RTCP XR Blocks for multimedia quality metric reporting
draft-wu-xrblock-rtcp-xr-quality-monitoring-02

Abstract

This document defines an RTCP XR Report Block and associated SDP parameters that allows the reporting of multimedia quality metrics for use in a range of RTP applications.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 2.1. Standards Language
• 3. Applicability
• 4. Synthetical Multimedia Quality Metrics Block
• 4.1. Metric Block Structure
• 4.2. Definition of Fields in Multimedia Quality Metrics Block
• 5. SDP Signaling
• 6. IANA Considerations
• 7. Security Considerations
• 8. Acknowledgements
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Appendix A. Change Log
• Authors' Addresses

1. Introduction

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 provides information on multimedia quality using one of several standard metrics.

The metrics belong to the class of application level metrics defined in [MONARCH] (work in progress).

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. Applicability

The Multimedia Quality Metrics Report Block can be used in any real-time AV application.

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:

• Tuning the content encoder algorithm to satisfy real time data quality requirements
• Determining which system techniques to use in a given situation and when to switch from one technique to another as system parameters change
• Verifying the continued correct operation of an existing system

4. Synthetical Multimedia Quality Metrics Block

This block reports the multimedia application performance or quality metrics beyond the information carried in the standard RTCP packet format. Information is recorded about multimedia application QoE metric which is 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 to estimate the multimedia quality. However Subjective testing is 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 recommendation [G.1082][P.NAMS][P.NBAMS] defines a methodology for verifying the performance of QoE estimation algorithms for video and audio. Hence this document recommends vendors and implementers to use International Telecommunication Union (ITU)-specified methodologies to measure parameters when possible.

4.1. 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 Perceptual Quality Metrics Block with a non-zero value in any field flagged as unreported.

   
    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=TBD    |I| tag |   MC  |        block length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        SSRC of source                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         MOS Value                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Synthetical Multimedia Quality Metrics Block has the following format:

4.2. Definition of Fields in Multimedia Quality Metrics Block

Block type (BT): 8 bits

The Perceptual Quality Metrics Block is identified by the constant <SMQM>.

Interval Metric flag (I): 1 bit

This field is used to indicate whether the Basic Loss/Discard 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=1) (the Interval Duration) or to the accumulation period characteristic of cumulative measurements (I=0) (the Cumulative Duration).

Measurement Identifier association (tag): 3 bits

This field is used to identify the Measurement Identifier block [MEASIDENT] which describes this measurement.

MoS Class (MC): 4 bits

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

• 0000 MOS-A - Audio Quality MOS [G.107][P.564].
• 0001 MOS-V - Video Quality MOS [P.NAMS][P.NBAMS].
• 0010 MOS-AV - Audio-Video Quality MOS[P.NAMS][P.NBAMS].
• 0100~1111 - Reserved

Rsd.: 7 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.

SSRC of source: 32 bits

As defined in Section 4.1 of [RFC3611].

MOS Value: Variable Length

The estimated mean opinion score for Audio Qulity, Video Quality or Audio-Video quality is defined as including the effects of delay and other effects that would affect Audio-Video quality [G.1082][P.NAMS][P.NBAMS]. It is expressed as an integer in the range 10 to 50, corresponding to MOS x 10, as for MOS. A value of 127 indicates that this parameter is unavailable. Values other than 127 and the valid range defined above MUST NOT be sent and MUST be ignored by the receiving system.

5. SDP Signaling

rtcp-xr-attrib =  "a=rtcp-xr:" 
                  [xr-format *(SP xr-format)] CRLF
      xr-format = multimedia-quality-metrics
         multimedia-quality-metrics = "multimedia-quality-metrics"
                               ["=" stat-flag *("," stat-flag)]
            stat-flag = "Interval Metrics"
                         /"Cumulative metrics"

One new parameter is defined for the six report blocks defined in this document to be used with Session Description Protocol (SDP) [RFC4566] using the Augmented Backus-Naur Form (ABNF) [RFC5234]. They have 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.

6. IANA Considerations

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

New report block types for RTCP XR are subject to IANA registration. For general guidelines on IANA allocations for RTCP XR, refer to Section 6.2 of [RFC3611].

This document assigns one new block type value in the RTCP XR Block Type Registry: [RFC4566] parameter for the "rtcp-xr" attribute in the RTCP XR SDP Parameters Registry:

The contact information for the registrations is:

• Name:

  SMQM

  Long Name:

  Synthetical Multimedia Quality Metric

  Value

  <SMQM>

  Reference:

  Section 4
  
  

This document also registers one new SDP

• • “multimedia-quality-metrics”

7. Security Considerations

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

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

9.2. Informative References

Appendix A. Change Log

This version focuses on multimedia quality metrics and separated other metrics block as independent documents.

Authors' Addresses