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Versions: (draft-singh-rmcat-cc-eval) 00 01 02 03 04 05 06 07 08

RMCAT WG                                                        V. Singh
Internet-Draft                                                    J. Ott
Intended status: Informational                          Aalto University
Expires: January 26, 2015                                  July 25, 2014


     Evaluating Congestion Control for Interactive Real-time Media
                   draft-ietf-rmcat-eval-criteria-02

Abstract

   The Real-time Transport Protocol (RTP) is used to transmit media in
   telephony and video conferencing applications.  This document
   describes the guidelines to evaluate new congestion control
   algorithms for interactive point-to-point real-time media.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 26, 2015.

Copyright Notice

   Copyright (c) 2014 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
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   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 are provided without warranty as
   described in the Simplified BSD License.




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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Metrics . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  RTP Log Format  . . . . . . . . . . . . . . . . . . . . .   4
   4.  Guidelines  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Avoiding Congestion Collapse  . . . . . . . . . . . . . .   5
     4.2.  Stability . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.3.  Media Traffic . . . . . . . . . . . . . . . . . . . . . .   5
     4.4.  Start-up Behaviour  . . . . . . . . . . . . . . . . . . .   6
     4.5.  Diverse Environments  . . . . . . . . . . . . . . . . . .   6
     4.6.  Varying Path Characteristics  . . . . . . . . . . . . . .   6
     4.7.  Reacting to Transient Events or Interruptions . . . . . .   6
     4.8.  Fairness With Similar Cross-Traffic . . . . . . . . . . .   7
     4.9.  Impact on Cross-Traffic . . . . . . . . . . . . . . . . .   7
     4.10. Extensions to RTP/RTCP  . . . . . . . . . . . . . . . . .   7
   5.  Minimum Requirements for Evaluation . . . . . . . . . . . . .   7
   6.  Status of Proposals . . . . . . . . . . . . . . . . . . . . .   7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .   8
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   8
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     11.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     11.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Appendix A.  Application Trade-off  . . . . . . . . . . . . . . .  10
     A.1.  Measuring Quality . . . . . . . . . . . . . . . . . . . .  10
   Appendix B.  Change Log . . . . . . . . . . . . . . . . . . . . .  10
     B.1.  Changes in draft-ietf-rmcat-eval-criteria-02  . . . . . .  10
     B.2.  Changes in draft-ietf-rmcat-eval-criteria-01  . . . . . .  10
     B.3.  Changes in draft-ietf-rmcat-eval-criteria-00  . . . . . .  10
     B.4.  Changes in draft-singh-rmcat-cc-eval-04 . . . . . . . . .  10
     B.5.  Changes in draft-singh-rmcat-cc-eval-03 . . . . . . . . .  11
     B.6.  Changes in draft-singh-rmcat-cc-eval-02 . . . . . . . . .  11
     B.7.  Changes in draft-singh-rmcat-cc-eval-01 . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   This memo describes the guidelines to help with evaluating new
   congestion control algorithms for interactive point-to-point real
   time media.  The requirements for the congestion control algorithm
   are outlined in [I-D.ietf-rmcat-cc-requirements]).  This document
   builds upon previous work at the IETF: Specifying New Congestion
   Control Algorithms [RFC5033] and Metrics for the Evaluation of
   Congestion Control Algorithms [RFC5166].




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   The guidelines proposed in the document are intended to help prevent
   a congestion collapse, promote fair capacity usage and optimize the
   media flow's throughput.  Furthermore, the proposed algorithms are
   expected to operate within the envelope of the circuit breakers
   defined in [I-D.ietf-avtcore-rtp-circuit-breakers].

   This document only provides broad-level criteria for evaluating a new
   congestion control algorithm and the working group should expect a
   thorough scientific study to make its decision.  The results of the
   evaluation are not expected to be included within the internet-draft
   but should be cited in the document.

2.  Terminology

   The terminology defined in RTP [RFC3550], RTP Profile for Audio and
   Video Conferences with Minimal Control [RFC3551], RTCP Extended
   Report (XR) [RFC3611], Extended RTP Profile for RTCP-based Feedback
   (RTP/AVPF) [RFC4585] and Support for Reduced-Size RTCP [RFC5506]
   apply.

3.  Metrics

   [RFC5166] describes the basic metrics for congestion control.
   Metrics that are of interest for interactive multimedia are:

   o  Throughput.

   o  Minimizing oscillations in the transmission rate (stability) when
      the end-to-end capacity varies slowly.

   o  Delay.

   o  Reactivity to transient events.

   o  Packet losses and discards.

   o  Section 2.1 of [RFC5166] discusses the tradeoff between
      throughput, delay and loss.

   Each experiment is expected to log every incoming and outgoing packet
   (the RTP logging format is described in Section 3.1).  The logging
   can be done inside the application or at the endpoints using pcap
   (packet capture, e.g., tcpdump, wireshark).  The following are
   calculated based on the information in the packet logs:

   1.  Sending rate, Receiver rate, Goodput

   2.  Packet delay



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   3.  Packet loss

   4.  If using, retransmission or FEC: residual loss

   5.  Packets discarded from the playout or de-jitter buffer

   6.  Fairness or Unfairness: Experiments testing the performance of an
       RMCAT proposal against any cross-traffic must define its expected
       criteria for fairness.  The "unfairness" test guideline (measured
       at 1s intervals) is:
       1.  Does not trigger the circuit breaker.
       2.  No RMCAT stream achieves more than 3 times the average
       throughput of the RMCAT stream with the lowest average
       throughput, for a case when the competing streams have similar
       RTTs.
       3.  RTT should not grow by a factor of 3 for the existing flows
       when a new flow is added.
       For example, see the test scenarios described in
       [I-D.sarker-rmcat-eval-test].

   7.  Convergence time: The time taken to reach a stable rate at
       startup, after the available link capacity changes, or when new
       flows get added to the bottleneck link.

   8.  Bandwidth Utilization, defined as ratio of the instantaneous
       sending rate to the instantaneous bottleneck capacity.  This
       metric is useful when an RMCAT flow is by itself or competing
       with similar cross-traffic.

   From the logs the statistical measures (min, max, mean, standard
   deviation and variance) for the whole duration or any specific part
   of the session can be calculated.  Also the metrics (sending rate,
   receiver rate, goodput, latency) can be visualized in graphs as
   variation over time, the measurements in the plot are at 1 second
   intervals.  Additionally, from the logs it is possible to plot the
   histogram or CDF of packet delay.

   [Open issue (1): Using Jain-fairness index (JFI) for measuring self-
   fairness between RTP flows? measured at what intervals? visualized as
   a CDF or a timeseries?  Additionally: Use JFI for comparing fairness
   between RTP and long TCP flows? ]

3.1.  RTP Log Format

   The log file is tab or comma separated containing the following
   details:





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           Send or receive timestamp (unix)
           RTP payload type
           SSRC
           RTP sequence no
           RTP timestamp
           marker bit
           payload size

   If the congestion control implements, retransmissions or FEC, the
   evaluation should report both packet loss (before applying error-
   resilience) and residual packet loss (after applying error-
   resilience).

4.  Guidelines

   A congestion control algorithm should be tested in simulation or a
   testbed environment, and the experiments should be repeated multiple
   times to infer statistical significance.  The following guidelines
   are considered for evaluation:

4.1.  Avoiding Congestion Collapse

   The congestion control algorithm is expected to take an action, such
   as reducing the sending rate, when it detects congestion.  Typically,
   it should intervene before the circuit breaker
   [I-D.ietf-avtcore-rtp-circuit-breakers] is engaged.

   Does the congestion control propose any changes to (or diverge from)
   the circuit breaker conditions defined in
   [I-D.ietf-avtcore-rtp-circuit-breakers].

4.2.  Stability

   The congestion control should be assessed for its stability when the
   path characteristics do not change over time.  Changing the media
   encoding rate estimate too often or by too much may adversely affect
   the application layer performance.

4.3.  Media Traffic

   The congestion control algorithm should be assessed with different
   types of media behavior, i.e., the media should contain idle and
   data-limited periods.  For example, periods of silence for audio,
   varying amount of motion for video, or bursty nature of I-frames.

   The evaluation may be done in two stages.  In the first stage, the
   endpoint generates traffic at the rate calculated by the congestion
   controller.  In the second stage, real codecs or models of video



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   codecs are used to mimic application-limited data periods and varying
   video frame sizes.

4.4.  Start-up Behaviour

   The congestion control algorithm should be assessed with different
   start-rates.  The main reason is to observe the behavior of the
   congestion control in different test scenarios, such as when
   competing with varying amount of cross-traffic or how quickly does
   the congestion control algorithm achieve a stable sending rate.

4.5.  Diverse Environments

   The congestion control algorithm should be assessed in heterogeneous
   environments, containing both wired and wireless paths.  Examples of
   wireless access technologies are: 802.11, GPRS, HSPA, or LTE.  One of
   the main challenges of the wireless environments for the congestion
   control algorithm is to distinguish between congestion induced loss
   and transmission (bit-error) loss.  Congestion control algorithms may
   incorrectly identify transmission loss as congestion loss and reduce
   the media encoding rate by too much, which may cause oscillatory
   behavior and deteriorate the users' quality of experience.
   Furthermore, packet loss may induce additional delay in networks with
   wireless paths due to link-layer retransmissions.

4.6.  Varying Path Characteristics

   The congestion control algorithm should be evaluated for a range of
   path characteristics such as, different end-to-end capacity and
   latency, varying amount of cross traffic on a bottleneck link and a
   router's queue length.  For the moment, only DropTail queues are
   used.  However, if new Active Queue Management (AQM) schemes become
   available, the performance of the congestion control algorithm should
   be again evaluated.

   In an experiment, if the media only flows in a single direction, the
   feedback path should also be tested with varying amounts of
   impairments.

   The main motivation for the previous and current criteria is to
   identify situations in which the proposed congestion control is less
   performant.

4.7.  Reacting to Transient Events or Interruptions

   The congestion control algorithm should be able to handle changes in
   end-to-end capacity and latency.  Latency may change due to route
   updates, link failures, handovers etc.  In mobile environment the



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   end-to-end capacity may vary due to the interference, fading,
   handovers, etc.  In wired networks the end-to-end capacity may vary
   due to changes in resource reservation.

4.8.  Fairness With Similar Cross-Traffic

   The congestion control algorithm should be evaluated when competing
   with other RTP flows using the same or another candidate congestion
   control algorithm.  The proposal should highlight the bottleneck
   capacity share of each RTP flow.

4.9.  Impact on Cross-Traffic

   The congestion control algorithm should be evaluated when competing
   with standard TCP.  Short TCP flows may be considered as transient
   events and the RTP flow may give way to the short TCP flow to
   complete quickly.  However, long-lived TCP flows may starve out the
   RTP flow depending on router queue length.

   The proposal should also measure the impact on varied number of
   cross-traffic sources, i.e., few and many competing flows, or mixing
   various amounts of TCP and similar cross-traffic.

4.10.  Extensions to RTP/RTCP

   The congestion control algorithm should indicate if any protocol
   extensions are required to implement it and should carefully describe
   the impact of the extension.

5.  Minimum Requirements for Evaluation

   The minimal requirements for RMCAT proposals is to produce or present
   results for the test scenarios described in Section 5 of
   [I-D.sarker-rmcat-eval-test] (Basic Test Cases).

6.  Status of Proposals

   Congestion control algorithms are expected to be published as
   "Experimental" documents until they are shown to be safe to deploy.
   An algorithm published as a draft should be experimented in
   simulation, or a controlled environment (testbed) to show its
   applicability.  Every congestion control algorithm should include a
   note describing the environments in which the algorithm is tested and
   safe to deploy.  It is possible that an algorithm is not recommended
   for certain environments or perform sub-optimally for the user.

   [Editor's Note: Should there be a distinction between "Informational"
   and "Experimental" drafts for congestion control algorithms in RMCAT.



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   [RFC5033] describes Informational proposals as algorithms that are
   not safe for deployment but are proposals to experiment with in
   simulation/testbeds.  While Experimental algorithms are ones that are
   deemed safe in some environments but require a more thorough
   evaluation (from the community).]

7.  Security Considerations

   Security issues have not been discussed in this memo.

8.  IANA Considerations

   There are no IANA impacts in this memo.

9.  Contributors

   The content and concepts within this document are a product of the
   discussion carried out in the Design Team.

   Michael Ramalho provided the text for a specific scenario, which is
   now covered in [I-D.sarker-rmcat-eval-test].

10.  Acknowledgements

   Much of this document is derived from previous work on congestion
   control at the IETF.

   The authors would like to thank Harald Alvestrand, Anna Brunstrom,
   Luca De Cicco, Wesley Eddy, Lars Eggert, Kevin Gross, Vinayak Hegde,
   Stefan Holmer, Randell Jesup, Karen Nielsen, Piers O'Hanlon, Colin
   Perkins, Michael Ramalho, Zaheduzzaman Sarker, Timothy B. Terriberry,
   Michael Welzl, and Mo Zanaty for providing valuable feedback on
   earlier versions of this draft.  Additionally, also thank the
   participants of the design team for their comments and discussion
   related to the evaluation criteria.

11.  References

11.1.  Normative References

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [RFC3551]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and
              Video Conferences with Minimal Control", STD 65, RFC 3551,
              July 2003.




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   [RFC3611]  Friedman, T., Caceres, R., and A. Clark, "RTP Control
              Protocol Extended Reports (RTCP XR)", RFC 3611, November
              2003.

   [RFC4585]  Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
              "Extended RTP Profile for Real-time Transport Control
              Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, July
              2006.

   [RFC5506]  Johansson, I. and M. Westerlund, "Support for Reduced-Size
              Real-Time Transport Control Protocol (RTCP): Opportunities
              and Consequences", RFC 5506, April 2009.

   [I-D.ietf-rmcat-cc-requirements]
              Jesup, R., "Congestion Control Requirements For RMCAT",
              draft-ietf-rmcat-cc-requirements-02 (work in progress),
              February 2014.

   [I-D.ietf-avtcore-rtp-circuit-breakers]
              Perkins, C. and V. Singh, "Multimedia Congestion Control:
              Circuit Breakers for Unicast RTP Sessions", draft-ietf-
              avtcore-rtp-circuit-breakers-05 (work in progress),
              February 2014.

11.2.  Informative References

   [RFC5033]  Floyd, S. and M. Allman, "Specifying New Congestion
              Control Algorithms", BCP 133, RFC 5033, August 2007.

   [RFC5166]  Floyd, S., "Metrics for the Evaluation of Congestion
              Control Mechanisms", RFC 5166, March 2008.

   [RFC5681]  Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
              Control", RFC 5681, September 2009.

   [I-D.sarker-rmcat-eval-test]
              Sarker, Z., Singh, V., Zhu, X., and M. Ramalho, "Test
              Cases for Evaluating RMCAT Proposals", draft-sarker-rmcat-
              eval-test-00 (work in progress), February 2014.

   [SA4-EVAL]
              R1-081955, 3GPP., "LTE Link Level Throughput Data for SA4
              Evaluation Framework", 3GPP R1-081955, 5 2008.

   [SA4-LR]   S4-050560, 3GPP., "Error Patterns for MBMS Streaming over
              UTRAN and GERAN", 3GPP S4-050560, 5 2008.





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   [TCP-eval-suite]
              Lachlan, A., Marcondes, C., Floyd, S., Dunn, L., Guillier,
              R., Gang, W., Eggert, L., Ha, S., and I. Rhee, "Towards a
              Common TCP Evaluation Suite", Proc. PFLDnet. 2008, August
              2008.

Appendix A.  Application Trade-off

   Application trade-off is yet to be defined. see RMCAT requirements
   [I-D.ietf-rmcat-cc-requirements] document.  Perhaps each experiment
   should define the application's expectation or trade-off.

A.1.  Measuring Quality

   No quality metric is defined for performance evaluation, it is
   currently an open issue.  However, there is consensus that congestion
   control algorithm should be able to show that it is useful for
   interactive video by performing analysis using a real codec and video
   sequences.

Appendix B.  Change Log

   Note to the RFC-Editor: please remove this section prior to
   publication as an RFC.

B.1.  Changes in draft-ietf-rmcat-eval-criteria-02

   o  Incorporated fairness test as a working test.

   o  Updated text on mimimum evaluation requirements.

B.2.  Changes in draft-ietf-rmcat-eval-criteria-01

   o  Removed Appendix B.

   o  Removed Section on Evaluation Parameters.

B.3.  Changes in draft-ietf-rmcat-eval-criteria-00

   o  Updated references.

   o  Resubmitted as WG draft.

B.4.  Changes in draft-singh-rmcat-cc-eval-04

   o  Incorporate feedback from IETF 87, Berlin.

   o  Clarified metrics: convergence time, bandwidth utilization.



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   o  Changed fairness criteria to fairness test.

   o  Added measuring pre- and post-repair loss.

   o  Added open issue of measuring video quality to appendix.

   o  clarified use of DropTail and AQM.

   o  Updated text in "Minimum Requirements for Evaluation"

B.5.  Changes in draft-singh-rmcat-cc-eval-03

   o  Incorporate the discussion within the design team.

   o  Added a section on evaluation parameters, it describes the flow
      and network characteristics.

   o  Added Appendix with self-fairness experiment.

   o  Changed bottleneck parameters from a proposal to an example set.

   o

B.6.  Changes in draft-singh-rmcat-cc-eval-02

   o  Added scenario descriptions.

B.7.  Changes in draft-singh-rmcat-cc-eval-01

   o  Removed QoE metrics.

   o  Changed stability to steady-state.

   o  Added measuring impact against few and many flows.

   o  Added guideline for idle and data-limited periods.

   o  Added reference to TCP evaluation suite in example evaluation
      scenarios.

Authors' Addresses










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   Varun Singh
   Aalto University
   School of Electrical Engineering
   Otakaari 5 A
   Espoo, FIN  02150
   Finland

   Email: varun@comnet.tkk.fi
   URI:   http://www.netlab.tkk.fi/~varun/


   Joerg Ott
   Aalto University
   School of Electrical Engineering
   Otakaari 5 A
   Espoo, FIN  02150
   Finland

   Email: jo@comnet.tkk.fi
































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