Audio/Video Transport Working Group G. Hunt
Internet-Draft Unaffiliated
Intended status: Standards Track A. Clark
Expires: January 31, 2013 Telchemy
R. Huang
Q. Wu, Ed.
Huawei
July 30, 2012
RTCP XR Report Block for Burst/Gap Discard metric Reporting
draft-ietf-xrblock-rtcp-xr-burst-gap-discard-05.txt
Abstract
This document defines an RTCP XR Report Block that allows the
reporting of Burst and Gap Discard metrics for use in a range of RTP
applications.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Burst and Gap Discard Report Block . . . . . . . . . . . . 3
1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Standards Language . . . . . . . . . . . . . . . . . . . . 4
3. Burst/Gap Discard Block . . . . . . . . . . . . . . . . . . . 5
3.1. Report Block Structure . . . . . . . . . . . . . . . . . . 5
3.2. Definition of Fields in Burst/Gap Discard Report Block . . 5
3.3. Derived metrics based on reported metrics . . . . . . . . 7
4. Considerations for Voice-over-IP applications . . . . . . . . 8
5. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6.1. New RTCP XR Block Type value . . . . . . . . . . . . . . . 10
6.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 10
6.3. Contact information for registrations . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
1.1. Burst and Gap Discard Report Block
This document defines a new block type to augment those defined in
[RFC3611] for use in a range of RTP applications. The new block type
supports the reporting of the proportion of packets discarded by the
receiver due to jitter. The discards during discard bursts are
reported, together with the number of bursts. This block is intended
to be used in conjunction with [DISCARD] which provides the total
packets discarded, and on which this block therefore depends.
However the metric in [DISCARD] may be used independently of the
metrics in this block.
This block provides information on transient IP problems. Burst/Gap
metrics are typically used in Cumulative reports however MAY be used
in Interval reports. The burstiness of packet discard affects user
experience, may influence any sender strategies to mitigate the
problem, and may also have diagnostic value.
The metric belongs to the class of transport-related terminal metrics
defined in [MONARCH].
The definitions of Burst, Gap, Loss and Discard are consistent with
definitions in [RFC3611]. 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[RFC3611].
1.2. RTCP and RTCP XR Reports
The use of RTCP for reporting is defined in [RFC3550]. [RFC3611]
defined an extensible structure for reporting using an RTCP Extended
Report (XR). This document defines a new Extended Report block. The
use of Extended Report blocks is defined by [RFC3611].
1.3. Performance Metrics Framework
The Performance Metrics Framework [RFC6390] provides guidance on the
definition and specification of performance metrics. Metrics
described in this draft either reference external definitions or
define metrics generally in accordance with the guidelines in
[RFC6390].
1.4. Applicability
These metrics are applicable to a range of RTP applications which
don't use stream repair means.
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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].
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 [RFC3550] reports a
count of packets lost from the media stream (single SSRC within
single RTP session). Similarly the metric "number of packets
discarded" defined in [DISCARD] reports a count of packets
discarded from the media stream (single SSRC within single RTP
session) arriving at the receiver. Another metric defined in
[RFC5725] is available to report on packets which are not
recovered by any repair techniques which may be in use.
Bursts and Gaps
The terms Burst and Gap are used in a manner consistent with that
of RTCP XR [RFC3611]. RTCP XR views a RTP stream as being divided
into bursts, which are periods during which the discard rate is
high enough to cause noticeable quality degradation (generally
over 5 percent discard rate), and gaps, which are periods during
which discarded packets are infrequent and hence quality is
generally acceptable.
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3. Burst/Gap Discard Block
Metrics in this block report on Burst/Gap Discard in the stream
arriving at the RTP system.
3.1. Report Block Structure
Burst/Gap Discard metrics block
0 1 2 3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BT=NBGD | I | resv. | block length = 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold | Packets Discarded in Bursts |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Packets expected in bursts | Reserved. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
3.2. Definition of Fields in Burst/Gap Discard Report Block
Block type (BT): 8 bits
A Burst/Gap Discard Report Block is identified by the constant
NBGD.
[Note to RFC Editor: please replace NBGD with the IANA provided
RTCP XR block type for this block.]
Interval Metric flag (I): 2 bits
This field is used to indicate whether the Burst/Gap Discard
metrics are Sampled, Interval or Cumulative metrics, that is,
whether the reported values applies to the most recent measurement
interval duration between successive metrics reports (I=10) (the
Interval Duration) or to the accumulation period characteristic of
cumulative measurements (I=11) (the Cumulative Duration) or is a
sampled instantaneous value (I=01) (Sampled Value). In this
document, Burst/Gap Discard Metric is not measured at a particular
time instant but over one or several reporting intervals.
Therefore Burst/Gap Discard Metric MUST NOT be chosen as Sampled
Metric.
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Reserved (resv): 6 bits
These bits are reserved. They SHOULD be set to zero by senders
and MUST be ignored by receivers.
block length: 16 bits
The length of this report block in 32-bit words, minus one. For
the Burst/Gap discard block, the block length is equal to 3.
SSRC of source: 32 bits
As defined in Section 4.1 of [RFC3611].
Threshold: 8 bits
The Threshold is equivalent to Gmin in [RFC3611], i.e. the number
of successive packets that must not be discarded prior to and
following a discard packet in order for this discarded packet to
be regarded as part of a gap.
Packets discarded in bursts: 24 bits
The total number of packets discarded during discard bursts.
If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE SHOULD
be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFF SHOULD be reported.
Total packets expected in bursts: 24 bits
The total number of packets expected during discarded bursts (that
is, the sum of received packets and lost packets).
If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE SHOULD
be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFF SHOULD be reported.
Reserved (resv): 8 bits
These bits are reserved. They SHOULD be set to zero by senders
and MUST be ignored by receivers.
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3.3. Derived metrics based on reported metrics
The metrics described here are intended to be used in conjunction
with information from the Measurement Information block [MEASID],
discard block [DISCARD] (which MUST be present in the same RTCP
packet as the Burst/Gap Discard block).
These metrics provides the following information relevant to
statistical parameters, including:
o The fraction of packets discarded during bursts (burst discard
rate in [SUMSTAT])
o The fraction of packets discarded during gaps (gap discard rate in
[SUMSTAT])
The details on calculation these parameters in the metrics are
described in [SUMSTAT].
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4. Considerations for Voice-over-IP applications
This metric block is applicable to a broad range of RTP applications.
Where the metric is used with a Voice-overIP (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
during which the discard rate is high enough to cause noticeable call
quality degradation (generally over 5 percent discard rate), and
gaps, which are periods during which discarded packets are infrequent
and hence call quality is generally acceptable.
If Voice Activity Detection is used the Burst and Gap Duration shall
be determined as if silence packets had been sent, i.e. a period of
silence in excess of Gmin packets MUST terminate a burst condition.
The recommended value for the threshold Gmin in [RFC3611] results in
a Burst being a period of time during which the call quality is
degraded to a similar extent to a typical PCM Severely Errored Second
[PSES].
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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.
This section augments the SDP [RFC4566] attribute "rtcp-xr" defined
in [RFC3611] by providing an additional value of "xr-format" to
signal the use of the report block defined in this document.
rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF
(defined in [RFC3611])
xr-format =/ xr-bgd-block
xr-bgd-block = "brst-gap-dscrd"
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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 value
This document assigns the block type value NBGD in the IANA "RTCP XR
Block Type Registry" to the "Burst/Gap Discard Metrics Block".
[Note to RFC Editor: please replace NBGD with the IANA provided RTCP
XR block type for this block.]
6.2. New RTCP XR SDP Parameter
This document also registers a new parameter "brst-gap-dscrd" in the
"RTCP XR SDP Parameters Registry".
6.3. Contact information for registrations
The contact information for the registrations is:
Qin Wu (sunseawq@huawei.com)
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
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7. Security Considerations
It is believed that this proposed RTCP XR report block introduces no
new security considerations beyond those described in [RFC3611].
This block does not provide per-packet statistics so the risk to
confidentiality documented in Section 7, paragraph 3 of [RFC3611]
does not apply.
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8. Acknowledgments
The authors gratefully acknowledge the comments and contributions
made 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, and Hideaki Yamada.
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[RFC3550] Schulzrinne, H., "RTP: A Transport Protocol for Real-Time
Applications", RFC 3550, July 2003.
[RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control
Protocol Extended Reports (RTCP XR)", November 2003.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", July 2006.
[RFC5725] Begen, A., Hsu, D., and M. Lague, "Post-Repair Loss RLE
Report Block Type for RTP Control Protocol (RTCP) Extended
Reports (XRs)", RFC 5725, February 2020.
9.2. Informative References
[DISCARD] Hunt, G., "RTCP XR Report Block for Discard metric
Reporting", ID draft-ietf-xrblock-rtcp-xr-discard-05,
July 2012.
[MEASID] Wu, Q., "Measurement Identity and information Reporting
using SDES item and XR Block",
ID draft-ietf-xrblock-rtcp-xr-meas-identity-09, July 2012.
[MONARCH] Hunt, G., "Monitoring Architectures for RTP",
ID draft-ietf-avtcore-monarch-12, June 2012.
[PSES] "URL", http://www.its.bldrdoc.gov/projects/devglossary/
_severely_errored_second.html, October 2011.
[RFC6390] Clark, A. and B. Claise, "Framework for Performance Metric
Development", RFC 6390, October 2011.
[SUMSTAT] Zorn, G., "RTCP XR for Summary Statistics Metrics
Reporting", ID draft-zorn-xrblock-rtcp-xr-al-stat-06,
July 2012.
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Authors' Addresses
Geoff Hunt
Unaffiliated
Email: r.geoff.hunt@gmail.com
Alan Clark
Telchemy Incorporated
2905 Premiere Parkway, Suite 280
Duluth, GA 30097
USA
Email: alan.d.clark@telchemy.com
Rachel Huang
Huawei Technologies Co., Ltd.
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: Rachel@huawei.com
Qin Wu (editor)
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
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