RTCP XR for Application Layer Statistics Metrics Reporting
draft-zorn-xrblock-rtcp-xr-al-stat-02

Abstract

This document defines a set of RTCP XR Report Blocks and associated Session Description Protocol (SDP) parameters allowing the report of application layer summary, loss discard and burst metrics for use in a range of RTP applications.

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This Internet-Draft will expire on December 11, 2011.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Standards Language
• 4. Applicability
• 5. Application Layer Metrics
• 5.1. Application Layer Statistics Summary Report Block
• 5.2. Application Layer Loss and Discard Metrics Block
• 5.3. Application Layer Burst Metrics Block
• 6. SDP Signaling
• 7. IANA Considerations
• 8. Security Considerations
• 9. Acknowledgements
• 10. References
• 10.1. Normative References
• 10.2. 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, 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 video-related parameters at the application layer that are generically designed for use in audio and video services.

The metrics belong to the class of application layer metrics defined in [I-D.hunt-avtcore-monarch].

2. Terminology

FEC

Forward Error Correction

Picture Type

Picture types used in the different video algorithms are composed 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 a Key-frame using prediction from the reference frame.

RTP

Real-time Transport Protocol [RFC3550].

RTCP

RTP Control Protocol [RFC3550].

RTCP XR

RTP Control Protocol Extended Reports [RFC3611].

3. 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].

4. Applicability

The Report Blocks defined in this document can be applied to any real-time applications that convey video-related parameters at the application layer.

5. Application Layer Metrics

5.1. Application Layer Statistics Summary Report Block

    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    |  rsd. |T|P|rsd|        block length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          begin_seq            |             end_seq           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Number of frames expected                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      lost_full_frames                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          dup_frames                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      lost_partial_frames                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

The Application Layer Statistics Summary Report Block has the following format:

block_type (BT): 8 bits

The Application Layer Statistics Summary Report Block is identified by the constant <ALSS>.

rsvd: 4 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.

picture_type_indicator (T): 1 bit

This field is used to indicate the frame type being reported. 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.

R: 2 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 5, in accordance with the definition of this field in Section 3 of RFC 3611 [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 of the type indicated by the picture_type_indicator field expected, estimated if necessary. If no such frames have been received then this count shall be set to zero (0).

lost_full_frames: 32 bits

If a frame is completely lost, this frame is regarded as one lost full frame. The lost_full_frames field is equivalent to the number of full frames of the type indicated by the picture_type_indicator field lost in the above sequence number interval.

dup_frames: 32 bits

Number of duplicate 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 field is equivalent to the number of lost fractional frames in the above sequence number interval.

5.2. Application Layer Loss and Discard Metrics Block

    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 |T| rsv.|        block length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Frame Loss rate        |     Frame Discard rate        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

A frame shall be regarded as lost if it fails to arrive within an implementation-specific time window. A frame that arrives within this time window but is too early or late to be played out shall be regarded as discarded. A frame shall be classified as one of received (or OK), discarded or lost.

This block reports Loss and Discard metrics statistics beyond the information carried in the standard RTCP packet format. The block reports separately on packets lost on the IP channel, and those that have been received but then discarded by the receiving jitter buffer.

It is very useful to distinguish between frames lost by the network and those discarded due to jitter. Both have equal effect on the quality of the video stream, however, having separate counts helps identify the source of quality degradation. These fields MUST be populated, and MUST be set to zero if no frames have been received.

The Loss and Discard metrics are determined after the effects of FEC, redundancy [RFC2198] or other similar processes. Implementations MUST provide values for all the fields defined here. For certain metrics, if the value is undefined or unknown, then the specified default or unknown field value MUST be provided.

The block is encoded as six 32-bit words:

block type (BT): 8 bits

An Application Layer Loss and Discard Metrics Block is identified by the constant <ALLDM>.

Interval Metric flag (I): 1 bit

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

reserved: 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.

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 picture type to be reported. Bits set to 0 if the Loss rate field and discard rate field contain a Key_frame report or reference frame report, 1 if the Loss rate field and discard rate field contain other derivation frame reports.

reserved: 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.

block length: 16 bits

The constant 1, in accordance with the definition of this field in Section 3 of RFC 3611 [RFC3611].

Frame Loss rate: 8 bits

The proportion of frames lost 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 total number of lost frames containing specified frame (e.g., Key frame) (after the effects of applying any error protection such as FEC) by the total number of frames expected, multiplying the result of the division by 256, limiting the maximum value to 255 (to avoid overflow), and taking the integer part. The numbers of duplicated frames and discarded frames do not enter into this calculation. Since receivers cannot be required to maintain unlimited buffers, a receiver MAY categorize late-arriving frames as lost. The degree of lateness that triggers a loss SHOULD be significantly greater than that which triggers a discard.

Frame Discard rate: 8 bits

The proportion of frames discarded since the beginning of reception, due to late or early arrival, under-run or overflow at the receiving jitter buffer. This value is expressed as a fixed point number with the binary point at the left edge of the field. It is calculated by dividing the total number of discarded frames containing specified frame (e.g., Key Frame) (excluding duplicate frames discards) by the total number of frames expected, multiplying the result of the division by 256, limiting the maximum value to 255 (to avoid overflow), and taking the integer part.

5.3. Application Layer Burst Metrics Block

   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           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Loss Distance        |          Loss Period          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Threshold            |           Reserved.           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

This block reports Burst metrics statistics beyond the information carried in the standard RTCP packet format. It reports on the combined effect of losses and discards, as both have equal effect on video quality.

In order to properly assess the quality of a video stream, it is desirable to consider the degree of burstiness of packet loss [RFC3357]. Following the one-way loss pattern sample metrics discussed in [RFC3357], a measure of the spacing between consecutive network packet loss or error events, is a "loss distance". The loss distance metric captures the spacing between the loss periods. The duration of a loss or error event (e.g. and how many packets are lost in that duration) is a "loss period", the loss period metric captures the frequency and length (burstiness) of loss once it starts. Delay reports include the transit delay between RTP end points and the end system processing delays, both of which contribute to the user perceived delay.

Implementations MUST provide values for all the fields defined here. For certain metrics, if the value is undefined or unknown, then the specified default or unknown field value MUST be provided.

The block is encoded as three 32-bit words:

block type (BT): 8 bits

The Application Layer Burst Metrics Block is identified by the constant <ALBM>.

Interval Metric flag (I): 1 bit

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

rsvd: 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].

Loss Distance: 16 bits

The average duration of periods between bursts. The mean duration, expressed in milliseconds, of the gap periods that have occurred since the beginning of reception [DSLF]. The duration of each period is calculated based upon the frame packets that marks the end of the prior burst and the frame packet that marks the beginning of the subsequent burst. It is equal to the timestamp of the subsequent burst frame packet, minus the timestamp of the prior burst frame packet, plus the duration of the prior burst frame packet. If the actual values are not available, estimated values MUST be used. In the case of a gap that occurs at the beginning of reception, the sum of the timestamp of the prior burst packet and the duration of the prior burst packet are replaced by the reception start time. In the case of a gap that occurs at the end of reception, the timestamp of the subsequent burst packet is replaced by the reception end time. If there have been no gap periods, the gap duration value MUST be zero.

Loss Period: 16 bits

The average duration of a burst of lost and discarded frames. The mean duration, expressed in milliseconds, of the loss intervals that have occurred since the beginning of reception [DSLF]. The duration of each loss period is calculated based upon the frame packets that mark the beginning and end of that period. It is equal to the timestamp of the end frame, plus the duration of the end frame, minus the timestamp of the beginning frame. If the actual values are not available, estimated values MUST be used. If there have been no burst periods, the burst duration value MUST be zero.

Threshold: 16 bits

The maximum duration, expressed in milliseconds, of the loss distance that have occurred since the beginning of reception.

Reserved: 16 bits

All bits SHALL be set to 0 by the sender and SHALL be ignored on reception.

6. SDP Signaling

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

application-burst-metrics = " application-burst-metrics"
                              ["=" max-size]
      max-size = 1*DIGIT ; maximum block size in octets

application--loss-metrics = " application-loss-metrics"
                       ["=" stat-flag *("," stat-flag)]
         stat-flag = "key Frame loss and duplication"
                        / "derivation Frame loss and duplication"

application-stat-summary = "application-stat-summary"
                      ["=" stat-flag *("," stat-flag)]
            stat-flag = "key Frame loss and duplication"
                   / "derivation Frame loss and duplication"

Three new parameters are defined for the three report blocks defined in this document to be used with 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.

7. IANA Considerations

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

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 three new block type value in the RTCP XR Block Type Registry: [RFC4566] parameters for the "rtcp-xr" attribute in the RTCP XR SDP Parameters Registry:

The contact information for the registrations is:

• Name:

  ALSS

  Long Name:

  Application Layer Statistics Summary

  Value

  <ALSS>

  Reference:

  Section 5.1
  
  

  Name:

  ALLDM

  Long Name:

  Application Layer Loss and Discard Metrics

  Value

  <ALLDM>

  Reference:

  Section 5.2
  
  

  Name:

  ALBM

  Long Name:

  Application Layer Burst Metrics

  Value

  <ALBM>

  Reference:

  Section 5.3
  
  

This document also registers three new SDP

• • "application-layer-loss-metrics"
  • "application-layer-burst-metrics"
  • "application-layer-stat-summary"

8. Security Considerations

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

9. 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.

10. References

10.1. Normative References

10.2. 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 application layer summary, loss, discard, and burst metrics.

Authors' Addresses