--- 1/draft-ietf-rmcat-coupled-cc-00.txt 2016-03-21 11:23:28.379628040 -0700 +++ 2/draft-ietf-rmcat-coupled-cc-01.txt 2016-03-21 11:23:28.619634044 -0700 @@ -1,50 +1,51 @@ RTP Media Congestion Avoidance S. Islam Techniques (rmcat) M. Welzl Internet-Draft S. Gjessing Intended status: Experimental University of Oslo -Expires: March 17, 2016 September 14, 2015 +Expires: September 22, 2016 March 21, 2016 Coupled congestion control for RTP media - draft-ietf-rmcat-coupled-cc-00 + draft-ietf-rmcat-coupled-cc-01 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 the NADA congestion control algorithm. + how to apply the method for both the NADA and Google 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 March 17, 2016. + This Internet-Draft will expire on September 22, 2016. Copyright Notice - Copyright (c) 2015 IETF Trust and the persons identified as the + 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 @@ -53,35 +54,46 @@ Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Limitations . . . . . . . . . . . . . . . . . . . . . . . . . 4 4. Architectural overview . . . . . . . . . . . . . . . . . . . . 5 5. Roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. SBD . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. FSE . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.3. Flows . . . . . . . . . . . . . . . . . . . . . . . . . . 7 - 5.3.1. Example algorithm 1 - Active FSE . . . . . . . . . . . 7 + 5.3.1. Example algorithm 1 - Active FSE . . . . . . . . . . . 8 5.3.2. Example algorithm 2 - Conservative Active FSE . . . . 8 6. Application . . . . . . . . . . . . . . . . . . . . . . . . . 10 6.1. NADA . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 - 6.2. General recommendations . . . . . . . . . . . . . . . . . 10 + 6.2. GCC . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 + 6.3. General recommendations . . . . . . . . . . . . . . . . . 11 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 9. Security Considerations . . . . . . . . . . . . . . . . . . . 11 - 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 - 10.1. Normative References . . . . . . . . . . . . . . . . . . . 11 + 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 + 10.1. Normative References . . . . . . . . . . . . . . . . . . . 12 10.2. Informative References . . . . . . . . . . . . . . . . . . 12 Appendix A. Scheduling . . . . . . . . . . . . . . . . . . . . . 13 Appendix B. Example algorithm - Passive FSE . . . . . . . . . . . 13 - B.1. Example operation (passive) . . . . . . . . . . . . . . . 15 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20 + B.1. Example operation (passive) . . . . . . . . . . . . . . . 16 + Appendix C. Change log . . . . . . . . . . . . . . . . . . . . . 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.1.4. 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.2.2. Changes from -00 to -01 . . . . . . . . . . . . . . . 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. @@ -90,21 +102,21 @@ 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 behavior by sharing information between existing congestion controllers. It is able to honor user-specified priorities, which is - required by rtcweb [rtcweb-usecases]. + required by rtcweb [RFC7478]. 2. Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Available Bandwidth: The available bandwidth is the nominal link capacity minus the amount of traffic that traversed the link during a certain time @@ -174,21 +186,23 @@ it initiates communication with flows and SBD. However, in the passive version, it does not actively initiate communication with 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). + 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. ------- <--- Flow 1 | FSE | <--- Flow 2 .. ------- <--- .. Flow N ^ | | ------- | | SBD | <-------| ------- @@ -222,72 +236,77 @@ 1. From multiplexing: it can be based on the simple assumption that packets sharing the same five-tuple (IP source and destination address, protocol, and transport layer port number pair) and having the same Differentiated Services Code Point (DSCP) in the IP header are typically treated in the same way along the path. The latter method is the only one specified in this document: SBD MAY consider all flows that use the same five-tuple and DSCP to belong to the same FG. This classification applies to certain tunnels, or RTP flows that are multiplexed over one transport - (cf. [transport-multiplex]). In one way or another, such - multiplexing will probably be recommended for use with rtcweb - [rtcweb-rtp-usage]. + (cf. [transport-multiplex]). Such multiplexing is also a + recommended usage of RTP in rtcweb [rtcweb-rtp-usage]. 2. Via configuration: e.g. by assuming that a common wireless uplink 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 [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 [sbd] for details). + 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). 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 be in only one FG) 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). A negative value is used to indicate that a - flow has terminated + (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]. + 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. - In the FSE, each FG contains one static variable S_CR which is meant - to be the sum of the calculated rates of all flows in the same FG - (including the flow itself). This value is used to calculate the - sending rate. + 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. 5.3. Flows Flows register themselves with SBD and FSE when they start, deregister from the FSE when they stop, and carry out an UPDATE @@ -399,57 +418,69 @@ end for 6. Application This section specifies how the FSE can be applied to specific congestion control mechanisms and makes general recommendations that facilitate applying the FSE to future congestion controls. 6.1. NADA - Network-Assisted Dynamic Adapation (NADA) [nada] is a congestion - control scheme for rtcweb. It calculates a reference rate R_n upon - receiving an acknowledgment, and then, based on the reference rate, - it calculates a video target rate R_v and a sending rate for the - flows, R_s. + Network-Assisted Dynamic Adapation (NADA) [I-D.ietf-rmcat-nada] is a + congestion control scheme for rtcweb. It calculates a reference rate + r_ref upon receiving an acknowledgment, and then, based on the + 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_n. 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_v and R_s of flow i with the value of FSE_R(i). + 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). - NADA simulation results are available from - http://heim.ifi.uio.no/safiquli/coupled-cc/. The next version of - this document will refer to a technical report that will be made - available at the same URL. +6.2. GCC -6.2. General recommendations + 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 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. 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 This document has benefitted from discussions with and feedback from - David Hayes, Mirja Kuehlewind, Andreas Petlund, David Ros (who also - gave the FSE its name), Zaheduzzaman Sarker and Varun Singh. The - authors would like to thank Xiaoqing Zhu for helping with NADA. + David Hayes, Mirja Kuehlewind, Karen Nielsen, Andreas Petlund, David + Ros (who also gave the FSE its name), Zaheduzzaman Sarker, Varun + Singh and Kristian Hiorth. The authors would like to 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). 8. IANA Considerations This memo includes no request to IANA. 9. Security Considerations @@ -488,47 +519,61 @@ 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, . 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. + + [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. + + [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. + + [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); extended version - available as a technical report from + 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. - [nada] Zhu, X., Pan, R., Ramalho, M., Mena, S., Ganzhorn, C., - Jones, P., and S. De Aronco, "NADA: A Unified Congestion - Control Scheme for Real-Time Media", - draft-ietf-rmcat-nada-00 (work in progress), April 2015. - [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-18.txt (work in progress), - October 2014. - - [rtcweb-usecases] - Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real- - Time Communication Use-cases and Requirements", - draft-ietf-rtcweb-use-cases-and-requirements-14.txt (work - in progress), February 2014. - - [sbd] Hayes, D., Ferlin, S., and M. Welzl, "Shared Bottleneck - Detection for Coupled Congestion Control for RTP Media", - draft-ietf-rmcat-sbd-00.txt (work in progress), May 2015. + 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 When connections originate from the same host, it would be possible @@ -813,20 +858,75 @@ 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 + +C.1. draft-welzl-rmcat-coupled-cc + +C.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 + + 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 + + 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 + + o Extended SBD section. + + o Added a note about window-based controllers. + +C.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 + +C.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 + + 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. + 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