RFC 7294

Abstract ✨

RFC 7294 💖 RTP Control Protocol (RTCP) Extended Report (XR) Blocks for Concealment Metrics Reporting on Audio Applications

• Stream: Internet Engineering Task Force (IETF) 🌸
• Authors: A. Clark (Telchemy), G. Zorn (Network Zen), C. Bi (STTRI), Q. Wu (Huawei) 🧚
• Category: Standards Track 🎀
• ISSN: 2070-1721
• Date: July 2014 🦋
• Obsoletes / Updates: the header doesn't list anything it obsoletes or updates 🤷‍♀️

This document defines two RTP Control Protocol (RTCP) Extended Report (XR) blocks that let you report concealment metrics for audio applications of RTP. 🎧✨

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Status of This Memo

Okay so this one is an Internet Standards Track document, which is the official, legit, we-mean-it category. 💅

It's a product of the Internet Engineering Task Force (IETF), and it represents the consensus of the IETF community. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). If you want more on Internet Standards, check out Section 2 of RFC 5741. 📚

For the current status, any errata, and how to give feedback, go to http://www.rfc-editor.org/info/rfc7294. 🔥

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Copyright Notice

Copyright (c) 2014 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. 🙈

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Table of Contents 🗂️

1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
  1.1.  Loss Concealment and Concealed Seconds Metrics
        Blocks  . . . . . . . . . . . . . . . . . . . . . . . . .   2
  1.2.  RTCP and RTCP Extended Reports  . . . . . . . . . . . . .   3
  1.3.  Performance Metrics Framework . . . . . . . . . . . . . .   4
  1.4.  Applicability . . . . . . . . . . . . . . . . . . . . . .   4
2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
  2.1.  Standards Language  . . . . . . . . . . . . . . . . . . .   4
  2.2.  Notations . . . . . . . . . . . . . . . . . . . . . . . .   4
3.  Loss Concealment Metrics Block  . . . . . . . . . . . . . . .   5
  3.1.  Report Block Structure  . . . . . . . . . . . . . . . . .   5
  3.2.  Definition of Fields in Loss Concealment Metrics Block  .   5
4.  Concealed Seconds Metrics Block . . . . . . . . . . . . . . .   9
  4.1.  Report Block Structure  . . . . . . . . . . . . . . . . .  10
  4.2.  Definition of Fields in Concealed Seconds Metrics Block .  10
5.  SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . .  14
  5.1.  SDP rtcp-xr-attrib Attribute Extension  . . . . . . . . .  14
  5.2.  Offer/Answer Usage  . . . . . . . . . . . . . . . . . . .  14
6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
  6.1.  New RTCP XR Block Type Values . . . . . . . . . . . . . .  14
  6.2.  New RTCP XR SDP Parameters  . . . . . . . . . . . . . . .  15
  6.3.  Contact Information for Registrations . . . . . . . . . .  15
7.  Security Considerations . . . . . . . . . . . . . . . . . . .  15
8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  15
9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
  10.1.  Normative References . . . . . . . . . . . . . . . . . .  16
  10.2.  Informative References . . . . . . . . . . . . . . . . .  16
Appendix A.  Metrics Represented Using the Template from RFC 6390  17

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1. Introduction 🎀

1.1. Loss Concealment and Concealed Seconds Metrics Blocks

Okay so at any instant, the audio output at a receiver can be classified as either 'normal' or 'concealed'. 🎶 'Normal' means playout of audio payload received from the remote end, and it also covers locally generated signals like announcements, tones, and comfort noise. 'Concealed' means playout of locally generated signals used to mask the impact of network impairments or to reduce how audible jitter buffer adaptations are. 🫶

This document defines two new concealment-related block types that augment the ones defined in [RFC3611], for use in a range of RTP applications. Both of them extend the packet loss concealment mechanism defined in Section 4.7.6 of [RFC3611]. ✨

The first one is the Loss Concealment Metrics Block. It gives you metrics for the actions the receiver takes to soften the blow of packet loss and packet discard. 🌈 The first metric, On-Time Playout Duration, reports how long the receiver played normal data it actually got from the sender's stream. A second metric, Loss Concealment Duration, reports the total time the receiver played locally made media, because the sender's data for those periods never showed up due to packet loss or discard. A similar one, Buffer Adjustment Concealment Duration, reports how long it played locally made data to replace data that was unavailable because an adaptive de-jitter buffer was adjusting. Then there are Playout Interrupt Count and Mean Playout Interrupt Size, which report how many times normal playout got interrupted and the average length of those interruptions. 💅

Loss Concealment Duration and Buffer Adjustment Concealment Duration are reported separately, and that's honestly iconic of them. 👑 Buffer adjustment is usually arranged to happen during silence periods, so it may barely affect user experience, whilst loss concealment can happen at any time. 😭

The second one is the Concealed Seconds Metrics Block. It gives you metrics for Concealed Seconds, which are measured at the receiving end of the RTP stream. 🦋 The first metric, Unimpaired Seconds, reports the number of whole seconds occupied only with normal playout of data the receiver got from the sender's stream. The second, Concealed Seconds, reports the number of whole seconds in which the receiver played any locally generated media. A third metric, Severely Concealed Seconds (SCSs), reports the number of whole seconds in which the receiver played locally generated data to conceal a lost or discarded frame percentage above the configured SCS Threshold. 🔥

These metrics belong to the class of transport-related terminal metrics defined in [RFC6792]. 🧚

1.2. RTCP and RTCP Extended Reports

RTCP is used for reporting, and that's defined in [RFC3550]. [RFC3611] gives us an extensible structure for reporting using an RTCP Extended Report (XR). 🍓 This document defines a new Extended Report block that MUST be used as defined in [RFC3550] and [RFC3611]. No skipping the rules, bestie. 🙅‍♀️

1.3. Performance Metrics Framework

The Performance Metrics Framework [RFC6390] gives guidance on defining and specifying performance metrics. 📐 The RTP Monitoring Framework [RFC6792] gives guidelines for reporting block format using RTCP XR. The metrics blocks described in this document follow those guidelines. 💜

1.4. Applicability

These metrics apply to audio applications of RTP, and to the audio component of audio/video applications, where the packet loss concealment machinery lives at the receiving end. Its job is to soften the impact of network impairments on the user's perception of media quality. 🎧🌸

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]. 🫶

2.2. Notations

The report blocks in this document use binary fractions. Here's the terminology:

Numeric formats S X:Y, where S says whether it's a two's complement signed representation, X is the number of bits before the decimal place, and Y is the number of bits after it. 🧮

So 8:8 is an unsigned number from 0.0 to 255.996, with a granularity of 0.0039. S7:8 covers -127.996 to +127.996. And 0:16 is a proper binary fraction with range 0.0 to 1 - 1/65536 = 0.9999847. 🦋

BUT, and this is a big but 🙈, using flag values at the top of the numeric range slightly shrinks that upper limit. For example, if the 16-bit values 0xFFFE and 0xFFFF are used as flags for "over-range" and "unavailable" conditions, a 0:16 quantity has range 0.0 to 1 - 3/65536 = 0.9999542. 🚩

3. Loss Concealment Metrics Block 💖

The Loss Concealment Metrics Block is meant to be used as described in this section, together with information from the Measurement Information Block [RFC6776]. Instances of this metrics block refer, by synchronization source (SSRC), to the separate auxiliary Measurement Information Block [RFC6776], which describes the measurement periods in use (see [RFC6776], Section 4.2). 🗓️ This metrics block relies on the measurement period in the Measurement Information Block to show the span of the report, and it SHOULD be sent in the same compound RTCP packet as the Measurement Information Block. ⭐ If the measurement period doesn't arrive in the same compound RTCP packet as this metrics block, this metrics block MUST be discarded. 💀

3.1. Report Block Structure

Here's how the Loss Concealment Metrics Block is laid out. 🗺️

     0               1               2               3
     0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    BT=30      | I |plc|  resv |       block length=6          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         SSRC of Source                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 On-Time Playout Duration                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                  Loss Concealment Duration                    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |              Buffer Adjustment Concealment Duration           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Playout Interrupt Count    |           Reserved            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 Mean Playout Interrupt Size                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: Loss Concealment Metrics Block 🌈

3.2. Definition of Fields in Loss Concealment Metrics Block ✨

Block type (BT): 8 bits 🎀

A Loss Concealment Metrics Block is identified by the constant 30. 💖

Interval Metric flag (I): 2 bits 🦋

okay so this field tells you whether the loss concealment metrics are Sampled, Interval, or Cumulative. it's giving "which kind of measurement am I looking at" 👀

• I=10: Interval Duration. The value applies to the most recent measurement interval duration between successive metrics reports. 🌸
• I=11: Cumulative Duration. The value applies to the accumulation period that's characteristic of cumulative measurements. 💜
• I=01: Sampled Value. The value is a sampled instantaneous value, which is not allowed in this block 🙅‍♀️
• I=00: Reserved value. This one is saved for future use. 🧚

In this document, Loss Concealment metrics can only be measured over definite intervals and cannot be sampled, so it's giving no sampling vibes. Senders MUST NOT use the values I=00 or I=01. If a block is received with I=00 or I=01, the receiver MUST discard the block. 💀

Packet Loss Concealment Method (plc): 2 bits 🌈

this field tells you which packet loss concealment method the receiver is using, using this code:

• bits 014-015
• 0 = silence insertion 🤫
• 1 = simple replay, no attenuation
• 2 = simple replay, with attenuation
• 3 = enhancement ✨

Other values are reserved. 🔒

ngl the enhancement method (plc=3) is my fave here. It offers improved audio quality and better robustness against packet losses [G.711], and it's equivalent to "enhanced" in Section 4.7.6 of [RFC3611]. literally iconic 👑

Reserved (resv): 4 bits 🍓

These bits are reserved. They MUST be set to zero by senders and ignored by receivers (see [RFC6709], Section 4.2). 🫶

block length: 16 bits 📏

This is the length of this report block in 32-bit words, minus one. For the Loss Concealment Metrics Block, the block length is equal to 6. ✨

SSRC of Source: 32 bits 🎧

As defined in Section 4.1 of [RFC3611]. 💅

On-Time Playout Duration: 32 bits ⏱️

'On-time playout' is the uninterrupted, in-sequence playout of valid decoded audio that comes from the remote endpoint. This includes comfort noise during remote talker silence (if Voice Activity Detection (VAD) [VAD] is used), plus locally generated or regenerated tones and announcements. 🎶

An equivalent way to say it: on-time playout is playout of any signal other than the ones used for concealment. 🧠

On-time playout duration is expressed in units of RTP timestamp. It MUST include both speech and silence intervals, whether VAD is used or not. 🫠

Two values are reserved: 0xFFFFFFFE means out of range (a measured value exceeding 0xFFFFFFFD), and 0xFFFFFFFF means the measurement is unavailable. 🙈

Loss Concealment Duration: 32 bits 🫧

This is the duration, in units of RTP timestamp, of audio playout corresponding to Loss-Type concealment.

Loss-Type concealment is reactive insertion or deletion of samples in the audio playout stream because of effective frame loss at the audio decoder. Effective frame loss is when a frame of coded audio is simply not there at the audio decoder when it's needed. In that case, substitute audio samples are usually formed (at the decoder or somewhere else) to reduce audible impairment. 🎭

Two values are reserved: 0xFFFFFFFE means out of range (a measured value exceeding 0xFFFFFFFD), and 0xFFFFFFFF means the measurement is unavailable. 💖

Buffer Adjustment Concealment Duration: 32 bits 🪄

This is the duration, in units of RTP timestamp, of audio playout corresponding to Buffer Adjustment-Type concealment, if it's known. 🤍

Buffer Adjustment-Type concealment is proactive or controlled insertion or deletion of samples in the audio playout stream. It happens because of jitter buffer adaptation, re-sizing decisions, or re-centering decisions within the endpoint. 🔧

Because this insertion is controlled instead of happening randomly in response to losses, it's typically less audible than Loss-Type concealment. For example, jitter buffer adaptation events may be constrained to happen during periods of talker silence, in which case only silence duration is affected. Or sophisticated time-stretching methods for insertion/deletion may be used during favorable periods in active speech. so smart 🧚‍♀️

Concealment events that cannot be classified as Buffer Adjustment-Type MUST be classified as Loss-Type. 📌

Two values are reserved: 0xFFFFFFFE means out of range (a measured value exceeding 0xFFFFFFFD), and 0xFFFFFFFF means the measurement is unavailable. 🌸

Playout Interrupt Count: 16 bits ⏸️

This is the number of interruptions to normal playout that happened during the reporting period. 📊

Two values are reserved: 0xFFFE means out of range (a measured value exceeding 0xFFFD), and 0xFFFF means the measurement is unavailable. 🥺

Reserved: 16 bits 🫙

These bits are reserved. They MUST be set to zero by senders and ignored by receivers (see [RFC6709], Section 4.2). 🌷

Mean Playout Interrupt Size: 32 bits 📐

This is the mean duration, in units of RTP timestamp, of interruptions to normal playout that happened during the reporting period. 🧮

Two values are reserved: 0xFFFFFFFE means out of range (a measured value exceeding 0xFFFFFFFD), and 0xFFFFFFFF means the measurement is unavailable. 💜

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4. Concealed Seconds Metrics Block 🌟

The Concealed Seconds Metrics Block is meant to be used the way this section describes, together with information from the Measurement Information Block [RFC6776]. It describes potentially audible impairments caused by lost and discarded packets at the endpoint. It's expressed on a time basis that's kind of like a traditional Public Switched Telephone Network (PSTN) T1/E1 errored seconds metric. 📞

Instances of this metrics block refer, by synchronization source (SSRC), to the separate auxiliary Measurement Information Block [RFC6776]. That one describes the measurement periods in use (see [RFC6776], Section 4.2). 🗂️

This metrics block relies on the measurement period in the Measurement Information Block to show the span of the report. It SHOULD be sent in the same compound RTCP packet as the Measurement Information Block. If the measurement period is not received in the same compound RTCP packet as this metrics block, this metrics block MUST be discarded. 🚫

The following metrics are based on successive one-second intervals, as declared by an RTP clock. This RTP clock does not need to be synchronized to any external time reference. The starting time of this clock is unspecified. ⏰

Note that this means the same loss pattern could give slightly different count values, depending on where the losses happen relative to the particular one-second demarcation points. For example, two loss events occurring 50 ms apart could result in either one Concealed Second or two, depending on the particular one-second boundaries used. it's giving chaos 🌀

The seconds in this sub-block are not necessarily calendar seconds. At the tail end of a session, periods of time of less than one second shall be incorporated into these counts if they exceed 500 ms, and shall be disregarded if they are less than 500 ms. 🧾

4.1. Report Block Structure 🧩

The structure of the Concealed Seconds Metrics Block is as follows. 🍭

     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=31      | I |plc|  resv |       block length=4          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                         SSRC of Source                        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Unimpaired Seconds                         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                    Concealed Seconds                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Severely Concealed Seconds    | Reserved      | SCS Threshold |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Concealed Seconds Metrics Block 📸

4.2. Definition of Fields in Concealed Seconds Metrics Block 🎀

okay so this is where we go field by field, bestie 💅

Block type (BT): 8 bits

A Concealed Seconds Metrics Block is identified by the constant 31 🦋

Interval Metric flag (I): 2 bits

this field tells you whether the Concealed Seconds numbers are Sampled, Interval, or Cumulative metrics 🌈

• I=10: Interval Duration. The reported value applies to the most recent measurement interval duration between successive metrics reports.
• I=11: Cumulative Duration. The reported value applies to the accumulation period characteristic of cumulative measurements.
• I=01: Sampled Value. The reported value is a sampled instantaneous value (Not allowed in this block).
• I=00: Reserved value. This value is reserved for future use.

In this document, Concealed Seconds metrics can only be measured over definite intervals and cannot be sampled. Senders MUST NOT use the values I=00 or I=01. If a block is received with I=00 or I=01, the receiver MUST discard the block. 🚫

Packet Loss Concealment Method (plc): 2 bits

this one says which packet loss concealment method the receiver is using 🎧 the code goes like this:

bits 014-015

   0 = silence insertion
   1 = simple replay, no attenuation
   2 = simple replay, with attenuation
   3 = enhancement

Other values are reserved.

ngl the enhancement method (plc=3) is the iconic one ✨ it offers improved audio quality and better robustness against packet losses [G.711], and it is equivalent to "enhanced" in Section 4.7.6 of [RFC3611]. main character energy 👑

Reserved (resv): 4 bits

these bits are reserved 🔒 They MUST be set to zero by senders and ignored by receivers (see [RFC6709], Section 4.2).

Block Length: 16 bits

this is the length of this report block in 32-bit words, minus one 📏 For the Concealed Seconds Metrics Block, the block length is equal to 4.

SSRC of Source: 32 bits

as defined in Section 4.1 of [RFC3611] 🫶

Unimpaired Seconds: 32 bits

a count of the number of Unimpaired Seconds that have occurred ✨

An Unimpaired Second is a continuous one-second period during which no frame loss or discard due to late arrival has occurred. Every second in a session must be classified as either OK or Concealed.

Normal playout of comfort noise or other silence-concealment signals during periods of talker silence, if VAD is used, shall be counted as Unimpaired Seconds 🤫

two values are reserved 🙈 0xFFFFFFFE indicates out of range (that is, a measured value exceeding 0xFFFFFFFD), and 0xFFFFFFFF indicates that the measurement is unavailable.

Concealed Seconds: 32 bits

okay this is the big one 👑 a count of the number of Concealed Seconds that have occurred.

A Concealed Second is a continuous one-second period during which any frame loss or discard due to late arrival has happened 💀

Equivalently, a Concealed Second is one in which some Loss-Type concealment has occurred. Buffer Adjustment-Type concealment SHOULD NOT cause Concealed Seconds to be incremented, with the following exception. An implementation MAY cause Concealed Seconds to be incremented for 'emergency' buffer adjustments made during talkspurts ⚡

Loss-Type concealment is reactive insertion or deletion of samples in the audio playout stream, caused by effective frame loss at the audio decoder. "Effective frame loss" is the event where a frame of coded audio is simply not present at the audio decoder when it's needed 😭 In this case, substitute audio samples are generally formed, at the decoder or elsewhere, to reduce audible impairment.

Buffer Adjustment-Type concealment is proactive or controlled insertion or deletion of samples in the audio playout stream. It happens due to jitter buffer adaptation, re-sizing decisions, or re-centering decisions within the endpoint 🧚

Because this insertion is controlled, rather than happening randomly in response to losses, it is typically less audible than Loss-Type concealment. For example, jitter buffer adaptation events may be constrained to occur during periods of talker silence, in which case only silence duration is affected. Or sophisticated time-stretching methods for insertion/deletion during favorable periods in active speech may be employed 🎀 For these reasons, Buffer Adjustment-Type concealment MAY be exempted from inclusion in calculations of Concealed Seconds and Severely Concealed Seconds.

However, an implementation SHOULD include Buffer Adjustment-Type concealment in counts of Concealed Seconds and Severely Concealed Seconds if the event occurs at an 'inopportune' moment. Think an emergency or large, immediate adaptation during active speech, or an unsophisticated adaptation during speech without regard for the underlying signal. In these cases, the assumption of low audibility cannot hold 🙈 In other words, jitter buffer adaptation events that may be presumed to be audible SHOULD be included in Concealed Seconds and Severely Concealed Seconds counts.

Concealment events that cannot be classified as Buffer Adjustment-Type MUST be classified as Loss-Type 📌

For clarification, the count of Concealed Seconds MUST include the count of Severely Concealed Seconds 💖

two values are reserved again 🙈 0xFFFFFFFE indicates out of range (that is, a measured value exceeding 0xFFFFFFFD), and 0xFFFFFFFF indicates that the measurement is unavailable.

Severely Concealed Seconds: 16 bits

a count of the number of Severely Concealed Seconds 🔥

A Severely Concealed Second is a non-overlapping one-second period during which the cumulative amount of time that has been subject to frame loss or discard due to late arrival exceeds the SCS Threshold. Lowkey the worst kind of second 😭

Two values are reserved: 0xFFFE indicates out of range (that is, a measured value exceeding 0xFFFD), and 0xFFFF indicates that the measurement is unavailable.

Reserved: 8 bits

these bits are reserved 🔒 They MUST be set to zero by senders and ignored by receivers (see [RFC6709], Section 4.2).

SCS Threshold: 8 bits

the SCS Threshold is the percentage of packets corresponding to lost or discarded frames that must occur within a one-second period for that second to be classified as a Severely Concealed Second 📊 It's expressed in numeric format 0:8, so it can represent a range of 0 to 99.6 percent loss or discard.

A default threshold of 5 percent effective frame loss (50 ms effective frame loss ) per second is suggested. That corresponds to an SCS Threshold in hexadecimal of 0x0D 🍓

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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 🦋

5.1. SDP rtcp-xr-attrib Attribute Extension 🌸

this section augments the SDP attribute "rtcp-xr" [RFC3611] by adding two more values of "xr-format" so you can signal the use of the two report blocks defined in this document 💅

   xr-format =/ xr-conceal-block
              / xr-conc-sec-block

   xr-conceal-block = "loss-conceal"
   xr-conc-sec-block = "conc-sec" ["=" thresh]

   thresh      = 1*DIGIT          ; threshold for SCS (ms)
   DIGIT =     <as defined in Section 3 of [RFC5234]>

5.2. Offer/Answer Usage 🤝

when SDP is used in an Offer/Answer context, the SDP Offer/Answer usage defined in [RFC3611] applies. Note that "thresh" is declared by the offer 💜

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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 🎀

this document assigns two block type values in the IANA "RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry" under the subregistry "RTCP XR Block Type" 🧁

   Name:       LCB
   Long Name:  Loss Concealment Metrics Block
   Value       30
   Reference:  Section 3.1
   Name:       CSB
   Long Name:  Concealed Seconds Metrics Block
   Value       31
   Reference:  Section 4.1

6.2. New RTCP XR SDP Parameters 🌈

this document also registers two new parameters in the "RTP Control Protocol Extended Reports (RTCP XR) Session Description Protocol (SDP) Parameters Registry" 🫶

• "loss-conceal"
• "conc-sec"

6.3. Contact Information for Registrations 📬

the contact information for the registrations is:

RAI Area Directors

rai-ads@tools.ietf.org

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7. Security Considerations 🔐

It is believed that the RTCP XR blocks defined in this document introduce no new security considerations beyond those described in [RFC3611]. These blocks do not provide per-packet statistics, so the risk to confidentiality documented in Section 7, Paragraph 3 of [RFC3611] does not apply 🛡️ no per-packet stats means no per-packet leaks, so this is a very safe, very slay situation 💖

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8. Contributors 🧚

Geoff Hunt wrote the initial version of this document 🌟

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9. Acknowledgements 💌

the authors gratefully acknowledge reviews and feedback provided by Bruce Adams, Philip Arden, Amit Arora, Bob Biskner, Kevin Connor, Alissa Cooper, Claus Dahm, Randy Ethier, Roni Even, Adrian Farrel, Jim Frauenthal, Albert Higashi, Tom Hock, Shane Holthaus, Paul Jones, Rajesh Kumar, Keith Lantz, Alfred C. Morton, Mohamed Mostafa, Amy Pendleton, Colin Perkins, Mike Ramalho, Ravi Raviraj, Pete Resnick, Albrecht Schwarz, Meral Shirazipour, Tom Taylor, and Hideaki Yamada 🙌

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10. References 📖

10.1. Normative References 🔥

[RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
           Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
           Jacobson, "RTP: A Transport Protocol for Real-Time
           Applications", STD 64, RFC 3550, July 2003.

[RFC3611]  Friedman, T., Caceres, R., and A. Clark, "RTP Control
           Protocol Extended Reports (RTCP XR)", RFC 3611, November
           2003.

[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.

[RFC6776]  Clark, A. and Q. Wu, "Measurement Identity and Information
           Reporting Using a Source Description (SDES) Item and an
           RTCP Extended Report (XR) Block", RFC 6776, October 2012.

10.2. Informative References 🌷

[G.711]    ITU-T, "Pulse Code Modulation (PCM) of Voice Frequencies",
           ITU-T Recommendation G.711, 1988.

[RFC6390]  Clark, A. and B. Claise, "Guidelines for Considering New
           Performance Metric Development", BCP 170, RFC 6390,
           October 2011.

[RFC6709]  Carpenter, B., Aboba, B., and S. Cheshire, "Design
           Considerations for Protocol Extensions", RFC 6709,
           September 2012.

[RFC6792]  Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the
           RTP Monitoring Framework", RFC 6792, November 2012.

[VAD]      Wikipedia, "Voice activity detection", January 2014,
           <http://en.wikipedia.org/w/index.php?title=Voice_activity_detection&oldid=593287643>.

Appendix A. Metrics Represented Using the Template from RFC 6390 ✨

Okay bestie, this appendix is basically a checklist of metrics, each one filled out using the RFC 6390 template. Every metric gets the same fields, so you can compare them easily 🧚

a. On-Time Playout Duration Metric

• Metric Name: On-Time Playout Duration
• Metric Description: "On-time playout" means audio playout that is uninterrupted and in sequence, made from valid decoded audio that comes from the remote endpoint. On-time playout duration is the playout duration of any signal that isn't used for concealment 🎀
• Method of Measurement or Calculation: See Section 3.2, On-Time Playout Duration definition.
• Units of Measurement: See Section 3.2, On-Time Playout Duration definition.
• Measurement Point(s) with Potential Measurement Domain: See Section 1.1, 3rd paragraph.
• Measurement Timing: See Section 3, 1st paragraph for measurement timing and Section 3.2 for Interval Metric flag.
• Use and Applications: See Section 1.4.
• Reporting Model: See RFC 3611.

b. Loss Concealment Duration Metric

• Metric Name: Loss Concealment Duration
• Metric Description: The duration of audio playout that corresponds to Loss-Type concealment 🦋
• Method of Measurement or Calculation: See Section 3.2, Loss Concealment Duration definition.
• Units of Measurement: See Section 3.2, Loss Concealment Duration definition.
• Measurement Point(s) with Potential Measurement Domain: See Section 1.1, 3rd paragraph.
• Measurement Timing: See Section 3, 1st paragraph for measurement timing and Section 3.2 for Interval Metric flag.
• Use and Applications: See Section 1.4.
• Reporting Model: See RFC 3611.

c. Buffer Adjustment Concealment Duration Metric

• Metric Name: Buffer Adjustment Concealment Duration
• Metric Description: The duration of audio playout that corresponds to Buffer Adjustment-Type concealment 🌸
• Method of Measurement or Calculation: See Section 3.2, Buffer Adjustment Concealment Duration definition.
• Units of Measurement: See Section 3.2, Buffer Adjustment Concealment Duration definition.
• Measurement Point(s) with Potential Measurement Domain: See Section 1.1, 3rd paragraph.
• Measurement Timing: See Section 3, 1st paragraph for measurement timing and Section 3.2 for Interval Metric flag.
• Use and Applications: See Section 1.4.
• Reporting Model: See RFC 3611.

d. Playout Interrupt Count Metric

• Metric Name: Playout Interrupt Count
• Metric Description: The number of times normal playout got interrupted during the reporting period 💅
• Method of Measurement or Calculation: See Section 3.2, Playout Interrupt Count definition.
• Units of Measurement: See Section 3.2, Playout Interrupt Count definition.
• Measurement Point(s) with Potential Measurement Domain: See Section 1.1, 3rd paragraph.
• Measurement Timing: See Section 3, 1st paragraph for measurement timing and Section 3.2 for Interval Metric flag.
• Use and Applications: See Section 1.4.
• Reporting Model: See RFC 3611.

e. Mean Playout Interrupt Size Metric

• Metric Name: Mean Playout Interrupt Size
• Metric Description: The mean duration of the interruptions to normal playout that happened during the reporting period. Iconic averaging energy 📊✨
• Method of Measurement or Calculation: See Section 3.2, Playout Interrupt Count definition.
• Units of Measurement: See Section 3.2, Playout Interrupt Count definition.
• Measurement Point(s) with Potential Measurement Domain: See Section 1.1, 3rd paragraph.
• Measurement Timing: See Section 3, 1st paragraph for measurement timing and Section 3.2 for Interval Metric flag.
• Use and Applications: See Section 1.4.
• Reporting Model: See RFC 3611.

f. Unimpaired Seconds Metric

• Metric Name: Unimpaired Seconds
• Metric Description: A count of how many Unimpaired Seconds have happened 🌈
• Method of Measurement or Calculation: See Section 4.2, Unimpaired Seconds definition.
• Units of Measurement: See Section 4.2, Unimpaired Seconds definition.
• Measurement Point(s) with Potential Measurement Domain: See Section 1.1, 5th paragraph.
• Measurement Timing: See Section 4, 1st paragraph for measurement timing and Section 4.2 paragraph for Interval Metric flag.
• Use and Applications: See Section 1.4.
• Reporting Model: See RFC 3611.

g. Concealed Seconds Metric

• Metric Name: Concealed Seconds
• Metric Description: A count of how many Concealed Seconds have happened 🙈
• Method of Measurement or Calculation: See Section 4.2, Concealed Seconds definition.
• Units of Measurement: See Section 4.2, Concealed Seconds definition.
• Measurement Point(s) with Potential Measurement Domain: See Section 1.1, 5th paragraph.
• Measurement Timing: See Section 4, 1st paragraph for measurement timing and Section 4.2 for Interval Metric flag.
• Use and Applications: See Section 1.4.
• Reporting Model: See RFC 3611.

h. Severely Concealed Seconds Metric

• Metric Name: Severely Concealed Seconds
• Metric Description: A count of how many Severely Concealed Seconds have happened. This one is a little dramatic, but it's giving important 😭
• Method of Measurement or Calculation: See Section 4.2, Severely Concealed Seconds definition.
• Units of Measurement: See Section 4.2, Severely Concealed Seconds definition.
• Measurement Point(s) with Potential Measurement Domain: See Section 1.1, 5th paragraph.
• Measurement Timing: See Section 4, 1st paragraph for measurement timing and Section 4.2 for Interval Metric flag.
• Use and Applications: See Section 1.4.
• Reporting Model: See RFC 3611.

i. SCS Threshold Metric

• Metric Name: SCS Threshold
• Metric Description: The amount of time that lost or discarded frames have to add up to within a one-second period before that second gets classified as a Severely Concealed Second. Main character threshold energy 👑
• Method of Measurement or Calculation: See Section 4.2, SCS Threshold definition.
• Units of Measurement: See Section 4.2, SCS Threshold definition.
• Measurement Point(s) with Potential Measurement Domain: See Section 1.1, 5th paragraph.
• Measurement Timing: See Section 4, 1st paragraph for measurement timing and Section 4.2 for Interval Metric flag.
• Use and Applications: See Section 1.4.
• Reporting Model: See RFC 3611.

---

Authors' Addresses 💖

Here's where you can find the authors, so you know exactly who to thank for all this 🫶

Alan Clark, from Telchemy Incorporated 🌸

Alan Clark
Telchemy Incorporated
2905 Premiere Parkway, Suite 280
Duluth, GA  30097
USA

EMail: alan.d.clark@telchemy.com

Glen Zorn, from Network Zen 🍓

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

Claire Bi, from the Shanghai Research Institute of China Telecom Corporation Limited 🦋

Claire Bi
Shanghai Research Institute of China Telecom Corporation Limited
No. 1835, South Pudong Road
Shanghai  200122
China

EMail: bijy@sttri.com.cn

Qin Wu, from Huawei 🌈

Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu  210012
China

EMail: sunseawq@huawei.com