Audio/Video Transport Working Group A. Clark
Internet-Draft Telchemy
Intended status: Standards Track G. Zorn
Expires: April 15, 2013 Network Zen
Q. Wu
Huawei
October 12, 2012
RTP Control Protocol (RTCP) Extended Report (XR) Block for Discard Count
metric Reporting
draft-ietf-xrblock-rtcp-xr-discard-09.txt
Abstract
This document defines an RTP Control Protocol(RTCP) Extended Report
(XR) Block that allows the reporting of a simple discard count metric
for use in a range of RTP applications.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Discard Count Report Block . . . . . . . . . . . . . . . . 3
1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Standards Language . . . . . . . . . . . . . . . . . . . . 5
3. Discard Count Metric Report Block . . . . . . . . . . . . . . 6
3.1. Report Block Structure . . . . . . . . . . . . . . . . . . 6
3.2. Definition of Fields in Discard Count Metric Report
Block . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 9
4.1. SDP rtcp-xr-attrib Attribute Extension . . . . . . . . . . 9
4.2. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . . 9
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 . . . . . . . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References . . . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 15
A.1. draft-ietf-xrblock-rtcp-xr-discard-09 . . . . . . . . . . 15
A.2. draft-ietf-xrblock-rtcp-xr-discard-08 . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
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1. Introduction
1.1. Discard Count Report 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
supports the reporting of the number of packets which are received
correctly but are never played out, typically because they arrive too
late to be played out (buffer underflow) or too early (buffer
overflow). The metric is applicable both to systems which use packet
loss repair techniques (such as forward error correction [RFC5109] or
retransmission [RFC4588]) and to those which do not.
This metric is useful for identifying the existence, and
characterizing the severity, of a packet transport problem which may
affect users' perception of a service delivered over RTP.
This block may be used in conjunction with [BGDISCARD] which provides
additional information on the pattern of discarded packets. However
the metric in [BGDISCARD] may be used independently of the metrics in
this block.
In case of Discard count metric block sent together with Burst gap
discard metric block defined in [BGDISCARD] to the media sender or
RTP based network management system, information carried in the
discard count metric block and Burst gap discard metric block allows
them calculate the some bust gap summary statistics, e.g., gap
discard rate.
The metric belongs to the class of transport-related end system
metrics defined in [MONARCH].
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 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 [MONARCH] provides guideline for reporting
block format using RTCP XR. The Metrics Block described in this
document are in accordance with the guidelines in [RFC6390] and
[MONARCH].
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1.4. Applicability
This metric is believed to be applicable to a large class of RTP
applications which use a jitter buffer.
Discards due to late or early arriving packets affects user
experience. The reporting of discards alerts senders and other
receivers to the need to adjust their transmission or reception
strategies. The reports allow network managers to diagnose these
user experience problems.
The ability to detect duplicate packets can be used by managers to
detect network layer or sender behavior which may indicate network or
device issues. Based on the reports, these issues may be addressed
prior to any impact on user experience.
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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].
In addition, the following terms are defined:
Received, Lost and Discarded
A packet shall be regarded as lost if it fails to arrive within an
implementation-specific time window. A packet that arrives within
this time window but is too early or late to be played out or
thrown away before playout due to packet duplication or redundancy
shall be regarded as discarded. A packet shall be classified as
one of received (or OK), discarded or lost. The Discard Count
Metric counts only discarded packets. The metric "cumulative
number of packets lost" defined in [RFC3550] reports a count of
packets lost from the media stream (single SSRC within single RTP
session). Similarly the metric "number of packets discarded"
reports a count of packets discarded from the media stream (single
SSRC within single RTP session) arriving at the receiver. Another
metric defined in [RFC5725] is available to report on packets
which are not recovered by any repair techniques which may be in
use.
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3. Discard Count Metric Report Block
3.1. Report Block Structure
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=PDC | I |DT | resv.| block length = 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| number of packets discarded |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
3.2. Definition of Fields in Discard Count Metric Report Block
Block type (BT): 8 bits
A Discard Count Metric Report Block is identified by the constant
PDC.
[Note to RFC Editor: please replace PDC with the IANA provided
RTCP XR block type for this block.]
Interval Metric flag (I): 2 bits
This field indicates whether the reported metric is an interval,
cumulative, or sampled metric [MONARCH]. The Discard Count Metric
value can be reported as either an interval metric (I=10) or a
cumulative metric (I=11). It does not make sense to report the
Discard Count Metric as a sampled metric, so the value I=01 MUST
NOT be used. The value I=00 is reserved, and MUST NOT be used.
Discard Type (DT): 2bits
This field is used to identify the discard type used in this
report block. The discard type is defined as follows:
00: Report packet discarded or being thrown away before playout
due to packets duplication.
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01: Report packet discarded due to too early to be played out.
10: Report packet discarded due to too late to be played out.
11: Report the total number of discarded packets due to both
early and late to be played out.
An endpoint MAY report only one of the above four discard types
blocks in an compound RTCP report in a reporting interval. It MAY
also report a combination of discard types in a compound RTCP
report but not all combinations are valid. The endpoint MAY
report duplicate packet discard (DT=0) block with any other
discard (DT=1, 2, or 3) block. Additionally, an endpoint MUST NOT
report combined discard (DT=3) block with early discard (DT=1) or
late discard (DT=2) report block.
Some systems send duplicate RTP packets for robustness or error
resilience. This is NOT RECOMMENDED since it breaks RTCP packet
statistics. If duplication is desired for error resilience, the
mechanism described in [RTPDUP] can be used, since this will not
cause breakage of RTP streams or RTCP statistics.
Reserved (resv): 4 bits
These bits are reserved. They MUST be set to zero by senders and
ignored by receivers.
block length: 16 bits
The length of this report block in 32-bit words, minus one. For
the Discard Count block, the block length is equal to 2.
SSRC of source: 32 bits
As defined in Section 4.1 of [RFC3611].
number of packets discarded: 32 bits
Number of packets discarded over the period (Interval or
Cumulative) covered by this report.
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.
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Note that the number of packets expected in the period associated
with this metric (whether interval or cumulative) is available
from the difference between a pair of extended sequence numbers in
the Measurement Information block [MEASI], so need not be repeated
in this block.
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4. 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.
4.1. 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-pdc-block
xr-pdc-block = "pkt-dscrd-count"
4.2. Offer/Answer Usage
When SDP is used in offer-answer context, the SDP Offer/Answer usage
defined in [RFC3611] applies.
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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
[RFC3611].
5.1. New RTCP XR Block Type value
This document assigns the block type value PDC in the IANA "RTCP XR
Block Type Registry" to the "Discard Count Metrics Block".
[Note to RFC Editor: please replace PDC 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 "pkt-dscrd-count" in the
"RTCP XR SDP Parameters Registry".
5.3. Contact information for registrations
The following contact information is provided for all
registrations in this document:
Qin Wu (sunseawq@huawei.com)
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
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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 [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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7. Contributors
Geoff Hunt wrote the initial draft of this document.
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8. 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, and Hideaki Yamada,Kevin
Gross, Varun Singh, Claire Bi, Roni Even, Dan Romascanu.
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9. References
9.1. 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.
9.2. Informative References
[BGDISCARD]
Hunt, G., "RTCP XR Report Block for Burst Gap Discard
metric Reporting",
ID draft-ietf-xrblock-rtcp-xr-burst-gap-discard-06,
October 2012.
[MEASI] Hunt, G., "Measurement Identity and information Reporting
using SDES item and XR Block",
ID draft-ietf-xrblock-rtcp-xr-meas-identity-10,
August 2012.
[MONARCH] Wu, Q., "Monitoring Architectures for RTP",
ID draft-ietf-avtcore-monarch-22, September 2012.
[RFC4588] Rey, J., "RTP Retransmission Payload Format", RFC 4588,
July 2006.
[RFC5109] Li, A., "RTP Payload Format for Generic Forward Error
Correction", RFC 5109, July 2006.
[RFC5725] Begen, A., "RTCP XR Report Block for Post-Repair Loss
metric Reporting", RFC 5725, February 2010.
[RFC6390] Clark, A. and B. Claise, "Framework for Performance Metric
Development", RFC 6390, October 2011.
[RTPDUP] Begen, A. and C. Perkins, "Duplicating RTP Streams",
ID draft-ietf-avtext-rtp-duplication-00, July 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-discard-09
The following are the major changes compared to previous version:
o SDP Duplicated Parameter Deleting.
A.2. draft-ietf-xrblock-rtcp-xr-discard-08
The following are the major changes compared to previous version:
o Outdated reference update.
o Editorial changes based on comments that applied to PDV and Delay
drafts.
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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
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
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
Email: sunseawq@huawei.com
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