Audio/Video Transport Working G. Hunt
Group BT
Internet-Draft A. Clark
Intended status: Standards Track Telchemy
Expires: August 29, 2009 February 25, 2009
RTCP XR Report Block for Measurement Identity
draft-ietf-avt-rtcp-xr-meas-identity-01.txt
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Abstract
This document defines an RTCP XR Report Block carrying parameters
which identify a measurement, to which one or more other RTCP XR
Report Blocks may refer.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Measurement Identity Report Block . . . . . . . . . . . . 3
1.2. RTCP and RTCP XR Reports . . . . . . . . . . . . . . . . . 4
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 4
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 4
2. Measurement Identity Block . . . . . . . . . . . . . . . . . . 5
2.1. Report Block Structure . . . . . . . . . . . . . . . . . . 5
2.2. Definition of Fields in Measurement Identity Report
Block . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
4.1. New RTCP XR Block Type value . . . . . . . . . . . . . . . 9
4.2. Contact information for registration . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. Changes since last version . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
1.1. Measurement Identity Report Block
This draft defines a new block type to augment those defined in
[RFC3611] for use in a range of RTP applications. This block type
does not itself contain any measurement results (metrics). However,
this new block type provides information relevant to a measurement
reported in one or more other block types, including
o a tag or key by which other blocks (containing metrics
information) may refer to this block
o the SSRC of the measured stream,
o a field for incorporation of an application-specific auxiliary
identifier,
o the sequence number of the first packet of the RTP session,
o the extended sequence numbers of the first packet of the current
measurement interval, and the last packet included in the
measurement,
o the duration of the most recent measurement interval and
o the duration of the interval applicable to cumulative measurements
(which may be the duration of the RTP session to date).
The method for calculation of the extended RTP sequence number is
provide in [RFC3550].
This block is intended to provide a single copy of the information
necessary to relate measurement data in other blocks to the stream,
and measurement period, to which they refer. Commonly, multiple
other small blocks contain measurement data for the same stream and
period, and it would be a large overhead if all of these blocks
carried duplicated data for measurement identification. Other blocks
make a reference to this block (by tag).
A Measurement Identity block is associated with the set of RTCP XR
metrics blocks which share its tag value. There MAY be several such
sets in an RTCP packet, up to a limit of 8 arising from the use of
3-bit tags. There MAY also be RTCP XR blocks in the packet which are
not associated with a Measurement Identity block, for example blocks
which were defined before the Measurement Identity mechanism was
introduced by this document.
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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 block provides identification information for members of a
family of RTCP XR metrics blocks which are designed to use it. To
use the mechanism defined here, a metrics block must be in the same
RTCP packet as the Measurement Identity block and must refer to the
Measurement Identity block via the 3-bit tag field defined below.
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2. Measurement Identity Block
2.1. 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=NMI |0| tag | resv | block length = 7 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of stream source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| reserved | first seq num |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| extended first sequence number of interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| extended last sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Duration (Cumulative) (ms) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Duration (Interval) (ms) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
2.2. Definition of Fields in Measurement Identity Report Block
Bits shown as '0' in the figure SHOULD be set to zero.
block type (BT): 8 bits
A Measurement Identity Report Block is identified by the constant
NMI.
[Note to RFC Editor: please replace NMI with the IANA provided RTCP
XR block type for this block.]
tag: 3 bits
This field is a tag or key which identifies this Measurement
Identity block within the scope of an RTCP packet. If an RTCP
packet contains more than one Measurement Identity block, each
Measurement Identity block MUST have a unique tag field to enable
metrics blocks in the same RTCP packet to refer unambiguously to
the correct Measurement Identity block. The 3-bit field allows up
to 8 Measurement Identity blocks in each RTCP packet. If
additional metrics must be sent at a given time, and they require
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more than 8 blocks of Measurement Identity information, then the
metrics must be sent in multiple RTCP packets.
resv: 4 bits
These bits are reserved. They MUST be set to zero by senders.
They MUST be ignored by receivers.
block length: 16 bits
The length of this report block in 32-bit words minus one. For
the Measurement Identity block, the block length is equal to 7.
SSRC of source: 32 bits
The SSRC [RFC3550] of the source of the stream being reported.
Note that the SSRC of the reporting RTP system (the originator of
the report block) is present in the RTCP XR header defined in
Section 2 of [RFC3611].
sub-identifier: 32 bits
An additional identifier which is useful in the context of a
specific application, e.g. an MPEG-2 transport identifier [MPEG2].
Where the identifier is less than 32 bits, the identifier SHOULD
be mapped into the most significant bits of the field. If no
additional identifier is provided, all bits of the field MUST be
set to zero. This field MUST be ignored by applications which are
not configured to make use of it.
reserved: 16 bits
These bits are reserved. They MUST be ignored by receivers. They
MUST be set to zero by senders.
first seq num: 16 bits
The RTP sequence number of the first received RTP packet of the
session, used to determine the number of packets contributing to
cumulative measurements.
extended first sequence number of interval: 32 bits
The extended RTP sequence number of the first received RTP packet
of the current measurement interval.
extended last sequence number: 32 bits
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The extended RTP sequence number of the last received RTP packet
which contributed to this measurement.
Measurement Duration (Cumulative) (ms): 32 bits
The duration in ms of the reporting interval applicable to
Cumulative reports which use this Measurement Identity block.
Measurement Duration (Interval) (ms): 32 bits
The duration in ms of the reporting interval applicable to
Interval reports which use this Measurement Identity block.
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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.
No additional SDP signaling is defined for this block. Instead, the
need for this block SHOULD be inferred from a request in SDP
signalling for a block type (such as [DISCARD]) which depends on it.
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4. 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].
4.1. New RTCP XR Block Type value
This document assigns the block type value NMI in the IANA "RTCP XR
Block Type Registry" to the "Measurement Identity Block".
[Note to RFC Editor: please replace NMI with the IANA provided RTCP
XR block type for this block.]
4.2. Contact information for registration
The contact information for the registration is:
Geoff Hunt (geoff.hunt@bt.com)
Orion 2 PP3, Adastral Park, Martlesham Heath, Ipswich IP5 3RE, United
Kingdom
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5. Security Considerations
RTCP reports can contain sensitive information since they can provide
information about the nature and duration of a session established
between two or more endpoints.
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6. Changes since last version
Expanded and clarified IANA Considerations section
Changed to remove explicit SDP signalling for this block - need for
block is implicit if a metrics block is requested which depends on
this block.
Modified block structure to send first sequence number without
extension, rather than extend to 32-bit number with leading 16 bits
set to 0. These 16 bits are now reserved. Addresses Colin Perkins'
comment of 15-Nov-2008
Removed "forwarding count" field following Colin Perkins' request for
a use case. The field had been intended for use by translators to
establish the "distance" (as a count of forwarding systems) to the
point at which a measurement was made. However a recommendation to
increment the count could have forced forwarding translator devices
to parse the packet on a slow (CPU) path, possibly compromising RTCP
measurement of round-trip delay [RFC3550].
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7. References
7.1. Normative References
[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
[DISCARD] Hunt, G., "RTCP XR Report Block for Discard metric
Reporting", ID draft-ietf-avt-rtcp-xr-discard-01,
February 2009.
[MONARCH] Hunt, G., "Monitoring Architectures for RTP",
ID draft-hunt-avt-monarch-01, August 2008.
[MPEG2] ISO/IEC, "Standard 13818-1", December 2000.
[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 2 PP3
Adastral Park
Martlesham Heath
Ipswich, Suffolk IP5 3RE
United Kingdom
Phone: +44 1473 651704
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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