draft-fairhurst-tsvwg-transport-encrypt-04.txt		draft-fairhurst-tsvwg-transport-encrypt-05.txt
	TSVWG G. Fairhurst		TSVWG G. Fairhurst
	Internet-Draft University of Aberdeen		Internet-Draft University of Aberdeen
	Intended status: Informational C.S. Perkins		Intended status: Informational C.S. Perkins
	Expires: March 29, 2018 University of Glasgow		Expires: June 20, 2018 University of Glasgow
	September 27, 2017		December 19, 2017
	The Impact of Transport Header Encryption on Operation and Evolution of		The Impact of Transport Header Encryption on Network Operation and
	the Internet		Evolution of the Internet
	draft-fairhurst-tsvwg-transport-encrypt-04		draft-fairhurst-tsvwg-transport-encrypt-05
	Abstract		Abstract
	This document describes implications of applying end-to-end		This document describes implications of applying end-to-end
	encryption at the transport layer. It identifies some in-network		encryption at the transport layer. It identifies in-network uses of
	uses of transport layer header information that can be used with a		transport layer header information. It then reviews the implications
	transport header integrity check. It reviews the implication of		of developing encrypted end-to-end transport protocols on transport
	developing encrypted end-to-end transport protocols and examines the		protocol design and the implications on network operation. Since
	implication of developing and deploying encrypted end-to-end		transport measurement and analysis of the impact of network
	transport protocols. Since transport measurement and analysis of the		characteristics have been important to the design of current
	impact of network characteristics have been important to the design		transport protocols, it also considers some anticipated implications
	of current transport protocols, it also considers some anticipated		on transport and application evolution.
	implications on transport and application evolution.
	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.
	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 http://datatracker.ietf.org/drafts/current/.		Drafts is at http://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 March 29, 2018.		This Internet-Draft will expire on June 20, 2018.
	Copyright Notice		Copyright Notice
	Copyright (c) 2017 IETF Trust and the persons identified as the		Copyright (c) 2017 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 (http://trustee.ietf.org/		Provisions Relating to IETF Documents (http://trustee.ietf.org/
	license-info) in effect on the date of publication of this document.		license-info) in effect on the date of publication of this document.
	Please review these documents carefully, as they describe your rights		Please review these documents carefully, as they describe your rights
	and restrictions with respect to this document. Code Components		and restrictions with respect to this document. Code Components
	extracted from this document must include Simplified BSD License text		extracted from this document must include Simplified BSD License text
	as described in Section 4.e of the Trust Legal Provisions and are		as described in Section 4.e of the Trust Legal Provisions and are
	provided without warranty as described in the Simplified BSD License.		provided without warranty as described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
	1.1. Current uses of Transport Headers within the Network . . . 6		2. Current uses of Transport Headers within the Network . . . . . 7
	1.1.1. Observing Transport Information in the Network . . . . 7		2.1. Observing Transport Information in the Network . . . . . . 7
	1.1.1.1. Flow Identification . . . . . . . . . . . . . . . 7		2.1.1. Flow Identification . . . . . . . . . . . . . . . . . 7
	1.1.1.2. Metrics derived from Transport Layer Headers . . . 7		2.1.2. Metrics derived from Transport Layer Headers . . . . . 8
	1.1.1.3. Metrics derived from Network Layer Headers . . . . 10		2.1.3. Metrics derived from Network Layer Headers . . . . . . 11
	1.1.2. Transport Measurement . . . . . . . . . . . . . . . . 12		2.2. Transport Measurement . . . . . . . . . . . . . . . . . . 12
	1.1.2.1. Point of Measurement . . . . . . . . . . . . . . . 12		2.2.1. Point of Measurement . . . . . . . . . . . . . . . . . 13
	1.1.2.2. Use by Operators to Plan and Provision Networks . 13		2.2.2. Use by Operators to Plan and Provision Networks . . . 14
	1.1.2.3. Service Performance Measurement . . . . . . . . . 13		2.2.3. Service Performance Measurement . . . . . . . . . . . 14
	1.1.2.4. Measuring Transport to Support Network Operations 13		2.2.4. Measuring Transport to Support Network Operations . . 14
	1.1.3. Use for Network Diagnostics and Troubleshooting . . . 15		2.3. Use for Network Diagnostics and Troubleshooting . . . . . 15
	1.1.4. Observing Headers to Implement Network Policy . . . . 15		2.4. Observing Headers to Implement Network Policy . . . . . . 16
	2. Encryption and Authentication of Transport Headers . . . . . . 15		3. Encryption and Authentication of Transport Headers . . . . . . 16
	2.1. Authenticating the Transport Protocol Header . . . . . . . 17		3.1. Authenticating the Transport Protocol Header . . . . . . . 18
	2.2. Encrypting the Transport Payload . . . . . . . . . . . . . 17		3.2. Encrypting the Transport Payload . . . . . . . . . . . . . 18
	2.3. Encrypting the Transport Header . . . . . . . . . . . . . 18		3.3. Encrypting the Transport Header . . . . . . . . . . . . . 18
	2.4. Authenticating Transport Information and Selectively		3.4. Authenticating Transport Information and Selectively
	Encrypting the Transport Header . . . . . . . . . . . . . 18		Encrypting the Transport Header . . . . . . . . . . . . . 19
	2.5. Adding Transport Information to Network-Layer Protocol		3.5. Adding Transport Information to Network-Layer Protocol
	Headers . . . . . . . . . . . . . . . . . . . . . . . . . 18		Headers . . . . . . . . . . . . . . . . . . . . . . . . . 19
	3. Implications of Protecting the Transport Headers . . . . . . . 19		4. Implications of Protecting the Transport Headers . . . . . . . 20
	3.1. Independent Measurement . . . . . . . . . . . . . . . . . 19		4.1. Independent Measurement . . . . . . . . . . . . . . . . . 20
	3.2. Characterising "Unknown" Network Traffic . . . . . . . . . 20		4.2. Characterising "Unknown" Network Traffic . . . . . . . . . 21
	3.3. Accountability and Internet Transport Protocols . . . . . 20		4.3. Accountability and Internet Transport Protocols . . . . . 21
	3.4. Impact on Research, Development and Deployment . . . . . . 21		4.4. Impact on Research, Development and Deployment . . . . . . 22
	4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21		5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22
	5. Security Considerations . . . . . . . . . . . . . . . . . . . 22		6. Security Considerations . . . . . . . . . . . . . . . . . . . 23
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
	7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22		8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
	7.1. Normative References . . . . . . . . . . . . . . . . . . . 22		8.1. Normative References . . . . . . . . . . . . . . . . . . . 23
	7.2. Informative References . . . . . . . . . . . . . . . . . . 22		8.2. Informative References . . . . . . . . . . . . . . . . . . 23
	Appendix A. Revision information . . . . . . . . . . . . . . . . . 26		Appendix A. Revision information . . . . . . . . . . . . . . . . . 28
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
	1. Introduction		1. Introduction
	This document discusses the implications of end-to-end encryption		This document discusses the implications of end-to-end encryption
	applied at the transport layer, and examines the impact on transport		applied at the transport layer, and examines the impact on transport
	protocol design, usage, and network operations and management. It		protocol design, transport usage, and network operations and
	also considers anticipated implications on transport and application		management. It also considers anticipated implications on transport
	evolution.		and application evolution.
	The transport layer provides the first end-to-end interactions across		The transport layer provides the first end-to-end interactions across
	the Internet. Transport protocols layer directly over the network-		the Internet. Transport protocols layer directly over the network-
	layer service and are sent in the payload of network-layer packets.		layer service and are sent in the payload of network-layer packets.
	They support end-to-end communication between applications, supported		They support end-to-end communication between applications, supported
	by higher-layer protocols, running on the end systems (or transport		by higher-layer protocols, running on the end systems (or transport
	endpoint). This simple architectural view hides one of the core		endpoints). This simple architectural view hides one of the core
	functions of the transport, however - to discover and adapt to the		functions of the transport, however - to discover and adapt to the
	properties of the Internet path that is currently being used. The		properties of the Internet path that is currently being used. The
	design of Internet transport protocols is as much about trying to		design of Internet transport protocols is as much about trying to
	avoid the unwanted side effects of congestion on a flow and other		avoid the unwanted side effects of congestion on a flow and other
	capacity-sharing flows, avoiding congestion collapse, adapting to		capacity-sharing flows, avoiding congestion collapse, adapting to
	changes in the path characteristics, etc., as it is about end-to-end		changes in the path characteristics, etc., as it is about end-to-end
	feature negotiation, flow control and optimising for performance of a		feature negotiation, flow control and optimising for performance of a
	specific application.		specific application.
	To achieve stable Internet operations the IETF transport community		To achieve stable Internet operations the IETF transport community
	has to date relied heavily on measurement and insights of the network		has to date relied heavily on measurement and insights of the network
	operations community to understand the trade-offs, and to inform		operations community to understand the trade-offs, and to inform
	selection of select appropriate mechanisms, to ensure a safe,		selection of appropriate mechanisms, to ensure a safe, reliable, and
	reliable and robust Internet. In turn, the network operations		robust Internet (e.g., [RFC1273]). In turn, the network operations
	community relies on being able to understand the traffic passing over		community relies on being able to understand the pattern and
	the Internet, both in aggregate and at the flow level -- inspecting		requirements of traffic passing over the Internet, both in aggregate
	transport layer headers to help understand traffic dynamics.		and at the flow level - inspecting transport layer headers to help
			understand traffic dynamics.
	There are many motivations for deploying encrypted transports, and		There are many motivations for deploying encrypted transports, and
	encryption of transport payloads. The increasing public concerns		encryption of transport payloads. The increasing public concerns
	about the interference with Internet traffic have led to a rapidly		about the interference with Internet traffic have led to a rapidly
	expanding deployment of encryption to protect end-user privacy, in		expanding deployment of encryption to protect end-user privacy, in
	protocols like QUIC. At the same time, network operators and access		protocols like QUIC. At the same time, network operators and access
	providers, especially in mobile networks, have come to rely on the		providers, especially in mobile networks, have come to rely on the
	in-network measurement of transport properties and the functionality		in-network measurement of transport properties and the functionality
	provided by middleboxes to both support network operations and		provided by middleboxes to both support network operations and
	enhance performance.		enhance performance (e.g., [I-D.dolson-plus-middlebox-benefits]).
	This document considers some implications of working with encrypted		This document considers some implications of working with encrypted
	transport protocols, and discusses trade-offs around authentication,		transport protocols, and discusses trade-offs around authentication,
	encryption of transport protocol headers. It describes some of the		and encryption of transport protocol headers. It describes some of
	architectural challenges and considerations in the way transport		the architectural challenges and considerations in the way transport
	protocols are designed when using encryption [Measure].		protocols are designed when using encryption [Measure].
	Encryption of the transport layer brings some well-known privacy and		Encryption of the transport layer brings some well-known privacy and
	security benefits, but also introduces various costs that need to be		security benefits, but also introduces various costs that need to be
	considered. Specifically, it can impact the following activities		considered. Specifically, it can impact the following activities
	that rely on measurement and analysis of traffic flows:		that rely on measurement and analysis of traffic flows:
	o Network Operations and Research: Observable transport headers		Network Operations and Research: Observable transport headers enable
	enable operators and the research community to measure and analyse		both operators and the research community to measure and analyse
	protocol performance, network anomalies, and failure pathologies.		protocol performance, network anomalies, and failure pathologies.
	This information can help inform capacity planning, and assist in		This information can help inform capacity planning, and assist in
	determining the need for equipment and/or configuration changes by		determining the need for equipment and/or configuration changes by
	network operators. This data also can inform Internet engineering		network operators.
	research, and help the develop of new protocols and procedures.
	Encryption of the entire transport protocol, including header
	information, will restrict the availability of data, and might
	lead to the development of alternative, and potentially more
	intrusive, methods to acquire the needed data. Encrypting the
	transport payload, but leaving some, or all, of the transport
	headers unencrypted but authenticated can provide the majority of
	the privacy and security benefits while allowing some measurement.
	o Network Troubleshooting and diagnostics: Encrypting transport		This data information can inform Internet engineering research,
	header information eliminates the incentive for operators to		and help the development of new protocols, methodologies, and
	troubleshoot what they cannot interpret. A flow experiencing		procedures. Encryption of the entire transport protocol,
	packet loss looks like an unaffected flow when only observing		including header information, will restrict the availability of
	network layer headers (if transport sequence numbers and flow		data, and might lead to the development of alternative, and
	identifiers are obscured). This limits understanding of the impact		potentially more intrusive, methods to acquire the needed data.
	of packet loss on the flows that share a network segment.
	Encrypted traffic therefore implies "don't touch", and a likely
	trouble-shooting response will be "can't help, no trouble found".
	The additional mechanisms that will need to be introduced to help
	reconstruct transport-level metrics add complexity and operational
	costs [I-D.mm-wg-effect-encrypt].
	o Network Traffic Analysis: The use of encryption can make it harder		Encrypting the transport payload, but leaving some, or all, of the
	to determine which transport protocols and features are being used		transport headers unencrypted, possibly with authentication, can
			provide the majority of the privacy and security benefits while
			allowing some measurement.
			Protection from Denial of Service: Observable transport headers can
			provide useful input to classification of traffic and detection of
			anomalous events, such as distributed denial of service attacks.
			To be effective, this protection needs to be able to uniquely
			disambiguate unwanted traffic. An inability to separate this
			traffic using packet header information is expected to lead to
			less precise pattern matching techniques or resort to
			indiscriminately (rate) limiting uncharacterised traffic.
			Network Troubleshooting and Diagnostics: Encrypting transport header
			information eliminates the incentive for operators to troubleshoot
			what they cannot interpret. A flow experiencing packet loss looks
			like an unaffected flow when only observing network layer headers
			(if transport sequence numbers and flow identifiers are obscured).
			This limits understanding of the impact of packet loss on the
			flows that share a network segment. Encrypted traffic therefore
			implies "don't touch", and a likely trouble-shooting response will
			be "can't help, no trouble found". The additional mechanisms that
			will need to be introduced to help reconstruct transport-level
			metrics add complexity and operational costs [I-D.mm-wg-effect-
			encrypt].
			Network Traffic Analysis: The use of encryption can make it harder to
			determine which transport protocols and features are being used
	across a network segment. The trends in usage. This could impact		across a network segment. The trends in usage. This could impact
	the ability for an operator to anticipate the need for network		the ability for an operator to anticipate the need for network
	upgrades and roll-out. It can also impact the on-going traffic		upgrades and roll-out. It can also impact the on-going traffic
	engineering activities performed by operators. While the impact		engineering activities performed by operators. While the impact
	may, in many cases, be small there are scenarios where operators		may, in many cases, be small there are scenarios where operators
	directly support particular services (e.g., in radio links, or to		directly support particular services (e.g., in radio links, or to
	troubleshoot issues realting to Quality of Service, QoS). The more		troubleshoot issues relating to Quality of Service, QoS; the
	complex the underlying infrastructure the more important this		ability to perform fast re-routing of critical traffic, or support
			to mitigate the characteristics of specific radio links). The
			more complex the underlying infrastructure the more important this
	impact.		impact.
	o Open and Verifiable Network Data: The use of transport header		Open and Verifiable Network Data: The use of transport header
	encryption reduces the range of actors that can capture useful		encryption reduces the range of actors that can capture useful
	measurement data. This is, of course, its goal. Doing so,		measurement data. This is, of course, its goal. Doing so,
	however, limits the information sources available to the Internet		however, limits the information sources available to the Internet
	community to understand the operation of transport protocols, so		community to understand the operation of transport protocols, so
	preventing access to the information necessary to inform design		preventing access to the information necessary to inform design
	decisions and standards for new protocols and related operational		decisions and standards for new protocols and related operational
	practices. There are dangers in a model where only endpoints		practices.
	(i.e., at user devices and within service platforms) can observe
	performance, and this cannot be independently verified. To ensure		There are dangers in a model where only endpoints (i.e., at user
	the health of the standards and research communities, we need		devices and within service platforms) can observe performance, and
	independently captured data to develop on the behaviour of the		this cannot be independently verified.
	transports. Independently verifiable performance metrics might
	also important in order to demonstrate regulatory compliance in		To ensure the health of the standards and research communities, we
	some jurisdictions.		need independently captured data to develop new transport protocol
			mechanisms based on the behaviour experienced in deployed
			networks.
			Independently verifiable performance metrics might also important
			in order to demonstrate regulatory compliance in some
			jurisdictions.
	The last point leads us to consider the impact of encrypting all the		The last point leads us to consider the impact of encrypting all the
	transport headers the specification and development of protocols and		transport headers the specification and development of protocols and
	standards. It has potential impact on:		standards. It has potential impact on:
	o Understanding Feature Interactions: An appropriate vantage point,		o Understanding Feature Interactions: An appropriate vantage point,
	coupled with timing information about traffic flows, provides a		coupled with timing information about traffic flows, provides a
	valuable tool for benchmarking equipment and/or configurations,		valuable tool for benchmarking equipment, functions, and/or
	and to understand complex feature interactions. Transport header		configurations, and to understand complex feature interactions.
	encryption limits the ability to diagnose and explore interactions		Transport header encryption limits the ability to diagnose and
	between features at different protocol layers, a side-effect of		explore interactions between features at different protocol
	not allowing a choice of vantage point from which this information		layers, a side-effect of not allowing a choice of vantage point
	is observed.		from which this information is observed.
	o Supporting Common Specifications: The Transmission Control Protocl		o Supporting Common Specifications: The Transmission Control
	(TCP) is the predominant transport protocol. Its many variants		Protocol (TCP) is the predominant transport protocol used over
	have broadly consistent approaches to avoiding congestion		Internet paths. Its many variants have broadly consistent
	collapse, and to ensuring the stability of the network. Increased		approaches to avoiding congestion collapse, and to ensuring the
	use of transport layer encryption can overcome ossification,		stability of the network. Increased use of transport layer
	allowing deployment of new transports with different types of		encryption can overcome ossification, allowing deployment of new
	congestion control. This flexibility can be beneficial, but it		transports with different types of congestion control. This
	comes at the cost of fragmenting the ecosystem. There's little		flexibility can be beneficial, but it comes at the cost of
	doubt that developers will try to produce high quality transports		fragmenting the ecosystem. There's little doubt that developers
	for their target uses, but it is not clear there are sufficient		will try to produce high quality transports for their target uses,
	incentives to ensure good practice that benefits the wide		but it is not clear there are sufficient incentives to ensure good
	diversity of requirements for the Internet community as a whole.		practice that benefits the wide diversity of requirements for the
	Increased diversity, and the ability to innovate without public		Internet community as a whole. Increased diversity, and the
	scrutiny, risks point solutions that optimise for specific needs,		ability to innovate without public scrutiny, risks point solutions
	but accidentally disrupt operations of/in different parts of the		that optimise for specific needs, but accidentally disrupt
	network. The social compact that maintains the stability of the		operations of/in different parts of the network. The social
	network relies on accepting common specifications, and on the		contract that maintains the stability of the network relies on
	ability to verify that others also conform.		accepting common specifications, and on the ability to verify that
			others also conform.
	o Operational practice: Published transport specifications allow		o Operational practice: Published transport specifications allow
	operators to check compliance. This can bring assurance to those		operators to check compliance. This can bring assurance to those
	operating networks, often avoiding the need to deploy complex		operating networks, often avoiding the need to deploy complex
	techniques that routinely monitor and manage TCP/IP traffic flows		techniques that routinely monitor and manage TCP/IP traffic flows
	(e.g. Avoiding the capital and operational costs of deploying		(e.g. Avoiding the capital and operational costs of deploying
	flow rate-limiting and network circuit-breaker methods). This		flow rate-limiting and network circuit-breaker methods [RFC8084]).
	should continue when encrypted transport headers are used, but		This should continue when encrypted transport headers are used,
	methods need to confirm that the traffic produced conforms to the		but methods need to confirm that the traffic produced conforms to
	expectations of the operator or developer.		the expectations of the operator or developer.
	o Restricting research and development: The use of encryption may		o Restricting research and development: The use of encryption may
	impede independent research into new mechanisms, measurement of		impede independent research into new mechanisms, measurement of
	behaviour, and development initiatives. Experience shows that		behaviour, and development initiatives. Experience shows that
	transport protocols are complicated to design and complex to		transport protocols are complicated to design and complex to
	deploy, and that individual mechanisms need to be evaluated while		deploy, and that individual mechanisms need to be evaluated while
	considering other mechanism, across a broad range of network		considering other mechanisms, across a broad range of network
	topologies and with attention to the impact on traffic sharing the		topologies and with attention to the impact on traffic sharing the
	capacity. Adopting pervasive encryption of transport information		capacity. Adopting pervasive encryption of transport information
	could eliminate the independent self-checks that have previously		could eliminate the independent self-checks that have previously
	been in place from research and academic contributors (e.g., the		been in place from research and academic contributors (e.g., the
	role of the IRTF ICCRG, and research publications in reviewing new		role of the IRTF ICCRG, and research publications in reviewing new
	transport mechanisms and assessing the impact of their		transport mechanisms and assessing the impact of their
	experimental deployment).		experimental deployment).
	Pervasive use of transport header encryption can impact the ways that		Pervasive use of transport header encryption can impact the ways that
	protocols are designed, standardised, deployed, and operated. The		protocols are designed, standardised, deployed, and operated. The
	choice of whether future transport protocols encrypt their protocol		choice of whether future transport protocols encrypt their protocol
	headers therefore needs to be taken based not solely on security and		headers therefore needs to be taken based not solely on security and
	privacy considerations, but also taking into account the impact on		privacy considerations, but also taking into account the impact on
	operations, standards, and research. A network that is secure but		operations, standards, and research. A network that is secure but
	unusable due to persistent congestion collapse is not an improvement,		unusable due to persistent congestion collapse is not an improvement,
	and while that would be an extreme outcome proposals that impose high		and while that would be an extreme outcome proposals that impose high
	costs for very limited benefits need to be considered carefully, to		costs for very limited benefits need to be considered carefully, to
	ensure the benefits outweigh the costs.		ensure the benefits outweigh the costs.
	1.1. Current uses of Transport Headers within the Network		2. Current uses of Transport Headers within the Network
	The transport layer is the first end-to-end layer in the network		Despite transport headers having end-to-end meaning, some of these
	stack. Despite headers having end-to-end meaning, some transport		transport headers have come to be used in various ways within the
	headers have come to be used in various ways within the Internet. In		Internet. In response to pervasive monitoring [RFC7624] revelations
	response to pervasive monitoring [RFC7624] revelations and the IETF		and the IETF consensus that "Pervasive Monitoring is an Attack"
	consensus that "Pervasive Monitoring is an Attack" [RFC7258], efforts		[RFC7258], efforts are underway to increase encryption of Internet
	are underway to increase encryption of Internet traffic, which would		traffic, which would prevent visibility of transport headers. This
	prevent visibility of transport headers. This affects on how network		affects on how network protocols are designed and used [I-D.mm-wg-
	protocols are designed and used [I-D.mm-wg-effect-encrypt]. To		effect-encrypt]. To understand these implications, it is first
	understand these implications, it is first necessary to understand		necessary to understand how transport layer headers are currently
	how transport layer headers are currently observed and/or modified by		observed and/or modified by middleboxes within the network.
	middleboxes within the network.
	Transport protocols can be designed to encrypt or authenticate		Transport protocols can be designed to encrypt or authenticate
	transport header fields. Authentication methods at the transport		transport header fields. Authentication methods at the transport
	layer can be sued to detect any changes to an immutable header field		layer can be used to detect any changes to an immutable header field
	that were made by a network device along a path. The intentional		that were made by a network device along a path. The intentional
	modification of transport headers by middleboxes (such as Network		modification of transport headers by middleboxes (such as Network
	Address Translation with Protocol Translation, NAT-PT, or Firewalls)		Address Translation, NAT, or Firewalls) is not considered. Common
	is not considered.		issues concerning IP address sharing are described in [RFC6269].
	1.1.1. Observing Transport Information in the Network		2.1. Observing Transport Information in the Network
	In-network observation of transport protocol headers requires		In-network observation of transport protocol headers requires
	knowledge of the format of the transport header:		knowledge of the format of the transport header:
	o Flows need to be identified at the level required for monitoring;		o Flows need to be identified at the level required for monitoring;
	o The protocol and version of the header need to be observable. As		o The protocol and version of the header need to be observable. As
	protocols evolve over time and there may be a need to introduce		protocols evolve over time and there may be a need to introduce
	new transport headers. This may require interpretation of		new transport headers. This may require interpretation of
	protocol version information or connection setup information;		protocol version information or connection setup information;
	o Location and syntax of any transport headers to be observed. IETF		o Location and syntax of any transport headers to be observed. IETF
	transport protocols specify this information.		transport protocols specify this information.
	The following subsections describe various ways that observable		The following subsections describe various ways that observable
	transport information may be utilised.		transport information may be utilised.
	1.1.1.1. Flow Identification		2.1.1. Flow Identification
			Transport protocol header information (with information in the
			network header), can identify a flow and the connection state of the
			flow, together with the protocol options being used. In some usages,
			a low-numbered (well-known ) port number can identify a protocol
			(although port information alone is not sufficient to guarantee
			identification of a protocol). Transport protocols, such as TCP and
			Stream Control Transport Protocol (SCTP) specify a standard base
			header that includes sequence number information and other data, with
			the possibility to negotiate additional headers at connection setup,
			identified by an option number in the transport header. UDP-based
			protocols can use, but sometimes do not use, well-known port numbers.
			Some can instead be identified by signalling protocols or through the
			use of magic numbers placed in the first byte(s) of the datagram
			payload.
	Transport protocol header information can identify a flow and the		Flow identification is more complex and less easily achieved when
	connection state of the flow, together with the protocol options		multiplexing is used at or above the transport layer.
	being used. In some usages, a low-numbered (well-known ) port can
	identify a protocol (although port information alone is not
	sufficient to guarantee identification of a protocol). Transport
	protocols, such as TCP and Stream Control Transport Protocol (SCTP)
	specify a standard base header that includes sequence number
	information and other data, with the possibility to negotiate
	additional headers at connection setup, identified by an option
	number in the transport header. UDP-based protocols can use, but
	sometimes do not use, well-known ports. Some can instead be
	identified by signalling protocols or through the use of magic
	numbers placed in the first byte(s) of the datagram payload.
	1.1.1.2. Metrics derived from Transport Layer Headers		2.1.2. Metrics derived from Transport Layer Headers
	Some actors have a need to characterise the performance of link/		Some actors have a need to characterise the performance of link/
	network segments. Passive monitoring uses observed traffic to makes		network segments. Passive monitoring uses observed traffic to makes
	inferences from transport headers to derive these measurements. A		inferences from transport headers to derive these measurements. A
	variety of open source and commercial tools have been deployed that		variety of open source and commercial tools have been deployed that
	utilise this information. The following metrics can be derived from		utilise this information. The following metrics can be derived from
	transport header information:		transport header information:
	Traffic Rate and Volume: Header infromation may allow derivation of		Traffic Rate and Volume: Header information may allow derivation of
	volume measures per-application, to characterise the traffic that		volume measures per-application, to characterise the traffic that
	uses a network segment or the pattern of network usage. This may		uses a network segment or the pattern of network usage. This may
	be measured per endpoint or aggregate of endpoint (e.g., by an		be measured per endpoint or for an aggregate of endpoints (e.g.,
	operator to assess subscriber usage). It can also be used to		by an operator to assess subscriber usage). It can also be used to
	trigger measurement-based traffic shaping and to implement QoS		trigger measurement-based traffic shaping and to implement QoS
	support within the network and lower layers. Volume measures can		support within the network and lower layers. Volume measures can
	be valuable for capacity planning (providing detail of trends		be valuable for capacity planning (providing detail of trends
	rather than the volume per subscriber).		rather than the volume per subscriber).
	Loss Rate and Loss Pattern: Flow loss rate may be derived and is		Loss Rate and Loss Pattern: Flow loss rate may be derived and is
	often used as a metric for performance assessment and to		often used as a metric for performance assessment and to
	characterise transport behaviour. Understanding the root cause of		characterise transport behaviour. Understanding the root cause of
	loss can help an operator determine whether this requires		loss can help an operator determine whether this requires
	corrective action.		corrective action. Network operators may also use the variation
			in patterns of loss as a key performance metric, utilising this to
			detect changes in the offered service.
	There are various cause of loss, including: corruption on a link		There are various cause of loss, including: corruption on a link
	(e.g., interference on a radio link), buffer overflow (e.g., due		(e.g., interference on a radio link), buffer overflow (e.g., due
	to congestion), policing (traffic management), buffer management		to congestion), policing (traffic management), buffer management
	(e.g., Active Queue Management, AQM). Understanding flow loss		(e.g., Active Queue Management, AQM), inadequate provision of
	rate requires either maintaining per flow packet counters or by		traffic preemption. Understanding flow loss rate requires either
	observing sequence numbers in transport headers. Loss can be		maintaining per flow packet counters or by observing sequence
	monitored at the interface level by devices in the network. It is		numbers in transport headers. Loss can be monitored at the
	often important to understand the conditions under which packet		interface level by devices in the network. It is often important
	loss occurs. This usually requires relating loss to the traffic		to understand the conditions under which packet loss occurs. This
	flowing on the network segment at the time of loss.		usually requires relating loss to the traffic flowing on the
			network node/segment at the time of loss.
	Observation of transport feedback information (observing loss		Observation of transport feedback information (observing loss
	reports, e.g., RTP Control Protocol (RTCP), TCP SACK) can increase		reports, e.g., RTP Control Protocol (RTCP), TCP SACK) can increase
	understanding of the impact of loss and help identify cases where		understanding of the impact of loss and help identify cases where
	loss may have been wrongly identified, or the transport did not		loss may have been wrongly identified, or the transport did not
	require the lost packet. It is sometimes more important to		require the lost packet. It is sometimes more important to
	understand the pattern of loss, than the loss rate - since losses		understand the pattern of loss, than the loss rate - since losses
	can often occur as bursts, rather than randomly-timed events.		can often occur as bursts, rather than randomly-timed events.
	Throughput and Goodput: The throughput observed by a flow can be		Throughput and Goodput: The throughput observed by a flow can be
	skipping to change at page 9, line 20 ¶		skipping to change at page 9, line 47 ¶
	determines the reaction time of the transport protocol itself,		determines the reaction time of the transport protocol itself,
	impacting flow setup, congestion control, loss recovery, and other		impacting flow setup, congestion control, loss recovery, and other
	transport mechanisms. The observed latency can have many		transport mechanisms. The observed latency can have many
	components [Latency]. Of these, unnecessary/unwanted queuing in		components [Latency]. Of these, unnecessary/unwanted queuing in
	network buffers has often been observed as a significant factor.		network buffers has often been observed as a significant factor.
	Once the cause of unwanted latency has been identified, this can		Once the cause of unwanted latency has been identified, this can
	often be eliminated, and determining latency metrics is a key		often be eliminated, and determining latency metrics is a key
	driver in the deployment of AQM [RFC7567], DiffServ [RFC2474], and		driver in the deployment of AQM [RFC7567], DiffServ [RFC2474], and
	Explicit Congestion Notification (ECN) [RFC3168] [RFC8087].		Explicit Congestion Notification (ECN) [RFC3168] [RFC8087].
	To measure latency across a part of the path, an observation point		To measure latency across a part of a path, an observation point
	can measure the experienced round trip time (RTT) using packet		can measure the experienced round trip time (RTT) using packet
	sequence numbers, and acknowledgements, or by observing header		sequence numbers, and acknowledgements, or by observing header
	timestamp information. Such information allows an observation		timestamp information. Such information allows an observation
	point in the network to determine not only the path RTT, but also		point in the network to determine not only the path RTT, but also
	to measure the upstream and downstream contribution to the RTT.		to measure the upstream and downstream contribution to the RTT.
	This may be used to locate a source of latency, e.g., by observing		This may be used to locate a source of latency, e.g., by observing
	cases where the ratio of median to minimum RTT is large for a part		cases where the ratio of median to minimum RTT is large for a part
	of a path.		of a path.
	An example usage of this method could identify excessive buffers		An example usage of this method could identify excessive buffers
	skipping to change at page 10, line 4 ¶		skipping to change at page 10, line 28 ¶
	Jitter: Some network applications are sensitive to changes in packet		Jitter: Some network applications are sensitive to changes in packet
	timing. For such applications, it can be necessary to measure the		timing. For such applications, it can be necessary to measure the
	jitter observed along a portion of the path. The requirements to		jitter observed along a portion of the path. The requirements to
	measure jitter resemble those for the measurement of latency.		measure jitter resemble those for the measurement of latency.
	Flow Reordering: Significant flow reordering can impact time-critical		Flow Reordering: Significant flow reordering can impact time-critical
	applications and can be interpreted as loss by reliable		applications and can be interpreted as loss by reliable
	transports. Many transport protocol techniques are impacted by		transports. Many transport protocol techniques are impacted by
	reordering (e.g., triggering TCP retransmission, or re-buffering		reordering (e.g., triggering TCP retransmission, or re-buffering
	of real-time applications). Packet reordering can occur for many		of real-time applications). Packet reordering can occur for many
	reasons (from equipment design to misconfiguration of forwarding		reasons (from equipment design to misconfiguration of forwarding
	rules).		rules).
	As in the drive to reduce network latency, there is a need for		As in the drive to reduce network latency, there is a need for
	operational tools to detect mis-ordered packet flows and quantify		operational tools to detect mis-ordered packet flows and quantify
	the degree or reordering. Techniques for measuring reordering		the degree or reordering. Techniques for measuring reordering
	typically observe packet sequence numbers. Metrics have been		typically observe packet sequence numbers. Metrics have been
	defined that evaluate whether a network has maintained packet		defined that evaluate whether a network has maintained packet
	order on a packet-by-packet basis [RFC4737] and [RFC5236].		order on a packet-by-packet basis [RFC4737] and [RFC5236].
	There has been initiatives in the IETF transport area to reduce		There have been initiatives in the IETF transport area to reduce
	the impact of reordering within a transport flow, possibly leading		the impact of reordering within a transport flow, possibly leading
	to reduced the requirements for ordering. These have promise to		to reduce the requirements for ordering. These have promise to
	simplify network equipment design as well as the potential to		simplify network equipment design as well as the potential to
	improve robustness of the transport service. Measurements of		improve robustness of the transport service. Measurements of
	reordering can help understand the level of reordering within		reordering can help understand the level of reordering within
	deployed infrastructure, and inform decisions about how to		deployed infrastructure, and inform decisions about how to
	progress such mechanisms.		progress such mechanisms.
	Some protocols provide in-built monitoring and reporting functions.		Some protocols provide in-built monitoring and reporting functions.
	Transport fields in the RTP header [RFC3550] [RFC4585] can be		Transport fields in the RTP header [RFC3550] [RFC4585] can be
	observed to derive traffic volume measurements and provide		observed to derive traffic volume measurements and provide
	information on the progress and quality of a session using RTP. Key		information on the progress and quality of a session using RTP. Key
	performance indicators are retransmission rate, packet drop rate,		performance indicators are retransmission rate, packet drop rate,
	sector utilization level, a measure of reordering, peak rate, the CE-		sector utilisation level, a measure of reordering, peak rate, the CE-
	marking rate, etc. Metadata is often important to understand the		marking rate, etc. Metadata is often important to understand the
	context under which the data was collected, including the time,		context under which the data was collected, including the time,
	observation point, and way in which metrics were accumulated. The		observation point, and way in which metrics were accumulated. The
	RTCP protocol directly reports some of this information in a form		RTCP protocol directly reports some of this information in a form
	that can be directly visible in the network. A user of summary		that can be directly visible in the network. A user of summary
	measurement data needs to trust the source of this data and the		measurement data needs to trust the source of this data and the
	method used to generate the summary information.		method used to generate the summary information.
	When encryption conceals information in packet headers, measurements		When encryption conceals information in packet headers, measurements
	need to rely on pattern inferences and other heuristics grows, and		need to rely on pattern inferences and other heuristics grows, and
	accuracy suffers [I-D.mm-wg-effect-encrypt].		accuracy suffers [I-D.mm-wg-effect-encrypt].
	1.1.1.3. Metrics derived from Network Layer Headers		2.1.3. Metrics derived from Network Layer Headers
	Some transport information is made visible in the network-layer		Some transport information is made visible in the network-layer
	protocol header. These header fields are not encrypted and can be		protocol header. These header fields are not encrypted and can be
	used to make flow observations.		used to make flow observations.
	Use of IPv6 Network-Layer Flow Label: Endpoints are encouraged expose		Use of IPv6 Network-Layer Flow Label: Endpoints are encouraged expose
	flow information in the IPv6 Flow Label field of the network-layer		flow information in the IPv6 Flow Label field of the network-layer
	header (e..g. [RFC8085]). This can be used to inform network-		header (e.g., [RFC8085]). This can be used to inform network-layer
	layer queuing, forwarding (e.g., for equal cost multi-path (ECMP)		queuing, forwarding (e.g., for equal cost multi-path (ECMP)
	routing, and Link Aggregation, LAG). This can provide useful		routing, and Link Aggregation, LAG). This can provide useful
	information to assign packets to flows in the data collected by		information to assign packets to flows in the data collected by
	measurement campaigns. Although important to characterising a		measurement campaigns. Although important to characterising a
	path, it does not directly provide any performance data.		path, it does not directly provide any performance data.
	Use Network-Layer Differentiated Services Code Point Point: Applicati		Use Network-Layer Differentiated Services Code Point Point: Applicati
	on can expose their delivery expectations to the network by		ons can expose their delivery expectations to the network by
	setting the Differentiated Services Code Point (DSCP) field of		setting the Differentiated Services Code Point (DSCP) field of
	IPv4 and IPv6 packets. This can be used to inform network-layer		IPv4 and IPv6 packets. This can be used to inform network-layer
	queuing and forwarding, and can also provide information on the		queuing and forwarding, and can also provide information on the
	relative importance of packet information collected by measurement		relative importance of packet information collected by measurement
	campaigns, but does not directly provide any performance data.		campaigns, but does not directly provide any performance data.
	This field provides explicit information that can be used in place		This field provides explicit information that can be used in place
	of inferring traffic requirements (e.g., by inferring QoS		of inferring traffic requirements (e.g., by inferring QoS
	requirements from port information via a multi-field classifier).		requirements from port information via a multi-field classifier).
	The DSCP value can therefore impact the quality of experience for		The DSCP value can therefore impact the quality of experience for
	a flow. Observations of service performance need to consider this		a flow. Observations of service performance need to consider this
	field when a network path has support for differentiated service		field when a network path has support for differentiated service
	treatment.		treatment.
	Use of Explicit Congestion Marking: ECN[RFC3168] is an optional		Use of Explicit Congestion Marking: ECN [RFC3168] is an optional
	transport mechanism that uses a code point in the network-layer		transport mechanism that uses a code point in the network-layer
	header. Use of ECN can offer gains in terms of increased		header. Use of ECN can offer gains in terms of increased
	throughput, reduced delay, and other benefits when used over a		throughput, reduced delay, and other benefits when used over a
	path that includes equipment that supports an AQM method that		path that includes equipment that supports an AQM method that
	performs Congestion Experienced (CE) marking of IP packets		performs Congestion Experienced (CE) marking of IP packets
	[RFC8087].		[RFC8087].
	ECN exposes the presence of congestion on a network path to the		ECN exposes the presence of congestion on a network path to the
	transport and network layer. The reception of CE-marked packets		transport and network layer. The reception of CE-marked packets
	can therefore be used to monitor the presence and estimate the		can therefore be used to monitor the presence and estimate the
	skipping to change at page 11, line 44 ¶		skipping to change at page 12, line 28 ¶
	ECN marks carried in the IP protocol header, it is much easier to		ECN marks carried in the IP protocol header, it is much easier to
	measure ECN than metering packet loss. However, interpreting the		measure ECN than metering packet loss. However, interpreting the
	marking behaviour (i.e., assessing congestion and diagnosing		marking behaviour (i.e., assessing congestion and diagnosing
	faults) requires context from the transport layer (path RTT,		faults) requires context from the transport layer (path RTT,
	visibility of loss - that could be due to queue overflow,		visibility of loss - that could be due to queue overflow,
	congestion response, etc) [RFC7567].		congestion response, etc) [RFC7567].
	Some ECN-capable network devices can provide richer (more frequent		Some ECN-capable network devices can provide richer (more frequent
	and fine-grained) indication of their congestion state. Setting		and fine-grained) indication of their congestion state. Setting
	congestion marks proportional to the level of congestion (e.g.,		congestion marks proportional to the level of congestion (e.g.,
	Data Center TCP, DCTP [I-D.ietf-tcpm-dctcp], and Low Latency Low		Data Center TCP, DCTP [RFC8257], and Low Latency Low Loss Scalable
	Loss Scalable throughput, L4S, [I-D.ietf-tsvwg-l4s-arch].		throughput, L4S, [I-D.ietf-tsvwg-l4s-arch].
	Use of ECN requires feedback a transport to feed back reception		Use of ECN requires a transport to feed back reception information
	information on the path towards the data sender. Exposure of this		on the path towards the data sender. Exposure of this Transport
	Transport ECN feedback provides an additional powerful tool to		ECN feedback provides an additional powerful tool to understand
	understand ECN-enabled AQM-based networks [RFC8087].		ECN-enabled AQM-based networks [RFC8087].
	AQM and ECN offer a range of algorithms and configuration options,		AQM and ECN offer a range of algorithms and configuration options,
	it is therefore important for tools to be available to network		it is therefore important for tools to be available to network
	operators and researchers to understand the implication of		operators and researchers to understand the implication of
	configuration choices and transport behaviour as use of ECN		configuration choices and transport behaviour as use of ECN
	increases and new methods emerge [RFC7567] [RFC8087]. ECN-		increases and new methods emerge [RFC7567] [RFC8087]. ECN-
	monitoring is expected to become important as AQM is deployed that		monitoring is expected to become important as AQM is deployed that
	supports ECN [RFC8087].		supports ECN [RFC8087].
	1.1.2. Transport Measurement		2.2. Transport Measurement
	The common language between network operators and application/content		The common language between network operators and application/content
	providers/users is packet transfer performance at a layer that all		providers/users is packet transfer performance at a layer that all
	can view and analyse. For most packets, this has been transport		can view and analyse. For most packets, this has been transport
	layer, until the emergence of QUIC, with the obvious exception of		layer, until the emergence of QUIC, with the obvious exception of
	VPNs and IPsec. When encryption conceals more layers in a packet,		VPNs and IPsec. When encryption conceals more layers in a packet,
	people seeking understanding of the network operation need to rely		people seeking understanding of the network operation need to rely
	more on pattern inferences and other heuristics. The accuracy of		more on pattern inferences and other heuristics. The accuracy of
	measurements therefore suffers, as does the ability to investigate		measurements therefore suffers, as does the ability to investigate
	and troubleshoot interactions between different anomalies. For		and troubleshoot interactions between different anomalies. For
	example, the traffic patterns between a web server and a browser are		example, the traffic patterns between a web server and a browser are
	skipping to change at page 13, line 5 ¶		skipping to change at page 13, line 34 ¶
	the packet header information of (randomly) selected packets. The		the packet header information of (randomly) selected packets. The
	utility of these measurements depends on the type of bearer and		utility of these measurements depends on the type of bearer and
	number of mechanisms used by network devices. Simple routers are		number of mechanisms used by network devices. Simple routers are
	relatively easy to manage, a device with more complexity demands		relatively easy to manage, a device with more complexity demands
	understanding of the choice of many system parameters. This level of		understanding of the choice of many system parameters. This level of
	complexity exists when several network methods are combined.		complexity exists when several network methods are combined.
	This section discusses topics concerning observation of transport		This section discusses topics concerning observation of transport
	flows, with a focus on transport measurement.		flows, with a focus on transport measurement.
	1.1.2.1. Point of Measurement		2.2.1. Point of Measurement
	Often measurements can only be understood in the context of the other		Often measurements can only be understood in the context of the other
	flows that share a bottleneck. A simple example is monitoring of		flows that share a bottleneck. A simple example is monitoring of
	AQM. For example, FQ-CODEL [I-D.ietf-aqm-fq-codel], combines sub		AQM. For example, FQ-CODEL [I-D.ietf-aqm-fq-codel], combines sub
	queues (statistically assigned per flow), management of the queue		queues (statistically assigned per flow), management of the queue
	length (CODEL), flow-scheduling, and a starvation prevention		length (CODEL), flow-scheduling, and a starvation prevention
	mechanism. Usually such algorithms are designed to be self-tuning,		mechanism. Usually such algorithms are designed to be self-tuning,
	but current methods typically employ heuristics that can result in		but current methods typically employ heuristics that can result in
	more loss under certain path conditions (e.g., large RTT, effects of		more loss under certain path conditions (e.g., large RTT, effects of
	multiple bottlenecks [RFC7567]).		multiple bottlenecks [RFC7567]).
	In-network measurements can distinguish between upstream and		In-network measurements can distinguish between upstream and
	downstream metrics with respect to the measurement point. These are		downstream metrics with respect to a measurement point. These are
	particularly useful for locating the source of problems or to assess		particularly useful for locating the source of problems or to assess
	the performance of a network segment or a particular device		the performance of a network segment or a particular device
	configuration.		configuration.
	By correlating observations at multiple points along the path (e.g.,		By correlating observations at multiple points along the path (e.g.,
	at the ingress and egress of a network segment), an observer can		at the ingress and egress of a network segment), an observer can
	determine the contribution of a portion of the path to an observed		determine the contribution of a portion of the path to an observed
	metric (to locate a source of delay, jitter, loss, reordering,		metric (to locate a source of delay, jitter, loss, reordering,
	congestion marking, etc.).		congestion marking, etc.).
	1.1.2.2. Use by Operators to Plan and Provision Networks		2.2.2. Use by Operators to Plan and Provision Networks
	Traffic measurements (e.g., traffic volume, loss, latency) is used by		Traffic measurements (e.g., traffic volume, loss, latency) is used by
	operators to help plan deployment of new equipment and configurations		operators to help plan deployment of new equipment and configurations
	in their networks. Data is also important to equipment vendors who		in their networks. Data is also important to equipment vendors who
	need to understand traffic trends traffic and patterns of usage as		need to understand traffic trends and patterns of usage as inputs to
	inputs to decisions about planning products and provisioning for new		decisions about planning products and provisioning for new
	deployments. This measurement information can also be correlated		deployments. This measurement information can also be correlated
	with billing information when this is also collected by an operator.		with billing information when this is also collected by an operator.
	A network operator supporting traffic that uses transport header		A network operator supporting traffic that uses transport header
	encryption may not have access to per-flow measurement data. Trends		encryption may not have access to per-flow measurement data. Trends
	in aggregate traffic can be observed and can be related this to the		in aggregate traffic can be observed and can be related this to the
	endpoint addresses being used, but it may not be possible to		endpoint addresses being used, but it may not be possible to
	correlate patterns in measurements with changes in transport		correlate patterns in measurements with changes in transport
	protocols (e.g., the impact of changes in introducing a new transport		protocols (e.g., the impact of changes in introducing a new transport
	protocol mechanism). This increases the dependency on other indirect		protocol mechanism). This increases the dependency on other indirect
	sources of information to inform planning and provisioning.		sources of information to inform planning and provisioning.
	1.1.2.3. Service Performance Measurement		2.2.3. Service Performance Measurement
	Traffic measurements (e.g., traffic volume, loss, latency) can be		Traffic measurements (e.g., traffic volume, loss, latency) can be
	used by various actors to help analyse the performance available to		used by various actors to help analyse the performance available to
	users of a network segment, and inform operational practice. While		users of a network segment, and inform operational practice. While
	active measurements may be used in-network passive measurements can		active measurements may be used in-network passive measurements can
	have advantages in terms of eliminating unproductive traffic,		have advantages in terms of eliminating unproductive traffic,
	reducing the influence of test traffic on the overall traffic mix,		reducing the influence of test traffic on the overall traffic mix,
	and the ability to choose the point of measurement Section 1.1.2.1.		and the ability to choose the point of measurement Section 2.2.1.
			2.2.4. Measuring Transport to Support Network Operations
	1.1.2.4. Measuring Transport to Support Network Operations
	Information provided by tools observing transport headers can help		Information provided by tools observing transport headers can help
	determine whether mechanisms are needed in the network to prevent		determine whether mechanisms are needed in the network to prevent
	flows from acquiring excessive network capacity. Operators can		flows from acquiring excessive network capacity. Operators can
	implement operational practices to manage traffic flows (e.g., to		implement operational practices to manage traffic flows (e.g., to
	prevent flows from acquiring excessive network capacity under severe		prevent flows from acquiring excessive network capacity under severe
	congestion) by deploying rate-limiters, traffic shaping or network		congestion) by deploying rate-limiters, traffic shaping or network
	transport circuit breakers [RFC8084].		transport circuit breakers [RFC8084].
	Congestion Control Compliance of Traffic: Congestion control is a key		Congestion Control Compliance of Traffic: Congestion control is a key
	transport function. Many network operators implicitly accept that		transport function. Many network operators implicitly accept that
	skipping to change at page 14, line 28 ¶		skipping to change at page 15, line 13 ¶
	struggle to easily duplicate [RFC8085].		struggle to easily duplicate [RFC8085].
	A standards-compliant TCP stack provides congestion control may		A standards-compliant TCP stack provides congestion control may
	therefore be judged safe for use across the Internet.		therefore be judged safe for use across the Internet.
	Applications developed on top of well-designed transports can be		Applications developed on top of well-designed transports can be
	expected to appropriately control their network usage, reacting		expected to appropriately control their network usage, reacting
	when the network experiences congestion, by back-off and reduce		when the network experiences congestion, by back-off and reduce
	the load placed on the network. This is the normal expected		the load placed on the network. This is the normal expected
	behaviour for TCP and SCTP.		behaviour for TCP and SCTP.
	However when anomolies are detected, tools can interpret the		However when anomalies are detected, tools can interpret the
	transport protocol header information to help understand the		transport protocol header information to help understand the
	impact of specific transport protocols (or protocol mechanisms) on		impact of specific transport protocols (or protocol mechanisms) on
	the other traffic that shares a network. An observation in the		the other traffic that shares a network. An observation in the
	network can gain understanding of the dynamics of a flow and its		network can gain understanding of the dynamics of a flow and its
	congestion control behaviour. Analysing observed packet sequence		congestion control behaviour. Analysing observed packet sequence
	numbers can be used to help build confidence that an application		numbers can be used to help build confidence that an application
	flow backs-off its share of the network load in the face of		flow backs-off its share of the network load in the face of
	persistent congestion, and hence to understand whether the		persistent congestion, and hence to understand whether the
	behaviour is appropriate for sharing limited network capacity.		behaviour is appropriate for sharing limited network capacity.
	For example, it is common to visualise plots of TCP sequence		For example, it is common to visualise plots of TCP sequence
	numbers versus time for a flow to understand how a flow shares		numbers versus time for a flow to understand how a flow shares
	available capacity, deduce its dynamics in response to congestion,		available capacity, deduce its dynamics in response to congestion,
	etc.		etc.
	Congestion Control Compliance for UDP Traffic UDP provides a minimal		Congestion Control Compliance for UDP traffic UDP provides a minimal
	message-passing transport that has no inherent congestion control		message-passing transport that has no inherent congestion control
	mechanisms. Because congestion control is critical to the stable		mechanisms. Because congestion control is critical to the stable
	operation of the Internet, applications and other protocols that		operation of the Internet, applications and other protocols that
	choose to use UDP as an Internet transport are required to employ		choose to use UDP as a transport are required to employ mechanisms
	mechanisms to prevent congestion collapse, avoid unacceptable		to prevent congestion collapse, avoid unacceptable contributions
	contributions to jitter/latency, and to establish an acceptable		to jitter/latency, and to establish an acceptable share of
	share of capacity with concurrent traffic [RFC8085].		capacity with concurrent traffic [RFC8085].
	A network operator needs tools to understand if UDP flows comply		A network operator needs tools to understand if UDP flows comply
	with congestion control expectations and therefore whether there		with congestion control expectations and therefore whether there
	is a need to deploy methods such as rate-limiters, transport		is a need to deploy methods such as rate-limiters, transport
	circuit breakers or other methods to enforce acceptable usage for		circuit breakers or other methods to enforce acceptable usage for
	the offered service.		the offered service.
	UDP flows that expose a well-known header by specifying the format		UDP flows that expose a well-known header by specifying the format
	of header fields can allow information to be observed to gain		of header fields can allow information to be observed to gain
	understanding of the dynamics of a flow and its congestion control		understanding of the dynamics of a flow and its congestion control
	behaviour. For example, tools exist to monitor various aspects of		behaviour. For example, tools exist to monitor various aspects of
	the RTP and RTCP header information of real-time flows (see		the RTP and RTCP header information of real-time flows (see
	Section 1.1.1.2.		Section 2.1.2.
	1.1.3. Use for Network Diagnostics and Troubleshooting		2.3. Use for Network Diagnostics and Troubleshooting
	Transport header information is useful for a variety of operational		Transport header information is useful for a variety of operational
	tasks [I-D.mm-wg-effect-encrypt]: to diagnose network problems,		tasks [I-D.mm-wg-effect-encrypt]: to diagnose network problems,
	assess performance, capacity planning, management of denial of		assess performance, capacity planning, management of denial of
	service threats, and responding to user performance questions. These		service threats, and responding to user performance questions. These
	tasks seldom involve the need to determine the contents of the		tasks seldom involve the need to determine the contents of the
	transport payload, or other application details.		transport payload, or other application details.
	A network operator supporting traffic that uses transport header		A network operator supporting traffic that uses transport header
	encryption can see only encrypted transport headers. This prevents		encryption can see only encrypted transport headers. This prevents
	skipping to change at page 15, line 39 ¶		skipping to change at page 16, line 23 ¶
	response to tracing issues, making appropriate Quality of Service,		response to tracing issues, making appropriate Quality of Service,
	QoS, decisions). For some this will be blessing, for others it may be		QoS, decisions). For some this will be blessing, for others it may be
	a curse. For example, operational performance data about encrypted		a curse. For example, operational performance data about encrypted
	flows needs to be determined by traffic pattern analysis, rather than		flows needs to be determined by traffic pattern analysis, rather than
	relying on traditional tools. This can impact the ability of the		relying on traditional tools. This can impact the ability of the
	operator to respond to faults, it could require reliance on endpoint		operator to respond to faults, it could require reliance on endpoint
	diagnostic tools or user involvement in diagnosing and		diagnostic tools or user involvement in diagnosing and
	troubleshooting unusual use cases or non-trivial problems. A key		troubleshooting unusual use cases or non-trivial problems. A key
	need here is that tools need to provide useful information during		need here is that tools need to provide useful information during
	network anomalies (e.g., significant reordering, high or intermittent		network anomalies (e.g., significant reordering, high or intermittent
	loss). Although many network operators utilise transport information		loss). Although many network operators utilise transport information
	as a part of their operational practice, the network will not break		as a part of their operational practice, the network will not break
	because transport headers are encrypted.		because transport headers are encrypted.
	1.1.4. Observing Headers to Implement Network Policy		2.4. Observing Headers to Implement Network Policy
	Information from the transport protocol can be used by a multi-field		Information from the transport protocol can be used by a multi-field
	classifier as a part of policy framework. Policies are commonly used		classifier as a part of policy framework. Policies are commonly used
	for QoS management for resource-constrained networks and by firewalls		for QoS management for resource-constrained networks and by firewalls
	that use the information to implement access rules. Traffic that		that use the information to implement access rules. Traffic that
	cannot be classified, will typically receive a default treatment.		cannot be classified, will typically receive a default treatment.
	2. Encryption and Authentication of Transport Headers		3. Encryption and Authentication of Transport Headers
	End-to-end encryption can be applied at various protocol layers. It		End-to-end encryption can be applied at various protocol layers. It
	can be applied above the transport to encrypt the transport payload.		can be applied above the transport to encrypt the transport payload.
	Encryption methods can hide information from an eavesdropper in the		Encryption methods can hide information from an eavesdropper in the
	network. Encryption can also help protect the privacy of a user, by		network. Encryption can also help protect the privacy of a user, by
	hiding data relating to user/device identity or location. Neither an		hiding data relating to user/device identity or location. Neither an
	integrity check nor encryption methods prevent traffic analysis, and		integrity check nor encryption methods prevent traffic analysis, and
	usage needs to reflect that profiling of users, identification of		usage needs to reflect that profiling of users, identification of
	location and fingerprinting of behaviour can take place even on		location and fingerprinting of behaviour can take place even on
	encrypted traffic flows.		encrypted traffic flows.
	skipping to change at page 16, line 30 ¶		skipping to change at page 17, line 21 ¶
	this, a method that authenticates transport headers may help improve		this, a method that authenticates transport headers may help improve
	the pace of transport development, by eliminating the need to always		the pace of transport development, by eliminating the need to always
	consider deployed middleboxes [I-D.trammell-plus-abstract-mech], or		consider deployed middleboxes [I-D.trammell-plus-abstract-mech], or
	potentially to only explicitly enable middlebox use for particular		potentially to only explicitly enable middlebox use for particular
	paths with particular middleboxes that are deliberately deployed to		paths with particular middleboxes that are deliberately deployed to
	realise a useful function for the network and/or users[RFC3135].		realise a useful function for the network and/or users[RFC3135].
	Another motivation stems from increased concerns about privacy and		Another motivation stems from increased concerns about privacy and
	surveillance. Some Internet users have valued the ability to protect		surveillance. Some Internet users have valued the ability to protect
	identity, user location, and defend against traffic analysis, and		identity, user location, and defend against traffic analysis, and
	have used methods such as IPsec ESP and Tor [Tor]. Revelations about		have used methods such as IPsec ESP. Revelations about the use of
	the use of pervasive surveillance [RFC7624] have, to some extent,		pervasive surveillance [RFC7624] have, to some extent, eroded trust
	eroded trust in the service offered by network operators, and		in the service offered by network operators, and following the
	following the Snowden revelation in the USA in 2013 has led to an		Snowden revelation in the USA in 2013 has led to an increased desire
	increased desire for people to employ encryption to avoid unwanted		for people to employ encryption to avoid unwanted "eavesdropping" on
	"eavesdropping" on their communications. Whatever the reasons, there		their communications. Whatever the reasons, there are now activities
	are now activities in the IETF to design new protocols that may		in the IETF to design new protocols that may include some form of
	include some form of transport header encryption (e.g., QUIC [I-D		transport header encryption (e.g., QUIC [I-D.ietf-quic-transport]).
	.ietf-quic-transport]).
	Authentication methods (that provide integrity checks of protocols		Authentication methods (that provide integrity checks of protocols
	fields) have also been specified at the network layer, and this also		fields) have also been specified at the network layer, and this also
	protects transport header fields. The network layer itself carries		protects transport header fields. The network layer itself carries
	protocol header fields that are increasingly used to help forwarding		protocol header fields that are increasingly used to help forwarding
	decisions reflect the need of transport protocols, such the IPv6 Flow		decisions reflect the need of transport protocols, such the IPv6 Flow
	Label [RFC6437], the Differentiated Services Code Point (DSCP)		Label [RFC6437], the DSCP and ECN.
	[RFC2474] and Explicit Congestion Notification (ECN) [RFC3168].
	The use of transport layer authentication and encryption exposes a		The use of transport layer authentication and encryption exposes a
	tussle between middlebox vendors, operators, applications developers		tussle between middlebox vendors, operators, applications developers
	and users.		and users.
	o On the one hand, future Internet protocols that enable large-scale		o On the one hand, future Internet protocols that enable large-scale
	encryption assist in the restoration of the end-to-end nature of		encryption assist in the restoration of the end-to-end nature of
	the Internet by returning complex processing to the endpoints,		the Internet by returning complex processing to the endpoints,
	since middleboxes cannot modify what they cannot see.		since middleboxes cannot modify what they cannot see.
	skipping to change at page 17, line 18 ¶		skipping to change at page 18, line 16 ¶
	understand the dynamics of protocols and traffic patterns.		understand the dynamics of protocols and traffic patterns.
	Whatever the motives, a decision to use pervasive of transport header		Whatever the motives, a decision to use pervasive of transport header
	encryption will have implications on the way in which design and		encryption will have implications on the way in which design and
	evaluation is performed, and which can in turn impact the direction		evaluation is performed, and which can in turn impact the direction
	of evolution of the TCP/IP stack.		of evolution of the TCP/IP stack.
	The next subsections briefly review some security design options for		The next subsections briefly review some security design options for
	transport protocols.		transport protocols.
	2.1. Authenticating the Transport Protocol Header		3.1. Authenticating the Transport Protocol Header
	Transport layer header information can be authenticated. An		Transport layer header information can be authenticated. An
	integrity check that protects the immutable transport header fields,		integrity check that protects the immutable transport header fields,
	but can still expose the transport protocol header information in the		but can still expose the transport protocol header information in the
	clear, allowing in-network devices to observes these fields. An		clear, allowing in-network devices to observes these fields. An
	integrity check can not prevent in-network modification, but can		integrity check can not prevent in-network modification, but can
	avoid a receiving accepting changes and avoid impact on the transport		avoid a receiving accepting changes and avoid impact on the transport
	protocol operation.		protocol operation.
	An example transport authentication mechanism is TCP-Authentication		An example transport authentication mechanism is TCP-Authentication
	skipping to change at page 17, line 40 ¶		skipping to change at page 18, line 38 ¶
	including the IP pseudo header, TCP header, and TCP data. TCP-AO		including the IP pseudo header, TCP header, and TCP data. TCP-AO
	protects the transport layer, preventing attacks from disabling the		protects the transport layer, preventing attacks from disabling the
	TCP connection itself. TCP-AO may interact with middleboxes,		TCP connection itself. TCP-AO may interact with middleboxes,
	depending on their behaviour [RFC3234].		depending on their behaviour [RFC3234].
	The IPsec Authentication Header (AH) [RFC4302] works at the network		The IPsec Authentication Header (AH) [RFC4302] works at the network
	layer and authenticates the IP payload. This therefore also		layer and authenticates the IP payload. This therefore also
	authenticates all transport headers, and verifies their integrity at		authenticates all transport headers, and verifies their integrity at
	the receiver, preventing in-network modification.		the receiver, preventing in-network modification.
	2.2. Encrypting the Transport Payload		3.2. Encrypting the Transport Payload
	The transport layer payload can be encrypted to protect the content		The transport layer payload can be encrypted to protect the content
	of transport segments. This leaves transport protocol header		of transport segments. This leaves transport protocol header
	information in the clear. The integrity of immutable transport		information in the clear. The integrity of immutable transport
	header fields could be protected by combining this with an integrity		header fields could be protected by combining this with an integrity
	check (Section 2.1).		check (Section 3.1).
	Examples of encrypting the payload include Transport Layer Security		Examples of encrypting the payload include Transport Layer Security
	(TLS) over TCP [RFC5246] [RFC7525] or Datagram TLS (DTLS) over UDP		(TLS) over TCP [RFC5246] [RFC7525] or Datagram TLS (DTLS) over UDP
	[RFC6347] [RFC7525].		[RFC6347] [RFC7525].
	2.3. Encrypting the Transport Header		3.3. Encrypting the Transport Header
	The network layer payload could be encrypted (including the entire		The network layer payload could be encrypted (including the entire
	transport header and payload). This method does not expose any		transport header and payload). This method does not expose any
	transport information to devices in the network, which also prevents		transport information to devices in the network, which also prevents
	modification along the network path.		modification along a network path.
	The IPsec Encapsulating Security Payload (ESP) [RFC4303] is an		The IPsec Encapsulating Security Payload (ESP) [RFC4303] is an
	example of encryption at the network layer, it encrypts and		example of encryption at the network layer, it encrypts and
	authenticates all transport headers, preventing visibility of the		authenticates all transport headers, preventing visibility of the
	headers by in-network devices. Some Virtual Private Network (VPN)		headers by in-network devices. Some Virtual Private Network (VPN)
	methods also encrypt these headers.		methods also encrypt these headers.
	2.4. Authenticating Transport Information and Selectively Encrypting		3.4. Authenticating Transport Information and Selectively Encrypting
	the Transport Header		the Transport Header
	A transport protocol design can encrypt selected header fields, while		A transport protocol design can encrypt selected header fields, while
	also choosing to authenticate fields in the transport header. This		also choosing to authenticate fields in the transport header. This
	allows specific transport header fields to be made observable by		allows specific transport header fields to be made observable by
	network devices. End-to end integrity checks can prevent an endpoint		network devices. End-to end integrity checks can prevent an endpoint
	from undetected modification of the immutable transport headers.		from undetected modification of the immutable transport headers.
	The choice of which fields to expose and which to encrypt is a design		The choice of which fields to expose and which to encrypt is a design
	choice for the transport protocol. Any selective encryption method		choice for the transport protocol. Any selective encryption method
	skipping to change at page 18, line 46 ¶		skipping to change at page 19, line 33 ¶
	designer to decide which header fields to encrypt. On the one hand,		designer to decide which header fields to encrypt. On the one hand,
	security work typically employs a design technique that seeks to		security work typically employs a design technique that seeks to
	expose only what is needed. On the other hand, there may be		expose only what is needed. On the other hand, there may be
	performance and operational benefits in exposing selected information		performance and operational benefits in exposing selected information
	to network tools.		to network tools.
	Mutable fields in the transport header provide opportunities for		Mutable fields in the transport header provide opportunities for
	middleboxes to modify the transport behaviour (e.g., the extended		middleboxes to modify the transport behaviour (e.g., the extended
	headers described in [I-D.trammell-plus-abstract-mech]). This		headers described in [I-D.trammell-plus-abstract-mech]). This
	considers only immutable fields in the transport headers, that is,		considers only immutable fields in the transport headers, that is,
	fields that may be authenticated end-to-end across a path.		fields that may be authenticated End-to-End across a path.
	An example of a method that encrypts some, but not all, transport		An example of a method that encrypts some, but not all, transport
	information is GRE-in-UDP [RFC8086] when used with GRE encryption.		information is GRE-in-UDP [RFC8086] when used with GRE encryption.
	2.5. Adding Transport Information to Network-Layer Protocol Headers		3.5. Adding Transport Information to Network-Layer Protocol Headers
	The transport information can be made visible in a network-layer		The transport information can be made visible in a network-layer
	header. This has the advantage that this information can then be		header. This has the advantage that this information can then be
	observed by in-network devices. This has the advantage that a single		observed by in-network devices. This has the advantage that a single
	header can support all transport protocols, but there may also be		header can support all transport protocols, but there may also be
	less desirable implications of separating the operation of the		less desirable implications of separating the operation of the
	transport protocol from the measurement framework.		transport protocol from the measurement framework.
	Some measurements may be made by adding additional protocol headers		Some measurements may be made by adding additional protocol headers
	carrying operations, administration and management (OAM) information		carrying operations, administration and management (OAM) information
	to packets at the ingress to a maintenance domain (e.g., an Ethernet		to packets at the ingress to a maintenance domain (e.g., an Ethernet
	protocol header with timestamps and sequence number information using		protocol header with timestamps and sequence number information using
	a method such as 802.11ag) and removing the additional header at the		a method such as 802.11ag or in-situ OAM [I-D.ietf-ippm-ioam-data])
	egress of the maintenance domain. This approach enables some types		and removing the additional header at the egress of the maintenance
	of measurements, but does not cover the entire range of measurements		domain. This approach enables some types of measurements, but does
	described in this document.		not cover the entire range of measurements described in this
			document. In some cases, it can be difficult to position measurement
			tools at the required segments/nodes and there can be challenges in
			correlating the downsream/upstream information when in-band OAM data
			is inserted by an on-path device.
	Another example of a network-layer approach is the IPv6 Performance		Another example of a network-layer approach is the IPv6 Performance
	and Diagnostic Metrics (PDM) Destination Option [I-D.ietf-ippm-6man-		and Diagnostic Metrics (PDM) Destination Option [I-D.ietf-ippm-6man-
	pdm-option]. This allows a sender to optionally include a		pdm-option]. This allows a sender to optionally include a
	destination option that caries header fields that can be used to		destination option that caries header fields that can be used to
	observe timestamps and packet sequence numbers. This information		observe timestamps and packet sequence numbers. This information
	could be authenticated by receiving transport endpoints when the		could be authenticated by receiving transport endpoints when the
	information is added at the sender and visible at the receiving		information is added at the sender and visible at the receiving
	endpoint, although methods to do this have not currently been		endpoint, although methods to do this have not currently been
	proposed. This method needs to be explicitly enabled at the sender.		proposed. This method needs to be explicitly enabled at the sender.
	A drawback of using extension headers is that IPv4 network options		It can be undesirable to rely on methods requiring options or
	are often not supported (or are carried on a slower processing path)		extension headers. IPv4 network options are often not supported (or
	and some IPv6 networks are also known to drop packets that set an		are carried on a slower processing path) and some IPv6 networks are
	IPv6 header extension. Another disadvantage is that protocols that		also known to drop packets that set an IPv6 header extension (e.g.,
	separately expose header information do not necessarily have an		[RFC7872]). Another disadvantage is that protocols that separately
	advantage to expose the information that is utilised by the protocol		expose header information do not necessarily have an advantage to
	itself, and could manipulate this header information to gain an		expose the information that is utilised by the protocol itself, and
	advantage from the network.		could manipulate this header information to gain an advantage from
			the network.
	3. Implications of Protecting the Transport Headers		4. Implications of Protecting the Transport Headers
	This section explores key implications of working with encrypted		This section explores key implications of working with encrypted
	transport protocols.		transport protocols.
	3.1. Independent Measurement		4.1. Independent Measurement
	Independent observation by multiple actors is important for		Independent observation by multiple actors is important for
	scientific analysis. Encrypting transport header encryption changes		scientific analysis. Encrypting transport header encryption changes
	the ability for other actors to collect and independently analyse		the ability for other actors to collect and independently analyse
	data. Internet transport protocols employ a set of mechanisms. Some		data. Internet transport protocols employ a set of mechanisms. Some
	of these need to work in cooperation with the network layer - loss		of these need to work in cooperation with the network layer - loss
	detection and recovery, congestion detection and congestion control,		detection and recovery, congestion detection and congestion control,
	some of these need to work only end-to-end (e.g., parameter		some of these need to work only End-to-End (e.g., parameter
	negotiation, flow-control).		negotiation, flow-control).
	When encryption conceals information in the transport header, it		When encryption conceals information in the transport header, it
	could be possible for an applications to provide summary data on		could be possible for an applications to provide summary data on
	performance and usage of the network. This data could be made		performance and usage of the network. This data could be made
	available to other actors. However, this data needs to contain		available to other actors. However, this data needs to contain
	sufficient detail to understand (and possibly reconstruct the network		sufficient detail to understand (and possibly reconstruct the network
	traffic pattern for further testing) and to be correlated with the		traffic pattern for further testing) and to be correlated with the
	configuration of the network paths being measured. Sharing		configuration of the network paths being measured. Sharing
	information between actors needs also to consider the privacy of the		information between actors needs also to consider the privacy of the
	skipping to change at page 20, line 28 ¶		skipping to change at page 21, line 24 ¶
	information. Protocols that expose the state information used by the		information. Protocols that expose the state information used by the
	transport protocol in their header information (e.g., timestamps used		transport protocol in their header information (e.g., timestamps used
	to calculate the RTT, packet numbers used to asses congestion and		to calculate the RTT, packet numbers used to asses congestion and
	requests for retransmission) provide an incentive for the sending		requests for retransmission) provide an incentive for the sending
	endpoint to provide correct information, increasing confidence that		endpoint to provide correct information, increasing confidence that
	the observer understands the transport interaction with the network.		the observer understands the transport interaction with the network.
	This becomes important when considering changes to transport		This becomes important when considering changes to transport
	protocols, changes in network infrastructure, or the emergence of new		protocols, changes in network infrastructure, or the emergence of new
	traffic patterns.		traffic patterns.
	3.2. Characterising "Unknown" Network Traffic		4.2. Characterising "Unknown" Network Traffic
	The patterns and types of traffic that share Internet capacity		The patterns and types of traffic that share Internet capacity
	changes with time as networked applications, usage patterns and		changes with time as networked applications, usage patterns and
	protocols continue to evolve.		protocols continue to evolve.
	If "unknown" or "uncharacterised" traffic patterns form a small part		If "unknown" or "uncharacterised" traffic patterns form a small part
	of the traffic aggregate passing through a network device or segment		of the traffic aggregate passing through a network device or segment
	of the network the path, the dynamics of the uncharacterised traffic		of the network the path, the dynamics of the uncharacterised traffic
	may not have a significant collateral impact on the performance of		may not have a significant collateral impact on the performance of
	other traffic that shares this network segment. Once the proportion		other traffic that shares this network segment. Once the proportion
	skipping to change at page 20, line 50 ¶		skipping to change at page 21, line 46 ¶
	determine if appropriate safety measures need to be put in place.		determine if appropriate safety measures need to be put in place.
	Tracking the impact of new mechanisms and protocols requires traffic		Tracking the impact of new mechanisms and protocols requires traffic
	volume to be measured and new transport behaviours to be identified.		volume to be measured and new transport behaviours to be identified.
	This is especially true of protocols operating over a UDP substrate.		This is especially true of protocols operating over a UDP substrate.
	The level and style of encryption needs to be considered in		The level and style of encryption needs to be considered in
	determining how this activity is performed. On a shorter timescale,		determining how this activity is performed. On a shorter timescale,
	information may also need to be collected to manage denial of service		information may also need to be collected to manage denial of service
	attacks against the infrastructure.		attacks against the infrastructure.
	3.3. Accountability and Internet Transport Protocols		4.3. Accountability and Internet Transport Protocols
	Information provided by tools observing transport headers can help		Information provided by tools observing transport headers can help
	determine whether mechanisms are needed in the network to prevent		determine whether mechanisms are needed in the network to prevent
	flows from acquiring excessive network capacity, and where needed to		flows from acquiring excessive network capacity, and where needed to
	deploy appropriate tools Section 1.1.2.4. Obfuscating or hiding this		deploy appropriate tools Section 2.2.4. Obfuscating or hiding this
	information using encryption is expected to lead operators and		information using encryption is expected to lead operators and
	maintainers of middleboxes (firewalls, etc.) to seek other methods to		maintainers of middleboxes (firewalls, etc.) to seek other methods to
	classify and mechanisms to condition network traffic. A lack of data		classify and mechanisms to condition network traffic.
	seems likely to reduce the level of precision with which these
	mechanisms are applied, and this needs to be considered when
	evaluating the impact of designs for transport encryption.
	3.4. Impact on Research, Development and Deployment		A lack of data seems likely to reduce the level of precision with
			which these mechanisms are applied, and this needs to be considered
			when evaluating the impact of designs for transport encryption. This
			could lead to increased use of rate limiting, circuit breaker
			techniques [RFC8084], or even blocking of uncharacterised traffic.
			This would hinder deployment of new mechanisms and/or protocols.
			4.4. Impact on Research, Development and Deployment
	Measurement data is increasingly being used to inform design		Measurement data is increasingly being used to inform design
	decisions in networking research, during development of new		decisions in networking research, during development of new
	mechanisms and protocols and in standardisation. Measurement has a		mechanisms and protocols and in standardisation. Measurement has a
	critical role in the design of transport protocol mechanisms and		critical role in the design of transport protocol mechanisms and
	their acceptance by the wider community (e.g., as a method to judge		their acceptance by the wider community (e.g., as a method to judge
	the safety for Internet deployment). Observation of pathologies are		the safety for Internet deployment). Observation of pathologies are
	also important in understanding the interactions between cooperating		also important in understanding the interactions between cooperating
	protocols and network mechanism, the implications of sharing capacity		protocols and network mechanism, the implications of sharing capacity
	with other traffic and the impact of different patterns of usage.		with other traffic and the impact of different patterns of usage.
	skipping to change at page 21, line 41 ¶		skipping to change at page 22, line 38 ¶
	therefore typically evolve as a protocol matures, or in response to		therefore typically evolve as a protocol matures, or in response to
	changes in network conditions, changes in network traffic or changes		changes in network conditions, changes in network traffic or changes
	to application usage.		to application usage.
	The growth and diversity of applications and protocols using the		The growth and diversity of applications and protocols using the
	Internet continues to expand - and there has been recent interest in		Internet continues to expand - and there has been recent interest in
	a wide range of new transport methods, e.g., Larger Initial Window,		a wide range of new transport methods, e.g., Larger Initial Window,
	Proportional Rate Reduction (PRR), congestion control methods based		Proportional Rate Reduction (PRR), congestion control methods based
	on measuring bottleneck bandwidth and round-trip propagation time,		on measuring bottleneck bandwidth and round-trip propagation time,
	the introduction of AQM techniques and new forms of ECN response		the introduction of AQM techniques and new forms of ECN response
	(e.g., Data Centre TCP, DCTP [I-D.ietf-tcpm-dctcp], and methods		(e.g., DCTP, and methods proposed for L4S). For each new method it is
	proposed for Low Latency Low Loss Scalable throughput, L4S). For		desirable to build a body of data reflecting its behaviour under a
	each new method it is desirable to build a body of data reflecting		wide range of deployment scenarios, traffic load, and interactions
	its behaviour under a wide range of deployment scenarios, traffic		with other deployed/candidate methods.
	load, and interactions with other deployed/candidate methods.
	Open standards motivate a desire for this evaluation to include		Open standards motivate a desire for this evaluation to include
	independent observation and evaluation of performance data, which in		independent observation and evaluation of performance data, which in
	turn suggests control over where and when measurement samples are		turn suggests control over where and when measurement samples are
	collected. This requires consideration of the appropriate balance		collected. This requires consideration of the appropriate balance
	between encrypting all and no transport information.		between encrypting all and no transport information.
	4. Acknowledgements		5. Acknowledgements
	The author would like to thank all who have talked to him face-to-		The author would like to thank all who have talked to him face-to-
	face or via email. ...		face or via email. ...
	This work has received funding from the European Union's Horizon 2020		This work has received funding from the European Union's Horizon 2020
	research and innovation programme under grant agreement No 688421.The		research and innovation programme under grant agreement No 688421.The
	opinions expressed and arguments employed reflect only the authors'		opinions expressed and arguments employed reflect only the authors'
	view. The European Commission is not responsible for any use that		view. The European Commission is not responsible for any use that
	may be made of that information.		may be made of that information.
	5. Security Considerations		6. Security Considerations
	This document is about design and deployment considerations for		This document is about design and deployment considerations for
	transport protocols. Authentication, confidentiality protection, and		transport protocols. Authentication, confidentiality protection, and
	integrity protection are identified as Transport Features by		integrity protection are identified as Transport Features by
	RFC8095". As currently deployed in the Internet, these features are		RFC8095". As currently deployed in the Internet, these features are
	generally provided by a protocol or layer on top of the transport		generally provided by a protocol or layer on top of the transport
	protocol; no current full-featured standards-track transport protocol		protocol; no current full-featured standards-track transport protocol
	provides these features on its own. Therefore, these features are		provides these features on its own. Therefore, these features are
	not considered in this document, with the exception of native		not considered in this document, with the exception of native
	authentication capabilities of TCP and SCTP for which the security		authentication capabilities of TCP and SCTP for which the security
	skipping to change at page 22, line 34 ¶		skipping to change at page 23, line 34 ¶
	Open data, and accessibility to tools that can help understand trends		Open data, and accessibility to tools that can help understand trends
	in application deployment, network traffic and usage patterns can all		in application deployment, network traffic and usage patterns can all
	contribute to understanding security challenges. Standard protocols		contribute to understanding security challenges. Standard protocols
	and understanding of the interactions between mechanisms and traffic		and understanding of the interactions between mechanisms and traffic
	patterns can also provide valuable insight into appropriate security		patterns can also provide valuable insight into appropriate security
	design. Like congestion control mechanisms, security mechanisms are		design. Like congestion control mechanisms, security mechanisms are
	difficult to design and implement correctly. It is hence recommended		difficult to design and implement correctly. It is hence recommended
	that applications employ well-known standard security mechanisms such		that applications employ well-known standard security mechanisms such
	as DTLS, TLS or IPsec, rather than inventing their own.		as DTLS, TLS or IPsec, rather than inventing their own.
	6. IANA Considerations		7. IANA Considerations
	XX RFC ED - PLEASE REMOVE THIS SECTION XXX		XX RFC ED - PLEASE REMOVE THIS SECTION XXX
	This memo includes no request to IANA.		This memo includes no request to IANA.
	7. References		8. References
	7.1. Normative References		8.1. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/		Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
	RFC2119, March 1997, <http://www.rfc-editor.org/info/		RFC2119, March 1997, <http://www.rfc-editor.org/info/
	rfc2119>.		rfc2119>.
	7.2. Informative References		8.2. Informative References
	[I-D.dolson-plus-middlebox-benefits]		[I-D.dolson-plus-middlebox-benefits]
	Dolson, D., Snellman, J., Boucadair, M. and C. Jacquenet,		Dolson, D., Snellman, J., Boucadair, M. and C. Jacquenet,
	"Beneficial Functions of Middleboxes", Internet-Draft		"Beneficial Functions of Middleboxes", Internet-Draft
	draft-dolson-plus-middlebox-benefits-03, March 2017.		draft-dolson-plus-middlebox-benefits-03, March 2017.
	[I-D.ietf-aqm-codel]		[I-D.ietf-aqm-codel]
	Nichols, K., Jacobson, V., McGregor, A. and J. Jana,		Nichols, K., Jacobson, V., McGregor, A. and J. Jana,
	"Controlled Delay Active Queue Management", Internet-Draft		"Controlled Delay Active Queue Management", Internet-Draft
	draft-ietf-aqm-codel-00, October 2014.		draft-ietf-aqm-codel-00, October 2014.
	skipping to change at page 23, line 25 ¶		skipping to change at page 24, line 25 ¶
	Lightweight Control Scheme To Address the Bufferbloat		Lightweight Control Scheme To Address the Bufferbloat
	Problem", Internet-Draft draft-ietf-aqm-pie-00, October		Problem", Internet-Draft draft-ietf-aqm-pie-00, October
	2014.		2014.
	[I-D.ietf-ippm-6man-pdm-option]		[I-D.ietf-ippm-6man-pdm-option]
	Elkins, N., Hamilton, R. and m. mackermann@bcbsm.com,		Elkins, N., Hamilton, R. and m. mackermann@bcbsm.com,
	"IPv6 Performance and Diagnostic Metrics (PDM) Destination		"IPv6 Performance and Diagnostic Metrics (PDM) Destination
	Option", Internet-Draft draft-ietf-ippm-6man-pdm-		Option", Internet-Draft draft-ietf-ippm-6man-pdm-
	option-10, May 2017.		option-10, May 2017.
			[I-D.ietf-ippm-ioam-data]
			Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
			Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
			P., Chang, R. and d. daniel.bernier@bell.ca, "Data Fields
			for In-situ OAM", Internet-Draft draft-ietf-ippm-ioam-
			data-01, October 2017.
	[I-D.ietf-quic-transport]		[I-D.ietf-quic-transport]
	Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed		Iyengar, J. and M. Thomson, "QUIC: A UDP-Based Multiplexed
	and Secure Transport", Internet-Draft draft-ietf-quic-		and Secure Transport", Internet-Draft draft-ietf-quic-
	transport-03, May 2017.		transport-03, May 2017.
	[I-D.ietf-tcpm-accurate-ecn]		[I-D.ietf-tcpm-accurate-ecn]
	Briscoe, B., Kuehlewind, M. and R. Scheffenegger, "More		Briscoe, B., Kuehlewind, M. and R. Scheffenegger, "More
	Accurate ECN Feedback in TCP", Internet-Draft draft-ietf-		Accurate ECN Feedback in TCP", Internet-Draft draft-ietf-
	tcpm-accurate-ecn-00, December 2015.		tcpm-accurate-ecn-00, December 2015.
	[I-D.ietf-tcpm-dctcp]
	Bensley, S., Thaler, D., Balasubramanian, P., Eggert, L.
	and G. Judd, "Datacenter TCP (DCTCP): TCP Congestion
	Control for Datacenters", Internet-Draft draft-ietf-tcpm-
	dctcp-06, May 2017.
	[I-D.ietf-tsvwg-l4s-arch]		[I-D.ietf-tsvwg-l4s-arch]
	Briscoe, B., Schepper, K. and M. Bagnulo, "Low Latency,		Briscoe, B., Schepper, K. and M. Bagnulo, "Low Latency,
	Low Loss, Scalable Throughput (L4S) Internet Service:		Low Loss, Scalable Throughput (L4S) Internet Service:
	Architecture", Internet-Draft draft-ietf-tsvwg-l4s-		Architecture", Internet-Draft draft-ietf-tsvwg-l4s-
	arch-00, May 2017.		arch-00, May 2017.
	[I-D.mm-wg-effect-encrypt]		[I-D.mm-wg-effect-encrypt]
	Moriarty, K. and A. Morton, "Effect of Pervasive		Moriarty, K. and A. Morton, "Effect of Pervasive
	Encryption on Operators", Internet-Draft draft-mm-wg-		Encryption on Operators", Internet-Draft draft-mm-wg-
	effect-encrypt-11, April 2017.		effect-encrypt-11, April 2017.
	skipping to change at page 24, line 15 ¶		skipping to change at page 25, line 17 ¶
	"Transport-Independent Path Layer State Management",		"Transport-Independent Path Layer State Management",
	Internet-Draft draft-trammell-plus-statefulness-02,		Internet-Draft draft-trammell-plus-statefulness-02,
	December 2016.		December 2016.
	[Latency] Briscoe, B., "Reducing Internet Latency: A Survey of		[Latency] Briscoe, B., "Reducing Internet Latency: A Survey of
	Techniques and Their Merits", November 2014.		Techniques and Their Merits", November 2014.
	[Measure] Fairhurst, G., Kuehlewind, M. and D. Lopez, "Measurement-		[Measure] Fairhurst, G., Kuehlewind, M. and D. Lopez, "Measurement-
	based Protocol Design", June 2017.		based Protocol Design", June 2017.
			[RFC1273] Schwartz, M.F., "Measurement Study of Changes in Service-
			Level Reachability in the Global TCP/IP Internet: Goals,
			Experimental Design, Implementation, and Policy
			Considerations", RFC 1273, DOI 10.17487/RFC1273, November
			1991, <https://www.rfc-editor.org/info/rfc1273>.
	[RFC2474] Nichols, K., Blake, S., Baker, F. and D. Black,		[RFC2474] Nichols, K., Blake, S., Baker, F. and D. Black,
	"Definition of the Differentiated Services Field (DS		"Definition of the Differentiated Services Field (DS
	Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI		Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI
	10.17487/RFC2474, December 1998, <http://www.rfc-		10.17487/RFC2474, December 1998, <http://www.rfc-
	editor.org/info/rfc2474>.		editor.org/info/rfc2474>.
	[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G. and Z.		[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G. and Z.
	Shelby, "Performance Enhancing Proxies Intended to		Shelby, "Performance Enhancing Proxies Intended to
	Mitigate Link-Related Degradations", RFC 3135, DOI		Mitigate Link-Related Degradations", RFC 3135, DOI
	10.17487/RFC3135, June 2001, <http://www.rfc-editor.org/		10.17487/RFC3135, June 2001, <http://www.rfc-editor.org/
	skipping to change at page 25, line 42 ¶		skipping to change at page 26, line 52 ¶
	rfc5246>.		rfc5246>.
	[RFC5559] Eardley, P., Ed., "Pre-Congestion Notification (PCN)		[RFC5559] Eardley, P., Ed., "Pre-Congestion Notification (PCN)
	Architecture", RFC 5559, DOI 10.17487/RFC5559, June 2009,		Architecture", RFC 5559, DOI 10.17487/RFC5559, June 2009,
	<http://www.rfc-editor.org/info/rfc5559>.		<http://www.rfc-editor.org/info/rfc5559>.
	[RFC5925] Touch, J., Mankin, A. and R. Bonica, "The TCP		[RFC5925] Touch, J., Mankin, A. and R. Bonica, "The TCP
	Authentication Option", RFC 5925, DOI 10.17487/RFC5925,		Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
	June 2010, <http://www.rfc-editor.org/info/rfc5925>.		June 2010, <http://www.rfc-editor.org/info/rfc5925>.
			[RFC6269] Ford, M., Ed., Boucadair, M., Durand, A., Levis, P. and P.
			Roberts, "Issues with IP Address Sharing", RFC 6269, DOI
			10.17487/RFC6269, June 2011, <https://www.rfc-editor.org/
			info/rfc6269>.
	[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer		[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
	Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,		Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
	January 2012, <http://www.rfc-editor.org/info/rfc6347>.		January 2012, <http://www.rfc-editor.org/info/rfc6347>.
	[RFC6437] Amante, S., Carpenter, B., Jiang, S. and J. Rajahalme,		[RFC6437] Amante, S., Carpenter, B., Jiang, S. and J. Rajahalme,
	"IPv6 Flow Label Specification", RFC 6437, DOI 10.17487/		"IPv6 Flow Label Specification", RFC 6437, DOI 10.17487/
	RFC6437, November 2011, <http://www.rfc-editor.org/info/		RFC6437, November 2011, <http://www.rfc-editor.org/info/
	rfc6437>.		rfc6437>.
	[RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.		[RFC6679] Westerlund, M., Johansson, I., Perkins, C., O'Hanlon, P.
	skipping to change at page 26, line 32 ¶		skipping to change at page 27, line 46 ¶
	"Confidentiality in the Face of Pervasive Surveillance: A		"Confidentiality in the Face of Pervasive Surveillance: A
	Threat Model and Problem Statement", RFC 7624, DOI		Threat Model and Problem Statement", RFC 7624, DOI
	10.17487/RFC7624, August 2015, <http://www.rfc-editor.org/		10.17487/RFC7624, August 2015, <http://www.rfc-editor.org/
	info/rfc7624>.		info/rfc7624>.
	[RFC7713] Mathis, M. and B. Briscoe, "Congestion Exposure (ConEx)		[RFC7713] Mathis, M. and B. Briscoe, "Congestion Exposure (ConEx)
	Concepts, Abstract Mechanism, and Requirements", RFC 7713,		Concepts, Abstract Mechanism, and Requirements", RFC 7713,
	DOI 10.17487/RFC7713, December 2015, <http://www.rfc-		DOI 10.17487/RFC7713, December 2015, <http://www.rfc-
	editor.org/info/rfc7713>.		editor.org/info/rfc7713>.
			[RFC7872] Gont, F., Linkova, J., Chown, T. and W. Liu, "Observations
			on the Dropping of Packets with IPv6 Extension Headers in
			the Real World", RFC 7872, DOI 10.17487/RFC7872, June
			2016, <https://www.rfc-editor.org/info/rfc7872>.
	[RFC7928] Kuhn, N., Ed., Natarajan, P., Ed., Khademi, N.Ed., and D.		[RFC7928] Kuhn, N., Ed., Natarajan, P., Ed., Khademi, N.Ed., and D.
	Ros, "Characterization Guidelines for Active Queue		Ros, "Characterization Guidelines for Active Queue
	Management (AQM)", RFC 7928, DOI 10.17487/RFC7928, July		Management (AQM)", RFC 7928, DOI 10.17487/RFC7928, July
	2016, <http://www.rfc-editor.org/info/rfc7928>.		2016, <http://www.rfc-editor.org/info/rfc7928>.
	[RFC8084] Fairhurst, G., "Network Transport Circuit Breakers", BCP		[RFC8084] Fairhurst, G., "Network Transport Circuit Breakers", BCP
	208, RFC 8084, DOI 10.17487/RFC8084, March 2017, <http://		208, RFC 8084, DOI 10.17487/RFC8084, March 2017, <http://
	www.rfc-editor.org/info/rfc8084>.		www.rfc-editor.org/info/rfc8084>.
	[RFC8085] Eggert, L., Fairhurst, G. and G. Shepherd, "UDP Usage		[RFC8085] Eggert, L., Fairhurst, G. and G. Shepherd, "UDP Usage
	skipping to change at page 26, line 54 ¶		skipping to change at page 28, line 22 ¶
	[RFC8086] Yong, L., Ed., Crabbe, E., Xu, X. and T. Herbert, "GRE-in-		[RFC8086] Yong, L., Ed., Crabbe, E., Xu, X. and T. Herbert, "GRE-in-
	UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, March		UDP Encapsulation", RFC 8086, DOI 10.17487/RFC8086, March
	2017, <http://www.rfc-editor.org/info/rfc8086>.		2017, <http://www.rfc-editor.org/info/rfc8086>.
	[RFC8087] Fairhurst, G. and M. Welzl, "The Benefits of Using		[RFC8087] Fairhurst, G. and M. Welzl, "The Benefits of Using
	Explicit Congestion Notification (ECN)", RFC 8087, DOI		Explicit Congestion Notification (ECN)", RFC 8087, DOI
	10.17487/RFC8087, March 2017, <http://www.rfc-editor.org/		10.17487/RFC8087, March 2017, <http://www.rfc-editor.org/
	info/rfc8087>.		info/rfc8087>.
			[RFC8257] Bensley, S., Thaler, D., Balasubramanian, P., Eggert, L.
			and G. Judd, "Data Center TCP (DCTCP): TCP Congestion
			Control for Data Centers", RFC 8257, DOI 10.17487/RFC8257,
			October 2017, <https://www.rfc-editor.org/info/rfc8257>.
	[Tor] The Tor Project, ., "https://www.torproject.org", June		[Tor] The Tor Project, ., "https://www.torproject.org", June
	2017.		2017.
	Appendix A. Revision information		Appendix A. Revision information
	-00 This is an individual draft for the IETF community.		-00 This is an individual draft for the IETF community.
	-01 This draft was a result of walking away from the text for a few		-01 This draft was a result of walking away from the text for a few
	days and then reorganising the content.		days and then reorganising the content.
	-02 This draft fixes textual errors.		-02 This draft fixes textual errors.
	-03 This draft follows feedback from people reading this draft.		-03 This draft follows feedback from people reading this draft.
	-04 This adds an additional contributore and includes significant		-04 This adds an additional contributor and includes significant
	reworking to ready this for review by the wider IETF community Colin		reworking to ready this for review by the wider IETF community Colin
	Perkins joined the author list.		Perkins joined the author list.
	Comments from the community are welcome on the text and		Comments from the community are welcome on the text and
	recommendations.		recommendations.
	Authors' Addresses		-05 Corrections received and helpful inputs from Mohamed Boucadair.
			Authors' Addresses
	Godred Fairhurst		Godred Fairhurst
	University of Aberdeen		University of Aberdeen
	Department of Engineering		Department of Engineering
	Fraser Noble Building		Fraser Noble Building
	Aberdeen, AB24 3UE		Aberdeen, AB24 3UE
	Scotland		Scotland
	Email: gorry@erg.abdn.ac.uk		Email: gorry@erg.abdn.ac.uk
	URI: http://www.erg.abdn.ac.uk/		URI: http://www.erg.abdn.ac.uk/
End of changes. 99 change blocks.
	266 lines changed or deleted		327 lines changed or added
This html diff was produced by rfcdiff 1.45. The latest version is available from http://tools.ietf.org/tools/rfcdiff/