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<pre>Internet Engineering Task Force (IETF) A. Clark
Request for Comments: 6958 Telchemy
Category: Standards Track S. Zhang
ISSN: 2070-1721 J. Zhao
STTRI
Q. Wu, Ed.
Huawei
May 2013
<span class="h1">RTP Control Protocol (RTCP) Extended Report (XR) Block for</span>
<span class="h1">Burst/Gap Loss Metric Reporting</span>
Abstract
This document defines an RTP Control Protocol (RTCP) Extended Report
(XR) Block that allows the reporting of burst and gap loss metrics
for use in a range of RTP applications.
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/rfc6958">http://www.rfc-editor.org/info/rfc6958</a>.
Copyright Notice
Copyright (c) 2013 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="./rfc6958">RFC 6958</a> RTCP XR Burst/Gap Loss May 2013</span>
Table of Contents
<a href="#section-1">1</a>. Introduction . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-2">2</a>
<a href="#section-1.1">1.1</a>. Burst/Gap Loss Metrics Block . . . . . . . . . . . . . . <a href="#page-2">2</a>
<a href="#section-1.2">1.2</a>. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . <a href="#page-3">3</a>
<a href="#section-1.3">1.3</a>. Performance Metrics Framework . . . . . . . . . . . . . . <a href="#page-3">3</a>
<a href="#section-1.4">1.4</a>. Applicability . . . . . . . . . . . . . . . . . . . . . . <a href="#page-3">3</a>
<a href="#section-2">2</a>. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-3">3</a>
<a href="#section-3">3</a>. Burst/Gap Loss Metrics Block . . . . . . . . . . . . . . . . <a href="#page-4">4</a>
<a href="#section-3.1">3.1</a>. Report Block Structure . . . . . . . . . . . . . . . . . <a href="#page-5">5</a>
<a href="#section-3.2">3.2</a>. Definition of Fields in Burst/Gap Loss Metrics Block . . <a href="#page-5">5</a>
<a href="#section-3.3">3.3</a>. Derived Metrics Based on Reported Metrics . . . . . . . . <a href="#page-7">7</a>
<a href="#section-4">4</a>. Considerations for Voice-over-IP Applications . . . . . . . . <a href="#page-8">8</a>
<a href="#section-5">5</a>. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
<a href="#section-5.1">5.1</a>. SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . <a href="#page-9">9</a>
<a href="#section-5.2">5.2</a>. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
<a href="#section-6">6</a>. IANA Considerations . . . . . . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
<a href="#section-6.1">6.1</a>. New RTCP XR Block Type Value . . . . . . . . . . . . . . <a href="#page-9">9</a>
<a href="#section-6.2">6.2</a>. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . <a href="#page-9">9</a>
<a href="#section-6.3">6.3</a>. Contact Information for Registrations . . . . . . . . . . <a href="#page-10">10</a>
<a href="#section-7">7</a>. Security Considerations . . . . . . . . . . . . . . . . . . . <a href="#page-10">10</a>
<a href="#section-8">8</a>. Contributors . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-10">10</a>
<a href="#section-9">9</a>. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-10">10</a>
<a href="#section-10">10</a>. References . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-11">11</a>
<a href="#section-10.1">10.1</a>. Normative References . . . . . . . . . . . . . . . . . . <a href="#page-11">11</a>
<a href="#section-10.2">10.2</a>. Informative References . . . . . . . . . . . . . . . . . <a href="#page-11">11</a>
<a href="#appendix-A">Appendix A</a>. Metrics Represented Using the Template from <a href="./rfc6390">RFC 6390</a> 13
<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>. Burst/Gap Loss Metrics Block</span>
This document defines a new block type 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. The new block type
supports the reporting of the proportion of packets lost by the
network. The losses during loss bursts are reported, together with
the number of bursts and additional data, allowing the calculation of
statistical parameters (mean and variance) of the distribution of
burst lengths. Some uses of these metrics depend on the availability
of the metric "cumulative number of packets lost" from RTCP
[<a href="./rfc3550" title=""RTP: A Transport Protocol for Real-Time Applications"">RFC3550</a>].
This block provides information on transient IP problems. Burst/gap
metrics are typically used in Cumulative reports; however, they also
may be used in Interval reports. The burstiness of packet loss
affects user experience, may influence any sender strategies to
mitigate the problem, and may also have diagnostic value.
<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="./rfc6958">RFC 6958</a> RTCP XR Burst/Gap Loss May 2013</span>
The metric belongs to the class of transport-related end system
metrics defined in [<a href="./rfc6792" title=""Guidelines for Use of the RTP Monitoring Framework"">RFC6792</a>].
The definitions of "burst", "gap", "loss", and "discard" are
consistent with definitions in [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>]. To accommodate the range
of jitter buffer algorithms and packet discard logic that may be used
by implementors, the method used to distinguish between bursts and
gaps may be an equivalent method to that defined in [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>]. The
method used should produce the same result as that defined in
[<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>] for conditions of burst packet loss but may produce
different results for conditions of time-varying jitter.
<span class="h3"><a class="selflink" id="section-1.2" href="#section-1.2">1.2</a>. RTCP and RTCP XR 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 by using an RTCP
Extended Report (XR). This document defines a new Extended Report
block for use with [<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="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 "Guidelines
for Use of 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
Block described in this document is in accordance with the guidelines
in [<a href="./rfc6390" title=""Guidelines for Considering New Performance Metric Development"">RFC6390</a>] and [<a href="./rfc6792" title=""Guidelines for Use of the RTP Monitoring Framework"">RFC6792</a>].
<span class="h3"><a class="selflink" id="section-1.4" href="#section-1.4">1.4</a>. Applicability</span>
These metrics are applicable to a range of RTP applications that
contain jitter buffers and don't use stream repair means, e.g.,
Forward Error Correction (FEC) [<a href="./rfc5109" title=""RTP Payload Format for Generic Forward Error Correction"">RFC5109</a>] and/or retransmission
[<a href="./rfc4588" title=""RTP Retransmission Payload Format"">RFC4588</a>].
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. Terminology</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="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="./rfc6958">RFC 6958</a> RTCP XR Burst/Gap Loss May 2013</span>
In addition, the following terms are defined:
Received, Lost, and Discarded
A packet shall be regarded as lost if it fails to arrive within an
implementation-specific time window. A packet that arrives within
this time window but is too early or late to be played out or
thrown away before playout due to packet duplication or redundancy
shall be regarded as discarded. A packet shall be classified as
one of received (or OK), discarded, or lost. The metric
"cumulative number of packets lost" defined in [<a href="./rfc3550" title=""RTP: A Transport Protocol for Real-Time Applications"">RFC3550</a>] reports a
count of packets lost from the media stream (single
Synchronization Source (SSRC) within a single RTP session).
Similarly, the metric "number of packets discarded" defined in
[<a href="#ref-DISCARD" title=""RTP Control Protocol (RTCP) Extended Report (XR) Block for Discard Count metric Reporting"">DISCARD</a>] reports a count of packets discarded from the media
stream (single SSRC within single RTP session) arriving at the
receiver. The post-repair Loss RLE metric, which is defined in
[<a href="./rfc5725" title=""Post-Repair Loss RLE Report Block Type for RTP Control Protocol (RTCP) Extended Reports (XRs)"">RFC5725</a>], can be used to report the number of packets that are
not recovered by any repair techniques that are in use.
Bursts and Gaps
The terms "burst" and "gap" are used in a manner consistent with
that of RTCP XR [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>]. RTCP XR views an RTP stream as being
divided into bursts, which are periods when the loss rate is high
enough to cause noticeable quality degradation (generally over 5
percent loss rate) and gaps, which are periods when lost packets
are infrequent and hence quality is generally acceptable.
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. Burst/Gap Loss Metrics Block</span>
Metrics in this block report on burst/gap loss in the stream arriving
at the RTP system. The measurement of these metrics is made at the
receiving end of the RTP stream. Each instance of this Metrics Block
refers by SSRC to a 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 the measurement periods in use (see <a href="./rfc6776">RFC</a>
<a href="./rfc6776">6776</a>, <a href="#section-4.2">Section 4.2</a>).
This Metrics Block relies on the measurement period in the
Measurement Information Block indicating the span of the report.
Senders MUST send this block in the same compound RTCP packet as the
Measurement Information Block. Receivers MUST verify that the
measurement period is received in the same compound RTCP packet as
this Metrics Block. If not, this Metrics Block MUST be discarded.
<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="./rfc6958">RFC 6958</a> RTCP XR Burst/Gap Loss May 2013</span>
<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 Burst/Gap Loss 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=20 | I |C| resv. | Block Length = 5 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ -+-+-+-+-+-+-+-+
| Threshold | Sum of Burst Durations (ms) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packets Lost in Bursts | Total... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...Packets Expected in Bursts | Number of Bursts | Sum of|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ...Squares of Burst Durations (ms-squared) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
<span class="h3"><a class="selflink" id="section-3.2" href="#section-3.2">3.2</a>. Definition of Fields in Burst/Gap Loss Metrics Block</span>
Block Type (BT): 8 bits
A Burst/Gap Loss Metrics Block is identified by the constant 20.
Interval Metric flag (I): 2 bits
This field is used to indicate whether the burst/gap loss 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.
In this document, burst/gap loss metrics can only be measured over
definite intervals and cannot be sampled. Also, the value I=00 is
reserved for future use. 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.
<span class="grey">Clark, et al. Standards Track [Page 5]</span></pre>
<hr class='noprint'/><!--NewPage--><pre class='newpage'><span id="page-6" ></span>
<span class="grey"><a href="./rfc6958">RFC 6958</a> RTCP XR Burst/Gap Loss May 2013</span>
Loss and Discard Combination flag (C): 1 bit
The 'C' flag is used to indicate whether the loss/discard report
is combined with the burst/gap loss report in the same compound
RTCP packet. The value is set to '1' if the loss/discard report
and the burst gap loss report are combined. Otherwise, the value
is set to '0'. If the 'C' flag is set to '1' but the burst/gap
discard was not sent, the receiver MUST discard the burst/gap
loss.
Reserved (resv.): 5 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 Burst/Gap Loss Metrics Block, the block length is equal to 5.
The block MUST be discarded if the block length is set to a
different value.
SSRC of Source: 32 bits
As defined in <a href="./rfc3611#section-4.1">Section 4.1 of [RFC3611]</a>.
Threshold: 8 bits
The Threshold is equivalent to Gmin in [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>], i.e., the number
of successive packets that must be received prior to and following
a lost packet in order for this lost packet to be regarded as part
of a gap. Note that the threshold is calculated in accordance
with the Gmin Calculation defined in <a href="./rfc3611#section-4.7.2">Section 4.7.2 of RFC 3611</a>.
Sum of Burst Durations (ms): 24 bits
The total duration of bursts of lost packets in the period of the
report (Interval or Cumulative).
The measured value is an unsigned value. If the measured value
exceeds 0xFFFFFD, the value 0xFFFFFE MUST be reported to indicate
an over-range measurement. If the measurement is unavailable, the
value 0xFFFFFF MUST be reported.
<span class="grey">Clark, et al. Standards Track [Page 6]</span></pre>
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Packets Lost in Bursts: 24 bits
The total number of packets lost during loss bursts.
The measured value is an unsigned value. If the measured value
exceeds 0xFFFFFD, the value 0xFFFFFE MUST be reported to indicate
an over-range measurement. If the measurement is unavailable, the
value 0xFFFFFF MUST be reported.
Total Packets Expected in Bursts: 24 bits
The total number of packets expected during loss bursts (that is,
the sum of received packets and lost packets).
The measured value is an unsigned value. If the measured value
exceeds 0xFFFFFD, the value 0xFFFFFE MUST be reported to indicate
an over-range measurement. If the measurement is unavailable, the
value 0xFFFFFF MUST be reported.
Number of Bursts: 16 bits
The number of bursts in the period of the report (Interval or
Cumulative).
The measured value is an unsigned value. If the measured value
exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an
over-range measurement. If the measurement is unavailable, the
value 0xFFFF MUST be reported.
Sum of Squares of Burst Durations (ms-squared): 36 bits
The sum of the squares of burst durations (where individual burst
durations are expressed in ms) in the period of the report
(Interval or Cumulative). The units for this quantity are
milliseconds-squared.
The measured value is an unsigned value. If the measured value
exceeds 0xFFFFFFFFD, the value 0xFFFFFFFFE MUST be reported to
indicate an over-range measurement. If the measurement is
unavailable, the value 0xFFFFFFFFF MUST be reported.
<span class="h3"><a class="selflink" id="section-3.3" href="#section-3.3">3.3</a>. Derived Metrics Based on Reported Metrics</span>
The metrics described here are 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>] and also with the metric "cumulative
number of packets lost" provided in standard RTCP [<a href="./rfc3550" title=""RTP: A Transport Protocol for Real-Time Applications"">RFC3550</a>].
<span class="grey">Clark, et al. Standards Track [Page 7]</span></pre>
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These metrics provide information relevant to statistical parameters,
including:
o the fraction of packets lost during bursts (i.e., Burst Loss Rate
in [<a href="#ref-SUMSTAT" title=""RTP Control Protocol (RTCP) Extended Report (XR) Blocks for Summary Statistics Metrics Reporting"">SUMSTAT</a>]), which can be calculated using the metric "Packets
Loss in Bursts" and the metric "Total Packets Expected in Bursts"
provided in the Burst/Gap Loss Metrics Block.
o the fraction of packets lost during gaps (i.e., Gap Loss Rate in
[<a href="#ref-SUMSTAT" title=""RTP Control Protocol (RTCP) Extended Report (XR) Blocks for Summary Statistics Metrics Reporting"">SUMSTAT</a>]), which can be calculated using the metric "Packets Loss
in Bursts" and the metric "Total Packets Expected in Bursts"
provided in the Burst/Gap Loss Metrics Block.
o burst duration mean [<a href="#ref-SUMSTAT" title=""RTP Control Protocol (RTCP) Extended Report (XR) Blocks for Summary Statistics Metrics Reporting"">SUMSTAT</a>], which can be calculated using the
metric "Packets Loss in Bursts" and the metric "Total Packets
Expected in Bursts" provided in the Burst/Gap Loss Metrics Block.
o burst duration variance [<a href="#ref-SUMSTAT" title=""RTP Control Protocol (RTCP) Extended Report (XR) Blocks for Summary Statistics Metrics Reporting"">SUMSTAT</a>], which can be calculated using
the metric "Packets Loss in Bursts" and the metric "Total Packets
Expected in Bursts" provided in the Burst/Gap Loss Metrics Block.
The details on calculation of these parameters in the metrics are
described in [<a href="#ref-SUMSTAT" title=""RTP Control Protocol (RTCP) Extended Report (XR) Blocks for Summary Statistics Metrics Reporting"">SUMSTAT</a>].
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. Considerations for Voice-over-IP Applications</span>
This Metrics Block is applicable to a broad range of RTP
applications. Where the metric is used with a Voice-over-IP (VoIP)
application and the stream repair means is not available, the
following considerations apply.
RTCP XR views a call as being divided into bursts, which are periods
when the loss rate is high enough to cause noticeable call quality
degradation (generally over 5 percent loss rate), and gaps, which are
periods when lost packets are infrequent and hence call quality is
generally acceptable.
If Voice Activity Detection is used, the Burst and Gap Durations
shall be determined as if silence packets had been sent, i.e., a
period of silence in excess of Gmin packets will terminate a burst
condition.
The recommended value for the threshold Gmin in [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>] causes a
burst during which the call quality is degraded to a similar extent
as it would be during a typical Pulse Code Modulation (PCM) Severely
Errored Second.
<span class="grey">Clark, et al. Standards Track [Page 8]</span></pre>
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<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 the Session Description Protocol (SDP)
[<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 [<a href="./rfc4566" title=""SDP: Session Description Protocol"">RFC4566</a>] attribute "rtcp-xr" defined
in [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>] by providing an additional value of "xr-format" to
signal the use of the report block defined in this document. The
ABNF [<a href="./rfc5234" title=""Augmented BNF for Syntax Specifications: ABNF"">RFC5234</a>] syntax is below.
xr-format =/ xr-bgl-block
xr-bgl-block = "burst-gap-loss"
<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 the offer/answer context, the SDP Offer/Answer
usage defined in [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>] for unilateral "rtcp-xr" attribute
parameters applies. For detailed usage of offer/answer for
unilateral parameters, refer to <a href="./rfc3611#section-5.2">Section 5.2 of [RFC3611]</a>.
<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 Value</span>
This document assigns the block type value 20 in the IANA "RTP
Control Protocol Extended Reports (RTCP XR) Block Type Registry" to
the "Burst/Gap Loss Metrics Block".
<span class="h3"><a class="selflink" id="section-6.2" href="#section-6.2">6.2</a>. New RTCP XR SDP Parameter</span>
This document also registers a new parameter "burst-gap-loss" in the
"RTP Control Protocol Extended Reports (RTCP XR) Session Description
Protocol (SDP) Parameters Registry".
<span class="grey">Clark, et al. Standards Track [Page 9]</span></pre>
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<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:
Qin Wu (sunseawq@huawei.com)
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>. Security Considerations</span>
This block does 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. However, the gaps indicated within this block could
be used to detect the timing of other events on the path between the
sender and receiver. For example, a competing multimedia stream
might cause a loss burst for the duration of the stream, allowing the
receiver of this block to know when the competing stream was active.
This risk is not a significant threat since the only information
leaked is the timing of the loss, not the cause. Besides this, it is
believed that this proposed RTCP XR report block introduces no other
new security considerations beyond those described in [<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>].
<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>. Contributors</span>
Geoff Hunt wrote the initial draft of this document.
<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>. Acknowledgments</span>
The authors gratefully acknowledge reviews and feedback provided by
Bruce Adams, Philip Arden, Amit Arora, Bob Biskner, Kevin Connor,
Claus Dahm, Randy Ethier, Roni Even, Jim Frauenthal, Albert Higashi,
Tom Hock, Shane Holthaus, Paul Jones, Rajesh Kumar, Keith Lantz,
Mohamed Mostafa, Amy Pendleton, Colin Perkins, Mike Ramalho, Ravi
Raviraj, Albrecht Schwarz, Tom Taylor, Hideaki Yamada, Adam Roach,
Dan Romascanu, Chris Lonvick, Alfred C. Morton Jr., Pete Resnick, Ted
Lemon, Stephen Farrell, Richard Barnes, and Benoit Claise.
<span class="grey">Clark, et al. Standards Track [Page 10]</span></pre>
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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-RFC5725">RFC5725</a>] Begen, A., Hsu, D., and M. Lague, "Post-Repair Loss RLE
Report Block Type for RTP Control Protocol (RTCP) Extended
Reports (XRs)", <a href="./rfc5725">RFC 5725</a>, February 2010.
<span class="h3"><a class="selflink" id="section-10.2" href="#section-10.2">10.2</a>. Informative References</span>
[<a id="ref-DISCARD">DISCARD</a>] Clark, A., Huang, R., and Q. Wu, Ed., "RTP Control
Protocol (RTCP) Extended Report (XR) Block for Discard
Count metric Reporting", Work in Progress, April 2013.
[<a id="ref-RFC4588">RFC4588</a>] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", <a href="./rfc4588">RFC 4588</a>,
July 2006.
[<a id="ref-RFC5109">RFC5109</a>] Li, A., "RTP Payload Format for Generic Forward Error
Correction", <a href="./rfc5109">RFC 5109</a>, December 2007.
[<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.
<span class="grey">Clark, et al. Standards Track [Page 11]</span></pre>
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[<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.
[<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-SUMSTAT">SUMSTAT</a>] Zorn, G., Schott, R., Wu, Q., Ed., and R. Huang, "RTP
Control Protocol (RTCP) Extended Report (XR) Blocks for
Summary Statistics Metrics Reporting", Work in Progress,
March 2013.
<span class="grey">Clark, et al. Standards Track [Page 12]</span></pre>
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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>
The six metrics defined in this document are described below using
the template from <a href="./rfc6390#section-5.4.4">Section 5.4.4 of RFC 6390</a>.
a. Threshold Metric
* Metric Name: Threshold in RTP
* Metric Description: The Threshold is equivalent to Gmin in
[<a href="./rfc3611" title=""RTP Control Protocol Extended Reports (RTCP XR)"">RFC3611</a>], i.e., the number of successive RTP packets that
must be received prior to and following a lost RTP packet in
order for this lost RTP packet to be regarded as part of a
gap.
* Method of Measurement or Calculation: See <a href="#section-3.2">Section 3.2</a>,
Threshold definition.
* Units of Measurement: See <a href="#section-3.2">Section 3.2</a>, Threshold definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-3">Section 3</a>, 1st paragraph.
* Measurement Timing: See <a href="#section-3">Section 3</a>, 2nd 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. Sum of Burst Durations Metric
* Metric Name: Sum of Burst Durations in RTP
* Metric Description: The total duration of bursts of lost RTP
packets in the period of the report.
* Method of Measurement or Calculation: See <a href="#section-3.2">Section 3.2</a>, Sum of
Burst Durations definition.
* Units of Measurement: See <a href="#section-3.2">Section 3.2</a>, Sum of Burst Durations
definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-3">Section 3</a>, 1st paragraph.
* Measurement Timing: See <a href="#section-3">Section 3</a>, 2nd paragraph for
measurement timing and <a href="#section-3.2">Section 3.2</a> for Interval Metric flag.
<span class="grey">Clark, et al. Standards Track [Page 13]</span></pre>
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* Use and Applications: See <a href="#section-1.4">Section 1.4</a>.
* Reporting Model: See <a href="./rfc3611">RFC 3611</a>.
c. Packets Lost in Bursts Metric
* Metric Name: RTP Packets lost in bursts
* Metric Description: The total number of RTP packets lost
during loss bursts.
* Method of Measurement or Calculation: See <a href="#section-3.2">Section 3.2</a>, Packets
Lost in Bursts definition.
* Units of Measurement: See <a href="#section-3.2">Section 3.2</a>, Packets lost in bursts
definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-3">Section 3</a>, 1st paragraph.
* Measurement Timing: See <a href="#section-3">Section 3</a>, 2nd 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. Total Packets Expected in Bursts Metric
* Metric Name: Total RTP packets expected in bursts
* Metric Description: The total number of RTP packets expected
during loss bursts (that is, the sum of received RTP packets
and lost RTP packets).
* Method of Measurement or Calculation: See <a href="#section-3.2">Section 3.2</a>, Total
packets expected in bursts definition.
* Units of Measurement: See <a href="#section-3.2">Section 3.2</a>, Total packets expected
in bursts definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-3">Section 3</a>, 1st paragraph.
* Measurement Timing: See <a href="#section-3">Section 3</a>, 2nd 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>.
<span class="grey">Clark, et al. Standards Track [Page 14]</span></pre>
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* Reporting Model: See <a href="./rfc3611">RFC 3611</a>.
e. Number of Bursts Metric
* Metric Name: Number of bursts in RTP
* Metric Description: The total duration of bursts of lost RTP
packets in the period of the report.
* Method of Measurement or Calculation: See <a href="#section-3.2">Section 3.2</a>, Number
of bursts definition.
* Units of Measurement: See <a href="#section-3.2">Section 3.2</a>, Number of bursts
definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-3">Section 3</a>, 1st paragraph.
* Measurement Timing: See <a href="#section-3">Section 3</a>, 2nd 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. Sum of Squares of Burst Durations Metric
* Metric Name: Sum of Squares of Burst Durations in RTP
* Metric Description: The sum of the squares of burst durations
(where individual burst durations are expressed in ms) over in
the period of the report.
* Method of Measurement or Calculation: See <a href="#section-3.2">Section 3.2</a>, Sum of
Squares of Burst Durations definition.
* Units of Measurement: See <a href="#section-3.2">Section 3.2</a>, Sum of Squares of Burst
Durations definition.
* Measurement Point(s) with Potential Measurement Domain: See
<a href="#section-3">Section 3</a>, 1st paragraph.
* Measurement Timing: See <a href="#section-3">Section 3</a>, 2nd 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>.
<span class="grey">Clark, et al. Standards Track [Page 15]</span></pre>
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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
Sunshine Zhang
Shanghai Research Institute of China Telecom Corporation Limited
No. 1835, South Pudong Road
Shanghai 200122
China
EMail: zhangyx@sttri.com.cn
Jing Zhao
Shanghai Research Institute of China Telecom Corporation Limited
No. 1835, South Pudong Road
Shanghai 200122
China
EMail: zhaojing@sttri.com.cn
Qin Wu (editor)
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
EMail: sunseawq@huawei.com
Clark, et al. Standards Track [Page 16]
</pre>
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