QUIC Loss Detection and Congestion Control
draft-ietf-quic-recovery-32
QUIC J. Iyengar, Ed.
Internet-Draft Fastly
Intended status: Standards Track I. Swett, Ed.
Expires: 23 April 2021 Google
20 October 2020
QUIC Loss Detection and Congestion Control
draft-ietf-quic-recovery-32
Abstract
This document describes loss detection and congestion control
mechanisms for QUIC.
Note to Readers
Discussion of this draft takes place on the QUIC working group
mailing list (quic@ietf.org (mailto:quic@ietf.org)), which is
archived at https://mailarchive.ietf.org/arch/
search/?email_list=quic.
Working Group information can be found at https://github.com/quicwg;
source code and issues list for this draft can be found at
https://github.com/quicwg/base-drafts/labels/-recovery.
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
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This Internet-Draft will expire on 23 April 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
Iyengar & Swett Expires 23 April 2021 [Page 1]
Internet-Draft QUIC Loss Detection October 2020
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Design of the QUIC Transmission Machinery . . . . . . . . . . 5
4. Relevant Differences Between QUIC and TCP . . . . . . . . . . 6
4.1. Separate Packet Number Spaces . . . . . . . . . . . . . . 6
4.2. Monotonically Increasing Packet Numbers . . . . . . . . . 6
4.3. Clearer Loss Epoch . . . . . . . . . . . . . . . . . . . 7
4.4. No Reneging . . . . . . . . . . . . . . . . . . . . . . . 7
4.5. More ACK Ranges . . . . . . . . . . . . . . . . . . . . . 7
4.6. Explicit Correction For Delayed Acknowledgements . . . . 7
4.7. Probe Timeout Replaces RTO and TLP . . . . . . . . . . . 7
4.8. The Minimum Congestion Window is Two Packets . . . . . . 8
5. Estimating the Round-Trip Time . . . . . . . . . . . . . . . 8
5.1. Generating RTT samples . . . . . . . . . . . . . . . . . 8
5.2. Estimating min_rtt . . . . . . . . . . . . . . . . . . . 9
5.3. Estimating smoothed_rtt and rttvar . . . . . . . . . . . 10
6. Loss Detection . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Acknowledgement-Based Detection . . . . . . . . . . . . . 12
6.1.1. Packet Threshold . . . . . . . . . . . . . . . . . . 13
6.1.2. Time Threshold . . . . . . . . . . . . . . . . . . . 13
6.2. Probe Timeout . . . . . . . . . . . . . . . . . . . . . . 14
6.2.1. Computing PTO . . . . . . . . . . . . . . . . . . . . 15
6.2.2. Handshakes and New Paths . . . . . . . . . . . . . . 16
6.2.3. Speeding Up Handshake Completion . . . . . . . . . . 17
6.2.4. Sending Probe Packets . . . . . . . . . . . . . . . . 18
6.3. Handling Retry Packets . . . . . . . . . . . . . . . . . 19
6.4. Discarding Keys and Packet State . . . . . . . . . . . . 19
7. Congestion Control . . . . . . . . . . . . . . . . . . . . . 20
7.1. Explicit Congestion Notification . . . . . . . . . . . . 20
7.2. Initial and Minimum Congestion Window . . . . . . . . . . 21
7.3. Congestion Control States . . . . . . . . . . . . . . . . 21
7.3.1. Slow Start . . . . . . . . . . . . . . . . . . . . . 22
7.3.2. Recovery . . . . . . . . . . . . . . . . . . . . . . 22
7.3.3. Congestion Avoidance . . . . . . . . . . . . . . . . 23
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