Audio/Video Transport Working Group A. Clark
Internet-Draft Telchemy
Intended status: Standards Track G. Zorn, Ed.
Expires: July 28, 2013 Network Zen
C. Bi
STTRI
Q. Wu, Ed.
Huawei
January 24, 2013
RTCP XR Report Block for Concealment metrics Reporting on Audio
Applications
draft-ietf-xrblock-rtcp-xr-loss-conceal-04.txt
Abstract
This document defines two RTCP XR Report Blocks that allows the
reporting of loss concealment metrics for audio applications of RTP.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Loss Concealment and Concealment Seconds Metrics
Reporting Block . . . . . . . . . . . . . . . . . . . . . 3
1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 4
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 4
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Standards Language . . . . . . . . . . . . . . . . . . . . 5
3. Loss Concealment Block . . . . . . . . . . . . . . . . . . . . 6
3.1. Report Block Structure . . . . . . . . . . . . . . . . . . 6
3.2. Definition of Fields in Loss Concealment Report Block . . 6
4. Concealment Seconds Block . . . . . . . . . . . . . . . . . . 10
4.1. Report Block Structure . . . . . . . . . . . . . . . . . . 10
4.2. Definition of Fields in Concealed Seconds Metrics Block . 10
5. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . . 15
5.2. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
6.1. New RTCP XR Block Type values . . . . . . . . . . . . . . 16
6.2. New RTCP XR SDP Parameters . . . . . . . . . . . . . . . . 16
6.3. Contact information for registrations . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 18
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
10.1. Normative References . . . . . . . . . . . . . . . . . . . 20
10.2. Informative References . . . . . . . . . . . . . . . . . . 20
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 21
A.1. draft-ietf-xrblock-rtcp-xr-loss-conceal-04 . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
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1. Introduction
1.1. Loss Concealment and Concealment Seconds Metrics Reporting Block
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 or to reduce the audibility of
jitter buffer adaptations.
This draft defines two new concealment related block types to augment
those defined in [RFC3611] for use in a range of RTP applications.
The first block type 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 which 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 which 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 which
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 may have very little impact
on user experience, whilst loss concealment may occur at any time.
The second 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).
These metrics belongs to the class of transport-related terminal
metrics defined in [RFC6792].
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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 [RFC6792] provides guideline for reporting
block format using RTCP XR. The Metrics Block described in this
document are in accordance with those guidelines.
1.4. Applicability
These metrics are only applicable to audio applications of RTP.
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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 RFC2119 [RFC2119].
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3. Loss Concealment Block
3.1. 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=5 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| On-time Playout Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Loss Concealment Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Buffer Adjustment Concealment Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Playout Interrupt Count | Mean Playout Interrupt Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
3.2. Definition of Fields in Loss Concealment Report Block
Block type (BT): 8 bits
A Loss Concealment Metrics Report Block is identified by the
constant NLC.
[Note to RFC Editor: please replace NLC 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 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.
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I=01: Sampled Value - the reported value is a sampled
instantaneous 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 MUST be set to zero by senders and
ignored by receivers (See [RFC6709] section 4.2).
block length: 16 bits
The length of this report block in 32-bit words, minus one. For
the Loss Concealment block, the block length is equal to 5.
SSRC of source: 32 bits
As defined in Section 4.1 of [RFC3611].
On-time Playout Duration (ms): 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 VAD is used, and locally generated or
regenerated tones and announcements.
An equivalent definition is that on-time playout is playout of any
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signal other than those used for concealment.
On-time playout duration MUST include both speech and silence
intervals, whether VAD is used or not. This duration is reported
in millisecond units.
If the measured value exceeds 0xFFFFFFFD, the value 0xFFFFFFFE
MUST be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFFFF MUST be reported.
Loss Concealment Duration (ms): 32 bits
The duration, in milliseconds, 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.
If the measured value exceeds 0xFFFFFFFD, the value 0xFFFFFFFE
MUST be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFFFF MUST be reported.
Buffer Adjustment Concealment Duration (ms): 32 bits
The duration, in milliseconds, of audio playout corresponding to
Buffer Adjustment-type concealment, if known.
If the measured value exceeds 0xFFFFFFFD, the value 0xFFFFFFFE
MUST be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFFFF MUST be reported.
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 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
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sophisticated time-stretching methods for insertion/deletion
during favorable periods in active speech may be employed.
Concealment events which cannot be classified as Buffer
Adjustment- type MUST be classified as Loss-type.
Playout Interrupt Count: 16 bits
The number of interruptions to normal playout which occurred
during the reporting period.
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.
Mean Playout Interrupt Size (ms): 16 bits
The mean duration, in ms, of interruptions to normal playout which
occurred during the reporting period.
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.
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4. Concealment Seconds 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 session, 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.
4.1. Report Block Structure
Concealed Seconds metrics block
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=NCS | I |plc|Rserved| block length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unimpaired Seconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Concealed Seconds |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Severely Concealed Seconds | RESERVED | SCS Threshold |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
4.2. 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 Concealment 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.
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 MUST be set to zero by senders and
ignored by receivers (See [RFC6709] section 4.2).
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Block Length: 16 bits
The length of this report block in 32-bit words, minus one. For
the Concealment Seconds block, the block length is equal to 4.
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 session 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 [VAD] is used,
shall be counted as unimpaired seconds.
If the measured value exceeds 0xFFFFFFFD, the value 0xFFFFFFFE
MUST be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFFFF MUST 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
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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 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
MUST be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFFFF MUST 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.
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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.
Reserved: 8 bits
These bits are reserved. They MUST be set to zero by senders and
ignored by receivers (See [RFC6709] section 4.2).
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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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.
5.1. SDP rtcp-xr-attrib Attribute Extension
This section augments the SDP attribute "rtcp-xr" [RFC3611] by
providing two additional values of "xr-format" to signal the use of
the report block defined in this document.
xr-format =/ xr-conceal-block
xr-format =/ xr-conc-sec-block
xr-conceal-block = "loss-conceal"
xr-conc-sec-block = "conc-sec" ["=" thresh]
thresh = 1*DIGIT ; threshold for SCS (ms)
DIGIT = %x30-39
5.2. Offer/Answer Usage
When SDP is used in offer-answer context, the SDP Offer/Answer usage
defined in [RFC3611] applies.
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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 values
This document assigns two block type values in the IANA "RTCP XR
Block Type Registry":
Name: NLC
Long Name: Loss Concealment Block
Value <NLC>
Reference: Section 3.1
Name: NCS
Long Name: Concealment Seconds Block
Value <NCS>
Reference: Section 4.1
[Note to RFC Editor: please replace <NLC> and <NCS> with the RTCP XR
block type assigned by IANA for this block.]
6.2. New RTCP XR SDP Parameters
This document also registers two new parameters in the "RTCP XR SDP
Parameters Registry":
o "loss-conceal"
o "conc-sec"
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
Geoff Hunt wrote the initial draft of this document.
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9. Acknowledgements
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, and Hideaki Yamada.
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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
[RFC6390] Clark, A. and B. Claise, "Framework for Performance Metric
Development", RFC 6390, October 2011.
[RFC6709] Carpenter, B., Aboba, B., and S. Cheshire, "Design
Considerations for Protocol Extensions", RFC 6709,
September 2012.
[RFC6792] Hunt, G., "Monitoring Architectures for RTP", RFC 6792,
November 2012.
[VAD] "http://en.wikipedia.org/wiki/Voice_activity_detection".
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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-loss-conceal-04
The following are the major changes to previous version :
o Merge Concealment Seconds draft into this draft (i.e.,Loss
Concealment draft).
o Updated references.
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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 (editor)
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 (editor)
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
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