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rfc:rfc7294

Internet Engineering Task Force (IETF) A. Clark Request for Comments: 7294 Telchemy Category: Standards Track G. Zorn ISSN: 2070-1721 Network Zen

                                                                 C. Bi
                                                                 STTRI
                                                                 Q. Wu
                                                                Huawei
                                                             July 2014
      RTP Control Protocol (RTCP) Extended Report (XR) Blocks
      for Concealment Metrics Reporting on Audio Applications

Abstract

 This document defines two RTP Control Protocol (RTCP) Extended Report
 (XR) blocks that allow the reporting of concealment metrics for audio
 applications of RTP.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7294.

Copyright Notice

 Copyright (c) 2014 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Clark, et al. Standards Track [Page 1] RFC 7294 RTCP XR Concealment July 2014

Table of Contents

 1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   1.1.  Loss Concealment and Concealed Seconds Metrics
         Blocks  . . . . . . . . . . . . . . . . . . . . . . . . .   2
   1.2.  RTCP and RTCP Extended Reports  . . . . . . . . . . . . .   3
   1.3.  Performance Metrics Framework . . . . . . . . . . . . . .   4
   1.4.  Applicability . . . . . . . . . . . . . . . . . . . . . .   4
 2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.1.  Standards Language  . . . . . . . . . . . . . . . . . . .   4
   2.2.  Notations . . . . . . . . . . . . . . . . . . . . . . . .   4
 3.  Loss Concealment Metrics Block  . . . . . . . . . . . . . . .   5
   3.1.  Report Block Structure  . . . . . . . . . . . . . . . . .   5
   3.2.  Definition of Fields in Loss Concealment Metrics Block  .   5
 4.  Concealed Seconds Metrics Block . . . . . . . . . . . . . . .   9
   4.1.  Report Block Structure  . . . . . . . . . . . . . . . . .  10
   4.2.  Definition of Fields in Concealed Seconds Metrics Block .  10
 5.  SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . .  14
   5.1.  SDP rtcp-xr-attrib Attribute Extension  . . . . . . . . .  14
   5.2.  Offer/Answer Usage  . . . . . . . . . . . . . . . . . . .  14
 6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   6.1.  New RTCP XR Block Type Values . . . . . . . . . . . . . .  14
   6.2.  New RTCP XR SDP Parameters  . . . . . . . . . . . . . . .  15
   6.3.  Contact Information for Registrations . . . . . . . . . .  15
 7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
 8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  15
 9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
 10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
   10.1.  Normative References . . . . . . . . . . . . . . . . . .  16
   10.2.  Informative References . . . . . . . . . . . . . . . . .  16
 Appendix A.  Metrics Represented Using the Template from RFC 6390  17

1. Introduction

1.1. Loss Concealment and Concealed Seconds Metrics Blocks

 At any instant, the audio output at a receiver may be classified as
 either 'normal' or 'concealed'.  'Normal' refers to playout of audio
 payload received from the remote end and also includes locally
 generated signals such as announcements, tones, and comfort noise.
 'Concealed' refers to playout of locally generated signals used to
 mask the impact of network impairments or to reduce the audibility of
 jitter buffer adaptations.
 This document defines two new concealment-related block types to
 augment those defined in [RFC3611] for use in a range of RTP
 applications.  These two block types extend the packet loss
 concealment mechanism defined in Section 4.7.6 of [RFC3611].

Clark, et al. Standards Track [Page 2] RFC 7294 RTCP XR Concealment July 2014

 The first block type, the Loss Concealment Metrics Block, provides
 metrics for actions taken by the receiver to mitigate the effect of
 packet loss and packet discard.  Specifically, the first metric
 (On-Time Playout Duration) reports the duration of normal playout of
 data that the receiver obtained from the sender's stream.  A second
 metric (Loss Concealment Duration) reports the total time during
 which the receiver played out media data that was manufactured
 locally, because the sender's data for these periods was not
 available due to packet loss or discard.  A similar metric (Buffer
 Adjustment Concealment Duration) reports the duration of playout of
 locally manufactured data replacing data that is unavailable due to
 adaptation of an adaptive de-jitter buffer.  Further metrics (Playout
 Interrupt Count and Mean Playout Interrupt Size) report the number of
 times normal playout was interrupted and the mean duration of these
 interruptions.
 Loss Concealment Duration and Buffer Adjustment Concealment Duration
 are reported separately because buffer adjustment is typically
 arranged to occur in silence periods, so it may have very little
 impact on user experience, whilst loss concealment may occur at any
 time.
 The second block type, the Concealed Seconds Metrics Block, provides
 metrics for Concealed Seconds, which are measured at the receiving
 end of the RTP stream.  Specifically, the first metric (Unimpaired
 Seconds) reports the number of whole seconds occupied only with
 normal playout of data that the receiver obtained from the sender's
 stream.  The second metric (Concealed Seconds) reports the number of
 whole seconds during which the receiver played out any locally
 generated media data.  A third metric, Severely Concealed Seconds
 (SCSs), reports the number of whole seconds during which the receiver
 played out locally generated data to conceal a lost or discarded
 frame percentage in excess of the configured SCS Threshold.
 These metrics belongs to the class of transport-related terminal
 metrics defined in [RFC6792].

1.2. RTCP and RTCP Extended Reports

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

Clark, et al. Standards Track [Page 3] RFC 7294 RTCP XR Concealment July 2014

1.3. Performance Metrics Framework

 The Performance Metrics Framework [RFC6390] provides guidance on the
 definition and specification of performance metrics.  The RTP
 Monitoring Framework [RFC6792] provides guidelines for reporting
 block format using RTCP XR.  The metrics blocks described in this
 document are in accordance with those guidelines.

1.4. Applicability

 These metrics are applicable to audio applications of RTP and the
 audio component of audio/video applications in which the packet loss
 concealment machinery is contained at the receiving end to mitigate
 the impact of network impairments to user's perception of media
 quality.

2. Terminology

2.1. Standards Language

 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 [RFC2119].

2.2. Notations

 The report blocks in this document make use of binary fractions.  The
 following terminology is used:
    Numeric formats S X:Y
       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.
       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
       0.0 to 1 - 1/65536 = 0.9999847
       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
       0.0 to 1 - 3/65536 = 0.9999542

Clark, et al. Standards Track [Page 4] RFC 7294 RTCP XR Concealment July 2014

3. Loss Concealment Metrics Block

 The Loss Concealment Metrics Block is intended to be used as
 described in this section, in conjunction with information from the
 Measurement Information Block [RFC6776].  Instances of this metrics
 block refer by synchronization source (SSRC) to the separate
 auxiliary Measurement Information Block [RFC6776], which describes
 measurement periods in use (see [RFC6776], Section 4.2).  This
 metrics block relies on the measurement period 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 period is not received in the same
 compound RTCP packet as this metrics block, this metrics block MUST
 be discarded.

3.1. Report Block Structure

 The structure of the Loss Concealment Metrics Block is as follows.
   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=30      | I |plc|  resv |       block length=6          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         SSRC of Source                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 On-Time Playout Duration                      |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                  Loss Concealment Duration                    |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |              Buffer Adjustment Concealment Duration           |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |    Playout Interrupt Count    |           Reserved            |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                 Mean Playout Interrupt Size                   |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 1: Loss Concealment Metrics Block

3.2. Definition of Fields in Loss Concealment Metrics Block

 Block type (BT): 8 bits
    A Loss Concealment Metrics Block is identified by the constant 30.

Clark, et al. Standards Track [Page 5] RFC 7294 RTCP XR Concealment July 2014

 Interval Metric flag (I): 2 bits
    This field is used to indicate whether the loss concealment
    metrics are Sampled, Interval, or Cumulative metrics:
       I=10: Interval Duration - the reported value applies to the
       most recent measurement interval duration between successive
       metrics reports.
       I=11: Cumulative Duration - the reported value applies to the
       accumulation period characteristic of cumulative measurements.
       I=01: Sampled Value - the reported value is a sampled
       instantaneous value (not allowed in this block).
       I=00: Reserved value - this value is reserved for future use.
    In this document, Loss Concealment metrics can only be measured
    over definite intervals and cannot be sampled.  Senders MUST NOT
    use the values I=00 or I=01.  If a block is received with I=00 or
    I=01, the receiver MUST discard the block.
 Packet Loss Concealment Method (plc): 2 bits
    This field is used to identify the packet loss concealment method
    in use at the receiver, according to the following code:
       bits 014-015
          0 = silence insertion
          1 = simple replay, no attenuation
          2 = simple replay, with attenuation
          3 = enhancement
          Other values are reserved.
    Note that the enhancement method (plc=3) for packet loss
    concealment offers an improved audio quality and better robustness
    against packet losses [G.711] and is equivalent to "enhanced" in
    Section 4.7.6 of [RFC3611].
 Reserved (resv): 4 bits
    These bits are reserved.  They MUST be set to zero by senders and
    ignored by receivers (see [RFC6709], Section 4.2).

Clark, et al. Standards Track [Page 6] RFC 7294 RTCP XR Concealment July 2014

 block length: 16 bits
    The length of this report block in 32-bit words, minus one.  For
    the Loss Concealment Metrics Block, the block length is equal to
    6.
 SSRC of Source: 32 bits
    As defined in Section 4.1 of [RFC3611].
 On-Time Playout Duration: 32 bits
    'On-time playout' is the uninterrupted, in-sequence playout of
    valid decoded audio information originating from the remote
    endpoint.  This includes comfort noise during periods of remote
    talker silence, if Voice Activity Detection (VAD) [VAD] is used,
    and locally generated or regenerated tones and announcements.
    An equivalent definition is that on-time playout is playout of any
    signal other than those used for concealment.
    On-time playout duration is expressed in units of RTP timestamp
    and MUST include both speech and silence intervals, whether VAD is
    used or not.
    Two values are reserved: a value of 0xFFFFFFFE indicates out of
    range (that is, a measured value exceeding 0xFFFFFFFD), and a
    value of 0xFFFFFFFF indicates that the measurement is unavailable.
 Loss Concealment Duration: 32 bits
    The duration, expressed in units of RTP timestamp, of audio
    playout corresponding to Loss-Type concealment.
    Loss-Type concealment is reactive insertion or deletion of samples
    in the audio playout stream due to effective frame loss at the
    audio decoder.  Effective frame loss is the event in which a frame
    of coded audio is simply not present at the audio decoder when
    required.  In this case, substitute audio samples are generally
    formed, at the decoder or elsewhere, to reduce audible impairment.
    Two values are reserved: a value of 0xFFFFFFFE indicates out of
    range (that is, a measured value exceeding 0xFFFFFFFD), and a
    value of 0xFFFFFFFF indicates that the measurement is unavailable.

Clark, et al. Standards Track [Page 7] RFC 7294 RTCP XR Concealment July 2014

 Buffer Adjustment Concealment Duration: 32 bits
    The duration, expressed in units of RTP timestamp, of audio
    playout corresponding to Buffer Adjustment-Type concealment, if
    known.
    Buffer Adjustment-Type concealment is proactive or controlled
    insertion or deletion of samples in the audio playout stream due
    to jitter buffer adaptation, re-sizing decisions, or re-centering
    decisions within the endpoint.
    Because this insertion is controlled, rather than occurring
    randomly in response to losses, it is typically less audible than
    Loss-Type concealment.  For example, jitter buffer adaptation
    events may be constrained to occur during periods of talker
    silence, in which case only silence duration is affected, or
    sophisticated time-stretching methods for insertion/deletion
    during favorable periods in active speech may be employed.
    Concealment events that cannot be classified as Buffer Adjustment-
    Type MUST be classified as Loss-Type.
    Two values are reserved: a value of 0xFFFFFFFE indicates out of
    range (that is, a measured value exceeding 0xFFFFFFFD), and a
    value of 0xFFFFFFFF indicates that the measurement is unavailable.
 Playout Interrupt Count: 16 bits
    The number of interruptions to normal playout that occurred during
    the reporting period.
    Two values are reserved: a value of 0xFFFE indicates out of range
    (that is, a measured value exceeding 0xFFFD), and a value of
    0xFFFF indicates that the measurement is unavailable.
 Reserved: 16 bits
    These bits are reserved.  They MUST be set to zero by senders and
    ignored by receivers (see [RFC6709], Section 4.2).

Clark, et al. Standards Track [Page 8] RFC 7294 RTCP XR Concealment July 2014

 Mean Playout Interrupt Size: 32 bits
    The mean duration, expressed in units of RTP timestamp, of
    interruptions to normal playout that occurred during the reporting
    period.
    Two values are reserved: a value of 0xFFFFFFFE indicates out of
    range (that is, a measured value exceeding 0xFFFFFFFD), and a
    value of 0xFFFFFFFF indicates that the measurement is unavailable.

4. Concealed Seconds Metrics Block

 The Concealed Seconds Metrics Block is intended to be used as
 described in this section, in conjunction with information from the
 Measurement Information Block [RFC6776].  It provides a description
 of potentially audible impairments due to lost and discarded packets
 at the endpoint, expressed on a time basis analogous to a traditional
 Public Switched Telephone Network (PSTN) T1/E1 errored seconds
 metric.  Instances of this metrics block refer by synchronization
 source (SSRC) to the separate auxiliary Measurement Information Block
 [RFC6776] that describes measurement periods in use (see [RFC6776],
 Section 4.2).  This metrics block relies on the measurement period 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 period is not
 received in the same compound RTCP packet as this metrics block, this
 metrics block MUST be discarded.
 The following metrics are based on successive one-second intervals as
 declared by an RTP clock.  This RTP clock does not need to be
 synchronized to any external time reference.  The starting time of
 this clock is unspecified.  Note that this implies that the same loss
 pattern could result in slightly different count values, depending on
 where the losses occur relative to the particular one-second
 demarcation points.  For example, two loss events occurring 50 ms
 apart could result in either one Concealed Second or two, depending
 on the particular one-second boundaries used.
 The seconds in this sub-block are not necessarily calendar seconds.
 At the tail end of a session, periods of time of less than one second
 shall be incorporated into these counts if they exceed 500 ms and
 shall be disregarded if they are less than 500 ms.

Clark, et al. Standards Track [Page 9] RFC 7294 RTCP XR Concealment July 2014

4.1. Report Block Structure

 The structure of the Concealed Seconds Metrics Block is as follows.
   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
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |    BT=31      | I |plc|  resv |       block length=4          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                         SSRC of Source                        |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Unimpaired Seconds                         |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  |                    Concealed Seconds                          |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  | Severely Concealed Seconds    | Reserved      | SCS Threshold |
  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
               Figure 2: Concealed Seconds Metrics Block

4.2. Definition of Fields in Concealed Seconds Metrics Block

 Block type (BT): 8 bits
    A Concealed Seconds Metrics Block is identified by the constant
    31.
 Interval Metric flag (I): 2 bits
    This field is used to indicate whether the Concealed Seconds
    metrics are Sampled, Interval, or Cumulative metrics:
       I=10: Interval Duration - the reported value applies to the
       most recent measurement interval duration between successive
       metrics reports.
       I=11: Cumulative Duration - the reported value applies to the
       accumulation period characteristic of cumulative measurements.
       I=01: Sampled Value - the reported value is a sampled
       instantaneous value (Not allowed in this block).
       I=00: Reserved value - this value is reserved for future use.
    In this document, Concealed Seconds metrics can only be measured
    over definite intervals and cannot be sampled.  Senders MUST NOT
    use the values I=00 or I=01.  If a block is received with I=00 or
    I=01, the receiver MUST discard the block.

Clark, et al. Standards Track [Page 10] RFC 7294 RTCP XR Concealment July 2014

 Packet Loss Concealment Method (plc): 2 bits
    This field is used to identify the packet loss concealment method
    in use at the receiver, according to the following code:
       bits 014-015
          0 = silence insertion
          1 = simple replay, no attenuation
          2 = simple replay, with attenuation
          3 = enhancement
          Other values are reserved.
    Note that the enhancement method (plc=3) for packet loss
    concealment offers an improved audio quality and a better
    robustness against packet losses [G.711] and is equivalent to
    "enhanced" in Section 4.7.6 of [RFC3611].
 Reserved (resv): 4 bits
    These bits are reserved.  They MUST be set to zero by senders and
    ignored by receivers (see [RFC6709], Section 4.2).
 Block Length: 16 bits
    The length of this report block in 32-bit words, minus one.  For
    the Concealed Seconds Metrics Block, the block length is equal to
    4.
 SSRC of Source: 32 bits
    As defined in Section 4.1 of [RFC3611].
 Unimpaired Seconds: 32 bits
    A count of the number of Unimpaired Seconds that have occurred.
    An Unimpaired Second is defined as a continuous period of one
    second during which no frame loss or discard due to late arrival
    has occurred.  Every second in a session must be classified as
    either OK or Concealed.

Clark, et al. Standards Track [Page 11] RFC 7294 RTCP XR Concealment July 2014

    Normal playout of comfort noise or other silence-concealment
    signals during periods of talker silence, if VAD is used, shall be
    counted as Unimpaired Seconds.
    Two values are reserved: a value of 0xFFFFFFFE indicates out of
    range (that is, a measured value exceeding 0xFFFFFFFD), and a
    value of 0xFFFFFFFF indicates that the measurement is unavailable.
 Concealed Seconds: 32 bits
    A count of the number of Concealed Seconds that have occurred.
    A Concealed Second is defined as a continuous period of one second
    during which any frame loss or discard due to late arrival has
    occurred.
    Equivalently, a Concealed Second is one in which some Loss-Type
    concealment has occurred.  Buffer Adjustment-Type concealment
    SHOULD NOT cause Concealed Seconds to be incremented, with the
    following exception.  An implementation MAY cause Concealed
    Seconds to be incremented for 'emergency' buffer adjustments made
    during talkspurts.
    Loss-Type concealment is reactive insertion or deletion of samples
    in the audio playout stream due to effective frame loss at the
    audio decoder.  "Effective frame loss" is the event in which a
    frame of coded audio is simply not present at the audio decoder
    when required.  In this case, substitute audio samples are
    generally formed, at the decoder or elsewhere, to reduce audible
    impairment.
    Buffer Adjustment-Type concealment is proactive or controlled
    insertion or deletion of samples in the audio playout stream due
    to jitter buffer adaptation, re-sizing decisions, or re-centering
    decisions within the endpoint.
    Because this insertion is controlled, rather than occurring
    randomly in response to losses, it is typically less audible than
    Loss-Type concealment.  For example, jitter buffer adaptation
    events may be constrained to occur during periods of talker
    silence, in which case only silence duration is affected, or
    sophisticated time-stretching methods for insertion/deletion
    during favorable periods in active speech may be employed.  For
    these reasons, Buffer Adjustment-Type concealment MAY be exempted
    from inclusion in calculations of Concealed Seconds and Severely
    Concealed Seconds.

Clark, et al. Standards Track [Page 12] RFC 7294 RTCP XR Concealment July 2014

    However, an implementation SHOULD include Buffer Adjustment-Type
    concealment in counts of Concealed Seconds and Severely Concealed
    Seconds if the event occurs at an 'inopportune' moment, such as an
    emergency or large, immediate adaptation during active speech or
    an unsophisticated adaptation during speech without regard for the
    underlying signal.  In these cases, the assumption of low
    audibility cannot hold.  In other words, jitter buffer adaptation
    events that may be presumed to be audible SHOULD be included in
    Concealed Seconds and Severely Concealed Seconds counts.
    Concealment events that cannot be classified as Buffer Adjustment-
    Type MUST be classified as Loss-Type.
    For clarification, the count of Concealed Seconds MUST include the
    count of Severely Concealed Seconds.
    Two values are reserved: a value of 0xFFFFFFFE indicates out of
    range (that is, a measured value exceeding 0xFFFFFFFD), and a
    value of 0xFFFFFFFF indicates that the measurement is unavailable.
 Severely Concealed Seconds: 16 bits
    A count of the number of Severely Concealed Seconds.
    A Severely Concealed Second is defined as a non-overlapping period
    of one second during which the cumulative amount of time that has
    been subject to frame loss or discard due to late arrival exceeds
    the SCS Threshold.
    Two values are reserved: a value of 0xFFFE indicates out of range
    (that is, a measured value exceeding 0xFFFD), and a value of
    0xFFFF indicates that the measurement is unavailable.
 Reserved: 8 bits
    These bits are reserved.  They MUST be set to zero by senders and
    ignored by receivers (see [RFC6709], Section 4.2).
 SCS Threshold: 8 bits
    The SCS Threshold is defined as the percentage of packets
    corresponding to lost or discarded frames that must occur within a
    one second period in order for the second to be classified as a
    Severely Concealed Second.  This is expressed in numeric format
    0:8 and hence can represent a range of 0 to 99.6 percent loss or
    discard.

Clark, et al. Standards Track [Page 13] RFC 7294 RTCP XR Concealment July 2014

    A default threshold of 5 percent effective frame loss (50 ms
    effective frame loss ) per second is suggested.  This corresponds
    to an SCS Threshold in hexadecimal of 0x0D.

5. 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.

5.1. SDP rtcp-xr-attrib Attribute Extension

 This section augments the SDP attribute "rtcp-xr" [RFC3611] by
 providing two additional values of "xr-format" to signal the use of
 the two report blocks defined in this document.
 xr-format =/ xr-conceal-block
            / xr-conc-sec-block
 xr-conceal-block = "loss-conceal"
 xr-conc-sec-block = "conc-sec" ["=" thresh]
 thresh      = 1*DIGIT          ; threshold for SCS (ms)
 DIGIT =     <as defined in Section 3 of [RFC5234]>

5.2. Offer/Answer Usage

 When SDP is used in Offer/Answer context, the SDP Offer/Answer usage
 defined in [RFC3611] applies.  Note that "thresh" is declared by the
 offer.

6. 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].

6.1. New RTCP XR Block Type Values

 This document assigns two block type values in the IANA "RTP Control
 Protocol Extended Reports (RTCP XR) Block Type Registry" under the
 subregistry "RTCP XR Block Type":
 Name:       LCB
 Long Name:  Loss Concealment Metrics Block
 Value       30
 Reference:  Section 3.1

Clark, et al. Standards Track [Page 14] RFC 7294 RTCP XR Concealment July 2014

 Name:       CSB
 Long Name:  Concealed Seconds Metrics Block
 Value       31
 Reference:  Section 4.1

6.2. New RTCP XR SDP Parameters

 This document also registers two new parameters in the "RTP Control
 Protocol Extended Reports (RTCP XR) Session Description Protocol
 (SDP) Parameters Registry":
 o  "loss-conceal"
 o  "conc-sec"

6.3. Contact Information for Registrations

 The contact information for the registrations is:
 RAI Area Directors
 rai-ads@tools.ietf.org

7. Security Considerations

 It is believed that the RTCP XR blocks defined in this document
 introduce no new security considerations beyond those described in
 [RFC3611].  These blocks do not provide per-packet statistics, so the
 risk to confidentiality documented in Section 7, Paragraph 3 of
 [RFC3611] does not apply.

8. Contributors

 Geoff Hunt wrote the initial version of this document.

9. Acknowledgements

 The authors gratefully acknowledge reviews and feedback provided by
 Bruce Adams, Philip Arden, Amit Arora, Bob Biskner, Kevin Connor,
 Alissa Cooper, Claus Dahm, Randy Ethier, Roni Even, Adrian Farrel,
 Jim Frauenthal, Albert Higashi, Tom Hock, Shane Holthaus, Paul Jones,
 Rajesh Kumar, Keith Lantz, Alfred C. Morton, Mohamed Mostafa, Amy
 Pendleton, Colin Perkins, Mike Ramalho, Ravi Raviraj, Pete Resnick,
 Albrecht Schwarz, Meral Shirazipour, Tom Taylor, and Hideaki Yamada.

Clark, et al. Standards Track [Page 15] RFC 7294 RTCP XR Concealment July 2014

10. References

10.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
            Jacobson, "RTP: A Transport Protocol for Real-Time
            Applications", STD 64, RFC 3550, July 2003.
 [RFC3611]  Friedman, T., Caceres, R., and A. Clark, "RTP Control
            Protocol Extended Reports (RTCP XR)", RFC 3611, November
            2003.
 [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
            Description Protocol", RFC 4566, July 2006.
 [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
            Specifications: ABNF", STD 68, RFC 5234, January 2008.
 [RFC6776]  Clark, A. and Q. Wu, "Measurement Identity and Information
            Reporting Using a Source Description (SDES) Item and an
            RTCP Extended Report (XR) Block", RFC 6776, October 2012.

10.2. Informative References

 [G.711]    ITU-T, "Pulse Code Modulation (PCM) of Voice Frequencies",
            ITU-T Recommendation G.711, 1988.
 [RFC6390]  Clark, A. and B. Claise, "Guidelines for Considering New
            Performance Metric Development", BCP 170, RFC 6390,
            October 2011.
 [RFC6709]  Carpenter, B., Aboba, B., and S. Cheshire, "Design
            Considerations for Protocol Extensions", RFC 6709,
            September 2012.
 [RFC6792]  Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the
            RTP Monitoring Framework", RFC 6792, November 2012.
 [VAD]      Wikipedia, "Voice activity detection", January 2014,
            <http://en.wikipedia.org/w/
            index.php?title=Voice_activity_detection&oldid=593287643>.

Clark, et al. Standards Track [Page 16] RFC 7294 RTCP XR Concealment July 2014

Appendix A. Metrics Represented Using the Template from RFC 6390

 a.  On-Time Playout Duration Metric
  • Metric Name: On-Time Playout Duration
  • Metric Description: 'On-time playout' is the uninterrupted,

in-sequence playout of valid decoded audio information

        originating from the remote endpoint.  On-time playout
        duration is playout duration of any signal other than those
        used for concealment.
  • Method of Measurement or Calculation: See Section 3.2, On-Time

Playout Duration definition.

  • Units of Measurement: See Section 3.2, On-Time Playout

Duration definition.

  • Measurement Point(s) with Potential Measurement Domain: See

Section 1.1, 3rd paragraph.

  • Measurement Timing: See Section 3, 1st paragraph for

measurement timing and Section 3.2 for Interval Metric flag.

  • Use and Applications: See Section 1.4.
  • Reporting Model: See RFC 3611.
 b.  Loss Concealment Duration Metric
  • Metric Name: Loss Concealment Duration
  • Metric Description: The duration of audio playout

corresponding to Loss-Type concealment.

  • Method of Measurement or Calculation: See Section 3.2, Loss

Concealment Duration definition.

  • Units of Measurement: See Section 3.2, Loss Concealment

Duration definition.

  • Measurement Point(s) with Potential Measurement Domain: See

Section 1.1, 3rd paragraph.

  • Measurement Timing: See Section 3, 1st paragraph for

measurement timing and Section 3.2 for Interval Metric flag.

  • Use and Applications: See Section 1.4.

Clark, et al. Standards Track [Page 17] RFC 7294 RTCP XR Concealment July 2014

  • Reporting Model: See RFC 3611.
 c.  Buffer Adjustment Concealment Duration Metric
  • Metric Name: Buffer Adjustment Concealment Duration
  • Metric Description: The duration of audio playout

corresponding to Buffer Adjustment-Type concealment.

  • Method of Measurement or Calculation: See Section 3.2, Buffer

Adjustment Concealment Duration definition.

  • Units of Measurement: See Section 3.2, Buffer Adjustment

Concealment Duration definition.

  • Measurement Point(s) with Potential Measurement Domain: See

Section 1.1, 3rd paragraph.

  • Measurement Timing: See Section 3, 1st paragraph for

measurement timing and Section 3.2 for Interval Metric flag.

  • Use and Applications: See Section 1.4.
  • Reporting Model: See RFC 3611.
 d.  Playout Interrupt Count Metric
  • Metric Name: Playout Interrupt Count
  • Metric Description: The number of interruptions to normal

playout that occurred during the reporting period.

  • Method of Measurement or Calculation: See Section 3.2, Playout

Interrupt Count definition.

  • Units of Measurement: See Section 3.2, Playout Interrupt Count

definition.

  • Measurement Point(s) with Potential Measurement Domain: See

Section 1.1, 3rd paragraph.

  • Measurement Timing: See Section 3, 1st paragraph for

measurement timing and Section 3.2 for Interval Metric flag.

  • Use and Applications: See Section 1.4.
  • Reporting Model: See RFC 3611.

Clark, et al. Standards Track [Page 18] RFC 7294 RTCP XR Concealment July 2014

 e.  Mean Playout Interrupt Size Metric
  • Metric Name: Mean Playout Interrupt Size
  • Metric Description: The mean duration of interruptions to

normal playout that occurred during the reporting period.

  • Method of Measurement or Calculation: See Section 3.2, Playout

Interrupt Count definition.

  • Units of Measurement: See Section 3.2, Playout Interrupt Count

definition.

  • Measurement Point(s) with Potential Measurement Domain: See

Section 1.1, 3rd paragraph.

  • Measurement Timing: See Section 3, 1st paragraph for

measurement timing and Section 3.2 for Interval Metric flag.

  • Use and Applications: See Section 1.4.
  • Reporting Model: See RFC 3611.
 f.  Unimpaired Seconds Metric
  • Metric Name: Unimpaired Seconds
  • Metric Description: A count of the number of Unimpaired

Seconds that have occurred.

  • Method of Measurement or Calculation: See Section 4.2,

Unimpaired Seconds definition.

  • Units of Measurement: See Section 4.2, Unimpaired Seconds

definition.

  • Measurement Point(s) with Potential Measurement Domain: See

Section 1.1, 5th paragraph.

  • Measurement Timing: See Section 4, 1st paragraph for

measurement timing and Section 4.2 paragraph for Interval

        Metric flag.
  • Use and Applications: See Section 1.4.
  • Reporting Model: See RFC 3611.

Clark, et al. Standards Track [Page 19] RFC 7294 RTCP XR Concealment July 2014

 g.  Concealed Seconds Metric
  • Metric Name: Concealed Seconds
  • Metric Description: A count of the number of Concealed Seconds

that have occurred.

  • Method of Measurement or Calculation: See Section 4.2,

Concealed Seconds definition.

  • Units of Measurement: See Section 4.2, Concealed Seconds

definition.

  • Measurement Point(s) with Potential Measurement Domain: See

Section 1.1, 5th paragraph.

  • Measurement Timing: See Section 4, 1st paragraph for

measurement timing and Section 4.2 for Interval Metric flag.

  • Use and Applications: See Section 1.4.
  • Reporting Model: See RFC 3611.
 h.  Severely Concealed Seconds Metric
  • Metric Name: Severely Concealed Seconds
  • Metric Description: A count of the number of Severely

Concealed Seconds that have occurred.

  • Method of Measurement or Calculation: See Section 4.2,

Severely Concealed Seconds definition.

  • Units of Measurement: See Section 4.2, Severely Concealed

Seconds definition.

  • Measurement Point(s) with Potential Measurement Domain: See

Section 1.1, 5th paragraph.

  • Measurement Timing: See Section 4, 1st paragraph for

measurement timing and Section 4.2 for Interval Metric flag.

  • Use and Applications: See Section 1.4.
  • Reporting Model: See RFC 3611.

Clark, et al. Standards Track [Page 20] RFC 7294 RTCP XR Concealment July 2014

 i.  SCS Threshold Metric
  • Metric Name: SCS Threshold
  • Metric Description: The amount of time corresponding to lost

or discarded frames that must occur within a one-second period

        in order for the second to be classified as a Severely
        Concealed Second.
  • Method of Measurement or Calculation: See Section 4.2, SCS

Threshold definition.

  • Units of Measurement: See Section 4.2, SCS Threshold

definition.

  • Measurement Point(s) with Potential Measurement Domain: See

Section 1.1, 5th paragraph.

  • Measurement Timing: See Section 4, 1st paragraph for

measurement timing and Section 4.2 for Interval Metric flag.

  • Use and Applications: See Section 1.4.
  • Reporting Model: See RFC 3611.

Clark, et al. Standards Track [Page 21] RFC 7294 RTCP XR Concealment July 2014

Authors' Addresses

 Alan Clark
 Telchemy Incorporated
 2905 Premiere Parkway, Suite 280
 Duluth, GA  30097
 USA
 EMail: alan.d.clark@telchemy.com
 Glen Zorn
 Network Zen
 77/440 Soi Phoomjit, Rama IV Road
 Phra Khanong, Khlong Toie
 Bangkok  10110
 Thailand
 Phone: +66 (0) 87 502 4274
 EMail: gwz@net-zen.net
 Claire Bi
 Shanghai Research Institute of China Telecom Corporation Limited
 No. 1835, South Pudong Road
 Shanghai  200122
 China
 EMail: bijy@sttri.com.cn
 Qin Wu
 Huawei
 101 Software Avenue, Yuhua District
 Nanjing, Jiangsu  210012
 China
 EMail: sunseawq@huawei.com

Clark, et al. Standards Track [Page 22]

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