Audio/Video Transport Working Group G. Zorn
Internet-Draft Network Zen
Intended status: Standards Track Q. Wu
Expires: April 25, 2013 Huawei
A. Clark
Telchemy
C. Bi
STTRI
October 22, 2012
RTP Control Protocol (RTCP) Extended Report (XR) Block for Concealed
Seconds Metric Reporting
draft-ietf-xrblock-rtcp-xr-concsec-03.txt
Abstract
This document defines an RTP Control Protocol(RTCP) Extended Report
(XR) Block that allows the reporting of Concealed Seconds metrics,
primarily for audio applications of RTP.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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to this document. Code Components extracted from this document must
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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 . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Standards Language . . . . . . . . . . . . . . . . . . . . 4
3. Concealment Seconds Block . . . . . . . . . . . . . . . . . . 4
3.1. Report Block Structure . . . . . . . . . . . . . . . . . . 5
3.2. Definition of Fields in Concealed Seconds Metrics Block . 5
4. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . . 9
4.2. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . 10
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5.1. New RTCP XR Block Type value . . . . . . . . . . . . . . . 10
5.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 10
5.3. Contact information for registrations . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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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.
'Concealed' 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.
Editor's Note: For video applications, the output at a receiver
should also be classified as either normal or concealed. Should
this paragraph be clear about this?
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 (SCS)) reports the number of whole
seconds during which the receiver played out locally-generated data
for longer than SCS Threshold milliseconds.
The metric belongs to the class of transport-related end system
metrics defined in Wu, Hunt & Arden [I-D.ietf-avtcore-monarch].
1.2. RTCP and RTCP XR Reports
The use of RTCP for reporting is defined in Schulzrinne et al.
[RFC3550]. Freidman, et al. [RFC3611] defines an extensible
structure for reporting using an RTCP Extended Report (XR). This
draft defines a new Extended Report block that MUST be used as
specified in RFC 3550 and RFC 3611.
1.3. Performance Metrics Framework
The Performance Metrics Framework [RFC6390] provides guidance on the
definition and specification of performance metrics. The RTP
Monitoring Architecture [I-D.ietf-avtcore-monarch] provides
guidelines for formatting RTCP XR blocks. The Metrics Block
described in this document are in accordance with the guidelines in
[RFC6390] and [I-D.ietf-avtcore-monarch].
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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?
Editor's Note: note that with video it is possible to use RTP based
retransmission and also FEC (e.g. COP3) - typically these would only
be used with IPTV as this is less delay sensitive than interactive
services.
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:
Editor's Note: For Video loss concealment, at least the following
four methods are used,i.e., Frame freeze,inter-frame
extrapolation, interpolation, Noise insertation, should this
section consider giving definition of these four methods for video
loss concealment?
3. Concealment Seconds Block
This 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.
Editor's Note: Should impairment also cover video application?
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
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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.
3.1. 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
3.2. Definition of Fields in Concealed Seconds Metrics Block
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 Concealed Seconds
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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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
Editor's Note 1 : In the packet loss concealment
methods,"Enhanced" is defines as one new Packet loss
Concealment method? However it is not clear what this
packet loss concealment method looks like?
Editor's Note 2: For Video loss concealment, there are a
range of methods used, for example:
(i) Frame freeze In this case the impaired video frame
is not displayed and the previously displayed frame is
hence "frozen" for the duration of the loss event
(ii) Inter-frame extrapolation If an area of the video
frame is damaged by loss, the same area from the
previous frame(s) can be used to estimate what the
missing pixels would have been. This can work well in
a scene with no motion but can be very noticeable if
there is significant movement from one frame to
another. Simple decoders may simply re-use the pixels
that were in the missing area, more complex decoders
may try to use several frames to do a more complex
extrapolation.
(iii) Interpolation A decoder may use the undamaged
pixels in the image to estimate what the missing block
of image should have
(iv) Noise insertion A decoder may insert random pixel
values - which would generally be less noticeable than
a blank rectangle in the image.
Therefore more text required in the future draft to
discuss Techniques for Video Loss Concealment method in
this document.
Reserved (resv): 4 bits
These bits are reserved. They SHOULD be set to zero by senders
and MUST be ignored by receivers.
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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.
SSRC of source: 32 bits
As defined in Section 4.1 of RFC 3611.
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.
If voice activity detection [VAD] is used, normal playout of
comfort noise or other silence concealment signals during periods
of talker silence SHALL be counted as unimpaired seconds.
Editor's Note: It should be clear that voice activity detection
does not apply to video.
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
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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.
Editor's Note: In this document, two kind of concealments are
defined: a. Loss-type concealment b. Buffer Adjustment-type
concealment Loss-type concealment is applicable to both audio
and video. However Buffer Adjustment-type concealment is
usually applied to audio. Should this section be clear about
this?
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
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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.
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.
4. SDP Signaling
RFC 3611 defines the use of Session Description Protocol (SDP,
[RFC4566] for signaling the use of XR blocks. XR blocks MAY be used
without prior signaling.
4.1. SDP rtcp-xr-attrib Attribute Extension
This section augments the SDP attribute "rtcp-xr" defined in Section
5.1 of RFC 3611 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.
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xr-format =/ xr-conc-sec-block
xr-conc-sec-block = "conc-sec" ["=" thresh]
thresh = 1*DIGIT ; threshold for SCS (ms)
DIGIT = <as defined in Section 3.4 of [RFC5234]>
4.2. Offer/Answer Usage
When SDP is used in offer-answer context, the SDP Offer/Answer usage
defined in Section 5.2 of RFC 3611 applies.
5. IANA Considerations
New block types for RTCP XR are subject to IANA registration. For
general guidelines on IANA considerations for RTCP XR, refer to
Section 6 of RFC 3611.
5.1. New RTCP XR Block Type value
This document assigns the block type value <NCS> 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.]
5.2. New RTCP XR SDP Parameter
This document also registers a new parameter "conc-sec" in the "RTCP
XR SDP Parameters Registry".
5.3. 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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6. Security Considerations
It is believed that this proposed RTCP XR report block introduces no
new security considerations beyond those described in RFC 3611. This
block does not provide per-packet statistics so the risk to
confidentiality documented in Section 7, paragraph 3 of [RFC3611]
does not apply.
7. Contributors
Geoff Hunt wrote the initial draft of this document.
8. 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.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control
Protocol Extended Reports (RTCP XR)", RFC 3611,
November 2003.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
9.2. Informative References
[I-D.ietf-avtcore-monarch]
Wu, W., Hunt, G., and P. Arden, "Guidelines for Use of the
RTP Monitoring Framework", draft-ietf-avtcore-monarch-22
(work in progress), September 2012.
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[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390,
October 2011.
[VAD] "http://en.wikipedia.org/wiki/Voice_activity_detection".
Authors' Addresses
Glen Zorn
Network Zen
227/358 Thanon Sanphawut
Bang Na, Bangkok 10260
Thailand
Phone: +66 (0) 909-0201060
Email: glenzorn@gmail.com
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
Alan Clark
Telchemy Incorporated
2905 Premiere Parkway, Suite 280
Duluth, GA 30097
USA
Email: alan.d.clark@telchemy.com
Claire Bi
Shanghai Research Institure of China Telecom Corporation Limited
No.1835,South Pudong Road
Shanghai 200122
China
Email: bijy@sttri.com.cn
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