Audio/Video Transport Working Group G. Hunt
Internet-Draft Unaffiliated
Intended status: Standards Track A. Clark
Expires: June 11, 2012 Telchemy
G. Zorn
Network Zen
Q. Wu
Huawei
December 9, 2011
RTCP XR Report Block for Discard metric Reporting
draft-ietf-xrblock-rtcp-xr-discard-01.txt
Abstract
This document defines an RTCP XR Report 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 Report 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. Discard Metric Report Block . . . . . . . . . . . . . . . . . 5
3.1. Report Block Structure . . . . . . . . . . . . . . . . . . 5
3.2. Definition of Fields in Discard Metric Report Block . . . 5
4. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5.1. New RTCP XR Block Type value . . . . . . . . . . . . . . . 8
5.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 8
5.3. Contact information for registrations . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 10
8. Changes from previous version . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
1.1. Discard Report Block
This draft 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
characterising the severity, of a packet transport problem which may
affect users' perception of a service delivered over RTP.
The metric belongs to the class of transport-related terminal metrics
defined in [MONARCH] (work in progress).
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 [RFC6390] 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
[RFC6390].
1.4. Applicability
This metric is believed to be applicable to a large class of RTP
applications which use a jitter buffer.
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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 shall
be regarded as discarded. A packet shall be classified as one of
received (or OK), discarded or lost. The Discard 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 Metric Report Block
3.1. Report Block Structure
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=NBGD | I |E| resv. | block length = 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| number of packets discarded |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
3.2. Definition of Fields in Discard Metric Report Block
Block type (BT): 8 bits
A Discard Metric Report Block is identified by the constant ND.
[Note to RFC Editor: please replace ND 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 Basic Loss/Discard
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 to the
value of a continuously measured or calculated that has been
sampled at end of the interval (I=01) (Sampled Value).
Early indication flag (E): 1bit
This field is used to indicate whether packets are discarded due
to early arrival or due to late arrival. This field MUST be set
to '1' if packets are discarded due to too early arrival and MUST
be set to '0' otherwise.
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Reserved (resv): 5 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 Delay 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
SHOULD be reported to indicate an over-range measurement. If the
measurement is unavailable, the value 0xFFFFFFFF SHOULD be
reported.
Note that the number of packets expected in the period covered by
the metric (whether interval or cumulative) is available from the
difference between a pair of extended sequence numbers in the
Measurement Identity block, 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.
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-pd-block
xr-pd-block = "pkt-dscrd"
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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 ND in the IANA "RTCP XR
Block Type Registry" to the "Discard Metrics Block".
[Note to RFC Editor: please replace ND 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" in the "RTCP
XR SDP Parameters Registry".
5.3. Contact information for registrations
The contact information for the registrations is:
Geoff Hunt (r.geoff.hunt@gmail.com)
Orion 2 PP3, Adastral Park, Martlesham Heath, Ipswich IP5 3RE, United
Kingdom
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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
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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8. Changes from previous version
Changed BNF for SDP following Christian Groves' and Tom Taylor's
comments (4th and 5th May 2009), now aligned with RFC 5234 section
3.3 "Incremental Alternatives".
Updated references.
Allocate 1 bit to distinguish early discard from later discard.
Expand Interval Metric flag to 2 bit to allow using sampled metric.
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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
[MONARCH] Wu, Q., "Monitoring Architectures for RTP",
ID draft-ietf-avtcore-monarch-04, August 2011.
[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",
ID draft-ietf-rtcp-xr-postrepair-loss-02, February 2010.
[RFC6390] Clark, A. and B. Claise, "Framework for Performance Metric
Development", RFC 6390, October 2011.
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Authors' Addresses
Geoff Hunt
Unaffiliated
Email: r.geoff.hunt@gmail.com
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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