RFC 7002
RTP Control Protocol (RTCP) Extended Report (XR) Block for Discard Count Metric Reporting
RFC 7002: RTCP XR Block for Discard Count Metric Reporting 🎀
Internet Engineering Task Force (IETF) 💅 Authors: A. Clark (Telchemy), G. Zorn (Network Zen), Q. Wu (Huawei) ✨ Category: Standards Track 🔥 Date: September 2013 🌸 ISSN: 2070-1721 Obsoletes / Updates: the header doesn't list any 🙈
Abstract ✨
okay so this doc defines an RTP Control Protocol (RTCP) Extended Report (XR) block 🦋 that lets you report a simple discard count metric, and it's built to work across a whole range of RTP apps. it's giving clean and useful, bestie 💖
Status of This Memo
ok this one is an Internet Standards Track document 👑 which means 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 Section 2 of RFC 5741 🧚
for the current status, any errata, and how to give feedback, go to http://www.rfc-editor.org/info/rfc7002 🌈
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. 🔒
this doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they were in effect on the date of publication. please read these carefully, bestie, because they explain your rights and restrictions for this doc 📜 Code Components pulled out of this document must include Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come without warranty, as the Simplified BSD License describes 🫶
Table of Contents 🗂️
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Discard Count Report Block . . . . . . . . . . . . . . . 2
1.2. RTCP and RTCP Extended Reports . . . . . . . . . . . . . 3
1.3. Performance Metrics Framework . . . . . . . . . . . . . . 3
1.4. Applicability . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Discard Count Metrics Block . . . . . . . . . . . . . . . . . 4
3.1. Report Block Structure . . . . . . . . . . . . . . . . . 5
3.2. Definition of Fields in the Discard Count Metrics Block . 5
4. SDP Signaling . . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. SDP rtcp-xr Attribute Extension . . . . . . . . . . . . . 7
4.2. Offer/Answer Usage . . . . . . . . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
5.1. New RTCP XR Block Type Value . . . . . . . . . . . . . . 8
5.2. New RTCP XR SDP Parameter . . . . . . . . . . . . . . . . 8
5.3. Contact Information for Registrations . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. Metrics Represented Using the Template from RFC 6390 111. Introduction ✨
1.1. Discard Count Report Block 🍓
this doc defines a brand-new block type that augments the ones already defined in [RFC3611], and it's made for a range of RTP apps 💅 the new block type lets you report how many packets were received correctly but never get played out. usually that's because they showed up too late (buffer underflow) or too early (buffer overflow) to be played out 😭 this metric works for systems that use packet loss repair techniques (like forward error correction [RFC5109] or retransmission [RFC4588]) and for systems that don't 🦋
this metric is so useful for spotting that packet transport problems exist and for figuring out how bad they are, and those problems can affect how users feel about a service delivered over RTP 🥺
this block may be used together with [RFC7003], which gives more info on the pattern of discarded packets. the metric in [RFC7003] can also be used on its own, though, without the metrics in this block 💜
when a Discard Count Metrics Block is sent along with a Burst/Gap Discard Metrics Block (defined in [RFC7003]) to the media sender or an RTP-based network management system, the info in both blocks lets the systems that receive them calculate burst/gap summary statistics, like the gap discard rate 🧮 it's giving analytics era ✨
this metric belongs to the class of transport-related end-system metrics defined in [RFC6792] 🎀
1.2. RTCP and RTCP Extended Reports 🌸
RTCP reporting is defined in [RFC3550]. [RFC3611] set up an extensible structure for reporting with an RTCP Extended Report (XR) 🧚 this document defines a new Extended Report block that's meant to be used with both [RFC3550] and [RFC3611] 💖
1.3. Performance Metrics Framework 📊
"Guidelines for Considering New Performance Metric Development" [RFC6390] gives guidance on defining and specifying performance metrics 🤓 "Guidelines for Use of the RTP Monitoring Framework" [RFC6792] gives guidance on the reporting block format using RTCP XR 🫶 the metrics block described here follows the guidelines in both [RFC6390] and [RFC6792], so it's giving "properly done" 👑
1.4. Applicability 🦋
this metric is believed to be applicable to a large class of RTP apps that use a de-jitter buffer [RFC5481] 🌈
discards caused by late or early packets hurt user experience, ngl 😭 reporting discards alerts senders and other receivers that they need to adjust how they transmit or receive 🔥 the reports also let network managers diagnose these user experience problems 🩺
being able to detect duplicate packets lets managers spot network layer or sender behavior that might point to network or device issues 👀 based on the reports, those issues can get fixed before they affect user experience at all, which is literally the dream ✨
2. Terminology 🧠
the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this doc are to be interpreted as described in RFC 2119 [RFC2119] 📖
also, these terms are defined:
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 either too early or too late to be played out, or is 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 😤 every packet shall be classified as one of the following: received (or OK), discarded, or lost 💅 the discard count metric counts only discarded packets 🎯
the metric "cumulative number of packets lost" defined in [RFC3550] reports a count of packets lost from the media stream (a single synchronization source (SSRC) within a single RTP session) 📉 similarly, the metric "number of packets discarded" reports a count of packets discarded from the media stream (a 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 🩹
3. Discard Count Metrics Block 🎀
metrics in this block report on the number of packets discarded in the stream arriving at the RTP end system 💜 the measurement of these metrics is made at the receiving end of the RTP stream 👂 instances of this metrics block use the 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 interval in the Measurement Information Block to indicate the span of the report, so it MUST be sent in the same compound RTCP packet as the Measurement Information Block 🚨 if the measurement interval is not received in the same compound RTCP packet as this metrics block, this metrics block MUST be discarded 💀
3.1. Report Block Structure 🧱
the structure of the Discard Count 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=24 | I |DT | resv | Block Length = 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of Source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discard Count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Figure 1: Report Block Structure 🖼️
3.2. Definition of Fields in the Discard Count Metrics Block ✨
okay bestie, let's go through the fields one by one 💅🎀
Block Type (BT): 8 bits 🌸
A Discard Count Metrics Block is identified by the constant 24. 🧚
Interval Metric flag (I): 2 bits 🦋
This field tells you whether the reported metric is an Interval, Cumulative, or Sampled metric [RFC6792]:
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 use. ➕I=01: Sampled Value. The reported value is a sampled instantaneous value. 📸
So here's the tea: in this document, the discard count metric can only be measured over definite intervals and can never be sampled 🙅♀️. That means I=01, the sampled value, MUST NOT be sent, and MUST be discarded when received. Also, I=00 is reserved, so it MUST NOT be sent either, and MUST be discarded when received. 💀
Discard Type (DT): 2 bits 🍓
This field identifies the discard type used in this report block. The discard types go like this:
00: Report packet discarded or being thrown away before playout due to packet duplication. 👯01: Report packet discarded due to too early to be played out. ⏰10: Report packet discarded due to too late to be played out. 🐢
DT=11 is reserved for future definition, so it MUST NOT be sent, and MUST be discarded when received. 🔒
An endpoint MAY report any combination of discard types in each reporting interval by including several Discard Count Metrics Blocks in a single RTCP XR packet. Main character energy, literally 👑
Some systems send duplicate RTP packets for robustness or error resilience. This is NOT RECOMMENDED, since it breaks RTCP packet statistics 😭. If you do want duplication for error resilience, the mechanism described in [RTPDUP] can be used, since it won't cause breakage of RTP streams or RTCP statistics. ✨
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, following the definition in [RFC3611]. This field MUST be set to 2 to match the fixed length of the report block. The block MUST be discarded if the block length is set to a different value. No cap, the length has to be exactly right 🎯
SSRC of Source: 32 bits 🎶
As defined in Section 4.1 of [RFC3611]. 💜
Discard Count 🔢
This is the number of packets discarded over the period (Interval or Cumulative) covered by this report.
The measured value is an unsigned value. If the measured value exceeds 0xFFFFFFFD, then the value 0xFFFFFFFE MUST be reported to indicate an over-range measurement. If the measurement is unavailable, the value 0xFFFFFFFF MUST be reported. The over-range and unavailable values are the special ones, bestie, so don't mix them up 🚨
Note that the number of packets expected in the period for this metric (whether Interval or Cumulative) is available from the difference between a pair of extended sequence numbers in the Measurement Information Block [RFC6776]. So it doesn't need to be repeated in this block. Efficient and iconic 🫶
4. SDP Signaling 🎀
[RFC3611] defines how to use the Session Description Protocol (SDP) [RFC4566] to signal the use of XR blocks. However, XR blocks MAY be used without prior signaling (see Section 5 of RFC 3611). Flexible, the way that's giving 🦋
4.1. SDP rtcp-xr Attribute Extension 💅
This section extends the SDP [RFC4566] attribute "rtcp-xr", which is defined in [RFC3611]. It adds one more value of "xr-format" to signal the use of the report block defined in this document. The ABNF [RFC5234] syntax goes like this:
xr-format =/ xr-pdc-block
xr-pdc-block = "pkt-discard-count"4.2. Offer/Answer Usage 🤝
When SDP is used in an Offer/Answer context, the SDP Offer/Answer usage defined in [RFC3611] for unilateral "rtcp-xr" attribute parameters applies. For detailed usage of Offer/Answer for unilateral parameters, check Section 5.2 of [RFC3611]. ✨
5. 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]. 📋
5.1. New RTCP XR Block Type Value 🔢
This document assigns the block type value 24 in the IANA "RTP Control Protocol Extended Reports (RTCP XR) Block Type Registry" to the "Discard Count Metrics Block". 🎯
5.2. New RTCP XR SDP Parameter 🧩
This document also registers a new parameter, "pkt-discard-count", in the "RTP Control Protocol Extended Reports (RTCP XR) Session Description Protocol (SDP) Parameters Registry". 💖
5.3. Contact Information for Registrations 📮
The following contact information is provided for all registrations in this document:
Qin Wu (sunseawq@huawei.com)
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China6. Security Considerations 🔐💀
Okay, this section is serious, so listen up 👀
In some situations, returning very detailed error information (for example, an over-range measurement or a measurement that's unavailable) using this report block can give an attacker insight into the security processing. Where this is a concern, the implementation should apply encryption and authentication to this report block. For example, this can be achieved by using the Audio-Visual Profile with Feedback (AVPF) profile together with the Secure RTP profile, as defined in [RFC3711]. An appropriate combination of those two profiles ("SAVPF") is specified in [RFC5124]. 🛡️
Besides this, it is believed that this RTCP XR block introduces no new security considerations beyond those described in [RFC3611]. This block doesn't provide per-packet statistics, so the risk to confidentiality documented in Section 7, paragraph 3 of [RFC3611] does not apply. Phew, we're safe on that one 🙌
7. Contributors 🫶
Geoff Hunt wrote the initial draft of this document. The OG who started it all 👑
8. Acknowledgments 💐
The authors gratefully acknowledge the reviews and feedback provided by Bruce Adams, Philip Arden, Amit Arora, Claire Bi, Bob Biskner, Gonzalo Camarillo, Benoit Claise, Kevin Connor, Claus Dahm, Spencer Dawkins, Randy Ethier, Roni Even, Stephen Farrel, Jim Frauenthal, Kevin Gross, Albert Higashi, Tom Hock, Shane Holthaus, Paul Jones, Rajesh Kumar, Keith Lantz, Jonathan Lennox, Mohamed Mostafa, Amy Pendleton, Colin Perkins, Mike Ramalho, Ravi Raviraj, Dan Romascanu, Albrecht Schwarz, Varun Singh, Tom Taylor, Dan Wing, and Hideaki Yamada. Thank you all, you're iconic 🥰
9. References 📚
9.1. 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.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006.
[RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for Real-time Transport Control Protocol (RTCP)-Based Feedback (RTP/SAVPF)", RFC 5124, February 2008.
[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008.
[RFC6709] Carpenter, B., Aboba, B., and S. Cheshire, "Design Considerations for Protocol Extensions", RFC 6709, September 2012.
[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.
9.2. 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.
[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.
[RFC6390] Clark, A. and B. Claise, "Guidelines for Considering New Performance Metric Development", BCP 170, RFC 6390, October 2011.
[RFC6792] Wu, Q., Hunt, G., and P. Arden, "Guidelines for Use of the RTP Monitoring Framework", RFC 6792, November 2012.
[RFC7003] Clark, A., Huang, R., and Q. Wu, Ed., "RTP Control Protocol(RTCP) Extended Report (XR) Block for Burst/Gap Discard Metric Reporting", RFC 7003, September 2013.
[RTPDUP] Begen, A. and C. Perkins, "Duplicating RTP Streams", Work in Progress, March 2013.
Appendix A. Metrics Represented Using the Template from RFC 6390 🧁
a. Number of Packets Discarded Metric 🍰
- Metric Name: Number of RTP packets discarded.
- Metric Description: Number of RTP packets discarded over the period covered by this report.
- Method of Measurement or Calculation: See Section 3.2, Discard Count definition.
- Units of Measurement: See Section 3.2, Discard Count definition.
- Measurement Point(s) with Potential Measurement Domain: See Section 3, 1st 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.
Authors' Addresses 🦋
Alan Clark
Telchemy Incorporated
2905 Premiere Parkway, Suite 280
Duluth, GA 30097
USA
EMail: alan.d.clark@telchemy.com
Glen Zorn
Network Zen
227/358 Thanon Sanphawut
Bang Na, Bangkok 10260
Thailand
Phone: +66 (0) 8-1000-4155
EMail: glenzorn@gmail.com
Qin Wu
Huawei
101 Software Avenue, Yuhua District
Nanjing, Jiangsu 210012
China
EMail: sunseawq@huawei.com📦 where this page comes from
- ietf: rfc7002 2013-09
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms