Audio/Video Transport Working Group G. Hunt
Internet-Draft Unaffiliated
Intended status: Standards Track A. Clark
Expires: December 14, 2012 Telchemy
G. Zorn
Network Zen
C. Bi
STTRI
Q. Wu
Huawei
June 12, 2012
RTCP XR Report Block for Concealed Seconds metric Reporting
draft-ietf-xrblock-rtcp-xr-concsec-00.txt
Abstract
This document defines an RTCP XR Report Block that allows the
reporting of Concealed Seconds metrics primarily for audio
applications of RTP.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Concealed Seconds Block . . . . . . . . . . . . . . . . . 3
1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 3
2. Loss Concealment Block . . . . . . . . . . . . . . . . . . . . 5
2.1. Report Block Structure . . . . . . . . . . . . . . . . . . 5
2.2. Definition of Fields in Concealed Seconds Metrics Block . 5
3. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 10
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
4.1. New RTCP XR Block Type value . . . . . . . . . . . . . . . 11
4.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 11
4.3. Contact information for registrations . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1. Normative References . . . . . . . . . . . . . . . . . . . 14
7.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 15
A.1. draft-ietf-xrblock-rtcp-xr-concsec-00 . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
1.1. Concealed Seconds Block
This draft defines a new block type to augment those defined in
[RFC3611], for use primarily in audio applications of RTP.
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.
Concealment refers to playout of locally-generated signals used to
mask the impact of network impairments such as lost packets or to
reduce the audibility of jitter buffer adaptations.
The new block type provides metrics for concealment. Specifically,
the first metric (Unimpaired Seconds) reports the number of whole
seconds occupied only with normal playout of data which 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) reports the number of whole seconds
during which the receiver played out locally-generated data for more
than SCS Threshold (ms).
The metric belongs to the class of transport-related terminal metrics
defined in [MONARCH].
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 draft defines a new Extended Report block that
MUST be used as defined in [RFC3550] and [RFC3611].
1.3. Performance Metrics Framework
The Performance Metrics Framework [RFC6390] provides guidance on the
definition and specification of performance metrics. The RTP
Monitoring Architectures [MONARCH] provides guideline for reporting
block format using RTCP XR. The Metrics Block described in this
document are in accordance with the guidelines in [RFC6390] and
[MONARCH].
1.4. Applicability
This metric is primarily applicable to audio applications of RTP.
EDITOR'S NOTE: are there metrics for concealment of transport errors
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for video?
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2. Loss Concealment Block
This sub-block 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 PSTN T1/E1
errored seconds metric.
The following metrics are based on successive one second intervals as
declared by a local clock. This local 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 50ms
apart could result in either one concealed second or two, depending
on the particular 1000 ms boundaries used.
The seconds in this sub-block are not necessarily calendar seconds.
At the tail end of a call, periods of time of less than 1000ms shall
be incorporated into these counts if they exceed 500ms and shall be
disregarded if they are less than 500ms.
2.1. Report Block Structure
Loss Concealment 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=NLC | I |plc| rsv. | block length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unimpaired Seconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Concealed Seconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Severely Concealed Seconds | RESERVED | SCS Threshold |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
2.2. Definition of Fields in Concealed Seconds Metrics Block
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Block type (BT): 8 bits
A Concealed Seconds Metrics Report Block is identified by the
constant NCS.
[Note to RFC Editor: please replace NCS 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 Delay 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).
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 = enhanced
Other values reserved
Reserved (resv): 4 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 4.
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SSRC of source: 32 bits
As defined in Section 4.1 of [RFC3611].
Unimpaired Seconds: 32 bits
A count of the number of unimpaired Seconds that have occurred.
An unimpaired Second is defined as a continuous period of 1000ms
during which no frame loss or discard due to late arrival has
occurred. Every second in a call must be classified as either OK
or Concealed.
Normal playout of comfort noise or other silence concealment
signal during periods of talker silence, if VAD is used, shall be
counted as unimpaired seconds.
If the measured value exceeds 0xFFFFFFFD, the value 0xFFFFFFFE
SHOULD be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFFFF SHOULD be
reported.
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 1000ms
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
SHALL 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
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insertion or deletion of samples in the audio playout stream due
to jitter buffer adaptation, re-sizing 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. .
However, an implementation SHOULD include buffer-type concealment
in counts of Concealed Seconds and Severely Concealed Seconds if
the event occurs at an 'inopportune' moment, with an emergency or
large, immediate adaptation during active speech, or for
unsophisticated adaptation during speech without regard for the
underlying signal, in which cases the assumption of low-audibility
cannot hold. In other words, jitter buffer adaptation events
which may be presumed to be audible SHOULD be included in
Concealed Seconds and Severely Concealed Seconds counts.
Concealment events which 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.
If the measured value exceeds 0xFFFFFFFD, the value 0xFFFFFFFE
SHOULD be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFFFF SHOULD be
reported.
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 1000 ms during which the cumulative amount of time that has
been subject to frame loss or discard due to late arrival, exceeds
the SCS Threshold.
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.
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RESERVED: 8 bits
These bits are reserved. They SHOULD be set to zero by senders
and MUST be ignored by receivers.
SCS Threshold: 8 bits
The SCS Threshold defines 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. This is expressed in milliseconds and hence can represent
a range of 0.1 to 25.5 percent loss or discard.
A default threshold of 50ms (5% effective frame loss per second)
is suggested.
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3. 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.
The SDP attribute for the block has an additional optional paremeter,
"thresh", used to supply a value for the SCS Threshold parameter. If
this parameter is present, the RTP system receiving the SDP SHOULD
use this value for the current session. If the parameter is not
present, the RTP system SHOULD use a locally configured value.
rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF
(defined in [RFC3611])
xr-format =/ xr-conc-sec-block
xr-conc-sec-block = "conc-sec" ["=" thresh]
thresh = 1*DIGIT ; threshold for SCS (ms)
DIGIT = %x30-39
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4. 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].
4.1. New RTCP XR Block Type value
This document assigns the block type value NJB in the IANA "RTCP XR
Block Type Registry" to the "Concealed Seconds Metrics Block".
[Note to RFC Editor: please replace NCS with the IANA provided RTCP
XR block type for this block.]
4.2. New RTCP XR SDP Parameter
This document also registers a new parameter "conc-sec" in the "RTCP
XR SDP Parameters Registry".
4.3. Contact information for registrations
The contact information for the registrations is:
Alan Clark (alan.d.clark@telchemy.com)
2905 Premiere Parkway, Suite 280
Duluth, GA 30097
USA
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5. 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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6. Acknowledgements
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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7. References
7.1. 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.
7.2. Informative References
[MONARCH] Hunt, G., "Monitoring Architectures for RTP",
ID draft-ietf-avtcore-monarch-04, August 2011.
[RFC6390] Clark, A. and B. Claise, "Framework for Performance Metric
Development", RFC 6390, October 2011.
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Appendix A. Change Log
Note to the RFC-Editor: please remove this section prior to
publication as an RFC.
A.1. draft-ietf-xrblock-rtcp-xr-concsec-00
The following are the major changes to previous version :
o Updated references.
o Allocate two bits for interval metric flag and 32 bit for SSRC
o Other editorial changes to get in line with MONARCH and MeasID
draft.
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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
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 Institure of China Telecom Corporation Limited
No.1835,South Pudong Road
Shanghai 200122
China
Email: bijy@sttri.com.cn
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
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