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 Concealed Seconds metric Reporting
draft-ietf-avt-rtcp-xr-concsec-00.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 28, 2009.
Hunt & Clark Expires April 28, 2009 [Page 1]
Internet-Draft RTCP XR Concealed Seconds October 2008
Abstract
This document defines an RTCP XR Report Block that allows the
reporting of Concealed Seconds metrics primarily for audio
applications of RTP.
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. Concealed Seconds Metrics Block . . . . . . . . . . . . . . . 5
2.1. Report Block Structure . . . . . . . . . . . . . . . . . . 5
2.2. Definition of Fields in Concealed Seconds Metrics 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
Hunt & Clark Expires April 28, 2009 [Page 2]
Internet-Draft RTCP XR Concealed Seconds October 2008
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 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] (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
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].
Hunt & Clark Expires April 28, 2009 [Page 3]
Internet-Draft RTCP XR Concealed Seconds October 2008
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?
Hunt & Clark Expires April 28, 2009 [Page 4]
Internet-Draft RTCP XR Concealed Seconds October 2008
2. Concealed Seconds Metrics 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
Concealed seconds 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=NCS |I| tag |plc|rsv| block length = 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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
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.]
Hunt & Clark Expires April 28, 2009 [Page 5]
Internet-Draft RTCP XR Concealed Seconds October 2008
Interval Metric flag (I): 1 bit
This field is used to indicate whether the Concealed Seconds
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
Concealed Seconds Metrics block. Note that there may be more than
one 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 0-3
0 = silence insertion
1 = simple replay, no attenuation
2 = simple replay, with attenuation
3 = enhanced
Other values reserved
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 Concealed Seconds block, the block length is equal to 3.
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
Hunt & Clark Expires April 28, 2009 [Page 6]
Internet-Draft RTCP XR Concealed Seconds October 2008
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 (defined in Section 3.6) 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.
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. The duration, in milliseconds, of audio playout
corresponding to Loss-type concealment.
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.
Hunt & Clark Expires April 28, 2009 [Page 7]
Internet-Draft RTCP XR Concealed Seconds October 2008
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.
Hunt & Clark Expires April 28, 2009 [Page 8]
Internet-Draft RTCP XR Concealed Seconds October 2008
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-format / xr-conc-sec-block
xr-conc-sec-block = "xr-concsec" ["=" thresh]
thresh = 1*DIGIT ; threshold for SCS (ms)
DIGIT = %x30-39
Hunt & Clark Expires April 28, 2009 [Page 9]
Internet-Draft RTCP XR Concealed Seconds October 2008
4. IANA Considerations
This document creates a new block type within the IANA "RTCP XR Block
Type Registry" called the Concealed Seconds Metrics Block, and a new
parameter xr-concsec within the "RTCP XR SDP Parameters Registry".
Hunt & Clark Expires April 28, 2009 [Page 10]
Internet-Draft RTCP XR Concealed Seconds October 2008
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.
Hunt & Clark Expires April 28, 2009 [Page 11]
Internet-Draft RTCP XR Concealed Seconds October 2008
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.
Hunt & Clark Expires April 28, 2009 [Page 12]
Internet-Draft RTCP XR Concealed Seconds October 2008
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.
Hunt & Clark Expires April 28, 2009 [Page 13]
Internet-Draft RTCP XR Concealed Seconds October 2008
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
Hunt & Clark Expires April 28, 2009 [Page 14]
Internet-Draft RTCP XR Concealed Seconds October 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Hunt & Clark Expires April 28, 2009 [Page 15]
