Network Working Group A. Clark
Internet-Draft Telchemy
Intended status: Standards Track Q. Wu
Expires: April 19, 2013 Huawei
R. Schott
DT
G. Zorn
Network Zen
October 18, 2012

RTP Control Protocol (RTCP) Extended Report (XR) Blocks for QoE Metric Reporting
draft-ietf-xrblock-rtcp-xr-qoe-03

Abstract

This document defines an RTP Control Protocol (RTCP) Extended Report (XR) Block including two new segment types and associated SDP parameters that allow the reporting of QoE 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/⁠.

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 April 19, 2013.

Copyright Notice

Copyright (c) 2012 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. QoE Metrics Report 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 multimedia quality using one of several standard metrics.

The metrics belong to the class of application level metrics defined in [MONARCH].

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 draft 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 [MONARCH] provides guideline for reporting block format using RTCP XR. The XR Block described in this document are in accordance with the guidelines in [RFC6390] and [MONARCH].

1.4. Applicability

The QoE Metrics Report Block can be used in any application of RTP for which QoE measurement algorithms are defined.

The factors that affect real-time AV application quality can be split into two categories. The first category consists of transport- dependent factors such as packet loss, delay and jitter (which also translates into losses in the playback buffer). The factors in the second category are application-specific factors that affect real time application (e.g., video) quality and are sensitivity to network errors. These factors can be but not limited to video codec and loss recovery technique, coding bit rate, packetization scheme, and content characteristics.

Compared with application-specific factors, the transport-dependent factors sometimes are not sufficient to measure real time data quality, since the ability to analyze the real time data in the application layer provides quantifiable measurements for subscriber Quality of Experience (QoE) that may not be captured in the transmission layers or from the RTP layer down. In a typical scenario, monitoring of the transmission layers can produce statistics suggesting that quality is not an issue, such as the fact that network jitter is not excessive. However, problems may occur in the service layers leading to poor subscriber QoE. Therefore monitoring using only network-level measurements may be insufficient when application layer content quality is required.

In order to provide accurate measures of real time application quality when transporting real time contents across a network, the synthentical multimedia quality Metrics is highly required which can be conveyed in the RTCP XR packets[RFC3611] and may have the following three benefits:

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].

The terminology used is

3. QoE Metrics Block

This block reports the multimedia application performance or quality beyond the information carried in the standard RTCP packet format. Information is recorded about multimedia application QoE metric which provides a measure that is indicative of the user's view of a service. Multimedia application QoE metric is commonly expressed as a MOS ("Mean Opinion Score"), MOS is on a scale from 1 to 5, in which 5 represents excellent and 1 represents unacceptable. MOS scores are usually obtained using subjective testing or using objective algorithm. However Subjective testing to estimate the multimedia quality may be not suitable for measuring the multimedia quality since the results may vary from test to test. Therefore using objective algorithm to calculate MOS scores is recommended. ITU-T recommendations define the methodologies for assessment of the performance of multimedia stream [G.107][P.564][G.1082][P.1201][P.1202] and provides a method to evaluate QoE estimation algorithms and objective model for video and audio. Hence this document recommends vendors and implementers to use these International Telecommunication Union (ITU)-specified methodologies to measure parameters when possible.



3.1. Metric Block Structure

The report block contents are dependent upon a series of flag bits carried in the first part of the header. Not all parameters need to be reported in each block. Flags indicate which are and which are not reported. The fields corresponding to unreported parameters MUST be present, but are set to zero. The receiver MUST ignore any QoE Metrics Block with a non-zero value in any field flagged as unreported. The encoding of QoE metrics block payload consists of a series of 32 bit units called segments that describe MOS Type, MoS algorithm and MoS value.

   
    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=QMB    | I |  Reserved |       Block Length            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        SSRC of source                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Segment  1                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Segment 2                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ..................
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          Segment n                            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The QoE Metrics Block has the following format:

3.2. Definition of Fields in QoE Metrics Block

Block type (BT): 8 bits


The QoE Metrics Block is identified by the constant <QMB>.

Interval Metric flag (I): 2 bits


This field is used to indicate whether the QoE metrics are Interval or Cumulative metrics, that is, whether the reported values applies to the most recent measurement interval duration between successive metrics reports (I=10) (the Interval Duration) or to the accumulation period characteristic of cumulative measurements (I=11) (the Cumulative Duration) or is a sampled instantaneous value (I=01) (Sampled Value).

Reserved.: 6 bits


This field is reserved for future definition. In the absence of such a definition, the bits in this field MUST be set to zero and MUST be ignored by the receiver.

Block Length: 16 bits


The length of this report block in 32-bit words, minus one. For the QoE Metrics Block, the block length is variable length.

SSRC of source: 32 bits


As defined in Section 4.1 of [RFC3611].

Segment i: 32 bits


There are two segment types defined in this document: single stream per SSRC segment, multi-channel audio per SSRC segment. Multi-channel audio per SSRC segment is used to deal with the case where Multi-channel audios are carried in one RTP stream while single stream per SSRC segment is used to deal with the case where each media stream is identified by SSRC and sent in separate RTP stream. The left two bits of the section determine its type. If the leftmost bit of the segment is zero, then it is single stream segment. If the leftmost bit is one, then it is multi-channel audio segment. Note that two segment types can not be present in the same metric block.

3.2.1. Single Stream per SSRC Segment

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S|  MT   |CAlg |    PT       |Rsv. |         MOS Value         |      
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Editor's Note: If we add MoS reference concept, we should give a definition of MoS reference which covers both audio application and video application. Editor's Note: Shall we need to support MoS Scaling concept in the future draft? One point on the list is MoS Scaling concept is implicitly used within the industry when quoting MOS scores for codecs and measurements.

Segment Type (S): 1 bit


This field is used to identify the segment type used in this report block. A zero identifies this as a single stream segment. Single stream means there is only one media stream carried in one RTP stream. The single stream segment can be used to report the MoS value associated with this media stream identified by SSRC. If there are multiple media streams and they want to use the single stream per SSRC segment to report the MOS value, they should be carried in the separate RTP streams with different SSRC. In this case, multiple QoE Metrics Blocks are required to report the MOS value corresponding to each media stream using single stream segment.

MoS Type (MT): 4 bits


This field is used to indicate the MOS type to be reported. The MOS type is defined as follows:

MoS-LQ measures the quality of audio for listening purposes only while MoS-CQ measures the quality of audio for conversation purpose only. MoS-A,MoS-V and MoS-AV measures the quality of audio application, the quality of video application and Audio-Video application respectively. Both MoS-LQ and MoS-CQ are commonly used in VoIP applications. MOS-LQ uses either wideband audio codec or narrowband audio codec, or both and does not take into account any of bidirectional effects, such as delay and echo. MOS-CQ uses narrowband codec and takes into account listening quality in each direction, as well as the bidirectional effects.



Calculation Algorithm (CALg):3 bits


G.107 and P.564 and ETSI TS101 329-5 specify three Calculation algorithms or MoS algorithms that are used to estimate speech quality or conversation quality. P.NAMS and P.NBAMS specify two MoS algorithms that are used to estimate multimedia quality including video quality, audio quality and audio-video quality. If MoS type is MoS-LQ and MoS-CQ, the MoS value can be calculated based on ITU-T G.107

[G.107], ITU-T P.564 [P.564]or ETSI TS 101 329-5 [ETSI], if the Mos type is MoS-V or MoS-AV, the Mos value can be calculated based on ITU-T P.NAMS [P.1201]or ITU-T P.NBAMS [P.1202]. If new MOS types are defined, they can be added by an update to this document. If the receiver does not understand the MOS type defined in this document it should discard this report. If MoS Type does not match the MoS algorithm in the report (e.g., specify a voice MOS algorithm for a video quality MOS), the receiver should also discard this report.

Payload Type (PT): 7 bits


QoE metrics reporting depends on the payload format in use. This field identifies the format of the RTP payload. For RTP sessions where multiple payload formats can be negotiated or the payload format changes during the mid-session), the value of this field will be used to indicate what payload format was in use for the reporting interval.

Rsd.:3 bits


This field is reserved for future definition. In the absence of such a definition, the bits in this field MUST be set to zero and MUST be ignored by the receiver.

MOS Value: 14 bits


The estimated mean opinion score for multimedia application quality is defined as including the effects of delay,loss, discard,jitter and other effects that would affect multimedia quality . It is expressed in numeric format 6:8 with the value in the range 0.0 to 63.996. The valid the measured value ranges from 0.0 to 50.0, corresponding to MoS x 10 as for MoS. If the measured value is over ranged, the value 0xFFFE SHOULD be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFF SHOULD be reported. Values other than 0xFFFE,0xFFFF and the valid range defined above MUST NOT be sent and MUST be ignored by the receiving system.

3.2.2. Multi-Channel audio per SSRC Segment

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |S|  MT   |CAlg |     PT      |CHID |         MOS Value         |      
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Segement Type (S): 1 bit


This field is used to identify the segment type used in this report block. A one identifies this as a multi-channel audio segment.

Media Type (M): 1bit


A zero identifies this as a multi-channel per SSRC segment.

MoS Type (MT): 4 bits


As defined in Section 3.2.1 of this document. If the value of this field is not corresponding to MoS-CQ or MoS-LQ, the receiver using multi-channel segment should discard this invalid segment with the wrong MoS Type.

Calculation Algorithm (CALg):3 bits


Payload Type (PT): 7 bits


As defined in Section 3.2.1 of this document.

Channel Identifier (CHID): 3 bits


If multiple channels of audio are carried in one RTP stream, each channel of audio will be viewed as a independent channel(e.g., left channel audio, right channel audio). This field is used to identify each channel carried in the same media stream. The default Channel mapping follows static ordering rule described in the section 4.1 of [RFC3551]. However there are some payload formats that use different channel mappings, e.g., AC-3 audio over RTP [RFC4184] only follow AC-3 channel order scheme defined in [ATSC]. Enhanced AC-3 Audio over RTP [RFC4598] uses dynamic channel transform mechanism. In order that the appropriate channel mapping can be determined, QoE reports need to be tied to an RTP payload format, i.e., including the payload type of the reported media according to [MONARCH] and using Payload Type to determine the appropriate channel mapping.

Rsd.:3 bits


This field is reserved for future definition. In the absence of such a definition, the bits in this field MUST be set to zero and MUST be ignored by the receiver.

MOS Value: 14 bits


As defined in Section 3.2.1 of this document.

4. SDP Signaling

      xr-format = qoe-metrics
         qoe-metrics = "QoE metrics"

One new parameter is defined for the report block defined in this document to be used with Session Description Protocol (SDP) [RFC4566] using the Augmented Backus-Naur Form (ABNF) [RFC5234]. It has the following syntax within the "rtcp-xr" attribute [RFC3611]: RFC 3611 [RFC3611] for a detailed description and the full syntax of the "rtcp-xr" attribute.

5. 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].

5.1. New RTCP XR Block Type value

This document assigns the block type value MMQ in the IANA "RTCP XR Block Type Registry" to the "QoE Metrics Block".

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

5.2. New RTCP XR SDP Parameter

This document also registers a new parameter "qoe-metrics" in the "RTCP XR SDP Parameters Registry".

5.3. 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:

5.4. New registry of calculation algorithms for single stream segment

This document creates a new registry for single stream per SSRC segment defined in the section 3.2.1 to be called "RTCP XR QoE metric block - multimedia application Calculation Algorithm" as a sub-registry of the "RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry". This registry applies to the multimedia session where each type of media are sent in a separate RTP stream. Specially this registry also applies to the layered video session where each layer video are sent in a separate RTP stream. Policies for this new registry are as follows:

5.5. New registry of calculation algorithms for multi-channel audio segment

This document creates a new registry for multi-channel audio per SSRC segment defined in the section 3.2.2 to be called "RTCP XR QoE metric block – multi-channel application Calculation Algorithm" as a sub-registry of the "RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry" if multi-channel voice data are carried in the same RTP stream. Policies for this new registry are as follows:

6. Security Considerations

The new RTCP XR report blocks proposed in this document introduces no new security considerations beyond those described in [RFC3611].

7. Authors

This draft merges ideas from two drafts addressing the QoE metric Reporting issue. The authors of these drafts are listed below (in alphabetical order):

8. Acknowledgements

The authors would like to thank Bill Ver Steeg, David R Oran, Ali Begen,Colin Perkins, Roni Even,Youqing Yang, Wenxiao Yu and Yinliang Hu for their valuable comments and suggestions on this document.

9. References

9.1. Normative References

[RFC3611] Friedman, T., Caceres, R. and A. Clark, "RTP Control Protocol Extended Reports (RTCP XR)", RFC 3611, November 2003.
[RFC3550] Schulzrinne, H., "RTP: A Transport Protocol for Real-Time Applications", RFC 3550, July 2003.
[RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", RFC 3551, July 2003.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4566] Handley, M., Jacobson, V. and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC5226] Narten, T., "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 5226, May 2008.
[ATSC] U.S. Advanced Television Systems Committee (ATSC), "ATSC Standard: Digital Audio Compression (AC-3), Revision B", ATSC Doc A/52B, June 2005.

9.2. Informative References

[G.1082] ITU-T, "Measurement-based methods for improving the robustness of IPTV performance", ITU-T Recommendation G.1082, April 2009.
[P.564] ITU-T, "Conformance testing for narrowband Voice over IP transmission quality assessment models", ITU-T Recommendation P.564, July 2006.
[G.107] ITU-T, "The E Model, a computational model for use in transmission planning", ITU-T Recommendation G.107, April 2009.
[ETSI] ETSI, "Quality of Service (QoS) measurement methodologies", ETSI TS 101 329-5 V1.1.1, November 2000.
[P.1201] ITU-T, "Parametric non-intrusive assessment of audiovisual media streaming quality", ITU-T Recommendation P.1201, October 2012.
[P.1202] ITU-T, "non-intrusive bit-stream model for assessment of performance of multimedia streaming", ITU-T Recommendation P.1202, October 2012.
[MONARCH] Wu, Q., "Monitoring Architectures for RTP", ID draft-ietf-avtcore-monarch-22, September 2012.
[TTC] TTC 201.01 (Japan), "A method for speech quality assessment for Voice over IP", .
[RFC6390] Clark, A. and B. Claise, "Framework for Performance Metric Development", RFC 6390, October 2011.
[RFC4598] Link, B., "Real-time Transport Protocol (RTP) Payload Format for Enhanced AC-3 (E-AC-3) Audio", RFC 4598, July 2006.
[RFC4184] Link, B., Hager, T. and J. Flaks, "RTP Payload Format for AC-3 Audio", RFC 4184, October 2005.

Appendix A. Change Log

Appendix A.1. draft-ietf-xrblock-rtcp-xr-qoe-03

The following are the major changes compared to previous version:

Appendix A.2. draft-ietf-xrblock-rtcp-xr-qoe-02

The following are the major changes compared to previous version:

Appendix A.3. draft-ietf-xrblock-rtcp-xr-qoe-01

The following are the major changes compared to previous version:

Appendix A.4. draft-ietf-xrblock-rtcp-xr-qoe-00

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
Qin Wu Huawei 101 Software Avenue, Yuhua District Nanjing, Jiangsu 210012 China EMail: sunseawq@huawei.com
Roland Schott Deutsche Telekom Laboratories Deutsche-Telekom-Allee 7 Darmstadt, 64295 Germany EMail: Roland.Schott@telekom.de
Glen Zorn Network Zen 77/440 Soi Phoomjit, Rama IV Road Phra Khanong, Khlong Toie Bangkok, 10110 Thailand Phone: +66 (0) 87 502 4274 EMail: gwz@net-zen.net