draft-ietf-taps-arch-02.txt   draft-ietf-taps-arch-03.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: April 25, 2019 ETH Zurich Expires: September 12, 2019 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.
October 22, 2018 March 11, 2019
An Architecture for Transport Services An Architecture for Transport Services
draft-ietf-taps-arch-02 draft-ietf-taps-arch-03
Abstract Abstract
This document provides an overview of the architecture of Transport This document provides an overview of the architecture of Transport
Services, a system for exposing the features of transport protocols Services, a model for exposing transport protocol features to
to applications. This architecture serves as a basis for Application applications for network communication. In contrast to what is
Programming Interfaces (APIs) and implementations that provide provided by most existing Application Programming Interfaces (APIs),
flexible transport networking services. It defines the common set of Transport Services is based on an asynchronous, event-driven
terminology and concepts to be used in more detailed discussion of interaction pattern; it uses messages for representing data transfer
Transport Services. to applications; and it assumes an implementation that can use
multiple IP addresses, multiple protocols, and multiple paths, and
provide multiple application streams. This document further defines
the common set of terminology and concepts to be used in definitions
of Transport Services APIs and implementations.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 12, 2019.
This Internet-Draft will expire on April 25, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 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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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Event-Driven API . . . . . . . . . . . . . . . . . . . . 5 1.2. Event-Driven API . . . . . . . . . . . . . . . . . . . . 5
1.3. Data Transfer Using Messages . . . . . . . . . . . . . . 5 1.3. Data Transfer Using Messages . . . . . . . . . . . . . . 5
1.4. Flexibile Implementation . . . . . . . . . . . . . . . . 6 1.4. Flexibile Implementation . . . . . . . . . . . . . . . . 6
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Design Principles . . . . . . . . . . . . . . . . . . . . . . 7 2.1. Specification of Requirements . . . . . . . . . . . . . . 7
3.1. Common APIs for Common Features . . . . . . . . . . . . . 7 3. Design Principles . . . . . . . . . . . . . . . . . . . . . . 8
3.2. Access to Specialized Features . . . . . . . . . . . . . 7 3.1. Common APIs for Common Features . . . . . . . . . . . . . 8
3.3. Scope for API and Implementation Definitions . . . . . . 8 3.2. Access to Specialized Features . . . . . . . . . . . . . 8
4. Transport Services Architecture and Concepts . . . . . . . . 9 3.3. Scope for API and Implementation Definitions . . . . . . 9
4.1. Transport Services API Concepts . . . . . . . . . . . . . 10 4. Transport Services Architecture and Concepts . . . . . . . . 10
4.1.1. Basic Objects . . . . . . . . . . . . . . . . . . . . 12 4.1. Transport Services API Concepts . . . . . . . . . . . . . 11
4.1.2. Pre-Establishment . . . . . . . . . . . . . . . . . . 13 4.1.1. Basic Objects . . . . . . . . . . . . . . . . . . . . 13
4.1.3. Establishment Actions . . . . . . . . . . . . . . . . 14 4.1.2. Pre-Establishment . . . . . . . . . . . . . . . . . . 14
4.1.4. Data Transfer Objects and Actions . . . . . . . . . . 14 4.1.3. Establishment Actions . . . . . . . . . . . . . . . . 15
4.1.5. Event Handling . . . . . . . . . . . . . . . . . . . 15 4.1.4. Data Transfer Objects and Actions . . . . . . . . . . 16
4.1.6. Termination Actions . . . . . . . . . . . . . . . . . 16 4.1.5. Event Handling . . . . . . . . . . . . . . . . . . . 16
4.2. Transport System Implementation Concepts . . . . . . . . 16 4.1.6. Termination Actions . . . . . . . . . . . . . . . . . 17
4.2.1. Candidate Gathering . . . . . . . . . . . . . . . . . 17 4.2. Transport System Implementation Concepts . . . . . . . . 17
4.2.2. Candidate Racing . . . . . . . . . . . . . . . . . . 17 4.2.1. Candidate Gathering . . . . . . . . . . . . . . . . . 19
4.3. Protocol Stack Equivalence . . . . . . . . . . . . . . . 18 4.2.2. Candidate Racing . . . . . . . . . . . . . . . . . . 19
4.3.1. Transport Security Equivalence . . . . . . . . . . . 19 4.2.3. Protocol Stack Equivalence . . . . . . . . . . . . . 19
4.4. Message Framing, Parsing, and Serialization . . . . . . . 19 4.2.4. Separating Connection Groups . . . . . . . . . . . . 21
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
6. Security Considerations . . . . . . . . . . . . . . . . . . . 20 6. Security Considerations . . . . . . . . . . . . . . . . . . . 21
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
8. Informative References . . . . . . . . . . . . . . . . . . . 21 8. Informative References . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
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 names and imitated being the BSD socket() [POSIX] interface. The naming of
functions between these APIs are not consistent, and vary depending objects and functions across these APIs is not consistent, and varies
on the protocol being used. For example, sending and receiving on a depending on the protocol being used. For example, sending and
stream of data is conceptually the same between operating on 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
on an encrypted Transport Layer Security (TLS) [I-D.ietf-tls-tls13] on an encrypted Transport Layer Security (TLS) [RFC8446] stream over
stream over TCP, but applications cannot use the same socket send() TCP, but applications cannot use the same socket send() and recv()
and recv() calls on top of both kinds of connections. Similarly, calls on top of both kinds of connections. Similarly, terminology
terminology for the implementation of protocols offering transport for the implementation of transport protocols varies based on the
services vary based on the context of the protocols themselves. This context of the protocols themselves: terms such as "flow", "stream",
variety can lead to confusion when trying to understand the "message", and "connection" can take on many different meanings.
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. application requirements and network conditions, without requiring
changes to the applications. This flexibility does not only enable
faster deployment of new feature and protocols, but it can also
support applications with racing and fallback mechanisms which
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
[I-D.ietf-taps-impl] documents. Guidelines [I-D.ietf-taps-impl]. Although following the Transport
Services Architecture does of course not mean that all APIs and
implementations have to be identical, a common minimal set of
features represented in a consistent fashion will enable applications
to be easily ported from one system to the another.
1.1. Overview 1.1. Overview
The model for using sockets for networking can be represented as The model of using sockets for networking can be represented as
follows: applications create connections and transfer data using the follows: applications create connections and transfer data using the
socket API, which provides the interface to the implementations of socket API, which provides the interface to the implementations of
UDP and TCP (typically implemented in the system's kernel), which in UDP and TCP (typically implemented in the system's kernel), which in
turn send data over the available network layer interfaces. turn send data over the available network layer interfaces.
+-----------------------------------------------------+ +-----------------------------------------------------+
| Application | | Application |
+-----------------------------------------------------+ +-----------------------------------------------------+
| | | |
+---------------------+ +-----------------------+ +---------------------+ +-----------------------+
skipping to change at page 4, line 22 skipping to change at page 4, line 22
| | | |
+-----------------------------------------------------+ +-----------------------------------------------------+
| TCP UDP | | TCP UDP |
| Kernel Protocol Implementation | | Kernel Protocol Implementation |
+-----------------------------------------------------+ +-----------------------------------------------------+
| |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Network Layer Interface | | Network Layer Interface |
+-----------------------------------------------------+ +-----------------------------------------------------+
Figure 1: socket() API Model
The Transport Services architecture maintains this general model of The Transport Services architecture maintains this general model of
interaction, but aims to both modernize the API surface exposed for interaction, but aims to both modernize the API surface exposed for
transport protocols and enrich the capabilities of the transport transport protocols and enrich the capabilities of the transport
system implementation. system implementation.
+-----------------------------------------------------+ +-----------------------------------------------------+
| Application | | Application |
+-----------------------------------------------------+ +-----------------------------------------------------+
| |
+-----------------------------------------------------+ +-----------------------------------------------------+
skipping to change at page 4, line 44 skipping to change at page 4, line 46
| |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Transport System Implementation | | Transport System Implementation |
| (UDP, TCP, SCTP, DCCP, TLS, QUIC, etc) | | (UDP, TCP, SCTP, DCCP, TLS, QUIC, etc) |
+-----------------------------------------------------+ +-----------------------------------------------------+
| |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Network Layer Interface | | Network Layer Interface |
+-----------------------------------------------------+ +-----------------------------------------------------+
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 and monitor network mechanism for an application to create network connections and
connections, and transfer data. The Implementation transfer data. The Implementation [I-D.ietf-taps-impl] is
[I-D.ietf-taps-impl] is responsible for mapping the API into the responsible for mapping the API into the various available transport
various available transport protocols and managing the available protocols and managing the available network interfaces and paths.
network interfaces and paths.
There are a few key departures that Transport Services makes from the There are a few key departures that Transport Services makes from the
sockets API: it presents an asynchronous, event-driven API; it uses sockets API: it presents an asynchronous, event-driven API; it uses
messages for respresenting data transfer to applications; and it messages for representing data transfer to applications; and it
assumes an implementation that can use multiple IP addresses, assumes an implementation that can use multiple IP addresses,
multiple protocols, multiple paths, and provide multiple application multiple protocols, multiple paths, and provide multiple application
streams. streams.
1.2. Event-Driven API 1.2. 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 for a notification that it should try again. 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 to available network links,
which were not previously made explicit in sockets. which were not previously made explicit in sockets.
skipping to change at page 5, line 44 skipping to change at page 5, line 46
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 1.3. 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.
HTTP/1.1 uses character delimiters to segment messages over a stream; For example, HTTP/1.1 uses character delimiters to segment messages
TLS record headers carry a version, content type, and length; and over a stream; TLS record headers carry a version, content type, and
HTTP/2 uses frames to segment its headers and bodies. length; and HTTP/2 uses frames to segment its headers and bodies.
In order to more closely match the way applications use the network, The Transport Services API represents data as messages, so that it
the Transport Services API respresents data as messages. 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 the records, but can also be used over a stream by defining an
application-layer framing being used Section 4.4. application-layer framer Section 4.1.4. When framing protocols are
placed on top of unstructured streams, the messages used in the API
represent the framed messages within the stream. In the absence of a
framer, protocols that deal only in byte streams, such as TCP,
represent their data in each direction as a single, long message.
Providing a message-based abstraction provides many benefits, such
as:
o the ability to associate deadlines with messages, for applications
that care about timing;
o the ability to provide control of reliability, choosing which
messages to retransmit in the event of packet loss, and how best
to make use of the data that arrived;
o the ability to manage dependencies between messages, when the
transport system could decide to not deliver a message, either
following packet loss or because it has missed a deadline. In
particular, this can avoid (re-)sending data that relies on a
previous transmission that was never received.
Allowing applications to interact with messages is backwards-
compatible with existings protocols and APIs, as it does not change
the wire format of any protocol. Instead, it gives the protocol
stack additional information to allow it to make better use of modern
transport services, while simplifying the application's role in
parsing data.
1.4. Flexibile Implementation 1.4. 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
connection establishment time, considering many different options and connection establishment time, considering many different options and
trying to select the most optimal combinations (Section 4.2.1 and trying to select the most optimal combinations (Section 4.2.1 and
Section 4.2.2). This requires applications to provide higher-level Section 4.2.2). This requires applications to provide higher-level
endpoints than IP addresses, such as hostnames and URLs, which are endpoints than IP addresses, such as hostnames and URLs, which are
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 2. Background
The Transport Services architecture is based on the survey of The Transport Services architecture is based on the survey of
Services Provided by IETF Transport Protocols and Congestion Control Services Provided by IETF Transport Protocols and Congestion Control
Mechanisms [RFC8095], and the distilled minimal set of the features Mechanisms [RFC8095], and the distilled minimal set of the features
offered by transport protocols [I-D.ietf-taps-minset]. This work has offered by transport protocols [I-D.ietf-taps-minset]. These
identified common features and patterns across all transport documents identified common features and patterns across all
protocols developed thus far in the IETF. transport protocols developed thus far in the IETF.
Since transport security is an increasingly relevant aspect of using Since transport security is an increasingly relevant aspect of using
transport protocols on the Internet, this architecture also considers transport protocols on the Internet, this architecture also considers
the impact of transport security protocols on the feature set exposed the impact of transport security protocols on the feature-set exposed
by transport services [I-D.ietf-taps-transport-security]. by transport services [I-D.ietf-taps-transport-security].
One of the key insights to come from identifying the minimal set of One of the key insights to come from identifying the minimal set of
features provided by transport protocols [I-D.ietf-taps-minset] was features provided by transport protocols [I-D.ietf-taps-minset] was
that features either require application interaction and guidance that features either require application interaction and guidance
(referred to as Functional Features), or else can be handled (referred to as Functional Features), or else can be handled
automatically by a system implementing Transport Services (referred automatically by a system implementing Transport Services (referred
to as Automatable Features). Among the Functional Features, some to as Automatable Features). Among the Functional Features, some
were common across all or nearly all transport protocols, while were common across all or nearly all transport protocols, while
others could be seen as features that, if specified, would only be others could be seen as features that, if specified, would only be
useful with a subset of protocols, or perhaps even a single transport useful with a subset of protocols, but would not harm the
protocol, but would not harm the functionality of other protocols. functionality of other protocols. For example, some protocols can
For example, some protocols can deliver messages faster for deliver messages faster for applications that do not require messages
applications that do not require them to arrive in the order in which to arrive in the order in which they were sent. However, this
they were sent. However, this functionality must be explicitly functionality needs to be explicitly allowed by the application,
allowed by the application, since reordering messages would be since reordering messages would be undesirable in many cases.
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 can
offer flexibility to an application: it can provide access to offer flexibility to an application: it can provide access to
multiple sets of protocols and protocol features, it can use these multiple sets of protocols and protocol features; it can use these
protocols across multiple paths that may have different performance protocols across multiple paths that could have different performance
and functional characteristics, and it can communicate with different and functional characteristics; and it can communicate with different
Remote Endpoints to optimize performance, robustness to failure, or remote systems to optimize performance, robustness to failure, or
some other metric. Beyond these, if the API for the system remains some other metric. Beyond these, if the API for the system remains
the same over time, new protocols and features may be added to the the same over time, new protocols and features could be added to the
system's implementation without requiring changes in applications for system's implementation without requiring changes in applications for
adoption. adoption.
The following considerations were used in the design of this The following considerations were used in the design of this
architecture. 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 should 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 must allow access to the distilled minimal Any Transport Services API is REQUIRED to allow access to the
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 peers,. A Transport Services system will compatibility with remote systems. A Transport Services system
therefore also needs to allow more specialized protocol features to therefore SHOULD also permit more specialized protocol features to be
be used. The interface for these specialized options should be used. The interface for these specialized options should be exposed
exposed differently from the common options to ensure flexibility. 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 should expose the features in such a options. In such cases, the API ought to expose the features in such
way that they take effect when a particular protocol is selected, but a way that they take effect when a particular protocol is selected,
do not imply that only that protocol could be used if there are but do not imply that only that protocol could be used. For example,
equivalent options. if the API allows an application to specify a preference for
constrained checksum usage, communication would not fail when a
protocol such as TCP is selected, which uses a checksum covering the
entire payload.
Other specialized features, however, may 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 some transport security
protocol are eligible to be used. A Transport Services API must protocol are eligible to be used. A Transport Services API MUST
allow applications to define such requirements and constrain the allow applications to define such requirements and constrain the
system's options. Since such options are not part of the core/common system's options. Since such options are not part of the core/common
features, it should be simple for an application to modify its set of features, it will generally be simple for an application to modify
constraints and change the set of allowable protocol features without its set of constraints and change the set of allowable protocol
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 is aimed at
application developers. 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, but that some features will not be functional in certain
implementations. All implementations must offer sufficient APIs to implementations. All implementations are REQUIRED to offer
use the distilled minimal set of features offered by transport sufficient APIs to use the distilled minimal set of features offered
protocols [I-D.ietf-taps-minset], including API support for TCP and by transport protocols [I-D.ietf-taps-minset], including API support
UDP transport, but it is possible that some very constrained devices for TCP and UDP transport, but it is possible that some very
might not have, for example, a full TCP implementation. constrained devices might not have, for example, a full 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
[TAPS-IMPL], which also explain the implications of the feature [I-D.ietf-taps-impl] along with the implications of the feature on
provided by existing protocols. It is expected that this document existing protocols. It is expected that this document will be
will be updated and supplemented as new protocols and protocol updated and supplemented as new protocols and protocol features are
features are developed. developed.
It is important to note that neither the Transport Services API nor It is important to note that neither the Transport Services API
the Implementation document defines new protocols that require any [I-D.ietf-taps-interface] nor the Implementation document
changes to a remote host. The Transport Services system must be [I-D.ietf-taps-impl] defines new protocols that require any changes
deployable on one side only, as a way to allow an application to make to a remote system. The Transport Services system MUST be deployable
better use of available capabilities on a system and protocol on one side only.
features that may be supported by peers across the network.
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 may 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
categories: categories:
1. API concepts, which are meant to be exposed to applications; and 1. API concepts, which are intended to be exposed to applications;
and
2. System-implementation concepts, which are meant to be internally 2. System-implementation concepts, which are intended to be
used when building systems that implement Transport Services. internally used when building systems that implement Transport
Services.
The following diagram summarizes the top-level concepts in the The following diagram summarizes the top-level concepts in the
architecture and how they relate to one another. architecture and how they relate to one another.
+-----------------------------------------------------+ +-----------------------------------------------------+
| Application | | Application |
+-+----------------+------^-------+--------^----------+ +-+----------------+------^-------+--------^----------+
| | | | | | | | | |
pre- | data | events pre- | data | events
establishment | transfer | | establishment | transfer | |
| establishment | termination | | establishment | termination |
| | | | | | | | | |
| +--v------v-------v+ | | +--v------v-------v+ |
+-v-------------+ Basic Objects +-------+----------+ +-v-------------+ Connection(s) +-------+----------+
| Transport +--------+---------+ | | Transport +--------+---------+ |
| Services | | | Services | |
| API | | | API | |
+------------------------|----------------------------+ +------------------------|----------------------------+
| |
+------------------------|----------------------------+ +------------------------|----------------------------+
| Transport | | | Transport | |
| System | +-----------------+ | | System | +-----------------+ |
| Implementation | | Cached | | | Implementation | | Cached | |
| | | State | | | | | State | |
skipping to change at page 10, line 37 skipping to change at page 11, line 37
| (Candidate Racing) | +-----------------+ | | (Candidate Racing) | +-----------------+ |
| | | System | | | | | System | |
| | | Policy | | | | | Policy | |
| +----------v-----+ +-----------------+ | | +----------v-----+ +-----------------+ |
| | Protocol | | | | Protocol | |
+-------------+ Stack(s) +----------------------+ +-------------+ Stack(s) +----------------------+
+-------+--------+ +-------+--------+
V V
Network Layer Interface Network Layer Interface
Figure 1: 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 basic
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 may be exposed as communication and send and receive data. These could be exposed as
handles or referenced objects, depending on the language. handles or referenced objects, depending on the language.
Beyond the basic objects, there are several high-level groups of Beyond the basic objects, there are several high-level groups of
actions that any Transport Services API must provide: actions that any Transport Services API implementing this
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 primarily be defined to apply to multiple properties SHOULD be defined to apply to multiple transport
transports. Properties may have a large impact on the rest of the protocols. Properties specified during Pre-Establishment can have
aspects of the interface: they can modify how establishment a large impact on the rest of the interface: they modify how
occurs, they can influence the expectations around data transfer, establishment occurs, they influence the expectations around data
and they determine the set of events that will be supported. transfer, and they determine the set of events that will be
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 basic 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 data to be sent and received, the functions required to represents the data to be sent and received, the functions
send and receive that data, and how the application is notified of required to send and receive that data, and how the application is
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 can 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 taken
during the lifetime of a connection. during the lifetime of a connection. Note that some actions are
alternatives (e.g., whether to initiate a connection or to listen for
incoming connections), others are optional (e.g., setting Connection
and Message Properties in Pre-Establishment), or have been omitted
for brevity.
Pre-Establishment : Established : Termination Pre-Establishment : Established : Termination
----------------- : ----------- : ----------- ----------------- : ----------- : -----------
: Close() : : Close() :
+---------------+ Initiate() +------------+ Abort() : +---------------+ Initiate() +------------+ Abort() :
+-->| Preconnection |----------->| Connection |---------------> Closed +-->| Preconnection |----------->| Connection |---------------> Closed
| +---------------+ : +------------+ Connection: | +---------------+ : +------------+ Connection:
| : ^ ^ | Finished : | : ^ ^ ^ | Finished :
+-- Local Endpoint : | | | : +-- Local Endpoint : | | | | :
| : | | +---------+ : | : | | | +---------+ :
+-- Remote Endpoint : | | | : +-- Remote Endpoint : +----+ | +-----+ | :
| : | |Send() | : | : | |Send() | | :
+-- Path Selection : | +---------+ v : +-- Selection Properties : | +---------+ | v :
| Properties : | | Message | Message : +-- Connection Properties ---+ | Message | | Message :
| : | | to send | Received : +-- Message Properties -------->| to send | | Received :
+-- Protocol Selection : | +---------+ : | : +---------+ | :
| Properties : | : | +----------+ : | :
| : | : +-->| Listener |------------------------------+ :
+-- Specific Protocol : | :
| Properties : | :
| : | :
| +----------+ : | :
+-->| Listener |-----------------+ :
+----------+ Connection Received : +----------+ Connection Received :
^ : : ^ : :
| : : | : :
Listen() : : Listen() : :
Figure 2: The lifetime of a connection Figure 4: The lifetime of a connection
4.1.1. Basic Objects 4.1.1. Basic 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 to which that Connection will be established, the Remote Endpoint
which it will connect, and Path Selection Properties, Protocol (Section 4.1.2) to which it will connect, and Selection Properties
Selection Properties, and Specific Protocol Properties that (Section 4.1.2) that influence the paths and protocols a
influence the choice of transport that a Connection will use. A Connection will use. A Preconnection can be fully specified and
Preconnection can be fully specified and represent a single represent a single possible Connection, or it can be partially
possible Connection, or it can be partially specified such that it specified such that it represents a family of possible
represents a family of possible Connections. The Local Endpoint Connections. The Local Endpoint (Section 4.1.2) MUST be specified
must be specified if the Preconnection is used to Listen for if the Preconnection is used to Listen for incoming connections.
incoming connections, but 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, but is optional if Preconnection is used to Initiate connections. The Remote
it is used to Listen for incoming connections. The Local Endpoint Endpoint is OPTIONAL if it is used to Listen for incoming
and the Remote Endpoint must both be specified if a peer-to-peer connections. The Local Endpoint and the Remote Endpoint MUST both
Rendezvous is to occur based on the Preconnection. be specified if a peer-to-peer Rendezvous is to occur based on the
Preconnection.
* Transport Properties: Transport Properties can be specified as
part of a Preconnection to allow the application to configure
the Transport System and express their requirements,
prohibitions, and preferences. There are three kinds of
Transport Properties: Selection Properties (Section 4.1.2),
Connection Properties (Section 4.1.2), and Message Properties
(Section 4.1.4). Message Properties can also be specified
during data transfer to affect specific Messages.
o Connection: A Connection object represents an active transport o Connection: A Connection object represents an active transport
protocol instance that can send and/or receive Messages between a protocol instance that can send and/or receive Messages between
Local Endpoint and a Remote Endpoint. It holds state pertaining local and remote systems. It holds state pertaining to the
to the underlying transport protocol instance and any ongoing data underlying transport protocol instance and any ongoing data
transfer. This represents, for example, an active connection in a transfer. This represents, for example, an active connection in a
connection-oriented protocol such as TCP, or a fully-specified connection-oriented protocol such as TCP, or a fully-specified
5-tuple for a connectionless protocol such as UDP. 5-tuple for a connectionless protocol such as UDP.
o Listener: A Listener object accepts incoming transport protocol o Listener: A Listener object accepts incoming transport protocol
connections from Remote Endpoints and generates corresponding connections from remote systems and generates corresponding
Connection objects. It is created from a Preconnection object Connection objects. It is created from a Preconnection object
that specifies the type of incoming connections it will accept. that specifies the type of incoming connections it will accept.
4.1.2. Pre-Establishment 4.1.2. Pre-Establishment
o Endpoint: An Endpoint represents one side of a transport o Endpoint: An Endpoint represents an identifier for one side of a
connection. Endpoints can be Local Endpoints or Remote Endpoints, transport connection. Endpoints can be Local Endpoints or Remote
and respectively represent an identity that the application uses Endpoints, and respectively represent an identity that the
for the source or destination of a connection. An Endpoint may be application uses for the source or destination of a connection.
specified at various levels, and an Endpoint with wider scope An Endpoint can be specified at various levels, and an Endpoint
(such as a hostname) can be resolved to more concrete identities with wider scope (such as a hostname) can be resolved to more
(such as IP addresses). concrete identities (such as IP addresses).
o Remote Endpoint: The Remote Endpoint represents the application's o Remote Endpoint: The Remote Endpoint represents the application's
name for a peer that can participate in a transport connection. identifier for a peer that can participate in a transport
For example, the combination of a DNS name for the peer and a connection. For example, the combination of a DNS name for the
service name/port. peer and a service name/port.
o Local Endpoint: The Local Endpoint represents the application's o Local Endpoint: The Local Endpoint represents the application's
name for itself that it uses for transport connections. For identifier for itself that it uses for transport connections. For
example, a local IP address and port. example, a local IP address and port.
o Path Selection Properties: The Path Selection Properties consist o Selection Properties: The Selection Properties consist of the
of the options that an application may set to influence the options that an application can set to influence the selection of
selection of paths between the Local Endpoint and the Remote paths between the local and remote systems, to influence the
Endpoint. These options can take the form of requirements, selection of transport protocols, or to configure the behavior of
prohibitions, or preferences. Examples of options that may generic transport protocol features. These options can take the
influence path selection include the interface type (such as a Wi- form of requirements, prohibitions, or preferences. Examples of
Fi Ethernet connection, or a Cellular LTE connection), options that influence path selection include the interface type
characteristics of the path that are locally known like Maximum (such as a Wi-Fi Ethernet connection, or a Cellular LTE
Transmission Unit (MTU) or discovered like Path MTU (PMTU), or connection), requirements around the Maximum Transmission Unit
predicted based on cached information like expected throughput or (MTU) or path MTU (PMTU), or preferences for throughput and
latency. latency properties. Examples of options that influence protocol
selection and configuration of transport protocol features include
o Protocol Selection Properties: The Protocol Selection Properties reliability, service class, multipath support, and fast open
consist of the options that an application may set to influence support.
the selection of transport protocol, or to configure the behavior
of generic transport protocol features. These options can take
the form of requirements, prohibitions, and preferences. Examples
include reliability, service class, multipath support, and fast
open support.
o Specific Protocol Properties: The Specific Protocol Properties o Connection Properties: The Connection Properties are used to
refer to the subset of Protocol Properties options that apply to a configure protocol-specific options and control per-connection
single protocol (transport protocol, IP, or security protocol). behavior of the Transport System. For example, a protocol-
The presence of such Properties does not necessarily require that specific Connection Property can express that if UDP is used, the
a specific protocol must be used when a Connection is established, implementation ought to use checksums. Note that the presence of
but that if this protocol is employed, a particular set of options such a property does not require that a specific protocol will be
should then be used.. used. In general, these properties do not explicitly determine
the selection of paths or protocols, but MAY be used in this way
by an implementation during connection establishment. Connection
Properties SHOULD be specified on a Preconnection prior to
Connection establishment, but MAY be modified later. Changes made
to Connection Properties after establishment take effect on a
best-effort basis.
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 be able to send and/or receive Messages.
For some protocols, this may initiate a client-to-server style For some protocols, this will initiate a client-to-server style
handshake; for other protocols, this may 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
with a Remote Endpoint. It simultaneously attempts to initiate a with a Remote Endpoint. It simultaneously attempts to initiate a
skipping to change at page 14, line 44 skipping to change at page 16, line 8
connection from that endpoint. This corresponds, for example, to connection from that endpoint. This corresponds, for example, to
a TCP simultaneous open [RFC0793]. The process of identifying a TCP simultaneous open [RFC0793]. The process of identifying
options for the connection, such as resolution of the Remote options for the connection, such as resolution of the Remote
Endpoint, occurs during the Rendezvous call. If successful, the Endpoint, occurs during the Rendezvous call. If successful, the
rendezvous call returns a Connection object to represent the rendezvous call returns a Connection object to represent the
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 endpoints 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. If a received Message is incomplete or corrupted, it
may or may not be usable by certain applications. Boundaries of a might or might not be usable by certain applications. Boundaries
Message may or may not be understood or transmitted by transport of a Message might or might not be understood or transmitted by
protocols. Specifically, what one application considers to be two transport protocols. Specifically, what one application considers
Messages sent on a stream-based transport may be treated as a to be two Messages sent on a stream-based transport can be treated
single Message by the 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
specific Messages. These properties can specify how the transport
will send the Message (for prioritization and reliability), along
with any per-protocol properties to send with the Message.
Message Properties MAY be set on a Preconnection to define
defaults properties for sending. When receiving Messages, Message
Properties can contain per-protocol properties.
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 a Remote Endpoint. The interface to Send may Connection to the remote system. The interface to Send MAY
include options specific to how the Message's content is to be include Message Properties specific to how the Message's content
sent. Status of the Send operation may be delivered back to the is to be sent. Status of the Send operation can be delivered back
application in an event (Section 4.1.5). to the 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
Endpoint, 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
options specific to the Message that is to be delivered to the Message Properties specific to the Message that is to be delivered
application. to the application.
o Framer: A Framer is a data translation layer that can be added to
a Connection to define how application-level Messages are
transmitted over a transport protocol. This is particularly
relevant for protocols that otherwise present unstructured
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 list of events that can be delivered to an application is not
exhaustive, but gives the top-level categories of events. The API exhaustive, but gives the top-level categories of events. The API
may expand this list. 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.
This should deliver an error to the application that describes the The event SHOULD deliver a reason or error to the application that
nature of the termination. describes the nature of the termination.
o Connection Received: Signals to an application that a given o Connection Received: Signals to an application that a given
Listener has passively received a Connection. Listener has passively received a Connection.
o Message Received: Delivers received Message content to the o Message Received: Delivers received Message content to the
application, based on a Receive action. This may include an error application, based on a Receive action. This MAY include an error
if the Receive action cannot be satisfied due to the Connection if the Receive action cannot be satisfied due to the Connection
being closed. being closed.
o Message Sent: Notifies the application of the status of its Send o Message Sent: Notifies the application of the status of its Send
action. This may be an error if the Message cannot be sent, or an action. This might indicate a failure if the Message cannot be
indication that Message has been processed by the protocol stack. sent, or an indication that Message has been processed by the
protocol stack.
o Path Properties Changed: Notifies the application that some o Path Properties Changed: Notifies the application that some
property of the Connection has changed that may influence how and property of the Connection has changed that might influence how
where data is sent and/or received. and where data is sent and/or received.
4.1.6. Termination Actions 4.1.6. Termination Actions
o Close: The action an application may take on a Connection to o Close: The action an application takes on a Connection to indicate
indicate that it no longer intends to send data, is no longer that it no longer intends to send data, is no longer willing to
willing to receive data, and that the protocol should signal this receive data, and that the protocol SHOULD signal this state to
state to the remote endpoint if applicable. the remote system if the transport protocol allows this.
o Abort: The action the application may take on a Connection to o Abort: The action the application takes on a Connection to
indicate a Close, but with the additional indication that the indicate a Close and also indicate that the transport system
transport system should not attempt to deliver any outstanding SHOULD NOT attempt to deliver any outstanding data.
data.
4.2. Transport System Implementation Concepts 4.2. Transport System Implementation Concepts
The Transport System Implementation Concepts define the set of The Transport System Implementation Concepts define the set of
objects used internally to a system or library to provide the objects used internally to a system or library to implement the
functionality required to provide a transport service across a functionality needed to provide a transport service across a network,
network, as required by the abstract interface. as required by the abstract interface.
o Connection Group: A set of Connections that share properties. For o Connection Group: A set of Connections that share properties and
multiplexing transport protocols, the Connection Group defines the caches. For multiplexing transport protocols, only Connections
set of Connections that can be multiplexed together. within the same Connection Group are allowed be multiplexed
together. Applications can use their explicitly defined
Connection Groups to control caching boundaries, as discussed in
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
Endpoint may use to send or receive packets with a Remote system can use to communicate with a remote system, such as
Endpoint. 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 it has necessary to establish connectivity or send and
receive Messages. receive 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 may 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).
o Candidate Path: One path that is available to an application and o Candidate Path: One path that is available to an application and
conforms to the Path Selection Properties and System Policy. conforms to the Selection Properties and System Policy. Candidate
Candidate Paths are identified during the gathering phase Paths are identified during the gathering phase (Section 4.2.1)
(Section 4.2.1) and may be used during the racing phase and can be used during the racing phase (Section 4.2.2).
(Section 4.2.2).
o Candidate Protocol Stack: One protocol stack that may be used by
an application for a connection, of which there may be several.
o Candidate Protocol Stack: One protocol stack that can be used by
an application for a connection, of which there can be several.
Candidate Protocol Stacks are identified during the gathering Candidate Protocol Stacks are identified during the gathering
phase (Section 4.2.1) and may be started during the racing phase phase (Section 4.2.1) and are started during the racing phase
(Section 4.2.2). (Section 4.2.2).
o System Policy: Represents the input from an operating system or o System Policy: Represents the input from an operating system or
other global preferences that can constrain or influence how an other global preferences that can constrain or influence how an
implementation will gather candidate paths and protocol stacks implementation will gather candidate paths and protocol stacks
(Section 4.2.1) and race the candidates during establishment (Section 4.2.1) and race the candidates during establishment
(Section 4.2.2). Specific aspects of the System Policy may apply (Section 4.2.2). Specific aspects of the System Policy either
to all Connections, or only certain ones depending on the runtime apply to all Connections or only certain ones, depending on the
context and properties of the Connection. runtime context and properties of the Connection.
o Cached State: The state and history that the implementation keeps o Cached State: The state and history that the implementation keeps
for each set of associated endpoints that have been used for each set of associated Endpoints that have been used
previously. This can include DNS results, TLS session state, previously. This can include DNS results, TLS session state,
previous success and quality of transport protocols over certain previous success and quality of transport protocols over certain
paths. paths.
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 Path or more paths that are available to use based on the Selection
Selection Properties provided by the application, and a Transport Properties provided by the application, the policies and
Services system's policies and heuristics. 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 Protocol 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 a Transport Services system's policies and
heuristics. heuristics.
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
differ based on a selection from the available Paths. differ based on a selection from the available Paths. Since
different Paths will have distinct configurations for local
addresses and DNS servers, attempts across different Paths will
perform separate DNS resolution stepss, which can lead to further
racing of the resolved Remote Endpoints.
o Endpoint Racing: Endpoint Racing is the act of attempting to o Remote Endpoint Racing: Remote Endpoint Racing is the act of
establish, or scheduling attempts to establish, multiple Protocol attempting to establish, or scheduling attempts to establish,
Stacks that differ based on the specific representation of the multiple Protocol Stacks that differ based on the specific
Remote Endpoint and the Local Endpoint, such as IP addresses representation of the Remote Endpoint, such as IP addresses
resolved from a DNS hostname. resolved from a DNS hostname.
4.3. 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 may in some Stacks. Transitioning between different Protocol Stacks is in some
cases be controlled by properties that only change when application cases controlled by properties that only change when application code
code is updated. For example, an application may enable the use of a is updated. For example, an application can enable the use of a
multipath or multistreaming transport protocol by modifying the multipath or multistreaming transport protocol by modifying the
properties in its Pre-Connection configuration. In some cases, properties in its Pre-Connection configuration. In some cases,
however, the Transport Services system will be able to automatically however, the Transport Services system will be able to automatically
change Protocol Stacks without an update to the application, either change Protocol Stacks without an update to the application, either
by selecting a new stack entirely, or racing multiple candidate by selecting a new stack entirely, or by racing multiple candidate
Protocol Stacks during connection establishment. This functionality Protocol Stacks during connection establishment. This functionality
can be a powerful driver of new protocol adoption, but must be can be a powerful driver of new protocol adoption, but needs to be
constrained carefully to avoid unexpected behavior that can lead to constrained carefully to avoid unexpected behavior that can lead to
functional or security problems. 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 must 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 Endpoint, 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 same transport services, as 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 unnecessary reliability might be allowed as an
equivalent Protocol Stack as long as it does not conflict with equivalent Protocol Stack as long as it does not conflict with
any other application-requested properties. any other application-requested properties.
3. Both stacks must offer the same security properties. See the 3. Both stacks MUST offer the same security properties. The
security protocol equivalence section below for futher discussion inclusion of transport security protocols
(Section 4.3.1). [I-D.ietf-taps-transport-security] in a Protocol Stack adds
additional restrictions to Protocol Stack equivalence. Security
4.3.1. Transport Security Equivalence features and properties, such as cryptographic algorithms, peer
authentication, and identity privacy vary across security
The inclusion of transport security protocols protocols, and across versions of security protocols. Protocol
[I-D.ietf-taps-transport-security] in a Protocol Stack adds extra equivalence ought not to be assumed for different protocols or
restrictions to Protocol Stack equivalence. Security features and protocol versions, even if they offer similar application
properties, such as cryptographic algorithms, peer authentication, configuration options. To ensure that security protocols are not
and identity privacy vary across security protocols, and across incorrectly swapped, Transport Services systems SHOULD only
versions of security protocols. Protocol equivalence should not be automatically generate equivalent Protocol Stacks when the
assumed for different protocols or protocol versions, even if they transport security protocols within the stacks are identical.
offer similar application configuration options. Specifically, a transport system would consider protocols
identical only if they are of the same type and version. For
To ensure that security protocols are not incorrectly swapped, example, the same version of TLS running over two different
Transport Services systems should only automatically generate transport protocol stacks are considered equivalent, whereas TLS
equivalent Protocol Stacks when the transport security protocols 1.2 and TLS 1.3 [RFC8446] are not considered equivalent.
within the stacks are identical. Specifically, a system should
consider protocols identical only if they are of the same type and
version. For example, the same version of TLS running over two
different transport protocol stacks may be considered equivalent,
whereas TLS 1.2 and TLS 1.3 [I-D.ietf-tls-tls13] should not be
considered equivalent.
4.4. Message Framing, Parsing, and Serialization 4.2.4. Separating Connection Groups
While some transports expose a byte stream abstraction, most higher By default, all stored properties of the Implementation are shared
level protocols impose some structure onto that byte stream. That within a process, such as cached protocol state, cached path state,
is, the higher level protocol operates in terms of messages, protocol and heuristics. This provides efficiency and convenience for the
data units (PDUs), rather than using unstructured sequences of bytes, application, since the Transport System Implementation can
with each message being processed in turn. Protocols are specified automatically optimize behavior.
in terms of state machines acting on semantic messages, with parsing
the byte stream into messages being a necessary annoyance, rather
than a semantic concern. Accordingly, the Transport Services
architecture exposes messages as the primary abstraction. Protocols
that deal only in byte streams, such as TCP, represent their data in
each direction as a single, long message. When framing protocols are
placed on top of byte streams, the messages used in the API represent
the framed messages within the stream.
Providing a message-based abstraction also provides: There are several reasons, however, that an application might want to
isolate some Connections within a single process. These reasons
include:
o the ability to associate deadlines with messages, for transports o Privacy concerns about re-using cached protocol state that can
that care about timing; lead to linkability. Sensitive state may include TLS session
state [RFC8446] and HTTP cookies [RFC6265].
o the ability to provide control of reliability, choosing what o Privacy concerns about allowing Connections to multiplex together,
messages to retransmit in the event of packet loss, and how best which can tell a Remote Endpoint that all of the Connections are
to make use of the data that arrived; coming from the same application (for example, when Connections
are multiplexed HTTP/2 or QUIC streams).
o the ability to manage dependencies between messages, when some o Performance concerns about Connections introducing head-of-line
messages may not be delivered due to either packet loss or missing blocking due to multiplexing or needing to share state on a single
a deadline, in particular the ability to avoid (re-)sending data thread.
that relies on a previous transmission that was never received.
All require explicit message boundaries, and application-level The Transport Services API SHOULD allow applications to explicitly
framing of messages, to be effective. Once a message is passed to define Connection Groups that force separation of Cached State and
the transport, it can not be cancelled or paused, but prioritization Protocol Stacks. For example, a web browser application might use
as well as lifetime and retransmission management will provide the Connection Groups with separate caches for different tabs in the
protocol stack with all needed information to send the messages as browser to decrease linkability.
quickly as possible without blocking transmission unnecessarily. The
transport services architecture facilitates this by handling
messages, with known identity (sequence numbers, in the simple case),
lifetimes, niceness, and antecedents.
Transport protocols such as SCTP provide a message-oriented API that The interface to specify these Groups MAY expose fine-grained tuning
has similar features to those we describe. Other transports, such as for which properties and cached state is allowed to be shared with
TCP, do not. To support a message oriented API, while still being other Connections. For example, an application might want to allow
compatible with stream-based transport protocols, implementations of sharing TCP Fast Open cookies across groups, but not TLS session
the transport services architecture should provide APIs for framing state.
and de-framing messages. That is, we push message framing down into
the transport services API, allowing applications to send and receive
complete messages. This is backwards compatible with existing
protocols and APIs, since the wire format of messages does not
change, but gives the protocol stack additional information to allow
it to make better use of modern transport services.
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.
6. Security Considerations 6. Security Considerations
The Transport Services architecture does not recommend use of The Transport Services architecture does not recommend use of
specific security protocols or algorithms. Its goal is to offer ease specific security protocols or algorithms. Its goal is to offer ease
of use for existing protocols by providing a generic security-related of use for existing protocols by providing a generic security-related
interface. Each provided interface mimics an existing protocol- interface. Each provided interface translates to an existing
specific interface provided by supported security protocols. For protocol-specific interface provided by supported security protocols.
example, trust verification callbacks are common parts of TLS APIs. For example, trust verification callbacks are common parts of TLS
Transport Services APIs will expose similar functionality. APIs. Transport Services APIs will expose similar functionality
[I-D.ietf-taps-transport-security].
Clients must take care to use security APIs appropriately. In cases As described above in Section 4.2.3, if a Transport Services system
where clients use said interface to provide sensitive keying races between two different Protocol Stacks, both MUST use the same
security protocols and options.
Clients need to ensure that security APIs are used appropriately. In
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 must be validated. For example, clients should not (PSKs), key use needs to be validated. For example, clients ought
use PSK material created for the Encapsulating Security Protocol not to use PSK material created for the Encapsulating Security
(ESP, part of IPsec) [RFC4303] with QUIC, and clients must not use Protocol (ESP, part of IPsec) [RFC4303] with QUIC, and clients ought
private keys intended for server authentication as a keys for client not to use private keys intended for server authentication as a keys
authentication. Moreover, unlike certain transport features such as for client authentication.
TCP Fast Open (TFO) [RFC7413] or Explicit Congestion Notification
(ECN) [RFC3168] which can fall back to standard configurations, Moreover, unlike certain transport features such as TCP Fast Open
Transport Services systems must not permit fallback for security (TFO) [RFC7413] or Explicit Congestion Notification (ECN) [RFC3168]
protocols. For example, if a client requests TLS, yet TLS or the which can fall back to standard configurations, Transport Services
desired version are not available, its connection must fail. Clients systems MUST prohibit fallback for security protocols. For example,
are responsible for implementing protocol or version fallback using a if a client requests TLS, yet TLS or the desired version are not
Transport Services API if so desired. available, its connection will fail. Clients are thus responsible
for implementing security protocol fallback or version fallback by
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 agreement No. 644334 research and innovation programme under grant agreements No. 644334
(NEAT). (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. 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-01 (work in progress), July 2018. ietf-taps-impl-02 (work in progress), October 2018.
[I-D.ietf-taps-interface] [I-D.ietf-taps-interface]
Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G., Trammell, B., Welzl, M., Enghardt, T., Fairhurst, G.,
Kuehlewind, M., Perkins, C., Tiesel, P., and C. Wood, "An Kuehlewind, M., Perkins, C., Tiesel, P., and C. Wood, "An
Abstract Application Layer Interface to Transport Abstract Application Layer Interface to Transport
Services", draft-ietf-taps-interface-01 (work in Services", draft-ietf-taps-interface-02 (work in
progress), July 2018. progress), October 2018.
[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]
Pauly, T., Perkins, C., Rose, K., and C. Wood, "A Survey Wood, C., Enghardt, T., Pauly, T., Perkins, C., and K.
of Transport Security Protocols", draft-ietf-taps- Rose, "A Survey of Transport Security Protocols", draft-
transport-security-02 (work in progress), June 2018. ietf-taps-transport-security-06 (work in progress), March
2019.
[I-D.ietf-tls-tls13]
Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", draft-ietf-tls-tls13-28 (work in progress),
March 2018.
[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 [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>.
[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,
DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/info/rfc6265>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP [RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014, Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<https://www.rfc-editor.org/info/rfc7413>. <https://www.rfc-editor.org/info/rfc7413>.
[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>.
[TAPS-IMPL] [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
Brunstrom, A., Pauly, T., Enghardt, T., Grinnemo, K., 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
Jones, T., Tiesel, P., Perkins, C., and M. Welzl, May 2017, <https://www.rfc-editor.org/info/rfc8174>.
"Implementing Interfaces to Transport Services", draft-
ietf-taps-impl-01 (work in progress), July 2018. [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
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
United States of America United States of America
Email: tpauly@apple.com Email: tpauly@apple.com
Brian Trammell (editor) Brian Trammell (editor)
ETH Zurich Google
Gloriastrasse 35 Gustav-Gull-Platz 1
8092 Zurich 8004 Zurich
Switzerland Switzerland
Email: ietf@trammell.ch Email: ietf@trammell.ch
Anna Brunstrom Anna Brunstrom
Karlstad University Karlstad University
Universitetsgatan 2 Universitetsgatan 2
651 88 Karlstad 651 88 Karlstad
Sweden Sweden
Email: anna.brunstrom@kau.se Email: anna.brunstrom@kau.se
Godred Fairhurst Godred Fairhurst
University of Aberdeen University of Aberdeen
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