RTP Control Protocol (RTCP) Extended Report (XR) Blocks for Concealment Metrics Reporting on Audio Applications
RFC 7294

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]
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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]
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 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].
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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
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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.
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 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).
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 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.
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 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).
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 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.
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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]
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 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.
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 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.
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 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.
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 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
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 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.
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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>.
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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.
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 * 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.
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 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.
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 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.
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 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.
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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
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