Audio/Video Transport Working G. Hunt
Group BT
Internet-Draft A. Clark
Intended status: Standards Track Telchemy
Expires: April 28, 2009 October 25, 2008
RTCP XR Report Block for Loss Concealment metric Reporting
draft-ietf-avt-rtcp-xr-loss-conceal-00.txt
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Abstract
This document defines an RTCP XR Report Block that allows the
reporting of Loss Concealment metrics primarily for audio
applications of RTP.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Loss Concealment Report Block . . . . . . . . . . . . . . 3
1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 4
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 4
2. Loss Concealment Block . . . . . . . . . . . . . . . . . . . . 5
2.1. Report Block Structure . . . . . . . . . . . . . . . . . . 5
2.2. Definition of Fields in Loss Concealment Report Block . . 5
3. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 9
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
Intellectual Property and Copyright Statements . . . . . . . . . . 15
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1. Introduction
1.1. Loss Concealment Report Block
This draft defines a new block type to augment those defined in
[RFC3611], for use in a range of RTP applications.
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.
The new 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. 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 metric belongs to the class of transport-related terminal metrics
defined in [MONARCH] (work in progress).
Instances of this Metrics Block refer by tag to the separate
auxiliary Measurement Identity block [MEASIDENT] which contains
information such as the SSRC of the measured stream, and RTP sequence
numbers and time intervals indicating the span of the report.
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
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MUST be used as defined in [RFC3550] and [RFC3611].
1.3. Performance Metrics Framework
The Performance Metrics Framework [PMOLFRAME] 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
[PMOLFRAME].
1.4. Applicability
This metric is primarily applicable to audio applications of RTP.
EDITOR'S NOTE: are there metrics for concealment of transport errors
for video?
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2. Loss Concealment Block
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| tag |plc|rsv| block length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| On-time Playout Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Loss Concealment Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Buffer Adjustment Concealment Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Playout Interrupt Count | Mean Playout Interrupt Size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
2.2. 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): 1 bit
This field is used to indicate whether the Loss Concealment metric
block is an Interval or a Cumulative report, that is, whether the
reported values apply to the most recent measurement interval
duration between successive metrics reports (I=1) (the Interval
Duration) or to the accumulation period characteristic of
cumulative measurements (I=0) (the Cumulative Duration).
Numerical values for both these intervals are provided in the
Measurement Identifier block referenced by the tag field below.
Measurement Identifier association (tag): 3 bits
This field is used to identify the Measurement Identifier block
[MEASIDENT] which describes this measurement. The relevant
Measurement Identifier block has the same tag value as the Loss
Concealment Metrics block. Note that there may be more than one
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Measurement Identifier block per RTCP packet.
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
Reserved (rsv): 2 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 Loss Concealment Metrics block, the block length is equal to
4.
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
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
SHOULD be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFFFF SHOULD be
reported.
Loss Concealment Duration (ms): 32 bits
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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
SHOULD be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFFFF SHOULD 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
SHOULD be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFFFF SHOULD 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
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.
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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.
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 SHOULD be
reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFF SHOULD be reported.
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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.
rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)] CRLF
(defined in [RFC3611])
xr-format = xr-format / xr-conceal-block
xr-bgld-block = "xr-conceal"
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4. IANA Considerations
This document creates a new block type within the IANA "RTCP XR Block
Type Registry" called the Loss Concealment Metrics Block, and a new
parameter xr-conceal within the "RTCP XR SDP Parameters Registry".
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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. 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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7. References
7.1. Normative References
[MEASIDENT]
Hunt, G., "RTCP XR Measurement Identifier Block",
ID draft-ietf-avt-rtcp-xr-measid-00, August 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC3550] Schulzrinne, H., "RTP: A Transport Protocol for Real-Time
Applications", RFC 3550, July 2003.
[RFC3611] Friedman, T., "RTP Control Protocol Extended Reports (RTCP
XR)", RFC 3611, November 2003.
[RFC4566] Handley, M., "SDP: Session Description Protocol",
RFC 4566, July 2006.
7.2. Informative References
[MONARCH] Hunt, G., "Monitoring Architectures for RTP",
ID draft-hunt-avt-monarch-01, August 2008.
[PMOLFRAME]
Clark, A., "Framework for Performance Metric Development",
ID draft-ietf-pmol-metrics-framework-00, July 2008.
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Authors' Addresses
Geoff Hunt
BT
Orion 1 PP9
Adastral Park
Martlesham Heath
Ipswich, Suffolk IP4 2TH
United Kingdom
Phone: +44 1473 608325
Email: geoff.hunt@bt.com
Alan Clark
Telchemy Incorporated
2905 Premiere Parkway, Suite 280
Duluth, GA 30097
USA
Email: alan.d.clark@telchemy.com
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