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<pre>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
<span class="h1">RTP Control Protocol (RTCP) Extended Report (XR) Blocks</span>
<span class="h1">for Concealment Metrics Reporting on Audio Applications</span>
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 <a href="./rfc5741#section-2">Section 2 of RFC 5741</a>.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
<a href="http://www.rfc-editor.org/info/rfc7294">http://www.rfc-editor.org/info/rfc7294</a>.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
Provisions Relating to IETF Documents
(<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) 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.
<span class="grey">Clark, et al. Standards Track [Page 1]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-2" ></span>
<span class="grey"><a href="./rfc7294">RFC 7294</a> RTCP XR Concealment July 2014</span>
Table of Contents
<a href="#section-1">1</a>. Introduction . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-2">2</a>
1.1. Loss Concealment and Concealed Seconds Metrics
Blocks . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-2">2</a>
<a href="#section-1.2">1.2</a>. RTCP and RTCP Extended Reports . . . . . . . . . . . . . <a href="#page-3">3</a>
<a href="#section-1.3">1.3</a>. Performance Metrics Framework . . . . . . . . . . . . . . <a href="#page-4">4</a>
<a href="#section-1.4">1.4</a>. Applicability . . . . . . . . . . . . . . . . . . . . . . <a href="#page-4">4</a>
<a href="#section-2">2</a>. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-4">4</a>
<a href="#section-2.1">2.1</a>. Standards Language . . . . . . . . . . . . . . . . . . . <a href="#page-4">4</a>
<a href="#section-2.2">2.2</a>. Notations . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-4">4</a>
<a href="#section-3">3</a>. Loss Concealment Metrics Block . . . . . . . . . . . . . . . <a href="#page-5">5</a>
<a href="#section-3.1">3.1</a>. Report Block Structure . . . . . . . . . . . . . . . . . <a href="#page-5">5</a>
3.2. Definition of Fields in Loss Concealment Metrics Block . 5
<a href="#section-4">4</a>. Concealed Seconds Metrics Block . . . . . . . . . . . . . . . <a href="#page-9">9</a>
<a href="#section-4.1">4.1</a>. Report Block Structure . . . . . . . . . . . . . . . . . <a href="#page-10">10</a>
4.2. Definition of Fields in Concealed Seconds Metrics Block . 10
<a href="#section-5">5</a>. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-14">14</a>
<a href="#section-5.1">5.1</a>. SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . <a href="#page-14">14</a>
<a href="#section-5.2">5.2</a>. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . <a href="#page-14">14</a>
<a href="#section-6">6</a>. IANA Considerations . . . . . . . . . . . . . . . . . . . . . <a href="#page-14">14</a>
<a href="#section-6.1">6.1</a>. New RTCP XR Block Type Values . . . . . . . . . . . . . . <a href="#page-14">14</a>
<a href="#section-6.2">6.2</a>. New RTCP XR SDP Parameters . . . . . . . . . . . . . . . <a href="#page-15">15</a>
<a href="#section-6.3">6.3</a>. Contact Information for Registrations . . . . . . . . . . <a href="#page-15">15</a>
<a href="#section-7">7</a>. Security Considerations . . . . . . . . . . . . . . . . . . . <a href="#page-15">15</a>
<a href="#section-8">8</a>. Contributors . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-15">15</a>
<a href="#section-9">9</a>. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . <a href="#page-15">15</a>
<a href="#section-10">10</a>. References . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-16">16</a>
<a href="#section-10.1">10.1</a>. Normative References . . . . . . . . . . . . . . . . . . <a href="#page-16">16</a>
<a href="#section-10.2">10.2</a>. Informative References . . . . . . . . . . . . . . . . . <a href="#page-16">16</a>
<a href="#appendix-A">Appendix A</a>. Metrics Represented Using the Template from <a href="./rfc6390">RFC 6390</a> 17
<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
<span class="h3"><a class="selflink" id="section-1.1" href="#section-1.1">1.1</a>. Loss Concealment and Concealed Seconds Metrics Blocks</span>
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 [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>] for use in a range of RTP
applications. These two block types extend the packet loss
concealment mechanism defined in <a href="./rfc3611#section-4.7.6">Section 4.7.6 of [RFC3611]</a>.
<span class="grey">Clark, et al. Standards Track [Page 2]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-3" ></span>
<span class="grey"><a href="./rfc7294">RFC 7294</a> RTCP XR Concealment July 2014</span>
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 [<a href="./rfc6792" title=""Guidelines for Use of the RTP Monitoring Framework"">RFC6792</a>].
<span class="h3"><a class="selflink" id="section-1.2" href="#section-1.2">1.2</a>. RTCP and RTCP Extended Reports</span>
The use of RTCP for reporting is defined in [<a href="./rfc3550" title=""RTP: A Transport Protocol for Real-Time Applications"">RFC3550</a>]. [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>]
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 [<a href="./rfc3550" title=""RTP: A Transport Protocol for Real-Time Applications"">RFC3550</a>] and [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>].
<span class="grey">Clark, et al. Standards Track [Page 3]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-4" ></span>
<span class="grey"><a href="./rfc7294">RFC 7294</a> RTCP XR Concealment July 2014</span>
<span class="h3"><a class="selflink" id="section-1.3" href="#section-1.3">1.3</a>. Performance Metrics Framework</span>
The Performance Metrics Framework [<a href="./rfc6390" title=""Guidelines for Considering New Performance Metric Development"">RFC6390</a>] provides guidance on the
definition and specification of performance metrics. The RTP
Monitoring Framework [<a href="./rfc6792" title=""Guidelines for Use of the RTP Monitoring Framework"">RFC6792</a>] provides guidelines for reporting
block format using RTCP XR. The metrics blocks described in this
document are in accordance with those guidelines.
<span class="h3"><a class="selflink" id="section-1.4" href="#section-1.4">1.4</a>. Applicability</span>
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.
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Terminology</span>
<span class="h3"><a class="selflink" id="section-2.1" href="#section-2.1">2.1</a>. Standards Language</span>
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 <a href="./rfc2119">RFC 2119</a> [<a href="./rfc2119" title=""Key words for use in RFCs to Indicate Requirement Levels"">RFC2119</a>].
<span class="h3"><a class="selflink" id="section-2.2" href="#section-2.2">2.2</a>. Notations</span>
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
<span class="grey">Clark, et al. Standards Track [Page 4]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-5" ></span>
<span class="grey"><a href="./rfc7294">RFC 7294</a> RTCP XR Concealment July 2014</span>
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. Loss Concealment Metrics Block</span>
The Loss Concealment Metrics Block is intended to be used as
described in this section, in conjunction with information from the
Measurement Information Block [<a href="./rfc6776" title=""Measurement Identity and Information Reporting Using a Source Description (SDES) Item and an RTCP Extended Report (XR) Block"">RFC6776</a>]. Instances of this metrics
block refer by synchronization source (SSRC) to the separate
auxiliary Measurement Information Block [<a href="./rfc6776" title=""Measurement Identity and Information Reporting Using a Source Description (SDES) Item and an RTCP Extended Report (XR) Block"">RFC6776</a>], which describes
measurement periods in use (see <a href="./rfc6776#section-4.2">[RFC6776], Section 4.2</a>). 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.
<span class="h3"><a class="selflink" id="section-3.1" href="#section-3.1">3.1</a>. Report Block Structure</span>
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
<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>. Definition of Fields in Loss Concealment Metrics Block</span>
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 [<a href="#ref-G.711" title=""Pulse Code Modulation (PCM) of Voice Frequencies"">G.711</a>] and is equivalent to "enhanced" in
<a href="./rfc3611#section-4.7.6">Section 4.7.6 of [RFC3611]</a>.
Reserved (resv): 4 bits
These bits are reserved. They MUST be set to zero by senders and
ignored by receivers (see <a href="./rfc6709#section-4.2">[RFC6709], Section 4.2</a>).
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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 <a href="./rfc3611#section-4.1">Section 4.1 of [RFC3611]</a>.
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) [<a href="#ref-VAD" title=""Voice activity detection"">VAD</a>] 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 <a href="./rfc6709#section-4.2">[RFC6709], Section 4.2</a>).
<span class="grey">Clark, et al. Standards Track [Page 8]</span></pre>
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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.
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. Concealed Seconds Metrics Block</span>
The Concealed Seconds Metrics Block is intended to be used as
described in this section, in conjunction with information from the
Measurement Information Block [<a href="./rfc6776" title=""Measurement Identity and Information Reporting Using a Source Description (SDES) Item and an RTCP Extended Report (XR) Block"">RFC6776</a>]. 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
[<a href="./rfc6776" title=""Measurement Identity and Information Reporting Using a Source Description (SDES) Item and an RTCP Extended Report (XR) Block"">RFC6776</a>] that describes measurement periods in use (see <a href="./rfc6776#section-4.2">[RFC6776],
Section 4.2</a>). 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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<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a>. Report Block Structure</span>
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
<span class="h3"><a class="selflink" id="section-4.2" href="#section-4.2">4.2</a>. Definition of Fields in Concealed Seconds Metrics Block</span>
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.
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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 [<a href="#ref-G.711" title=""Pulse Code Modulation (PCM) of Voice Frequencies"">G.711</a>] and is equivalent to
"enhanced" in <a href="./rfc3611#section-4.7.6">Section 4.7.6 of [RFC3611]</a>.
Reserved (resv): 4 bits
These bits are reserved. They MUST be set to zero by senders and
ignored by receivers (see <a href="./rfc6709#section-4.2">[RFC6709], Section 4.2</a>).
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 <a href="./rfc3611#section-4.1">Section 4.1 of [RFC3611]</a>.
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 <a href="./rfc6709#section-4.2">[RFC6709], Section 4.2</a>).
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.
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. SDP Signaling</span>
[<a id="ref-RFC3611">RFC3611</a>] defines the use of SDP (Session Description Protocol)
[<a href="./rfc4566" title=""SDP: Session Description Protocol"">RFC4566</a>] for signaling the use of XR blocks. XR blocks MAY be used
without prior signaling.
<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>. SDP rtcp-xr-attrib Attribute Extension</span>
This section augments the SDP attribute "rtcp-xr" [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>] 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 <a href="./rfc5234#section-3">Section 3 of [RFC5234]</a>>
<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>. Offer/Answer Usage</span>
When SDP is used in Offer/Answer context, the SDP Offer/Answer usage
defined in [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>] applies. Note that "thresh" is declared by the
offer.
<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. IANA Considerations</span>
New block types for RTCP XR are subject to IANA registration. For
general guidelines on IANA considerations for RTCP XR, refer to
[<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>].
<span class="h3"><a class="selflink" id="section-6.1" href="#section-6.1">6.1</a>. New RTCP XR Block Type Values</span>
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: <a href="#section-3.1">Section 3.1</a>
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Name: CSB
Long Name: Concealed Seconds Metrics Block
Value 31
Reference: <a href="#section-4.1">Section 4.1</a>
<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>. New RTCP XR SDP Parameters</span>
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"
<span class="h3"><a class="selflink" id="section-6.3" href="#section-6.3">6.3</a>. Contact Information for Registrations</span>
The contact information for the registrations is:
RAI Area Directors
rai-ads@tools.ietf.org
<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>. Security Considerations</span>
It is believed that the RTCP XR blocks defined in this document
introduce no new security considerations beyond those described in
[<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>]. These blocks do not provide per-packet statistics, so the
risk to confidentiality documented in <a href="#section-7">Section 7</a>, Paragraph 3 of
[<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>] does not apply.
<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>. Contributors</span>
Geoff Hunt wrote the initial version of this document.
<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>. Acknowledgements</span>
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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<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a>. References</span>
<span class="h3"><a class="selflink" id="section-10.1" href="#section-10.1">10.1</a>. Normative References</span>
[<a id="ref-RFC2119">RFC2119</a>] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.
[<a id="ref-RFC3550">RFC3550</a>] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, <a href="./rfc3550">RFC 3550</a>, July 2003.
[<a id="ref-RFC3611">RFC3611</a>] Friedman, T., Caceres, R., and A. Clark, "RTP Control
Protocol Extended Reports (RTCP XR)", <a href="./rfc3611">RFC 3611</a>, November
2003.
[<a id="ref-RFC4566">RFC4566</a>] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", <a href="./rfc4566">RFC 4566</a>, July 2006.
[<a id="ref-RFC5234">RFC5234</a>] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, <a href="./rfc5234">RFC 5234</a>, January 2008.
[<a id="ref-RFC6776">RFC6776</a>] Clark, A. and Q. Wu, "Measurement Identity and Information
Reporting Using a Source Description (SDES) Item and an
RTCP Extended Report (XR) Block", <a href="./rfc6776">RFC 6776</a>, October 2012.
<span class="h3"><a class="selflink" id="section-10.2" href="#section-10.2">10.2</a>. Informative References</span>
[<a id="ref-G.711">G.711</a>] ITU-T, "Pulse Code Modulation (PCM) of Voice Frequencies",
ITU-T Recommendation G.711, 1988.
[<a id="ref-RFC6390">RFC6390</a>] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", <a href="https://www.rfc-editor.org/bcp/bcp170">BCP 170</a>, <a href="./rfc6390">RFC 6390</a>,
October 2011.
[<a id="ref-RFC6709">RFC6709</a>] Carpenter, B., Aboba, B., and S. Cheshire, "Design
Considerations for Protocol Extensions", <a href="./rfc6709">RFC 6709</a>,
September 2012.
[<a id="ref-RFC6792">RFC6792</a>] Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the
RTP Monitoring Framework", <a href="./rfc6792">RFC 6792</a>, November 2012.
[<a id="ref-VAD">VAD</a>] Wikipedia, "Voice activity detection", January 2014,
<<a href="http://en.wikipedia.org/w/index.php?title=Voice_activity_detection&oldid=593287643">http://en.wikipedia.org/w/</a>
<a href="http://en.wikipedia.org/w/index.php?title=Voice_activity_detection&oldid=593287643">index.php?title=Voice_activity_detection&oldid=593287643</a>>.
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<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>. Metrics Represented Using the Template from <a href="./rfc6390">RFC 6390</a></span>
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 <a href="#section-3.2">Section 3.2</a>, On-Time
Playout Duration definition.
* Units of Measurement: See <a href="#section-3.2">Section 3.2</a>, On-Time Playout
Duration definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-1.1">Section 1.1</a>, 3rd paragraph.
* Measurement Timing: See <a href="#section-3">Section 3</a>, 1st paragraph for
measurement timing and <a href="#section-3.2">Section 3.2</a> for Interval Metric flag.
* Use and Applications: See <a href="#section-1.4">Section 1.4</a>.
* Reporting Model: See <a href="./rfc3611">RFC 3611</a>.
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 <a href="#section-3.2">Section 3.2</a>, Loss
Concealment Duration definition.
* Units of Measurement: See <a href="#section-3.2">Section 3.2</a>, Loss Concealment
Duration definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-1.1">Section 1.1</a>, 3rd paragraph.
* Measurement Timing: See <a href="#section-3">Section 3</a>, 1st paragraph for
measurement timing and <a href="#section-3.2">Section 3.2</a> for Interval Metric flag.
* Use and Applications: See <a href="#section-1.4">Section 1.4</a>.
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* Reporting Model: See <a href="./rfc3611">RFC 3611</a>.
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 <a href="#section-3.2">Section 3.2</a>, Buffer
Adjustment Concealment Duration definition.
* Units of Measurement: See <a href="#section-3.2">Section 3.2</a>, Buffer Adjustment
Concealment Duration definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-1.1">Section 1.1</a>, 3rd paragraph.
* Measurement Timing: See <a href="#section-3">Section 3</a>, 1st paragraph for
measurement timing and <a href="#section-3.2">Section 3.2</a> for Interval Metric flag.
* Use and Applications: See <a href="#section-1.4">Section 1.4</a>.
* Reporting Model: See <a href="./rfc3611">RFC 3611</a>.
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 <a href="#section-3.2">Section 3.2</a>, Playout
Interrupt Count definition.
* Units of Measurement: See <a href="#section-3.2">Section 3.2</a>, Playout Interrupt Count
definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-1.1">Section 1.1</a>, 3rd paragraph.
* Measurement Timing: See <a href="#section-3">Section 3</a>, 1st paragraph for
measurement timing and <a href="#section-3.2">Section 3.2</a> for Interval Metric flag.
* Use and Applications: See <a href="#section-1.4">Section 1.4</a>.
* Reporting Model: See <a href="./rfc3611">RFC 3611</a>.
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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 <a href="#section-3.2">Section 3.2</a>, Playout
Interrupt Count definition.
* Units of Measurement: See <a href="#section-3.2">Section 3.2</a>, Playout Interrupt Count
definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-1.1">Section 1.1</a>, 3rd paragraph.
* Measurement Timing: See <a href="#section-3">Section 3</a>, 1st paragraph for
measurement timing and <a href="#section-3.2">Section 3.2</a> for Interval Metric flag.
* Use and Applications: See <a href="#section-1.4">Section 1.4</a>.
* Reporting Model: See <a href="./rfc3611">RFC 3611</a>.
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 <a href="#section-4.2">Section 4.2</a>,
Unimpaired Seconds definition.
* Units of Measurement: See <a href="#section-4.2">Section 4.2</a>, Unimpaired Seconds
definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-1.1">Section 1.1</a>, 5th paragraph.
* Measurement Timing: See <a href="#section-4">Section 4</a>, 1st paragraph for
measurement timing and <a href="#section-4.2">Section 4.2</a> paragraph for Interval
Metric flag.
* Use and Applications: See <a href="#section-1.4">Section 1.4</a>.
* Reporting Model: See <a href="./rfc3611">RFC 3611</a>.
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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 <a href="#section-4.2">Section 4.2</a>,
Concealed Seconds definition.
* Units of Measurement: See <a href="#section-4.2">Section 4.2</a>, Concealed Seconds
definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-1.1">Section 1.1</a>, 5th paragraph.
* Measurement Timing: See <a href="#section-4">Section 4</a>, 1st paragraph for
measurement timing and <a href="#section-4.2">Section 4.2</a> for Interval Metric flag.
* Use and Applications: See <a href="#section-1.4">Section 1.4</a>.
* Reporting Model: See <a href="./rfc3611">RFC 3611</a>.
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 <a href="#section-4.2">Section 4.2</a>,
Severely Concealed Seconds definition.
* Units of Measurement: See <a href="#section-4.2">Section 4.2</a>, Severely Concealed
Seconds definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-1.1">Section 1.1</a>, 5th paragraph.
* Measurement Timing: See <a href="#section-4">Section 4</a>, 1st paragraph for
measurement timing and <a href="#section-4.2">Section 4.2</a> for Interval Metric flag.
* Use and Applications: See <a href="#section-1.4">Section 1.4</a>.
* Reporting Model: See <a href="./rfc3611">RFC 3611</a>.
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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 <a href="#section-4.2">Section 4.2</a>, SCS
Threshold definition.
* Units of Measurement: See <a href="#section-4.2">Section 4.2</a>, SCS Threshold
definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-1.1">Section 1.1</a>, 5th paragraph.
* Measurement Timing: See <a href="#section-4">Section 4</a>, 1st paragraph for
measurement timing and <a href="#section-4.2">Section 4.2</a> for Interval Metric flag.
* Use and Applications: See <a href="#section-1.4">Section 1.4</a>.
* Reporting Model: See <a href="./rfc3611">RFC 3611</a>.
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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
Clark, et al. Standards Track [Page 22]
</pre>
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