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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 RMCAT WG V. Singh 3 Internet-Draft J. Ott 4 Intended status: Informational Aalto University 5 Expires: January 26, 2015 July 25, 2014 7 Evaluating Congestion Control for Interactive Real-time Media 8 draft-ietf-rmcat-eval-criteria-02 10 Abstract 12 The Real-time Transport Protocol (RTP) is used to transmit media in 13 telephony and video conferencing applications. This document 14 describes the guidelines to evaluate new congestion control 15 algorithms for interactive point-to-point real-time media. 17 Status of This Memo 19 This Internet-Draft is submitted in full conformance with the 20 provisions of BCP 78 and BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF). Note that other groups may also distribute 24 working documents as Internet-Drafts. The list of current Internet- 25 Drafts is at http://datatracker.ietf.org/drafts/current/. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 This Internet-Draft will expire on January 26, 2015. 34 Copyright Notice 36 Copyright (c) 2014 IETF Trust and the persons identified as the 37 document authors. All rights reserved. 39 This document is subject to BCP 78 and the IETF Trust's Legal 40 Provisions Relating to IETF Documents 41 (http://trustee.ietf.org/license-info) in effect on the date of 42 publication of this document. Please review these documents 43 carefully, as they describe your rights and restrictions with respect 44 to this document. Code Components extracted from this document must 45 include Simplified BSD License text as described in Section 4.e of 46 the Trust Legal Provisions and are provided without warranty as 47 described in the Simplified BSD License. 49 Table of Contents 51 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 52 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 53 3. Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 3.1. RTP Log Format . . . . . . . . . . . . . . . . . . . . . 4 55 4. Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . 5 56 4.1. Avoiding Congestion Collapse . . . . . . . . . . . . . . 5 57 4.2. Stability . . . . . . . . . . . . . . . . . . . . . . . . 5 58 4.3. Media Traffic . . . . . . . . . . . . . . . . . . . . . . 5 59 4.4. Start-up Behaviour . . . . . . . . . . . . . . . . . . . 6 60 4.5. Diverse Environments . . . . . . . . . . . . . . . . . . 6 61 4.6. Varying Path Characteristics . . . . . . . . . . . . . . 6 62 4.7. Reacting to Transient Events or Interruptions . . . . . . 6 63 4.8. Fairness With Similar Cross-Traffic . . . . . . . . . . . 7 64 4.9. Impact on Cross-Traffic . . . . . . . . . . . . . . . . . 7 65 4.10. Extensions to RTP/RTCP . . . . . . . . . . . . . . . . . 7 66 5. Minimum Requirements for Evaluation . . . . . . . . . . . . . 7 67 6. Status of Proposals . . . . . . . . . . . . . . . . . . . . . 7 68 7. Security Considerations . . . . . . . . . . . . . . . . . . . 8 69 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 70 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8 71 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 72 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 73 11.1. Normative References . . . . . . . . . . . . . . . . . . 8 74 11.2. Informative References . . . . . . . . . . . . . . . . . 9 75 Appendix A. Application Trade-off . . . . . . . . . . . . . . . 10 76 A.1. Measuring Quality . . . . . . . . . . . . . . . . . . . . 10 77 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 10 78 B.1. Changes in draft-ietf-rmcat-eval-criteria-02 . . . . . . 10 79 B.2. Changes in draft-ietf-rmcat-eval-criteria-01 . . . . . . 10 80 B.3. Changes in draft-ietf-rmcat-eval-criteria-00 . . . . . . 10 81 B.4. Changes in draft-singh-rmcat-cc-eval-04 . . . . . . . . . 10 82 B.5. Changes in draft-singh-rmcat-cc-eval-03 . . . . . . . . . 11 83 B.6. Changes in draft-singh-rmcat-cc-eval-02 . . . . . . . . . 11 84 B.7. Changes in draft-singh-rmcat-cc-eval-01 . . . . . . . . . 11 85 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11 87 1. Introduction 89 This memo describes the guidelines to help with evaluating new 90 congestion control algorithms for interactive point-to-point real 91 time media. The requirements for the congestion control algorithm 92 are outlined in [I-D.ietf-rmcat-cc-requirements]). This document 93 builds upon previous work at the IETF: Specifying New Congestion 94 Control Algorithms [RFC5033] and Metrics for the Evaluation of 95 Congestion Control Algorithms [RFC5166]. 97 The guidelines proposed in the document are intended to help prevent 98 a congestion collapse, promote fair capacity usage and optimize the 99 media flow's throughput. Furthermore, the proposed algorithms are 100 expected to operate within the envelope of the circuit breakers 101 defined in [I-D.ietf-avtcore-rtp-circuit-breakers]. 103 This document only provides broad-level criteria for evaluating a new 104 congestion control algorithm and the working group should expect a 105 thorough scientific study to make its decision. The results of the 106 evaluation are not expected to be included within the internet-draft 107 but should be cited in the document. 109 2. Terminology 111 The terminology defined in RTP [RFC3550], RTP Profile for Audio and 112 Video Conferences with Minimal Control [RFC3551], RTCP Extended 113 Report (XR) [RFC3611], Extended RTP Profile for RTCP-based Feedback 114 (RTP/AVPF) [RFC4585] and Support for Reduced-Size RTCP [RFC5506] 115 apply. 117 3. Metrics 119 [RFC5166] describes the basic metrics for congestion control. 120 Metrics that are of interest for interactive multimedia are: 122 o Throughput. 124 o Minimizing oscillations in the transmission rate (stability) when 125 the end-to-end capacity varies slowly. 127 o Delay. 129 o Reactivity to transient events. 131 o Packet losses and discards. 133 o Section 2.1 of [RFC5166] discusses the tradeoff between 134 throughput, delay and loss. 136 Each experiment is expected to log every incoming and outgoing packet 137 (the RTP logging format is described in Section 3.1). The logging 138 can be done inside the application or at the endpoints using pcap 139 (packet capture, e.g., tcpdump, wireshark). The following are 140 calculated based on the information in the packet logs: 142 1. Sending rate, Receiver rate, Goodput 144 2. Packet delay 145 3. Packet loss 147 4. If using, retransmission or FEC: residual loss 149 5. Packets discarded from the playout or de-jitter buffer 151 6. Fairness or Unfairness: Experiments testing the performance of an 152 RMCAT proposal against any cross-traffic must define its expected 153 criteria for fairness. The "unfairness" test guideline (measured 154 at 1s intervals) is: 155 1. Does not trigger the circuit breaker. 156 2. No RMCAT stream achieves more than 3 times the average 157 throughput of the RMCAT stream with the lowest average 158 throughput, for a case when the competing streams have similar 159 RTTs. 160 3. RTT should not grow by a factor of 3 for the existing flows 161 when a new flow is added. 162 For example, see the test scenarios described in 163 [I-D.sarker-rmcat-eval-test]. 165 7. Convergence time: The time taken to reach a stable rate at 166 startup, after the available link capacity changes, or when new 167 flows get added to the bottleneck link. 169 8. Bandwidth Utilization, defined as ratio of the instantaneous 170 sending rate to the instantaneous bottleneck capacity. This 171 metric is useful when an RMCAT flow is by itself or competing 172 with similar cross-traffic. 174 From the logs the statistical measures (min, max, mean, standard 175 deviation and variance) for the whole duration or any specific part 176 of the session can be calculated. Also the metrics (sending rate, 177 receiver rate, goodput, latency) can be visualized in graphs as 178 variation over time, the measurements in the plot are at 1 second 179 intervals. Additionally, from the logs it is possible to plot the 180 histogram or CDF of packet delay. 182 [Open issue (1): Using Jain-fairness index (JFI) for measuring self- 183 fairness between RTP flows? measured at what intervals? visualized as 184 a CDF or a timeseries? Additionally: Use JFI for comparing fairness 185 between RTP and long TCP flows? ] 187 3.1. RTP Log Format 189 The log file is tab or comma separated containing the following 190 details: 192 Send or receive timestamp (unix) 193 RTP payload type 194 SSRC 195 RTP sequence no 196 RTP timestamp 197 marker bit 198 payload size 200 If the congestion control implements, retransmissions or FEC, the 201 evaluation should report both packet loss (before applying error- 202 resilience) and residual packet loss (after applying error- 203 resilience). 205 4. Guidelines 207 A congestion control algorithm should be tested in simulation or a 208 testbed environment, and the experiments should be repeated multiple 209 times to infer statistical significance. The following guidelines 210 are considered for evaluation: 212 4.1. Avoiding Congestion Collapse 214 The congestion control algorithm is expected to take an action, such 215 as reducing the sending rate, when it detects congestion. Typically, 216 it should intervene before the circuit breaker 217 [I-D.ietf-avtcore-rtp-circuit-breakers] is engaged. 219 Does the congestion control propose any changes to (or diverge from) 220 the circuit breaker conditions defined in 221 [I-D.ietf-avtcore-rtp-circuit-breakers]. 223 4.2. Stability 225 The congestion control should be assessed for its stability when the 226 path characteristics do not change over time. Changing the media 227 encoding rate estimate too often or by too much may adversely affect 228 the application layer performance. 230 4.3. Media Traffic 232 The congestion control algorithm should be assessed with different 233 types of media behavior, i.e., the media should contain idle and 234 data-limited periods. For example, periods of silence for audio, 235 varying amount of motion for video, or bursty nature of I-frames. 237 The evaluation may be done in two stages. In the first stage, the 238 endpoint generates traffic at the rate calculated by the congestion 239 controller. In the second stage, real codecs or models of video 240 codecs are used to mimic application-limited data periods and varying 241 video frame sizes. 243 4.4. Start-up Behaviour 245 The congestion control algorithm should be assessed with different 246 start-rates. The main reason is to observe the behavior of the 247 congestion control in different test scenarios, such as when 248 competing with varying amount of cross-traffic or how quickly does 249 the congestion control algorithm achieve a stable sending rate. 251 4.5. Diverse Environments 253 The congestion control algorithm should be assessed in heterogeneous 254 environments, containing both wired and wireless paths. Examples of 255 wireless access technologies are: 802.11, GPRS, HSPA, or LTE. One of 256 the main challenges of the wireless environments for the congestion 257 control algorithm is to distinguish between congestion induced loss 258 and transmission (bit-error) loss. Congestion control algorithms may 259 incorrectly identify transmission loss as congestion loss and reduce 260 the media encoding rate by too much, which may cause oscillatory 261 behavior and deteriorate the users' quality of experience. 262 Furthermore, packet loss may induce additional delay in networks with 263 wireless paths due to link-layer retransmissions. 265 4.6. Varying Path Characteristics 267 The congestion control algorithm should be evaluated for a range of 268 path characteristics such as, different end-to-end capacity and 269 latency, varying amount of cross traffic on a bottleneck link and a 270 router's queue length. For the moment, only DropTail queues are 271 used. However, if new Active Queue Management (AQM) schemes become 272 available, the performance of the congestion control algorithm should 273 be again evaluated. 275 In an experiment, if the media only flows in a single direction, the 276 feedback path should also be tested with varying amounts of 277 impairments. 279 The main motivation for the previous and current criteria is to 280 identify situations in which the proposed congestion control is less 281 performant. 283 4.7. Reacting to Transient Events or Interruptions 285 The congestion control algorithm should be able to handle changes in 286 end-to-end capacity and latency. Latency may change due to route 287 updates, link failures, handovers etc. In mobile environment the 288 end-to-end capacity may vary due to the interference, fading, 289 handovers, etc. In wired networks the end-to-end capacity may vary 290 due to changes in resource reservation. 292 4.8. Fairness With Similar Cross-Traffic 294 The congestion control algorithm should be evaluated when competing 295 with other RTP flows using the same or another candidate congestion 296 control algorithm. The proposal should highlight the bottleneck 297 capacity share of each RTP flow. 299 4.9. Impact on Cross-Traffic 301 The congestion control algorithm should be evaluated when competing 302 with standard TCP. Short TCP flows may be considered as transient 303 events and the RTP flow may give way to the short TCP flow to 304 complete quickly. However, long-lived TCP flows may starve out the 305 RTP flow depending on router queue length. 307 The proposal should also measure the impact on varied number of 308 cross-traffic sources, i.e., few and many competing flows, or mixing 309 various amounts of TCP and similar cross-traffic. 311 4.10. Extensions to RTP/RTCP 313 The congestion control algorithm should indicate if any protocol 314 extensions are required to implement it and should carefully describe 315 the impact of the extension. 317 5. Minimum Requirements for Evaluation 319 The minimal requirements for RMCAT proposals is to produce or present 320 results for the test scenarios described in Section 5 of 321 [I-D.sarker-rmcat-eval-test] (Basic Test Cases). 323 6. Status of Proposals 325 Congestion control algorithms are expected to be published as 326 "Experimental" documents until they are shown to be safe to deploy. 327 An algorithm published as a draft should be experimented in 328 simulation, or a controlled environment (testbed) to show its 329 applicability. Every congestion control algorithm should include a 330 note describing the environments in which the algorithm is tested and 331 safe to deploy. It is possible that an algorithm is not recommended 332 for certain environments or perform sub-optimally for the user. 334 [Editor's Note: Should there be a distinction between "Informational" 335 and "Experimental" drafts for congestion control algorithms in RMCAT. 337 [RFC5033] describes Informational proposals as algorithms that are 338 not safe for deployment but are proposals to experiment with in 339 simulation/testbeds. While Experimental algorithms are ones that are 340 deemed safe in some environments but require a more thorough 341 evaluation (from the community).] 343 7. Security Considerations 345 Security issues have not been discussed in this memo. 347 8. IANA Considerations 349 There are no IANA impacts in this memo. 351 9. Contributors 353 The content and concepts within this document are a product of the 354 discussion carried out in the Design Team. 356 Michael Ramalho provided the text for a specific scenario, which is 357 now covered in [I-D.sarker-rmcat-eval-test]. 359 10. Acknowledgements 361 Much of this document is derived from previous work on congestion 362 control at the IETF. 364 The authors would like to thank Harald Alvestrand, Anna Brunstrom, 365 Luca De Cicco, Wesley Eddy, Lars Eggert, Kevin Gross, Vinayak Hegde, 366 Stefan Holmer, Randell Jesup, Karen Nielsen, Piers O'Hanlon, Colin 367 Perkins, Michael Ramalho, Zaheduzzaman Sarker, Timothy B. Terriberry, 368 Michael Welzl, and Mo Zanaty for providing valuable feedback on 369 earlier versions of this draft. Additionally, also thank the 370 participants of the design team for their comments and discussion 371 related to the evaluation criteria. 373 11. References 375 11.1. Normative References 377 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 378 Jacobson, "RTP: A Transport Protocol for Real-Time 379 Applications", STD 64, RFC 3550, July 2003. 381 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 382 Video Conferences with Minimal Control", STD 65, RFC 3551, 383 July 2003. 385 [RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control 386 Protocol Extended Reports (RTCP XR)", RFC 3611, November 387 2003. 389 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 390 "Extended RTP Profile for Real-time Transport Control 391 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July 392 2006. 394 [RFC5506] Johansson, I. and M. Westerlund, "Support for Reduced-Size 395 Real-Time Transport Control Protocol (RTCP): Opportunities 396 and Consequences", RFC 5506, April 2009. 398 [I-D.ietf-rmcat-cc-requirements] 399 Jesup, R., "Congestion Control Requirements For RMCAT", 400 draft-ietf-rmcat-cc-requirements-02 (work in progress), 401 February 2014. 403 [I-D.ietf-avtcore-rtp-circuit-breakers] 404 Perkins, C. and V. Singh, "Multimedia Congestion Control: 405 Circuit Breakers for Unicast RTP Sessions", draft-ietf- 406 avtcore-rtp-circuit-breakers-05 (work in progress), 407 February 2014. 409 11.2. Informative References 411 [RFC5033] Floyd, S. and M. Allman, "Specifying New Congestion 412 Control Algorithms", BCP 133, RFC 5033, August 2007. 414 [RFC5166] Floyd, S., "Metrics for the Evaluation of Congestion 415 Control Mechanisms", RFC 5166, March 2008. 417 [RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion 418 Control", RFC 5681, September 2009. 420 [I-D.sarker-rmcat-eval-test] 421 Sarker, Z., Singh, V., Zhu, X., and M. Ramalho, "Test 422 Cases for Evaluating RMCAT Proposals", draft-sarker-rmcat- 423 eval-test-00 (work in progress), February 2014. 425 [SA4-EVAL] 426 R1-081955, 3GPP., "LTE Link Level Throughput Data for SA4 427 Evaluation Framework", 3GPP R1-081955, 5 2008. 429 [SA4-LR] S4-050560, 3GPP., "Error Patterns for MBMS Streaming over 430 UTRAN and GERAN", 3GPP S4-050560, 5 2008. 432 [TCP-eval-suite] 433 Lachlan, A., Marcondes, C., Floyd, S., Dunn, L., Guillier, 434 R., Gang, W., Eggert, L., Ha, S., and I. Rhee, "Towards a 435 Common TCP Evaluation Suite", Proc. PFLDnet. 2008, August 436 2008. 438 Appendix A. Application Trade-off 440 Application trade-off is yet to be defined. see RMCAT requirements 441 [I-D.ietf-rmcat-cc-requirements] document. Perhaps each experiment 442 should define the application's expectation or trade-off. 444 A.1. Measuring Quality 446 No quality metric is defined for performance evaluation, it is 447 currently an open issue. However, there is consensus that congestion 448 control algorithm should be able to show that it is useful for 449 interactive video by performing analysis using a real codec and video 450 sequences. 452 Appendix B. Change Log 454 Note to the RFC-Editor: please remove this section prior to 455 publication as an RFC. 457 B.1. Changes in draft-ietf-rmcat-eval-criteria-02 459 o Incorporated fairness test as a working test. 461 o Updated text on mimimum evaluation requirements. 463 B.2. Changes in draft-ietf-rmcat-eval-criteria-01 465 o Removed Appendix B. 467 o Removed Section on Evaluation Parameters. 469 B.3. Changes in draft-ietf-rmcat-eval-criteria-00 471 o Updated references. 473 o Resubmitted as WG draft. 475 B.4. Changes in draft-singh-rmcat-cc-eval-04 477 o Incorporate feedback from IETF 87, Berlin. 479 o Clarified metrics: convergence time, bandwidth utilization. 481 o Changed fairness criteria to fairness test. 483 o Added measuring pre- and post-repair loss. 485 o Added open issue of measuring video quality to appendix. 487 o clarified use of DropTail and AQM. 489 o Updated text in "Minimum Requirements for Evaluation" 491 B.5. Changes in draft-singh-rmcat-cc-eval-03 493 o Incorporate the discussion within the design team. 495 o Added a section on evaluation parameters, it describes the flow 496 and network characteristics. 498 o Added Appendix with self-fairness experiment. 500 o Changed bottleneck parameters from a proposal to an example set. 502 o 504 B.6. Changes in draft-singh-rmcat-cc-eval-02 506 o Added scenario descriptions. 508 B.7. Changes in draft-singh-rmcat-cc-eval-01 510 o Removed QoE metrics. 512 o Changed stability to steady-state. 514 o Added measuring impact against few and many flows. 516 o Added guideline for idle and data-limited periods. 518 o Added reference to TCP evaluation suite in example evaluation 519 scenarios. 521 Authors' Addresses 522 Varun Singh 523 Aalto University 524 School of Electrical Engineering 525 Otakaari 5 A 526 Espoo, FIN 02150 527 Finland 529 Email: varun@comnet.tkk.fi 530 URI: http://www.netlab.tkk.fi/~varun/ 532 Joerg Ott 533 Aalto University 534 School of Electrical Engineering 535 Otakaari 5 A 536 Espoo, FIN 02150 537 Finland 539 Email: jo@comnet.tkk.fi