Audio/Video Transport Working Group A. Clark
Internet-Draft Telchemy
Intended status: Standards Track V. Singh
Expires: August 27, 2013 Aalto University
Q. Wu
Huawei
February 23, 2013
RTP Control Protocol (RTCP) Extended Report (XR) Block for Jitter Buffer
Metric Reporting
draft-ietf-xrblock-rtcp-xr-jb-08.txt
Abstract
This document defines an RTP Control Protocol (RTCP) Extended Report
(XR) Block that allows the reporting of Jitter Buffer metrics for a
range of RTP applications.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Jitter Buffer Metrics Block . . . . . . . . . . . . . . . 3
1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Standards Language . . . . . . . . . . . . . . . . . . . . 4
3. Jitter Buffer Operation . . . . . . . . . . . . . . . . . . . 5
3.1. Fixed Jitter Buffer . . . . . . . . . . . . . . . . . . . 5
3.2. Adaptive Jitter Buffer . . . . . . . . . . . . . . . . . . 5
4. Jitter Buffer Metrics Block . . . . . . . . . . . . . . . . . 6
4.1. Report Block Structure . . . . . . . . . . . . . . . . . . 6
4.2. Definition of Fields in Jitter Buffer Metrics Block . . . 6
5. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . . 9
5.2. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6.1. New RTCP XR Block Type value . . . . . . . . . . . . . . . 10
6.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 10
6.3. Contact information for registrations . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 12
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 15
A.1. draft-ietf-xrblock-rtcp-xr-jb-08 . . . . . . . . . . . . . 15
A.2. draft-ietf-xrblock-rtcp-xr-jb-07 . . . . . . . . . . . . . 15
A.3. draft-ietf-xrblock-rtcp-xr-jb-05 . . . . . . . . . . . . . 15
A.4. draft-ietf-xrblock-rtcp-xr-jb-03 . . . . . . . . . . . . . 15
A.5. draft-ietf-xrblock-rtcp-xr-jb-02 . . . . . . . . . . . . . 15
A.6. draft-ietf-xrblock-rtcp-xr-jb-01 . . . . . . . . . . . . . 15
A.7. draft-ietf-xrblock-rtcp-xr-jb-00 . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
1.1. Jitter Buffer Metrics Block
This document defines a new block type to augment those defined in
[RFC3611], for use in a range of RTP applications.
The new block type provides information on jitter buffer
configuration and performance.
The metric belongs to the class of transport-related end system
metrics defined in [RFC6792].
Instances of this Metrics Block refer by Synchronization source
(SSRC) to the separate auxiliary Measurement Information block
[RFC6776] 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]
defines an extensible structure for reporting using an RTCP Extended
Report (XR). This document defines a new Extended Report block for
use with [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. Metrics described in this draft are in
accordance with the guidelines in [RFC6390]and [RFC6792].
1.4. Applicability
Real-time applications employ a jitter buffer to absorb jitter
introduced on the path from source to destination. These metrics are
used to report how the jitter buffer at the receiving end of RTP
stream behaves as a result of jitter in the network and are
applicable to a range of RTP applications.
These metrics reflect how terminal-related factors affect real-time
application quality and are useful to provide better end-user quality
of experience (QoE).
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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 RFC 2119 [RFC2119].
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3. Jitter Buffer Operation
A jitter buffer is required to absorb delay variation in network
delivery of media packets. A jitter buffer works by holding media
data for a period of time after it is received and before it is
played out. Packets that arrive early are held in the jitter buffer
longer. If packets arrive too early they may be discarded if there
is no available jitter buffer space. If packets are delayed
excessively by the network they may be discarded if they miss their
playout time.
The jitter buffer can be considered as a time window with one side
(the early window) aligned with the delay corresponding to the
earliest arriving packet and the other side (the late window)
representing the maximum permissible delay before a late arriving
packet would be discarded. The delay applied to packets that arrive
at their expected time is known as the Nominal Delay and this is
equivalent to the late window.
The "expected arrival time" is the time that a packet would arrive if
there was no delay variation. If all packets arrived at their
expected arrival time then every packet would be delayed by exactly
the Nominal Delay. Early packets arrive before their expected
arrival time and late packets arrive after. The reference for the
expected arrival time may, for example, be the first packet in the
session or the running average delay.
Jitter Buffer delay is the time spent by a packet in the jitter
buffer. The Jitter Buffer Nominal Delay is the delay applied to
packets arriving at their expected time. The Jitter Buffer maximum
delay is the delay that is applied to an earliest arriving packet
that is not discarded and corresponds to the early window of the
jitter buffer.
3.1. Fixed Jitter Buffer
A receiver can use either a fixed or adaptive jitter buffer. A fixed
jitter buffer is a simple implementation however may not give optimum
performance in terms of packet discard rate and delay.
3.2. Adaptive Jitter Buffer
An adaptive jitter buffer allows the nominal delay to be set to a low
value initially, to minimize user perceived delay, however can
automatically increase the late window if a significant proportion of
packets are arriving late (and hence being discarded).
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4. Jitter Buffer Metrics Block
This block describes the configuration and operating parameters of
the jitter buffer in the receiver of the RTP end system or RTP mixer
which sends the report. Instances of this Metrics Block refer by
SSRC to the separate auxiliary Measurement Information block
[RFC6776] which describes the measurement interval in use. This
Metrics Block relies on the measurement interval in the Measurement
Information block indicating the span of the report and should be
sent in the same compound RTCP packet as the measurement information
block. If the measurement interval is not received in the same
compound RTCP packet as this Metrics Block, this Metrics Block should
be discarded.
4.1. Report Block Structure
JB 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=NJB | I |C| Rsvd. | block length=3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| JB nominal | JB maximum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| JB high water mark | JB low water mark |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
4.2. Definition of Fields in Jitter Buffer Metrics Block
Block type (BT): 8 bits
A Jitter Buffer Metrics Report Block is identified by the constant
NJB.
[Note to RFC Editor: please replace NJB with the IANA provided
RTCP XR block type for this block.]
Interval Metric flag (I): 2 bits
This field is used to indicate whether the Jitter Buffer metrics
are Sampled, Interval or Cumulative metrics:
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I=01: Sampled Value - the reported value is a sampled
instantaneous value.
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.
Jitter Buffer Configuration (C): 1 bit
This field is used to identify the jitter buffer method in use at
the receiver, according to the following code:
0 = Fixed jitter buffer
1 = Adaptive jitter buffer
Reserved (Rsvd.): 5 bits
These bits are reserved. They MUST be set to zero by senders
ignored by receivers (See [RFC6709] section 4.2).
Block Length: 16 bits
The length of this report block in 32-bit words, minus one, in
accordance with the definition in [RFC3611]. This field MUST be
set to 3 to match the fixed length of the report block.
jitter buffer nominal delay (JB nominal): 16 bits
This is the current nominal jitter buffer delay in milliseconds,
which corresponds to the nominal jitter buffer delay for packets
that arrive exactly on time. It is calculated based on the time
spend in the jitter buffer for the packet that arrives exactly on
time. This parameter MUST be provided for both fixed and adaptive
jitter buffer implementations.
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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jitter buffer maximum delay (JB maximum): 16 bits
This is the current maximum jitter buffer delay in milliseconds
which corresponds to the earliest arriving packet that would not
be discarded. It is calculated based on the time spent in the
jitter buffer for the earliest arriving packet In simple queue
implementations this may correspond to the size of the jitter
buffer. In adaptive jitter buffer implementations, this value may
vary dynamically. This parameter MUST be provided for both fixed
and adaptive jitter buffer implementations.
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.
jitter buffer high water mark (JB high water mark): 16 bits
This is the highest value of the jitter buffer nominal delay in
milliseconds which occurred at any time during the reporting
interval. This parameter MUST be provided for adaptive jitter
buffer implementations and its value MUST be set to JB maximum for
fixed jitter buffer implementations.
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.
jitter buffer low water mark (JB low water mark): 16 bits
This is the lowest value of the jitter buffer nominal delay in
milliseconds which occurred at any time during the reporting
interval. This parameter MUST be provided for adaptive jitter
buffer implementations and its value MUST be set to JB maximum for
fixed jitter buffer implementations.
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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5. SDP Signaling
[RFC3611] defines the use of SDP (Session Description Protocol)
[RFC4566] for signaling the use of XR blocks. However XR blocks MAY
be used without prior signaling (see section 5 of RFC3611).
5.1. SDP rtcp-xr-attrib Attribute Extension
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.
xr-format =/ xr-jb-block
xr-jb-block = "jitter-bfr"
5.2. Offer/Answer Usage
When SDP is used in offer-answer context, the SDP Offer/Answer usage
defined in [RFC3611] for unilateral "rtcp-xr" attribute parameters
applies. For detailed usage of Offer/Answer for unilateral
parameter, refer to section 5.2 of [RFC3611].
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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 value
This document assigns the block type value NJB in the IANA "RTCP XR
Block Type Registry" to the "JB Metrics Block".
[Note to RFC Editor: please replace NJB with the IANA provided RTCP
XR block type for this block.]
6.2. New RTCP XR SDP Parameter
This document also registers a new parameter "jitter-bfr" in the
"RTCP XR SDP Parameters Registry".
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. Acknowledgments
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, Hideaki Yamada,Claire Bi,Colin
Perkin, Dan Romascanu, Kevin Gross and Glen Zorn.
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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.
[RFC6709] Carpenter, B., Aboba, B., and S. Cheshire, "Design
Considerations for Protocol Extensions", RFC 6709,
September 2012.
[RFC6776] Wu, Q., "Measurement Identity and information Reporting
using SDES item and XR Block", RFC 6776, August 2012.
10.2. Informative References
[RFC6390] Clark, A. and B. Claise, "Framework for Performance Metric
Development", RFC 6390, October 2011.
[RFC6792] Hunt, G., Wu, Q., and P. Arden, "Monitoring Architectures
for RTP", RFC 6792, November 2012.
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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-jb-08
The following are the major changes to previous version :
o Rewrote descriptive text and definitions for clarification.
A.2. draft-ietf-xrblock-rtcp-xr-jb-07
The following are the major changes to previous version :
o Add one new section to discuss jitter buffer operation.
A.3. draft-ietf-xrblock-rtcp-xr-jb-05
The following are the major changes to previous version :
o Some editorial change changes based on the discussion with Glen
and Kevin on the list.
A.4. draft-ietf-xrblock-rtcp-xr-jb-03
The following are the major changes to previous version :
o Reduce the "jb cfg" to 1-bit based on discussion in the WGLC.
o Other editorial change changes aligning with PDV,Delay draft.
A.5. draft-ietf-xrblock-rtcp-xr-jb-02
The following are the major changes to previous version :
o Add some explanation text in the SDP offer/answer section.
o Add some text in applicability section to explain the use to
report jitter buffer metrics.
o Other editorial change changes aligning with PDV,Delay draft.
A.6. draft-ietf-xrblock-rtcp-xr-jb-01
The following are the major changes to previous version :
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o Outdated reference update
o Add one Editor notes to ask clarification on the use of reporting
jitter buffer metrics.
o Other Editorial changes.
A.7. draft-ietf-xrblock-rtcp-xr-jb-00
The following are the major changes to previous version :
o Boilerplate updates.
o references updates
o allocate 32 bit field in report block for SSRC
o Other editorial changes to get alignment with MONARCH draft.
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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
Varun Singh
Aalto University
School of Electrical Engineering
Otakaari 5 A
Espoo, FIN 02150
Finland
Email: varun@comnet.tkk.fi
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
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