--- 1/draft-ietf-rmcat-coupled-cc-04.txt 2016-12-07 06:13:39.747669989 -0800 +++ 2/draft-ietf-rmcat-coupled-cc-05.txt 2016-12-07 06:13:39.815671667 -0800 @@ -1,47 +1,48 @@ RTP Media Congestion Avoidance S. Islam Techniques (rmcat) M. Welzl Internet-Draft S. Gjessing Intended status: Experimental University of Oslo -Expires: May 4, 2017 October 31, 2016 +Expires: June 10, 2017 December 7, 2016 Coupled congestion control for RTP media - draft-ietf-rmcat-coupled-cc-04 + draft-ietf-rmcat-coupled-cc-05 Abstract When multiple congestion controlled RTP sessions traverse the same network bottleneck, combining their controls can improve the total on-the-wire behavior in terms of delay, loss and fairness. This document describes such a method for flows that have the same sender, in a way that is as flexible and simple as possible while minimizing the amount of changes needed to existing RTP applications. It - specifies how to apply the method for both the NADA and Google + specifies how to apply the method for the NADA congestion control + algorithm, and provides suggestions on how to apply it to other congestion control algorithms. 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 May 4, 2017. + This Internet-Draft will expire on June 10, 2017. Copyright Notice Copyright (c) 2016 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 @@ -58,46 +59,47 @@ 3. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Architectural overview . . . . . . . . . . . . . . . . . . . . 4 5. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. SBD . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. FSE . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 5.3. Flows . . . . . . . . . . . . . . . . . . . . . . . . . . 8 5.3.1. Example algorithm 1 - Active FSE . . . . . . . . . . . 8 5.3.2. Example algorithm 2 - Conservative Active FSE . . . . 9 6. Application . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1. NADA . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 - 6.2. GCC . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 - 6.3. General recommendations . . . . . . . . . . . . . . . . . 11 - 7. Expected feedback from experiments . . . . . . . . . . . . . . 11 + 6.2. General recommendations . . . . . . . . . . . . . . . . . 11 + 7. Expected feedback from experiments . . . . . . . . . . . . . . 12 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 10. Security Considerations . . . . . . . . . . . . . . . . . . . 12 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 11.1. Normative References . . . . . . . . . . . . . . . . . . . 13 11.2. Informative References . . . . . . . . . . . . . . . . . . 13 - Appendix A. Scheduling . . . . . . . . . . . . . . . . . . . . . 15 - Appendix B. Example algorithm - Passive FSE . . . . . . . . . . . 15 - B.1. Example operation (passive) . . . . . . . . . . . . . . . 18 - Appendix C. Change log . . . . . . . . . . . . . . . . . . . . . 22 - C.1. draft-welzl-rmcat-coupled-cc . . . . . . . . . . . . . . . 22 - C.1.1. Changes from -00 to -01 . . . . . . . . . . . . . . . 22 - C.1.2. Changes from -01 to -02 . . . . . . . . . . . . . . . 22 - C.1.3. Changes from -02 to -03 . . . . . . . . . . . . . . . 22 - C.1.4. Changes from -03 to -04 . . . . . . . . . . . . . . . 22 - C.1.5. Changes from -04 to -05 . . . . . . . . . . . . . . . 22 - C.2. draft-ietf-rmcat-coupled-cc . . . . . . . . . . . . . . . 23 - C.2.1. Changes from draft-welzl-rmcat-coupled-cc-05 . . . . . 23 - C.2.2. Changes from -00 to -01 . . . . . . . . . . . . . . . 23 - C.2.3. Changes from -01 to -02 . . . . . . . . . . . . . . . 23 - C.2.4. Changes from -02 to -03 . . . . . . . . . . . . . . . 23 - C.2.5. Changes from -03 to -04 . . . . . . . . . . . . . . . 23 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23 + Appendix A. Application to GCC . . . . . . . . . . . . . . . . . 15 + Appendix B. Scheduling . . . . . . . . . . . . . . . . . . . . . 15 + Appendix C. Example algorithm - Passive FSE . . . . . . . . . . . 15 + C.1. Example operation (passive) . . . . . . . . . . . . . . . 18 + Appendix D. Change log . . . . . . . . . . . . . . . . . . . . . 22 + D.1. draft-welzl-rmcat-coupled-cc . . . . . . . . . . . . . . . 22 + D.1.1. Changes from -00 to -01 . . . . . . . . . . . . . . . 22 + D.1.2. Changes from -01 to -02 . . . . . . . . . . . . . . . 22 + D.1.3. Changes from -02 to -03 . . . . . . . . . . . . . . . 23 + D.1.4. Changes from -03 to -04 . . . . . . . . . . . . . . . 23 + D.1.5. Changes from -04 to -05 . . . . . . . . . . . . . . . 23 + D.2. draft-ietf-rmcat-coupled-cc . . . . . . . . . . . . . . . 23 + D.2.1. Changes from draft-welzl-rmcat-coupled-cc-05 . . . . . 23 + D.2.2. Changes from -00 to -01 . . . . . . . . . . . . . . . 23 + D.2.3. Changes from -01 to -02 . . . . . . . . . . . . . . . 23 + D.2.4. Changes from -02 to -03 . . . . . . . . . . . . . . . 24 + D.2.5. Changes from -03 to -04 . . . . . . . . . . . . . . . 24 + D.2.6. Changes from -04 to -05 . . . . . . . . . . . . . . . 24 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24 1. Introduction When there is enough data to send, a congestion controller must increase its sending rate until the path's capacity has been reached; depending on the controller, sometimes the rate is increased further, until packets are ECN-marked or dropped. This process inevitably creates undesirable queuing delay when multiple congestion controlled connections traverse the same network bottleneck. @@ -466,64 +468,63 @@ reference rate, it calculates a video target rate r_vin and a sending rate for the flows, r_send. When applying the FSE to NADA, the UPDATE function call described in Section 5.3 gives the FSE NADA's reference rate r_ref. The recommended algorithm for NADA is the Active FSE in Section 5.3.1. In step 3 (c), when the FSE_R(i) is "sent" to the flow i, this means updating r_ref(r_vin and r_send) of flow i with the value of FSE_R(i). -6.2. GCC - - Google Congestion Control (GCC) [I-D.ietf-rmcat-gcc] is another - congestion control scheme for rtcweb. The rate control of GCC - employs two parts: controlling the bandwidth estimate based on delay, - and controlling the bandwidth estimate based on loss. Both are - designed to estimate the available bandwidth, A_hat. - - When applying the FSE to GCC, the UPDATE function call described in - Section 5.3 gives the FSE GCC's estimate of available bandwidth - A_hat. The recommended algorithm for GCC is the Active FSE in - Section 5.3.1. In step 3 (c), when the FSE_R(i) is "sent" to the - flow i, this means updating A_hat of flow i with the value of - FSE_R(i). - -6.3. General recommendations +6.2. General recommendations This section provides general advice for applying the FSE to congestion control mechanisms. Receiver-side calculations: When receiver-side calculations make assumptions about the rate of the sender, the calculations need to be synchronized or the receiver needs to be updated accordingly. This applies to TFRC [RFC5348], for example, where simulations showed somewhat less favorable results when using the FSE without a receiver-side change [fse]. + Stateful algorithms: + When a congestion control algorithm is stateful (e.g., TCP, + with Slow Start, Congestion Avoidance and Fast Recovery), these + states should be carefully considered such that the overall + state of the aggregate flow is correct. This may require + sharing more information in the UPDATE call. + + Rate jumps: + The FSE-based coupling algorithms can let a flow quickly + increase its rate to its fair share, e.g. when a new flow joins + or after a quiescent period. In case of window-based + congestion controls, this may produce a burst which should be + mitigated in some way. An example of how this could be done + without using a timer is presented in [anrw2016], using TCP as + an example. + 7. Expected feedback from experiments The algorithm described in this memo has so far been evaluated using simulations covering all the tests for more than one flow from - [I-D.ietf-rmcat-eval-test] (see [IETF-93], [IETF-94]). Experiments - should confirm these results using at least one of the same - congestion control algorithms (GCC or NADA) with real-life code - (e.g., browsers communicating over an emulated network covering the - conditions in [I-D.ietf-rmcat-eval-test]. The tests with real-life - code should be repeated afterwards in real network environments and - monitored. Experiments should investigate cases where the media - coder's output rate is below the rate that is calculated by the - coupling algorithm (FSE_R in algorithms 1 and 2, section 5.3). - Implementers and testers are invited to document their findings in an - Internet draft. + should confirm these results using at least the NADA congestion + control algorithm with real-life code (e.g., browsers communicating + over an emulated network covering the conditions in + [I-D.ietf-rmcat-eval-test]. The tests with real-life code should be + repeated afterwards in real network environments and monitored. + Experiments should investigate cases where the media coder's output + rate is below the rate that is calculated by the coupling algorithm + (FSE_R in algorithms 1 and 2, section 5.3). Implementers and testers + are invited to document their findings in an Internet draft. 8. Acknowledgements This document has benefitted from discussions with and feedback from Andreas Petlund, Anna Brunstrom, David Hayes, David Ros (who also gave the FSE its name), Ingemar Johansson, Karen Nielsen, Kristian Hiorth, Mirja Kuehlewind, Martin Stiemerling, Varun Singh , Xiaoqing Zhu, and Zaheduzzaman Sarker. The authors would like to especially thank Xiaoqing Zhu and Stefan Holmer for helping with NADA and GCC. @@ -555,26 +556,20 @@ may not be given, and one could imagine the worst case of an "arms race" situation, where applications end up setting their priorities to the maximum value. If all applications do this, the end result is a fair allocation in which the priority mechanism is implicitly eliminated, and no major harm is done. 11. References 11.1. Normative References - [I-D.ietf-rmcat-gcc] - Holmer, S., Lundin, H., Carlucci, G., Cicco, L., and S. - Mascolo, "A Google Congestion Control Algorithm for Real- - Time Communication", draft-ietf-rmcat-gcc-02 (work in - progress), July 2016. - [I-D.ietf-rmcat-nada] Zhu, X., Pan, R., Ramalho, M., Cruz, S., Jones, P., Fu, J., D'Aronco, S., and C. Ganzhorn, "NADA: A Unified Congestion Control Scheme for Real-Time Media", draft-ietf-rmcat-nada-03 (work in progress), September 2016. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ RFC2119, March 1997, @@ -590,20 +585,26 @@ . 11.2. Informative References [I-D.ietf-rmcat-eval-test] Sarker, Z., Singh, V., Zhu, X., and M. Ramalho, "Test Cases for Evaluating RMCAT Proposals", draft-ietf-rmcat-eval-test-04 (work in progress), October 2016. + [I-D.ietf-rmcat-gcc] + Holmer, S., Lundin, H., Carlucci, G., Cicco, L., and S. + Mascolo, "A Google Congestion Control Algorithm for Real- + Time Communication", draft-ietf-rmcat-gcc-02 (work in + progress), July 2016. + [I-D.ietf-rmcat-sbd] Hayes, D., Ferlin, S., Welzl, M., and K. Hiorth, "Shared Bottleneck Detection for Coupled Congestion Control for RTP Media.", draft-ietf-rmcat-sbd-04 (work in progress), March 2016. [I-D.ietf-rtcweb-transports] Alvestrand, H., "Transports for WebRTC", draft-ietf-rtcweb-transports-11.txt (work in progress), January 2016. @@ -614,20 +615,26 @@ [IETF-94] Islam, S., Welzl, M., and S. Gjessing, "Updates on Coupled Congestion Control for RTP Media", November 2015, . [RFC7478] Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real- Time Communication Use Cases and Requirements", RFC 7478, DOI 10.17487/RFC7478, March 2015, . + [anrw2016] + Islam, S. and M. Welzl, "Start Me Up:Determining and + Sharing TCP's Initial Congestion Window", ACM, IRTF, ISOC + Applied Networking Research Workshop 2016 (ANRW 2016) , + 2016. + [fse] Islam, S., Welzl, M., Gjessing, S., and N. Khademi, "Coupled Congestion Control for RTP Media", ACM SIGCOMM Capacity Sharing Workshop (CSWS 2014) and ACM SIGCOMM CCR 44(4) 2014; extended version available as a technical report from http://safiquli.at.ifi.uio.no/paper/fse-tech-report.pdf , 2014. [fse-noms] Islam, S., Welzl, M., Hayes, D., and S. Gjessing, @@ -639,46 +646,63 @@ Communication (WebRTC): Media Transport and Use of RTP", draft-ietf-rtcweb-rtp-usage-26.txt (work in progress), March 2016. [transport-multiplex] Westerlund, M. and C. Perkins, "Multiple RTP Sessions on a Single Lower-Layer Transport", draft-westerlund-avtcore-transport-multiplexing-07.txt (work in progress), October 2013. -Appendix A. Scheduling +Appendix A. Application to GCC + + Google Congestion Control (GCC) [I-D.ietf-rmcat-gcc] is another + congestion control scheme for RTP flows that is under development. + GCC is not yet finalised, but at the time of this writing, the rate + control of GCC employs two parts: controlling the bandwidth estimate + based on delay, and controlling the bandwidth estimate based on loss. + Both are designed to estimate the available bandwidth, A_hat. + + When applying the FSE to GCC, the UPDATE function call described in + Section 5.3 gives the FSE GCC's estimate of available bandwidth + A_hat. The recommended algorithm for GCC is the Active FSE in + Section 5.3.1. In step 3 (c), when the FSE_R(i) is "sent" to the + flow i, this means updating A_hat of flow i with the value of + FSE_R(i). + +Appendix B. Scheduling When connections originate from the same host, it would be possible to use only one single sender-side congestion controller which determines the overall allowed sending rate, and then use a local scheduler to assign a proportion of this rate to each RTP session. This way, priorities could also be implemented as a function of the scheduler. The Congestion Manager (CM) [RFC3124] also uses such a scheduling function. -Appendix B. Example algorithm - Passive FSE +Appendix C. Example algorithm - Passive FSE Active algorithms calculate the rates for all the flows in the FG and actively distribute them. In a passive algorithm, UPDATE returns a rate that should be used instead of the rate that the congestion controller has determined. This can make a passive algorithm easier to implement; however, when round-trip times of flows are unequal, - shorter-RTT flows will update and react to the overall FSE state more - often than longer-RTT flows, which can produce unwanted side effects. - This problem is more significant when the congestion control - convergence depends on the RTT. While the passive algorithm works - better for congestion controls with RTT-independent convergence, it - can still produce oscillations on short time scales. The algorithm - described below is therefore considered as highly experimental. - Results of a simplified passive FSE algorithm with both NADA and GCC - can be found in [fse-noms]. + shorter-RTT flows may (depending on the congestion control algorithm) + update and react to the overall FSE state more often than longer-RTT + flows, which can produce unwanted side effects. This problem is more + significant when the congestion control convergence depends on the + RTT. While the passive algorithm works better for congestion + controls with RTT-independent convergence, it can still produce + oscillations on short time scales. The algorithm described below is + therefore considered as highly experimental. Results of a simplified + passive FSE algorithm with both NADA and GCC can be found in + [fse-noms]. This passive version of the FSE stores the following information in addition to the variables described in Section 5.2: o The desired rate DR. This can be smaller than the calculated rate if the application feeding into the flow has less data to send than the congestion controller would allow. In case of a bulk transfer, DR must be set to CC_R received from the flow's congestion module. @@ -772,21 +796,21 @@ homogeneous controllers being in different states, are also subject to experimentation. This algorithm gives all the leftover rate of application-limited flows to the first flow that updates its sending rate, provided that this flow needs it all (otherwise, its own leftover rate can be taken by the next flow that updates its rate). Other policies could be applied, e.g. to divide the leftover rate of a flow equally among all other flows in the FGI. -B.1. Example operation (passive) +C.1. Example operation (passive) In order to illustrate the operation of the passive coupled congestion control algorithm, this section presents a toy example of two flows that use it. Let us assume that both flows traverse a common 10 Mbit/s bottleneck and use a simplistic congestion controller that starts out with 1 Mbit/s, increases its rate by 1 Mbit/s in the absence of congestion and decreases it by 2 Mbit/s in the presence of congestion. For simplicity, flows are assumed to always operate in a round-robin fashion. Rate numbers below without units are assumed to be in Mbit/s. For illustration purposes, the @@ -933,101 +956,112 @@ 3 e) FSE_R(f) = DR(f) = 9.33. The resulting FSE looks as follows: ------------------------------------------- | # | FGI | P | FSE_R | DR | Rate | | | | | | | | | 2 | 1 | 0.5 | 9.33 | 9.33 | 9.33 | ------------------------------------------- S_CR = 9.33, TLO = 0 -Appendix C. Change log +Appendix D. Change log -C.1. draft-welzl-rmcat-coupled-cc +D.1. draft-welzl-rmcat-coupled-cc -C.1.1. Changes from -00 to -01 +D.1.1. Changes from -00 to -01 o Added change log. o Updated the example algorithm and its operation. -C.1.2. Changes from -01 to -02 +D.1.2. Changes from -01 to -02 o Included an active version of the algorithm which is simpler. o Replaced "greedy flow" with "bulk data transfer" and "non-greedy" with "application-limited". o Updated new_CR to CC_R, and CR to FSE_R for better understanding. -C.1.3. Changes from -02 to -03 +D.1.3. Changes from -02 to -03 o Included an active conservative version of the algorithm which reduces queue growth and packet loss; added a reference to a technical report that shows these benefits with simulations. o Moved the passive variant of the algorithm to appendix. -C.1.4. Changes from -03 to -04 +D.1.4. Changes from -03 to -04 o Extended SBD section. o Added a note about window-based controllers. -C.1.5. Changes from -04 to -05 +D.1.5. Changes from -04 to -05 o Added a section about applying the FSE to specific congestion control algorithms, with a subsection specifying its use with NADA. -C.2. draft-ietf-rmcat-coupled-cc +D.2. draft-ietf-rmcat-coupled-cc -C.2.1. Changes from draft-welzl-rmcat-coupled-cc-05 +D.2.1. Changes from draft-welzl-rmcat-coupled-cc-05 o Moved scheduling section to the appendix. -C.2.2. Changes from -00 to -01 +D.2.2. Changes from -00 to -01 o Included how to apply the algorithm to GCC. o Updated variable names of NADA to be in line with the latest version. o Added a reference to [I-D.ietf-rtcweb-transports] to make a connection to the prioritization text there. -C.2.3. Changes from -01 to -02 +D.2.3. Changes from -01 to -02 o Minor changes. o Moved references of NADA and GCC from informative to normative. o Added a reference for the passive variant of the algorithm. -C.2.4. Changes from -02 to -03 +D.2.4. Changes from -02 to -03 o Minor changes. o Added a section about expected feedback from experiments. -C.2.5. Changes from -03 to -04 +D.2.5. Changes from -03 to -04 o Described the names of variables used in the algorithms. o Added a diagram to illustrate the interaction between flows and the FSE. o Added text on the trade-off of using the configuration based approach. o Minor changes to enhance the readability. +D.2.6. Changes from -04 to -05 + + o Changed several occurrences of "NADA and GCC" to "NADA", including + the abstract. + + o Moved the application to GCC to an appendix, and made the GCC + reference informative. + + o Provided a few more general recommendations on applying the + coupling algorithm. + Authors' Addresses Safiqul Islam University of Oslo PO Box 1080 Blindern Oslo, N-0316 Norway Phone: +47 22 84 08 37 Email: safiquli@ifi.uio.no