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<rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std"
     docName="draft-ietf-avtcore-rtp-multi-stream-optimisation-12"
     number="8861" ipr="trust200902" updates=""> updates="" obsoletes=""
     submissionType="IETF" consensus="true" xml:lang="en" tocInclude="true" sortRefs="true" symRefs="true" version="3">
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  <front>
    <title abbrev="Grouping RTCP Reception Statistics">Sending Multiple RTP
    Streams in a Single RTP Session: Grouping RTCP RTP Control Protocol (RTCP) Reception Statistics and
    Other Feedback</title>

    <seriesInfo name="RFC" value="8861"/>

    <author fullname="Jonathan Lennox" initials="J." surname="Lennox">
      <organization abbrev="Vidyo">Vidyo, Inc.</organization> abbrev="8x8 / Jitsi">8x8, Inc. / Jitsi</organization>
      <address>
        <postal>
          <street>433 Hackensack Avenue</street>

          <street>Seventh Floor</street>

          <city>Hackensack</city>
          <city>Jersey City</city>
          <region>NJ</region>

          <code>07601</code>

          <country>US</country>
          <code>07302</code>
          <country>United States of America</country>
        </postal>

        <email>jonathan@vidyo.com</email>
        <email>jonathan.lennox@8x8.com</email>
      </address>
    </author>
    <author fullname="Magnus Westerlund" initials="M." surname="Westerlund">
      <organization>Ericsson</organization>
      <address>
        <postal>
          <street>Farogatan 2</street>

          <city>SE-164 80 Kista</city>
          <city>Kista</city>
          <code>164 80</code>
          <country>Sweden</country>
        </postal>
        <phone>+46 10 714 82 87</phone>
        <email>magnus.westerlund@ericsson.com</email>
      </address>
    </author>
    <author fullname="Qin Wu" initials="Q." surname="Wu">
      <organization>Huawei</organization>
      <address>
        <postal>
          <street>101 Software Avenue, Yuhua District</street>
          <city>Nanjing, Jiangsu 210012</city>
          <country>China</country>
        </postal>
        <email>bill.wu@huawei.com</email>
      </address>
    </author>
    <author fullname="Colin Perkins" initials="C. " surname="Perkins">
      <organization>University of Glasgow</organization>
      <address>
        <postal>
          <street>School of Computing Science</street>
          <city>Glasgow</city>
          <code>G12 8QQ</code>
          <country>United Kingdom</country>
        </postal>
        <email>csp@csperkins.org</email>
      </address>
    </author>

    <date/>

    <workgroup>AVTCORE WG</workgroup>
    <date month="September" year="2020"/>

<keyword>RGRP</keyword>
<keyword>SDES</keyword>
<keyword>XR</keyword>
<keyword>Reporting</keyword>
<keyword>Group</keyword>

    <abstract>
      <t>RTP allows multiple RTP streams to be sent in a single session, session but
      requires each Synchronisation Synchronization Source (SSRC) to send RTCP RTP Control Protocol
      (RTCP)
      reception quality reports for every other SSRC visible in the session. This causes
      the number of RTCP reception reports to grow with the number of SSRCs,
      rather than the number of endpoints. In many cases cases, most of these RTCP
      reception reports are unnecessary, since all SSRCs of an endpoint are
      normally co-located and see the same reception quality. This memo
      defines a Reporting Group extension to RTCP to reduce the reporting
      overhead in such scenarios.</t>
    </abstract>
  </front>
  <middle>
    <section anchor="introduction" title="Introduction"> numbered="true" toc="default">
      <name>Introduction</name>
      <t>The Real-time Transport Protocol (RTP) <xref target="RFC3550"/> target="RFC3550" format="default"/> is a
      protocol for group communication, supporting multiparty multimedia
      sessions. A single RTP session can support multiple participants sending
      data at once, once and can also support participants sending multiple simultaneous
      RTP streams. Examples of the latter might include a participant with
      multiple cameras who chooses to send multiple views of a scene, or a
      participant that sends audio and video flows multiplexed in a single RTP
      session. Rules for handling RTP sessions containing multiple RTP streams
      are described in <xref target="RFC3550"/> target="RFC3550" format="default"/>, with some clarifications in
      <xref target="I-D.ietf-avtcore-rtp-multi-stream"/>.</t> target="RFC8108" format="default"/>.</t>
      <t>An RTP endpoint will have one or more synchronisation sources Synchronization Sources
      (SSRCs). It will have at least one RTP Stream, stream, and thus at least one SSRC, for each
      media source it sends, and it might use multiple SSRCs per media source
      when using <xref target="RFC6190">media target="RFC6190" format="default">media scalability features</xref>,
      forward error correction, <xref target="RFC4588">RTP target="RFC4588" format="default">RTP
      retransmission</xref>, or similar mechanisms. An endpoint that is not
      sending any RTP stream, streams will have at least one SSRC to use for reporting
      and any feedback messages. Each SSRC has to send RTCP sender reports RTP Control Protocol
      (RTCP) Sender Reports (SRs) corresponding to the RTP packets it sends, sends
      and receiver reports Receiver Reports (RRs) for traffic it receives. (SRs and RRs are
      described in <xref target="RFC3550"/>.) That is, every SSRC will send RTCP packets to
      report on every other SSRC. This rule is simple, but it can be quite
      inefficient for endpoints that send large numbers of RTP streams in a
      single RTP session. Consider a session comprising ten participants, each
      sending three media sources, each media source associated with their its own RTP stream. There will
      be 30 SSRCs in such an RTP session, and each of those 30 SSRCs will send
      an RTCP Sender Report/Receiver Report SR/RR packet (containing several report
      blocks) per reporting interval as each SSRC reports on all the others.
      However, the three SSRCs comprising each participant are commonly
      co-located such that they see identical reception quality. If there was
      a way to indicate that several SSRCs are co-located, co-located and see the same
      reception quality, then two-thirds of those RTCP reports could be
      suppressed. This would allow the remaining RTCP reports to be sent more
      often, while keeping within the same RTCP bandwidth fraction.</t>
      <t>This memo defines such an RTCP extension, extension: RTCP Reporting Groups. This
      extension is used to indicate the SSRCs that originate from the same
      endpoint,
      endpoint and therefore have identical reception quality, hence allowing
      the endpoints to suppress unnecessary RTCP reception quality
      reports.</t>
    </section>
    <section title="Terminology"> numbered="true" toc="default">
      <name>Terminology</name>
      <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
      "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", "<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 "OPTIONAL" "<bcp14>OPTIONAL</bcp14>" in this document are
      to be interpreted as described in BCP&nbsp;14 <xref
      target="RFC2119"/>.</t> target="RFC2119"/>
      <xref target="RFC8174"/> when, and only when, they appear in all
      capitals, as shown here.</t>
    </section>
    <section anchor="reportgroups" title="RTCP numbered="true" toc="default">
      <name>RTCP Reporting Groups"> Groups</name>
      <t>An RTCP Reporting Group is a set of synchronization sources (SSRCs) SSRCs that are co-located co&nbhy;located at a single endpoint (which could be an end host or
      a middlebox) in an RTP session. Since they are co-located, every SSRC in
      the RTCP reporting group Reporting Group will have an identical view of the network
      conditions,
      conditions and will see the same lost packets, jitter, etc. This allows a
      single representative to send RTCP reception quality reports on behalf
      of the rest of the reporting group, Reporting Group, reducing the number of RTCP packets
      that need to be sent without loss of information.</t>
      <section title="Semantics numbered="true" toc="default">
        <name>Semantics and Behaviour Behavior of RTCP Reporting Groups"> Groups</name>
        <t>A group of co-located SSRCs that see identical network conditions
        can form an RTCP reporting group. Reporting Group. If reporting groups Reporting Groups are in use, an
        RTP endpoint with multiple SSRCs MAY <bcp14>MAY</bcp14> put those SSRCs into a reporting
        group Reporting
        Group if their view of the network is identical; identical, i.e., if they report
        on traffic received at the same interface of an RTP endpoint. SSRCs
        with different views of the network MUST NOT <bcp14>MUST NOT</bcp14> be put into the same
        reporting group.</t>
        Reporting Group.</t>
        <t>An endpoint that has combined its SSRCs into an RTCP reporting
        group Reporting
        Group will choose one (or a subset) of those SSRCs to act as
        "reporting source(s)" for that RTCP reporting group. Reporting Group. A reporting
        source will send RTCP SR/RR reception quality reports on behalf of the
        other members of the RTCP reporting group. Reporting Group. A reporting source MUST <bcp14>MUST</bcp14>
        suppress the RTCP SR/RR reports that relate to other members of the
        reporting group,
        Reporting Group and only report on remote SSRCs. The other members
        (non reporting
        (non-reporting sources) of the RTCP reporting group Reporting Group will suppress
        their RTCP reception quality reports, reports and will instead send an
        RTCP RGRS Reporting Group Reporting Sources (RGRS)
        packet (see <xref target="sec-rgrs"/>) target="sec-rgrs" format="default"/>) to indicate that they are part
        of an RTCP reporting group Reporting Group and give the SSRCs of the reporting
        sources.</t>
        <t>If there are large numbers of remote SSRCs in the RTP session, then
        the reception quality reports generated by the reporting source might
        grow too large to fit into a single compound RTCP packet, forcing the
        reporting source to use a round-robin policy to determine what remote
        SSRCs it includes in each compound RTCP packet, and so reducing the
        frequency of reports on each SSRC. To avoid this, in sessions with
        large numbers of remote SSRCs, an RTCP reporting group MAY Reporting Group <bcp14>MAY</bcp14> use more
        than one reporting source. If several SSRCs are acting as reporting
        sources for an RTCP reporting group, Reporting Group, then each reporting source MUST <bcp14>MUST</bcp14>
        have non-overlapping sets of remote SSRCs it reports on.</t>
        <t>An endpoint MUST NOT <bcp14>MUST NOT</bcp14> create an RTCP reporting group Reporting Group that comprises
        only a single local SSRC (i.e., an RTCP reporting group Reporting Group where the
        reporting source is the only member of the group), unless it is
        anticipated that the group might have additional SSRCs added to it in
        the future.</t>
        <t>If a reporting source leaves the RTP session (i.e., if it sends a an
        RTCP BYE packet, packet or it leaves the session without sending a BYE under
        according to the
        rules of <xref target="RFC3550"/> section 6.3.7), target="RFC3550" sectionFormat="comma" section="6.3.7"/>), the remaining
        members of the RTCP reporting group MUST either (a) have Reporting Group <bcp14>MUST</bcp14> (a)&nbsp;have another
        reporting source, source -- if one exists, exists -- report on the remote SSRCs that
        the leaving SSRC had reported on, (b) choose (b)&nbsp;choose a new reporting source, or (c)
        disband (c)&nbsp;disband the RTCP reporting group Reporting Group and begin sending reception quality
        reports following per <xref target="RFC3550"/> target="RFC3550" format="default"/> and <xref
        target="I-D.ietf-avtcore-rtp-multi-stream"/>.</t> target="RFC8108" format="default"/>.</t>
        <t>The RTCP timing rules assign different bandwidth fractions to
        senders and receivers. This lets senders transmit RTCP reception
        quality reports more often than receivers. If a reporting source in an
        RTCP reporting group Reporting Group is a receiver, receiver but one or more non-reporting
        SSRCs in the RTCP reporting group Reporting Group are senders, then the endpoint MAY <bcp14>MAY</bcp14>
        treat the reporting source as a sender for the purpose of RTCP
        bandwidth allocation, increasing its RTCP bandwidth allocation,
        provided it also treats one of the senders as if it were a receiver
        and makes the corresponding reduction in RTCP bandwidth for that SSRC.
        However, the application needs to consider the impact on the frequency
        of transmitting of the synchronization information included in RTCP
        Sender Reports.</t> SRs.</t>
      </section>
      <section title="Identifying numbered="true" toc="default">
        <name>Identifying Members of an RTCP Reporting Group"> Group</name>
        <t>When RTCP Reporting Groups are in use, the other SSRCs in the RTP
        session need to be able to identify which SSRCs are members of an RTCP
        reporting group.
        Reporting Group. Two RTCP extensions are defined to support this: the
        RTCP RGRP SDES Reporting Group (RGRP) Source Description (SDES) item is used by the reporting source(s) to identify an
        RTCP reporting group, Reporting Group, and the RTCP RGRS packet is used by other
        members of an RTCP reporting group Reporting Group to identify the reporting
        source(s).</t>
        <section anchor="sec-rgrp"
                 title="Definition numbered="true" toc="default">
          <name>Definition and Use of the RTCP RGRP SDES Item"> Item</name>
          <t>This document defines a new RTCP RGRP SDES item to identify an RTCP
          reporting group.
          Reporting Group. The motivation for giving a reporting group Reporting Group an
          identify
          identifier is to ensure that the (1)&nbsp;the RTCP reporting group Reporting Group and its member
          SSRCs can be correctly associated when there are multiple reporting
          sources,
          sources and to ensure that a (2)&nbsp;a reporting SSRC can be associated with
          the correct reporting group Reporting Group if an SSRC collision occurs.</t>
          <t>This document defines the RTCP Source Description (SDES) RGRP SDES item.
 The RTCP SDES RGRP SDES item MUST <bcp14>MUST</bcp14> be sent by the reporting sources
          in a reporting group, Reporting Group and MUST NOT <bcp14>MUST NOT</bcp14> be sent by other members of the
          reporting group
          Reporting Group or by SSRCs that are not members of any RTCP
          reporting group.
          Reporting Group. Specifically, every reporting source in an RTCP
          reporting group MUST
          Reporting Group <bcp14>MUST</bcp14> include an RTCP SDES packet containing an RGRP
          item in every compound RTCP packet in which it sends an RR or SR
          packet (i.e., in every RTCP packet it sends, unless <xref
          target="RFC5506">Reduced-Size target="RFC5506" format="default">Reduced-Size RTCP</xref> is in use).</t>

          <t>Syntactically, the format of the RTCP SDES RGRP SDES item is identical
          to that of the <xref target="RFC7022">RTCP target="RFC7022" format="default">RTCP SDES CNAME item</xref>,
          except that the SDES item type field MUST <bcp14>MUST</bcp14> have value RGRP=(TBA) RGRP=11
          instead of CNAME=1. The value of the RTCP SDES RGRP SDES item MUST <bcp14>MUST</bcp14> be
          chosen with the same concerns about global uniqueness and the same
          privacy considerations as the RTCP SDES CNAME. The value of the RTCP
          SDES
          RGRP SDES item MUST <bcp14>MUST</bcp14> be stable throughout the lifetime of the
          reporting group,
          Reporting Group, even if some or all of the reporting sources change
          their SSRC due to collisions, collisions or if the set of reporting sources
          changes.</t>

          <t><list style="empty">
              <t>Note to RFC Editor: please replace (TBA) in the above
              paragraph with the RTCP SDES item type number assigned to the
              RGRP item, then delete this note.</t>
            </list></t>
          <t>An RTP mixer or translator that forwards RTCP SR or RR packets
          from members of a reporting group MUST Reporting Group <bcp14>MUST</bcp14> forward the corresponding
          RTCP SDES RGRP SDES items as well, even if it otherwise strips SDES items
          other than the CNAME item.</t>
        </section>
        <section anchor="sec-rgrs"
                 title="Definition numbered="true" toc="default">
          <name>Definition and Use of the RTCP RGRS Packet"> Packet</name>
          <t>A new RTCP packet type is defined to allow the members of an RTCP
          reporting group
          Reporting Group to identify the reporting sources for that group.
          This allows participants in an RTP session to distinguish an SSRC
          that is sending empty RTCP reception reports because it is a member
          of an RTCP reporting group, Reporting Group from an SSRC that is sending empty RTCP
          reception reports because it is not receiving any traffic. It also
          explicitly identifies the reporting sources, allowing other members
          of the RTP session to know (1)&nbsp;know which SSRCs are acting as the reporting
          sources for an RTCP reporting group, Reporting Group and allowing them to detect (2)&nbsp;detect if
          RTCP packets from any of the reporting sources are being lost.</t>
          <t>The format of the RTCP RGRS packet is defined below. It comprises
          the fixed RTCP header that indicates the packet type and length, the
          SSRC of the packet sender, and a list of reporting sources for the
          RTCP reporting group Reporting Group of which the packet sender is a member.</t>

          <figure>
            <artwork><![CDATA[
          <artwork name="" type="" align="left" alt=""><![CDATA[
 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|V=2|P|    SC   | PT=RGRS(TBA) PT=RGRS(212)  |             length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     SSRC of packet sender                     |
+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+
:          List of SSRC(s) for the Reporting Source(s)          :
:                              ...                              :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+]]></artwork>
          </figure>
          <t>The fields in the RTCP RGRS packet have the following definition:
          <list style="hanging">
              <t hangText="version (V):">2 bits definitions:
          </t>
          <dl newline="false" spacing="normal">
            <dt>version (V):</dt>
            <dd>2-bit unsigned integer. This field
              identifies the RTP version. The current RTP version is 2.</t>

              <t hangText="padding (P):">1 2.</dd>
            <dt>padding (P):</dt>
            <dd>1 bit. If set, the padding bit
              indicates that the RTCP packet contains additional padding
              octets at the end that are not part of the control information
              but are included in the length field. See <xref
              target="RFC3550"/>.</t>

              <t hangText="Source target="RFC3550" format="default"/>.</dd>
            <dt>Source Count (SC):">5 bits (SC):</dt>
            <dd>5-bit unsigned integer.
              Indicates the number of reporting source SSRCs that are included
              in this RTCP packet. As the RTCP RGRS packet MUST NOT <bcp14>MUST NOT</bcp14> be not sent by reporting sources, all the SSRCs in the list of
              reporting sources will be different from the SSRC of the packet
              sender. Every RTCP RGRS packet MUST <bcp14>MUST</bcp14> contain at least one
              reporting source SSRC.</t>

              <t hangText="Payload SSRC.</dd>
            <dt>Payload type (PT):">8 bits (PT):</dt>
            <dd>
              <t>8-bit unsigned integer. The
              RTCP packet type number that identifies the packet as being an
              RTCP RGRS packet. The RGRS RTCP packet has the value [TBA].
              <list style="empty">
                  <t>Note to RFC Editor: please replace [TBA] here, and in the
                  packet format diagram above, with the RTCP packet type that
                  IANA assigns to the RTCP RGRS packet.</t>
                </list></t>

              <t hangText="Length:">16 bits 212.
              </t>
            </dd>
            <dt>Length:</dt>
            <dd>16-bit unsigned integer. The length of
              this packet in 32-bit words minus one, including the header and
              any padding. This is in line with the definition of the length
              field used in RTCP sender SRs and receiver reports RRs <xref
              target="RFC3550"/>. target="RFC3550" format="default"/>. Since all RTCP RGRS packets include at least
              one reporting source SSRC, the length will always be 2 or
              greater.</t>

              <t hangText="SSRC
              greater.</dd>
            <dt>SSRC of packet sender:">32 sender:</dt>
            <dd>32 bits. The SSRC of the
              sender of this packet.</t>

              <t hangText="List packet.</dd>
            <dt>List of SSRCs for the Reporting Source(s):">A Source(s):</dt>
            <dd>A variable length size number (as indicated by the SC header field) of the 32
              bit
              32&nbhy;bit SSRC values of the reporting sources for the
RTCP Reporting Group of which the packet sender is a member.</t>
            </list></t> member.</dd>
          </dl>
          <t>Every source that belongs to an RTCP reporting group Reporting Group but is not a
          reporting source MUST <bcp14>MUST</bcp14> include an RTCP RGRS packet in every compound
          RTCP packet in which it sends an RR or SR packet (i.e., in every
          RTCP packet it sends, unless <xref target="RFC5506"> target="RFC5506" format="default"> Reduced-Size
          RTCP</xref> is in use). Each RTCP RGRS packet MUST <bcp14>MUST</bcp14> contain the SSRC
          identifier of at least one reporting source. If there are more
          reporting sources in an RTCP reporting group Reporting Group than can fit into an
          RTCP RGRS packet, the members of that reporting group MUST Reporting Group <bcp14>MUST</bcp14> send the
          SSRCs of the reporting sources in a round-robin fashion in
          consecutive RTCP RGRS packets, such that all the SSRCs of the
          reporting sources are included over the course of several RTCP
          reporting intervals.</t>
          <t>An RTP mixer or translator that forwards RTCP SR or RR packets
          from members of a reporting group MUST Reporting Group <bcp14>MUST</bcp14> also forward the
          corresponding RGRS RTCP packets. If the RTP mixer or translator
          rewrites SSRC values of the packets it forwards, it MUST <bcp14>MUST</bcp14> make the
          corresponding changes to the RTCP RGRS packets.</t>
        </section>
      </section>
      <section title="Interactions numbered="true" toc="default">
        <name>Interactions with the RTP/AVPF Feedback Profile">
        <t>Use Profile</name>
        <t>The use of the RTP/AVPF Feedback Profile <xref target="RFC4585"/> target="RFC4585" format="default"/>
        allows SSRCs to send rapid RTCP feedback requests and codec control
        messages. If the use of the RTP/AVPF profile has been negotiated in an RTP
        session, members of an RTCP reporting group Reporting Group can send rapid RTCP
        feedback and codec control messages following per <xref target="RFC4585"/>
        and target="RFC5104"
        format="default"/>, per <xref target="RFC5104"/>, target="RFC4585" format="default"/>
        as updated by Section 5.4 of <xref
        target="I-D.ietf-avtcore-rtp-multi-stream"/>, target="RFC8108" sectionFormat="of"
        section="5.4"/>, and by the following considerations.</t>
        <t>The members of an RTCP reporting group Reporting Group will all see identical
        network conditions. Accordingly, one might therefore think that it
        doesn't matter which SSRC in the reporting group Reporting Group sends the RTP/AVPF
        feedback or codec control messages. There might be, however, cases
        where the sender of the feedback/codec control message has semantic
        importance, or when only a subset of the members of an RTCP reporting
        group Reporting
        Group might want to send RTP/AVPF feedback or a codec control message
        in response to a particular event. For example, an RTP video sender
        might choose to treat packet loss feedback received from SSRCs known
        to be audio receivers with less urgency than feedback that it receives
        from video receivers when deciding what packets to retransmit, and a
        multimedia receiver using reporting groups Reporting Groups might want to choose the
        outgoing SSRC for feedback packets to reflect this.</t>
        <t>Each member of an RTCP reporting group SHOULD Reporting Group <bcp14>SHOULD</bcp14> therefore send
        RTP/AVPF feedback/codec control messages independently of the other
        members of the reporting group, Reporting Group, to respect the semantic meaning of the
        message sender. The suppression rules of <xref target="RFC4585"/> target="RFC4585" format="default"/> will
        ensure that only a single copy of each feedback packet is (typically)
        generated, even if several members of a reporting group Reporting Group send the same
        feedback. When an endpoint knows that several members of its RTCP
        reporting group
        Reporting Group will be sending identical feedback, feedback and that the
        sender of the feedback is not semantically important, then that
        endpoint MAY <bcp14>MAY</bcp14> choose to send all its feedback from the reporting source
        and deterministically suppress feedback packets generated by the other
        sources in the reporting group.</t> Reporting Group.</t>
        <t>It is important to note that the RTP/AVPF timing rules operate on a
        per-SSRC basis. Using a single reporting source to send all feedback
        for a reporting group Reporting Group will hence limit the amount of feedback that can
        be sent to that which can be sent by one SSRC. If this limit is a
        problem, then the reporting group Reporting Group can allow each of its members to
        send its own feedback, using its own SSRC.</t>
        <t>If the RTP/AVPF feedback messages or codec control requests are
        sent as compound RTCP packets, then those compound RTCP packets MUST <bcp14>MUST</bcp14>
        include either an RTCP RGRS packet or an RTCP SDES RGRP SDES item,
        depending on whether they are sent by the reporting source or a
        non-reporting
        non&nbhy;reporting source in the RTCP reporting group Reporting Group, respectively. The
        contents of non-compound noncompound RTCP feedback or codec control messages are
        not affected by the use of RTCP reporting groups.</t> Reporting Groups.</t>
      </section>
      <section title="Interactions numbered="true" toc="default">
        <name>Interactions with RTCP Extended Report (XR) Packets"> Packets</name>
        <t>When using RTCP Extended Reports Report (XR) packets <xref target="RFC3611"/> target="RFC3611" format="default"/> with
        RTCP reporting groups, Reporting Groups, it is RECOMMENDED <bcp14>RECOMMENDED</bcp14> that the reporting source is be
        used to send the RTCP XR packets. If multiple reporting sources are in
        use, the reporting source that sends the SR/RR packets that relate to
        a particular remote SSRC SHOULD <bcp14>SHOULD</bcp14> send the RTCP XR reports about that
        SSRC. This is motivated as one commonly combine the RTCP XR metrics
        with the regular report block to more fully understand the situation.
        Receiving these blocks in different compound packets reduces their
        value
        value, as the measuring intervals are not synchronized in those
        cases.</t>
        <t>Some RTCP XR report blocks are specific to particular types of
        media,
        media and might be relevant to only some members of a reporting
        group. Reporting
        Group. For example, it would make no sense for an SSRC that is
        receiving video to send a VoIP Voice over IP (VoIP) metric RTCP XR report block. Such media
        specific
        media-specific RTCP XR report blocks MUST <bcp14>MUST</bcp14> be sent by the SSRC to which they
        are relevant, relevant and MUST NOT <bcp14>MUST NOT</bcp14> be included in the common report sent by
        the reporting source. This might mean that some SSRCs send RTCP XR
        packets in compound RTCP packets that contain an empty RTCP SR/RR
        packet,
        packet and that the time period covered by the RTCP XR packet is
        different to from that covered by the RTCP SR/RR packet. If it is important
        that the RTCP XR packet and RTCP SR/RR packet cover the same time
        period, then that source SHOULD <bcp14>SHOULD</bcp14> be removed from the RTCP reporting
        group, Reporting
        Group, and send standard RTCP packets be sent instead.</t>
      </section>
      <section title="Middlebox Considerations"> numbered="true" toc="default">
        <name>Middlebox Considerations</name>
        <t>Many different types of middlebox middleboxes are used with RTP. RTCP reporting
        groups Reporting
        Groups are potentially relevant to those types of RTP middlebox middleboxes that
        have their own SSRCs and generate RTCP reports for the traffic they
        receive. RTP middleboxes that do not have their own SSRC, SSRC and that
        don't do not
        send RTCP reports on the traffic they receive, receive cannot use the
        RTCP reporting groups Reporting Group extension, since they generate no RTCP reports
        to that group.</t>
        <t>An RTP middlebox that has several SSRCs of its own can use the RTCP
        reporting groups
        Reporting Group extension to group the RTCP reports it generates.
        This can occur, for example, if a middlebox is acting as an RTP mixer
        for both audio and video flows that are multiplexed onto a single RTP
        session, where the middlebox has one SSRC for the audio mixer and one
        for the video mixer part, and when the middlebox wants to avoid cross
        reporting
        cross-reporting between audio and video.</t>
        <t>A middlebox cannot use the RTCP reporting groups Reporting Group extension to group
        RTCP packets from the SSRCs that it is forwarding. It can, however,
        group the RTCP packets from the SSRCs it is forwarding into compound
        RTCP packets packets, following the rules in Section 6.1 of <xref
        target="RFC3550"/> target="RFC3550" sectionFormat="of" section="6.1"/> and Section 5.3 of <xref
        target="I-D.ietf-avtcore-rtp-multi-stream"/>. target="RFC8108" sectionFormat="of" section="5.3"/>. If the middlebox is
        using RTCP reporting groups Reporting Groups for its own SSRCs, it MAY <bcp14>MAY</bcp14> include RTCP
        packets from the SSRCs that it is forwarding as part of the compound
        RTCP packets its reporting source generates.</t>
        <t>A middlebox that forwards RTCP SR or RR packets sent by members of
        a reporting group MUST Reporting Group <bcp14>MUST</bcp14> forward the corresponding RTCP SDES
        RGRP SDES items,
        as described in <xref target="sec-rgrp"/>. target="sec-rgrp" format="default"/>. A middlebox that forwards
        RTCP SR or RR packets sent by member members of a reporting group MUST Reporting Group <bcp14>MUST</bcp14> also
        forward the corresponding RTCP RGRS packets, as described in <xref
        target="sec-rgrs"/>. target="sec-rgrs" format="default"/>. Failure to forward these packets can cause
        compatibility problems, as described in <xref target="compat"/>.</t> target="compat" format="default"/>.</t>
        <t>If a middlebox rewrites SSRC values in the RTP and RTCP packets
        that it is forwarding, then it MUST <bcp14>MUST</bcp14> make the corresponding changes in
        RTCP SDES packets containing RGRP items and in RTCP RGRS packets, to
        allow them to be associated with the rewritten SSRCs.</t>
      </section>
      <section anchor="sdp" title="SDP Signalling numbered="true" toc="default">
        <name>SDP Signaling for Reporting Groups"> Groups</name>
        <t>This document defines the "a=rtcp-rgrp" <xref
        target="RFC4566">Session target="RFC4566" format="default">Session Description Protocol (SDP)</xref> attribute
        to indicate if the session participant is capable of supporting RTCP
        Reporting Groups for applications that use SDP for configuration of
        RTP sessions. It is a property attribute, attribute and hence takes no value.
        The <xref target="I-D.ietf-mmusic-sdp-mux-attributes">multiplexing target="RFC8859" format="default">multiplexing
        category</xref> is IDENTICAL, as the functionality applies on at the RTP
        session level. A participant that proposes the use of RTCP Reporting
        Groups SHALL <bcp14>SHALL</bcp14> itself support the reception of RTCP Reporting Groups.
        The formal definition of this attribute is:</t>

        <figure>
          <artwork><![CDATA[
   Name: rtcp-rgrp
   Value:
   Usage Level: session, media
   Charset Dependent: no
   Example:
      a=rtcp-rgrp
]]></artwork>
        </figure> is as follows:</t>

        <ul empty="true"><li>
          <dl spacing="compact">
            <dt>Name:</dt><dd>rtcp-rgrp</dd>
            <dt>Value:</dt><dd>None</dd>
            <dt>Usage Level:</dt><dd>session, media</dd>
            <dt>Charset Dependent:</dt><dd>no</dd>
            <dt>Example:</dt><dd>a=rtcp-rgrp</dd>
          </dl>
        </li>
        </ul>

        <t>When using SDP Offer/Answer <xref target="RFC3264"/>, target="RFC3264" format="default"/>, the following
        procedures are to be used: <list style="symbols">
            <t>Generating </t>
        <dl newline="true" spacing="normal">
          <dt>Generating the initial SDP offer: If offer:</dt>
            <dd>If the offerer supports the
            RTCP reporting group extensions, Reporting Group extensions and is willing to accept RTCP
            packets containing those extensions, then it MUST <bcp14>MUST</bcp14> include an
            "a=rtcp-rgrp" attribute in the initial offer. If the offerer does
            not support RTCP reporting groups extensions, Reporting Group extensions or is not willing to
            accept RTCP packets containing those extensions, then it MUST NOT <bcp14>MUST NOT</bcp14>
            include the "a=rtcp-rgrp" attribute in the offer.</t>

            <t>Generating offer.</dd>
          <dt>Generating the SDP answer: If answer:</dt>
            <dd>If the SDP offer contains an
            "a=rtcp-rgrp"
            "a=rtcp&nbhy;rgrp" attribute, and if the answerer supports RTCP
            reporting groups
            Reporting Groups and is willing to receive RTCP packets using the
            RTCP reporting groups Reporting Group extensions, then the answerer MAY <bcp14>MAY</bcp14> include an
            "a=rtcp-rgrp" attribute in the answer and MAY <bcp14>MAY</bcp14> send RTCP packets
            containing the RTCP reporting groups Reporting Group extensions. If the offer does
            not contain an "a=rtcp-rgrp" attribute, or if the offer does
            contain such an attribute but the answerer does not wish to accept
            RTCP packets using the RTCP reporting groups Reporting Group extensions, then the
            answer MUST NOT <bcp14>MUST NOT</bcp14> include an "a=rtcp-rgrp" attribute.</t>

            <t>Offerer Processing attribute.</dd>
          <dt>Offerer processing of the SDP Answer: If answer:</dt>
            <dd>If the SDP answer
            contains an "a=rtcp-rgrp" attribute, attribute and the corresponding offer
            also contained an "a=rtcp-rgrp" attribute, then the offerer MUST <bcp14>MUST</bcp14>
            be prepared to accept and process RTCP packets that contain the
            reporting groups extension,
            Reporting Group extensions and MAY <bcp14>MAY</bcp14> send RTCP packets that contain
            the reporting groups extension. Reporting Group extensions. If the SDP answer contains an
            "a=rtcp-rgrp" attribute, attribute but the corresponding offer did not
            contain the "a=rtcp-rgrp" "a=rtcp&nbhy;rgrp" attribute, then the offerer MUST <bcp14>MUST</bcp14> reject
            the call. If the SDP answer does not contain an "a=rtcp-rgrp"
            attribute, then the offerer MUST NOT <bcp14>MUST NOT</bcp14> send packets containing the
            RTCP reporting groups extensions, Reporting Group extensions and does not need to process
            packet
            packets containing the RTCP reporting groups extensions.</t>
          </list></t> Reporting Group extensions.</dd>
        </dl>
        <t>In declarative usage of SDP, such as the <xref
        target="RFC2326">Real Time target="RFC7826" format="default">Real-Time Streaming Protocol (RTSP)</xref> and the
        <xref target="RFC2974">Session target="RFC2974" format="default">Session Announcement Protocol (SAP)</xref>, the
        presence of the attribute indicates that the session participant MAY <bcp14>MAY</bcp14>
        use RTCP Reporting Groups in its RTCP transmissions. An implementation
        that doesn't explicitly support RTCP Reporting Groups MAY <bcp14>MAY</bcp14> join a an RTP
        session as long as it has been verified that the implementation
        doesn't suffer from the problems discussed in <xref
        target="compat"/>.</t> target="compat" format="default"/>.</t>
      </section>
    </section>
    <section title="Properties numbered="true" toc="default">
      <name>Properties of RTCP Reporting Groups"> Groups</name>
      <t>This section provides additional information on what the resulting
      properties are with (i.e., resulting effects or impacts) as related to the design specified in <xref
      target="reportgroups"/>. target="reportgroups"
      format="default"/>. The content of this section is
      non-normative.</t>
      <section anchor="reportgroups-bw"
               title="Bandwidth numbered="true" toc="default">
        <name>Bandwidth Benefits of RTCP Reporting Groups"> Groups</name>
        <t>To understand the benefits of RTCP reporting groups, Reporting Groups, consider a
        scenario in which the two endpoints in a session each have a hundred
        sources, of which eight each are sending within any given reporting
        interval.</t>
        <t>For ease of analysis, we can make the simplifying approximation
        that the duration of the RTCP reporting interval is equal to the total
        size of the RTCP packets sent during an RTCP interval, divided by the
        RTCP bandwidth. (This will be approximately true in scenarios where
        the bandwidth is not so high that the minimum RTCP interval is
        reached.) For To further simplification, simplify, we can assume that RTCP senders are
        following the recommendations regarding Compound compound RTCP Packets packets in <xref
        target="I-D.ietf-avtcore-rtp-multi-stream"/>; target="RFC8108" format="default"/>; thus, the per-packet
        transport-layer overhead will be small relative to the RTCP data.
        Thus, only the actual RTCP data itself need be considered.</t>
        <t>In a report interval in this scenario, there will, as a baseline,
        be 200 SDES packets, 184 RR packets, and 16 SR packets. This amounts
        to approximately 6.5 kB KB of RTCP packets per report interval, assuming 16-byte
        CNAMEs and no other SDES information.</t>
        <t>Using the original <xref target="RFC3550"/>
        everyone-reports-on-every-sender "everyone reports on every sender" feedback rules, rules
        <xref target="RFC3550" format="default"/>, each of the 184
        receivers will send 16 report blocks, and each of the 16 senders will
        send 15. This amounts to approximately 76 kB KB of report block traffic
        per interval; 92% of RTCP traffic consists of report blocks.</t>
        <t>If reporting groups Reporting Groups are used, however, there is only 0.4 kB KB of
        reports per interval, with no loss of useful information.
        Additionally, there will be (assuming 16-byte RGRPs, RGRPs and a single
        reporting source per reporting group) Reporting Group) an additional 2.4 kB KB per cycle
        of RTCP RGRP SDES items and RGRS packets. Put another way, the unmodified
        <xref target="RFC3550"/>
        reporting interval per <xref target="RFC3550" format="default"/> is approximately 9 times
        longer than if reporting groups Reporting Groups are in use.</t>
      </section>
      <section anchor="compat" title="Compatibility numbered="true" toc="default">
        <name>Compatibility of RTCP Reporting Groups"> Groups</name>
        <t>The RTCP traffic generated by receivers using RTCP Reporting Groups
        might appear, to observers unaware of these semantics, to be generated
        by receivers who are experiencing a network disconnection, as the
        non-reporting sources appear not to be receiving a given sender at
        all.</t>
        <t>This could be a potentially critical problem for such a sender
        using RTCP for congestion control, as such a sender might think that
        it is sending so much traffic that it is causing complete congestion
        collapse.</t>
        <t>However, such an interpretation of the session statistics would
        require a fairly sophisticated RTCP analysis. Any receiver of RTCP
        statistics which that is just interested in information about itself needs
        to be prepared for the possibility that any given reception report might not contain
        information about a specific media source, because reception reports
        in large conferences can be round-robined.</t>
        <t>Thus, it is unclear to what the extent to which such backward compatibility backward-compatibility
        issues would actually cause trouble in practice.</t> practice is unclear.</t>
      </section>
    </section>
    <section title="Security Considerations"> numbered="true" toc="default">
      <name>Security Considerations</name>
      <t>The security considerations of <xref target="RFC3550"/> target="RFC3550" format="default"/> and <xref
      target="I-D.ietf-avtcore-rtp-multi-stream"/> target="RFC8108" format="default"/> apply. If the RTP/AVPF
      profile is in use, then the security considerations of <xref
      target="RFC4585"/> target="RFC4585" format="default"/> (and <xref target="RFC5104"/>, target="RFC5104" format="default"/>, if used) also apply.
      If RTCP XR is used, the security consideration considerations of <xref
      target="RFC3611"/> and
      target="RFC3611" format="default"/>, including security considerations regarding any XR report blocks used used, also apply.</t>
      <t>The RTCP SDES RGRP SDES item is vulnerable to malicious modifications
      unless integrity protected protection is used. A modification of this item's length
      field cause causes the parsing of the RTCP packet in which it is contained to
      fail. Depending on the implementation, parsing of the full compound RTCP
      packet can also fail fail, causing the whole packet to be discarded. A
      modification to of the value of this SDES item would make the receiver of
      the report think that the sender of the report was a member of a
      different RTCP reporting group. Reporting Group. This will potentially create an
      inconsistency, when the RGRS reports the source as being in the same
      reporting group
      Reporting Group as another source with another reporting group Reporting Group
      identifier. What impact The impacts on a receiver implementation that such
      inconsistencies would have could cause are difficult to fully predict. One case is
      that when congestion control or other adaptation mechanisms are used, an
      inconsistent report can result in a media sender to reduce reducing its bit-rate. bitrate.
      However, a direct modification of the receiver report RR or a feedback
      message itself would be a more efficient attack, attack and would be equally costly to
      perform.</t>
      <t>The new RGRS RTCP Packet packet type is very simple. The common RTCP packet
      type header shares the same security risks with as those that affect previous RTCP packet types.
      Errors or modification of the length field can cause the full compound
      packet to fail header validation (see Appendix A.2 in <xref
      target="RFC3550"/>) target="RFC3550" sectionFormat="of" section="A.2"/>), resulting in the whole compound RTCP packet being
      discarded. Modification of the SC field or the P fields field would cause an inconsistency
      when processing the RTCP packet, likely resulting it in the packet being classified as
      invalid. A modification of the PT field would cause the packet being to be
      interpreted under according to some other packet type's rules. In such case a case, the
      result might be more or less predictable but would be specific to the packet type specific. type.
      Modification of the SSRC "SSRC of packet sender sender" field would attribute this packet to
      another sender. Resulting sender, resulting in a receiver believing that the reporting group
      applies Reporting
      Group also applies for this SSRC, if it exists. If it doesn't exist, unless
      also
      corresponding modifications are also done on a an SR/RR packet and a an SDES
      packet
      packet, the RTCP packet SHOULD <bcp14>SHOULD</bcp14> be discarded. If consistent changes are
      done, that such a scenario could be part of a resource exhaustion attack on a receiver
      implementation. Modification of the "List of SSRCs for the Reporting
      Source(s)" field would change the SSRC the receiver expect expects to report on behalf
      of this SSRC. If that SSRC exist, that exists, this situation could potentially change the
      report group
      Reporting Group used for this SSRC. A change to another reporting group Reporting Group
      belonging to another endpoint is likely detectable detectable, as there would be a
      mismatch between the SSRC of the packet sender's endpoint information,
      transport addresses, SDES CNAME etc CNAME, etc., and the corresponding information
      from the reporting group Reporting Group indicated.</t>
      <t>In general general, the reporting group Reporting Group is providing limited impacts attacks. limited-impact attacks
      on the endpoints.  The most significant result from an a deliberate attack would be to cause
      the information to be discarded or be inconsistent, including discard the
      discarding of
      all RTCP packets that are modified. This causes a lack of information at
      any receiver entity, possibly disregarding the endpoints endpoint's participation
      in the session.</t>
      <t>To protect against this type of such attacks from external non trusted non-trusted
      entities, integrity and source authentication SHOULD <bcp14>SHOULD</bcp14> be applied. This
      can be done, for example, by using <xref target="RFC3711">SRTP</xref> target="RFC3711"
      format="default">the Secure Real-time Transport Protocol (SRTP)</xref>
      with appropriate key-management, key management; other options exist exist, as discussed in
      <xref target="RFC7201">RTP Security Options</xref>.</t> target="RFC7201" format="default">"Options for Securing RTP Sessions"</xref>.</t>
      <t>The Report Reporting Group Identifier has a potential privacy impacting
      properties. properties that could potentially
      impact privacy. If this would identifier were to be generated by an implementation in such a
      way that is long term makes it long-term stable or predictable, it could be used for
      tracking a particular end-point. Therefore endpoint. Therefore, it is RECOMMENDED <bcp14>RECOMMENDED</bcp14> that it be
      generated as a short-term persistent RGRP, following the rules for
      short-term persistent CNAMEs in <xref target="RFC7022"/>. target="RFC7022" format="default"/>. The rest of
      the information revealed, i.e. i.e., the SSRCs, the size of reporting group the Reporting Group,
      and the number of reporting sources in a reporting group Reporting Group, is of a less
      sensitive nature, considering that the SSRCs and the communication would
      anyway
      be revealed without this extension. extension anyway. By encrypting the report
      group extensions Reporting
      Group extensions, the confidentiality of the SSRC values would preserved confidential, be preserved, but
      the values can
      still be revealed if <xref target="RFC3711">SRTP</xref> target="RFC3711" format="default">SRTP</xref>
      is used. The
      size of the reporting groups Reporting Groups and the number of reporting sources are
      likely determinable from analysis of the packet pattern and sizes. However,
      this information appears to have limited value.</t>
    </section>
    <section title="IANA Considerations">
      <t>(Note to the RFC-Editor: in the following, please replace "TBA" with
      the IANA-assigned value, and "XXXX" with the number of this document,
      then delete this note)</t>

      <t>The IANA is requested to register one numbered="true" toc="default">

      <name>IANA Considerations</name>
      <t>IANA has registered a new RTCP RGRP SDES items item in the
      "RTCP
      "RTP SDES Item Types" registry, as follows:</t>

      <figure>
        <artwork><![CDATA[
   Value  Abbrev  Name                         Reference
   TBA

<table anchor="new-RTCP-SDES-item">
  <name>New RTCP RGRP SDES Item: Reporting Group Identifier   [RFCXXXX]
      ]]></artwork>
      </figure> Identifier</name>
  <thead>
    <tr>
      <th>Value</th>
      <th>Abbrev</th>
      <th>Name</th>
      <th>Reference</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>11</td>
      <td>RGRP</td>
      <td>Reporting Group Identifier</td>
      <td>RFC 8861</td>
    </tr>
  </tbody>
</table>

      <t>The definition of the RTCP SDES RGRP SDES item is given in <xref
      target="sec-rgrp"/>
      target="sec-rgrp" format="default"/> of this memo.</t>

      <t>The IANA is also requested to register one

      <t>IANA has registered a new RTCP packet type in
      the "RTCP Control Packet Types (PT)" Registry registry, as follows:</t>

      <figure>
        <artwork><![CDATA[
   Value  Abbrev  Name                               Reference
   TBA    RGRS

<table anchor="new-RTCP-packet-type">
  <name>New RTCP Packet Type: Reporting Group Reporting Sources  [RFCXXXX]
      ]]></artwork>
      </figure> Sources</name>
  <thead>
    <tr>
      <th>Value</th>
      <th>Abbrev</th>
      <th>Name</th>
      <th>Reference</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>212</td>
      <td>RGRS</td>
      <td>Reporting Group Reporting Sources</td>
      <td>RFC 8861</td>
    </tr>
  </tbody>
</table>

      <t>The definition of the RTCP RGRS packet type is given in <xref
      target="sec-rgrs"/> target="sec-rgrs" format="default"/> of this memo.</t>

      <t>The IANA is also requested

<!-- 8/5/2020:  Changed "Values:" to register one "Value:" per
     <https://www.iana.org/assignments/rtp-parameters/> -->

      <t>IANA has also registered a new SDP attribute:</t>

      <figure>
        <artwork><![CDATA[
   SDP Attribute ("att-field"): attribute.</t>
      <t>SDP Attribute name:     rtcp-rgrp
      Long form:          RTCP ("att-field"):</t>
      <ul empty="true" spacing="normal"><li>
      <dl indent="22" spacing="normal">
      <dt>Contact Name:</dt><dd>IESG</dd>
      <dt>Contact Email:</dt><dd>iesg@ietf.org</dd>
      <dt>Attribute name:</dt><dd>rtcp-rgrp</dd>
      <dt>Long form:</dt><dd>RTCP Reporting Groups
      Type Groups</dd>
      <dt>Type of name:       att-field
      Type name:</dt><dd>att-field</dd>
      <dt>Type of attribute:  Media attribute:</dt><dd>Media or session level
      Subject level</dd>
      <dt>Subject to charset: No
      Purpose:            Negotiate charset:</dt><dd>No</dd>
      <dt>Purpose:</dt><dd>To negotiate or configure the use of the RTCP Reporting Group Extension.
      Reference:          [RFCXXXX]
      Values:             None
       ]]></artwork>
      </figure> extension</dd>
      <dt>Reference:</dt><dd>RFC 8861</dd>
      <dt>Value:</dt><dd>None</dd>
      <dt>Mux Category:</dt><dd>IDENTICAL</dd>
      </dl>
    </li>
  </ul>

      <t>The definition of the "a=rtcp-rgrp" SDES attribute is given in <xref
      target="sdp"/> target="sdp" format="default"/> of this memo.</t>
    </section>
  </middle>
  <back>
    <references title="Normative References">
      <?rfc include="reference.RFC.2119"?>

      <?rfc include='reference.RFC.3264'?>

      <?rfc include='reference.RFC.3550'?>

      <?rfc include='reference.RFC.4566'?>

      <?rfc include='reference.RFC.7022'?>

      <?rfc include="reference.I-D.ietf-avtcore-rtp-multi-stream"?>

      <?rfc include='reference.I-D.ietf-mmusic-sdp-mux-attributes'?>
    <references>
      <name>References</name>
      <references>
        <name>Normative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3264.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3550.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4566.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7022.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8108.xml"/>

<!-- draft-ietf-mmusic-sdp-mux-attributes-17 (RFC 8859) -->
        <reference anchor="RFC8859" target="https://www.rfc-editor.org/info/rfc8859">
          <front>
            <title>A Framework for Session Description Protocol (SDP)
            Attributes When Multiplexing</title>
            <author initials="S" surname="Nandakumar" fullname="Suhas Nandakumar">
              <organization/>
            </author>
            <date month="September" year="2020"/>
          </front>
            <seriesInfo name="RFC" value="8859"/>
            <seriesInfo name="DOI" value="10.17487/RFC8859"/>
        </reference>
      </references>

      <references>
        <name>Informative References</name>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2974.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3611.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3711.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4585.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4588.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5104.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5506.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6190.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7201.xml"/>
        <xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7826.xml"/>
      </references>

    <references title="Informative References">
      <?rfc include='reference.RFC.2326'?>

      <?rfc include='reference.RFC.2974'?>

      <?rfc include='reference.RFC.3611'?>

      <?rfc include='reference.RFC.3711'?>

      <?rfc include='reference.RFC.4585'?>

      <?rfc include='reference.RFC.4588'?>

      <?rfc include='reference.RFC.5104'?>

      <?rfc include='reference.RFC.5506'?>

      <?rfc include='reference.RFC.6190'?>

      <?rfc include='reference.RFC.7201'?>
    </references>
  </back>
</rfc>