RTCP XR for Summary Statistics Metrics Reporting
draft-zorn-xrblock-rtcp-xr-al-stat-04

Abstract

This document defines three RTCP XR Report Blocks and associated SDP parameters that allows the reporting of loss, duplication and discard summary statistics metrics for use in a range of RTP applications.

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Table of Contents

• 1. Introduction
• 1.1. Applicability
• 2. Terminology
• 2.1. Standards Language
• 3. Transport Layer Metrics
• 3.1. Burst/Gap Loss Summsary Statistics Block
• 3.1.1. Report Block Structure
• 3.1.2. Definition of Fields in Loss Summary Statistics Block
• 3.2. Burst/Gap Discard Summary Statistics Block
• 3.2.1. Report Block Structure
• 3.2.2. Definition of Fields in Discard Summary Statistics Block
• 4. Application Layer Metrics
• 4.1. Application Layer Loss/Duplication Statistics Summary Block
• 4.1.1. Report Block Structure
• 4.1.2. Definition of Fields in Loss/Duplication Summary Statistics Block
• 5. SDP Signaling
• 6. IANA Considerations
• 6.1. New RTCP XR Block Type values
• 6.2. New RTCP XR SDP Parameters
• 6.3. Contact information for registrations
• 7. Security Considerations
• 8. Acknowledgements
• 9. References
• 9.1. Normative References
• 9.2. Informative References
• Appendix A. Change Log
• Authors' Addresses

1. Introduction

RFC 3611 [RFC3611] defines seven report block formats for network management and quality monitoring. However, some of these metrics are mostly for multicast inference of network characteristics (MINC) or voice over IP (VoIP) monitoring and not widely applicable to other applications, e.g., video quality monitoring. This document focuses on specifying new additional report block types used to convey loss, duplication and discard summary statistics that are generically designed for use in audio and video services.

The metrics belong to both the class of application layer metrics and transport layer metrics defined in [MONARCH] (work in progress).

1.1. Applicability

The Report Blocks defined in this document can be applied to any real-time applications that convey loss, duplication and discard summary statistics.

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:

Picture Type

Picture types used in the different video algorithms compose of the key-frame and the Derivation frame. Key-frame is also called a reference frame and used as a reference for predicting other pictures. It is coded without prediction from other pictures. The Derivation frame is derived from Key-frame using prediction from the reference frame.

3. Transport Layer Metrics

3.1. Burst/Gap Loss Summsary Statistics Block

The metrics described here are intended to be used as described in this section, in conjunction with information from the Measurement Information block (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].

3.1.1. 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=TBD    |I|    rsv.     |        block length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         SSRC of Source                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Burst Loss Rate        |         Gap Loss Rate         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Burst duration Mean     |    Burst duration Varianc     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.1.2. Definition of Fields in Loss Summary Statistics Block

block type (BT): 8 bits

Burst/Gap Loss Summsary Statistics Block is identified by the constant <BGLSS>.

Interval Metric flag (I): 1 bit

This field is used to indicate whether the metrics block is an Interval or a Cumulative report,

reserved: 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.

block length: 16 bits

The constant 2, in accordance with the definition of this field in Section 3 of RFC 3611 [RFC3611].

SSRC of source: 32 bits

As defined in Section 4.1 of RFC3611 [RFC3611].

Burst Loss Rate: 16 bits

The fraction of packets lost during bursts since the beginning of reception, expressed as a fixed point number with the binary point at the left edge of the field. This value is calculated by dividing Packets Discarded in Bursts by Total Packets expected in Bursts as follows:

Packets Loss in Bursts / Total Packets expected in Bursts

Gap Loss Rate: 16 bits

The fraction of packets lost during gaps since the beginning of reception expressed as a fixed point number with the binary point at the left edge of the field. This value is calculated by dividing the difference between number of packets lost and Packets lost in Bursts by the difference between Packets Expected and Total Packets expected in Bursts as follows:

(number of packets lost - Packets Lost in Bursts) / (Packets Expected - Total Packets expected in Bursts)

where "number of packets lost" is obtained from standard RTCP [RFC3550] and Packets Expected is calculated as the difference between "extended last sequence number" and "extended first sequence number" (Interval or Cumulative) provided in the Measurement Identity and Information block [MEASIDENT].

Note that if the metric is to be calculated on an Interval basis, a difference must be taken between the current and preceding values of "cumulative number of packets lost" in RTCP, to obtain the "number of packets lost" for the reporting interval.

Burst duration Mean:16bits

The mean burst duration is obtained as the quotient:

mean = Sum of Burst Durations / Number of Bursts

where " Sum of Burst Durations " and “Number of Bursts”is obtained from the RTCP XR Burst/Gap Discard Block.

Burst Duration Variance:16bits

The variance of the burst duration is obtained using the standard result:

var = ( Sum of Squares of Burst Durations - Number of Bursts * mean^2 ) / (Number of Bursts - 1)

where " Sum of Squares of Burst Durations " and “Number of Bursts”is obtained from the RTCP XR Burst/Gap Discard Block.

3.2. Burst/Gap Discard Summary Statistics Block

The metrics described here are intended to be used as described in this section, in conjunction with information from the Measurement Identity block (which MUST be present in the same RTCP packet as the Burst/Gap Discard block) and also with the metric "number of packets discarded" provided in the RTCP XR Discard Block [DISCARD]. The RTCP XR Discard Block SHOULD be sent if the Burst/Gap Discard block is sent, but the converse does not apply.

3.2.1. 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=TBD    |I|     Rsv.    |        block length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          SSRC of Source                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Burst Discard Rate   |        Gap Discard Rate       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.2.2. Definition of Fields in Discard Summary Statistics Block

block type (BT): 8 bits

Burst/Gap Discard Summary Statistics Block is identified by the constant <BGDSS>.

reserved: 8 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.

Interval Metric flag (I): 1 bit

This field is used to indicate whether the metrics block is an Interval or a Cumulative report,

reserved: 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.

block length: 16 bits

The constant 3, in accordance with the definition of this field in Section 3 of RFC 3611 [RFC3611].

SSRC of source: 32 bits

As defined in Section 4.1 of RFC3611 [RFC3611].

Burst Discard Rate: 16 bits

The fraction of packets discarded during bursts since the beginning of reception, expressed as a fixed point number with the binary point at the left edge of the field. This value is calculated by dividing Packets Discarded in Bursts by Total Packets expected in Bursts as follows:

Packets Discarded in Bursts / Total Packets expected in Bursts

Gap Discard Rate: 16 bits

The fraction of packets discarded during gaps since the beginning of reception expressed as a fixed point number with the binary point at the left edge of the field. This value is calculated by dividing the difference between number of packets discarded and Packets Discarded in Bursts by the difference between Packets Expected and Total Packets expected in Bursts as follows:

(number of packets discarded - Packets Discarded in Bursts) / (Packets Expected - Total Packets expected in Bursts)

where "number of packets discarded" is obtained from the RTCP XR Discard Block [DISCARD] and Packets Expected is calculated as the difference between "extended last sequence number" and "extended first sequence number" (Interval or Cumulative) provided in the Measurement Information block [MEASIDENT].

4. Application Layer Metrics

4.1. Application Layer Loss/Duplication Statistics Summary Block

This block reports statistics beyond the information carried in the Statistics Summary Report Block RTCP packet specified in the section 4.6 of RFC 3611 [RFC3611]. Information is recorded about lost frames ,duplicated frames, lost partial frames. Such information can be useful for network management and video quality monitoring.

4.1.1. 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=TBD    | |T|P|   rsv.  |        block length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        SSRC of Source                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          begin_seq            |             end_seq           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Number of frames expected                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      lost_full_frames                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          dup_frames                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      lost_partial_frames                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.1.2. Definition of Fields in Loss/Duplication Summary Statistics Block

Block type (BT): 8 bits

Application Layer Loss/Duplication Statistics Summary Bloc is identified by the constant <ALDSS>.

Picture type indicator (T): 1 bit

Picture types used in the different video algorithms compose of key-frame and derivation frame. This field is used to indicate the frame type to be reported. Bits set to 0 if the lost_frames field or dup_frames field contain a key_frame report or reference frame report, 1 if the lost_frames field and dup_frames field contain other derivation frame report.

P: 1 bit

Bit set to 1 if the partial_lost_frames field or the partial_dup_ frames field contains a report, 0 otherwise.

Rsv.: 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 constant 6, in accordance with the definition of this field in Section 3 of RFC 3611 [RFC3611].

SSRC of source: 32 bits

As defined in Section 4.1 of RFC3611 [RFC3611].

begin_seq: 16 bits

As defined in Section 4.1 of RFC 3611 [RFC3611].

end_seq: 16 bits

As defined in Section 4.1 of RFC 3611 [RFC3611].

number of frames expected:32bits

A count of the number of frames expected, estimated if necessary. If no frames have been received then this count shall be set to Zero.

lost_full_frames: 32 bits

If one frame is completely lost, this frame is regarded as one lost full_frame. The lost_full_frames is equivalent to the number of lost_full_frames in the above sequence number interval.

dup_frames: 32 bits

Number of dup_frames in the above sequence number interval.

lost_partial_frames: 32 bits

If one frame is partially lost, this frame is regarded as one lost fractional frame. The lost_partial_frames is equivalent to the number of lost_partial_frames in the above sequence number interval.

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.

This section augments the SDP [RFC4566] attribute "rtcp-xr" defined in [RFC3611] by providing three additional value of "xr-format" to signal the use of the report block defined in this document.

     rtcp-xr-attrib =  "a=rtcp-xr:"
                       [xr-format *(SP xr-format)] CRLF
           xr-format =
                       / burst-gap-loss-stat
                       / burst-gap-discard-stat
                       / application-loss-dup-stat

Refer to Section 5.1 of RFC 3611 [RFC3611] for a detailed description and the full syntax of the "rtcp-xr" attribute.

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 values

    
      Name:       BGLSS
      Long Name:  Burst/Gap Loss Summsary Statistics Block
      Value       <BGLSS>
      Reference:  Section 5.1

      Name:       BGDSS
      Long Name:  Burst/Gap Discard Summary Statistics Block
      Value       <BGDSS>
      Reference:  Section 5.2

      Name:       ALDSS
      Long Name:  Application Layer Loss/Duplication Statistics Summary
      Value       <ALDSS>
      Reference:  Section 6.1

This document assigns three new block type value in the RTCP XR Block Type Registry:

6.2. New RTCP XR SDP Parameters

 *  " burst-gap-loss-stat "
 *  " burst-gap-discard-stat "
 *  "application-loss-dup-stat "

This document also registers three new SDP [RFC4566] parameters for the "rtcp-xr" attribute in the RTCP XR SDP Parameters Registry:

6.3. Contact information for registrations

The contact information for the registrations is:

    Glen Zorn
    Network Zen
    227/358 Thanon Sanphawut
    Bang Na, Bangkok  10110
    Thailand

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 document is separated from draft-wu-xrblock-rtcp-xr-quality-monitoring-01 with a few editorial changes and focuses on loss,duplication, discard, and summary statistics metrics.

Authors' Addresses