< draft-irtf-nwcrg-coding-and-congestion-09.txt		draft-irtf-nwcrg-coding-and-congestion-10.txt >
	NWCRG N. Kuhn		NWCRG N. Kuhn
	Internet-Draft CNES		Internet-Draft CNES
	Intended status: Informational E. Lochin		Intended status: Informational E. Lochin
	Expires: December 27, 2021 ENAC		Expires: July 19, 2022 ENAC
	F. Michel		F. Michel
	UCLouvain		UCLouvain
	M. Welzl		M. Welzl
	University of Oslo		University of Oslo
	June 25, 2021		January 15, 2022
	Coding and congestion control in transport		Coding and congestion control in transport
	draft-irtf-nwcrg-coding-and-congestion-09		draft-irtf-nwcrg-coding-and-congestion-10
	Abstract		Abstract
	Forward Erasure Correction (FEC) is a reliability mechanism that is		Forward Erasure Correction (FEC) is a reliability mechanism that is
	distinct and separate from the retransmission logic in reliable		distinct and separate from the retransmission logic in reliable
	transfer protocols such as TCP. FEC coding can help deal with losses		transfer protocols such as TCP. FEC coding can help deal with losses
	at the end of transfers or with networks having non-congestion		at the end of transfers or with networks having non-congestion
	losses. However, FEC coding mechanisms should not hide congestion		losses. However, FEC coding mechanisms should not hide congestion
	signals. This memo offers a discussion of how FEC coding and		signals. This memo offers a discussion of how FEC coding and
	congestion control can coexist. Another objective is to encourage		congestion control can coexist. Another objective is to encourage
	skipping to change at page 1, line 49 ¶		skipping to change at page 1, line 49 ¶
	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
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	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 December 27, 2021.		This Internet-Draft will expire on July 19, 2022.
	Copyright Notice		Copyright Notice
	Copyright (c) 2021 IETF Trust and the persons identified as the		Copyright (c) 2022 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
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	skipping to change at page 2, line 43 ¶		skipping to change at page 2, line 43 ¶
	3.2. Congestion control and recovered symbols . . . . . . . . 11		3.2. Congestion control and recovered symbols . . . . . . . . 11
	3.3. Interactions between congestion control and coding rates 11		3.3. Interactions between congestion control and coding rates 11
	3.4. On useless repair symbols . . . . . . . . . . . . . . . . 11		3.4. On useless repair symbols . . . . . . . . . . . . . . . . 11
	3.5. On partial ordering . . . . . . . . . . . . . . . . . . . 11		3.5. On partial ordering . . . . . . . . . . . . . . . . . . . 11
	3.6. On partial reliability . . . . . . . . . . . . . . . . . 12		3.6. On partial reliability . . . . . . . . . . . . . . . . . 12
	3.7. On multipath transport . . . . . . . . . . . . . . . . . 12		3.7. On multipath transport . . . . . . . . . . . . . . . . . 12
	4. FEC within the transport . . . . . . . . . . . . . . . . . . 12		4. FEC within the transport . . . . . . . . . . . . . . . . . . 12
	4.1. Fairness and impact on non-coded flows . . . . . . . . . 13		4.1. Fairness and impact on non-coded flows . . . . . . . . . 13
	4.2. Congestion control and recovered symbols . . . . . . . . 13		4.2. Congestion control and recovered symbols . . . . . . . . 13
	4.3. Interactions between congestion control and coding rates 13		4.3. Interactions between congestion control and coding rates 13
	4.4. On useless repair symbols . . . . . . . . . . . . . . . . 13		4.4. On useless repair symbols . . . . . . . . . . . . . . . . 14
	4.5. On partial ordering . . . . . . . . . . . . . . . . . . . 14		4.5. On partial ordering . . . . . . . . . . . . . . . . . . . 14
	4.6. On partial reliability . . . . . . . . . . . . . . . . . 14		4.6. On partial reliability . . . . . . . . . . . . . . . . . 14
	4.7. On transport multipath . . . . . . . . . . . . . . . . . 14		4.7. On transport multipath . . . . . . . . . . . . . . . . . 14
	5. FEC below the transport . . . . . . . . . . . . . . . . . . . 14		5. FEC below the transport . . . . . . . . . . . . . . . . . . . 14
	5.1. Fairness and impact on non-coded flows . . . . . . . . . 15		5.1. Fairness and impact on non-coded flows . . . . . . . . . 16
	5.2. Congestion control and recovered symbols . . . . . . . . 16		5.2. Congestion control and recovered symbols . . . . . . . . 16
	5.3. Interactions between congestion control and coding rates 16		5.3. Interactions between congestion control and coding rates 16
	5.4. On useless repair symbols . . . . . . . . . . . . . . . . 16		5.4. On useless repair symbols . . . . . . . . . . . . . . . . 16
	5.5. On partial ordering . . . . . . . . . . . . . . . . . . . 16		5.5. On partial ordering . . . . . . . . . . . . . . . . . . . 17
	5.6. On partial reliability . . . . . . . . . . . . . . . . . 16		5.6. On partial reliability . . . . . . . . . . . . . . . . . 17
	5.7. On transport multipath . . . . . . . . . . . . . . . . . 16		5.7. On transport multipath . . . . . . . . . . . . . . . . . 17
	6. Research recommendations and questions . . . . . . . . . . . 17		6. Research recommendations and questions . . . . . . . . . . . 17
	6.1. Activities related to congestion control and coding . . . 17		6.1. Activities related to congestion control and coding . . . 17
	6.2. Open research questions . . . . . . . . . . . . . . . . . 17		6.2. Open research questions . . . . . . . . . . . . . . . . . 18
	6.2.1. Parameter derivation . . . . . . . . . . . . . . . . 17		6.2.1. Parameter derivation . . . . . . . . . . . . . . . . 18
	6.2.2. New signaling methods and fairness . . . . . . . . . 18		6.2.2. New signaling methods and fairness . . . . . . . . . 18
	6.3. Recommendations and advice for evaluating coding		6.3. Recommendations and advice for evaluating coding
	mechanisms . . . . . . . . . . . . . . . . . . . . . . . 18		mechanisms . . . . . . . . . . . . . . . . . . . . . . . 19
	7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19		7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 19		9. Security Considerations . . . . . . . . . . . . . . . . . . . 19
	10. Informative References . . . . . . . . . . . . . . . . . . . 19		10. Informative References . . . . . . . . . . . . . . . . . . . 20
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
	1. Introduction		1. Introduction
	There are cases where deploying FEC coding improves the performance		There are cases where deploying FEC coding improves the performance
	of a transmission. As an example, it may take time for a sender to		of a transmission. As an example, it may take time for a sender to
	detect transfer tail losses (losses that occur at the end of a		detect transfer tail losses (losses that occur at the end of a
	transfer, where, e.g., TCP obtains no more ACKs that would enable it		transfer, where, e.g., TCP obtains no more ACKs that would enable it
	to quickly repair the loss via retransmission). Allowing the		to quickly repair the loss via retransmission). Allowing the
	receiver to recover such losses instead of having to rely on a		receiver to recover such losses instead of having to rely on a
	retransmission could improve the experience of applications using		retransmission could improve the experience of applications using
	skipping to change at page 12, line 45 ¶		skipping to change at page 12, line 45 ¶
	Figure 7: FEC in the transport		Figure 7: FEC in the transport
	Figure 7 presents an architecture where FEC operates within the		Figure 7 presents an architecture where FEC operates within the
	transport. The repair symbols are sent within what the congestion		transport. The repair symbols are sent within what the congestion
	window or calculated rate allows, such as in [CTCP].		window or calculated rate allows, such as in [CTCP].
	The advantage of this approach is that it allows a joint optimization		The advantage of this approach is that it allows a joint optimization
	of CC and FEC. Moreover, the transmission of repair symbols does not		of CC and FEC. Moreover, the transmission of repair symbols does not
	add congestion in potentially congested networks but helps repair		add congestion in potentially congested networks but helps repair
	lost packets (such as tail losses).		lost packets (such as tail losses). This joint optimization is the
			key to prevent flows to consume the whole available capacity. The
			amount of repair traffic injected should not lead to congestion. As
			denoted in [I-D.singh-rmcat-adaptive-fec], an increase of the repair
			ratio should be done conjointly with a decrease of the source sending
			rate.
	For reliable transfers, including redundancy reduces goodput for long		For reliable transfers, including redundancy reduces goodput for long
	transfers but the amount of repair symbols can be adapted, e.g.		transfers but the amount of repair symbols can be adapted, e.g.
	depending on the congestion window size. There is a trade-off		depending on the congestion window size. There is a trade-off
	between 1) the capacity that could have been exploited by application		between 1) the capacity that could have been exploited by application
	data instead of transmitting source packets, and 2) the benefits		data instead of transmitting source packets, and 2) the benefits
	derived from transmitting repair symbols (e.g. unlocking the receive		derived from transmitting repair symbols (e.g. unlocking the receive
	buffer if it is limiting). The coding ratio needs to be carefully		buffer if it is limiting). The coding ratio needs to be carefully
	designed. For small files, sending repair symbols when there is no		designed. For small files, sending repair symbols when there is no
	more data to transmit could help to reduce the transfer time.		more data to transmit could help to reduce the transfer time.
	skipping to change at page 19, line 51 ¶		skipping to change at page 20, line 29 ¶
	arXiv 1212.2291v3, 2013.		arXiv 1212.2291v3, 2013.
	[I-D.briscoe-tsvarea-fair]		[I-D.briscoe-tsvarea-fair]
	Briscoe, B., "Flow Rate Fairness: Dismantling a Religion",		Briscoe, B., "Flow Rate Fairness: Dismantling a Religion",
	draft-briscoe-tsvarea-fair-02 (work in progress), July		draft-briscoe-tsvarea-fair-02 (work in progress), July
	2007.		2007.
	[I-D.detchart-nwcrg-tetrys]		[I-D.detchart-nwcrg-tetrys]
	Detchart, J., Lochin, E., Lacan, J., and V. Roca, "Tetrys,		Detchart, J., Lochin, E., Lacan, J., and V. Roca, "Tetrys,
	an On-the-Fly Network Coding protocol", draft-detchart-		an On-the-Fly Network Coding protocol", draft-detchart-
	nwcrg-tetrys-06 (work in progress), December 2020.		nwcrg-tetrys-08 (work in progress), October 2021.
	[I-D.ietf-quic-datagram]		[I-D.ietf-quic-datagram]
	Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable		Pauly, T., Kinnear, E., and D. Schinazi, "An Unreliable
	Datagram Extension to QUIC", draft-ietf-quic-datagram-02		Datagram Extension to QUIC", draft-ietf-quic-datagram-07
	(work in progress), February 2021.		(work in progress), December 2021.
			[I-D.singh-rmcat-adaptive-fec]
			Singh, V., Nagy, M., Ott, J., and L. Eggert, "Congestion
			Control Using FEC for Conversational Media", draft-singh-
			rmcat-adaptive-fec-03 (work in progress), March 2016.
	[I-D.swett-nwcrg-coding-for-quic]		[I-D.swett-nwcrg-coding-for-quic]
	Swett, I., Montpetit, M., Roca, V., and F. Michel, "Coding		Swett, I., Montpetit, M., Roca, V., and F. Michel, "Coding
	for QUIC", draft-swett-nwcrg-coding-for-quic-04 (work in		for QUIC", draft-swett-nwcrg-coding-for-quic-04 (work in
	progress), March 2020.		progress), March 2020.
	[NCTCP] Sundararajan (et al.), J., "Network Coding Meets TCP:		[NCTCP] Sundararajan (et al.), J., "Network Coding Meets TCP:
	Theory and Implementation", IEEE		Theory and Implementation", IEEE
	INFOCOM 10.1109/JPROC.2010.2093850, 2009.		INFOCOM 10.1109/JPROC.2010.2093850, 2009.
	skipping to change at page 21, line 40 ¶		skipping to change at page 22, line 27 ¶
	January 2020, <https://www.rfc-editor.org/info/rfc8699>.		January 2020, <https://www.rfc-editor.org/info/rfc8699>.
	[TENTET] Lochin, E., "On the joint use of TCP and Network Coding",		[TENTET] Lochin, E., "On the joint use of TCP and Network Coding",
	NWCRG session IETF 100, 2017.		NWCRG session IETF 100, 2017.
	Authors' Addresses		Authors' Addresses
	Nicolas Kuhn		Nicolas Kuhn
	CNES		CNES
	Email: nicolas.kuhn@cnes.fr		Email: nicolas.kuhn@ietf.gmail.com
	Emmanuel Lochin		Emmanuel Lochin
	ENAC		ENAC
	Email: emmanuel.lochin@enac.fr		Email: emmanuel.lochin@enac.fr
	Francois Michel		Francois Michel
	UCLouvain		UCLouvain
	Email: francois.michel@uclouvain.be		Email: francois.michel@uclouvain.be
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