draft-ietf-quic-recovery-10.txt   draft-ietf-quic-recovery-11.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: September 6, 2018 Google Expires: October 19, 2018 Google
March 05, 2018 April 17, 2018
QUIC Loss Detection and Congestion Control QUIC Loss Detection and Congestion Control
draft-ietf-quic-recovery-10 draft-ietf-quic-recovery-11
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), which is archived at mailing list (quic@ietf.org), which is archived at
skipping to change at page 1, line 42 skipping to change at page 1, line 42
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-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 6, 2018. This Internet-Draft will expire on October 19, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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publication of this document. Please review these documents publication of this document. Please review these documents
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to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 4
2. Design of the QUIC Transmission Machinery . . . . . . . . . . 4 2. Design of the QUIC Transmission Machinery . . . . . . . . . . 4
2.1. Relevant Differences Between QUIC and TCP . . . . . . . . 4 2.1. Relevant Differences Between QUIC and TCP . . . . . . . . 4
2.1.1. Monotonically Increasing Packet Numbers . . . . . . . 4 2.1.1. Monotonically Increasing Packet Numbers . . . . . . . 5
2.1.2. No Reneging . . . . . . . . . . . . . . . . . . . . . 5 2.1.2. No Reneging . . . . . . . . . . . . . . . . . . . . . 5
2.1.3. More ACK Ranges . . . . . . . . . . . . . . . . . . . 5 2.1.3. More ACK Ranges . . . . . . . . . . . . . . . . . . . 5
2.1.4. Explicit Correction For Delayed Acks . . . . . . . . 5 2.1.4. Explicit Correction For Delayed ACKs . . . . . . . . 5
3. Loss Detection . . . . . . . . . . . . . . . . . . . . . . . 5 3. Loss Detection . . . . . . . . . . . . . . . . . . . . . . . 6
3.1. Computing the RTT estimate . . . . . . . . . . . . . . . 6 3.1. Computing the RTT estimate . . . . . . . . . . . . . . . 6
3.2. Ack-based Detection . . . . . . . . . . . . . . . . . . . 6 3.2. Ack-based Detection . . . . . . . . . . . . . . . . . . . 6
3.2.1. Fast Retransmit . . . . . . . . . . . . . . . . . . . 6 3.2.1. Fast Retransmit . . . . . . . . . . . . . . . . . . . 6
3.2.2. Early Retransmit . . . . . . . . . . . . . . . . . . 7 3.2.2. Early Retransmit . . . . . . . . . . . . . . . . . . 7
3.3. Timer-based Detection . . . . . . . . . . . . . . . . . . 8 3.3. Timer-based Detection . . . . . . . . . . . . . . . . . . 8
3.3.1. Tail Loss Probe . . . . . . . . . . . . . . . . . . . 8 3.3.1. Handshake Timeout . . . . . . . . . . . . . . . . . . 8
3.3.2. Retransmission Timeout . . . . . . . . . . . . . . . 9 3.3.2. Tail Loss Probe . . . . . . . . . . . . . . . . . . . 9
3.3.3. Handshake Timeout . . . . . . . . . . . . . . . . . . 10 3.3.3. Retransmission Timeout . . . . . . . . . . . . . . . 10
3.4. Pseudocode . . . . . . . . . . . . . . . . . . . . . . . 11 3.4. Generating Acknowledgements . . . . . . . . . . . . . . . 11
3.4.1. Constants of interest . . . . . . . . . . . . . . . . 11 3.4.1. ACK Ranges . . . . . . . . . . . . . . . . . . . . . 11
3.4.2. Variables of interest . . . . . . . . . . . . . . . . 12 3.4.2. Receiver Tracking of ACK Frames . . . . . . . . . . . 12
3.4.3. Initialization . . . . . . . . . . . . . . . . . . . 13 3.5. Pseudocode . . . . . . . . . . . . . . . . . . . . . . . 12
3.4.4. On Sending a Packet . . . . . . . . . . . . . . . . . 13 3.5.1. Constants of interest . . . . . . . . . . . . . . . . 12
3.4.5. On Ack Receipt . . . . . . . . . . . . . . . . . . . 14 3.5.2. Variables of interest . . . . . . . . . . . . . . . . 13
3.4.6. On Packet Acknowledgment . . . . . . . . . . . . . . 15 3.5.3. Initialization . . . . . . . . . . . . . . . . . . . 14
3.4.7. Setting the Loss Detection Alarm . . . . . . . . . . 16 3.5.4. On Sending a Packet . . . . . . . . . . . . . . . . . 15
3.4.8. On Alarm Firing . . . . . . . . . . . . . . . . . . . 17 3.5.5. On Ack Receipt . . . . . . . . . . . . . . . . . . . 16
3.4.9. Detecting Lost Packets . . . . . . . . . . . . . . . 18 3.5.6. On Packet Acknowledgment . . . . . . . . . . . . . . 17
3.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . 19 3.5.7. Setting the Loss Detection Alarm . . . . . . . . . . 18
4. Congestion Control . . . . . . . . . . . . . . . . . . . . . 19 3.5.8. On Alarm Firing . . . . . . . . . . . . . . . . . . . 20
4.1. Slow Start . . . . . . . . . . . . . . . . . . . . . . . 20 3.5.9. Detecting Lost Packets . . . . . . . . . . . . . . . 20
4.2. Congestion Avoidance . . . . . . . . . . . . . . . . . . 20 3.6. Discussion . . . . . . . . . . . . . . . . . . . . . . . 21
4.3. Recovery Period . . . . . . . . . . . . . . . . . . . . . 20 4. Congestion Control . . . . . . . . . . . . . . . . . . . . . 22
4.4. Tail Loss Probe . . . . . . . . . . . . . . . . . . . . . 20 4.1. Slow Start . . . . . . . . . . . . . . . . . . . . . . . 22
4.5. Retransmission Timeout . . . . . . . . . . . . . . . . . 20 4.2. Congestion Avoidance . . . . . . . . . . . . . . . . . . 22
4.6. Pacing . . . . . . . . . . . . . . . . . . . . . . . . . 21 4.3. Recovery Period . . . . . . . . . . . . . . . . . . . . . 22
4.7. Pseudocode . . . . . . . . . . . . . . . . . . . . . . . 21 4.4. Tail Loss Probe . . . . . . . . . . . . . . . . . . . . . 23
4.7.1. Constants of interest . . . . . . . . . . . . . . . . 21 4.5. Retransmission Timeout . . . . . . . . . . . . . . . . . 23
4.7.2. Variables of interest . . . . . . . . . . . . . . . . 21 4.6. Pacing . . . . . . . . . . . . . . . . . . . . . . . . . 23
4.7.3. Initialization . . . . . . . . . . . . . . . . . . . 22 4.7. Pseudocode . . . . . . . . . . . . . . . . . . . . . . . 24
4.7.4. On Packet Sent . . . . . . . . . . . . . . . . . . . 22 4.7.1. Constants of interest . . . . . . . . . . . . . . . . 24
4.7.5. On Packet Acknowledgement . . . . . . . . . . . . . . 22 4.7.2. Variables of interest . . . . . . . . . . . . . . . . 24
4.7.6. On Packets Lost . . . . . . . . . . . . . . . . . . . 23 4.7.3. Initialization . . . . . . . . . . . . . . . . . . . 24
4.7.7. On Retransmission Timeout Verified . . . . . . . . . 23 4.7.4. On Packet Sent . . . . . . . . . . . . . . . . . . . 25
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 4.7.5. On Packet Acknowledgement . . . . . . . . . . . . . . 25
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 4.7.6. On Packets Lost . . . . . . . . . . . . . . . . . . . 25
6.1. Normative References . . . . . . . . . . . . . . . . . . 24 4.7.7. On Retransmission Timeout Verified . . . . . . . . . 26
6.2. Informative References . . . . . . . . . . . . . . . . . 25 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
6.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 25 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 25 6.1. Normative References . . . . . . . . . . . . . . . . . . 26
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 25 6.2. Informative References . . . . . . . . . . . . . . . . . 26
B.1. Since draft-ietf-quic-recovery-09 . . . . . . . . . . . . 25 6.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 27
B.2. Since draft-ietf-quic-recovery-08 . . . . . . . . . . . . 26 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 28
B.3. Since draft-ietf-quic-recovery-07 . . . . . . . . . . . . 26 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 28
B.4. Since draft-ietf-quic-recovery-06 . . . . . . . . . . . . 26 B.1. Since draft-ietf-quic-recovery-10 . . . . . . . . . . . . 28
B.5. Since draft-ietf-quic-recovery-05 . . . . . . . . . . . . 26 B.2. Since draft-ietf-quic-recovery-09 . . . . . . . . . . . . 28
B.6. Since draft-ietf-quic-recovery-04 . . . . . . . . . . . . 26 B.3. Since draft-ietf-quic-recovery-08 . . . . . . . . . . . . 28
B.7. Since draft-ietf-quic-recovery-03 . . . . . . . . . . . . 26 B.4. Since draft-ietf-quic-recovery-07 . . . . . . . . . . . . 28
B.8. Since draft-ietf-quic-recovery-02 . . . . . . . . . . . . 26 B.5. Since draft-ietf-quic-recovery-06 . . . . . . . . . . . . 28
B.9. Since draft-ietf-quic-recovery-01 . . . . . . . . . . . . 26 B.6. Since draft-ietf-quic-recovery-05 . . . . . . . . . . . . 29
B.10. Since draft-ietf-quic-recovery-00 . . . . . . . . . . . . 27 B.7. Since draft-ietf-quic-recovery-04 . . . . . . . . . . . . 29
B.11. Since draft-iyengar-quic-loss-recovery-01 . . . . . . . . 27 B.8. Since draft-ietf-quic-recovery-03 . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 27 B.9. Since draft-ietf-quic-recovery-02 . . . . . . . . . . . . 29
B.10. Since draft-ietf-quic-recovery-01 . . . . . . . . . . . . 29
B.11. Since draft-ietf-quic-recovery-00 . . . . . . . . . . . . 29
B.12. Since draft-iyengar-quic-loss-recovery-01 . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30
1. Introduction 1. Introduction
QUIC is a new multiplexed and secure transport atop UDP. QUIC builds QUIC is a new multiplexed and secure transport atop UDP. QUIC builds
on decades of transport and security experience, and implements on decades of transport and security experience, and implements
mechanisms that make it attractive as a modern general-purpose mechanisms that make it attractive as a modern general-purpose
transport. The QUIC protocol is described in [QUIC-TRANSPORT]. transport. The QUIC protocol is described in [QUIC-TRANSPORT].
QUIC implements the spirit of known TCP loss recovery mechanisms, QUIC implements the spirit of known TCP loss recovery mechanisms,
described in RFCs, various Internet-drafts, and also those prevalent described in RFCs, various Internet-drafts, and also those prevalent
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connection, and are monotonically increasing, which prevents connection, and are monotonically increasing, which prevents
ambiguity. This fundamental design decision obviates the need for ambiguity. This fundamental design decision obviates the need for
disambiguating between transmissions and retransmissions and disambiguating between transmissions and retransmissions and
eliminates significant complexity from QUIC's interpretation of TCP eliminates significant complexity from QUIC's interpretation of TCP
loss detection mechanisms. loss detection mechanisms.
Every packet may contain several frames. We outline the frames that Every packet may contain several frames. We outline the frames that
are important to the loss detection and congestion control machinery are important to the loss detection and congestion control machinery
below. below.
o Retransmittable frames are frames requiring reliable delivery. o Retransmittable frames are those that count towards bytes in
The most common are STREAM frames, which typically contain flight and need acknowledgement. The most common are STREAM
application data. frames, which typically contain application data.
o Retransmittable packets are those that contain at least one
retransmittable frame.
o Crypto handshake data is sent on stream 0, and uses the o Crypto handshake data is sent on stream 0, and uses the
reliability machinery of QUIC underneath. reliability machinery of QUIC underneath.
o ACK frames contain acknowledgment information. ACK frames contain o ACK frames contain acknowledgment information. ACK frames contain
one or more ranges of acknowledged packets. one or more ranges of acknowledged packets.
2.1. Relevant Differences Between QUIC and TCP 2.1. Relevant Differences Between QUIC and TCP
Readers familiar with TCP's loss detection and congestion control Readers familiar with TCP's loss detection and congestion control
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implementations on both sides and reducing memory pressure on the implementations on both sides and reducing memory pressure on the
sender. sender.
2.1.3. More ACK Ranges 2.1.3. More ACK Ranges
QUIC supports many ACK ranges, opposed to TCP's 3 SACK ranges. In QUIC supports many ACK ranges, opposed to TCP's 3 SACK ranges. In
high loss environments, this speeds recovery, reduces spurious high loss environments, this speeds recovery, reduces spurious
retransmits, and ensures forward progress without relying on retransmits, and ensures forward progress without relying on
timeouts. timeouts.
2.1.4. Explicit Correction For Delayed Acks 2.1.4. Explicit Correction For Delayed ACKs
QUIC ACKs explicitly encode the delay incurred at the receiver QUIC ACKs explicitly encode the delay incurred at the receiver
between when a packet is received and when the corresponding ACK is between when a packet is received and when the corresponding ACK is
sent. This allows the receiver of the ACK to adjust for receiver sent. This allows the receiver of the ACK to adjust for receiver
delays, specifically the delayed ack timer, when estimating the path delays, specifically the delayed ack timer, when estimating the path
RTT. This mechanism also allows a receiver to measure and report the RTT. This mechanism also allows a receiver to measure and report the
delay from when a packet was received by the OS kernel, which is delay from when a packet was received by the OS kernel, which is
useful in receivers which may incur delays such as context-switch useful in receivers which may incur delays such as context-switch
latency before a userspace QUIC receiver processes a received packet. latency before a userspace QUIC receiver processes a received packet.
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RTT is calculated when an ACK frame arrives by computing the RTT is calculated when an ACK frame arrives by computing the
difference between the current time and the time the largest newly difference between the current time and the time the largest newly
acked packet was sent. If no packets are newly acknowledged, RTT acked packet was sent. If no packets are newly acknowledged, RTT
cannot be calculated. When RTT is calculated, the ack delay field cannot be calculated. When RTT is calculated, the ack delay field
from the ACK frame SHOULD be subtracted from the RTT as long as the from the ACK frame SHOULD be subtracted from the RTT as long as the
result is larger than the Min RTT. If the result is smaller than the result is larger than the Min RTT. If the result is smaller than the
min_rtt, the RTT should be used, but the ack delay field should be min_rtt, the RTT should be used, but the ack delay field should be
ignored. ignored.
Like TCP, QUIC calculates both smoothed RTT and RTT variance as Like TCP, QUIC calculates both smoothed RTT and RTT variance similar
specified in [RFC6298]. to those specified in [RFC6298].
Min RTT is the minimum RTT measured over the connection, prior to Min RTT is the minimum RTT measured over the connection, prior to
adjusting by ack delay. Ignoring ack delay for min RTT prevents adjusting by ack delay. Ignoring ack delay for min RTT prevents
intentional or unintentional underestimation of min RTT, which in intentional or unintentional underestimation of min RTT, which in
turn prevents underestimating smoothed RTT. turn prevents underestimating smoothed RTT.
3.2. Ack-based Detection 3.2. Ack-based Detection
Ack-based loss detection implements the spirit of TCP's Fast Ack-based loss detection implements the spirit of TCP's Fast
Retransmit [RFC5681], Early Retransmit [RFC5827], FACK, and SACK loss Retransmit [RFC5681], Early Retransmit [RFC5827], FACK, and SACK loss
recovery [RFC6675]. This section provides an overview of how these recovery [RFC6675]. This section provides an overview of how these
algorithms are implemented in QUIC. algorithms are implemented in QUIC.
(TODO: Define unacknowledged packet, ackable packet, outstanding
bytes.)
3.2.1. Fast Retransmit 3.2.1. Fast Retransmit
An unacknowledged packet is marked as lost when an acknowledgment is An unacknowledged packet is marked as lost when an acknowledgment is
received for a packet that was sent a threshold number of packets received for a packet that was sent a threshold number of packets
(kReorderingThreshold) after the unacknowledged packet. Receipt of (kReorderingThreshold) after the unacknowledged packet. Receipt of
the ack indicates that a later packet was received, while the ack indicates that a later packet was received, while
kReorderingThreshold provides some tolerance for reordering of kReorderingThreshold provides some tolerance for reordering of
packets in the network. packets in the network.
The RECOMMENDED initial value for kReorderingThreshold is 3. The RECOMMENDED initial value for kReorderingThreshold is 3.
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QUIC's reordering resilience, though care should be taken to map TCP QUIC's reordering resilience, though care should be taken to map TCP
specifics to QUIC correctly. Similarly, using time-based loss specifics to QUIC correctly. Similarly, using time-based loss
detection to deal with reordering, such as in PR-TCP, should be more detection to deal with reordering, such as in PR-TCP, should be more
readily usable in QUIC. Making QUIC deal with such networks is readily usable in QUIC. Making QUIC deal with such networks is
important open research, and implementers are encouraged to explore important open research, and implementers are encouraged to explore
this space. this space.
3.2.2. Early Retransmit 3.2.2. Early Retransmit
Unacknowledged packets close to the tail may have fewer than Unacknowledged packets close to the tail may have fewer than
kReorderingThreshold number of ackable packets sent after them. Loss kReorderingThreshold retransmittable packets sent after them. Loss
of such packets cannot be detected via Fast Retransmit. To enable of such packets cannot be detected via Fast Retransmit. To enable
ack-based loss detection of such packets, receipt of an ack-based loss detection of such packets, receipt of an
acknowledgment for the last outstanding ackable packet triggers the acknowledgment for the last outstanding retransmittable packet
Early Retransmit process, as follows. triggers the Early Retransmit process, as follows.
If there are unacknowledged ackable packets still pending, they ought If there are unacknowledged retransmittable packets still pending,
to be marked as lost. To compensate for the reduced reordering they should be marked as lost. To compensate for the reduced
resilience, the sender SHOULD set an alarm for a small period of reordering resilience, the sender SHOULD set an alarm for a small
time. If the unacknowledged ackable packets are not acknowledged period of time. If the unacknowledged retransmittable packets are
during this time, then these packets MUST be marked as lost. not acknowledged during this time, then these packets MUST be marked
as lost.
An endpoint SHOULD set the alarm such that a packet is marked as lost An endpoint SHOULD set the alarm such that a packet is marked as lost
no earlier than 1.25 * max(SRTT, latest_RTT) since when it was sent. no earlier than 1.25 * max(SRTT, latest_RTT) since when it was sent.
Using max(SRTT, latest_RTT) protects from the two following cases: Using max(SRTT, latest_RTT) protects from the two following cases:
o the latest RTT sample is lower than the SRTT, perhaps due to o the latest RTT sample is lower than the SRTT, perhaps due to
reordering where packet whose ack triggered the Early Retransit reordering where packet whose ack triggered the Early Retransit
process encountered a shorter path; process encountered a shorter path;
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This mechanism is based on Early Retransmit for TCP [RFC5827]. This mechanism is based on Early Retransmit for TCP [RFC5827].
However, [RFC5827] does not include the alarm described above. Early However, [RFC5827] does not include the alarm described above. Early
Retransmit is prone to spurious retransmissions due to its reduced Retransmit is prone to spurious retransmissions due to its reduced
reordering resilence without the alarm. This observation led Linux reordering resilence without the alarm. This observation led Linux
TCP implementers to implement an alarm for TCP as well, and this TCP implementers to implement an alarm for TCP as well, and this
document incorporates this advancement. document incorporates this advancement.
3.3. Timer-based Detection 3.3. Timer-based Detection
Timer-based loss detection implements the spirit of TCP's Tail Loss Timer-based loss detection implements a handshake retransmission
Probe and Retransmission Timeout mechanisms. timer that is optimized for QUIC as well as the spirit of TCP's Tail
Loss Probe and Retransmission Timeout mechanisms.
3.3.1. Tail Loss Probe 3.3.1. Handshake Timeout
Handshake packets, which contain STREAM frames for stream 0, are
critical to QUIC transport and crypto negotiation, so a separate
alarm is used for them.
The initial handshake timeout SHOULD be set to twice the initial RTT.
At the beginning, there are no prior RTT samples within a connection.
Resumed connections over the same network SHOULD use the previous
connection's final smoothed RTT value as the resumed connection's
initial RTT.
If no previous RTT is available, or if the network changes, the
initial RTT SHOULD be set to 100ms.
When a handshake packet is sent, the sender SHOULD set an alarm for
the handshake timeout period.
When the alarm fires, the sender MUST retransmit all unacknowledged
handshake data, by calling RetransmitAllUnackedHandshakeData(). On
each consecutive firing of the handshake alarm, the sender SHOULD
double the handshake timeout and set an alarm for this period.
When an acknowledgement is received for a handshake packet, the new
RTT is computed and the alarm SHOULD be set for twice the newly
computed smoothed RTT.
Handshake data may be cancelled by handshake state transitions. In
particular, all non-protected data SHOULD no longer be transmitted
once packet protection is available.
(TODO: Work this section some more. Add text on client vs. server,
and on stateless retry.)
3.3.2. Tail Loss Probe
The algorithm described in this section is an adaptation of the Tail The algorithm described in this section is an adaptation of the Tail
Loss Probe algorithm proposed for TCP [TLP]. Loss Probe algorithm proposed for TCP [TLP].
A packet sent at the tail is particularly vulnerable to slow loss A packet sent at the tail is particularly vulnerable to slow loss
detection, since acks of subsequent packets are needed to trigger detection, since acks of subsequent packets are needed to trigger
ack-based detection. To ameliorate this weakness of tail packets, ack-based detection. To ameliorate this weakness of tail packets,
the sender schedules an alarm when the last ackable packet before the sender schedules an alarm when the last retransmittable packet
quiescence is transmitted. When this alarm fires, a Tail Loss Probe before quiescence is transmitted. When this alarm fires, a Tail Loss
(TLP) packet is sent to evoke an acknowledgement from the receiver. Probe (TLP) packet is sent to evoke an acknowledgement from the
receiver.
The alarm duration, or Probe Timeout (PTO), is set based on the The alarm duration, or Probe Timeout (PTO), is set based on the
following conditions: following conditions:
o PTO SHOULD be scheduled for max(1.5*SRTT+MaxAckDelay, 10ms) o PTO SHOULD be scheduled for max(1.5*SRTT+MaxAckDelay,
kMinTLPTimeout)
o If RTO (Section 3.3.2) is earlier, schedule a TLP alarm in its o If RTO (Section 3.3.3) is earlier, schedule a TLP alarm in its
place. That is, PTO SHOULD be scheduled for min(RTO, PTO). place. That is, PTO SHOULD be scheduled for min(RTO, PTO).
MaxAckDelay is the maximum ack delay supplied in an incoming ACK MaxAckDelay is the maximum ack delay supplied in an incoming ACK
frame. MaxAckDelay excludes ack delays that aren't included in an frame. MaxAckDelay excludes ack delays that aren't included in an
RTT sample because they're too large and excludes those which RTT sample because they're too large and excludes those which
reference an ack-only packet. reference an ack-only packet.
QUIC diverges from TCP by calculating MaxAckDelay dynamically, QUIC diverges from TCP by calculating MaxAckDelay dynamically,
instead of assuming a constant delayed ack timeout for all instead of assuming a constant delayed ack timeout for all
connections. QUIC includes this in all probe timeouts, because it connections. QUIC includes this in all probe timeouts, because it
assume the ack delay may come into play, regardless of the number of assume the ack delay may come into play, regardless of the number of
packets outstanding. TCP's TLP assumes if at least 2 packets are packets outstanding. TCP's TLP assumes if at least 2 packets are
outstanding, acks will not be delayed. outstanding, acks will not be delayed.
A PTO value of at least 1.5*SRTT ensures that the ACK is overdue. A PTO value of at least 1.5*SRTT ensures that the ACK is overdue.
The 1.5 is based on [LOSS-PROBE], but implementations MAY experiment The 1.5 is based on [TLP], but implementations MAY experiment with
with other constants. other constants.
To reduce latency, it is RECOMMENDED that the sender set and allow To reduce latency, it is RECOMMENDED that the sender set and allow
the TLP alarm to fire twice before setting an RTO alarm. In other the TLP alarm to fire twice before setting an RTO alarm. In other
words, when the TLP alarm fires the first time, a TLP packet is sent, words, when the TLP alarm fires the first time, a TLP packet is sent,
and it is RECOMMENDED that the TLP alarm be scheduled for a second and it is RECOMMENDED that the TLP alarm be scheduled for a second
time. When the TLP alarm fires the second time, a second TLP packet time. When the TLP alarm fires the second time, a second TLP packet
is sent, and an RTO alarm SHOULD be scheduled Section 3.3.2. is sent, and an RTO alarm SHOULD be scheduled Section 3.3.3.
A TLP packet SHOULD carry new data when possible. If new data is A TLP packet SHOULD carry new data when possible. If new data is
unavailable or new data cannot be sent due to flow control, a TLP unavailable or new data cannot be sent due to flow control, a TLP
packet MAY retransmit unacknowledged data to potentially reduce packet MAY retransmit unacknowledged data to potentially reduce
recovery time. Since a TLP alarm is used to send a probe into the recovery time. Since a TLP alarm is used to send a probe into the
network prior to establishing any packet loss, prior unacknowledged network prior to establishing any packet loss, prior unacknowledged
packets SHOULD NOT be marked as lost when a TLP alarm fires. packets SHOULD NOT be marked as lost when a TLP alarm fires.
A TLP packet MUST NOT be blocked by the sender's congestion
controller. The sender MUST however count these bytes as additional
bytes in flight, since a TLP adds network load without establishing
packet loss.
A sender may not know that a packet being sent is a tail packet. A sender may not know that a packet being sent is a tail packet.
Consequently, a sender may have to arm or adjust the TLP alarm on Consequently, a sender may have to arm or adjust the TLP alarm on
every sent ackable packet. every sent retransmittable packet.
3.3.2. Retransmission Timeout 3.3.3. Retransmission Timeout
A Retransmission Timeout (RTO) alarm is the final backstop for loss A Retransmission Timeout (RTO) alarm is the final backstop for loss
detection. The algorithm used in QUIC is based on the RTO algorithm detection. The algorithm used in QUIC is based on the RTO algorithm
for TCP [RFC5681] and is additionally resilient to spurious RTO for TCP [RFC5681] and is additionally resilient to spurious RTO
events [RFC5682]. events [RFC5682].
When the last TLP packet is sent, an alarm is scheduled for the RTO When the last TLP packet is sent, an alarm is scheduled for the RTO
period. When this alarm fires, the sender sends two packets, to period. When this alarm fires, the sender sends two packets, to
evoke acknowledgements from the receiver, and restarts the RTO alarm. evoke acknowledgements from the receiver, and restarts the RTO alarm.
Similar to TCP [RFC6298], the RTO period is set based on the Similar to TCP [RFC6298], the RTO period is set based on the
following conditions: following conditions:
o When the final TLP packet is sent, the RTO period is set to o When the final TLP packet is sent, the RTO period is set to
max(SRTT + 4*RTTVAR + MaxAckDelay, minRTO) max(SRTT + 4*RTTVAR + MaxAckDelay, kMinRTOTimeout)
o When an RTO alarm fires, the RTO period is doubled. o When an RTO alarm fires, the RTO period is doubled.
The sender typically has incurred a high latency penalty by the time The sender typically has incurred a high latency penalty by the time
an RTO alarm fires, and this penalty increases exponentially in an RTO alarm fires, and this penalty increases exponentially in
subsequent consecutive RTO events. Sending a single packet on an RTO subsequent consecutive RTO events. Sending a single packet on an RTO
event therefore makes the connection very sensitive to single packet event therefore makes the connection very sensitive to single packet
loss. Sending two packets instead of one significantly increases loss. Sending two packets instead of one significantly increases
resilience to packet drop in both directions, thus reducing the resilience to packet drop in both directions, thus reducing the
probability of consecutive RTO events. probability of consecutive RTO events.
skipping to change at page 10, line 28 skipping to change at page 11, line 20
or unacknowledged data to potentially reduce recovery time. Since or unacknowledged data to potentially reduce recovery time. Since
this packet is sent as a probe into the network prior to establishing this packet is sent as a probe into the network prior to establishing
any packet loss, prior unacknowledged packets SHOULD NOT be marked as any packet loss, prior unacknowledged packets SHOULD NOT be marked as
lost. lost.
A packet sent on an RTO alarm MUST NOT be blocked by the sender's A packet sent on an RTO alarm MUST NOT be blocked by the sender's
congestion controller. A sender MUST however count these bytes as congestion controller. A sender MUST however count these bytes as
additional bytes in flight, since this packet adds network load additional bytes in flight, since this packet adds network load
without establishing packet loss. without establishing packet loss.
3.3.3. Handshake Timeout 3.4. Generating Acknowledgements
Handshake packets, which contain STREAM frames for stream 0, are QUIC SHOULD delay sending acknowledgements in response to packets,
critical to QUIC transport and crypto negotiation, so a separate but MUST NOT excessively delay acknowledgements of packets containing
alarm is used for them. non-ack frames. Specifically, implementaions MUST attempt to enforce
a maximum ack delay to avoid causing the peer spurious timeouts. The
default maximum ack delay in QUIC is 25ms.
The initial handshake timeout SHOULD be set to twice the initial RTT. An acknowledgement MAY be sent for every second full-sized packet, as
TCP does [RFC5681], or may be sent less frequently, as long as the
delay does not exceed the maximum ack delay. QUIC recovery
algorithms do not assume the peer generates an acknowledgement
immediately when receiving a second full-sized packet.
At the beginning, there are no prior RTT samples within a connection. Out-of-order packets SHOULD be acknowledged more quickly, in order to
Resumed connections over the same network SHOULD use the previous accelerate loss recovery. The receiver SHOULD send an immediate ACK
connection's final smoothed RTT value as the resumed connection's when it receives a new packet which is not one greater than the
initial RTT. largest received packet number.
If no previous RTT is available, or if the network changes, the As an optimization, a receiver MAY process multiple packets before
initial RTT SHOULD be set to 100ms. sending any ACK frames in response. In this case they can determine
whether an immediate or delayed acknowledgement should be generated
after processing incoming packets.
When the first handshake packet is sent, the sender SHOULD set an 3.4.1. ACK Ranges
alarm for the handshake timeout period.
When the alarm fires, the sender MUST retransmit all unacknowledged When an ACK frame is sent, one or more ranges of acknowledged packets
handshake data. On each consecutive firing of the handshake alarm, are included. Including older packets reduces the chance of spurious
the sender SHOULD double the handshake timeout and set an alarm for retransmits caused by losing previously sent ACK frames, at the cost
this period. of larger ACK frames.
When an acknowledgement is received for a handshake packet, the new ACK frames SHOULD always acknowledge the most recently received
RTT is computed and the alarm SHOULD be set for twice the newly packets, and the more out-of-order the packets are, the more
computed smoothed RTT. important it is to send an updated ACK frame quickly, to prevent the
peer from declaring a packet as lost and spuriusly retransmitting the
frames it contains.
Handshake data may be cancelled by handshake state transitions. In Below is one recommended approach for determining what packets to
particular, all non-protected data SHOULD no longer be transmitted include in an ACK frame.
once packet protection is available.
(TODO: Work this section some more. Add text on client vs. server, 3.4.2. Receiver Tracking of ACK Frames
and on stateless retry.)
3.4. Pseudocode When a packet containing an ACK frame is sent, the largest
acknowledged in that frame may be saved. When a packet containing an
ACK frame is acknowledged, the receiver can stop acknowledging
packets less than or equal to the largest acknowledged in the sent
ACK frame.
3.4.1. Constants of interest In cases without ACK frame loss, this algorithm allows for a minimum
of 1 RTT of reordering. In cases with ACK frame loss, this approach
does not guarantee that every acknowledgement is seen by the sender
before it is no longer included in the ACK frame. Packets could be
received out of order and all subsequent ACK frames containing them
could be lost. In this case, the loss recovery algorithm may cause
spurious retransmits, but the sender will continue making forward
progress.
3.5. Pseudocode
3.5.1. Constants of interest
Constants used in loss recovery are based on a combination of RFCs, Constants used in loss recovery are based on a combination of RFCs,
papers, and common practice. Some may need to be changed or papers, and common practice. Some may need to be changed or
negotiated in order to better suit a variety of environments. negotiated in order to better suit a variety of environments.
kMaxTLPs (default 2): Maximum number of tail loss probes before an kMaxTLPs (default 2): Maximum number of tail loss probes before an
RTO fires. RTO fires.
kReorderingThreshold (default 3): Maximum reordering in packet kReorderingThreshold (default 3): Maximum reordering in packet
number space before FACK style loss detection considers a packet number space before FACK style loss detection considers a packet
skipping to change at page 12, line 5 skipping to change at page 13, line 14
kMinRTOTimeout (default 200ms): Minimum time in the future an RTO kMinRTOTimeout (default 200ms): Minimum time in the future an RTO
alarm may be set for. alarm may be set for.
kDelayedAckTimeout (default 25ms): The length of the peer's delayed kDelayedAckTimeout (default 25ms): The length of the peer's delayed
ack timer. ack timer.
kDefaultInitialRtt (default 100ms): The default RTT used before an kDefaultInitialRtt (default 100ms): The default RTT used before an
RTT sample is taken. RTT sample is taken.
3.4.2. Variables of interest 3.5.2. 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.
loss_detection_alarm: Multi-modal alarm used for loss detection. loss_detection_alarm: Multi-modal alarm used for loss detection.
handshake_count: The number of times the handshake packets have been handshake_count: The number of times the handshake packets have been
retransmitted without receiving an ack. retransmitted without receiving an ack.
tlp_count: The number of times a tail loss probe has been sent tlp_count: The number of times a tail loss probe has been sent
without receiving an ack. without receiving an ack.
rto_count: The number of times an rto has been sent without rto_count: The number of times an rto has been sent without
receiving an ack. receiving an ack.
largest_sent_before_rto: The last packet number sent prior to the largest_sent_before_rto: The last packet number sent prior to the
first retransmission timeout. first retransmission timeout.
time_of_last_sent_packet: The time the most recent packet was sent. time_of_last_sent_retransmittable_packet: The time the most recent
retransmittable packet was sent.
time_of_last_sent_handshake_packet: The time the most recent packet
containing handshake data was sent.
largest_sent_packet: The packet number of the most recently sent largest_sent_packet: The packet number of the most recently sent
packet. packet.
largest_acked_packet: The largest packet number acknowledged in an largest_acked_packet: The largest packet number acknowledged in an
ACK frame. ACK frame.
latest_rtt: The most recent RTT measurement made when receiving an latest_rtt: The most recent RTT measurement made when receiving an
ack for a previously unacked packet. ack for a previously unacked packet.
skipping to change at page 12, line 39 skipping to change at page 14, line 4
largest_acked_packet: The largest packet number acknowledged in an largest_acked_packet: The largest packet number acknowledged in an
ACK frame. ACK frame.
latest_rtt: The most recent RTT measurement made when receiving an latest_rtt: The most recent RTT measurement made when receiving an
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 [RFC6298] described in [RFC6298]
rttvar: The RTT variance, computed as described in [RFC6298] rttvar: The RTT variance, computed as described in [RFC6298]
min_rtt: The minimum RTT seen in the connection, ignoring ack delay. min_rtt: The minimum RTT seen in the connection, ignoring ack delay.
max_ack_delay: The maximum ack delay in an incoming ACK frame for max_ack_delay: The maximum ack delay in an incoming ACK frame for
this connection. Excludes ack delays for ack only packets and this connection. Excludes ack delays for ack only packets and
those that create an RTT sample less than min_rtt. those that create an RTT sample less than min_rtt.
reordering_threshold: The largest delta between the largest acked reordering_threshold: The largest packet number gap between the
retransmittable packet and a packet containing retransmittable largest acked retransmittable packet and an unacknowledged
frames before it's declared lost. retransmittable packet before it is declared lost.
time_reordering_fraction: The reordering window as a fraction of time_reordering_fraction: The reordering window as a fraction of
max(smoothed_rtt, latest_rtt). max(smoothed_rtt, latest_rtt).
loss_time: The time at which the next packet will be considered lost loss_time: The time at which the next packet will be considered lost
based on early transmit or exceeding the reordering window in based on early transmit or exceeding the reordering window in
time. time.
sent_packets: An association of packet numbers to information about sent_packets: An association of packet numbers to information about
them, including a number field indicating the packet number, a them, including a number field indicating the packet number, a
time field indicating the time a packet was sent, a boolean time field indicating the time a packet was sent, a boolean
indicating whether the packet is ack only, and a bytes field indicating whether the packet is ack only, and a bytes field
indicating the packet's size. sent_packets is ordered by packet indicating the packet's size. sent_packets is ordered by packet
number, and packets remain in sent_packets until acknowledged or number, and packets remain in sent_packets until acknowledged or
lost. lost.
3.4.3. Initialization 3.5.3. Initialization
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_alarm.reset() loss_detection_alarm.reset()
handshake_count = 0 handshake_count = 0
tlp_count = 0 tlp_count = 0
rto_count = 0 rto_count = 0
if (kUsingTimeLossDetection) if (kUsingTimeLossDetection)
reordering_threshold = infinite reordering_threshold = infinite
time_reordering_fraction = kTimeReorderingFraction time_reordering_fraction = kTimeReorderingFraction
else: else:
reordering_threshold = kReorderingThreshold reordering_threshold = kReorderingThreshold
time_reordering_fraction = infinite time_reordering_fraction = infinite
loss_time = 0 loss_time = 0
smoothed_rtt = 0 smoothed_rtt = 0
rttvar = 0 rttvar = 0
min_rtt = 0 min_rtt = infinite
max_ack_delay = 0 max_ack_delay = 0
largest_sent_before_rto = 0 largest_sent_before_rto = 0
time_of_last_sent_packet = 0 time_of_last_sent_retransmittable_packet = 0
time_of_last_sent_handshake_packet = 0
largest_sent_packet = 0 largest_sent_packet = 0
3.4.4. On Sending a Packet 3.5.4. On Sending a Packet
After any packet is sent, be it a new transmission or a rebundled After any packet is sent, be it a new transmission or a rebundled
transmission, the following OnPacketSent function is called. The transmission, the following OnPacketSent function is called. The
parameters to OnPacketSent are as follows: parameters to OnPacketSent are as follows:
o packet_number: The packet number of the sent packet. o packet_number: The packet number of the sent packet.
o is_ack_only: A boolean that indicates whether a packet only o is_ack_only: A boolean that indicates whether a packet only
contains an ACK frame. If true, it is still expected an ack will contains an ACK frame. If true, it is still expected an ack will
be received for this packet, but it is not congestion controlled. be received for this packet, but it is not retransmittable.
o is_handshake_packet: A boolean that indicates whether a packet
contains handshake data.
o sent_bytes: The number of bytes sent in the packet, not including o sent_bytes: The number of bytes sent in the packet, not including
UDP or IP overhead, but including QUIC framing overhead. UDP or IP overhead, but including QUIC framing overhead.
Pseudocode for OnPacketSent follows: Pseudocode for OnPacketSent follows:
OnPacketSent(packet_number, is_ack_only, sent_bytes): OnPacketSent(packet_number, is_ack_only, is_handshake_packet,
time_of_last_sent_packet = now sent_bytes):
largest_sent_packet = packet_number largest_sent_packet = packet_number
sent_packets[packet_number].packet_number = packet_number sent_packets[packet_number].packet_number = packet_number
sent_packets[packet_number].time = now sent_packets[packet_number].time = now
sent_packets[packet_number].ack_only = is_ack_only sent_packets[packet_number].ack_only = is_ack_only
if !is_ack_only: if !is_ack_only:
if is_handshake_packet:
time_of_last_sent_handshake_packet = now
time_of_last_sent_retransmittable_packet = now
OnPacketSentCC(sent_bytes) OnPacketSentCC(sent_bytes)
sent_packets[packet_number].bytes = sent_bytes sent_packets[packet_number].bytes = sent_bytes
SetLossDetectionAlarm() SetLossDetectionAlarm()
3.4.5. On Ack Receipt 3.5.5. On Ack Receipt
When an ack is received, it may acknowledge 0 or more packets. When an ack is received, it may acknowledge 0 or more packets.
Pseudocode for OnAckReceived and UpdateRtt follow: Pseudocode for OnAckReceived and UpdateRtt follow:
OnAckReceived(ack): OnAckReceived(ack):
largest_acked_packet = ack.largest_acked largest_acked_packet = ack.largest_acked
// If the largest acked is newly acked, update the RTT. // If the largest acked is newly acked, update the RTT.
if (sent_packets[ack.largest_acked]): if (sent_packets[ack.largest_acked]):
latest_rtt = now - sent_packets[ack.largest_acked].time latest_rtt = now - sent_packets[ack.largest_acked].time
skipping to change at page 15, line 37 skipping to change at page 17, line 37
max_ack_delay = max(max_ack_delay, ack_delay) max_ack_delay = max(max_ack_delay, ack_delay)
// Based on {{RFC6298}}. // Based on {{RFC6298}}.
if (smoothed_rtt == 0): if (smoothed_rtt == 0):
smoothed_rtt = latest_rtt smoothed_rtt = latest_rtt
rttvar = latest_rtt / 2 rttvar = latest_rtt / 2
else: else:
rttvar_sample = abs(smoothed_rtt - latest_rtt) rttvar_sample = abs(smoothed_rtt - latest_rtt)
rttvar = 3/4 * rttvar + 1/4 * rttvar_sample rttvar = 3/4 * rttvar + 1/4 * rttvar_sample
smoothed_rtt = 7/8 * smoothed_rtt + 1/8 * latest_rtt smoothed_rtt = 7/8 * smoothed_rtt + 1/8 * latest_rtt
3.4.6. On Packet Acknowledgment 3.5.6. On Packet Acknowledgment
When a packet is acked for the first time, the following When a packet is acked for the first time, the following
OnPacketAcked function is called. Note that a single ACK frame may OnPacketAcked function is called. Note that a single ACK frame may
newly acknowledge several packets. OnPacketAcked must be called once newly acknowledge several packets. OnPacketAcked must be called once
for each of these newly acked packets. for each of these newly acked packets.
OnPacketAcked takes one parameter, acked_packet_number, which is the OnPacketAcked takes one parameter, acked_packet, which is the struct
packet number of the newly acked packet, and returns a list of packet of the newly acked packet.
numbers that are detected as lost.
If this is the first acknowledgement following RTO, check if the If this is the first acknowledgement following RTO, check if the
smallest newly acknowledged packet is one sent by the RTO, and if so, smallest newly acknowledged packet is one sent by the RTO, and if so,
inform congestion control of a verified RTO, similar to F-RTO inform congestion control of a verified RTO, similar to F-RTO
[RFC5682] [RFC5682]
Pseudocode for OnPacketAcked follows: Pseudocode for OnPacketAcked follows:
OnPacketAcked(acked_packet_number): OnPacketAcked(acked_packet):
OnPacketAckedCC(acked_packet_number) if (!acked_packet.is_ack_only):
OnPacketAckedCC(acked_packet)
// If a packet sent prior to RTO was acked, then the RTO // If a packet sent prior to RTO was acked, then the RTO
// was spurious. Otherwise, inform congestion control. // was spurious. Otherwise, inform congestion control.
if (rto_count > 0 && if (rto_count > 0 &&
acked_packet_number > largest_sent_before_rto) acked_packet.packet_number > largest_sent_before_rto)
OnRetransmissionTimeoutVerified() OnRetransmissionTimeoutVerified()
handshake_count = 0 handshake_count = 0
tlp_count = 0 tlp_count = 0
rto_count = 0 rto_count = 0
sent_packets.remove(acked_packet_number) sent_packets.remove(acked_packet.packet_number)
3.4.7. Setting the Loss Detection Alarm 3.5.7. Setting the Loss Detection Alarm
QUIC loss detection uses a single alarm for all timer-based loss QUIC loss detection uses a single alarm for all timer-based loss
detection. The duration of the alarm is based on the alarm's mode, detection. The duration of the alarm is based on the alarm's mode,
which is set in the packet and timer events further below. The which is set in the packet and timer events further below. The
function SetLossDetectionAlarm defined below shows how the single function SetLossDetectionAlarm defined below shows how the single
timer is set based on the alarm mode. timer is set based on the alarm mode.
3.4.7.1. Handshake Alarm 3.5.7.1. Handshake Alarm
When a connection has unacknowledged handshake data, the handshake When a connection has unacknowledged handshake data, the handshake
alarm is set and when it expires, all unacknowledgedd handshake data alarm is set and when it expires, all unacknowledgedd handshake data
is retransmitted. is retransmitted.
When stateless rejects are in use, the connection is considered When stateless rejects are in use, the connection is considered
immediately closed once a reject is sent, so no timer is set to immediately closed once a reject is sent, so no timer is set to
retransmit the reject. retransmit the reject.
Version negotiation packets are always stateless, and MUST be sent Version negotiation packets are always stateless, and MUST be sent
once per handshake packet that uses an unsupported QUIC version, and once per handshake packet that uses an unsupported QUIC version, and
MAY be sent in response to 0RTT packets. MAY be sent in response to 0RTT packets.
3.4.7.2. Tail Loss Probe and Retransmission Alarm 3.5.7.2. Tail Loss Probe and Retransmission Alarm
Tail loss probes [LOSS-PROBE] and retransmission timeouts [RFC6298] Tail loss probes [TLP] and retransmission timeouts [RFC6298] are an
are an alarm based mechanism to recover from cases when there are alarm based mechanism to recover from cases when there are
outstanding retransmittable packets, but an acknowledgement has not outstanding retransmittable packets, but an acknowledgement has not
been received in a timely manner. been received in a timely manner.
The TLP and RTO timers are armed when there is not unacknowledged The TLP and RTO timers are armed when there is not unacknowledged
handshake data. The TLP alarm is set until the max number of TLP handshake data. The TLP alarm is set until the max number of TLP
packets have been sent, and then the RTO timer is set. packets have been sent, and then the RTO timer is set.
3.4.7.3. Early Retransmit Alarm 3.5.7.3. Early Retransmit Alarm
Early retransmit [RFC5827] is implemented with a 1/4 RTT timer. It Early retransmit [RFC5827] is implemented with a 1/4 RTT timer. It
is part of QUIC's time based loss detection, but is always enabled, is part of QUIC's time based loss detection, but is always enabled,
even when only packet reordering loss detection is enabled. even when only packet reordering loss detection is enabled.
3.4.7.4. Pseudocode 3.5.7.4. Pseudocode
Pseudocode for SetLossDetectionAlarm follows: Pseudocode for SetLossDetectionAlarm follows:
SetLossDetectionAlarm(): SetLossDetectionAlarm():
// Don't arm the alarm if there are no packets with // Don't arm the alarm if there are no packets with
// retransmittable data in flight. // retransmittable data in flight.
if (num_retransmittable_packets_outstanding == 0): if (bytes_in_flight == 0):
loss_detection_alarm.cancel() loss_detection_alarm.cancel()
return return
if (handshake packets are outstanding): if (handshake packets are outstanding):
// Handshake retransmission alarm. // Handshake retransmission alarm.
if (smoothed_rtt == 0): if (smoothed_rtt == 0):
alarm_duration = 2 * kDefaultInitialRtt alarm_duration = 2 * kDefaultInitialRtt
else: else:
alarm_duration = 2 * smoothed_rtt alarm_duration = 2 * smoothed_rtt
alarm_duration = max(alarm_duration + max_ack_delay, alarm_duration = max(alarm_duration + max_ack_delay,
kMinTLPTimeout) kMinTLPTimeout)
alarm_duration = alarm_duration * (2 ^ handshake_count) alarm_duration = alarm_duration * (2 ^ handshake_count)
loss_detection_alarm.set(
time_of_last_sent_handshake_packet + alarm_duration)
return;
else if (loss_time != 0): else if (loss_time != 0):
// Early retransmit timer or time loss detection. // Early retransmit timer or time loss detection.
alarm_duration = loss_time - time_of_last_sent_packet alarm_duration = loss_time -
else if (tlp_count < kMaxTLPs): time_of_last_sent_retransmittable_packet
// Tail Loss Probe
alarm_duration = max(1.5 * smoothed_rtt + max_ack_delay,
kMinTLPTimeout)
else: else:
// RTO alarm // RTO or TLP alarm
// Calculate RTO duration
alarm_duration = alarm_duration =
smoothed_rtt + 4 * rttvar + max_ack_delay smoothed_rtt + 4 * rttvar + max_ack_delay
alarm_duration = max(alarm_duration, kMinRTOTimeout) alarm_duration = max(alarm_duration, kMinRTOTimeout)
alarm_duration = alarm_duration * (2 ^ rto_count) alarm_duration = alarm_duration * (2 ^ rto_count)
if (tlp_count < kMaxTLPs):
// Tail Loss Probe
tlp_alarm_duration = max(1.5 * smoothed_rtt
+ max_ack_delay, kMinTLPTimeout)
alarm_duration = min(tlp_alarm_duration, alarm_duration)
loss_detection_alarm.set(time_of_last_sent_packet loss_detection_alarm.set(
+ alarm_duration) time_of_last_sent_retransmittable_packet + alarm_duration)
3.4.8. On Alarm Firing 3.5.8. On Alarm Firing
QUIC uses one loss recovery alarm, which when set, can be in one of QUIC uses one loss recovery alarm, which when set, can be in one of
several modes. When the alarm fires, the mode determines the action several modes. When the alarm fires, the mode determines the action
to be performed. to be performed.
Pseudocode for OnLossDetectionAlarm follows: Pseudocode for OnLossDetectionAlarm follows:
OnLossDetectionAlarm(): OnLossDetectionAlarm():
if (handshake packets are outstanding): if (handshake packets are outstanding):
// Handshake retransmission alarm. // Handshake retransmission alarm.
RetransmitAllHandshakePackets() RetransmitAllUnackedHandshakeData()
handshake_count++ handshake_count++
else if (loss_time != 0): else if (loss_time != 0):
// Early retransmit or Time Loss Detection // Early retransmit or Time Loss Detection
DetectLostPackets(largest_acked_packet) DetectLostPackets(largest_acked_packet)
else if (tlp_count < kMaxTLPs): else if (tlp_count < kMaxTLPs):
// Tail Loss Probe. // Tail Loss Probe.
SendOnePacket() SendOnePacket()
tlp_count++ tlp_count++
else: else:
// RTO. // RTO.
if (rto_count == 0) if (rto_count == 0)
largest_sent_before_rto = largest_sent_packet largest_sent_before_rto = largest_sent_packet
SendTwoPackets() SendTwoPackets()
rto_count++ rto_count++
SetLossDetectionAlarm() SetLossDetectionAlarm()
3.4.9. Detecting Lost Packets 3.5.9. Detecting Lost Packets
Packets in QUIC are only considered lost once a larger packet number Packets in QUIC are only considered lost once a larger packet number
is acknowledged. DetectLostPackets is called every time an ack is is acknowledged. DetectLostPackets is called every time an ack is
received. If the loss detection alarm fires and the loss_time is received. If the loss detection alarm fires and the loss_time is
set, the previous largest acked packet is supplied. set, the previous largest acked packet is supplied.
3.4.9.1. Handshake Packets 3.5.9.1. Handshake Packets
The receiver MUST close the connection with an error of type The receiver MUST close the connection with an error of type
OPTIMISTIC_ACK when receiving an unprotected packet that acks OPTIMISTIC_ACK when receiving an unprotected packet that acks
protected packets. The receiver MUST trust protected acks for protected packets. The receiver MUST trust protected acks for
unprotected packets, however. Aside from this, loss detection for unprotected packets, however. Aside from this, loss detection for
handshake packets when an ack is processed is identical to other handshake packets when an ack is processed is identical to other
packets. packets.
3.4.9.2. Pseudocode 3.5.9.2. Pseudocode
DetectLostPackets takes one parameter, acked, which is the largest DetectLostPackets takes one parameter, acked, which is the largest
acked packet. acked packet.
Pseudocode for DetectLostPackets follows: Pseudocode for DetectLostPackets follows:
DetectLostPackets(largest_acked): DetectLostPackets(largest_acked):
loss_time = 0 loss_time = 0
lost_packets = {} lost_packets = {}
delay_until_lost = infinite delay_until_lost = infinite
if (kUsingTimeLossDetection): if (kUsingTimeLossDetection):
delay_until_lost = delay_until_lost =
(1 + time_reordering_fraction) * (1 + time_reordering_fraction) *
max(latest_rtt, smoothed_rtt) max(latest_rtt, smoothed_rtt)
else if (largest_acked.packet_number == largest_sent_packet): else if (largest_acked.packet_number == largest_sent_packet):
// Early retransmit alarm. // Early retransmit alarm.
delay_until_lost = 5/4 * max(latest_rtt, smoothed_rtt) delay_until_lost = 5/4 * max(latest_rtt, smoothed_rtt)
foreach (unacked < largest_acked.packet_number): foreach (unacked < largest_acked.packet_number):
time_since_sent = now() - unacked.time_sent time_since_sent = now() - unacked.time_sent
delta = largest_acked.packet_number - unacked.packet_number delta = largest_acked.packet_number - unacked.packet_number
if (time_since_sent > delay_until_lost): if (time_since_sent > delay_until_lost ||
lost_packets.insert(unacked) delta > reordering_threshold):
else if (delta > reordering_threshold) sent_packets.remove(unacked.packet_number)
lost_packets.insert(unacked) if (!unacked.is_ack_only):
lost_packets.insert(unacked)
else if (loss_time == 0 && delay_until_lost != infinite): else if (loss_time == 0 && delay_until_lost != infinite):
loss_time = now() + delay_until_lost - time_since_sent loss_time = now() + delay_until_lost - time_since_sent
// Inform the congestion controller of lost packets and // Inform the congestion controller of lost packets and
// lets it decide whether to retransmit immediately. // lets it decide whether to retransmit immediately.
if (!lost_packets.empty()) if (!lost_packets.empty()):
OnPacketsLost(lost_packets) OnPacketsLost(lost_packets)
foreach (packet in lost_packets)
sent_packets.remove(packet.packet_number)
3.5. Discussion 3.6. Discussion
The majority of constants were derived from best common practices The majority of constants were derived from best common practices
among widely deployed TCP implementations on the internet. among widely deployed TCP implementations on the internet.
Exceptions follow. Exceptions follow.
A shorter delayed ack time of 25ms was chosen because longer delayed A shorter delayed ack time of 25ms was chosen because longer delayed
acks can delay loss recovery and for the small number of connections acks can delay loss recovery and for the small number of connections
where less than packet per 25ms is delivered, acking every packet is where less than packet per 25ms is delivered, acking every packet is
beneficial to congestion control and loss recovery. beneficial to congestion control and loss recovery.
skipping to change at page 20, line 7 skipping to change at page 22, line 12
higher than both the median and mean min_rtt typically observed on higher than both the median and mean min_rtt typically observed on
the public internet. the public internet.
4. Congestion Control 4. Congestion Control
QUIC's congestion control is based on TCP NewReno [RFC6582] QUIC's congestion control is based on TCP NewReno [RFC6582]
congestion control to determine the congestion window. QUIC congestion control to determine the congestion window. QUIC
congestion control is specified in bytes due to finer control and the congestion control is specified in bytes due to finer control and the
ease of appropriate byte counting [RFC3465]. ease of appropriate byte counting [RFC3465].
QUIC hosts MUST NOT send packets if they would increase
bytes_in_flight (defined in Section 4.7.2) beyond the available
congestion window, unless the packet is a probe packet sent after the
TLP or RTO alarm fires, as described in Section 3.3.2 and
Section 3.3.3.
4.1. Slow Start 4.1. Slow Start
QUIC begins every connection in slow start and exits slow start upon QUIC begins every connection in slow start and exits slow start upon
loss. QUIC re-enters slow start anytime the congestion window is loss. QUIC re-enters slow start anytime the congestion window is
less than sshthresh, which typically only occurs after an RTO. While less than sshthresh, which typically only occurs after an RTO. While
in slow start, QUIC increases the congestion window by the number of in slow start, QUIC increases the congestion window by the number of
acknowledged bytes when each ack is processed. acknowledged bytes when each ack is processed.
4.2. Congestion Avoidance 4.2. Congestion Avoidance
skipping to change at page 20, line 42 skipping to change at page 23, line 7
During recovery, the congestion window is not increased or decreased. During recovery, the congestion window is not increased or decreased.
As such, multiple lost packets only decrease the congestion window As such, multiple lost packets only decrease the congestion window
once as long as they're lost before exiting recovery. This causes once as long as they're lost before exiting recovery. This causes
QUIC to decrease the congestion window multiple times if QUIC to decrease the congestion window multiple times if
retransmisions are lost, but limits the reduction to once per round retransmisions are lost, but limits the reduction to once per round
trip. trip.
4.4. Tail Loss Probe 4.4. Tail Loss Probe
If recovery sends a tail loss probe, no change is made to the A TLP packet MUST NOT be blocked by the sender's congestion
congestion window. Acknowledgement or loss of tail loss probes are controller. The sender MUST however count these bytes as additional
treated like any other packet. bytes-in-flight, since a TLP adds network load without establishing
packet loss.
Acknowledgement or loss of tail loss probes are treated like any
other packet.
4.5. Retransmission Timeout 4.5. Retransmission Timeout
When retransmissions are sent due to a retransmission timeout alarm, When retransmissions are sent due to a retransmission timeout alarm,
no change is made to the congestion window until the next no change is made to the congestion window until the next
acknowledgement arrives. The retransmission timeout is considered acknowledgement arrives. The retransmission timeout is considered
spurious when this acknowledgement acknowledges packets sent prior to spurious when this acknowledgement acknowledges packets sent prior to
the first retransmission timeout. The retransmission timeout is the first retransmission timeout. The retransmission timeout is
considered valid when this acknowledgement acknowledges no packets considered valid when this acknowledgement acknowledges no packets
sent prior to the first retransmission timeout. In this case, the sent prior to the first retransmission timeout. In this case, the
congestion window MUST be reduced to the minimum congestion window congestion window MUST be reduced to the minimum congestion window
and slow start is re-entered. and slow start is re-entered.
4.6. Pacing 4.6. Pacing
It is RECOMMENDED that a sender pace sending of all data, This document does not specify a pacer, but it is RECOMMENDED that a
distributing the congestion window over the SRTT. This document does sender pace sending of all retransmittable packets based on input
not specify a pacer. As an example pacer, implementers are referred from the congestion controller. For example, a pacer might
to the Fair Queue packet scheduler (fq qdisc) in Linux (3.11 onwards) distribute the congestion window over the SRTT when used with a
as a well-known and publicly available implementation of a flow window-based controller, and a pacer might use the rate estimate of a
pacer. rate-based controller.
An implementation should take care to architect its congestion
controller to work well with a pacer. For instance, a pacer might
wrap the congestion controller and control the availability of the
congestion window, or a pacer might pace out packets handed to it by
the congestion controller. Timely delivery of ACK frames is
important for efficient loss recovery. Packets containing only ACK
frames should therefore not be paced, to avoid delaying their
delivery to the peer.
As an example of a well-known and publicly available implementation
of a flow pacer, implementers are referred to the Fair Queue packet
scheduler (fq qdisc) in Linux (3.11 onwards).
4.7. Pseudocode 4.7. Pseudocode
4.7.1. Constants of interest 4.7.1. 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. Some may need to be changed or RFCs, papers, and common practice. Some may need to be changed or
negotiated in order to better suit a variety of environments. negotiated in order to better suit a variety of environments.
kDefaultMss (default 1460 bytes): The default max packet size used kDefaultMss (default 1460 bytes): The default max packet size used
skipping to change at page 21, line 45 skipping to change at page 24, line 31
kLossReductionFactor (default 0.5): Reduction in congestion window kLossReductionFactor (default 0.5): Reduction in congestion window
when a new loss event is detected. when a new loss event is detected.
4.7.2. Variables of interest 4.7.2. 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.
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 retransmittable or PADDING frame, and that contain at least one retransmittable frame, and have not been
have not been acked or declared lost. The size does not include acked or declared lost. The size does not include IP or UDP
IP or UDP overhead. Packets only containing ACK frames do not overhead. Packets only containing ACK frames do not count towards
count towards byte_in_flight to ensure congestion control does not bytes_in_flight to ensure congestion control does not impede
impede congestion feedback. congestion feedback.
congestion_window: Maximum number of bytes in flight that may be congestion_window: Maximum number of bytes-in-flight that may be
sent. sent.
end_of_recovery: The largest packet number sent when QUIC detects a end_of_recovery: The largest packet number sent when QUIC detects a
loss. When a larger packet is acknowledged, QUIC exits recovery. loss. When a larger packet is acknowledged, QUIC exits 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.
4.7.3. Initialization 4.7.3. Initialization
skipping to change at page 24, line 12 skipping to change at page 26, line 37
This document has no IANA actions. Yet. This document has no IANA actions. Yet.
6. References 6. References
6.1. Normative References 6.1. Normative References
[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", draft-ietf-quic- Multiplexed and Secure Transport", draft-ietf-quic-
transport-10 (work in progress), March 2018. transport-11 (work in progress), April 2018.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
6.2. Informative References
[RFC3465] Allman, M., "TCP Congestion Control with Appropriate Byte
Counting (ABC)", RFC 3465, DOI 10.17487/RFC3465, February
2003, <https://www.rfc-editor.org/info/rfc3465>.
[RFC4653] Bhandarkar, S., Reddy, A., Allman, M., and E. Blanton, [RFC4653] Bhandarkar, S., Reddy, A., Allman, M., and E. Blanton,
"Improving the Robustness of TCP to Non-Congestion "Improving the Robustness of TCP to Non-Congestion
Events", RFC 4653, DOI 10.17487/RFC4653, August 2006, Events", RFC 4653, DOI 10.17487/RFC4653, August 2006,
<https://www.rfc-editor.org/info/rfc4653>. <https://www.rfc-editor.org/info/rfc4653>.
[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 24, line 45 skipping to change at page 27, line 31
P. Hurtig, "Early Retransmit for TCP and Stream Control P. Hurtig, "Early Retransmit for TCP and Stream Control
Transmission Protocol (SCTP)", RFC 5827, Transmission Protocol (SCTP)", RFC 5827,
DOI 10.17487/RFC5827, May 2010, DOI 10.17487/RFC5827, May 2010,
<https://www.rfc-editor.org/info/rfc5827>. <https://www.rfc-editor.org/info/rfc5827>.
[RFC6298] Paxson, V., Allman, M., Chu, J., and M. Sargent, [RFC6298] Paxson, V., Allman, M., Chu, J., and M. Sargent,
"Computing TCP's Retransmission Timer", RFC 6298, "Computing TCP's Retransmission Timer", RFC 6298,
DOI 10.17487/RFC6298, June 2011, DOI 10.17487/RFC6298, June 2011,
<https://www.rfc-editor.org/info/rfc6298>. <https://www.rfc-editor.org/info/rfc6298>.
[RFC6582] Henderson, T., Floyd, S., Gurtov, A., and Y. Nishida, "The
NewReno Modification to TCP's Fast Recovery Algorithm",
RFC 6582, DOI 10.17487/RFC6582, April 2012,
<https://www.rfc-editor.org/info/rfc6582>.
[RFC6675] Blanton, E., Allman, M., Wang, L., Jarvinen, I., Kojo, M., [RFC6675] Blanton, E., Allman, M., Wang, L., Jarvinen, I., Kojo, M.,
and Y. Nishida, "A Conservative Loss Recovery Algorithm and Y. Nishida, "A Conservative Loss Recovery Algorithm
Based on Selective Acknowledgment (SACK) for TCP", Based on Selective Acknowledgment (SACK) for TCP",
RFC 6675, DOI 10.17487/RFC6675, August 2012, RFC 6675, DOI 10.17487/RFC6675, August 2012,
<https://www.rfc-editor.org/info/rfc6675>. <https://www.rfc-editor.org/info/rfc6675>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
6.2. Informative References
[LOSS-PROBE]
Dukkipati, N., Cardwell, N., Cheng, Y., and M. Mathis,
"Tail Loss Probe (TLP): An Algorithm for Fast Recovery of
Tail Losses", draft-dukkipati-tcpm-tcp-loss-probe-01 (work
in progress), February 2013.
[RFC3465] Allman, M., "TCP Congestion Control with Appropriate Byte
Counting (ABC)", RFC 3465, DOI 10.17487/RFC3465, February
2003, <https://www.rfc-editor.org/info/rfc3465>.
[RFC6582] Henderson, T., Floyd, S., Gurtov, A., and Y. Nishida, "The
NewReno Modification to TCP's Fast Recovery Algorithm",
RFC 6582, DOI 10.17487/RFC6582, April 2012,
<https://www.rfc-editor.org/info/rfc6582>.
[TLP] Dukkipati, N., Cardwell, N., Cheng, Y., and M. Mathis, [TLP] Dukkipati, N., Cardwell, N., Cheng, Y., and M. Mathis,
"Tail Loss Probe (TLP): An Algorithm for Fast Recovery of "Tail Loss Probe (TLP): An Algorithm for Fast Recovery of
Tail Losses", draft-dukkipati-tcpm-tcp-loss-probe-01 (work Tail Losses", draft-dukkipati-tcpm-tcp-loss-probe-01 (work
in progress), February 2013. in progress), February 2013.
6.3. URIs 6.3. URIs
[1] https://mailarchive.ietf.org/arch/search/?email_list=quic [1] https://mailarchive.ietf.org/arch/search/?email_list=quic
[2] https://github.com/quicwg [2] https://github.com/quicwg
[3] https://github.com/quicwg/base-drafts/labels/-recovery [3] https://github.com/quicwg/base-drafts/labels/-recovery
Appendix A. Acknowledgments Appendix A. Acknowledgments
Appendix B. Change Log Appendix B. 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.
B.1. Since draft-ietf-quic-recovery-09 B.1. Since draft-ietf-quic-recovery-10
o Improved text on ack generation (#1139, #1159)
o Make references to TCP recovery mechanisms informational (#1195)
o Define time_of_last_sent_handshake_packet (#1171)
o Added signal from TLS the data it includes needs to be sent in a
Retry packet (#1061, #1199)
o Minimum RTT (min_rtt) is initialized with an infinite value
(#1169)
B.2. Since draft-ietf-quic-recovery-09
No significant changes. No significant changes.
B.2. Since draft-ietf-quic-recovery-08 B.3. Since draft-ietf-quic-recovery-08
o Clarified pacing and RTO (#967, #977) o Clarified pacing and RTO (#967, #977)
B.3. Since draft-ietf-quic-recovery-07 B.4. Since draft-ietf-quic-recovery-07
o Include Ack Delay in RTO(and TLP) computations (#981) o Include Ack Delay in RTO(and TLP) computations (#981)
o Ack Delay in SRTT computation (#961) o Ack Delay in SRTT computation (#961)
o Default RTT and Slow Start (#590) o Default RTT and Slow Start (#590)
o Many editorial fixes. o Many editorial fixes.
B.4. Since draft-ietf-quic-recovery-06 B.5. Since draft-ietf-quic-recovery-06
No significant changes. No significant changes.
B.5. Since draft-ietf-quic-recovery-05 B.6. Since draft-ietf-quic-recovery-05
o Add more congestion control text (#776) o Add more congestion control text (#776)
B.6. Since draft-ietf-quic-recovery-04 B.7. Since draft-ietf-quic-recovery-04
No significant changes. No significant changes.
B.7. Since draft-ietf-quic-recovery-03 B.8. Since draft-ietf-quic-recovery-03
No significant changes. No significant changes.
B.8. Since draft-ietf-quic-recovery-02 B.9. Since draft-ietf-quic-recovery-02
o Integrate F-RTO (#544, #409) o Integrate F-RTO (#544, #409)
o Add congestion control (#545, #395) o Add congestion control (#545, #395)
o Require connection abort if a skipped packet was acknowledged o Require connection abort if a skipped packet was acknowledged
(#415) (#415)
o Simplify RTO calculations (#142, #417) o Simplify RTO calculations (#142, #417)
B.9. Since draft-ietf-quic-recovery-01 B.10. Since draft-ietf-quic-recovery-01
o Overview added to loss detection o Overview added to loss detection
o Changes initial default RTT to 100ms o Changes initial default RTT to 100ms
o Added time-based loss detection and fixes early retransmit o Added time-based loss detection and fixes early retransmit
o Clarified loss recovery for handshake packets o Clarified loss recovery for handshake packets
o Fixed references and made TCP references informative o Fixed references and made TCP references informative
B.10. Since draft-ietf-quic-recovery-00 B.11. Since draft-ietf-quic-recovery-00
o Improved description of constants and ACK behavior o Improved description of constants and ACK behavior
B.11. Since draft-iyengar-quic-loss-recovery-01 B.12. Since draft-iyengar-quic-loss-recovery-01
o Adopted as base for draft-ietf-quic-recovery o Adopted as base for draft-ietf-quic-recovery
o Updated authors/editors list o Updated authors/editors list
o Added table of contents o Added table of contents
Authors' Addresses Authors' Addresses
Jana Iyengar (editor) Jana Iyengar (editor)
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