draft-ietf-taps-arch-04.txt   draft-ietf-taps-arch-05.txt 
TAPS Working Group T. Pauly, Ed. TAPS Working Group T. Pauly, Ed.
Internet-Draft Apple Inc. Internet-Draft Apple Inc.
Intended status: Standards Track B. Trammell, Ed. Intended status: Standards Track B. Trammell, Ed.
Expires: January 9, 2020 Google Expires: May 7, 2020 Google
A. Brunstrom A. Brunstrom
Karlstad University Karlstad University
G. Fairhurst G. Fairhurst
University of Aberdeen University of Aberdeen
C. Perkins C. Perkins
University of Glasgow University of Glasgow
P. Tiesel P. Tiesel
TU Berlin TU Berlin
C. Wood C. Wood
Apple Inc. Apple Inc.
July 08, 2019 November 04, 2019
An Architecture for Transport Services An Architecture for Transport Services
draft-ietf-taps-arch-04 draft-ietf-taps-arch-05
Abstract Abstract
This document provides an overview of the architecture of Transport This document provides an overview of the architecture of Transport
Services, a model for exposing transport protocol features to Services, a model for exposing transport protocol features to
applications for network communication. In contrast to what is applications for network communication. In contrast to what is
provided by most existing Application Programming Interfaces (APIs), provided by most existing Application Programming Interfaces (APIs),
Transport Services is based on an asynchronous, event-driven Transport Services is based on an asynchronous, event-driven
interaction pattern; it uses messages for representing data transfer interaction pattern; it uses messages for representing data transfer
to applications; and it assumes an implementation that can use to applications; and it assumes an implementation that can use
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 9, 2020. This Internet-Draft will expire on May 7, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Background . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Event-Driven API . . . . . . . . . . . . . . . . . . . . 5 1.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Data Transfer Using Messages . . . . . . . . . . . . . . 5 1.3. Specification of Requirements . . . . . . . . . . . . . . 5
1.4. Flexibile Implementation . . . . . . . . . . . . . . . . 6 2. API Model . . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Event-Driven API . . . . . . . . . . . . . . . . . . . . 6
2.1. Specification of Requirements . . . . . . . . . . . . . . 7 2.2. Data Transfer Using Messages . . . . . . . . . . . . . . 7
2.3. Flexibile Implementation . . . . . . . . . . . . . . . . 8
3. Design Principles . . . . . . . . . . . . . . . . . . . . . . 8 3. Design Principles . . . . . . . . . . . . . . . . . . . . . . 8
3.1. Common APIs for Common Features . . . . . . . . . . . . . 8 3.1. Common APIs for Common Features . . . . . . . . . . . . . 9
3.2. Access to Specialized Features . . . . . . . . . . . . . 8 3.2. Access to Specialized Features . . . . . . . . . . . . . 9
3.3. Scope for API and Implementation Definitions . . . . . . 9 3.3. Scope for API and Implementation Definitions . . . . . . 10
4. Transport Services Architecture and Concepts . . . . . . . . 10 4. Transport Services Architecture and Concepts . . . . . . . . 11
4.1. Transport Services API Concepts . . . . . . . . . . . . . 11 4.1. Transport Services API Concepts . . . . . . . . . . . . . 12
4.1.1. Basic Objects . . . . . . . . . . . . . . . . . . . . 13 4.1.1. Connection Objects . . . . . . . . . . . . . . . . . 14
4.1.2. Pre-Establishment . . . . . . . . . . . . . . . . . . 14 4.1.2. Pre-Establishment . . . . . . . . . . . . . . . . . . 15
4.1.3. Establishment Actions . . . . . . . . . . . . . . . . 15 4.1.3. Establishment Actions . . . . . . . . . . . . . . . . 16
4.1.4. Data Transfer Objects and Actions . . . . . . . . . . 16 4.1.4. Data Transfer Objects and Actions . . . . . . . . . . 17
4.1.5. Event Handling . . . . . . . . . . . . . . . . . . . 16 4.1.5. Event Handling . . . . . . . . . . . . . . . . . . . 18
4.1.6. Termination Actions . . . . . . . . . . . . . . . . . 17 4.1.6. Termination Actions . . . . . . . . . . . . . . . . . 18
4.2. Transport System Implementation Concepts . . . . . . . . 17 4.2. Transport System Implementation Concepts . . . . . . . . 18
4.2.1. Candidate Gathering . . . . . . . . . . . . . . . . . 19 4.2.1. Candidate Gathering . . . . . . . . . . . . . . . . . 20
4.2.2. Candidate Racing . . . . . . . . . . . . . . . . . . 19 4.2.2. Candidate Racing . . . . . . . . . . . . . . . . . . 20
4.2.3. Protocol Stack Equivalence . . . . . . . . . . . . . 19 4.2.3. Protocol Stack Equivalence . . . . . . . . . . . . . 20
4.2.4. Separating Connection Groups . . . . . . . . . . . . 21 4.2.4. Separating Connection Groups . . . . . . . . . . . . 22
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
6. Security Considerations . . . . . . . . . . . . . . . . . . . 21 6. Security Considerations . . . . . . . . . . . . . . . . . . . 23
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 23
8. Informative References . . . . . . . . . . . . . . . . . . . 23 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24 8.1. Normative References . . . . . . . . . . . . . . . . . . 24
8.2. Informative References . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction 1. Introduction
Many application programming interfaces (APIs) to perform transport Many application programming interfaces (APIs) to perform transport
networking have been deployed, perhaps the most widely known and networking have been deployed, perhaps the most widely known and
imitated being the BSD socket() [POSIX] interface. The naming of imitated being the BSD socket() [POSIX] interface. The naming of
objects and functions across these APIs is not consistent, and varies objects and functions across these APIs is not consistent, and varies
depending on the protocol being used. For example, sending and depending on the protocol being used. For example, sending and
receiving streams of data is conceptually the same for both an receiving streams of data is conceptually the same for both an
unencrypted Transmission Control Protocol (TCP) stream and operating unencrypted Transmission Control Protocol (TCP) stream and operating
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This variety can lead to confusion when trying to understand the This variety can lead to confusion when trying to understand the
similarities and differences between protocols, and how applications similarities and differences between protocols, and how applications
can use them effectively. can use them effectively.
The goal of the Transport Services architecture is to provide a The goal of the Transport Services architecture is to provide a
common, flexible, and reusable interface for transport protocols. As common, flexible, and reusable interface for transport protocols. As
applications adopt this interface, they will benefit from a wide set applications adopt this interface, they will benefit from a wide set
of transport features that can evolve over time, and ensure that the of transport features that can evolve over time, and ensure that the
system providing the interface can optimize its behavior based on the system providing the interface can optimize its behavior based on the
application requirements and network conditions, without requiring application requirements and network conditions, without requiring
changes to the applications. This flexibility does not only enable changes to the applications. This flexibility enables faster
faster deployment of new feature and protocols, but it can also deployment of new features and protocols. It can also support
support applications with racing and fallback mechanisms which applications by offering racing and fallback mechanisms, which
otherwise need to be implemented in each application separately. otherwise need to be implemented in each application separately.
This document is developed in parallel with the specification of the This document is developed in parallel with the specification of the
Transport Services API [I-D.ietf-taps-interface] and Implementation Transport Services API [I-D.ietf-taps-interface] and Implementation
Guidelines [I-D.ietf-taps-impl]. Although following the Transport Guidelines [I-D.ietf-taps-impl]. Although following the Transport
Services Architecture does of course not mean that all APIs and Services Architecture does not require that all APIs and
implementations have to be identical, a common minimal set of implementations are identical, a common minimal set of features
features represented in a consistent fashion will enable applications represented in a consistent fashion will enable applications to be
to be easily ported from one system to the another. easily ported from one system to another.
1.1. Overview 1.1. Background
The model of using sockets for networking can be represented as The Transport Services architecture is based on the survey of
follows: applications create connections and transfer data using the Services Provided by IETF Transport Protocols and Congestion Control
socket API, which provides the interface to the implementations of Mechanisms [RFC8095], and the distilled minimal set of the features
UDP and TCP (typically implemented in the system's kernel), which in offered by transport protocols [I-D.ietf-taps-minset]. These
turn send data over the available network layer interfaces. documents identified common features and patterns across all
transport protocols developed thus far in the IETF.
Since transport security is an increasingly relevant aspect of using
transport protocols on the Internet, this architecture also considers
the impact of transport security protocols on the feature-set exposed
by transport services [I-D.ietf-taps-transport-security].
One of the key insights to come from identifying the minimal set of
features provided by transport protocols [I-D.ietf-taps-minset] was
that features either require application interaction and guidance
(referred to as Functional or Optimizing Features), or else can be
handled automatically by a system implementing Transport Services
(referred to as Automatable Features). Among the Functional and
Optimizing Features, some were common across all or nearly all
transport protocols, while others could be seen as features that, if
specified, would only be useful with a subset of protocols, but would
not harm the functionality of other protocols. For example, some
protocols can deliver messages faster for applications that do not
require messages to arrive in the order in which they were sent.
However, this functionality needs to be explicitly allowed by the
application, since reordering messages would be undesirable in many
cases.
1.2. Overview
This document describes the Transport Services architecture in three
sections:
o Section 2 describes how the API model of Transport Services
differs from traditional socket-based APIs. Specifically, it
offers asynchronous event-driven interaction, the use of messages
for data transfer, and the ability to easily adopt different
transport protocols.
o Section 3 explains the design principles that guide the Transport
Services API. These principles are intended to make sure that
transport protocols can continue to be enhanced and evolve without
requiring too many changes by application developers.
o Section 4 presents the Transport Services architecture diagram and
defines the concepts that are used by both the API and
implementation documents. The Preconnection allows applications
to configure connection properties, and the Connection represents
an object that can be used to send and receive Messages.
1.3. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. API Model
The traditional model of using sockets for networking can be
represented as follows:
o Applications create connections and transfer data using the socket
API.
o The socket API provides the interface to the implementations of
TCP and UDP (typically implemented in the system's kernel).
o TCP and UDP in the kernel send and receive data over the available
network layer interfaces.
+-----------------------------------------------------+ +-----------------------------------------------------+
| Application | | Application |
+-----------------------------------------------------+ +-----------------------------------------------------+
| | | |
+---------------------+ +-----------------------+ +---------------------+ +-----------------------+
| Socket Stream API | | Socket Datagram API | | Socket Stream API | | Socket Datagram API |
+---------------------+ +-----------------------+ +---------------------+ +-----------------------+
| | | |
+-----------------------------------------------------+ +-----------------------------------------------------+
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+-----------------------------------------------------+ +-----------------------------------------------------+
| |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Network Layer Interface | | Network Layer Interface |
+-----------------------------------------------------+ +-----------------------------------------------------+
Figure 2: Transport Services API Model Figure 2: Transport Services API Model
The Transport Services API [I-D.ietf-taps-interface] defines the The Transport Services API [I-D.ietf-taps-interface] defines the
mechanism for an application to create network connections and mechanism for an application to create network connections and
transfer data. The Implementation [I-D.ietf-taps-impl] is transfer data. The implementation [I-D.ietf-taps-impl] is
responsible for mapping the API into the various available transport responsible for mapping the API to the various available transport
protocols and managing the available network interfaces and paths. protocols and managing the available network interfaces and paths.
There are a few key departures that Transport Services makes from the There are key differences between the architecture of the Transport
sockets API: it presents an asynchronous, event-driven API; it uses Services system and the architecture of the sockets API: it presents
messages for representing data transfer to applications; and it an asynchronous, event-driven API; it uses messages for representing
assumes an implementation that can use multiple IP addresses, data transfer to applications; and it assumes an implementation that
multiple protocols, multiple paths, and provide multiple application can use multiple IP addresses, multiple protocols, multiple paths,
streams. and provide multiple application streams.
1.2. Event-Driven API 2.1. Event-Driven API
Originally, sockets presented a blocking interface for establishing Originally, sockets presented a blocking interface for establishing
connections and transferring data. However, most modern applications connections and transferring data. However, most modern applications
interact with the network asynchronously. When sockets are presented interact with the network asynchronously. When sockets are presented
as an asynchronous interface, they generally use a try-and-fail as an asynchronous interface, they generally use a try-and-fail
model. If the application wants to read, but data has not yet been model. If the application wants to read, but data has not yet been
received from the peer, the call to read will fail. The application received from the peer, the call to read will fail. The application
then waits and can try again later. then waits and can try again later.
All interaction with a Transport Services system is expected to be All interaction with a Transport Services system is expected to be
asynchronous, and use an event-driven model unlike sockets asynchronous, and use an event-driven model unlike sockets
Section 4.1.5. For example, if the application wants to read, its Section 4.1.5. For example, if the application wants to read, its
call to read will not fail, but will deliver an event containing the call to read will not fail, but will deliver an event containing the
received data once it is available. received data once it is available.
The Transport Services API also delivers events regarding the The Transport Services API also delivers events regarding the
lifetime of a connection and changes to available network links, lifetime of a connection and changes in the available network links,
which were not previously made explicit in sockets. which were not previously made explicit in sockets.
Using asynchronous events allows for a much simpler interaction model Using asynchronous events allows for a much simpler interaction model
when establishing connections and transferring data. Events in time when establishing connections and transferring data. Events in time
more closely reflect the nature of interactions over networks, as more closely reflect the nature of interactions over networks, as
opposed to how sockets represent network resources as file system opposed to how sockets represent network resources as file system
objects that may be temporarily unavailable. objects that may be temporarily unavailable.
1.3. Data Transfer Using Messages 2.2. Data Transfer Using Messages
Sockets provide a message interface for datagram protocols like UDP, Sockets provide a message interface for datagram protocols like UDP,
but provide an unstructured stream abstraction for TCP. While TCP but provide an unstructured stream abstraction for TCP. While TCP
does indeed provide the ability to send and receive data as streams, does indeed provide the ability to send and receive data as streams,
most applications need to interpret structure within these streams. most applications need to interpret structure within these streams.
For example, HTTP/1.1 uses character delimiters to segment messages For example, HTTP/1.1 uses character delimiters to segment messages
over a stream; TLS record headers carry a version, content type, and over a stream [RFC7230]; TLS record headers carry a version, content
length; and HTTP/2 uses frames to segment its headers and bodies. type, and length [RFC8446]; and HTTP/2 uses frames to segment its
headers and bodies [RFC7540].
The Transport Services API represents data as messages, so that it The Transport Services API represents data as messages, so that it
more closely matches the way applications use the network. Messages more closely matches the way applications use the network. Messages
seamlessly work with transport protocols that support datagrams or seamlessly work with transport protocols that support datagrams or
records, but can also be used over a stream by defining an records, but can also be used over a stream by defining an
application-layer framer Section 4.1.4. When framing protocols are application-layer framer Section 4.1.4. When framing protocols are
placed on top of unstructured streams, the messages used in the API placed on top of unstructured streams, the messages used in the API
represent the framed messages within the stream. In the absence of a represent the framed messages within the stream. In the absence of a
framer, protocols that deal only in byte streams, such as TCP, framer, protocols that deal only in byte streams, such as TCP,
represent their data in each direction as a single, long message. represent their data in each direction as a single, long message.
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underlaying transport connections to utilize multi-streaming and underlaying transport connections to utilize multi-streaming and
pooled connections. pooled connections.
Allowing applications to interact with messages is backwards- Allowing applications to interact with messages is backwards-
compatible with existings protocols and APIs, as it does not change compatible with existings protocols and APIs, as it does not change
the wire format of any protocol. Instead, it gives the protocol the wire format of any protocol. Instead, it gives the protocol
stack additional information to allow it to make better use of modern stack additional information to allow it to make better use of modern
transport services, while simplifying the application's role in transport services, while simplifying the application's role in
parsing data. parsing data.
1.4. Flexibile Implementation 2.3. Flexibile Implementation
Sockets, for protocols like TCP, are generally limited to connecting Sockets, for protocols like TCP, are generally limited to connecting
to a single address over a single interface. They also present a to a single address over a single interface. They also present a
single stream to the application. Software layers built upon sockets single stream to the application. Software layers built upon sockets
often propagate this limitation of a single-address single-stream often propagate this limitation of a single-address single-stream
model. The Transport Services architecture is designed to handle model. The Transport Services architecture is designed to handle
multiple candidate endpoints, protocols, and paths; and support multiple candidate endpoints, protocols, and paths; and support
multipath and multistreaming protocols. multipath and multistreaming protocols.
Transport Services implementations are meant to be flexible at Transport Services implementations are meant to be flexible at
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used by a Transport Services implementation for resolution, path used by a Transport Services implementation for resolution, path
selection, and racing. selection, and racing.
Flexibility after connection establishment is also important. Flexibility after connection establishment is also important.
Transport protocols that can migrate between multiple network-layer Transport protocols that can migrate between multiple network-layer
interfaces need to be able to process and react to interface changes. interfaces need to be able to process and react to interface changes.
Protocols that support multiple application-layer streams need to Protocols that support multiple application-layer streams need to
support initiating and receiving new streams using existing support initiating and receiving new streams using existing
connections. connections.
2. Background
The Transport Services architecture is based on the survey of
Services Provided by IETF Transport Protocols and Congestion Control
Mechanisms [RFC8095], and the distilled minimal set of the features
offered by transport protocols [I-D.ietf-taps-minset]. These
documents identified common features and patterns across all
transport protocols developed thus far in the IETF.
Since transport security is an increasingly relevant aspect of using
transport protocols on the Internet, this architecture also considers
the impact of transport security protocols on the feature-set exposed
by transport services [I-D.ietf-taps-transport-security].
One of the key insights to come from identifying the minimal set of
features provided by transport protocols [I-D.ietf-taps-minset] was
that features either require application interaction and guidance
(referred to as Functional Features), or else can be handled
automatically by a system implementing Transport Services (referred
to as Automatable Features). Among the Functional Features, some
were common across all or nearly all transport protocols, while
others could be seen as features that, if specified, would only be
useful with a subset of protocols, but would not harm the
functionality of other protocols. For example, some protocols can
deliver messages faster for applications that do not require messages
to arrive in the order in which they were sent. However, this
functionality needs to be explicitly allowed by the application,
since reordering messages would be undesirable in many cases.
2.1. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Design Principles 3. Design Principles
The goal of the Transport Services architecture is to redefine the The goal of the Transport Services architecture is to redefine the
interface between applications and transports in a way that allows interface between applications and transports in a way that allows
the transport layer to evolve and improve without fundamentally the transport layer to evolve and improve without fundamentally
changing the contract with the application. This requires a careful changing the contract with the application. This requires a careful
consideration of how to expose the capabilities of protocols. consideration of how to expose the capabilities of protocols.
There are several degrees in which a Transport Services system can There are several degrees in which a Transport Services system is
offer flexibility to an application: it can provide access to intended to offer flexibility to an application: it can provide
multiple sets of protocols and protocol features; it can use these access to multiple sets of protocols and protocol features; it can
protocols across multiple paths that could have different performance use these protocols across multiple paths that could have different
and functional characteristics; and it can communicate with different performance and functional characteristics; and it can communicate
remote systems to optimize performance, robustness to failure, or with different remote systems to optimize performance, robustness to
some other metric. Beyond these, if the API for the system remains failure, or some other metric. Beyond these, if the API for the
the same over time, new protocols and features could be added to the system remains the same over time, new protocols and features could
system's implementation without requiring changes in applications for be added to the system's implementation without requiring changes in
adoption. applications for adoption.
The following considerations were used in the design of this
architecture.
3.1. Common APIs for Common Features 3.1. Common APIs for Common Features
Functionality that is common across multiple transport protocols Functionality that is common across multiple transport protocols
SHOULD be accessible through a unified set of API calls. An SHOULD be accessible through a unified set of API calls. An
application ought to be able to implement logic for its basic use of application ought to be able to implement logic for its basic use of
transport networking (establishing the transport, and sending and transport networking (establishing the transport, and sending and
receiving data) once, and expect that implementation to continue to receiving data) once, and expect that implementation to continue to
function as the transports change. function as the transports change.
Any Transport Services API is REQUIRED to allow access to the Any Transport Services API is REQUIRED to allow access to the
distilled minimal set of features offered by transport protocols distilled minimal set of features offered by transport protocols
[I-D.ietf-taps-minset]. [I-D.ietf-taps-minset].
3.2. Access to Specialized Features 3.2. Access to Specialized Features
There are applications that will need to control fine-grained details There are applications that will need to control fine-grained details
of transport protocols to optimize their behavior and ensure of transport protocols to optimize their behavior and ensure
compatibility with remote systems. A Transport Services system compatibility with remote systems. A Transport Services system
therefore SHOULD also permit more specialized protocol features to be therefore SHOULD also permit more specialized protocol features to be
used. The interface for these specialized options should be exposed used. The interface for these specialized options ought to be
differently from the common options to ensure flexibility. exposed differently from the common options to ensure flexibility.
A specialized feature could be required by an application only when A specialized feature could be required by an application only when
using a specific protocol, and not when using others. For example, using a specific protocol, and not when using others. For example,
if an application is using UDP, it could require control over the if an application is using UDP, it could require control over the
checksum or fragmentation behavior for UDP; if it used a protocol to checksum or fragmentation behavior for UDP; if it used a protocol to
frame its data over a byte stream like TCP, it would not need these frame its data over a byte stream like TCP, it would not need these
options. In such cases, the API ought to expose the features in such options. In such cases, the API ought to expose the features in such
a way that they take effect when a particular protocol is selected, a way that they take effect when a particular protocol is selected,
but do not imply that only that protocol could be used. For example, but do not imply that only that protocol could be used. For example,
if the API allows an application to specify a preference for if the API allows an application to specify a preference for
constrained checksum usage, communication would not fail when a constrained checksum usage, communication would not fail when a
protocol such as TCP is selected, which uses a checksum covering the protocol such as TCP is selected, which uses a checksum covering the
entire payload. entire payload.
Other specialized features, however, could be strictly required by an Other specialized features, however, could be strictly required by an
application and thus constrain the set of protocols that can be used. application and thus constrain the set of protocols that can be used.
For example, if an application requires encryption of its transport For example, if an application requires encryption of its transport
data, only protocol stacks that include some transport security data, only protocol stacks that include a transport security function
protocol are eligible to be used. A Transport Services API MUST are eligible to be used. A Transport Services API MUST allow
allow applications to define such requirements and constrain the applications to define such requirements and constrain the system's
system's options. Since such options are not part of the core/common options. Since such options are not part of the core/common
features, it will generally be simple for an application to modify features, it will generally be simple for an application to modify
its set of constraints and change the set of allowable protocol its set of constraints and change the set of allowable protocol
features without changing the core implementation. features without changing the core implementation.
3.3. Scope for API and Implementation Definitions 3.3. Scope for API and Implementation Definitions
The Transport Services API is envisioned as the abstract model for a The Transport Services API is envisioned as the abstract model for a
family of APIs that share a common way to expose transport features family of APIs that share a common way to expose transport features
and encourage flexibility. The abstract API definition and encourage flexibility. The abstract API definition
[I-D.ietf-taps-interface] describes this interface and is aimed at [I-D.ietf-taps-interface] describes this interface and how it can be
application developers. exposed to application developers.
Implementations that provide the Transport Services API Implementations that provide the Transport Services API
[I-D.ietf-taps-impl] will vary due to system-specific support and the [I-D.ietf-taps-impl] will vary due to system-specific support and the
needs of the deployment scenario. It is expected that all needs of the deployment scenario. It is expected that all
implementations of Transport Services will offer the entire mandatory implementations of Transport Services will offer the entire mandatory
API, but that some features will not be functional in certain API. All implementations are REQUIRED to offer an API that is
implementations. All implementations are REQUIRED to offer sufficient to use the distilled minimal set of features offered by
sufficient APIs to use the distilled minimal set of features offered transport protocols [I-D.ietf-taps-minset], including API support for
by transport protocols [I-D.ietf-taps-minset], including API support TCP and UDP transport. However, some features provided by this API
for TCP and UDP transport, but it is possible that some very will not be functional in certain implementations. For example, it
constrained devices might not have, for example, a full TCP is possible that some very constrained devices might not have a full
implementation beneath the API. TCP implementation beneath the API.
To preserve flexibility and compatibility with future protocols, top- To preserve flexibility and compatibility with future protocols, top-
level features in the Transport Services API SHOULD avoid referencing level features in the Transport Services API SHOULD avoid referencing
particular transport protocols. The mappings of these API features particular transport protocols. The mappings of these API features
to specific implementations of each feature is explained in the to specific implementations of each feature is explained in the
[I-D.ietf-taps-impl] along with the implications of the feature on [I-D.ietf-taps-impl] along with the implications of the feature on
existing protocols. It is expected that this document will be existing protocols. It is expected that [I-D.ietf-taps-interface]
updated and supplemented as new protocols and protocol features are will be updated and supplemented as new protocols and protocol
developed. features are developed.
It is important to note that neither the Transport Services API It is important to note that neither the Transport Services API
[I-D.ietf-taps-interface] nor the Implementation document [I-D.ietf-taps-interface] nor the Implementation document
[I-D.ietf-taps-impl] defines new protocols that require any changes [I-D.ietf-taps-impl] define new protocols or protocol capabilities
to a remote system. The Transport Services system MUST be deployable that affect what is communicated across the network. The Transport
on one side only. Services system MUST be deployable on one side only. A Transport
Services system acting as a connection initiator can communicate with
any existing system that implements the transport protocol(s)
selected by the Transport Services system. Similarly, a Transport
Services system acting as a listener can receive connections for any
protocol that is supported by the system, from existing initiators.
4. Transport Services Architecture and Concepts 4. Transport Services Architecture and Concepts
The concepts defined in this document are intended primarily for use The concepts defined in this document are intended primarily for use
in the documents and specifications that describe the Transport in the documents and specifications that describe the Transport
Services architecture and API. While the specific terminology can be Services architecture and API. While the specific terminology can be
used in some implementations, it is expected that there will remain a used in some implementations, it is expected that there will remain a
variety of terms used by running code. variety of terms used by running code.
The architecture divides the concepts for Transport Services into two The architecture divides the concepts for Transport Services into two
skipping to change at page 11, line 42 skipping to change at page 12, line 42
+-------------+ Stack(s) +----------------------+ +-------------+ Stack(s) +----------------------+
+-------+--------+ +-------+--------+
V V
Network Layer Interface Network Layer Interface
Figure 3: Concepts and Relationships in the Transport Services Figure 3: Concepts and Relationships in the Transport Services
Architecture Architecture
4.1. Transport Services API Concepts 4.1. Transport Services API Concepts
Fundamentally, a Transport Services API needs to provide basic Fundamentally, a Transport Services API needs to provide connection
objects (Section 4.1.1) that allow applications to establish objects (Section 4.1.1) that allow applications to establish
communication and send and receive data. These could be exposed as communication, and then send and receive data. These could be
handles or referenced objects, depending on the language. exposed as handles or referenced objects, depending on the language.
Beyond the basic objects, there are several high-level groups of Beyond the connection objects, there are several high-level groups of
actions that any Transport Services API implementing this actions that any Transport Services API implementing this
specification MUST provide: specification MUST provide:
o Pre-Establishment (Section 4.1.2) encompasses the properties that o Pre-Establishment (Section 4.1.2) encompasses the properties that
an application can pass to describe its intent, requirements, an application can pass to describe its intent, requirements,
prohibitions, and preferences for its networking operations. For prohibitions, and preferences for its networking operations. For
any system that provides generic Transport Services, these any system that provides generic Transport Services, these
properties SHOULD be defined to apply to multiple transport properties SHOULD be defined to apply to multiple transport
protocols. Properties specified during Pre-Establishment can have protocols. Properties specified during Pre-Establishment can have
a large impact on the rest of the interface: they modify how a large impact on the rest of the interface: they modify how
establishment occurs, they influence the expectations around data establishment occurs, they influence the expectations around data
transfer, and they determine the set of events that will be transfer, and they determine the set of events that will be
supported. supported.
o Establishment (Section 4.1.3) focuses on the actions that an o Establishment (Section 4.1.3) focuses on the actions that an
application takes on the basic objects to prepare for data application takes on the connection objects to prepare for data
transfer. transfer.
o Data Transfer (Section 4.1.4) consists of how an application o Data Transfer (Section 4.1.4) consists of how an application
represents the data to be sent and received, the functions represents the data to be sent and received, the functions
required to send and receive that data, and how the application is required to send and receive that data, and how the application is
notified of the status of its data transfer. notified of the status of its data transfer.
o Event Handling (Section 4.1.5) defines the set of properties about o Event Handling (Section 4.1.5) defines the set of properties about
which an application can receive notifications during the lifetime which an application can receive notifications during the lifetime
of transport objects. Events MAY also provide opportunities for of transport objects. Events MAY also provide opportunities for
the application to interact with the underlying transport by the application to interact with the underlying transport by
querying state or updating maintenance options. querying state or updating maintenance options.
o Termination (Section 4.1.6) focuses on the methods by which data o Termination (Section 4.1.6) focuses on the methods by which data
transmission is stopped, and state is torn down in the transport. transmission is stopped, and state is torn down in the transport.
The diagram below provides a high-level view of the actions taken The diagram below provides a high-level view of the actions and
during the lifetime of a connection. Note that some actions are events during the lifetime of a connection. Note that some actions
alternatives (e.g., whether to initiate a connection or to listen for are alternatives (e.g., whether to initiate a connection or to listen
incoming connections), others are optional (e.g., setting Connection for incoming connections), others are optional (e.g., setting
and Message Properties in Pre-Establishment), or have been omitted Connection and Message Properties in Pre-Establishment), or have been
for brevity. omitted for brevity.
Pre-Establishment : Established : Termination Pre-Establishment : Established : Termination
----------------- : ----------- : ----------- ----------------- : ----------- : -----------
: Close() : : Close() :
+---------------+ Initiate() +------------+ Abort() : +---------------+ Initiate() +------------+ Abort() :
+-->| Preconnection |----------->| Connection |---------------> Closed +-->| Preconnection |------------->| Connection |-----------> Closed
| +---------------+ : +------------+ Connection: | +---------------+ Rendezvous() +------------+ Conn. :
| : ^ ^ ^ | Finished : | : ^ | Finished :
+-- Local Endpoint : | | | | : +-- Local Endpoint : | | :
| : | | | +---------+ : | : | | :
+-- Remote Endpoint : +----+ | +-----+ | : +-- Remote Endpoint : | v :
| : | |Send() | | : | : | Connection :
+-- Selection Properties : | +---------+ | v : +-- Selection Properties : | Ready :
+-- Connection Properties ---+ | Message | | Message : +-- Connection Properties : | :
+-- Message Properties -------->| to send | | Received : +-- Message Properties : | :
| : +---------+ | : | : | :
| +----------+ : | : | +----------+ : | :
+-->| Listener |------------------------------+ : +-->| Listener |----------------------+ :
+----------+ Connection Received : +----------+ Connection Received :
^ : : ^ : :
| : : | : :
Listen() : : Listen() : :
Figure 4: The lifetime of a connection Figure 4: The lifetime of a connection
4.1.1. Basic Objects 4.1.1. Connection Objects
o Preconnection: A Preconnection object is a representation of a o Preconnection: A Preconnection object is a representation of a
potential connection. It has state that describes parameters of a potential connection. It has state that describes parameters of a
Connection that might exist in the future: the Local Endpoint from Connection that might exist in the future: the Local Endpoint from
which that Connection will be established, the Remote Endpoint which that Connection will be established, the Remote Endpoint
(Section 4.1.2) to which it will connect, and Selection Properties (Section 4.1.2) to which it will connect, and Selection Properties
(Section 4.1.2) that influence the paths and protocols a (Section 4.1.2) that influence the paths and protocols a
Connection will use. A Preconnection can be fully specified and Connection will use. A Preconnection can be fully specified such
represent a single possible Connection, or it can be partially that it represents a single possible Connection, or it can be
specified such that it represents a family of possible partially specified such that it represents a family of possible
Connections. The Local Endpoint (Section 4.1.2) MUST be specified Connections. The Local Endpoint (Section 4.1.2) MUST be specified
if the Preconnection is used to Listen for incoming connections. if the Preconnection is used to Listen for incoming connections.
The Local Endpoint is OPTIONAL if it is used to Initiate The Local Endpoint is OPTIONAL if it is used to Initiate
connections. The Remote Endpoint MUST be specified in the connections. The Remote Endpoint MUST be specified in the
Preconnection is used to Initiate connections. The Remote Preconnection that is used to Initiate connections. The Remote
Endpoint is OPTIONAL if it is used to Listen for incoming Endpoint is OPTIONAL if it is used to Listen for incoming
connections. The Local Endpoint and the Remote Endpoint MUST both connections. The Local Endpoint and the Remote Endpoint MUST both
be specified if a peer-to-peer Rendezvous is to occur based on the be specified if a peer-to-peer Rendezvous is to occur based on the
Preconnection. Preconnection.
* Transport Properties: Transport Properties can be specified as o Transport Properties: Transport Properties can be specified as
part of a Preconnection to allow the application to configure part of a Preconnection to allow the application to configure the
the Transport System and express their requirements, Transport System and express their requirements, prohibitions, and
prohibitions, and preferences. There are three kinds of preferences. There are three kinds of Transport Properties:
Transport Properties: Selection Properties (Section 4.1.2),
Connection Properties (Section 4.1.2), and Message Properties * Selection Properties (Section 4.1.2)
(Section 4.1.4). Message Properties can also be specified
during data transfer to affect specific Messages. * Connection Properties (Section 4.1.2)
* and Message Properties (Section 4.1.4); note that Message
Properties can also be specified during data transfer to affect
specific Messages.
o Connection: A Connection object represents one or more active o Connection: A Connection object represents one or more active
transport protocol instances that can send and/or receive Messages transport protocol instances that can send and/or receive Messages
between local and remote systems. It holds state pertaining to between local and remote systems. It holds state pertaining to
the underlying transport protocol instances and any ongoing data the underlying transport protocol instances and any ongoing data
transfers. This represents, for example, an active connection in transfers. This represents, for example, an active connection in
a connection-oriented protocol such as TCP, or a fully-specified a connection-oriented protocol such as TCP, or a fully-specified
5-tuple for a connectionless protocol such as UDP. It can also 5-tuple for a connectionless protocol such as UDP. It can also
represent a pool of transport protocol instance, e.g., a set of represent a pool of transport protocol instance, e.g., a set of
TCP and QUIC connections to equivalent endpoints, or a stream of a TCP and QUIC connections to equivalent endpoints, or a stream of a
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behavior of the Transport System. For example, a protocol- behavior of the Transport System. For example, a protocol-
specific Connection Property can express that if UDP is used, the specific Connection Property can express that if UDP is used, the
implementation ought to use checksums. Note that the presence of implementation ought to use checksums. Note that the presence of
such a property does not require that a specific protocol will be such a property does not require that a specific protocol will be
used. In general, these properties do not explicitly determine used. In general, these properties do not explicitly determine
the selection of paths or protocols, but MAY be used in this way the selection of paths or protocols, but MAY be used in this way
by an implementation during connection establishment. Connection by an implementation during connection establishment. Connection
Properties SHOULD be specified on a Preconnection prior to Properties SHOULD be specified on a Preconnection prior to
Connection establishment, but MAY be modified later. Changes made Connection establishment, but MAY be modified later. Changes made
to Connection Properties after establishment take effect on a to Connection Properties after establishment take effect on a
best-effort basis. best-effort basis. Such changes do not affect protocol or path
selection, but only modify the manner in which a connection sends
and receives data.
4.1.3. Establishment Actions 4.1.3. Establishment Actions
o Initiate: The primary action that an application can take to o Initiate: The primary action that an application can take to
create a Connection to a Remote Endpoint, and prepare any required create a Connection to a Remote Endpoint, and prepare any required
local or remote state to be able to send and/or receive Messages. local or remote state to enable the transmission of Messages. For
For some protocols, this will initiate a client-to-server style some protocols, this will initiate a client-to-server style
handshake; for other protocols, this will just establish local handshake; for other protocols, this will just establish local
state. The process of identifying options for connecting, such as state. The process of identifying options for connecting, such as
resolution of the Remote Endpoint, occurs in response the Initiate resolution of the Remote Endpoint, occurs in response the Initiate
call. call.
o Listen: The action of marking a Listener as willing to accept o Listen: The action of marking a Listener as willing to accept
incoming Connections. The Listener will then create Connection incoming Connections. The Listener will then create Connection
objects as incoming connections are accepted (Section 4.1.5). objects as incoming connections are accepted (Section 4.1.5).
o Rendezvous: The action of establishing a peer-to-peer connection o Rendezvous: The action of establishing a peer-to-peer connection
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established peer-to-peer connection. established peer-to-peer connection.
4.1.4. Data Transfer Objects and Actions 4.1.4. Data Transfer Objects and Actions
o Message: A Message object is a unit of data that can be o Message: A Message object is a unit of data that can be
represented as bytes that can be transferred between two systems represented as bytes that can be transferred between two systems
over a transport connection. The bytes within a Message are over a transport connection. The bytes within a Message are
assumed to be ordered within the Message. If an application does assumed to be ordered within the Message. If an application does
not care about the order in which a peer receives two distinct not care about the order in which a peer receives two distinct
spans of bytes, those spans of bytes are considered independent spans of bytes, those spans of bytes are considered independent
Messages. If a received Message is incomplete or corrupted, it Messages. Boundaries of a Message might or might not be
might or might not be usable by certain applications. Boundaries understood or transmitted by transport protocols. Specifically,
of a Message might or might not be understood or transmitted by what one application considers to be two Messages sent on a
transport protocols. Specifically, what one application considers stream-based transport can be treated as a single Message by the
to be two Messages sent on a stream-based transport can be treated application on the other side.
as a single Message by the application on the other side.
o Message Properties: Message Properties can be used to annotate o Message Properties: Message Properties can be used to annotate
specific Messages. These properties can specify how the transport specific Messages. These properties might only apply to how
will send the Message (for prioritization and reliability), along Message is sent (such as how the transport will treat
with any per-protocol properties to send with the Message. prioritization and reliability), but can also include properties
Message Properties MAY be set on a Preconnection to define that specific protocols encode and communicate to the Remote
defaults properties for sending. When receiving Messages, Message Endpoint. Message Properties MAY be set on a Preconnection to
Properties can contain per-protocol properties. define defaults properties for sending. When receiving Messages,
Message Properties can contain per-protocol properties for
properties that are sent between the endpoints.
o Send: The action to transmit a Message or partial Message over a o Send: The action to transmit a Message or partial Message over a
Connection to the remote system. The interface to Send MAY Connection to the remote system. The interface to Send MAY
include Message Properties specific to how the Message's content include Message Properties specific to how the Message content is
is to be sent. Status of the Send operation can be delivered back to be sent. The status of the Send operation can be delivered
to the application in an event (Section 4.1.5). back to the sending application in an event (Section 4.1.5).
o Receive: An action that indicates that the application is ready to o Receive: An action that indicates that the application is ready to
asynchronously accept a Message over a Connection from a remote asynchronously accept a Message over a Connection from a remote
system, while the Message content itself will be delivered in an system, while the Message content itself will be delivered in an
event (Section 4.1.5). The interface to Receive MAY include event (Section 4.1.5). The interface to Receive MAY include
Message Properties specific to the Message that is to be delivered Message Properties specific to the Message that is to be delivered
to the application. to the application.
o Framer: A Framer is a data translation layer that can be added to o Framer: A Framer is a data translation layer that can be added to
a Connection to define how application-level Messages are a Connection to define how application-level Messages are
transmitted over a transport protocol. This is particularly transmitted over a transport protocol. This is particularly
relevant for protocols that otherwise present unstructured relevant for protocols that otherwise present unstructured
streams, such as TCP. streams, such as TCP.
4.1.5. Event Handling 4.1.5. Event Handling
This list of events that can be delivered to an application is not This section provides the top-level categories of events events that
exhaustive, but gives the top-level categories of events. The API can be delivered to an application. This list is not exhaustive.
MAY expand this list.
o Connection Ready: Signals to an application that a given o Connection Ready: Signals to an application that a given
Connection is ready to send and/or receive Messages. If the Connection is ready to send and/or receive Messages. If the
Connection relies on handshakes to establish state between peers, Connection relies on handshakes to establish state between peers,
then it is assumed that these steps have been taken. then it is assumed that these steps have been taken.
o Connection Finished: Signals to an application that a given o Connection Finished: Signals to an application that a given
Connection is no longer usable for sending or receiving Messages. Connection is no longer usable for sending or receiving Messages.
The event SHOULD deliver a reason or error to the application that The event SHOULD deliver a reason or error to the application that
describes the nature of the termination. describes the nature of the termination.
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that it no longer intends to send data, is no longer willing to that it no longer intends to send data, is no longer willing to
receive data, and that the protocol SHOULD signal this state to receive data, and that the protocol SHOULD signal this state to
the remote system if the transport protocol allows this. the remote system if the transport protocol allows this.
o Abort: The action the application takes on a Connection to o Abort: The action the application takes on a Connection to
indicate a Close and also indicate that the transport system indicate a Close and also indicate that the transport system
SHOULD NOT attempt to deliver any outstanding data. SHOULD NOT attempt to deliver any outstanding data.
4.2. Transport System Implementation Concepts 4.2. Transport System Implementation Concepts
The Transport System Implementation Concepts define the set of This section defines the set of objects used internally to a system
objects used internally to a system or library to implement the or library to implement the functionality needed to provide a
functionality needed to provide a transport service across a network, transport service across a network, as required by the abstract
as required by the abstract interface. interface.
o Connection Group: A set of Connections that share properties and o Connection Group: A set of Connections that share properties and
caches. For multiplexing transport protocols, only Connections caches. For multiplexing transport protocols, only Connections
within the same Connection Group are allowed be multiplexed within the same Connection Group are allowed to be multiplexed
together. Applications can use their explicitly defined together. An application can explicitly define Connection Groups
Connection Groups to control caching boundaries, as discussed in to control caching boundaries, as discussed in Section 4.2.4.
Section 4.2.4.
o Path: Represents an available set of properties that a local o Path: Represents an available set of properties that a local
system can use to communicate with a remote system, such as system can use to communicate with a remote system, such as
routes, addresses, and physical and virtual network interfaces. routes, addresses, and physical and virtual network interfaces.
o Protocol Instance: A single instance of one protocol, including o Protocol Instance: A single instance of one protocol, including
any state it has necessary to establish connectivity or send and any state necessary to establish connectivity or send and receive
receive Messages. Messages.
o Protocol Stack: A set of Protocol Instances (including relevant o Protocol Stack: A set of Protocol Instances (including relevant
application, security, transport, or Internet protocols) that are application, security, transport, or Internet protocols) that are
used together to establish connectivity or send and receive used together to establish connectivity or send and receive
Messages. A single stack can be simple (a single transport Messages. A single stack can be simple (a single transport
protocol instance over IP), or complex (multiple application protocol instance over IP), or complex (multiple application
protocol streams going through a single security and transport protocol streams going through a single security and transport
protocol, over IP; or, a multi-path transport protocol over protocol, over IP; or, a multi-path transport protocol over
multiple transport sub-flows). multiple transport sub-flows).
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4.2.1. Candidate Gathering 4.2.1. Candidate Gathering
o Path Selection: Path Selection represents the act of choosing one o Path Selection: Path Selection represents the act of choosing one
or more paths that are available to use based on the Selection or more paths that are available to use based on the Selection
Properties provided by the application, the policies and Properties provided by the application, the policies and
heuristics of a Transport Services system. heuristics of a Transport Services system.
o Protocol Selection: Protocol Selection represents the act of o Protocol Selection: Protocol Selection represents the act of
choosing one or more sets of protocol options that are available choosing one or more sets of protocol options that are available
to use based on the Transport Properties provided by the to use based on the Transport Properties provided by the
application, and a Transport Services system's policies and application, and the heuristics or policies within the Transport
heuristics. Services system.
4.2.2. Candidate Racing 4.2.2. Candidate Racing
o Protocol Option Racing: Protocol Racing is the act of attempting o Protocol Option Racing: Protocol Racing is the act of attempting
to establish, or scheduling attempts to establish, multiple to establish, or scheduling attempts to establish, multiple
Protocol Stacks that differ based on the composition of protocols Protocol Stacks that differ based on the composition of protocols
or the options used for protocols. or the options used for protocols.
o Path Racing: Path Racing is the act of attempting to establish, or o Path Racing: Path Racing is the act of attempting to establish, or
scheduling attempts to establish, multiple Protocol Stacks that scheduling attempts to establish, multiple Protocol Stacks that
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o Remote Endpoint Racing: Remote Endpoint Racing is the act of o Remote Endpoint Racing: Remote Endpoint Racing is the act of
attempting to establish, or scheduling attempts to establish, attempting to establish, or scheduling attempts to establish,
multiple Protocol Stacks that differ based on the specific multiple Protocol Stacks that differ based on the specific
representation of the Remote Endpoint, such as IP addresses representation of the Remote Endpoint, such as IP addresses
resolved from a DNS hostname. resolved from a DNS hostname.
4.2.3. Protocol Stack Equivalence 4.2.3. Protocol Stack Equivalence
The Transport Services architecture defines a mechanism that allows The Transport Services architecture defines a mechanism that allows
applications to easily use different network paths and Protocol applications to easily use different network paths and Protocol
Stacks. Transitioning between different Protocol Stacks is in some Stacks. In some cases, changing which Protocol Stacks or network
cases controlled by properties that only change when application code paths are used will require updating the preferences expressed by the
is updated. For example, an application can enable the use of a application that uses the Transport Services system. For example, an
multipath or multistreaming transport protocol by modifying the application can enable the use of a multipath or multistreaming
properties in its Pre-Connection configuration. In some cases, transport protocol by modifying the properties in its Pre-Connection
however, the Transport Services system will be able to automatically configuration. In some cases, however, the Transport Services system
change Protocol Stacks without an update to the application, either will be able to automatically change Protocol Stacks without an
by selecting a new stack entirely, or by racing multiple candidate update to the application, either by selecting a new stack entirely,
Protocol Stacks during connection establishment. This functionality or by racing multiple candidate Protocol Stacks during connection
can be a powerful driver of new protocol adoption, but needs to be establishment. This functionality in the API can be a powerful
constrained carefully to avoid unexpected behavior that can lead to driver of new protocol adoption, but needs to be constrained
functional or security problems. carefully to avoid unexpected behavior that can lead to functional or
security problems.
If two different Protocol Stacks can be safely swapped, or raced in If two different Protocol Stacks can be safely swapped, or raced in
parallel (see Section 4.2.2), then they are considered to be parallel (see Section 4.2.2), then they are considered to be
"equivalent". Equivalent Protocol Stacks need to meet the following "equivalent". Equivalent Protocol Stacks need to meet the following
criteria: criteria:
1. Both stacks MUST offer the same interface to the application for 1. Both stacks MUST offer the same interface to the application for
connection establishment and data transmission. For example, if connection establishment and data transmission. For example, if
one Protocol Stack has UDP as the top-level interface to the one Protocol Stack has UDP as the top-level interface to the
application, then it is not equivalent to a Protocol Stack that application, then it is not equivalent to a Protocol Stack that
runs TCP as the top-level interface. Among other differences, runs TCP as the top-level interface. Among other differences,
the UDP stack would allow an application to read out message the UDP stack would allow an application to read out message
boundaries based on datagrams sent from the remote system, boundaries based on datagrams sent from the remote system,
whereas TCP does not preserve message boundaries on its own. whereas TCP does not preserve message boundaries on its own.
2. Both stacks MUST offer the same transport services, as required 2. Both stacks MUST offer the transport services that are required
by the application. For example, if an application specifies by the application. For example, if an application specifies
that it requires reliable transmission of data, then a Protocol that it requires reliable transmission of data, then a Protocol
Stack using UDP without any reliability layer on top would not be Stack using UDP without any reliability layer on top would not be
allowed to replace a Protocol Stack using TCP. However, if the allowed to replace a Protocol Stack using TCP. However, if the
application does not require reliability, then a Protocol Stack application does not require reliability, then a Protocol Stack
that adds unnecessary reliability might be allowed as an that adds reliability could be regarded as an equivalent Protocol
equivalent Protocol Stack as long as it does not conflict with Stack as long providing this would not conflict with any other
any other application-requested properties. application-requested properties.
3. Both stacks MUST offer the same security properties. The 3. Both stacks MUST offer the same security properties. The
inclusion of transport security protocols inclusion of transport security protocols
[I-D.ietf-taps-transport-security] in a Protocol Stack adds [I-D.ietf-taps-transport-security] in a Protocol Stack adds
additional restrictions to Protocol Stack equivalence. Security additional restrictions to Protocol Stack equivalence. Security
features and properties, such as cryptographic algorithms, peer features and properties, such as cryptographic algorithms, peer
authentication, and identity privacy vary across security authentication, and identity privacy vary across security
protocols, and across versions of security protocols. Protocol protocols, and across versions of security protocols. Protocol
equivalence ought not to be assumed for different protocols or equivalence ought not to be assumed for different protocols or
protocol versions, even if they offer similar application protocol versions, even if they offer similar application
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automatically generate equivalent Protocol Stacks when the automatically generate equivalent Protocol Stacks when the
transport security protocols within the stacks are identical. transport security protocols within the stacks are identical.
Specifically, a transport system would consider protocols Specifically, a transport system would consider protocols
identical only if they are of the same type and version. For identical only if they are of the same type and version. For
example, the same version of TLS running over two different example, the same version of TLS running over two different
transport protocol stacks are considered equivalent, whereas TLS transport protocol stacks are considered equivalent, whereas TLS
1.2 and TLS 1.3 [RFC8446] are not considered equivalent. 1.2 and TLS 1.3 [RFC8446] are not considered equivalent.
4.2.4. Separating Connection Groups 4.2.4. Separating Connection Groups
By default, all stored properties of the Implementation are shared By default, all stored properties of the implementation are shared
within a process, such as cached protocol state, cached path state, within a process, such as cached protocol state, cached path state,
and heuristics. This provides efficiency and convenience for the and heuristics. This provides efficiency and convenience for the
application, since the Transport System Implementation can application, since the Transport System implementation can
automatically optimize behavior. automatically optimize behavior.
There are several reasons, however, that an application might want to There are several reasons, however, that an application might want to
isolate some Connections within a single process. These reasons isolate some Connections within a single process. These reasons
include: include:
o Privacy concerns about re-using cached protocol state that can o Privacy concerns about re-using cached protocol state that can
lead to linkability. Sensitive state may include TLS session lead to linkability. Sensitive state may include TLS session
state [RFC8446] and HTTP cookies [RFC6265]. state [RFC8446] and HTTP cookies [RFC6265].
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o Performance concerns about Connections introducing head-of-line o Performance concerns about Connections introducing head-of-line
blocking due to multiplexing or needing to share state on a single blocking due to multiplexing or needing to share state on a single
thread. thread.
The Transport Services API SHOULD allow applications to explicitly The Transport Services API SHOULD allow applications to explicitly
define Connection Groups that force separation of Cached State and define Connection Groups that force separation of Cached State and
Protocol Stacks. For example, a web browser application might use Protocol Stacks. For example, a web browser application might use
Connection Groups with separate caches for different tabs in the Connection Groups with separate caches for different tabs in the
browser to decrease linkability. browser to decrease linkability.
The interface to specify these Groups MAY expose fine-grained tuning The interface to specify these groups MAY expose fine-grained tuning
for which properties and cached state is allowed to be shared with for which properties and cached state is allowed to be shared with
other Connections. For example, an application might want to allow other Connections. For example, an application might want to allow
sharing TCP Fast Open cookies across groups, but not TLS session sharing TCP Fast Open cookies across groups, but not TLS session
state. state.
5. IANA Considerations 5. IANA Considerations
RFC-EDITOR: Please remove this section before publication. RFC-EDITOR: Please remove this section before publication.
This document has no actions for IANA. This document has no actions for IANA.
skipping to change at page 22, line 23 skipping to change at page 23, line 29
Clients need to ensure that security APIs are used appropriately. In Clients need to ensure that security APIs are used appropriately. In
cases where clients use an interface to provide sensitive keying cases where clients use an interface to provide sensitive keying
material, e.g., access to private keys or copies of pre-shared keys material, e.g., access to private keys or copies of pre-shared keys
(PSKs), key use needs to be validated. For example, clients ought (PSKs), key use needs to be validated. For example, clients ought
not to use PSK material created for the Encapsulating Security not to use PSK material created for the Encapsulating Security
Protocol (ESP, part of IPsec) [RFC4303] with QUIC, and clients ought Protocol (ESP, part of IPsec) [RFC4303] with QUIC, and clients ought
not to use private keys intended for server authentication as a keys not to use private keys intended for server authentication as a keys
for client authentication. for client authentication.
Moreover, unlike certain transport features such as TCP Fast Open Moreover, Transport Services systems MUST NOT automatically fall back
(TFO) [RFC7413] or Explicit Congestion Notification (ECN) [RFC3168] from secure protocols to insecure protocols, or to weaker versions of
which can fall back to standard configurations, Transport Services secure protocols. For example, if a client requests TLS, but the
systems MUST prohibit fallback for security protocols. For example, desired version of TLS is not available, its connection will fail.
if a client requests TLS, yet TLS or the desired version are not Clients are thus responsible for implementing security protocol
available, its connection will fail. Clients are thus responsible fallback or version fallback by creating multiple Transport Services
for implementing security protocol fallback or version fallback by Connections, if so desired.
creating multiple Transport Services Connections, if so desired.
7. Acknowledgements 7. Acknowledgements
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 agreements No. 644334 research and innovation programme under grant agreements No. 644334
(NEAT) and No. 688421 (MAMI). (NEAT) and No. 688421 (MAMI).
This work has been supported by Leibniz Prize project funds of DFG - This work has been supported by Leibniz Prize project funds of DFG -
German Research Foundation: Gottfried Wilhelm Leibniz-Preis 2011 (FKZ German Research Foundation: Gottfried Wilhelm Leibniz-Preis 2011 (FKZ
FE 570/4-1). FE 570/4-1).
This work has been supported by the UK Engineering and Physical This work has been supported by the UK Engineering and Physical
Sciences Research Council under grant EP/R04144X/1. Sciences Research Council under grant EP/R04144X/1.
Thanks to Stuart Cheshire, Josh Graessley, David Schinazi, and Eric Thanks to Stuart Cheshire, Josh Graessley, David Schinazi, and Eric
Kinnear for their implementation and design efforts, including Happy Kinnear for their implementation and design efforts, including Happy
Eyeballs, that heavily influenced this work. Eyeballs, that heavily influenced this work.
8. Informative References 8. References
8.1. Normative References
[I-D.ietf-taps-interface]
Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G.,
Kuehlewind, M., Perkins, C., Tiesel, P., Wood, C., and T.
Pauly, "An Abstract Application Layer Interface to
Transport Services", draft-ietf-taps-interface-04 (work in
progress), July 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
8.2. Informative References
[I-D.ietf-taps-impl] [I-D.ietf-taps-impl]
Brunstrom, A., Pauly, T., Enghardt, T., Grinnemo, K., Brunstrom, A., Pauly, T., Enghardt, T., Grinnemo, K.,
Jones, T., Tiesel, P., Perkins, C., and M. Welzl, Jones, T., Tiesel, P., Perkins, C., and M. Welzl,
"Implementing Interfaces to Transport Services", draft- "Implementing Interfaces to Transport Services", draft-
ietf-taps-impl-03 (work in progress), March 2019. ietf-taps-impl-04 (work in progress), July 2019.
[I-D.ietf-taps-interface]
Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G.,
Kuehlewind, M., Perkins, C., Tiesel, P., and C. Wood, "An
Abstract Application Layer Interface to Transport
Services", draft-ietf-taps-interface-03 (work in
progress), March 2019.
[I-D.ietf-taps-minset] [I-D.ietf-taps-minset]
Welzl, M. and S. Gjessing, "A Minimal Set of Transport Welzl, M. and S. Gjessing, "A Minimal Set of Transport
Services for End Systems", draft-ietf-taps-minset-11 (work Services for End Systems", draft-ietf-taps-minset-11 (work
in progress), September 2018. in progress), September 2018.
[I-D.ietf-taps-transport-security] [I-D.ietf-taps-transport-security]
Wood, C., Enghardt, T., Pauly, T., Perkins, C., and K. Wood, C., Enghardt, T., Pauly, T., Perkins, C., and K.
Rose, "A Survey of Transport Security Protocols", draft- Rose, "A Survey of Transport Security Protocols", draft-
ietf-taps-transport-security-06 (work in progress), March ietf-taps-transport-security-09 (work in progress),
2019. September 2019.
[POSIX] "IEEE Std. 1003.1-2008 Standard for Information Technology [POSIX] "IEEE Std. 1003.1-2008 Standard for Information Technology
-- Portable Operating System Interface (POSIX). Open -- Portable Operating System Interface (POSIX). Open
group Technical Standard: Base Specifications, Issue 7", group Technical Standard: Base Specifications, Issue 7",
n.d.. n.d..
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981, RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>. <https://www.rfc-editor.org/info/rfc793>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[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>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011, DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/info/rfc6265>. <https://www.rfc-editor.org/info/rfc6265>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, Protocol (HTTP/1.1): Message Syntax and Routing",
<https://www.rfc-editor.org/info/rfc7413>. RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7540] Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
DOI 10.17487/RFC7540, May 2015,
<https://www.rfc-editor.org/info/rfc7540>.
[RFC8095] Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind, [RFC8095] Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind,
Ed., "Services Provided by IETF Transport Protocols and Ed., "Services Provided by IETF Transport Protocols and
Congestion Control Mechanisms", RFC 8095, Congestion Control Mechanisms", RFC 8095,
DOI 10.17487/RFC8095, March 2017, DOI 10.17487/RFC8095, March 2017,
<https://www.rfc-editor.org/info/rfc8095>. <https://www.rfc-editor.org/info/rfc8095>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
Authors' Addresses Authors' Addresses
Tommy Pauly (editor) Tommy Pauly (editor)
Apple Inc. Apple Inc.
One Apple Park Way One Apple Park Way
Cupertino, California 95014 Cupertino, California 95014
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