draft-ietf-tcpm-alternativebackoff-ecn-04.txt		draft-ietf-tcpm-alternativebackoff-ecn-05.txt
	Network Working Group N. Khademi		Network Working Group N. Khademi
	Internet-Draft M. Welzl		Internet-Draft M. Welzl
	Intended status: Experimental University of Oslo		Intended status: Experimental University of Oslo
	Expires: May 19, 2018 G. Armitage		Expires: June 14, 2018 G. Armitage
	Swinburne University of Technology		Swinburne University of Technology
	G. Fairhurst		G. Fairhurst
	University of Aberdeen		University of Aberdeen
	November 15, 2017		December 11, 2017
	TCP Alternative Backoff with ECN (ABE)		TCP Alternative Backoff with ECN (ABE)
	draft-ietf-tcpm-alternativebackoff-ecn-04		draft-ietf-tcpm-alternativebackoff-ecn-05
	Abstract		Abstract
	Recent Active Queue Management (AQM) mechanisms allow for burst		Recent Active Queue Management (AQM) mechanisms allow for burst
	tolerance while enforcing short queues to minimise the time that		tolerance while enforcing short queues to minimise the time that
	packets spend enqueued at a bottleneck. This can cause noticeable		packets spend enqueued at a bottleneck. This can cause noticeable
	performance degradation for TCP connections traversing such a		performance degradation for TCP connections traversing such a
	bottleneck, especially if they are only a few or their bandwidth-		bottleneck, especially if there are only a few flows or their
	delay-product is large. An Explicit Congestion Notification (ECN)		bandwidth-delay-product is large. An Explicit Congestion
	signal indicates that an AQM mechanism is used at the bottleneck, and		Notification (ECN) signal indicates that an AQM mechanism is used at
	therefore the bottleneck network queue is likely to be short. This		the bottleneck, and therefore the bottleneck network queue is likely
	document therefore proposes an update to the TCP sender-side ECN		to be short. This document therefore proposes an update to RFC3168,
	reaction in congestion avoidance to reduce the Congestion Window		which changes the TCP sender-side ECN reaction in congestion
	(cwnd) by a smaller amount than the congestion control algorithm's		avoidance to reduce the Congestion Window (cwnd) by a smaller amount
	reaction to inferred packet loss.		than the congestion control algorithm's reaction to inferred packet
			loss.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
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	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
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	Copyright Notice		Copyright Notice
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	document authors. All rights reserved.		document authors. All rights reserved.
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	Table of Contents		Table of Contents
	1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 4		3. Specification . . . . . . . . . . . . . . . . . . . . . . . . 3
	4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 4		4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 4
	4.1. Why Use ECN to Vary the Degree of Backoff? . . . . . . . 4		4.1. Why Use ECN to Vary the Degree of Backoff? . . . . . . . 4
	4.2. Focus on ECN as Defined in RFC3168 . . . . . . . . . . . 5		4.2. Focus on ECN as Defined in RFC3168 . . . . . . . . . . . 5
	4.3. Choice of ABE Multiplier . . . . . . . . . . . . . . . . 5		4.3. Choice of ABE Multiplier . . . . . . . . . . . . . . . . 5
	5. ABE Requirements . . . . . . . . . . . . . . . . . . . . . . 7		5. ABE Requirements . . . . . . . . . . . . . . . . . . . . . . 7
	6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7		6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
	8. Implementation Status . . . . . . . . . . . . . . . . . . . . 8		8. Implementation Status . . . . . . . . . . . . . . . . . . . . 8
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 8		9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
	10. Revision Information . . . . . . . . . . . . . . . . . . . . 9		10. Revision Information . . . . . . . . . . . . . . . . . . . . 9
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10		11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
	11.1. Normative References . . . . . . . . . . . . . . . . . . 10		11.1. Normative References . . . . . . . . . . . . . . . . . . 10
	11.2. Informative References . . . . . . . . . . . . . . . . . 10		11.2. Informative References . . . . . . . . . . . . . . . . . 11
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
	1. Definitions		1. Definitions
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in RFC 2119 [RFC2119].		document are to be interpreted as described in RFC 2119 [RFC2119].
	2. Introduction		2. Introduction
	Explicit Congestion Notification (ECN) [RFC3168] makes it possible		Explicit Congestion Notification (ECN) [RFC3168] makes it possible
	for an Active Queue Management (AQM) mechanism to signal the presence		for an Active Queue Management (AQM) mechanism to signal the presence
	of incipient congestion without incurring packet loss. This lets the		of incipient congestion without incurring packet loss. This lets the
	network deliver some packets to an application that would have been		network deliver some packets to an application that would have been
	dropped if the application or transport did not support ECN. This		dropped if the application or transport did not support ECN. This
	packet loss reduction is the most obvious benefit of ECN, but it is		packet loss reduction is the most obvious benefit of ECN, but it is
	often relatively modest. There are also significant other benefits		often relatively modest. Other benefits of deploying ECN have been
	from deploying ECN [RFC8087], including reduced end-to-end network		documented in RFC8087 [RFC8087].
	latency.
	The rules for ECN were originally written to be very conservative,		The rules for ECN were originally written to be very conservative,
	and required the congestion control algorithms of ECN-capable		and required the congestion control algorithms of ECN-Capable
	transport protocols to treat ECN congestion signals exactly the same		transport protocols to treat ECN congestion signals exactly the same
	as they would treat an inferred packet loss [RFC3168].		as they would treat an inferred packet loss [RFC3168].
	Research has demonstrated the benefits of reducing network delays		Research has demonstrated the benefits of reducing network delays
	that are caused by interaction of loss-based TCP congestion control		that are caused by interaction of loss-based TCP congestion control
	and excessive buffering [BUFFERBLOAT]. This has led to the creation		and excessive buffering [BUFFERBLOAT]. This has led to the creation
	of new AQM mechanisms like PIE [RFC8033] and CoDel		of new AQM mechanisms like PIE [RFC8033] and CoDel
	[CODEL2012][I-D.CoDel], which prevent bloated queues that are common		[CODEL2012][I-D.CoDel], which prevent bloated queues that are common
	with unmanaged and excessively large buffers deployed across the		with unmanaged and excessively large buffers deployed across the
	Internet [BUFFERBLOAT].		Internet [BUFFERBLOAT].
	skipping to change at page 4, line 7 ¶		skipping to change at page 3, line 49 ¶
	changes in modern AQM practices, more recent rules have relaxed the		changes in modern AQM practices, more recent rules have relaxed the
	strict requirement that ECN signals be treated identically to		strict requirement that ECN signals be treated identically to
	inferred packet loss [I-D.ECN-exp]. Following these newer, more		inferred packet loss [I-D.ECN-exp]. Following these newer, more
	flexible rules, this document defines a new sender-side-only		flexible rules, this document defines a new sender-side-only
	congestion control response, called "ABE" (Alternative Backoff with		congestion control response, called "ABE" (Alternative Backoff with
	ECN). ABE improves TCP's average throughput when routers use AQM		ECN). ABE improves TCP's average throughput when routers use AQM
	controlled buffers that allow for short queues only.		controlled buffers that allow for short queues only.
	3. Specification		3. Specification
	This specification describes an update to the congestion control		This specification updates the congestion control algorithm of an
	algorithm of an ECN-capable TCP transport protocol. It allows a TCP		ECN-Capable TCP transport protocol by changing the TCP sender
	stack to update the TCP sender response when it receives feedback		response to feedback from the TCP receiver that indicates reception
	indicating reception of a CE-marked packet (ECN-signalled congestion		of a CE-marked packet, i.e., receipt of a packet with the ECN-Echo
	hereafter) per Equation 4 of [RFC5681]. It RECOMMENDS that a TCP		flag (defined in [RFC3168]) set.
	sender multiplies the slow start threshold (ssthresh) by 0.8 times of
	the FlightSize (with its minimum value set to 2 * SMSS) and reduces		It updates the following text in section 6.1.2 of the ECN
	the cwnd in congestion avoidance following reception of a TCP segment		specification [RFC3168] :
	that sets the ECN-Echo flag (defined in [RFC3168]). While this
	specification concerns TCP, other transports also support a per-RTT		The indication of congestion should be treated just as a
	response to ECN. The method defined in this document is also		congestion loss in non-ECN-Capable TCP. That is, the TCP source
	applicable for such transports.		halves the congestion window "cwnd" and reduces the slow start
			threshold "ssthresh".
			Replacing this with:
			Receipt of a packet with the ECN-Echo flag SHOULD trigger the TCP
			source to set the slow start threshold (ssthresh) to 0.8 times the
			FlightSize, with a lower bound of 2 * SMSS applied to the result.
			As in [RFC5681], the TCP sender also reduces the cwnd value to
			that new ssthresh value.
	4. Discussion		4. Discussion
	Much of the technical background to ABE can be found in a research		Much of the technical background to ABE can be found in a research
	paper [ABE2017]. This paper used a mix of experiments, theory and		paper [ABE2017]. This paper used a mix of experiments, theory and
	simulations with standard NewReno and CUBIC to evaluate the		simulations with NewReno [RFC5681] and CUBIC [I-D.CUBIC] to evaluate
	technique. The technique was shown to present "...significant		the technique. The technique was shown to present "...significant
	performance gains in lightly-multiplexed [few concurrent flows]		performance gains in lightly-multiplexed [few concurrent flows]
	scenarios, without losing the delay-reduction benefits of deploying		scenarios, without losing the delay-reduction benefits of deploying
	CoDel or PIE". The performance improvement is achieved when reacting		CoDel or PIE". The performance improvement is achieved when reacting
	to ECN-Echo in congestion avoidance by multiplying cwnd and ssthresh		to ECN-Echo in congestion avoidance by multiplying cwnd and ssthresh
	with a value in the range [0.7,0.85].		with a value in the range [0.7,0.85].
	4.1. Why Use ECN to Vary the Degree of Backoff?		4.1. Why Use ECN to Vary the Degree of Backoff?
	The classic rule-of-thumb dictates that a network path needs to		The classic rule-of-thumb dictates that a network path needs to
	provide a BDP of bottleneck buffering if a TCP connection wishes to		provide a BDP of bottleneck buffering if a TCP connection wishes to
	skipping to change at page 5, line 12 ¶		skipping to change at page 5, line 16 ¶
	default delay targets, CoDel and PIE both effectively emulate a		default delay targets, CoDel and PIE both effectively emulate a
	bottleneck with a short queue (section II, [ABE2017]) while also		bottleneck with a short queue (section II, [ABE2017]) while also
	allowing short traffic bursts into the queue. This provides		allowing short traffic bursts into the queue. This provides
	acceptable performance for TCP connections over a path with a low		acceptable performance for TCP connections over a path with a low
	BDP, or in highly multiplexed scenarios (many concurrent transport		BDP, or in highly multiplexed scenarios (many concurrent transport
	flows). However, in a lightly-multiplexed case over a path with a		flows). However, in a lightly-multiplexed case over a path with a
	large BDP, conventional TCP backoff leads to gaps in packet		large BDP, conventional TCP backoff leads to gaps in packet
	transmission and under-utilisation of the path.		transmission and under-utilisation of the path.
	Instead of discarding packets, an AQM mechanism is allowed to mark		Instead of discarding packets, an AQM mechanism is allowed to mark
	ECN-capable packets with an ECN CE-mark. The reception of a CE-mark		ECN-Capable packets with an ECN CE-mark. The reception of a CE-mark
	feedback not only indicates congestion on the network path, it also		feedback not only indicates congestion on the network path, it also
	indicates that an AQM mechanism exists at the bottleneck along the		indicates that an AQM mechanism exists at the bottleneck along the
	path, and hence the CE-mark likely came from a bottleneck with a		path, and hence the CE-mark likely came from a bottleneck with a
	controlled short queue. Reacting differently to an ECN-signalled		controlled short queue. Reacting differently to an ECN-signalled
	congestion than to an inferred packet loss can then yield the benefit		congestion than to an inferred packet loss can then yield the benefit
	of a reduced back-off when queues are short. Using ECN can also be		of a reduced back-off when queues are short. Using ECN can also be
	advantageous for several other reasons [RFC8087].		advantageous for several other reasons [RFC8087].
	The idea of reacting differently to inferred packet loss and		The idea of reacting differently to inferred packet loss and
	detection of an ECN-signalled congestion pre-dates this document.		detection of an ECN-signalled congestion pre-dates this document.
	For example, previous research proposed using ECN CE-marked feedback		For example, previous research proposed using ECN CE-marked feedback
	to modify TCP congestion control behaviour via a larger		to modify TCP congestion control behaviour via a larger
	multiplicative decrease factor in conjunction with a smaller additive		multiplicative decrease factor in conjunction with a smaller additive
	increase factor [ICC2002]. The goal of this former work was to		increase factor [ICC2002]. The goal of this former work was to
	operate across AQM bottlenecks using Random Early Detection (RED)		operate across AQM bottlenecks using Random Early Detection (RED)
	that were not necessarily configured to emulate a short queue		that were not necessarily configured to emulate a short queue (The
	([RFC7567] notes the current status of RED as an AQM method.)		current usage of RED as an Internet AQM method is limited [RFC7567]).
	4.2. Focus on ECN as Defined in RFC3168		4.2. Focus on ECN as Defined in RFC3168
	Some transport protocol mechanisms rely on ECN semantics that differ		Some transport protocol mechanisms rely on ECN semantics that differ
	from the original ECN definition [RFC3168] -- for example, Congestion		from the original ECN definition [RFC3168] -- for example, Congestion
	Exposure (ConEx) [RFC7713] and Datacenter TCP (DCTCP)		Exposure (ConEx) [RFC7713] and Datacenter TCP (DCTCP)
	[I-D.ietf-tcpm-dctcp] need more accurate ECN information than that		[I-D.ietf-tcpm-dctcp] need more accurate ECN information than that
	offered by the original feedback method. Other mechanisms (e.g.,		offered by the original feedback method. Other mechanisms (e.g.,
	[I-D.ietf-tcpm-accurate-ecn]) allow the sender to adjust the rate		[I-D.ietf-tcpm-accurate-ecn]) allow the sender to adjust the rate
	more frequently than once each path RTT. Use of these mechanisms is		more frequently than once each path RTT. Use of these mechanisms is
	skipping to change at page 6, line 13 ¶		skipping to change at page 6, line 17 ¶
	enabled TCP connections, only beta_{loss} applies.		enabled TCP connections, only beta_{loss} applies.
	In other words, in response to inferred packet loss:		In other words, in response to inferred packet loss:
	ssthresh = max (FlightSize * beta_{loss}, 2 * SMSS)		ssthresh = max (FlightSize * beta_{loss}, 2 * SMSS)
	and in response to an indication of an ECN-signalled congestion:		and in response to an indication of an ECN-signalled congestion:
	ssthresh = max (FlightSize * beta_{ecn}, 2 * SMSS)		ssthresh = max (FlightSize * beta_{ecn}, 2 * SMSS)
	and		and
	cwnd = ssthresh		cwnd = ssthresh
	where FlightSize is the amount of outstanding data in the network,		where FlightSize is the amount of outstanding data in the network,
	upper-bounded by the smaller of the sender's cwnd and the receiver's		upper-bounded by the smaller of the sender's cwnd and the receiver's
	advertised window (rwnd) [RFC5681]. The higher the values of		advertised window (rwnd) [RFC5681]. The higher the values of
	beta_{loss} and beta_{ecn}, the less aggressive the response of any		beta_{loss} and beta_{ecn}, the less aggressive the response of any
	individual backoff event.		individual backoff event.
	The appropriate choice for beta_{loss} and beta_{ecn} values is a		The appropriate choice for beta_{loss} and beta_{ecn} values is a
	skipping to change at page 6, line 42 ¶		skipping to change at page 6, line 46 ¶
	a multiplier of 0.7 since kernel version 2.6.25 released in 2008.		a multiplier of 0.7 since kernel version 2.6.25 released in 2008.
	ABE proposes no change to beta_{loss} used by current TCP		ABE proposes no change to beta_{loss} used by current TCP
	implementations.		implementations.
	beta_{ecn} depends on how the response of a TCP connection to shallow		beta_{ecn} depends on how the response of a TCP connection to shallow
	AQM marking thresholds is optimised. beta_{loss} reflects the		AQM marking thresholds is optimised. beta_{loss} reflects the
	preferred response of each congestion control algorithm when faced		preferred response of each congestion control algorithm when faced
	with exhaustion of buffers (of unknown depth) signalled by packet		with exhaustion of buffers (of unknown depth) signalled by packet
	loss. Consequently, for any given TCP congestion control algorithm		loss. Consequently, for any given TCP congestion control algorithm
	the choice of beta_{ecn} is likely to be algorithm-specific, rather		the choice of beta_{ecn} is likely to be algorithm-specific, rather
	than a constant multiple of the algorithm's existing beta_{loss}.		than a constant multiple of the algorithm's existing beta_{loss}. The
	The recommended beta_{ecn} value in this document is only applicable		recommended beta_{ecn} value in this document is only applicable for
	for Standard TCP congestion control.		Standard TCP congestion control.
	A range of tests (section IV, [ABE2017]) with NewReno and CUBIC over		A range of tests (section IV, [ABE2017]) with NewReno and CUBIC over
	CoDel and PIE in lightly-multiplexed scenarios have explored this		CoDel and PIE in lightly-multiplexed scenarios have explored this
	choice of parameter. The results of these tests indicate that CUBIC		choice of parameter. The results of these tests indicate that CUBIC
	connections benefit from beta_{ecn} of 0.85 (cf. beta_{loss} = 0.7),		connections benefit from beta_{ecn} of 0.85 (cf. beta_{loss} = 0.7),
	and NewReno connections see improvements with beta_{ecn} in the range		and NewReno connections see improvements with beta_{ecn} in the range
	0.7 to 0.85 (cf. beta_{loss} = 0.5).		0.7 to 0.85 (cf. beta_{loss} = 0.5).
	5. ABE Requirements		5. ABE Requirements
	This update is a sender-side only change. Like other changes to		This update is a sender-side only change. Like other changes to
	congestion control algorithms, it does not require any change to the		congestion control algorithms, it does not require any change to the
	TCP receiver or to network devices. It does not require any ABE-		TCP receiver or to network devices. It does not require any ABE-
	specific changes in routers or the use of Accurate ECN feedback		specific changes in routers or the use of Accurate ECN feedback
	[I-D.ietf-tcpm-accurate-ecn] by a receiver.		[I-D.ietf-tcpm-accurate-ecn] by a receiver.
	RFC 3168 states that the congestion control response to an ECN-		RFC3168 states that the congestion control response to an ECN-
	signalled congestion is the same as the response to a dropped packet		signalled congestion is the same as the response to a dropped packet
	[RFC3168]. [I-D.ECN-exp] updates this specification to allow systems		[RFC3168]. [I-D.ECN-exp] updates this specification to allow systems
	to provide a different behaviour when they experience ECN-signalled		to provide a different behaviour when they experience ECN-signalled
	congestion rather than packet loss. The present specification		congestion rather than packet loss. The present specification
	defines such an experiment and has thus been assigned an Experimental		defines such an experiment and has thus been assigned an Experimental
	status before being proposed as a Standards-Track update.		status before being proposed as a Standards-Track update.
	The purpose of the Internet experiment is to collect experience with		The purpose of the Internet experiment is to collect experience with
	deployment of ABE, and confirm the safety in deployed networks using		deployment of ABE, and confirm the safety in deployed networks using
	this update to TCP congestion control.		this update to TCP congestion control.
	When used with bottlenecks that do not support ECN-marking the		When used with bottlenecks that do not support ECN-marking the
	specification does not modify the transport protocol.		specification does not modify the transport protocol.
	To evaluate the benefit, this experiment therefore requires support		To evaluate the benefit, this experiment therefore requires support
	in AQM routers (except to enable an ECN-marking mechanism [RFC3168]		in AQM routers for ECN-marking of packets carrying the ECN-Capable
	[RFC7567]) for ECN-marking of packets carrying the ECN Capable
	Transport, ECT(0), codepoint [RFC3168].		Transport, ECT(0), codepoint [RFC3168].
	If the method is only deployed by some senders, and not by others,		If the method is only deployed by some senders, and not by others,
	the senders that use this method can gain some advantage, possibly at		the senders that use this method can gain some advantage, possibly at
	the expense of other flows that do not use this updated method.		the expense of other flows that do not use this updated method.
	Because this advantage applies only to ECN-marked packets and not to		Because this advantage applies only to ECN-marked packets and not to
	packet loss indications, in the worst-case (e.g., an ABE-compliant		packet loss indications, in the worst case (e.g., an ABE-compliant
	TCP sender using beta_{ecn} = 1.0) the ECN-capable bottleneck will		TCP sender using beta_{ecn} = 1.0) the ECN-Capable bottleneck will
	still fall back to dropping packets, and the result is no different		still fall back to dropping packets, and the result is no different
	than if the TCP sender was using traditional loss-based congestion		than if the TCP sender was using traditional loss-based congestion
	control.		control.
	The result of this Internet experiment will be reported by		A TCP sender reacts to loss or ECN marks only once per round-trip
			time. Hence, if a sender would first be notified of an ECN mark and
			then learn about loss in the same round-trip, it would only react to
			the first notification (ECN) but not to the second (loss). RFC3168
			specified a reaction to ECN that was equal to the reaction to loss
			[RFC3168].
			ABE also makes one congestion-response each RTT that congestion is
			signalled, and therefore there is no response to loss within the same
			round-trip time, since ABE has already made a reduction of the
			congestion window. ABE will however respond for each round-trip time
			that congestion continues to be signaled. This consecutive reduction
			can protect the network against long-standing unfairness in the case
			of AQM algorithms that do not keep a small average queue length.
			The result of this Internet experiment will include an investigation
			of cases such as the ones listed above, and be reported by
	presentation to the TCPM WG (or IESG) or an implementation report at		presentation to the TCPM WG (or IESG) or an implementation report at
	the end of the experiment.		the end of the experiment.
	6. Acknowledgements		6. Acknowledgements
	Authors N. Khademi, M. Welzl and G. Fairhurst were part-funded by		Authors N. Khademi, M. Welzl and G. Fairhurst were part-funded by
	the European Community under its Seventh Framework Programme through		the European Community under its Seventh Framework Programme through
	the Reducing Internet Transport Latency (RITE) project (ICT-317700).		the Reducing Internet Transport Latency (RITE) project (ICT-317700).
	The views expressed are solely those of the authors.		The views expressed are solely those of the authors.
	The authors would like to thank Stuart Cheshire for many suggestions		The authors would like to thank Stuart Cheshire for many suggestions
	when revising the draft, and the following people for their		when revising the draft, and the following people for their
	contributions to [ABE2017]: Chamil Kulatunga, David Ros, Stein		contributions to [ABE2017]: Chamil Kulatunga, David Ros, Stein
	Gjessing, Sebastian Zander. Thanks also to (in alphabetical order)		Gjessing, Sebastian Zander. Thanks also to (in alphabetical order)
	Bob Briscoe, Markku Kojo, John Leslie, Dave Taht and the TCPM working		Roland Bless, Bob Briscoe, David Black, Markku Kojo, John Leslie,
	group for providing valuable feedback on this document.		Lawrence Stewart, Dave Taht and the TCPM working group for providing
			valuable feedback on this document.
	The authors would finally like to thank everyone who provided		The authors would finally like to thank everyone who provided
	feedback on the congestion control behaviour specified in this update		feedback on the congestion control behaviour specified in this update
	received from the IRTF Internet Congestion Control Research Group		received from the IRTF Internet Congestion Control Research Group
	(ICCRG).		(ICCRG).
	7. IANA Considerations		7. IANA Considerations
	XX RFC ED - PLEASE REMOVE THIS SECTION XXX		XX RFC ED - PLEASE REMOVE THIS SECTION XXX
	skipping to change at page 9, line 9 ¶		skipping to change at page 9, line 26 ¶
	mechanisms that have been in use in the Internet for many years		mechanisms that have been in use in the Internet for many years
	(e.g., CUBIC [I-D.CUBIC]). Unfairness may also be a result of other		(e.g., CUBIC [I-D.CUBIC]). Unfairness may also be a result of other
	factors, including the round trip time experienced by a flow. ABE		factors, including the round trip time experienced by a flow. ABE
	applies only when ECN-marked packets are received, not when packets		applies only when ECN-marked packets are received, not when packets
	are lost, hence use of ABE cannot lead to congestion collapse.		are lost, hence use of ABE cannot lead to congestion collapse.
	10. Revision Information		10. Revision Information
	XX RFC ED - PLEASE REMOVE THIS SECTION XXX		XX RFC ED - PLEASE REMOVE THIS SECTION XXX
	-04. Incorporates review comments from Larence Stewart and the		-05. Refined the description of the experiment based on feedback at
			IETF-100. Incorporated comments from David Black.
			-04. Incorporates review comments from Lawrence Stewart and the
	remaining comments from Roland Bless. References are updated.		remaining comments from Roland Bless. References are updated.
	-03. Several review comments from Roland Bless are addressed.		-03. Several review comments from Roland Bless are addressed.
	Consistent terminology and equations. Clarification on the scope of		Consistent terminology and equations. Clarification on the scope of
	recommended beta_{ecn} value.		recommended beta_{ecn} value.
	-02. Corrected the equations in Section 4.3. Updated the		-02. Corrected the equations in Section 4.3. Updated the
	affiliations. Lower bound for cwnd is defined. A recommendation for		affiliations. Lower bound for cwnd is defined. A recommendation for
	window-based transport protocols is changed to cover all transport		window-based transport protocols is changed to cover all transport
	protocols that implement a congestion control reduction to an ECN		protocols that implement a congestion control reduction to an ECN
End of changes. 23 change blocks.
	50 lines changed or deleted		78 lines changed or added
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