--- 1/draft-ietf-rmcat-coupled-cc-01.txt 2016-04-14 05:15:57.923755860 -0700 +++ 2/draft-ietf-rmcat-coupled-cc-02.txt 2016-04-14 05:15:57.967756954 -0700 @@ -1,99 +1,100 @@ -RTP Media Congestion Avoidance S. Islam -Techniques (rmcat) M. Welzl -Internet-Draft S. Gjessing -Intended status: Experimental University of Oslo -Expires: September 22, 2016 March 21, 2016 +RTP Media Congestion Avoidance Techniques (rmcat) S. Islam +Internet-Draft M. Welzl +Intended status: Experimental S. Gjessing +Expires: October 16, 2016 University of Oslo + April 14, 2016 Coupled congestion control for RTP media - draft-ietf-rmcat-coupled-cc-01 + draft-ietf-rmcat-coupled-cc-02 Abstract When multiple congestion controlled RTP sessions traverse the same network bottleneck, it can be beneficial to combine their controls such that the total on-the-wire behavior is improved. 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 congestion control algorithms. -Status of this Memo +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 September 22, 2016. + This Internet-Draft will expire on October 16, 2016. 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 carefully, as they describe your rights and restrictions with respect 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. Table of Contents - 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 4. Architectural overview . . . . . . . . . . . . . . . . . . . . 5 - 5. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 - 5.1. SBD . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 + 4. Architectural overview . . . . . . . . . . . . . . . . . . . 4 + 5. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 5.1. SBD . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5.2. FSE . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.3. Flows . . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 5.3.1. Example algorithm 1 - Active FSE . . . . . . . . . . . 8 + 5.3.1. Example algorithm 1 - Active FSE . . . . . . . . . . 7 5.3.2. Example algorithm 2 - Conservative Active FSE . . . . 8 - 6. Application . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 6.1. NADA . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 + 6. Application . . . . . . . . . . . . . . . . . . . . . . . . . 9 + 6.1. NADA . . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.2. GCC . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 6.3. General recommendations . . . . . . . . . . . . . . . . . 11 - 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 + 6.3. General recommendations . . . . . . . . . . . . . . . . . 10 + 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 9. Security Considerations . . . . . . . . . . . . . . . . . . . 11 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 10.1. Normative References . . . . . . . . . . . . . . . . . . . 12 - 10.2. Informative References . . . . . . . . . . . . . . . . . . 12 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 + 10.1. Normative References . . . . . . . . . . . . . . . . . . 11 + 10.2. Informative References . . . . . . . . . . . . . . . . . 12 Appendix A. Scheduling . . . . . . . . . . . . . . . . . . . . . 13 - Appendix B. Example algorithm - Passive FSE . . . . . . . . . . . 13 + Appendix B. Example algorithm - Passive FSE . . . . . . . . . . 13 B.1. Example operation (passive) . . . . . . . . . . . . . . . 16 Appendix C. Change log . . . . . . . . . . . . . . . . . . . . . 20 - C.1. draft-welzl-rmcat-coupled-cc . . . . . . . . . . . . . . . 20 + C.1. draft-welzl-rmcat-coupled-cc . . . . . . . . . . . . . . 20 C.1.1. Changes from -00 to -01 . . . . . . . . . . . . . . . 20 C.1.2. Changes from -01 to -02 . . . . . . . . . . . . . . . 20 - C.1.3. Changes from -02 to -03 . . . . . . . . . . . . . . . 21 + C.1.3. Changes from -02 to -03 . . . . . . . . . . . . . . . 20 C.1.4. Changes from -03 to -04 . . . . . . . . . . . . . . . 21 C.1.5. Changes from -04 to -05 . . . . . . . . . . . . . . . 21 C.2. draft-ietf-rmcat-coupled-cc . . . . . . . . . . . . . . . 21 - C.2.1. Changes from draft-welzl-rmcat-coupled-cc-05 . . . . . 21 + C.2.1. Changes from draft-welzl-rmcat-coupled-cc-05 . . . . 21 C.2.2. Changes from -00 to -01 . . . . . . . . . . . . . . . 21 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 + C.2.3. Changes from -01 to -02 . . . . . . . . . . . . . . . 21 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21 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 -- an effect that is amplified when multiple congestion controlled connections traverse the same network bottleneck. @@ -279,30 +281,29 @@ o a priority P, which here is assumed to be represented as a floating point number in the range from 0.1 (unimportant) to 1 (very important). o The rate used by the flow in bits per second, FSE_R. Note that the priority does not need to be a floating point value and its value range does not matter for this algorithm: the algorithm works with a flow's priority portion of the sum of all priority - values. Priority values can therefore also be mapped to the "very- - low", "low", "medium" or "high" priority levels described in - [I-D.ietf-rtcweb-transports]. + values. Priorities can therefore be mapped to the "very-low", "low", + "medium" or "high" priority levels described in + [I-D.ietf-rtcweb-transports] using the values 1, 2, 4 and 8, + respectively. The FSE can operate on window-based as well as rate-based congestion - controllers (TEMPORARY NOTE: and probably -- not yet tested -- - combinations thereof, with calculations to convert from one to the - other). In case of a window-based controller, FSE_R is a window, and - all the text below should be considered to refer to window, not - rates. + controllers. In case of a window-based controller, FSE_R is a + window, and all the text below should be considered to refer to + window, not rates. In the FSE, each FG contains one static variable S_CR which is the sum of the calculated rates of all flows in the same FG. This value is used to calculate the sending rate. The information listed here is enough to implement the sample flow algorithm given below. FSE implementations could easily be extended to store, e.g., a flow's current sending rate for statistics gathering or future potential optimizations. @@ -448,23 +449,22 @@ 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 - This section will provides general advice for applying the FSE to - congestion control mechanisms. TEMPORARY NOTE: Future versions of - this document will contain a longer list. + 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]. 7. Acknowledgements @@ -503,83 +503,87 @@ 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. 10. References 10.1. 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-01 (work in + progress), October 2015. + + [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-02 (work in progress), March 2016. + [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ RFC2119, March 1997, . [RFC3124] Balakrishnan, H. and S. Seshan, "The Congestion Manager", RFC 3124, DOI 10.17487/RFC3124, June 2001, . [RFC5348] Floyd, S., Handley, M., Padhye, J., and J. Widmer, "TCP - Friendly Rate Control (TFRC): Protocol Specification", - RFC 5348, DOI 10.17487/RFC5348, September 2008, + Friendly Rate Control (TFRC): Protocol Specification", RFC + 5348, DOI 10.17487/RFC5348, September 2008, . 10.2. Informative 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-01 (work in - progress), October 2015. + [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. - [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-02 (work in progress), March 2016. + [fse-noms] + Islam, S., Welzl, M., Hayes, D., and S. Gjessing, + "Managing Real-Time Media Flows through a Flow State + Exchange", IEEE NOMS 2016, Istanbul, Turkey , 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. + Alvestrand, H., "Transports for WebRTC", Internet-draft + draft-ietf-rtcweb-transports-11.txt, January 2016. [RFC7478] Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real- Time Communication Use Cases and Requirements", RFC 7478, DOI 10.17487/RFC7478, March 2015, . - [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. - [rtcweb-rtp-usage] Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time Communication (WebRTC): Media Transport and Use of RTP", - draft-ietf-rtcweb-rtp-usage-26.txt (work in progress), - March 2016. + Internet-draft draft-ietf-rtcweb-rtp-usage-26.txt, 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. + Single Lower-Layer Transport", Internet-draft draft- + westerlund-avtcore-transport-multiplexing-07.txt, October + 2013. Appendix A. 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. @@ -591,20 +595,22 @@ 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]. 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. @@ -722,55 +727,56 @@ Flow #1 begins. It is a bulk data transfer and considers itself to have top priority. This is the FSE after the flow algorithm's step 1: ---------------------------------------- | # | FGI | P | FSE_R | DR | Rate | | | | | | | | | 1 | 1 | 1 | 1 | 1 | 1 | ---------------------------------------- S_CR = 1, TLO = 0 + Its congestion controller gradually increases its rate. Eventually, at some point, the FSE should look like this: - -------------------------------------- + ----------------------------------------- | # | FGI | P | FSE_R | DR | Rate | | | | | | | | | 1 | 1 | 1 | 10 | 10 | 10 | ----------------------------------------- S_CR = 10, TLO = 0 Now another flow joins. It is also a bulk data transfer, and has a lower priority (0.5): - ---------------------------------------- + ------------------------------------------ | # | FGI | P | FSE_R | DR | Rate | | | | | | | | | 1 | 1 | 1 | 10 | 10 | 10 | | 2 | 1 | 0.5 | 1 | 1 | 1 | ------------------------------------------ S_CR = 11, TLO = 0 Now assume that the first flow updates its rate to 8, because the total sending rate of 11 exceeds the total capacity. Let us take a closer look at what happens in step 3 of the flow algorithm. CC_R = 8. new_DR = infinity. 3 a) new_S_CR = 11; DELTA = 8 - 10 = -2. 3 b) FSE_Rf) = 8. DELTA is negative, hence S_CR = 9; DR(f) = 8. 3 c) S_P = 1.5. 3 d) new sending rate = min(infinity, 1/1.5 * 9 + 0) = 6. 3 e) FSE_R(f) = 6. The resulting FSE looks as follows: - ---------------------------------------- + ------------------------------------------- | # | FGI | P | FSE_R | DR | Rate | | | | | | | | | 1 | 1 | 1 | 6 | 8 | 6 | | 2 | 1 | 0.5 | 1 | 1 | 1 | ------------------------------------------- S_CR = 9, TLO = 0 The effect is that flow #1 is sending with 6 Mbit/s instead of the 8 Mbit/s that the congestion controller derived. Let us now assume that flow #2 updates its rate. Its congestion controller detects that the network is not fully saturated (the actual total sending @@ -913,37 +919,45 @@ C.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 + + 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. + Authors' Addresses Safiqul Islam University of Oslo PO Box 1080 Blindern - Oslo, N-0316 + Oslo N-0316 Norway Phone: +47 22 84 08 37 Email: safiquli@ifi.uio.no Michael Welzl University of Oslo PO Box 1080 Blindern - Oslo, N-0316 + Oslo N-0316 Norway Phone: +47 22 85 24 20 Email: michawe@ifi.uio.no Stein Gjessing University of Oslo PO Box 1080 Blindern - Oslo, N-0316 + Oslo N-0316 Norway Phone: +47 22 85 24 44 Email: steing@ifi.uio.no