RFC6776
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/rfc6776.
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4.2. Definition of Fields in Measurement Information Report
Contents
Introduction
This document defines one new RTP Control Protocol (RTCP) Source Description (SDES) RFC3550 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,
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) RFC3550.
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.
RTCP and RTCP XRs
The use of RTCP for reporting is defined in RFC3550. RFC3611 defines an extensible structure for reporting by using an RTCP XR. RFC3611 also defines the use of XR blocks. This document defines a new Extended Report block.
Performance Metrics Framework
The Performance Metrics Framework RFC6390 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 RFC6390 and [MONARCH].
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.
Terminology
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.
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 RFC3550. 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).
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.
Measurement Information XR Block
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
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 RFC3611.
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 RFC3550.
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 RFC5905, 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 RFC3550.
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 RFC3550 for RTCP SDES and RFC3611 for RTCP XR.
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
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".
Contact Information for Registrations
The contact information for the registrations is:
Qin Wu ([email protected]) 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China
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 RFC3550, applies.
References
Normative References
RFC2119 Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
RFC3550 Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
RFC3611 Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed.,
"RTP Control Protocol Extended Reports (RTCP XR)",
RFC 3611, November 2003.
RFC5905 Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
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.
RFC6390 Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390, October 2011.
Authors' Addresses
Alan Clark Telchemy Incorporated 2905 Premiere Parkway, Suite 280 Duluth, GA 30097 United States
EMail: [email protected]
Qin Wu Huawei 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China
EMail: [email protected]
