draft-ietf-quic-recovery-06.txt   draft-ietf-quic-recovery-07.txt 
QUIC J. Iyengar, Ed. QUIC J. Iyengar, Ed.
Internet-Draft I. Swett, Ed. Internet-Draft I. Swett, Ed.
Intended status: Standards Track Google Intended status: Standards Track Google
Expires: March 26, 2018 September 22, 2017 Expires: May 18, 2018 November 14, 2017
QUIC Loss Detection and Congestion Control QUIC Loss Detection and Congestion Control
draft-ietf-quic-recovery-06 draft-ietf-quic-recovery-07
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
https://mailarchive.ietf.org/arch/search/?email_list=quic . https://mailarchive.ietf.org/arch/search/?email_list=quic [1].
Working Group information can be found at https://github.com/quicwg ; Working Group information can be found at https://github.com/quicwg
source code and issues list for this draft can be found at [2]; source code and issues list for this draft can be found at
https://github.com/quicwg/base-drafts/labels/recovery . https://github.com/quicwg/base-drafts/labels/recovery [3].
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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 http://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 March 26, 2018. This Internet-Draft will expire on May 18, 2018.
Copyright Notice Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the Copyright (c) 2017 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 . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3 1.1. Notational Conventions . . . . . . . . . . . . . . . . . 3
2. Design of the QUIC Transmission Machinery . . . . . . . . . . 3 2. Design of the QUIC Transmission Machinery . . . . . . . . . . 3
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 . . . . . . . 4
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 . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Computing the RTT estimate . . . . . . . . . . . . . . . 5
3.2. Algorithm Details . . . . . . . . . . . . . . . . . . . . 6 3.2. Ack-based Detection . . . . . . . . . . . . . . . . . . . 5
3.2.1. Constants of interest . . . . . . . . . . . . . . . . 6 3.2.1. Fast Retransmit . . . . . . . . . . . . . . . . . . . 6
3.2.2. Variables of interest . . . . . . . . . . . . . . . . 7 3.2.2. Early Retransmit . . . . . . . . . . . . . . . . . . 6
3.2.3. Initialization . . . . . . . . . . . . . . . . . . . 8 3.3. Timer-based Detection . . . . . . . . . . . . . . . . . . 7
3.2.4. On Sending a Packet . . . . . . . . . . . . . . . . . 8 3.3.1. Tail Loss Probe . . . . . . . . . . . . . . . . . . . 7
3.2.5. On Ack Receipt . . . . . . . . . . . . . . . . . . . 9 3.3.2. Retransmission Timeout . . . . . . . . . . . . . . . 9
3.2.6. On Packet Acknowledgment . . . . . . . . . . . . . . 9 3.3.3. Handshake Timeout . . . . . . . . . . . . . . . . . . 10
3.2.7. Setting the Loss Detection Alarm . . . . . . . . . . 10 3.4. Algorithm Details . . . . . . . . . . . . . . . . . . . . 10
3.2.8. On Alarm Firing . . . . . . . . . . . . . . . . . . . 12 3.4.1. Constants of interest . . . . . . . . . . . . . . . . 10
3.2.9. Detecting Lost Packets . . . . . . . . . . . . . . . 13 3.4.2. Variables of interest . . . . . . . . . . . . . . . . 11
3.3. Discussion . . . . . . . . . . . . . . . . . . . . . . . 14 3.4.3. Initialization . . . . . . . . . . . . . . . . . . . 12
4. Congestion Control . . . . . . . . . . . . . . . . . . . . . 14 3.4.4. On Sending a Packet . . . . . . . . . . . . . . . . . 13
4.1. Slow Start . . . . . . . . . . . . . . . . . . . . . . . 15 3.4.5. On Ack Receipt . . . . . . . . . . . . . . . . . . . 13
4.2. Congestion Avoidance . . . . . . . . . . . . . . . . . . 15 3.4.6. On Packet Acknowledgment . . . . . . . . . . . . . . 14
4.3. Recovery Period . . . . . . . . . . . . . . . . . . . . . 15 3.4.7. Setting the Loss Detection Alarm . . . . . . . . . . 15
4.4. Tail Loss Probe . . . . . . . . . . . . . . . . . . . . . 15 3.4.8. On Alarm Firing . . . . . . . . . . . . . . . . . . . 17
4.5. Retransmission Timeout . . . . . . . . . . . . . . . . . 15 3.4.9. Detecting Lost Packets . . . . . . . . . . . . . . . 17
4.6. Pacing Rate . . . . . . . . . . . . . . . . . . . . . . . 16 3.5. Discussion . . . . . . . . . . . . . . . . . . . . . . . 18
4.7. Pseudocode . . . . . . . . . . . . . . . . . . . . . . . 16 4. Congestion Control . . . . . . . . . . . . . . . . . . . . . 19
4.7.1. Constants of interest . . . . . . . . . . . . . . . . 16 4.1. Slow Start . . . . . . . . . . . . . . . . . . . . . . . 19
4.7.2. Variables of interest . . . . . . . . . . . . . . . . 16 4.2. Congestion Avoidance . . . . . . . . . . . . . . . . . . 19
4.7.3. Initialization . . . . . . . . . . . . . . . . . . . 17 4.3. Recovery Period . . . . . . . . . . . . . . . . . . . . . 19
4.7.4. On Packet Sent . . . . . . . . . . . . . . . . . . . 17 4.4. Tail Loss Probe . . . . . . . . . . . . . . . . . . . . . 19
4.7.5. On Packet Acknowledgement . . . . . . . . . . . . . . 17 4.5. Retransmission Timeout . . . . . . . . . . . . . . . . . 20
4.7.6. On Packets Lost . . . . . . . . . . . . . . . . . . . 17 4.6. Pacing Rate . . . . . . . . . . . . . . . . . . . . . . . 20
4.7.7. On Retransmission Timeout Verified . . . . . . . . . 18 4.7. Pseudocode . . . . . . . . . . . . . . . . . . . . . . . 20
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18 4.7.1. Constants of interest . . . . . . . . . . . . . . . . 20
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 18 4.7.2. Variables of interest . . . . . . . . . . . . . . . . 20
6.1. Normative References . . . . . . . . . . . . . . . . . . 18 4.7.3. Initialization . . . . . . . . . . . . . . . . . . . 21
6.2. Informative References . . . . . . . . . . . . . . . . . 18 4.7.4. On Packet Sent . . . . . . . . . . . . . . . . . . . 21
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 19 4.7.5. On Packet Acknowledgement . . . . . . . . . . . . . . 21
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 19 4.7.6. On Packets Lost . . . . . . . . . . . . . . . . . . . 22
B.1. Since draft-ietf-quic-recovery-05 . . . . . . . . . . . . 19 4.7.7. On Retransmission Timeout Verified . . . . . . . . . 22
B.2. Since draft-ietf-quic-recovery-04 . . . . . . . . . . . . 19 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
B.3. Since draft-ietf-quic-recovery-03 . . . . . . . . . . . . 19 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 23
B.4. Since draft-ietf-quic-recovery-02 . . . . . . . . . . . . 20 6.1. Normative References . . . . . . . . . . . . . . . . . . 23
B.5. Since draft-ietf-quic-recovery-01 . . . . . . . . . . . . 20 6.2. Informative References . . . . . . . . . . . . . . . . . 24
B.6. Since draft-ietf-quic-recovery-00 . . . . . . . . . . . . 20 6.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 24
B.7. Since draft-iyengar-quic-loss-recovery-01 . . . . . . . . 20 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20 Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 24
B.1. Since draft-ietf-quic-recovery-06 . . . . . . . . . . . . 24
B.2. Since draft-ietf-quic-recovery-05 . . . . . . . . . . . . 24
B.3. Since draft-ietf-quic-recovery-04 . . . . . . . . . . . . 25
B.4. Since draft-ietf-quic-recovery-03 . . . . . . . . . . . . 25
B.5. Since draft-ietf-quic-recovery-02 . . . . . . . . . . . . 25
B.6. Since draft-ietf-quic-recovery-01 . . . . . . . . . . . . 25
B.7. Since draft-ietf-quic-recovery-00 . . . . . . . . . . . . 25
B.8. Since draft-iyengar-quic-loss-recovery-01 . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
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
skipping to change at page 4, line 13 skipping to change at page 4, line 21
below. below.
o Retransmittable frames are frames requiring reliable delivery. o Retransmittable frames are frames requiring reliable delivery.
The most common are STREAM frames, which typically contain The most common are STREAM frames, which typically contain
application data. application data.
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. QUIC uses a SACK- o ACK frames contain acknowledgment information. QUIC uses a SACK-
based scheme, where acks express up to 256 ranges. The ACK frame based scheme, where acks express up to 256 ranges.
also includes a receive timestamp for each packet newly acked.
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
will find algorithms here that parallel well-known TCP ones. will find algorithms here that parallel well-known TCP ones.
Protocol differences between QUIC and TCP however contribute to Protocol differences between QUIC and TCP however contribute to
algorithmic differences. We briefly describe these protocol algorithmic differences. We briefly describe these protocol
differences below. differences below.
2.1.1. Monotonically Increasing Packet Numbers 2.1.1. Monotonically Increasing Packet Numbers
skipping to change at page 5, line 30 skipping to change at page 5, line 37
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.
3. Loss Detection 3. Loss Detection
3.1. Overview QUIC senders use both ack information and timeouts to detect lost
packets, and this section provides a description of these algorithms.
Estimating the network round-trip time (RTT) is critical to these
algorithms and is described first.
QUIC uses a combination of ack information and alarms to detect lost 3.1. Computing the RTT estimate
packets. An unacknowledged QUIC packet is marked as lost in one of
the following ways:
o A packet is marked as lost if at least one packet that was sent a (To be filled)
threshold number of packets (kReorderingThreshold) after it has
been acknowledged. This indicates that the unacknowledged packet
is either lost or reordered beyond the specified threshold. This
mechanism combines both TCP's FastRetransmit and FACK mechanisms.
o If a packet is near the tail, where fewer than 3.2. Ack-based Detection
kReorderingThreshold packets are sent after it, the sender cannot
expect to detect loss based on the previous mechanism. In this
case, a sender uses both ack information and an alarm to detect
loss. Specifically, when the last sent packet is acknowledged,
the sender waits a short period of time to allow for reordering
and then marks any unacknowledged packets as lost. This mechanism
is based on the Linux implementation of TCP Early Retransmit.
o If a packet is sent at the tail, there are no packets sent after Ack-based loss detection implements the spirit of TCP's Fast
it, and the sender cannot use ack information to detect its loss. Retransmit [RFC5681], Early Retransmit [RFC5827], FACK, and SACK loss
recovery [RFC6675]. This section provides an overview of how these
algorithms are implemented in QUIC.
The sender therefore relies on an alarm to detect such tail (TODO: Define unacknowledged packet, ackable packet, outstanding
losses. This mechanism is based on TCP's Tail Loss Probe. bytes.)
o If all else fails, a Retransmission Timeout (RTO) alarm is always 3.2.1. Fast Retransmit
set when any retransmittable packet is outstanding. When this
alarm fires, all unacknowledged packets are marked as lost.
o Instead of a packet threshold to tolerate reordering, a QUIC An unacknowledged packet is marked as lost when an acknowledgment is
sender may use a time threshold. This allows for senders to be received for a packet that was sent a threshold number of packets
tolerant of short periods of significant reordering. In this (kReorderingThreshold) after the unacknowledged packet. Receipt of
mechanism, a QUIC sender marks a packet as lost when a larger the ack indicates that a later packet was received, while
packet number is acknowledged and a threshold amount of time has kReorderingThreshold provides some tolerance for reordering of
passed since the packet was sent. packets in the network.
o Handshake packets, which contain STREAM frames for stream 0, are The RECOMMENDED initial value for kReorderingThreshold is 3.
critical to QUIC transport and crypto negotiation, so a separate
alarm period is used for them.
3.2. Algorithm Details We derive this default from recommendations for TCP loss recovery
[RFC5681] [RFC6675]. It is possible for networks to exhibit higher
degrees of reordering, causing a sender to detect spurious losses.
Detecting spurious losses leads to unnecessary retransmissions and
may result in degraded performance due to the actions of the
congestion controller upon detecting loss. Implementers MAY use
algorithms developed for TCP, such as TCP-NCR [RFC4653], to improve
QUIC's reordering resilience, though care should be taken to map TCP
specifics to QUIC correctly. Similarly, using time-based loss
detection to deal with reordering, such as in PR-TCP, should be more
readily usable in QUIC. Making QUIC deal with such networks is
important open research, and implementers are encouraged to explore
this space.
3.2.1. Constants of interest 3.2.2. Early Retransmit
Unacknowledged packets close to the tail may have fewer than
kReorderingThreshold number of ackable packets sent after them. Loss
of such packets cannot be detected via Fast Retransmit. To enable
ack-based loss detection of such packets, receipt of an
acknowledgment for the last outstanding ackable packet triggers the
Early Retransmit process, as follows.
If there are unacknowledged ackable packets still pending, they ought
to be marked as lost. To compensate for the reduced reordering
resilience, the sender SHOULD set an alarm for a small period of
time. If the unacknowledged ackable packets are 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
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:
o the latest RTT sample is lower than the SRTT, perhaps due to
reordering where packet whose ack triggered the Early Retransit
process encountered a shorter path;
o the latest RTT sample is higher than the SRTT, perhaps due to a
sustained increase in the actual RTT, but the smoothed SRTT has
not yet caught up.
The 1.25 multiplier increases reordering resilience. Implementers
MAY experiment with using other multipliers, bearing in mind that a
lower multiplier reduces reordering resilience and increases spurious
retransmissions, and a higher multipler increases loss recovery
delay.
This mechanism is based on Early Retransmit for TCP [RFC5827].
However, [RFC5827] does not include the alarm described above. Early
Retransmit is prone to spurious retransmissions due to its reduced
reordering resilence without the alarm. This observation led Linux
TCP implementers to implement an alarm for TCP as well, and this
document incorporates this advancement.
3.3. Timer-based Detection
Timer-based loss detection implements the spirit of TCP's Tail Loss
Probe and Retransmission Timeout mechanisms.
3.3.1. Tail Loss Probe
The algorithm described in this section is an adaptation of the Tail
Loss Probe algorithm proposed for TCP [TLP].
A packet sent at the tail is particularly vulnerable to slow loss
detection, since acks of subsequent packets are needed to trigger
ack-based detection. To ameliorate this weakness of tail packets,
the sender schedules an alarm when the last ackable packet before
quiescence is transmitted. When this alarm fires, a Tail Loss Probe
(TLP) packet is sent to evoke an acknowledgement from the receiver.
The alarm duration, or Probe Timeout (PTO), is set based on the
following conditions:
o If there is exactly one unacknowledged packet, PTO SHOULD be
scheduled for max(2_SRTT, 1.5_SRTT+kDelayedAckTimeout)
o If there are more than one unacknowledged packets, PTO SHOULD be
scheduled for max(2*SRTT, 10ms).
o If RTO is earlier, schedule a TLP alarm in its place. That is,
PTO SHOULD be scheduled for min(RTO, PTO).
kDelayedAckTimeout is the expected delayed ACK timer. When there is
exactly one unacknowledged packet, the alarm duration includes time
for an acknowledgment to be received, and additionally, a
kDelayedAckTimeout period to compensate for the delayed
acknowledgment timer at the receiver.
The RECOMMENDED value for kDelayedAckTimeout is 25ms.
(TODO: Add negotiability of delayed ack timeout.)
A PTO value of at least 2_SRTT ensures that the ACK is overdue.
Using a PTO of exactly 1_SRTT may generate spurious probes, and
2*SRTT is simply the next integral value of RTT.
(TODO: These values of 2 and 1.5 are a bit arbitrary. Reconsider
these.)
If the Retransmission Timeout (RTO, Section 3.3.2) period is smaller
than the computed PTO, then a PTO is scheduled for the smaller RTO
period.
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
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
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.
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
packet MAY retransmit unacknowledged data to potentially reduce
recovery time. Since a TLP alarm is used to send a probe into the
network prior to establishing any packet loss, prior unacknowledged
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 will commonly not know that a packet being sent is a tail
packet. Consequently, a sender may have to arm or adjust the TLP
alarm on every sent ackable packet.
3.3.2. Retransmission Timeout
A Retransmission Timeout (RTO) alarm is the final backstop for loss
detection. The algorithm used in QUIC is based on the RTO algorithm
for TCP [RFC5681] and is additionally resilient to spurious RTO
events [RFC5682].
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
evoke acknowledgements from the receiver, and restarts the RTO alarm.
Similar to TCP [RFC6298], the RTO period is set based on the
following conditions:
o When the final TLP packet is sent, the RTO period is set to
max(SRTT + 4*RTTVAR, minRTO)
o When an RTO alarm fires, the RTO period is doubled.
The sender typically has incurred a high latency penalty by the time
an RTO alarm fires, and this penalty increases exponentially in
subsequent consecutive RTO events. Sending a single packet on an RTO
event therefore makes the connection very sensitive to single packet
loss. Sending two packets instead of one significantly increases
resilience to packet drop in both directions, thus reducing the
probability of consecutive RTO events.
QUIC's RTO algorithm differs from TCP in that the firing of an RTO
alarm is not considered a strong enough signal of packet loss. An
RTO alarm fires only when there's a prolonged period of network
silence, which could be caused by a change in the underlying network
RTT.
When an acknowledgment is received for a packet sent on an RTO event,
any unacknowledged packets with lower packet numbers than those
acknowledged MUST be marked as lost.
A packet sent when an RTO alarm fires MAY carry new data if available
or unacknowledged data to potentially reduce recovery time. Since
this packet is sent as a probe into the network prior to establishing
any packet loss, prior unacknowledged packets SHOULD NOT be marked as
lost.
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
additional bytes in flight, since this packet adds network load
without establishing packet loss.
3.3.3. 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 handshake timeout SHOULD be set to twice the initial RTT.
There are no prior RTT samples within this connection. However, this
may be a resumed connection over the same network, in which case, a
client 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 the first 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 frames. The sender SHOULD double the handshake timeout and
set an alarm for this period.
On each consecutive firing of the handshake alarm, the sender SHOULD
double the handshake timeout 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 frames may be cancelled by handshake state transitions. In
particular, all non-protected frames 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.)
3.4. Algorithm Details
3.4.1. 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 7, line 5 skipping to change at page 11, line 25
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.
3.2.2. Variables of interest 3.4.2. 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
skipping to change at page 8, line 9 skipping to change at page 12, line 31
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, and a bytes time field indicating the time a packet was sent, and a bytes
field indicating the packet's size. sent_packets is ordered by field indicating the packet's size. sent_packets is ordered by
packet number, and packets remain in sent_packets until packet number, and packets remain in sent_packets until
acknowledged or lost. acknowledged or lost.
3.2.3. Initialization 3.4.3. 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 (UsingTimeLossDetection()) if (UsingTimeLossDetection())
reordering_threshold = infinite reordering_threshold = infinite
skipping to change at page 8, line 31 skipping to change at page 13, line 5
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
largest_sent_before_rto = 0 largest_sent_before_rto = 0
time_of_last_sent_packet = 0 time_of_last_sent_packet = 0
largest_sent_packet = 0 largest_sent_packet = 0
3.2.4. On Sending a Packet 3.4.4. 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 congestion controlled.
skipping to change at page 9, line 15 skipping to change at page 13, line 32
OnPacketSent(packet_number, is_ack_only, sent_bytes): OnPacketSent(packet_number, is_ack_only, sent_bytes):
time_of_last_sent_packet = now time_of_last_sent_packet = now
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
if !is_ack_only: if !is_ack_only:
OnPacketSentCC(sent_bytes) OnPacketSentCC(sent_bytes)
sent_packets[packet_number].bytes = sent_bytes sent_packets[packet_number].bytes = sent_bytes
SetLossDetectionAlarm() SetLossDetectionAlarm()
3.2.5. On Ack Receipt 3.4.5. 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 9, line 45 skipping to change at page 14, line 29
UpdateRtt(latest_rtt): UpdateRtt(latest_rtt):
// 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 = 3/4 * rttvar + 1/4 * abs(smoothed_rtt - latest_rtt) rttvar = 3/4 * rttvar + 1/4 * abs(smoothed_rtt - latest_rtt)
smoothed_rtt = 7/8 * smoothed_rtt + 1/8 * latest_rtt smoothed_rtt = 7/8 * smoothed_rtt + 1/8 * latest_rtt
3.2.6. On Packet Acknowledgment 3.4.6. 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, which is the packet OnPacketAcked takes one parameter, acked_packet, which is the packet
number of the newly acked packet, and returns a list of packet number of the newly acked packet, and returns a list of packet
numbers that are detected as lost. numbers that are detected as lost.
skipping to change at page 10, line 28 skipping to change at page 15, line 17
// 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_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_number)
3.2.7. Setting the Loss Detection Alarm 3.4.7. 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.
3.2.7.1. Handshake Packets 3.4.7.1. Handshake Packets
The initial flight has no prior RTT sample. A client SHOULD remember The initial flight has no prior RTT sample. A client SHOULD remember
the previous RTT it observed when resumption is attempted and use the previous RTT it observed when resumption is attempted and use
that for an initial RTT value. If no previous RTT is available, the that for an initial RTT value. If no previous RTT is available, the
initial RTT defaults to 100ms. initial RTT defaults to 100ms.
Endpoints MUST retransmit handshake frames if not acknowledged within Endpoints MUST retransmit handshake frames if not acknowledged within
a time limit. This time limit will start as the largest of twice the a time limit. This time limit will start as the largest of twice the
RTT value and MinTLPTimeout. Each consecutive handshake RTT value and MinTLPTimeout. Each consecutive handshake
retransmission doubles the time limit, until an acknowledgement is retransmission doubles the time limit, until an acknowledgement is
skipping to change at page 11, line 13 skipping to change at page 16, line 5
transmitted once packet protection is available. transmitted once packet protection is available.
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.
3.2.7.2. Tail Loss Probe and Retransmission Timeout 3.4.7.2. Tail Loss Probe and Retransmission Timeout
Tail loss probes [LOSS-PROBE] and retransmission timeouts [RFC6298] Tail loss probes [LOSS-PROBE] and retransmission timeouts [RFC6298]
are an alarm based mechanism to recover from cases when there are are an 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.
3.2.7.3. Early Retransmit 3.4.7.3. Early Retransmit
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.
3.2.7.4. Pseudocode 3.4.7.4. Pseudocode
Pseudocode for SetLossDetectionAlarm follows: Pseudocode for SetLossDetectionAlarm follows:
SetLossDetectionAlarm(): SetLossDetectionAlarm():
if (retransmittable packets are not outstanding): if (retransmittable packets are not outstanding):
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.
skipping to change at page 12, line 36 skipping to change at page 17, line 5
alarm_duration = kMinTLPTimeout alarm_duration = kMinTLPTimeout
alarm_duration = max(alarm_duration, 2 * smoothed_rtt) alarm_duration = max(alarm_duration, 2 * smoothed_rtt)
else: else:
// RTO alarm // RTO alarm
alarm_duration = smoothed_rtt + 4 * rttvar alarm_duration = smoothed_rtt + 4 * rttvar
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)
loss_detection_alarm.set(now + alarm_duration) loss_detection_alarm.set(now + alarm_duration)
3.2.8. On Alarm Firing 3.4.8. 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.
skipping to change at page 13, line 26 skipping to change at page 17, line 34
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()
3.2.9. Detecting Lost Packets 3.4.9. 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.
3.2.9.1. Handshake Packets 3.4.9.1. Handshake Packets
The receiver MUST ignore unprotected packets that ack protected The receiver MUST close the connection with an error of type
packets. The receiver MUST trust protected acks for unprotected OPTIMISTIC_ACK when receiving an unprotected packet that acks
packets, however. Aside from this, loss detection for handshake protected packets. The receiver MUST trust protected acks for
packets when an ack is processed is identical to other packets. unprotected packets, however. Aside from this, loss detection for
handshake packets when an ack is processed is identical to other
packets.
3.2.9.2. Pseudocode 3.4.9.2. 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 (time_reordering_fraction != infinite): if (time_reordering_fraction != infinite):
delay_until_lost = delay_until_lost =
(1 + time_reordering_fraction) * max(latest_rtt, smoothed_rtt) (1 + time_reordering_fraction) * 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 = 9/8 * max(latest_rtt, smoothed_rtt) delay_until_lost = 9/8 * 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
packet_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) lost_packets.insert(unacked)
else if (packet_delta > reordering_threshold) else if (delta > reordering_threshold)
lost_packets.insert(unacked) 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) foreach (packet in lost_packets)
sent_packets.remove(packet.packet_number) sent_packets.remove(packet.packet_number)
3.3. Discussion 3.5. 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 15, line 24 skipping to change at page 19, line 31
Slow start exits to congestion avoidance. Congestion avoidance in Slow start exits to congestion avoidance. Congestion avoidance in
NewReno uses an additive increase multiplicative decrease (AIMD) NewReno uses an additive increase multiplicative decrease (AIMD)
approach that increases the congestion window by one MSS of bytes per approach that increases the congestion window by one MSS of bytes per
congestion window acknowledged. When a loss is detected, NewReno congestion window acknowledged. When a loss is detected, NewReno
halves the congestion window and sets the slow start threshold to the halves the congestion window and sets the slow start threshold to the
new congestion window. new congestion window.
4.3. Recovery Period 4.3. Recovery Period
Recovery is a period of time beginning with detection of a lost Recovery is a period of time beginning with detection of a lost
packet. Because QUIC retransmits frames, not packets, it defines the packet. Because QUIC retransmits stream data and control frames, not
end of recovery as all packets outstanding at the start of recovery packets, it defines the end of recovery as a packet sent after the
being acknowledged or lost. This is slightly different from TCP's start of recovery being acknowledged. This is slightly different
definition of recovery ending when the lost packet that started from TCP's definition of recovery ending when the lost packet that
recovery is acknowledged. During recovery, the congestion window is started recovery is acknowledged.
not increased or decreased. As such, multiple lost packets only
decrease the congestion window once as long as they're lost before During recovery, the congestion window is not increased or decreased.
exiting recovery. This causes QUIC to decrease the congestion window As such, multiple lost packets only decrease the congestion window
multiple times if retransmisions are lost, but limits the reduction once as long as they're lost before exiting recovery. This causes
to once per round trip. QUIC to decrease the congestion window multiple times if
retransmisions are lost, but limits the reduction to once per round
trip.
4.4. Tail Loss Probe 4.4. Tail Loss Probe
If recovery sends a tail loss probe, no change is made to the If recovery sends a tail loss probe, no change is made to the
congestion window or pacing rate. Acknowledgement or loss of tail congestion window or pacing rate. Acknowledgement or loss of tail
loss probes are treated like any other packet. 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,
skipping to change at page 16, line 11 skipping to change at page 20, line 22
retransmission timeout are acknowledged, the retransmission timeout retransmission timeout are acknowledged, the retransmission timeout
has been validated and the congestion window must be reduced to the has been validated and the congestion window must be reduced to the
minimum congestion window and slow start is begun. minimum congestion window and slow start is begun.
4.6. Pacing Rate 4.6. Pacing Rate
The pacing rate is a function of the mode, the congestion window, and The pacing rate is a function of the mode, the congestion window, and
the smoothed rtt. Specifically, the pacing rate is 2 times the the smoothed rtt. Specifically, the pacing rate is 2 times the
congestion window divided by the smoothed RTT during slow start and congestion window divided by the smoothed RTT during slow start and
1.25 times the congestion window divided by the smoothed RTT during 1.25 times the congestion window divided by the smoothed RTT during
slow start. In order to fairly compete with flows that are not congestion avoidance. In order to fairly compete with flows that are
pacing, it is recommended to not pace the first 10 sent packets when not pacing, it is recommended to not pace the first 10 sent packets
exiting quiescence. when exiting quiescence.
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 18, line 37 skipping to change at page 23, line 12
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 (work in progress), September 2017. transport-07 (work in progress), November 2017.
[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, <https://www.rfc- DOI 10.17487/RFC2119, March 1997,
editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
6.2. Informative References
[LOSS-PROBE] [RFC4653] Bhandarkar, S., Reddy, A., Allman, M., and E. Blanton,
Dukkipati, N., Cardwell, N., Cheng, Y., and M. Mathis, "Improving the Robustness of TCP to Non-Congestion
"Tail Loss Probe (TLP): An Algorithm for Fast Recovery of Events", RFC 4653, DOI 10.17487/RFC4653, August 2006,
Tail Losses", draft-dukkipati-tcpm-tcp-loss-probe-01 (work <https://www.rfc-editor.org/info/rfc4653>.
in progress), February 2013.
[RFC3465] Allman, M., "TCP Congestion Control with Appropriate Byte [RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
Counting (ABC)", RFC 3465, DOI 10.17487/RFC3465, February Control", RFC 5681, DOI 10.17487/RFC5681, September 2009,
2003, <https://www.rfc-editor.org/info/rfc3465>. <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,
"Forward RTO-Recovery (F-RTO): An Algorithm for Detecting "Forward RTO-Recovery (F-RTO): An Algorithm for Detecting
Spurious Retransmission Timeouts with TCP", RFC 5682, Spurious Retransmission Timeouts with TCP", RFC 5682,
DOI 10.17487/RFC5682, September 2009, <https://www.rfc- DOI 10.17487/RFC5682, September 2009,
editor.org/info/rfc5682>. <https://www.rfc-editor.org/info/rfc5682>.
[RFC5827] Allman, M., Avrachenkov, K., Ayesta, U., Blanton, J., and [RFC5827] Allman, M., Avrachenkov, K., Ayesta, U., Blanton, J., and
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, <https://www.rfc- DOI 10.17487/RFC5827, May 2010,
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, <https://www.rfc- DOI 10.17487/RFC6298, June 2011,
editor.org/info/rfc6298>. <https://www.rfc-editor.org/info/rfc6298>.
[RFC6675] Blanton, E., Allman, M., Wang, L., Jarvinen, I., Kojo, M.,
and Y. Nishida, "A Conservative Loss Recovery Algorithm
Based on Selective Acknowledgment (SACK) for TCP",
RFC 6675, DOI 10.17487/RFC6675, August 2012,
<https://www.rfc-editor.org/info/rfc6675>.
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 [RFC6582] Henderson, T., Floyd, S., Gurtov, A., and Y. Nishida, "The
NewReno Modification to TCP's Fast Recovery Algorithm", NewReno Modification to TCP's Fast Recovery Algorithm",
RFC 6582, DOI 10.17487/RFC6582, April 2012, RFC 6582, DOI 10.17487/RFC6582, April 2012,
<https://www.rfc-editor.org/info/rfc6582>. <https://www.rfc-editor.org/info/rfc6582>.
[TLP] 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.
6.3. URIs
[1] https://mailarchive.ietf.org/arch/search/?email_list=quic
[2] https://github.com/quicwg
[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-05 B.1. Since draft-ietf-quic-recovery-06
Nothing yet.
B.2. Since draft-ietf-quic-recovery-05
o Add more congestion control text (#776) o Add more congestion control text (#776)
B.2. Since draft-ietf-quic-recovery-04 B.3. Since draft-ietf-quic-recovery-04
No significant changes. No significant changes.
B.3. Since draft-ietf-quic-recovery-03 B.4. Since draft-ietf-quic-recovery-03
No significant changes. No significant changes.
B.4. Since draft-ietf-quic-recovery-02 B.5. 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.5. Since draft-ietf-quic-recovery-01 B.6. 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.6. Since draft-ietf-quic-recovery-00 B.7. Since draft-ietf-quic-recovery-00
o Improved description of constants and ACK behavior o Improved description of constants and ACK behavior
B.7. Since draft-iyengar-quic-loss-recovery-01 B.8. 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)
Google Google
Email: jri@google.com Email: jri@google.com
Ian Swett (editor) Ian Swett (editor)
Google Google
Email: ianswett@google.com Email: ianswett@google.com
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