Audio/Video Transport Working Group A. Clark
Internet-Draft Telchemy
Intended status: Standards Track S. Zhang, Ed.
Expires: June 08, 2013 J. Zhao
STTRI
Q. Wu
Huawei
December 05, 2012

RTP Control Protocol (RTCP) Extended Report (XR) Block for Burst/Gap Loss metric Reporting
draft-ietf-xrblock-rtcp-xr-burst-gap-loss-06.txt

Abstract

This document defines an RTP Control Protocol (RTCP) Extended Report (XR) Block that allows the reporting of Burst and Gap Loss metrics for use in 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/⁠.

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This Internet-Draft will expire on June 08, 2013.

Copyright Notice

Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

1. Introduction

1.1. Burst and Gap Loss Report Block

This draft 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 proportion of packets lost by the network. The losses during loss bursts are reported, together with the number of bursts and additional data allowing the calculation of statistical parameters (mean and variance) of the distribution of burst lengths. Some uses of these metrics depend on the availability of the metric "cumulative number of packets lost" from RTCP [RFC3550].

This block provides information on transient IP problems. Burst/Gap metrics are typically used in Cumulative reports however MAY be used in Interval reports. The burstiness of packet loss affects user experience, may influence any sender strategies to mitigate the problem, and may also have diagnostic value.

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

The definitions of Burst, Gap, Loss and Discard are consistent with definitions in [RFC3611]. To accommodate the range of jitter buffer algorithms and packet discard logic that may be used by implementors, the method used to distinguish between bursts and gaps may be an equivalent method to that defined in [RFC3611]. The method used SHOULD produce the same result as that defined in [RFC3611] for conditions of burst packet loss, but MAY produce different results for conditions of time varying jitter.

1.2. 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].

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. The Metrics Block described in this document are in accordance with the guidelines in [RFC6390] and [RFC6792].

1.4. Applicability

These metrics are applicable to a range of RTP applications which don't use stream repair means.

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].

In addition, the following terms are defined:

Received, Lost and Discarded


A packet shall be regarded as lost if it fails to arrive within an implementation-specific time window. A packet that arrives within this time window but is too early or late to be played out or thrown away before playout due to packet duplication or redundancy shall be regarded as discarded. A packet shall be classified as one of received (or OK), discarded or lost. The metric "cumulative number of packets lost" defined in [RFC3550] reports a count of packets lost from the media stream (single SSRC within single RTP session). Similarly the metric "number of packets discarded" defined in [DISCARD] reports a count of packets discarded from the media stream (single SSRC within single RTP session) arriving at the receiver. Another metric defined in [RFC5725] is available to report on packets which are not recovered by any repair techniques which may be in use.

Bursts and Gaps


The terms Burst and Gap are used in a manner consistent with that of RTCP XR [RFC3611]. RTCP XR views a RTP stream as being divided into bursts, which are periods during which the loss rate is high enough to cause noticeable quality degradation (generally over 5 percent loss rate), and gaps, which are periods during which lost packets are infrequent and hence quality is generally acceptable.

3. Burst/Gap Loss Block

Metrics in this block report on Burst/Gap Loss in the stream arriving at the RTP system. The measurement of these metrics are made at the receiving 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 metric 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 metric block, this metric block MUST be discarded.

3.1. 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=NBGL    | I |C|  resv.  |      block length = 5         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        SSRC of Source                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Threshold     |         Sum of Burst Durations (ms)           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            Packets Lost in Bursts             |    Total...   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | ...Packets expected in bursts |    Number of bursts   | Sum of|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                ...Squares of Burst Durations (ms-squared)     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Burst/Gap Loss metrics block

3.2. Definition of Fields in Burst/Gap Loss Report Block

Block type (BT): 8 bits


A Burst/Gap Loss Report Block is identified by the constant NBGL.

[Note to RFC Editor: please replace NBGL 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 Burst/Gap Loss metrics are Sampled, Interval or Cumulative metrics:

In this document, Burst/Gap Loss Metric is not measured at a particular time instant but over one or several reporting intervals. Therefore Burst/Gap Loss Metric MUST NOT be chosen as Sampled Metric.



Loss and Discard Combination flag (C): 1 bit


The 'C' flag is used to indicate whether combining loss/discard report is needed. This field MUST be set to '1' if the burst gap loss report is present in conjunction with the burst gap discard report in the same compound RTCP packet and MUST be set to '0' otherwise. If the burst gap discard is not sent with the burst gap loss, then the receiver MUST discard the burst gap loss with 'C' flag set to 1. If the 'C' flag is set to 0, then receiver MUST NOT discard the burst gap loss metric block when the burst gap discard is not received.

Reserved (resv): 5 bits


These bits are reserved. They SHOULD be set to zero by senders and MUST be ignored by receivers.

block length: 16 bits


The length of this report block in 32-bit words, minus one. For the Burst/Gap Loss block, the block length is equal to 5.

SSRC of source: 32 bits


As defined in Section 4.1 of [RFC3611].

Threshold: 8 bits


The Threshold is equivalent to Gmin in [RFC3611], i.e. the number of successive packets that must be received prior to and following a lost packet in order for this lost packet to be regarded as part of a gap.

Sum of Burst Durations (ms): 24 bits


The total duration of bursts of lost packets in the period of the report (Interval or Cumulative).

If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE SHOULD be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFF SHOULD be reported.

Packets lost in bursts: 24 bits


The total number of packets lost during loss bursts.

If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE SHOULD be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFF SHOULD be reported.

Total packets expected in bursts: 24 bits


The total number of packets expected during loss bursts (that is, the sum of received packets and lost packets).

If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE SHOULD be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFF SHOULD be reported.

Number of bursts: 16 bits


The number of bursts in the period of the report (Interval or Cumulative).

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

Sum of Squares of Burst Durations (ms-squared): 36 bits


The sum of the squares of burst durations (where individual burst durations are expressed in ms) over in the period of the report (Interval or Cumulative). The units for this quantity are milliseconds-squared.

If the measured value exceeds 0xFFFFFFFFD, the value 0xFFFFFFFFE SHOULD be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFFFFF SHOULD be reported.

3.3. Derived metrics based on reported metrics

The metrics described here are intended to be used as described in this section, in conjunction with information from the Measurement Information block [RFC6776] (which MUST be present in the same RTCP packet as the Burst/Gap Loss block) and also with the metric "cumulative number of packets lost" provided in standard RTCP [RFC3550].

These metrics provides information relevant to statistical parameters, including:

The details on calculation these parameters in the metrics are described in [SUMSTAT].

4. Considerations for Voice-over-IP applications

This metric block is applicable to a broad range of RTP applications. Where the metric is used with a Voice-overIP (VoIP) application and the stream repair means is not available, the following considerations apply.

RTCP XR views a call as being divided into bursts, which are periods during which the loss rate is high enough to cause noticeable call quality degradation (generally over 5 percent loss rate), and gaps, which are periods during which lost packets are infrequent and hence call quality is generally acceptable.

If Voice Activity Detection is used the Burst and Gap Duration shall be determined as if silence packets had been sent, i.e. a period of silence in excess of Gmin packets MUST terminate a burst condition.

The recommended value for the threshold Gmin in [RFC3611] results in a Burst being a period of time during which the call quality is degraded to a similar extent to a typical PCM Severely Errored Second [PSES].

5. 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.

5.1. SDP rtcp-xr-attrib Attribute Extension

xr-format =/ xr-bgl-block

xr-bgl-block = "brst-gap-loss"

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, the SDP Offer/Answer usage defined in [RFC3611] for unilateral "rtcp-xr" attribute parameters applies. For detailed usage in 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 NBGL in the IANA " RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry " to the "Burst/Gap Loss Metrics Block".

[Note to RFC Editor: please replace NBGL 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 "brst-gap-loss" in the " RTP Control Protocol Extended Reports (RTCP XR) Session Description Protocol (SDP) Parameters Registry".

6.3. 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



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 and Adam Roach.

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.
[RFC5725] Begen, A., Hsu, D. and M. Lague, "Post-Repair Loss RLE Report Block Type for RTP Control Protocol (RTCP) Extended Reports (XRs)", RFC 5725, February 2020.

10.2. Informative References

, "
[DISCARD] Wu, Q., "RTCP XR Report Block for Discard metric Reporting", ID draft-ietf-xrblock-rtcp-xr-discard-09, October 2012.
[SUMSTAT] Zorn, G., "RTCP XR for Summary Statistics Metrics Reporting", ID draft-ietf-xrblock-rtcp-xr-summary-stat-03, November 2012.
[RFC6776] Wu, Q., "Measurement Identity and information Reporting using SDES item and XR Block", RFC 6776, October 2012.
[RFC6792] Hunt, G., "Monitoring Architectures for RTP", RFC 6792, November 2012.
[RFC6390] Clark, A. and B. Claise, "Framework for Performance Metric Development", RFC 6390, July 2011.
[PSES]URL", http://www.its.bldrdoc.gov/projects/devglossary/_severely_errored_second.html, October 2011.

Appendix A. Change Log

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

A.1. draft-ietf-xrblock-rtcp-xr-burst-gap-loss-06

The following are the major changes compared to previous version:

A.2. draft-ietf-xrblock-rtcp-xr-burst-gap-loss-04

The following are the major changes compared to previous version:

Authors' Addresses

Alan Clark Telchemy Incorporated 2905 Premiere Parkway, Suite 280 Duluth, GA 30097 USA EMail: alan.d.clark@telchemy.com
Sunshine Zhang (editor) Shanghai Research Institute of China Telecom Corporation Limited No.1835,South Pudong Road Shanghai, 200122 China EMail: zhangyx@sttri.com.cn
Jing Zhao Shanghai Research Institute of China Telecom Corporation Limited No.1835,South Pudong Road Shanghai, 200122 China EMail: zhaojing@sttri.com.cn
Qin Wu Huawei 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China EMail: sunseawq@huawei.com