draft-ietf-quic-recovery-22.txt		draft-ietf-quic-recovery-latest.txt
	QUIC Working Group J. Iyengar, Ed.		QUIC Working Group J. Iyengar, Ed.
	Internet-Draft Fastly		Internet-Draft Fastly
	Intended status: Standards Track I. Swett, Ed.		Intended status: Standards Track I. Swett, Ed.
	Expires: January 10, 2020 Google		Expires: February 17, 2020 Google
	July 9, 2019		August 16, 2019
	QUIC Loss Detection and Congestion Control		QUIC Loss Detection and Congestion Control
	draft-ietf-quic-recovery-22		draft-ietf-quic-recovery-latest
	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 January 10, 2020.		This Internet-Draft will expire on February 17, 2020.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2019 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	skipping to change at page 2, line 36 ¶		skipping to change at page 2, line 36 ¶
	3.1.6. Explicit Correction For Delayed Acknowledgements . . 7		3.1.6. Explicit Correction For Delayed Acknowledgements . . 7
	4. Generating Acknowledgements . . . . . . . . . . . . . . . . . 7		4. Generating Acknowledgements . . . . . . . . . . . . . . . . . 7
	4.1. Crypto Handshake Data . . . . . . . . . . . . . . . . . . 8		4.1. Crypto Handshake Data . . . . . . . . . . . . . . . . . . 8
	4.2. ACK Ranges . . . . . . . . . . . . . . . . . . . . . . . 8		4.2. ACK Ranges . . . . . . . . . . . . . . . . . . . . . . . 8
	4.3. Receiver Tracking of ACK Frames . . . . . . . . . . . . . 8		4.3. Receiver Tracking of ACK Frames . . . . . . . . . . . . . 8
	4.4. Measuring and Reporting Host Delay . . . . . . . . . . . 9		4.4. Measuring and Reporting Host Delay . . . . . . . . . . . 9
	5. Estimating the Round-Trip Time . . . . . . . . . . . . . . . 9		5. Estimating the Round-Trip Time . . . . . . . . . . . . . . . 9
	5.1. Generating RTT samples . . . . . . . . . . . . . . . . . 9		5.1. Generating RTT samples . . . . . . . . . . . . . . . . . 9
	5.2. Estimating min_rtt . . . . . . . . . . . . . . . . . . . 10		5.2. Estimating min_rtt . . . . . . . . . . . . . . . . . . . 10
	5.3. Estimating smoothed_rtt and rttvar . . . . . . . . . . . 10		5.3. Estimating smoothed_rtt and rttvar . . . . . . . . . . . 10
	6. Loss Detection . . . . . . . . . . . . . . . . . . . . . . . 11		6. Loss Detection . . . . . . . . . . . . . . . . . . . . . . . 12
	6.1. Acknowledgement-based Detection . . . . . . . . . . . . . 12		6.1. Acknowledgement-based Detection . . . . . . . . . . . . . 12
	6.1.1. Packet Threshold . . . . . . . . . . . . . . . . . . 12		6.1.1. Packet Threshold . . . . . . . . . . . . . . . . . . 12
	6.1.2. Time Threshold . . . . . . . . . . . . . . . . . . . 12		6.1.2. Time Threshold . . . . . . . . . . . . . . . . . . . 13
	6.2. Crypto Retransmission Timeout . . . . . . . . . . . . . . 13		6.2. Probe Timeout . . . . . . . . . . . . . . . . . . . . . . 13
	6.3. Probe Timeout . . . . . . . . . . . . . . . . . . . . . . 14		6.2.1. Computing PTO . . . . . . . . . . . . . . . . . . . . 13
	6.3.1. Computing PTO . . . . . . . . . . . . . . . . . . . . 15		6.3. Handshakes and New Paths . . . . . . . . . . . . . . . . 14
	6.3.2. Sending Probe Packets . . . . . . . . . . . . . . . . 15		6.3.1. Sending Probe Packets . . . . . . . . . . . . . . . . 15
	6.3.3. Loss Detection . . . . . . . . . . . . . . . . . . . 16		6.3.2. Loss Detection . . . . . . . . . . . . . . . . . . . 16
	6.4. Retry and Version Negotiation . . . . . . . . . . . . . . 16		6.4. Retry and Version Negotiation . . . . . . . . . . . . . . 16
	6.5. Discarding Keys and Packet State . . . . . . . . . . . . 17		6.5. Discarding Keys and Packet State . . . . . . . . . . . . 17
	6.6. Discussion . . . . . . . . . . . . . . . . . . . . . . . 17		6.6. Discussion . . . . . . . . . . . . . . . . . . . . . . . 17
	7. Congestion Control . . . . . . . . . . . . . . . . . . . . . 17		7. Congestion Control . . . . . . . . . . . . . . . . . . . . . 17
	7.1. Explicit Congestion Notification . . . . . . . . . . . . 18		7.1. Explicit Congestion Notification . . . . . . . . . . . . 18
	7.2. Slow Start . . . . . . . . . . . . . . . . . . . . . . . 18		7.2. Slow Start . . . . . . . . . . . . . . . . . . . . . . . 18
	7.3. Congestion Avoidance . . . . . . . . . . . . . . . . . . 18		7.3. Congestion Avoidance . . . . . . . . . . . . . . . . . . 18
	7.4. Recovery Period . . . . . . . . . . . . . . . . . . . . . 18		7.4. Recovery Period . . . . . . . . . . . . . . . . . . . . . 18
	7.5. Ignoring Loss of Undecryptable Packets . . . . . . . . . 19		7.5. Ignoring Loss of Undecryptable Packets . . . . . . . . . 19
	7.6. Probe Timeout . . . . . . . . . . . . . . . . . . . . . . 19		7.6. Probe Timeout . . . . . . . . . . . . . . . . . . . . . . 19
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	10.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 24		10.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 24
	Appendix A. Loss Recovery Pseudocode . . . . . . . . . . . . . . 24		Appendix A. Loss Recovery Pseudocode . . . . . . . . . . . . . . 24
	A.1. Tracking Sent Packets . . . . . . . . . . . . . . . . . . 25		A.1. Tracking Sent Packets . . . . . . . . . . . . . . . . . . 25
	A.1.1. Sent Packet Fields . . . . . . . . . . . . . . . . . 25		A.1.1. Sent Packet Fields . . . . . . . . . . . . . . . . . 25
	A.2. Constants of interest . . . . . . . . . . . . . . . . . . 25		A.2. Constants of interest . . . . . . . . . . . . . . . . . . 25
	A.3. Variables of interest . . . . . . . . . . . . . . . . . . 26		A.3. Variables of interest . . . . . . . . . . . . . . . . . . 26
	A.4. Initialization . . . . . . . . . . . . . . . . . . . . . 27		A.4. Initialization . . . . . . . . . . . . . . . . . . . . . 27
	A.5. On Sending a Packet . . . . . . . . . . . . . . . . . . . 27		A.5. On Sending a Packet . . . . . . . . . . . . . . . . . . . 27
	A.6. On Receiving an Acknowledgment . . . . . . . . . . . . . 28		A.6. On Receiving an Acknowledgment . . . . . . . . . . . . . 28
	A.7. On Packet Acknowledgment . . . . . . . . . . . . . . . . 29		A.7. On Packet Acknowledgment . . . . . . . . . . . . . . . . 29
	A.8. Setting the Loss Detection Timer . . . . . . . . . . . . 30		A.8. Setting the Loss Detection Timer . . . . . . . . . . . . 29
	A.9. On Timeout . . . . . . . . . . . . . . . . . . . . . . . 32		A.9. On Timeout . . . . . . . . . . . . . . . . . . . . . . . 30
	A.10. Detecting Lost Packets . . . . . . . . . . . . . . . . . 32		A.10. Detecting Lost Packets . . . . . . . . . . . . . . . . . 31
	Appendix B. Congestion Control Pseudocode . . . . . . . . . . . 33		Appendix B. Congestion Control Pseudocode . . . . . . . . . . . 32
	B.1. Constants of interest . . . . . . . . . . . . . . . . . . 33		B.1. Constants of interest . . . . . . . . . . . . . . . . . . 32
	B.2. Variables of interest . . . . . . . . . . . . . . . . . . 34		B.2. Variables of interest . . . . . . . . . . . . . . . . . . 33
	B.3. Initialization . . . . . . . . . . . . . . . . . . . . . 35		B.3. Initialization . . . . . . . . . . . . . . . . . . . . . 34
	B.4. On Packet Sent . . . . . . . . . . . . . . . . . . . . . 35		B.4. On Packet Sent . . . . . . . . . . . . . . . . . . . . . 34
	B.5. On Packet Acknowledgement . . . . . . . . . . . . . . . . 35		B.5. On Packet Acknowledgement . . . . . . . . . . . . . . . . 34
	B.6. On New Congestion Event . . . . . . . . . . . . . . . . . 36		B.6. On New Congestion Event . . . . . . . . . . . . . . . . . 35
	B.7. Process ECN Information . . . . . . . . . . . . . . . . . 36		B.7. Process ECN Information . . . . . . . . . . . . . . . . . 35
	B.8. On Packets Lost . . . . . . . . . . . . . . . . . . . . . 37		B.8. On Packets Lost . . . . . . . . . . . . . . . . . . . . . 36
	Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 37		Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 36
	C.1. Since draft-ietf-quic-recovery-21 . . . . . . . . . . . . 37		C.1. Since draft-ietf-quic-recovery-21 . . . . . . . . . . . . 36
	C.2. Since draft-ietf-quic-recovery-20 . . . . . . . . . . . . 37		C.2. Since draft-ietf-quic-recovery-20 . . . . . . . . . . . . 36
	C.3. Since draft-ietf-quic-recovery-19 . . . . . . . . . . . . 38		C.3. Since draft-ietf-quic-recovery-19 . . . . . . . . . . . . 37
	C.4. Since draft-ietf-quic-recovery-18 . . . . . . . . . . . . 38		C.4. Since draft-ietf-quic-recovery-18 . . . . . . . . . . . . 37
	C.5. Since draft-ietf-quic-recovery-17 . . . . . . . . . . . . 38		C.5. Since draft-ietf-quic-recovery-17 . . . . . . . . . . . . 37
	C.6. Since draft-ietf-quic-recovery-16 . . . . . . . . . . . . 39		C.6. Since draft-ietf-quic-recovery-16 . . . . . . . . . . . . 38
	C.7. Since draft-ietf-quic-recovery-14 . . . . . . . . . . . . 40		C.7. Since draft-ietf-quic-recovery-14 . . . . . . . . . . . . 39
	C.8. Since draft-ietf-quic-recovery-13 . . . . . . . . . . . . 40		C.8. Since draft-ietf-quic-recovery-13 . . . . . . . . . . . . 39
	C.9. Since draft-ietf-quic-recovery-12 . . . . . . . . . . . . 40		C.9. Since draft-ietf-quic-recovery-12 . . . . . . . . . . . . 39
	C.10. Since draft-ietf-quic-recovery-11 . . . . . . . . . . . . 40		C.10. Since draft-ietf-quic-recovery-11 . . . . . . . . . . . . 39
	C.11. Since draft-ietf-quic-recovery-10 . . . . . . . . . . . . 40		C.11. Since draft-ietf-quic-recovery-10 . . . . . . . . . . . . 39
	C.12. Since draft-ietf-quic-recovery-09 . . . . . . . . . . . . 41		C.12. Since draft-ietf-quic-recovery-09 . . . . . . . . . . . . 40
	C.13. Since draft-ietf-quic-recovery-08 . . . . . . . . . . . . 41		C.13. Since draft-ietf-quic-recovery-08 . . . . . . . . . . . . 40
	C.14. Since draft-ietf-quic-recovery-07 . . . . . . . . . . . . 41		C.14. Since draft-ietf-quic-recovery-07 . . . . . . . . . . . . 40
	C.15. Since draft-ietf-quic-recovery-06 . . . . . . . . . . . . 41		C.15. Since draft-ietf-quic-recovery-06 . . . . . . . . . . . . 40
	C.16. Since draft-ietf-quic-recovery-05 . . . . . . . . . . . . 41		C.16. Since draft-ietf-quic-recovery-05 . . . . . . . . . . . . 40
	C.17. Since draft-ietf-quic-recovery-04 . . . . . . . . . . . . 41		C.17. Since draft-ietf-quic-recovery-04 . . . . . . . . . . . . 40
	C.18. Since draft-ietf-quic-recovery-03 . . . . . . . . . . . . 41		C.18. Since draft-ietf-quic-recovery-03 . . . . . . . . . . . . 40
	C.19. Since draft-ietf-quic-recovery-02 . . . . . . . . . . . . 41		C.19. Since draft-ietf-quic-recovery-02 . . . . . . . . . . . . 40
	C.20. Since draft-ietf-quic-recovery-01 . . . . . . . . . . . . 42		C.20. Since draft-ietf-quic-recovery-01 . . . . . . . . . . . . 41
	C.21. Since draft-ietf-quic-recovery-00 . . . . . . . . . . . . 42		C.21. Since draft-ietf-quic-recovery-00 . . . . . . . . . . . . 41
	C.22. Since draft-iyengar-quic-loss-recovery-01 . . . . . . . . 42		C.22. Since draft-iyengar-quic-loss-recovery-01 . . . . . . . . 41
	Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 42		Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 41
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
	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 existing TCP loss recovery mechanisms,		QUIC implements the spirit of existing 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 5, line 44 ¶		skipping to change at page 5, line 44 ¶
	delivery are acknowledged or declared lost and sent in new packets as		delivery are acknowledged or declared lost and sent in new packets as
	necessary. The types of frames contained in a packet affect recovery		necessary. The types of frames contained in a packet affect recovery
	and congestion control logic:		and congestion control logic:
	o All packets are acknowledged, though packets that contain no ack-		o All packets are acknowledged, though packets that contain no ack-
	eliciting frames are only acknowledged along with ack-eliciting		eliciting frames are only acknowledged along with ack-eliciting
	packets.		packets.
	o Long header packets that contain CRYPTO frames are critical to the		o Long header packets that contain CRYPTO frames are critical to the
	performance of the QUIC handshake and use shorter timers for		performance of the QUIC handshake and use shorter timers for
	acknowledgement and retransmission.		acknowledgement.
	o Packets that contain only ACK frames do not count toward		o Packets that contain only ACK frames do not count toward
	congestion control limits and are not considered in-flight.		congestion control limits and are not considered in-flight.
	o PADDING frames cause packets to contribute toward bytes in flight		o PADDING frames cause packets to contribute toward bytes in flight
	without directly causing an acknowledgment to be sent.		without directly causing an acknowledgment to be sent.
	3.1. Relevant Differences Between QUIC and TCP		3.1. 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
	skipping to change at page 7, line 43 ¶		skipping to change at page 7, line 43 ¶
	a peer to maintain a more accurate round-trip time estimate (see		a peer to maintain a more accurate round-trip time estimate (see
	Section 4.4).		Section 4.4).
	4. Generating Acknowledgements		4. Generating Acknowledgements
	An acknowledgement SHOULD be sent immediately upon receipt of a		An acknowledgement SHOULD be sent immediately upon receipt of a
	second ack-eliciting packet. QUIC recovery algorithms do not assume		second ack-eliciting packet. QUIC recovery algorithms do not assume
	the peer sends an ACK immediately when receiving a second ack-		the peer sends an ACK immediately when receiving a second ack-
	eliciting packet.		eliciting packet.
	In order to accelerate loss recovery and reduce timeouts, the		In order to accelerate loss recovery and reduce timeouts, an endpoint
	receiver SHOULD send an immediate ACK after it receives an out-of-		SHOULD immediately send an ACK frame when it receives an out-of-order
	order packet. It could send immediate ACKs for in-order packets for		packet that is ACK-eliciting. The endpoint MAY continue sending ACK
	a period of time that SHOULD NOT exceed 1/8 RTT unless more out-of-		frames immediately on each subsequently received packet, but the
	order packets arrive. If every packet arrives out-of- order, then an		endpoint SHOULD return to acknowledging every other packet after a
	immediate ACK SHOULD be sent for every received packet.		period of 1/8 x RTT, unless more ACK-eliciting packets are received
			out of order. If every subsequent ACK-eliciting packet arrives out
			of order, then an ACK frame SHOULD be sent immediately for every
			received ACK-eliciting packet.
	Similarly, packets marked with the ECN Congestion Experienced (CE)		If a packet is received with the ECN Congestion Experienced (CE)
	codepoint in the IP header SHOULD be acknowledged immediately, to		codepoint in the IP header, the endpoint SHOULD respond with an ACK
	reduce the peer's response time to congestion events.		frame immediately, even if the packet is received in order. Doing so
			reduces the peer's response time to congestion events.
	As an optimization, a receiver MAY process multiple packets before		If multiple packets are already available at an endpoint, the
	sending any ACK frames in response. In this case the receiver can		endpoint MAY process them all before sending an ACK frame in
	determine whether an immediate or delayed acknowledgement should be		response. The endpoint can determine whether an acknowledgement
	generated after processing incoming packets.		should be sent immediately or delayed after processing the batch.
	4.1. Crypto Handshake Data		4.1. Crypto Handshake Data
	In order to quickly complete the handshake and avoid spurious		In order to quickly complete the handshake and avoid spurious
	retransmissions due to crypto retransmission timeouts, crypto packets		retransmissions due to crypto retransmission timeouts, crypto packets
	SHOULD use a very short ack delay, such as the local timer		SHOULD use a very short ack delay, such as the local timer
	granularity. ACK frames SHOULD be sent immediately when the crypto		granularity. ACK frames SHOULD be sent immediately when the crypto
	stack indicates all data for that packet number space has been		stack indicates all data for that packet number space has been
	received.		received.
	skipping to change at page 9, line 20 ¶		skipping to change at page 9, line 23 ¶
	largest acknowledged packet in the Ack Delay field of an ACK frame		largest acknowledged packet in the Ack Delay field of an ACK frame
	(see Section 19.3 of [QUIC-TRANSPORT]). This allows the receiver of		(see Section 19.3 of [QUIC-TRANSPORT]). This allows the receiver of
	the ACK to adjust for any intentional delays, which is important for		the ACK to adjust for any intentional delays, which is important for
	delayed acknowledgements, when estimating the path RTT. A packet		delayed acknowledgements, when estimating the path RTT. A packet
	might be held in the OS kernel or elsewhere on the host before being		might be held in the OS kernel or elsewhere on the host before being
	processed. An endpoint SHOULD NOT include these unintentional delays		processed. An endpoint SHOULD NOT include these unintentional delays
	when populating the Ack Delay field in an ACK frame.		when populating the Ack Delay field in an ACK frame.
	An endpoint MUST NOT excessively delay acknowledgements of ack-		An endpoint MUST NOT excessively delay acknowledgements of ack-
	eliciting packets. The maximum ack delay is communicated in the		eliciting packets. The maximum ack delay is communicated in the
	max_ack_delay transport parameter; see Section 18.1 of		max_ack_delay transport parameter; see Section 18.2 of
	[QUIC-TRANSPORT]. max_ack_delay implies an explicit contract: an		[QUIC-TRANSPORT]. max_ack_delay implies an explicit contract: an
	endpoint promises to never delay acknowledgments of an ack-eliciting		endpoint promises to never delay acknowledgments of an ack-eliciting
	packet by more than the indicated value. If it does, any excess		packet by more than the indicated value. If it does, any excess
	accrues to the RTT estimate and could result in spurious		accrues to the RTT estimate and could result in spurious
	retransmissions from the peer. For Initial and Handshake packets, a		retransmissions from the peer. For Initial and Handshake packets, a
	max_ack_delay of 0 is used.		max_ack_delay of 0 is used.
	5. Estimating the Round-Trip Time		5. Estimating the Round-Trip Time
	At a high level, an endpoint measures the time from when a packet was		At a high level, an endpoint measures the time from when a packet was
	skipping to change at page 13, line 28 ¶		skipping to change at page 13, line 36 ¶
	The RECOMMENDED time threshold (kTimeThreshold), expressed as a		The RECOMMENDED time threshold (kTimeThreshold), expressed as a
	round-trip time multiplier, is 9/8.		round-trip time multiplier, is 9/8.
	Implementations MAY experiment with absolute thresholds, thresholds		Implementations MAY experiment with absolute thresholds, thresholds
	from previous connections, adaptive thresholds, or including RTT		from previous connections, adaptive thresholds, or including RTT
	variance. Smaller thresholds reduce reordering resilience and		variance. Smaller thresholds reduce reordering resilience and
	increase spurious retransmissions, and larger thresholds increase		increase spurious retransmissions, and larger thresholds increase
	loss detection delay.		loss detection delay.
	6.2. Crypto Retransmission Timeout		6.2. Probe Timeout
	Data in CRYPTO frames is critical to QUIC transport and crypto
	negotiation, so a more aggressive timeout is used to retransmit it.
	The initial crypto retransmission 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 500ms, resulting in a 1
	second initial handshake timeout as recommended in [RFC6298].
	A connection MAY use the delay between sending a PATH_CHALLENGE and
	receiving a PATH_RESPONSE to seed initial_rtt for a new path, but the
	delay SHOULD NOT be considered an RTT sample.
	When a crypto packet is sent, the sender MUST set a timer for twice
	the smoothed RTT. This timer MUST be updated when a new crypto
	packet is sent and when an acknowledgement is received which computes
	a new RTT sample. Upon timeout, the sender MUST retransmit all
	unacknowledged CRYPTO data if possible. The sender MUST NOT declare
	in-flight crypto packets as lost when the crypto timer expires.
	On each consecutive expiration of the crypto timer without receiving
	an acknowledgement for a new packet, the sender MUST double the
	crypto retransmission timeout and set a timer for this period.
	Until the server has validated the client's address on the path, the
	amount of data it can send is limited, as specified in Section 8.1 of
	[QUIC-TRANSPORT]. If not all unacknowledged CRYPTO data can be sent,
	then all unacknowledged CRYPTO data sent in Initial packets should be
	retransmitted. If no data can be sent, then no alarm should be armed
	until data has been received from the client.
	Because the server could be blocked until more packets are received,
	the client MUST ensure that the crypto retransmission timer is set if
	there is unacknowledged crypto data or if the client does not yet
	have 1-RTT keys. If the crypto retransmission timer expires before
	the client has 1-RTT keys, it is possible that the client may not
	have any crypto data to retransmit. However, the client MUST send a
	new packet, containing only PADDING frames if necessary, to allow the
	server to continue sending data. If Handshake keys are available to
	the client, it MUST send a Handshake packet, and otherwise it MUST
	send an Initial packet in a UDP datagram of at least 1200 bytes.
	Because packets only containing PADDING do not elicit an
	acknowledgement, they may never be acknowledged, but they are removed
	from bytes in flight when the client gets Handshake keys and the
	Initial keys are discarded.
	The crypto retransmission timer is not set if the time threshold
	Section 6.1.2 loss detection timer is set. The time threshold loss
	detection timer is expected to both expire earlier than the crypto
	retransmission timeout and be less likely to spuriously retransmit
	data. The Initial and Handshake packet number spaces will typically
	contain a small number of packets, so losses are less likely to be
	detected using packet-threshold loss detection.
	When the crypto retransmission timer is active, the probe timer
	(Section 6.3) is not active.
	6.3. Probe Timeout
	A Probe Timeout (PTO) triggers a probe packet when ack-eliciting data		A Probe Timeout (PTO) triggers sending one or two probe datagrams
	is in flight but an acknowledgement is not received within the		when ack-eliciting packets are not acknowledged within the expected
	expected period of time. A PTO enables a connection to recover from		period of time or the handshake has not been completed. A PTO
	loss of tail packets or acks. The PTO algorithm used in QUIC		enables a connection to recover from loss of tail packets or
	implements the reliability functions of Tail Loss Probe [TLP] [RACK],		acknowledgements. The PTO algorithm used in QUIC implements the
	RTO [RFC5681] and F-RTO algorithms for TCP [RFC5682], and the timeout		reliability functions of Tail Loss Probe [TLP] [RACK], RTO [RFC5681]
	computation is based on TCP's retransmission timeout period		and F-RTO algorithms for TCP [RFC5682], and the timeout computation
	[RFC6298].		is based on TCP's retransmission timeout period [RFC6298].
	6.3.1. Computing PTO		6.2.1. Computing PTO
	When an ack-eliciting packet is transmitted, the sender schedules a		When an ack-eliciting packet is transmitted, the sender schedules a
	timer for the PTO period as follows:		timer for the PTO period as follows:
	PTO = smoothed_rtt + max(4*rttvar, kGranularity) + max_ack_delay		PTO = smoothed_rtt + max(4*rttvar, kGranularity) + max_ack_delay
	kGranularity, smoothed_rtt, rttvar, and max_ack_delay are defined in		kGranularity, smoothed_rtt, rttvar, and max_ack_delay are defined in
	Appendix A.2 and Appendix A.3.		Appendix A.2 and Appendix A.3.
	The PTO period is the amount of time that a sender ought to wait for		The PTO period is the amount of time that a sender ought to wait for
	an acknowledgement of a sent packet. This time period includes the		an acknowledgement of a sent packet. This time period includes the
	estimated network roundtrip-time (smoothed_rtt), the variance in the		estimated network roundtrip-time (smoothed_rtt), the variance in the
	estimate (4*rttvar), and max_ack_delay, to account for the maximum		estimate (4*rttvar), and max_ack_delay, to account for the maximum
	time by which a receiver might delay sending an acknowledgement.		time by which a receiver might delay sending an acknowledgement.
	The PTO value MUST be set to at least kGranularity, to avoid the		The PTO value MUST be set to at least kGranularity, to avoid the
	timer expiring immediately.		timer expiring immediately.
	When a PTO timer expires, the sender probes the network as described		When a PTO timer expires, the PTO period MUST be set to twice its
	in the next section. The PTO period MUST be set to twice its current		current value. This exponential reduction in the sender's rate is
	value. This exponential reduction in the sender's rate is important		important because the PTOs might be caused by loss of packets or
	because the PTOs might be caused by loss of packets or		acknowledgements due to severe congestion. The life of a connection
	acknowledgements due to severe congestion.		that is experiencing consecutive PTOs is limited by the endpoint's
			idle timeout.
	A sender computes its PTO timer every time an ack-eliciting packet is		A sender computes its PTO timer every time an ack-eliciting packet is
	sent. A sender might choose to optimize this by setting the timer		sent. A sender might choose to optimize this by setting the timer
	fewer times if it knows that more ack-eliciting packets will be sent		fewer times if it knows that more ack-eliciting packets will be sent
	within a short period of time.		within a short period of time.
	6.3.2. Sending Probe Packets		The probe timer is not set if the time threshold Section 6.1.2 loss
			detection timer is set. The time threshold loss detection timer is
			expected to both expire earlier than the PTO and be less likely to
			spuriously retransmit data.
			6.3. Handshakes and New Paths
			The initial probe timeout for a new connection or new path SHOULD be
			set to twice the initial RTT. 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, the initial RTT SHOULD be set to 500ms, resulting in a 1
			second initial timeout as recommended in [RFC6298].
			A connection MAY use the delay between sending a PATH_CHALLENGE and
			receiving a PATH_RESPONSE to seed initial_rtt for a new path, but the
			delay SHOULD NOT be considered an RTT sample.
			Until the server has validated the client's address on the path, the
			amount of data it can send is limited, as specified in Section 8.1 of
			[QUIC-TRANSPORT]. Data at Initial encryption MUST be retransmitted
			before Handshake data and data at Handshake encryption MUST be
			retransmitted before any ApplicationData data. If no data can be
			sent, then the PTO alarm MUST NOT be armed until data has been
			received from the client.
			Because the server could be blocked until more packets are received,
			the client MUST ensure that the retransmission timer is set if the
			client does not yet have 1-RTT keys. If the probe timer expires
			before the client has 1-RTT keys, it is possible that the client may
			not have any crypto data to retransmit. However, the client MUST
			send a new packet to allow the server to continue sending data. At
			this stage in the connection, when few to none RTT samples have been
			generated, it is possible that the probe timer expiration is due to
			an incorrect RTT estimate at the client. To allow the client to
			improve its RTT estimate, the new packet that it sends MUST be ack-
			eliciting. If Handshake keys are available to the client, it MUST
			send a Handshake packet, and otherwise it MUST send an Initial packet
			in a UDP datagram of at least 1200 bytes.
			Initial packets and Handshake packets may never be acknowledged, but
			they are removed from bytes in flight when the Initial and Handshake
			keys are discarded.
			6.3.1. Sending Probe Packets
	When a PTO timer expires, a sender MUST send at least one ack-		When a PTO timer expires, a sender MUST send at least one ack-
	eliciting packet as a probe, unless there is no data available to		eliciting packet as a probe, unless there is no data available to
	send. An endpoint MAY send up to two ack-eliciting packets, to avoid		send. An endpoint MAY send up to two full-sized datagrams containing
	an expensive consecutive PTO expiration due to a single packet loss.		ack-eliciting packets, to avoid an expensive consecutive PTO
			expiration due to a single lost datagram.
	It is possible that the sender has no new or previously-sent data to		It is possible that the sender has no new or previously-sent data to
	send. As an example, consider the following sequence of events: new		send. As an example, consider the following sequence of events: new
	application data is sent in a STREAM frame, deemed lost, then		application data is sent in a STREAM frame, deemed lost, then
	retransmitted in a new packet, and then the original transmission is		retransmitted in a new packet, and then the original transmission is
	acknowledged. In the absence of any new application data, a PTO		acknowledged. In the absence of any new application data, a PTO
	timer expiration now would find the sender with no new or previously-		timer expiration now would find the sender with no new or previously-
	sent data to send.		sent data to send.
	When there is no data to send, the sender SHOULD send a PING or other		When there is no data to send, the sender SHOULD send a PING or other
	skipping to change at page 16, line 33 ¶		skipping to change at page 16, line 24 ¶
	packets, including sending new or retransmitted data based on the		packets, including sending new or retransmitted data based on the
	application's priorities.		application's priorities.
	When the PTO timer expires multiple times and new data cannot be		When the PTO timer expires multiple times and new data cannot be
	sent, implementations must choose between sending the same payload		sent, implementations must choose between sending the same payload
	every time or sending different payloads. Sending the same payload		every time or sending different payloads. Sending the same payload
	may be simpler and ensures the highest priority frames arrive first.		may be simpler and ensures the highest priority frames arrive first.
	Sending different payloads each time reduces the chances of spurious		Sending different payloads each time reduces the chances of spurious
	retransmission.		retransmission.
	6.3.3. Loss Detection		6.3.2. Loss Detection
	Delivery or loss of packets in flight is established when an ACK		Delivery or loss of packets in flight is established when an ACK
	frame is received that newly acknowledges one or more packets.		frame is received that newly acknowledges one or more packets.
	A PTO timer expiration event does not indicate packet loss and MUST		A PTO timer expiration event does not indicate packet loss and MUST
	NOT cause prior unacknowledged packets to be marked as lost. When an		NOT cause prior unacknowledged packets to be marked as lost. When an
	acknowledgement is received that newly acknowledges packets, loss		acknowledgement is received that newly acknowledges packets, loss
	detection proceeds as dictated by packet and time threshold		detection proceeds as dictated by packet and time threshold
	mechanisms; see Section 6.1.		mechanisms; see Section 6.1.
	skipping to change at page 18, line 8 ¶		skipping to change at page 17, line 51 ¶
	7. Congestion Control		7. Congestion Control
	QUIC's congestion control is based on TCP NewReno [RFC6582]. NewReno		QUIC's congestion control is based on TCP NewReno [RFC6582]. NewReno
	is a congestion window based congestion control. QUIC specifies the		is a congestion window based congestion control. QUIC specifies the
	congestion window in bytes rather than packets due to finer control		congestion window in bytes rather than packets due to finer control
	and the ease of appropriate byte counting [RFC3465].		and the ease of appropriate byte counting [RFC3465].
	QUIC hosts MUST NOT send packets if they would increase		QUIC hosts MUST NOT send packets if they would increase
	bytes_in_flight (defined in Appendix B.2) beyond the available		bytes_in_flight (defined in Appendix B.2) beyond the available
	congestion window, unless the packet is a probe packet sent after a		congestion window, unless the packet is a probe packet sent after a
	PTO timer expires, as described in Section 6.3.		PTO timer expires, as described in Section 6.2.
	Implementations MAY use other congestion control algorithms, such as		Implementations MAY use other congestion control algorithms, such as
	Cubic [RFC8312], and endpoints MAY use different algorithms from one		Cubic [RFC8312], and endpoints MAY use different algorithms from one
	another. The signals QUIC provides for congestion control are		another. The signals QUIC provides for congestion control are
	generic and are designed to support different algorithms.		generic and are designed to support different algorithms.
	7.1. Explicit Congestion Notification		7.1. Explicit Congestion Notification
	If a path has been verified to support ECN, QUIC treats a Congestion		If a path has been verified to support ECN, QUIC treats a Congestion
	Experienced codepoint in the IP header as a signal of congestion.		Experienced codepoint in the IP header as a signal of congestion.
	skipping to change at page 22, line 38 ¶		skipping to change at page 22, line 38 ¶
	9. IANA Considerations		9. IANA Considerations
	This document has no IANA actions. Yet.		This document has no IANA actions. Yet.
	10. References		10. References
	10.1. Normative References		10.1. Normative References
	[QUIC-TLS]		[QUIC-TLS]
	Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure		Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
	QUIC", draft-ietf-quic-tls-22 (work in progress).		QUIC", draft-ietf-quic-tls-latest (work in progress).
	[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-22 (work in progress).		transport-latest (work in progress).
	[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		[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
	2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,		2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
	May 2017, <https://www.rfc-editor.org/info/rfc8174>.		May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	skipping to change at page 25, line 33 ¶		skipping to change at page 25, line 33 ¶
	packet_number: The packet number of the sent packet.		packet_number: The packet number of the sent packet.
	ack_eliciting: A boolean that indicates whether a packet is ack-		ack_eliciting: A boolean that indicates whether a packet is ack-
	eliciting. If true, it is expected that an acknowledgement will		eliciting. If true, it is expected that an acknowledgement will
	be received, though the peer could delay sending the ACK frame		be received, though the peer could delay sending the ACK frame
	containing it by up to the MaxAckDelay.		containing it by up to the MaxAckDelay.
	in_flight: A boolean that indicates whether the packet counts		in_flight: A boolean that indicates whether the packet counts
	towards bytes in flight.		towards bytes in flight.
	is_crypto_packet: A boolean that indicates whether the packet
	contains cryptographic handshake messages critical to the
	completion of the QUIC handshake. In this version of QUIC, this
	includes any packet with the long header that includes a CRYPTO
	frame.
	sent_bytes: The number of bytes sent in the packet, not including		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.
	time_sent: The time the packet was sent.		time_sent: The time the packet was sent.
	A.2. Constants of interest		A.2. 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.
	skipping to change at page 26, line 31 ¶		skipping to change at page 26, line 27 ¶
	ApplicationData,		ApplicationData,
	}		}
	A.3. Variables of interest		A.3. 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_timer: Multi-modal timer used for loss detection.		loss_detection_timer: Multi-modal timer used for loss detection.
	crypto_count: The number of times all unacknowledged CRYPTO data has
	been retransmitted without receiving an ack.
	pto_count: The number of times a PTO has been sent without receiving		pto_count: The number of times a PTO has been sent without receiving
	an ack.		an ack.
	time_of_last_sent_ack_eliciting_packet: The time the most recent		time_of_last_sent_ack_eliciting_packet: The time the most recent
	ack-eliciting packet was sent.		ack-eliciting packet was sent.
	time_of_last_sent_crypto_packet: The time the most recent crypto
	packet was sent.
	largest_acked_packet[kPacketNumberSpace]: The largest packet number		largest_acked_packet[kPacketNumberSpace]: The largest packet number
	acknowledged in the packet number space so far.		acknowledged in the packet number space so far.
	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]
	skipping to change at page 27, line 26 ¶		skipping to change at page 27, line 19 ¶
	sent_packets[kPacketNumberSpace]: An association of packet numbers		sent_packets[kPacketNumberSpace]: An association of packet numbers
	in a packet number space to information about them. Described in		in a packet number space to information about them. Described in
	detail above in Appendix A.1.		detail above in Appendix A.1.
	A.4. Initialization		A.4. 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_timer.reset()		loss_detection_timer.reset()
	crypto_count = 0
	pto_count = 0		pto_count = 0
	latest_rtt = 0		latest_rtt = 0
	smoothed_rtt = 0		smoothed_rtt = 0
	rttvar = 0		rttvar = 0
	min_rtt = 0		min_rtt = 0
	max_ack_delay = 0		max_ack_delay = 0
	time_of_last_sent_ack_eliciting_packet = 0		time_of_last_sent_ack_eliciting_packet = 0
	time_of_last_sent_crypto_packet = 0
	for pn_space in [ Initial, Handshake, ApplicationData ]:		for pn_space in [ Initial, Handshake, ApplicationData ]:
	largest_acked_packet[pn_space] = infinite		largest_acked_packet[pn_space] = infinite
	loss_time[pn_space] = 0		loss_time[pn_space] = 0
	A.5. On Sending a Packet		A.5. On Sending a Packet
	After a packet is sent, information about the packet is stored. The		After a packet is sent, information about the packet is stored. The
	parameters to OnPacketSent are described in detail above in		parameters to OnPacketSent are described in detail above in
	Appendix A.1.1.		Appendix A.1.1.
	Pseudocode for OnPacketSent follows:		Pseudocode for OnPacketSent follows:
	OnPacketSent(packet_number, pn_space, ack_eliciting,		OnPacketSent(packet_number, pn_space, ack_eliciting,
	in_flight, is_crypto_packet, sent_bytes):		in_flight, sent_bytes):
	sent_packets[pn_space][packet_number].packet_number =		sent_packets[pn_space][packet_number].packet_number =
	packet_number		packet_number
	sent_packets[pn_space][packet_number].time_sent = now		sent_packets[pn_space][packet_number].time_sent = now
	sent_packets[pn_space][packet_number].ack_eliciting =		sent_packets[pn_space][packet_number].ack_eliciting =
	ack_eliciting		ack_eliciting
	sent_packets[pn_space][packet_number].in_flight = in_flight		sent_packets[pn_space][packet_number].in_flight = in_flight
	if (in_flight):		if (in_flight):
	if (is_crypto_packet):
	time_of_last_sent_crypto_packet = now
	if (ack_eliciting):		if (ack_eliciting):
	time_of_last_sent_ack_eliciting_packet = now		time_of_last_sent_ack_eliciting_packet = now
	OnPacketSentCC(sent_bytes)		OnPacketSentCC(sent_bytes)
	sent_packets[pn_space][packet_number].size = sent_bytes		sent_packets[pn_space][packet_number].size = sent_bytes
	SetLossDetectionTimer()		SetLossDetectionTimer()
	A.6. On Receiving an Acknowledgment		A.6. On Receiving an Acknowledgment
	When an ACK frame is received, it may newly acknowledge any number of		When an ACK frame is received, it may newly acknowledge any number of
	packets.		packets.
	skipping to change at page 28, line 44 ¶		skipping to change at page 28, line 27 ¶
	max(largest_acked_packet[pn_space], ack.largest_acked)		max(largest_acked_packet[pn_space], ack.largest_acked)
	// Nothing to do if there are no newly acked packets.		// Nothing to do if there are no newly acked packets.
	newly_acked_packets = DetermineNewlyAckedPackets(ack, pn_space)		newly_acked_packets = DetermineNewlyAckedPackets(ack, pn_space)
	if (newly_acked_packets.empty()):		if (newly_acked_packets.empty()):
	return		return
	// If the largest acknowledged is newly acked and		// If the largest acknowledged is newly acked and
	// at least one ack-eliciting was newly acked, update the RTT.		// at least one ack-eliciting was newly acked, update the RTT.
	if (sent_packets[pn_space][ack.largest_acked] &&		if (sent_packets[pn_space][ack.largest_acked] &&
	IncludesAckEliciting(newly_acked_packets))		IncludesAckEliciting(newly_acked_packets)):
	latest_rtt =		latest_rtt =
	now - sent_packets[pn_space][ack.largest_acked].time_sent		now - sent_packets[pn_space][ack.largest_acked].time_sent
	ack_delay = 0		ack_delay = 0
	if pn_space == ApplicationData:		if (pn_space == ApplicationData):
	ack_delay = ack.ack_delay		ack_delay = ack.ack_delay
	UpdateRtt(ack_delay)		UpdateRtt(ack_delay)
	// Process ECN information if present.		// Process ECN information if present.
	if (ACK frame contains ECN information):		if (ACK frame contains ECN information):
	ProcessECN(ack)		ProcessECN(ack, pn_space)
	for acked_packet in newly_acked_packets:		for acked_packet in newly_acked_packets:
	OnPacketAcked(acked_packet.packet_number, pn_space)		OnPacketAcked(acked_packet.packet_number, pn_space)
	DetectLostPackets(pn_space)		DetectLostPackets(pn_space)
	crypto_count = 0
	pto_count = 0		pto_count = 0
	SetLossDetectionTimer()		SetLossDetectionTimer()
	UpdateRtt(ack_delay):		UpdateRtt(ack_delay):
	// First RTT sample.		// First RTT sample.
	if (smoothed_rtt == 0):		if (smoothed_rtt == 0):
	min_rtt = latest_rtt		min_rtt = latest_rtt
	smoothed_rtt = latest_rtt		smoothed_rtt = latest_rtt
	rttvar = latest_rtt / 2		rttvar = latest_rtt / 2
	skipping to change at page 31, line 11 ¶		skipping to change at page 30, line 11 ¶
	fire immediately.		fire immediately.
	Pseudocode for SetLossDetectionTimer follows:		Pseudocode for SetLossDetectionTimer follows:
	// Returns the earliest loss_time and the packet number		// Returns the earliest loss_time and the packet number
	// space it's from. Returns 0 if all times are 0.		// space it's from. Returns 0 if all times are 0.
	GetEarliestLossTime():		GetEarliestLossTime():
	time = loss_time[Initial]		time = loss_time[Initial]
	space = Initial		space = Initial
	for pn_space in [ Handshake, ApplicationData ]:		for pn_space in [ Handshake, ApplicationData ]:
	if loss_time[pn_space] != 0 &&		if (loss_time[pn_space] != 0 &&
	(time == 0 || loss_time[pn_space] < time):		(time == 0 || loss_time[pn_space] < time)):
	time = loss_time[pn_space];		time = loss_time[pn_space];
	space = pn_space		space = pn_space
	return time, space		return time, space
	SetLossDetectionTimer():		SetLossDetectionTimer():
	loss_time, _ = GetEarliestLossTime()		loss_time, _ = GetEarliestLossTime()
	if (loss_time != 0):		if (loss_time != 0):
	// Time threshold loss detection.		// Time threshold loss detection.
	loss_detection_timer.update(loss_time)		loss_detection_timer.update(loss_time)
	return		return
	if (has unacknowledged crypto data
	|| endpoint is client without 1-RTT keys):
	// Crypto retransmission timer.
	if (smoothed_rtt == 0):
	timeout = 2 * kInitialRtt
	else:
	timeout = 2 * smoothed_rtt
	timeout = max(timeout, kGranularity)
	timeout = timeout * (2 ^ crypto_count)
	loss_detection_timer.update(
	time_of_last_sent_crypto_packet + timeout)
	return
	// Don't arm timer if there are no ack-eliciting packets		// Don't arm timer if there are no ack-eliciting packets
	// in flight.		// in flight and the handshake is complete.
	if (no ack-eliciting packets in flight):		if (endpoint is client with 1-RTT keys &&
			no ack-eliciting packets in flight):
	loss_detection_timer.cancel()		loss_detection_timer.cancel()
	return		return
	// Calculate PTO duration		// Use a default timeout if there are no RTT measurements
	timeout =		if (smoothed_rtt == 0):
	smoothed_rtt + max(4 * rttvar, kGranularity) + max_ack_delay		timeout = 2 * kInitialRtt
			else:
			// Calculate PTO duration
			timeout = smoothed_rtt + max(4 * rttvar, kGranularity) +
			max_ack_delay
	timeout = timeout * (2 ^ pto_count)		timeout = timeout * (2 ^ pto_count)
	loss_detection_timer.update(		loss_detection_timer.update(
	time_of_last_sent_ack_eliciting_packet + timeout)		time_of_last_sent_ack_eliciting_packet + timeout)
	A.9. On Timeout		A.9. On Timeout
	When the loss detection timer expires, the timer's mode determines		When the loss detection timer expires, the timer's mode determines
	the action to be performed.		the action to be performed.
	Pseudocode for OnLossDetectionTimeout follows:		Pseudocode for OnLossDetectionTimeout follows:
	OnLossDetectionTimeout():		OnLossDetectionTimeout():
	loss_time, pn_space = GetEarliestLossTime()		loss_time, pn_space = GetEarliestLossTime()
	if (loss_time != 0):		if (loss_time != 0):
	// Time threshold loss Detection		// Time threshold loss Detection
	DetectLostPackets(pn_space)		DetectLostPackets(pn_space)
	// Retransmit crypto data if no packets were lost		SetLossDetectionTimer()
	// and there is crypto data to retransmit.		return
	else if (has unacknowledged crypto data):
	// Crypto retransmission timeout.		if (endpoint is client without 1-RTT keys):
	RetransmitUnackedCryptoData()
	crypto_count++
	else if (endpoint is client without 1-RTT keys):
	// Client sends an anti-deadlock packet: Initial is padded		// Client sends an anti-deadlock packet: Initial is padded
	// to earn more anti-amplification credit,		// to earn more anti-amplification credit,
	// a Handshake packet proves address ownership.		// a Handshake packet proves address ownership.
	if (has Handshake keys):		if (has Handshake keys):
	SendOneHandshakePacket()		SendOneAckElicitingHandshakePacket()
	else:		else:
	SendOnePaddedInitialPacket()		SendOneAckElicitingPaddedInitialPacket()
	crypto_count++
	else:		else:
	// PTO. Send new data if available, else retransmit old data.		// PTO. Send new data if available, else retransmit old data.
	// If neither is available, send a single PING frame.		// If neither is available, send a single PING frame.
	SendOneOrTwoPackets()		SendOneOrTwoAckElicitingPackets()
	pto_count++
			pto_count++
	SetLossDetectionTimer()		SetLossDetectionTimer()
	A.10. Detecting Lost Packets		A.10. Detecting Lost Packets
	DetectLostPackets is called every time an ACK is received and		DetectLostPackets is called every time an ACK is received and
	operates on the sent_packets for that packet number space.		operates on the sent_packets for that packet number space.
	Pseudocode for DetectLostPackets follows:		Pseudocode for DetectLostPackets follows:
	DetectLostPackets(pn_space):		DetectLostPackets(pn_space):
	skipping to change at page 34, line 34 ¶		skipping to change at page 33, line 34 ¶
	TCP does with a Retransmission Timeout (RTO) [RFC5681]. The		TCP does with a Retransmission Timeout (RTO) [RFC5681]. The
	RECOMMENDED value for kPersistentCongestionThreshold is 3, which		RECOMMENDED value for kPersistentCongestionThreshold is 3, which
	is approximately equivalent to having two TLPs before an RTO in		is approximately equivalent to having two TLPs before an RTO in
	TCP.		TCP.
	B.2. Variables of interest		B.2. Variables of interest
	Variables required to implement the congestion control mechanisms are		Variables required to implement the congestion control mechanisms are
	described in this section.		described in this section.
	ecn_ce_counter: The highest value reported for the ECN-CE counter by		ecn_ce_counters[kPacketNumberSpace]: The highest value reported for
	the peer in an ACK frame. This variable is used to detect		the ECN-CE counter in the packet number space by the peer in an
	increases in the reported ECN-CE counter.		ACK frame. This value is used to detect increases in the reported
			ECN-CE counter.
	bytes_in_flight: The sum of the size in bytes of all sent packets		bytes_in_flight: The sum of the size in bytes of all sent packets
	that contain at least one ack-eliciting or PADDING frame, and have		that contain at least one ack-eliciting or PADDING frame, and have
	not been acked or declared lost. The size does not include IP or		not been acked or declared lost. The size does not include IP or
	UDP overhead, but does include the QUIC header and AEAD overhead.		UDP overhead, but does include the QUIC header and AEAD overhead.
	Packets only containing ACK frames do not count towards		Packets only containing ACK frames do not count towards
	bytes_in_flight to ensure congestion control does not impede		bytes_in_flight to ensure congestion control does not 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
	skipping to change at page 35, line 20 ¶		skipping to change at page 34, line 20 ¶
	B.3. Initialization		B.3. Initialization
	At the beginning of the connection, initialize the congestion control		At the beginning of the connection, initialize the congestion control
	variables as follows:		variables as follows:
	congestion_window = kInitialWindow		congestion_window = kInitialWindow
	bytes_in_flight = 0		bytes_in_flight = 0
	congestion_recovery_start_time = 0		congestion_recovery_start_time = 0
	ssthresh = infinite		ssthresh = infinite
	ecn_ce_counter = 0		for pn_space in [ Initial, Handshake, ApplicationData ]:
			ecn_ce_counters[pn_space] = 0
	B.4. On Packet Sent		B.4. On Packet Sent
	Whenever a packet is sent, and it contains non-ACK frames, the packet		Whenever a packet is sent, and it contains non-ACK frames, the packet
	increases bytes_in_flight.		increases bytes_in_flight.
	OnPacketSentCC(bytes_sent):		OnPacketSentCC(bytes_sent):
	bytes_in_flight += bytes_sent		bytes_in_flight += bytes_sent
	B.5. On Packet Acknowledgement		B.5. On Packet Acknowledgement
	skipping to change at page 36, line 14 ¶		skipping to change at page 35, line 14 ¶
	InCongestionRecovery(sent_time):		InCongestionRecovery(sent_time):
	return sent_time <= congestion_recovery_start_time		return sent_time <= congestion_recovery_start_time
	OnPacketAckedCC(acked_packet):		OnPacketAckedCC(acked_packet):
	// Remove from bytes_in_flight.		// Remove from bytes_in_flight.
	bytes_in_flight -= acked_packet.size		bytes_in_flight -= acked_packet.size
	if (InCongestionRecovery(acked_packet.time_sent)):		if (InCongestionRecovery(acked_packet.time_sent)):
	// Do not increase congestion window in recovery period.		// Do not increase congestion window in recovery period.
	return		return
	if (IsAppLimited())		if (IsAppLimited()):
	// Do not increase congestion_window if application		// Do not increase congestion_window if application
	// limited.		// limited.
	return		return
	if (congestion_window < ssthresh):		if (congestion_window < ssthresh):
	// Slow start.		// Slow start.
	congestion_window += acked_packet.size		congestion_window += acked_packet.size
	else:		else:
	// Congestion avoidance.		// Congestion avoidance.
	congestion_window += kMaxDatagramSize * acked_packet.size		congestion_window += kMaxDatagramSize * acked_packet.size
	/ congestion_window		/ congestion_window
	skipping to change at page 36, line 46 ¶		skipping to change at page 35, line 46 ¶
	congestion_recovery_start_time = Now()		congestion_recovery_start_time = Now()
	congestion_window *= kLossReductionFactor		congestion_window *= kLossReductionFactor
	congestion_window = max(congestion_window, kMinimumWindow)		congestion_window = max(congestion_window, kMinimumWindow)
	ssthresh = congestion_window		ssthresh = congestion_window
	B.7. Process ECN Information		B.7. Process ECN Information
	Invoked when an ACK frame with an ECN section is received from the		Invoked when an ACK frame with an ECN section is received from the
	peer.		peer.
	ProcessECN(ack):		ProcessECN(ack, pn_space):
	// If the ECN-CE counter reported by the peer has increased,		// If the ECN-CE counter reported by the peer has increased,
	// this could be a new congestion event.		// this could be a new congestion event.
	if (ack.ce_counter > ecn_ce_counter):		if (ack.ce_counter > ecn_ce_counters[pn_space]):
	ecn_ce_counter = ack.ce_counter		ecn_ce_counters[pn_space] = ack.ce_counter
	CongestionEvent(sent_packets[ack.largest_acked].time_sent)		CongestionEvent(sent_packets[ack.largest_acked].time_sent)
	B.8. On Packets Lost		B.8. On Packets Lost
	Invoked from DetectLostPackets when packets are deemed lost.		Invoked from DetectLostPackets when packets are deemed lost.
	InPersistentCongestion(largest_lost_packet):		InPersistentCongestion(largest_lost_packet):
	pto = smoothed_rtt + max(4 * rttvar, kGranularity) +		pto = smoothed_rtt + max(4 * rttvar, kGranularity) +
	max_ack_delay		max_ack_delay
	congestion_period = pto * kPersistentCongestionThreshold		congestion_period = pto * kPersistentCongestionThreshold
End of changes. 47 change blocks.
	213 lines changed or deleted		170 lines changed or added
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