Audio/Video Transport Working Group A. Clark
Internet-Draft Telchemy
Intended status: Standards Track V. Singh
Expires: December 30, 2013 Aalto University
Q. Wu
Huawei
June 28, 2013

RTP Control Protocol (RTCP) Extended Report (XR) Block for De-Jitter Buffer Metric Reporting
draft-ietf-xrblock-rtcp-xr-jb-14.txt

Abstract

This document defines an RTP Control Protocol (RTCP) Extended Report (XR) Block that allows the reporting of De-Jitter Buffer metrics for a range of RTP applications.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on December 30, 2013.

Copyright Notice

Copyright (c) 2013 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.


Table of Contents

1. Introduction

1.1. De-Jitter Buffer 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 provides information on jitter buffer configuration and performance.

The metric belongs to the class of transport-related end system metrics defined in [RFC6792].

Instances of this metrics block refer by Synchronization source (SSRC) to the separate auxiliary Measurement Information block [RFC6776] which contains information such as the SSRC of the measured stream, and RTP sequence numbers and time intervals indicating the span of the report.

1.2. RTCP and RTCP XR Reports

The use of RTCP for reporting is defined in [RFC3550]. [RFC3611] defines 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].

1.3. Performance Metrics Framework

The Performance Metrics Framework [RFC6390] provides guidance on the definition and specification of performance metrics. The RTP Monitoring Architectures [RFC6792] provides guideline for reporting block format using RTCP XR. Metrics described in this draft are in accordance with the guidelines in [RFC6390]and [RFC6792].

1.4. Applicability

Real-time applications employ a de-jitter buffer [RFC5481] to absorb jitter introduced on the path from source to destination. These metrics are used to report how the de-jitter buffer at the receiving end of RTP stream behaves as a result of jitter in the network; and they are applicable to a range of RTP applications.

These metrics are corresponding to terminal related factors that affect real-time application quality and are useful to provide better end-user quality of experience (QoE) when these terminal-related factors are used as inputs to calculate QoE metrics [QMB].

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 [RFC2119].

3. De-Jitter Buffer Operation

A de-jitter buffer is required to absorb delay variation in network delivery of media packets. A de-jitter buffer works by holding media data for a period of time after it is received and before it is played out. Packets that arrive early are held in the de-jitter buffer longer. If packets arrive too early they may be discarded if there is no available de-jitter buffer space. If packets are delayed excessively by the network they may be discarded if they miss their playout time.

The de-jitter buffer can be considered as a time window with early edge aligned with the delay corresponding to the earliest arriving packet and late edge representing the maximum permissible delay before a late arriving packet would be discarded. The delay applied to packets that arrive on time or at their expected arrival time is known as the Nominal Delay and this is equivalent to the time difference/ buffer size difference between the on-time packets insertion point and the point at which packets are read out.

The reference for the expected arrival time may, for example, be the first packet in the session or the running average delay. If all packets arrived at their expected arrival time, then every packet would be held in the de-jitter buffer exactly the Nominal Delay.

The de-jitter buffer maximum delay is the delay that is applied to an earliest arriving packet that is not discarded and corresponds to the early edge of the de-jitter buffer time window.

3.1. Idealized De-Jitter Buffer

In practice de-jitter buffer implementations vary considerably however they should behave in a manner conceptually consistent with an idealized de-jitter buffer described as follows:

Note that this idealized implementation assumes that the sender's RTP clock is synchronized to the clock in the receiver which is used to timestamp packet arrivals. If there is no such inherent synchronization, the system may need to use an adaptive de-jitter buffer or other techniques to ensure reliable reception.

3.2. Fixed De-Jitter Buffer

A fixed de-jitter buffer lacks provision to track network condition and has a fixed size and packets leaving the de-jitter buffer have a constant delay. For fixed de-jitter buffer implementation, the nominal delay is set to a constant value corresponding to the packets that arrive at their expected arrival time while the maximum delay is set to a constant value corresponding to the fixed size of the de-jitter buffer.

3.3. Adaptive De-Jitter Buffer

An adaptive de-jitter buffer can adapt to the change in the network’s delay and has variable size or variable delay. It allows the nominal delay to be set to a low value initially, to minimize user perceived delay, however can automatically extend the late edge (and possibly also retract the early edge) of buffer window if a significant proportion of packets are arriving late (and hence being discarded).

4. De-Jitter Buffer Metrics Block

This block describes the configuration and operating parameters of the de-jitter buffer in the receiver of the RTP end system or RTP mixer which sends the report. Instances of this metrics block refer by SSRC to the separate auxiliary Measurement Information Block [RFC6776] which describes the measurement interval in use. This metrics block relies on the measurement interval in the Measurement Information Block indicating the span of the report and MUST be sent in the same compound RTCP packet as the Measurement Information Block. If the measurement interval is not received in the same compound RTCP packet as this metrics block, this metrics block MUST be discarded.

4.1. Report Block Structure

       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 
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     BT=DJB    | I |C|  Rsvd.  |       block length=3          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           SSRC of Source                      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          DJB nominal          |        DJB maximum            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     DJB high water mark       |      DJB low water mark       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: Report Block Structure

De-Jitter Buffer (DJB) Metrics Block

4.2. Definition of Fields in De-Jitter Buffer Metrics Block

Block type (BT): 8 bits


A de-jitter buffer Metrics Report Block is identified by the constant DJB.

[Note to RFC Editor: please replace DJB with the IANA provided RTCP XR block type for this block.]

Interval Metric flag (I): 2 bits


This field is used to indicate whether the de-jitter buffer metrics are Sampled, Interval or Cumulative metrics:

In this document, de-jitter buffer Metrics can only be sampled , and cannot be measured over definite intervals. Also, the value I=00 is reserved for future use. Senders MUST NOT use the values I=00 or I=10 or I=11. If a block is received with I=00 or I=10 or I=11, the receiver MUST discard the block.



Jitter Buffer Configuration (C): 1 bit


This field is used to identify the de-jitter buffer method in use at the receiver, according to the following code:

Reserved (Rsvd.): 5 bits


These bits are reserved. They MUST be set to zero by senders ignored by receivers (See [RFC6709] section 4.2).

Block Length: 16 bits


The length of this report block in 32-bit words, minus one, in accordance with the definition in [RFC3611]. This field MUST be set to 3 to match the fixed length of the report block.

de-jitter buffer nominal delay (DJB nominal): 16 bits


This is the current nominal de-jitter buffer delay in milliseconds, which corresponds to the nominal de-jitter buffer delay for packets that arrive exactly on time. It is calculated based on the time spent in the de-jitter buffer for the packet that arrives exactly on time. This parameter MUST be provided for both fixed and adaptive de-jitter buffer implementations.

The measured value is unsigned value. If the measured value exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFF MUST be reported.

de-jitter buffer maximum delay (DJB maximum): 16 bits


This is the current maximum de-jitter buffer delay in milliseconds which corresponds to the earliest arriving packet that would not be discarded. It is calculated based on the time spent in the de-jitter buffer for the earliest arriving packet In simple queue implementations this may correspond to the size of the de-jitter buffer. In adaptive de-jitter buffer implementations, this value may vary dynamically. This parameter MUST be provided for both fixed and adaptive de-jitter buffer implementations.

The measured value is unsigned value. If the measured value exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFF MUST be reported.

de-jitter buffer high water mark (DJB high water mark): 16 bits


This is the highest value of the de-jitter buffer nominal delay in milliseconds which occurred at any time during the reporting interval. This parameter MUST be provided for adaptive de-jitter buffer implementations and its value MUST be set to JB maximum for fixed de-jitter buffer implementations.

The measured value is unsigned value. If the measured value exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFF MUST be reported.

de-jitter buffer low water mark (DJB low water mark): 16 bits


This is the lowest value of the de-jitter buffer nominal delay in milliseconds which occurred at any time during the reporting interval. This parameter MUST be provided for adaptive de-jitter buffer implementations and its value MUST be set to JB maximum for fixed de-jitter buffer implementations.

The measured value is unsigned value. If the measured value exceeds 0xFFFD, the value 0xFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFF MUST be reported.

5. SDP Signaling

[RFC3611] defines the use of SDP (Session Description Protocol) [RFC4566] for signaling the use of XR blocks. However XR blocks MAY be used without prior signaling (see section 5 of RFC3611).

5.1. SDP rtcp-xr-attrib Attribute Extension

xr-format =/ xr-djb-block

xr-djb-block = "de-jitter-buffer"

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.

5.2. Offer/Answer Usage

When SDP is used in offer-answer context [RFC3264], the SDP Offer/Answer usage defined in [RFC3611] for unilateral "rtcp-xr" attribute parameters applies. For detailed usage of Offer/Answer for unilateral parameter, refer to section 5.2 of [RFC3611].

6. 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].

6.1. New RTCP XR Block Type value

This document assigns the block type value DJB in the IANA "RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry" to the "De-Jitter Buffer Metrics Block".

[Note to RFC Editor: please replace DJB with the IANA provided RTCP XR block type for this block.]

6.2. New RTCP XR SDP Parameter

This document also registers a new parameter "de-jitter-buffer" in the "RTP Control Protocol Extended Reports (RTCP XR) Session Description Protocol (SDP) Parameters Registry".

6.3. Contact information for registrations

Qin Wu (sunseawq@huawei.com)
101 Software Avenue, Yuhua District
Nanjing, Jiangsu  210012
China

The contact information for the registrations is:

7. 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.

8. Contributors

Geoff Hunt wrote the initial draft of this document.

9. Acknowledgments

The authors gratefully acknowledge reviews and feedback provided 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, Hideaki Yamada,Claire Bi,Colin Perkin, Dan Romascanu, Kevin Gross ,Glen Zorn, Spencer Dawkins and Benoit Claise.

10. References

10.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", March 1997.
[RFC3611] Friedman, T., Caceres, R. and A. Clark, "RTP Control Protocol Extended Reports (RTCP XR)", November 2003.
[RFC4566] Handley, M., Jacobson, V. and C. Perkins, "SDP: Session Description Protocol", July 2006.
[RFC3550] Schulzrinne, H., "RTP: A Transport Protocol for Real-Time Applications", RFC 3550, July 2003.
[RFC6776] Wu, Q., "Measurement Identity and information Reporting using SDES item and XR Block", RFC 6776, August 2012.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with the Session Description Protocol (SDP)", RFC 3264, June 2002.

10.2. Informative References

[RFC6792] Hunt, G., Wu, Q. and P. Arden, "Monitoring Architectures for RTP", RFC 6792, November 2012.
[RFC6390] Clark, A. and B. Claise, "Framework for Performance Metric Development", RFC 6390, October 2011.
[RFC6709] Carpenter, B., Aboba, B. and S. Cheshire, "Design Considerations for Protocol Extensions", RFC 6709, September 2012.
[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation Applicability Statement", RFC 5481, March 2009.
[QMB] Clark, A., "RTP Control Protocol (RTCP) Extended Report (XR) Blocks for QoE Metric Reporting", ID draft-ietf-xrblock-rtcp-xr-qoe-08, May 2013.

Appendix A. Metrics represented using RFC6390 Template

RFC EDITOR NOTE: please change XXXX in [RFCXXXX] by the new RFC number, when assigned.

  1. de-jitter buffer nominal delay Metric

  2. de-jitter buffer maximum delay Metric

  3. de-jitter buffer high water mark Metric

  4. de-jitter buffer low water mark Metric

Appendix B. Change Log

Note to the RFC-Editor: please remove this section prior to publication as an RFC.

B.1. draft-ietf-xrblock-rtcp-xr-jb-12

The following are the major changes to previous version :

B.2. draft-ietf-xrblock-rtcp-xr-jb-11

The following are the major changes to previous version :

B.3. draft-ietf-xrblock-rtcp-xr-jb-10

The following are the major changes to previous version :

B.4. draft-ietf-xrblock-rtcp-xr-jb-09

The following are the major changes to previous version :

B.5. draft-ietf-xrblock-rtcp-xr-jb-08

The following are the major changes to previous version :

B.6. draft-ietf-xrblock-rtcp-xr-jb-07

The following are the major changes to previous version :

B.7. draft-ietf-xrblock-rtcp-xr-jb-05

The following are the major changes to previous version :

B.8. draft-ietf-xrblock-rtcp-xr-jb-03

The following are the major changes to previous version :

B.9. draft-ietf-xrblock-rtcp-xr-jb-02

The following are the major changes to previous version :

B.10. draft-ietf-xrblock-rtcp-xr-jb-01

The following are the major changes to previous version :

B.11. draft-ietf-xrblock-rtcp-xr-jb-00

The following are the major changes to previous version :

Authors' Addresses

Alan Clark Telchemy Incorporated 2905 Premiere Parkway, Suite 280 Duluth, GA 30097 USA EMail: alan.d.clark@telchemy.com
Varun Singh Aalto University School of Electrical Engineering Otakaari 5 A Espoo, FIN 02150 Finland EMail: varun@comnet.tkk.fi
Qin Wu Huawei 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China EMail: sunseawq@huawei.com