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 Delay metric Reporting
draft-ietf-avt-rtcp-xr-delay-00.txt
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Abstract
This document defines an RTCP XR Report Block that allows the
reporting of Delay metrics for use in a range of RTP applications.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Delay Report Block . . . . . . . . . . . . . . . . . . . . 3
1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 3
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Delay Block . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Report Block Structure . . . . . . . . . . . . . . . . . . 5
3.2. Definition of Fields in Delay Metrics Report Block . . . . 5
4. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
Intellectual Property and Copyright Statements . . . . . . . . . . 14
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1. Introduction
1.1. Delay 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 mean, minimum and maximum values of the
network round-trip delay between RTP interfaces in peer RTP end
systems as measured, for example, using the RTCP method described in
[RFC3550]. It also supports reporting of the component of the round-
trip delay internal to the local RTP system.
The network metrics belong to the class of packet transport delay
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].
1.4. Applicability
This metric is believed to be applicable to all RTP applications.
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2. Definitions
Numeric formats
This report block makes use of binary fractions. The terminology
used is
S X:Y
where S indicates a two's complement signed representation, X the
number of bits prior to the decimal place and Y the number of bits
after the decimal place.
Hence 8:8 represents an unsigned number in the range 0.0 to
255.996 with a granularity of 0.0039. S7:8 would represent the
range -128.000 to +127.996. 0:16 represents a proper binary
fraction with range
0.0 to 1 - 1/65536 = 0.9999847
though note that use of flag values at the top of the numeric
range slightly reduces this upper limit. For example, if the 16-
bit values 0xfffe and 0xffff are used as flags for "over-range"
and "unavailable" conditions, a 0:16 quantity has range
0.0 to 1 - 3/65536 = 0.9999542
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3. Delay Block
3.1. Report Block Structure
Delay 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=NDEL |I| tag | resv | block length = 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mean Network Round Trip Delay | End System Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Min Network Round Trip Delay | Max Network Round Trip Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
3.2. Definition of Fields in Delay Metrics Report Block
block type (BT): 8 bits
A Delay Report Block is identified by the constant NDEL.
[Note to RFC Editor: please replace NDEL with the IANA provided RTCP
XR block type for this block.]
Interval Metric flag (I): 1 bit
This field is used to indicate whether the Delay metric block is
an Interval or a Cumulative metric block, 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 Delay
block. Note that there may be more than one Measurement
Identifier block per RTCP packet.
Reserved (resv): 4 bits
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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.
Mean Network Round Trip Delay (ms): 16 bits
The Mean Network Round Trip Delay is the mean value of the RTP-to-
RTP interface round trip delay in ms over the measurement period,
typically determined using RTCP SR/RR.
If only one measurement of Round Trip Delay is available for the
timespan of the report (whether Interval or Cumulative), this
single value should be reported as the mean value.
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.
End System Delay (ms): 16 bits
The End System Delay is the internal round trip delay within the
reporting endpoint, calculated using the nominal value of the
jitter buffer delay plus the accumulation/ encoding and decoding /
playout delay associated with the codec being used.
If the measured or estimated 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.
Min Network Round Trip Delay (ms): 16 bits
The Min Network Round Trip Delay is the minimum value of the RTP-
to-RTP interface round trip delay in ms over the measurement
period, typically determined using RTCP SR/RR.
If only one measurement of Round Trip Delay is available for the
timespan of the report (whether Interval or Cumulative), this
single value should be reported as the minimum value.
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.
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Max Network Round Trip Delay (ms): 16 bits
The Max Network Round Trip Delay is the maximum value of the RTP-
to-RTP interface round trip delay in ms over the measurement
period, typically determined using RTCP SR/RR.
If only one measurement of Round Trip Delay is available for the
timespan of the report (whether Interval or Cumulative), this
single value should be reported as the maximum value.
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.
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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-format / xr-delay-block
xr-delay-block = "xr-delay"
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5. IANA Considerations
This document creates a new block type within the IANA "RTCP XR Block
Type Registry" called the Delay Block, and a new parameter xr-delay
within the "RTCP XR SDP Parameters Registry".
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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. References
8.1. 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.
8.2. 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.
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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
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