fullname='Zach Shelby'>
<organization />
</author>
<date month='July' day='9' year='2012' />
<abstract><t>This memo describes a new Uniform Resource Name (URN) namespace for hardware device identifiers. A general representation of device identity can be useful in many applications, such as in sensor data streams and storage, or equipment inventories. A URN-based representation can be easily passed along in any application that needs the information.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-arkko-core-dev-urn-03' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-arkko-core-dev-urn-03.txt' />
</reference>
<reference anchor='I-D.greevenbosch-appsawg-cbor-cddl'>
<front>
<title>CBOR data definition language (CDDL): a notational convention to express CBOR data structures</title>
<author initials='C' surname='Vigano' fullname='Christoph Vigano'>
<organization />
</author>
<author initials='H' surname='Birkholz' fullname='Henk Birkholz'>
<organization />
</author>
<date month='March' day='21' year='2016' />
<abstract><t>This document proposes a notational convention to express CBOR data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-greevenbosch-appsawg-cbor-cddl-08' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-greevenbosch-appsawg-cbor-cddl-08.txt' />
</reference>
<reference anchor='I-D.ietf-core-links-json'>
<front>
<title>Representing CoRE Formats in JSON and CBOR</title>
<author initials='K' surname='Li' fullname='Kepeng Li'>
<organization />
</author>
<author initials='A' surname='Rahman' fullname='Akbar Rahman'>
<organization />
</author>
<author initials='C' surname='Bormann' fullname='Carsten Bormann'>
<organization />
</author>
<date month='November' day='1' year='2015' />
<abstract><t>JavaScript Object Notation, JSON (RFC7159) is a text-based data format which is popular for Web based data exchange. Concise Binary Object Representation, CBOR (RFC7049) is a binary data format which has been optimized for data exchange for the Internet of Things (IoT). For many IoT scenarios, CBOR formats will be preferred since it can help decrease transmission payload sizes as well as implementation code sizes compared to other data formats. Web Linking (RFC5988) provides a way to represent links between Web resources as well as the relations expressed by them and attributes of such a link. In constrained networks, a collection of Web links can be exchanged in the CoRE link format (RFC6690). Outside of constrained environments, it may be useful to represent these collections of Web links in JSON, and similarly, inside constrained environments, in CBOR. This specification defines a common format for this. Group Communication for the Constrained Application Protocol (RFC7390) defines a number of JSON formats for controlling communication between groups of nodes employing the Constrained Application Protocol (CoAP). In a similar vein, this specification defines CBOR variants of these formats.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-ietf-core-links-json-04' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-ietf-core-links-json-04.txt' />
</reference>
<reference anchor="UCUM" target="http://unitsofmeasure.org/ucum.html">
<front>
<title>The Unified Code for Units of Measure (UCUM)</title>
<author initials="G." surname="Schadow">
<organization></organization>
</author>
<author initials="C." surname="McDonald">
<organization></organization>
</author>
<date year="2013"/>
</front>
<seriesInfo name="Regenstrief Institute and Indiana University School of" value="Informatics"/>
</reference>
</references>
<section anchor="links-extension" title="Links extension">
<t>An extension to SenML to support links is expected to be registered and
defined by <xref target="I-D.ietf-core-links-json"/>.</t>
<t>The link extension can be an array of objects that can be used for
additional information. Each object in the Link array is constrained to
being a map of strings to strings with unique keys.</t>
<t>The following shows an example of the links extension.</t>
<figure><artwork><![CDATA[
[{"bn": "urn:dev:ow:10e2073a01080063/",
"bt": 1320078429,
"l": "[{\"href\":\"humidity\",\"foo\":\"bar1\"}\"
},
{ "n": "temperature", "v": 27.2, "u": "Cel" },
{ "n": "humidity", "v": 80, "u": "%RH" }
]
]]></artwork></figure>
</section>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-23 04:42:15 |