RTCP XR for Application Layer Statistics Metrics Reporting
draft-zorn-xrblock-rtcp-xr-al-stat-00

Abstract

This document defines an RTCP XR Report Block and associated SDP parameters that allows the reporting of application layer summary, loss discard and burst 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. Application Layer Metrics
• 4.1. Application Layer Statistics Summary Report Block
• 4.2. Application Layer Loss and Discard Metrics Block
• 4.3. Application Layer Burst 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

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 video related parameters at application layer that are genericly designed for use in voice, audio and video services.

The metrics belong to the class of transport 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].

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. Applicability

The Metric Block defined in this document can be applied to any real time applications that convey video related parameters at application layer.

4. Application Layer Metrics

4.1. 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    |I| tag |T|P|rsd|        block length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          begin_seq            |             end_seq           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         lost_frames                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                          dup frames                           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        partial_lost_frames                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        partial_dup_frames                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  key frames impairement proportion            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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 frame packets, duplicated frame packets, lost layered component packets, duplicated layered component packets. Such information can be useful for network management and video quality monitoring.

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 parameters are reported and which are not. The fields corresponding to unreported parameters MUST be present, but are set to zero. The receiver MUST ignore any Video Statistics Summary Report Block with a non-zero value in any field flagged as unreported.

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>.

Interval Metric flag (I): 1 bit

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

Measurement Identifier association (tag): 3 bits

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

Picture type indicator (T): 1 bits

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.

Rsd.: 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].

lost_frames: 32 bits

Number of lost_frames in the above sequence number interval.

dup_frames: 32 bits

Number of dup_frames in the above sequence number interval.

partial lost_frames: 32 bits

Number of partial lost_frames in the above sequence number interval.

partial dup_frames: 32 bits

Number of partial_dup_frames in the above sequence number interval.

key frames impairment proportion:32bits

The proportion of key frame impaired by packet loss,discard and duplication.

4.2. 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| tag |T| rsv.|        block length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Loss rate            |        Discard rate           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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 packets 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 packets have been received.

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

A Application Layer Metrics Report 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,

Measurement Identifier association (tag): 3 bits

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

Picture type indicator (T): 1 bits

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].

Loss rate: 8 bits

The fraction of RTP data packets from the source 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 packets containing specified frame (e.g., Key frame) (after the effects of applying any error protection such as FEC) by the total number of packets 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 packets and discarded packets do not enter into this calculation. Since receivers cannot be required to maintain unlimited buffers, a receiver MAY categorize late-arriving packets as lost. The degree of lateness that triggers a loss SHOULD be significantly greater than that which triggers a discard.

Discard rate: 8 bits

The fraction of RTP data packets from the source that have been 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 packets containing specified frame (e.g., Key Frame) (excluding duplicate packet discards) by the total number of packets expected, multiplying the result of the division by 256, limiting the maximum value to 255 (to avoid overflow), and taking the integer part.

4.3. 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| tag |  Rsv. |        block length           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Loss Distance        |          Loss Period          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Max Loss Duration        |           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 RFC 3357 [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

Appliation Layer Metrics Report Block is identified by the constant <ALBM>.

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,

Measurement Identifier association (tag): 3 bits

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

reserved: 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.

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 mean duration, expressed in milliseconds, of the loss intervals that have occurred since the beginning of reception [DSLF]. The duration of each loss distance is calculated based upon the frames 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.

Loss Period: 16 bits

The mean duration, expressed in milliseconds, of the burst loss periods that have occurred since the beginning of reception [DSLF]. The duration of each period is calculated based upon the frame that marks the end of the prior burst loss and the frame that marks the beginning of the subsequent burst loss. It is equal to the timestamp of the subsequent burst frame, minus the timestamp of the prior burst packet, plus the duration of the prior burst 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.

Max Loss Duration of a single error: 16 bits

The maximum loss duration, expressed in milliseconds, of the loss periods that have occurred since the beginning of reception. The recommended max loss duration is specified as less than 16 ms in [DSLF], which provides a balance between interleaver depth protection from xDSL errors induced by impulse noise, delay added to other applications and video service QoE requirements to reduce visible impairments.

Reserved: 16 bits

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

block length: 16 bits

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

5. 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 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 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 4.1
    
    

    Name:

    ALLDM

    Long Name:

    Application Layer Loss and Discard Metrics

    Value

    <ALLDM>

    Reference:

    Section 4.2
    
    

    Name:

    ALBM

    Long Name:

    Application Layer Burst Metrics

    Value

    <ALBM>

    Reference:

    Section 4.3

This document also registers three new SDP

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

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

Authors' Addresses