File: rfc8852.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 8852: RTP Stream Identifier Source Description (SDES)</title>
<meta content="Adam Roach" name="author">
<meta content="Suhas Nandakumar" name="author">
<meta content="Peter Thatcher" name="author">
<meta content="
       
   This document defines and registers two new Real-time Transport Control
   Protocol (RTCP) Stream Identifier
   Source Description (SDES) items.  One, named RtpStreamId, is used for
   unique identification of RTP streams.  The other,
   RepairedRtpStreamId, can be used to identify which stream is to be repaired
   using a redundancy RTP stream. 
    " name="description">
<meta content="xml2rfc 3.5.0" name="generator">
<meta content="WebRTC" name="keyword">
<meta content="Multiplexing" name="keyword">
<meta content="8852" 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="rfc8852.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;
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<table class="ears">
<thead><tr>
<td class="left">RFC 8852</td>
<td class="center">RtpStreamId SDES</td>
<td class="right">January 2021</td>
</tr></thead>
<tfoot><tr>
<td class="left">Roach, 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/rfc8852" class="eref">8852</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">A.B. Roach</div>
<div class="org">Mozilla</div>
</div>
<div class="author">
      <div class="author-name">S. Nandakumar</div>
<div class="org">Cisco Systems</div>
</div>
<div class="author">
      <div class="author-name">P. Thatcher</div>
<div class="org">Google</div>
</div>
</dd>
</dl>
</div>
<h1 id="rfcnum">RFC 8852</h1>
<h1 id="title">RTP Stream Identifier Source Description (SDES)</h1>
<section id="section-abstract">
      <h2 id="abstract"><a href="#abstract" class="selfRef">Abstract</a></h2>
<p id="section-abstract-1">
   This document defines and registers two new Real-time Transport Control
   Protocol (RTCP) Stream Identifier
   Source Description (SDES) items.  One, named RtpStreamId, is used for
   unique identification of RTP streams.  The other,
   RepairedRtpStreamId, can be used to identify which stream is to be repaired
   using a redundancy RTP stream.<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/rfc8852">https://www.rfc-editor.org/info/rfc8852</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 ulEmpty toc">
<li class="compact ulEmpty 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="compact ulEmpty 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="compact ulEmpty toc" 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-usage-of-rtpstreamid-and-re" class="xref">Usage of RtpStreamId and RepairedRtpStreamId in RTP and RTCP</a><a href="#section-toc.1-1.3.1" class="pilcrow">¶</a></p>
<ul class="compact ulEmpty toc">
<li class="compact ulEmpty toc" 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-rtcp-rtpstreamid-sdes-exten" class="xref">RTCP "RtpStreamId" SDES Extension</a><a href="#section-toc.1-1.3.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" 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-rtcp-repairedrtpstreamid-sd" class="xref">RTCP "RepairedRtpStreamId" SDES Extension</a><a href="#section-toc.1-1.3.2.2.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" 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-rtp-rtpstreamid-and-repaire" class="xref">RTP "RtpStreamId" and "RepairedRtpStreamId" Header Extensions</a><a href="#section-toc.1-1.3.2.3.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="compact ulEmpty 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-iana-considerations" class="xref">IANA Considerations</a><a href="#section-toc.1-1.4.1" class="pilcrow">¶</a></p>
<ul class="compact ulEmpty toc">
<li class="compact ulEmpty toc" 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-new-rtpstreamid-sdes-item" class="xref">New RtpStreamId SDES Item</a><a href="#section-toc.1-1.4.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" 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-new-repairrtpstreamid-sdes-" class="xref">New RepairRtpStreamId SDES Item</a><a href="#section-toc.1-1.4.2.2.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.4.2.3">
                <p id="section-toc.1-1.4.2.3.1"><a href="#section-4.3" class="xref">4.3</a>.  <a href="#name-new-rtpstreamid-header-exte" class="xref">New RtpStreamId Header Extension URI</a><a href="#section-toc.1-1.4.2.3.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.4.2.4">
                <p id="section-toc.1-1.4.2.4.1"><a href="#section-4.4" class="xref">4.4</a>.  <a href="#name-new-repairrtpstreamid-heade" class="xref">New RepairRtpStreamId Header Extension URI</a><a href="#section-toc.1-1.4.2.4.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="compact ulEmpty 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-security-considerations" class="xref">Security Considerations</a><a href="#section-toc.1-1.5.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact ulEmpty 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-references" class="xref">References</a><a href="#section-toc.1-1.6.1" class="pilcrow">¶</a></p>
<ul class="compact ulEmpty toc">
<li class="compact ulEmpty toc" id="section-toc.1-1.6.2.1">
                <p id="section-toc.1-1.6.2.1.1"><a href="#section-6.1" class="xref">6.1</a>.  <a href="#name-normative-references" class="xref">Normative References</a><a href="#section-toc.1-1.6.2.1.1" class="pilcrow">¶</a></p>
</li>
              <li class="compact ulEmpty toc" id="section-toc.1-1.6.2.2">
                <p id="section-toc.1-1.6.2.2.1"><a href="#section-6.2" class="xref">6.2</a>.  <a href="#name-informative-references" class="xref">Informative References</a><a href="#section-toc.1-1.6.2.2.1" class="pilcrow">¶</a></p>
</li>
            </ul>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.7">
            <p id="section-toc.1-1.7.1"><a href="#section-appendix.a" class="xref"></a><a href="#name-acknowledgements" class="xref">Acknowledgements</a><a href="#section-toc.1-1.7.1" class="pilcrow">¶</a></p>
</li>
          <li class="compact ulEmpty toc" id="section-toc.1-1.8">
            <p id="section-toc.1-1.8.1"><a href="#section-appendix.b" class="xref"></a><a href="#name-authors-addresses" class="xref">Authors' Addresses</a><a href="#section-toc.1-1.8.1" class="pilcrow">¶</a></p>
</li>
        </ul>
</nav>
</section>
</div>
<div id="intro">
<section id="section-1">
      <h2 id="name-introduction">
<a href="#section-1" class="section-number selfRef">1. </a><a href="#name-introduction" class="section-name selfRef">Introduction</a>
      </h2>
<p id="section-1-1">
   RTP sessions frequently consist of multiple streams, each of which is
   identified at any given time by its synchronization source (SSRC); however,
   the SSRC associated with a stream is not guaranteed to be stable over its
   lifetime.  Within a session, these streams can be tagged with a
   number of identifiers, including CNAMEs and MediaStream Identification
   (MSID) <span>[<a href="#RFC8830" class="xref">RFC8830</a>]</span>.
   Unfortunately, none of these have the proper
   ordinality to refer to an individual stream; all such identifiers can
   appear in more than one stream at a time.  While approaches that use
   unique payload types (PTs) per stream have been used in some
   applications, this is a semantic overloading of that field, and one
   for which its size is inadequate: in moderately complex systems that
   use PT to uniquely identify every potential combination of codec
   configuration and unique stream, it is possible to simply run out of
   values.<a href="#section-1-1" class="pilcrow">¶</a></p>
<p id="section-1-2">
   To address this situation, we define a new RTCP Stream Identifier
   Source Description (SDES) identifier, RtpStreamId, that uniquely
   identifies a single RTP stream.  A key motivator for defining this
   identifier is the ability to differentiate among different encodings
   of a single source stream that are sent simultaneously (i.e.,
   simulcast).  This need for unique identification extends to dependent
   streams (e.g., where layers used by a layered codec are transmitted
   on separate streams).<a href="#section-1-2" class="pilcrow">¶</a></p>
<p id="section-1-3">
   At the same time, when redundancy RTP streams are in use, we also
   need an identifier that connects such streams to the RTP stream for
   which they are providing redundancy.  For this purpose, we define an
   additional SDES identifier, RepairedRtpStreamId.  This identifier can
   appear only in packets associated with a redundancy RTP stream.  They
   carry the same value as the RtpStreamId of the RTP stream that the
   redundant RTP stream is correcting.<a href="#section-1-3" class="pilcrow">¶</a></p>
</section>
</div>
<div id="terminology">
<section id="section-2">
      <h2 id="name-terminology">
<a href="#section-2" class="section-number selfRef">2. </a><a href="#name-terminology" class="section-name selfRef">Terminology</a>
      </h2>
<p id="section-2-1">
   In this document, the terms "source stream", "RTP stream", "source RTP stream", "dependent stream", "received RTP stream", and
   "redundancy RTP stream" are used as defined in <span>[<a href="#RFC7656" class="xref">RFC7656</a>]</span>.<a href="#section-2-1" class="pilcrow">¶</a></p>
<p id="section-2-2">
   The following acronyms are also used:<a href="#section-2-2" class="pilcrow">¶</a></p>
<ul class="normal">
<li class="normal" id="section-2-3.1">CNAME: Canonical Endpoint Identifier, defined in <span>[<a href="#RFC3550" class="xref">RFC3550</a>]</span><a href="#section-2-3.1" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-2-3.2">MID: Media Identification, defined in
      <span>[<a href="#RFC8843" class="xref">RFC8843</a>]</span><a href="#section-2-3.2" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-2-3.3">MSID: MediaStream Identification, defined in <span>[<a href="#RFC8830" class="xref">RFC8830</a>]</span><a href="#section-2-3.3" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-2-3.4">RTCP: Real-time Transport Control Protocol, defined in <span>[<a href="#RFC3550" class="xref">RFC3550</a>]</span><a href="#section-2-3.4" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-2-3.5">RTP: Real-time Transport Protocol, defined in <span>[<a href="#RFC3550" class="xref">RFC3550</a>]</span><a href="#section-2-3.5" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-2-3.6">SDES: Source Description, defined in <span>[<a href="#RFC3550" class="xref">RFC3550</a>]</span><a href="#section-2-3.6" class="pilcrow">¶</a>
</li>
        <li class="normal" id="section-2-3.7">SSRC: Synchronization Source, defined in <span>[<a href="#RFC3550" class="xref">RFC3550</a>]</span><a href="#section-2-3.7" class="pilcrow">¶</a>
</li>
      </ul>
</section>
</div>
<div id="StreamId">
<section id="section-3">
      <h2 id="name-usage-of-rtpstreamid-and-re">
<a href="#section-3" class="section-number selfRef">3. </a><a href="#name-usage-of-rtpstreamid-and-re" class="section-name selfRef">Usage of RtpStreamId and RepairedRtpStreamId in RTP and RTCP</a>
      </h2>
<p id="section-3-1">
   The RTP fixed header includes the payload type number and the SSRC
   values of the RTP stream.  RTP defines how to demultiplex streams
   within an RTP session; however, in some use cases, applications need
   further identifiers in order to effectively map the individual RTP
   streams to their equivalent payload configurations in the SDP.<a href="#section-3-1" class="pilcrow">¶</a></p>
<p id="section-3-2">
   This specification defines two new RTCP SDES items <span>[<a href="#RFC3550" class="xref">RFC3550</a>]</span>.  The
   first item is "RtpStreamId", which is used to carry RTP stream
   identifiers within RTCP SDES packets.  This makes it possible for a
   receiver to associate received RTP packets (identifying the RTP
   stream) with a media description having the format constraint
   specified.  The second is "RepairedRtpStreamId", which can be used in
   redundancy RTP streams to indicate the RTP stream repaired by a
   redundancy RTP stream.<a href="#section-3-2" class="pilcrow">¶</a></p>
<p id="section-3-3">
   To be clear: the value carried in a RepairedRtpStreamId will always
   match the RtpStreamId value from another RTP stream in the same
   session.  For example, if a source RTP stream is identified by
   RtpStreamId "A", then any redundancy RTP stream that repairs that
   source RTP stream will contain a RepairedRtpStreamId of "A" (if this
   mechanism is being used to perform such correlation).  These
   redundant RTP streams may also contain their own unique RtpStreamId.<a href="#section-3-3" class="pilcrow">¶</a></p>
<p id="section-3-4">
   This specification also uses the RTP header extension for RTCP SDES
   items <span>[<a href="#RFC7941" class="xref">RFC7941</a>]</span> to allow carrying RtpStreamId
   and RepairedRtpStreamId values in RTP packets.  This allows
   correlation at stream startup, or after stream changes where the use
   of RTCP may not be sufficiently responsive.  This speed of response
   is necessary since, in many cases, the stream cannot be properly
   processed until it can be identified.<a href="#section-3-4" class="pilcrow">¶</a></p>
<p id="section-3-5">
   RtpStreamId and RepairedRtpStreamId values are scoped by source
   identifier (e.g., CNAME) and by media session.  When the media is
   multiplexed using the BUNDLE extension
   <span>[<a href="#RFC8843" class="xref">RFC8843</a>]</span>, these values are further
   scoped by their associated MID values.  For example: an RtpStreamId
   of "1" may be present in the stream identified with a CNAME of
   "1234@example.com" and may also be present in a stream with a CNAME
   of "5678@example.org", and these would refer to different streams.
   Similarly, an RtpStreamId of "1" may be present with an MID of "A",
   and again with a MID of "B", and also refer to two different streams.<a href="#section-3-5" class="pilcrow">¶</a></p>
<p id="section-3-6">
   Note that the RepairedRtpStreamId mechanism is limited to indicating
   one repaired stream per redundancy stream.  If systems require
   correlation for schemes in which a redundancy stream contains
   information used to repair more than one stream, they will have to
   use a more complex mechanism than the one defined in this
   specification.<a href="#section-3-6" class="pilcrow">¶</a></p>
<p id="section-3-7">
   As with all SDES items, RtpStreamId and RepairedRtpStreamId are
   limited to a total of 255 octets in length.  RtpStreamId and
   RepairedRtpStreamId are constrained to contain only alphanumeric
   characters.  For avoidance of doubt, the only allowed byte values for
   these IDs are decimal 48 through 57, 65 through 90, and 97 through
   122.<a href="#section-3-7" class="pilcrow">¶</a></p>
<div id="RtpStreamId-ext">
<section id="section-3.1">
        <h3 id="name-rtcp-rtpstreamid-sdes-exten">
<a href="#section-3.1" class="section-number selfRef">3.1. </a><a href="#name-rtcp-rtpstreamid-sdes-exten" class="section-name selfRef">RTCP "RtpStreamId" SDES Extension</a>
        </h3>
<div class="artwork art-text alignLeft" id="section-3.1-1">
<pre>
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |RtpStreamId=12 |     length    | RtpStreamId                 ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</pre><a href="#section-3.1-1" class="pilcrow">¶</a>
</div>
<p id="section-3.1-2">
The RtpStreamId payload is ASCII encoded and is not null terminated.<a href="#section-3.1-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="Repaired-ext">
<section id="section-3.2">
        <h3 id="name-rtcp-repairedrtpstreamid-sd">
<a href="#section-3.2" class="section-number selfRef">3.2. </a><a href="#name-rtcp-repairedrtpstreamid-sd" class="section-name selfRef">RTCP "RepairedRtpStreamId" SDES Extension</a>
        </h3>
<div class="artwork art-text alignLeft" id="section-3.2-1">
<pre>
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |Repaired...=13 |     length    | RepairRtpStreamId           ...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+</pre><a href="#section-3.2-1" class="pilcrow">¶</a>
</div>
<p id="section-3.2-2">
The RepairedRtpStreamId payload is ASCII encoded and is not null terminated.<a href="#section-3.2-2" class="pilcrow">¶</a></p>
</section>
</div>
<div id="Header-ext">
<section id="section-3.3">
        <h3 id="name-rtp-rtpstreamid-and-repaire">
<a href="#section-3.3" class="section-number selfRef">3.3. </a><a href="#name-rtp-rtpstreamid-and-repaire" class="section-name selfRef">RTP "RtpStreamId" and "RepairedRtpStreamId" Header Extensions</a>
        </h3>
<p id="section-3.3-1">
   Because recipients of RTP packets will typically need to know which
   streams they correspond to immediately upon receipt, this
   specification also defines a means of carrying RtpStreamId and
   RepairedRtpStreamId identifiers in RTP extension headers, using the
   technique described in <span>[<a href="#RFC7941" class="xref">RFC7941</a>]</span>.<a href="#section-3.3-1" class="pilcrow">¶</a></p>
<p id="section-3.3-2">
   As described in that document, the header extension element can be
   encoded using either the one-byte or two-byte header, and the
   identification-tag payload is ASCII encoded.<a href="#section-3.3-2" class="pilcrow">¶</a></p>
<p id="section-3.3-3">
   As the identifier is included in an RTP header extension, there
   should be some consideration given to the packet expansion caused by
   the identifier.  To avoid Maximum Transmission Unit (MTU) issues for
   the RTP packets, the header extension's size needs to be taken into
   account when encoding media.  Note that the set of header extensions
   included in the packet needs to be padded to the next 32-bit boundary
   <span>[<a href="#RFC8285" class="xref">RFC8285</a>]</span>.<a href="#section-3.3-3" class="pilcrow">¶</a></p>
<p id="section-3.3-4">
   In many cases, a one-byte identifier will be sufficient to
   distinguish streams in a session; implementations are strongly
   encouraged to use the shortest identifier that fits their purposes.
   Implementors are warned, in particular, not to include any
   information in the identifier that is derived from potentially user-
   identifying information, such as user ID or IP address.  To avoid
   identification of specific implementations based on their pattern of
   tag generation, implementations are encouraged to use a simple scheme
   that starts with the ASCII digit "1", and increments by one for each
   subsequent identifier.<a href="#section-3.3-4" class="pilcrow">¶</a></p>
</section>
</div>
</section>
</div>
<div id="IANA">
<section id="section-4">
      <h2 id="name-iana-considerations">
<a href="#section-4" class="section-number selfRef">4. </a><a href="#name-iana-considerations" class="section-name selfRef">IANA Considerations</a>
      </h2>
<div id="New-RtpStreamId">
<section id="section-4.1">
        <h3 id="name-new-rtpstreamid-sdes-item">
<a href="#section-4.1" class="section-number selfRef">4.1. </a><a href="#name-new-rtpstreamid-sdes-item" class="section-name selfRef">New RtpStreamId SDES Item</a>
        </h3>
<p id="section-4.1-1">
   This document adds the RtpStreamId SDES item to the IANA "RTP SDES Item
 Types" registry as follows:<a href="#section-4.1-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel dlCompact" id="section-4.1-2">
          <dt id="section-4.1-2.1">Value:</dt>
          <dd style="margin-left: 6.0em" id="section-4.1-2.2">12<a href="#section-4.1-2.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-4.1-2.3">Abbrev.:</dt>
          <dd style="margin-left: 6.0em" id="section-4.1-2.4">RtpStreamId<a href="#section-4.1-2.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-4.1-2.5">Name:</dt>
          <dd style="margin-left: 6.0em" id="section-4.1-2.6">RTP Stream Identifier<a href="#section-4.1-2.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-4.1-2.7">Reference:</dt>
          <dd style="margin-left: 6.0em" id="section-4.1-2.8">RFC 8852<a href="#section-4.1-2.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
</section>
</div>
<div id="New-Repair">
<section id="section-4.2">
        <h3 id="name-new-repairrtpstreamid-sdes-">
<a href="#section-4.2" class="section-number selfRef">4.2. </a><a href="#name-new-repairrtpstreamid-sdes-" class="section-name selfRef">New RepairRtpStreamId SDES Item</a>
        </h3>
<p id="section-4.2-1">
   This document adds the RepairedRtpStreamId SDES item to the IANA "RTP SDES
 Item Types" registry as follows:<a href="#section-4.2-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel dlCompact" id="section-4.2-2">
          <dt id="section-4.2-2.1">Value:</dt>
          <dd style="margin-left: 6.0em" id="section-4.2-2.2">13<a href="#section-4.2-2.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-4.2-2.3">Abbrev.:</dt>
          <dd style="margin-left: 6.0em" id="section-4.2-2.4">RepairedRtpStreamId<a href="#section-4.2-2.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-4.2-2.5">Name:</dt>
          <dd style="margin-left: 6.0em" id="section-4.2-2.6">Repaired RTP Stream Identifier<a href="#section-4.2-2.6" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-4.2-2.7">Reference:</dt>
          <dd style="margin-left: 6.0em" id="section-4.2-2.8">RFC 8852<a href="#section-4.2-2.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
</section>
</div>
<div id="New-Str-header">
<section id="section-4.3">
        <h3 id="name-new-rtpstreamid-header-exte">
<a href="#section-4.3" class="section-number selfRef">4.3. </a><a href="#name-new-rtpstreamid-header-exte" class="section-name selfRef">New RtpStreamId Header Extension URI</a>
        </h3>
<p id="section-4.3-1">
   This document defines a new extension URI in the "RTP SDES Compact
   Header Extensions" subregistry of the "RTP Compact Header Extensions"
   subregistry, as follows:<a href="#section-4.3-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel dlCompact" id="section-4.3-2">
          <dt id="section-4.3-2.1">Extension URI:</dt>
          <dd style="margin-left: 1.5em" id="section-4.3-2.2">urn:ietf:params:rtp-hdrext:sdes:rtp-stream-id<a href="#section-4.3-2.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-4.3-2.3">Description:</dt>
          <dd style="margin-left: 1.5em" id="section-4.3-2.4">RTP Stream Identifier<a href="#section-4.3-2.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-4.3-2.5">Contact:</dt>
          <dd style="margin-left: 1.5em" id="section-4.3-2.6">
            <p id="section-4.3-2.6.1"><span class="contact-name">Adam Roach</span> &lt;adam@nostrum.com&gt;<a href="#section-4.3-2.6.1" class="pilcrow">¶</a></p>
</dd>
          <dd class="break"></dd>
<dt id="section-4.3-2.7">Reference:</dt>
          <dd style="margin-left: 1.5em" id="section-4.3-2.8">RFC 8852<a href="#section-4.3-2.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
</section>
</div>
<div id="New-Repair-Header">
<section id="section-4.4">
        <h3 id="name-new-repairrtpstreamid-heade">
<a href="#section-4.4" class="section-number selfRef">4.4. </a><a href="#name-new-repairrtpstreamid-heade" class="section-name selfRef">New RepairRtpStreamId Header Extension URI</a>
        </h3>
<p id="section-4.4-1">
   This document defines a new extension URI in the "RTP SDES Compact
   Header Extensions" subregistry of the "RTP Compact Header Extensions"
   subregistry, as follows:<a href="#section-4.4-1" class="pilcrow">¶</a></p>
<span class="break"></span><dl class="dlParallel dlCompact" id="section-4.4-2">
          <dt id="section-4.4-2.1">Extension URI:</dt>
          <dd style="margin-left: 1.5em" id="section-4.4-2.2">urn:ietf:params:rtp-hdrext:sdes:repaired-rtp-stream-id<a href="#section-4.4-2.2" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-4.4-2.3">Description:</dt>
          <dd style="margin-left: 1.5em" id="section-4.4-2.4">RTP Repaired Stream Identifier<a href="#section-4.4-2.4" class="pilcrow">¶</a>
</dd>
          <dd class="break"></dd>
<dt id="section-4.4-2.5">Contact:</dt>
          <dd style="margin-left: 1.5em" id="section-4.4-2.6">
            <p id="section-4.4-2.6.1"><span class="contact-name">Adam Roach</span> &lt;adam@nostrum.com&gt;<a href="#section-4.4-2.6.1" class="pilcrow">¶</a></p>
</dd>
          <dd class="break"></dd>
<dt id="section-4.4-2.7">Reference:</dt>
          <dd style="margin-left: 1.5em" id="section-4.4-2.8">RFC 8852<a href="#section-4.4-2.8" class="pilcrow">¶</a>
</dd>
        <dd class="break"></dd>
</dl>
</section>
</div>
</section>
</div>
<div id="Security">
<section id="section-5">
      <h2 id="name-security-considerations">
<a href="#section-5" class="section-number selfRef">5. </a><a href="#name-security-considerations" class="section-name selfRef">Security Considerations</a>
      </h2>
<p id="section-5-1">
   Although the identifiers defined in this document are limited to be
   strictly alphanumeric, SDES items have the potential to carry any
   string.  As a consequence, there exists a risk that they might carry
   privacy-sensitive information.  Implementations need to take care
   when generating identifiers so that they do not contain information
   that can identify the user or allow for long-term tracking of the
   device.  Following the generation recommendations in <a href="#Header-ext" class="xref">Section 3.3</a> will
   result in non-instance-specific labels, with only minor
   fingerprinting possibilities in the total number of used RtpStreamIds
   and RepairedRtpStreamIds.<a href="#section-5-1" class="pilcrow">¶</a></p>
<p id="section-5-2">
   Even if the SDES items are generated to convey as little information
   as possible, implementors are strongly encouraged to encrypt SDES
   items -- both in RTCP and RTP header extensions -- so as to preserve
   privacy against third parties.<a href="#section-5-2" class="pilcrow">¶</a></p>
<p id="section-5-3">
   As the SDES items are used for identification of the RTP streams for
   different application purposes, it is important that the intended
   values are received.  An attacker, either a third party or malicious
   RTP middlebox, that removes or changes the values for these SDES
   items can severely impact the application.  The impact can include
   failure to decode or display the media content of the RTP stream.  It
   can also result in incorrectly attributing media content to
   identifiers of the media source, such as incorrectly identifying the
   speaker.  To prevent this from occurring due to third-party attacks,
   integrity and source authentication is needed.<a href="#section-5-3" class="pilcrow">¶</a></p>
<p id="section-5-4">
   "Options for Securing RTP Sessions" <span>[<a href="#RFC7201" class="xref">RFC7201</a>]</span> discusses options for how
   encryption, integrity, and source authentication can be accomplished.<a href="#section-5-4" class="pilcrow">¶</a></p>
</section>
</div>
<section id="section-6">
      <h2 id="name-references">
<a href="#section-6" class="section-number selfRef">6. </a><a href="#name-references" class="section-name selfRef">References</a>
      </h2>
<section id="section-6.1">
        <h3 id="name-normative-references">
<a href="#section-6.1" class="section-number selfRef">6.1. </a><a href="#name-normative-references" class="section-name selfRef">Normative References</a>
        </h3>
<dl class="references">
<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="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="RFC7941">[RFC7941]</dt>
        <dd>
<span class="refAuthor">Westerlund, M.</span><span class="refAuthor">, Burman, B.</span><span class="refAuthor">, Even, R.</span><span class="refAuthor">, and M. Zanaty</span>, <span class="refTitle">"RTP Header Extension for the RTP Control Protocol (RTCP) Source Description Items"</span>, <span class="seriesInfo">RFC 7941</span>, <span class="seriesInfo">DOI 10.17487/RFC7941</span>, <time datetime="2016-08" class="refDate">August 2016</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7941">https://www.rfc-editor.org/info/rfc7941</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8285">[RFC8285]</dt>
        <dd>
<span class="refAuthor">Singer, D.</span><span class="refAuthor">, Desineni, H.</span><span class="refAuthor">, and R. Even, Ed.</span>, <span class="refTitle">"A General Mechanism for RTP Header Extensions"</span>, <span class="seriesInfo">RFC 8285</span>, <span class="seriesInfo">DOI 10.17487/RFC8285</span>, <time datetime="2017-10" class="refDate">October 2017</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8285">https://www.rfc-editor.org/info/rfc8285</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8843">[RFC8843]</dt>
      <dd>
<span class="refAuthor">Holmberg, C.</span><span class="refAuthor">, Alvestrand, H.</span><span class="refAuthor">, and C. Jennings</span>, <span class="refTitle">"Negotiating Media Multiplexing Using the Session Description Protocol (SDP)"</span>, <span class="seriesInfo">RFC 8843</span>, <span class="seriesInfo">DOI 10.17487/RFC8843</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8843">https://www.rfc-editor.org/info/rfc8843</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
<section id="section-6.2">
        <h3 id="name-informative-references">
<a href="#section-6.2" class="section-number selfRef">6.2. </a><a href="#name-informative-references" class="section-name selfRef">Informative References</a>
        </h3>
<dl class="references">
<dt id="RFC7201">[RFC7201]</dt>
        <dd>
<span class="refAuthor">Westerlund, M.</span><span class="refAuthor"> and C. Perkins</span>, <span class="refTitle">"Options for Securing RTP Sessions"</span>, <span class="seriesInfo">RFC 7201</span>, <span class="seriesInfo">DOI 10.17487/RFC7201</span>, <time datetime="2014-04" class="refDate">April 2014</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc7201">https://www.rfc-editor.org/info/rfc7201</a>&gt;</span>. </dd>
<dd class="break"></dd>
<dt id="RFC8830">[RFC8830]</dt>
      <dd>
<span class="refAuthor">Alvestrand, H.</span>, <span class="refTitle">"WebRTC MediaStream Identification in the Session Description Protocol"</span>, <span class="seriesInfo">RFC 8830</span>, <span class="seriesInfo">DOI 10.17487/RFC8830</span>, <time datetime="2021-01" class="refDate">January 2021</time>, <span>&lt;<a href="https://www.rfc-editor.org/info/rfc8830">https://www.rfc-editor.org/info/rfc8830</a>&gt;</span>. </dd>
<dd class="break"></dd>
</dl>
</section>
</section>
<div id="Ack">
<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">
   Many thanks to <span class="contact-name">Cullen Jennings</span>, <span class="contact-name">Magnus Westerlund</span>, <span class="contact-name">Colin Perkins</span>,
   <span class="contact-name">Jonathan Lennox</span>, and <span class="contact-name">Paul    Kyzivat</span> for review and input.  <span class="contact-name">Magnus Westerlund</span>
   provided nearly all of the Security Considerations section.<a href="#section-appendix.a-1" class="pilcrow">¶</a></p>
</section>
</div>
<div id="authors-addresses">
<section id="section-appendix.b">
      <h2 id="name-authors-addresses">
<a href="#name-authors-addresses" class="section-name selfRef">Authors' Addresses</a>
      </h2>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Adam Roach</span></div>
<div dir="auto" class="left"><span class="org">Mozilla</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:adam@nostrum.com" class="email">adam@nostrum.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Suhas Nandakumar</span></div>
<div dir="auto" class="left"><span class="org">Cisco Systems</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:snandaku@cisco.com" class="email">snandaku@cisco.com</a>
</div>
</address>
<address class="vcard">
        <div dir="auto" class="left"><span class="fn nameRole">Peter Thatcher</span></div>
<div dir="auto" class="left"><span class="org">Google</span></div>
<div class="email">
<span>Email:</span>
<a href="mailto:pthatcher@google.com" class="email">pthatcher@google.com</a>
</div>
</address>
</section>
</div>
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