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Audio/Video Transport Working                                    G. Hunt
Group                                                                 BT
Internet-Draft                                                  A. Clark
Intended status: Standards Track                                Telchemy
Expires: November 16, 2009                                  May 15, 2009


    RTCP XR Report Block for Packet Delay Variation Metric Reporting
                   draft-ietf-avt-rtcp-xr-pdv-03.txt

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Abstract

   This document defines an RTCP XR Report Block that allows the
   reporting of Packet Delay Variation metrics for a range of RTP
   applications.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Packet Delay Variation Metrics Block . . . . . . . . . . .  3
     1.2.  RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . .  3
     1.3.  Performance Metrics Framework  . . . . . . . . . . . . . .  3
     1.4.  Applicability  . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Packet Delay Variation Metrics Block . . . . . . . . . . . . .  4
     2.1.  Report Block Structure . . . . . . . . . . . . . . . . . .  4
     2.2.  Definition of Fields in PDV Metrics Block  . . . . . . . .  4
     2.3.  Guidance on use of PDV metrics . . . . . . . . . . . . . .  7
     2.4.  Examples of use  . . . . . . . . . . . . . . . . . . . . .  8
   3.  SDP Signaling  . . . . . . . . . . . . . . . . . . . . . . . .  9
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
     4.1.  New RTCP XR Block Type value . . . . . . . . . . . . . . . 10
     4.2.  New RTCP XR SDP Parameter  . . . . . . . . . . . . . . . . 10
     4.3.  Contact information for registrations  . . . . . . . . . . 10
     4.4.  New registry of PDV types  . . . . . . . . . . . . . . . . 10
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   6.  Changes from previous version  . . . . . . . . . . . . . . . . 13
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 14
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 14
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15




















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1.  Introduction

1.1.  Packet Delay Variation Metrics Block

   This draft defines a new block type to augment those defined in
   [RFC3611], for use in a range of RTP applications.

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

   The metrics belong to the class of transport metrics defined in
   [MONARCH] (work in progress).

   Instances of this Metrics Block refer by tag to the separate
   auxiliary Measurement Identity block [MEASIDENT] which contains
   information such as the SSRC of the measured stream, and RTP sequence
   numbers and time intervals indicating the span of the report.

1.2.  RTCP and RTCP XR Reports

   The use of RTCP for reporting is defined in [RFC3550].  [RFC3611]
   defined an extensible structure for reporting using an RTCP Extended
   Report (XR).  This draft defines a new Extended Report block that
   MUST be used as defined in [RFC3550] and [RFC3611].

1.3.  Performance Metrics Framework

   The Performance Metrics Framework [PMOLFRAME] provides guidance on
   the definition and specification of performance metrics.  Metrics
   described in this draft either reference external definitions or
   define metrics generally in accordance with the guidelines in
   [PMOLFRAME].

1.4.  Applicability

   These metrics are applicable to a range of RTP applications.















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2.  Packet Delay Variation Metrics Block

   Metrics in this block report on packet delay variation in the stream
   arriving at the RTP system.

2.1.  Report Block Structure

      PDV metrics block
       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| tag |pdvtyp |        block length=3         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Pos Threshold/Peak PDV     |     Pos PDV Percentile        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |    Neg Threshold/Peak PDV     |     Neg PDV Percentile        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Mean PDV             |            unused             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 1: Report Block Structure

2.2.  Definition of Fields in PDV Metrics Block

   block type (BT): 8 bits

      A Packet Delay Variation Metrics Report Block is identified by the
      constant NPDV.

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

   Interval Metric flag (I): 1 bit

      This field is used to indicate whether the Packet Delay Variation
      metrics block is an Interval or a Cumulative report, that is,
      whether the reported values apply to the most recent measurement
      interval duration between successive metrics reports (I=1) (the
      Interval Duration) or to the accumulation period characteristic of
      cumulative measurements (I=0) (the Cumulative Duration).
      Numerical values for both these intervals are provided in the
      Measurement Identifier block referenced by the tag field below.

   Measurement Identifier association (tag): 3 bits

      This field is used to identify the Measurement Identifier block
      [MEASIDENT] which describes this measurement.  The relevant
      Measurement Identifier block has the same tag value as the Packet



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      Delay Variation Metrics block.  Note that there may be more than
      one Measurement Identifier block per RTCP packet.

   Packet Delay Variation Metric Type (pdvtyp): 4 bits

      This field is used to identify the Packet Delay Variation Metric
      Type used in this report block, according to the following code:


       bits 014-017
           0: interarrival jitter, Section 6.4.1 of [RFC3550],
           1: MAPDV2, Clause 6.2.3.2 of [G.1020],
           2: 2-point PDV, Clause 6.2.4 of [Y.1540]

      Other values as registered by IANA in new registry "RTCP XR PDV
      block - PDV type", see Section 4.4.

   block length: 16 bits

      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 3.

   Positive Threshold/Peak PDV: 16 bit, S11:4 format

      The PDV associated with the Positive PDV percentile expressed in
      milliseconds.  The term Positive is associated with packets
      arriving later than the expected time.

      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 SHOULD be reported.

   Positive PDV Percentile: 16 bit, 8:8 format

      The percentage of packets on the call for which individual packet
      delays were less than the Positive Threshold PDV.

      If the measurement is unavailable, the value 0xFFFF SHOULD be
      reported.

   Negative Threshold/Peak PDV: 16 bit, S11:4 format





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      The PDV associated with the Negative PDV percentile expressed in
      milliseconds.  The term Negative is associated with packets
      arriving earlier than the expected time.

      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 SHOULD be reported.

   Negative PDV Percentile: 16 bit, 8:8 format

      The percentage of packets on the call for which individual packet
      delays were more than the Negative Threshold PDV.

      If the measurement is unavailable, the value 0xFFFF SHOULD be
      reported.

   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.

   Mean PDV: (16 bit, S11:4 format) expressed in milliseconds

      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.

      For interarrival jitter, the value reported is the value of J(i)
      calculated according to [RFC3550] at the time the report is
      generated.

      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.




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      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 SHOULD be reported.

   unused: 16 bits

      These bits are unused.  They SHOULD be set to zero by the sender
      and MUST be ignored by the receiver.

2.3.  Guidance on use of PDV metrics

   This subsection provides informative guidance on when it might be
   appropriate to use each of the PDV metric types.

   Interarrival jitter (Section 6.4.1 of [RFC3550]) allows comparison of
   results with those from RTP end systems which support only RTCP as
   defined in [RFC3550].

   MAPDV2 (Clause 6.2.3.2 of [G.1020]) compares instantaneous (per-
   packet) delay variation against a moving average delay variation.
   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 MAPDV2 algorithm and the
   adaptive de-jitter buffer have similar averaging behaviour.

   2-point PDV (Clause 6.2.4 of [Y.1540]) reports absolute packet delay
   variation with respect to the time of arrival of the first packet of
   the connection.  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
   [RFC3550] if the packet index i is set equal to 1, that is, the
   reference packet for the metric is the first packet of the
   connection.  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 [RFC4040].  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.



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2.4.  Examples of use

   (a) To report interarrival jitter [RFC3550]:

   Threshold PDV = FFFF (Undefined); PDV Percentile = FFFF (Undefined);
   PDV type = 0 (interarrival jitter)

   causes interarrival jitter to be reported in the Mean PDV field.

   (b) To report MAPDV2 [G.1020]:

   Pos Threshold PDV = 50.0; Pos PDV Percentile = 95.3; Neg Threshold
   PDV = 50.0 (note this implies -50ms); Neg PDV Percentile = 98.4; PDV
   type = 1 (MAPDV2)

   causes average MAPDV2 to be reported in the Mean PDV field.

   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).

   2-point PDV, according to [Y.1540] is the difference in delay between
   the current packet and the first packet of the stream.  If the
   sending and receiving clocks are not synchronized, this metric
   includes the effect of relative timing drift.























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3.  SDP Signaling

   [RFC3611] defines the use of SDP (Session Description Protocol)
   [RFC4566] for signaling the use of XR blocks.  XR blocks MAY be used
   without prior signaling.

   This section augments the SDP [RFC4566] attribute "rtcp-xr" defined
   in [RFC3611] by providing an additional value of "xr-format" to
   signal the use of the report block defined in this document.

   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      ; interarrival jitter  RFC 3550
                              / 1      ; MAPDV2 ITU-T G.1020
                              / 2      ; 2-point PDV ITU-T Y.1540
        nspec       = "nthr=" fixpoint     ; negative threshold PDV (ms)
                    / "npc=" fixpoint    ; negative PDV percentile
        pspec       = "pthr=" fixpoint     ; positive threshold PDV (ms)
                    / "ppc=" fixpoint    ; positive PDV percentile


        fixpoint       = 1*DIGIT "." 1*DIGIT  ; fixed point decimal
        DIGIT          = %x30-39

   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 SHOULD
   send the flag value indicating that the metric is unavailable.













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4.  IANA Considerations

   New block types for RTCP XR are subject to IANA registration.  For
   general guidelines on IANA considerations for RTCP XR, refer to
   [RFC3611].

4.1.  New RTCP XR Block Type value

   This document assigns the block type value NPDV in the IANA "RTCP XR
   Block Type Registry" to the "Packet Delay Variation Metrics Block".

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

4.2.  New RTCP XR SDP Parameter

   This document also registers a new parameter "pkt-dly-var" in the
   "RTCP XR SDP Parameters Registry".

4.3.  Contact information for registrations

   The contact information for the registrations is:

   Geoff Hunt (geoff.hunt@bt.com)

   Orion 2 PP3, Adastral Park, Martlesham Heath, Ipswich IP5 3RE, United
   Kingdom

4.4.  New registry of PDV types

   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:

   o  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
      Threshold/Peak PDV", "Neg Threshold/Peak PDV" and "Mean PDV"
      within the report block, and how the metric uses the two 16-bit
      fields "Pos PDV Percentile" and "Neg PDV Percentile".

   o  The review process for the registry is "Specification Required" as
      described in Section 4.1 of [RFC5226].





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   o  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.

   o  Initial assignments are as follows:


           0: interarrival jitter, Section 6.4.1 of [RFC3550],
           1: MAPDV2, Clause 6.2.3.2 of [G.1020],
           2: 2-point PDV, Clause 6.2.4 of [Y.1540]









































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5.  Security Considerations

   It is believed that this proposed RTCP XR report block introduces no
   new security considerations beyond those described in [RFC3611].
   This block does not provide per-packet statistics so the risk to
   confidentiality documented in Section 7, paragraph 3 of [RFC3611]
   does not apply.












































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6.  Changes from previous version

   Changed BNF for SDP following Christian Groves' and Tom Taylor's
   comments (4th and 5th May 2009), now aligned with RFC 5234 section 
   3.3 "Incremental Alternatives".

   Updated references.












































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7.  References

7.1.  Normative References

   [G.1020]   ITU-T, "ITU-T Rec. G.1020, Performance parameter
              definitions for quality of speech and other voiceband
              applications utilizing IP networks", July 2006.

   [MEASIDENT]
              Hunt, G., "RTCP XR Measurement Identifier Block",
              ID draft-ietf-avt-rtcp-xr-meas-identity-02, May 2009.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, BCP 14, March 1997.

   [RFC3550]  Schulzrinne, H., "RTP: A Transport Protocol for Real-Time
              Applications", RFC 3550, July 2003.

   [RFC3611]  Friedman, T., "RTP Control Protocol Extended Reports (RTCP
              XR)", RFC 3611, November 2003.

   [RFC4040]  Kreuter, R., "RTP Payload Format for a 64 kbit/s
              Transparent Call", RFC 4040, April 2005.

   [RFC4566]  Handley, M., "SDP: Session Description Protocol",
              RFC 4566, July 2006.

   [RFC5226]  Narten, T., "Guidelines for Writing an IANA Considerations
              Section in RFCs", RFC 5226, BCP 26, May 2008.

   [Y.1540]   ITU-T, "ITU-T Rec. Y.1540, IP packet transfer and
              availability performance parameters", November 2007.

7.2.  Informative References

   [MONARCH]  Hunt, G., "Monitoring Architectures for RTP",
              ID draft-hunt-avt-monarch-01, August 2008.

   [PMOLFRAME]
              Clark, A., "Framework for Performance Metric Development",
              ID draft-ietf-pmol-metrics-framework-02, March 2009.










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Authors' Addresses

   Geoff Hunt
   BT
   Orion 2 PP3
   Adastral Park
   Martlesham Heath
   Ipswich, Suffolk  IP5 3RE
   United Kingdom

   Phone: +44 1473 651704
   Email: geoff.hunt@bt.com


   Alan Clark
   Telchemy Incorporated
   2905 Premiere Parkway, Suite 280
   Duluth, GA  30097
   USA

   Email: alan.d.clark@telchemy.com






























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