Audio/Video Transport Working Group G. Hunt
Internet-Draft Unaffiliated
Intended status: Standards Track A. Clark
Expires: January 11, 2013 Telchemy
S. Zhang, Ed.
J. Zhao
STTRI
Q. Wu
Huawei
July 10, 2012
RTCP XR Report Block for Burst/Gap Loss metric Reporting
draft-ietf-xrblock-rtcp-xr-burst-gap-loss-02.txt
Abstract
This document defines an RTCP XR Report Block that allows the
reporting of Burst and Gap Loss 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 Loss Report Block . . . . . . . . . . . . . 3
1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Standards Language . . . . . . . . . . . . . . . . . . . . 5
3. Burst/Gap Loss Block . . . . . . . . . . . . . . . . . . . . . 6
3.1. Report Block Structure . . . . . . . . . . . . . . . . . . 6
3.2. Definition of Fields in Burst/Gap Loss Report Block . . . 6
3.3. Derived metrics based on reported metrics . . . . . . . . 8
4. Considerations for Voice-over-IP applications . . . . . . . . 10
5. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
6.1. New RTCP XR Block Type value . . . . . . . . . . . . . . . 12
6.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 12
6.3. Contact information for registrations . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 14
9. Changes from previous version . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
1.1. Burst and Gap Loss Report Block
This draft 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 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
[RFC3550].
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 loss 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]. The method used
SHOULD produce the same result as that defined in [RFC3611] for
conditions of burst packet loss, but MAY produce different results
for conditions of time varying jitter.
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].
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1.4. Applicability
These metrics are applicable to a range of RTP applications.
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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 shall
be regarded as discarded. A packet shall be classified as one of
received (or OK), discarded or lost.
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 loss rate is high
enough to cause noticeable quality degradation (generally over 5
percent loss rate), and gaps, which are periods during which lost
packets are infrequent and hence quality is generally acceptable.
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3. Burst/Gap Loss Block
Metrics in this block report on Burst/Gap Loss in the stream arriving
at the RTP system.
3.1. Report Block Structure
Burst/Gap Loss 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=NBGL | 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
3.2. Definition of Fields in Burst/Gap Loss Report Block
Block type (BT): 8 bits
A Burst/Gap Loss Report Block is identified by the constant NBGL.
[Note to RFC Editor: please replace NBGL with the IANA provided
RTCP XR block type for this block.]
Interval Metric flag (I): 2 bit
This field is used to indicate whether the Burst/Gap Loss 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).
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Loss and Discard Combination flag (C): 1 bit
The 'C' flag is used to indicate whether combining loss/discard
report is needed. This field MUST be set to '1' if the burst gap
loss report is present in conjunction with the burst gap discard
report in the same compound RTCP packet and MUST be set to '0'
otherwise. If the burst gap discard is not sent with burst gap
loss, then the receiver should discard burst gap loss with 'C'
flag set to 1. If the 'C' flag is set to 0, then receiver should
not discard burst gap loss metric block when burst gap discard is
not received.
Reserved (resv): 5 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 Delay block, the block length is equal to 5.
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 be received prior to and following
a lost packet in order for this lost packet to be regarded as part
of a gap.
Sum of Burst Durations (ms): 24 bits
The total duration of bursts of lost packets in the period of the
report (Interval or Cumulative).
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.
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Packets lost in bursts: 24 bits
The total number of packets lost during loss 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 loss 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.
Number of bursts: 16 bits
The number of bursts in the period of the report (Interval or
Cumulative).
If the measured value exceeds 0xFFFD, the value 0xFFFE SHOULD be
reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFF SHOULD 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) over in the period of the report
(Interval or Cumulative). The units for this quantity are
milliseconds-squared.
If the measured value exceeds 0xFFFFFFFFD, the value 0xFFFFFFFFE
SHOULD be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFFFFF SHOULD be
reported.
3.3. Derived metrics based on reported metrics
The metrics described here are intended to be used as described in
this section, in conjunction with information from the Measurement
Information block [MEASID] (which MUST be present in the same RTCP
packet as the Burst/Gap Loss block) and also with the metric
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"cumulative number of packets lost" provided in standard RTCP
[RFC3550].
These metrics provides information relevant to statistical
parameters, including:
o The fraction of packets lost during bursts (i.e., Burst Loss Rate
in [SUMSTAT])
o The fraction of packets lost during gaps (i.e., Gap Loss Rate in
[SUMSTAT])
o burst duration mean [SUMSTAT]
o burst duration variance [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, the
following considerations apply.
RTCP XR views a call as being divided into bursts, which are periods
during which the loss rate is high enough to cause noticeable call
quality degradation (generally over 5 percent loss rate), and gaps,
which are periods during which lost 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-bgl-block
xr-bgl-block = "brst-gap-loss"
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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 NDEL in the IANA "RTCP XR
Block Type Registry" to the "Burst/Gap Loss Metrics Block".
[Note to RFC Editor: please replace NBGL 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-loss" 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. Contributors
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. Changes from previous version
Changed BNF for SDP following Christian Groves' and Tom Taylor's
comments (4th and 5th May 2009), now aligned with RFC 5234 section
3.3 "Incremental Alternatives".
Updated references.
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10. References
10.1. 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.
10.2. Informative References
[DISCARD] Hunt, G., "RTCP XR Report Block for Discard metric
Reporting", ID draft-ietf-rtcp-xr-discard-02, May 2009.
[MEASID] Wu, Q., "Measurement Identity and information Reporting
using SDES item and XR Block",
ID draft-ietf-xrblock-rtcp-xr-meas-identity-01,
October 2011.
[MONARCH] Hunt, G., "Monitoring Architectures for RTP",
ID draft-ietf-avtcore-monarch-04, August 2011.
[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, July 2011.
[SUMSTAT] Zorn, G., "RTCP XR for Summary Statistics Metrics
Reporting", ID draft-zorn-xrblock-rtcp-xr-al-stat-03,
October 2011.
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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
Sunshine Zhang (editor)
Shanghai Research Institure of China Telecom Corporation Limited
No.1835,South Pudong Road
Shanghai 200122
China
Email: zhangyx@sttri.com.cn
Jing Zhao
Shanghai Research Institure of China Telecom Corporation Limited
No.1835,South Pudong Road
Shanghai 200122
China
Email: zhaojing@sttri.com.cn
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
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