File: rfc8837.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 8837: Differentiated Services Code Point (DSCP) Packet Markings for WebRTC QoS</title>
<meta content="Paul E. Jones" name="author">
<meta content="Subha Dhesikan" name="author">
<meta content="Cullen Jennings" name="author">
<meta content="Dan Druta" name="author">
<meta content="
       
        Networks can provide different forwarding treatments for individual
        packets based on Differentiated Services Code Point (DSCP)
        values on a per-hop basis.  This document provides the
        recommended DSCP values for web browsers to use for various
        classes of Web Real-Time Communication (WebRTC) traffic.
       
    " name="description">
<meta content="xml2rfc 3.5.0" name="generator">
<meta content="Diffserv" name="keyword">
<meta content="rtcweb" name="keyword">
<meta content="8837" 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="rfc8837.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;
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<table class="ears">
<thead><tr>
<td class="left">RFC 8837</td>
<td class="center">WebRTC QoS</td>
<td class="right">January 2021</td>
</tr></thead>
<tfoot><tr>
<td class="left">Jones, et al.</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/rfc8837" class="eref">8837</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">Authors:</dt>
<dd class="authors">
<div class="author">
      <div class="author-name">P. Jones</div>
<div class="org">Cisco Systems</div>
</div>
<div class="author">
      <div class="author-name">S. Dhesikan</div>
<div class="org">Individual</div>
</div>
<div class="author">
      <div class="author-name">C. Jennings</div>
<div class="org">Cisco Systems</div>
</div>
<div class="author">
      <div class="author-name">D. Druta</div>
<div class="org">AT&amp;T</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 8837</h1>
<h1 id="title">Differentiated Services Code Point (DSCP) Packet Markings for WebRTC QoS</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">
        Networks can provide different forwarding treatments for individual
        packets based on Differentiated Services Code Point (DSCP)
        values on a per-hop basis.  This document provides the
        recommended DSCP values for web browsers to use for various
        classes of Web Real-Time Communication (WebRTC) traffic.<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/rfc8837">https://www.rfc-editor.org/info/rfc8837</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="ulEmpty compact toc">
<li class="ulEmpty compact toc" 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="ulEmpty compact toc" 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><a href="#section-toc.1-1.2.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty compact toc" id="section-toc.1-1.3">
            <p id="section-toc.1-1.3.1" class="keepWithNext"><a href="#section-3" class="xref">3</a>.  <a href="#name-relation-to-other-specifica" class="xref">Relation to Other Specifications</a><a href="#section-toc.1-1.3.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty compact toc" 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-inputs" class="xref">Inputs</a><a href="#section-toc.1-1.4.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty compact toc" 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-dscp-mappings" class="xref">DSCP Mappings</a><a href="#section-toc.1-1.5.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty compact toc" 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="ulEmpty compact toc" 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-iana-considerations" class="xref">IANA Considerations</a><a href="#section-toc.1-1.7.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty compact toc" 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-downward-references" class="xref">Downward References</a><a href="#section-toc.1-1.8.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty compact toc" 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><a href="#section-toc.1-1.9.1" class="pilcrow">¶</a></p>
<ul class="ulEmpty compact toc">
<li class="ulEmpty compact toc" 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><a href="#section-toc.1-1.9.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="ulEmpty compact toc" 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><a href="#section-toc.1-1.9.2.2.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="ulEmpty compact toc" id="section-toc.1-1.10">
            <p id="section-toc.1-1.10.1"><a href="#section-appendix.a" class="xref"></a><a href="#name-acknowledgements" class="xref">Acknowledgements</a><a href="#section-toc.1-1.10.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty compact toc" id="section-toc.1-1.11">
            <p id="section-toc.1-1.11.1"><a href="#section-appendix.b" class="xref"></a><a href="#name-dedication" class="xref">Dedication</a><a href="#section-toc.1-1.11.1" class="pilcrow">¶</a></p>
</li>
          <li class="ulEmpty compact toc" id="section-toc.1-1.12">
            <p id="section-toc.1-1.12.1"><a href="#section-appendix.c" class="xref"></a><a href="#name-authors-addresses" class="xref">Authors' Addresses</a><a href="#section-toc.1-1.12.1" 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">
        Differentiated Services Code Point (DSCP) <span>[<a href="#RFC2474" class="xref">RFC2474</a>]</span>
        packet marking can help provide QoS in some environments.
        This specification provides default packet marking for browsers
        that support WebRTC applications, but does not change any advice
        or requirements in other RFCs.  The contents of this
        specification are intended to be a simple set of implementation
        recommendations based on previous RFCs.<a href="#section-1-1" class="pilcrow">¶</a></p>
<p id="section-1-2">
        Networks in which these DSCP markings are beneficial (likely to
        improve QoS for WebRTC traffic) include:<a href="#section-1-2" class="pilcrow">¶</a></p>
<ol start="1" type="1" class="normal type-1" id="section-1-3">
        <li id="section-1-3.1">
            Private, wide-area networks.  Network administrators have
            control over remarking packets and treatment of packets.<a href="#section-1-3.1" class="pilcrow">¶</a>
</li>
        <li id="section-1-3.2">
            Residential Networks.  If the congested link is the
            broadband uplink in a cable or DSL scenario, residential
     routers/NAT often support preferential treatment based
            on DSCP.<a href="#section-1-3.2" class="pilcrow">¶</a>
</li>
        <li id="section-1-3.3">
            Wireless Networks.  If the congested link is a local
            wireless network, marking may help.<a href="#section-1-3.3" class="pilcrow">¶</a>
</li>
      </ol>
<p id="section-1-4">
        There are cases where these DSCP markings do not help but,
        aside from possible priority inversion for "Less-than-Best-Effort
 traffic" (see <a href="#dscp-mappings" class="xref">Section 5</a>), they seldom make things worse
        if packets are marked appropriately.<a href="#section-1-4" class="pilcrow">¶</a></p>
<p id="section-1-5">
        DSCP values are, in principle, site specific with each site
        selecting its own code points for controlling per-hop behavior
        to influence the QoS for transport-layer flows.  However, in the
        WebRTC use cases, the browsers need to set them to something
        when there is no site-specific information.  This document
        describes a subset of DSCP code point values drawn from existing
        RFCs and common usage for use with WebRTC applications.  These
        code points are intended to be the default values used by a
        WebRTC application.  While other values could be used, using a
        non-default value may result in unexpected per-hop behavior.  It
        is <span class="bcp14">RECOMMENDED</span> that WebRTC applications use non-default values
        only in private networks that are configured to use different
        values.<a href="#section-1-5" class="pilcrow">¶</a></p>
<p id="section-1-6">

        This specification defines inputs that are provided by the
        WebRTC application hosted in the browser that aid the browser in
        determining how to set the various packet markings.  The
        specification also defines the mapping from abstract QoS
        policies (flow type, priority level) to those packet markings.<a href="#section-1-6" class="pilcrow">¶</a></p>
</section>
<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 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>
<p id="section-2-2">
        The terms "browser" and "non-browser" are defined in
        <span>[<a href="#RFC7742" class="xref">RFC7742</a>]</span> and carry the same meaning in this
        document.<a href="#section-2-2" class="pilcrow">¶</a></p>
</section>
<section id="section-3">
      <h2 id="name-relation-to-other-specifica">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-relation-to-other-specifica" class="section-name selfRef">Relation to Other Specifications</a>
      </h2>
<p id="section-3-1">
        This document is a complement to <span>[<a href="#RFC7657" class="xref">RFC7657</a>]</span>, which
        describes the interaction between DSCP and real-time
        communications.  That RFC covers the implications of using
        various DSCP values, particularly focusing on the Real-time
        Transport Protocol (RTP) <span>[<a href="#RFC3550" class="xref">RFC3550</a>]</span> streams that
        are multiplexed onto a single transport-layer flow.<a href="#section-3-1" class="pilcrow">¶</a></p>
<p id="section-3-2">
        There are a number of guidelines specified in
        <span>[<a href="#RFC7657" class="xref">RFC7657</a>]</span> that apply to marking traffic sent by
        WebRTC applications, as it is common for multiple RTP streams to
        be multiplexed on the same transport-layer flow.  Generally, the
        RTP streams would be marked with a value as appropriate from
        <a href="#tab-dscp" class="xref">Table 1</a>.  A WebRTC application might also
        multiplex data channel
        <span>[<a href="#RFC8831" class="xref">RFC8831</a>]</span> traffic over the
        same 5-tuple as RTP streams, which would also be marked per
        that table.  The guidance in <span>[<a href="#RFC7657" class="xref">RFC7657</a>]</span> says that
        all data channel traffic would be marked with a single value
        that is typically different from the value(s) used for RTP
        streams multiplexed with the data channel traffic over the same
        5-tuple, assuming RTP streams are marked with a value other than
        Default Forwarding (DF).  This is expanded upon further in the
        next section.<a href="#section-3-2" class="pilcrow">¶</a></p>
<p id="section-3-3">
        This specification does not change or override the advice in any
        other RFCs about setting packet markings.  Rather, it
        simply selects a subset of DSCP values that is relevant in the
        WebRTC context.<a href="#section-3-3" class="pilcrow">¶</a></p>
<p id="section-3-4">
        The DSCP value set by the endpoint is not trusted by the
        network.  In addition, the DSCP value may be remarked at any
        place in the network for a variety of reasons to any other DSCP
        value, including the DF value to provide basic
        best-effort service.  Even so, there is a benefit to marking
        traffic even if it only benefits the first few hops.  The
        implications are discussed in 
        <span><a href="https://www.rfc-editor.org/rfc/rfc7657#section-3.2" class="relref">Section 3.2</a> of [<a href="#RFC7657" class="xref">RFC7657</a>]</span>.  Further, a mitigation for such action
        is through an authorization mechanism.  Such an authorization
        mechanism is outside the scope of this document.<a href="#section-3-4" class="pilcrow">¶</a></p>
</section>
<section id="section-4">
      <h2 id="name-inputs">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-inputs" class="section-name selfRef">Inputs</a>
      </h2>
<p id="section-4-1">
        This document recommends DSCP values for two classes of WebRTC flows:<a href="#section-4-1" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4-2.1">
           media flows that are RTP streams
            <span>[<a href="#RFC8834" class="xref">RFC8834</a>]</span><a href="#section-4-2.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-4-2.2">
           data flows that are data channels
            <span>[<a href="#RFC8831" class="xref">RFC8831</a>]</span><a href="#section-4-2.2" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-4-3">
        Each of the RTP streams and distinct data channels consist of
        all of the packets associated with an independent media entity,
        so an RTP stream or distinct data channel is not always
        equivalent to a transport-layer flow defined by a 5-tuple
        (source address, destination address, source port, destination
        port, and protocol).  There may be multiple RTP streams and data
        channels multiplexed over the same 5-tuple, with each having a
        different level of importance to the application and, therefore,
        potentially marked using different DSCP values than another RTP
        stream or data channel within the same transport-layer flow.
        (Note that there are restrictions with respect to marking
        different data channels carried within the same Stream Control
 Transmission Protocol (SCTP) association
        as outlined in <a href="#dscp-mappings" class="xref">Section 5</a>.)<a href="#section-4-3" class="pilcrow">¶</a></p>
<p id="section-4-4">
        The following are the inputs provided by the WebRTC application
        to the browser:<a href="#section-4-4" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-4-5.1">
            Flow Type: The application provides this input because it knows
            if the flow is audio, interactive video (<span>[<a href="#RFC4594" class="xref">RFC4594</a>]</span>
          <span>[<a href="#G.1010" class="xref">G.1010</a>]</span>) with or without audio, or data.<a href="#section-4-5.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-4-5.2">
            Application Priority: Another input is the relative
            importance of an RTP stream or data channel.  Many
            applications have multiple flows of the same flow type and
            some flows are often more important than others.  For
            example, in a video conference where there are usually audio
            and video flows, the audio flow may be more important than
            the video flow.  JavaScript applications can tell the
            browser whether a particular flow is of High, Medium, Low, or
            Very Low importance to the application.<a href="#section-4-5.2" class="pilcrow">¶</a>
</li>
      </ul>
<p id="section-4-6">
        <span>[<a href="#RFC8835" class="xref">RFC8835</a>]</span> defines in more
        detail what an individual flow is within the WebRTC
        context and priorities for media and data flows.<a href="#section-4-6" class="pilcrow">¶</a></p>
<p id="section-4-7">
        Currently in WebRTC, media sent over RTP is assumed to be
        interactive <span>[<a href="#RFC8835" class="xref">RFC8835</a>]</span> and
        browser APIs do not exist to allow an application to
        differentiate between interactive and non-interactive video.<a href="#section-4-7" class="pilcrow">¶</a></p>
</section>
<div id="dscp-mappings">
<section id="section-5">
      <h2 id="name-dscp-mappings">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-dscp-mappings" class="section-name selfRef">DSCP Mappings</a>
      </h2>
<p id="section-5-1"> 
        The DSCP values for each flow type of interest to WebRTC based
        on application priority are shown in <a href="#tab-dscp" class="xref">Table 1</a>.
        These values are based on the framework and recommended values in
        <span>[<a href="#RFC4594" class="xref">RFC4594</a>]</span>.  A web browser <span class="bcp14">SHOULD</span> use these values
        to mark the appropriate media packets.  More information on Expedited
 Forwarding (EF) and Assured Forwarding (AF) can be found in <span>[<a href="#RFC3246" class="xref">RFC3246</a>]</span> and <span>[<a href="#RFC2597" class="xref">RFC2597</a>]</span>, respectively.  DF is Default Forwarding, which provides the basic best-effort service
        <span>[<a href="#RFC2474" class="xref">RFC2474</a>]</span>.<a href="#section-5-1" class="pilcrow">¶</a></p>
<p id="section-5-2">
        WebRTC's use of multiple DSCP values may result in packets with
        certain DSCP values being blocked by a network.  See 
        <span><a href="https://www.rfc-editor.org/rfc/rfc8835#section-4.2" class="relref">Section 4.2</a> of [<a href="#RFC8835" class="xref">RFC8835</a>]</span> for further
        discussion, including how WebRTC implementations establish and
        maintain connectivity when such blocking is encountered.<a href="#section-5-2" class="pilcrow">¶</a></p>
<span id="name-recommended-dscp-values-for"></span><div id="tab-dscp">
<table class="center" id="table-1">
        <caption>
<a href="#table-1" class="selfRef">Table 1</a>:
<a href="#name-recommended-dscp-values-for" class="selfRef">Recommended DSCP Values for WebRTC Applications</a>
        </caption>
<thead>
          <tr>
            <th class="text-center" rowspan="1" colspan="1">Flow Type</th>
            <th class="text-center" rowspan="1" colspan="1">Very Low</th>
            <th class="text-center" rowspan="1" colspan="1">Low</th>
            <th class="text-center" rowspan="1" colspan="1">Medium</th>
            <th class="text-center" rowspan="1" colspan="1">High</th>
          </tr>
        </thead>
        <tbody>
          <tr>
            <td class="text-center" rowspan="1" colspan="1">Audio</td>
            <td class="text-center" rowspan="1" colspan="1">LE (1)</td>
            <td class="text-center" rowspan="1" colspan="1">DF (0)</td>
            <td class="text-center" rowspan="1" colspan="1">EF (46)</td>
            <td class="text-center" rowspan="1" colspan="1">EF (46)</td>
          </tr>
          <tr>
            <td class="text-center" rowspan="1" colspan="1"> </td>
            <td class="text-center" rowspan="1" colspan="1"> </td>
            <td class="text-center" rowspan="1" colspan="1"> </td>
            <td class="text-center" rowspan="1" colspan="1"> </td>
            <td class="text-center" rowspan="1" colspan="1"> </td>
          </tr>
          <tr>
            <td class="text-center" rowspan="1" colspan="1">Interactive Video with or without Audio</td>
            <td class="text-center" rowspan="1" colspan="1">LE (1)</td>
            <td class="text-center" rowspan="1" colspan="1">DF (0)</td>
            <td class="text-center" rowspan="1" colspan="1">AF42, AF43 (36, 38)</td>
            <td class="text-center" rowspan="1" colspan="1">AF41, AF42 (34, 36)</td>
          </tr>
          <tr>
            <td class="text-center" rowspan="1" colspan="1"> </td>
            <td class="text-center" rowspan="1" colspan="1"> </td>
            <td class="text-center" rowspan="1" colspan="1"> </td>
            <td class="text-center" rowspan="1" colspan="1"> </td>
            <td class="text-center" rowspan="1" colspan="1"> </td>
          </tr>
          <tr>
            <td class="text-center" rowspan="1" colspan="1">Non-Interactive Video with or without Audio</td>
            <td class="text-center" rowspan="1" colspan="1">LE (1)</td>
            <td class="text-center" rowspan="1" colspan="1">DF (0)</td>
            <td class="text-center" rowspan="1" colspan="1">AF32, AF33 (28, 30)</td>
            <td class="text-center" rowspan="1" colspan="1">AF31, AF32 (26, 28)</td>
          </tr>
          <tr>
            <td class="text-center" rowspan="1" colspan="1"> </td>
            <td class="text-center" rowspan="1" colspan="1"> </td>
            <td class="text-center" rowspan="1" colspan="1"> </td>
            <td class="text-center" rowspan="1" colspan="1"> </td>
            <td class="text-center" rowspan="1" colspan="1"> </td>
          </tr>
          <tr>
            <td class="text-center" rowspan="1" colspan="1">Data</td>
            <td class="text-center" rowspan="1" colspan="1">LE (1)</td>
            <td class="text-center" rowspan="1" colspan="1">DF (0)</td>
            <td class="text-center" rowspan="1" colspan="1">AF11</td>
            <td class="text-center" rowspan="1" colspan="1">AF21</td>
          </tr>
        </tbody>
      </table>
</div>
<p id="section-5-4">
        The application priority, indicated by the columns "Very Low",
        "Low", "Medium", and "High", signifies the relative importance
        of the flow within the application.  It is an input that the
        browser receives to assist in selecting the DSCP value and
        adjusting the network transport behavior.<a href="#section-5-4" class="pilcrow">¶</a></p>
<p id="section-5-5">
   The above table assumes that packets marked with LE are treated as
   lower effort (i.e., "less than best effort"), such as the LE behavior
   described in <span>[<a href="#RFC8622" class="xref">RFC8622</a>]</span>.  However, the treatment of LE is
   implementation dependent.  If an implementation treats LE as other
   than "less than best effort", then the actual priority (or, more
   precisely, the per-hop behavior) of the packets may be changed from
   what is intended.  It is common for LE to be treated the same as DF,
   so applications and browsers using LE cannot assume that LE will be
   treated differently than DF <span>[<a href="#RFC7657" class="xref">RFC7657</a>]</span>.  During development of this
   document, the CS1 DSCP was recommended for "very low" application
   priority traffic; implementations that followed that recommendation
   <span class="bcp14">SHOULD</span> be updated to use the LE DSCP instead of the CS1 DSCP.<a href="#section-5-5" class="pilcrow">¶</a></p>
<p id="section-5-6">
        Implementers should also note that excess EF traffic is dropped.
        This could mean that a packet marked as EF may not get through, 
        although the same packet marked with a different DSCP value would
        have gotten through.  This is not a flaw, but how excess EF
        traffic is intended to be treated.<a href="#section-5-6" class="pilcrow">¶</a></p>
<p id="section-5-7">
        The browser <span class="bcp14">SHOULD</span> first select the flow type of the flow.
        Within the flow type, the relative importance of the flow
        <span class="bcp14">SHOULD</span> be used to select the appropriate DSCP value.<a href="#section-5-7" class="pilcrow">¶</a></p>
<p id="section-5-8">
        Currently, all WebRTC video is assumed to be interactive
        <span>[<a href="#RFC8835" class="xref">RFC8835</a>]</span>, for which the
        interactive video DSCP values in Table 1 <span class="bcp14">SHOULD</span> be used.
        Browsers <span class="bcp14">MUST NOT</span> use the AF3x DSCP values (for non-interactive
        video in Table 1) for WebRTC applications.  Non-browser
        implementations of WebRTC <span class="bcp14">MAY</span> use the AF3x DSCP values for video
        that is known not to be interactive, e.g., all video in a WebRTC
        video playback application that is not implemented  in a
        browser.<a href="#section-5-8" class="pilcrow">¶</a></p>
<p id="section-5-9">
        The combination of flow type and application priority provides
        specificity and helps in selecting the right DSCP value for the
        flow.  All packets within a flow <span class="bcp14">SHOULD</span> have the same application
        priority.  In some cases, the selected application priority cell
        may have multiple DSCP values, such as AF41 and AF42.  These offer
        different drop precedences.  The different drop precedence
        values provide additional granularity in classifying packets
        within a flow.  For example, in a video conference, the video
        flow may have medium application priority, thus either AF42 or
        AF43 may be selected.  More important video packets (e.g., a
        video picture or frame encoded without any dependency on any
        prior pictures or frames) might be marked with AF42 and less
        important packets (e.g., a video picture or frame encoded based
        on the content of one or more prior pictures or frames) might be
        marked with AF43 (e.g., receipt of the more important packets
        enables a video renderer to continue after one or more packets
        are lost).<a href="#section-5-9" class="pilcrow">¶</a></p>
<p id="section-5-10">
        It is worth noting that the application priority is utilized by
        the coupled congestion control mechanism for media flows per
        <span>[<a href="#RFC8699" class="xref">RFC8699</a>]</span> and the SCTP
        scheduler for data channel traffic per
        <span>[<a href="#RFC8831" class="xref">RFC8831</a>]</span>.<a href="#section-5-10" class="pilcrow">¶</a></p>
<p id="section-5-11">
        For reasons discussed in 
        <span><a href="https://www.rfc-editor.org/rfc/rfc7657#section-6" class="relref">Section 6</a> of [<a href="#RFC7657" class="xref">RFC7657</a>]</span>, if multiple flows are multiplexed
        using a reliable transport (e.g., TCP), then all of the packets
        for all flows multiplexed over that transport-layer flow <span class="bcp14">MUST</span> be
        marked using the same DSCP value.  Likewise, all WebRTC data
        channel packets transmitted over an SCTP association <span class="bcp14">MUST</span> be
        marked using the same DSCP value, regardless of how many data
        channels (streams) exist or what kind of traffic is carried over
        the various SCTP streams.  In the event that the browser wishes
        to change the DSCP value in use for an SCTP association, it <span class="bcp14">MUST</span>
        reset the SCTP congestion controller after changing values.
        However, frequent changes in the DSCP value used for an SCTP association
        are discouraged, as this would defeat any attempts at
        effectively managing congestion.  It should also be noted that
        any change in DSCP value that results in a reset of the
        congestion controller puts the SCTP association back into slow
        start, which may have undesirable effects on application
        performance.<a href="#section-5-11" class="pilcrow">¶</a></p>
<p id="section-5-12">
        For the data channel traffic multiplexed over an SCTP
        association, it is <span class="bcp14">RECOMMENDED</span> that the DSCP value selected be
        the one associated with the highest priority requested for all
        data channels multiplexed over the SCTP association.  Likewise,
        when multiplexing multiple flows over a TCP connection,
        the DSCP value selected <span class="bcp14">SHOULD</span> be the one associated with the
        highest priority requested for all multiplexed flows.<a href="#section-5-12" class="pilcrow">¶</a></p>
<p id="section-5-13"> 
        If a packet enters a network that has no support for a flow-type-application priority combination specified in
        <a href="#tab-dscp" class="xref">Table 1</a>, then the network node at the edge
        will remark the DSCP value based on policies.  This could result
        in the flow not getting the network treatment it expects based
        on the original DSCP value in the packet.  Subsequently, if the
        packet enters a network that supports a larger number of these
        combinations, there may not be sufficient information in the
        packet to restore the original markings.  Mechanisms for
        restoring such original DSCP is outside the scope of this
        document.<a href="#section-5-13" class="pilcrow">¶</a></p>
<p id="section-5-14">
        In summary, DSCP marking provides neither guarantees nor
        promised levels of service.  However, DSCP marking is expected
        to provide a statistical improvement in real-time service as a
        whole.  The service provided to a packet is dependent upon the
        network design along the path, as well as the network conditions
        at every hop.<a href="#section-5-14" class="pilcrow">¶</a></p>
</section>
</div>
<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">
        Since the JavaScript application specifies the flow type and
        application priority that determine the media flow DSCP values
        used by the browser, the browser could consider application use
        of a large number of higher priority flows to be suspicious.
        If the server hosting the JavaScript application is compromised,
        many browsers within the network might simultaneously transmit
        flows with the same DSCP marking.  The Diffserv architecture
        requires ingress traffic conditioning for reasons that include
        protecting the network from this sort of attack.<a href="#section-6-1" class="pilcrow">¶</a></p>
<p id="section-6-2">
        Otherwise, this specification does not add any additional
        security implications beyond those addressed in the following
        DSCP-related specifications.  For security implications on use
        of DSCP, please refer to <span><a href="https://www.rfc-editor.org/rfc/rfc7657#section-7" class="relref">Section 7</a> of [<a href="#RFC7657" class="xref">RFC7657</a>]</span>
        and <span><a href="https://www.rfc-editor.org/rfc/rfc4594#section-6" class="relref">Section 6</a> of [<a href="#RFC4594" class="xref">RFC4594</a>]</span>.  Please also see
        <span>[<a href="#RFC8826" class="xref">RFC8826</a>]</span> as an additional
        reference.<a href="#section-6-2" class="pilcrow">¶</a></p>
</section>
<section id="section-7">
      <h2 id="name-iana-considerations">
<a href="#section-7" class="section-number selfRef">7. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<p id="section-7-1">This document has no IANA actions.<a href="#section-7-1" class="pilcrow">¶</a></p>
</section>
<section id="section-8">
      <h2 id="name-downward-references">
<a href="#section-8" class="section-number selfRef">8. </a><a href="#name-downward-references" class="section-name selfRef">Downward References</a>
      </h2>
<p id="section-8-1">
        This specification contains downwards references to
        <span>[<a href="#RFC4594" class="xref">RFC4594</a>]</span> and <span>[<a href="#RFC7657" class="xref">RFC7657</a>]</span>.  However,
        the parts of the former RFCs used by this specification are
        sufficiently stable for these downward references.  The guidance
        in the latter RFC is necessary to understand the Diffserv
        technology used in this document and the motivation
        for the recommended DSCP values and procedures.<a href="#section-8-1" class="pilcrow">¶</a></p>
</section>
<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="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="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="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="RFC7742">[RFC7742]</dt>
        <dd>
<span class="refAuthor">Roach, A.B.</span>, <span class="refTitle">"WebRTC Video Processing and Codec Requirements"</span>, <span class="seriesInfo">RFC 7742</span>, <span class="seriesInfo">DOI 10.17487/RFC7742</span>, <time datetime="2016-03" class="refDate">March 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7742">https://www.rfc-editor.org/info/rfc7742</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="RFC8622">[RFC8622]</dt>
        <dd>
<span class="refAuthor">Bless, R.</span>, <span class="refTitle">"A Lower-Effort Per-Hop Behavior (LE PHB) for Differentiated Services"</span>, <span class="seriesInfo">RFC 8622</span>, <span class="seriesInfo">DOI 10.17487/RFC8622</span>, <time datetime="2019-06" class="refDate">June 2019</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8622">https://www.rfc-editor.org/info/rfc8622</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="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="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="RFC8835">[RFC8835]</dt>
      <dd>
<span class="refAuthor">Alvestrand, H.</span>, <span class="refTitle">"Transports for WebRTC"</span>, <span class="seriesInfo">RFC 8835</span>, <span class="seriesInfo">DOI 10.17487/RFC8835</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8835">https://www.rfc-editor.org/info/rfc8835</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="G.1010">[G.1010]</dt>
        <dd>
<span class="refAuthor">ITU-T</span>, <span class="refTitle">"End-user multimedia QoS categories"</span>, <span class="seriesInfo">ITU-T Recommendation G.1010</span>, <time datetime="2001-11" class="refDate">November 2001</time>, <span>&lt;<a href="https://www.itu.int/rec/T-REC-G.1010-200111-I/en">https://www.itu.int/rec/T-REC-G.1010-200111-I/en</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC2474">[RFC2474]</dt>
        <dd>
<span class="refAuthor">Nichols, K.</span><span class="refAuthor">, Blake, S.</span><span class="refAuthor">, Baker, F.</span><span class="refAuthor">, and D. Black</span>, <span class="refTitle">"Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers"</span>, <span class="seriesInfo">RFC 2474</span>, <span class="seriesInfo">DOI 10.17487/RFC2474</span>, <time datetime="1998-12" class="refDate">December 1998</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2474">https://www.rfc-editor.org/info/rfc2474</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC2597">[RFC2597]</dt>
        <dd>
<span class="refAuthor">Heinanen, J.</span><span class="refAuthor">, Baker, F.</span><span class="refAuthor">, Weiss, W.</span><span class="refAuthor">, and J. Wroclawski</span>, <span class="refTitle">"Assured Forwarding PHB Group"</span>, <span class="seriesInfo">RFC 2597</span>, <span class="seriesInfo">DOI 10.17487/RFC2597</span>, <time datetime="1999-06" class="refDate">June 1999</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc2597">https://www.rfc-editor.org/info/rfc2597</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3246">[RFC3246]</dt>
        <dd>
<span class="refAuthor">Davie, B.</span><span class="refAuthor">, Charny, A.</span><span class="refAuthor">, Bennet, J.C.R.</span><span class="refAuthor">, Benson, K.</span><span class="refAuthor">, Le Boudec, J.Y.</span><span class="refAuthor">, Courtney, W.</span><span class="refAuthor">, Davari, S.</span><span class="refAuthor">, Firoiu, V.</span><span class="refAuthor">, and D. Stiliadis</span>, <span class="refTitle">"An Expedited Forwarding PHB (Per-Hop Behavior)"</span>, <span class="seriesInfo">RFC 3246</span>, <span class="seriesInfo">DOI 10.17487/RFC3246</span>, <time datetime="2002-03" class="refDate">March 2002</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3246">https://www.rfc-editor.org/info/rfc3246</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC3550">[RFC3550]</dt>
        <dd>
<span class="refAuthor">Schulzrinne, H.</span><span class="refAuthor">, Casner, S.</span><span class="refAuthor">, Frederick, R.</span><span class="refAuthor">, and V. Jacobson</span>, <span class="refTitle">"RTP: A Transport Protocol for Real-Time Applications"</span>, <span class="seriesInfo">STD 64</span>, <span class="seriesInfo">RFC 3550</span>, <span class="seriesInfo">DOI 10.17487/RFC3550</span>, <time datetime="2003-07" class="refDate">July 2003</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc3550">https://www.rfc-editor.org/info/rfc3550</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>
<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">
        Thanks to <span class="contact-name">David Black</span>, <span class="contact-name">Magnus  Westerlund</span>, <span class="contact-name">Paolo Severini</span>, <span class="contact-name">Jim         Hasselbrook</span>, <span class="contact-name">Joe Marcus</span>, <span class="contact-name">Erik  Nordmark</span>, <span class="contact-name">Michael Tüxen</span>, and
        <span class="contact-name">Brian Carpenter</span> for their invaluable input.<a href="#section-appendix.a-1" class="pilcrow">¶</a></p>
</section>
<section id="section-appendix.b">
      <h2 id="name-dedication">
<a href="#name-dedication" class="section-name selfRef">Dedication</a>
      </h2>
<p id="section-appendix.b-1">
        This document is dedicated to the memory of <span class="contact-name">James Polk</span>, a
        long-time friend and colleague.  James made important
        contributions to this specification, including serving initially
        as one of the primary authors.  The IETF global community mourns
        his loss and he will be missed dearly.<a href="#section-appendix.b-1" class="pilcrow">¶</a></p>
</section>
<div id="authors-addresses">
<section id="section-appendix.c">
      <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">Paul E. Jones</span></div>
<div dir="auto" class="left"><span class="org">Cisco Systems</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:paulej@packetizer.com" class="email">paulej@packetizer.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Subha Dhesikan</span></div>
<div dir="auto" class="left"><span class="org">Individual</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:sdhesikan@gmail.com" class="email">sdhesikan@gmail.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Cullen Jennings</span></div>
<div dir="auto" class="left"><span class="org">Cisco Systems</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:fluffy@cisco.com" class="email">fluffy@cisco.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Dan Druta</span></div>
<div dir="auto" class="left"><span class="org">AT&amp;T</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:dd5826@att.com" class="email">dd5826@att.com</a>
</div>
</address>
</section>
</div>
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