RFC 7003
RTP Control Protocol (RTCP) Extended Report (XR) Block for Burst/Gap Discard Metric Reporting
RFC 7003 🎀
Okay bestie, let's get into RFC 7003 💅 This is Part 1 of 3.
It's an IETF document on the Standards Track 🦋, published September 2013. The authors are A. Clark (Telchemy), R. Huang, and Q. Wu, Ed. (Huawei). Its ISSN is 2070-1721. The title is "RTP Control Protocol (RTCP) Extended Report (XR) Block for Burst/Gap Discard Metric Reporting" ✨ The header doesn't list anything it obsoletes or updates, so there's no drama there 🙈
Abstract
This document defines an RTP Control Protocol (RTCP) Extended Report (XR) block that lets you report burst and gap discard metrics for a range of RTP applications 💜
Status of This Memo
This is an Internet Standards Track document 🌸
It's a product of the Internet Engineering Task Force (IETF) and represents the IETF community's consensus 🫶 It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). For more on Internet Standards, check Section 2 of RFC 5741.
For the current status, errata, and how to send feedback, go to http://www.rfc-editor.org/info/rfc7003 🧚
Copyright Notice
Copyright (c) 2013 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, since 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 they are provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction ....................................................2
1.1. Burst/Gap Discard Metrics Block ............................2
1.2. RTCP and RTCP Extended Reports .............................3
1.3. Performance Metrics Framework ..............................3
1.4. Applicability ..............................................3
2. Terminology .....................................................3
3. Burst/Gap Discard Metrics Block .................................4
3.1. Report Block Structure .....................................5
3.2. Definition of Fields in Burst/Gap Discard Metrics Block ....5
3.3. Derived Metrics Based on Reported Metrics ..................7
4. Considerations for Voice-over-IP Applications ...................7
5. SDP Signaling ...................................................8
5.1. SDP rtcp-xr Attribute Extension ............................8
5.2. Offer/Answer Usage .........................................8
6. IANA Considerations .............................................8
6.1. New RTCP XR Block Type Value ...............................8
6.2. New RTCP XR SDP Parameter ..................................9
6.3. Contact Information for Registrations ......................9
7. Security Considerations .........................................9
8. Contributors ....................................................9
9. Acknowledgments .................................................9
10. References ....................................................10
10.1. Normative References .....................................10
10.2. Informative References ...................................10
Appendix A. Metrics Represented Using the Template from RFC 6390..121. Introduction ✨
1.1. Burst/Gap Discard Metrics Block
This document defines a new block type that augments the ones defined in [RFC3611] for a range of RTP applications 🦋 The new block type reports the proportion of packets the jitter buffer at the receiver discards, using packet discard logic that follows the jitter buffer algorithms. The discards during discard bursts get reported, along with the number of bursts. This block is meant to be used together with [RFC7002], which provides the total packets discarded, so this block depends on it. The metric in [RFC7002] can still be used on its own, though, without the metrics in this block.
This block gives you info on transient IP problems 👀 Burst/gap metrics are typically used in cumulative reports, but they can also be used in interval reports (see the Interval Metric flag in Section 3.2). Burstiness of packet discard affects user experience, may influence any sender strategies for mitigating the problem, and may have diagnostic value too 💖
The metric belongs to the class of transport-related end-system metrics defined in [RFC6792].
The definitions of "burst", "gap", "loss", and "discard" match the ones in [RFC3611]. To cover the range of jitter buffer algorithms and packet discard logic that implementors might use, the method for telling bursts and gaps apart shall use an equivalent method to the one defined in Section 4.7.2 of [RFC3611]. Note that reporting the specific jitter buffer algorithms and/or packet discard logic is out of scope for this document 🙈
1.2. RTCP and RTCP Extended Reports
RTCP reporting is defined in [RFC3550]. [RFC3611] defined an extensible structure for reporting using an RTCP Extended Report (XR). This document defines a new Extended Report block for use with [RFC3550] and [RFC3611] 🎀
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 block in this document follows the guidelines in [RFC6390] and [RFC6792] 🧚
1.4. Applicability
These metrics apply to a range of RTP applications that have de-jitter buffers [RFC5481] at the receiving end to smooth out variation in packet-arrival time, and that don't use stream repair means, like Forward Error Correction (FEC) [RFC5109] and/or retransmission [RFC4588] 🌈
2. Terminology 💜
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].
Besides those, a few terms get defined here 🍓
Received, Lost, and Discarded
A packet shall be regarded as "lost" if it fails to arrive within an implementation-specific time window. A packet that does arrive within this time window but is too early to be played out, too late to be played out, or thrown away before playout due to packet duplication or redundancy shall be regarded as discarded. A packet shall not be regarded as discarded if it arrives within this time window but gets dropped during decoding by some higher-layer decoder, e.g., due to a decoding error. A packet shall be classified as one of received (or OK), discarded, or lost 😭
The metric "cumulative number of packets lost" defined in [RFC3550] reports a count of packets lost from the media stream (single synchronization source (SSRC) within a single RTP session). Similarly, the metric "number of packets discarded" defined in [RFC7002] reports a count of packets discarded from the media stream (single SSRC within a single RTP session) arriving at the receiver. Another metric, defined in [RFC5725], is available to report on packets that aren't recovered by any repair techniques that may be in use. Note that the term "discard" defined here builds on the "discard" definition in [RFC3611] but extends the concept to take into account packet duplication, and it reports different types of discard counts [RFC7002] 💅
Bursts and Gaps
The terms "burst" and "gap" are used in a manner consistent with RTCP XR [RFC3611]. RTCP XR views an RTP stream as divided into bursts, which are periods during which the discard rate is high enough to cause noticeable quality degradation (generally over 5 percent discard rate), and gaps, which are periods during which discarded packets are infrequent and so quality is generally acceptable 🦋
3. Burst/Gap Discard Metrics Block 🌸
Metrics in this block report on burst/gap discard in the stream arriving at the RTP system. Measurements of these metrics are made at the receiving end of the RTP stream. Instances of this metrics block use the synchronization source (SSRC) to refer 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 indicate the span of the report. Senders MUST send this block in the same compound RTCP packet as the Measurement Information Block. Receivers MUST verify that the measurement period is received in the same compound RTCP packet as this metrics block. If not, this metrics block MUST be discarded 🙈
3.1. Report Block Structure
The structure of the Burst/Gap Discard Metrics Block looks like this 🧚
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=20 | I | resv | Block Length = 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Threshold | Packets Discarded in Bursts |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Packets Expected in Bursts | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Figure 1: Report Block Structure
Part 1 ends here, bestie 🫶 Section 3.2 (the field definitions) is up next in Part 2 👀
3.2. Definition of Fields in Burst/Gap Discard Metrics Block 🎀
okay bestie, let's walk through every field, one by one 💅
Block Type (BT): 8 bits 🧚
A Burst/Gap Discard Metrics Block is identified by the constant 20. ✨
Interval Metric flag (I): 2 bits 🌈
This field tells you whether the burst/gap discard metrics are Sampled, Interval, or Cumulative metrics [RFC6792]. the vibes are very specific here 😭
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 that cumulative measurements have. 💜I=01: Sampled Value. The reported value is a sampled instantaneous value. 🦋
In this document, burst/gap discard metrics can only be measured over definite intervals and cannot be sampled. ngl that's a big rule 🙈 Also, the value I=00 is reserved for future use. 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. no exceptions, periodt 💅
Reserved (resv): 6 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 Burst/Gap Discard Metrics Block, the block length is equal to 3. The block MUST be discarded if the block length is set to a different value. so if the length is off, it's getting tossed 🗑️
SSRC of Source: 32 bits 🌸
This is as defined in Section 4.1 of [RFC3611].
Threshold: 8 bits 👑
The Threshold is equivalent to Gmin in [RFC3611]. Basically it's the number of successive packets that must not be discarded prior to and following a discard packet, in order for this discarded packet to count as part of a gap. Note that the Threshold is set in accordance with the Gmin calculation defined in Section 4.7.2 of [RFC3611]. the math is giving precision ✨
Packets Discarded in Bursts: 24 bits 💖
This is the total number of packets discarded during discard bursts.
The measured value is unsigned value. If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFF MUST be reported. 🙈
Total Packets Expected in Bursts: 24 bits 🦋
This is the total number of packets expected during discard bursts. In other words, it's the sum of received packets and lost packets.
The measured value is unsigned value. If the measured value exceeds 0xFFFFFD, the value 0xFFFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFF MUST be reported. same rules, same energy 💅
Reserved: 8 bits 🫧
These bits are reserved. They MUST be set to zero by senders and ignored by receivers (See [RFC6709], Section 4.2).
3.3. Derived Metrics Based on Reported Metrics 🔥
okay so these metrics are meant to be used together with the Measurement Information Block [RFC6776], and also with the metric "number of packets discarded" from the RTCP XR Discard Count Metrics Block [RFC7002]. it's a whole team effort 🫶
These metrics give you info for statistical parameters, including:
- The fraction of packets discarded during bursts (Burst Discard Rate in [RFC7004]). You can calculate this using the metric "Packets Discarded in Bursts" and the metric "Total Packets Expected in Bursts" from the Burst/Gap Discard Metrics Block. 💜
- The fraction of packets discarded during gaps (Gap Discard Rate in [RFC7004]). You can calculate this using the same two metrics, "Packets Discarded in Bursts" and "Total Packets Expected in Bursts," from the Burst/Gap Discard Metrics Block. 🌈
The details on calculating these parameters from the metrics are described in [RFC7004]. go read that one, it's the main character of the calc stuff ✨
4. Considerations for Voice-over-IP Applications 📞
This metrics block is applicable to a broad range of RTP applications. Where the metric is used with a Voice-over-IP (VoIP) application and the stream repair means is not available, the following considerations apply. 🎧
RTCP XR views a call as being divided into bursts and gaps. Bursts are periods during which the discard rate is high enough to cause noticeable call quality degradation (generally over 5 percent discard rate). Gaps are periods during which discarded packets are infrequent, and hence call quality is generally acceptable. 🌸
If voice activity detection is used, the burst and gap duration shall be determined as if silence packets had been sent. In other words, a period of silence in excess of Gmin packets will terminate a burst condition. 🤫
The recommended value for the threshold Gmin in [RFC3611] results in a burst being a period of time during which the call quality is degraded to a similar extent to a typical pulse code modulation (PCM) severely errored second. this is the kind of detail that makes me obsessed 😭
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. no permission slip needed 🦋
5.1. SDP rtcp-xr Attribute Extension 💖
This section augments the SDP [RFC4566] attribute "rtcp-xr" defined in [RFC3611] by providing an additional value of "xr-format" to signal the use of the report block defined in this document. The ABNF [RFC5234] syntax is as follows. 🧾
xr-format =/ xr-bgd-block
xr-bgd-block = "burst-gap-discard"5.2. Offer/Answer Usage 🤝
When SDP is used in Offer/Answer context, the SDP Offer/Answer usage defined in [RFC3611] for unilateral "rtcp-xr" attribute parameters applies. For detailed usage in Offer/Answer for unilateral parameters, refer to Section 5.2 of [RFC3611]. 🫶
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 Value 🔢
This document assigns the block type value 20 in the IANA "RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry" to the "Burst/Gap Discard Metrics Block". 🦋
6.2. New RTCP XR SDP Parameter 🌈
This document also registers a new parameter "burst-gap-discard" in the "RTP Control Protocol Extended Reports (RTCP XR) Session Description Protocol (SDP) Parameters Registry". 💜
6.3. Contact Information for Registrations 📬
The contact information for the registrations is:
Qin Wu (sunseawq@huawei.com)
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China7. Security Considerations 🔐
⚠️ this part is serious, so read it carefully bestie 😭
It is believed that this RTCP XR block introduces no new security considerations beyond those described in [RFC3611]. This block does not provide per-packet statistics, so the risk to confidentiality documented in Section 7, paragraph 3 of [RFC3611] does not apply. 🛡️
8. Contributors 🫶
Geoff Hunt wrote the initial draft of this document. the OG 🧚
9. Acknowledgments 💐
The authors gratefully acknowledge reviews and feedback provided by Bruce Adams, Philip Arden, Amit Arora, Claire Bi, Bob Biskner, Benoit Claise, Kevin Connor, Claus Dahm, Randy Ethier, Roni Even, Stephen Farrell, Jim Frauenthal, Albert Higashi, Tom Hock, Shane Holthaus, Paul Jones, Rajesh Kumar, Paul Kyzivat, Keith Lantz, Mohamed Mostafa, Amy Pendleton, Colin Perkins, Mike Ramalho, Ravi Raviraj, Dan Romascanu, Albrecht Schwarz, Tom Taylor, and Hideaki Yamada. the whole squad showed up for this one 👑💖
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.
[RFC5725] Begen, A., Hsu, D., and M. Lague, "Post-Repair Loss RLE
Report Block Type for RTP Control Protocol (RTCP) Extended
Reports (XRs)", RFC 5725, February 2010.
[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.
[RFC7002] Clark, A., Zorn, G., and Q. Wu, "RTP Control Protocol
(RTCP) Extended Report (XR) for Discard Count Metric
Reporting", RFC 7002, September 2013.
[RFC7004] Zorn, G., Schott, R., Wu, Q., Ed., and R. Huang, "RTP
Control Protocol (RTCP) Extended Report (XR) Blocks for
Summary Statistics Metrics Reporting", RFC 7004, September
2013.10.2. Informative References 🦋
[RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R.
Hakenberg, "RTP Retransmission Payload Format", RFC 4588,
July 2006.
[RFC5109] Li, A., "RTP Payload Format for Generic Forward Error
Correction", RFC 5109, December 2007.
[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation
Applicability Statement", RFC 5481, March 2009.
[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.Appendix A. Metrics Represented Using the Template from RFC 6390 ✨
okay so this appendix is basically the metrics cheat sheet 🧚 it lists three metrics written up with the RFC 6390 template, and each one points back to the main sections for the juicy details 💅
a. Burst/Gap Discard Threshold in RTP Metric
- Metric Name: Burst/gap discard threshold in RTP
- Metric Description: The Threshold is equivalent to Gmin in [RFC3611], i.e., the number of successive packets that must not be discarded prior to and following a discard packet in order for this discarded packet to be regarded as part of a gap. 🔥
- Method of Measurement or Calculation: See Section 3.2, Threshold definition.
- Units of Measurement: See Section 3.2, Threshold definition.
- Measurement Point(s) with Potential Measurement Domain: See Section 3, 1st paragraph.
- Measurement Timing: See Section 3, 2nd 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. Packets Discarded in Bursts Metric
- Metric Name: RTP packets discarded in bursts
- Metric Description: The total number of RTP packets discarded during discard bursts. 💀
- Method of Measurement or Calculation: See Section 3.2, Packets Discarded in Bursts definition.
- Units of Measurement: See Section 3.2, Packets Discarded in Bursts definition.
- Measurement Point(s) with Potential Measurement Domain: See Section 3, 1st paragraph.
- Measurement Timing: See Section 3, 2nd 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. Total Packets Expected in Discard Bursts Metric
- Metric Name: Total RTP packets expected in discard bursts
- Metric Description: The total number of packets expected during discard bursts (that is, the sum of received packets and lost packets). 🎀
- Method of Measurement or Calculation: See Section 3.2, Total Packets Expected in Bursts definition.
- Units of Measurement: See Section 3.2, Total Packets Expected in Bursts definition.
- Measurement Point(s) with Potential Measurement Domain: See Section 3, 1st paragraph.
- Measurement Timing: See Section 3, 2nd paragraph for measurement timing and Section 3.2 for Interval Metric flag.
- Use and Applications: See Section 1.4.
- Reporting Model: See RFC 3611.
Authors' Addresses 🫶
And that's the whole squad, bestie 🌸 here's who wrote it:
Alan Clark
Telchemy Incorporated
2905 Premiere Parkway, Suite 280
Duluth, GA 30097
USA
EMail: alan.d.clark@telchemy.comRachel Huang
Huawei Technologies Co., Ltd.
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
EMail: Rachel@huawei.comQin Wu (editor)
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
EMail: sunseawq@huawei.com📦 where this page comes from
- ietf: rfc7003 2013-09
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms