RFC6843
Internet Engineering Task Force (IETF) A. Clark Request for Comments: 6843 Telchemy Category: Standards Track K. Gross ISSN: 2070-1721 AVA Networks
Q. Wu
Huawei
January 2013
RTP Control Protocol (RTCP) Extended Report (XR)
Block for Delay Metric Reporting
Abstract
This document defines an RTP Control Protocol (RTCP) Extended Report (XR) block that allows the reporting of delay metrics for use in a range of Real-time Transport Protocol (RTP) applications.
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/rfc6843.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved.
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Contents
Introduction
Packet Delay Metrics Block
This document 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 transport metrics defined in RFC6792.
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 document defines a new Extended Report block for use with RFC3550 and RFC3611.
Performance Metrics Framework
The Performance Metrics Framework RFC6390 provides guidance on the definition and specification of performance metrics. The RTP Monitoring Architectures RFC6792 provides guidelines for reporting block format using RTCP XR. The metrics block described in this document is in accordance with the guidelines in RFC6390 and RFC6792.
Applicability
These metrics are applicable to a range of RTP applications in which this report block would be useful, such as multimedia conferencing and streaming audio and video. Knowledge of the round-trip delay and delay characteristics can aid other receivers in sizing their receive buffers and selecting a playout delay. The same information is also valuable to network managers in troubleshooting network and user experience issues.
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.
Delay Block
Metrics in this block report on packet delay in the stream arriving at the RTP system. The measurement of these metrics is made either at the receiving end of the RTP stream or at the sending end of the RTP stream. Instances of this metrics block refer by synchronization source (SSRC) to the separate auxiliary Measurement Information block RFC6776, which contains measurement periods (see RFC6776, Section 4.2). This metrics block relies on the measurement period in the Measurement Information block indicating the span of the report and SHOULD be sent in the same compound RTCP packet as the Measurement Information block. If the measurement period is not received in the same compound RTCP packet as this metrics block, this metrics block MUST be discarded.
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=16 | I | resv. | block length = 6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mean Network Round-Trip Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Min Network Round-Trip Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max Network Round-Trip Delay |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| End System Delay - Seconds (bit 0-31) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| End System Delay - Fraction (bit 0-31) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Report Block Structure
Definition of Fields in Delay Metrics Report Block
Block type (BT): 8 bits
A Delay Report Block is identified by the constant 16.
Interval Metric flag (I): 2 bit
This field is used to indicate whether the delay metrics are Sampled, Interval or Cumulative metrics:
I=10: Interval Duration - the reported value applies to the
most recent measurement interval duration between successive
metrics reports.
I=11: Cumulative Duration - the reported value applies to the
accumulation period characteristic of cumulative measurements.
I=01: Sampled Value - the reported value is a sampled
instantaneous value.
Reserved (resv): 6 bits
These bits are reserved. They MUST be set to zero by senders and ignored by receivers (see RFC6709, Section 4.2).
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 6.
SSRC of source: 32 bits
As defined in Section 4.1 of RFC3611.
Mean Network Round-Trip Delay: 32 bits
The Mean Network Round-Trip Delay is the mean value of the RTP-to- RTP interface round-trip delay over the measurement period, expressed in units of 1/65536 seconds. This value is typically determined using "the NTP timestamp field" in the RTCP sender report (SR) and "the last SR (LSR) field","delay since last SR (DLSR) field" in the RTCP receiver report (RR) (see RFC3550, Section 6.4.1 and Figure 2). It also can be determined using "the NTP timestamp field" in the RTCP Receiver Reference Time Report Block and "last RR (LRR) field", "delay since last RR (DLRR) field" in the DLRR Report Block (see RFC3611, Section 4.5).
If only one measurement of Round-Trip Delay is available for the time span of the report (i.e., the measurement period) (whether Interval or Cumulative), this single value SHOULD be reported as the mean value.
If the measurement is unavailable, the value of this field with all bits set to 1 MUST be reported.
Min Network Round-Trip Delay: 32 bits
The Min Network Round Trip Delay is the minimum value of the RTP- to-RTP interface round-trip delay over the measurement period, expressed in units of 1/65536 seconds. This value is typically determined using the NTP timestamp field in the RTCP SR and LSR field and DLSR field in the RTCP RR. It also can be determined using the NTP timestamp field in the RTCP Receiver Reference Time Report Block and LRR field and DLRR field in the DLRR Report Block.
If only one measurement of Round Trip Delay is available for the time span of the report (i.e., the measurement period) (whether Interval or Cumulative), this single value SHOULD be reported as the minimum value.
If the measurement is unavailable, the value of this field with all bits set to 1 MUST be reported.
Max Network Round-Trip Delay: 32 bits
The Max Network Round-Trip Delay is the maximum value of the RTP- to-RTP interface round-trip delay over the measurement period, expressed in units of 1/65536 seconds. This value is typically determined using the NTP timestamp field in the RTCP SR and LSR field and DLSR field in the RTCP RR. It also can be determined using the NTP timestamp field in the RTCP Receiver Reference Time Report Block and LRR field and DLRR field in the DLRR Report Block.
If only one measurement of Round-Trip Delay is available for the time span of the report (i.e.,the measurement period) (whether Interval or Cumulative), this single value SHOULD be reported as the maximum value.
If the measurement is unavailable, the value of this field with all bits set to 1 MUST be reported.
End System Delay: 64 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. 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.
If the measurement is unavailable, the value of this field with all bits set to 1 MUST be reported.
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.
SDP rtcp-xr-attrib Attribute Extension
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.
xr-format =/ xr-delay-block
xr-delay-block ="delay"
Offer/Answer Usage
When SDP is used in offer/answer context, the SDP Offer/Answer usage defined in RFC3611 applies.
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.
New RTCP XR Block Type Value
This document assigns the block type value 16 in the IANA "RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry" to the "Delay Metrics Block".
New RTCP XR SDP Parameter
This document also registers a new parameter "delay" in the "RTP Control Protocol Extended Reports (RTCP XR) Session Description Protocol (SDP) Parameters" registry.
Contact Information for Registrations
The contact information for the registrations is:
Qin Wu ([email protected]) Huawei 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China
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.
Contributors
Geoff Hunt wrote the initial version of this document.
Acknowledgments
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, Jing Zhao, Kevin Gross, Colin Perkins, Charles Eckel, Glen Zorn, Shida Schubert, Barry Leiba, Sean Turner, Robert Sparks, Benoit Claise, and Stephen Farrell.
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., Caceres, R., and A. Clark, "RTP Control
Protocol Extended Reports (RTCP XR)", RFC 3611, November 2003.
RFC4566 Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
RFC5905 Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
RFC6709 Carpenter, B., Aboba, B., and S. Cheshire, "Design
Considerations for Protocol Extensions", RFC 6709, September 2012.
Informative References
RFC6390 Clark, A. and B. Claise, "Guidelines for Considering New
Performance Metric Development", BCP 170, RFC 6390, October 2011.
RFC6776 Clark, A. and Q. Wu, "Measurement Identity and Information
Reporting Using a Source Description (SDES) Item and an
RTCP Extended Report (XR) Block", RFC 6776, October 2012.
RFC6792 Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the
RTP Monitoring Framework", RFC 6792, November 2012.
Authors' Addresses
Alan Clark Telchemy Incorporated 2905 Premiere Parkway, Suite 280 Duluth, GA 30097 USA
EMail: [email protected]
Kevin Gross AVA Networks
EMail: [email protected]
Qin Wu Huawei 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China
EMail: [email protected]
