<?xml version='1.0' encoding='utf-8'?>
<rfc xmlns:xi="http://www.w3.org/2001/XInclude" version="3" category="exp" docName="draft-ietf-avtext-framemarking-16" number="9626" consensus="true" updates="" obsoletes="" ipr="trust200902" submissionType="IETF" symRefs="true" sortRefs="true" tocInclude="true" tocDepth="4" xml:lang="en" prepTime="2025-03-27T17:04:02" indexInclude="true" scripts="Common,Latin">
  <link href="https://datatracker.ietf.org/doc/draft-ietf-avtext-framemarking-16" rel="prev"/>
  <link href="https://dx.doi.org/10.17487/rfc9626" rel="alternate"/>
  <link href="urn:issn:2070-1721" rel="alternate"/>
  <front>
    <title abbrev="Video Frame Marking">Video Frame Marking RTP Header Extension</title>
    <seriesInfo name="RFC" value="9626" stream="IETF"/>
    <author fullname="Mo Zanaty" initials="M" surname="Zanaty">
      <organization showOnFrontPage="true">Cisco Systems</organization>
      <address>
        <postal>
          <street>170 West Tasman Drive</street>
          <city>San Jose</city>
          <region>CA</region>
          <code>95134</code>
          <country>United States of America</country>
        </postal>
        <email>mzanaty@cisco.com</email>
      </address>
    </author>
    <author initials="E." surname="Berger" fullname="Espen Berger">
      <organization showOnFrontPage="true">Cisco Systems</organization>
      <address>
        <email>espeberg@cisco.com</email>
      </address>
    </author>
    <author fullname="Suhas Nandakumar" initials="S" surname="Nandakumar">
      <organization showOnFrontPage="true">Cisco Systems</organization>
      <address>
        <postal>
          <street>170 West Tasman Drive</street>
          <city>San Jose</city>
          <region>CA</region>
          <code>95134</code>
          <country>United States of America</country>
        </postal>
        <email>snandaku@cisco.com</email>
      </address>
    </author>
    <date month="03" year="2025"/>
    <area>WIT</area>
    <workgroup>avtcore</workgroup>
    <abstract pn="section-abstract">
      <t indent="0" pn="section-abstract-1">This document describes a Video Frame Marking RTP header extension used to
      convey information about video frames that is critical for error recovery
      and packet forwarding in RTP middleboxes or network nodes. It is most
      useful when media is encrypted and essential when the middlebox or node
      has no access to the media decryption keys. It is also useful for
      codec-agnostic processing of encrypted or unencrypted media, while it also
      supports extensions for codec-specific information.</t>
    </abstract>
    <boilerplate>
      <section anchor="status-of-memo" numbered="false" removeInRFC="false" toc="exclude" pn="section-boilerplate.1">
        <name slugifiedName="name-status-of-this-memo">Status of This Memo</name>
        <t indent="0" pn="section-boilerplate.1-1">
            This document is not an Internet Standards Track specification; it is
            published for examination, experimental implementation, and
            evaluation.
        </t>
        <t indent="0" pn="section-boilerplate.1-2">
            This document defines an Experimental Protocol for the Internet
            community.  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).  Not all documents
            approved by the IESG are candidates for any level of Internet
            Standard; see Section 2 of RFC 7841. 
        </t>
        <t indent="0" pn="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
            <eref target="https://www.rfc-editor.org/info/rfc9626" brackets="none"/>.
        </t>
      </section>
      <section anchor="copyright" numbered="false" removeInRFC="false" toc="exclude" pn="section-boilerplate.2">
        <name slugifiedName="name-copyright-notice">Copyright Notice</name>
        <t indent="0" pn="section-boilerplate.2-1">
            Copyright (c) 2025 IETF Trust and the persons identified as the
            document authors. All rights reserved.
        </t>
        <t indent="0" pn="section-boilerplate.2-2">
            This document is subject to BCP 78 and the IETF Trust's Legal
            Provisions Relating to IETF Documents
            (<eref target="https://trustee.ietf.org/license-info" brackets="none"/>) in effect on the date of
            publication of this document. Please review these documents
            carefully, as they describe your rights and restrictions with
            respect to this document. Code Components extracted from this
            document must include Revised BSD License text as described in
            Section 4.e of the Trust Legal Provisions and are provided without
            warranty as described in the Revised BSD License.
        </t>
      </section>
    </boilerplate>
    <toc>
      <section anchor="toc" numbered="false" removeInRFC="false" toc="exclude" pn="section-toc.1">
        <name slugifiedName="name-table-of-contents">Table of Contents</name>
        <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1">
          <li pn="section-toc.1-1.1">
            <t indent="0" keepWithNext="true" pn="section-toc.1-1.1.1"><xref derivedContent="1" format="counter" sectionFormat="of" target="section-1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-introduction">Introduction</xref></t>
          </li>
          <li pn="section-toc.1-1.2">
            <t indent="0" keepWithNext="true" pn="section-toc.1-1.2.1"><xref derivedContent="2" format="counter" sectionFormat="of" target="section-2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-requirements-language">Requirements Language</xref></t>
          </li>
          <li pn="section-toc.1-1.3">
            <t indent="0" pn="section-toc.1-1.3.1"><xref derivedContent="3" format="counter" sectionFormat="of" target="section-3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-video-frame-marking-rtp-hea">Video Frame Marking RTP Header Extension</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.3.2">
              <li pn="section-toc.1-1.3.2.1">
                <t indent="0" keepWithNext="true" pn="section-toc.1-1.3.2.1.1"><xref derivedContent="3.1" format="counter" sectionFormat="of" target="section-3.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-long-extension-for-scalable">Long Extension for Scalable Streams</xref></t>
              </li>
              <li pn="section-toc.1-1.3.2.2">
                <t indent="0" pn="section-toc.1-1.3.2.2.1"><xref derivedContent="3.2" format="counter" sectionFormat="of" target="section-3.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-short-extension-for-non-sca">Short Extension for Non-Scalable Streams</xref></t>
              </li>
              <li pn="section-toc.1-1.3.2.3">
                <t indent="0" pn="section-toc.1-1.3.2.3.1"><xref derivedContent="3.3" format="counter" sectionFormat="of" target="section-3.3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-lid-mappings-for-scalable-s">LID Mappings for Scalable Streams</xref></t>
                <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.3.2.3.2">
                  <li pn="section-toc.1-1.3.2.3.2.1">
                    <t indent="0" pn="section-toc.1-1.3.2.3.2.1.1"><xref derivedContent="3.3.1" format="counter" sectionFormat="of" target="section-3.3.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-vp9-lid-mapping">VP9 LID Mapping</xref></t>
                  </li>
                  <li pn="section-toc.1-1.3.2.3.2.2">
                    <t indent="0" pn="section-toc.1-1.3.2.3.2.2.1"><xref derivedContent="3.3.2" format="counter" sectionFormat="of" target="section-3.3.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-h265-lid-mapping">H265 LID Mapping</xref></t>
                  </li>
                  <li pn="section-toc.1-1.3.2.3.2.3">
                    <t indent="0" pn="section-toc.1-1.3.2.3.2.3.1"><xref derivedContent="3.3.3" format="counter" sectionFormat="of" target="section-3.3.3"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-h264-scalable-video-coding-">H264 Scalable Video Coding (SVC) LID Mapping</xref></t>
                  </li>
                  <li pn="section-toc.1-1.3.2.3.2.4">
                    <t indent="0" pn="section-toc.1-1.3.2.3.2.4.1"><xref derivedContent="3.3.4" format="counter" sectionFormat="of" target="section-3.3.4"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-h264-advanced-video-coding-">H264 Advanced Video Coding (AVC) LID Mapping</xref></t>
                  </li>
                  <li pn="section-toc.1-1.3.2.3.2.5">
                    <t indent="0" pn="section-toc.1-1.3.2.3.2.5.1"><xref derivedContent="3.3.5" format="counter" sectionFormat="of" target="section-3.3.5"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-vp8-lid-mapping">VP8 LID Mapping</xref></t>
                  </li>
                  <li pn="section-toc.1-1.3.2.3.2.6">
                    <t indent="0" pn="section-toc.1-1.3.2.3.2.6.1"><xref derivedContent="3.3.6" format="counter" sectionFormat="of" target="section-3.3.6"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-future-codec-lid-mapping">Future Codec LID Mapping</xref></t>
                  </li>
                </ul>
              </li>
              <li pn="section-toc.1-1.3.2.4">
                <t indent="0" pn="section-toc.1-1.3.2.4.1"><xref derivedContent="3.4" format="counter" sectionFormat="of" target="section-3.4"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-signaling-information">Signaling Information</xref></t>
              </li>
              <li pn="section-toc.1-1.3.2.5">
                <t indent="0" pn="section-toc.1-1.3.2.5.1"><xref derivedContent="3.5" format="counter" sectionFormat="of" target="section-3.5"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-usage-considerations">Usage Considerations</xref></t>
                <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.3.2.5.2">
                  <li pn="section-toc.1-1.3.2.5.2.1">
                    <t indent="0" pn="section-toc.1-1.3.2.5.2.1.1"><xref derivedContent="3.5.1" format="counter" sectionFormat="of" target="section-3.5.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-relation-to-layer-refresh-r">Relation to Layer Refresh Request (LRR)</xref></t>
                  </li>
                  <li pn="section-toc.1-1.3.2.5.2.2">
                    <t indent="0" pn="section-toc.1-1.3.2.5.2.2.1"><xref derivedContent="3.5.2" format="counter" sectionFormat="of" target="section-3.5.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-scalability-structures">Scalability Structures</xref></t>
                  </li>
                </ul>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.4">
            <t indent="0" pn="section-toc.1-1.4.1"><xref derivedContent="4" format="counter" sectionFormat="of" target="section-4"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-security-and-privacy-consid">Security and Privacy Considerations</xref></t>
          </li>
          <li pn="section-toc.1-1.5">
            <t indent="0" pn="section-toc.1-1.5.1"><xref derivedContent="5" format="counter" sectionFormat="of" target="section-5"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-iana-considerations">IANA Considerations</xref></t>
          </li>
          <li pn="section-toc.1-1.6">
            <t indent="0" pn="section-toc.1-1.6.1"><xref derivedContent="6" format="counter" sectionFormat="of" target="section-6"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-references">References</xref></t>
            <ul bare="true" empty="true" indent="2" spacing="compact" pn="section-toc.1-1.6.2">
              <li pn="section-toc.1-1.6.2.1">
                <t indent="0" pn="section-toc.1-1.6.2.1.1"><xref derivedContent="6.1" format="counter" sectionFormat="of" target="section-6.1"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-normative-references">Normative References</xref></t>
              </li>
              <li pn="section-toc.1-1.6.2.2">
                <t indent="0" pn="section-toc.1-1.6.2.2.1"><xref derivedContent="6.2" format="counter" sectionFormat="of" target="section-6.2"/>.  <xref derivedContent="" format="title" sectionFormat="of" target="name-informative-references">Informative References</xref></t>
              </li>
            </ul>
          </li>
          <li pn="section-toc.1-1.7">
            <t indent="0" pn="section-toc.1-1.7.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.a"/><xref derivedContent="" format="title" sectionFormat="of" target="name-acknowledgements">Acknowledgements</xref></t>
          </li>
          <li pn="section-toc.1-1.8">
            <t indent="0" pn="section-toc.1-1.8.1"><xref derivedContent="" format="none" sectionFormat="of" target="section-appendix.b"/><xref derivedContent="" format="title" sectionFormat="of" target="name-authors-addresses">Authors' Addresses</xref></t>
          </li>
        </ul>
      </section>
    </toc>
  </front>
  <middle>
    <section anchor="intro" numbered="true" removeInRFC="false" toc="include" pn="section-1">
      <name slugifiedName="name-introduction">Introduction</name>
      <t indent="0" pn="section-1-1">Many widely deployed RTP <xref target="RFC3550" format="default" sectionFormat="of" derivedContent="RFC3550"/> topologies
        <xref target="RFC7667" format="default" sectionFormat="of" derivedContent="RFC7667"/> used in modern voice and video
      conferencing systems include a centralized component that acts as an RTP switch.
      It receives voice and video streams from each participant, which may be encrypted using
      Secure Real-time Transport Protocol (SRTP) <xref target="RFC3711" format="default" sectionFormat="of" derivedContent="RFC3711"/> or extensions that provide participants with
      private media <xref target="RFC8871" format="default" sectionFormat="of" derivedContent="RFC8871"/>
      via end-to-end encryption where the switch has no access to media decryption keys.
      The goal is to provide a set of streams back to
      the participants, which enable them to render the right media content. For example, in a 
      simple video configuration, the goal will be that each participant 
      sees and hears just the active speaker. In that case, the goal of the switch is to 
      receive the voice and video streams from each participant, determine the active 
      speaker based on energy in the voice packets, possibly using the client-to-mixer
      audio level RTP header extension <xref target="RFC6464" format="default" sectionFormat="of" derivedContent="RFC6464"/>, and select the corresponding video
        stream for transmission to participants; see <xref target="rtpswitch" format="default" sectionFormat="of" derivedContent="Figure 1"/>.</t>
      <t indent="0" pn="section-1-2">In this document, an "RTP switch" is used as shorthand for the terms 
      "switching RTP mixer", "source projecting middlebox",
      "source forwarding unit/middlebox" and "video switching Multipoint Control Unit (MCU)", as
      discussed in <xref target="RFC7667" format="default" sectionFormat="of" derivedContent="RFC7667"/>.</t>
      <figure anchor="rtpswitch" align="left" suppress-title="false" pn="figure-1">
        <name slugifiedName="name-rtp-switch">RTP Switch</name>
        <artwork align="left" pn="section-1-3.1">
         +---+      +------------+      +---+
         | A |&lt;----&gt;|            |&lt;----&gt;| B |
         +---+      |            |      +---+
                    |    RTP     |
         +---+      |   Switch   |      +---+
         | C |&lt;----&gt;|            |&lt;----&gt;| D |
         +---+      +------------+      +---+

    </artwork>
      </figure>
      <t indent="0" pn="section-1-4">In order to properly support the switching of video streams, the RTP switch typically needs 
    some critical information about video frames in order to start and stop forwarding streams.
      </t>
      <ul bare="false" empty="false" indent="3" spacing="normal" pn="section-1-5">
        <li pn="section-1-5.1">
          <t indent="0" pn="section-1-5.1.1">Because of inter-frame dependencies, it should ideally switch video streams at a point 
        where the first frame from the new speaker can be decoded by recipients without prior 
        frames, e.g., switch on an intra-frame.</t>
        </li>
        <li pn="section-1-5.2">
          <t indent="0" pn="section-1-5.2.1">In many cases, the switch may need to drop frames in order to realize congestion control 
        techniques, and it needs to know which frames can be dropped with minimal impact to video quality.</t>
        </li>
        <li pn="section-1-5.3">
          <t indent="0" pn="section-1-5.3.1">For scalable streams with dependent layers, the switch may need to selectively forward
        specific layers to specific recipients due to recipient bandwidth or decoder limits.</t>
        </li>
      </ul>
      <t indent="0" pn="section-1-6">Furthermore, it is highly desirable to do this in a payload format-agnostic way that is not
        specific to each different video codec.
        Most modern video codecs share common concepts around frame types and other critical information
          to make this codec-agnostic handling possible.</t>
      <t indent="0" pn="section-1-7">It is also desirable to be able to do this for SRTP without requiring the video switch to 
        decrypt the packets. SRTP will encrypt the RTP payload format contents; consequently, this 
        data is not usable for the switching function without decryption, which may not even
        be possible in the case of end-to-end encryption of private media
        <xref target="RFC8871" format="default" sectionFormat="of" derivedContent="RFC8871"/>.</t>
      <t indent="0" pn="section-1-8">By providing meta-information about the RTP streams outside the encrypted media payload, an
      RTP switch can do codec-agnostic selective forwarding without decrypting the payload.
      This document specifies the necessary meta-information in an RTP header extension.
      </t>
    </section>
    <section numbered="true" removeInRFC="false" toc="include" pn="section-2">
      <name slugifiedName="name-requirements-language">Requirements Language</name>
      <t indent="0" pn="section-2-1">
    The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>",
    "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>",
    "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
    "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
    "<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this document are to be
    interpreted as described in BCP 14 <xref target="RFC2119" format="default" sectionFormat="of" derivedContent="RFC2119"/> <xref target="RFC8174" format="default" sectionFormat="of" derivedContent="RFC8174"/> when, and only when, they appear in all capitals, as
    shown here.
      </t>
    </section>
    <section numbered="true" removeInRFC="false" toc="include" pn="section-3">
      <name slugifiedName="name-video-frame-marking-rtp-hea">Video Frame Marking RTP Header Extension</name>
      <t indent="0" pn="section-3-1">This specification uses RTP header extensions as defined in <xref target="RFC8285" format="default" sectionFormat="of" derivedContent="RFC8285"/>. A subset of
      meta-information from the video stream is provided as an RTP header extension to allow an RTP switch
      to do generic selective forwarding of video streams encoded with potentially different video codecs.</t>
      <t indent="0" pn="section-3-2">The Video Frame Marking RTP header extension is encoded
      	using the one-byte header or two-byte header as described in <xref target="RFC8285" format="default" sectionFormat="of" derivedContent="RFC8285"/>.
        The one-byte header format is used for examples in this document.
        The two-byte header format is used when other two-byte header extensions
        are present in the same RTP packet since mixing one-byte and two-byte extensions
        is not possible in the same RTP packet.</t>
      <t indent="0" pn="section-3-3">This extension is only specified for Source (not Redundancy) RTP Streams
            <xref target="RFC7656" format="default" sectionFormat="of" derivedContent="RFC7656"/> that carry video payloads.
            It is not specified for audio payloads, nor is it specified for Redundancy RTP Streams.
            The (separate) specifications for Redundancy RTP Streams often include
            provisions for recovering any header extensions that were part of the original source packet.
            Such provisions can be followed to recover the Video Frame Marking RTP header extension of the
            original source packet.
            Source packet frame markings may be useful when generating Redundancy RTP Streams;
            for example, the I (Independent Frame) and D (Discardable Frame) bits,
            defined in <xref target="mandatory-scalable" format="default" sectionFormat="of" derivedContent="Section 3.1"/>, 
            can be used to generate extra or no redundancy, respectively,
            and redundancy schemes with source blocks can align source block boundaries with
            independent frame boundaries as marked by the I bit.
      </t>
      <t indent="0" pn="section-3-4">A frame, in the context of this specification, is the set of RTP packets
          with the same RTP timestamp from a specific RTP Synchronization Source (SSRC).
          A frame within a layer is the set of RTP packets with the same RTP timestamp, SSRC,
          Temporal-layer ID (TID), and Layer ID (LID).</t>
      <section anchor="mandatory-scalable" numbered="true" removeInRFC="false" toc="include" pn="section-3.1">
        <name slugifiedName="name-long-extension-for-scalable">Long Extension for Scalable Streams</name>
        <t indent="0" pn="section-3.1-1">The following RTP header extension is <bcp14>RECOMMENDED</bcp14> for scalable streams.
           It <bcp14>MAY</bcp14> also be used for non-scalable streams, in which case the TID, LID, and TL0PICIDX <bcp14>MUST</bcp14> be 0 or omitted.
           The ID is assigned per <xref target="RFC8285" format="default" sectionFormat="of" derivedContent="RFC8285"/>.
           The length is encoded as follows:</t>
        <ul bare="false" empty="false" indent="3" spacing="normal" pn="section-3.1-2">
          <li pn="section-3.1-2.1">L=2 to indicate 3 octets of data when nothing is omitted,</li>
          <li pn="section-3.1-2.2">L=1 for 2 octets when TL0PICIDX is omitted, or</li>
          <li pn="section-3.1-2.3">L=0 for 1 octet when both the LID and TL0PICIDX are omitted.</li>
        </ul>
        <artwork align="left" pn="section-3.1-3">
 0                   1                   2                   3
 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  ID=? |  L=2  |S|E|I|D|B| TID |   LID         |    TL0PICIDX  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           or
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  ID=? |  L=1  |S|E|I|D|B| TID |   LID         | (TL0PICIDX omitted)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
           or
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  ID=? |  L=0  |S|E|I|D|B| TID | (LID and TL0PICIDX omitted)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
        <t indent="0" pn="section-3.1-4">The following information is extracted from the media payload and sent in the Video Frame Marking RTP header extension.
        </t>
        <dl newline="true" indent="3" spacing="normal" pn="section-3.1-5">
          <dt pn="section-3.1-5.1">S: Start of Frame (1 bit)</dt>
          <dd pn="section-3.1-5.2">
            <bcp14>MUST</bcp14> be 1 in the first packet in a frame
                within a layer; otherwise, <bcp14>MUST</bcp14> be 0.</dd>
          <dt pn="section-3.1-5.3">E: End of Frame (1 bit)</dt>
          <dd pn="section-3.1-5.4">
            <bcp14>MUST</bcp14> be 1 in the last packet in a frame
                within a layer; otherwise, <bcp14>MUST</bcp14> be 0.
                Note that the RTP header marker bit <bcp14>MAY</bcp14> be used to infer the last packet of the highest enhancement layer in payload formats with such semantics.</dd>
          <dt pn="section-3.1-5.5">I: Independent Frame  (1 bit)</dt>
          <dd pn="section-3.1-5.6">
            <bcp14>MUST</bcp14> be 1 for a frame within a layer that can be
               decoded independent of temporally prior frames, e.g., intra-frame, VPX keyframe,
               H.264 Instantaneous Decoding Refresh (IDR) <xref target="RFC6184" format="default" sectionFormat="of" derivedContent="RFC6184"/>, or
               H.265 IDR / Clean Random Access (CRA) / Broken Link Access (BLA) / Random Access Point (RAP) <xref target="RFC7798" format="default" sectionFormat="of" derivedContent="RFC7798"/>; 
               otherwise, <bcp14>MUST</bcp14> be 0.
               Note that this bit only signals temporal independence, so it can be
               1 in spatial or quality enhancement layers that depend on temporally
               co-located layers but not temporally prior frames.</dd>
          <dt pn="section-3.1-5.7">D: Discardable Frame (1 bit)</dt>
          <dd pn="section-3.1-5.8">
            <bcp14>MUST</bcp14> be 1 for a frame within a layer the sender knows can be discarded
                and still provide a decodable media stream; otherwise, <bcp14>MUST</bcp14> be 0. </dd>
          <dt pn="section-3.1-5.9">B: Base Layer Sync (1 bit)</dt>
          <dd pn="section-3.1-5.10">When the TID is not 0, this <bcp14>MUST</bcp14> be 1 if the sender knows this frame within a layer only depends
                on the base temporal layer; otherwise, <bcp14>MUST</bcp14> be 0. When the TID is 0 or if no scalability is used, this <bcp14>MUST</bcp14> be 0.
          </dd>
          <dt pn="section-3.1-5.11">TID: Temporal-layer ID (3 bits)</dt>
          <dd pn="section-3.1-5.12">Identifies the temporal layer/sub-layer encoded,
               starting with 0 for the base layer and increasing with higher temporal fidelity.
               If no scalability is used, this <bcp14>MUST</bcp14> be 0. It is implicitly 0 in the short extension format.
          </dd>
          <dt pn="section-3.1-5.13">LID: Layer ID (8 bits)</dt>
          <dd pn="section-3.1-5.14">Identifies the spatial and quality layer encoded, 
               starting with 0 for the base layer and increasing with higher fidelity.
               If no scalability is used, this <bcp14>MUST</bcp14> be 0 or omitted to reduce length.
               When the LID is omitted, TL0PICIDX <bcp14>MUST</bcp14> also be omitted. It is implicitly 0 in the short extension format
               or when omitted in the long extension format.</dd>
          <dt pn="section-3.1-5.15">TL0PICIDX: Temporal Layer 0 Picture Index (8 bits)</dt>
          <dd pn="section-3.1-5.16">When the TID is 0 and the LID is 0, this is a cyclic counter labeling
               base layer frames. When the TID is not 0 or the LID is not 0,
               the indication is that a dependency on the given index, such that this frame within this layer
               depends on the frame with this label in the layer with a TID 0 and LID 0.
               If no scalability is used, or the cyclic counter is unknown, TL0PICIDX <bcp14>MUST</bcp14> be omitted to reduce length.
               Note that 0 is a valid index value for TL0PICIDX.</dd>
        </dl>
        <t indent="0" pn="section-3.1-6">The layer information contained in the TID and LID convey useful aspects of the layer structure that
          can be utilized in selective forwarding.</t>
        <t indent="0" pn="section-3.1-7">Without further information about the layer structure,
          these TID/LID identifiers can only be used for relative priority of layers
          and implicit dependencies between layers.
          They convey a layer hierarchy with TID = 0 and LID = 0 identifying the base layer.
          Higher values of TID identify higher temporal layers with higher frame rates.
          Higher values of LID identify higher spatial and/or quality layers with higher resolutions and/or bitrates.
          Implicit dependencies between layers assume that a layer with a given TID/LID <bcp14>MAY</bcp14> depend
          on a layer or layers with the same or lower TID/LID, but they <bcp14>MUST NOT</bcp14> depend on a layer or layers with higher TID/LID.
        </t>
        <t indent="0" pn="section-3.1-8">
          With further information,
          for example, possible future RTCP source description (SDES) items that convey full layer structure information, it may
          be possible to map these TIDs and LIDs to specific absolute frame rates, resolutions, bitrates, and explicit dependencies between layers.
          Such additional layer information may be useful for forwarding decisions in the RTP switch
          but is beyond the scope of this document. The relative layer information is still useful
          for many selective forwarding decisions, even without such additional layer information.
        </t>
      </section>
      <section anchor="mandatory-non-scalable" numbered="true" removeInRFC="false" toc="include" pn="section-3.2">
        <name slugifiedName="name-short-extension-for-non-sca">Short Extension for Non-Scalable Streams</name>
        <t indent="0" pn="section-3.2-1">The following RTP header extension is <bcp14>RECOMMENDED</bcp14> for non-scalable streams.
           It is identical to the shortest form of the extension for scalable streams,
           except the last four bits (B and TID) are replaced with zeros.
           It <bcp14>MAY</bcp14> also be used for scalable streams if the sender has limited or no
           information about stream scalability.
           The ID is assigned per <xref target="RFC8285" format="default" sectionFormat="of" derivedContent="RFC8285"/>;
           the length is encoded as L=0, which indicates 1 octet of data.</t>
        <artwork align="left" pn="section-3.2-2">
 0                   1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  ID=? |  L=0  |S|E|I|D|0 0 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


</artwork>
        <t indent="0" pn="section-3.2-3">The following information is extracted from the media payload and sent in the Video Frame Marking RTP header extension.
        </t>
        <dl newline="true" indent="3" spacing="normal" pn="section-3.2-4">
          <dt pn="section-3.2-4.1">S: Start of Frame (1 bit)</dt>
          <dd pn="section-3.2-4.2">
            <bcp14>MUST</bcp14> be 1 in the first packet in a frame; otherwise, <bcp14>MUST</bcp14> be 0.</dd>
          <dt pn="section-3.2-4.3">E: End of Frame (1 bit)</dt>
          <dd pn="section-3.2-4.4">
            <bcp14>MUST</bcp14> be 1 in the last packet in a frame; otherwise, <bcp14>MUST</bcp14> be 0.
            <bcp14>SHOULD</bcp14> match the RTP header marker bit in payload formats with such semantics for marking end of frame.</dd>
          <dt pn="section-3.2-4.5">I: Independent Frame  (1 bit)</dt>
          <dd pn="section-3.2-4.6">
            <bcp14>MUST</bcp14> be 1 for frames that can be
               decoded independent of temporally prior frames, e.g., intra-frame, VPX keyframe,
               H.264 IDR <xref target="RFC6184" format="default" sectionFormat="of" derivedContent="RFC6184"/>, or
               H.265 IDR/CRA/BLA/IRAP <xref target="RFC7798" format="default" sectionFormat="of" derivedContent="RFC7798"/>;
               otherwise, <bcp14>MUST</bcp14> be 0. </dd>
          <dt pn="section-3.2-4.7">D: Discardable Frame (1 bit)</dt>
          <dd pn="section-3.2-4.8">
            <bcp14>MUST</bcp14> be 1 for frames the sender knows can be discarded
                and still provide a decodable media stream; otherwise, <bcp14>MUST</bcp14> be 0. </dd>
          <dt pn="section-3.2-4.9">The remaining (4 bits)</dt>
          <dd pn="section-3.2-4.10">These are reserved/fixed values and not used for non-scalable streams;
              they <bcp14>MUST</bcp14> be set to zero upon transmission and ignored upon reception.</dd>
        </dl>
      </section>
      <section numbered="true" removeInRFC="false" toc="include" pn="section-3.3">
        <name slugifiedName="name-lid-mappings-for-scalable-s">LID Mappings for Scalable Streams</name>
        <t indent="0" pn="section-3.3-1"> This section maps the specific Layer ID (LID) information contained in specific scalable codecs to the generic LID and TID fields. </t>
        <t indent="0" pn="section-3.3-2"> Note that non-scalable streams have no LID information; thus, they have no mappings. </t>
        <section numbered="true" removeInRFC="false" toc="include" pn="section-3.3.1">
          <name slugifiedName="name-vp9-lid-mapping">VP9 LID Mapping</name>
          <t indent="0" pn="section-3.3.1-1"> The VP9 <xref target="RFC9628" format="default" sectionFormat="of" derivedContent="RFC9628"/>
           Spatial-layer ID (SID, 3 bits) and Temporal-layer ID (TID, 3 bits)
           in the VP9 payload descriptor are mapped to the generic LID and TID fields
           in the header extension as shown in the following figure.</t>
          <artwork align="left" pn="section-3.3.1-2">
   0                   1                   2                   3
   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |  ID=? |  L=2  |S|E|I|D|B| TID |0|0|0|0|0| SID |    TL0PICIDX  |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  </artwork>
          <t indent="0" pn="section-3.3.1-3"> The S bit <bcp14>MUST</bcp14> match the B bit in the VP9 payload descriptor.</t>
          <t indent="0" pn="section-3.3.1-4"> The E bit <bcp14>MUST</bcp14> match the E bit in the VP9 payload descriptor.</t>
          <t indent="0" pn="section-3.3.1-5"> The I bit <bcp14>MUST</bcp14> match the inverse of the P bit in the VP9 payload descriptor.</t>
          <t indent="0" pn="section-3.3.1-6"> The D bit <bcp14>MUST</bcp14> be 1 if the refresh_frame_flags bits in the VP9 payload uncompressed header are all 0; otherwise, it <bcp14>MUST</bcp14> be 0.</t>
          <t indent="0" pn="section-3.3.1-7"> The B bit <bcp14>MUST</bcp14> be 0 if the TID is 0; if the TID is not 0, it <bcp14>MUST</bcp14> match the U bit in the VP9 payload descriptor.</t>
          <aside pn="section-3.3.1-8">
            <t indent="0" pn="section-3.3.1-8.1">Note: when using temporally nested scalability structures as recommended in <xref target="scalable-structures" format="default" sectionFormat="of" derivedContent="Section 3.5.2"/>, the B bit and VP9 U bit will always be 1 if the TID is not 0 since it is always
           possible to switch up to a higher temporal layer in such nested structures.</t>
          </aside>
          <t indent="0" pn="section-3.3.1-9">The TID, SID, and TL0PICIDX <bcp14>MUST</bcp14> match the correspondingly named fields in the VP9 payload descriptor,
           with SID aligned in the least significant 3 bits of the 8-bit LID field and zeros
           in the most significant 5 bits.</t>
        </section>
        <section numbered="true" removeInRFC="false" toc="include" pn="section-3.3.2">
          <name slugifiedName="name-h265-lid-mapping">H265 LID Mapping</name>
          <t indent="0" pn="section-3.3.2-1"> The H265 <xref target="RFC7798" format="default" sectionFormat="of" derivedContent="RFC7798"/> layer ID (6 bits), and TID (3 bits) 
             from the Network Abstraction Layer (NAL) unit header are mapped to the generic LID and TID fields 
             in the header extension as shown in the following figure.</t>
          <artwork align="left" pn="section-3.3.2-2">
 0                   1                   2                   3
 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  ID=? |  L=2  |S|E|I|D|B| TID |0|0| layer ID  |    TL0PICIDX  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
          <t indent="0" pn="section-3.3.2-3">The S and E bits <bcp14>MUST</bcp14> match the correspondingly named bits in PACI:PHES:TSCI payload structures.</t>
          <t indent="0" pn="section-3.3.2-4">The I bit <bcp14>MUST</bcp14> be 1 when the NAL unit type is 16-23 (inclusive) or 32-34 (inclusive), or an aggregation packet or fragmentation unit encapsulating any of these types; otherwise, it <bcp14>MUST</bcp14> be 0. These ranges cover intra (IRAP) frames as well as
          critical parameter sets (Video Parameter Set (VPS), Sequence Parameter Set (SPS), Picture Parameter Set (PPS)).</t>
          <t indent="0" pn="section-3.3.2-5">The D bit <bcp14>MUST</bcp14> be 1 if either:</t>
          <ul bare="false" empty="false" indent="3" spacing="normal" pn="section-3.3.2-6">
            <li pn="section-3.3.2-6.1">the payload's NAL unit header's NRI field is 0, or</li>
            <li pn="section-3.3.2-6.2">the payload is an aggregation packet or fragmentation unit encapsulating only NAL units with NRI = 0.</li>
          </ul>
          <t indent="0" pn="section-3.3.2-7">Otherwise, it <bcp14>MUST</bcp14> be 0.</t>
          <t indent="0" pn="section-3.3.2-8">The NRI = 0 condition signals non-reference frames.</t>
          <t indent="0" pn="section-3.3.2-9">The B bit cannot be determined reliably from simple inspection of payload headers; therefore, it is determined by implementation-specific means. For example, internal codec interfaces may provide information to set this reliably.</t>
          <t indent="0" pn="section-3.3.2-10">The TID and layer ID <bcp14>MUST</bcp14> match the correspondingly named fields in the H265 NAL unit header,
           with layer ID aligned in the least significant 6 bits of the 8-bit LID field and zeros
           in the most significant 2 bits.</t>
        </section>
        <section numbered="true" removeInRFC="false" toc="include" pn="section-3.3.3">
          <name slugifiedName="name-h264-scalable-video-coding-">H264 Scalable Video Coding (SVC) LID Mapping</name>
          <t indent="0" pn="section-3.3.3-1"> The following shows H264-SVC <xref target="RFC6190" format="default" sectionFormat="of" derivedContent="RFC6190"/> Layer encoding information (3 bits for
   spatial/dependency layer (DID), 4 bits for quality layer (QID), and 3 bits for temporal layer) mapped to the generic LID and TID fields.</t>
          <t indent="0" pn="section-3.3.3-2">The S, E, I, and D bits <bcp14>MUST</bcp14> match the correspondingly named bits in Payload Content Scalability Information (PACSI) payload structures.</t>
          <t indent="0" pn="section-3.3.3-3">The I bit <bcp14>MUST</bcp14> be 1 when the NAL unit type is 5, 7, 8, 13, 15,
     or an aggregation packet or fragmentation unit encapsulating any of these types; otherwise, it <bcp14>MUST</bcp14> be 0. These ranges cover intra (IDR) frames as well as
       critical parameter sets (SPS/PPS variants).</t>
          <t indent="0" pn="section-3.3.3-4">The D bit <bcp14>MUST</bcp14> be 1 if either:</t>
          <ul bare="false" empty="false" indent="3" spacing="normal" pn="section-3.3.3-5">
            <li pn="section-3.3.3-5.1">the payload's NAL unit header's NRI field is 0, or</li>
            <li pn="section-3.3.3-5.2">the payload is an aggregation packet or fragmentation unit encapsulating only NAL units with NRI = 0.</li>
          </ul>
          <t indent="0" pn="section-3.3.3-6">Otherwise, it <bcp14>MUST</bcp14> be 0.</t>
          <t indent="0" pn="section-3.3.3-7">The NRI = 0 condition signals non-reference frames.</t>
          <t indent="0" pn="section-3.3.3-8">The B bit cannot be determined reliably from simple inspection of payload headers; therefore, it is determined by implementation-specific means. For example, internal codec interfaces may provide information to set this reliably.</t>
          <artwork align="left" pn="section-3.3.3-9">
 0                   1                   2                   3
 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  ID=? |  L=2  |S|E|I|D|B| TID |0| DID |  QID  |    TL0PICIDX  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
        </section>
        <section numbered="true" removeInRFC="false" toc="include" pn="section-3.3.4">
          <name slugifiedName="name-h264-advanced-video-coding-">H264 Advanced Video Coding (AVC) LID Mapping</name>
          <t indent="0" pn="section-3.3.4-1"> The following  shows the header extension for H264 (AVC) <xref target="RFC6184" format="default" sectionFormat="of" derivedContent="RFC6184"/> that contains
    only temporal layer information.</t>
          <t indent="0" pn="section-3.3.4-2"> The S bit <bcp14>MUST</bcp14> be 1 when the timestamp in the RTP header differs from the timestamp
     in the prior RTP sequence number from the same SSRC; otherwise, it <bcp14>MUST</bcp14> be 0.</t>
          <t indent="0" pn="section-3.3.4-3"> The E bit <bcp14>MUST</bcp14> match the M bit in the RTP header.</t>
          <t indent="0" pn="section-3.3.4-4">The I bit <bcp14>MUST</bcp14> be 1 when the NAL unit type is 5, 7, or 8,
     or an aggregation packet or fragmentation unit encapsulating any of these types;
     otherwise, it <bcp14>MUST</bcp14> be 0. These ranges cover intra (IDR) frames as well as
     critical parameter sets (SPS/PPS).</t>
          <t indent="0" pn="section-3.3.4-5">The D bit <bcp14>MUST</bcp14> be 1 if either:</t>
          <ul bare="false" empty="false" indent="3" spacing="normal" pn="section-3.3.4-6">
            <li pn="section-3.3.4-6.1">the payload's NAL unit header's NRI field is 0,
       or</li>
            <li pn="section-3.3.4-6.2">the payload is an aggregation packet or fragmentation unit encapsulating only
       NAL units with NRI = 0.</li>
          </ul>
          <t indent="0" pn="section-3.3.4-7">Otherwise, it <bcp14>MUST</bcp14> be 0.</t>
          <t indent="0" pn="section-3.3.4-8">The NRI = 0 condition signals non-reference frames.</t>
          <t indent="0" pn="section-3.3.4-9">The B bit cannot be determined reliably from simple inspection of payload headers; therefore, it is determined by implementation-specific means. For example, internal codec interfaces may provide information to set this reliably.</t>
          <artwork align="left" pn="section-3.3.4-10">
 0                   1                   2                   3
 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  ID=? |  L=2  |S|E|I|D|B| TID |0|0|0|0|0|0|0|0|    TL0PICIDX  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
        </section>
        <section numbered="true" removeInRFC="false" toc="include" pn="section-3.3.5">
          <name slugifiedName="name-vp8-lid-mapping">VP8 LID Mapping</name>
          <t indent="0" pn="section-3.3.5-1"> The following  shows the header extension for VP8 <xref target="RFC7741" format="default" sectionFormat="of" derivedContent="RFC7741"/> that contains
    only temporal layer information.</t>
          <t indent="0" pn="section-3.3.5-2"> The S bit <bcp14>MUST</bcp14> match the correspondingly named bit in the VP8 payload descriptor when PID=0; otherwise, it <bcp14>MUST</bcp14> be 0.</t>
          <t indent="0" pn="section-3.3.5-3"> The E bit <bcp14>MUST</bcp14> match the M bit in the RTP header. </t>
          <t indent="0" pn="section-3.3.5-4"> The I bit <bcp14>MUST</bcp14> match the inverse of the P bit in the VP8 payload header.</t>
          <t indent="0" pn="section-3.3.5-5"> The D bit <bcp14>MUST</bcp14> match the N bit in the VP8 payload descriptor.</t>
          <t indent="0" pn="section-3.3.5-6"> The B bit <bcp14>MUST</bcp14> match the Y bit in the VP8 payload descriptor.</t>
          <aside pn="section-3.3.5-7">
            <t indent="0" pn="section-3.3.5-7.1">Note: when using temporally nested scalability structures as recommended in <xref target="scalable-structures" format="default" sectionFormat="of" derivedContent="Section 3.5.2"/>, the B bit and VP8 Y bit will always be 1 if the TID is not 0 since it is always
       possible to switch up to a higher temporal layer in such nested structures.</t>
          </aside>
          <t indent="0" pn="section-3.3.5-8">The TID and TL0PICIDX <bcp14>MUST</bcp14> match the correspondingly named fields in the VP8 payload descriptor. </t>
          <artwork align="left" pn="section-3.3.5-9">
 0                   1                   2                   3
 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  ID=? |  L=2  |S|E|I|D|B| TID |0|0|0|0|0|0|0|0|    TL0PICIDX  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
        </section>
        <section numbered="true" removeInRFC="false" toc="include" pn="section-3.3.6">
          <name slugifiedName="name-future-codec-lid-mapping">Future Codec LID Mapping</name>
          <t indent="0" pn="section-3.3.6-1">The RTP payload format specification for future video codecs <bcp14>SHOULD</bcp14> include a section describing
        the LID mapping and TID mapping for the codec.</t>
        </section>
      </section>
      <section numbered="true" removeInRFC="false" toc="include" pn="section-3.4">
        <name slugifiedName="name-signaling-information">Signaling Information</name>
        <t indent="0" pn="section-3.4-1">The URI for declaring this header extension in an extmap attribute is 
      "urn:ietf:params:rtp-hdrext:framemarking". It does not contain any
      extension attributes. </t>
        <t indent="0" pn="section-3.4-2">An example attribute line in SDP:</t>
        <artwork align="left" pn="section-3.4-3">
   a=extmap:3 urn:ietf:params:rtp-hdrext:framemarking
</artwork>
      </section>
      <section numbered="true" removeInRFC="false" toc="include" pn="section-3.5">
        <name slugifiedName="name-usage-considerations">Usage Considerations</name>
        <t indent="0" pn="section-3.5-1">The header extension values <bcp14>MUST</bcp14> represent what is already in the RTP payload.</t>
        <t indent="0" pn="section-3.5-2">When an RTP switch needs to discard received video frames due to congestion control considerations,
	it is <bcp14>RECOMMENDED</bcp14> that it drop:</t>
        <ul bare="false" empty="false" indent="3" spacing="normal" pn="section-3.5-3">
          <li pn="section-3.5-3.1">frames marked with the D bit set,
          or</li>
          <li pn="section-3.5-3.2">frames with the highest values of TID and LID (which indicate the highest temporal and spatial/quality enhancement layers) since those typically have fewer dependencies on them than lower layers.</li>
        </ul>
        <t indent="0" pn="section-3.5-4"> When an RTP switch wants to forward a new video stream to a receiver, it is <bcp14>RECOMMENDED</bcp14> to
	select the new video stream from the first switching point with the I bit set in all spatial layers and forward the video stream from that point on. An RTP switch can request that a media source generate a switching point by sending an RTCP
      Full Intra Request (FIR) as defined in <xref target="RFC5104" format="default" sectionFormat="of" derivedContent="RFC5104"/>, for example. </t>
        <section numbered="true" removeInRFC="false" toc="include" pn="section-3.5.1">
          <name slugifiedName="name-relation-to-layer-refresh-r">Relation to Layer Refresh Request (LRR)</name>
          <t indent="0" pn="section-3.5.1-1">Receivers can use the Layer Refresh Request (LRR) <xref target="RFC9627" format="default" sectionFormat="of" derivedContent="RFC9627"/>
          RTCP feedback message
          to upgrade to a higher layer in scalable encodings. The TID/LID values
          and formats used in LRR messages <bcp14>MUST</bcp14> correspond to the same values and formats
          specified in <xref target="mandatory-scalable" format="default" sectionFormat="of" derivedContent="Section 3.1"/>.
          </t>
          <t indent="0" pn="section-3.5.1-2">Because frame marking can only be used with temporally nested streams,
            temporal-layer refreshes requested with an LRR message are unnecessary for frame-marked streams.
          Other refreshes can be detected based on the I bit being set for the specific spatial layers.
          </t>
        </section>
        <section anchor="scalable-structures" numbered="true" removeInRFC="false" toc="include" pn="section-3.5.2">
          <name slugifiedName="name-scalability-structures">Scalability Structures</name>
          <t indent="0" pn="section-3.5.2-1">The LID and TID information is most useful for fixed scalability structures,
            such as nested hierarchical temporal layering structures, where each temporal
            layer only references lower temporal layers or the base temporal layer.
            The LID and TID information is less useful, or even not useful at all,
            for complex, irregular scalability structures that do not conform to common,
            fixed patterns of inter-layer dependencies and referencing structures.
            Therefore, it is <bcp14>RECOMMENDED</bcp14> to use LID and TID information for
            RTP switch forwarding decisions only in the case of temporally nested
            scalability structures, and it is <bcp14>NOT RECOMMENDED</bcp14> for other
            (more complex or irregular) scalability structures.</t>
        </section>
      </section>
    </section>
    <section numbered="true" removeInRFC="false" toc="include" pn="section-4">
      <name slugifiedName="name-security-and-privacy-consid">Security and Privacy Considerations</name>
      <t indent="0" pn="section-4-1">In "<xref target="RFC3711" format="title" sectionFormat="of" derivedContent="The Secure Real-time Transport Protocol (SRTP)"/>" <xref target="RFC3711" format="default" sectionFormat="of" derivedContent="RFC3711"/>, RTP header extensions are
      authenticated and optionally encrypted <xref target="RFC9335" format="default" sectionFormat="of" derivedContent="RFC9335"/>.
      When unencrypted header extensions are used, some metadata is
      exposed and visible to middleboxes on the network path,
      while encrypted media data and metadata in encrypted header extensions are not exposed.</t>
      <t indent="0" pn="section-4-2">The primary utility of this specification is for RTP switches to make proper media forwarding decisions. 
      RTP switches are the SRTP peers of endpoints, so they can access encrypted header extensions, 
      but not end-to-end encrypted private media payloads. Other middleboxes on the network path can only access
      unencrypted header extensions since they are not SRTP peers.</t>
      <t indent="0" pn="section-4-3">RTP endpoints that negotiate this extension should consider whether:
      </t>
      <ul bare="false" empty="false" indent="3" spacing="normal" pn="section-4-4">
        <li pn="section-4-4.1">this video frame marking metadata
      needs to be exposed to the SRTP peer only, in which case the header extension can be encrypted; or</li>
        <li pn="section-4-4.2">other middleboxes on the network path also need this metadata, for example, to optimize packet drop decisions
      that minimize media quality impacts, in which case the header extension can be unencrypted, if the endpoint
      accepts the potential privacy leakage of this metadata.</li>
      </ul>
      <t indent="0" pn="section-4-5">
      For example, it would be possible to determine
      keyframes and their frequency in unencrypted header extensions. This information can often be obtained via
      statistical analysis of encrypted data. For example, keyframes are usually much larger than other frames, 
      so frame size alone can leak this in the absence of any unencrypted metadata. However, unencrypted metadata
      provides a reliable signal rather than a statistical probability; so endpoints should take that into consideration
      to balance the privacy leakage risk against the potential benefit of optimized media delivery when deciding
      whether to negotiate and encrypt this header extension.</t>
    </section>
    <section numbered="true" removeInRFC="false" toc="include" pn="section-5">
      <name slugifiedName="name-iana-considerations">IANA Considerations</name>
      <t indent="0" pn="section-5-1">This document defines a new extension URI listed in the "RTP Compact Header Extensions" registry of the 
      	"Real-Time Transport Protocol (RTP) Parameters" registry group, according to the following data:</t>
      <t indent="0" pn="section-5-2">Extension URI:  urn:ietf:params:rtp-hdrext:framemarking </t>
      <t indent="0" pn="section-5-3">Description: Frame marking information for video streams </t>
      <t indent="0" pn="section-5-4">Contact: mzanaty@cisco.com </t>
      <t indent="0" pn="section-5-5">Reference: RFC 9626</t>
    </section>
  </middle>
  <back>
    <references pn="section-6">
      <name slugifiedName="name-references">References</name>
      <references pn="section-6.1">
        <name slugifiedName="name-normative-references">Normative References</name>
        <reference anchor="RFC2119" target="https://www.rfc-editor.org/info/rfc2119" quoteTitle="true" derivedAnchor="RFC2119">
          <front>
            <title>Key words for use in RFCs to Indicate Requirement Levels</title>
            <author fullname="S. Bradner" initials="S." surname="Bradner"/>
            <date month="March" year="1997"/>
            <abstract>
              <t indent="0">In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="2119"/>
          <seriesInfo name="DOI" value="10.17487/RFC2119"/>
        </reference>
        <reference anchor="RFC6184" target="https://www.rfc-editor.org/info/rfc6184" quoteTitle="true" derivedAnchor="RFC6184">
          <front>
            <title>RTP Payload Format for H.264 Video</title>
            <author fullname="Y.-K. Wang" initials="Y.-K." surname="Wang"/>
            <author fullname="R. Even" initials="R." surname="Even"/>
            <author fullname="T. Kristensen" initials="T." surname="Kristensen"/>
            <author fullname="R. Jesup" initials="R." surname="Jesup"/>
            <date month="May" year="2011"/>
            <abstract>
              <t indent="0">This memo describes an RTP Payload format for the ITU-T Recommendation H.264 video codec and the technically identical ISO/IEC International Standard 14496-10 video codec, excluding the Scalable Video Coding (SVC) extension and the Multiview Video Coding extension, for which the RTP payload formats are defined elsewhere. The RTP payload format allows for packetization of one or more Network Abstraction Layer Units (NALUs), produced by an H.264 video encoder, in each RTP payload. The payload format has wide applicability, as it supports applications from simple low bitrate conversational usage, to Internet video streaming with interleaved transmission, to high bitrate video-on-demand.</t>
              <t indent="0">This memo obsoletes RFC 3984. Changes from RFC 3984 are summarized in Section 14. Issues on backward compatibility to RFC 3984 are discussed in Section 15. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="6184"/>
          <seriesInfo name="DOI" value="10.17487/RFC6184"/>
        </reference>
        <reference anchor="RFC6190" target="https://www.rfc-editor.org/info/rfc6190" quoteTitle="true" derivedAnchor="RFC6190">
          <front>
            <title>RTP Payload Format for Scalable Video Coding</title>
            <author fullname="S. Wenger" initials="S." surname="Wenger"/>
            <author fullname="Y.-K. Wang" initials="Y.-K." surname="Wang"/>
            <author fullname="T. Schierl" initials="T." surname="Schierl"/>
            <author fullname="A. Eleftheriadis" initials="A." surname="Eleftheriadis"/>
            <date month="May" year="2011"/>
            <abstract>
              <t indent="0">This memo describes an RTP payload format for Scalable Video Coding (SVC) as defined in Annex G of ITU-T Recommendation H.264, which is technically identical to Amendment 3 of ISO/IEC International Standard 14496-10. The RTP payload format allows for packetization of one or more Network Abstraction Layer (NAL) units in each RTP packet payload, as well as fragmentation of a NAL unit in multiple RTP packets. Furthermore, it supports transmission of an SVC stream over a single as well as multiple RTP sessions. The payload format defines a new media subtype name "H264-SVC", but is still backward compatible to RFC 6184 since the base layer, when encapsulated in its own RTP stream, must use the H.264 media subtype name ("H264") and the packetization method specified in RFC 6184. The payload format has wide applicability in videoconferencing, Internet video streaming, and high-bitrate entertainment-quality video, among others. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="6190"/>
          <seriesInfo name="DOI" value="10.17487/RFC6190"/>
        </reference>
        <reference anchor="RFC7741" target="https://www.rfc-editor.org/info/rfc7741" quoteTitle="true" derivedAnchor="RFC7741">
          <front>
            <title>RTP Payload Format for VP8 Video</title>
            <author fullname="P. Westin" initials="P." surname="Westin"/>
            <author fullname="H. Lundin" initials="H." surname="Lundin"/>
            <author fullname="M. Glover" initials="M." surname="Glover"/>
            <author fullname="J. Uberti" initials="J." surname="Uberti"/>
            <author fullname="F. Galligan" initials="F." surname="Galligan"/>
            <date month="March" year="2016"/>
            <abstract>
              <t indent="0">This memo describes an RTP payload format for the VP8 video codec. The payload format has wide applicability, as it supports applications from low-bitrate peer-to-peer usage to high-bitrate video conferences.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7741"/>
          <seriesInfo name="DOI" value="10.17487/RFC7741"/>
        </reference>
        <reference anchor="RFC7798" target="https://www.rfc-editor.org/info/rfc7798" quoteTitle="true" derivedAnchor="RFC7798">
          <front>
            <title>RTP Payload Format for High Efficiency Video Coding (HEVC)</title>
            <author fullname="Y.-K. Wang" initials="Y.-K." surname="Wang"/>
            <author fullname="Y. Sanchez" initials="Y." surname="Sanchez"/>
            <author fullname="T. Schierl" initials="T." surname="Schierl"/>
            <author fullname="S. Wenger" initials="S." surname="Wenger"/>
            <author fullname="M. M. Hannuksela" initials="M. M." surname="Hannuksela"/>
            <date month="March" year="2016"/>
            <abstract>
              <t indent="0">This memo describes an RTP payload format for the video coding standard ITU-T Recommendation H.265 and ISO/IEC International Standard 23008-2, both also known as High Efficiency Video Coding (HEVC) and developed by the Joint Collaborative Team on Video Coding (JCT-VC). The RTP payload format allows for packetization of one or more Network Abstraction Layer (NAL) units in each RTP packet payload as well as fragmentation of a NAL unit into multiple RTP packets. Furthermore, it supports transmission of an HEVC bitstream over a single stream as well as multiple RTP streams. When multiple RTP streams are used, a single transport or multiple transports may be utilized. The payload format has wide applicability in videoconferencing, Internet video streaming, and high-bitrate entertainment-quality video, among others.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7798"/>
          <seriesInfo name="DOI" value="10.17487/RFC7798"/>
        </reference>
        <reference anchor="RFC8174" target="https://www.rfc-editor.org/info/rfc8174" quoteTitle="true" derivedAnchor="RFC8174">
          <front>
            <title>Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words</title>
            <author fullname="B. Leiba" initials="B." surname="Leiba"/>
            <date month="May" year="2017"/>
            <abstract>
              <t indent="0">RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings.</t>
            </abstract>
          </front>
          <seriesInfo name="BCP" value="14"/>
          <seriesInfo name="RFC" value="8174"/>
          <seriesInfo name="DOI" value="10.17487/RFC8174"/>
        </reference>
        <reference anchor="RFC8285" target="https://www.rfc-editor.org/info/rfc8285" quoteTitle="true" derivedAnchor="RFC8285">
          <front>
            <title>A General Mechanism for RTP Header Extensions</title>
            <author fullname="D. Singer" initials="D." surname="Singer"/>
            <author fullname="H. Desineni" initials="H." surname="Desineni"/>
            <author fullname="R. Even" initials="R." role="editor" surname="Even"/>
            <date month="October" year="2017"/>
            <abstract>
              <t indent="0">This document provides a general mechanism to use the header extension feature of RTP (the Real-time Transport Protocol). It provides the option to use a small number of small extensions in each RTP packet, where the universe of possible extensions is large and registration is decentralized. The actual extensions in use in a session are signaled in the setup information for that session. This document obsoletes RFC 5285.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8285"/>
          <seriesInfo name="DOI" value="10.17487/RFC8285"/>
        </reference>
      </references>
      <references pn="section-6.2">
        <name slugifiedName="name-informative-references">Informative References</name>
        <reference anchor="RFC3550" target="https://www.rfc-editor.org/info/rfc3550" quoteTitle="true" derivedAnchor="RFC3550">
          <front>
            <title>RTP: A Transport Protocol for Real-Time Applications</title>
            <author fullname="H. Schulzrinne" initials="H." surname="Schulzrinne"/>
            <author fullname="S. Casner" initials="S." surname="Casner"/>
            <author fullname="R. Frederick" initials="R." surname="Frederick"/>
            <author fullname="V. Jacobson" initials="V." surname="Jacobson"/>
            <date month="July" year="2003"/>
            <abstract>
              <t indent="0">This memorandum describes RTP, the real-time transport protocol. RTP provides end-to-end network transport functions suitable for applications transmitting real-time data, such as audio, video or simulation data, over multicast or unicast network services. RTP does not address resource reservation and does not guarantee quality-of- service for real-time services. The data transport is augmented by a control protocol (RTCP) to allow monitoring of the data delivery in a manner scalable to large multicast networks, and to provide minimal control and identification functionality. RTP and RTCP are designed to be independent of the underlying transport and network layers. The protocol supports the use of RTP-level translators and mixers. Most of the text in this memorandum is identical to RFC 1889 which it obsoletes. There are no changes in the packet formats on the wire, only changes to the rules and algorithms governing how the protocol is used. The biggest change is an enhancement to the scalable timer algorithm for calculating when to send RTCP packets in order to minimize transmission in excess of the intended rate when many participants join a session simultaneously. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="STD" value="64"/>
          <seriesInfo name="RFC" value="3550"/>
          <seriesInfo name="DOI" value="10.17487/RFC3550"/>
        </reference>
        <reference anchor="RFC3711" target="https://www.rfc-editor.org/info/rfc3711" quoteTitle="true" derivedAnchor="RFC3711">
          <front>
            <title>The Secure Real-time Transport Protocol (SRTP)</title>
            <author fullname="M. Baugher" initials="M." surname="Baugher"/>
            <author fullname="D. McGrew" initials="D." surname="McGrew"/>
            <author fullname="M. Naslund" initials="M." surname="Naslund"/>
            <author fullname="E. Carrara" initials="E." surname="Carrara"/>
            <author fullname="K. Norrman" initials="K." surname="Norrman"/>
            <date month="March" year="2004"/>
            <abstract>
              <t indent="0">This document describes the Secure Real-time Transport Protocol (SRTP), a profile of the Real-time Transport Protocol (RTP), which can provide confidentiality, message authentication, and replay protection to the RTP traffic and to the control traffic for RTP, the Real-time Transport Control Protocol (RTCP). [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="3711"/>
          <seriesInfo name="DOI" value="10.17487/RFC3711"/>
        </reference>
        <reference anchor="RFC5104" target="https://www.rfc-editor.org/info/rfc5104" quoteTitle="true" derivedAnchor="RFC5104">
          <front>
            <title>Codec Control Messages in the RTP Audio-Visual Profile with Feedback (AVPF)</title>
            <author fullname="S. Wenger" initials="S." surname="Wenger"/>
            <author fullname="U. Chandra" initials="U." surname="Chandra"/>
            <author fullname="M. Westerlund" initials="M." surname="Westerlund"/>
            <author fullname="B. Burman" initials="B." surname="Burman"/>
            <date month="February" year="2008"/>
            <abstract>
              <t indent="0">This document specifies a few extensions to the messages defined in the Audio-Visual Profile with Feedback (AVPF). They are helpful primarily in conversational multimedia scenarios where centralized multipoint functionalities are in use. However, some are also usable in smaller multicast environments and point-to-point calls.</t>
              <t indent="0">The extensions discussed are messages related to the ITU-T Rec. H.271 Video Back Channel, Full Intra Request, Temporary Maximum Media Stream Bit Rate, and Temporal-Spatial Trade-off. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="5104"/>
          <seriesInfo name="DOI" value="10.17487/RFC5104"/>
        </reference>
        <reference anchor="RFC6464" target="https://www.rfc-editor.org/info/rfc6464" quoteTitle="true" derivedAnchor="RFC6464">
          <front>
            <title>A Real-time Transport Protocol (RTP) Header Extension for Client-to-Mixer Audio Level Indication</title>
            <author fullname="J. Lennox" initials="J." role="editor" surname="Lennox"/>
            <author fullname="E. Ivov" initials="E." surname="Ivov"/>
            <author fullname="E. Marocco" initials="E." surname="Marocco"/>
            <date month="December" year="2011"/>
            <abstract>
              <t indent="0">This document defines a mechanism by which packets of Real-time Transport Protocol (RTP) audio streams can indicate, in an RTP header extension, the audio level of the audio sample carried in the RTP packet. In large conferences, this can reduce the load on an audio mixer or other middlebox that wants to forward only a few of the loudest audio streams, without requiring it to decode and measure every stream that is received. [STANDARDS-TRACK]</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="6464"/>
          <seriesInfo name="DOI" value="10.17487/RFC6464"/>
        </reference>
        <reference anchor="RFC7656" target="https://www.rfc-editor.org/info/rfc7656" quoteTitle="true" derivedAnchor="RFC7656">
          <front>
            <title>A Taxonomy of Semantics and Mechanisms for Real-Time Transport Protocol (RTP) Sources</title>
            <author fullname="J. Lennox" initials="J." surname="Lennox"/>
            <author fullname="K. Gross" initials="K." surname="Gross"/>
            <author fullname="S. Nandakumar" initials="S." surname="Nandakumar"/>
            <author fullname="G. Salgueiro" initials="G." surname="Salgueiro"/>
            <author fullname="B. Burman" initials="B." role="editor" surname="Burman"/>
            <date month="November" year="2015"/>
            <abstract>
              <t indent="0">The terminology about, and associations among, Real-time Transport Protocol (RTP) sources can be complex and somewhat opaque. This document describes a number of existing and proposed properties and relationships among RTP sources and defines common terminology for discussing protocol entities and their relationships.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7656"/>
          <seriesInfo name="DOI" value="10.17487/RFC7656"/>
        </reference>
        <reference anchor="RFC7667" target="https://www.rfc-editor.org/info/rfc7667" quoteTitle="true" derivedAnchor="RFC7667">
          <front>
            <title>RTP Topologies</title>
            <author fullname="M. Westerlund" initials="M." surname="Westerlund"/>
            <author fullname="S. Wenger" initials="S." surname="Wenger"/>
            <date month="November" year="2015"/>
            <abstract>
              <t indent="0">This document discusses point-to-point and multi-endpoint topologies used in environments based on the Real-time Transport Protocol (RTP). In particular, centralized topologies commonly employed in the video conferencing industry are mapped to the RTP terminology.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="7667"/>
          <seriesInfo name="DOI" value="10.17487/RFC7667"/>
        </reference>
        <reference anchor="RFC8871" target="https://www.rfc-editor.org/info/rfc8871" quoteTitle="true" derivedAnchor="RFC8871">
          <front>
            <title>A Solution Framework for Private Media in Privacy-Enhanced RTP Conferencing (PERC)</title>
            <author fullname="P. Jones" initials="P." surname="Jones"/>
            <author fullname="D. Benham" initials="D." surname="Benham"/>
            <author fullname="C. Groves" initials="C." surname="Groves"/>
            <date month="January" year="2021"/>
            <abstract>
              <t indent="0">This document describes a solution framework for ensuring that media confidentiality and integrity are maintained end to end within the context of a switched conferencing environment where Media Distributors are not trusted with the end-to-end media encryption keys. The solution builds upon existing security mechanisms defined for the Real-time Transport Protocol (RTP).</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="8871"/>
          <seriesInfo name="DOI" value="10.17487/RFC8871"/>
        </reference>
        <reference anchor="RFC9335" target="https://www.rfc-editor.org/info/rfc9335" quoteTitle="true" derivedAnchor="RFC9335">
          <front>
            <title>Completely Encrypting RTP Header Extensions and Contributing Sources</title>
            <author fullname="J. Uberti" initials="J." surname="Uberti"/>
            <author fullname="C. Jennings" initials="C." surname="Jennings"/>
            <author fullname="S. Murillo" initials="S." surname="Murillo"/>
            <date month="January" year="2023"/>
            <abstract>
              <t indent="0">While the Secure Real-time Transport Protocol (SRTP) provides confidentiality for the contents of a media packet, a significant amount of metadata is left unprotected, including RTP header extensions and contributing sources (CSRCs). However, this data can be moderately sensitive in many applications. While there have been previous attempts to protect this data, they have had limited deployment, due to complexity as well as technical limitations.</t>
              <t indent="0">This document updates RFC 3711, the SRTP specification, and defines Cryptex as a new mechanism that completely encrypts header extensions and CSRCs and uses simpler Session Description Protocol (SDP) signaling with the goal of facilitating deployment.</t>
            </abstract>
          </front>
          <seriesInfo name="RFC" value="9335"/>
          <seriesInfo name="DOI" value="10.17487/RFC9335"/>
        </reference>
        <reference anchor="RFC9627" target="https://www.rfc-editor.org/info/rfc9627" quoteTitle="true" derivedAnchor="RFC9627">
          <front>
            <title>The Layer Refresh Request (LRR) RTCP Feedback Message</title>
            <author initials="J." surname="Lennox" fullname="Jonathan Lennox">
              <organization showOnFrontPage="true">8x8, Inc. / Jitsi</organization>
            </author>
            <author initials="D." surname="Hong" fullname="Danny Hong">
              <organization showOnFrontPage="true">Google, Inc.</organization>
            </author>
            <author initials="J." surname="Uberti" fullname="Justin Uberti">
              <organization showOnFrontPage="true">OpenAI</organization>
            </author>
            <author initials="S." surname="Holmer" fullname="Stefan Holmer">
              <organization showOnFrontPage="true">Google, Inc.</organization>
            </author>
            <author initials="M." surname="Flodman" fullname="Magnus Flodman">
              <organization showOnFrontPage="true">Google, Inc.</organization>
            </author>
            <date month="March" year="2025"/>
          </front>
          <seriesInfo name="RFC" value="9627"/>
          <seriesInfo name="DOI" value="10.17487/RFC9627"/>
        </reference>
        <reference anchor="RFC9628" target="https://www.rfc-editor.org/info/rfc9628" quoteTitle="true" derivedAnchor="RFC9628">
          <front>
            <title>RTP Payload Format for VP9 Video</title>
            <author initials="J." surname="Uberti" fullname="Justin Uberti">
              <organization showOnFrontPage="true">OpenAI</organization>
            </author>
            <author initials="S." surname="Holmer" fullname="Stefan Holmer">
              <organization showOnFrontPage="true">Google, Inc.</organization>
            </author>
            <author initials="M." surname="Flodman" fullname="Magnus Flodman">
              <organization showOnFrontPage="true">Google, Inc.</organization>
            </author>
            <author initials="D." surname="Hong" fullname="Danny Hong">
              <organization showOnFrontPage="true">Google, Inc.</organization>
            </author>
            <author initials="J." surname="Lennox" fullname="Jonathan Lennox">
              <organization showOnFrontPage="true">8x8, Inc. / Jitsi</organization>
            </author>
            <date month="March" year="2025"/>
          </front>
          <seriesInfo name="RFC" value="9628"/>
          <seriesInfo name="DOI" value="10.17487/RFC9628"/>
        </reference>
      </references>
    </references>
    <section numbered="false" removeInRFC="false" toc="include" pn="section-appendix.a">
      <name slugifiedName="name-acknowledgements">Acknowledgements</name>
      <t indent="0" pn="section-appendix.a-1">Many thanks to  <contact fullname="Bernard Aboba"/>,  <contact fullname="Jonathan Lennox"/>,  <contact fullname="Stephan Wenger"/>,  <contact fullname="Dale Worley"/>, and  <contact fullname="Magnus Westerlund"/> for their inputs.</t>
    </section>
    <section anchor="authors-addresses" numbered="false" removeInRFC="false" toc="include" pn="section-appendix.b">
      <name slugifiedName="name-authors-addresses">Authors' Addresses</name>
      <author fullname="Mo Zanaty" initials="M" surname="Zanaty">
        <organization showOnFrontPage="true">Cisco Systems</organization>
        <address>
          <postal>
            <street>170 West Tasman Drive</street>
            <city>San Jose</city>
            <region>CA</region>
            <code>95134</code>
            <country>United States of America</country>
          </postal>
          <email>mzanaty@cisco.com</email>
        </address>
      </author>
      <author initials="E." surname="Berger" fullname="Espen Berger">
        <organization showOnFrontPage="true">Cisco Systems</organization>
        <address>
          <email>espeberg@cisco.com</email>
        </address>
      </author>
      <author fullname="Suhas Nandakumar" initials="S" surname="Nandakumar">
        <organization showOnFrontPage="true">Cisco Systems</organization>
        <address>
          <postal>
            <street>170 West Tasman Drive</street>
            <city>San Jose</city>
            <region>CA</region>
            <code>95134</code>
            <country>United States of America</country>
          </postal>
          <email>snandaku@cisco.com</email>
        </address>
      </author>
    </section>
  </back>
</rfc>
