File: rfc8835.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 8835: Transports for WebRTC</title>
<meta content="Harald Alvestrand" name="author">
<meta content="
       This document describes the data transport protocols used by Web
      Real-Time Communication (WebRTC),
      including the protocols used for interaction with intermediate boxes
      such as firewalls, relays, and NAT boxes. 
    " name="description">
<meta content="xml2rfc 3.5.0" name="generator">
<meta content="8835" name="rfc.number">
<!-- Generator version information:
  xml2rfc 3.5.0
    Python 3.6.10
    appdirs 1.4.4
    ConfigArgParse 1.2.3
    google-i18n-address 2.3.5
    html5lib 1.0.1
    intervaltree 3.0.2
    Jinja2 2.11.2
    kitchen 1.2.6
    lxml 4.4.2
    pycairo 1.19.0
    pycountry 19.8.18
    pyflakes 2.1.1
    PyYAML 5.3.1
    requests 2.22.0
    setuptools 40.6.2
    six 1.14.0
    WeasyPrint 51
-->
<link href="rfc8835.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;
  /* this isn't optimal, but it's an existence proof.  PrinceXML doesn't
     support flexbox yet.
  */
  display: table;
  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.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;
}
#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;
  }
  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;
}
/* In print, the pilcrow won't show on hover, so prevent it from taking up space,
   possibly even requiring a new line */
@media print {
  a.pilcrow {
    display: none;
  }
}
/* Styling for the external metadata */
div#external-metadata {
  background-color: #eee;
  padding: 0.5em;
  margin-bottom: 0.5em;
  display: none;
}
div#internal-metadata {
  padding: 0.5em;                       /* to match the external-metadata padding */
}
/* Styling for title RFC Number */
h1#rfcnum {
  clear: both;
  margin: 0 0 -1em;
  padding: 1em 0 0 0;
}
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<table class="ears">
<thead><tr>
<td class="left">RFC 8835</td>
<td class="center">WebRTC Transports</td>
<td class="right">January 2021</td>
</tr></thead>
<tfoot><tr>
<td class="left">Alvestrand</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/rfc8835" class="eref">8835</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="2021-01" class="published">January 2021</time>
    </dd>
<dt class="label-issn">ISSN:</dt>
<dd class="issn">2070-1721</dd>
<dt class="label-authors">Author:</dt>
<dd class="authors">
<div class="author">
      <div class="author-name">H. Alvestrand</div>
<div class="org">Google</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 8835</h1>
<h1 id="title">Transports for WebRTC</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">This document describes the data transport protocols used by Web
      Real-Time Communication (WebRTC),
      including the protocols used for interaction with intermediate boxes
      such as firewalls, relays, and NAT boxes.<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/rfc8835">https://www.rfc-editor.org/info/rfc8835</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) 2021 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 Simplified BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Simplified 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 ulEmpty">
<li class="compact toc 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><a href="#section-toc.1-1.1.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact toc 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-requirements-language" class="xref">Requirements Language</a><a href="#section-toc.1-1.2.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact toc 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-transport-and-middlebox-spe" class="xref">Transport and Middlebox Specification</a><a href="#section-toc.1-1.3.1" class="pilcrow">¶</a></p>
<ul class="compact toc ulEmpty">
<li class="compact toc ulEmpty" id="section-toc.1-1.3.2.1">
                <p id="section-toc.1-1.3.2.1.1" class="keepWithNext"><a href="#section-3.1" class="xref">3.1</a>.  <a href="#name-system-provided-interfaces" class="xref">System-Provided Interfaces</a><a href="#section-toc.1-1.3.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact toc ulEmpty" id="section-toc.1-1.3.2.2">
                <p id="section-toc.1-1.3.2.2.1"><a href="#section-3.2" class="xref">3.2</a>.  <a href="#name-ability-to-use-ipv4-and-ipv" class="xref">Ability to Use IPv4 and IPv6</a><a href="#section-toc.1-1.3.2.2.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact toc ulEmpty" id="section-toc.1-1.3.2.3">
                <p id="section-toc.1-1.3.2.3.1"><a href="#section-3.3" class="xref">3.3</a>.  <a href="#name-usage-of-temporary-ipv6-add" class="xref">Usage of Temporary IPv6 Addresses</a><a href="#section-toc.1-1.3.2.3.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact toc ulEmpty" id="section-toc.1-1.3.2.4">
                <p id="section-toc.1-1.3.2.4.1"><a href="#section-3.4" class="xref">3.4</a>.  <a href="#name-middlebox-related-functions" class="xref">Middlebox-Related Functions</a><a href="#section-toc.1-1.3.2.4.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact toc ulEmpty" id="section-toc.1-1.3.2.5">
                <p id="section-toc.1-1.3.2.5.1"><a href="#section-3.5" class="xref">3.5</a>.  <a href="#name-transport-protocols-impleme" class="xref">Transport Protocols Implemented</a><a href="#section-toc.1-1.3.2.5.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="compact toc 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-media-prioritization" class="xref">Media Prioritization</a><a href="#section-toc.1-1.4.1" class="pilcrow">¶</a></p>
<ul class="compact toc ulEmpty">
<li class="compact toc ulEmpty" id="section-toc.1-1.4.2.1">
                <p id="section-toc.1-1.4.2.1.1"><a href="#section-4.1" class="xref">4.1</a>.  <a href="#name-local-prioritization" class="xref">Local Prioritization</a><a href="#section-toc.1-1.4.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact toc ulEmpty" id="section-toc.1-1.4.2.2">
                <p id="section-toc.1-1.4.2.2.1"><a href="#section-4.2" class="xref">4.2</a>.  <a href="#name-usage-of-quality-of-service" class="xref">Usage of Quality of Service -- DSCP and Multiplexing</a><a href="#section-toc.1-1.4.2.2.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="compact toc 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-iana-considerations" class="xref">IANA Considerations</a><a href="#section-toc.1-1.5.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact toc 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-security-considerations" class="xref">Security Considerations</a><a href="#section-toc.1-1.6.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact toc 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-references" class="xref">References</a><a href="#section-toc.1-1.7.1" class="pilcrow">¶</a></p>
<ul class="compact toc ulEmpty">
<li class="compact toc ulEmpty" id="section-toc.1-1.7.2.1">
                <p id="section-toc.1-1.7.2.1.1"><a href="#section-7.1" class="xref">7.1</a>.  <a href="#name-normative-references" class="xref">Normative References</a><a href="#section-toc.1-1.7.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact toc ulEmpty" id="section-toc.1-1.7.2.2">
                <p id="section-toc.1-1.7.2.2.1"><a href="#section-7.2" class="xref">7.2</a>.  <a href="#name-informative-references" class="xref">Informative References</a><a href="#section-toc.1-1.7.2.2.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="compact toc ulEmpty" id="section-toc.1-1.8">
            <p id="section-toc.1-1.8.1"><a href="#section-appendix.a" class="xref"></a><a href="#name-acknowledgements" class="xref">Acknowledgements</a><a href="#section-toc.1-1.8.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact toc ulEmpty" id="section-toc.1-1.9">
            <p id="section-toc.1-1.9.1"><a href="#section-appendix.b" class="xref"></a><a href="#name-authors-address" class="xref">Author's Address</a><a href="#section-toc.1-1.9.1" class="pilcrow">¶</a></p>
</li>
        </ul>
</nav>
</section>
</div>
<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">WebRTC is a protocol suite aimed at real-time multimedia exchange
      between browsers, and between browsers and other entities.<a href="#section-1-1" class="pilcrow">¶</a></p>
<p id="section-1-2">WebRTC is described in the WebRTC overview document <span>[<a href="#RFC8825" class="xref">RFC8825</a>]</span>, which also defines terminology used
      in this document, including the terms "WebRTC endpoint" and "WebRTC
      browser".<a href="#section-1-2" class="pilcrow">¶</a></p>
<p id="section-1-3">Terminology for RTP sources is taken from <span>[<a href="#RFC7656" class="xref">RFC7656</a>]</span>.<a href="#section-1-3" class="pilcrow">¶</a></p>
<p id="section-1-4">This document focuses on the data transport protocols that are used
      by conforming implementations, including the protocols used for
      interaction with intermediate boxes such as firewalls, relays, and NAT
      boxes.<a href="#section-1-4" class="pilcrow">¶</a></p>
<p id="section-1-5">This protocol suite is intended to satisfy the security considerations
      described in the WebRTC security documents, <span>[<a href="#RFC8826" class="xref">RFC8826</a>]</span> and <span>[<a href="#RFC8827" class="xref">RFC8827</a>]</span>.<a href="#section-1-5" class="pilcrow">¶</a></p>
<p id="section-1-6">This document describes requirements that apply to all WebRTC
      endpoints. When there are requirements that apply only to WebRTC
      browsers, this is called out explicitly.<a href="#section-1-6" class="pilcrow">¶</a></p>
</section>
<section id="section-2">
      <h2 id="name-requirements-language">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-requirements-language" class="section-name selfRef">Requirements Language</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 NOT</span>", "<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>
</section>
<div id="app-transport">
<section id="section-3">
      <h2 id="name-transport-and-middlebox-spe">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-transport-and-middlebox-spe" class="section-name selfRef">Transport and Middlebox Specification</a>
      </h2>
<p id="section-3-1"></p>
<section id="section-3.1">
        <h3 id="name-system-provided-interfaces">
<a href="#section-3.1" class="section-number selfRef">3.1. </a><a href="#name-system-provided-interfaces" class="section-name selfRef">System-Provided Interfaces</a>
        </h3>
<p id="section-3.1-1">The protocol specifications used here assume that the following
        protocols are available to the implementations of the WebRTC
        protocols:<a href="#section-3.1-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-3.1-2">
          <dt id="section-3.1-2.1">UDP <span>[<a href="#RFC0768" class="xref">RFC0768</a>]</span>:</dt>
          <dd style="margin-left: 1.5em" id="section-3.1-2.2">This is the protocol assumed by
            most protocol elements described.<a href="#section-3.1-2.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-3.1-2.3">TCP <span>[<a href="#RFC0793" class="xref">RFC0793</a>]</span>:</dt>
          <dd style="margin-left: 1.5em" id="section-3.1-2.4">This is used for HTTP/WebSockets,
            as well as TURN/TLS and
            ICE-TCP.<a href="#section-3.1-2.4" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
<p id="section-3.1-3">For both protocols, IPv4 and IPv6 support is assumed.<a href="#section-3.1-3" class="pilcrow">¶</a></p>
<p id="section-3.1-4">For UDP, this specification assumes the ability to set the
        Differentiated Services Code Point (DSCP) of the sockets opened on a per-packet basis, in order to
        achieve the prioritizations described in <span>[<a href="#RFC8837" class="xref">RFC8837</a>]</span> (see <a href="#s-qos" class="xref">Section 4.2</a> of this document) when
        multiple media types are multiplexed. It does not assume that the DSCPs
        will be honored and does assume that they may be zeroed or
        changed, since this is a local configuration issue.<a href="#section-3.1-4" class="pilcrow">¶</a></p>
<p id="section-3.1-5">Platforms that do not give access to these interfaces will not be
        able to support a conforming WebRTC endpoint.<a href="#section-3.1-5" class="pilcrow">¶</a></p>
<p id="section-3.1-6">This specification does not assume that the implementation will
        have access to ICMP or raw IP.<a href="#section-3.1-6" class="pilcrow">¶</a></p>
<p id="section-3.1-7">The following protocols may be used, but they can be implemented by a
        WebRTC endpoint and are therefore not defined as "system-provided
        interfaces":<a href="#section-3.1-7" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel" id="section-3.1-8">
          <dt id="section-3.1-8.1">TURN:</dt>
          <dd style="margin-left: 1.5em" id="section-3.1-8.2">Traversal Using Relays Around NAT <span>[<a href="#RFC8656" class="xref">RFC8656</a>]</span><a href="#section-3.1-8.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-3.1-8.3">STUN:</dt>
          <dd style="margin-left: 1.5em" id="section-3.1-8.4">Session Traversal Utilities for NAT <span>[<a href="#RFC5389" class="xref">RFC5389</a>]</span><a href="#section-3.1-8.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-3.1-8.5">ICE:</dt>
          <dd style="margin-left: 1.5em" id="section-3.1-8.6">Interactive Connectivity Establishment <span>[<a href="#RFC8445" class="xref">RFC8445</a>]</span><a href="#section-3.1-8.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-3.1-8.7">TLS:</dt>
          <dd style="margin-left: 1.5em" id="section-3.1-8.8">Transport Layer Security <span>[<a href="#RFC8446" class="xref">RFC8446</a>]</span><a href="#section-3.1-8.8" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-3.1-8.9">DTLS:</dt>
          <dd style="margin-left: 1.5em" id="section-3.1-8.10">Datagram Transport Layer Security <span>[<a href="#RFC6347" class="xref">RFC6347</a>]</span><a href="#section-3.1-8.10" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
</section>
<section id="section-3.2">
        <h3 id="name-ability-to-use-ipv4-and-ipv">
<a href="#section-3.2" class="section-number selfRef">3.2. </a><a href="#name-ability-to-use-ipv4-and-ipv" class="section-name selfRef">Ability to Use IPv4 and IPv6</a>
        </h3>
<p id="section-3.2-1">Web applications running in a WebRTC browser <span class="bcp14">MUST</span> be able to
        utilize both IPv4 and IPv6 where available -- that is, when two peers
        have only IPv4 connectivity to each other, or they have only IPv6
        connectivity to each other, applications running in the WebRTC browser
        <span class="bcp14">MUST</span> be able to communicate.<a href="#section-3.2-1" class="pilcrow">¶</a></p>
<p id="section-3.2-2">When TURN is used, and the TURN server has IPv4 or IPv6
        connectivity to the peer or the peer's TURN server, candidates of the
        appropriate types <span class="bcp14">MUST</span> be supported. The "Happy Eyeballs"
        specification for ICE <span>[<a href="#RFC8421" class="xref">RFC8421</a>]</span> <span class="bcp14">SHOULD</span> be
        supported.<a href="#section-3.2-2" class="pilcrow">¶</a></p>
</section>
<section id="section-3.3">
        <h3 id="name-usage-of-temporary-ipv6-add">
<a href="#section-3.3" class="section-number selfRef">3.3. </a><a href="#name-usage-of-temporary-ipv6-add" class="section-name selfRef">Usage of Temporary IPv6 Addresses</a>
        </h3>
<p id="section-3.3-1">The IPv6 default address selection specification <span>[<a href="#RFC6724" class="xref">RFC6724</a>]</span> specifies that temporary addresses
        <span>[<a href="#RFC4941" class="xref">RFC4941</a>]</span> are to be preferred over
        permanent addresses. This
        is a change from the rules specified by <span>[<a href="#RFC3484" class="xref">RFC3484</a>]</span>. For
        applications that select a single address, this is usually done by the
        IPV6_PREFER_SRC_TMP preference flag specified in <span>[<a href="#RFC5014" class="xref">RFC5014</a>]</span>. However, this rule, which is intended to ensure
        that privacy-enhanced addresses are used in preference to static
        addresses, doesn't have the right effect in ICE, where all addresses
        are gathered and therefore revealed to the application. Therefore, the
        following rule is applied instead:<a href="#section-3.3-1" class="pilcrow">¶</a></p>
<p style="margin-left: 1.5em" id="section-3.3-2">When a WebRTC endpoint gathers all IPv6 addresses on its host, and
        both nondeprecated temporary addresses and permanent addresses of the
        same scope are present, the WebRTC endpoint <span class="bcp14">SHOULD</span> discard the
        permanent addresses before exposing addresses to the application or
        using them in ICE. This is consistent with the default policy
        described in <span>[<a href="#RFC6724" class="xref">RFC6724</a>]</span>.<a href="#section-3.3-2" class="pilcrow">¶</a></p>
<p style="margin-left: 1.5em" id="section-3.3-3">If some, but not all, of the temporary IPv6 addresses are marked
        deprecated, the WebRTC endpoint <span class="bcp14">SHOULD</span> discard the deprecated
        addresses, unless they are used by an ongoing connection. In an ICE
        restart, deprecated addresses that are currently in use <span class="bcp14">MAY</span> be
        retained.<a href="#section-3.3-3" class="pilcrow">¶</a></p>
</section>
<div id="s-middlebox">
<section id="section-3.4">
        <h3 id="name-middlebox-related-functions">
<a href="#section-3.4" class="section-number selfRef">3.4. </a><a href="#name-middlebox-related-functions" class="section-name selfRef">Middlebox-Related Functions</a>
        </h3>
<p id="section-3.4-1">The primary mechanism for dealing with middleboxes is ICE, which is an
        appropriate way to deal with NAT boxes and firewalls that accept
        traffic from the inside, but only from the outside if it is in
        response to inside traffic (simple stateful firewalls).<a href="#section-3.4-1" class="pilcrow">¶</a></p>
<p id="section-3.4-2">ICE <span>[<a href="#RFC8445" class="xref">RFC8445</a>]</span> <span class="bcp14">MUST</span> be supported. The
        implementation <span class="bcp14">MUST</span> be a full ICE implementation, not ICE-Lite. A full
        ICE implementation allows interworking with both ICE and ICE-Lite
        implementations when they are deployed appropriately.<a href="#section-3.4-2" class="pilcrow">¶</a></p>
<p id="section-3.4-3">In order to deal with situations where both parties are behind NATs
        of the type that perform endpoint-dependent mapping (as defined in
        <span>[<a href="#RFC5128" class="xref">RFC5128</a>], <a href="https://www.rfc-editor.org/rfc/rfc5128#section-2.4" class="relref">Section 2.4</a></span>), TURN <span>[<a href="#RFC8656" class="xref">RFC8656</a>]</span>
          <span class="bcp14">MUST</span> be supported.<a href="#section-3.4-3" class="pilcrow">¶</a></p>
<p id="section-3.4-4">WebRTC browsers <span class="bcp14">MUST</span> support configuration of STUN and TURN
        servers, from both browser configuration and an application.<a href="#section-3.4-4" class="pilcrow">¶</a></p>
<p id="section-3.4-5">Note that other work exists around STUN and TURN server discovery
        and management, including <span>[<a href="#RFC8155" class="xref">RFC8155</a>]</span> for server discovery,
        as well as <span>[<a href="#I-D.ietf-rtcweb-return" class="xref">RETURN</a>]</span>.<a href="#section-3.4-5" class="pilcrow">¶</a></p>
<p id="section-3.4-6">In order to deal with firewalls that block all UDP traffic, the
        mode of TURN that uses TCP between the WebRTC endpoint and the TURN
        server <span class="bcp14">MUST</span> be supported, and the mode of TURN that uses TLS over TCP
        between the WebRTC endpoint and the TURN server <span class="bcp14">MUST</span> be supported. See
        <span><a href="https://www.rfc-editor.org/rfc/rfc8656#section-3.1" class="relref">Section 3.1</a> of [<a href="#RFC8656" class="xref">RFC8656</a>]</span>, for details.<a href="#section-3.4-6" class="pilcrow">¶</a></p>
<p id="section-3.4-7">In order to deal with situations where one party is on an IPv4
        network and the other party is on an IPv6 network, TURN extensions for
        IPv6 <span class="bcp14">MUST</span> be supported.<a href="#section-3.4-7" class="pilcrow">¶</a></p>
<p id="section-3.4-8">TURN TCP candidates, where the connection from the WebRTC
        endpoint's TURN server to the peer is a TCP connection, <span>[<a href="#RFC6062" class="xref">RFC6062</a>]</span> <span class="bcp14">MAY</span> be supported.<a href="#section-3.4-8" class="pilcrow">¶</a></p>
<p id="section-3.4-9">However, such candidates are not seen as providing any significant
        benefit, for the following reasons.<a href="#section-3.4-9" class="pilcrow">¶</a></p>
<p id="section-3.4-10">First, use of TURN TCP candidates would only be relevant in cases
        where both peers are required to use TCP to establish a
        connection.<a href="#section-3.4-10" class="pilcrow">¶</a></p>
<p id="section-3.4-11">Second, that use case is supported in a different way by both sides
        establishing UDP relay candidates using TURN over TCP to connect to
        their respective relay servers.<a href="#section-3.4-11" class="pilcrow">¶</a></p>
<p id="section-3.4-12">Third, using TCP between the WebRTC endpoint's TURN server and the
        peer may result in more performance problems than using UDP, e.g., due
        to head of line blocking.<a href="#section-3.4-12" class="pilcrow">¶</a></p>
<p id="section-3.4-13">ICE-TCP candidates <span>[<a href="#RFC6544" class="xref">RFC6544</a>]</span> <span class="bcp14">MUST</span> be supported; this
        may allow applications to communicate to peers with public IP
        addresses across UDP-blocking firewalls without using a TURN
        server.<a href="#section-3.4-13" class="pilcrow">¶</a></p>
<p id="section-3.4-14">If TCP connections are used, RTP framing according to <span>[<a href="#RFC4571" class="xref">RFC4571</a>]</span> <span class="bcp14">MUST</span> be used for all packets. This includes the RTP
        packets, DTLS packets used to carry data channels, and STUN
        connectivity check packets.<a href="#section-3.4-14" class="pilcrow">¶</a></p>
<p id="section-3.4-15">The ALTERNATE-SERVER mechanism specified in <span><a href="https://www.rfc-editor.org/rfc/rfc5389#section-11" class="relref">Section 11</a> of [<a href="#RFC5389" class="xref">RFC5389</a>]</span> (300 Try Alternate) <span class="bcp14">MUST</span> be
        supported.<a href="#section-3.4-15" class="pilcrow">¶</a></p>
<p id="section-3.4-16">The WebRTC endpoint <span class="bcp14">MAY</span> support accessing the Internet through an
        HTTP proxy. If it does so, it <span class="bcp14">MUST</span> include the "ALPN" header as
        specified in <span>[<a href="#RFC7639" class="xref">RFC7639</a>]</span>, and proxy authentication as
        described in <span><a href="https://www.rfc-editor.org/rfc/rfc7231#section-4.3.6" class="relref">Section 4.3.6</a> of [<a href="#RFC7231" class="xref">RFC7231</a>]</span> and <span>[<a href="#RFC7235" class="xref">RFC7235</a>]</span> <span class="bcp14">MUST</span> also be supported.<a href="#section-3.4-16" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-3.5">
        <h3 id="name-transport-protocols-impleme">
<a href="#section-3.5" class="section-number selfRef">3.5. </a><a href="#name-transport-protocols-impleme" class="section-name selfRef">Transport Protocols Implemented</a>
        </h3>
<p id="section-3.5-1">For transport of media, secure RTP is used. The details of the
        RTP profile used are described in "Media Transport and Use of RTP in WebRTC" <span>[<a href="#RFC8834" class="xref">RFC8834</a>]</span>, which mandates the use of a
        circuit breaker <span>[<a href="#RFC8083" class="xref">RFC8083</a>]</span>
        and congestion control (see <span>[<a href="#RFC8836" class="xref">RFC8836</a>]</span> for further guidance).<a href="#section-3.5-1" class="pilcrow">¶</a></p>
<p id="section-3.5-2">Key exchange <span class="bcp14">MUST</span> be done using DTLS-SRTP, as described in <span>[<a href="#RFC8827" class="xref">RFC8827</a>]</span>.<a href="#section-3.5-2" class="pilcrow">¶</a></p>
<p id="section-3.5-3">For data transport over the WebRTC data channel <span>[<a href="#RFC8831" class="xref">RFC8831</a>]</span>, WebRTC endpoints <span class="bcp14">MUST</span> support
        SCTP over DTLS over ICE. This encapsulation is specified in <span>[<a href="#RFC8261" class="xref">RFC8261</a>]</span>. Negotiation of this
        transport in the Session Description Protocol (SDP) is defined in <span>[<a href="#RFC8841" class="xref">RFC8841</a>]</span>. The SCTP extension for I-DATA
        <span>[<a href="#RFC8260" class="xref">RFC8260</a>]</span> <span class="bcp14">MUST</span> be supported.<a href="#section-3.5-3" class="pilcrow">¶</a></p>
<p id="section-3.5-4">The setup protocol for WebRTC data channels described in <span>[<a href="#RFC8832" class="xref">RFC8832</a>]</span> <span class="bcp14">MUST</span> be supported.<a href="#section-3.5-4" class="pilcrow">¶</a></p>
<aside id="section-3.5-5">
          <p id="section-3.5-5.1">Note: The interaction between DTLS-SRTP as defined in <span>[<a href="#RFC5764" class="xref">RFC5764</a>]</span> and ICE as defined in <span>[<a href="#RFC8445" class="xref">RFC8445</a>]</span> is described in <span><a href="https://www.rfc-editor.org/rfc/rfc8842#section-6" class="relref">Section 6</a> of [<a href="#RFC8842" class="xref">RFC8842</a>]</span>. The effect of this specification
        is that all ICE candidate pairs associated with a single component are
        part of the same DTLS association. Thus, there will only be one DTLS
        handshake, even if there are multiple valid candidate pairs.<a href="#section-3.5-5.1" class="pilcrow">¶</a></p>
</aside>
<p id="section-3.5-6">WebRTC endpoints <span class="bcp14">MUST</span> support multiplexing of DTLS and RTP over the
        same port pair, as described in the DTLS-SRTP specification <span>[<a href="#RFC5764" class="xref">RFC5764</a>], <a href="https://www.rfc-editor.org/rfc/rfc5764#section-5.1.2" class="relref">Section 5.1.2</a></span>, with clarifications in <span>[<a href="#RFC7983" class="xref">RFC7983</a>]</span>. All application-layer
        protocol payloads over this DTLS connection are SCTP packets.<a href="#section-3.5-6" class="pilcrow">¶</a></p>
<p id="section-3.5-7">Protocol identification <span class="bcp14">MUST</span> be supplied as part of the DTLS
        handshake, as specified in <span>[<a href="#RFC8833" class="xref">RFC8833</a>]</span>.<a href="#section-3.5-7" class="pilcrow">¶</a></p>
</section>
</section>
</div>
<section id="section-4">
      <h2 id="name-media-prioritization">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-media-prioritization" class="section-name selfRef">Media Prioritization</a>
      </h2>
<p id="section-4-1">In the WebRTC prioritization model, the application tells the
      WebRTC endpoint about the priority of media and data that is controlled
      from the API.<a href="#section-4-1" class="pilcrow">¶</a></p>
<p id="section-4-2">In this context, a "flow" is used for the units that are given a
      specific priority through the WebRTC API.<a href="#section-4-2" class="pilcrow">¶</a></p>
<p id="section-4-3">For media, a "media flow", which can be an "audio flow" or a "video
      flow", is what <span>[<a href="#RFC7656" class="xref">RFC7656</a>]</span> calls a "media source", which
      results in a "source RTP stream" and one or more "redundancy RTP
      streams". This specification does not describe prioritization between
      the RTP streams that come from a single media source.<a href="#section-4-3" class="pilcrow">¶</a></p>
<p id="section-4-4">All media flows in WebRTC are assumed to be interactive, as defined
      in <span>[<a href="#RFC4594" class="xref">RFC4594</a>]</span>; there is no browser API support for
      indicating whether media is interactive or noninteractive.<a href="#section-4-4" class="pilcrow">¶</a></p>
<p id="section-4-5">A "data flow" is the outgoing data on a single WebRTC data
      channel.<a href="#section-4-5" class="pilcrow">¶</a></p>
<p id="section-4-6">The priority associated with a media flow or data flow is classified
      as "very-low", "low", "medium", or "high". There are only four priority
      levels in the API.<a href="#section-4-6" class="pilcrow">¶</a></p>
<p id="section-4-7">The priority settings affect two pieces of behavior: packet send
      sequence decisions and packet markings. Each is described in its own
      section below.<a href="#section-4-7" class="pilcrow">¶</a></p>
<section id="section-4.1">
        <h3 id="name-local-prioritization">
<a href="#section-4.1" class="section-number selfRef">4.1. </a><a href="#name-local-prioritization" class="section-name selfRef">Local Prioritization</a>
        </h3>
<p id="section-4.1-1">Local prioritization is applied at the local node, before the
        packet is sent. This means that the prioritization has full access to
        the data about the individual packets and can choose differing
        treatment based on the stream a packet belongs to.<a href="#section-4.1-1" class="pilcrow">¶</a></p>
<p id="section-4.1-2">When a WebRTC endpoint has packets to send on multiple streams
        that are congestion controlled under the same congestion control
        regime, the WebRTC endpoint <span class="bcp14">SHOULD</span> cause data to be emitted in such a
        way that each stream at each level of priority is being given
        approximately twice the transmission capacity (measured in payload
        bytes) of the level below.<a href="#section-4.1-2" class="pilcrow">¶</a></p>
<p id="section-4.1-3">Thus, when congestion occurs, a high-priority flow will have the
        ability to send 8 times as much data as a very-low-priority flow if
        both have data to send. This prioritization is independent of the
        media type. The details of which packet to send first are
        implementation defined.<a href="#section-4.1-3" class="pilcrow">¶</a></p>
<p id="section-4.1-4">For example, if there is a high-priority audio flow sending
        100-byte packets and a low-priority video flow sending 1000-byte
        packets, and outgoing capacity exists for sending &gt; 5000 payload bytes, it
        would be appropriate to send 4000 bytes (40 packets) of audio and 1000
        bytes (one packet) of video as the result of a single pass of sending
        decisions.<a href="#section-4.1-4" class="pilcrow">¶</a></p>
<p id="section-4.1-5">Conversely, if the audio flow is marked low priority and the video
        flow is marked high priority, the scheduler may decide to send 2 video
        packets (2000 bytes) and 5 audio packets (500 bytes) when outgoing
        capacity exists for sending &gt; 2500 payload bytes.<a href="#section-4.1-5" class="pilcrow">¶</a></p>
<p id="section-4.1-6">If there are two high-priority audio flows, each will be able to
        send 4000 bytes in the same period where a low-priority video flow is
        able to send 1000 bytes.<a href="#section-4.1-6" class="pilcrow">¶</a></p>
<p id="section-4.1-7">Two example implementation strategies are:<a href="#section-4.1-7" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4.1-8.1">When the available bandwidth is known from the congestion
            control algorithm, configure each codec and each data channel with
            a target send rate that is appropriate to its share of the
            available bandwidth.<a href="#section-4.1-8.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-4.1-8.2">When congestion control indicates that a specified number of
            packets can be sent, send packets that are available to send using
            a weighted round-robin scheme across the connections.<a href="#section-4.1-8.2" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-4.1-9">Any combination of these, or other schemes that have the same
        effect, is valid, as long as the distribution of transmission capacity
        is approximately correct.<a href="#section-4.1-9" class="pilcrow">¶</a></p>
<p id="section-4.1-10">For media, it is usually inappropriate to use deep queues for
        sending; it is more useful to, for instance, skip intermediate frames
        that have no dependencies on them in order to achieve a lower bitrate.
        For reliable data, queues are useful.<a href="#section-4.1-10" class="pilcrow">¶</a></p>
<p id="section-4.1-11">Note that this specification doesn't dictate when disparate streams
        are to be "congestion controlled under the same congestion control
        regime". The issue of coupling congestion controllers is explored
        further in <span>[<a href="#RFC8699" class="xref">RFC8699</a>]</span>.<a href="#section-4.1-11" class="pilcrow">¶</a></p>
</section>
<div id="s-qos">
<section id="section-4.2">
        <h3 id="name-usage-of-quality-of-service">
<a href="#section-4.2" class="section-number selfRef">4.2. </a><a href="#name-usage-of-quality-of-service" class="section-name selfRef">Usage of Quality of Service -- DSCP and Multiplexing</a>
        </h3>
<p id="section-4.2-1">When the packet is sent, the network will make decisions about
        queueing and/or discarding the packet that can affect the quality of
        the communication. The sender can attempt to set the DSCP field of the
        packet to influence these decisions.<a href="#section-4.2-1" class="pilcrow">¶</a></p>
<p id="section-4.2-2">Implementations <span class="bcp14">SHOULD</span> attempt to set QoS on the packets sent,
        according to the guidelines in <span>[<a href="#RFC8837" class="xref">RFC8837</a>]</span>. It is appropriate to depart from
        this recommendation when running on platforms where QoS marking is not
        implemented.<a href="#section-4.2-2" class="pilcrow">¶</a></p>
<p id="section-4.2-3">The implementation <span class="bcp14">MAY</span> turn off use of DSCP markings if it detects
        symptoms of unexpected behavior such as priority inversion or blocking
        of packets with certain DSCP markings. Some examples of such behaviors
        are described in <span>[<a href="#ANRW16" class="xref">ANRW16</a>]</span>. The detection of these
        conditions is implementation dependent.<a href="#section-4.2-3" class="pilcrow">¶</a></p>
<p id="section-4.2-4">A particularly hard problem is when one media transport uses
        multiple DSCPs, where one may be blocked and another may be
        allowed. This is allowed even within a single media flow for video in
        <span>[<a href="#RFC8837" class="xref">RFC8837</a>]</span>. Implementations need to
        diagnose this scenario; one possible implementation is to send initial
        ICE probes with DSCP 0, and send ICE probes on all the DSCPs
        that are intended to be used once a candidate pair has been
        selected. If one or more of the DSCP-marked probes fail, the sender
        will switch the media type to using DSCP 0. This can be carried out
        simultaneously with the initial media traffic; on failure, the initial
        data may need to be resent. This switch will, of course, invalidate any
        congestion information gathered up to that point.<a href="#section-4.2-4" class="pilcrow">¶</a></p>
<p id="section-4.2-5">Failures can also start happening during the lifetime of the call;
        this case is expected to be rarer and can be handled by the normal
        mechanisms for transport failure, which may involve an ICE
        restart.<a href="#section-4.2-5" class="pilcrow">¶</a></p>
<p id="section-4.2-6">Note that when a DSCP causes nondelivery, one has to
        switch the whole media flow to DSCP 0, since all traffic for a single
        media flow needs to be on the same queue for congestion control
        purposes. Other flows on the same transport, using different DSCPs, don't need to change.<a href="#section-4.2-6" class="pilcrow">¶</a></p>
<p id="section-4.2-7">All packets carrying data from the SCTP association supporting the
        data channels <span class="bcp14">MUST</span> use a single DSCP. The code point used
        <span class="bcp14">SHOULD</span> be that recommended by <span>[<a href="#RFC8837" class="xref">RFC8837</a>]</span> for the highest-priority data
        channel carried. Note that this means that all data packets, no matter
        what their relative priority is, will be treated the same by the
        network.<a href="#section-4.2-7" class="pilcrow">¶</a></p>
<p id="section-4.2-8">All packets on one TCP connection, no matter what it carries, <span class="bcp14">MUST</span>
        use a single DSCP.<a href="#section-4.2-8" class="pilcrow">¶</a></p>
<p id="section-4.2-9">More advice on the use of DSCPs with RTP, as well as the
        relationship between DSCP and congestion control, is given in <span>[<a href="#RFC7657" class="xref">RFC7657</a>]</span>.<a href="#section-4.2-9" class="pilcrow">¶</a></p>
<p id="section-4.2-10">There exist a number of schemes for achieving quality of service
        that do not depend solely on DSCPs. Some of these schemes
        depend on classifying the traffic into flows based on 5-tuple (source
        address, source port, protocol, destination address, destination port)
        or 6-tuple (5-tuple + DSCP). Under differing conditions, it
        may therefore make sense for a sending application to choose any of
        the following configurations:<a href="#section-4.2-10" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4.2-11.1">Each media stream carried on its own 5-tuple<a href="#section-4.2-11.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-4.2-11.2">Media streams grouped by media type into 5-tuples (such as
            carrying all audio on one 5-tuple)<a href="#section-4.2-11.2" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-4.2-11.3">All media sent over a single 5-tuple, with or without
            differentiation into 6-tuples based on DSCPs<a href="#section-4.2-11.3" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-4.2-12">In each of the configurations mentioned, data channels may be
        carried in their own 5-tuple or multiplexed together with one of the
        media flows.<a href="#section-4.2-12" class="pilcrow">¶</a></p>
<p id="section-4.2-13">More complex configurations, such as sending a high-priority video
        stream on one 5-tuple and sending all other video streams multiplexed
        together over another 5-tuple, can also be envisioned. More
        information on mapping media flows to 5-tuples can be found in <span>[<a href="#RFC8834" class="xref">RFC8834</a>]</span>.<a href="#section-4.2-13" class="pilcrow">¶</a></p>
<p id="section-4.2-14">A sending implementation <span class="bcp14">MUST</span> be able to support the following
        configurations:<a href="#section-4.2-14" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4.2-15.1">Multiplex all media and data on a single 5-tuple (fully
            bundled)<a href="#section-4.2-15.1" class="pilcrow">¶</a>
</li>
          <li class="normal" id="section-4.2-15.2">Send each media stream on its own 5-tuple and data on its own
            5-tuple (fully unbundled)<a href="#section-4.2-15.2" class="pilcrow">¶</a>
</li>
        </ul>
<p id="section-4.2-16">The sending implementation <span class="bcp14">MAY</span> choose to support other
          configurations, such as
        bundling each media type (audio, video, or data) into its own 5-tuple
        (bundling by media type).<a href="#section-4.2-16" class="pilcrow">¶</a></p>
<p id="section-4.2-17">Sending data channel data over multiple 5-tuples is not
        supported.<a href="#section-4.2-17" class="pilcrow">¶</a></p>
<p id="section-4.2-18">A receiving implementation <span class="bcp14">MUST</span> be able to receive media and data
        in all these configurations.<a href="#section-4.2-18" class="pilcrow">¶</a></p>
</section>
</div>
</section>
<div id="IANA">
<section id="section-5">
      <h2 id="name-iana-considerations">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<p id="section-5-1">This document has no IANA actions.<a href="#section-5-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="Security">
<section id="section-6">
      <h2 id="name-security-considerations">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<p id="section-6-1">WebRTC security considerations are enumerated in <span>[<a href="#RFC8826" class="xref">RFC8826</a>]</span>.<a href="#section-6-1" class="pilcrow">¶</a></p>
<p id="section-6-2">Security considerations pertaining to the use of DSCP are enumerated
      in <span>[<a href="#RFC8837" class="xref">RFC8837</a>]</span>.<a href="#section-6-2" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-7">
      <h2 id="name-references">
<a href="#section-7" class="section-number selfRef">7. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-7.1">
        <h3 id="name-normative-references">
<a href="#section-7.1" class="section-number selfRef">7.1. </a><a href="#name-normative-references" class="section-name selfRef">Normative References</a>
        </h3>
<dl class="references">
<dt id="RFC0768">[RFC0768]</dt>
        <dd>
<span class="refAuthor">Postel, J.</span>, <span class="refTitle">"User Datagram Protocol"</span>, <span class="seriesInfo">STD 6</span>, <span class="seriesInfo">RFC 768</span>, <span class="seriesInfo">DOI 10.17487/RFC0768</span>, <time datetime="1980-08" class="refDate">August 1980</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc768">https://www.rfc-editor.org/info/rfc768</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC0793">[RFC0793]</dt>
        <dd>
<span class="refAuthor">Postel, J.</span>, <span class="refTitle">"Transmission Control Protocol"</span>, <span class="seriesInfo">STD 7</span>, <span class="seriesInfo">RFC 793</span>, <span class="seriesInfo">DOI 10.17487/RFC0793</span>, <time datetime="1981-09" class="refDate">September 1981</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc793">https://www.rfc-editor.org/info/rfc793</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="RFC4571">[RFC4571]</dt>
        <dd>
<span class="refAuthor">Lazzaro, J.</span>, <span class="refTitle">"Framing Real-time Transport Protocol (RTP) and RTP Control Protocol (RTCP) Packets over Connection-Oriented Transport"</span>, <span class="seriesInfo">RFC 4571</span>, <span class="seriesInfo">DOI 10.17487/RFC4571</span>, <time datetime="2006-07" class="refDate">July 2006</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4571">https://www.rfc-editor.org/info/rfc4571</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4594">[RFC4594]</dt>
        <dd>
<span class="refAuthor">Babiarz, J.</span><span class="refAuthor">, Chan, K.</span><span class="refAuthor">, and F. Baker</span>, <span class="refTitle">"Configuration Guidelines for DiffServ Service Classes"</span>, <span class="seriesInfo">RFC 4594</span>, <span class="seriesInfo">DOI 10.17487/RFC4594</span>, <time datetime="2006-08" class="refDate">August 2006</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4594">https://www.rfc-editor.org/info/rfc4594</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC4941">[RFC4941]</dt>
        <dd>
<span class="refAuthor">Narten, T.</span><span class="refAuthor">, Draves, R.</span><span class="refAuthor">, and S. Krishnan</span>, <span class="refTitle">"Privacy Extensions for Stateless Address Autoconfiguration in IPv6"</span>, <span class="seriesInfo">RFC 4941</span>, <span class="seriesInfo">DOI 10.17487/RFC4941</span>, <time datetime="2007-09" class="refDate">September 2007</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc4941">https://www.rfc-editor.org/info/rfc4941</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5389">[RFC5389]</dt>
        <dd>
<span class="refAuthor">Rosenberg, J.</span><span class="refAuthor">, Mahy, R.</span><span class="refAuthor">, Matthews, P.</span><span class="refAuthor">, and D. Wing</span>, <span class="refTitle">"Session Traversal Utilities for NAT (STUN)"</span>, <span class="seriesInfo">RFC 5389</span>, <span class="seriesInfo">DOI 10.17487/RFC5389</span>, <time datetime="2008-10" class="refDate">October 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5389">https://www.rfc-editor.org/info/rfc5389</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5764">[RFC5764]</dt>
        <dd>
<span class="refAuthor">McGrew, D.</span><span class="refAuthor"> and E. Rescorla</span>, <span class="refTitle">"Datagram Transport Layer Security (DTLS) Extension to Establish Keys for the Secure Real-time Transport Protocol (SRTP)"</span>, <span class="seriesInfo">RFC 5764</span>, <span class="seriesInfo">DOI 10.17487/RFC5764</span>, <time datetime="2010-05" class="refDate">May 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5764">https://www.rfc-editor.org/info/rfc5764</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6062">[RFC6062]</dt>
        <dd>
<span class="refAuthor">Perreault, S., Ed.</span><span class="refAuthor"> and J. Rosenberg</span>, <span class="refTitle">"Traversal Using Relays around NAT (TURN) Extensions for TCP Allocations"</span>, <span class="seriesInfo">RFC 6062</span>, <span class="seriesInfo">DOI 10.17487/RFC6062</span>, <time datetime="2010-11" class="refDate">November 2010</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6062">https://www.rfc-editor.org/info/rfc6062</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6347">[RFC6347]</dt>
        <dd>
<span class="refAuthor">Rescorla, E.</span><span class="refAuthor"> and N. Modadugu</span>, <span class="refTitle">"Datagram Transport Layer Security Version 1.2"</span>, <span class="seriesInfo">RFC 6347</span>, <span class="seriesInfo">DOI 10.17487/RFC6347</span>, <time datetime="2012-01" class="refDate">January 2012</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6347">https://www.rfc-editor.org/info/rfc6347</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6544">[RFC6544]</dt>
        <dd>
<span class="refAuthor">Rosenberg, J.</span><span class="refAuthor">, Keranen, A.</span><span class="refAuthor">, Lowekamp, B. B.</span><span class="refAuthor">, and A. B. Roach</span>, <span class="refTitle">"TCP Candidates with Interactive Connectivity Establishment (ICE)"</span>, <span class="seriesInfo">RFC 6544</span>, <span class="seriesInfo">DOI 10.17487/RFC6544</span>, <time datetime="2012-03" class="refDate">March 2012</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6544">https://www.rfc-editor.org/info/rfc6544</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC6724">[RFC6724]</dt>
        <dd>
<span class="refAuthor">Thaler, D., Ed.</span><span class="refAuthor">, Draves, R.</span><span class="refAuthor">, Matsumoto, A.</span><span class="refAuthor">, and T. Chown</span>, <span class="refTitle">"Default Address Selection for Internet Protocol Version 6 (IPv6)"</span>, <span class="seriesInfo">RFC 6724</span>, <span class="seriesInfo">DOI 10.17487/RFC6724</span>, <time datetime="2012-09" class="refDate">September 2012</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc6724">https://www.rfc-editor.org/info/rfc6724</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7231">[RFC7231]</dt>
        <dd>
<span class="refAuthor">Fielding, R., Ed.</span><span class="refAuthor"> and J. Reschke, Ed.</span>, <span class="refTitle">"Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content"</span>, <span class="seriesInfo">RFC 7231</span>, <span class="seriesInfo">DOI 10.17487/RFC7231</span>, <time datetime="2014-06" class="refDate">June 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7231">https://www.rfc-editor.org/info/rfc7231</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7235">[RFC7235]</dt>
        <dd>
<span class="refAuthor">Fielding, R., Ed.</span><span class="refAuthor"> and J. Reschke, Ed.</span>, <span class="refTitle">"Hypertext Transfer Protocol (HTTP/1.1): Authentication"</span>, <span class="seriesInfo">RFC 7235</span>, <span class="seriesInfo">DOI 10.17487/RFC7235</span>, <time datetime="2014-06" class="refDate">June 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7235">https://www.rfc-editor.org/info/rfc7235</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7639">[RFC7639]</dt>
        <dd>
<span class="refAuthor">Hutton, A.</span><span class="refAuthor">, Uberti, J.</span><span class="refAuthor">, and M. Thomson</span>, <span class="refTitle">"The ALPN HTTP Header Field"</span>, <span class="seriesInfo">RFC 7639</span>, <span class="seriesInfo">DOI 10.17487/RFC7639</span>, <time datetime="2015-08" class="refDate">August 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7639">https://www.rfc-editor.org/info/rfc7639</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7656">[RFC7656]</dt>
        <dd>
<span class="refAuthor">Lennox, J.</span><span class="refAuthor">, Gross, K.</span><span class="refAuthor">, Nandakumar, S.</span><span class="refAuthor">, Salgueiro, G.</span><span class="refAuthor">, and B. Burman, Ed.</span>, <span class="refTitle">"A Taxonomy of Semantics and Mechanisms for Real-Time Transport Protocol (RTP) Sources"</span>, <span class="seriesInfo">RFC 7656</span>, <span class="seriesInfo">DOI 10.17487/RFC7656</span>, <time datetime="2015-11" class="refDate">November 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7656">https://www.rfc-editor.org/info/rfc7656</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7983">[RFC7983]</dt>
        <dd>
<span class="refAuthor">Petit-Huguenin, M.</span><span class="refAuthor"> and G. Salgueiro</span>, <span class="refTitle">"Multiplexing Scheme Updates for Secure Real-time Transport Protocol (SRTP) Extension for Datagram Transport Layer Security (DTLS)"</span>, <span class="seriesInfo">RFC 7983</span>, <span class="seriesInfo">DOI 10.17487/RFC7983</span>, <time datetime="2016-09" class="refDate">September 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7983">https://www.rfc-editor.org/info/rfc7983</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8083">[RFC8083]</dt>
        <dd>
<span class="refAuthor">Perkins, C.</span><span class="refAuthor"> and V. Singh</span>, <span class="refTitle">"Multimedia Congestion Control: Circuit Breakers for Unicast RTP Sessions"</span>, <span class="seriesInfo">RFC 8083</span>, <span class="seriesInfo">DOI 10.17487/RFC8083</span>, <time datetime="2017-03" class="refDate">March 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8083">https://www.rfc-editor.org/info/rfc8083</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="RFC8260">[RFC8260]</dt>
        <dd>
<span class="refAuthor">Stewart, R.</span><span class="refAuthor">, Tuexen, M.</span><span class="refAuthor">, Loreto, S.</span><span class="refAuthor">, and R. Seggelmann</span>, <span class="refTitle">"Stream Schedulers and User Message Interleaving for the Stream Control Transmission Protocol"</span>, <span class="seriesInfo">RFC 8260</span>, <span class="seriesInfo">DOI 10.17487/RFC8260</span>, <time datetime="2017-11" class="refDate">November 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8260">https://www.rfc-editor.org/info/rfc8260</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8261">[RFC8261]</dt>
        <dd>
<span class="refAuthor">Tuexen, M.</span><span class="refAuthor">, Stewart, R.</span><span class="refAuthor">, Jesup, R.</span><span class="refAuthor">, and S. Loreto</span>, <span class="refTitle">"Datagram Transport Layer Security (DTLS) Encapsulation of SCTP Packets"</span>, <span class="seriesInfo">RFC 8261</span>, <span class="seriesInfo">DOI 10.17487/RFC8261</span>, <time datetime="2017-11" class="refDate">November 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8261">https://www.rfc-editor.org/info/rfc8261</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8421">[RFC8421]</dt>
        <dd>
<span class="refAuthor">Martinsen, P.</span><span class="refAuthor">, Reddy, T.</span><span class="refAuthor">, and P. Patil</span>, <span class="refTitle">"Guidelines for Multihomed and IPv4/IPv6 Dual-Stack Interactive Connectivity Establishment (ICE)"</span>, <span class="seriesInfo">BCP 217</span>, <span class="seriesInfo">RFC 8421</span>, <span class="seriesInfo">DOI 10.17487/RFC8421</span>, <time datetime="2018-07" class="refDate">July 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8421">https://www.rfc-editor.org/info/rfc8421</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8445">[RFC8445]</dt>
        <dd>
<span class="refAuthor">Keranen, A.</span><span class="refAuthor">, Holmberg, C.</span><span class="refAuthor">, and J. Rosenberg</span>, <span class="refTitle">"Interactive Connectivity Establishment (ICE): A Protocol for Network Address Translator (NAT) Traversal"</span>, <span class="seriesInfo">RFC 8445</span>, <span class="seriesInfo">DOI 10.17487/RFC8445</span>, <time datetime="2018-07" class="refDate">July 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8445">https://www.rfc-editor.org/info/rfc8445</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8446">[RFC8446]</dt>
        <dd>
<span class="refAuthor">Rescorla, E.</span>, <span class="refTitle">"The Transport Layer Security (TLS) Protocol Version 1.3"</span>, <span class="seriesInfo">RFC 8446</span>, <span class="seriesInfo">DOI 10.17487/RFC8446</span>, <time datetime="2018-08" class="refDate">August 2018</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8446">https://www.rfc-editor.org/info/rfc8446</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8656">[RFC8656]</dt>
        <dd>
<span class="refAuthor">Reddy, T., Ed.</span><span class="refAuthor">, Johnston, A., Ed.</span><span class="refAuthor">, Matthews, P.</span><span class="refAuthor">, and J. Rosenberg</span>, <span class="refTitle">"Traversal Using Relays around NAT (TURN): Relay Extensions to Session Traversal Utilities for NAT (STUN)"</span>, <span class="seriesInfo">RFC 8656</span>, <span class="seriesInfo">DOI 10.17487/RFC8656</span>, <time datetime="2020-02" class="refDate">February 2020</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8656">https://www.rfc-editor.org/info/rfc8656</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8825">[RFC8825]</dt>
        <dd>
<span class="refAuthor">Alvestrand, H.</span>, <span class="refTitle">"Overview: Real-Time Protocols for Browser-Based Applications"</span>, <span class="seriesInfo">RFC 8825</span>, <span class="seriesInfo">DOI 10.17487/RFC8825</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8825">https://www.rfc-editor.org/info/rfc8825</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8826">[RFC8826]</dt>
        <dd>
<span class="refAuthor">Rescorla, E.</span>, <span class="refTitle">"Security Considerations for WebRTC"</span>, <span class="seriesInfo">RFC 8826</span>, <span class="seriesInfo">DOI 10.17487/RFC8826</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8826">https://www.rfc-editor.org/info/rfc8826</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8827">[RFC8827]</dt>
        <dd>
<span class="refAuthor">Rescorla, E.</span>, <span class="refTitle">"WebRTC Security Architecture"</span>, <span class="seriesInfo">RFC 8827</span>, <span class="seriesInfo">DOI 10.17487/RFC8827</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8827">https://www.rfc-editor.org/info/rfc8827</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8831">[RFC8831]</dt>
        <dd>
<span class="refAuthor">Jesup, R.</span><span class="refAuthor">, Loreto, S.</span><span class="refAuthor">, and M. Tüxen</span>, <span class="refTitle">"WebRTC Data Channels"</span>, <span class="seriesInfo">RFC 8831</span>, <span class="seriesInfo">DOI 10.17487/RFC8831</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8831">https://www.rfc-editor.org/info/rfc8831</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8832">[RFC8832]</dt>
        <dd>
<span class="refAuthor">Jesup, R.</span><span class="refAuthor">, Loreto, S.</span><span class="refAuthor">, and M. Tüxen</span>, <span class="refTitle">"WebRTC Data Channel Establishment Protocol"</span>, <span class="seriesInfo">RFC 8832</span>, <span class="seriesInfo">DOI 10.17487/RFC8832</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8832">https://www.rfc-editor.org/info/rfc8832</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8833">[RFC8833]</dt>
        <dd>
<span class="refAuthor">Thomson, M.</span>, <span class="refTitle">"Application-Layer Protocol Negotiation (ALPN) for WebRTC"</span>, <span class="seriesInfo">RFC 8833</span>, <span class="seriesInfo">DOI 10.17487/RFC8833</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8833">https://www.rfc-editor.org/info/rfc8833</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8834">[RFC8834]</dt>
        <dd>
<span class="refAuthor">Perkins, C.</span><span class="refAuthor">, Westerlund, M.</span><span class="refAuthor">, and J. Ott</span>, <span class="refTitle">"Media Transport and Use of RTP in WebRTC"</span>, <span class="seriesInfo">RFC 8834</span>, <span class="seriesInfo">DOI 10.17487/RFC8834</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8834">https://www.rfc-editor.org/info/rfc8834</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8836">[RFC8836]</dt>
        <dd>
<span class="refAuthor">Jesup, R.</span><span class="refAuthor"> and Z. Sarker, Ed.</span>, <span class="refTitle">"Congestion Control Requirements for Interactive Real-Time Media"</span>, <span class="seriesInfo">RFC 8836</span>, <span class="seriesInfo">DOI 10.17487/RFC8836</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8836">https://www.rfc-editor.org/info/rfc8836</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8837">[RFC8837]</dt>
        <dd>
<span class="refAuthor">Jones, P.</span><span class="refAuthor">, Dhesikan, S.</span><span class="refAuthor">, Jennings, C.</span><span class="refAuthor">, and D. Druta</span>, <span class="refTitle">"Differentiated Services Code Point (DSCP) Packet Markings for WebRTC QoS"</span>, <span class="seriesInfo">RFC 8837</span>, <span class="seriesInfo">DOI 10.17487/RFC8837</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8837">https://www.rfc-editor.org/info/rfc8837</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8841">[RFC8841]</dt>
        <dd>
<span class="refAuthor">Holmberg, C.</span><span class="refAuthor">, Shpount, R.</span><span class="refAuthor">, Loreto, S.</span><span class="refAuthor">, and G. Camarillo</span>, <span class="refTitle">"Session Description Protocol (SDP) Offer/Answer Procedures for Stream Control Transmission Protocol (SCTP) over Datagram Transport Layer Security (DTLS) Transport"</span>, <span class="seriesInfo">RFC 8841</span>, <span class="seriesInfo">DOI 10.17487/RFC8841</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8841">https://www.rfc-editor.org/info/rfc8841</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8842">[RFC8842]</dt>
      <dd>
<span class="refAuthor">Holmberg, C.</span><span class="refAuthor"> and R. Shpount</span>, <span class="refTitle">"Session Description Protocol (SDP) Offer/Answer Considerations for Datagram Transport Layer Security (DTLS) and Transport Layer Security (TLS)"</span>, <span class="seriesInfo">RFC 8842</span>, <span class="seriesInfo">DOI 10.17487/RFC8842</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8842">https://www.rfc-editor.org/info/rfc8842</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
<section id="section-7.2">
        <h3 id="name-informative-references">
<a href="#section-7.2" class="section-number selfRef">7.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="ANRW16">[ANRW16]</dt>
        <dd>
<span class="refAuthor">Barik, R.</span><span class="refAuthor">, Welzl, M.</span><span class="refAuthor">, and A. Elmokashfi</span>, <span class="refTitle">"How to say that you're special: Can we use bits in the IPv4 header?"</span>, <span class="refContent">ANRW '16: Proceedings of the 2016 Applied Networking
          Research Workshop, pages 68-70</span>, <span class="seriesInfo">DOI 10.1145/2959424.2959442</span>, <time datetime="2016-07" class="refDate">July 2016</time>, <span>&lt;<a href="https://irtf.org/anrw/2016/anrw16-final17.pdf">https://irtf.org/anrw/2016/anrw16-final17.pdf</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="I-D.ietf-rtcweb-return">[RETURN]</dt>
        <dd>
<span class="refAuthor">Schwartz, B.</span><span class="refAuthor"> and J. Uberti</span>, <span class="refTitle">"Recursively Encapsulated TURN (RETURN) for Connectivity and Privacy in WebRTC"</span>, <span class="refContent">Work in Progress</span>, <span class="seriesInfo">Internet-Draft, draft-ietf-rtcweb-return-02</span>, <time datetime="2017-03-27" class="refDate">27 March 2017</time>, <span>&lt;<a href="https://tools.ietf.org/html/draft-ietf-rtcweb-return-02">https://tools.ietf.org/html/draft-ietf-rtcweb-return-02</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3484">[RFC3484]</dt>
        <dd>
<span class="refAuthor">Draves, R.</span>, <span class="refTitle">"Default Address Selection for Internet Protocol version 6 (IPv6)"</span>, <span class="seriesInfo">RFC 3484</span>, <span class="seriesInfo">DOI 10.17487/RFC3484</span>, <time datetime="2003-02" class="refDate">February 2003</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3484">https://www.rfc-editor.org/info/rfc3484</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5014">[RFC5014]</dt>
        <dd>
<span class="refAuthor">Nordmark, E.</span><span class="refAuthor">, Chakrabarti, S.</span><span class="refAuthor">, and J. Laganier</span>, <span class="refTitle">"IPv6 Socket API for Source Address Selection"</span>, <span class="seriesInfo">RFC 5014</span>, <span class="seriesInfo">DOI 10.17487/RFC5014</span>, <time datetime="2007-09" class="refDate">September 2007</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5014">https://www.rfc-editor.org/info/rfc5014</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC5128">[RFC5128]</dt>
        <dd>
<span class="refAuthor">Srisuresh, P.</span><span class="refAuthor">, Ford, B.</span><span class="refAuthor">, and D. Kegel</span>, <span class="refTitle">"State of Peer-to-Peer (P2P) Communication across Network Address Translators (NATs)"</span>, <span class="seriesInfo">RFC 5128</span>, <span class="seriesInfo">DOI 10.17487/RFC5128</span>, <time datetime="2008-03" class="refDate">March 2008</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc5128">https://www.rfc-editor.org/info/rfc5128</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC7657">[RFC7657]</dt>
        <dd>
<span class="refAuthor">Black, D., Ed.</span><span class="refAuthor"> and P. Jones</span>, <span class="refTitle">"Differentiated Services (Diffserv) and Real-Time Communication"</span>, <span class="seriesInfo">RFC 7657</span>, <span class="seriesInfo">DOI 10.17487/RFC7657</span>, <time datetime="2015-11" class="refDate">November 2015</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7657">https://www.rfc-editor.org/info/rfc7657</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8155">[RFC8155]</dt>
        <dd>
<span class="refAuthor">Patil, P.</span><span class="refAuthor">, Reddy, T.</span><span class="refAuthor">, and D. Wing</span>, <span class="refTitle">"Traversal Using Relays around NAT (TURN) Server Auto Discovery"</span>, <span class="seriesInfo">RFC 8155</span>, <span class="seriesInfo">DOI 10.17487/RFC8155</span>, <time datetime="2017-04" class="refDate">April 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8155">https://www.rfc-editor.org/info/rfc8155</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8699">[RFC8699]</dt>
      <dd>
<span class="refAuthor">Islam, S.</span><span class="refAuthor">, Welzl, M.</span><span class="refAuthor">, and S. Gjessing</span>, <span class="refTitle">"Coupled Congestion Control for RTP Media"</span>, <span class="seriesInfo">RFC 8699</span>, <span class="seriesInfo">DOI 10.17487/RFC8699</span>, <time datetime="2020-01" class="refDate">January 2020</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8699">https://www.rfc-editor.org/info/rfc8699</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
</section>
<div id="Acknowledgements">
<section id="section-appendix.a">
      <h2 id="name-acknowledgements">
<a href="#name-acknowledgements" class="section-name selfRef">Acknowledgements</a>
      </h2>
<p id="section-appendix.a-1">This document is based on earlier draft versions embedded in <span>[<a href="#RFC8825" class="xref">RFC8825</a>]</span>, which were the result of contributions from many RTCWEB Working Group
      members.<a href="#section-appendix.a-1" class="pilcrow">¶</a></p>
<p id="section-appendix.a-2">Special thanks for reviews of earlier draft versions of this document go to
      <span class="contact-name">Eduardo Gueiros</span>, <span class="contact-name">Magnus         Westerlund</span>, <span class="contact-name">Markus Isomaki</span>, and <span class="contact-name">Dan Wing</span>; the
      contributions from <span class="contact-name">Andrew Hutton</span> also deserve special mention.<a href="#section-appendix.a-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="authors-addresses">
<section id="section-appendix.b">
      <h2 id="name-authors-address">
<a href="#name-authors-address" class="section-name selfRef">Author's Address</a>
      </h2>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Harald Alvestrand</span></div>
<div dir="auto" class="left"><span class="org">Google</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:harald@alvestrand.no" class="email">harald@alvestrand.no</a>
</div>
</address>
</section>
</div>
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