QUIC L. Eggert Internet-Draft Mozilla Updates: 9002 (if approved) 17 September 2024 Intended status: Standards Track Expires: 21 March 2025 Maximum Acknowledgment Delay and QUIC Loss Recovery draft-eggert-quic-9002-mad-latest Abstract This document updates RFC9002 by specifying how the max_ack_delay is incorporated into the computation of the loss_delay used for time- based loss recovery. About This Document This note is to be removed before publishing as an RFC. The latest revision of this draft can be found at https://larseggert.github.io/quic-9002-mad/draft-eggert-quic- 9002-mad.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-eggert-quic-9002-mad/. Discussion of this document takes place on the QUIC Working Group mailing list (mailto:quic@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/quic/. Subscribe at https://www.ietf.org/mailman/listinfo/quic/. Source for this draft and an issue tracker can be found at https://github.com/larseggert/quic-9002-mad. 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 https://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 21 March 2025. Copyright Notice Copyright (c) 2024 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. Conventions and Definitions 3. Updates to RFC9002 3.1. Detecting Lost Packets 4. Security Considerations 5. IANA Considerations 6. Normative References Acknowledgments Author's Address 1. Introduction The maximum acknowledgement delay (max_ack_delay) is the maximum amount of time by which the receiver intends to delay acknowledgments for packets in the Application Data packet number space, as defined by the eponymous transport parameter (Section 18.2 of [RFC9000]). This document updates [RFC9002] by specifying how the max_ack_delay is incorporated into the computation of the loss_delay used for time- based loss recovery. 2. Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 3. Updates to RFC9002 3.1. Detecting Lost Packets Appendix A.10 of [RFC9002] contains pseudo code for detecting lost packets in a packet number space. That code includes a computation of loss_delay, i.e., a time in the past before which all sent packets are deemed lost. loss_delay = kTimeThreshold * max(latest_rtt, smoothed_rtt) This computation of loss_delay does not take max_ack_delay into account; kTimeThreshold (which is 9/8) is the only stretch factor that adds some affordance for delayed ACK delivery. When the peer ACK delay approaches or (especially) when it exceeds 1/8 * RTT, this can cause the sender to declare sent packets as lost, causing unneeded early retransmissions. This document updates this calculation of loss_delay to take max_ack_delay into account: loss_delay = kTimeThreshold * max(latest_rtt, smoothed_rtt) + max_ack_delay As in Section 6.2.1 of [RFC9002], when loss_delay is calculated for Initial or Handshake packet number spaces, the max_ack_delay in the loss_delay computation is set to 0, since the peer is expected to not delay ACKs in these packet number spaces intentionally; see Section 13.2.1 of [RFC9000]. 4. Security Considerations No security considerations are introduced by this document. 5. IANA Considerations This document has no IANA actions. 6. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Multiplexed and Secure Transport", RFC 9000, DOI 10.17487/RFC9000, May 2021, . [RFC9002] Iyengar, J., Ed. and I. Swett, Ed., "QUIC Loss Detection and Congestion Control", RFC 9002, DOI 10.17487/RFC9002, May 2021, . Acknowledgments These individuals suggested improvements to this document: Author's Address Lars Eggert Mozilla Stenbergintie 12 B FI-02700 Kauniainen Finland Email: lars@eggert.org URI: https://eggert.org/