rfc9937v4.txt		rfc9937.txt
	skipping to change at line 353 ¶		skipping to change at line 353 ¶
	could, in some cases, be worse than [RFC6675] recovery, which simply		could, in some cases, be worse than [RFC6675] recovery, which simply
	sets cwnd to ssthresh at the start of recovery. This behavior of		sets cwnd to ssthresh at the start of recovery. This behavior of
	setting cwnd to ssthresh at the end of recovery has been implemented		setting cwnd to ssthresh at the end of recovery has been implemented
	since the first widely deployed TCP PRR implementation in 2011		since the first widely deployed TCP PRR implementation in 2011
	[First_TCP_PRR] and is similar to [RFC6675], which specifies setting		[First_TCP_PRR] and is similar to [RFC6675], which specifies setting
	cwnd to ssthresh at the start of recovery.		cwnd to ssthresh at the start of recovery.
	Since [RFC6937] was written, PRR has also been adapted to perform		Since [RFC6937] was written, PRR has also been adapted to perform
	multiplicative window reduction for non-loss-based congestion control		multiplicative window reduction for non-loss-based congestion control
	algorithms, such as for Explicit Congestion Notification (ECN) as		algorithms, such as for Explicit Congestion Notification (ECN) as
	described in [RFC3168]. This can be done by using some parts of the		specified in [RFC3168]. This can be done by using some parts of the
	loss recovery state machine (in particular, the RecoveryPoint from		loss recovery state machine (in particular, the RecoveryPoint from
	[RFC6675]) to invoke the PRR ACK processing for exactly one round		[RFC6675]) to invoke the PRR ACK processing for exactly one round
	trip worth of ACKs. However, note that using PRR for cwnd reductions		trip worth of ACKs. However, there can be interactions between using
	for the [RFC3168] variant of ECN has been observed, with some		PRR and approaches to Active Queue Management (AQM) and ECN; guidance
	approaches to Active Queue Management (AQM), to cause an excess cwnd		on the development and assessment of congestion control mechanisms is
	reduction during ECN-triggered congestion episodes, as noted in		provided in [RFC9743].
	[VCC].
	5. Relationships to Other Standards		5. Relationships to Other Standards
	PRR MAY be used in conjunction with any congestion control algorithm		PRR MAY be used in conjunction with any congestion control algorithm
	that intends to make a multiplicative decrease in its sending rate		that intends to make a multiplicative decrease in its sending rate
	over approximately the time scale of one round-trip time, as long as		over approximately the time scale of one round-trip time, as long as
	the current volume of in-flight data is limited by a congestion		the current volume of in-flight data is limited by a congestion
	window (cwnd) and the target volume of in-flight data during that		window (cwnd) and the target volume of in-flight data during that
	reduction is a fixed value given by ssthresh. In particular, PRR is		reduction is a fixed value given by ssthresh. In particular, PRR is
	applicable to both Reno [RFC5681] and CUBIC [RFC9438] congestion		applicable to both Reno [RFC5681] and CUBIC [RFC9438] congestion
	skipping to change at line 802 ¶		skipping to change at line 801 ¶
	require any changes at data receivers or in networks. This allows		require any changes at data receivers or in networks. This allows
	data senders using PRR to work correctly with any existing data		data senders using PRR to work correctly with any existing data
	receivers or networks. PRR does not require any changes to or		receivers or networks. PRR does not require any changes to or
	assistance from routers, switches, or other devices in the network.		assistance from routers, switches, or other devices in the network.
	11.2. Fairness		11.2. Fairness
	PRR is designed to maintain the fairness properties of the congestion		PRR is designed to maintain the fairness properties of the congestion
	control algorithm with which it is deployed. PRR only operates		control algorithm with which it is deployed. PRR only operates
	during a congestion control response episode, such as fast recovery		during a congestion control response episode, such as fast recovery
	or response to the [RFC3168] variant of ECN, and only makes short-		or when there is a step reduction in the cwnd from the TCP ECN
	term, per-acknowledgment decisions to smoothly regulate the volume of		reaction defined in [RFC3168], and only makes short-term, per-
	in-flight data during an episode such that at the end of the episode		acknowledgment decisions to smoothly regulate the volume of in-flight
	it will be as close as possible to the slow start threshold		data during an episode such that at the end of the episode it will be
	(ssthresh), as determined by the congestion control algorithm. PRR		as close as possible to the slow start threshold (ssthresh), as
	does not modify the congestion control cwnd increase or decrease		determined by the congestion control algorithm. PRR does not modify
	mechanisms outside of congestion control response episodes.		the congestion control cwnd increase or decrease mechanisms outside
			of congestion control response episodes.
	11.3. Protecting the Network Against Excessive Queuing and Packet Loss		11.3. Protecting the Network Against Excessive Queuing and Packet Loss
	Over long time scales, PRR is designed to maintain the queuing and		Over long time scales, PRR is designed to maintain the queuing and
	packet loss properties of the congestion control algorithm with which		packet loss properties of the congestion control algorithm with which
	it is deployed. As noted above, PRR only operates during a		it is deployed. As noted above, PRR only operates during a
	congestion control response episode, such as fast recovery or		congestion control response episode, such as fast recovery or
	response to ECN, and only makes short-term, per-acknowledgment		response to ECN, and only makes short-term, per-acknowledgment
	decisions to smoothly regulate the volume of in-flight data during an		decisions to smoothly regulate the volume of in-flight data during an
	episode such that at the end of the episode it will be as close as		episode such that at the end of the episode it will be as close as
	skipping to change at line 982 ¶		skipping to change at line 982 ¶
	[RFC3517] Blanton, E., Allman, M., Fall, K., and L. Wang, "A		[RFC3517] Blanton, E., Allman, M., Fall, K., and L. Wang, "A
	Conservative Selective Acknowledgment (SACK)-based Loss		Conservative Selective Acknowledgment (SACK)-based Loss
	Recovery Algorithm for TCP", RFC 3517,		Recovery Algorithm for TCP", RFC 3517,
	DOI 10.17487/RFC3517, April 2003,		DOI 10.17487/RFC3517, April 2003,
	<https://www.rfc-editor.org/info/rfc3517>.		<https://www.rfc-editor.org/info/rfc3517>.
	[RFC6937] Mathis, M., Dukkipati, N., and Y. Cheng, "Proportional		[RFC6937] 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>.
			[RFC9743] Duke, M., Ed. and G. Fairhurst, Ed., "Specifying New
			Congestion Control Algorithms", BCP 133, RFC 9743,
			DOI 10.17487/RFC9743, March 2025,
			<https://www.rfc-editor.org/info/rfc9743>.
	[Savage99] Savage, S., Cardwell, N., Wetherall, D., and T. Anderson,		[Savage99] Savage, S., Cardwell, N., Wetherall, D., and T. Anderson,
	"TCP Congestion Control with a Misbehaving Receiver", ACM		"TCP Congestion Control with a Misbehaving Receiver", ACM
	SIGCOMM Computer Communication Review, vol. 29, no. 5, pp.		SIGCOMM Computer Communication Review, vol. 29, no. 5, pp.
	71-78, DOI 10.1145/505696.505704, October 1999,		71-78, DOI 10.1145/505696.505704, October 1999,
	<https://doi.org/10.1145/505696.505704>.		<https://doi.org/10.1145/505696.505704>.
	[TCP-RH] Mathis, M., Mahdavi, J., and J. Semke, "The Rate-Halving		[TCP-RH] Mathis, M., Mahdavi, J., and J. Semke, "The Rate-Halving
	Algorithm for TCP Congestion Control", Work in Progress,		Algorithm for TCP Congestion Control", Work in Progress,
	Internet-Draft, draft-mathis-tcp-ratehalving-00, 30 August		Internet-Draft, draft-mathis-tcp-ratehalving-00, 30 August
	1999, <https://datatracker.ietf.org/doc/html/draft-mathis-		1999, <https://datatracker.ietf.org/doc/html/draft-mathis-
	tcp-ratehalving-00>.		tcp-ratehalving-00>.
	[VCC] Cronkite-Ratcliff, B., Bergman, A., Vargaftik, S., Ravi,
	M., McKeown, N., Abraham, I., and I. Keslassy,
	"Virtualized Congestion Control (Extended Version)",
	SIGCOMM '16: Proceedings of the 2016 ACM SIGCOMM
	Conference pp. 230-243, DOI 10.1145/2934872.2934889,
	August 2016, <http://www.ee.technion.ac.il/~isaac/p/
	sigcomm16_vcc_extended.pdf>.
	Appendix A. Strong Packet Conservation Bound		Appendix A. Strong Packet Conservation Bound
	PRR-CRB is based on a conservative, philosophically pure, and		PRR-CRB is based on a conservative, philosophically pure, and
	aesthetically appealing Strong Packet Conservation Bound, described		aesthetically appealing Strong Packet Conservation Bound, described
	here. Although inspired by the packet conservation principle		here. Although inspired by the packet conservation principle
	[Jacobson88], it differs in how it treats segments that are missing		[Jacobson88], it differs in how it treats segments that are missing
	and presumed lost. Under all conditions and sequences of events		and presumed lost. Under all conditions and sequences of events
	during recovery, PRR-CRB strictly bounds the data transmitted to be		during recovery, PRR-CRB strictly bounds the data transmitted to be
	equal to or less than the amount of data delivered to the receiver.		equal to or less than the amount of data delivered to the receiver.
	Note that the effects of presumed losses are included in the inflight		Note that the effects of presumed losses are included in the inflight
End of changes. 5 change blocks.
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