draft-ietf-quic-recovery-30.txt		draft-ietf-quic-recovery-31.txt
	QUIC J. Iyengar, Ed.		QUIC J. Iyengar, Ed.
	Internet-Draft Fastly		Internet-Draft Fastly
	Intended status: Standards Track I. Swett, Ed.		Intended status: Standards Track I. Swett, Ed.
	Expires: March 14, 2021 Google		Expires: 29 March 2021 Google
	September 10, 2020		25 September 2020
	QUIC Loss Detection and Congestion Control		QUIC Loss Detection and Congestion Control
	draft-ietf-quic-recovery-30		draft-ietf-quic-recovery-31
	Abstract		Abstract
	This document describes loss detection and congestion control		This document describes loss detection and congestion control
	mechanisms for QUIC.		mechanisms for QUIC.
	Note to Readers		Note to Readers
	Discussion of this draft takes place on the QUIC working group		Discussion of this draft takes place on the QUIC working group
	mailing list (quic@ietf.org (mailto:quic@ietf.org)), which is		mailing list (quic@ietf.org (mailto:quic@ietf.org)), which is
	skipping to change at page 1, line 43 ¶		skipping to change at page 1, line 43 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	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 March 14, 2021.		This Internet-Draft will expire on 29 March 2021.
	Copyright Notice		Copyright Notice
	Copyright (c) 2020 IETF Trust and the persons identified as the		Copyright (c) 2020 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	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 (https://trustee.ietf.org/		Provisions Relating to IETF Documents (https://trustee.ietf.org/
	license-info) in effect on the date of publication of this document.		license-info) in effect on the date of publication of this document.
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	skipping to change at page 3, line 40 ¶		skipping to change at page 3, line 40 ¶
	B.1. Constants of interest . . . . . . . . . . . . . . . . . . 39		B.1. Constants of interest . . . . . . . . . . . . . . . . . . 39
	B.2. Variables of interest . . . . . . . . . . . . . . . . . . 40		B.2. Variables of interest . . . . . . . . . . . . . . . . . . 40
	B.3. Initialization . . . . . . . . . . . . . . . . . . . . . 40		B.3. Initialization . . . . . . . . . . . . . . . . . . . . . 40
	B.4. On Packet Sent . . . . . . . . . . . . . . . . . . . . . 41		B.4. On Packet Sent . . . . . . . . . . . . . . . . . . . . . 41
	B.5. On Packet Acknowledgement . . . . . . . . . . . . . . . . 41		B.5. On Packet Acknowledgement . . . . . . . . . . . . . . . . 41
	B.6. On New Congestion Event . . . . . . . . . . . . . . . . . 42		B.6. On New Congestion Event . . . . . . . . . . . . . . . . . 42
	B.7. Process ECN Information . . . . . . . . . . . . . . . . . 43		B.7. Process ECN Information . . . . . . . . . . . . . . . . . 43
	B.8. On Packets Lost . . . . . . . . . . . . . . . . . . . . . 43		B.8. On Packets Lost . . . . . . . . . . . . . . . . . . . . . 43
	B.9. Upon dropping Initial or Handshake keys . . . . . . . . . 43		B.9. Upon dropping Initial or Handshake keys . . . . . . . . . 43
	Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 44		Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 44
	C.1. Since draft-ietf-quic-recovery-29 . . . . . . . . . . . . 44		C.1. Since draft-ietf-quic-recovery-30 . . . . . . . . . . . . 44
	C.2. Since draft-ietf-quic-recovery-28 . . . . . . . . . . . . 44		C.2. Since draft-ietf-quic-recovery-29 . . . . . . . . . . . . 44
	C.3. Since draft-ietf-quic-recovery-27 . . . . . . . . . . . . 44		C.3. Since draft-ietf-quic-recovery-28 . . . . . . . . . . . . 44
	C.4. Since draft-ietf-quic-recovery-26 . . . . . . . . . . . . 45		C.4. Since draft-ietf-quic-recovery-27 . . . . . . . . . . . . 45
	C.5. Since draft-ietf-quic-recovery-25 . . . . . . . . . . . . 45		C.5. Since draft-ietf-quic-recovery-26 . . . . . . . . . . . . 45
	C.6. Since draft-ietf-quic-recovery-24 . . . . . . . . . . . . 45		C.6. Since draft-ietf-quic-recovery-25 . . . . . . . . . . . . 45
	C.7. Since draft-ietf-quic-recovery-23 . . . . . . . . . . . . 45		C.7. Since draft-ietf-quic-recovery-24 . . . . . . . . . . . . 45
	C.8. Since draft-ietf-quic-recovery-22 . . . . . . . . . . . . 46		C.8. Since draft-ietf-quic-recovery-23 . . . . . . . . . . . . 45
	C.9. Since draft-ietf-quic-recovery-21 . . . . . . . . . . . . 46		C.9. Since draft-ietf-quic-recovery-22 . . . . . . . . . . . . 46
	C.10. Since draft-ietf-quic-recovery-20 . . . . . . . . . . . . 46		C.10. Since draft-ietf-quic-recovery-21 . . . . . . . . . . . . 46
	C.11. Since draft-ietf-quic-recovery-19 . . . . . . . . . . . . 46		C.11. Since draft-ietf-quic-recovery-20 . . . . . . . . . . . . 46
	C.12. Since draft-ietf-quic-recovery-18 . . . . . . . . . . . . 46		C.12. Since draft-ietf-quic-recovery-19 . . . . . . . . . . . . 46
	C.13. Since draft-ietf-quic-recovery-17 . . . . . . . . . . . . 47		C.13. Since draft-ietf-quic-recovery-18 . . . . . . . . . . . . 47
	C.14. Since draft-ietf-quic-recovery-16 . . . . . . . . . . . . 47		C.14. Since draft-ietf-quic-recovery-17 . . . . . . . . . . . . 47
	C.15. Since draft-ietf-quic-recovery-14 . . . . . . . . . . . . 48		C.15. Since draft-ietf-quic-recovery-16 . . . . . . . . . . . . 47
	C.16. Since draft-ietf-quic-recovery-13 . . . . . . . . . . . . 48		C.16. Since draft-ietf-quic-recovery-14 . . . . . . . . . . . . 48
	C.17. Since draft-ietf-quic-recovery-12 . . . . . . . . . . . . 48		C.17. Since draft-ietf-quic-recovery-13 . . . . . . . . . . . . 48
	C.18. Since draft-ietf-quic-recovery-11 . . . . . . . . . . . . 49		C.18. Since draft-ietf-quic-recovery-12 . . . . . . . . . . . . 48
	C.19. Since draft-ietf-quic-recovery-10 . . . . . . . . . . . . 49		C.19. Since draft-ietf-quic-recovery-11 . . . . . . . . . . . . 49
	C.20. Since draft-ietf-quic-recovery-09 . . . . . . . . . . . . 49		C.20. Since draft-ietf-quic-recovery-10 . . . . . . . . . . . . 49
	C.21. Since draft-ietf-quic-recovery-08 . . . . . . . . . . . . 49		C.21. Since draft-ietf-quic-recovery-09 . . . . . . . . . . . . 49
	C.22. Since draft-ietf-quic-recovery-07 . . . . . . . . . . . . 49		C.22. Since draft-ietf-quic-recovery-08 . . . . . . . . . . . . 49
	C.23. Since draft-ietf-quic-recovery-06 . . . . . . . . . . . . 49		C.23. Since draft-ietf-quic-recovery-07 . . . . . . . . . . . . 49
	C.24. Since draft-ietf-quic-recovery-05 . . . . . . . . . . . . 49		C.24. Since draft-ietf-quic-recovery-06 . . . . . . . . . . . . 49
	C.25. Since draft-ietf-quic-recovery-04 . . . . . . . . . . . . 50		C.25. Since draft-ietf-quic-recovery-05 . . . . . . . . . . . . 49
	C.26. Since draft-ietf-quic-recovery-03 . . . . . . . . . . . . 50		C.26. Since draft-ietf-quic-recovery-04 . . . . . . . . . . . . 50
	C.27. Since draft-ietf-quic-recovery-02 . . . . . . . . . . . . 50		C.27. Since draft-ietf-quic-recovery-03 . . . . . . . . . . . . 50
	C.28. Since draft-ietf-quic-recovery-01 . . . . . . . . . . . . 50		C.28. Since draft-ietf-quic-recovery-02 . . . . . . . . . . . . 50
	C.29. Since draft-ietf-quic-recovery-00 . . . . . . . . . . . . 50		C.29. Since draft-ietf-quic-recovery-01 . . . . . . . . . . . . 50
	C.30. Since draft-iyengar-quic-loss-recovery-01 . . . . . . . . 50		C.30. Since draft-ietf-quic-recovery-00 . . . . . . . . . . . . 50
			C.31. Since draft-iyengar-quic-loss-recovery-01 . . . . . . . . 50
	Appendix D. Contributors . . . . . . . . . . . . . . . . . . . . 51		Appendix D. Contributors . . . . . . . . . . . . . . . . . . . . 51
	Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 51		Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 51
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51
	1. Introduction		1. Introduction
	QUIC is a new multiplexed and secure transport protocol atop UDP,		QUIC is a new multiplexed and secure transport protocol atop UDP,
	specified in [QUIC-TRANSPORT]. This document describes congestion		specified in [QUIC-TRANSPORT]. This document describes congestion
	control and loss recovery for QUIC. Mechanisms described in this		control and loss recovery for QUIC. Mechanisms described in this
	document follow the spirit of existing TCP congestion control and		document follow the spirit of existing TCP congestion control and
	skipping to change at page 13, line 16 ¶		skipping to change at page 13, line 16 ¶
	The RECOMMENDED initial value for the packet reordering threshold		The RECOMMENDED initial value for the packet reordering threshold
	(kPacketThreshold) is 3, based on best practices for TCP loss		(kPacketThreshold) is 3, based on best practices for TCP loss
	detection ([RFC5681], [RFC6675]). In order to remain similar to TCP,		detection ([RFC5681], [RFC6675]). In order to remain similar to TCP,
	implementations SHOULD NOT use a packet threshold less than 3; see		implementations SHOULD NOT use a packet threshold less than 3; see
	[RFC5681].		[RFC5681].
	Some networks may exhibit higher degrees of packet reordering,		Some networks may exhibit higher degrees of packet reordering,
	causing a sender to detect spurious losses. Additionally, packet		causing a sender to detect spurious losses. Additionally, packet
	reordering could be more common with QUIC than TCP, because network		reordering could be more common with QUIC than TCP, because network
	elements that could observe and reorder out-of-order TCP packets		elements that could observe and reorder TCP packets cannot do that
	cannot do that for QUIC, because packet numbers are encrypted.		for QUIC, because QUIC packet numbers are encrypted. Algorithms that
	Algorithms that increase the reordering threshold after spuriously		increase the reordering threshold after spuriously detecting losses,
	detecting losses, such as RACK [RACK], have proven to be useful in		such as RACK [RACK], have proven to be useful in TCP and are expected
	TCP and are expected to be at least as useful in QUIC.		to be at least as useful in QUIC.
	6.1.2. Time Threshold		6.1.2. Time Threshold
	Once a later packet within the same packet number space has been		Once a later packet within the same packet number space has been
	acknowledged, an endpoint SHOULD declare an earlier packet lost if it		acknowledged, an endpoint SHOULD declare an earlier packet lost if it
	was sent a threshold amount of time in the past. To avoid declaring		was sent a threshold amount of time in the past. To avoid declaring
	packets as lost too early, this time threshold MUST be set to at		packets as lost too early, this time threshold MUST be set to at
	least the local timer granularity, as indicated by the kGranularity		least the local timer granularity, as indicated by the kGranularity
	constant. The time threshold is:		constant. The time threshold is:
	skipping to change at page 14, line 5 ¶		skipping to change at page 13, line 51 ¶
	path;		path;
	* the latest RTT sample is higher than the smoothed RTT, perhaps due		* the latest RTT sample is higher than the smoothed RTT, perhaps due
	to a sustained increase in the actual RTT, but the smoothed RTT		to a sustained increase in the actual RTT, but the smoothed RTT
	has not yet caught up.		has not yet caught up.
	The RECOMMENDED time threshold (kTimeThreshold), expressed as a		The RECOMMENDED time threshold (kTimeThreshold), expressed as a
	round-trip time multiplier, is 9/8. The RECOMMENDED value of the		round-trip time multiplier, is 9/8. The RECOMMENDED value of the
	timer granularity (kGranularity) is 1ms.		timer granularity (kGranularity) is 1ms.
			Note: TCP's RACK ([RACK]) specifies a slightly larger threshold,
			equivalent to 5/4, for a similar purpose. Experience with QUIC
			shows that 9/8 works well.
	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
	variation. Smaller thresholds reduce reordering resilience and		variation. 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. Probe Timeout		6.2. Probe Timeout
	A Probe Timeout (PTO) triggers sending one or two probe datagrams		A Probe Timeout (PTO) triggers sending one or two probe datagrams
	when ack-eliciting packets are not acknowledged within the expected		when ack-eliciting packets are not acknowledged within the expected
	skipping to change at page 15, line 48 ¶		skipping to change at page 15, line 51 ¶
	This exponential reduction in the sender's rate is important because		This exponential reduction in the sender's rate is important because
	consecutive PTOs might be caused by loss of packets or		consecutive PTOs might be caused by loss of packets or
	acknowledgements due to severe congestion. Even when there are ack-		acknowledgements due to severe congestion. Even when there are ack-
	eliciting packets in-flight in multiple packet number spaces, the		eliciting packets in-flight in multiple packet number spaces, the
	exponential increase in probe timeout occurs across all spaces to		exponential increase in probe timeout occurs across all spaces to
	prevent excess load on the network. For example, a timeout in the		prevent excess load on the network. For example, a timeout in the
	Initial packet number space doubles the length of the timeout in the		Initial packet number space doubles the length of the timeout in the
	Handshake packet number space.		Handshake packet number space.
	The time length of a connection that is experiencing consecutive PTOs		The total length of time over which consecutive PTOs expire is
	is limited by the endpoint's idle timeout.		limited by the idle timeout.
	The probe timer MUST NOT be set if the time threshold (Section 6.1.2)		The probe timer MUST NOT be set if the time threshold (Section 6.1.2)
	loss detection timer is set. The time threshold loss detection timer		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		is expected to both expire earlier than the PTO and be less likely to
	spuriously retransmit data.		spuriously retransmit data.
	6.2.2. Handshakes and New Paths		6.2.2. Handshakes and New Paths
	Resumed connections over the same network MAY use the previous		Resumed connections over the same network MAY use the previous
	connection's final smoothed RTT value as the resumed connection's		connection's final smoothed RTT value as the resumed connection's
	skipping to change at page 16, line 51 ¶		skipping to change at page 16, line 51 ¶
	Since the server could be blocked until more datagrams are received		Since the server could be blocked until more datagrams are received
	from the client, it is the client's responsibility to send packets to		from the client, it is the client's responsibility to send packets to
	unblock the server until it is certain that the server has finished		unblock the server until it is certain that the server has finished
	its address validation (see Section 8 of [QUIC-TRANSPORT]). That is,		its address validation (see Section 8 of [QUIC-TRANSPORT]). That is,
	the client MUST set the probe timer if the client has not received an		the client MUST set the probe timer if the client has not received an
	acknowledgement for one of its Handshake packets and the handshake is		acknowledgement for one of its Handshake packets and the handshake is
	not confirmed (see Section 4.1.2 of [QUIC-TLS]), even if there are no		not confirmed (see Section 4.1.2 of [QUIC-TLS]), even if there are no
	packets in flight. When the PTO fires, the client MUST send a		packets in flight. When the PTO fires, the client MUST send a
	Handshake packet if it has Handshake keys, otherwise it MUST send an		Handshake packet if it has Handshake keys, otherwise it MUST send an
	Initial packet in a UDP datagram of at least 1200 bytes.		Initial packet in a UDP datagram with a payload of at least 1200
			bytes.
	6.2.3. Speeding Up Handshake Completion		6.2.3. Speeding Up Handshake Completion
	When a server receives an Initial packet containing duplicate CRYPTO		When a server receives an Initial packet containing duplicate CRYPTO
	data, it can assume the client did not receive all of the server's		data, it can assume the client did not receive all of the server's
	CRYPTO data sent in Initial packets, or the client's estimated RTT is		CRYPTO data sent in Initial packets, or the client's estimated RTT is
	too small. When a client receives Handshake or 1-RTT packets prior		too small. When a client receives Handshake or 1-RTT packets prior
	to obtaining Handshake keys, it may assume some or all of the		to obtaining Handshake keys, it may assume some or all of the
	server's Initial packets were lost.		server's Initial packets were lost.
	To speed up handshake completion under these conditions, an endpoint		To speed up handshake completion under these conditions, an endpoint
	MAY send a packet containing unacknowledged CRYPTO data earlier than		MAY send a packet containing unacknowledged CRYPTO data earlier than
	the PTO expiry, subject to the address validation limits in		the PTO expiry, subject to the address validation limits in
	Section 8.1 of [QUIC-TRANSPORT].		Section 8.1 of [QUIC-TRANSPORT].
	Endpoints can also use coalesced packets to ensure that each datagram		Endpoints can also use coalesced packets (see Section 12.2 of
	elicits at least one acknowledgement. For example, a client can		[QUIC-TRANSPORT]) to ensure that each datagram elicits at least one
	coalesce an Initial packet containing PING and PADDING frames with a		acknowledgement. For example, a client can coalesce an Initial
	0-RTT data packet and a server can coalesce an Initial packet		packet containing PING and PADDING frames with a 0-RTT data packet
	containing a PING frame with one or more packets in its first flight.		and a server can coalesce an Initial packet containing a PING frame
			with one or more packets in its first flight.
	6.2.4. Sending Probe Packets		6.2.4. 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 in the packet number space as a probe. An endpoint		eliciting packet in the packet number space as a probe. An endpoint
	MAY send up to two full-sized datagrams containing ack-eliciting		MAY send up to two full-sized datagrams containing ack-eliciting
	packets, to avoid an expensive consecutive PTO expiration due to a		packets, to avoid an expensive consecutive PTO expiration due to a
	single lost datagram or transmit data from multiple packet number		single lost datagram or transmit data from multiple packet number
	spaces. All probe packets sent on a PTO MUST be ack-eliciting.		spaces. All probe packets sent on a PTO MUST be ack-eliciting.
	skipping to change at page 20, line 12 ¶		skipping to change at page 20, line 12 ¶
	The algorithm in this document specifies and uses the controller's		The algorithm in this document specifies and uses the controller's
	congestion window in bytes.		congestion window in bytes.
	An endpoint MUST NOT send a packet if it would cause bytes_in_flight		An endpoint MUST NOT send a packet if it would cause bytes_in_flight
	(see Appendix B.2) to be larger than the congestion window, unless		(see Appendix B.2) to be larger than the congestion window, unless
	the packet is sent on a PTO timer expiration (see Section 6.2) or		the packet is sent on a PTO timer expiration (see Section 6.2) or
	when entering recovery (see Section 7.3.2).		when entering recovery (see Section 7.3.2).
	7.1. Explicit Congestion Notification		7.1. Explicit Congestion Notification
	If a path has been verified to support ECN ([RFC3168], [RFC8311]),		If a path has been validated to support ECN ([RFC3168], [RFC8311]),
	QUIC treats a Congestion Experienced (CE) codepoint in the IP header		QUIC treats a Congestion Experienced (CE) codepoint in the IP header
	as a signal of congestion. This document specifies an endpoint's		as a signal of congestion. This document specifies an endpoint's
	response when its peer receives packets with the ECN-CE codepoint.		response when its peer receives packets with the ECN-CE codepoint.
	7.2. Initial and Minimum Congestion Window		7.2. Initial and Minimum Congestion Window
	QUIC begins every connection in slow start with the congestion window		QUIC begins every connection in slow start with the congestion window
	set to an initial value. Endpoints SHOULD use an initial congestion		set to an initial value. Endpoints SHOULD use an initial congestion
	window of 10 times the maximum datagram size (max_datagram_size),		window of 10 times the maximum datagram size (max_datagram_size),
	limited to the larger of 14720 or twice the maximum datagram size.		limited to the larger of 14720 bytes or twice the maximum datagram
	This follows the analysis and recommendations in [RFC6928],		size. This follows the analysis and recommendations in [RFC6928],
	increasing the byte limit to account for the smaller 8 byte overhead		increasing the byte limit to account for the smaller 8 byte overhead
	of UDP compared to the 20 byte overhead for TCP.		of UDP compared to the 20 byte overhead for TCP.
	If the maximum datagram size changes during the connection, the		If the maximum datagram size changes during the connection, the
	initial congestion window SHOULD be recalculated with the new size.		initial congestion window SHOULD be recalculated with the new size.
	If the maximum datagram size is decreased in order to complete the		If the maximum datagram size is decreased in order to complete the
	handshake, the congestion window SHOULD be set to the new initial		handshake, the congestion window SHOULD be set to the new initial
	congestion window.		congestion window.
	Prior to validating the client's address, the server can be further		Prior to validating the client's address, the server can be further
	skipping to change at page 26, line 36 ¶		skipping to change at page 26, line 36 ¶
	trip time. Expressed as a rate in bytes:		trip time. Expressed as a rate in bytes:
	rate = N * congestion_window / smoothed_rtt		rate = N * congestion_window / smoothed_rtt
	Or, expressed as an inter-packet interval:		Or, expressed as an inter-packet interval:
	interval = smoothed_rtt * packet_size / congestion_window / N		interval = smoothed_rtt * packet_size / congestion_window / N
	Using a value for "N" that is small, but at least 1 (for example,		Using a value for "N" that is small, but at least 1 (for example,
	1.25) ensures that variations in round-trip time do not result in		1.25) ensures that variations in round-trip time do not result in
	under-utilization of the congestion window. Values of 'N' larger		under-utilization of the congestion window.
	than 1 ultimately result in sending packets as acknowledgments are
	received rather than when timers fire, provided the congestion window
	is fully utilized and acknowledgments arrive at regular intervals.
	Practical considerations, such as packetization, scheduling delays,		Practical considerations, such as packetization, scheduling delays,
	and computational efficiency, can cause a sender to deviate from this		and computational efficiency, can cause a sender to deviate from this
	rate over time periods that are much shorter than a round-trip time.		rate over time periods that are much shorter than a round-trip time.
	One possible implementation strategy for pacing uses a leaky bucket		One possible implementation strategy for pacing uses a leaky bucket
	algorithm, where the capacity of the "bucket" is limited to the		algorithm, where the capacity of the "bucket" is limited to the
	maximum burst size and the rate the "bucket" fills is determined by		maximum burst size and the rate the "bucket" fills is determined by
	the above function.		the above function.
	skipping to change at page 28, line 31 ¶		skipping to change at page 28, line 31 ¶
	9. IANA Considerations		9. IANA Considerations
	This document has no IANA actions.		This document has no IANA actions.
	10. References		10. References
	10.1. Normative References		10.1. Normative References
	[QUIC-TLS] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure		[QUIC-TLS] Thomson, M., Ed. and S. Turner, Ed., "Using TLS to Secure
	QUIC", Work in Progress, Internet-Draft, draft-ietf-quic-		QUIC", Work in Progress, Internet-Draft, draft-ietf-quic-
	tls-30, September 10, 2020,		tls-31, 25 September 2020,
	<https://tools.ietf.org/html/draft-ietf-quic-tls-30>.		<https://tools.ietf.org/html/draft-ietf-quic-tls-31>.
	[QUIC-TRANSPORT]		[QUIC-TRANSPORT]
	Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based		Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
	Multiplexed and Secure Transport", Work in Progress,		Multiplexed and Secure Transport", Work in Progress,
	Internet-Draft, draft-ietf-quic-transport-30, September		Internet-Draft, draft-ietf-quic-transport-31, 25 September
	10, 2020, <https://tools.ietf.org/html/draft-ietf-quic-		2020, <https://tools.ietf.org/html/draft-ietf-quic-
	transport-30>.		transport-31>.
	[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>.
	[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage		[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
	Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,		Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
	March 2017, <https://www.rfc-editor.org/info/rfc8085>.		March 2017, <https://www.rfc-editor.org/info/rfc8085>.
	skipping to change at page 29, line 17 ¶		skipping to change at page 29, line 17 ¶
	[FACK] Mathis, M. and J. Mahdavi, "Forward Acknowledgement:		[FACK] Mathis, M. and J. Mahdavi, "Forward Acknowledgement:
	Refining TCP Congestion Control", ACM SIGCOMM , August		Refining TCP Congestion Control", ACM SIGCOMM , August
	1996.		1996.
	[PRR] Mathis, M., Dukkipati, N., and Y. Cheng, "Proportional		[PRR] Mathis, M., Dukkipati, N., and Y. Cheng, "Proportional
	Rate Reduction for TCP", RFC 6937, DOI 10.17487/RFC6937,		Rate Reduction for TCP", RFC 6937, DOI 10.17487/RFC6937,
	May 2013, <https://www.rfc-editor.org/info/rfc6937>.		May 2013, <https://www.rfc-editor.org/info/rfc6937>.
	[RACK] Cheng, Y., Cardwell, N., Dukkipati, N., and P. Jha, "The		[RACK] Cheng, Y., Cardwell, N., Dukkipati, N., and P. Jha, "The
	RACK-TLP loss detection algorithm for TCP", Work in		RACK-TLP loss detection algorithm for TCP", Work in
	Progress, Internet-Draft, draft-ietf-tcpm-rack-10, August		Progress, Internet-Draft, draft-ietf-tcpm-rack-10, 22
	22, 2020, <http://www.ietf.org/internet-drafts/draft-ietf-		August 2020, <http://www.ietf.org/internet-drafts/draft-
	tcpm-rack-10.txt>.		ietf-tcpm-rack-10.txt>.
	[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition		[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
	of Explicit Congestion Notification (ECN) to IP",		of Explicit Congestion Notification (ECN) to IP",
	RFC 3168, DOI 10.17487/RFC3168, September 2001,		RFC 3168, DOI 10.17487/RFC3168, September 2001,
	<https://www.rfc-editor.org/info/rfc3168>.		<https://www.rfc-editor.org/info/rfc3168>.
	[RFC3465] Allman, M., "TCP Congestion Control with Appropriate Byte		[RFC3465] Allman, M., "TCP Congestion Control with Appropriate Byte
	Counting (ABC)", RFC 3465, DOI 10.17487/RFC3465, February		Counting (ABC)", RFC 3465, DOI 10.17487/RFC3465, February
	2003, <https://www.rfc-editor.org/info/rfc3465>.		2003, <https://www.rfc-editor.org/info/rfc3465>.
	skipping to change at page 44, line 25 ¶		skipping to change at page 44, line 25 ¶
	pto_count = 0		pto_count = 0
	SetLossDetectionTimer()		SetLossDetectionTimer()
	Appendix C. Change Log		Appendix C. Change Log
	*RFC Editor's Note:* Please remove this section prior to		*RFC Editor's Note:* Please remove this section prior to
	publication of a final version of this document.		publication of a final version of this document.
	Issue and pull request numbers are listed with a leading octothorp.		Issue and pull request numbers are listed with a leading octothorp.
	C.1. Since draft-ietf-quic-recovery-29		C.1. Since draft-ietf-quic-recovery-30
			Editorial changes only.
			C.2. Since draft-ietf-quic-recovery-29
	* Allow caching of packets that can't be decrypted, by allowing the		* Allow caching of packets that can't be decrypted, by allowing the
	reported acknowledgment delay to exceed max_ack_delay prior to		reported acknowledgment delay to exceed max_ack_delay prior to
	confirming the handshake (#3821, #3980, #4035, #3874)		confirming the handshake (#3821, #3980, #4035, #3874)
	* Persistent congestion cannot include packets sent before the first		* Persistent congestion cannot include packets sent before the first
	RTT sample for the path (#3875, #3889)		RTT sample for the path (#3875, #3889)
	* Recommend reset of min_rtt in persistent congestion (#3927, #3975)		* Recommend reset of min_rtt in persistent congestion (#3927, #3975)
	* Persistent congestion is independent of packet number space		* Persistent congestion is independent of packet number space
	(#3939, #3961)		(#3939, #3961)
	* Only limit bursts to the initial window without information about		* Only limit bursts to the initial window without information about
	the path (#3892, #3936)		the path (#3892, #3936)
	* Add normative requirements for increasing and reducing the		* Add normative requirements for increasing and reducing the
	congestion window (#3944, #3978, #3997, #3998)		congestion window (#3944, #3978, #3997, #3998)
	C.2. Since draft-ietf-quic-recovery-28		C.3. Since draft-ietf-quic-recovery-28
	* Refactored pseudocode to correct PTO calculation (#3564, #3674,		* Refactored pseudocode to correct PTO calculation (#3564, #3674,
	#3681)		#3681)
	C.3. Since draft-ietf-quic-recovery-27		C.4. Since draft-ietf-quic-recovery-27
	* Added recommendations for speeding up handshake under some loss		* Added recommendations for speeding up handshake under some loss
	conditions (#3078, #3080)		conditions (#3078, #3080)
	* PTO count is reset when handshake progress is made (#3272, #3415)		* PTO count is reset when handshake progress is made (#3272, #3415)
	* PTO count is not reset by a client when the server might be		* PTO count is not reset by a client when the server might be
	awaiting address validation (#3546, #3551)		awaiting address validation (#3546, #3551)
	* Recommend repairing losses immediately after entering the recovery		* Recommend repairing losses immediately after entering the recovery
	period (#3335, #3443)		period (#3335, #3443)
	* Clarified what loss conditions can be ignored during the handshake		* Clarified what loss conditions can be ignored during the handshake
	(#3456, #3450)		(#3456, #3450)
	* Allow, but don't recommend, using RTT from previous connection to		* Allow, but don't recommend, using RTT from previous connection to
	seed RTT (#3464, #3496)		seed RTT (#3464, #3496)
	* Recommend use of adaptive loss detection thresholds (#3571, #3572)		* Recommend use of adaptive loss detection thresholds (#3571, #3572)
	C.4. Since draft-ietf-quic-recovery-26		C.5. Since draft-ietf-quic-recovery-26
	No changes.		No changes.
	C.5. Since draft-ietf-quic-recovery-25		C.6. Since draft-ietf-quic-recovery-25
	No significant changes.		No significant changes.
	C.6. Since draft-ietf-quic-recovery-24		C.7. Since draft-ietf-quic-recovery-24
	* Require congestion control of some sort (#3247, #3244, #3248)		* Require congestion control of some sort (#3247, #3244, #3248)
	* Set a minimum reordering threshold (#3256, #3240)		* Set a minimum reordering threshold (#3256, #3240)
	* PTO is specific to a packet number space (#3067, #3074, #3066)		* PTO is specific to a packet number space (#3067, #3074, #3066)
	C.7. Since draft-ietf-quic-recovery-23		C.8. Since draft-ietf-quic-recovery-23
	* Define under-utilizing the congestion window (#2630, #2686, #2675)		* Define under-utilizing the congestion window (#2630, #2686, #2675)
	* PTO MUST send data if possible (#3056, #3057)		* PTO MUST send data if possible (#3056, #3057)
	* Connection Close is not ack-eliciting (#3097, #3098)		* Connection Close is not ack-eliciting (#3097, #3098)
	* MUST limit bursts to the initial congestion window (#3160)		* MUST limit bursts to the initial congestion window (#3160)
	* Define the current max_datagram_size for congestion control		* Define the current max_datagram_size for congestion control
	(#3041, #3167)		(#3041, #3167)
	C.8. Since draft-ietf-quic-recovery-22		C.9. Since draft-ietf-quic-recovery-22
	* PTO should always send an ack-eliciting packet (#2895)		* PTO should always send an ack-eliciting packet (#2895)
	* Unify the Handshake Timer with the PTO timer (#2648, #2658, #2886)		* Unify the Handshake Timer with the PTO timer (#2648, #2658, #2886)
	* Move ACK generation text to transport draft (#1860, #2916)		* Move ACK generation text to transport draft (#1860, #2916)
	C.9. Since draft-ietf-quic-recovery-21		C.10. Since draft-ietf-quic-recovery-21
	* No changes		* No changes
	C.10. Since draft-ietf-quic-recovery-20		C.11. Since draft-ietf-quic-recovery-20
	* Path validation can be used as initial RTT value (#2644, #2687)		* Path validation can be used as initial RTT value (#2644, #2687)
	* max_ack_delay transport parameter defaults to 0 (#2638, #2646)		* max_ack_delay transport parameter defaults to 0 (#2638, #2646)
	* ACK delay only measures intentional delays induced by the		* ACK delay only measures intentional delays induced by the
	implementation (#2596, #2786)		implementation (#2596, #2786)
	C.11. Since draft-ietf-quic-recovery-19		C.12. Since draft-ietf-quic-recovery-19
	* Change kPersistentThreshold from an exponent to a multiplier		* Change kPersistentThreshold from an exponent to a multiplier
	(#2557)		(#2557)
	* Send a PING if the PTO timer fires and there's nothing to send		* Send a PING if the PTO timer fires and there's nothing to send
	(#2624)		(#2624)
	* Set loss delay to at least kGranularity (#2617)		* Set loss delay to at least kGranularity (#2617)
	* Merge application limited and sending after idle sections. Always		* Merge application limited and sending after idle sections. Always
	skipping to change at page 46, line 51 ¶		skipping to change at page 47, line 5 ¶
	packet is ack-eliciting but the largest_acked is not (#2592)		packet is ack-eliciting but the largest_acked is not (#2592)
	* Don't arm the handshake timer if there is no handshake data		* Don't arm the handshake timer if there is no handshake data
	(#2590)		(#2590)
	* Clarify that the time threshold loss alarm takes precedence over		* Clarify that the time threshold loss alarm takes precedence over
	the crypto handshake timer (#2590, #2620)		the crypto handshake timer (#2590, #2620)
	* Change initial RTT to 500ms to align with RFC6298 (#2184)		* Change initial RTT to 500ms to align with RFC6298 (#2184)
	C.12. Since draft-ietf-quic-recovery-18		C.13. Since draft-ietf-quic-recovery-18
	* Change IW byte limit to 14720 from 14600 (#2494)		* Change IW byte limit to 14720 from 14600 (#2494)
	* Update PTO calculation to match RFC6298 (#2480, #2489, #2490)		* Update PTO calculation to match RFC6298 (#2480, #2489, #2490)
	* Improve loss detection's description of multiple packet number		* Improve loss detection's description of multiple packet number
	spaces and pseudocode (#2485, #2451, #2417)		spaces and pseudocode (#2485, #2451, #2417)
	* Declare persistent congestion even if non-probe packets are sent		* Declare persistent congestion even if non-probe packets are sent
	and don't make persistent congestion more aggressive than RTO		and don't make persistent congestion more aggressive than RTO
	verified was (#2365, #2244)		verified was (#2365, #2244)
	* Move pseudocode to the appendices (#2408)		* Move pseudocode to the appendices (#2408)
	* What to send on multiple PTOs (#2380)		* What to send on multiple PTOs (#2380)
	C.13. Since draft-ietf-quic-recovery-17		C.14. Since draft-ietf-quic-recovery-17
	* After Probe Timeout discard in-flight packets or send another		* After Probe Timeout discard in-flight packets or send another
	(#2212, #1965)		(#2212, #1965)
	* Endpoints discard initial keys as soon as handshake keys are		* Endpoints discard initial keys as soon as handshake keys are
	available (#1951, #2045)		available (#1951, #2045)
	* 0-RTT state is discarded when 0-RTT is rejected (#2300)		* 0-RTT state is discarded when 0-RTT is rejected (#2300)
	* Loss detection timer is cancelled when ack-eliciting frames are in		* Loss detection timer is cancelled when ack-eliciting frames are in
	skipping to change at page 47, line 45 ¶		skipping to change at page 47, line 48 ¶
	controller (#2138, 2187)		controller (#2138, 2187)
	* Process ECN counts before marking packets lost (#2142)		* Process ECN counts before marking packets lost (#2142)
	* Mark packets lost before resetting crypto_count and pto_count		* Mark packets lost before resetting crypto_count and pto_count
	(#2208, #2209)		(#2208, #2209)
	* Congestion and loss recovery state are discarded when keys are		* Congestion and loss recovery state are discarded when keys are
	discarded (#2327)		discarded (#2327)
	C.14. Since draft-ietf-quic-recovery-16		C.15. Since draft-ietf-quic-recovery-16
	* Unify TLP and RTO into a single PTO; eliminate min RTO, min TLP		* Unify TLP and RTO into a single PTO; eliminate min RTO, min TLP
	and min crypto timeouts; eliminate timeout validation (#2114,		and min crypto timeouts; eliminate timeout validation (#2114,
	#2166, #2168, #1017)		#2166, #2168, #1017)
	* Redefine how congestion avoidance in terms of when the period		* Redefine how congestion avoidance in terms of when the period
	starts (#1928, #1930)		starts (#1928, #1930)
	* Document what needs to be tracked for packets that are in flight		* Document what needs to be tracked for packets that are in flight
	(#765, #1724, #1939)		(#765, #1724, #1939)
	skipping to change at page 48, line 30 ¶		skipping to change at page 48, line 30 ¶
	* Limit ack_delay by max_ack_delay (#2060, #2099)		* Limit ack_delay by max_ack_delay (#2060, #2099)
	* Initial keys are discarded once Handshake keys are available		* Initial keys are discarded once Handshake keys are available
	(#1951, #2045)		(#1951, #2045)
	* Reorder ECN and loss detection in pseudocode (#2142)		* Reorder ECN and loss detection in pseudocode (#2142)
	* Only cancel loss detection timer if ack-eliciting packets are in		* Only cancel loss detection timer if ack-eliciting packets are in
	flight (#2093, #2117)		flight (#2093, #2117)
	C.15. Since draft-ietf-quic-recovery-14		C.16. Since draft-ietf-quic-recovery-14
	* Used max_ack_delay from transport params (#1796, #1782)		* Used max_ack_delay from transport params (#1796, #1782)
	* Merge ACK and ACK_ECN (#1783)		* Merge ACK and ACK_ECN (#1783)
	C.16. Since draft-ietf-quic-recovery-13		C.17. Since draft-ietf-quic-recovery-13
	* Corrected the lack of ssthresh reduction in CongestionEvent		* Corrected the lack of ssthresh reduction in CongestionEvent
	pseudocode (#1598)		pseudocode (#1598)
	* Considerations for ECN spoofing (#1426, #1626)		* Considerations for ECN spoofing (#1426, #1626)
	* Clarifications for PADDING and congestion control (#837, #838,		* Clarifications for PADDING and congestion control (#837, #838,
	#1517, #1531, #1540)		#1517, #1531, #1540)
	* Reduce early retransmission timer to RTT/8 (#945, #1581)		* Reduce early retransmission timer to RTT/8 (#945, #1581)
	* Packets are declared lost after an RTO is verified (#935, #1582)		* Packets are declared lost after an RTO is verified (#935, #1582)
	C.17. Since draft-ietf-quic-recovery-12		C.18. Since draft-ietf-quic-recovery-12
	* Changes to manage separate packet number spaces and encryption		* Changes to manage separate packet number spaces and encryption
	levels (#1190, #1242, #1413, #1450)		levels (#1190, #1242, #1413, #1450)
	* Added ECN feedback mechanisms and handling; new ACK_ECN frame		* Added ECN feedback mechanisms and handling; new ACK_ECN frame
	(#804, #805, #1372)		(#804, #805, #1372)
	C.18. Since draft-ietf-quic-recovery-11		C.19. Since draft-ietf-quic-recovery-11
	No significant changes.		No significant changes.
	C.19. Since draft-ietf-quic-recovery-10		C.20. Since draft-ietf-quic-recovery-10
	* Improved text on ack generation (#1139, #1159)		* Improved text on ack generation (#1139, #1159)
	* Make references to TCP recovery mechanisms informational (#1195)		* Make references to TCP recovery mechanisms informational (#1195)
	* Define time_of_last_sent_handshake_packet (#1171)		* Define time_of_last_sent_handshake_packet (#1171)
	* Added signal from TLS the data it includes needs to be sent in a		* Added signal from TLS the data it includes needs to be sent in a
	Retry packet (#1061, #1199)		Retry packet (#1061, #1199)
	* Minimum RTT (min_rtt) is initialized with an infinite value		* Minimum RTT (min_rtt) is initialized with an infinite value
	(#1169)		(#1169)
	C.20. Since draft-ietf-quic-recovery-09		C.21. Since draft-ietf-quic-recovery-09
	No significant changes.		No significant changes.
	C.21. Since draft-ietf-quic-recovery-08		C.22. Since draft-ietf-quic-recovery-08
	* Clarified pacing and RTO (#967, #977)		* Clarified pacing and RTO (#967, #977)
	C.22. Since draft-ietf-quic-recovery-07		C.23. Since draft-ietf-quic-recovery-07
	* Include ACK delay in RTO(and TLP) computations (#981)		* Include ACK delay in RTO(and TLP) computations (#981)
	* ACK delay in SRTT computation (#961)		* ACK delay in SRTT computation (#961)
	* Default RTT and Slow Start (#590)		* Default RTT and Slow Start (#590)
	* Many editorial fixes.		* Many editorial fixes.
	C.23. Since draft-ietf-quic-recovery-06		C.24. Since draft-ietf-quic-recovery-06
	No significant changes.		No significant changes.
	C.24. Since draft-ietf-quic-recovery-05		C.25. Since draft-ietf-quic-recovery-05
	* Add more congestion control text (#776)		* Add more congestion control text (#776)
	C.25. Since draft-ietf-quic-recovery-04		C.26. Since draft-ietf-quic-recovery-04
	No significant changes.		No significant changes.
	C.26. Since draft-ietf-quic-recovery-03		C.27. Since draft-ietf-quic-recovery-03
	No significant changes.		No significant changes.
	C.27. Since draft-ietf-quic-recovery-02		C.28. Since draft-ietf-quic-recovery-02
	* Integrate F-RTO (#544, #409)		* Integrate F-RTO (#544, #409)
	* Add congestion control (#545, #395)		* Add congestion control (#545, #395)
	* Require connection abort if a skipped packet was acknowledged		* Require connection abort if a skipped packet was acknowledged
	(#415)		(#415)
	* Simplify RTO calculations (#142, #417)		* Simplify RTO calculations (#142, #417)
	C.28. Since draft-ietf-quic-recovery-01		C.29. Since draft-ietf-quic-recovery-01
	* Overview added to loss detection		* Overview added to loss detection
	* Changes initial default RTT to 100ms		* Changes initial default RTT to 100ms
	* Added time-based loss detection and fixes early retransmit		* Added time-based loss detection and fixes early retransmit
	* Clarified loss recovery for handshake packets		* Clarified loss recovery for handshake packets
	* Fixed references and made TCP references informative		* Fixed references and made TCP references informative
	C.29. Since draft-ietf-quic-recovery-00		C.30. Since draft-ietf-quic-recovery-00
	* Improved description of constants and ACK behavior		* Improved description of constants and ACK behavior
	C.30. Since draft-iyengar-quic-loss-recovery-01		C.31. Since draft-iyengar-quic-loss-recovery-01
	* Adopted as base for draft-ietf-quic-recovery		* Adopted as base for draft-ietf-quic-recovery
	* Updated authors/editors list		* Updated authors/editors list
	* Added table of contents		* Added table of contents
	Appendix D. Contributors		Appendix D. Contributors
	The IETF QUIC Working Group received an enormous amount of support		The IETF QUIC Working Group received an enormous amount of support
	from many people. The following people provided substantive		from many people. The following people provided substantive
	contributions to this document: Alessandro Ghedini, Benjamin		contributions to this document:
	Saunders, Gorry Fairhurst, 奥 一穂 (Kazuho Oku), Lars Eggert, Magnus
	Westerlund, Marten Seemann, Martin Duke, Martin Thomson, Nick Banks,		* Alessandro Ghedini
	Praveen Balasubramanian.
			* Benjamin Saunders
			* Gorry Fairhurst
			* 山本和彦 (Kazu Yamamoto)
			* 奥 一穂 (Kazuho Oku)
			* Lars Eggert
			* Magnus Westerlund
			* Marten Seemann
			* Martin Duke
			* Martin Thomson
			* Mirja Kühlewind
			* Nick Banks
			* Praveen Balasubramanian
	Acknowledgments		Acknowledgments
	Authors' Addresses		Authors' Addresses
	Jana Iyengar (editor)		Jana Iyengar (editor)
	Fastly		Fastly
	Email: jri.ietf@gmail.com		Email: jri.ietf@gmail.com
End of changes. 47 change blocks.
	97 lines changed or deleted		129 lines changed or added
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