File: rfc9193.html

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<!DOCTYPE html>
<html lang="en" class="RFC">
<head>
<meta charset="utf-8">
<meta content="Common,Latin" name="scripts">
<meta content="initial-scale=1.0" name="viewport">
<title>RFC 9193: Sensor Measurement Lists (SenML) Fields for Indicating Data Value Content-Format</title>
<meta content="Ari Keränen" name="author">
<meta content="Carsten Bormann" name="author">
<meta content="
       The Sensor Measurement Lists (SenML) media types support multiple types
of values, from numbers to text strings and arbitrary binary Data Values.
In order to facilitate processing of binary Data Values, this document
specifies a pair of new SenML fields for indicating the
content format of those binary Data Values, i.e., their Internet media
type, including parameters as well as any content codings applied. 
    " name="description">
<meta content="xml2rfc 3.12.10" name="generator">
<meta content="Internet of Things (IoT)" name="keyword">
<meta content="Internet of Things" name="keyword">
<meta content="IOT" name="keyword">
<meta content="data model" name="keyword">
<meta content="media type" name="keyword">
<meta content="9193" name="rfc.number">
<!-- Generator version information:
  xml2rfc 3.12.10
    Python 3.6.15
    appdirs 1.4.4
    ConfigArgParse 1.4.1
    google-i18n-address 2.4.0
    html5lib 1.0.1
    intervaltree 3.0.2
    Jinja2 2.11.3
    kitchen 1.2.6
    lxml 4.7.1
    MarkupSafe 2.0.1
    pycairo 1.15.1
    pycountry 19.8.18
    pyflakes 2.1.1
    PyYAML 5.4.1
    requests 2.24.0
    setuptools 40.5.0
    six 1.14.0
    WeasyPrint 52.5
-->
<link href="rfc9193.xml" rel="alternate" type="application/rfc+xml">
<link href="#copyright" rel="license">
<style type="text/css">/*

  NOTE: Changes at the bottom of this file overrides some earlier settings.

  Once the style has stabilized and has been adopted as an official RFC style,
  this can be consolidated so that style settings occur only in one place, but
  for now the contents of this file consists first of the initial CSS work as
  provided to the RFC Formatter (xml2rfc) work, followed by itemized and
  commented changes found necssary during the development of the v3
  formatters.

*/

/* fonts */
@import url('https://fonts.googleapis.com/css?family=Noto+Sans'); /* Sans-serif */
@import url('https://fonts.googleapis.com/css?family=Noto+Serif'); /* Serif (print) */
@import url('https://fonts.googleapis.com/css?family=Roboto+Mono'); /* Monospace */

@viewport {
  zoom: 1.0;
  width: extend-to-zoom;
}
@-ms-viewport {
  width: extend-to-zoom;
  zoom: 1.0;
}
/* general and mobile first */
html {
}
body {
  max-width: 90%;
  margin: 1.5em auto;
  color: #222;
  background-color: #fff;
  font-size: 14px;
  font-family: 'Noto Sans', Arial, Helvetica, sans-serif;
  line-height: 1.6;
  scroll-behavior: smooth;
}
.ears {
  display: none;
}

/* headings */
#title, h1, h2, h3, h4, h5, h6 {
  margin: 1em 0 0.5em;
  font-weight: bold;
  line-height: 1.3;
}
#title {
  clear: both;
  border-bottom: 1px solid #ddd;
  margin: 0 0 0.5em 0;
  padding: 1em 0 0.5em;
}
.author {
  padding-bottom: 4px;
}
h1 {
  font-size: 26px;
  margin: 1em 0;
}
h2 {
  font-size: 22px;
  margin-top: -20px;  /* provide offset for in-page anchors */
  padding-top: 33px;
}
h3 {
  font-size: 18px;
  margin-top: -36px;  /* provide offset for in-page anchors */
  padding-top: 42px;
}
h4 {
  font-size: 16px;
  margin-top: -36px;  /* provide offset for in-page anchors */
  padding-top: 42px;
}
h5, h6 {
  font-size: 14px;
}
#n-copyright-notice {
  border-bottom: 1px solid #ddd;
  padding-bottom: 1em;
  margin-bottom: 1em;
}
/* general structure */
p {
  padding: 0;
  margin: 0 0 1em 0;
  text-align: left;
}
div, span {
  position: relative;
}
div {
  margin: 0;
}
.alignRight.art-text {
  background-color: #f9f9f9;
  border: 1px solid #eee;
  border-radius: 3px;
  padding: 1em 1em 0;
  margin-bottom: 1.5em;
}
.alignRight.art-text pre {
  padding: 0;
}
.alignRight {
  margin: 1em 0;
}
.alignRight > *:first-child {
  border: none;
  margin: 0;
  float: right;
  clear: both;
}
.alignRight > *:nth-child(2) {
  clear: both;
  display: block;
  border: none;
}
svg {
  display: block;
}
.alignCenter.art-text {
  background-color: #f9f9f9;
  border: 1px solid #eee;
  border-radius: 3px;
  padding: 1em 1em 0;
  margin-bottom: 1.5em;
}
.alignCenter.art-text pre {
  padding: 0;
}
.alignCenter {
  margin: 1em 0;
}
.alignCenter > *:first-child {
  border: none;
  margin: 0 auto;
}

/* lists */
ol, ul {
  padding: 0;
  margin: 0 0 1em 2em;
}
ol ol, ul ul, ol ul, ul ol {
  margin-left: 1em;
}
li {
  margin: 0 0 0.25em 0;
}
.ulCompact li {
  margin: 0;
}
ul.empty, .ulEmpty {
  list-style-type: none;
}
ul.empty li, .ulEmpty li {
  margin-top: 0.5em;
}
ul.ulBare, li.ulBare {
  margin-left: 0em !important;
}
ul.compact, .ulCompact,
ol.compact, .olCompact {
  line-height: 100%;
  margin: 0 0 0 2em;
}

/* definition lists */
dl {
}
dl > dt {
  float: left;
  margin-right: 1em;
}
/* 
dl.nohang > dt {
  float: none;
}
*/
dl > dd {
  margin-bottom: .8em;
  min-height: 1.3em;
}
dl.compact > dd, .dlCompact > dd {
  margin-bottom: 0em;
}
dl > dd > dl {
  margin-top: 0.5em;
  margin-bottom: 0em;
}

/* links */
a {
  text-decoration: none;
}
a[href] {
  color: #22e; /* Arlen: WCAG 2019 */
}
a[href]:hover {
  background-color: #f2f2f2;
}
figcaption a[href],
a[href].selfRef {
  color: #222;
}
/* XXX probably not this:
a.selfRef:hover {
  background-color: transparent;
  cursor: default;
} */

/* Figures */
tt, code, pre, code {
  background-color: #f9f9f9;
  font-family: 'Roboto Mono', monospace;
}
pre {
  border: 1px solid #eee;
  margin: 0;
  padding: 1em;
}
img {
  max-width: 100%;
}
figure {
  margin: 0;
}
figure blockquote {
  margin: 0.8em 0.4em 0.4em;
}
figcaption {
  font-style: italic;
  margin: 0 0 1em 0;
}
@media screen {
  pre {
    overflow-x: auto;
    max-width: 100%;
    max-width: calc(100% - 22px);
  }
}

/* aside, blockquote */
aside, blockquote {
  margin-left: 0;
  padding: 1.2em 2em;
}
blockquote {
  background-color: #f9f9f9;
  color: #111; /* Arlen: WCAG 2019 */
  border: 1px solid #ddd;
  border-radius: 3px;
  margin: 1em 0;
}
cite {
  display: block;
  text-align: right;
  font-style: italic;
}

/* tables */
table {
  width: 100%;
  margin: 0 0 1em;
  border-collapse: collapse;
  border: 1px solid #eee;
}
th, td {
  text-align: left;
  vertical-align: top;
  padding: 0.5em 0.75em;
}
th {
  text-align: left;
  background-color: #e9e9e9;
}
tr:nth-child(2n+1) > td {
  background-color: #f5f5f5;
}
table caption {
  font-style: italic;
  margin: 0;
  padding: 0;
  text-align: left;
}
table p {
  /* XXX to avoid bottom margin on table row signifiers. If paragraphs should
     be allowed within tables more generally, it would be far better to select on a class. */
  margin: 0;
}

/* pilcrow */
a.pilcrow {
  color: #666; /* Arlen: AHDJ 2019 */
  text-decoration: none;
  visibility: hidden;
  user-select: none;
  -ms-user-select: none;
  -o-user-select:none;
  -moz-user-select: none;
  -khtml-user-select: none;
  -webkit-user-select: none;
  -webkit-touch-callout: none;
}
@media screen {
  aside:hover > a.pilcrow,
  p:hover > a.pilcrow,
  blockquote:hover > a.pilcrow,
  div:hover > a.pilcrow,
  li:hover > a.pilcrow,
  pre:hover > a.pilcrow {
    visibility: visible;
  }
  a.pilcrow:hover {
    background-color: transparent;
  }
}

/* misc */
hr {
  border: 0;
  border-top: 1px solid #eee;
}
.bcp14 {
  font-variant: small-caps;
}

.role {
  font-variant: all-small-caps;
}

/* info block */
#identifiers {
  margin: 0;
  font-size: 0.9em;
}
#identifiers dt {
  width: 3em;
  clear: left;
}
#identifiers dd {
  float: left;
  margin-bottom: 0;
}
/* Fix PDF info block run off issue */
@media print {
  #identifiers dd {
    float: none;
  }
}
#identifiers .authors .author {
  display: inline-block;
  margin-right: 1.5em;
}
#identifiers .authors .org {
  font-style: italic;
}

/* The prepared/rendered info at the very bottom of the page */
.docInfo {
  color: #666; /* Arlen: WCAG 2019 */
  font-size: 0.9em;
  font-style: italic;
  margin-top: 2em;
}
.docInfo .prepared {
  float: left;
}
.docInfo .prepared {
  float: right;
}

/* table of contents */
#toc  {
  padding: 0.75em 0 2em 0;
  margin-bottom: 1em;
}
nav.toc ul {
  margin: 0 0.5em 0 0;
  padding: 0;
  list-style: none;
}
nav.toc li {
  line-height: 1.3em;
  margin: 0.75em 0;
  padding-left: 1.2em;
  text-indent: -1.2em;
}
/* references */
.references dt {
  text-align: right;
  font-weight: bold;
  min-width: 7em;
}
.references dd {
  margin-left: 8em;
  overflow: auto;
}

.refInstance {
  margin-bottom: 1.25em;
}

.references .ascii {
  margin-bottom: 0.25em;
}

/* index */
.index ul {
  margin: 0 0 0 1em;
  padding: 0;
  list-style: none;
}
.index ul ul {
  margin: 0;
}
.index li {
  margin: 0;
  text-indent: -2em;
  padding-left: 2em;
  padding-bottom: 5px;
}
.indexIndex {
  margin: 0.5em 0 1em;
}
.index a {
  font-weight: 700;
}
/* make the index two-column on all but the smallest screens */
@media (min-width: 600px) {
  .index ul {
    -moz-column-count: 2;
    -moz-column-gap: 20px;
  }
  .index ul ul {
    -moz-column-count: 1;
    -moz-column-gap: 0;
  }
}

/* authors */
address.vcard {
  font-style: normal;
  margin: 1em 0;
}

address.vcard .nameRole {
  font-weight: 700;
  margin-left: 0;
}
address.vcard .label {
  font-family: "Noto Sans",Arial,Helvetica,sans-serif;
  margin: 0.5em 0;
}
address.vcard .type {
  display: none;
}
.alternative-contact {
  margin: 1.5em 0 1em;
}
hr.addr {
  border-top: 1px dashed;
  margin: 0;
  color: #ddd;
  max-width: calc(100% - 16px);
}

/* temporary notes */
.rfcEditorRemove::before {
  position: absolute;
  top: 0.2em;
  right: 0.2em;
  padding: 0.2em;
  content: "The RFC Editor will remove this note";
  color: #9e2a00; /* Arlen: WCAG 2019 */
  background-color: #ffd; /* Arlen: WCAG 2019 */
}
.rfcEditorRemove {
  position: relative;
  padding-top: 1.8em;
  background-color: #ffd; /* Arlen: WCAG 2019 */
  border-radius: 3px;
}
.cref {
  background-color: #ffd; /* Arlen: WCAG 2019 */
  padding: 2px 4px;
}
.crefSource {
  font-style: italic;
}
/* alternative layout for smaller screens */
@media screen and (max-width: 1023px) {
  body {
    padding-top: 2em;
  }
  #title {
    padding: 1em 0;
  }
  h1 {
    font-size: 24px;
  }
  h2 {
    font-size: 20px;
    margin-top: -18px;  /* provide offset for in-page anchors */
    padding-top: 38px;
  }
  #identifiers dd {
    max-width: 60%;
  }
  #toc {
    position: fixed;
    z-index: 2;
    top: 0;
    right: 0;
    padding: 0;
    margin: 0;
    background-color: inherit;
    border-bottom: 1px solid #ccc;
  }
  #toc h2 {
    margin: -1px 0 0 0;
    padding: 4px 0 4px 6px;
    padding-right: 1em;
    min-width: 190px;
    font-size: 1.1em;
    text-align: right;
    background-color: #444;
    color: white;
    cursor: pointer;
  }
  #toc h2::before { /* css hamburger */
    float: right;
    position: relative;
    width: 1em;
    height: 1px;
    left: -164px;
    margin: 6px 0 0 0;
    background: white none repeat scroll 0 0;
    box-shadow: 0 4px 0 0 white, 0 8px 0 0 white;
    content: "";
  }
  #toc nav {
    display: none;
    padding: 0.5em 1em 1em;
    overflow: auto;
    height: calc(100vh - 48px);
    border-left: 1px solid #ddd;
  }
}

/* alternative layout for wide screens */
@media screen and (min-width: 1024px) {
  body {
    max-width: 724px;
    margin: 42px auto;
    padding-left: 1.5em;
    padding-right: 29em;
  }
  #toc {
    position: fixed;
    top: 42px;
    right: 42px;
    width: 25%;
    margin: 0;
    padding: 0 1em;
    z-index: 1;
  }
  #toc h2 {
    border-top: none;
    border-bottom: 1px solid #ddd;
    font-size: 1em;
    font-weight: normal;
    margin: 0;
    padding: 0.25em 1em 1em 0;
  }
  #toc nav {
    display: block;
    height: calc(90vh - 84px);
    bottom: 0;
    padding: 0.5em 0 0;
    overflow: auto;
  }
  img { /* future proofing */
    max-width: 100%;
    height: auto;
  }
}

/* pagination */
@media print {
  body {

    width: 100%;
  }
  p {
    orphans: 3;
    widows: 3;
  }
  #n-copyright-notice {
    border-bottom: none;
  }
  #toc, #n-introduction {
    page-break-before: always;
  }
  #toc {
    border-top: none;
    padding-top: 0;
  }
  figure, pre {
    page-break-inside: avoid;
  }
  figure {
    overflow: scroll;
  }
  pre.breakable {
    break-inside: auto;
  }
  h1, h2, h3, h4, h5, h6 {
    page-break-after: avoid;
  }
  h2+*, h3+*, h4+*, h5+*, h6+* {
    page-break-before: avoid;
  }
  pre {
    white-space: pre-wrap;
    word-wrap: break-word;
    font-size: 10pt;
  }
  table {
    border: 1px solid #ddd;
  }
  td {
    border-top: 1px solid #ddd;
  }
}

/* This is commented out here, as the string-set: doesn't
   pass W3C validation currently */
/*
.ears thead .left {
  string-set: ears-top-left content();
}

.ears thead .center {
  string-set: ears-top-center content();
}

.ears thead .right {
  string-set: ears-top-right content();
}

.ears tfoot .left {
  string-set: ears-bottom-left content();
}

.ears tfoot .center {
  string-set: ears-bottom-center content();
}

.ears tfoot .right {
  string-set: ears-bottom-right content();
}
*/

@page :first {
  padding-top: 0;
  @top-left {
    content: normal;
    border: none;
  }
  @top-center {
    content: normal;
    border: none;
  }
  @top-right {
    content: normal;
    border: none;
  }
}

@page {
  size: A4;
  margin-bottom: 45mm;
  padding-top: 20px;
  /* The follwing is commented out here, but set appropriately by in code, as
     the content depends on the document */
  /*
  @top-left {
    content: 'Internet-Draft';
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-left {
    content: string(ears-top-left);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-center {
    content: string(ears-top-center);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @top-right {
    content: string(ears-top-right);
    vertical-align: bottom;
    border-bottom: solid 1px #ccc;
  }
  @bottom-left {
    content: string(ears-bottom-left);
    vertical-align: top;
    border-top: solid 1px #ccc;
  }
  @bottom-center {
    content: string(ears-bottom-center);
    vertical-align: top;
    border-top: solid 1px #ccc;
  }
  @bottom-right {
      content: '[Page ' counter(page) ']';
      vertical-align: top;
      border-top: solid 1px #ccc;
  }
  */

}

/* Changes introduced to fix issues found during implementation */
/* Make sure links are clickable even if overlapped by following H* */
a {
  z-index: 2;
}
/* Separate body from document info even without intervening H1 */
section {
  clear: both;
}


/* Top align author divs, to avoid names without organization dropping level with org names */
.author {
  vertical-align: top;
}

/* Leave room in document info to show Internet-Draft on one line */
#identifiers dt {
  width: 8em;
}

/* Don't waste quite as much whitespace between label and value in doc info */
#identifiers dd {
  margin-left: 1em;
}

/* Give floating toc a background color (needed when it's a div inside section */
#toc {
  background-color: white;
}

/* Make the collapsed ToC header render white on gray also when it's a link */
@media screen and (max-width: 1023px) {
  #toc h2 a,
  #toc h2 a:link,
  #toc h2 a:focus,
  #toc h2 a:hover,
  #toc a.toplink,
  #toc a.toplink:hover {
    color: white;
    background-color: #444;
    text-decoration: none;
  }
}

/* Give the bottom of the ToC some whitespace */
@media screen and (min-width: 1024px) {
  #toc {
    padding: 0 0 1em 1em;
  }
}

/* Style section numbers with more space between number and title */
.section-number {
  padding-right: 0.5em;
}

/* prevent monospace from becoming overly large */
tt, code, pre, code {
  font-size: 95%;
}

/* Fix the height/width aspect for ascii art*/
pre.sourcecode,
.art-text pre {
  line-height: 1.12;
}


/* Add styling for a link in the ToC that points to the top of the document */
a.toplink {
  float: right;
  margin-right: 0.5em;
}

/* Fix the dl styling to match the RFC 7992 attributes */
dl > dt,
dl.dlParallel > dt {
  float: left;
  margin-right: 1em;
}
dl.dlNewline > dt {
  float: none;
}

/* Provide styling for table cell text alignment */
table td.text-left,
table th.text-left {
  text-align: left;
}
table td.text-center,
table th.text-center {
  text-align: center;
}
table td.text-right,
table th.text-right {
  text-align: right;
}

/* Make the alternative author contact informatio look less like just another
   author, and group it closer with the primary author contact information */
.alternative-contact {
  margin: 0.5em 0 0.25em 0;
}
address .non-ascii {
  margin: 0 0 0 2em;
}

/* With it being possible to set tables with alignment
  left, center, and right, { width: 100%; } does not make sense */
table {
  width: auto;
}

/* Avoid reference text that sits in a block with very wide left margin,
   because of a long floating dt label.*/
.references dd {
  overflow: visible;
}

/* Control caption placement */
caption {
  caption-side: bottom;
}

/* Limit the width of the author address vcard, so names in right-to-left
   script don't end up on the other side of the page. */

address.vcard {
  max-width: 30em;
  margin-right: auto;
}

/* For address alignment dependent on LTR or RTL scripts */
address div.left {
  text-align: left;
}
address div.right {
  text-align: right;
}

/* Provide table alignment support.  We can't use the alignX classes above
   since they do unwanted things with caption and other styling. */
table.right {
 margin-left: auto;
 margin-right: 0;
}
table.center {
 margin-left: auto;
 margin-right: auto;
}
table.left {
 margin-left: 0;
 margin-right: auto;
}

/* Give the table caption label the same styling as the figcaption */
caption a[href] {
  color: #222;
}

@media print {
  .toplink {
    display: none;
  }

  /* avoid overwriting the top border line with the ToC header */
  #toc {
    padding-top: 1px;
  }

  /* Avoid page breaks inside dl and author address entries */
  .vcard {
    page-break-inside: avoid;
  }

}
/* Tweak the bcp14 keyword presentation */
.bcp14 {
  font-variant: small-caps;
  font-weight: bold;
  font-size: 0.9em;
}
/* Tweak the invisible space above H* in order not to overlay links in text above */
 h2 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 31px;
 }
 h3 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
 h4 {
  margin-top: -18px;  /* provide offset for in-page anchors */
  padding-top: 24px;
 }
/* Float artwork pilcrow to the right */
@media screen {
  .artwork a.pilcrow {
    display: block;
    line-height: 0.7;
    margin-top: 0.15em;
  }
}
/* Make pilcrows on dd visible */
@media screen {
  dd:hover > a.pilcrow {
    visibility: visible;
  }
}
/* Make the placement of figcaption match that of a table's caption
   by removing the figure's added bottom margin */
.alignLeft.art-text,
.alignCenter.art-text,
.alignRight.art-text {
   margin-bottom: 0;
}
.alignLeft,
.alignCenter,
.alignRight {
  margin: 1em 0 0 0;
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<table class="ears">
<thead><tr>
<td class="left">RFC 9193</td>
<td class="center">SenML Data Content-Format Indication</td>
<td class="right">June 2022</td>
</tr></thead>
<tfoot><tr>
<td class="left">Keränen &amp; Bormann</td>
<td class="center">Standards Track</td>
<td class="right">[Page]</td>
</tr></tfoot>
</table>
<div id="external-metadata" class="document-information"></div>
<div id="internal-metadata" class="document-information">
<dl id="identifiers">
<dt class="label-stream">Stream:</dt>
<dd class="stream">Internet Engineering Task Force (IETF)</dd>
<dt class="label-rfc">RFC:</dt>
<dd class="rfc"><a href="https://www.rfc-editor.org/rfc/rfc9193" class="eref">9193</a></dd>
<dt class="label-category">Category:</dt>
<dd class="category">Standards Track</dd>
<dt class="label-published">Published:</dt>
<dd class="published">
<time datetime="2022-06" class="published">June 2022</time>
    </dd>
<dt class="label-issn">ISSN:</dt>
<dd class="issn">2070-1721</dd>
<dt class="label-authors">Authors:</dt>
<dd class="authors">
<div class="author">
      <div class="author-name">A. Keränen</div>
<div class="org">Ericsson</div>
</div>
<div class="author">
      <div class="author-name">C. Bormann</div>
<div class="org">Universität Bremen TZI</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 9193</h1>
<h1 id="title">Sensor Measurement Lists (SenML) Fields for Indicating Data Value Content-Format</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">The Sensor Measurement Lists (SenML) media types support multiple types
of values, from numbers to text strings and arbitrary binary Data Values.
In order to facilitate processing of binary Data Values, this document
specifies a pair of new SenML fields for indicating the
content format of those binary Data Values, i.e., their Internet media
type, including parameters as well as any content codings applied.<a href="#section-abstract-1" class="pilcrow">¶</a></p>
</section>
<div id="status-of-memo">
<section id="section-boilerplate.1">
        <h2 id="name-status-of-this-memo">
<a href="#name-status-of-this-memo" class="section-name selfRef">Status of This Memo</a>
        </h2>
<p id="section-boilerplate.1-1">
            This is an Internet Standards Track document.<a href="#section-boilerplate.1-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-2">
            This document is a product of the Internet Engineering Task Force
            (IETF).  It represents the consensus of the IETF community.  It has
            received public review and has been approved for publication by
            the Internet Engineering Steering Group (IESG).  Further
            information on Internet Standards is available in Section 2 of 
            RFC 7841.<a href="#section-boilerplate.1-2" class="pilcrow">¶</a></p>
<p id="section-boilerplate.1-3">
            Information about the current status of this document, any
            errata, and how to provide feedback on it may be obtained at
            <span><a href="https://www.rfc-editor.org/info/rfc9193">https://www.rfc-editor.org/info/rfc9193</a></span>.<a href="#section-boilerplate.1-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="copyright">
<section id="section-boilerplate.2">
        <h2 id="name-copyright-notice">
<a href="#name-copyright-notice" class="section-name selfRef">Copyright Notice</a>
        </h2>
<p id="section-boilerplate.2-1">
            Copyright (c) 2022 IETF Trust and the persons identified as the
            document authors. All rights reserved.<a href="#section-boilerplate.2-1" class="pilcrow">¶</a></p>
<p id="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<span><a href="https://trustee.ietf.org/license-info">https://trustee.ietf.org/license-info</a></span>) in effect on the date of
            publication of this document. Please review these documents
            carefully, as they describe your rights and restrictions with
            respect to this document. Code Components extracted from this
            document must include Revised BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Revised BSD License.<a href="#section-boilerplate.2-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="toc">
<section id="section-toc.1">
        <a href="#" onclick="scroll(0,0)" class="toplink">▲</a><h2 id="name-table-of-contents">
<a href="#name-table-of-contents" class="section-name selfRef">Table of Contents</a>
        </h2>
<nav class="toc"><ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.1">
            <p id="section-toc.1-1.1.1" class="keepWithNext"><a href="#section-1" class="xref">1</a>.  <a href="#name-introduction" class="xref">Introduction</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.1.2.1">
                <p id="section-toc.1-1.1.2.1.1" class="keepWithNext"><a href="#section-1.1" class="xref">1.1</a>.  <a href="#name-evolution" class="xref">Evolution</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.2">
            <p id="section-toc.1-1.2.1" class="keepWithNext"><a href="#section-2" class="xref">2</a>.  <a href="#name-terminology" class="xref">Terminology</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.3">
            <p id="section-toc.1-1.3.1"><a href="#section-3" class="xref">3</a>.  <a href="#name-senml-content-format-ct-fie" class="xref">SenML Content-Format ("ct") Field</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.4">
            <p id="section-toc.1-1.4.1"><a href="#section-4" class="xref">4</a>.  <a href="#name-senml-base-content-format-b" class="xref">SenML Base Content-Format ("bct") Field</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.5">
            <p id="section-toc.1-1.5.1"><a href="#section-5" class="xref">5</a>.  <a href="#name-examples" class="xref">Examples</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.6">
            <p id="section-toc.1-1.6.1"><a href="#section-6" class="xref">6</a>.  <a href="#name-abnf" class="xref">ABNF</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.7">
            <p id="section-toc.1-1.7.1"><a href="#section-7" class="xref">7</a>.  <a href="#name-security-considerations" class="xref">Security Considerations</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.8">
            <p id="section-toc.1-1.8.1"><a href="#section-8" class="xref">8</a>.  <a href="#name-iana-considerations" class="xref">IANA Considerations</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.9">
            <p id="section-toc.1-1.9.1"><a href="#section-9" class="xref">9</a>.  <a href="#name-references" class="xref">References</a></p>
<ul class="compact toc ulBare ulEmpty">
<li class="compact toc ulBare ulEmpty" id="section-toc.1-1.9.2.1">
                <p id="section-toc.1-1.9.2.1.1"><a href="#section-9.1" class="xref">9.1</a>.  <a href="#name-normative-references" class="xref">Normative References</a></p>
</li>
              <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.9.2.2">
                <p id="section-toc.1-1.9.2.2.1"><a href="#section-9.2" class="xref">9.2</a>.  <a href="#name-informative-references" class="xref">Informative References</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.10">
            <p id="section-toc.1-1.10.1"><a href="#appendix-A" class="xref"></a><a href="#name-acknowledgments" class="xref">Acknowledgments</a></p>
</li>
          <li class="compact toc ulBare ulEmpty" id="section-toc.1-1.11">
            <p id="section-toc.1-1.11.1"><a href="#appendix-B" class="xref"></a><a href="#name-authors-addresses" class="xref">Authors' Addresses</a></p>
</li>
        </ul>
</nav>
</section>
</div>
<div id="intro">
<section id="section-1">
      <h2 id="name-introduction">
<a href="#section-1" class="section-number selfRef">1. </a><a href="#name-introduction" class="section-name selfRef">Introduction</a>
      </h2>
<p id="section-1-1">The Sensor Measurement Lists (SenML) media types <span>[<a href="#RFC8428" class="xref">RFC8428</a>]</span> can be used
to send various kinds of data.  In the example given in
<a href="#ex-1" class="xref">Figure 1</a>, a temperature value, an indication whether a lock is open, and
a Data Value (with SenML field "vd") read from a Near Field Communication (NFC) reader is sent in a
single SenML Pack.
The example is given in SenML JSON representation, so the "vd" (Data
Value) field is encoded as a base64url string (without
padding), as per <span><a href="https://www.rfc-editor.org/rfc/rfc8428#section-5" class="relref">Section 5</a> of [<a href="#RFC8428" class="xref">RFC8428</a>]</span>.<a href="#section-1-1" class="pilcrow">¶</a></p>
<span id="name-senml-pack-with-unidentifie"></span><div id="ex-1">
<figure id="figure-1">
        <div id="section-1-2.1">
<pre class="lang-senml-json sourcecode">
[
  {"bn":"urn:dev:ow:10e2073a01080063:","n":"temp","u":"Cel","v":7.1},
  {"n":"open","vb":false},
  {"n":"nfc-reader","vd":"aGkgCg"}
]
</pre>
</div>
<figcaption><a href="#figure-1" class="selfRef">Figure 1</a>:
<a href="#name-senml-pack-with-unidentifie" class="selfRef">SenML Pack with Unidentified Binary Data</a>
        </figcaption></figure>
</div>
<p id="section-1-3">The receiver is expected to know how to interpret the data in the "vd"
field based on the context, e.g., the name of the data source and out-of-band
knowledge of the application. However, this context may not always be
easily available to entities processing the SenML Pack, especially if
the Pack is propagated over time and via multiple entities. To facilitate
automatic interpretation, it is useful to be able to indicate an Internet
media type and, optionally, content codings right in the SenML Record.<a href="#section-1-3" class="pilcrow">¶</a></p>
<p id="section-1-4">The Constrained Application Protocol (CoAP)
Content-Format (<span><a href="https://www.rfc-editor.org/rfc/rfc7252#section-12.3" class="relref">Section 12.3</a> of [<a href="#RFC7252" class="xref">RFC7252</a>]</span>) provides this
information in the form of a single unsigned integer. For instance, <span>[<a href="#RFC8949" class="xref">RFC8949</a>]</span> defines the Content-Format number 60 for
Content-Type application/cbor. Enclosing this Content-Format number in the Record is illustrated in <a href="#ex-2" class="xref">Figure 2</a>. All registered CoAP Content-Format numbers are listed
in the "<a href="https://www.iana.org/assignments/core-parameters#content-formats" class="relref">CoAP Content-Formats</a>" registry <span>[<a href="#IANA.core-parameters" class="xref">IANA.core-parameters</a>]</span>, as specified by
<span><a href="https://www.rfc-editor.org/rfc/rfc7252#section-12.3" class="relref">Section 12.3</a> of [<a href="#RFC7252" class="xref">RFC7252</a>]</span>.
Note that, at the time of writing, the structure of this registry only
provides for zero or one content coding; nothing in the present
document needs to change if the registry is extended to allow
sequences of content codings.<a href="#section-1-4" class="pilcrow">¶</a></p>
<span id="name-senml-record-with-binary-da"></span><div id="ex-2">
<figure id="figure-2">
        <div id="section-1-5.1">
<pre class="lang-json sourcecode">
{"n":"nfc-reader", "vd":"gmNmb28YKg", "ct":"60"}
</pre>
</div>
<figcaption><a href="#figure-2" class="selfRef">Figure 2</a>:
<a href="#name-senml-record-with-binary-da" class="selfRef">SenML Record with Binary Data Identified as CBOR</a>
        </figcaption></figure>
</div>
<p id="section-1-6">In this example SenML Record, the Data Value contains a string "foo" and a
number 42 encoded in a Concise Binary Object Representation (CBOR) <span>[<a href="#RFC8949" class="xref">RFC8949</a>]</span> array. Since the example above
uses the JSON format of SenML, the Data Value containing the binary CBOR
value is base64 encoded (<span><a href="https://www.rfc-editor.org/rfc/rfc4648#section-5" class="relref">Section 5</a> of [<a href="#RFC4648" class="xref">RFC4648</a>]</span>).
The Data Value after base64 decoding is shown
with CBOR diagnostic notation in <a href="#ex-2-cbor" class="xref">Figure 3</a>.<a href="#section-1-6" class="pilcrow">¶</a></p>
<span id="name-example-data-value-in-cbor-"></span><div id="ex-2-cbor">
<figure id="figure-3">
        <div id="section-1-7.1">
<pre class="lang-cbor-pretty sourcecode">
82           # array(2)
   63        # text(3)
      666F6F # "foo"
   18 2A     # unsigned(42)
</pre>
</div>
<figcaption><a href="#figure-3" class="selfRef">Figure 3</a>:
<a href="#name-example-data-value-in-cbor-" class="selfRef">Example Data Value in CBOR Diagnostic Notation</a>
        </figcaption></figure>
</div>
<div id="evolution">
<section id="section-1.1">
        <h3 id="name-evolution">
<a href="#section-1.1" class="section-number selfRef">1.1. </a><a href="#name-evolution" class="section-name selfRef">Evolution</a>
        </h3>
<p id="section-1.1-1">As with SenML in general, there is no expectation that the creator of
a SenML Pack knows (or has negotiated with) each consumer of that Pack,
which may be very remote in space and particularly in time.
This means that the SenML creator in general has no way to know
whether the consumer knows:<a href="#section-1.1-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-1.1-2.1">each specific Media-Type-Name used,<a href="#section-1.1-2.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-1.1-2.2">each parameter and each parameter value used,<a href="#section-1.1-2.2" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-1.1-2.3">each content coding in use, and<a href="#section-1.1-2.3" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-1.1-2.4">each Content-Format number in use for a combination of these.<a href="#section-1.1-2.4" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-1.1-3">What SenML, as well as the new fields defined here, guarantees is that
a recipient implementation <em>knows</em> when it needs to be updated to
understand these field values and the values controlled by them;
registries are used to evolve these name spaces in a controlled way.
SenML Packs can be processed by a consumer while not understanding all
the information in them, and information can generally be preserved in
this processing such that it is useful for further consumers.<a href="#section-1.1-3" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="terminology">
<section id="section-2">
      <h2 id="name-terminology">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-terminology" class="section-name selfRef">Terminology</a>
      </h2>
<p id="section-2-1">The key words "<span class="bcp14">MUST</span>", "<span class="bcp14">MUST NOT</span>", "<span class="bcp14">REQUIRED</span>", "<span class="bcp14">SHALL</span>", "<span class="bcp14">SHALL</span>
NOT", "<span class="bcp14">SHOULD</span>", "<span class="bcp14">SHOULD NOT</span>", "<span class="bcp14">RECOMMENDED</span>", "<span class="bcp14">NOT RECOMMENDED</span>",
"<span class="bcp14">MAY</span>", and "<span class="bcp14">OPTIONAL</span>" in this document are to be interpreted as
described in BCP 14 <span>[<a href="#RFC2119" class="xref">RFC2119</a>]</span> <span>[<a href="#RFC8174" class="xref">RFC8174</a>]</span> when, and only when, they
appear in all capitals, as shown here.<a href="#section-2-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-2-2">
        <dt id="section-2-2.1">Media type:  </dt>
        <dd style="margin-left: 1.5em" id="section-2-2.2">A registered label for representations (byte strings) prepared for
interchange <span>[<a href="#RFC1590" class="xref">RFC1590</a>]</span>
          <span>[<a href="#RFC6838" class="xref">RFC6838</a>]</span>, identified by a Media-Type-Name.<a href="#section-2-2.2" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-2.3">Media-Type-Name:  </dt>
        <dd style="margin-left: 1.5em" id="section-2-2.4">A combination of a type-name and a subtype-name registered in
<span>[<a href="#IANA.media-types" class="xref">IANA.media-types</a>]</span>, as per <span>[<a href="#RFC6838" class="xref">RFC6838</a>]</span>, conventionally
identified by the two names separated by a slash.<a href="#section-2-2.4" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-2.5">Content-Type:  </dt>
        <dd style="margin-left: 1.5em" id="section-2-2.6">A Media-Type-Name, optionally associated with parameters
(<span><a href="https://www.rfc-editor.org/rfc/rfc2045#section-5" class="relref">Section 5</a> of [<a href="#RFC2045" class="xref">RFC2045</a>]</span>, separated from
the Media-Type-Name and from each other by a semicolon).
In HTTP and many other protocols, it is used in a <code>Content-Type</code> header field.<a href="#section-2-2.6" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-2.7">Content coding:  </dt>
        <dd style="margin-left: 1.5em" id="section-2-2.8">A name registered in the "<a href="https://www.iana.org/assignments/http-parameters#content-coding" class="relref">HTTP Content Coding Registry</a>" <span>[<a href="#IANA.http-parameters" class="xref">IANA.http-parameters</a>]</span>, as specified by
Sections <a href="https://www.rfc-editor.org/rfc/rfc9110#section-16.6.1" class="relref">16.6.1</a> and <a href="https://www.rfc-editor.org/rfc/rfc9110#section-18.6" class="relref">18.6</a> of <span>[<a href="#RFC9110" class="xref">RFC9110</a>]</span>, indicating an encoding
transformation with semantics further specified in <span><a href="https://www.rfc-editor.org/rfc/rfc9110#section-8.4.1" class="relref">Section 8.4.1</a> of [<a href="#RFC9110" class="xref">RFC9110</a>]</span>.
Confusingly, in HTTP, content coding values are found in a header field
called "Content-Encoding"; however, "content coding" is the correct
term for the process and the registered values.<a href="#section-2-2.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-2.9">Content format:  </dt>
        <dd style="margin-left: 1.5em" id="section-2-2.10">The combination of a Content-Type and zero or more content codings, identified
by (1) a numeric identifier defined in the "<a href="https://www.iana.org/assignments/core-parameters#content-formats" class="relref">CoAP Content-Formats</a>" registry <span>[<a href="#IANA.core-parameters" class="xref">IANA.core-parameters</a>]</span>,
as per <span><a href="https://www.rfc-editor.org/rfc/rfc7252#section-12.3" class="relref">Section 12.3</a> of [<a href="#RFC7252" class="xref">RFC7252</a>]</span> (referred to as Content-Format
number), or (2) a Content-Format-String.<a href="#section-2-2.10" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-2.11">Content-Format-String:</dt>
        <dd style="margin-left: 1.5em" id="section-2-2.12">The string representation of the combination of a Content-Type and
 zero or more content codings.<a href="#section-2-2.12" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
<dt id="section-2-2.13">Content-Format-Spec:</dt>
        <dd style="margin-left: 1.5em" id="section-2-2.14">The string representation of a content format; either a
 Content-Format-String or the (decimal) string representation of a
 Content-Format number.<a href="#section-2-2.14" class="pilcrow">¶</a>
</dd>
      <dd class="break"></dd>
</dl>
<p id="section-2-3">Readers should also be familiar with the terms and concepts discussed in
<span>[<a href="#RFC8428" class="xref">RFC8428</a>]</span>.<a href="#section-2-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="senml-content-format-ct-field">
<section id="section-3">
      <h2 id="name-senml-content-format-ct-fie">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-senml-content-format-ct-fie" class="section-name selfRef">SenML Content-Format ("ct") Field</a>
      </h2>
<p id="section-3-1">When a SenML Record contains a Data Value field ("vd"), the Record <span class="bcp14">MAY</span>
also include a Content-Format indication field, using label "ct".  The
value of this field is a Content-Format-Spec, i.e., one of the following:<a href="#section-3-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-3-2.1">a CoAP Content-Format number in decimal form with no leading
zeros (except for the value "0" itself). This value represents an
unsigned integer in the range of 0-65535, similar to the  "ct"
attribute defined in <span><a href="https://www.rfc-editor.org/rfc/rfc7252#section-7.2.1" class="relref">Section 7.2.1</a> of [<a href="#RFC7252" class="xref">RFC7252</a>]</span> for CoRE Link
Format <span>[<a href="#RFC6690" class="xref">RFC6690</a>]</span>.<a href="#section-3-2.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-3-2.2">a Content-Format-String containing a Content-Type and
zero or more content codings (see below).<a href="#section-3-2.2" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-3-3">The syntax of this field is formally defined in <a href="#abnf" class="xref">Section 6</a>.<a href="#section-3-3" class="pilcrow">¶</a></p>
<p id="section-3-4">The CoAP Content-Format number provides a simple and efficient way
to indicate the type of the data.  Since some Internet media types and
their content coding and parameter alternatives do not have assigned
CoAP Content-Format numbers, using Content-Type and zero or more
content codings
is also allowed. Both methods use a string value in the "ct" field to
keep its data type consistent across uses.  When the "ct" field
contains only digits, it is interpreted as a CoAP Content-Format
number.<a href="#section-3-4" class="pilcrow">¶</a></p>
<p id="section-3-5">To indicate that one or more content codings are used with a Content-Type,
each of the content coding values is appended to the Content-Type value (media
type and parameters, if any), separated by an "@" sign, in the order of when
the content codings were applied (the same order as in <span><a href="https://www.rfc-editor.org/rfc/rfc9110#section-8.4" class="relref">Section 8.4</a> of [<a href="#RFC9110" class="xref">RFC9110</a>]</span>).
For example (using a content coding value of "deflate", as defined in
<span><a href="https://www.rfc-editor.org/rfc/rfc9110#section-8.4.1.2" class="relref">Section 8.4.1.2</a> of [<a href="#RFC9110" class="xref">RFC9110</a>]</span>):<a href="#section-3-5" class="pilcrow">¶</a></p>
<div class="alignLeft art-text artwork" id="section-3-6">
<pre>
text/plain; charset=utf-8@deflate
</pre><a href="#section-3-6" class="pilcrow">¶</a>
</div>
<p id="section-3-7">If no "@" sign is present after the media type and parameters,
then no content coding has been specified, and the "identity"
content coding is used -- no encoding transformation is employed.<a href="#section-3-7" class="pilcrow">¶</a></p>
</section>
</div>
<div id="senml-base-content-format-bct-field">
<section id="section-4">
      <h2 id="name-senml-base-content-format-b">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-senml-base-content-format-b" class="section-name selfRef">SenML Base Content-Format ("bct") Field</a>
      </h2>
<p id="section-4-1">The Base Content-Format field, label "bct", provides a default value for
the Content-Format field (label "ct") within its range.  The range of the
base field includes the Record containing it, up to (but not including)
the next Record containing a "bct" field, if any, or up to the end of the
Pack otherwise.  The process of resolving (<span><a href="https://www.rfc-editor.org/rfc/rfc8428#section-4.6" class="relref">Section 4.6</a> of [<a href="#RFC8428" class="xref">RFC8428</a>]</span>) this base
field is performed by adding its value with the label "ct" to all Records
in this range that carry a "vd" field but do not already contain a
Content-Format ("ct") field.<a href="#section-4-1" class="pilcrow">¶</a></p>
<p id="section-4-2"><a href="#ex-bct" class="xref">Figure 4</a> shows a variation of <a href="#ex-2" class="xref">Figure 2</a> with multiple records, with the
"nfc-reader" records resolving to the base field value "60" and the
"iris-photo" record overriding this with the "image/png" media type
(actual data left out for brevity).<a href="#section-4-2" class="pilcrow">¶</a></p>
<span id="name-senml-pack-with-the-bct-fie"></span><div id="ex-bct">
<figure id="figure-4">
        <div id="section-4-3.1">
<pre class="lang-senml-json sourcecode">
[
  {"n":"nfc-reader", "vd":"gmNmb28YKg",
   "bct":"60", "bt":1627430700},
  {"n":"nfc-reader", "vd":"gmNiYXIYKw", "t":10},
  {"n":"iris-photo", "vd":".....", "ct":"image/png", "t":10},
  {"n":"nfc-reader", "vd":"gmNiYXoYLA", "t":20}
]
</pre>
</div>
<figcaption><a href="#figure-4" class="selfRef">Figure 4</a>:
<a href="#name-senml-pack-with-the-bct-fie" class="selfRef">SenML Pack with the bct Field</a>
        </figcaption></figure>
</div>
</section>
</div>
<div id="examples">
<section id="section-5">
      <h2 id="name-examples">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-examples" class="section-name selfRef">Examples</a>
      </h2>
<p id="section-5-1">The following examples are valid values for the "ct" and "bct" fields
(explanation/comments in parentheses):<a href="#section-5-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-5-2.1">"60" (CoAP Content-Format number for "application/cbor")<a href="#section-5-2.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-2.2">"0" (CoAP Content-Format number for "text/plain" with parameter
"charset=utf-8")<a href="#section-5-2.2" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-2.3">"application/json" (JSON Content-Type -- equivalent to "50" CoAP
Content-Format number)<a href="#section-5-2.3" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-2.4">"application/json@deflate" (JSON Content-Type with "deflate" as
content coding -- equivalent to "11050" CoAP Content-Format number)<a href="#section-5-2.4" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-2.5">"application/json@deflate@aes128gcm" (JSON Content-Type with
"deflate" followed by "aes128gcm" as content codings)<a href="#section-5-2.5" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-2.6">"text/csv" (Comma-Separated Values (CSV) <span>[<a href="#RFC4180" class="xref">RFC4180</a>]</span> Content-Type)<a href="#section-5-2.6" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-5-2.7">"text/csv;header=present@gzip" (CSV with header row, using "gzip" as
content coding)<a href="#section-5-2.7" class="pilcrow">¶</a>
</li>
      </ul>
</section>
</div>
<div id="abnf">
<section id="section-6">
      <h2 id="name-abnf">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-abnf" class="section-name selfRef">ABNF</a>
      </h2>
<p id="section-6-1">This specification provides a formal definition of the syntax of
Content-Format-Spec strings using ABNF notation <span>[<a href="#RFC5234" class="xref">RFC5234</a>]</span>, which
contains three new rules and a number of rules collected and adapted
from various RFCs <span>[<a href="#RFC9110" class="xref">RFC9110</a>]</span> <span>[<a href="#RFC6838" class="xref">RFC6838</a>]</span> <span>[<a href="#RFC5234" class="xref">RFC5234</a>]</span> <span>[<a href="#RFC8866" class="xref">RFC8866</a>]</span>.<a href="#section-6-1" class="pilcrow">¶</a></p>
<span id="name-abnf-syntax-of-content-form"></span><div id="content-format-spec">
<figure id="figure-5">
        <div id="section-6-2.1">
<pre class="breakable lang-abnf sourcecode">
; New in this document

Content-Format-Spec = Content-Format-Number / Content-Format-String

Content-Format-Number = "0" / (POS-DIGIT *DIGIT)
Content-Format-String   = Content-Type *("@" Content-Coding)

; Cleaned up from RFC 9110,
; leaving only SP as blank space,
; removing legacy 8-bit characters, and
; leaving the parameter as mandatory with each semicolon:

Content-Type   = Media-Type-Name *( *SP ";" *SP parameter )
parameter      = token "=" ( token / quoted-string )

token          = 1*tchar
tchar          = "!" / "#" / "$" / "%" / "&amp;" / "'" / "*"
               / "+" / "-" / "." / "^" / "_" / "`" / "|" / "~"
               / DIGIT / ALPHA
quoted-string  = %x22 *( qdtext / quoted-pair ) %x22
qdtext         = SP / %x21 / %x23-5B / %x5D-7E
quoted-pair    = "\" ( SP / VCHAR )

; Adapted from Section 8.4.1 of RFC 9110

Content-Coding   = token

; Adapted from various specs

Media-Type-Name = type-name "/" subtype-name

; From RFC 6838

type-name = restricted-name
subtype-name = restricted-name

restricted-name = restricted-name-first *126restricted-name-chars
restricted-name-first  = ALPHA / DIGIT
restricted-name-chars  = ALPHA / DIGIT / "!" / "#" /
                         "$" / "&amp;" / "-" / "^" / "_"
restricted-name-chars =/ "." ; Characters before first dot always
                             ; specify a facet name
restricted-name-chars =/ "+" ; Characters after last plus always
                             ; specify a structured syntax suffix


; Boilerplate from RFC 5234 and RFC 8866

DIGIT     =  %x30-39           ; 0 - 9
POS-DIGIT =  %x31-39           ; 1 - 9
ALPHA     =  %x41-5A / %x61-7A ; A - Z / a - z
SP        =  %x20
VCHAR     =  %x21-7E           ; printable ASCII (no SP)

</pre>
</div>
<figcaption><a href="#figure-5" class="selfRef">Figure 5</a>:
<a href="#name-abnf-syntax-of-content-form" class="selfRef">ABNF Syntax of Content-Format-Spec</a>
        </figcaption></figure>
</div>
</section>
</div>
<div id="seccons">
<section id="section-7">
      <h2 id="name-security-considerations">
<a href="#section-7" class="section-number selfRef">7. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<p id="section-7-1">The indication of a media type in the data does not exempt a consuming
application from properly checking its inputs.
Also, the ability for an attacker to supply crafted SenML data that
specifies media types chosen by the attacker may expose vulnerabilities
of handlers for these media types to the attacker.
This includes "decompression bombs", compressed data that is crafted
to decompress to extremely large data items.<a href="#section-7-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="iana">
<section id="section-8">
      <h2 id="name-iana-considerations">
<a href="#section-8" class="section-number selfRef">8. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<p id="section-8-1">IANA has assigned the following new labels in the 
"<a href="https://www.iana.org/assignments/senml#senml-labels" class="relref">SenML Labels</a>" subregistry
of the "Sensor Measurement Lists (SenML)" registry <span>[<a href="#IANA.senml" class="xref">IANA.senml</a>]</span> (as defined in <span><a href="https://www.rfc-editor.org/rfc/rfc8428#section-12.2" class="relref">Section 12.2</a> of [<a href="#RFC8428" class="xref">RFC8428</a>]</span>) for the
Content-Format indication, as per <a href="#tbl-senml-reg" class="xref">Table 1</a>:<a href="#section-8-1" class="pilcrow">¶</a></p>
<span id="name-iana-registration-for-new-s"></span><div id="tbl-senml-reg">
<table class="center" id="table-1">
        <caption>
<a href="#table-1" class="selfRef">Table 1</a>:
<a href="#name-iana-registration-for-new-s" class="selfRef">IANA Registration for New SenML Labels</a>
        </caption>
<thead>
          <tr>
            <th class="text-right" rowspan="1" colspan="1">Name</th>
            <th class="text-left" rowspan="1" colspan="1">Label</th>
            <th class="text-left" rowspan="1" colspan="1">JSON Type</th>
            <th class="text-left" rowspan="1" colspan="1">XML Type</th>
            <th class="text-left" rowspan="1" colspan="1">Reference</th>
          </tr>
        </thead>
        <tbody>
          <tr>
            <td class="text-right" rowspan="1" colspan="1">Base Content-Format</td>
            <td class="text-left" rowspan="1" colspan="1">bct</td>
            <td class="text-left" rowspan="1" colspan="1">String</td>
            <td class="text-left" rowspan="1" colspan="1">string</td>
            <td class="text-left" rowspan="1" colspan="1">RFC 9193</td>
          </tr>
          <tr>
            <td class="text-right" rowspan="1" colspan="1">Content-Format</td>
            <td class="text-left" rowspan="1" colspan="1">ct</td>
            <td class="text-left" rowspan="1" colspan="1">String</td>
            <td class="text-left" rowspan="1" colspan="1">string</td>
            <td class="text-left" rowspan="1" colspan="1">RFC 9193</td>
          </tr>
        </tbody>
      </table>
</div>
<p id="section-8-3">Note that, per <span><a href="https://www.rfc-editor.org/rfc/rfc8428#section-12.2" class="relref">Section 12.2</a> of [<a href="#RFC8428" class="xref">RFC8428</a>]</span>, no CBOR labels nor Efficient XML Interchange (EXI)
schemaId values (EXI ID column) are supplied.<a href="#section-8-3" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-9">
      <h2 id="name-references">
<a href="#section-9" class="section-number selfRef">9. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-9.1">
        <h3 id="name-normative-references">
<a href="#section-9.1" class="section-number selfRef">9.1. </a><a href="#name-normative-references" class="section-name selfRef">Normative References</a>
        </h3>
<dl class="references">
<dt id="IANA.core-parameters">[IANA.core-parameters]</dt>
        <dd>
<span class="refAuthor">IANA</span>, <span class="refTitle">"Constrained RESTful Environments (CoRE) Parameters"</span>, <span>&lt;<a href="https://www.iana.org/assignments/core-parameters">https://www.iana.org/assignments/core-parameters</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="IANA.http-parameters">[IANA.http-parameters]</dt>
        <dd>
<span class="refAuthor">IANA</span>, <span class="refTitle">"Hypertext Transfer Protocol (HTTP) Parameters"</span>, <span>&lt;<a href="https://www.iana.org/assignments/http-parameters">https://www.iana.org/assignments/http-parameters</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="IANA.media-types">[IANA.media-types]</dt>
        <dd>
<span class="refAuthor">IANA</span>, <span class="refTitle">"Media Types"</span>, <span>&lt;<a href="https://www.iana.org/assignments/media-types">https://www.iana.org/assignments/media-types</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="IANA.senml">[IANA.senml]</dt>
        <dd>
<span class="refAuthor">IANA</span>, <span class="refTitle">"Sensor Measurement Lists (SenML)"</span>, <span>&lt;<a href="https://www.iana.org/assignments/senml">https://www.iana.org/assignments/senml</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC2045">[RFC2045]</dt>
        <dd>
<span class="refAuthor">Freed, N.</span> and <span class="refAuthor">N. Borenstein</span>, <span class="refTitle">"Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies"</span>, <span class="seriesInfo">RFC 2045</span>, <span class="seriesInfo">DOI 10.17487/RFC2045</span>, <time datetime="1996-11" class="refDate">November 1996</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2045">https://www.rfc-editor.org/info/rfc2045</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC2119">[RFC2119]</dt>
        <dd>
<span class="refAuthor">Bradner, S.</span>, <span class="refTitle">"Key words for use in RFCs to Indicate Requirement Levels"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 2119</span>, <span class="seriesInfo">DOI 10.17487/RFC2119</span>, <time datetime="1997-03" class="refDate">March 1997</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2119">https://www.rfc-editor.org/info/rfc2119</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5234">[RFC5234]</dt>
        <dd>
<span class="refAuthor">Crocker, D., Ed.</span> and <span class="refAuthor">P. Overell</span>, <span class="refTitle">"Augmented BNF for Syntax Specifications: ABNF"</span>, <span class="seriesInfo">STD 68</span>, <span class="seriesInfo">RFC 5234</span>, <span class="seriesInfo">DOI 10.17487/RFC5234</span>, <time datetime="2008-01" class="refDate">January 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5234">https://www.rfc-editor.org/info/rfc5234</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7252">[RFC7252]</dt>
        <dd>
<span class="refAuthor">Shelby, Z.</span>, <span class="refAuthor">Hartke, K.</span>, and <span class="refAuthor">C. Bormann</span>, <span class="refTitle">"The Constrained Application Protocol (CoAP)"</span>, <span class="seriesInfo">RFC 7252</span>, <span class="seriesInfo">DOI 10.17487/RFC7252</span>, <time datetime="2014-06" class="refDate">June 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7252">https://www.rfc-editor.org/info/rfc7252</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8174">[RFC8174]</dt>
        <dd>
<span class="refAuthor">Leiba, B.</span>, <span class="refTitle">"Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words"</span>, <span class="seriesInfo">BCP 14</span>, <span class="seriesInfo">RFC 8174</span>, <span class="seriesInfo">DOI 10.17487/RFC8174</span>, <time datetime="2017-05" class="refDate">May 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8174">https://www.rfc-editor.org/info/rfc8174</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8428">[RFC8428]</dt>
        <dd>
<span class="refAuthor">Jennings, C.</span>, <span class="refAuthor">Shelby, Z.</span>, <span class="refAuthor">Arkko, J.</span>, <span class="refAuthor">Keranen, A.</span>, and <span class="refAuthor">C. Bormann</span>, <span class="refTitle">"Sensor Measurement Lists (SenML)"</span>, <span class="seriesInfo">RFC 8428</span>, <span class="seriesInfo">DOI 10.17487/RFC8428</span>, <time datetime="2018-08" class="refDate">August 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8428">https://www.rfc-editor.org/info/rfc8428</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC9110">[RFC9110]</dt>
      <dd>
<span class="refAuthor">Fielding, R.</span>, <span class="refAuthor">Nottingham, M.</span>, and <span class="refAuthor">J. Reschke</span>, <span class="refTitle">"HTTP Semantics"</span>, <span class="seriesInfo">STD 97</span>, <span class="seriesInfo">RFC 9110</span>, <span class="seriesInfo">DOI 10.17487/RFC9110</span>, <time datetime="2022-02" class="refDate">February 2022</time>, <span>&lt;<a href="https://www.rfc-editor.org/rfc/rfc9110">https://www.rfc-editor.org/rfc/rfc9110</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
<section id="section-9.2">
        <h3 id="name-informative-references">
<a href="#section-9.2" class="section-number selfRef">9.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="RFC1590">[RFC1590]</dt>
        <dd>
<span class="refAuthor">Postel, J.</span>, <span class="refTitle">"Media Type Registration Procedure"</span>, <span class="seriesInfo">RFC 1590</span>, <span class="seriesInfo">DOI 10.17487/RFC1590</span>, <time datetime="1994-03" class="refDate">March 1994</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc1590">https://www.rfc-editor.org/info/rfc1590</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4180">[RFC4180]</dt>
        <dd>
<span class="refAuthor">Shafranovich, Y.</span>, <span class="refTitle">"Common Format and MIME Type for Comma-Separated Values (CSV) Files"</span>, <span class="seriesInfo">RFC 4180</span>, <span class="seriesInfo">DOI 10.17487/RFC4180</span>, <time datetime="2005-10" class="refDate">October 2005</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4180">https://www.rfc-editor.org/info/rfc4180</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4648">[RFC4648]</dt>
        <dd>
<span class="refAuthor">Josefsson, S.</span>, <span class="refTitle">"The Base16, Base32, and Base64 Data Encodings"</span>, <span class="seriesInfo">RFC 4648</span>, <span class="seriesInfo">DOI 10.17487/RFC4648</span>, <time datetime="2006-10" class="refDate">October 2006</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4648">https://www.rfc-editor.org/info/rfc4648</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6690">[RFC6690]</dt>
        <dd>
<span class="refAuthor">Shelby, Z.</span>, <span class="refTitle">"Constrained RESTful Environments (CoRE) Link Format"</span>, <span class="seriesInfo">RFC 6690</span>, <span class="seriesInfo">DOI 10.17487/RFC6690</span>, <time datetime="2012-08" class="refDate">August 2012</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6690">https://www.rfc-editor.org/info/rfc6690</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6838">[RFC6838]</dt>
        <dd>
<span class="refAuthor">Freed, N.</span>, <span class="refAuthor">Klensin, J.</span>, and <span class="refAuthor">T. Hansen</span>, <span class="refTitle">"Media Type Specifications and Registration Procedures"</span>, <span class="seriesInfo">BCP 13</span>, <span class="seriesInfo">RFC 6838</span>, <span class="seriesInfo">DOI 10.17487/RFC6838</span>, <time datetime="2013-01" class="refDate">January 2013</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6838">https://www.rfc-editor.org/info/rfc6838</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8866">[RFC8866]</dt>
        <dd>
<span class="refAuthor">Begen, A.</span>, <span class="refAuthor">Kyzivat, P.</span>, <span class="refAuthor">Perkins, C.</span>, and <span class="refAuthor">M. Handley</span>, <span class="refTitle">"SDP: Session Description Protocol"</span>, <span class="seriesInfo">RFC 8866</span>, <span class="seriesInfo">DOI 10.17487/RFC8866</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8866">https://www.rfc-editor.org/info/rfc8866</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8949">[RFC8949]</dt>
      <dd>
<span class="refAuthor">Bormann, C.</span> and <span class="refAuthor">P. Hoffman</span>, <span class="refTitle">"Concise Binary Object Representation (CBOR)"</span>, <span class="seriesInfo">STD 94</span>, <span class="seriesInfo">RFC 8949</span>, <span class="seriesInfo">DOI 10.17487/RFC8949</span>, <time datetime="2020-12" class="refDate">December 2020</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8949">https://www.rfc-editor.org/info/rfc8949</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
</section>
<div id="acks">
<section id="appendix-A">
      <h2 id="name-acknowledgments">
<a href="#name-acknowledgments" class="section-name selfRef">Acknowledgments</a>
      </h2>
<p id="appendix-A-1">The authors would like to thank <span class="contact-name">Sérgio Abreu</span> for the discussions leading
to the design of this extension and <span class="contact-name">Isaac Rivera</span> for reviews and
feedback.
<span class="contact-name">Klaus Hartke</span> suggested not burdening this document with a separate
mandatory-to-implement version of the fields.
<span class="contact-name">Alexey Melnikov</span>, <span class="contact-name">Jim Schaad</span>, and <span class="contact-name">Thomas Fossati</span> provided helpful
comments at Working Group Last Call.
<span class="contact-name">Marco Tiloca</span> asked for clarifying and using the term Content-Format-Spec.<a href="#appendix-A-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="authors-addresses">
<section id="appendix-B">
      <h2 id="name-authors-addresses">
<a href="#name-authors-addresses" class="section-name selfRef">Authors' Addresses</a>
      </h2>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Ari Keränen</span></div>
<div dir="auto" class="left"><span class="org">Ericsson</span></div>
<div dir="auto" class="left">FI-<span class="postal-code">02420</span> <span class="locality">Jorvas</span>
</div>
<div dir="auto" class="left"><span class="country-name">Finland</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:ari.keranen@ericsson.com" class="email">ari.keranen@ericsson.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Carsten Bormann</span></div>
<div dir="auto" class="left"><span class="org">Universität Bremen TZI</span></div>
<div dir="auto" class="left"><span class="street-address">Postfach 330440</span></div>
<div dir="auto" class="left">
<span class="postal-code">D-28359</span> <span class="locality">Bremen</span>
</div>
<div dir="auto" class="left"><span class="country-name">Germany</span></div>
<div class="tel">
<span>Phone:</span>
<a href="tel:+49-421-218-63921" class="tel">+49-421-218-63921</a>
</div>
<div class="email">
<span>Email:</span>
<a href="mailto:cabo@tzi.org" class="email">cabo@tzi.org</a>
</div>
</address>
</section>
</div>
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