draft-ietf-tsvwg-transport-encrypt-02.txt   draft-ietf-tsvwg-transport-encrypt-03.txt 
TSVWG G. Fairhurst TSVWG G. Fairhurst
Internet-Draft University of Aberdeen Internet-Draft University of Aberdeen
Intended status: Informational C. Perkins Intended status: Informational C. Perkins
Expires: May 29, 2019 University of Glasgow Expires: May 29, 2019 University of Glasgow
November 25, 2018 November 25, 2018
The Impact of Transport Header Confidentiality on Network Operation and The Impact of Transport Header Confidentiality on Network Operation and
Evolution of the Internet Evolution of the Internet
draft-ietf-tsvwg-transport-encrypt-02 draft-ietf-tsvwg-transport-encrypt-03
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 in-network uses of encryption at the transport layer. It identifies in-network uses of
transport layer header information. It then reviews the implications transport layer header information. It then reviews the implications
of developing end-to-end transport protocols that use authentication of developing end-to-end transport protocols that use authentication
to protect the integrity of transport information or encryption to to protect the integrity of transport information or encryption to
provide confidentiality of the transport protocol header and expected provide confidentiality of the transport protocol header and expected
implications of transport protocol design and network operation. implications of transport protocol design and network operation.
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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Context and Rationale . . . . . . . . . . . . . . . . . . . . 3 2. Context and Rationale . . . . . . . . . . . . . . . . . . . . 3
3. Current uses of Transport Headers within the Network . . . . 10 3. Current uses of Transport Headers within the Network . . . . 10
3.1. Observing Transport Information in the Network . . . . . 10 3.1. Observing Transport Information in the Network . . . . . 10
3.2. Transport Measurement . . . . . . . . . . . . . . . . . . 15 3.2. Transport Measurement . . . . . . . . . . . . . . . . . . 16
3.3. Use for Network Diagnostics and Troubleshooting . . . . . 19 3.3. Use for Network Diagnostics and Troubleshooting . . . . . 19
3.4. Use of transport information to influence network 3.4. Header Compression . . . . . . . . . . . . . . . . . . . 20
forwarding . . . . . . . . . . . . . . . . . . . . . . . 20
4. Encryption and Authentication of Transport Headers . . . . . 21 4. Encryption and Authentication of Transport Headers . . . . . 21
5. Addition of Transport Information to Network-Layer Protocol 5. Addition of Transport Information to Network-Layer Protocol
Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Headers . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
5.1. Use of transport information to influence network 6. Implications of Protecting the Transport Headers . . . . . . 26
forwarding . . . . . . . . . . . . . . . . . . . . . . . 25 6.1. Independent Measurement . . . . . . . . . . . . . . . . . 26
5.2. Network-layer measurement . . . . . . . . . . . . . . . . 27 6.2. Characterising "Unknown" Network Traffic . . . . . . . . 27
6. Implications of Protecting the Transport Headers . . . . . . 28 6.3. Accountability and Internet Transport Protocols . . . . . 27
6.1. Independent Measurement . . . . . . . . . . . . . . . . . 28 6.4. Impact on Research, Development and Deployment . . . . . 28
6.2. Characterising "Unknown" Network Traffic . . . . . . . . 29 7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 29
6.3. Accountability and Internet Transport Protocols . . . . . 29 8. Security Considerations . . . . . . . . . . . . . . . . . . . 31
6.4. Impact on Research, Development and Deployment . . . . . 30 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 33
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 31 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 33
8. Security Considerations . . . . . . . . . . . . . . . . . . . 33 11. Informative References . . . . . . . . . . . . . . . . . . . 33
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35 Appendix A. Revision information . . . . . . . . . . . . . . . . 40
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 35 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 41
11. Informative References . . . . . . . . . . . . . . . . . . . 36
Appendix A. Revision information . . . . . . . . . . . . . . . . 42
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42
1. Introduction 1. Introduction
There is increased interest in, and deployment of, new protocols that There is increased interest in, and deployment of, new protocols that
employ end-to-end encryption at the transport layer, including the employ end-to-end encryption at the transport layer, including the
transport layer headers. An example of such a transport is the QUIC transport layer headers. An example of such a transport is the QUIC
transport protocol [I-D.ietf-quic-transport], currently being transport protocol [I-D.ietf-quic-transport], currently being
standardised in the IETF. Encryption of transport layer headers and standardised in the IETF. Encryption of transport layer headers and
payload data has many benefits in terms of protecting user privacy. payload data has many benefits in terms of protecting user privacy.
These benefits have been widely discussed, and we strongly support These benefits have been widely discussed [RFC7258], [RFC7624], and
them. There are also, however, some costs, in that the wide use of this document strongly supports the increased use of encryption in
transport encryption requires changes to network operations, and transport protocols. There are also, however, some costs, in that
complicates network measurement for research, operational, and the widespread use of transport encryption requires changes to
standardisation purposes. network operations, and complicates network measurement for research,
operational, and standardisation purposes.
This document discusses some consequences of applying end-to-end This document discusses some consequences of applying end-to-end
encryption at the transport layer. It reviews the implications of encryption at the transport layer. It reviews the implications of
developing end-to-end transport protocols that use encryption to developing end-to-end transport protocols that use encryption to
provide confidentiality of the transport protocol header, and provide confidentiality of the transport protocol header, and
consider the effect of such changes on transport protocol design and considers the effect of such changes on transport protocol design and
network operation. It also considers anticipated implications on network operations. It also considers anticipated implications on
transport and application evolution. transport and application evolution.
Transports are increasingly encrypting and authenticating the payload
(i.e., the application data carried within the transport connection)
end-to-end. Such protection is encouraged, and iits implications are
not further discussed in this memo.
2. Context and Rationale 2. Context and Rationale
The transport layer provides end-to-end interactions between The transport layer provides end-to-end interactions between
endpoints (processes) using an Internet path. Transport protocols endpoints (processes) using an Internet path. Transport protocols
layer directly over the network-layer service and are sent in the layer directly over the network-layer service and are sent in the
payload of network-layer packets. They support end-to-end payload of network-layer packets. They support end-to-end
communication between applications, supported by higher-layer communication between applications, supported by higher-layer
protocols, running on the end systems (or transport endpoints). This protocols, running on the end systems (or transport endpoints). This
simple architectural view hides one of the core functions of the simple architectural view hides one of the core functions of the
transport, however, to discover and adapt to the properties of the transport, however, to discover and adapt to the properties of the
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In both cases, the issue was caused by middleboxes that had a hard- In both cases, the issue was caused by middleboxes that had a hard-
coded understanding of transport behaviour, and that interacted coded understanding of transport behaviour, and that interacted
poorly with transports that tried to change that behaviour. Other poorly with transports that tried to change that behaviour. Other
examples have included middleboxes that rewrite TCP sequence and examples have included middleboxes that rewrite TCP sequence and
acknowledgement numbers but are unaware of the (newer) SACK option acknowledgement numbers but are unaware of the (newer) SACK option
and don't correctly rewrite selective acknowledgements to match the and don't correctly rewrite selective acknowledgements to match the
changes made to the fixed TCP header. changes made to the fixed TCP header.
A protocol design that uses header encryption can provide A protocol design that uses header encryption can provide
confidentiality of some or all of the protocol header information. confidentiality of some or all of the protocol header information.
This prevents an on-path device from knowledge of the header field. This prevents an on-path device from gaining knowledge of the header
It therefore prevents mechanisms being built that directly rely on field. It therefore prevents mechanisms being built that directly
the information or seek to infer semantics of an exposed header rely on the information or seek to infer semantics of an exposed
field. Using encryption to provide confidentiality of the transport header field. Using encryption to provide confidentiality of the
layer brings some well-known privacy and security benefits and can transport layer brings some well-known privacy and security benefits
therefore help reduce ossification of the transport layer. In and can therefore help reduce ossification of the transport layer.
particular, it is important that protocols either do not expose In particular, it is important that protocols either do not expose
information where the usage could change in future protocols, or that information where the usage could change in future protocols, or that
methods that utilise the information are robust to potential changes methods that utilise the information are robust to potential changes
as protocols evolve over time. To avoid unwanted inspection, a as protocols evolve over time. To avoid unwanted inspection, a
protocol could also intentionally vary the format and/or value of protocol could also intentionally vary the format and/or value of
header fields (sometimes known as Greasing header fields (sometimes known as Greasing
[I-D.thomson-quic-grease]). However, while encryption hides the [I-D.thomson-quic-grease]). However, while encryption hides the
protocol header information, it does not prevent ossification of the protocol header information, it does not prevent ossification of the
network service: People seeking understanding of network traffic network service. People seeking understanding of network traffic
could come to rely on pattern inferences and other heuristics as the could come to rely on pattern inferences and other heuristics as the
basis for network decision and to derive measurement data, creating basis for network decision and to derive measurement data, creating
new dependencies on the transport protocol. new dependencies on the transport protocol.
Specification of non-encrypted transport header fields explicitly Specification of non-encrypted transport header fields explicitly
allows protocol designers to make specific header information allows protocol designers to make specific header information
observable in the network. This supports other uses of this observable in the network. This supports other uses of this
information by on-path devices, and at the same time this can be information by on-path devices, and at the same time this can be
expected to lead to ossification of the transport header, because expected to lead to ossification of the transport header, because
network forwarding could evolve to depend on the presence and/or network forwarding could evolve to depend on the presence and/or
value of these fields. The decision about which transport headers value of these fields. The decision about which transport headers
fields are made observable offers trade-offs around authentication, fields are made observable offers trade-offs around authentication
and confidentiality. For example, a design that provides and confidentiality versus observability, network operations and
management, and ossification. For example, a design that provides
confidentiality of protocol header information can impact the confidentiality of protocol header information can impact the
following activities that rely on measurement and analysis of traffic following activities that rely on measurement and analysis of traffic
flows: flows:
Network Operations and Research: Observable transport headers enable Network Operations and Research: Observable transport headers enable
both 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
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The data can also inform Internet engineering research, and help The data can also inform Internet engineering research, and help
in the development of new protocols, methodologies, and in the development of new protocols, methodologies, and
procedures. Concealing the transport protocol header information procedures. Concealing the transport protocol header information
makes the stream performance unavailable to passive observers makes the stream performance unavailable to passive observers
along the path, and likely leads to the development of alternative along the path, and likely leads to the development of alternative
methods to collect or infer that data. methods to collect or infer that data.
Providing confidentiality of the transport payload, but leaving Providing confidentiality of the transport payload, but leaving
some, or all, of the transport headers unencrypted, possibly with some, or all, of the transport headers unencrypted, possibly with
authentication, can provide the majority of the privacy and authentication, can provide the majority of the privacy and
security benefits while supporting operations and research. security benefits while supporting operations and research, but at
the cost of ossifying the transport headers.
Protection from Denial of Service: Observable transport headers Protection from Denial of Service: Observable transport headers
currently provide useful input to classify traffic and detect currently provide useful input to classify traffic and detect
anomalous events (e.g., changes in application behaviour, anomalous events (e.g., changes in application behaviour,
distributed denial of service attacks). To be effective, this distributed denial of service attacks). To be effective, this
protection needs to be able to uniquely disambiguate unwanted protection needs to be able to uniquely disambiguate unwanted
traffic. An inability to separate this traffic using packet traffic. An inability to separate this traffic using packet
header information could result in less-efficient identification header information could result in less-efficient identification
of unwanted traffic or development of different methods (e.g. of unwanted traffic or development of different methods (e.g.
rate-limiting of uncharacterised traffic). rate-limiting of uncharacterised traffic).
Network Troubleshooting and Diagnostics: Encrypting transport Network Troubleshooting and Diagnostics: Encrypting transport
header information eliminates the incentive for operators to header information eliminates the incentive for operators to
troubleshoot what they cannot interpret. A flow experiencing troubleshoot since they cannot interpret the data. A flow
packet loss or jitter looks like an unaffected flow when only experiencing packet loss or jitter looks like an unaffected flow
observing network layer headers (if transport sequence numbers and when only observing network layer headers (if transport sequence
flow identifiers are obscured). This limits understanding of the numbers and flow identifiers are obscured). This limits
impact of packet loss or latency on the flows, or even localizing understanding of the impact of packet loss or latency on the
the network segment causing the packet loss or latency. Encrypted flows, or even localizing the network segment causing the packet
traffic could imply "don't touch" to some, and could limit a loss or latency. Encrypted traffic could imply "don't touch" to
trouble-shooting response to "can't help, no trouble found". The some, and could limit a trouble-shooting response to "can't help,
additional mechanisms that will need to be introduced to help no trouble found". Additional mechanisms will need to be
reconstruct transport-level metrics add complexity and operational introduced to help reconstruct or replace transport-level metrics
costs (e.g., in deploying additional functions in equipment or to support troubleshooting and diagnostics, but these add
adding traffic overhead). complexity and operational costs (e.g., in deploying additional
functions in equipment or adding traffic overhead).
Network Traffic Analysis: Hiding transport protocol header Network Traffic Analysis: Hiding transport protocol header
information can make it harder to determine which transport information can make it harder to determine which transport
protocols and features are being used across a network segment and protocols and features are being used across a network segment and
to measure trends in the pattern of usage. This could impact the to measure trends in the pattern of usage. This could impact the
ability for an operator to anticipate the need for network 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 (such as determining engineering activities performed by operators (such as determining
which parts of the path contribute delay, jitter or loss). While which parts of the path contribute delay, jitter or loss). While
the impact could, in many cases, be small there are scenarios the impact could, in many cases, be small there are scenarios
where operators directly support particular services (e.g., to where operators directly support particular services (e.g., to
troubleshoot issues relating to Quality of Service, QoS; the troubleshoot issues relating to Quality of Service, QoS; the
ability to perform fast re-routing of critical traffic, or support ability to perform fast re-routing of critical traffic, or support
to mitigate the characteristics of specific radio links). The to mitigate the characteristics of specific radio links). The
more complex the underlying infrastructure the more important this more complex the underlying infrastructure the more important this
impact. impact.
Open and Verifiable Network Data: Hiding transport protocol header Open and Verifiable Network Data: Hiding transport protocol header
information can reduce the range of actors that can capture useful information can reduce the range of actors that can capture useful
measurement data. For example, one approach could be to employ an measurement data. This limits the information sources available
existing transport protocol that reveals little information (e.g., to the Internet community to understand the operation of new
UDP), and perform traditional transport functions at higher layers transport protocols, so preventing access to the information
protecting the confidentiality of transport information. Such a necessary to inform design decisions and standardisation of the
design, limits the information sources available to the Internet new protocols and related operational practices.
community to understand the operation of new transport protocols,
so preventing access to the information necessary to inform design
decisions and standardisation of the new protocols and related
operational practices.
The cooperating dependence of network, application, and host to The cooperating dependence of network, application, and host to
provide communication performance on the Internet is uncertain provide communication performance on the Internet is uncertain
when only endpoints (i.e., at user devices and within service when only endpoints (i.e., at user devices and within service
platforms) can observe performance, and performance cannot be platforms) can observe performance, and when performance cannot be
independently verified by all parties. The ability of other independently verified by all parties. The ability of other
stakeholders to review code can help develop deeper insight. In stakeholders to review transport header traces can help develop
the heterogeneous Internet, this helps extend the range of deeper insight into performance. In the heterogeneous Internet,
topologies, vendor equipment, and traffic patterns that are this helps extend the range of topologies, vendor equipment, and
evaluated. traffic patterns that are evaluated.
Independently captured data is important to help ensure the health Independently captured data is important to help ensure the health
of the research and development communities. It can provide input of the research and development communities. It can provide input
and test scenarios to support development of new transport and test scenarios to support development of new transport
protocol mechanisms, especially when this analysis can be based on protocol mechanisms, especially when this analysis can be based on
the behaviour experienced in a diversity of deployed networks. the behaviour experienced in a diversity of deployed networks.
Independently verifiable performance metrics might also be Independently verifiable performance metrics might also be
utilised to demonstrate regulatory compliance in some utilised to demonstrate regulatory compliance in some
jurisdictions, and provides a basis for informing design jurisdictions, and to provide a basis for informing design
decisions. decisions.
The last point leads us to consider the impact of hiding transport The last point leads us to consider the impact of hiding transport
headers in the specification and development of protocols and headers in the specification and development of protocols and
standards. This has potential impact on: standards. This 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, functions, and/or valuable tool for benchmarking equipment, functions, and/or
configurations, and to understand complex feature interactions. configurations, and to understand complex feature interactions.
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accidentally disrupt operations of/in different parts of the accidentally disrupt operations of/in different parts of the
network. The social contract that maintains the stability of the network. The social contract that maintains the stability of the
Internet relies on accepting common specifications. Internet relies on accepting common specifications.
o Operational Practice: The network operations community relies on o Operational Practice: The network operations community relies on
being able to understand the pattern and requirements of traffic being able to understand the pattern and requirements of traffic
passing over the Internet, both in aggregate and at the flow passing over the Internet, both in aggregate and at the flow
level. These operational practices have developed based on the level. These operational practices have developed based on the
information available from unencrypted transport headers. If this information available from unencrypted transport headers. If this
information is only carried in encrypted transport headers, information is only carried in encrypted transport headers,
operators will not be able to use this information directly, but operators will not be able to use this information directly. If
if operators still wish to use these practices, they may turn to operators still wish to use these practices, they may turn to more
more ambitious ways of discovering this information. For example, ambitious ways of discovering this information. For example, if
if an operator wants to know that traffic is audio traffic, and no an operator wants to know that traffic is audio traffic, and no
longer has access to Session Description Protocol (SDP) session longer has access to Session Description Protocol (SDP) session
descriptions that would explicitly say a flow "is audio", the descriptions that would explicitly say a flow "is audio", the
operator might use heuristics to guess that short UDP packets with operator might use heuristics to guess that short UDP packets with
regular spacing are carrying audio traffic. Operational practices regular spacing are carrying audio traffic. Operational practices
aimed at guessing transport parameters are out of scope for this aimed at guessing transport parameters are out of scope for this
document, and are only mentioned here to recognize that encryption document, and are only mentioned here to recognize that encryption
may not prevent operators from attempting to apply the same may not prevent operators from attempting to apply the same
practices they used with unencrypted transport headers. practices they used with unencrypted transport headers.
o Compliance: Published transport specifications allow operators and o Compliance: Published transport specifications allow operators and
regulators to check compliance. This can bring assurance to those regulators 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 [RFC8084]). flow rate-limiting and network circuit-breaker methods [RFC8084]).
When it is not possible to observe transport header information, When it is not possible to observe transport header information,
methods are still needed to confirm that the traffic produced methods are still needed to confirm that the traffic produced
conforms to the expectations of the operator or developer. conforms to the expectations of the operator or developer.
o Restricting research and development: Hiding transport information o Restricting research and development: Hiding transport information
can impede independent research into new mechanisms, measurement can impede independent research into new mechanisms, measurement
of behaviour, and development initiatives. Experience shows that of 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 mechanisms, 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. If this results in reduced availability of open data, capacity. If this results in reduced availability of open data,
it could eliminate the independent self-checks to the it could eliminate the independent self-checks to the
standardisation process that have previously been in place from standardisation process that have previously been in place from
research and academic contributors (e.g., the role of the IRTF research and academic contributors (e.g., the role of the IRTF
ICCRG, and research publications in reviewing new transport Internet Congestion Control Research Groups (ICCRG) and research
mechanisms and assessing the impact of their experimental publications in reviewing new transport mechanisms and assessing
deployment) the impact of their experimental deployment)
In summary, there are trade offs. On the one hand, protocol In summary, there are trade-offs. On the one hand, transport
designers have often ignored the implications of whether the protocol designers have often ignored the implications of whether the
information in transport header fields can or will be used by in- information in transport header fields can or will be used by in-
network devices, and the implications this places on protocol network devices, and the implications this places on protocol
evolution. This motivates a design that provides confidentiality of evolution. This motivates a design that provides confidentiality of
the header information. On the other hand, it can be expected that a the header information. On the other hand, it can be expected that a
lack of visibility of transport header information can impact the lack of visibility of transport header information can impact the
ways that protocols are deployed, standardised, and their operational ways that protocols are deployed, standardised, and their operational
support. support.
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 appropriate mechanisms, to ensure a safe, reliable, and selection of appropriate mechanisms, to ensure a safe, reliable, and
robust Internet (e.g., [RFC1273],[RFC2914]). robust Internet (e.g., [RFC1273],[RFC2914]).
The choice of whether future transport protocols encrypt their The choice of whether future transport protocols encrypt their
protocol headers therefore needs to be taken based not solely on protocol headers therefore needs to be taken based not solely on
security and privacy considerations, but also taking into account the security and privacy considerations, but also taking into account the
impact on operations, standards, and research. Any new Internet impact on operations, standards, and research. As [RFC7258] notes:
transport will need to provide appropriate transport mechanisms and "Making networks unmanageable to mitigate [pervasive monitoring] is
operational support to assure the resulting traffic can not result in not an acceptable outcome, but ignoring [pervasive monitoring] would
persistent congestion collapse [RFC2914]. This document suggests go against the consensus documented here. An appropriate balance
that the balance between information exposed and concealed should be will emerge over time as real instances of this tension are
carefully considered when specifying new protocols. considered." This balance between information exposed and
information concealed ought to be carefully considered when
specifying new transport protocols.
3. Current uses of Transport Headers within the Network 3. Current uses of Transport Headers within the Network
Despite transport headers having end-to-end meaning, some of these Despite transport headers having end-to-end meaning, some of these
transport headers have come to be used in various ways within the transport headers have come to be used in various ways within the
Internet. In response to pervasive monitoring [RFC7624] revelations Internet. In response to pervasive monitoring [RFC7624] revelations
and the IETF consensus that "Pervasive Monitoring is an Attack" and the IETF consensus that "Pervasive Monitoring is an Attack"
[RFC7258], efforts are underway to increase encryption of Internet [RFC7258], efforts are underway to increase encryption of Internet
traffic,. Applying confidentiality to transport header fields would traffic,. Applying confidentiality to transport header fields would
affect how protocol information is used [RFC8404]. To understand affect how protocol information is used [RFC8404]. To understand
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Transport protocol header information (together with information in Transport protocol header information (together with information in
the network header), has been used to identify a flow and the the network header), has been used to identify a flow and the
connection state of the flow, together with the protocol options connection state of the flow, together with the protocol options
being used. In some usages, a low-numbered (well-known) transport being used. In some usages, a low-numbered (well-known) transport
port number has been used to identify a protocol (although port port number has been used to identify a protocol (although port
information alone is not sufficient to guarantee identification of a information alone is not sufficient to guarantee identification of a
protocol, since applications can use arbitrary ports, multiple protocol, since applications can use arbitrary ports, multiple
sessions can be multiplexed on a single port, and ports can be re- sessions can be multiplexed on a single port, and ports can be re-
used by subsequent sessions). used by subsequent sessions).
Transport protocols, such as TCP and Stream Control Transport Transport protocols, such as TCP and the Stream Control Transport
Protocol (SCTP) specify a standard base header that includes sequence Protocol (SCTP) specify a standard base header that includes sequence
number information and other data, with the possibility to negotiate number information and other data, with the possibility to negotiate
additional headers at connection setup, identified by an option additional headers at connection setup, identified by an option
number in the transport header. UDP-based protocols can use, but number in the transport header. UDP-based protocols can use, but
sometimes do not use, well-known port numbers. Some flows can sometimes do not use, well-known port numbers. Some flows can
instead be identified by signalling protocols or through the use of instead be identified by observing signalling protocol data (e.g.,
magic numbers placed in the first byte(s) of the datagram payload. [RFC3261], [I-D.ietf-rtcweb-overview]) or through the use of magic
numbers placed in the first byte(s) of the datagram payload
[RFC7983].
Flow identification is a common function. For example, performed by Flow identification is a common function. For example, performed by
measurement activities, QoS classification, firewalls, Denial of measurement activities, QoS classification, firewalls, Denial of
Service, DOS, prevention. It becomes more complex and less easily Service, DOS, prevention. It becomes more complex and less easily
achieved when multiplexing is used at or above the transport layer. achieved when multiplexing is used at or above the transport layer.
3.1.2. Metrics derived from Transport Layer Headers 3.1.2. Metrics derived from Transport Layer Headers
Some actors manage their portion of the Internet by characterizing Some actors manage their portion of the Internet by characterizing
the performance of link/network segments. Passive monitoring uses the performance of link/network segments. Passive monitoring uses
observed traffic to makes inferences from transport headers to derive observed traffic to make inferences from transport headers to derive
these measurements. A variety of open source and commercial tools these performance metrics. A variety of open source and commercial
have been deployed that utilise this information. The following tools have been deployed that utilise this information. The
metrics can be derived from transport header information: following metrics can be derived from transport header information:
Traffic Rate and Volume: Header information e.g., (sequence number, Traffic Rate and Volume: Header information (e.g., sequence number
length) allows derivation of volume measures per-application, to and packet size) allows derivation of volume measures per-
characterise the traffic that uses a network segment or the application, to characterise the traffic that uses a network
pattern of network usage. This can be measured per endpoint or segment or the pattern of network usage. This can be measured per
for an aggregate of endpoints (e.g., by an operator to assess endpoint or for an aggregate of endpoints (e.g., by an operator to
subscriber usage). It can also be used to trigger measurement- assess subscriber usage). It can also be used to trigger
based traffic shaping and to implement QoS support within the measurement-based traffic shaping and to implement QoS support
network and lower layers. Volume measures can be valuable for within the network and lower layers. Volume measures can be
capacity planning (providing detail of trends rather than the valuable for capacity planning and providing detail of trends,
volume per subscriber). rather than the volume per subscriber.
Loss Rate and Loss Pattern: Flow loss rate can be derived (e.g., Loss Rate and Loss Pattern: Flow loss rate can be derived (e.g.,
from sequence number) and has been used as a metric for from transport sequence numbers) and has been used as a metric for
performance assessment and to characterise transport behaviour. performance assessment and to characterise transport behaviour.
Understanding the root cause of loss can help an operator Understanding the location and root cause of loss can help an
determine whether this requires corrective action. Network operator determine whether this requires corrective action.
operators have used the variation in patterns of loss as a key Network operators have used the variation in patterns of loss as a
performance metric, utilising this to detect changes in the key performance metric, utilising this to detect changes in the
offered service. offered service.
There are various causes of loss, including: corruption of link There are various causes of loss, including corruption of link
frames (e.g., interference on a radio link), buffer overflow frames (e.g., interference on a radio link), buffer overflow
(e.g., due to congestion), policing (traffic management), buffer (e.g., due to congestion), policing (traffic management), buffer
management (e.g., Active Queue Management, AQM [RFC7567]), management (e.g., Active Queue Management, AQM [RFC7567]), and
inadequate provision of traffic preemption. Understanding flow inadequate provision of traffic pre-emption. Understanding flow
loss rate requires either maintaining per flow packet counters or loss rate requires either maintaining per flow packet counters or
by observing sequence numbers in transport headers. Loss can be by observing sequence numbers in transport headers. Loss can be
monitored at the interface level by devices in the network. It is monitored at the interface level by devices in the network. It is
often valuable to understand the conditions under which packet often valuable to understand the conditions under which packet
loss occurs. This usually requires relating loss to the traffic loss occurs. This usually requires relating loss to the traffic
flowing on the network node/segment at the time of loss. flowing on the network node/segment at the time of loss.
Observation of transport feedback information (observing loss Observation of transport feedback information (e.g., RTP Control
reports, e.g., RTP Control Protocol (RTCP) [RFC3550], TCP SACK) Protocol (RTCP) reception reports [RFC3550], TCP SACK blocks) can
can increase understanding of the impact of loss and help identify increase understanding of the impact of loss and help identify
cases where loss could have been wrongly identified, or the cases where loss could have been wrongly identified, or the
transport did not require the lost packet. It is sometimes more transport did not require the lost packet. It is sometimes more
helpful to understand the pattern of loss, than the loss rate, helpful to understand the pattern of loss, than the loss rate,
because losses can often occur as bursts, rather than randomly- because losses can often occur as bursts, rather than randomly-
timed events. timed events.
Throughput and Goodput: The throughput achieved by a flow can be Throughput and Goodput: The throughput achieved by a flow can be
determined even when a flow is encrypted, providing the individual determined even when a flow is encrypted, providing the individual
flow can be identified. Goodput [RFC7928] is a measure of useful flow can be identified. Goodput [RFC7928] is a measure of useful
data exchanged (the ratio of useful/total volume of traffic sent data exchanged (the ratio of useful/total volume of traffic sent
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numbers in the TCP or the Real-time Transport Protocol, RTP, numbers in the TCP or the Real-time Transport Protocol, RTP,
headers [RFC3550]). headers [RFC3550]).
Latency: Latency is a key performance metric that impacts Latency: Latency is a key performance metric that impacts
application response time and user-perceived response time. It application response time and user-perceived response time. It
often indirectly impacts throughput and flow completion time. often indirectly impacts throughput and flow completion time.
Latency determines the reaction time of the transport protocol Latency determines the reaction time of the transport protocol
itself, impacting flow setup, congestion control, loss recovery, itself, impacting flow setup, congestion control, loss recovery,
and other transport mechanisms. The observed latency can have and other transport mechanisms. The observed latency can have
many components [Latency]. Of these, unnecessary/unwanted queuing many components [Latency]. Of these, unnecessary/unwanted queuing
in network buffers has often been observed as a significant in network buffers has often been observed as a significant factor
factor. Once the cause of unwanted latency has been identified, [bufferbloat]. Once the cause of unwanted latency has been
this can often be eliminated. identified, this can often be eliminated.
To measure latency across a part of a 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 could be used to locate a source of latency, e.g., by This could be used to locate a source of latency, e.g., by
observing cases where the median RTT is much greater than the observing cases where the median RTT is much greater than the
minimum RTT for a part of a path. minimum RTT for a part of a path.
The service offered by operators can benefit from latency The service offered by network operators can benefit from latency
information to understand the impact of deployment and tune information to understand the impact of deployment and tune
deployed services. Latency metrics are key to evaluating and deployed services. Latency metrics are key to evaluating and
deploying AQM [RFC7567], DiffServ [RFC2474], and Explicit deploying AQM [RFC7567], DiffServ [RFC2474], and Explicit
Congestion Notification (ECN) [RFC3168] [RFC8087]. Measurements Congestion Notification (ECN) [RFC3168] [RFC8087]. Measurements
could identify excessively large buffers, indicating where to could identify excessively large buffers, indicating where to
deploy or configure AQM. An AQM method is often deployed in deploy or configure AQM. An AQM method is often deployed in
combination with other techniques, such as scheduling [RFC7567] combination with other techniques, such as scheduling [RFC7567]
[RFC8290] and although parameter-less methods are desired [RFC8290] and although parameter-less methods are desired
[RFC7567], current methods [RFC8290] [RFC8289] [RFC8033] often [RFC7567], current methods [RFC8290] [RFC8289] [RFC8033] often
cannot scale across all possible deployment scenarios. cannot scale across all possible deployment scenarios.
Variation in delay: Some network applications are sensitive to small Variation in delay: Some network applications are sensitive to small
changes in packet timing. To assess the performance of such changes in packet timing. To assess the performance of such
applications, it can be necessary to measure the variation in applications, it can be necessary to measure the variation in
delay observed along a portion of the path [RFC3393] [RFC5481]. delay observed along a portion of the path [RFC3393] [RFC5481].
The requirements resemble those for the measurement of latency. The requirements resemble those for the measurement of latency.
Flow Reordering: Significant flow reordering can impact time- Flow Reordering: Significant packet reordering within a flow can
critical applications and can be interpreted as loss by reliable impact time-critical applications and can be interpreted as loss
transports. Many transport protocol techniques are impacted by by reliable transports. Many transport protocol techniques are
reordering (e.g., triggering TCP retransmission, or re-buffering impacted by reordering (e.g., triggering TCP retransmission, or
of real-time applications). Packet reordering can occur for many re-buffering of real-time applications). Packet reordering can
reasons (from equipment design to misconfiguration of forwarding occur for many reasons, from equipment design to misconfiguration
rules). Since this impacts transport performance, network tools of forwarding rules. Since this impacts transport performance,
are needed to detect and measure unwanted/excessive reordering. network tools are needed to detect and measure unwanted/excessive
reordering.
There have 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 a reduction in the requirements for preserving ordering. These to a reduction in the requirements for preserving ordering. These
have promise to simplify network equipment design as well as the have promise to simplify network equipment design as well as the
potential to improve robustness of the transport service. potential to improve robustness of the transport service.
Measurements of reordering can help understand the present level Measurements of reordering can help understand the present level
of reordering within deployed infrastructure, and inform decisions of reordering within deployed infrastructure, and inform decisions
about how to progress such mechanisms. about how to progress such mechanisms. Key performance indicators
are retransmission rate, packet drop rate, sector utilisation
level, a measure of reordering, peak rate, the ECN congestion
experienced (CE) marking rate, etc.
Operational tools to detect mis-ordered packet flows and quantify the Metrics have been defined that evaluate whether a network has
degree or reordering. Key performance indicators are retransmission maintained packet order on a packet-by-packet basis [RFC4737] and
rate, packet drop rate, sector utilisation level, a measure of [RFC5236].
reordering, peak rate, the ECN congestion experienced (CE) marking
rate, etc.
Metrics have been defined that evaluate whether a network has Techniques for measuring reordering typically observe packet
maintained packet order on a packet-by-packet basis [RFC4737] and sequence numbers. Some protocols provide in-built monitoring and
[RFC5236]. reporting functions. Transport fields in the RTP header [RFC3550]
[RFC4585] can be observed to derive traffic volume measurements
and provide information on the progress and quality of a session
using RTP. As with other measurement, metadata is often needed to
understand the context under which the data was collected,
including the time, observation point, and way in which metrics
were accumulated. The RTCP protocol directly reports some of this
information in a form that can be directly visible in the network.
A user of summary measurement data needs to trust the source of
this data and the method used to generate the summary information.
Techniques for measuring reordering typically observe packet sequence The above passively monitor transport protocol headers to derive
numbers. Some protocols provide in-built monitoring and reporting metrics about network layer performance useful for operation and
functions. Transport fields in the RTP header [RFC3550] [RFC4585] management of a network.
can be observed to derive traffic volume measurements and provide
information on the progress and quality of a session using RTP. As
with other measurement, metadata is often needed to understand the
context under which the data was collected, including the time,
observation point, and way in which metrics were accumulated. The
RTCP protocol directly reports some of this information in a form
that can be directly visible in the network. A user of summary
measurement data needs to trust the source of this data and the
method used to generate the summary information.
3.1.3. Transport use of Network Layer Header Fields 3.1.3. Transport use of Network Layer Header Fields
Information from the transport protocol can be used by a multi-field
classifier as a part of policy framework. Policies are commonly used
for management of the QoS or Quality of Experience (QoE) in resource-
constrained networks and by firewalls that use the information to
implement access rules (see also section 2.2.2 of [RFC8404]).
Network-layer classification methods that rely on a multi-field Network-layer classification methods that rely on a multi-field
classifier (e.g. infering QoS from the 5-tuple or choice of classifier (e.g. Inferring QoS from the 5-tuple or choice of
application protocol) are incompatible with transport protocols that application protocol) are incompatible with transport protocols that
encrypt the transport information. encrypt the transport information. Traffic that cannot be
classified, will typically receive a default treatment.
In contrast, network-layer header fields are not encrypted and can Transport information can also be explicitly set in network-layer
explicitly provide information from the transport layer to enable a header fields that are not encrypted. This can provide information
different forwarding treatment by the network. This information can to enable a different forwarding treatment by the network, even when
be provided by a transport that employs encryption. a transport employs encryption to protect other header information.
When a transport multiplexes multiple subflows, the user of the On the one hand, the user of a transport that multiplexes multiple
transport could wish to hide the presence and characteristics of sub-flows could wish to hide the presence and characteristics of
these subflows. other uses of an encrypted transport could set the these sub-flows. On the other hand, an encrypted transport could set
network-layer information to indicate the presence of subflows and to the network-layer information to indicate the presence of sub-flows
reflect the network needs of individual subflows (e.g., a WebRTC can and to reflect the network needs of individual sub-flows. There are
identify different forwarding treatments for individual packets based several ways this could be done:
on the value of the Differentiated Services Code Point (DSCP) field
[I-D.ietf-tsvwg-rtcweb-qos]).
Use of IPv6 Network-Layer Flow Label: Endpoints are encouraged to Using the IPv6 Network-Layer Flow Label: Endpoints are encouraged to
set the IPv6 Flow Label field of the network-layer header (e.g., set the IPv6 Flow Label field of the network-layer header (e.g.,
[RFC8085]). The label can provide information that can help [RFC8085]). The label can provide information that can help
inform network-layer queuing, forwarding (e.g., for Equal Cost inform network-layer queuing, forwarding (e.g., for Equal Cost
Multi-Path, ECMP, routing, and Link Aggregation, LAG) [RFC6294]. Multi-Path, ECMP, routing, and Link Aggregation, LAG) [RFC6294].
A multiplexing transport could choose to use multiple flow labels A multiplexing transport could choose to use multiple flow labels
to allow the network to independently forward subflows. to allow the network to independently forward subflows.
Use Network-Layer Differentiated Services Code Point Point: Using the Network-Layer Differentiated Services Code Point:
Applications can expose their delivery expectations to the network Applications can expose their delivery expectations to the network
by setting the DSCP field of IPv4 and IPv6 packets [RFC2474].This by setting the Differentiated Services Code Point (DSCP) field of
provides explicit information to inform network-layer queuing and IPv4 and IPv6 packets [RFC2474]. For example, WebRTC applications
forwarding, rather than an operator inferring traffic requirements identify different forwarding treatments for individual sub-flows
from transport and application headers via a multi-field (audio vs. video) based on the value of the DSCP field
classifier. [I-D.ietf-tsvwg-rtcweb-qos]). This provides explicit information
to inform network-layer queuing and forwarding, rather than an
operator inferring traffic requirements from transport and
application headers via a multi-field classifier.
Since the DSCP value can impact the quality of experience for a Since the DSCP value can impact the quality of experience for a
flow., observations of service performance need to consider this 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 a transport Using Explicit Congestion Marking: ECN [RFC3168] is a transport
mechanism that utilises the ECN field in the network-layer header. mechanism that utilises the ECN field in the network-layer header.
Use of ECN explicitly informs the network-layer that a transport Use of ECN explicitly informs the network-layer that a transport
is ECN-capable, and requests ECN treatment of the flows packets. is ECN-capable, and requests ECN treatment of the flows packets.
An ECN-capable transport can offer benefits when used over a path An ECN-capable transport can offer benefits when used over a path
with equipment taht implements an AQM method with Congestion with equipment that implements an AQM method with Congestion
Experienced (CE) marking of IP packets [RFC8087]. Experienced (CE) marking of IP packets [RFC8087], since it can
react to congestion without also having to recover from lost
packets.
ECN exposes the presence of congestion. The reception of CE- ECN exposes the presence of congestion. The reception of CE-
marked packets can be used to estimate the level of incipient marked packets can be used to estimate the level of incipient
congestion on the upstream portion of the path from the point of congestion on the upstream portion of the path from the point of
observation (Section 2.5 of [RFC8087]). Interpreting the marking observation (Section 2.5 of [RFC8087]). Interpreting the marking
behaviour (i.e., assessing congestion and diagnosing faults) behaviour (i.e., assessing congestion and diagnosing faults)
requires context from the transport layer (such as path RTT). requires context from the transport layer (such as path RTT).
AQM and ECN offer a range of algorithms and configuration options. AQM and ECN offer a range of algorithms and configuration options.
Tools therefore need to be available to network operators and Tools therefore need to be available to network operators and
researchers to understand the implication of configuration choices researchers to understand the implication of configuration choices
and transport behaviour as use of ECN increases and new methods and transport behaviour as use of ECN increases and new methods
emerge [RFC7567]. emerge [RFC7567].
Careful use of the network layer features can therefore help address
some of the reasons why the network inspects transport protocol
headers.
3.2. Transport Measurement 3.2. 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 the transport
layer, until the emergence of QUIC, with the obvious exception of layer, until the emergence of QUIC, with the obvious exception of
Virtual Private Networks (VPNs) and IPsec. Virtual Private Networks (VPNs) and IPsec.
When encryption conceals more layers in each packet, people seeking When encryption conceals more layers in each packet, people seeking
understanding of the network operation rely more on pattern understanding of the network operation rely more on pattern
inferences and other heuristics reliance on pattern inferences and inferences and other heuristics reliance on pattern inferences and
accuracy suffers. For example, the traffic patterns between server accuracy suffers. For example, the traffic patterns between server
and browser are dependent on browser supplier and version, even when and browser are dependent on browser supplier and version, even when
the sessions use the same server application (e.g., web e-mail the sessions use the same server application (e.g., web e-mail
access). It remains to be seen whether more complex inferences can access). It remains to be seen whether more complex inferences can
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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.
3.2.1. Point of Observation 3.2.1. Point of Observation
On-path measurements are particularly useful for locating the source On-path measurements are particularly useful for locating the source
of problems or to assess the performance of a network segment or a of problems, or to assess the performance of a network segment or a
particular device configuration. Often issues can only be understood particular device configuration. Often issues can only be understood
in the context of the other flows that share a particular path, in the context of the other flows that share a particular path,
common network device, interface port, etc. A simple example is common network device, interface port, etc. A simple example is
monitoring of a network device that uses a scheduler or active queue monitoring of a network device that uses a scheduler or active queue
management technique [RFC7567], where it could be desirable to management technique [RFC7567], where it could be desirable to
understand whether algorithms are correctly controlling latency, or understand whether the algorithms are correctly controlling latency,
overload protection. This understanding implies knowledge of how or if overload protection is working. This understanding implies
traffic is assigned to any sub-queues used for flow scheduling, but knowledge of how traffic is assigned to any sub-queues used for flow
can also require information about how the traffic dynamics impact scheduling, but can also require information about how the traffic
active queue management, starvation prevention mechanisms and dynamics impact active queue management, starvation prevention
circuit-breakers. mechanisms, and circuit-breakers.
Sometimes multiple on-path observation points are needed. By Sometimes multiple on-path observation points are needed. By
correlating observations of headers at multiple points along the path correlating observations of headers at multiple points along the path
(e.g., at the ingress and egress of a network segment), an observer (e.g., at the ingress and egress of a network segment), an observer
can determine the contribution of a portion of the path to an can determine the contribution of a portion of the path to an
observed metric (to locate a source of delay, jitter, loss, observed metric, to locate a source of delay, jitter, loss,
reordering, congestion marking, etc.). reordering, congestion marking, etc.
3.2.2. Use by Operators to Plan and Provision Networks 3.2.2. 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 valuable to equipment vendors who in their networks. Data is also valuable to equipment vendors who
want to understand traffic trends and patterns of usage as inputs to want to understand traffic trends and patterns of usage as 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 might not have access to per-flow measurement data.
in aggregate traffic can be observed and can be related to the Trends in aggregate traffic can be observed and can be related to the
endpoint addresses being used, but it may be impossible to correlate endpoint addresses being used, but it may be impossible to correlate
patterns in measurements with changes in transport protocols (e.g., patterns in measurements with changes in transport protocols (e.g.,
the impact of changes in introducing a new transport protocol the impact of changes in introducing a new transport protocol
mechanism). This increases the dependency on other indirect sources mechanism). This increases the dependency on other indirect sources
of information to inform planning and provisioning. of information to inform planning and provisioning.
3.2.3. Service Performance Measurement 3.2.3. 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 offered to the used by various actors to help analyse the performance offered to the
users of a network segment, and inform operational practice. users of a network segment, and to inform operational practice.
While active measurements may be used in-network, passive While active measurements may be used within a network, passive
measurements can have advantages in terms of eliminating unproductive measurements can have advantages in terms of eliminating unproductive
test traffic, reducing the influence of test traffic on the overall test traffic, reducing the influence of test traffic on the overall
traffic mix, and the ability to choose the point of observation traffic mix, and the ability to choose the point of observation (see
Section 3.2.1. However, passive measurements can rely on observing Section 3.2.1). However, passive measurements can rely on observing
transport headers. transport headers which is not possible if those headers are
encrypted.
3.2.4. Measuring Transport to Support Network Operations 3.2.4. 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 Congestion Control Compliance of Traffic: Congestion control is a
key transport function [RFC2914]. Many network operators key transport function [RFC2914]. Many network operators
implicitly accept that TCP traffic complies with a behaviour that implicitly accept that TCP traffic complies with a behaviour that
is acceptable for use in the shared Internet. TCP algorithms have is acceptable for use in the shared Internet. TCP algorithms have
been continuously improved over decades, and they have reached a been continuously improved over decades, and they have reached a
level of efficiency and correctness that custom application-layer level of efficiency and correctness that custom application-layer
mechanisms will struggle to easily duplicate [RFC8085]. mechanisms will struggle to easily duplicate [RFC8085].
A standards-compliant TCP stack provides congestion control may A standards-compliant TCP stack provides congestion control that
therefore be judged safe for use across the Internet. may 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 IETF-specified transport (e.g., TCP and SCTP). behaviour for IETF-specified transport (e.g., TCP and SCTP).
However, when anomalies 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
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visualise plots of TCP sequence numbers versus time for a flow to visualise plots of TCP sequence numbers versus time for a flow to
understand how a flow shares available capacity, deduce its understand how a flow shares available capacity, deduce its
dynamics in response to congestion, etc. The ability to identify dynamics in response to congestion, etc. The ability to identify
sources that contribute excessive congestion is important to safe sources that contribute excessive congestion is important to safe
operation of network infrastructure, and mechanisms can inform operation of network infrastructure, and mechanisms can inform
configuration of network devices to complement the endpoint configuration of network devices to complement the endpoint
congestion avoidance mechanisms [RFC7567] [RFC8084] to avoid a congestion avoidance mechanisms [RFC7567] [RFC8084] to avoid a
portion of the network being driven into congestion collapse portion of the network being driven into congestion collapse
[RFC2914]. [RFC2914].
Congestion Control Compliance for UDP traffic UDP provides a minimal Congestion Control Compliance for UDP traffic: UDP provides a
message-passing datagram transport that has no inherent congestion minimal message-passing datagram transport that has no inherent
control mechanisms. Because congestion control is critical to the congestion control mechanisms. Because congestion control is
stable operation of the Internet, applications and other protocols critical to the stable operation of the Internet, applications and
that choose to use UDP as a transport are required to employ other protocols that choose to use UDP as a transport are required
mechanisms to prevent congestion collapse, avoid unacceptable to employ mechanisms to prevent congestion collapse, avoid
contributions to jitter/latency, and to establish an acceptable unacceptable contributions to jitter/latency, and to establish an
share of capacity with concurrent traffic [RFC8085]. acceptable share of capacity with concurrent traffic [RFC8085].
A network operator needs tools to understand if datagram flows A network operator needs tools to understand if datagram flows
comply with congestion control expectations and therefore whether comply with congestion control expectations and therefore whether
there is a need to deploy methods such as rate-limiters, transport there 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 3.1.2. Section 3.1.2, and the Secure RTP extensions [RFC3711] were
explicitly designed to expose header information to enable such
observation.
3.3. Use for Network Diagnostics and Troubleshooting 3.3. Use for Network Diagnostics and Troubleshooting
Transport header information can be useful for a variety of Transport header information can be useful for a variety of
operational tasks [RFC8404]: to diagnose network problems, assess operational tasks [RFC8404]: to diagnose network problems, assess
network provider performance, evaluate equipment/protocol network provider performance, evaluate equipment/protocol
performance, capacity planning, management of security threats performance, capacity planning, management of security threats
(including denial of service), and responding to user performance (including denial of service), and responding to user performance
questions. Sections 3.1.2 and 5 of [RFC8404] provide further questions. Sections 3.1.2 and 5 of [RFC8404] provide further
examples. These tasks seldom involve the need to determine the examples. These tasks seldom involve the need to determine the
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reliance on endpoint diagnostic tools or user involvement in reliance on endpoint diagnostic tools or user involvement in
diagnosing and troubleshooting unusual use cases or non-trivial diagnosing and troubleshooting unusual use cases or non-trivial
problems. A key need here is for tools to provide useful information problems. A key need here is for tools to provide useful information
during network anomalies (e.g., significant reordering, high or during network anomalies (e.g., significant reordering, high or
intermittent loss). Many network operators currently utilise intermittent loss). Many network operators currently utilise
observed transport information as a part of their operational observed transport information as a part of their operational
practice. However, the network will not break just because transport practice. However, the network will not break just because transport
headers are encrypted, although alternative diagnostic and headers are encrypted, although alternative diagnostic and
troubleshooting tools would need to be developed and deployed. troubleshooting tools would need to be developed and deployed.
3.3.1. Examples of measurements
Measurements can be used to monitor the health of a portion of the Measurements can be used to monitor the health of a portion of the
Internet, to provide early warning of the need to take action. They Internet, to provide early warning of the need to take action. They
can assist in debugging and diagnosing the root causes of faults that can assist in debugging and diagnosing the root causes of faults that
concern a particular user's traffic. They can also be used to concern a particular user's traffic. They can also be used to
support post-mortem investigation after an anomaly to determine the support post-mortem investigation after an anomaly to determine the
root cause of a problem. root cause of a problem.
In some case, measurements may involve active injection of test In some case, measurements may involve active injection of test
traffic to complete a measurement. However, most operators do not traffic to complete a measurement. However, most operators do not
have access to user equipment, and injection of test traffic may be have access to user equipment, and injection of test traffic may be
associated with costs in running such tests (e.g., the implications associated with costs in running such tests (e.g., the implications
of bandwidth tests in a mobile network are obvious). Some active of capacity tests in a mobile network are obvious). Some active
measurements (e.g., response under load or particular workloads) measurements (e.g., response under load or particular workloads)
perturb other traffic, and could require dedicated access to the perturb other traffic, and could require dedicated access to the
network segment. An alternative approach is to use in-network network segment. An alternative approach is to use in-network
techniques that observe transport packet headers in operational techniques that observe transport packet headers in operational
networks to make the measurements. networks to make the measurements.
In other cases, measurement involves dissecting network traffic In other cases, measurement involves dissecting network traffic
flows. The observed transport layer information can help identify flows. The observed transport layer information can help identify
whether the link/network tuning is effective and alert to potential whether the link/network tuning is effective and alert to potential
problems that can be hard to derive from link or device measurements problems that can be hard to derive from link or device measurements
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to-point radio) has the complexity of a subsystem that performs radio to-point radio) has the complexity of a subsystem that performs radio
resource management,s with direct impact on the available capacity, resource management,s with direct impact on the available capacity,
and potentially loss/reordering of packets. The impact of the and potentially loss/reordering of packets. The impact of the
pattern of loss and congestion, differs for different traffic types, pattern of loss and congestion, differs for different traffic types,
correlation with propagation and interference can all have correlation with propagation and interference can all have
significant impact on the cost and performance of a provided service. significant impact on the cost and performance of a provided service.
The need for this type of information is expected to increase as The need for this type of information is expected to increase as
operators bring together heterogeneous types of network equipment and operators bring together heterogeneous types of network equipment and
seek to deploy opportunistic methods to access radio spectrum. seek to deploy opportunistic methods to access radio spectrum.
3.4. Use of transport information to influence network forwarding 3.4. Header Compression
Information from the transport protocol can be used by a multi-field
classifier as a part of policy framework. Policies are commonly used
for management of the QoS or Quality of Experience (QoE) in resource-
constrained networks and by firewalls that use the information to
implement access rules (see also section 2.2.2 of [RFC8404]).
Network-layer classification methods that rely on a multi-field
classifier (e.g. Inferring QoS from the 5-tuple or choice of
application protocol) are incompatible with transport protocols that
encrypt the transport information. Traffic that cannot be
classified, will typically receive a default treatment.
Transport information can also be explicitly set in network-layer
header fields that are not encrypted. This can provide information
to enable a different forwarding treatment by the network, even when
a transport employs encryption to protect other header information.
When a transport multiplexes multiple subflows, a transport could
choose to hide the presence and characteristics of these subflows
from the network. However, a transport is permitted to set the
network-layer information to indicate the presence of subflows and to
reflect the needs of individual subflows (e.g., a WebRTC can identify
different forwarding treatments for individual packets based on the
value of the DS field [I-D.ietf-tsvwg-rtcweb-qos]).
Use of IPv6 Network-Layer Flow Label: Endpoints are encouraged to
set the IPv6 Flow Label field of the network-layer header (e.g.,
[RFC8085]). The label can provide information that can help
inform network-layer queuing, forwarding (e.g., for Equal Cost
Multi-Path, ECMP, routing, and Link Aggregation, LAG) [RFC6294].
A multiplexing transport could choose to use multiple flow labels
to allow the network to independently forward subflows.
Use Network-Layer Differentiated Services Code Point Point:
Applications can expose their delivery expectations to the network
by setting the DSCP field of IPv4 and IPv6 packets [RFC2474].
This provides explicit information to inform network-layer queuing
and forwarding, rather than an operator inferring traffic
requirements from transport and application headers via a multi-
field classifier.
Since the DSCP value can impact the quality of experience for a
flow, observations of service performance need to consider this
field when a network path has support for differentiated service
treatment.
Use of Explicit Congestion Marking: ECN [RFC3168] is a transport
mechanism that utilises the ECN field in the network-layer header
to explicitly inform the network-layer that a transport is ECN-
capable and request ECN treatment of the flows packets. This can
offer benefits when used over a path with equipment that
implements an AQM method with Congestion Experienced (CE) marking
of IP packets [RFC8087].
The reception of CE-marked packets can be used to estimate the Header compression saves link bandwidth by compressing network and
level of incipient congestion on the upstream portion of the path transport protocol headers on a per-hop basis. It was widely used
from the point of observation (Section 2.5 of [RFC8087]). with low bandwidth dial-up access links, and still finds application
Interpreting the marking behaviour (i.e., assessing congestion and on wireless links that are subject to capacity constraints. Header
diagnosing faults) requires context from the transport layer (such compression has been specified for use with TCP/IP and RTP/UDP/IP
as path RTT). flows [RFC2507], [RFC2508], [RFC4995].
AQM and ECN offer a range of algorithms and configuration options, While it is possible to compress only the network layer headers,
it is therefore important for tools to be available to network significant bandwidth savings can be made if both the network and
operators and researchers to understand the implication of transport layer headers are compressed together as a single unit.
configuration choices and transport behaviour as use of ECN The Secure RTP extensions [RFC3711] were explicitly designed to leave
increases and new methods emerge [RFC7567]. the transport protocol headers unencrypted, but authenticated, since
support for header compression was considered important. Encrypting
the transport protocol headers does not break such header
compression, but does cause it to fall back to compressing only the
network layer headers, with a significant reduction in efficiency.
This may have operational impact.
4. Encryption and Authentication of Transport Headers 4. 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
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allow or block content. Whatever the reasons, there are now allow or block content. Whatever the reasons, there are now
activities in the IETF to design new protocols that could include activities in the IETF to design new protocols that could include
some form of transport header encryption (e.g., QUIC some form of transport header encryption (e.g., QUIC
[I-D.ietf-quic-transport]). [I-D.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 as the IPv6 decisions reflect the need of transport protocols, such as the IPv6
Flow Label [RFC6437], the DSCP and ECN. Flow Label [RFC6437], DSCP, and ECN fields.
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.
o On the other hand, encryption of transport layer header o On the other hand, encryption of transport layer header
information has implications for people who are responsible for information has implications for people who are responsible for
operating networks and researchers and analysts seeking to operating networks and researchers and analysts seeking to
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 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. While the IETF can specify of evolution of the transport protocol stack. While the IETF can
protocols, the success in actual deployment is often determined by specify protocols, the success in actual deployment is often
many factors [RFC5218] that are not always clear at the time when determined by many factors [RFC5218] that are not always clear at the
protocols are being defined. time when protocols are being defined.
The following briefly reviews some security design options for The following briefly reviews some security design options for
transport protocols. A Survey of Transport Security Protocols transport protocols. A Survey of Transport Security Protocols
[I-D.ietf-taps-transport-security] provides more details concerning [I-D.ietf-taps-transport-security] provides more details concerning
commonly used encryption methods at the transport layer. commonly used encryption methods at the transport layer.
Authenticating the Transport Protocol Header: Transport layer header Authenticating the Transport Protocol Header: Transport layer header
information can be authenticated. An integrity check that information can be authenticated. An integrity check that
protects the immutable transport header fields, but can still protects the immutable transport header fields, but can still
expose the transport protocol header information in the clear, expose the transport protocol header information in the clear,
allowing in-network devices to observes these fields. An allowing in-network devices to observe these fields. An integrity
integrity check can not prevent in-network modification, but can check can not prevent in-network modification, but can prevent a
avoid a receiving accepting changes and avoid impact on the receiving from accepting changes and avoid impact on the transport
transport protocol operation. protocol operation.
An example transport authentication mechanism is TCP- An example transport authentication mechanism is TCP-
Authentication (TCP-AO) [RFC5925]. This TCP option authenticates Authentication (TCP-AO) [RFC5925]. This TCP option authenticates
the IP pseudo header, TCP header, and TCP data. TCP-AO protects the IP pseudo header, TCP header, and TCP data. TCP-AO protects
the transport layer, preventing attacks from disabling the TCP the transport layer, preventing attacks from disabling the TCP
connection itself and provides replay protection. TCP-AO may connection itself and provides replay protection. TCP-AO may
interact with middleboxes, depending on their behaviour [RFC3234]. interact with middleboxes, depending on their behaviour [RFC3234].
The IPsec Authentication Header (AH) [RFC4302] was designed to The IPsec Authentication Header (AH) [RFC4302] was designed to
work at the network layer and authenticate the IP payload. This work at the network layer and authenticate the IP payload. This
approach authenticates all transport headers, and verifies their approach authenticates all transport headers, and verifies their
integrity at the receiver, preventing in-network modification. integrity at the receiver, preventing in-network modification.
Secure RTP [RFC3711] is another example of a transport protocol
that allows header authentication.
Greasing Transport layer header information that is observable can Greasing: Transport layer header information that is observable can
be observed in the network. Protocols often provide extensibility be observed in the network. Protocols often provide extensibility
features, reserving fields or values for use by future versions of features, reserving fields or values for use by future versions of
a specification. The specification of receivers has traditionally a specification. The specification of receivers has traditionally
ignored unspecified values, however in-network devices have ignored unspecified values, however in-network devices have
emerged that ossify to require a certain value in a field, or re- emerged that ossify to require a certain value in a field, or re-
use a field for another purpose. When the speicfication is later use a field for another purpose. When the specification is later
updated, it is impossible to deploy the new use of the field, and updated, it is impossible to deploy the new use of the field, and
forwarding of the protocol could even become conditional on a forwarding of the protocol could even become conditional on a
specific header field value. specific header field value.
A protocol can intentionally vary the value, format, and/or A protocol can intentionally vary the value, format, and/or
presence of observable transport header fields. This behaviour, presence of observable transport header fields. This behaviour,
known as GREASE (Generate Random Extensions And Sustain known as GREASE (Generate Random Extensions And Sustain
Extensibility), is designed to avoid a network device ossifying Extensibility), is designed to avoid a network device ossifying
the use of a specific observable field. Greasing seeks to ease the use of a specific observable field. Greasing seeks to ease
deployment of new methods. It can be designed to avoid in-network deployment of new methods. It can be designed to prevent in-
devices utilising the information in a transport header, or can network devices utilising the information in a transport header,
make an observation robust to a set of changing values, rather or can make an observation robust to a set of changing values,
than a specific set of values. rather than a specific set of values.
Encrypting the Transport Payload: The transport layer payload can be Encrypting the Transport Payload: The transport layer payload can be
encrypted to protect the content of transport segments. This encrypted to protect the content of transport segments. This
leaves transport protocol header information in the clear. The leaves transport protocol header information in the clear. The
integrity of immutable transport header fields could be protected integrity of immutable transport header fields could be protected
by combining this with an integrity check. by combining this with an integrity check.
Examples of encrypting the payload include Transport Layer Examples of encrypting the payload include Transport Layer
Security (TLS) over TCP [RFC8446] [RFC7525], Datagram TLS (DTLS) Security (TLS) over TCP [RFC8446] [RFC7525], Datagram TLS (DTLS)
over UDP [RFC6347] [RFC7525], and TCPcrypt over UDP [RFC6347] [RFC7525], Secure RTP [RFC3711], and TCPcrypt
[I-D.ietf-tcpinc-tcpcrypt], which permits opportunistic encryption [I-D.ietf-tcpinc-tcpcrypt] which permits opportunistic encryption
of the TCP transport payload. of the TCP transport payload.
Encrypting the Transport Headers and Payload: The network layer Encrypting the Transport Headers and Payload: The network layer
payload could be encrypted (including the entire transport header payload could be encrypted (including the entire transport header
and the payload). This method provides confidentiality of the and the payload). This method provides confidentiality of the
entire transport packet. It therefore does not expose any entire transport packet. It therefore does not expose any
transport information to devices in the network, which also transport information to devices in the network, which also
prevents modification along a network path. prevents modification along a network path.
One example of encryption at the network layer is use of IPsec One example of encryption at the network layer is use of IPsec
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Optional Encryption of Header Information: There are implications to Optional Encryption of Header Information: There are implications to
the use of optional header encryption in the design of a transport the use of optional header encryption in the design of a transport
protocol, where support of optional mechanisms can increase the protocol, where support of optional mechanisms can increase the
complexity of the protocol and its implementation and in the complexity of the protocol and its implementation and in the
management decisions that are required to use variable format management decisions that are required to use variable format
fields. Instead, fields of a specific type ought to always be fields. Instead, fields of a specific type ought to always be
sent with the same level of confidentiality or integrity sent with the same level of confidentiality or integrity
protection. protection.
As seen, different transports use encryption to protect their header
information to varying degrees. There is, however, a trend towards
increased protection with newer transport protocols.
5. Addition of Transport Information to Network-Layer Protocol Headers 5. Addition of Transport Information to Network-Layer Protocol Headers
Transport protocol information can be made visible in a network-layer Transport protocol 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. observed by in-network devices.
5.1. Use of transport information to influence network forwarding
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 to prioritise flows as a part of a policy framework. This
for management of the QoS or Quality of Experience (QoE) in resource- was discussed in Section 3.1.3.
constrained networks and by firewalls that use the information to
implement access rules (see also section 2.2.2 of [RFC8404]).
Network-layer classification methods that rely on a multi-field
classifier (e.g. Inferring QoS from the 5-tuple or choice of
application protocol) are incompatible with transport protocols that
encrypt the transport information. Traffic that cannot be
classified, will typically receive a default treatment.
Transport information can also be explicitly set in network-layer
header fields that are not encrypted. This can provide information
to enable a different forwarding treatment by the network, even when
a transport employs encryption to protect other header information.
When a transport multiplexes multiple subflows, a transport could
choose to hide the presence and characteristics of these subflows
from the network. However, a transport is permitted to set the
network-layer information to indicate the presence of subflows and to
reflect the needs of individual subflows (e.g., a WebRTC can identify
different forwarding treatments for individual packets based on the
value of the Differentiated Services Code Point (DSCP) field
[I-D.ietf-tsvwg-rtcweb-qos]).
Use of IPv6 Network-Layer Flow Label: Endpoints are encouraged to
set the IPv6 Flow Label field of the network-layer header (e.g.,
[RFC8085]). The label can provide information that can help
inform network-layer queuing, forwarding (e.g., for Equal Cost
Multi-Path, ECMP, routing, and Link Aggregation, LAG) [RFC6294].
A multiplexing transport could choose to use multiple flow labels
to allow the network to independently forward subflows.
Use Network-Layer Differentiated Services Code Point Point:
Applications can expose their delivery expectations to the network
by setting the DSCP field of IPv4 and IPv6 packets [RFC2474].This
provides explicit information to inform network-layer queuing and
forwarding, rather than an operator inferring traffic requirements
from transport and application headers via a multi-field
classifier.
Since the DSCP value can impact the quality of experience for a
flow., observations of service performance need to consider this
field when a network path has support for differentiated service
treatment.
Use of Explicit Congestion Marking: ECN [RFC3168] is a transport
mechanism that utilises the ECN field in the network-layer header.
Use of ECN explicitly informs the network-layer that a transport
is ECN-capable, and requests ECN treatment of the flows packets.
An ECN-capable transport can offer benefits when used over a path
with equipment that implements an AQM method with Congestion
Experienced (CE) marking of IP packets [RFC8087].
ECN exposes the presence of congestion. The reception of CE-
marked packets can be used to estimate the level of incipient
congestion on the upstream portion of the path from the point of
observation (Section 2.5 of [RFC8087]). Interpreting the marking
behaviour (i.e., assessing congestion and diagnosing faults)
requires context from the transport layer (such as path RTT).
AQM and ECN offer a range of algorithms and configuration options,
it is therefore important for tools to be available to network
operators and researchers to understand the implication of
configuration choices and transport behaviour as use of ECN
increases and new methods emerge [RFC7567].
5.2. Network-layer measurement
Some measurements can be made by adding additional protocol headers Some measurements can 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 or in-situ OAM [I-D.ietf-ippm-ioam-data]) a method such as 802.11ag or in-situ OAM [I-D.ietf-ippm-ioam-data])
and removing the additional header at the egress of the maintenance and removing the additional header at the egress of the maintenance
domain. This approach enables some types of measurements, but does domain. This approach enables some types of measurements, but does
not cover the entire range of measurements described in this not cover the entire range of measurements described in this
document. In some cases, it can be difficult to position measurement document. In some cases, it can be difficult to position measurement
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the transport protocol from the measurement framework. the transport protocol from the measurement framework.
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 [RFC8250]. This and Diagnostic Metrics (PDM) Destination Option [RFC8250]. This
allows a sender to optionally include a destination option that allows a sender to optionally include a destination option that
caries header fields that can be used to observe timestamps and caries header fields that can be used to observe timestamps and
packet sequence numbers. This information could be authenticated by packet sequence numbers. This information could be authenticated by
receiving transport endpoints when the information is added at the receiving transport endpoints when the information is added at the
sender and visible at the receiving endpoint, although methods to do sender and visible at the receiving endpoint, although methods to do
this have not currently been proposed. This method needs to be this have not currently been proposed. This method needs to be
explicitly enabled at the sender.XXX explicitly enabled at the sender.
Current measurements suggest it can be undesirable to rely on methods Current measurements suggest it can be undesirable to rely on methods
requiring the presence of network options or extension headers. IPv4 requiring the presence of network options or extension headers. IPv4
network options are often not supported (or are carried on a slower network options are often not supported (or are carried on a slower
processing path) and some IPv6 networks are also known to drop processing path) and some IPv6 networks are also known to drop
packets that set an IPv6 header extension (e.g., [RFC7872]). Another packets that set an IPv6 header extension (e.g., [RFC7872]). Another
disadvantage is that protocols that separately expose header disadvantage is that protocols that separately expose header
information do not necessarily have an advantage to expose the information do not necessarily have an advantage to expose the
information that is utilised by the protocol itself, and could information that is utilised by the protocol itself, and could
manipulate this header information to gain an advantage from the manipulate this header information to gain an advantage from the
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transport protocols. transport protocols.
6.1. Independent Measurement 6.1. 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. configuration of the network paths being measured.
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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 can support decisions when considering changes to transport This can support decisions 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.
6.2. Characterising "Unknown" Network Traffic 6.2. Characterising "Unknown" Network Traffic
The patterns and types of traffic that share Internet capacity The patterns and types of traffic that share Internet capacity change
changes with time as networked applications, usage patterns and over time as networked applications, usage patterns and protocols
protocols continue to evolve. 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
of this traffic increases, the need to monitor the traffic and of this traffic increases, the need to monitor the traffic and
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
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6.3. Accountability and Internet Transport Protocols 6.3. Accountability and Internet Transport Protocols
Information provided by tools observing transport headers can be used Information provided by tools observing transport headers can be used
to classify traffic, and to limit the network capacity used by to classify traffic, and to limit the network capacity used by
certain flows. Operators can potentially use this information to certain flows. Operators can potentially use this information to
prioritise or de-prioritise certain flows or classes of flow, with prioritise or de-prioritise certain flows or classes of flow, with
potential implications for network neutrality, or to rate limit potential implications for network neutrality, or to rate limit
malicious or otherwise undesirable flows (e.g., for Distributed malicious or otherwise undesirable flows (e.g., for Distributed
Denial of Service, DDOS, protection, or to ensure compliance with a Denial of Service, DDOS, protection, or to ensure compliance with a
traffic profile Section 3.2.4). Equally, operators could use traffic profile, as discussed in Section 3.2.4). Equally, operators
analysis of transport headers and transport flow state to demonstrate could use analysis of transport headers and transport flow state to
that they are not providing differential treatment to certain flows. demonstrate that they are not providing differential treatment to
Obfuscating or hiding this information using encryption is expected certain flows. Obfuscating or hiding this information using
to lead operators and maintainers of middleboxes (firewalls, etc.) to encryption may lead operators and maintainers of middleboxes
seek other methods to classify, and potentially other mechanisms to (firewalls, etc.) to seek other methods to classify, and potentially
condition, network traffic. other mechanisms to condition, network traffic.
A lack of data reduces the level of precision with which flows can be A lack of data reduces the level of precision with which flows can be
classified and conditioning mechanisms are applied (e.g., rate classified and conditioning mechanisms can be applied (e.g., rate
limiting, circuit breaker techniques [RFC8084], or blocking of limiting, circuit breaker techniques [RFC8084], or blocking of
uncharacterised traffic), and this needs to be considered when uncharacterised traffic), and this needs to be considered when
evaluating the impact of designs for transport encryption [RFC5218]. evaluating the impact of designs for transport encryption [RFC5218].
6.4. Impact on Research, Development and Deployment 6.4. Impact on Research, Development and Deployment
The majority of present Internet applications use two well-known The majority of present Internet applications use two well-known
transport protocols: e.g., TCP and UDP. Although TCP represents the transport protocols, TCP and UDP. Although TCP represents the
majority of current traffic, some real-time applications use UDP, and majority of current traffic, some real-time applications use UDP, and
much of this traffic utilises RTP format headers in the payload of much of this traffic utilises RTP format headers in the payload of
the UDP datagram. Since these protocol headers have been fixed for the UDP datagram. Since these protocol headers have been fixed for
decades, a range of tools and analysis methods have became common and decades, a range of tools and analysis methods have became common and
well-understood. Over this period, the transport protocol headers well-understood. Over this period, the transport protocol headers
have mostly changed slowly, and so also the need to develop tools have mostly changed slowly, and so also the need to develop tools
track new versions of the protocol. track new versions of the protocol.
Looking ahead, there will be a need to update these protocols and to Looking ahead, there will be a need to update these protocols and to
develop and deploy new transport mechanisms and protocols. There are develop and deploy new transport mechanisms and protocols. There are
both opportunities and also challenges to the design, evaluation and both opportunities and also challenges to the design, evaluation and
deployment of new transport protocol mechanisms. deployment of new transport protocol mechanisms.
Integrity checks can protect an endpoint from undetected modification Integrity checks can protect an endpoint from undetected modification
of protocol fields by network devices, whereas encryption and of protocol fields by network devices, whereas encryption and
obfuscation can further prevent these headers being utilised by obfuscation can further prevent these headers from being utilised by
network devices. Hiding headers can therefore provide the network devices. Hiding headers can therefore provide the
opportunity for greater freedom to update the protocols and can ease opportunity for greater freedom to update the protocols, and can ease
experimentation with new techniques and their final deployment in experimentation with new techniques and their final deployment in
endpoints. endpoints.
Hiding headers can limit the ability to measure and characterise Hiding headers can limit the ability to measure and characterise
traffic. Measurement data is increasingly being used to inform traffic. Measurement data is increasingly being used to inform
design decisions in networking research, during development of new design 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
skipping to change at page 31, line 25 skipping to change at page 29, line 25
deployed/candidate methods. 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.
7. Conclusions 7. Conclusions
The majority of present Internet applications use two well-known
transport protocols: e.g., TCP and UDP. Although TCP represents the
majority of current traffic, some real-time applications have used
UDP, and much of this traffic utilises RTP format headers in the
payload of the UDP datagram. Since these protocol headers have been
fixed for decades, a range of tools and analysis methods have became
common and well-understood. Over this period, the transport protocol
headers have mostly changed slowly, and so also the need to develop
tools track new versions of the protocol.
Confidentiality and strong integrity checks have properties that are Confidentiality and strong integrity checks have properties that are
being incorporated into new protocols and that have important being incorporated into new protocols and that have important
benefits. The pace of development of transports using the WebRTC benefits. The pace of development of transports using the WebRTC
data channel and the rapid deployment of QUIC transport protocol can data channel and the rapid deployment of QUIC transport protocol can
both be attributed to using the combination of UDP as a substrate both be attributed to using the combination of UDP as a substrate
while providing confidentiality and authentication of the while providing confidentiality and authentication of the
encapsulated transport headers and payload. encapsulated transport headers and payload.
The traffic that can be observed by on-path network devices is a The traffic that can be observed by on-path network devices is a
function of transport protocol design/options, network use, function of transport protocol design/options, network use,
skipping to change at page 35, line 42 skipping to change at page 33, line 33
9. IANA Considerations 9. 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.
10. Acknowledgements 10. Acknowledgements
The authors would like to thank Mohamed Boucadair, Spencer Dawkins, The authors would like to thank Mohamed Boucadair, Spencer Dawkins,
Jana Iyengar, Mirja Kuehlewind, Kathleen Moriarty, Al Morton, Chris Tom Herbert, Jana Iyengar, Mirja Kuehlewind, Kyle Rose, Kathleen
Seal, Joe Touch, Brian Trammell, and other members of the TSVWG for Moriarty, Al Morton, Chris Seal, Joe Touch, Brian Trammell, and other
their comments and feedback. members of the TSVWG for their comments and feedback.
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.
This work has received funding from the UK Engineering and Physical This work has received funding from the UK Engineering and Physical
Sciences Research Council under grant EP/R04144X/1. Sciences Research Council under grant EP/R04144X/1.
11. Informative References 11. Informative References
[bufferbloat]
Gettys, J. and K. Nichols, "Bufferbloat: dark buffers in
the Internet. Communications of the ACM, 55(1):57-65",
January 2012.
[I-D.ietf-ippm-ioam-data] [I-D.ietf-ippm-ioam-data]
Brockners, F., Bhandari, S., Pignataro, C., Gredler, H., Brockners, F., Bhandari, S., Pignataro, C., Gredler, H.,
Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov, Leddy, J., Youell, S., Mizrahi, T., Mozes, D., Lapukhov,
P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon, P., Chang, R., daniel.bernier@bell.ca, d., and J. Lemon,
"Data Fields for In-situ OAM", draft-ietf-ippm-ioam- "Data Fields for In-situ OAM", draft-ietf-ippm-ioam-
data-03 (work in progress), June 2018. data-03 (work in progress), June 2018.
[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", draft-ietf-quic-transport-14 (work and Secure Transport", draft-ietf-quic-transport-14 (work
in progress), August 2018. in progress), August 2018.
[I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-19
(work in progress), November 2017.
[I-D.ietf-taps-transport-security] [I-D.ietf-taps-transport-security]
Pauly, T., Perkins, C., Rose, K., and C. Wood, "A Survey Pauly, T., Perkins, C., Rose, K., and C. Wood, "A Survey
of Transport Security Protocols", draft-ietf-taps- of Transport Security Protocols", draft-ietf-taps-
transport-security-02 (work in progress), June 2018. transport-security-02 (work in progress), June 2018.
[I-D.ietf-tcpinc-tcpcrypt] [I-D.ietf-tcpinc-tcpcrypt]
Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack, Bittau, A., Giffin, D., Handley, M., Mazieres, D., Slack,
Q., and E. Smith, "Cryptographic protection of TCP Streams Q., and E. Smith, "Cryptographic protection of TCP Streams
(tcpcrypt)", draft-ietf-tcpinc-tcpcrypt-12 (work in (tcpcrypt)", draft-ietf-tcpinc-tcpcrypt-12 (work in
progress), June 2018. progress), June 2018.
skipping to change at page 37, line 30 skipping to change at page 35, line 30
Experimental Design, Implementation, and Policy Experimental Design, Implementation, and Policy
Considerations", RFC 1273, DOI 10.17487/RFC1273, November Considerations", RFC 1273, DOI 10.17487/RFC1273, November
1991, <https://www.rfc-editor.org/info/rfc1273>. 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, Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998, DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>. <https://www.rfc-editor.org/info/rfc2474>.
[RFC2507] Degermark, M., Nordgren, B., and S. Pink, "IP Header
Compression", RFC 2507, DOI 10.17487/RFC2507, February
1999, <https://www.rfc-editor.org/info/rfc2507>.
[RFC2508] Casner, S. and V. Jacobson, "Compressing IP/UDP/RTP
Headers for Low-Speed Serial Links", RFC 2508,
DOI 10.17487/RFC2508, February 1999,
<https://www.rfc-editor.org/info/rfc2508>.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, [RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, DOI 10.17487/RFC2914, September 2000, RFC 2914, DOI 10.17487/RFC2914, September 2000,
<https://www.rfc-editor.org/info/rfc2914>. <https://www.rfc-editor.org/info/rfc2914>.
[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, Mitigate Link-Related Degradations", RFC 3135,
DOI 10.17487/RFC3135, June 2001, DOI 10.17487/RFC3135, June 2001,
<https://www.rfc-editor.org/info/rfc3135>. <https://www.rfc-editor.org/info/rfc3135>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition [RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP", of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001, RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>. <https://www.rfc-editor.org/info/rfc3168>.
[RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and [RFC3234] Carpenter, B. and S. Brim, "Middleboxes: Taxonomy and
Issues", RFC 3234, DOI 10.17487/RFC3234, February 2002, Issues", RFC 3234, DOI 10.17487/RFC3234, February 2002,
<https://www.rfc-editor.org/info/rfc3234>. <https://www.rfc-editor.org/info/rfc3234>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/info/rfc3261>.
[RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation [RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393, Metric for IP Performance Metrics (IPPM)", RFC 3393,
DOI 10.17487/RFC3393, November 2002, DOI 10.17487/RFC3393, November 2002,
<https://www.rfc-editor.org/info/rfc3393>. <https://www.rfc-editor.org/info/rfc3393>.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <https://www.rfc-editor.org/info/rfc3550>. July 2003, <https://www.rfc-editor.org/info/rfc3550>.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, DOI 10.17487/RFC3711, March 2004,
<https://www.rfc-editor.org/info/rfc3711>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, [RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005, DOI 10.17487/RFC4302, December 2005,
<https://www.rfc-editor.org/info/rfc4302>. <https://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005, RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>. <https://www.rfc-editor.org/info/rfc4303>.
[RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey, [RFC4585] Ott, J., Wenger, S., Sato, N., Burmeister, C., and J. Rey,
"Extended RTP Profile for Real-time Transport Control "Extended RTP Profile for Real-time Transport Control
Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585, Protocol (RTCP)-Based Feedback (RTP/AVPF)", RFC 4585,
DOI 10.17487/RFC4585, July 2006, DOI 10.17487/RFC4585, July 2006,
<https://www.rfc-editor.org/info/rfc4585>. <https://www.rfc-editor.org/info/rfc4585>.
[RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov, [RFC4737] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov,
S., and J. Perser, "Packet Reordering Metrics", RFC 4737, S., and J. Perser, "Packet Reordering Metrics", RFC 4737,
DOI 10.17487/RFC4737, November 2006, DOI 10.17487/RFC4737, November 2006,
<https://www.rfc-editor.org/info/rfc4737>. <https://www.rfc-editor.org/info/rfc4737>.
[RFC4995] Jonsson, L-E., Pelletier, G., and K. Sandlund, "The RObust
Header Compression (ROHC) Framework", RFC 4995,
DOI 10.17487/RFC4995, July 2007,
<https://www.rfc-editor.org/info/rfc4995>.
[RFC5218] Thaler, D. and B. Aboba, "What Makes for a Successful [RFC5218] Thaler, D. and B. Aboba, "What Makes for a Successful
Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008, Protocol?", RFC 5218, DOI 10.17487/RFC5218, July 2008,
<https://www.rfc-editor.org/info/rfc5218>. <https://www.rfc-editor.org/info/rfc5218>.
[RFC5236] Jayasumana, A., Piratla, N., Banka, T., Bare, A., and R. [RFC5236] Jayasumana, A., Piratla, N., Banka, T., Bare, A., and R.
Whitner, "Improved Packet Reordering Metrics", RFC 5236, Whitner, "Improved Packet Reordering Metrics", RFC 5236,
DOI 10.17487/RFC5236, June 2008, DOI 10.17487/RFC5236, June 2008,
<https://www.rfc-editor.org/info/rfc5236>. <https://www.rfc-editor.org/info/rfc5236>.
[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation [RFC5481] Morton, A. and B. Claise, "Packet Delay Variation
skipping to change at page 40, line 10 skipping to change at page 38, line 34
"Observations on the Dropping of Packets with IPv6 "Observations on the Dropping of Packets with IPv6
Extension Headers in the Real World", RFC 7872, Extension Headers in the Real World", RFC 7872,
DOI 10.17487/RFC7872, June 2016, DOI 10.17487/RFC7872, June 2016,
<https://www.rfc-editor.org/info/rfc7872>. <https://www.rfc-editor.org/info/rfc7872>.
[RFC7928] Kuhn, N., Ed., Natarajan, P., Ed., Khademi, N., Ed., and [RFC7928] Kuhn, N., Ed., Natarajan, P., Ed., Khademi, N., Ed., and
D. Ros, "Characterization Guidelines for Active Queue D. 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, <https://www.rfc-editor.org/info/rfc7928>. 2016, <https://www.rfc-editor.org/info/rfc7928>.
[RFC7983] Petit-Huguenin, M. and G. Salgueiro, "Multiplexing Scheme
Updates for Secure Real-time Transport Protocol (SRTP)
Extension for Datagram Transport Layer Security (DTLS)",
RFC 7983, DOI 10.17487/RFC7983, September 2016,
<https://www.rfc-editor.org/info/rfc7983>.
[RFC8033] Pan, R., Natarajan, P., Baker, F., and G. White, [RFC8033] Pan, R., Natarajan, P., Baker, F., and G. White,
"Proportional Integral Controller Enhanced (PIE): A "Proportional Integral Controller Enhanced (PIE): A
Lightweight Control Scheme to Address the Bufferbloat Lightweight Control Scheme to Address the Bufferbloat
Problem", RFC 8033, DOI 10.17487/RFC8033, February 2017, Problem", RFC 8033, DOI 10.17487/RFC8033, February 2017,
<https://www.rfc-editor.org/info/rfc8033>. <https://www.rfc-editor.org/info/rfc8033>.
[RFC8084] Fairhurst, G., "Network Transport Circuit Breakers", [RFC8084] Fairhurst, G., "Network Transport Circuit Breakers",
BCP 208, RFC 8084, DOI 10.17487/RFC8084, March 2017, BCP 208, RFC 8084, DOI 10.17487/RFC8084, March 2017,
<https://www.rfc-editor.org/info/rfc8084>. <https://www.rfc-editor.org/info/rfc8084>.
skipping to change at page 42, line 48 skipping to change at page 40, line 48
-10 Updated references, split the Introduction, and added a paragraph -10 Updated references, split the Introduction, and added a paragraph
giving some examples of why ossification has been an issue. giving some examples of why ossification has been an issue.
-01 This resolved some reference issues. Updated section on -01 This resolved some reference issues. Updated section on
observation by devices on the path. observation by devices on the path.
-02 Comments received from Kyle Rose, Spencer Dawkins and Tom -02 Comments received from Kyle Rose, Spencer Dawkins and Tom
Herbert. The network-layer information has also been re-organised Herbert. The network-layer information has also been re-organised
after comments at IETF-103. after comments at IETF-103.
-03 Added a section on header compression and rewriting of sections
refering to RTP transport. This version contains author editorial
work and removed duplicate section.
Authors' Addresses 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/
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