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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.
1.1. Measurement Identity Report Block
1.2. RTCP and RTCP XR Reports
1.3. Performance Metrics Framework
2. Measurement Identity Block
2.1. Report Block Structure
2.2. Definition of Fields in Measurement Identity Report Block
3. SDP Signaling
4. IANA Considerations
4.1. New RTCP XR Block Type value
4.2. Contact information for registration
5. Security Considerations
6. Changes since last version
7.1. Normative References
7.2. Informative References
§ Authors' Addresses
This draft defines a new block type to augment those defined in [RFC3611] (Friedman, T., “RTP Control Protocol Extended Reports (RTCP XR),” November 2003.) 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
The method for calculation of the extended RTP sequence number is provide in [RFC3550] (Schulzrinne, H., “RTP: A Transport Protocol for Real-Time Applications,” July 2003.).
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.
The use of RTCP for reporting is defined in [RFC3550] (Schulzrinne, H., “RTP: A Transport Protocol for Real-Time Applications,” July 2003.). [RFC3611] (Friedman, T., “RTP Control Protocol Extended Reports (RTCP XR),” November 2003.) 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] (Schulzrinne, H., “RTP: A Transport Protocol for Real-Time Applications,” July 2003.) and [RFC3611] (Friedman, T., “RTP Control Protocol Extended Reports (RTCP XR),” November 2003.).
The Performance Metrics Framework [PMOLFRAME] (Clark, A., “Framework for Performance Metric Development,” March 2009.) 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] (Clark, A., “Framework for Performance Metric Development,” March 2009.).
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.
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 |
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 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] (Schulzrinne, H., “RTP: A Transport Protocol for Real-Time Applications,” July 2003.) 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] (Friedman, T., “RTP Control Protocol Extended Reports (RTCP XR),” November 2003.).
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] (ISO/IEC, “Standard 13818-1,” December 2000.). 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
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.
[RFC3611] (Friedman, T., “RTP Control Protocol Extended Reports (RTCP XR),” November 2003.) defines the use of SDP (Session Description Protocol) [RFC4566] (Handley, M., “SDP: Session Description Protocol,” July 2006.) 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] (Hunt, G., “RTCP XR Report Block for Discard metric Reporting,” May 2009.)) which depends on it.
New block types for RTCP XR are subject to IANA registration. For general guidelines on IANA considerations for RTCP XR, refer to [RFC3611].
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.]
The contact information for the registration is:
Geoff Hunt (firstname.lastname@example.org)
Orion 2 PP3, Adastral Park, Martlesham Heath, Ipswich IP5 3RE, United Kingdom
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.
|[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.|
|[DISCARD]||Hunt, G., “RTCP XR Report Block for Discard metric Reporting,” ID draft-ietf-avt-rtcp-xr-discard-02, May 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-02, March 2009.|
|Orion 2 PP3|
|Ipswich, Suffolk IP5 3RE|
|Phone:||+44 1473 651704|
|2905 Premiere Parkway, Suite 280|
|Duluth, GA 30097|