--- 1/draft-ietf-rmcat-coupled-cc-03.txt 2016-10-31 03:16:25.337003789 -0700 +++ 2/draft-ietf-rmcat-coupled-cc-04.txt 2016-10-31 03:16:25.381004867 -0700 @@ -1,112 +1,112 @@ -RTP Media Congestion Avoidance Techniques (rmcat) S. Islam -Internet-Draft M. Welzl -Intended status: Experimental S. Gjessing -Expires: January 29, 2017 University of Oslo - July 28, 2016 +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 Coupled congestion control for RTP media - draft-ietf-rmcat-coupled-cc-03 + draft-ietf-rmcat-coupled-cc-04 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. + 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 + 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 January 29, 2017. + This Internet-Draft will expire on May 4, 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 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 4. Architectural overview . . . . . . . . . . . . . . . . . . . 4 - 5. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 + 4. Architectural overview . . . . . . . . . . . . . . . . . . . . 4 + 5. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. SBD . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 - 5.2. FSE . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 - 5.3. Flows . . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 5.3.1. Example algorithm 1 - Active FSE . . . . . . . . . . 7 - 5.3.2. Example algorithm 2 - Conservative Active FSE . . . . 8 + 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 6.2. GCC . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 6.3. General recommendations . . . . . . . . . . . . . . . . . 10 - 7. Expected feedback from experiments . . . . . . . . . . . . . 11 - 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 - 10. Security Considerations . . . . . . . . . . . . . . . . . . . 11 - 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 - 11.1. Normative References . . . . . . . . . . . . . . . . . . 12 - 11.2. Informative References . . . . . . . . . . . . . . . . . 12 - Appendix A. Scheduling . . . . . . . . . . . . . . . . . . . . . 14 - Appendix B. Example algorithm - Passive FSE . . . . . . . . . . 14 - B.1. Example operation (passive) . . . . . . . . . . . . . . . 17 - Appendix C. Change log . . . . . . . . . . . . . . . . . . . . . 21 - C.1. draft-welzl-rmcat-coupled-cc . . . . . . . . . . . . . . 21 - C.1.1. Changes from -00 to -01 . . . . . . . . . . . . . . . 21 - C.1.2. Changes from -01 to -02 . . . . . . . . . . . . . . . 21 - C.1.3. Changes from -02 to -03 . . . . . . . . . . . . . . . 21 + 6.1. NADA . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 + 6.2. GCC . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 + 6.3. General recommendations . . . . . . . . . . . . . . . . . 11 + 7. Expected feedback from experiments . . . . . . . . . . . . . . 11 + 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 . . . . . . . . . . . . . . . 22 - C.2.1. Changes from draft-welzl-rmcat-coupled-cc-05 . . . . 22 - C.2.2. Changes from -00 to -01 . . . . . . . . . . . . . . . 22 - C.2.3. Changes from -01 to -02 . . . . . . . . . . . . . . . 22 - C.2.4. Changes from -02 to -03 . . . . . . . . . . . . . . . 22 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 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 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. + creates undesirable queuing delay when multiple congestion controlled + connections traverse the same network bottleneck. The Congestion Manager (CM) [RFC3124] couples flows by providing a single congestion controller. It is hard to implement because it requires an additional congestion controller and removes all per- connection congestion control functionality, which is quite a significant change to existing RTP based applications. This document presents a method to combine the behavior of congestion control mechanisms that is easier to implement than the Congestion Manager [RFC3124] and also requires less significant changes to existing RTP based applications. It attempts to roughly approximate the CM @@ -150,21 +150,21 @@ The entity that determines which flows traverse the same bottleneck in the network, or the process of doing so. 3. Limitations Sender-side only: Coupled congestion control as described here only operates inside a single host on the sender side. This is because, irrespective of where the major decisions for congestion control are taken, the sender of a flow needs to eventually - decide the transmission rate. Additionally, the necessary + decide on the transmission rate. Additionally, the necessary information about how much data an application can currently send on a flow is often only available at the sender side, making the sender an obvious choice for placement of the elements and mechanisms described here. Shared bottlenecks do not change quickly: As per the definition above, a bottleneck depends on cross traffic, and since such traffic can heavily fluctuate, bottlenecks can change at a high frequency (e.g., there can be oscillation between two or more links). This means that, when @@ -191,33 +191,47 @@ flows and SBD; its only active role is internal state maintenance (e.g., an implementation could use soft state to remove a flow's data after long periods of inactivity). Every time a flow's congestion control mechanism would normally update its sending rate, the flow instead updates information in the FSE and performs a query on the FSE, leading to a sending rate that can be different from what the congestion controller originally determined. Using information about/from the currently active flows, SBD updates the FSE with the correct Flow State Identifiers (FSIs). This document describes both active and passive versions, however the passive version is put into - the appendix as it is extremely experimental. + the appendix as it is extremely experimental. Figure 2 shows the + interaction between flows and the FSE, using the variable names + defined in Section 5.2. ------- <--- Flow 1 | FSE | <--- Flow 2 .. ------- <--- .. Flow N ^ | | ------- | | SBD | <-------| ------- Figure 1: Coupled congestion control architecture + Flow#1(cc) FSE Flow#2(cc) + ---------- --- ---------- + #1 JOIN ----register--> REGISTER + + REGISTER <--register-- JOIN #1 + + #2 CC_R ----UPDATE----> UPDATE (in) + + #3 NEW RATE <---FSE_R------ UPDATE (out) --FSE_R----> #3 NEW RATE + + Figure 2: Flow-FSE interaction + Since everything shown in Figure 1 is assumed to operate on a single host (the sender) only, this document only describes aspects that have an influence on the resulting on-the-wire behavior. It does, for instance, not define how many bits must be used to represent FSIs, or in which way the entities communicate. Implementations can take various forms: for instance, all the elements in the figure could be implemented within a single application, thereby operating on flows generated by that application only. Another alternative could be to implement both the FSE and SBD together in a separate process which different applications communicate with via some form @@ -253,28 +267,32 @@ is also a shared bottleneck. 3. From measurements: e.g. by considering correlations among measured delay and loss as an indication of a shared bottleneck. The methods above have some essential trade-offs: e.g., multiplexing is a completely reliable measure, however it is limited in scope to two end points (i.e., it cannot be applied to couple congestion controllers of one sender talking to multiple receivers). A measurement-based SBD mechanism is described in [I-D.ietf-rmcat-sbd]. + Measurements can never be 100% reliable, in particular because they are based on the past but applying coupled congestion control means to make an assumption about the future; it is therefore recommended to implement cautionary measures, e.g. by disabling coupled congestion control if enabling it causes a significant increase in delay and/or packet loss. Measurements also take time, which entails a certain delay for turning on coupling (refer to - [I-D.ietf-rmcat-sbd] for details). + [I-D.ietf-rmcat-sbd] for details). Using system configuration to + decide about shared bottlenecks can be more efficient (faster to + obtain) than using measurements, but it relies on assumptions about + the network environment. 5.2. FSE The FSE contains a list of all flows that have registered with it. For each flow, it stores the following: o a unique flow number to identify the flow o the FGI of the FG that it belongs to (based on the definitions in this document, a flow has only one bottleneck, and can therefore @@ -308,21 +326,39 @@ Flows register themselves with SBD and FSE when they start, deregister from the FSE when they stop, and carry out an UPDATE function call every time their congestion controller calculates a new sending rate. Via UPDATE, they provide the newly calculated rate and optionally (if the algorithm supports it) the desired rate. The desired rate is less than the calculated rate in case of application- limited flows; otherwise, it is the same as the calculated rate. Below, two example algorithms are described. While other algorithms could be used instead, the same algorithm must be applied to all - flows. + flows. Names of variables used in the algorithms are explained + below. + + o CC_R - The rate received from a flow's congestion controller when + it calls UPDATE. + + o FSE_R - The rate calculated by the FSE for a flow. + + o S_CR - The sum of the calculated rates of all flows in the same + FG; this value is used to calculate the sending rate. + + o FG - A group of flows having the same FGI, and hence sharing the + same bottleneck. + + o P - The priority of a flow which is received from the flow's + congestion controller; the FSE uses this variable for calculating + FSE R. + + o S_P - The sum of all the priorities. 5.3.1. Example algorithm 1 - Active FSE This algorithm was designed to be the simplest possible method to assign rates according to the priorities of flows. Simulations results in [fse] indicate that it does however not significantly reduce queuing delay and packet loss. (1) When a flow f starts, it registers itself with SBD and the FSE. FSE_R is initialized with the congestion controller's initial @@ -462,37 +498,41 @@ 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. 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. Implementers and testers are invited to document their - findings in an Internet draft. + 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 - David Hayes, Mirja Kuehlewind, Karen Nielsen, Andreas Petlund, David - Ros (who also gave the FSE its name), Zaheduzzaman Sarker, Varun - Singh, Anna Brunstrom, Martin Stiemerling, and Kristian Hiorth. The - authors would like to thank Xiaoqing Zhu and Stefan Holmer for - helping with NADA and GCC. + 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. This work was partially funded by the European Community under its Seventh Framework Programme through the Reducing Internet Transport Latency (RITE) project (ICT-317700). 9. IANA Considerations This memo includes no request to IANA. 10. Security Considerations @@ -522,95 +562,96 @@ 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, D., Cruz, S., Jones, P., Fu, + 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. + 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, + 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, . 11.2. Informative References - [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, - "Managing Real-Time Media Flows through a Flow State - Exchange", IEEE NOMS 2016, Istanbul, Turkey , 2016. - [I-D.ietf-rmcat-eval-test] - Sarker, Z., Singh, V., Zhu, X., and D. Ramalho, "Test - Cases for Evaluating RMCAT Proposals", draft-ietf-rmcat- - eval-test-03 (work in progress), March 2016. + 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-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", Internet-draft - draft-ietf-rtcweb-transports-11.txt, January 2016. + Alvestrand, H., "Transports for WebRTC", + draft-ietf-rtcweb-transports-11.txt (work in progress), + January 2016. [IETF-93] Islam, S., Welzl, M., and S. Gjessing, "Updates on Coupled Congestion Control for RTP Media", July 2015, - . + . [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, . + [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, + "Managing Real-Time Media Flows through a Flow State + Exchange", IEEE NOMS 2016, Istanbul, Turkey , 2016. + [rtcweb-rtp-usage] Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time Communication (WebRTC): Media Transport and Use of RTP", - Internet-draft draft-ietf-rtcweb-rtp-usage-26.txt, March - 2016. + 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", Internet-draft draft- - westerlund-avtcore-transport-multiplexing-07.txt, October - 2013. + Single Lower-Layer Transport", + draft-westerlund-avtcore-transport-multiplexing-07.txt + (work in progress), 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. @@ -961,37 +1002,50 @@ 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 o Minor changes. o Added a section about expected feedback from experiments. +C.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. + 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