https://www.rfc-editor.org/rfc/rfc9743.txt

 Internet Engineering Task Force (IETF) M. Duke, Ed. Request for Comments: 9743 Google LLC BCP: 133 G. Fairhurst, Ed. Obsoletes: 5033 University of Aberdeen Category: Best Current Practice March 2025 ISSN: 2070-1721 Specifying New Congestion Control Algorithms Abstract RFC 5033 discusses the principles and guidelines for standardizing new congestion control algorithms. This document obsoletes RFC 5033 to reflect changes in the congestion control landscape by providing a framework for the development and assessment of congestion control mechanisms, promoting stability across diverse network paths. This document seeks to ensure that proposed congestion control algorithms operate efficiently and without harm when used in the global Internet. It emphasizes the need for comprehensive testing and validation to prevent adverse interactions with existing flows. Status of This Memo This memo documents an Internet Best Current Practice. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on BCPs is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc9743. Copyright Notice Copyright (c) 2025 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 (https://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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction 2. Specification of Requirements 3. Guidelines for Authors 3.1. Evaluation Guidelines 3.2. Document-Status Guidelines 4. Specifying Algorithms for Use in Controlled Environments 5. Evaluation Criteria 5.1. Single Algorithm Behavior 5.1.1. Protection Against Congestion Collapse 5.1.2. Protection Against Bufferbloat 5.1.3. Protection Against High Packet Loss 5.1.4. Fairness Within the Proposed Congestion Control Algorithm 5.1.5. Short Flows 5.2. Mixed Algorithm Behavior 5.2.1. Existing General-Purpose Congestion Control 5.2.2. Real-Time Congestion Control 5.2.3. Short and Long Flows 5.3. Other Criteria 5.3.1. Differences with Congestion Control Principles 5.3.2. Incremental Deployment 6. General Use 6.1. Paths with Tail-Drop Queues 6.2. Tunnel Behavior 6.3. Wired Paths 6.4. Wireless Paths 7. Special Cases 7.1. Active Queue Management (AQM) 7.2. Operation with the Envelope Set by Network Circuit Breakers 7.3. Paths with Varying Delay 7.4. Internet of Things and Constrained Nodes 7.5. Paths with High Delay 7.6. Misbehaving Nodes 7.7. Extreme Packet Reordering 7.8. Transient Events 7.9. Sudden Changes in the Path 7.10. Multipath Transport 7.11. Data Centers 8. Security Considerations 9. IANA Considerations 10. References 10.1. Normative References 10.2. Informative References Appendix A. Changes Since RFC 5033 Acknowledgments Contributors Authors' Addresses 1. Introduction This document provides guidelines for the IETF to use when evaluating a proposed congestion control algorithm that differs from the general congestion control principles outlined in [RFC2914]. The guidance is intended to be useful to authors proposing congestion control algorithms and for the IETF community when evaluating whether a proposal is appropriate for publication in the RFC Series and for deployment in the Internet. This document obsoletes [RFC5033], which was published in 2007 as a Best Current Practice for evaluating proposed congestion control algorithms for publication in Experimental or Proposed Standard RFCs. The IETF specifies standard Internet congestion control algorithms in the RFC Series. These congestion control algorithms can suffer performance challenges when used in differing environments (e.g., high-speed networks, cellular and Wi-Fi wireless technologies, and long-distance satellite links), and also when flows carry specific workloads (e.g., Voice over IP (VoIP), gaming, and videoconferencing). When [RFC5033] was published, TCP [RFC9293] was the primary focus of IETF congestion control efforts, with proposals typically discussed within the Internet Congestion Control Research Group (ICCRG). Concurrently, the Datagram Congestion Control Protocol (DCCP) [RFC4340] was developed to define new congestion control algorithms for datagram traffic, while the Stream Control Transmission Protocol (SCTP) [RFC9260] reused TCP congestion control algorithms. Since then, several changes have occurred. The range of protocols utilizing congestion control algorithms has expanded to include QUIC [RFC9000] and RTP Media Congestion Avoidance Techniques (RMCAT) (e.g., [RFC8836]). Additionally, some alternative congestion control algorithms have been tested and deployed at scale without full IETF review. There is increased interest in specialized use cases, such as data centers (e.g., [RFC8257]), and in supporting a variety of upper-layer protocols and applications, such as real-time protocols. Moreover, the community has gained significant experience with congestion indications beyond packet loss. Multicast congestion control is a considerably less mature field of study and is not in the scope of this document. However, Section 4 of [RFC8085] provides additional guidelines for multicast and broadcast usage of UDP. Congestion control algorithms have been developed outside of the IETF, including at least two that saw large scale deployment. These include CUBIC [HRX08