draft-ietf-quic-recovery-31.txt   draft-ietf-quic-recovery-32.txt 
QUIC J. Iyengar, Ed. QUIC J. Iyengar, Ed.
Internet-Draft Fastly Internet-Draft Fastly
Intended status: Standards Track I. Swett, Ed. Intended status: Standards Track I. Swett, Ed.
Expires: 29 March 2021 Google Expires: 23 April 2021 Google
25 September 2020 20 October 2020
QUIC Loss Detection and Congestion Control QUIC Loss Detection and Congestion Control
draft-ietf-quic-recovery-31 draft-ietf-quic-recovery-32
Abstract Abstract
This document describes loss detection and congestion control This document describes loss detection and congestion control
mechanisms for QUIC. mechanisms for QUIC.
Note to Readers Note to Readers
Discussion of this draft takes place on the QUIC working group Discussion of this draft takes place on the QUIC working group
mailing list (quic@ietf.org (mailto:quic@ietf.org)), which is mailing list (quic@ietf.org (mailto:quic@ietf.org)), which is
skipping to change at page 1, line 43 skipping to change at page 1, line 43
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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This Internet-Draft will expire on 29 March 2021. This Internet-Draft will expire on 23 April 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
3. Design of the QUIC Transmission Machinery . . . . . . . . . . 5 3. Design of the QUIC Transmission Machinery . . . . . . . . . . 5
4. Relevant Differences Between QUIC and TCP . . . . . . . . . . 5 4. Relevant Differences Between QUIC and TCP . . . . . . . . . . 6
4.1. Separate Packet Number Spaces . . . . . . . . . . . . . . 6 4.1. Separate Packet Number Spaces . . . . . . . . . . . . . . 6
4.2. Monotonically Increasing Packet Numbers . . . . . . . . . 6 4.2. Monotonically Increasing Packet Numbers . . . . . . . . . 6
4.3. Clearer Loss Epoch . . . . . . . . . . . . . . . . . . . 6 4.3. Clearer Loss Epoch . . . . . . . . . . . . . . . . . . . 7
4.4. No Reneging . . . . . . . . . . . . . . . . . . . . . . . 7 4.4. No Reneging . . . . . . . . . . . . . . . . . . . . . . . 7
4.5. More ACK Ranges . . . . . . . . . . . . . . . . . . . . . 7 4.5. More ACK Ranges . . . . . . . . . . . . . . . . . . . . . 7
4.6. Explicit Correction For Delayed Acknowledgements . . . . 7 4.6. Explicit Correction For Delayed Acknowledgements . . . . 7
4.7. Probe Timeout Replaces RTO and TLP . . . . . . . . . . . 7 4.7. Probe Timeout Replaces RTO and TLP . . . . . . . . . . . 7
4.8. The Minimum Congestion Window is Two Packets . . . . . . 8 4.8. The Minimum Congestion Window is Two Packets . . . . . . 8
5. Estimating the Round-Trip Time . . . . . . . . . . . . . . . 8 5. Estimating the Round-Trip Time . . . . . . . . . . . . . . . 8
5.1. Generating RTT samples . . . . . . . . . . . . . . . . . 8 5.1. Generating RTT samples . . . . . . . . . . . . . . . . . 8
5.2. Estimating min_rtt . . . . . . . . . . . . . . . . . . . 9 5.2. Estimating min_rtt . . . . . . . . . . . . . . . . . . . 9
5.3. Estimating smoothed_rtt and rttvar . . . . . . . . . . . 10 5.3. Estimating smoothed_rtt and rttvar . . . . . . . . . . . 10
6. Loss Detection . . . . . . . . . . . . . . . . . . . . . . . 12 6. Loss Detection . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. Acknowledgement-Based Detection . . . . . . . . . . . . . 12 6.1. Acknowledgement-Based Detection . . . . . . . . . . . . . 12
6.1.1. Packet Threshold . . . . . . . . . . . . . . . . . . 13 6.1.1. Packet Threshold . . . . . . . . . . . . . . . . . . 13
6.1.2. Time Threshold . . . . . . . . . . . . . . . . . . . 13 6.1.2. Time Threshold . . . . . . . . . . . . . . . . . . . 13
6.2. Probe Timeout . . . . . . . . . . . . . . . . . . . . . . 14 6.2. Probe Timeout . . . . . . . . . . . . . . . . . . . . . . 14
6.2.1. Computing PTO . . . . . . . . . . . . . . . . . . . . 14 6.2.1. Computing PTO . . . . . . . . . . . . . . . . . . . . 15
6.2.2. Handshakes and New Paths . . . . . . . . . . . . . . 16 6.2.2. Handshakes and New Paths . . . . . . . . . . . . . . 16
6.2.3. Speeding Up Handshake Completion . . . . . . . . . . 17 6.2.3. Speeding Up Handshake Completion . . . . . . . . . . 17
6.2.4. Sending Probe Packets . . . . . . . . . . . . . . . . 17 6.2.4. Sending Probe Packets . . . . . . . . . . . . . . . . 18
6.3. Handling Retry Packets . . . . . . . . . . . . . . . . . 18 6.3. Handling Retry Packets . . . . . . . . . . . . . . . . . 19
6.4. Discarding Keys and Packet State . . . . . . . . . . . . 19 6.4. Discarding Keys and Packet State . . . . . . . . . . . . 19
7. Congestion Control . . . . . . . . . . . . . . . . . . . . . 19 7. Congestion Control . . . . . . . . . . . . . . . . . . . . . 20
7.1. Explicit Congestion Notification . . . . . . . . . . . . 20 7.1. Explicit Congestion Notification . . . . . . . . . . . . 20
7.2. Initial and Minimum Congestion Window . . . . . . . . . . 20 7.2. Initial and Minimum Congestion Window . . . . . . . . . . 21
7.3. Congestion Control States . . . . . . . . . . . . . . . . 20 7.3. Congestion Control States . . . . . . . . . . . . . . . . 21
7.3.1. Slow Start . . . . . . . . . . . . . . . . . . . . . 21 7.3.1. Slow Start . . . . . . . . . . . . . . . . . . . . . 22
7.3.2. Recovery . . . . . . . . . . . . . . . . . . . . . . 21 7.3.2. Recovery . . . . . . . . . . . . . . . . . . . . . . 22
7.3.3. Congestion Avoidance . . . . . . . . . . . . . . . . 22 7.3.3. Congestion Avoidance . . . . . . . . . . . . . . . . 23
7.4. Ignoring Loss of Undecryptable Packets . . . . . . . . . 22 7.4. Ignoring Loss of Undecryptable Packets . . . . . . . . . 23
7.5. Probe Timeout . . . . . . . . . . . . . . . . . . . . . . 23 7.5. Probe Timeout . . . . . . . . . . . . . . . . . . . . . . 24
7.6. Persistent Congestion . . . . . . . . . . . . . . . . . . 23 7.6. Persistent Congestion . . . . . . . . . . . . . . . . . . 24
7.6.1. Duration . . . . . . . . . . . . . . . . . . . . . . 23 7.6.1. Duration . . . . . . . . . . . . . . . . . . . . . . 24
7.6.2. Establishing Persistent Congestion . . . . . . . . . 24 7.6.2. Establishing Persistent Congestion . . . . . . . . . 25
7.6.3. Example . . . . . . . . . . . . . . . . . . . . . . . 24 7.6.3. Example . . . . . . . . . . . . . . . . . . . . . . . 25
7.7. Pacing . . . . . . . . . . . . . . . . . . . . . . . . . 25 7.7. Pacing . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.8. Under-utilizing the Congestion Window . . . . . . . . . . 27 7.8. Under-utilizing the Congestion Window . . . . . . . . . . 28
8. Security Considerations . . . . . . . . . . . . . . . . . . . 27 8. Security Considerations . . . . . . . . . . . . . . . . . . . 28
8.1. Congestion Signals . . . . . . . . . . . . . . . . . . . 27 8.1. Congestion Signals . . . . . . . . . . . . . . . . . . . 28
8.2. Traffic Analysis . . . . . . . . . . . . . . . . . . . . 27 8.2. Traffic Analysis . . . . . . . . . . . . . . . . . . . . 28
8.3. Misreporting ECN Markings . . . . . . . . . . . . . . . . 27 8.3. Misreporting ECN Markings . . . . . . . . . . . . . . . . 28
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
10.1. Normative References . . . . . . . . . . . . . . . . . . 28 10.1. Normative References . . . . . . . . . . . . . . . . . . 29
10.2. Informative References . . . . . . . . . . . . . . . . . 29 10.2. Informative References . . . . . . . . . . . . . . . . . 30
Appendix A. Loss Recovery Pseudocode . . . . . . . . . . . . . . 30 Appendix A. Loss Recovery Pseudocode . . . . . . . . . . . . . . 31
A.1. Tracking Sent Packets . . . . . . . . . . . . . . . . . . 30 A.1. Tracking Sent Packets . . . . . . . . . . . . . . . . . . 32
A.1.1. Sent Packet Fields . . . . . . . . . . . . . . . . . 31 A.1.1. Sent Packet Fields . . . . . . . . . . . . . . . . . 32
A.2. Constants of Interest . . . . . . . . . . . . . . . . . . 31 A.2. Constants of Interest . . . . . . . . . . . . . . . . . . 32
A.3. Variables of interest . . . . . . . . . . . . . . . . . . 32 A.3. Variables of interest . . . . . . . . . . . . . . . . . . 33
A.4. Initialization . . . . . . . . . . . . . . . . . . . . . 33 A.4. Initialization . . . . . . . . . . . . . . . . . . . . . 34
A.5. On Sending a Packet . . . . . . . . . . . . . . . . . . . 33 A.5. On Sending a Packet . . . . . . . . . . . . . . . . . . . 34
A.6. On Receiving a Datagram . . . . . . . . . . . . . . . . . 33 A.6. On Receiving a Datagram . . . . . . . . . . . . . . . . . 35
A.7. On Receiving an Acknowledgment . . . . . . . . . . . . . 34 A.7. On Receiving an Acknowledgment . . . . . . . . . . . . . 35
A.8. Setting the Loss Detection Timer . . . . . . . . . . . . 35 A.8. Setting the Loss Detection Timer . . . . . . . . . . . . 37
A.9. On Timeout . . . . . . . . . . . . . . . . . . . . . . . 37 A.9. On Timeout . . . . . . . . . . . . . . . . . . . . . . . 38
A.10. Detecting Lost Packets . . . . . . . . . . . . . . . . . 38 A.10. Detecting Lost Packets . . . . . . . . . . . . . . . . . 39
Appendix B. Congestion Control Pseudocode . . . . . . . . . . . 39 A.11. Upon Dropping Initial or Handshake Keys . . . . . . . . . 40
B.1. Constants of interest . . . . . . . . . . . . . . . . . . 39 Appendix B. Congestion Control Pseudocode . . . . . . . . . . . 41
B.2. Variables of interest . . . . . . . . . . . . . . . . . . 40 B.1. Constants of interest . . . . . . . . . . . . . . . . . . 41
B.3. Initialization . . . . . . . . . . . . . . . . . . . . . 40 B.2. Variables of interest . . . . . . . . . . . . . . . . . . 41
B.4. On Packet Sent . . . . . . . . . . . . . . . . . . . . . 41 B.3. Initialization . . . . . . . . . . . . . . . . . . . . . 42
B.5. On Packet Acknowledgement . . . . . . . . . . . . . . . . 41 B.4. On Packet Sent . . . . . . . . . . . . . . . . . . . . . 42
B.6. On New Congestion Event . . . . . . . . . . . . . . . . . 42 B.5. On Packet Acknowledgement . . . . . . . . . . . . . . . . 43
B.7. Process ECN Information . . . . . . . . . . . . . . . . . 43 B.6. On New Congestion Event . . . . . . . . . . . . . . . . . 43
B.8. On Packets Lost . . . . . . . . . . . . . . . . . . . . . 43 B.7. Process ECN Information . . . . . . . . . . . . . . . . . 44
B.9. Upon dropping Initial or Handshake keys . . . . . . . . . 43 B.8. On Packets Lost . . . . . . . . . . . . . . . . . . . . . 44
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 44 B.9. Removing Discarded Packets From Bytes In Flight . . . . . 45
C.1. Since draft-ietf-quic-recovery-30 . . . . . . . . . . . . 44 Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 45
C.2. Since draft-ietf-quic-recovery-29 . . . . . . . . . . . . 44 C.1. Since draft-ietf-quic-recovery-31 . . . . . . . . . . . . 45
C.3. Since draft-ietf-quic-recovery-28 . . . . . . . . . . . . 44 C.2. Since draft-ietf-quic-recovery-30 . . . . . . . . . . . . 45
C.4. Since draft-ietf-quic-recovery-27 . . . . . . . . . . . . 45 C.3. Since draft-ietf-quic-recovery-29 . . . . . . . . . . . . 45
C.5. Since draft-ietf-quic-recovery-26 . . . . . . . . . . . . 45 C.4. Since draft-ietf-quic-recovery-28 . . . . . . . . . . . . 46
C.6. Since draft-ietf-quic-recovery-25 . . . . . . . . . . . . 45 C.5. Since draft-ietf-quic-recovery-27 . . . . . . . . . . . . 46
C.7. Since draft-ietf-quic-recovery-24 . . . . . . . . . . . . 45 C.6. Since draft-ietf-quic-recovery-26 . . . . . . . . . . . . 46
C.8. Since draft-ietf-quic-recovery-23 . . . . . . . . . . . . 45 C.7. Since draft-ietf-quic-recovery-25 . . . . . . . . . . . . 46
C.9. Since draft-ietf-quic-recovery-22 . . . . . . . . . . . . 46 C.8. Since draft-ietf-quic-recovery-24 . . . . . . . . . . . . 46
C.10. Since draft-ietf-quic-recovery-21 . . . . . . . . . . . . 46 C.9. Since draft-ietf-quic-recovery-23 . . . . . . . . . . . . 46
C.11. Since draft-ietf-quic-recovery-20 . . . . . . . . . . . . 46 C.10. Since draft-ietf-quic-recovery-22 . . . . . . . . . . . . 47
C.12. Since draft-ietf-quic-recovery-19 . . . . . . . . . . . . 46 C.11. Since draft-ietf-quic-recovery-21 . . . . . . . . . . . . 47
C.13. Since draft-ietf-quic-recovery-18 . . . . . . . . . . . . 47 C.12. Since draft-ietf-quic-recovery-20 . . . . . . . . . . . . 47
C.14. Since draft-ietf-quic-recovery-17 . . . . . . . . . . . . 47 C.13. Since draft-ietf-quic-recovery-19 . . . . . . . . . . . . 47
C.15. Since draft-ietf-quic-recovery-16 . . . . . . . . . . . . 47 C.14. Since draft-ietf-quic-recovery-18 . . . . . . . . . . . . 48
C.16. Since draft-ietf-quic-recovery-14 . . . . . . . . . . . . 48 C.15. Since draft-ietf-quic-recovery-17 . . . . . . . . . . . . 48
C.17. Since draft-ietf-quic-recovery-13 . . . . . . . . . . . . 48 C.16. Since draft-ietf-quic-recovery-16 . . . . . . . . . . . . 49
C.18. Since draft-ietf-quic-recovery-12 . . . . . . . . . . . . 48 C.17. Since draft-ietf-quic-recovery-14 . . . . . . . . . . . . 49
C.19. Since draft-ietf-quic-recovery-11 . . . . . . . . . . . . 49 C.18. Since draft-ietf-quic-recovery-13 . . . . . . . . . . . . 49
C.20. Since draft-ietf-quic-recovery-10 . . . . . . . . . . . . 49 C.19. Since draft-ietf-quic-recovery-12 . . . . . . . . . . . . 50
C.21. Since draft-ietf-quic-recovery-09 . . . . . . . . . . . . 49 C.20. Since draft-ietf-quic-recovery-11 . . . . . . . . . . . . 50
C.22. Since draft-ietf-quic-recovery-08 . . . . . . . . . . . . 49 C.21. Since draft-ietf-quic-recovery-10 . . . . . . . . . . . . 50
C.23. Since draft-ietf-quic-recovery-07 . . . . . . . . . . . . 49 C.22. Since draft-ietf-quic-recovery-09 . . . . . . . . . . . . 50
C.24. Since draft-ietf-quic-recovery-06 . . . . . . . . . . . . 49 C.23. Since draft-ietf-quic-recovery-08 . . . . . . . . . . . . 50
C.25. Since draft-ietf-quic-recovery-05 . . . . . . . . . . . . 49 C.24. Since draft-ietf-quic-recovery-07 . . . . . . . . . . . . 50
C.26. Since draft-ietf-quic-recovery-04 . . . . . . . . . . . . 50 C.25. Since draft-ietf-quic-recovery-06 . . . . . . . . . . . . 51
C.27. Since draft-ietf-quic-recovery-03 . . . . . . . . . . . . 50 C.26. Since draft-ietf-quic-recovery-05 . . . . . . . . . . . . 51
C.28. Since draft-ietf-quic-recovery-02 . . . . . . . . . . . . 50 C.27. Since draft-ietf-quic-recovery-04 . . . . . . . . . . . . 51
C.29. Since draft-ietf-quic-recovery-01 . . . . . . . . . . . . 50 C.28. Since draft-ietf-quic-recovery-03 . . . . . . . . . . . . 51
C.30. Since draft-ietf-quic-recovery-00 . . . . . . . . . . . . 50 C.29. Since draft-ietf-quic-recovery-02 . . . . . . . . . . . . 51
C.31. Since draft-iyengar-quic-loss-recovery-01 . . . . . . . . 50 C.30. Since draft-ietf-quic-recovery-01 . . . . . . . . . . . . 51
Appendix D. Contributors . . . . . . . . . . . . . . . . . . . . 51 C.31. Since draft-ietf-quic-recovery-00 . . . . . . . . . . . . 51
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 51 C.32. Since draft-iyengar-quic-loss-recovery-01 . . . . . . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51 Appendix D. Contributors . . . . . . . . . . . . . . . . . . . . 52
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 52
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 52
1. Introduction 1. Introduction
QUIC is a new multiplexed and secure transport protocol atop UDP, QUIC is a new multiplexed and secure transport protocol atop UDP,
specified in [QUIC-TRANSPORT]. This document describes congestion specified in [QUIC-TRANSPORT]. This document describes congestion
control and loss recovery for QUIC. Mechanisms described in this control and loss recovery for QUIC. Mechanisms described in this
document follow the spirit of existing TCP congestion control and document follow the spirit of existing TCP congestion control and
loss recovery mechanisms, described in RFCs, various Internet-drafts, loss recovery mechanisms, described in RFCs, various Internet-drafts,
or academic papers, and also those prevalent in TCP implementations. or academic papers, and also those prevalent in TCP implementations.
skipping to change at page 10, line 18 skipping to change at page 10, line 31
NOT refresh the min_rtt value too often, since the actual minimum RTT NOT refresh the min_rtt value too often, since the actual minimum RTT
of the path is not frequently observable. of the path is not frequently observable.
5.3. Estimating smoothed_rtt and rttvar 5.3. Estimating smoothed_rtt and rttvar
smoothed_rtt is an exponentially-weighted moving average of an smoothed_rtt is an exponentially-weighted moving average of an
endpoint's RTT samples, and rttvar is the variation in the RTT endpoint's RTT samples, and rttvar is the variation in the RTT
samples, estimated using a mean variation. samples, estimated using a mean variation.
The calculation of smoothed_rtt uses RTT samples after adjusting them The calculation of smoothed_rtt uses RTT samples after adjusting them
for acknowledgement delays. These delays are computed using the ACK for acknowledgement delays. These delays are decoded from the ACK
Delay field of the ACK frame as described in Section 19.3 of Delay field of ACK frames as described in Section 19.3 of
[QUIC-TRANSPORT]. [QUIC-TRANSPORT].
The peer might report acknowledgement delays that are larger than the The peer might report acknowledgement delays that are larger than the
peer's max_ack_delay during the handshake (Section 13.2.1 of peer's max_ack_delay during the handshake (Section 13.2.1 of
[QUIC-TRANSPORT]). To account for this, the endpoint SHOULD ignore [QUIC-TRANSPORT]). To account for this, the endpoint SHOULD ignore
max_ack_delay until the handshake is confirmed (Section 4.1.2 of max_ack_delay until the handshake is confirmed (Section 4.1.2 of
[QUIC-TLS]). When they occur, these large acknowledgement delays are [QUIC-TLS]). When they occur, these large acknowledgement delays are
likely to be non-repeating and limited to the handshake. The likely to be non-repeating and limited to the handshake. The
endpoint can therefore use them without limiting them to the endpoint can therefore use them without limiting them to the
max_ack_delay, avoiding unnecessary inflation of the RTT estimate. max_ack_delay, avoiding unnecessary inflation of the RTT estimate.
skipping to change at page 10, line 43 skipping to change at page 11, line 9
the peer's reporting of the acknowledgement delay or in the the peer's reporting of the acknowledgement delay or in the
endpoint's min_rtt estimate. Therefore, prior to handshake endpoint's min_rtt estimate. Therefore, prior to handshake
confirmation, an endpoint MAY ignore RTT samples if adjusting the RTT confirmation, an endpoint MAY ignore RTT samples if adjusting the RTT
sample for acknowledgement delay causes the sample to be less than sample for acknowledgement delay causes the sample to be less than
the min_rtt. the min_rtt.
After the handshake is confirmed, any acknowledgement delays reported After the handshake is confirmed, any acknowledgement delays reported
by the peer that are greater than the peer's max_ack_delay are by the peer that are greater than the peer's max_ack_delay are
attributed to unintentional but potentially repeating delays, such as attributed to unintentional but potentially repeating delays, such as
scheduler latency at the peer or loss of previous acknowledgements. scheduler latency at the peer or loss of previous acknowledgements.
Excess delays could also be due to a non-compliant receiver.
Therefore, these extra delays are considered effectively part of path Therefore, these extra delays are considered effectively part of path
delay and incorporated into the RTT estimate. delay and incorporated into the RTT estimate.
Therefore, when adjusting an RTT sample using peer-reported Therefore, when adjusting an RTT sample using peer-reported
acknowledgement delays, an endpoint: acknowledgement delays, an endpoint:
* MAY ignore the acknowledgement delay for Initial packets, since * MAY ignore the acknowledgement delay for Initial packets, since
these acknowledgements are not delayed by the peer (Section 13.2.1 these acknowledgements are not delayed by the peer (Section 13.2.1
of [QUIC-TRANSPORT]); of [QUIC-TRANSPORT]);
skipping to change at page 11, line 23 skipping to change at page 11, line 38
underestimation of the smoothed_rtt due to a misreporting peer. underestimation of the smoothed_rtt due to a misreporting peer.
Additionally, an endpoint might postpone the processing of Additionally, an endpoint might postpone the processing of
acknowledgements when the corresponding decryption keys are not acknowledgements when the corresponding decryption keys are not
immediately available. For example, a client might receive an immediately available. For example, a client might receive an
acknowledgement for a 0-RTT packet that it cannot decrypt because acknowledgement for a 0-RTT packet that it cannot decrypt because
1-RTT packet protection keys are not yet available to it. In such 1-RTT packet protection keys are not yet available to it. In such
cases, an endpoint SHOULD subtract such local delays from its RTT cases, an endpoint SHOULD subtract such local delays from its RTT
sample until the handshake is confirmed. sample until the handshake is confirmed.
smoothed_rtt and rttvar are computed as follows, similar to Similar to [RFC6298], smoothed_rtt and rttvar are computed as
[RFC6298]. follows.
When there are no samples for a network path, and on the first RTT An endpoint initializes the RTT estimator during connection
sample for the network path: establishment and when the estimator is reset during connection
migration; see Section 9.4 of [QUIC-TRANSPORT]. Before any RTT
samples are available for a new path or when the estimator is reset,
the estimator is initialized using the initial RTT; see
Section 6.2.2.
smoothed_rtt = rtt_sample smoothed_rtt and rttvar are initialized as follows, where kInitialRtt
rttvar = rtt_sample / 2 contains the initial RTT value:
Before any RTT samples are available, the initial RTT is used as smoothed_rtt = kInitialRtt
rtt_sample. On the first RTT sample for the network path, that rttvar = kInitialRtt / 2
sample is used as rtt_sample. This ensures that the first RTT samples for the network path are recorded in latest_rtt; see
measurement erases the history of any persisted or default values. Section 5.1. On the first RTT sample after initialization, the
estimator is reset using that sample. This ensures that the
estimator retains no history of past samples.
On the first RTT sample after initialization, smoothed_rtt and rttvar
are set as follows:
smoothed_rtt = latest_rtt
rttvar = latest_rtt / 2
On subsequent RTT samples, smoothed_rtt and rttvar evolve as follows: On subsequent RTT samples, smoothed_rtt and rttvar evolve as follows:
ack_delay = decoded acknowledgement delay from ACK frame ack_delay = decoded acknowledgement delay from ACK frame
if (handshake confirmed): if (handshake confirmed):
ack_delay = min(ack_delay, max_ack_delay) ack_delay = min(ack_delay, max_ack_delay)
adjusted_rtt = latest_rtt adjusted_rtt = latest_rtt
if (min_rtt + ack_delay < latest_rtt): if (min_rtt + ack_delay < latest_rtt):
adjusted_rtt = latest_rtt - ack_delay adjusted_rtt = latest_rtt - ack_delay
smoothed_rtt = 7/8 * smoothed_rtt + 1/8 * adjusted_rtt smoothed_rtt = 7/8 * smoothed_rtt + 1/8 * adjusted_rtt
skipping to change at page 12, line 34 skipping to change at page 13, line 8
Fast Retransmit ([RFC5681]), Early Retransmit ([RFC5827]), FACK Fast Retransmit ([RFC5681]), Early Retransmit ([RFC5827]), FACK
([FACK]), SACK loss recovery ([RFC6675]), and RACK ([RACK]). This ([FACK]), SACK loss recovery ([RFC6675]), and RACK ([RACK]). This
section provides an overview of how these algorithms are implemented section provides an overview of how these algorithms are implemented
in QUIC. in QUIC.
A packet is declared lost if it meets all the following conditions: A packet is declared lost if it meets all the following conditions:
* The packet is unacknowledged, in-flight, and was sent prior to an * The packet is unacknowledged, in-flight, and was sent prior to an
acknowledged packet. acknowledged packet.
* Either its packet number is kPacketThreshold smaller than an * The packet was sent kPacketThreshold packets before an
acknowledged packet (Section 6.1.1), or it was sent long enough in acknowledged packet (Section 6.1.1), or it was sent long enough in
the past (Section 6.1.2). the past (Section 6.1.2).
The acknowledgement indicates that a packet sent later was delivered, The acknowledgement indicates that a packet sent later was delivered,
and the packet and time thresholds provide some tolerance for packet and the packet and time thresholds provide some tolerance for packet
reordering. reordering.
Spuriously declaring packets as lost leads to unnecessary Spuriously declaring packets as lost leads to unnecessary
retransmissions and may result in degraded performance due to the retransmissions and may result in degraded performance due to the
actions of the congestion controller upon detecting loss. actions of the congestion controller upon detecting loss.
skipping to change at page 15, line 27 skipping to change at page 15, line 50
acknowledgements. For example, this can happen when a client sends acknowledgements. For example, this can happen when a client sends
0-RTT packets to the server; it does so without knowing whether the 0-RTT packets to the server; it does so without knowing whether the
server will be able to decrypt them. Similarly, this can happen when server will be able to decrypt them. Similarly, this can happen when
a server sends 1-RTT packets before confirming that the client has a server sends 1-RTT packets before confirming that the client has
verified the server's certificate and can therefore read these 1-RTT verified the server's certificate and can therefore read these 1-RTT
packets. packets.
A sender SHOULD restart its PTO timer every time an ack-eliciting A sender SHOULD restart its PTO timer every time an ack-eliciting
packet is sent or acknowledged, when the handshake is confirmed packet is sent or acknowledged, when the handshake is confirmed
(Section 4.1.2 of [QUIC-TLS]), or when Initial or Handshake keys are (Section 4.1.2 of [QUIC-TLS]), or when Initial or Handshake keys are
discarded (Section 9 of [QUIC-TLS]). This ensures the PTO is always discarded (Section 4.9 of [QUIC-TLS]). This ensures the PTO is
set based on the latest estimate of the round-trip time and for the always set based on the latest estimate of the round-trip time and
correct packet across packet number spaces. for the correct packet across packet number spaces.
When a PTO timer expires, the PTO backoff MUST be increased, When a PTO timer expires, the PTO backoff MUST be increased,
resulting in the PTO period being set to twice its current value. resulting in the PTO period being set to twice its current value.
The PTO backoff factor is reset when an acknowledgement is received, The PTO backoff factor is reset when an acknowledgement is received,
except in the following case. A server might take longer to respond except in the following case. A server might take longer to respond
to packets during the handshake than otherwise. To protect such a to packets during the handshake than otherwise. To protect such a
server from repeated client probes, the PTO backoff is not reset at a server from repeated client probes, the PTO backoff is not reset at a
client that is not yet certain that the server has finished client that is not yet certain that the server has finished
validating the client's address. That is, a client does not reset validating the client's address. That is, a client does not reset
the PTO backoff factor on receiving acknowledgements until the the PTO backoff factor on receiving acknowledgements in Initial
handshake is confirmed; see Section 4.1.2 of [QUIC-TLS]. packets.
This exponential reduction in the sender's rate is important because This exponential reduction in the sender's rate is important because
consecutive PTOs might be caused by loss of packets or consecutive PTOs might be caused by loss of packets or
acknowledgements due to severe congestion. Even when there are ack- acknowledgements due to severe congestion. Even when there are ack-
eliciting packets in-flight in multiple packet number spaces, the eliciting packets in-flight in multiple packet number spaces, the
exponential increase in probe timeout occurs across all spaces to exponential increase in probe timeout occurs across all spaces to
prevent excess load on the network. For example, a timeout in the prevent excess load on the network. For example, a timeout in the
Initial packet number space doubles the length of the timeout in the Initial packet number space doubles the length of the timeout in the
Handshake packet number space. Handshake packet number space.
The total length of time over which consecutive PTOs expire is The total length of time over which consecutive PTOs expire is
limited by the idle timeout. limited by the idle timeout.
The probe timer MUST NOT be set if the time threshold (Section 6.1.2) The PTO timer MUST NOT be set if a timer is set for time threshold
loss detection timer is set. The time threshold loss detection timer loss detection; see Section 6.1.2. A timer that is set for time
is expected to both expire earlier than the PTO and be less likely to threshold loss detection will expire earlier than the PTO timer in
spuriously retransmit data. most cases and is less likely to spuriously retransmit data.
6.2.2. Handshakes and New Paths 6.2.2. Handshakes and New Paths
Resumed connections over the same network MAY use the previous Resumed connections over the same network MAY use the previous
connection's final smoothed RTT value as the resumed connection's connection's final smoothed RTT value as the resumed connection's
initial RTT. When no previous RTT is available, the initial RTT initial RTT. When no previous RTT is available, the initial RTT
SHOULD be set to 333ms, resulting in a 1 second initial timeout, as SHOULD be set to 333ms, resulting in a 1 second initial timeout, as
recommended in [RFC6298]. recommended in [RFC6298].
A connection MAY use the delay between sending a PATH_CHALLENGE and A connection MAY use the delay between sending a PATH_CHALLENGE and
skipping to change at page 17, line 15 skipping to change at page 17, line 38
6.2.3. Speeding Up Handshake Completion 6.2.3. Speeding Up Handshake Completion
When a server receives an Initial packet containing duplicate CRYPTO When a server receives an Initial packet containing duplicate CRYPTO
data, it can assume the client did not receive all of the server's data, it can assume the client did not receive all of the server's
CRYPTO data sent in Initial packets, or the client's estimated RTT is CRYPTO data sent in Initial packets, or the client's estimated RTT is
too small. When a client receives Handshake or 1-RTT packets prior too small. When a client receives Handshake or 1-RTT packets prior
to obtaining Handshake keys, it may assume some or all of the to obtaining Handshake keys, it may assume some or all of the
server's Initial packets were lost. server's Initial packets were lost.
To speed up handshake completion under these conditions, an endpoint To speed up handshake completion under these conditions, an endpoint
MAY send a packet containing unacknowledged CRYPTO data earlier than MAY, for a limited number of occasions per each connection, send a
the PTO expiry, subject to the address validation limits in packet containing unacknowledged CRYPTO data earlier than the PTO
Section 8.1 of [QUIC-TRANSPORT]. expiry, subject to the address validation limits in Section 8.1 of
[QUIC-TRANSPORT]. Doing so at most once for each connection is
adequate to quickly recover from a single packet loss. Endpoints
that do not cease retransmitting packets in response to
unauthenticated data risk creating an infinite exchange of packets.
Endpoints can also use coalesced packets (see Section 12.2 of Endpoints can also use coalesced packets (see Section 12.2 of
[QUIC-TRANSPORT]) to ensure that each datagram elicits at least one [QUIC-TRANSPORT]) to ensure that each datagram elicits at least one
acknowledgement. For example, a client can coalesce an Initial acknowledgement. For example, a client can coalesce an Initial
packet containing PING and PADDING frames with a 0-RTT data packet packet containing PING and PADDING frames with a 0-RTT data packet
and a server can coalesce an Initial packet containing a PING frame and a server can coalesce an Initial packet containing a PING frame
with one or more packets in its first flight. with one or more packets in its first flight.
6.2.4. Sending Probe Packets 6.2.4. Sending Probe Packets
skipping to change at page 19, line 7 skipping to change at page 19, line 32
connection state, in particular cryptographic handshake messages, is connection state, in particular cryptographic handshake messages, is
retained; see Section 17.2.5 of [QUIC-TRANSPORT]. retained; see Section 17.2.5 of [QUIC-TRANSPORT].
The client MAY compute an RTT estimate to the server as the time The client MAY compute an RTT estimate to the server as the time
period from when the first Initial was sent to when a Retry or a period from when the first Initial was sent to when a Retry or a
Version Negotiation packet is received. The client MAY use this Version Negotiation packet is received. The client MAY use this
value in place of its default for the initial RTT estimate. value in place of its default for the initial RTT estimate.
6.4. Discarding Keys and Packet State 6.4. Discarding Keys and Packet State
When packet protection keys are discarded (see Section 4.8 of When packet protection keys are discarded (see Section 4.9 of
[QUIC-TLS]), all packets that were sent with those keys can no longer [QUIC-TLS]), all packets that were sent with those keys can no longer
be acknowledged because their acknowledgements cannot be processed be acknowledged because their acknowledgements cannot be processed
anymore. The sender MUST discard all recovery state associated with anymore. The sender MUST discard all recovery state associated with
those packets and MUST remove them from the count of bytes in flight. those packets and MUST remove them from the count of bytes in flight.
Endpoints stop sending and receiving Initial packets once they start Endpoints stop sending and receiving Initial packets once they start
exchanging Handshake packets; see Section 17.2.2.1 of exchanging Handshake packets; see Section 17.2.2.1 of
[QUIC-TRANSPORT]. At this point, recovery state for all in-flight [QUIC-TRANSPORT]. At this point, recovery state for all in-flight
Initial packets is discarded. Initial packets is discarded.
skipping to change at page 19, line 32 skipping to change at page 20, line 12
arrive before Initial packets, early 0-RTT packets will be declared arrive before Initial packets, early 0-RTT packets will be declared
lost, but that is expected to be infrequent. lost, but that is expected to be infrequent.
It is expected that keys are discarded after packets encrypted with It is expected that keys are discarded after packets encrypted with
them would be acknowledged or declared lost. However, Initial them would be acknowledged or declared lost. However, Initial
secrets are discarded as soon as handshake keys are proven to be secrets are discarded as soon as handshake keys are proven to be
available to both client and server; see Section 4.9.1 of [QUIC-TLS]. available to both client and server; see Section 4.9.1 of [QUIC-TLS].
7. Congestion Control 7. Congestion Control
This document specifies a congestion controller for QUIC similar to This document specifies a sender-side congestion controller for QUIC
TCP NewReno ([RFC6582]). similar to TCP NewReno ([RFC6582]).
The signals QUIC provides for congestion control are generic and are The signals QUIC provides for congestion control are generic and are
designed to support different algorithms. Endpoints can unilaterally designed to support different sender-side algorithms. A sender can
choose a different algorithm to use, such as Cubic ([RFC8312]). unilaterally choose a different algorithm to use, such as Cubic
([RFC8312]).
If an endpoint uses a different controller than that specified in If a sender uses a different controller than that specified in this
this document, the chosen controller MUST conform to the congestion document, the chosen controller MUST conform to the congestion
control guidelines specified in Section 3.1 of [RFC8085]. control guidelines specified in Section 3.1 of [RFC8085].
Similar to TCP, packets containing only ACK frames do not count Similar to TCP, packets containing only ACK frames do not count
towards bytes in flight and are not congestion controlled. Unlike towards bytes in flight and are not congestion controlled. Unlike
TCP, QUIC can detect the loss of these packets and MAY use that TCP, QUIC can detect the loss of these packets and MAY use that
information to adjust the congestion controller or the rate of ACK- information to adjust the congestion controller or the rate of ACK-
only packets being sent, but this document does not describe a only packets being sent, but this document does not describe a
mechanism for doing so. mechanism for doing so.
The algorithm in this document specifies and uses the controller's The algorithm in this document specifies and uses the controller's
skipping to change at page 20, line 15 skipping to change at page 20, line 44
An endpoint MUST NOT send a packet if it would cause bytes_in_flight An endpoint MUST NOT send a packet if it would cause bytes_in_flight
(see Appendix B.2) to be larger than the congestion window, unless (see Appendix B.2) to be larger than the congestion window, unless
the packet is sent on a PTO timer expiration (see Section 6.2) or the packet is sent on a PTO timer expiration (see Section 6.2) or
when entering recovery (see Section 7.3.2). when entering recovery (see Section 7.3.2).
7.1. Explicit Congestion Notification 7.1. Explicit Congestion Notification
If a path has been validated to support ECN ([RFC3168], [RFC8311]), If a path has been validated to support ECN ([RFC3168], [RFC8311]),
QUIC treats a Congestion Experienced (CE) codepoint in the IP header QUIC treats a Congestion Experienced (CE) codepoint in the IP header
as a signal of congestion. This document specifies an endpoint's as a signal of congestion. This document specifies an endpoint's
response when its peer receives packets with the ECN-CE codepoint. response when the peer-reported ECN-CE count increases; see
Section 13.4.2 of [QUIC-TRANSPORT].
7.2. Initial and Minimum Congestion Window 7.2. Initial and Minimum Congestion Window
QUIC begins every connection in slow start with the congestion window QUIC begins every connection in slow start with the congestion window
set to an initial value. Endpoints SHOULD use an initial congestion set to an initial value. Endpoints SHOULD use an initial congestion
window of 10 times the maximum datagram size (max_datagram_size), window of 10 times the maximum datagram size (max_datagram_size),
limited to the larger of 14720 bytes or twice the maximum datagram limited to the larger of 14720 bytes or twice the maximum datagram
size. This follows the analysis and recommendations in [RFC6928], size. This follows the analysis and recommendations in [RFC6928],
increasing the byte limit to account for the smaller 8 byte overhead increasing the byte limit to account for the smaller 8 byte overhead
of UDP compared to the 20 byte overhead for TCP. of UDP compared to the 20 byte overhead for TCP.
skipping to change at page 20, line 41 skipping to change at page 21, line 29
congestion window. congestion window.
Prior to validating the client's address, the server can be further Prior to validating the client's address, the server can be further
limited by the anti-amplification limit as specified in Section 8.1 limited by the anti-amplification limit as specified in Section 8.1
of [QUIC-TRANSPORT]. Though the anti-amplification limit can prevent of [QUIC-TRANSPORT]. Though the anti-amplification limit can prevent
the congestion window from being fully utilized and therefore slow the congestion window from being fully utilized and therefore slow
down the increase in congestion window, it does not directly affect down the increase in congestion window, it does not directly affect
the congestion window. the congestion window.
The minimum congestion window is the smallest value the congestion The minimum congestion window is the smallest value the congestion
window can decrease to as a response to loss, ECN-CE, or persistent window can decrease to as a response to loss, increase in the peer-
congestion. The RECOMMENDED value is 2 * max_datagram_size. reported ECN-CE count, or persistent congestion. The RECOMMENDED
value is 2 * max_datagram_size.
7.3. Congestion Control States 7.3. Congestion Control States
The NewReno congestion controller described in this document has The NewReno congestion controller described in this document has
three distinct states, as shown in Figure 1. three distinct states, as shown in Figure 1.
New Path or +------------+ New Path or +------------+
persistent congestion | Slow | persistent congestion | Slow |
(O)---------------------->| Start | (O)---------------------->| Start |
+------------+ +------------+
skipping to change at page 23, line 40 skipping to change at page 24, line 40
Unlike the PTO computation in Section 6.2, this duration includes the Unlike the PTO computation in Section 6.2, this duration includes the
max_ack_delay irrespective of the packet number spaces in which max_ack_delay irrespective of the packet number spaces in which
losses are established. losses are established.
This duration allows a sender to send as many packets before This duration allows a sender to send as many packets before
establishing persistent congestion, including some in response to PTO establishing persistent congestion, including some in response to PTO
expiration, as TCP does with Tail Loss Probes ([RACK]) and a expiration, as TCP does with Tail Loss Probes ([RACK]) and a
Retransmission Timeout ([RFC5681]). Retransmission Timeout ([RFC5681]).
Larger values of kPersistentCongestionThreshold cause the sender to
become less responsive to persistent congestion in the network, which
can result in aggressive sending into a congested network. Too small
a value can result in a sender declaring persistent congestion
unnecessarily, resulting in reduced throughput for the sender.
The RECOMMENDED value for kPersistentCongestionThreshold is 3, which The RECOMMENDED value for kPersistentCongestionThreshold is 3, which
is approximately equivalent to two TLPs before an RTO in TCP. results in behavior that is approximately equivalent to a TCP sender
declaring an RTO after two TLPs.
This design does not use consecutive PTO events to establish This design does not use consecutive PTO events to establish
persistent congestion, since application patterns impact PTO persistent congestion, since application patterns impact PTO
expirations. For example, a sender that sends small amounts of data expirations. For example, a sender that sends small amounts of data
with silence periods between them restarts the PTO timer every time with silence periods between them restarts the PTO timer every time
it sends, potentially preventing the PTO timer from expiring for a it sends, potentially preventing the PTO timer from expiring for a
long period of time, even when no acknowledgments are being received. long period of time, even when no acknowledgments are being received.
The use of a duration enables a sender to establish persistent The use of a duration enables a sender to establish persistent
congestion without depending on PTO expiration. congestion without depending on PTO expiration.
skipping to change at page 27, line 13 skipping to change at page 28, line 13
the above function. the above function.
7.8. Under-utilizing the Congestion Window 7.8. Under-utilizing the Congestion Window
When bytes in flight is smaller than the congestion window and When bytes in flight is smaller than the congestion window and
sending is not pacing limited, the congestion window is under- sending is not pacing limited, the congestion window is under-
utilized. When this occurs, the congestion window SHOULD NOT be utilized. When this occurs, the congestion window SHOULD NOT be
increased in either slow start or congestion avoidance. This can increased in either slow start or congestion avoidance. This can
happen due to insufficient application data or flow control limits. happen due to insufficient application data or flow control limits.
A sender MAY use the pipeACK method described in Section 4.3 of
[RFC7661] to determine if the congestion window is sufficiently
utilized.
A sender that paces packets (see Section 7.7) might delay sending A sender that paces packets (see Section 7.7) might delay sending
packets and not fully utilize the congestion window due to this packets and not fully utilize the congestion window due to this
delay. A sender SHOULD NOT consider itself application limited if it delay. A sender SHOULD NOT consider itself application limited if it
would have fully utilized the congestion window without pacing delay. would have fully utilized the congestion window without pacing delay.
A sender MAY implement alternative mechanisms to update its A sender MAY implement alternative mechanisms to update its
congestion window after periods of under-utilization, such as those congestion window after periods of under-utilization, such as those
proposed for TCP in [RFC7661]. proposed for TCP in [RFC7661].
8. Security Considerations 8. Security Considerations
skipping to change at page 28, line 5 skipping to change at page 29, line 5
other frames, or they can use PADDING frames at a potential cost to other frames, or they can use PADDING frames at a potential cost to
performance. performance.
8.3. Misreporting ECN Markings 8.3. Misreporting ECN Markings
A receiver can misreport ECN markings to alter the congestion A receiver can misreport ECN markings to alter the congestion
response of a sender. Suppressing reports of ECN-CE markings could response of a sender. Suppressing reports of ECN-CE markings could
cause a sender to increase their send rate. This increase could cause a sender to increase their send rate. This increase could
result in congestion and loss. result in congestion and loss.
A sender MAY attempt to detect suppression of reports by marking A sender can detect suppression of reports by marking occasional
occasional packets that they send with ECN-CE. If a packet sent with packets that it sends with an ECN-CE marking. If a packet sent with
ECN-CE is not reported as having been CE marked when the packet is an ECN-CE marking is not reported as having been CE marked when the
acknowledged, then the sender SHOULD disable ECN for that path. packet is acknowledged, then the sender can disable ECN for that path
by not setting ECT codepoints in subsequent packets sent on that path
[RFC3168].
Reporting additional ECN-CE markings will cause a sender to reduce Reporting additional ECN-CE markings will cause a sender to reduce
their sending rate, which is similar in effect to advertising reduced their sending rate, which is similar in effect to advertising reduced
connection flow control limits and so no advantage is gained by doing connection flow control limits and so no advantage is gained by doing
so. so.
Endpoints choose the congestion controller that they use. Congestion Endpoints choose the congestion controller that they use. Congestion
controllers respond to reports of ECN-CE by reducing their rate, but controllers respond to reports of ECN-CE by reducing their rate, but
the response may vary. Markings can be treated as equivalent to loss the response may vary. Markings can be treated as equivalent to loss
([RFC3168]), but other responses can be specified, such as ([RFC3168]), but other responses can be specified, such as
skipping to change at page 28, line 31 skipping to change at page 29, line 33
9. IANA Considerations 9. IANA Considerations
This document has no IANA actions. This document has no IANA actions.
10. References 10. References
10.1. Normative References 10.1. Normative References
[QUIC-TLS] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure [QUIC-TLS] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
QUIC", Work in Progress, Internet-Draft, draft-ietf-quic- QUIC", Work in Progress, Internet-Draft, draft-ietf-quic-
tls-31, 25 September 2020, tls-32, 20 October 2020,
<https://tools.ietf.org/html/draft-ietf-quic-tls-31>. <https://tools.ietf.org/html/draft-ietf-quic-tls-32>.
[QUIC-TRANSPORT] [QUIC-TRANSPORT]
Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", Work in Progress, Multiplexed and Secure Transport", Work in Progress,
Internet-Draft, draft-ietf-quic-transport-31, 25 September Internet-Draft, draft-ietf-quic-transport-32, 20 October
2020, <https://tools.ietf.org/html/draft-ietf-quic- 2020, <https://tools.ietf.org/html/draft-ietf-quic-
transport-31>. transport-32>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/info/rfc8085>. March 2017, <https://www.rfc-editor.org/info/rfc8085>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References 10.2. Informative References
[FACK] Mathis, M. and J. Mahdavi, "Forward Acknowledgement: [FACK] Mathis, M. and J. Mahdavi, "Forward Acknowledgement:
Refining TCP Congestion Control", ACM SIGCOMM , August Refining TCP Congestion Control", ACM SIGCOMM , August
1996. 1996.
[PRR] Mathis, M., Dukkipati, N., and Y. Cheng, "Proportional [PRR] Mathis, M., Dukkipati, N., and Y. Cheng, "Proportional
Rate Reduction for TCP", RFC 6937, DOI 10.17487/RFC6937, Rate Reduction for TCP", RFC 6937, DOI 10.17487/RFC6937,
May 2013, <https://www.rfc-editor.org/info/rfc6937>. May 2013, <https://www.rfc-editor.org/info/rfc6937>.
[RACK] Cheng, Y., Cardwell, N., Dukkipati, N., and P. Jha, "The [RACK] Cheng, Y., Cardwell, N., Dukkipati, N., and P. Jha, "The
RACK-TLP loss detection algorithm for TCP", Work in RACK-TLP loss detection algorithm for TCP", Work in
Progress, Internet-Draft, draft-ietf-tcpm-rack-10, 22 Progress, Internet-Draft, draft-ietf-tcpm-rack-11, 30
August 2020, <http://www.ietf.org/internet-drafts/draft- September 2020, <http://www.ietf.org/internet-drafts/
ietf-tcpm-rack-10.txt>. draft-ietf-tcpm-rack-11.txt>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC3465] Allman, M., "TCP Congestion Control with Appropriate Byte [RFC3465] Allman, M., "TCP Congestion Control with Appropriate Byte
Counting (ABC)", RFC 3465, DOI 10.17487/RFC3465, February Counting (ABC)", RFC 3465, DOI 10.17487/RFC3465, February
2003, <https://www.rfc-editor.org/info/rfc3465>. 2003, <https://www.rfc-editor.org/info/rfc3465>.
[RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion [RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
Control", RFC 5681, DOI 10.17487/RFC5681, September 2009, Control", RFC 5681, DOI 10.17487/RFC5681, September 2009,
<https://www.rfc-editor.org/info/rfc5681>. <https://www.rfc-editor.org/info/rfc5681>.
[RFC5682] Sarolahti, P., Kojo, M., Yamamoto, K., and M. Hata, [RFC5682] Sarolahti, P., Kojo, M., Yamamoto, K., and M. Hata,
skipping to change at page 30, line 46 skipping to change at page 31, line 46
[RFC8511] Khademi, N., Welzl, M., Armitage, G., and G. Fairhurst, [RFC8511] Khademi, N., Welzl, M., Armitage, G., and G. Fairhurst,
"TCP Alternative Backoff with ECN (ABE)", RFC 8511, "TCP Alternative Backoff with ECN (ABE)", RFC 8511,
DOI 10.17487/RFC8511, December 2018, DOI 10.17487/RFC8511, December 2018,
<https://www.rfc-editor.org/info/rfc8511>. <https://www.rfc-editor.org/info/rfc8511>.
Appendix A. Loss Recovery Pseudocode Appendix A. Loss Recovery Pseudocode
We now describe an example implementation of the loss detection We now describe an example implementation of the loss detection
mechanisms described in Section 6. mechanisms described in Section 6.
The pseudocode segments in this section are licensed as Code
Components; see the copyright notice.
A.1. Tracking Sent Packets A.1. Tracking Sent Packets
To correctly implement congestion control, a QUIC sender tracks every To correctly implement congestion control, a QUIC sender tracks every
ack-eliciting packet until the packet is acknowledged or lost. It is ack-eliciting packet until the packet is acknowledged or lost. It is
expected that implementations will be able to access this information expected that implementations will be able to access this information
by packet number and crypto context and store the per-packet fields by packet number and crypto context and store the per-packet fields
(Appendix A.1.1) for loss recovery and congestion control. (Appendix A.1.1) for loss recovery and congestion control.
After a packet is declared lost, the endpoint can still maintain After a packet is declared lost, the endpoint can still maintain
state for it for an amount of time to allow for packet reordering; state for it for an amount of time to allow for packet reordering;
skipping to change at page 32, line 27 skipping to change at page 33, line 33
ack for a previously unacked packet. ack for a previously unacked packet.
smoothed_rtt: The smoothed RTT of the connection, computed as smoothed_rtt: The smoothed RTT of the connection, computed as
described in Section 5.3. described in Section 5.3.
rttvar: The RTT variation, computed as described in Section 5.3. rttvar: The RTT variation, computed as described in Section 5.3.
min_rtt: The minimum RTT seen in the connection, ignoring min_rtt: The minimum RTT seen in the connection, ignoring
acknowledgment delay, as described in Section 5.2. acknowledgment delay, as described in Section 5.2.
first_rtt_sample: The time that the first RTT sample was obtained.
max_ack_delay: The maximum amount of time by which the receiver max_ack_delay: The maximum amount of time by which the receiver
intends to delay acknowledgments for packets in the Application intends to delay acknowledgments for packets in the Application
Data packet number space, as defined by the eponymous transport Data packet number space, as defined by the eponymous transport
parameter (Section 18.2 of [QUIC-TRANSPORT]). Note that the parameter (Section 18.2 of [QUIC-TRANSPORT]). Note that the
actual ack_delay in a received ACK frame may be larger due to late actual ack_delay in a received ACK frame may be larger due to late
timers, reordering, or loss. timers, reordering, or loss.
loss_detection_timer: Multi-modal timer used for loss detection. loss_detection_timer: Multi-modal timer used for loss detection.
pto_count: The number of times a PTO has been sent without receiving pto_count: The number of times a PTO has been sent without receiving
skipping to change at page 33, line 16 skipping to change at page 34, line 24
At the beginning of the connection, initialize the loss detection At the beginning of the connection, initialize the loss detection
variables as follows: variables as follows:
loss_detection_timer.reset() loss_detection_timer.reset()
pto_count = 0 pto_count = 0
latest_rtt = 0 latest_rtt = 0
smoothed_rtt = kInitialRtt smoothed_rtt = kInitialRtt
rttvar = kInitialRtt / 2 rttvar = kInitialRtt / 2
min_rtt = 0 min_rtt = 0
first_rtt_sample = 0
for pn_space in [ Initial, Handshake, ApplicationData ]: for pn_space in [ Initial, Handshake, ApplicationData ]:
largest_acked_packet[pn_space] = infinite largest_acked_packet[pn_space] = infinite
time_of_last_ack_eliciting_packet[pn_space] = 0 time_of_last_ack_eliciting_packet[pn_space] = 0
loss_time[pn_space] = 0 loss_time[pn_space] = 0
A.5. On Sending a Packet A.5. On Sending a Packet
After a packet is sent, information about the packet is stored. The After a packet is sent, information about the packet is stored. The
parameters to OnPacketSent are described in detail above in parameters to OnPacketSent are described in detail above in
Appendix A.1.1. Appendix A.1.1.
skipping to change at page 34, line 44 skipping to change at page 36, line 4
DetectAndRemoveAckedPackets(ack, pn_space) DetectAndRemoveAckedPackets(ack, pn_space)
// Nothing to do if there are no newly acked packets. // Nothing to do if there are no newly acked packets.
if (newly_acked_packets.empty()): if (newly_acked_packets.empty()):
return return
// Update the RTT if the largest acknowledged is newly acked // Update the RTT if the largest acknowledged is newly acked
// and at least one ack-eliciting was newly acked. // and at least one ack-eliciting was newly acked.
if (newly_acked_packets.largest().packet_number == if (newly_acked_packets.largest().packet_number ==
ack.largest_acked && ack.largest_acked &&
IncludesAckEliciting(newly_acked_packets)): IncludesAckEliciting(newly_acked_packets)):
latest_rtt = latest_rtt =
now() - newly_acked_packets.largest().time_sent now() - newly_acked_packets.largest().time_sent
UpdateRtt(ack.ack_delay) UpdateRtt(ack.ack_delay)
// Process ECN information if present. // Process ECN information if present.
if (ACK frame contains ECN information): if (ACK frame contains ECN information):
ProcessECN(ack, pn_space) ProcessECN(ack, pn_space)
lost_packets = DetectAndRemoveLostPackets(pn_space) lost_packets = DetectAndRemoveLostPackets(pn_space)
if (!lost_packets.empty()): if (!lost_packets.empty()):
OnPacketsLost(lost_packets) OnPacketsLost(lost_packets)
OnPacketsAcked(newly_acked_packets) OnPacketsAcked(newly_acked_packets)
// Reset pto_count unless the client is unsure if // Reset pto_count unless the client is unsure if
// the server has validated the client's address. // the server has validated the client's address.
if (PeerCompletedAddressValidation()): if (PeerCompletedAddressValidation()):
pto_count = 0 pto_count = 0
SetLossDetectionTimer() SetLossDetectionTimer()
UpdateRtt(ack_delay): UpdateRtt(ack_delay):
if (is first RTT sample): if (first_rtt_sample == 0):
min_rtt = latest_rtt min_rtt = latest_rtt
smoothed_rtt = latest_rtt smoothed_rtt = latest_rtt
rttvar = latest_rtt / 2 rttvar = latest_rtt / 2
first_rtt_sample = now()
return return
// min_rtt ignores acknowledgment delay. // min_rtt ignores acknowledgment delay.
min_rtt = min(min_rtt, latest_rtt) min_rtt = min(min_rtt, latest_rtt)
// Limit ack_delay by max_ack_delay after handshake // Limit ack_delay by max_ack_delay after handshake
// confirmation. Note that ack_delay is 0 for // confirmation. Note that ack_delay is 0 for
// acknowledgements of Initial and Handshake packets. // acknowledgements of Initial and Handshake packets.
if (handshake confirmed): if (handshake confirmed):
ack_delay = min(ack_delay, max_ack_delay) ack_delay = min(ack_delay, max_ack_delay)
skipping to change at page 39, line 22 skipping to change at page 40, line 22
loss_delay = max(loss_delay, kGranularity) loss_delay = max(loss_delay, kGranularity)
// Packets sent before this time are deemed lost. // Packets sent before this time are deemed lost.
lost_send_time = now() - loss_delay lost_send_time = now() - loss_delay
foreach unacked in sent_packets[pn_space]: foreach unacked in sent_packets[pn_space]:
if (unacked.packet_number > largest_acked_packet[pn_space]): if (unacked.packet_number > largest_acked_packet[pn_space]):
continue continue
// Mark packet as lost, or set time when it should be marked. // Mark packet as lost, or set time when it should be marked.
// Note: The use of kPacketThreshold here assumes that there
// were no sender-induced gaps in the packet number space.
if (unacked.time_sent <= lost_send_time || if (unacked.time_sent <= lost_send_time ||
largest_acked_packet[pn_space] >= largest_acked_packet[pn_space] >=
unacked.packet_number + kPacketThreshold): unacked.packet_number + kPacketThreshold):
sent_packets[pn_space].remove(unacked.packet_number) sent_packets[pn_space].remove(unacked.packet_number)
if (unacked.in_flight): if (unacked.in_flight):
lost_packets.insert(unacked) lost_packets.insert(unacked)
else: else:
if (loss_time[pn_space] == 0): if (loss_time[pn_space] == 0):
loss_time[pn_space] = unacked.time_sent + loss_delay loss_time[pn_space] = unacked.time_sent + loss_delay
else: else:
loss_time[pn_space] = min(loss_time[pn_space], loss_time[pn_space] = min(loss_time[pn_space],
unacked.time_sent + loss_delay) unacked.time_sent + loss_delay)
return lost_packets return lost_packets
A.11. Upon Dropping Initial or Handshake Keys
When Initial or Handshake keys are discarded, packets from the space
are discarded and loss detection state is updated.
Pseudocode for OnPacketNumberSpaceDiscarded follows:
OnPacketNumberSpaceDiscarded(pn_space):
assert(pn_space != ApplicationData)
RemoveFromBytesInFlight(sent_packets[pn_space])
sent_packets[pn_space].clear()
// Reset the loss detection and PTO timer
time_of_last_ack_eliciting_packet[pn_space] = 0
loss_time[pn_space] = 0
pto_count = 0
SetLossDetectionTimer()
Appendix B. Congestion Control Pseudocode Appendix B. Congestion Control Pseudocode
We now describe an example implementation of the congestion We now describe an example implementation of the congestion
controller described in Section 7. controller described in Section 7.
The pseudocode segments in this section are licensed as Code
Components; see the copyright notice.
B.1. Constants of interest B.1. Constants of interest
Constants used in congestion control are based on a combination of Constants used in congestion control are based on a combination of
RFCs, papers, and common practice. RFCs, papers, and common practice.
kInitialWindow: Default limit on the initial bytes in flight as kInitialWindow: Default limit on the initial bytes in flight as
described in Section 7.2. described in Section 7.2.
kMinimumWindow: Minimum congestion window in bytes as described in kMinimumWindow: Minimum congestion window in bytes as described in
Section 7.2. Section 7.2.
skipping to change at page 40, line 18 skipping to change at page 41, line 49
Section 7.6 recommends a value of 3. Section 7.6 recommends a value of 3.
B.2. Variables of interest B.2. Variables of interest
Variables required to implement the congestion control mechanisms are Variables required to implement the congestion control mechanisms are
described in this section. described in this section.
max_datagram_size: The sender's current maximum payload size. Does max_datagram_size: The sender's current maximum payload size. Does
not include UDP or IP overhead. The max datagram size is used for not include UDP or IP overhead. The max datagram size is used for
congestion window computations. An endpoint sets the value of congestion window computations. An endpoint sets the value of
this variable based on its PMTU (see Section 14.1 of this variable based on its Path Maximum Transmission Unit (PMTU;
[QUIC-TRANSPORT]), with a minimum value of 1200 bytes. see Section 14.2 of [QUIC-TRANSPORT]), with a minimum value of
1200 bytes.
ecn_ce_counters[kPacketNumberSpace]: The highest value reported for ecn_ce_counters[kPacketNumberSpace]: The highest value reported for
the ECN-CE counter in the packet number space by the peer in an the ECN-CE counter in the packet number space by the peer in an
ACK frame. This value is used to detect increases in the reported ACK frame. This value is used to detect increases in the reported
ECN-CE counter. ECN-CE counter.
bytes_in_flight: The sum of the size in bytes of all sent packets bytes_in_flight: The sum of the size in bytes of all sent packets
that contain at least one ack-eliciting or PADDING frame, and have that contain at least one ack-eliciting or PADDING frame, and have
not been acknowledged or declared lost. The size does not include not been acknowledged or declared lost. The size does not include
IP or UDP overhead, but does include the QUIC header and AEAD IP or UDP overhead, but does include the QUIC header and AEAD
skipping to change at page 40, line 46 skipping to change at page 42, line 30
congestion_recovery_start_time: The time when QUIC first detects congestion_recovery_start_time: The time when QUIC first detects
congestion due to loss or ECN, causing it to enter congestion congestion due to loss or ECN, causing it to enter congestion
recovery. When a packet sent after this time is acknowledged, recovery. When a packet sent after this time is acknowledged,
QUIC exits congestion recovery. QUIC exits congestion recovery.
ssthresh: Slow start threshold in bytes. When the congestion window ssthresh: Slow start threshold in bytes. When the congestion window
is below ssthresh, the mode is slow start and the window grows by is below ssthresh, the mode is slow start and the window grows by
the number of bytes acknowledged. the number of bytes acknowledged.
first_rtt_sample: The time that the first RTT sample was obtained. The congestion control pseudocode also accesses some of the variables
from the loss recovery pseudocode.
B.3. Initialization B.3. Initialization
At the beginning of the connection, initialize the congestion control At the beginning of the connection, initialize the congestion control
variables as follows: variables as follows:
congestion_window = kInitialWindow congestion_window = kInitialWindow
bytes_in_flight = 0 bytes_in_flight = 0
congestion_recovery_start_time = 0 congestion_recovery_start_time = 0
ssthresh = infinite ssthresh = infinite
first_rtt_sample = 0
for pn_space in [ Initial, Handshake, ApplicationData ]: for pn_space in [ Initial, Handshake, ApplicationData ]:
ecn_ce_counters[pn_space] = 0 ecn_ce_counters[pn_space] = 0
B.4. On Packet Sent B.4. On Packet Sent
Whenever a packet is sent, and it contains non-ACK frames, the packet Whenever a packet is sent, and it contains non-ACK frames, the packet
increases bytes_in_flight. increases bytes_in_flight.
OnPacketSentCC(bytes_sent): OnPacketSentCC(bytes_sent):
bytes_in_flight += bytes_sent bytes_in_flight += bytes_sent
skipping to change at page 42, line 9 skipping to change at page 43, line 19
In congestion avoidance, implementers that use an integer In congestion avoidance, implementers that use an integer
representation for congestion_window should be careful with division, representation for congestion_window should be careful with division,
and can use the alternative approach suggested in Section 2.1 of and can use the alternative approach suggested in Section 2.1 of
[RFC3465]. [RFC3465].
InCongestionRecovery(sent_time): InCongestionRecovery(sent_time):
return sent_time <= congestion_recovery_start_time return sent_time <= congestion_recovery_start_time
OnPacketsAcked(acked_packets): OnPacketsAcked(acked_packets):
if (first_rtt_sample == 0):
first_rtt_sample = now()
for acked_packet in acked_packets: for acked_packet in acked_packets:
OnPacketAcked(acked_packet) OnPacketAcked(acked_packet)
OnPacketAcked(acked_packet): OnPacketAcked(acked_packet):
// Remove from bytes_in_flight. // Remove from bytes_in_flight.
bytes_in_flight -= acked_packet.sent_bytes bytes_in_flight -= acked_packet.sent_bytes
// Do not increase congestion_window if application // Do not increase congestion_window if application
// limited or flow control limited. // limited or flow control limited.
if (IsAppOrFlowControlLimited()) if (IsAppOrFlowControlLimited())
return return
skipping to change at page 43, line 31 skipping to change at page 44, line 43
OnPacketsLost(lost_packets): OnPacketsLost(lost_packets):
// Remove lost packets from bytes_in_flight. // Remove lost packets from bytes_in_flight.
for lost_packet in lost_packets: for lost_packet in lost_packets:
bytes_in_flight -= lost_packet.sent_bytes bytes_in_flight -= lost_packet.sent_bytes
OnCongestionEvent(lost_packets.largest().time_sent) OnCongestionEvent(lost_packets.largest().time_sent)
// Reset the congestion window if the loss of these // Reset the congestion window if the loss of these
// packets indicates persistent congestion. // packets indicates persistent congestion.
// Only consider packets sent after getting an RTT sample. // Only consider packets sent after getting an RTT sample.
assert(first_rtt_sample != 0) if (first_rtt_sample == 0):
return
pc_lost = {} pc_lost = {}
for lost in lost_packets: for lost in lost_packets:
if lost.time_sent > first_rtt_sample: if lost.time_sent > first_rtt_sample:
pc_lost.insert(lost) pc_lost.insert(lost)
if (InPersistentCongestion(pc_lost)): if (InPersistentCongestion(pc_lost)):
congestion_window = kMinimumWindow congestion_window = kMinimumWindow
congestion_recovery_start_time = 0 congestion_recovery_start_time = 0
B.9. Upon dropping Initial or Handshake keys B.9. Removing Discarded Packets From Bytes In Flight
When Initial or Handshake keys are discarded, packets from the space When Initial or Handshake keys are discarded, packets sent in that
are discarded and loss detection state is updated. space no longer count toward bytes in flight.
Pseudocode for OnPacketNumberSpaceDiscarded follows: Pseudocode for RemoveFromBytesInFlight follows:
OnPacketNumberSpaceDiscarded(pn_space): RemoveFromBytesInFlight(discarded_packets):
assert(pn_space != ApplicationData)
// Remove any unacknowledged packets from flight. // Remove any unacknowledged packets from flight.
foreach packet in sent_packets[pn_space]: foreach packet in discarded_packets:
if packet.in_flight if packet.in_flight
bytes_in_flight -= size bytes_in_flight -= size
sent_packets[pn_space].clear()
// Reset the loss detection and PTO timer
time_of_last_ack_eliciting_packet[pn_space] = 0
loss_time[pn_space] = 0
pto_count = 0
SetLossDetectionTimer()
Appendix C. Change Log Appendix C. Change Log
*RFC Editor's Note:* Please remove this section prior to *RFC Editor's Note:* Please remove this section prior to
publication of a final version of this document. publication of a final version of this document.
Issue and pull request numbers are listed with a leading octothorp. Issue and pull request numbers are listed with a leading octothorp.
C.1. Since draft-ietf-quic-recovery-30 C.1. Since draft-ietf-quic-recovery-31
* Limit the number of Initial packets sent in response to
unauthenticated packets (#4183, #4188)
C.2. Since draft-ietf-quic-recovery-30
Editorial changes only. Editorial changes only.
C.2. Since draft-ietf-quic-recovery-29 C.3. Since draft-ietf-quic-recovery-29
* Allow caching of packets that can't be decrypted, by allowing the * Allow caching of packets that can't be decrypted, by allowing the
reported acknowledgment delay to exceed max_ack_delay prior to reported acknowledgment delay to exceed max_ack_delay prior to
confirming the handshake (#3821, #3980, #4035, #3874) confirming the handshake (#3821, #3980, #4035, #3874)
* Persistent congestion cannot include packets sent before the first * Persistent congestion cannot include packets sent before the first
RTT sample for the path (#3875, #3889) RTT sample for the path (#3875, #3889)
* Recommend reset of min_rtt in persistent congestion (#3927, #3975) * Recommend reset of min_rtt in persistent congestion (#3927, #3975)
* Persistent congestion is independent of packet number space * Persistent congestion is independent of packet number space
(#3939, #3961) (#3939, #3961)
* Only limit bursts to the initial window without information about * Only limit bursts to the initial window without information about
the path (#3892, #3936) the path (#3892, #3936)
* Add normative requirements for increasing and reducing the * Add normative requirements for increasing and reducing the
congestion window (#3944, #3978, #3997, #3998) congestion window (#3944, #3978, #3997, #3998)
C.3. Since draft-ietf-quic-recovery-28 C.4. Since draft-ietf-quic-recovery-28
* Refactored pseudocode to correct PTO calculation (#3564, #3674, * Refactored pseudocode to correct PTO calculation (#3564, #3674,
#3681) #3681)
C.4. Since draft-ietf-quic-recovery-27 C.5. Since draft-ietf-quic-recovery-27
* Added recommendations for speeding up handshake under some loss * Added recommendations for speeding up handshake under some loss
conditions (#3078, #3080) conditions (#3078, #3080)
* PTO count is reset when handshake progress is made (#3272, #3415) * PTO count is reset when handshake progress is made (#3272, #3415)
* PTO count is not reset by a client when the server might be * PTO count is not reset by a client when the server might be
awaiting address validation (#3546, #3551) awaiting address validation (#3546, #3551)
* Recommend repairing losses immediately after entering the recovery * Recommend repairing losses immediately after entering the recovery
period (#3335, #3443) period (#3335, #3443)
* Clarified what loss conditions can be ignored during the handshake * Clarified what loss conditions can be ignored during the handshake
(#3456, #3450) (#3456, #3450)
* Allow, but don't recommend, using RTT from previous connection to * Allow, but don't recommend, using RTT from previous connection to
seed RTT (#3464, #3496) seed RTT (#3464, #3496)
* Recommend use of adaptive loss detection thresholds (#3571, #3572) * Recommend use of adaptive loss detection thresholds (#3571, #3572)
C.5. Since draft-ietf-quic-recovery-26 C.6. Since draft-ietf-quic-recovery-26
No changes. No changes.
C.6. Since draft-ietf-quic-recovery-25 C.7. Since draft-ietf-quic-recovery-25
No significant changes. No significant changes.
C.7. Since draft-ietf-quic-recovery-24 C.8. Since draft-ietf-quic-recovery-24
* Require congestion control of some sort (#3247, #3244, #3248) * Require congestion control of some sort (#3247, #3244, #3248)
* Set a minimum reordering threshold (#3256, #3240) * Set a minimum reordering threshold (#3256, #3240)
* PTO is specific to a packet number space (#3067, #3074, #3066) * PTO is specific to a packet number space (#3067, #3074, #3066)
C.8. Since draft-ietf-quic-recovery-23 C.9. Since draft-ietf-quic-recovery-23
* Define under-utilizing the congestion window (#2630, #2686, #2675) * Define under-utilizing the congestion window (#2630, #2686, #2675)
* PTO MUST send data if possible (#3056, #3057) * PTO MUST send data if possible (#3056, #3057)
* Connection Close is not ack-eliciting (#3097, #3098) * Connection Close is not ack-eliciting (#3097, #3098)
* MUST limit bursts to the initial congestion window (#3160) * MUST limit bursts to the initial congestion window (#3160)
* Define the current max_datagram_size for congestion control * Define the current max_datagram_size for congestion control
(#3041, #3167) (#3041, #3167)
C.9. Since draft-ietf-quic-recovery-22 C.10. Since draft-ietf-quic-recovery-22
* PTO should always send an ack-eliciting packet (#2895) * PTO should always send an ack-eliciting packet (#2895)
* Unify the Handshake Timer with the PTO timer (#2648, #2658, #2886) * Unify the Handshake Timer with the PTO timer (#2648, #2658, #2886)
* Move ACK generation text to transport draft (#1860, #2916) * Move ACK generation text to transport draft (#1860, #2916)
C.10. Since draft-ietf-quic-recovery-21 C.11. Since draft-ietf-quic-recovery-21
* No changes * No changes
C.11. Since draft-ietf-quic-recovery-20 C.12. Since draft-ietf-quic-recovery-20
* Path validation can be used as initial RTT value (#2644, #2687) * Path validation can be used as initial RTT value (#2644, #2687)
* max_ack_delay transport parameter defaults to 0 (#2638, #2646) * max_ack_delay transport parameter defaults to 0 (#2638, #2646)
* ACK delay only measures intentional delays induced by the * ACK delay only measures intentional delays induced by the
implementation (#2596, #2786) implementation (#2596, #2786)
C.12. Since draft-ietf-quic-recovery-19 C.13. Since draft-ietf-quic-recovery-19
* Change kPersistentThreshold from an exponent to a multiplier * Change kPersistentThreshold from an exponent to a multiplier
(#2557) (#2557)
* Send a PING if the PTO timer fires and there's nothing to send * Send a PING if the PTO timer fires and there's nothing to send
(#2624) (#2624)
* Set loss delay to at least kGranularity (#2617) * Set loss delay to at least kGranularity (#2617)
* Merge application limited and sending after idle sections. Always * Merge application limited and sending after idle sections. Always
skipping to change at page 47, line 5 skipping to change at page 48, line 10
packet is ack-eliciting but the largest_acked is not (#2592) packet is ack-eliciting but the largest_acked is not (#2592)
* Don't arm the handshake timer if there is no handshake data * Don't arm the handshake timer if there is no handshake data
(#2590) (#2590)
* Clarify that the time threshold loss alarm takes precedence over * Clarify that the time threshold loss alarm takes precedence over
the crypto handshake timer (#2590, #2620) the crypto handshake timer (#2590, #2620)
* Change initial RTT to 500ms to align with RFC6298 (#2184) * Change initial RTT to 500ms to align with RFC6298 (#2184)
C.13. Since draft-ietf-quic-recovery-18 C.14. Since draft-ietf-quic-recovery-18
* Change IW byte limit to 14720 from 14600 (#2494) * Change IW byte limit to 14720 from 14600 (#2494)
* Update PTO calculation to match RFC6298 (#2480, #2489, #2490) * Update PTO calculation to match RFC6298 (#2480, #2489, #2490)
* Improve loss detection's description of multiple packet number * Improve loss detection's description of multiple packet number
spaces and pseudocode (#2485, #2451, #2417) spaces and pseudocode (#2485, #2451, #2417)
* Declare persistent congestion even if non-probe packets are sent * Declare persistent congestion even if non-probe packets are sent
and don't make persistent congestion more aggressive than RTO and don't make persistent congestion more aggressive than RTO
verified was (#2365, #2244) verified was (#2365, #2244)
* Move pseudocode to the appendices (#2408) * Move pseudocode to the appendices (#2408)
* What to send on multiple PTOs (#2380) * What to send on multiple PTOs (#2380)
C.14. Since draft-ietf-quic-recovery-17 C.15. Since draft-ietf-quic-recovery-17
* After Probe Timeout discard in-flight packets or send another * After Probe Timeout discard in-flight packets or send another
(#2212, #1965) (#2212, #1965)
* Endpoints discard initial keys as soon as handshake keys are * Endpoints discard initial keys as soon as handshake keys are
available (#1951, #2045) available (#1951, #2045)
* 0-RTT state is discarded when 0-RTT is rejected (#2300) * 0-RTT state is discarded when 0-RTT is rejected (#2300)
* Loss detection timer is cancelled when ack-eliciting frames are in * Loss detection timer is cancelled when ack-eliciting frames are in
skipping to change at page 47, line 48 skipping to change at page 49, line 5
controller (#2138, 2187) controller (#2138, 2187)
* Process ECN counts before marking packets lost (#2142) * Process ECN counts before marking packets lost (#2142)
* Mark packets lost before resetting crypto_count and pto_count * Mark packets lost before resetting crypto_count and pto_count
(#2208, #2209) (#2208, #2209)
* Congestion and loss recovery state are discarded when keys are * Congestion and loss recovery state are discarded when keys are
discarded (#2327) discarded (#2327)
C.15. Since draft-ietf-quic-recovery-16 C.16. Since draft-ietf-quic-recovery-16
* Unify TLP and RTO into a single PTO; eliminate min RTO, min TLP * Unify TLP and RTO into a single PTO; eliminate min RTO, min TLP
and min crypto timeouts; eliminate timeout validation (#2114, and min crypto timeouts; eliminate timeout validation (#2114,
#2166, #2168, #1017) #2166, #2168, #1017)
* Redefine how congestion avoidance in terms of when the period * Redefine how congestion avoidance in terms of when the period
starts (#1928, #1930) starts (#1928, #1930)
* Document what needs to be tracked for packets that are in flight * Document what needs to be tracked for packets that are in flight
(#765, #1724, #1939) (#765, #1724, #1939)
skipping to change at page 48, line 30 skipping to change at page 49, line 36
* Limit ack_delay by max_ack_delay (#2060, #2099) * Limit ack_delay by max_ack_delay (#2060, #2099)
* Initial keys are discarded once Handshake keys are available * Initial keys are discarded once Handshake keys are available
(#1951, #2045) (#1951, #2045)
* Reorder ECN and loss detection in pseudocode (#2142) * Reorder ECN and loss detection in pseudocode (#2142)
* Only cancel loss detection timer if ack-eliciting packets are in * Only cancel loss detection timer if ack-eliciting packets are in
flight (#2093, #2117) flight (#2093, #2117)
C.16. Since draft-ietf-quic-recovery-14 C.17. Since draft-ietf-quic-recovery-14
* Used max_ack_delay from transport params (#1796, #1782) * Used max_ack_delay from transport params (#1796, #1782)
* Merge ACK and ACK_ECN (#1783) * Merge ACK and ACK_ECN (#1783)
C.17. Since draft-ietf-quic-recovery-13 C.18. Since draft-ietf-quic-recovery-13
* Corrected the lack of ssthresh reduction in CongestionEvent * Corrected the lack of ssthresh reduction in CongestionEvent
pseudocode (#1598) pseudocode (#1598)
* Considerations for ECN spoofing (#1426, #1626) * Considerations for ECN spoofing (#1426, #1626)
* Clarifications for PADDING and congestion control (#837, #838, * Clarifications for PADDING and congestion control (#837, #838,
#1517, #1531, #1540) #1517, #1531, #1540)
* Reduce early retransmission timer to RTT/8 (#945, #1581) * Reduce early retransmission timer to RTT/8 (#945, #1581)
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* Corrected the lack of ssthresh reduction in CongestionEvent * Corrected the lack of ssthresh reduction in CongestionEvent
pseudocode (#1598) pseudocode (#1598)
* Considerations for ECN spoofing (#1426, #1626) * Considerations for ECN spoofing (#1426, #1626)
* Clarifications for PADDING and congestion control (#837, #838, * Clarifications for PADDING and congestion control (#837, #838,
#1517, #1531, #1540) #1517, #1531, #1540)
* Reduce early retransmission timer to RTT/8 (#945, #1581) * Reduce early retransmission timer to RTT/8 (#945, #1581)
* Packets are declared lost after an RTO is verified (#935, #1582) * Packets are declared lost after an RTO is verified (#935, #1582)
C.18. Since draft-ietf-quic-recovery-12 C.19. Since draft-ietf-quic-recovery-12
* Changes to manage separate packet number spaces and encryption * Changes to manage separate packet number spaces and encryption
levels (#1190, #1242, #1413, #1450) levels (#1190, #1242, #1413, #1450)
* Added ECN feedback mechanisms and handling; new ACK_ECN frame * Added ECN feedback mechanisms and handling; new ACK_ECN frame
(#804, #805, #1372) (#804, #805, #1372)
C.19. Since draft-ietf-quic-recovery-11 C.20. Since draft-ietf-quic-recovery-11
No significant changes. No significant changes.
C.20. Since draft-ietf-quic-recovery-10 C.21. Since draft-ietf-quic-recovery-10
* Improved text on ack generation (#1139, #1159) * Improved text on ack generation (#1139, #1159)
* Make references to TCP recovery mechanisms informational (#1195) * Make references to TCP recovery mechanisms informational (#1195)
* Define time_of_last_sent_handshake_packet (#1171) * Define time_of_last_sent_handshake_packet (#1171)
* Added signal from TLS the data it includes needs to be sent in a * Added signal from TLS the data it includes needs to be sent in a
Retry packet (#1061, #1199) Retry packet (#1061, #1199)
* Minimum RTT (min_rtt) is initialized with an infinite value * Minimum RTT (min_rtt) is initialized with an infinite value
(#1169) (#1169)
C.21. Since draft-ietf-quic-recovery-09 C.22. Since draft-ietf-quic-recovery-09
No significant changes. No significant changes.
C.22. Since draft-ietf-quic-recovery-08 C.23. Since draft-ietf-quic-recovery-08
* Clarified pacing and RTO (#967, #977) * Clarified pacing and RTO (#967, #977)
C.23. Since draft-ietf-quic-recovery-07 C.24. Since draft-ietf-quic-recovery-07
* Include ACK delay in RTO(and TLP) computations (#981) * Include ACK delay in RTO(and TLP) computations (#981)
* ACK delay in SRTT computation (#961) * ACK delay in SRTT computation (#961)
* Default RTT and Slow Start (#590) * Default RTT and Slow Start (#590)
* Many editorial fixes. * Many editorial fixes.
C.24. Since draft-ietf-quic-recovery-06 C.25. Since draft-ietf-quic-recovery-06
No significant changes. No significant changes.
C.25. Since draft-ietf-quic-recovery-05 C.26. Since draft-ietf-quic-recovery-05
* Add more congestion control text (#776) * Add more congestion control text (#776)
C.26. Since draft-ietf-quic-recovery-04 C.27. Since draft-ietf-quic-recovery-04
No significant changes. No significant changes.
C.27. Since draft-ietf-quic-recovery-03 C.28. Since draft-ietf-quic-recovery-03
No significant changes. No significant changes.
C.28. Since draft-ietf-quic-recovery-02 C.29. Since draft-ietf-quic-recovery-02
* Integrate F-RTO (#544, #409) * Integrate F-RTO (#544, #409)
* Add congestion control (#545, #395) * Add congestion control (#545, #395)
* Require connection abort if a skipped packet was acknowledged * Require connection abort if a skipped packet was acknowledged
(#415) (#415)
* Simplify RTO calculations (#142, #417) * Simplify RTO calculations (#142, #417)
C.29. Since draft-ietf-quic-recovery-01 C.30. Since draft-ietf-quic-recovery-01
* Overview added to loss detection * Overview added to loss detection
* Changes initial default RTT to 100ms * Changes initial default RTT to 100ms
* Added time-based loss detection and fixes early retransmit * Added time-based loss detection and fixes early retransmit
* Clarified loss recovery for handshake packets * Clarified loss recovery for handshake packets
* Fixed references and made TCP references informative * Fixed references and made TCP references informative
C.30. Since draft-ietf-quic-recovery-00 C.31. Since draft-ietf-quic-recovery-00
* Improved description of constants and ACK behavior * Improved description of constants and ACK behavior
C.31. Since draft-iyengar-quic-loss-recovery-01 C.32. Since draft-iyengar-quic-loss-recovery-01
* Adopted as base for draft-ietf-quic-recovery * Adopted as base for draft-ietf-quic-recovery
* Updated authors/editors list * Updated authors/editors list
* Added table of contents * Added table of contents
Appendix D. Contributors Appendix D. Contributors
The IETF QUIC Working Group received an enormous amount of support The IETF QUIC Working Group received an enormous amount of support
from many people. The following people provided substantive from many people. The following people provided substantive
contributions to this document: contributions to this document:
* Alessandro Ghedini * Alessandro Ghedini
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