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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Outdated reference: A later version (-12) exists of draft-ietf-rmcat-rtp-cc-feedback-04 ** Downref: Normative reference to an Informational draft: draft-ietf-rmcat-rtp-cc-feedback (ref. 'I-D.ietf-rmcat-rtp-cc-feedback') == Outdated reference: A later version (-13) exists of draft-ietf-rmcat-nada-09 Summary: 1 error (**), 0 flaws (~~), 3 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IETF RMCAT Working Group Z. Sarker 3 Internet-Draft Ericsson AB 4 Intended status: Standards Track C. Perkins 5 Expires: June 26, 2019 University of Glasgow 6 V. Singh 7 callstats.io 8 M. Ramalho 9 Cisco Systems 10 December 23, 2018 12 RTP Control Protocol (RTCP) Feedback for Congestion Control 13 draft-ietf-avtcore-cc-feedback-message-03 15 Abstract 17 This document describes an RTCP feedback message intended to enable 18 congestion control for interactive real-time traffic using RTP. The 19 feedback message is designed for use with a sender-based congestion 20 control algorithm, in which the receiver of an RTP flow sends RTCP 21 feedback packets to the sender containing the information the sender 22 needs to perform congestion control. 24 Status of This Memo 26 This Internet-Draft is submitted in full conformance with the 27 provisions of BCP 78 and BCP 79. 29 Internet-Drafts are working documents of the Internet Engineering 30 Task Force (IETF). Note that other groups may also distribute 31 working documents as Internet-Drafts. The list of current Internet- 32 Drafts is at http://datatracker.ietf.org/drafts/current/. 34 Internet-Drafts are draft documents valid for a maximum of six months 35 and may be updated, replaced, or obsoleted by other documents at any 36 time. It is inappropriate to use Internet-Drafts as reference 37 material or to cite them other than as "work in progress." 39 This Internet-Draft will expire on June 26, 2019. 41 Copyright Notice 43 Copyright (c) 2018 IETF Trust and the persons identified as the 44 document authors. All rights reserved. 46 This document is subject to BCP 78 and the IETF Trust's Legal 47 Provisions Relating to IETF Documents 48 (http://trustee.ietf.org/license-info) in effect on the date of 49 publication of this document. Please review these documents 50 carefully, as they describe your rights and restrictions with respect 51 to this document. Code Components extracted from this document must 52 include Simplified BSD License text as described in Section 4.e of 53 the Trust Legal Provisions and are provided without warranty as 54 described in the Simplified BSD License. 56 Table of Contents 58 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 59 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 3. RTCP Feedback for Congestion Control . . . . . . . . . . . . 3 61 3.1. RTCP Congestion Control Feedback Report . . . . . . . . . 4 62 4. Feedback Frequency and Overhead . . . . . . . . . . . . . . . 6 63 5. SDP Signalling . . . . . . . . . . . . . . . . . . . . . . . 7 64 6. Relation to RFC 6679 . . . . . . . . . . . . . . . . . . . . 7 65 7. Design Rationale . . . . . . . . . . . . . . . . . . . . . . 8 66 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 67 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 68 10. Security Considerations . . . . . . . . . . . . . . . . . . . 9 69 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 70 11.1. Normative References . . . . . . . . . . . . . . . . . . 10 71 11.2. Informative References . . . . . . . . . . . . . . . . . 11 72 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 74 1. Introduction 76 For interactive real-time traffic, such as video conferencing flows, 77 the typical protocol choice is the Real-time Transport Protocol (RTP) 78 running over the User Datagram Protocol (UDP). RTP does not provide 79 any guarantee of Quality of Service (QoS), reliability, or timely 80 delivery, and expects the underlying transport protocol to do so. 81 UDP alone certainly does not meet that expectation. However, the RTP 82 Control Protocol (RTCP) provides a mechanism by which the receiver of 83 an RTP flow can periodically send transport and media quality metrics 84 to the sender of that RTP flow. This information can be used by the 85 sender to perform congestion control. In the absence of standardized 86 messages for this purpose, designers of congestion control algorithms 87 have developed proprietary RTCP messages that convey only those 88 parameters needed for their respective designs. As a direct result, 89 the different congestion control (i.e., rate adaptation) designs are 90 not interoperable. To enable algorithm evolution as well as 91 interoperability across designs (e.g., different rate adaptation 92 algorithms), it is highly desirable to have generic congestion 93 control feedback format. 95 To help achieve interoperability for unicast RTP congestion control, 96 this memo proposes a common RTCP feedback packet format that can be 97 used by NADA [I-D.ietf-rmcat-nada], SCReAM [RFC8298], Google 98 Congestion Control [I-D.ietf-rmcat-gcc] and Shared Bottleneck 99 Detection [RFC8382], and hopefully also by future RTP congestion 100 control algorithms. 102 2. Terminology 104 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 105 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 106 document are to be interpreted as described in [RFC2119]. 108 In addition the terminology defined in [RFC3550], [RFC3551], 109 [RFC3611], [RFC4585], and [RFC5506] applies. 111 3. RTCP Feedback for Congestion Control 113 Based on an analysis of NADA [I-D.ietf-rmcat-nada], SCReAM [RFC8298], 114 Google Congestion Control [I-D.ietf-rmcat-gcc] and Shared Bottleneck 115 Detection [RFC8382], the following per-RTP packet congestion control 116 feedback information has been determined to be necessary: 118 o RTP sequence number: The receiver of an RTP flow needs to feedback 119 the sequence numbers of the received RTP packets to the sender, so 120 the sender can determine which packets were received and which 121 were lost. Packet loss is used as an indication of congestion by 122 many congestion control algorithms. 124 o Packet Arrival Time: The receiver of an RTP flow needs to feedback 125 the arrival time of each RTP packet to the sender. Packet delay 126 and/or delay variation (jitter) is used as a congestion signal by 127 some congestion control algorithms. 129 o Packet Explicit Congestion Notification (ECN) Marking: If ECN 130 [RFC3168], [RFC6679] is used, it is necessary to feedback the 131 2-bit ECN mark in received RTP packets, indicating for each RTP 132 packet whether it is marked not-ECT, ECT(0), ECT(1), or ECN-CE. 133 If the path used by the RTP traffic is ECN capable the sender can 134 use Congestion Experienced (ECN-CE) marking information as a 135 congestion control signal. 137 Every RTP flow is identified by its Synchronization Source (SSRC) 138 identifier. Accordingly, the RTCP feedback format needs to group its 139 reports by SSRC, sending one report block per received SSRC. 141 As a practical matter, we note that host operating system (OS) 142 process interruptions can occur at inopportune times. Accordingly, 143 recording RTP packet send times at the sender, and the corresponding 144 RTP packet arrival times at the receiver, needs to be done with 145 deliberate care. This is because the time duration of host OS 146 interruptions can be significant relative to the precision desired in 147 the one-way delay estimates. Specifically, the send time needs to be 148 recorded at the last opportunity prior to transmitting the RTP packet 149 at the sender, and the arrival time at the receiver needs to be 150 recorded at the earliest available opportunity. 152 3.1. RTCP Congestion Control Feedback Report 154 Congestion control feedback can be sent as part of a regular 155 scheduled RTCP report, or in an RTP/AVPF early feedback packet. If 156 sent as early feedback, congestion control feedback MAY be sent in a 157 non-compound RTCP packet [RFC5506] if the RTP/AVPF profile [RFC4585] 158 or the RTP/SAVPF profile [RFC5124] is used. 160 Irrespective of how it is transported, the congestion control 161 feedback is sent as a Transport Layer Feedback Message (RTCP packet 162 type 205). The format of this RTCP packet is shown in Figure 1: 164 0 1 2 3 165 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 1 166 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 167 |V=2|P| FMT=CCFB | PT = 205 | length | 168 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 169 | SSRC of RTCP packet sender | 170 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 171 | SSRC of 1st RTP Stream | 172 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 173 | begin_seq | num_reports | 174 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 175 |L|ECN| Arrival time offset | ... . 176 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 177 . . 178 . . 179 . . 180 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 181 | SSRC of nth RTP Stream | 182 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 183 | begin_seq | num_reports | 184 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 185 |L|ECN| Arrival time offset | ... | 186 . . 187 . . 188 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 189 | Report Timestamp (32bits) | 190 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 192 Figure 1: RTCP Congestion Control Feedback Packet Format 194 The first eight octets comprise a standard RTCP header, with PT=205 195 and FMT=CCFB indicating that this is a congestion control feedback 196 packet, and with the SSRC set to that of the sender of the RTCP 197 packet. (NOTE TO RFC EDITOR: please replace CCFB here and in the 198 above diagram with the IANA assigned RTCP feedback packet type, and 199 remove this note) 201 Section 6.1 of [RFC4585] requires the RTCP header to be followed by 202 the SSRC of the RTP flow being reported upon. Accordingly, the RTCP 203 header is followed by a report block for each SSRC from which RTP 204 packets have been received, followed by a Report Timestamp. 206 Each report block begins with the SSRC of the received RTP Stream on 207 which it is reporting. Following this, the report block contains a 208 16-bit packet metric block for each RTP packet with sequence number 209 in the range begin_seq to begin_seq+num_reports inclusive (calculated 210 using arithmetic modulo 65536 to account for possible sequence number 211 wrap-around). If the number of 16-bit packet metric blocks included 212 in the report block is not a multiple of two, then 16 bits of zero 213 padding MUST be added after the last packet metric block, to align 214 the end of the packet metric blocks with the next 32 bit boundary. 215 The value of num_reports MAY be zero, indicating that there are no 216 packet metric blocks included for that SSRC. Each report block MUST 217 NOT include more than 16384 packet metric blocks (i.e., it MUST NOT 218 report on more than one quarter of the sequence number space in a 219 single report). 221 The contents of each 16-bit packet metric block comprises the L, ECN, 222 and ATO fields are as follows: 224 o L (1 bit): is a boolean to indicate if the packet was received. 0 225 represents that the packet was not yet received and all the 226 subsequent bits (ECN and ATO) are also set to 0. 1 represent the 227 packet was received and the subsequent bits in the block need to 228 be parsed. 230 o ECN (2 bits): is the echoed ECN mark of the packet. These are set 231 to 00 if not received, or if ECN is not used. 233 o Arrival time offset (ATO, 13 bits): is the arrival time of the RTP 234 packet at the receiver, as an offset before the time represented 235 by the RTS field of this RTCP congestion control feedback report. 236 The ATO field is in units of 1/1024 seconds (this unit is chosen 237 to give exact offsets from the RTS field) so, for example, an ATO 238 value of 512 indicates that the corresponding RTP packet arrived 239 exactly half a second before the time instant represented by the 240 RTS field. If the measured value is greater than 8189/1024 241 seconds (the value that would be coded as 0x1FFD), the value 242 0x1FFE MUST be reported to indicate an over-range measurement. If 243 the measurement is unavailable, or if the arrival time of the RTP 244 packet is after the time represented by the RTS field, then an ATO 245 value of 0x1FFF MUST be reported for the packet. 247 The RTCP congestion control feedback report packet concludes with the 248 Report Timestamp field (RTS, 32 bits). This denotes the time instant 249 on which this packet is reporting, and is the instant from which the 250 arrival time offset values are calculated. The value of RTS field is 251 derived from the same clock used to generate the NTP timestamp field 252 in RTCP Sender Report (SR) packets. It is formatted as the middle 32 253 bits of an NTP format timestamp, as described in Section 4 of 254 [RFC3550]. 256 RTCP congestion control feedback packets SHOULD include a report 257 block for every active SSRC. The sequence number ranges reported on 258 in consecutive reports for a given SSRC will generally be contiguous, 259 but overlapping reports MAY be sent (and need to be sent in cases 260 where RTP packet reordering occurs across the boundary between 261 consecutive reports). If reports covering overlapping sequence 262 number ranges are sent, information in later reports updates that in 263 sent previous reports for RTP packets included in both reports. If 264 an RTP packet was reported as received in one report, that packet 265 MUST also be reported as received in any overlapping reports sent 266 later that cover its sequence number range. 268 If duplicate copies of a particular RTP packet are received, then the 269 arrival time of the first copy to arrive MUST be reported. If any of 270 the copies of the duplicated packet are ECN-CE marked, then an ECN-CE 271 mark MUST be reported that for packet; otherwise the ECN mark of the 272 first copy to arrive is reported. 274 If no packets are received from an SSRC in a reporting interval, a 275 report block MAY be sent with begin_seq set to the highest sequence 276 number previously received from that SSRC and num_reports set to zero 277 (or, the report can simply to omitted). The corresponding SR/RR 278 packet will have a non-increased extended highest sequence number 279 received field that will inform the sender that no packets have been 280 received, but it can ease processing to have that information 281 available in the congestion control feedback reports too. 283 4. Feedback Frequency and Overhead 285 There is a trade-off between speed and accuracy of reporting, and the 286 overhead of the reports. [I-D.ietf-rmcat-rtp-cc-feedback] discusses 287 this trade-off, suggests desirable RTCP feedback rates, and provides 288 guidance on how to configure the RTCP bandwidth fraction, etc., to 289 make appropriate use of the reporting block described in this memo. 291 Specifications for RTP congestion control algorithms can also provide 292 guidance. 294 It is a general understanding that the congestion control algorithms 295 will work better with more frequent feedback - per packet feedback. 296 However, RTCP bandwidth and transmission rules put some upper limits 297 on how frequently the RTCP feedback messages can be send from the RTP 298 receiver to the RTP sender. It has been shown 299 [I-D.ietf-rmcat-rtp-cc-feedback] that in most cases a per frame 300 feedback is a reasonable assumption on how frequent the RTCP feedback 301 messages can be transmitted. It has also been noted that even if a 302 higher frequency of feedback is desired it is not viable if the 303 feedback messages starts to compete against the RTP traffic on the 304 feedback path during congestion period. Analyzing the feedback 305 interval requirement [feedback-requirements] it can be seen that the 306 candidate algorithms can perform with a feedback interval range of 307 50-200ms. A value within this range need to be negotiated at session 308 setup. 310 5. SDP Signalling 312 A new "ack" feedback parameter, "ccfb", is defined for use with the 313 "a=rtcp-fb:" SDP extension to indicate the use of the RTP Congestion 314 Control feedback packet format defined in Section 3. The ABNF 315 definition of this SDP parameter extension is: 317 rtcp-fb-ack-param = 318 rtcp-fb-ack-param =/ ccfb-par 319 ccfb-par = SP "ccfb" 321 The offer/answer rules for these SDP feedback parameters are 322 specified in Section 4.2 of the RTP/AVPF profile [RFC4585]. When 323 used with "ccfb" feedback, the wildcard payload type ("*") MUST be 324 used. 326 6. Relation to RFC 6679 328 Use of Explicit Congestion Notification (ECN) with RTP is described 329 in [RFC6679]. That specifies how to negotiate the use of ECN with 330 RTP, and defines an RTCP ECN Feedback Packet to carry ECN feedback 331 reports. It uses an SDP "a=ecn-capaable-rtp:" attribute to negotiate 332 use of ECN, and the "a=rtcp-fb:" attributes with the "nack" parameter 333 "ecn" to negotiate the use of RTCP ECN Feedback Packets. 335 The RTCP ECN Feedback Packet is not useful when ECN is used with the 336 RTP Congestion Control Feedback Packet defined in this memo since it 337 provides duplicate information. Accordingly, when congestion control 338 feedback is to be used with RTP and ECN, the SDP offer generated MUST 339 include an "a=ecn-capable-rtp:" attribute to negotiate ECN support, 340 along with an "a=rtcp-fb:" attribute with the "ack" parameter "ccfb" 341 to indicate that the RTP Congestion Control Feedback Packet is to be 342 used for feedback. The "a=rtcp-fb:" attribute MUST NOT include the 343 "nack" parameter "ecn", so the RTCP ECN Feedback Packet will not be 344 used. 346 7. Design Rationale 348 The primary function of RTCP SR/RR packets is to report statistics on 349 the reception of RTP packets. The reception report blocks sent in 350 these packets contain information about observed jitter, fractional 351 packet loss, and cumulative packet loss. It was intended that this 352 information could be used to support congestion control algorithms, 353 but experience has shown that it is not sufficient for that purpose. 354 An efficient congestion control algorithm requires more fine grained 355 information on per packet reception quality than is provided by SR/RR 356 packets to react effectively. 358 The Codec Control Messages for the RTP/AVPF profile [RFC5104] include 359 a Temporary Maximum Media Bit Rate (TMMBR) message. This is used to 360 convey a temporary maximum bit rate limitation from a receiver of RTP 361 packets to their sender. Even though it was not designed to replace 362 congestion control, TMMBR has been used as a means to do receiver 363 based congestion control where the session bandwidth is high enough 364 to send frequent TMMBR messages, especially when used with non- 365 compound RTCP packets [RFC5506]. This approach requires the receiver 366 of the RTP packets to monitor their reception, determine the level of 367 congestion, and recommend a maximum bit rate suitable for current 368 available bandwidth on the path; it also assumes that the RTP sender 369 can/will respect that bit rate. This is the opposite of the sender 370 based congestion control approach suggested in this memo, so TMMBR 371 cannot be used to convey the information needed for a sender based 372 congestion control. TMMBR could, however, be viewed a complementary 373 mechanism that can inform the sender of the receiver's current view 374 of acceptable maximum bit rate. 376 A number of RTCP eXtended Report (XR) blocks have previously been 377 defined to report details of packet loss, arrival times [RFC3611], 378 delay [RFC6843], and ECN marking [RFC6679]. It is possible to 379 combine several such XR blocks to report the detailed loss, arrival 380 time, and ECN marking marking information needed for effective 381 sender-based congestion control. However, the result has high 382 overhead both in terms of bandwidth and complexity, due to the need 383 to stack multiple reports. 385 Considering these issues, we believe it appropriate to design a new 386 RTCP feedback mechanism to convey information for sender based 387 congestion control algorithms. The new congestion control feedback 388 RTCP packet described in Section 3 provides such a mechanism. 390 8. Acknowledgements 392 This document is based on the outcome of a design team discussion in 393 the RTP Media Congestion Avoidance Techniques (RMCAT) working group. 394 The authors would like to thank David Hayes, Stefan Holmer, Randell 395 Jesup, Ingemar Johansson, Jonathan Lennox, Sergio Mena, Nils 396 Ohlmeier, Magnus Westerlund, and Xiaoqing Zhu for their valuable 397 feedback. 399 9. IANA Considerations 401 The IANA is requested to register one new RTP/AVPF Transport-Layer 402 Feedback Message in the table for FMT values for RTPFB Payload Types 403 [RFC4585] as defined in Section 3.1: 405 Name: CCFB 406 Long name: RTP Congestion Control Feedback 407 Value: (to be assigned by IANA) 408 Reference: (RFC number of this document, when published) 410 The IANA is also requested to register one new SDP "rtcp-fb" 411 attribute "ack" parameter, "ccfb", in the SDP ("ack" and "nack" 412 Attribute Values) registry: 414 Value name: ccfb 415 Long name: Congestion Control Feedback 416 Usable with: ack 417 Reference: (RFC number of this document, when published) 419 10. Security Considerations 421 The security considerations of the RTP specification [RFC3550], the 422 applicable RTP profile (e.g., [RFC3551], [RFC3711], or [RFC4585]), 423 and the RTP congestion control algorithm that is in use (e.g., 424 [I-D.ietf-rmcat-nada], [RFC8298], [I-D.ietf-rmcat-gcc], or [RFC8382]) 425 apply. 427 A receiver that intentionally generates inaccurate RTCP congestion 428 control feedback reports might be able trick the sender into sending 429 at a greater rate than the path can support, thereby congesting the 430 path. This will negatively impact the quality of experience of that 431 receiver. Since RTP is an unreliable transport, a sender can 432 intentionally leave a gap in the RTP sequence number space without 433 causing harm, to check that the receiver is correctly reporting 434 losses. 436 An on-path attacker that can modify RTCP congestion control feedback 437 packets can change the reports to trick the sender into sending at 438 either an excessively high or excessively low rate, leading to denial 439 of service. The secure RTCP profile [RFC3711] can be used to 440 authenticate RTCP packets to protect against this attack. 442 11. References 444 11.1. Normative References 446 [I-D.ietf-rmcat-rtp-cc-feedback] 447 Perkins, C., "RTP Control Protocol (RTCP) Feedback for 448 Congestion Control in Interactive Multimedia Conferences", 449 draft-ietf-rmcat-rtp-cc-feedback-04 (work in progress), 450 July 2018. 452 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 453 Requirement Levels", BCP 14, RFC 2119, 454 DOI 10.17487/RFC2119, March 1997, . 457 [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition 458 of Explicit Congestion Notification (ECN) to IP", 459 RFC 3168, DOI 10.17487/RFC3168, September 2001, 460 . 462 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 463 Jacobson, "RTP: A Transport Protocol for Real-Time 464 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 465 July 2003, . 467 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 468 Video Conferences with Minimal Control", STD 65, RFC 3551, 469 DOI 10.17487/RFC3551, July 2003, . 472 [RFC3611] Friedman, T., Ed., Caceres, R., Ed., and A. Clark, Ed., 473 "RTP Control Protocol Extended Reports (RTCP XR)", 474 RFC 3611, DOI 10.17487/RFC3611, November 2003, 475 . 477 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 478 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 479 RFC 3711, DOI 10.17487/RFC3711, March 2004, 480 . 482 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 483 "Extended RTP Profile for Real-time Transport Control 484 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 485 DOI 10.17487/RFC4585, July 2006, . 488 [RFC5124] Ott, J. and E. Carrara, "Extended Secure RTP Profile for 489 Real-time Transport Control Protocol (RTCP)-Based Feedback 490 (RTP/SAVPF)", RFC 5124, DOI 10.17487/RFC5124, February 491 2008, . 493 [RFC5506] Johansson, I. and M. Westerlund, "Support for Reduced-Size 494 Real-Time Transport Control Protocol (RTCP): Opportunities 495 and Consequences", RFC 5506, DOI 10.17487/RFC5506, April 496 2009, . 498 [RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P., 499 and K. Carlberg, "Explicit Congestion Notification (ECN) 500 for RTP over UDP", RFC 6679, DOI 10.17487/RFC6679, August 501 2012, . 503 11.2. Informative References 505 [feedback-requirements] 506 "RMCAT Feedback Requirements", 507 <://www.ietf.org/proceedings/95/slides/slides-95-rmcat- 508 1.pdf>. 510 [I-D.ietf-rmcat-gcc] 511 Holmer, S., Lundin, H., Carlucci, G., Cicco, L., and S. 512 Mascolo, "A Google Congestion Control Algorithm for Real- 513 Time Communication", draft-ietf-rmcat-gcc-02 (work in 514 progress), July 2016. 516 [I-D.ietf-rmcat-nada] 517 Zhu, X., *, R., Ramalho, M., Cruz, S., Jones, P., Fu, J., 518 and S. D'Aronco, "NADA: A Unified Congestion Control 519 Scheme for Real-Time Media", draft-ietf-rmcat-nada-09 520 (work in progress), August 2018. 522 [RFC5104] Wenger, S., Chandra, U., Westerlund, M., and B. Burman, 523 "Codec Control Messages in the RTP Audio-Visual Profile 524 with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104, 525 February 2008, . 527 [RFC6843] Clark, A., Gross, K., and Q. Wu, "RTP Control Protocol 528 (RTCP) Extended Report (XR) Block for Delay Metric 529 Reporting", RFC 6843, DOI 10.17487/RFC6843, January 2013, 530 . 532 [RFC8298] Johansson, I. and Z. Sarker, "Self-Clocked Rate Adaptation 533 for Multimedia", RFC 8298, DOI 10.17487/RFC8298, December 534 2017, . 536 [RFC8382] Hayes, D., Ed., Ferlin, S., Welzl, M., and K. Hiorth, 537 "Shared Bottleneck Detection for Coupled Congestion 538 Control for RTP Media", RFC 8382, DOI 10.17487/RFC8382, 539 June 2018, . 541 Authors' Addresses 543 Zaheduzzaman Sarker 544 Ericsson AB 545 Luleae 546 Sweden 548 Phone: +46107173743 549 Email: zaheduzzaman.sarker@ericsson.com 551 Colin Perkins 552 University of Glasgow 553 School of Computing Science 554 Glasgow G12 8QQ 555 United Kingdom 557 Email: csp@csperkins.org 559 Varun Singh 560 CALLSTATS I/O Oy 561 Annankatu 31-33 C 42 562 Helsinki 00100 563 Finland 565 Email: varun.singh@iki.fi 566 URI: http://www.callstats.io/ 567 Michael A. Ramalho 568 Cisco Systems, Inc. 569 6310 Watercrest Way Unit 203 570 Lakewood Ranch, FL 34202 571 USA 573 Phone: +1 919 476 2038 574 Email: mramalho@cisco.com