RFC 9002 - QUIC Loss Detection and Congestion Control

Publication Date: May 2021
Status: Standards Track
Authors: J. Iyengar (Fastly), I. Swett (Google)

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Abstract

This document describes loss detection and congestion control mechanisms for QUIC.

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Table of Contents

• 1. Introduction
• 2. Conventions and Definitions
• 3. Design of the QUIC Transmission Machinery
• 4. Relevant Differences between QUIC and TCP
  • 4.1 Separate Packet Number Spaces
  • 4.2 Monotonically Increasing Packet Numbers
  • 4.3 Clearer Loss Epoch
  • 4.4 No Reneging
  • 4.5 More ACK Ranges
  • 4.6 Explicit Correction for Delayed Acknowledgments
  • 4.7 Probe Timeout Replaces RTO and TLP
  • 4.8 The Minimum Congestion Window Is Two Packets
  • 4.9 Handshake Packets Are Not Special
• 5. Estimating the Round-Trip Time
  • 5.1 Generating RTT Samples
  • 5.2 Estimating min_rtt
  • 5.3 Estimating smoothed_rtt and rttvar
• 6. Loss Detection
  • 6.1 Acknowledgment-Based Detection
  • 6.2 Probe Timeout
  • 6.3 Handling Retry Packets
  • 6.4 Discarding Keys and Packet State
• 7. Congestion Control
  • 7.1 Explicit Congestion Notification
  • 7.2 Initial and Minimum Congestion Window
  • 7.3 Congestion Control States
  • 7.4 Ignoring Loss of Undecryptable Packets
  • 7.5 Probe Timeout
  • 7.6 Persistent Congestion
  • 7.7 Pacing
  • 7.8 Underutilizing the Congestion Window
• 8. Security Considerations
  • 8.1 Loss and Congestion Signals
  • 8.2 Traffic Analysis
  • 8.3 Misreporting ECN Markings
• 9. References

Appendices

• Appendix A. Loss Recovery Pseudocode
• Appendix B. Congestion Control Pseudocode

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Related Resources

• Official Text: RFC 9002
• Official Page: RFC 9002 DataTracker
• Errata: RFC Editor Errata

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