< draft-gomez-tcpm-ack-rate-request-01.txt		draft-gomez-tcpm-ack-rate-request-02.txt >
	TCPM Working Group C. Gomez		TCPM Working Group C. Gomez
	Internet-Draft UPC		Internet-Draft UPC
	Intended status: Experimental J. Crowcroft		Intended status: Experimental J. Crowcroft
	Expires: May 4, 2021 University of Cambridge		Expires: August 23, 2021 University of Cambridge
	October 31, 2020		February 19, 2021
	TCP ACK Rate Request Option		TCP ACK Rate Request Option
	draft-gomez-tcpm-ack-rate-request-01		draft-gomez-tcpm-ack-rate-request-02
	Abstract		Abstract
	TCP Delayed Acknowledgments (ACKs) is a widely deployed mechanism		TCP Delayed Acknowledgments (ACKs) is a widely deployed mechanism
	that allows reducing protocol overhead in many scenarios. However,		that allows reducing protocol overhead in many scenarios. However,
	Delayed ACKs may also contribute to suboptimal performance. When a		Delayed ACKs may also contribute to suboptimal performance. When a
	relatively large congestion window (cwnd) can be used, less frequent		relatively large congestion window (cwnd) can be used, less frequent
	ACKs may be desirable. On the other hand, in relatively small cwnd		ACKs may be desirable. On the other hand, in relatively small cwnd
	scenarios, eliciting an immediate ACK may avoid unnecessary delays		scenarios, eliciting an immediate ACK may avoid unnecessary delays
	that may be incurred by the Delayed ACKs mechanism. This document		that may be incurred by the Delayed ACKs mechanism. This document
	skipping to change at page 1, line 40 ¶		skipping to change at page 1, line 40 ¶
	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 May 4, 2021.		This Internet-Draft will expire on August 23, 2021.
	Copyright Notice		Copyright Notice
	Copyright (c) 2020 IETF Trust and the persons identified as the		Copyright (c) 2021 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 20 ¶		skipping to change at page 2, line 20 ¶
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Conventions used in this document . . . . . . . . . . . . . . 3		2. Conventions used in this document . . . . . . . . . . . . . . 3
	3. TCP ACK Rate Request Functionality . . . . . . . . . . . . . 4		3. TCP ACK Rate Request Functionality . . . . . . . . . . . . . 4
	3.1. Sender behavior . . . . . . . . . . . . . . . . . . . . . 4		3.1. Sender behavior . . . . . . . . . . . . . . . . . . . . . 4
	3.2. Receiver behavior . . . . . . . . . . . . . . . . . . . . 4		3.2. Receiver behavior . . . . . . . . . . . . . . . . . . . . 4
	4. Option Format . . . . . . . . . . . . . . . . . . . . . . . . 5		4. Option Format . . . . . . . . . . . . . . . . . . . . . . . . 5
	5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6		5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 6		6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6		7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6		8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
	8.1. Normative References . . . . . . . . . . . . . . . . . . 6		8.1. Normative References . . . . . . . . . . . . . . . . . . 7
	8.2. Informative References . . . . . . . . . . . . . . . . . 7		8.2. Informative References . . . . . . . . . . . . . . . . . 8
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
	1. Introduction		1. Introduction
	Delayed Acknowledgments (ACKs) were specified for TCP with the aim to		Delayed Acknowledgments (ACKs) were specified for TCP with the aim to
	reduce protocol overhead [RFC1122]. With Delayed ACKs, a TCP delays		reduce protocol overhead [RFC1122]. With Delayed ACKs, a TCP delays
	sending an ACK by up to 500 ms (often 200 ms, with lower values in		sending an ACK by up to 500 ms (often 200 ms, with lower values in
	recent implementations such as ~50 ms also reported), and typically		recent implementations such as ~50 ms also reported), and typically
	sends an ACK for at least every second segment received in a stream		sends an ACK for at least every second segment received in a stream
	of full-sized segments. This allows combining several segments into		of full-sized segments. This allows combining several segments into
	a single one (e.g. the application layer response to an application		a single one (e.g. the application layer response to an application
	skipping to change at page 4, line 8 ¶		skipping to change at page 4, line 8 ¶
	2. Conventions used in this document		2. Conventions used in this document
	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 [RFC2119].		document are to be interpreted as described in [RFC2119].
	3. TCP ACK Rate Request Functionality		3. TCP ACK Rate Request Functionality
	A TCP endpoint announces that it supports the TARR option by		A TCP endpoint announces that it supports the TARR option by
	including the TARR option format in packets that have the SYN bit		including the TARR option format format (with the appropriate Length
	set. In such packets, the values carried by the TARR option format		value, see Section 4) in packets that have the SYN bit set.
	other than Kind, Length and ExID MUST be ignored by the receiving
	TCP.
	TBD1: perhaps two formats (with one codepoint each), a shorter one
	just to advertise that TARR is supported, and a larger one which is
	the current TARR option format defined in section 4?
	The next two subsections define the sender and receiver behaviors for		The next two subsections define the sender and receiver behaviors for
	devices that support the TARR option, respectively.		devices that support the TARR option, respectively.
	3.1. Sender behavior		3.1. Sender behavior
	A TCP sender MUST NOT include the TARR option in TCP data segments to		A TCP sender MUST NOT include the TARR option in TCP data segments to
	be sent if the TCP receiver does not support the TARR option.		be sent if the TCP receiver does not support the TARR option.
	A TCP sender MAY request a TARR-option-capable receiver to modify the		A TCP sender MAY request a TARR-option-capable receiver to modify the
	skipping to change at page 5, line 9 ¶		skipping to change at page 4, line 52 ¶
	option present in a received data segment.		option present in a received data segment.
	When the TARR option of a received segment carries an R value		When the TARR option of a received segment carries an R value
	different from zero, a TARR-option-capable receiving TCP MUST modify		different from zero, a TARR-option-capable receiving TCP MUST modify
	its ACK rate to one ACK every R full-sized received data segments		its ACK rate to one ACK every R full-sized received data segments
	from the sender, as long as packet reordering does not occur. When R		from the sender, as long as packet reordering does not occur. When R
	is different from zero, the receiving TCP MUST ignore the N field of		is different from zero, the receiving TCP MUST ignore the N field of
	the TARR option.		the TARR option.
	A TARR-option-capable TCP that receives a TARR option with the Ignore		A TARR-option-capable TCP that receives a TARR option with the Ignore
	Order field set to True (see Section 4), MUST NOT send an ACK after		Order (I) field set to True (see Section 4), MUST NOT send an ACK
	each reordered data segment. Instead, it MUST continue to send one		after each reordered data segment. Instead, it MUST continue to send
	ACK every R received data segments. Otherwise (i.e., Ignore Order =		one ACK every R received data segments. Otherwise (i.e., Ignore
	False), such a receiver will need to send an ACK after each reordered		Order = False), such a receiver will need to send an ACK after each
	data segment received.		reordered data segment received.
	If a TARR-option-capable TCP receives a segment carrying the TARR		If a TARR-option-capable TCP receives a segment carrying the TARR
	option with R=0, the receiving TCP MUST send an ACK immediately, and		option with R=0, the receiving TCP MUST send an ACK immediately, and
	it MUST also send an ACK immediately after each one of the N next		it MUST also send an ACK immediately after each one of the N next
	consecutive segments to be received. N refers to the corresponding		consecutive segments to be received. N refers to the corresponding
	field in the TARR option of the received segment (see Section 4).		field in the TARR option of the received segment (see Section 4).
	4. Option Format		4. Option Format
	The TARR option has the format and content shown in Fig. 1.		The TARR option presents two different formats that can be identified
			by the corresponding format length. For packets that have the SYN
			bit set, the TARR option has the format shown in Fig. 1.
	0 1 2 3		0 1 2 3
	01234567 89012345 67890123 45678901		0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
	+--------+--------+--------+--------+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| Kind | Length | ExID |		| Kind | Length | ExID |
	+--------+--------+--------+--------+		+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
	| R | IgnOrd | N |
	+--------+--------+--------+
	Figure 1: TCP ACK Rate Request option format.		Figure 1: TCP ACK Rate Request option format for packets that have
			the SYN bit set.
	Kind: The Kind field value is TBD.		Kind: The Kind field value is TBD.
	Length: The Length field value is 7 bytes.		Length: The Length field value is 4 bytes.
	ExID: The experiment ID field size is 2 bytes, and its value is		ExID: The experiment ID field size is 2 bytes, and its value is
	0x00AC.		0x00AC.
	R: The size of this field is 1 byte. If all bits of this field are		For packets that do not have the SYN bit set, the TARR option has the
			format and content shown in Fig. 2.
			0 1 2 3
			0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			| Kind | Length | ExID |
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			| R |I| N |
			+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
			Figure 2: TCP ACK Rate Request option format.
			Kind: The Kind field value is TBD.
			Length: The Length field value is 6 bytes.
			ExID: The experiment ID field size is 2 bytes, and its value is
			0x00AC.
			R: The size of this field is 7 bits. If all bits of this field are
	set to 0, the field indicates a request by the sender for the		set to 0, the field indicates a request by the sender for the
	receiver to trigger one or more ACKs immediately. Otherwise, the		receiver to trigger one or more ACKs immediately. Otherwise, the
	field carries the binary encoding of the number of full-sized		field carries the binary encoding of the number of full-sized
	segments received after which the receiver is requested by the sender		segments received after which the receiver is requested by the sender
	to send an ACK.		to send an ACK.
	Ignore Order: The size of this field is 1 byte. This field MUST have		Ignore Order (I): The size of this field is 1 bit. This field either
	the value 0x01 ("True") or 0x00 ("False"). When this field is set to		has the value 1 ("True") or 0 ("False"). When this field is set to
	True, the receiver MUST NOT send an ACK after each reordered data		True, the receiver MUST NOT send an ACK after each reordered data
	segment. Instead, it MUST continue to send one ACK every R received		segment. Instead, it MUST continue to send one ACK every R received
	data segments.		data segments.
	TBD2: perhaps 7 bits for R and 1 bit for Ignore Order?
	N: The size of this field is 1 byte. When R=0, the N field indicates		N: The size of this field is 1 byte. When R=0, the N field indicates
	the number of subsequent consecutive data segments to be sent for		the number of subsequent consecutive data segments to be sent for
	which immediate ACKs are requested by the sender.		which immediate ACKs are requested by the sender.
	5. IANA Considerations		5. IANA Considerations
	This document specifies a new TCP option (TCP ACK Rate Request) that		This document specifies a new TCP option (TCP ACK Rate Request) that
	uses the shared experimental options format [RFC6994], with ExID in		uses the shared experimental options format [RFC6994], with ExID in
	network-standard byte order.		network-standard byte order.
	The authors plan to request the allocation of ExID value 0x00AC for		The authors plan to request the allocation of ExID value 0x00AC for
	the TCP option specified in this document.		the TCP option specified in this document.
	6. Security Considerations		6. Security Considerations
	TBD		The TARR option opens the door to new security threats. This section
			discusses such new threats, and suggests mitigation techniques.
			An attacker might be able to impersonate a legitimate sender, and
			forge an apparently valid packet intended for the receiver, in order
			to intentionally communicate a bad R value to the latter with the aim
			to damage communication or device performance. For example, in a
			small cwnd scenario, using a too high R value may lead to exacerbated
			RTT increase and throughput decrease. In other scenarios, a too low
			R value may contribute to depleting the energy of a battery-operated
			receiver at a faster rate or may lead to increased network packet
			load.
			While Transport Layer Security (TLS) [RFC8446] is strongly
			recommended for securing TCP-based communication, TLS does not
			protect TCP headers, and thus cannot protect the TARR option fields
			carried by a segment. One approach to address the problem is using
			network-layer protection, such as Internet Protocol Security (IPsec)
			[RFC4301].
	7. Acknowledgments		7. Acknowledgments
	Bob Briscoe, Jonathan Morton, Richard Scheffenegger, Neal Cardwell,		Bob Briscoe, Jonathan Morton, Richard Scheffenegger, Neal Cardwell,
	Michael Tuexen, Yuchung Cheng, Matt Mathis, Jana Iyengar, Gorry		Michael Tuexen, Yuchung Cheng, Matt Mathis, Jana Iyengar, Gorry
	Fairhurst, and Stuart Cheshire provided useful comments and input for		Fairhurst, and Stuart Cheshire provided useful comments and input for
	this document. Jana Iyengar suggested including a field to allow a		this document. Jana Iyengar suggested including a field to allow a
	sender communicate its tolerance to reordering. Gorry Fairhurst		sender communicate its tolerance to reordering. Gorry Fairhurst
	suggested adding a mechanism to request a number of consecutive		suggested adding a mechanism to request a number of consecutive
	immediate ACKs.		immediate ACKs.
	skipping to change at page 7, line 21 ¶		skipping to change at page 8, line 21 ¶
	RFC 6994, DOI 10.17487/RFC6994, August 2013,		RFC 6994, DOI 10.17487/RFC6994, August 2013,
	<https://www.rfc-editor.org/info/rfc6994>.		<https://www.rfc-editor.org/info/rfc6994>.
	8.2. Informative References		8.2. Informative References
	[RFC3449] Balakrishnan, H., Padmanabhan, V., Fairhurst, G., and M.		[RFC3449] Balakrishnan, H., Padmanabhan, V., Fairhurst, G., and M.
	Sooriyabandara, "TCP Performance Implications of Network		Sooriyabandara, "TCP Performance Implications of Network
	Path Asymmetry", BCP 69, RFC 3449, DOI 10.17487/RFC3449,		Path Asymmetry", BCP 69, RFC 3449, DOI 10.17487/RFC3449,
	December 2002, <https://www.rfc-editor.org/info/rfc3449>.		December 2002, <https://www.rfc-editor.org/info/rfc3449>.
			[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
			Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
			December 2005, <https://www.rfc-editor.org/info/rfc4301>.
			[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
			Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
			<https://www.rfc-editor.org/info/rfc8446>.
	[RFC8490] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,		[RFC8490] Bellis, R., Cheshire, S., Dickinson, J., Dickinson, S.,
	Lemon, T., and T. Pusateri, "DNS Stateful Operations",		Lemon, T., and T. Pusateri, "DNS Stateful Operations",
	RFC 8490, DOI 10.17487/RFC8490, March 2019,		RFC 8490, DOI 10.17487/RFC8490, March 2019,
	<https://www.rfc-editor.org/info/rfc8490>.		<https://www.rfc-editor.org/info/rfc8490>.
	Authors' Addresses		Authors' Addresses
	Carles Gomez		Carles Gomez
	UPC		UPC
	C/Esteve Terradas, 7		C/Esteve Terradas, 7
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