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IETF RFC 6776
Last modified on Thursday, October 25th, 2012
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Internet Engineering Task Force (IETF) A. Clark
Request for Comments: 6776 Telchemy
Category: Standards Track Q. Wu
ISSN: 2070-1721 Huawei
October 2012
Measurement Identity and Information Reporting Using a
Source Description (SDES) Item and an RTCP Extended Report (XR) Block
 Abstract
This document defines an RTP Control Protocol (RTCP) Source
Description (SDES) item and an RTCP Extended Report (XR) block
carrying parameters that identify and describe a measurement period
to which one or more other RTCP XR blocks may refer.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 6776.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Clark & Wu Standards Track PAGE 1 
RFC 6776 Measurement Identity and Duration October 2012
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. RTCP and RTCP XRs . . . . . . . . . . . . . . . . . . . . . 3
1.2. Performance Metrics Framework . . . . . . . . . . . . . . . 3
1.3. Applicability . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Standards Language . . . . . . . . . . . . . . . . . . . . 4
3. Measurement Identity SDES Item . . . . . . . . . . . . . . . . 4
3.1. APSI: Application-Specific Identifier SDES Item . . . . . . 4
4. Measurement Information XR Block . . . . . . . . . . . . . . . 5
4.1. Report Block Structure . . . . . . . . . . . . . . . . . . 5
4.2. Definition of Fields in Measurement Information Report
Block . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
5.1. New RTCP SDES Item Type Value . . . . . . . . . . . . . . . 7
5.2. New RTCP XR Block Type Value . . . . . . . . . . . . . . . 7
5.3. Contact Information for Registrations . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . . 8
1. Introduction
This document defines one new RTP Control Protocol (RTCP) Source
Description (SDES) [RFC 3550] item and one new Extended Report (XR)
block carrying parameters that identify and describe a measurement
period to which one or more other RTCP XR blocks may refer.
The SDES item provides a field for an application-specific auxiliary
identifier. This identifier may be used to correlate data in XR
blocks within an RTP session with data from a non-RTP session.
An RTCP Measurement Identity SDES packet may be associated with a set
of RTCP XR metrics blocks that share the same application-specific
measurement identifier.
The XR block does not contain any measurement results (metrics).
Instead, it provides information relevant to a measurement reported
in one or more other block types, including:
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,
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RFC 6776 Measurement Identity and Duration October 2012
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 calculation method of the extended RTP sequence number is
provided in the Real-time Transport Protocol (RTP) [RFC 3550].
The RTCP XR block containing the measurement information is intended
to provide a single copy of the information necessary to relate
measurement data in the RTCP XR blocks to the stream and measurement
period to which they refer. Commonly, multiple other small metric
blocks contain measurement data for the same stream and period, and
overhead would be large if all of these metric blocks carried
duplicated data for measurement identification.
The RTCP XR block may be associated with a set of RTCP XR metrics
blocks that share the same information relevant to a reported
measurement. There may be several such sets in an RTCP packet, in
which each set shares the same information relevant to a reported
measurement. There may also be RTCP XR blocks in the packet that are
not associated with a Measurement Information block, for example,
blocks that were defined before the Measurement Identity and
information mechanism were introduced by this document.
1.1. RTCP and RTCP XRs
The use of RTCP for reporting is defined in [RFC 3550]. [RFC 3611]
defines an extensible structure for reporting by using an RTCP XR.
[RFC 3611] also defines the use of XR blocks. This document defines a
new Extended Report block.
1.2. Performance Metrics Framework
The Performance Metrics Framework [RFC 6390] provides guidance on the
definition and specification of performance metrics. The RTP
Monitoring Architectures [MONARCH] provides guidelines for reporting
block format using RTCP XR. The SDES item and XR block described in
this document are in accordance with [RFC 6390] and [MONARCH].
1.3. Applicability
The RTCP SDES item and the RTCP XR block defined in this document
provide information relevant to the measurements for members of a
family of RTCP XR metrics blocks that are designed to use it. To use
the mechanism defined here, the RTCP XR block containing measurement
information is not required to be in the same RTCP packet as the SDES
item containing measurement identity.
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RFC 6776 Measurement Identity and Duration October 2012
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 [RFC 2119].
3. Measurement Identity SDES Item
This section defines the format of the Measurement Identity SDES
item. The SDES item is carried in the RTCP SDES packet. The packet
format for the RTCP SDES is defined in Section 6.5 of [RFC 3550].
Each SDES packet is composed of a header with fixed-length fields for
version, source count, packet type (PT), and length, followed by zero
or more SDES items. In the SDES packet, the PT field is set to SDES
(202).
3.1. APSI: Application-Specific Identifier SDES Item
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| APSI=10 | length |application-specific identifier
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ....
+-+-+-+-+-+-+-+-+
The application-specific identifier is an additional identifier that
is useful in the context of a specific application, e.g., an MPEG-2
transport identifier [MPEG2]. This item MUST be ignored by
applications that are not configured to make use of it. The
identifier is variable length. Its length is described by the length
field. The value of the length field does not include the two-octet
SDES item header.
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RFC 6776 Measurement Identity and Duration October 2012
4. Measurement Information XR Block
4.1. 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=14 | Reserved | block length = 7 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of stream source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | first sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| extended first sequence number of interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| extended last sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Duration (Interval) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Duration (Cumulative) - Seconds (bit 0-31) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Measurement Duration (Cumulative) - Fraction (bit 0-31) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Report Block Structure
4.2. Definition of Fields in Measurement Information Report Block
Block type (BT): 8 bits
A Measurement Information Block is identified by the constant 14.
Reserved: 8 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 Measurement Information Block, the block length is equal to 7.
SSRC of source: 32 bits
As defined in Section 4.1 of [RFC 3611].
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RFC 6776 Measurement Identity and Duration October 2012
Reserved: 16 bits
These bits are reserved. They MUST be set to zero by senders and
ignored by receivers.
First sequence number: 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. The extended sequence number
is expressed as the low 16-bit value containing the sequence
number received in an RTP data packet and the most significant
16-bit value containing the corresponding count of sequence number
cycles. For additional information on extended sequence numbers,
see the "extended highest sequence number received" definition in
Section 6.4.1 of RFC 3550 and Appendix A.1 of RFC 3550.
Extended last sequence number: 32 bits
The extended RTP sequence number of the last received RTP packet
that contributed to this measurement. The extended sequence
number is expressed as the low 16-bit value containing the
sequence number received in an RTP data packet and the most
significant 16-bit value containing the corresponding count of
sequence number cycles. For additional information on extended
sequence numbers, see the "extended highest sequence number
received" definition in Section 6.4.1 of RFC 3550 and Appendix A.1
of RFC 3550.
Measurement Duration (Interval): 32 bits
The duration, expressed in units of 1/65536 seconds, of the
reporting interval applicable to Interval reports that use this
Measurement Information Block. The value of this field can be
calculated by the receiver of the RTP media stream, for example,
based on received RTP media packets or using the RTCP method
described in [RFC 3550].
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RFC 6776 Measurement Identity and Duration October 2012
Measurement Duration (Cumulative): 64 bits
The duration of the reporting interval applicable to Cumulative
reports that use this Measurement Information Block. The value of
this field is represented using a 64-bit NTP-format timestamp as
defined in [RFC 5905], which is a 64-bit unsigned fixed-point
number with the integer part in the first 32 bits and the
fractional part in the last 32 bits. It can be calculated by the
receiver of the RTP media stream, for example, based on received
RTP media packets or using the RTCP method described in [RFC 3550].
5. IANA Considerations
A new SDES item type for RTCP SDES and a new XR block type for RTCP
XR have been registered with IANA. For general guidelines on IANA
considerations, refer to [RFC 3550] for RTCP SDES and [RFC 3611] for
RTCP XR.
5.1. New RTCP SDES Item Type Value
This document adds the Measurement Identity SDES item to the IANA
"RTP SDES item types" registry as follows:
abbrev. name value
APSI Application-Specific Identifier 10
5.2. New RTCP XR Block Type Value
This document assigns the block type value 14 in the IANA "RTCP XR
Block Type Registry" to the "Measurement Information Block".
5.3. 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
6. Security Considerations
RTCP reports can contain sensitive information, including information
about the nature and duration of a session established between two or
more endpoints. Therefore, the use of security mechanisms with RTP,
as documented in Section 9 of [RFC 3550], applies.
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RFC 6776 Measurement Identity and Duration October 2012
7. References
7.1. Normative References
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC 3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed.,
"RTP Control Protocol Extended Reports (RTCP XR)",
RFC 3611, November 2003.
[RFC 5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
7.2. Informative References
[MONARCH] Wu, Q., Hunt, G., and P. Arden, "Monitoring Architectures
for RTP", Work in Progress, September 2012.
[MPEG2] ISO/IEC, "Standard 13818-1, Information technology --
Generic coding of moving pictures and associated audio
information: Systems", October 2007.
[RFC 6390] Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390,
October 2011.
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RFC 6776 Measurement Identity and Duration October 2012
Authors' Addresses
Alan Clark
Telchemy Incorporated
2905 Premiere Parkway, Suite 280
Duluth, GA 30097
United States
EMail: alan.d.clark@telchemy.com
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
EMail: sunseawq@huawei.com
Clark & Wu Standards Track PAGE 9
RFC TOTAL SIZE: 17259 bytes
PUBLICATION DATE: Thursday, October 25th, 2012
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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