draft-ietf-tcpm-alternativebackoff-ecn-09.txt		draft-ietf-tcpm-alternativebackoff-ecn-10.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: February 15, 2019 G. Armitage		Expires: March 4, 2019 G. Armitage
	Netflix		Netflix
	G. Fairhurst		G. Fairhurst
	University of Aberdeen		University of Aberdeen
	August 14, 2018		August 31, 2018
	TCP Alternative Backoff with ECN (ABE)		TCP Alternative Backoff with ECN (ABE)
	draft-ietf-tcpm-alternativebackoff-ecn-09		draft-ietf-tcpm-alternativebackoff-ecn-10
	Abstract		Abstract
	Active Queue Management (AQM) mechanisms allow for burst tolerance		Active Queue Management (AQM) mechanisms allow for burst tolerance
	while enforcing short queues to minimise the time that packets spend		while enforcing short queues to minimise the time that packets spend
	enqueued at a bottleneck. This can cause noticeable performance		enqueued at a bottleneck. This can cause noticeable performance
	degradation for TCP connections traversing such a bottleneck,		degradation for TCP connections traversing such a bottleneck,
	especially if there are only a few flows or their bandwidth-delay-		especially if there are only a few flows or their bandwidth-delay-
	product is large. The reception of a Congestion Experienced (CE) ECN		product is large. The reception of a Congestion Experienced (CE) ECN
	mark indicates that an AQM mechanism is used at the bottleneck, and		mark indicates that an AQM mechanism is used at the bottleneck, and
	skipping to change at page 1, line 47 ¶		skipping to change at page 1, line 47 ¶
	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 February 15, 2019.		This Internet-Draft will expire on March 4, 2019.
	Copyright Notice		Copyright Notice
	Copyright (c) 2018 IETF Trust and the persons identified as the		Copyright (c) 2018 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 39 ¶		skipping to change at page 2, line 39 ¶
	5. ABE Deployment Requirements . . . . . . . . . . . . . . . . . 7		5. ABE Deployment Requirements . . . . . . . . . . . . . . . . . 7
	6. ABE Experiment Goals . . . . . . . . . . . . . . . . . . . . 8		6. ABE Experiment Goals . . . . . . . . . . . . . . . . . . . . 8
	7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8		7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
	9. Implementation Status . . . . . . . . . . . . . . . . . . . . 9		9. Implementation Status . . . . . . . . . . . . . . . . . . . . 9
	10. Security Considerations . . . . . . . . . . . . . . . . . . . 9		10. Security Considerations . . . . . . . . . . . . . . . . . . . 9
	11. Revision Information . . . . . . . . . . . . . . . . . . . . 9		11. Revision Information . . . . . . . . . . . . . . . . . . . . 9
	12. References . . . . . . . . . . . . . . . . . . . . . . . . . 11		12. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
	12.1. Normative References . . . . . . . . . . . . . . . . . . 11		12.1. Normative References . . . . . . . . . . . . . . . . . . 11
	12.2. Informative References . . . . . . . . . . . . . . . . . 11		12.2. Informative References . . . . . . . . . . . . . . . . . 11
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
	1. Introduction		1. 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 necessarily incurring packet loss.		of incipient congestion without necessarily incurring packet loss.
	This lets the network deliver some packets to an application that		This lets the network deliver some packets to an application that
	would have been dropped if the application or transport did not		would have been dropped if the application or transport did not
	support ECN. This packet loss reduction is the most obvious benefit		support ECN. This packet loss reduction is the most obvious benefit
	of ECN, but it is often relatively modest. Other benefits of		of ECN, but it is often relatively modest. Other benefits of
	skipping to change at page 3, line 19 ¶		skipping to change at page 3, line 19 ¶
	[RFC3168]. Research has demonstrated the benefits of reducing		[RFC3168]. Research has demonstrated the benefits of reducing
	network delays that are caused by interaction of loss-based TCP		network delays that are caused by interaction of loss-based TCP
	congestion control and excessive buffering [BUFFERBLOAT]. This has		congestion control and excessive buffering [BUFFERBLOAT]. This has
	led to the creation of AQM mechanisms like PIE [RFC8033] and CoDel		led to the creation of AQM mechanisms like PIE [RFC8033] and CoDel
	[CODEL2012][RFC8289], which prevent bloated queues that are common		[CODEL2012][RFC8289], 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].
	The AQM mechanisms mentioned above aim to keep a sustained queue		The AQM mechanisms mentioned above aim to keep a sustained queue
	short while tolerating transient (short-term) packet bursts.		short while tolerating transient (short-term) packet bursts.
	However, currently used loss-based congestion control mechanisms		However, currently used loss-based congestion control mechanisms are
	cannot always utilise a bottleneck link well where there are short		not always able to effectively utilise a bottleneck link where there
	queues. For example, a TCP sender using the Reno congestion control		are short queues. For example, a TCP sender using the Reno
	needs to be able to store at least an end-to-end bandwidth-delay		congestion control needs to be able to store at least an end-to-end
	product (BDP) worth of data at the bottleneck buffer if it is to		bandwidth-delay product (BDP) worth of data at the bottleneck buffer
	maintain full path utilisation in the face of loss-induced reduction		if it is to maintain full path utilisation in the face of loss-
	of the congestion window (cwnd) [RFC5681], which effectively doubles		induced reduction of the congestion window (cwnd) [RFC5681], which
	the amount of data that can be in flight, the maximum round-trip time		effectively doubles the amount of data that can be in flight, the
	(RTT) experience, and the path's effective RTT using the network		maximum round-trip time (RTT) experience, and the path's effective
	path.		RTT using the network path.
	Modern AQM mechanisms can use ECN to signal the early signs of		Modern AQM mechanisms can use ECN to signal the early signs of
	impending queue buildup long before a tail-drop queue would be forced		impending queue buildup long before a tail-drop queue would be forced
	to resort to dropping packets. It is therefore appropriate for the		to resort to dropping packets. It is therefore appropriate for the
	transport protocol congestion control algorithm to have a more		transport protocol congestion control algorithm to have a more
	measured response when it receives an indication with an early-		measured response when it receives an indication with an early-
	warning of congestion after the remote endpoint receives an ECN CE-		warning of congestion after the remote endpoint receives an ECN CE-
	marked packet. Recognizing these changes in modern AQM practices,		marked packet. Recognizing these changes in modern AQM practices,
	the strict requirement that ECN CE signals be treated identically to		the strict requirement that ECN CE signals be treated identically to
	inferred packet loss have been relaxed [RFC8311]. This document		inferred packet loss have been relaxed [RFC8311]. This document
	therefore defines a new sender-side-only congestion control response,		therefore defines a new sender-side-only congestion control response,
	called "ABE" (Alternative Backoff with ECN). ABE improves TCP's		called "ABE" (Alternative Backoff with ECN). ABE improves TCP's
	average throughput when routers use AQM controlled buffers that allow		average throughput when routers use AQM controlled buffers that allow
	for short queues only.		only for short queues.
	2. Definitions		2. 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][RFC8174] .
	3. Specification		3. Specification
	This specification changes the congestion control algorithm of an		This specification changes the congestion control algorithm of an
	ECN-Capable TCP transport protocol by changing the TCP sender		ECN-Capable TCP transport protocol by changing the TCP sender
	response to feedback from the TCP receiver that indicates reception		response to feedback from the TCP receiver that indicates reception
	of a CE-marked packet, i.e., receipt of a packet with the ECN-Echo		of a CE-marked packet, i.e., receipt of a packet with the ECN-Echo
	flag (defined in [RFC3168]) set, following the process defined in		flag (defined in [RFC3168]) set, following the process defined in
	[RFC8311].		[RFC8311].
	The TCP sender response is currently specified in section 6.1.2 of		The TCP sender response is currently specified in section 6.1.2 of
	the ECN specification [RFC3168], updated by [RFC8311]:		the ECN specification [RFC3168], updated by [RFC8311]:
	The indication of congestion should be treated just as a		The indication of congestion should be treated just as a
	congestion loss in non-ECN-Capable TCP. That is, the TCP source		congestion loss in non-ECN-Capable TCP. That is, the TCP source
	halves the congestion window "cwnd" and reduces the slow start		halves the congestion window "cwnd" and reduces the slow start
	threshold "ssthresh", unless otherwise specified by an		threshold "ssthresh", unless otherwise specified by an
	Experimental RFC in the IETF document stream.		Experimental RFC in the IETF document stream.
	Following publication of RFC8311, this document specifies a sender-		Following publication of RFC 8311, this document specifies a sender-
	side change to TCP:		side change to TCP:
	Receipt of a packet with the ECN-Echo flag SHOULD trigger the TCP		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		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.		FlightSize, with a lower bound of 2 * SMSS applied to the result.
	As in [RFC5681], the TCP sender also reduces the cwnd value to no		As in [RFC5681], the TCP sender also reduces the cwnd value to no
	more than the new ssthresh value. RFC 3168 section 6.1.2 provides		more than the new ssthresh value. RFC 3168 section 6.1.2 provides
	guidance on setting a cwnd less than 2 * SMSS.		guidance on setting a cwnd less than 2 * SMSS.
	3.1. Choice of ABE Multiplier		3.1. Choice of ABE Multiplier
	skipping to change at page 8, line 7 ¶		skipping to change at page 8, line 7 ¶
	packet loss indications, an ECN-Capable bottleneck will still fall		packet loss indications, an ECN-Capable bottleneck will still fall
	back to dropping packets if an TCP sender using ABE is too		back to dropping packets if an TCP sender using ABE is too
	aggressive, and the result is no different than if the TCP sender was		aggressive, and the result is no different than if the TCP sender was
	using traditional loss-based congestion control.		using traditional loss-based 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.
	6. ABE Experiment Goals		6. ABE Experiment Goals
	RFC3168 states that the congestion control response following an		[RFC3168] states that the congestion control response following an
	indication of ECN-signalled congestion is the same as the response to		indication of ECN-signalled congestion is the same as the response to
	a dropped packet [RFC3168]. [RFC8311] updates this specification to		a dropped packet. [RFC8311] updates this specification to allow
	allow systems to provide a different behaviour when they experience		systems to provide a different behaviour when they experience ECN-
	ECN-signalled congestion rather than packet loss. The present		signalled congestion rather than packet loss. The present
	specification defines such an experiment and has thus been assigned		specification defines such an experiment and has thus been assigned
	an Experimental status before being proposed as a Standards-Track		an Experimental status before being proposed as a Standards-Track
	update.		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 acceptable safety in deployed networks		deployment of ABE, and confirm acceptable safety in deployed networks
	that use this update to TCP congestion control. To evaluate ABE,		that use this update to TCP congestion control. To evaluate ABE,
	this experiment therefore requires support in AQM routers for ECN-		this experiment therefore requires support in AQM routers for ECN-
	marking of packets carrying the ECN-Capable Transport, ECT(0),		marking of packets carrying the ECN-Capable Transport, ECT(0),
	codepoint [RFC3168].		codepoint [RFC3168].
	The result of this Internet experiment ought to include an		The result of this Internet experiment ought to include an
	investigation of the implications of experiencing an ECN-CE mark		investigation of the implications of experiencing an ECN-CE mark
	followed by loss within the same RTT. At the end of the experiment,		followed by loss within the same RTT. At the end of the experiment,
	this will be reported to the TCPM WG or IESG.		this will be reported to the TCPM WG or the IESG.
	7. Acknowledgements		7. 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.
	Author G. Armitage performed most of his work on this document while		Author G. Armitage performed most of his work on this document while
	employed by Swinburne University of Technology, Melbourne, Australia.		employed by Swinburne University of Technology, Melbourne, Australia.
	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)
	Roland Bless, Bob Briscoe, David Black, Markku Kojo, John Leslie,		Roland Bless, Bob Briscoe, David Black, Markku Kojo, John Leslie,
	Lawrence Stewart, Dave Taht and the TCPM working group for providing		Lawrence Stewart, Dave Taht and the TCPM Working Group for providing
	valuable feedback on this document.		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).
	8. IANA Considerations		8. IANA Considerations
	XX RFC ED - PLEASE REMOVE THIS SECTION XXX		XX RFC ED - PLEASE REMOVE THIS SECTION XXX
	This document includes no request to IANA.		This document includes no request to IANA.
	9. Implementation Status		9. Implementation Status
	ABE is implemented as a patch for Linux and FreeBSD. It is meant for		ABE is implemented as a patch for Linux and FreeBSD. This is meant
	research and available for download from		for research and available for download from
	http://heim.ifi.uio.no/naeemk/research/ABE/. This code was used to		http://heim.ifi.uio.no/michawe/research/abe/. This code was used to
	produce the test results that are reported in [ABE2017]. The FreeBSD		produce the test results that are reported in [ABE2017]. The FreeBSD
	code has been committed to the mainline kernel on March 19, 2018		code has been committed to the mainline kernel on March 19, 2018
	[ABE-FreeBSD].		[ABE-FreeBSD].
	10. Security Considerations		10. Security Considerations
	The described method is a sender-side only transport change, and does		The described method is a sender-side only transport change, and does
	not change the protocol messages exchanged. The security		not change the protocol messages exchanged. The security
	considerations for ECN [RFC3168] therefore still apply.		considerations for ECN [RFC3168] therefore still apply.
	skipping to change at page 9, line 41 ¶		skipping to change at page 9, line 41 ¶
	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 [RFC8312]). Unfairness may also be a result of other		(e.g., CUBIC [RFC8312]). 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.
	11. Revision Information		11. Revision Information
	XX RFC ED - PLEASE REMOVE THIS SECTION XXX		XX RFC ED - PLEASE REMOVE THIS SECTION XXX
	-09. Chnaged to "Following publication of RFC8311, this document		-10. Incorported changes following the Gen-ART review by Russ
			Housley. Correction to URL.
			-09. Changed to "Following publication of RFC 8311, this document
	specifies a sender-side change to TCP:"		specifies a sender-side change to TCP:"
	-08. Addressed comments from AD review on the document structure,		-08. Addressed comments from AD review on the document structure,
	and relationship to existing RFCs.		and relationship to existing RFCs.
	-07. Addressed comments following WGLC.		-07. Addressed comments following WGLC.
	o Updated Reference citations.		o Updated Reference citations.
	o Removed paragraph containing a wrong statement related to timeout		o Removed paragraph containing a wrong statement related to timeout
	skipping to change at page 10, line 43 ¶		skipping to change at page 10, line 46 ¶
	technical language and clarification on the intended purpose of the		technical language and clarification on the intended purpose of the
	experiments required by EXP status. There was no change to the		experiments required by EXP status. There was no change to the
	technical content.		technical content.
	-00. draft-ietf-tcpm-alternativebackoff-ecn-00 replaces draft-		-00. draft-ietf-tcpm-alternativebackoff-ecn-00 replaces draft-
	khademi-tcpm-alternativebackoff-ecn-01. Text describing the nature		khademi-tcpm-alternativebackoff-ecn-01. Text describing the nature
	of the experiment was added.		of the experiment was added.
	Individual draft -01. This I-D now refers to draft-black-tsvwg-ecn-		Individual draft -01. This I-D now refers to draft-black-tsvwg-ecn-
	experimentation-02, which replaces draft-khademi-tsvwg-ecn-		experimentation-02, which replaces draft-khademi-tsvwg-ecn-
	response-00 to make a broader update to RFC3168 for the sake of		response-00 to make a broader update to RFC 3168 for the sake of
	allowing experiments. As a result, some of the motivating and		allowing experiments. As a result, some of the motivating and
	discussing text that was moved from draft-khademi-alternativebackoff-		discussing text that was moved from draft-khademi-alternativebackoff-
	ecn-03 to draft-khademi-tsvwg-ecn-response-00 has now been re-		ecn-03 to draft-khademi-tsvwg-ecn-response-00 has now been re-
	inserted here.		inserted here.
	Individual draft -00. draft-khademi-tsvwg-ecn-response-00 and draft-		Individual draft -00. draft-khademi-tsvwg-ecn-response-00 and draft-
	khademi-tcpm-alternativebackoff-ecn-00 replace draft-khademi-		khademi-tcpm-alternativebackoff-ecn-00 replace draft-khademi-
	alternativebackoff-ecn-03, following discussion in the TSVWG and TCPM		alternativebackoff-ecn-03, following discussion in the TSVWG and TCPM
	working groups.		working groups.
	skipping to change at page 11, line 28 ¶		skipping to change at page 11, line 33 ¶
	[RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion		[RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
	Control", RFC 5681, DOI 10.17487/RFC5681, September 2009,		Control", RFC 5681, DOI 10.17487/RFC5681, September 2009,
	<https://www.rfc-editor.org/info/rfc5681>.		<https://www.rfc-editor.org/info/rfc5681>.
	[RFC7567] Baker, F., Ed. and G. Fairhurst, Ed., "IETF		[RFC7567] Baker, F., Ed. and G. Fairhurst, Ed., "IETF
	Recommendations Regarding Active Queue Management",		Recommendations Regarding Active Queue Management",
	BCP 197, RFC 7567, DOI 10.17487/RFC7567, July 2015,		BCP 197, RFC 7567, DOI 10.17487/RFC7567, July 2015,
	<https://www.rfc-editor.org/info/rfc7567>.		<https://www.rfc-editor.org/info/rfc7567>.
			[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
			2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
			May 2017, <https://www.rfc-editor.org/info/rfc8174>.
	[RFC8257] Bensley, S., Thaler, D., Balasubramanian, P., Eggert, L.,		[RFC8257] Bensley, S., Thaler, D., Balasubramanian, P., Eggert, L.,
	and G. Judd, "Data Center TCP (DCTCP): TCP Congestion		and G. Judd, "Data Center TCP (DCTCP): TCP Congestion
	Control for Data Centers", RFC 8257, DOI 10.17487/RFC8257,		Control for Data Centers", RFC 8257, DOI 10.17487/RFC8257,
	October 2017, <https://www.rfc-editor.org/info/rfc8257>.		October 2017, <https://www.rfc-editor.org/info/rfc8257>.
	[RFC8311] Black, D., "Relaxing Restrictions on Explicit Congestion		[RFC8311] Black, D., "Relaxing Restrictions on Explicit Congestion
	Notification (ECN) Experimentation", RFC 8311,		Notification (ECN) Experimentation", RFC 8311,
	DOI 10.17487/RFC8311, January 2018,		DOI 10.17487/RFC8311, January 2018,
	<https://www.rfc-editor.org/info/rfc8311>.		<https://www.rfc-editor.org/info/rfc8311>.
End of changes. 17 change blocks.
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