idnits 2.17.1 draft-singh-rmcat-cc-eval-01.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- No issues found here. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year -- The document date (October 22, 2012) is 4196 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- == Missing Reference: 'S1' is mentioned on line 246, but not defined == Missing Reference: 'S2' is mentioned on line 250, but not defined == Missing Reference: 'S3' is mentioned on line 256, but not defined == Missing Reference: 'S4' is mentioned on line 260, but not defined == Missing Reference: 'S5' is mentioned on line 265, but not defined == Outdated reference: A later version (-18) exists of draft-ietf-avtcore-rtp-circuit-breakers-00 Summary: 0 errors (**), 0 flaws (~~), 7 warnings (==), 1 comment (--). 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: April 25, 2013 October 22, 2012 7 Evaluating Congestion Control for Interactive Real-time Media. 8 draft-singh-rmcat-cc-eval-01.txt 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 April 25, 2013. 34 Copyright Notice 36 Copyright (c) 2012 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 52 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 53 3. Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 4. Guidelines . . . . . . . . . . . . . . . . . . . . . . . . . . 4 55 4.1. Avoiding Congestion Collapse . . . . . . . . . . . . . . . 4 56 4.2. Stability . . . . . . . . . . . . . . . . . . . . . . . . . 4 57 4.3. Media Traffic . . . . . . . . . . . . . . . . . . . . . . . 4 58 4.4. Diverse Environments . . . . . . . . . . . . . . . . . . . 5 59 4.5. Varying Path Characteristics . . . . . . . . . . . . . . . 5 60 4.6. Reacting to Transient Events or Interruptions . . . . . . . 5 61 4.7. Fairness With Similar Cross-Traffic . . . . . . . . . . . . 5 62 4.8. Impact on Cross-Traffic . . . . . . . . . . . . . . . . . . 6 63 4.9. Extensions to RTP/RTCP . . . . . . . . . . . . . . . . . . 6 64 5. Minimum Requirements for Evaluation . . . . . . . . . . . . . . 6 65 6. Example Evaluation Scenarios . . . . . . . . . . . . . . . . . 6 66 7. Status of Proposals . . . . . . . . . . . . . . . . . . . . . . 7 67 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 68 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8 69 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 70 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 71 11.1. Normative References . . . . . . . . . . . . . . . . . . . 8 72 11.2. Informative References . . . . . . . . . . . . . . . . . . 9 73 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . . 9 74 A.1. Changes in draft-singh-rmcat-cc-eval-01 . . . . . . . . . . 9 75 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 77 1. Introduction 79 This memo describes the guidelines to help with evaluating new 80 congestion control algorithms for interactive point-to-point real 81 time media. The requirements for the congestion control algorithm 82 are outlined in [I-D.jesup-rtp-congestion-reqs]). This document 83 builds upon previous work at the IETF: Specifying New Congestion 84 Control Algorithms [RFC5033] and Metrics for the Evaluation of 85 Congestion Control Algorithms [RFC5166]. 87 The guidelines proposed in the document are intended to prevent a 88 congestion collapse, promote fair capacity usage and optimize the 89 media flow's throughput, delay, loss and quality. Furthermore, the 90 proposed algorithms are expected to operate within the envelope of 91 the circuit breakers defined in 92 [I-D.ietf-avtcore-rtp-circuit-breakers]. 94 This document only provides broad-level criteria for evaluating a new 95 congestion control algorithm and the working group should expect a 96 thorough scientific study to make its decision. The results of the 97 evaluation are not expected to be included within the internet-draft 98 but should be cited in the document. 100 2. Terminology 102 The terminology defined in RTP [RFC3550], RTP Profile for Audio and 103 Video Conferences with Minimal Control [RFC3551], RTCP Extended 104 Report (XR) [RFC3611], Extended RTP Profile for RTCP-based Feedback 105 (RTP/AVPF) [RFC4585] and Support for Reduced-Size RTCP [RFC5506] 106 apply. 108 3. Metrics 110 [RFC5166] describes the basic metrics for congestion control. 111 Metrics that are important to interactive multimedia are: 113 * Delay 114 * Throughput 115 * Minimizing oscillations in encoding rate (stability) 116 * Reactivity to transient events 117 * Packet loss and discard rate 118 * Users' quality of experience 120 [Editor's Note: measurement interval and statistical measures 121 (min, max, mean, median) are yet to be specified.] 123 Section 2.1 of [RFC5166] discusses the tradeoff between throughput, 124 delay and loss. 126 (i) Bandwidth Utilization: is the ratio of the encoding rate to 127 the (available) end-to-end path capacity. 128 * Under-utilization: is the period of time when the endpoint's 129 encoding rate is lower than the end-to-end capacity, i.e., the 130 bandwidth utilization is less than 1. 131 * Overuse: is the period of time when the endpoint's encoding 132 rate is higher than the end-to-end capacity, i.e., the 133 bandwidth utilization is greater than 1. 134 * Steady-state: is the period of time when the endpoint's 135 encoding rate is relatively stable, i.e., the bandwidth 136 utilization is constant. 138 (ii) Packet Loss and Discard Rate. 140 (iii) Fair Share. 142 [Editor's Note: This metric should match the one defined in the 143 RMCAT requirements [I-D.jesup-rtp-congestion-reqs] document.] 145 4. Guidelines 147 A congestion control algorithm should be tested in simulation or a 148 testbed environment, and the experiments should be repeated multiple 149 times to infer statistical significance. The following guidelines 150 are considered for evaluation: 152 4.1. Avoiding Congestion Collapse 154 Does the congestion control propose any changes to (or diverge from) 155 the circuit breaker conditions defined in 156 [I-D.ietf-avtcore-rtp-circuit-breakers]. 158 4.2. Stability 160 The congestion control should be assessed for its stability when the 161 path characteristics do not change over time. Changing the media 162 encoding rate too often or by too much may adversely affect the 163 users' quality of experience. 165 4.3. Media Traffic 167 The congestion control algorithm should be assessed with different 168 types of media behavior, i.e., the media should contain idle and 169 data-limited periods. For example, periods of silence for audio or 170 varying amount of motion for video. 172 4.4. Diverse Environments 174 The congestion control algorithm should be assessed in heterogeneous 175 environments, containing both wired and wireless paths. Examples of 176 wireless access technologies are: 802.11x, HSPA, WCDMA, or GPRS. One 177 of the main challenges of the wireless environments is the inability 178 to distinguish congestion induced loss from transmission (bit-error) 179 loss. Congestion control algorithms may incorrectly identify 180 transmission loss as congestion loss and reduce the media encoding 181 rate too much, which may cause oscillatory behavior and deteriorate 182 the users' quality of experience. Furthermore, packet loss may 183 induce additional delay in networks with wireless paths due to link- 184 layer retransmissions. 186 4.5. Varying Path Characteristics 188 The congestion control algorithm should be evaluated for a range of 189 path characteristics such as, different end-to-end capacity and 190 latency, varying amount of cross traffic on a bottle-neck link and a 191 router's queue length. The main motivation for the previous and 192 current criteria is to determine under which circumstances will the 193 proposed congestion control algorithm break down and also determine 194 the operational range of the algorithm. 196 [Editor's Note: Different types of queueing mechanisms? Random Early 197 Detection or only DropTail?]. 199 4.6. Reacting to Transient Events or Interruptions 201 The congestion control algorithm should be able to handle changes in 202 end-to-end capacity and latency. Latency may change due to route 203 updates, link failures, handovers etc. In mobile environment the 204 end-to-end capacity may vary due to the interference, fading, 205 handovers, etc. In wired networks the end-to-end capacity may vary 206 due to changes in resource reservation. 208 4.7. Fairness With Similar Cross-Traffic 210 The congestion control algorithm should be evaluated when competing 211 with other RTP flows using the same congestion control algorithm. 212 The proposal should highlight the bottleneck capacity share of each 213 RTP flow. 215 4.8. Impact on Cross-Traffic 217 The congestion control algorithm should be evaluated when competing 218 with standard TCP. Short TCP flows may be considered as transient 219 events and the RTP flow may give way to the short TCP flow to 220 complete quickly. However, long-lived TCP flows may starve out the 221 RTP flow depending on router queue length. In the latter case the 222 proposed congestion control for RTP should be as aggressive as 223 standard TCP [RFC5681]. 225 The proposal should also measure the impact on varied number of 226 cross-traffic sources, i.e., few and many competing flows, or mixing 227 various amounts of TCP and similar cross-traffic. 229 4.9. Extensions to RTP/RTCP 231 The congestion control algorithm should indicate if any protocol 232 extensions are required to implement it and should carefully describe 233 the impact of the extension. 235 5. Minimum Requirements for Evaluation 237 [Editor's Note: If needed, a minimum evaluation criteria can be based 238 on the above guidelines] 240 6. Example Evaluation Scenarios 242 In the scenarios listed below, all RTP flows are bi-directional and 243 point-to-point. [TCP-eval-suite] contains examples of TCP traffic 244 load and scenario settings. 246 [S1] RTP flow on a fixed link: This scenario evaluates the ramp-up 247 to the bottleneck capacity and the stability of the proposed 248 congestion control algorithm. 250 [S2] RTP flow on a variable capacity link: This scenario evaluates 251 the reactivity of the proposed congestion control algorithm to 252 transient network events due to interference and handovers in 253 mobile environments. Sample 3G bandwidth traces are available at 254 [3GPP.R1.081955]. 256 [S3] Fairness to RTP flows running the same congestion control 257 algorithm: This scenario shows if the proposed algorithm can share 258 the bottleneck link equitably, irrespective of number of flows. 260 [S4] Competing with long-lived TCP flows: In this scenario the 261 proposed algorithm is expected to be TCP-friendly, i.e., it should 262 neither starve out the competing TCP flows (causing a congestion 263 collapse) nor should it be starved out by TCP. 265 [S5] Competing with short TCP flows: Depending on the level of 266 statistical multiplexing on the bottleneck link, the proposed 267 algorithm may behave differently. If there are a few short TCP 268 flows then the proposed algorithm may observe these flows as 269 transient events and let them complete quickly. Alternatively, if 270 there are many short flows then the proposed algorithm may have to 271 compete with the flows as if they were long lived TCP flows. 273 [Editor's Note: definition of many and few short TCP flows may 274 depend on the bottleneck link capacity.] 276 [Editor's Note: clarify if media packets are generated using a 277 traffic generator.] 279 7. Status of Proposals 281 Congestion control algorithms are expected to be published as 282 "Experimental" documents until they are shown to be safe to deploy. 283 An algorithm published as a draft should be experimented in 284 simulation, or a controlled environment (testbed) to show its 285 applicability. Every congestion control algorithm should include a 286 note describing the environments in which the algorithm is tested and 287 safe to deploy. It is possible that an algorithm is not recommended 288 for certain environments or perform sub-optimally for the user. 290 [Editor's Note: Should there be a distinction between "Informational" 291 and "Experimental" drafts for congestion control algorithms in RMCAT. 292 [RFC5033] describes Informational proposals as algorithms that are 293 not safe for deployment but are proposals to experiment with in 294 simulation/testbeds. While Experimental algorithms are ones that are 295 deemed safe in some environments but require a more thorough 296 evaluation (from the community).] 298 8. Security Considerations 300 Security issues have not been discussed in this memo. 302 9. IANA Considerations 304 There are no IANA impacts in this memo. 306 10. Acknowledgements 308 Much of this document is derived from previous work on congestion 309 control at the IETF. 311 The authors would like to thank Harald Alvestrand, Luca De Cicco, 312 Wesley Eddy, Lars Eggert, Stefan Holmer, Randell Jesup, Piers 313 O'Hanlon, Timothy B. Terriberry and Michael Welzl for providing 314 valuable feedback on earlier versions of this draft. 316 11. References 318 11.1. Normative References 320 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 321 Jacobson, "RTP: A Transport Protocol for Real-Time 322 Applications", STD 64, RFC 3550, July 2003. 324 [RFC3551] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and 325 Video Conferences with Minimal Control", STD 65, RFC 3551, 326 July 2003. 328 [RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control 329 Protocol Extended Reports (RTCP XR)", RFC 3611, 330 November 2003. 332 [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, 333 "Extended RTP Profile for Real-time Transport Control 334 Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, 335 July 2006. 337 [RFC5506] Johansson, I. and M. Westerlund, "Support for Reduced-Size 338 Real-Time Transport Control Protocol (RTCP): Opportunities 339 and Consequences", RFC 5506, April 2009. 341 [I-D.jesup-rtp-congestion-reqs] 342 Jesup, R. and H. Alvestrand, "Congestion Control 343 Requirements For Real Time Media", 344 draft-jesup-rtp-congestion-reqs-00 (work in progress), 345 March 2012. 347 [I-D.ietf-avtcore-rtp-circuit-breakers] 348 Perkins, C. and V. Singh, "RTP Congestion Control: Circuit 349 Breakers for Unicast Sessions", 350 draft-ietf-avtcore-rtp-circuit-breakers-00 (work in 351 progress), October 2012. 353 11.2. Informative References 355 [RFC5033] Floyd, S. and M. Allman, "Specifying New Congestion 356 Control Algorithms", BCP 133, RFC 5033, August 2007. 358 [RFC5166] Floyd, S., "Metrics for the Evaluation of Congestion 359 Control Mechanisms", RFC 5166, March 2008. 361 [RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion 362 Control", RFC 5681, September 2009. 364 [3GPP.R1.081955] 365 R1-081955, 3GPP., "LTE Link Level Throughput Data for SA4 366 Evaluation Framework", 3GPP R1-081955, 5 2008. 368 [TCP-eval-suite] 369 Lachlan, A., Marcondes, C., Floyd, S., Dunn, L., Guillier, 370 R., Gang, W., Eggert, L., Ha, S., and I. Rhee, "Towards a 371 Common TCP Evaluation Suite", Proc. PFLDnet. 2008, 372 August 2008. 374 Appendix A. Change Log 376 Note to the RFC-Editor: please remove this section prior to 377 publication as an RFC. 379 A.1. Changes in draft-singh-rmcat-cc-eval-01 381 o Removed QoE metrics. 382 o Changed stability to steady-state. 383 o Added measuring impact against few and many flows. 384 o Added guideline for idle and data-limited periods. 385 o Added reference to TCP evaluation suite in example evaluation 386 scenarios. 388 Authors' Addresses 390 Varun Singh 391 Aalto University 392 School of Electrical Engineering 393 Otakaari 5 A 394 Espoo, FIN 02150 395 Finland 397 Email: varun@comnet.tkk.fi 398 URI: http://www.netlab.tkk.fi/~varun/ 400 Joerg Ott 401 Aalto University 402 School of Electrical Engineering 403 Otakaari 5 A 404 Espoo, FIN 02150 405 Finland 407 Email: jo@comnet.tkk.fi