One document matched: draft-ietf-xrblock-rtcp-xr-pdv-03.xml


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<rfc category="std" docName="draft-ietf-xrblock-rtcp-xr-pdv-03.txt"
     ipr="trust200902">
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  <front>
    <title abbrev="RTCP XR Packet Delay Variation">RTCP XR Report Block for
    Packet Delay Variation Metric Reporting</title>

    <author fullname="Geoff Hunt" initials="G." surname="Hunt">
      <organization>Unaffiliated</organization>

      <address>
        <email>r.geoff.hunt@gmail.com</email>
      </address>
    </author>

    <author fullname="Alan Clark" initials="A." surname="Clark">
      <organization abbrev="Telchemy">Telchemy Incorporated</organization>

      <address>
        <postal>
          <street>2905 Premiere Parkway, Suite 280</street>

          <city>Duluth</city>

          <region>GA</region>

          <code>30097</code>

          <country>USA</country>
        </postal>

        <email>alan.d.clark@telchemy.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</city>

          <region>Jiangsu</region>

          <code>210012</code>

          <country>China</country>
        </postal>

        <email>sunseawq@huawei.com</email>
      </address>
    </author>

    <date year="2012" />

    <area>Real-time Applications and Infrastructure Area</area>

    <workgroup>Audio/Video Transport Working Group</workgroup>

    <keyword>RFC</keyword>

    <keyword>Request for Comments</keyword>

    <keyword>I-D</keyword>

    <keyword>Internet-Draft</keyword>

    <keyword>Real Time Control Protocol</keyword>

    <abstract>
      <t>This document defines an RTCP XR Report Block that allows the
      reporting of Packet Delay Variation metrics for a range of RTP
      applications.</t>
    </abstract>
  </front>

  <middle>
    <section anchor="intro" title="Introduction">
      <section title="Packet Delay Variation Metrics Block">
        <t>This draft defines a new block type to augment those defined in
        <xref target="RFC3611"></xref>, for use in a range of RTP
        applications.</t>

        <t>The new block type provides information on Packet Delay Variation
        using one of several standard metrics.</t>

        <t>The metrics belong to the class of transport metrics defined in
        <xref target="MONARCH"></xref> .</t>
      </section>

      <section title="RTCP and RTCP XR Reports">
        <t>The use of RTCP for reporting is defined in <xref
        target="RFC3550"></xref>. <xref target="RFC3611"></xref> defined an
        extensible structure for reporting using an RTCP Extended Report (XR).
        This draft defines a new Extended Report block that must be used in
        accordance with <xref target="RFC3550"></xref> and <xref
        target="RFC3611"></xref>.</t>
      </section>

      <section title="Performance Metrics Framework">
        <t>The Performance Metrics Framework <xref target="RFC6390"></xref>
        provides guidance on the definition and specification of performance
        metrics. The RTP Monitoring Architectures <xref
        target="MONARCH"></xref> provides guideline for reporting block format
        using RTCP XR. The XR Block described in this document are in
        accordance with the guidelines in <xref target="RFC6390"></xref> and
        <xref target="MONARCH"></xref>.</t>
      </section>

      <section title="Applicability">
        <t>These metrics are applicable to a wide range of RTP applications in
        which the application streams are sensitive to delay variation <xref
        target="RFC5481"></xref>. </t>
      </section>
    </section>

    <section title="Terminology">
      <section title="Standards Language">
        <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
        "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
        document are to be interpreted as described in RFC 2119 <xref
        target="RFC2119"></xref>.</t>
      </section>

      <section title="Notations">
        <t>This report block makes use of binary fractions. The terminology
        used is <list>
            <t>Numeric formats S X:Y<list>
                <t>where S indicates a two's complement signed representation,
                X the number of bits prior to the decimal place and Y the
                number of bits after the decimal place.</t>

                <t>Hence 8:8 represents an unsigned number in the range 0.0 to
                255.996 with a granularity of 0.0039. S7:8 would represent the
                range -127.996 to +127.996. 0:16 represents a proper binary
                fraction with range</t>

                <t>0.0 to 1 - 1/65536 = 0.9999847</t>

                <t>though note that use of flag values at the top of the
                numeric range slightly reduces this upper limit. For example,
                if the 16- bit values 0xfffe and 0xffff are used as flags for
                "over-range" and "unavailable" conditions, a 0:16 quantity has
                range</t>

                <t>0.0 to 1 - 3/65536 = 0.9999542</t>
              </list></t>
          </list></t>
      </section>
    </section>

    <section title="Packet Delay Variation Metrics Block">
      <t>Metrics in this block report on packet delay variation in the stream
      arriving at the RTP system. Instances of this Metrics Block refer by
      Synchronization source (SSRC) to the separate auxiliary Measurement
      Information block <xref target="MEASI"></xref> which contains
      measurement intervals. This metric block relies on the measurement
      interval in the Measurement Information block indicating the span of the
      report and SHOULD be sent in the same compound RTCP packet as the
      measurement information block. If the measurement interval is not
      received for this metric block, this metric block SHOULD be
      discarded.</t>

      <section title="Report Block Structure">
        <t>PDV metrics block<figure title="Figure 1: Report Block Structure">
            <artwork>
       0               1               2               3
       0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     BT=NPDV   | I |pdvtyp |Rsv|       block length=3          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        SSRC of Source                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Pos PDV Threshold/Peak     |     Pos PDV Percentile        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Neg PDV Threshold/Peak     |     Neg PDV Percentile        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Mean PDV             |            unused             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
          </figure></t>
      </section>

      <section title="Definition of Fields in PDV Metrics Block">
        <t><list style="hanging">
            <t hangText="Block type (BT): 8 bits"><vspace blankLines="1" /> A
            Packet Delay Variation Metrics Report Block is identified by the
            constant NPDV.<vspace blankLines="1" />[Note to RFC Editor: please
            replace NPDV with the IANA provided RTCP XR block type for this
            block.]<vspace blankLines="1" /></t>

            <t hangText="Interval Metric flag (I): 2 bit"><vspace
            blankLines="1" />This field is used to indicate whether the Packet
            Delay variation metrics are Sampled, Interval or Cumulative
            metrics, that is, whether the reported values applies to the most
            recent measurement interval duration between successive metrics
            reports (I=10) (the Interval Duration) or to the accumulation
            period characteristic of cumulative measurements (I=11) (the
            Cumulative Duration) or is a sampled instantaneous value (I=01)
            (Sampled Value). <vspace blankLines="1" /></t>

            <t
            hangText="Packet Delay Variation Metric Type (pdvtyp): 4 bits"><vspace
            blankLines="1" />Packet Delay Variation Metric Type is of type
            enumerated and should be interpreted as Integer. This field is
            used to identify the Packet Delay Variation Metric Type used in
            this report block, according to the following code:<vspace
            blankLines="1" /><list>
                <t>bits 014-011<list>
                    <t>0: MAPDV2, Clause 6.2.3.2 of <xref
                    target="G.1020"></xref>,</t>

                    <t>1: 2-point PDV, Clause 6.2.4 of <xref
                    target="Y.1540"></xref>.</t>
                  </list></t>
              </list><vspace blankLines="1" /></t>

            <t hangText="Rsv.: 2 bits"><vspace blankLines="1" />This field is
            reserved for future definition. In the absence of such a
            definition, the bits in this field SHOULD be set to zero and MUST
            be ignored by the receiver. <vspace blankLines="1" /></t>

            <t hangText="Block Length: 16 bits"><vspace blankLines="1" />The
            length of this report block in 32-bit words, minus one. For the
            Packet Delay Variation Metrics block, the block length is equal to
            4.<vspace blankLines="1" /></t>

            <t hangText="SSRC of source: 32 bits"><vspace blankLines="1" /> As
            defined in Section 4.1 of <xref target="RFC3611"></xref>. <vspace
            blankLines="1" /></t>

            <t hangText="Positive PDV Threshold/Peak: 16 bits"><vspace
            blankLines="1" />This field is associated with the Positive PDV
            percentile and expressed in Milliseconds with numeric format
            S11:4. The term Positive represents that the packets are arriving
            later than the expected time. <vspace blankLines="1" /> If the
            measured value is more negative than -2047.9375 (the value which
            would be coded as 0x8001), the value 0x8000 SHOULD be reported to
            indicate an over-range negative measurement. If the measured value
            is more positive than +2047.8125 (the value which would be coded
            as 0x7FFD), the value 0x7FFE SHOULD be reported to indicate an
            over-range positive measurement. If the measurement is
            unavailable, the value 0x7FFF MUST be reported.<vspace
            blankLines="1" /></t>

            <t hangText="Positive PDV Percentile: 16 bits"><vspace
            blankLines="1" />The percentages of packets in the RTP stream for
            which individual packet delays were less than the Positive PDV
            Threshold. It is expressed in numeric format 8:8 with values from
            0 to 100th percentile. <vspace blankLines="1" /> If the
            measurement is unavailable, the value 0xFFFF MUST be
            reported.<vspace blankLines="1" /></t>

            <t hangText="Negative PDV Threshold/Peak: 16 bits"><vspace
            blankLines="1" />This field is associated with the Negative PDV
            percentile and expressed in Milliseconds with numeric format
            S11:4. The term Negative represents that the packets are arriving
            earlier than the expected time. <vspace blankLines="1" />If the
            measured value is more negative than -2047.9375 (the value which
            would be coded as 0x8001), the value 0x8000 SHOULD be reported to
            indicate an over-range negative measurement. If the measured value
            is more positive than +2047.8125 (the value which would be coded
            as 0x7FFD), the value 0x7FFE SHOULD be reported to indicate an
            over-range positive measurement. If the measurement is
            unavailable, the value 0x7FFF MUST be reported.<vspace
            blankLines="1" /></t>

            <t hangText="Negative PDV Percentile: 16 bits"><vspace
            blankLines="1" />The percentages of packets in the RTP stream for
            which individual packet delays were more than the Negative PDV
            Threshold. It is expressed in numeric format 8:8 with values from
            0 to 100th percentile. <vspace blankLines="1" /> If the
            measurement is unavailable, the value 0xFFFF MUST be
            reported.<vspace blankLines="1" />If the PDV Type indicated is
            2-point PDV and the Positive and Negative PDV Percentiles are set
            to 100.0 then the Positive and Negative Threshold/Peak PDV values
            are the peak values measured during the reporting interval (which
            may be from the start of the call for cumulative reports). In this
            case, the difference between the Positive and Negative
            Threshold/Peak values defines the range of 2-point PDV.<vspace
            blankLines="1" /></t>

            <t hangText="Mean PDV: 16 bits"><vspace blankLines="1" />The mean
            PDV value of data packets is expressed in milliseconds with
            Numeric format S11:4 format.<vspace blankLines="1" /> For MAPDV2
            this value is generated according to Clause 6.2.3.2 of [G.1020].
            For interval reports the MAPDV2 value is reset at the start of the
            interval.<vspace blankLines="1" /> For 2-point PDV, the value
            reported is the mean of per-packet 2-point PDV values. This metric
            indicates the arrival time of the first media packet of the
            session with respect to the mean of the arrival times of every
            packet of the session. A single value of the metric (for a single
            session) may not be useful by itself, but its average over a
            number of sessions may be useful in diagnosing media delay at
            session startup. For example, this might occur if media packets
            are often delayed behind signalling packets due to head-of-line
            blocking.<vspace blankLines="1" /> If the measured value is more
            negative than -2047.9375 (the value which would be coded as
            0x8001), the value 0x8000 SHOULD be reported to indicate an
            over-range negative measurement. If the measured value is more
            positive than +2047.8125 (the value which would be coded as
            0x7FFD), the value 0x7FFE SHOULD be reported to indicate an
            over-range positive measurement. If the measurement is
            unavailable, the value 0x7FFF MUST be reported.<vspace
            blankLines="1" /></t>

            <t hangText="Reserved: 16 bits"><vspace blankLines="1" />These
            bits are reserved for future definition. They SHOULD be set to
            zero by the sender and MUST be ignored by the receiver. <vspace
            blankLines="1" /></t>
          </list></t>
      </section>

      <section title="Guidance on use of PDV metrics">
        <t>This subsection provides informative guidance on when it might be
        appropriate to use each of the PDV metric types.</t>

        <t>MAPDV2 (Clause 6.2.3.2 of <xref target="G.1020"></xref>) is the
        envelope of instantaneous (per-packet) delay when compared to the
        short term moving average delay. This metric could be useful in
        determining residual impairment when an RTP end system uses an
        adaptive de-jitter buffer which tracks the average delay variation,
        provided the adaptive de-jitter buffer have similar averaging
        behaviour as the MAPDV2 algorithm.</t>

        <t>2-point PDV (Clause 6.2.4 of <xref target="Y.1540"></xref>) reports
        absolute packet delay variation with respect to a defined reference
        packet transfer delay . Note that the reference packet is generally
        selected as the packet with minimum delay based on the most common
        criterion (See section 1 and section 5.1 of <xref
        target="RFC5481"></xref> ). In an RTP context, the two "points" are at
        the sender (the synchronization source which applies RTP timestamps)
        and at the receiver. The value of this metric for the packet with
        index j is identical to the quantity D(i,j) defined in Section 6.4.1
        of <xref target="RFC3550"></xref> and the packet index i should be set
        equal to the index of the reference packet for the metric in practice.
        The metric includes the effect of the frequency offsets of clocks in
        both the sender and receiver end systems, so it is useful mainly in
        network where synchronisation is distributed. As well as measuring
        packet delay variation in such networks, it may be used to ensure that
        synchronisation is effective, for example where the network carries
        ISDN data traffic over RTP <xref target="RFC4040"></xref>. The metric
        is likely to be useful in networks which use fixed de-jitter
        buffering, because it may be used to determine the length of the
        required de-jitter buffer, or to determine if network performance has
        deteriorated such that existing de-jitter buffers are too small to
        accommodate the observed delay variation.</t>
      </section>

      <section title="Examples of use">
        <t><list>
            <t>(b) To report MAPDV2 <xref target="G.1020"></xref>:<list>
                <t>Pos PDV Threshold = 50.0; Pos PDV Percentile = 95.3; Neg
                PDV Threshold = 50.0 (note this implies -50ms); Neg PDV
                Percentile = 98.4; PDV type = 1 (MAPDV2)</t>

                <t>causes average MAPDV2 to be reported in the Mean PDV
                field.</t>

                <t>Note that implementations may either fix the reported
                percentile and calculate the associated PDV level or may fix a
                threshold PDV level and calculate the associated percentile.
                From a practical implementation perspective it is simpler to
                use the second of these approaches (except of course in the
                extreme case of a 100% percentile).</t>
              </list></t>

            <t>(b) To report 2-point PDV <xref target="Y.1540"></xref>:<list>
                <t>Pos PDV Threshold = 60 (note this implies +60ms); Pos PDV
                Percentile = 96.3; Neg PDV Threshold = 0; Neg PDV Percentile =
                0; PDV type = 1 (2-point PDV) </t>

                <t>causes 2-point PDV to be reported in the Mean PDV field.
                </t>

                <t>2-point PDV, according to <xref target="Y.1540"></xref> is
                the difference in delay between the current packet and the
                referenced packet of the stream. If the sending and receiving
                clocks are not synchronized, this metric includes the effect
                of relative timing drift.</t>
              </list></t>
          </list></t>
      </section>
    </section>

    <section title="SDP Signaling">
      <t>[RFC3611] defines the use of SDP (Session Description Protocol) <xref
      target="RFC4566"></xref> for signaling the use of XR blocks. XR blocks
      MAY be used without prior signaling.</t>

      <t>This section augments the SDP <xref target="RFC4566"></xref>
      attribute "rtcp-xr" defined in <xref target="RFC3611"></xref> by
      providing an additional value of "xr-format" to signal the use of the
      report block defined in this document.<figure>
          <artwork>
   rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF

   (defined in [RFC3611])

   xr-format =/ xr-pdv-block

   xr-pdv-block  = "pkt-dly-var" [ "," pdvtype ] [ "," nspec "," pspec ]


        pdvtype     = "pdv="    0      ; MAPDV2 ITU-T G.1020
                              / 1      ; 2-point PDV ITU-T Y.1540
        nspec       = "nthr=" fixpoint     ; negative PDV threshold (ms)
                    / "npc=" fixpoint    ; negative PDV percentile
        pspec       = "pthr=" fixpoint     ; positive PDV threshold (ms)
                    / "ppc=" fixpoint    ; positive PDV percentile


        fixpoint       = 1*DIGIT "." 1*DIGIT  ; fixed point decimal
        DIGIT          = %x30-39
</artwork>
        </figure></t>

      <t>When SDP is used in offer-answer, a system sending SDP may request a
      specific type of PDV measurement. In addition, they may state a specific
      percentile or threshold value, and expect to receive the corresponding
      threshold or percentile metric, respectively. The system receiving the
      SDP SHOULD send the PDV metrics requested, but if the metric is not
      available, the system receiving the SDP MUST send the metric block with
      the flag value indicating that the metric is unavailable.</t>
    </section>

    <section title="IANA Considerations">
      <t>New block types for RTCP XR are subject to IANA registration. For
      general guidelines on IANA considerations for RTCP XR, refer to <xref
      target="RFC3611"></xref>.</t>

      <section title="New RTCP XR Block Type value">
        <t>This document assigns the block type value NPDV in the IANA "RTCP
        XR Block Type Registry" to the "Packet Delay Variation Metrics
        Block".</t>

        <t>[Note to RFC Editor: please replace NPDV with the IANA provided
        RTCP XR block type for this block.]</t>
      </section>

      <section title="New RTCP XR SDP Parameter">
        <t>This document also registers a new parameter "pkt-dly-var" in the
        "RTCP XR SDP Parameters Registry".</t>
      </section>

      <section title="Contact information for registrations">
        <t><figure>
            <artwork>
   The contact information for the registrations is:
   
   Qin Wu (sunseawq@huawei.com)

   101 Software Avenue, Yuhua District
   Nanjing, Jiangsu  210012
   China

</artwork>
          </figure><vspace blankLines="1" /></t>
      </section>

      <section title="New registry of PDV types">
        <t>This document creates a new registry to be called "RTCP XR PDV
        block - PDV type" as a sub-registry of the "RTP Control Protocol
        Extended Reports (RTCP XR) Block Type Registry". Policies for this new
        registry are as follows:<list style="symbols">
            <t>The information required to support an assignment is an
            unambiguous definition of the new metric, covering the base
            measurements and how they are processed to generate the reported
            metric. This should include the units of measurement, how values
            of the metric are reported in the three 16-bit fields "Pos PDV
            Threshold/Peak", "Neg PDV Threshold/Peak" and "Mean PDV" within
            the report block, and how the metric uses the two 16-bit fields
            "Pos PDV Percentile" and "Neg PDV Percentile".</t>

            <t>The review process for the registry is "Specification Required"
            as described in Section 4.1 of <xref target="RFC5226"></xref>.</t>

            <t>Entries in the registry are integers. The valid range is 0 to
            15 corresponding to the 4-bit field "pdvtyp" in the block. Values
            are to be recorded in decimal.</t>

            <t>Initial assignments are as follows:<list>
                <t>0: MAPDV2, Clause 6.2.3.2 of <xref
                target="G.1020"></xref>,</t>

                <t>1: 2-point PDV, Clause 6.2.4 of <xref
                target="Y.1540"></xref></t>
              </list></t>
          </list></t>
      </section>
    </section>

    <section title="Security Considerations">
      <t>It is believed that this proposed RTCP XR report block introduces no
      new security considerations beyond those described in <xref
      target="RFC3611"></xref>. This block does not provide per-packet
      statistics so the risk to confidentiality documented in Section 7,
      paragraph 3 of <xref target="RFC3611"></xref> does not apply.</t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <reference anchor="RFC2119">
        <front>
          <title abbrev="RFC Key Words">Key words for use in RFCs to Indicate
          Requirement Levels</title>

          <author fullname="Scott Bradner" initials="S." surname="Bradner">
            <organization>Harvard University</organization>

            <address>
              <postal>
                <street>1350 Mass. Ave.</street>

                <street>Cambridge</street>

                <street>MA 02138</street>
              </postal>

              <phone>- +1 617 495 3864</phone>

              <email>sob@harvard.edu</email>
            </address>
          </author>

          <date month="March" year="1997" />

          <area>General</area>

          <keyword>keyword</keyword>

          <abstract>
            <t>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. Authors who follow these
            guidelines should incorporate this phrase near the beginning of
            their document: <list>
                <t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
                "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
                "OPTIONAL" in this document are to be interpreted as described
                in RFC 2119.</t>
              </list></t>

            <t>Note that the force of these words is modified by the
            requirement level of the document in which they are used.</t>
          </abstract>
        </front>
      </reference>

      <reference anchor="G.1020">
        <front>
          <title>ITU-T Rec. G.1020, Performance parameter definitions for
          quality of speech and other voiceband applications utilizing IP
          networks</title>

          <author initials="" surname="">
            <organization>ITU-T</organization>
          </author>

          <date month="July" year="2006" />
        </front>
      </reference>

      <reference anchor="RFC3611">
        <front>
          <title>RTP Control Protocol Extended Reports (RTCP XR)</title>

          <author fullname="T. Friedman" initials="T." surname="Friedman">
            <organization></organization>
          </author>

          <author fullname="R. Caceres" initials="R." surname="Caceres">
            <organization></organization>
          </author>

          <author fullname="A. Clark" initials="A." surname="Clark">
            <organization></organization>
          </author>

          <date month="November" year="2003" />

          <abstract>
            <t>This document defines the Extended Report (XR) packet type for
            the RTP Control Protocol (RTCP), and defines how the use of XR
            packets can be signaled by an application if it employs the
            Session Description Protocol (SDP). XR packets are composed of
            report blocks, and seven block types are defined here. The purpose
            of the extended reporting format is to convey information that
            supplements the six statistics that are contained in the report
            blocks used by RTCP's Sender Report (SR) and Receiver Report (RR)
            packets. Some applications, such as multicast inference of network
            characteristics (MINC) or voice over IP (VoIP) monitoring, require
            other and more detailed statistics. In addition to the block types
            defined here, additional block types may be defined in the future
            by adhering to the framework that this document provides.</t>
          </abstract>
        </front>
      </reference>

      <reference anchor="RFC4566">
        <front>
          <title>SDP: Session Description Protocol</title>

          <author fullname="M. Handley" initials="M." surname="Handley">
            <organization></organization>
          </author>

          <author fullname="V. Jacobson" initials="V." surname="Jacobson">
            <organization></organization>
          </author>

          <author fullname="C. Perkins" initials="C." surname="Perkins">
            <organization></organization>
          </author>

          <date month="July" year="2006" />

          <abstract>
            <t>This memo defines the Session Description Protocol (SDP). SDP
            is intended for describing multimedia sessions for the purposes of
            session announcement, session invitation, and other forms of
            multimedia session initiation. [STANDARDS-TRACK]</t>
          </abstract>
        </front>
      </reference>

      <reference anchor="RFC3550">
        <front>
          <title>RTP: A Transport Protocol for Real-Time Applications</title>

          <author fullname="Henning Schulzrinne" initials="H."
                  surname="Schulzrinne">
            <organization>Columbia University</organization>
          </author>

          <date month="July" year="2003" />
        </front>

        <seriesInfo name="RFC" value="3550" />

        <format type="TXT" />
      </reference>

      <reference anchor="RFC4040">
        <front>
          <title>RTP Payload Format for a 64 kbit/s Transparent Call</title>

          <author fullname="R.,Kreuter" initials="R." surname="Kreuter">
            <organization></organization>
          </author>

          <date month="April" year="2005" />
        </front>
      </reference>

      <reference anchor="RFC5226">
        <front>
          <title>Guidelines for Writing an IANA Considerations Section in
          RFCs</title>

          <author fullname="T.,Narten" initials="T." surname="Narten">
            <organization></organization>
          </author>

          <date month="May" year="2008" />
        </front>

        <annotation>BCP 26</annotation>
      </reference>

      <reference anchor="Y.1540">
        <front>
          <title>ITU-T Rec. Y.1540, IP packet transfer and availability
          performance parameters</title>

          <author fullname="" initials="" surname="">
            <organization>ITU-T</organization>
          </author>

          <date month="November" year="2007" />
        </front>
      </reference>
    </references>

    <references title="Informative References">
      <reference anchor="MONARCH">
        <front>
          <title>Monitoring Architectures for RTP</title>

          <author fullname="Geoff Hunt" initials="G." surname="Hunt">
            <organization></organization>
          </author>

          <date month="May" year="2012" />
        </front>

        <seriesInfo name="ID" value="draft-ietf-avtcore-monarch-13" />

        <format type="TXT" />
      </reference>

      <reference anchor="MEASI">
        <front>
          <title>Measurement Identity and information Reporting using SDES
          item and XR Block</title>

          <author fullname="Geoff Hunt" initials="G." surname="Hunt">
            <organization></organization>
          </author>

          <date day="" month="April" year="2012" />
        </front>

        <seriesInfo name="ID"
                    value="draft-ietf-xrblock-rtcp-xr-meas-identity-06" />

        <format type="TXT" />
      </reference>

      <reference anchor="RFC6390">
        <front>
          <title>Framework for Performance Metric Development</title>

          <author fullname="Alan Clark" initials="A." surname="Clark">
            <organization></organization>
          </author>

          <author fullname="Benoit Claise " initials="B." surname="Claise">
            <organization></organization>
          </author>

          <date month="October" year="2011" />
        </front>

        <seriesInfo name="RFC" value="6390" />
      </reference>

      <reference anchor="RFC5481">
        <front>
          <title>Packet Delay Variation Applicability Statement </title>

          <author fullname="A. Morton" initials="A." surname="Morton">
            <organization></organization>
          </author>

          <author fullname="Benoit Claise " initials="B." surname="Claise">
            <organization></organization>
          </author>

          <date month="March" year="2009" />
        </front>

        <seriesInfo name="RFC" value="5481" />
      </reference>
    </references>

    <section title="Change Log">
      <t>Note to the RFC-Editor: please remove this section prior to
      publication as an RFC.</t>

      <section title="draft-ietf-xrblock-rtcp-xr-pdv-03">
        <t>The following are the major changes to previous version
        draft-ietf-xrblock-rtcp-xr-pdv-02: <list style="symbols">
            <t>Make definition of pdvtype get alignment with IANA section.</t>

            <t>Make Guidance on use of PDV metrics get alignment with
            RFC5481.</t>

            <t>Other Editorial changes.</t>
          </list></t>
      </section>

      <section title="draft-ietf-xrblock-rtcp-xr-pdv-02">
        <t>The following are the major changes to previous version
        draft-ietf-xrblock-rtcp-xr-pdv-01: <list style="symbols">
            <t>Updated references.</t>

            <t>Allocate one more bit for Interval metric flag to indicate
            sampled metric can be used.</t>

            <t>Add a few clarification text for failure mode.</t>
          </list></t>
      </section>

      <section title="draft-ietf-xrblock-rtcp-xr-pdv-01">
        <t>The following are the major changes to previous version
        draft-ietf-xrblock-rtcp-xr-pdv-00: <list style="symbols">
            <t>Fix typos or nits in the definition of Negative PDV
            Threshold/Peak.</t>

            <t>Fix nits in Numeric format S7:8.</t>

            <t>remove the text that is relevant to tag field.</t>

            <t>Add text in SDP signaling section to clarify indicationof
            metric unavailable.</t>
          </list></t>
      </section>

      <section title="draft-ietf-xrblock-rtcp-xr-pdv-00">
        <t>The following are the major changes to previous version
        draft-ietf-avt-rtcp-xr-pdv-03: <list style="symbols">
            <t>Updated references.</t>
          </list></t>
      </section>

      <section title="draft-ietf-avt-rtcp-xr-pdv-03">
        <t>The following are the major changes to previous version : <list
            style="symbols">
            <t>Changed BNF for SDP following Christian Groves' and Tom
            Taylor's comments (4th and 5th May 2009).</t>

            <t>Updated references.</t>
          </list></t>
      </section>
    </section>
  </back>
</rfc>

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