draft-ietf-taps-arch-18.txt   draft-ietf-taps-arch-19.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: 1 December 2023 Google Switzerland GmbH Expires: 12 May 2024 Google Switzerland GmbH
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
30 May 2023 9 November 2023
An Architecture for Transport Services Architecture and Requirements for Transport Services
draft-ietf-taps-arch-18 draft-ietf-taps-arch-19
Abstract Abstract
This document describes an architecture for exposing transport This document describes an architecture for exposing transport
protocol features to applications for network communication, a protocol features to applications for network communication. This
Transport Services system. The Transport Services Application system exposes transport protocol features to applications for
network communication. The Transport Services Application
Programming Interface (API) is based on an asynchronous, event-driven Programming Interface (API) is based on an asynchronous, event-driven
interaction pattern. This API uses messages for representing data interaction pattern. This API uses messages for representing data
transfer to applications, and describes how implementations can use transfer to applications, and describes how a Transport Services
multiple IP addresses, multiple protocols, and multiple paths, and Implementation can use multiple IP addresses, multiple protocols, and
provide multiple application streams. This document further defines multiple paths, and provide multiple application streams. This
document provides the architecture and requirements. It defines
common terminology and concepts to be used in definitions of a common terminology and concepts to be used in definitions of a
Transport Service API and a Transport Services implementation. Transport Service API and a Transport Services Implementation.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on 1 December 2023. This Internet-Draft will expire on 12 May 2024.
Copyright Notice Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/ Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document. license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
skipping to change at page 2, line 27 skipping to change at page 2, line 27
provided without warranty as described in the Revised BSD License. provided without warranty as described in the Revised BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Background . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Background . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
1.3. Specification of Requirements . . . . . . . . . . . . . . 5 1.3. Specification of Requirements . . . . . . . . . . . . . . 5
1.4. Glossary of Key Terms . . . . . . . . . . . . . . . . . . 5 1.4. Glossary of Key Terms . . . . . . . . . . . . . . . . . . 5
2. API Model . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2. API Model . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1. Event-Driven API . . . . . . . . . . . . . . . . . . . . 9 2.1. Event-Driven API . . . . . . . . . . . . . . . . . . . . 10
2.2. Data Transfer Using Messages . . . . . . . . . . . . . . 10 2.2. Data Transfer Using Messages . . . . . . . . . . . . . . 11
2.3. Flexible Implementation . . . . . . . . . . . . . . . . . 11 2.3. Flexible Implementation . . . . . . . . . . . . . . . . . 12
2.4. Coexistence . . . . . . . . . . . . . . . . . . . . . . . 12 2.4. Coexistence . . . . . . . . . . . . . . . . . . . . . . . 13
3. API and Implementation Requirements . . . . . . . . . . . . . 12 3. API and Implementation Requirements . . . . . . . . . . . . . 13
3.1. Provide Common APIs for Common Features . . . . . . . . . 13 3.1. Provide Common APIs for Common Features . . . . . . . . . 14
3.2. Allow Access to Specialized Features . . . . . . . . . . 14 3.2. Allow Access to Specialized Features . . . . . . . . . . 15
3.3. Select Between Equivalent Protocol Stacks . . . . . . . . 15 3.3. Select Between Equivalent Protocol Stacks . . . . . . . . 16
3.4. Maintain Interoperability . . . . . . . . . . . . . . . . 16 3.4. Maintain Interoperability . . . . . . . . . . . . . . . . 17
4. Transport Services Architecture and Concepts . . . . . . . . 16 3.5. Support Monitoring . . . . . . . . . . . . . . . . . . . 17
4.1. Transport Services API Concepts . . . . . . . . . . . . . 18 4. Transport Services Architecture and Concepts . . . . . . . . 18
4.1.1. Endpoint Objects . . . . . . . . . . . . . . . . . . 20 4.1. Transport Services API Concepts . . . . . . . . . . . . . 20
4.1.2. Connections and Related Objects . . . . . . . . . . . 20 4.1.1. Endpoint Objects . . . . . . . . . . . . . . . . . . 22
4.1.3. Pre-establishment . . . . . . . . . . . . . . . . . . 21 4.1.2. Connections and Related Objects . . . . . . . . . . . 22
4.1.4. Establishment Actions . . . . . . . . . . . . . . . . 22 4.1.3. Pre-establishment . . . . . . . . . . . . . . . . . . 24
4.1.5. Data Transfer Objects and Actions . . . . . . . . . . 23 4.1.4. Establishment Actions . . . . . . . . . . . . . . . . 24
4.1.6. Event Handling . . . . . . . . . . . . . . . . . . . 24 4.1.5. Data Transfer Objects and Actions . . . . . . . . . . 25
4.1.7. Termination Actions . . . . . . . . . . . . . . . . . 25 4.1.6. Event Handling . . . . . . . . . . . . . . . . . . . 26
4.1.8. Connection Groups . . . . . . . . . . . . . . . . . . 25 4.1.7. Termination Actions . . . . . . . . . . . . . . . . . 27
4.2. Transport Services Implementation . . . . . . . . . . . . 26 4.1.8. Connection Groups . . . . . . . . . . . . . . . . . . 28
4.2.1. Candidate Gathering . . . . . . . . . . . . . . . . . 27 4.2. Transport Services Implementation . . . . . . . . . . . . 28
4.2.2. Candidate Racing . . . . . . . . . . . . . . . . . . 27 4.2.1. Candidate Gathering . . . . . . . . . . . . . . . . . 30
4.2.3. Separating Connection Contexts . . . . . . . . . . . 28 4.2.2. Candidate Racing . . . . . . . . . . . . . . . . . . 30
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28 4.2.3. Separating Connection Contexts . . . . . . . . . . . 30
6. Security and Privacy Considerations . . . . . . . . . . . . . 29 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30 6. Security and Privacy Considerations . . . . . . . . . . . . . 31
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32
8.1. Normative References . . . . . . . . . . . . . . . . . . 30 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 32
8.2. Informative References . . . . . . . . . . . . . . . . . 30 8.1. Normative References . . . . . . . . . . . . . . . . . . 32
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 32 8.2. Informative References . . . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction 1. Introduction
Many application programming interfaces (APIs) to perform transport Many application programming interfaces (APIs) to provide transport
networking have been deployed, perhaps the most widely known and interfaces to networks have been deployed, perhaps the most widely
imitated being the BSD Socket [POSIX] interface (Socket API). The known and imitated being the BSD Socket [POSIX] interface (Socket
naming of objects and functions across these APIs is not consistent API). The naming of objects and functions across these APIs is not
and varies depending on the protocol being used. For example, consistent and varies depending on the protocol being used. For
sending and receiving streams of data is conceptually the same for example, sending and receiving streams of data is conceptually the
both an unencrypted Transmission Control Protocol (TCP) stream and same for both an unencrypted Transmission Control Protocol (TCP)
operating on an encrypted Transport Layer Security (TLS) [RFC8446] stream and operating on an encrypted Transport Layer Security (TLS)
stream over TCP, but applications cannot use the same socket send() [RFC8446] stream over TCP, but applications cannot use the same
and recv() calls on top of both kinds of connections. Similarly, socket send() and recv() calls on top of both kinds of connections.
terminology for the implementation of transport protocols varies Similarly, terminology for the implementation of transport protocols
based on the context of the protocols themselves: terms such as varies based on the context of the protocols themselves: terms such
"flow", "stream", "message", and "connection" can take on many as "flow", "stream", "message", and "connection" can take on many
different meanings. This variety can lead to confusion when trying different meanings. This variety can lead to confusion when trying
to understand the similarities and differences between protocols, and to understand the similarities and differences between protocols, and
how applications can use them effectively. how applications can use them effectively.
The goal of the Transport Services architecture is to provide a The goal of the Transport Services System architecture is to provide
flexible and reusable architecture that provides a common interface a flexible and reusable system with a common interface for transport
for transport protocols. As applications adopt this interface, they protocols. An application uses the Transport Services System through
will benefit from a wide set of transport features that can evolve an abstract Connection (we use capitalization to distinguish these
over time, and ensure that the system providing the interface can from the underlying connections of, e.g., TCP). This provides
optimize its behavior based on the application requirements and flexible connection establishment allowing an application to request
network conditions, without requiring changes to the applications. or require a set of properties.
This flexibility enables faster deployment of new features and
protocols. It can also support applications by offering racing As applications adopt this interface, they will benefit from a wide
set of transport features that can evolve over time, and ensure that
the system providing the interface can optimize its behavior based on
the application requirements and network conditions, without
requiring changes to the applications. This flexibility enables
faster deployment of new features and protocols.
This architecture can also support applications by offering racing
mechanisms (attempting multiple IP addresses, protocols, or network mechanisms (attempting multiple IP addresses, protocols, or network
paths in parallel), which otherwise need to be implemented in each paths in parallel), which otherwise need to be implemented in each
application separately (see Section 4.2.2). application separately (see Section 4.2.2). Racing selects one or
more candidates each with equivalent protocol stacks that are used to
identify an optimal combination of transport protocol instance such
as TCP, UDP, or another transport, together with configuration of
parameters and interfaces. A Connection represents an object that,
once established, can be used to send and receive messages. A
Connection can also be created from another Connection, by cloning,
and then forms a part of a Connection Group whose Connections share
properties.
This document was developed in parallel with the specification of the This document was developed in parallel with the specification of the
Transport Services API [I-D.ietf-taps-interface] and implementation Transport Services API [I-D.ietf-taps-interface] and implementation
guidelines [I-D.ietf-taps-impl]. Although following the Transport guidelines [I-D.ietf-taps-impl]. Although following the Transport
Services architecture does not require that all APIs and Services architecture does not require all APIs and implementations
implementations are identical, a common minimal set of features to be identical, a common minimal set of features represented in a
represented in a consistent fashion will enable applications to be consistent fashion will enable applications to be easily ported from
easily ported from one system to another. one implementation of the Transport Services System to another.
1.1. Background 1.1. Background
The Transport Services architecture is based on the survey of The architecture of the Transport Services System is based on the
services provided by IETF transport protocols and congestion control survey of services provided by IETF transport protocols and
mechanisms [RFC8095], and the distilled minimal set of the features congestion control mechanisms [RFC8095], and the distilled minimal
offered by transport protocols [RFC8923]. These documents identified set of the features offered by transport protocols [RFC8923]. These
common features and patterns across all transport protocols developed documents identified common features and patterns across all
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 document also considers the
the impact of transport security protocols on the feature-set exposed impact of transport security protocols on the feature-set exposed by
by Transport Services [RFC8922]. Transport Services [RFC8922].
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 [RFC8923] was that features features provided by transport protocols [RFC8923] was that features
either require application interaction and guidance (referred to in either require application interaction and guidance (referred to in
that document as Functional or Optimizing Features), or else can be that document as Functional or Optimizing Features), or else can be
handled automatically by a system implementing Transport Services handled automatically by an implementation of the Transport Services
(referred to as Automatable Features). Among the identified System (referred to as Automatable Features). Among the identified
Functional and Optimizing Features, some were common across all or Functional and Optimizing Features, some are common across all or
nearly all transport protocols, while others could be seen as nearly all transport protocols, while others present features that,
features that, if specified, would only be useful with a subset of if specified, would only be useful with a subset of protocols, but
protocols, but would not harm the functionality of other protocols. would not harm the functionality of other protocols. For example,
For example, some protocols can deliver messages faster for some protocols can deliver messages faster for applications that do
applications that do not require messages to arrive in the order in not require messages to arrive in the order in which they were sent.
which they were sent. However, this functionality needs to be This functionality needs to be explicitly allowed by the application,
explicitly allowed by the application, since reordering messages since reordering messages would be undesirable in many cases.
would be undesirable in many cases.
1.2. Overview 1.2. Overview
This document describes the Transport Services architecture in three This document describes the Transport Services System in three
sections: sections:
* Section 2 describes how the API model of Transport Services * Section 2 describes how the Transport Services API model differs
architecture differs from traditional socket-based APIs. from that of traditional socket-based APIs. Specifically, it
Specifically, it offers asynchronous event-driven interaction, the offers asynchronous event-driven interaction, the use of messages
use of messages for data transfer, and the flexibility to use for data transfer, and the flexibility to use different transport
different transport protocols and paths without requiring major protocols and paths without requiring major changes to the
changes to the application. application.
* Section 3 explains the fundamental requirements for a Transport * Section 3 explains the fundamental requirements for a Transport
Services system. These principles are intended to make sure that Services System. These principles are intended to make sure that
transport protocols can continue to be enhanced and evolve without transport protocols can continue to be enhanced and evolve without
requiring significant changes by application developers. requiring significant changes by application developers.
* Section 4 presents a diagram showing the Transport Services * Section 4 presents the Transport Services Implementation and
architecture and defines the concepts that are used by both the defines the concepts that are used by the API
API [I-D.ietf-taps-interface] and implementation guidelines [I-D.ietf-taps-interface] and described in the implementation
[I-D.ietf-taps-impl]. The Preconnection allows applications to guidelines [I-D.ietf-taps-impl]. This introduces the
configure Connection Properties. Preconnection, which allows applications to configure Connection
Properties.
* Section 4 also presents how an abstract Connection is used to
select a transport protocol instance such as TCP, UDP, or another
transport. The Connection represents an object that can be used
to send and receive messages.
1.3. Specification of Requirements 1.3. Specification of Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
1.4. Glossary of Key Terms 1.4. Glossary of Key Terms
This subsection provides a glossary of key terms related to the This subsection provides a glossary of key terms related to the
Transport Services architecture. It provides a short description of Transport Services architecture. It provides a short description of
key terms that are later defined in this document. key terms that are later defined in this document.
* Application: An entity that uses the transport layer for end-to- * Application: An entity that uses the transport layer for end-to-
end delivery of data across the network [RFC8095]. end delivery of data across the network [RFC8095].
* Cached State: The state and history that the implementation keeps * Cached State: The state and history that the Transport Services
for each set of associated Endpoints that have been used Implementation keeps for each set of the associated Endpoints that
previously. have been used previously.
* Candidate Path: One path that is available to an application and * Candidate Path: One path that is available to an application and
conforms to the Selection Properties and System Policy during conforms to the Selection Properties and System Policy during
racing. racing.
* Candidate Protocol Stack: One Protocol Stack that can be used by * Candidate Protocol Stack: One Protocol Stack that can be used by
an application for a Connection during racing. an application for a Connection during racing.
* Client: The peer responsible for initiating a Connection. * Client: The peer responsible for initiating a Connection.
* Clone: A Connection that was created from another Connection, and * Clone: A Connection that was created from another Connection, and
forms a part of a Connection Group. forms a part of a Connection Group.
* Connection: Shared state of two or more endpoints that persists * Connection: Shared state of two or more Endpoints that persists
across Messages that are transmitted and received between these across Messages that are transmitted and received between these
Endpoints [RFC8303]. When this document (and other Transport Endpoints [RFC8303]. When this document (and other Transport
Services documents) use the capitalized "Connection" term, it Services documents) use the capitalized "Connection" term, it
refers to a Connection Object that is being offered by the refers to a Connection object that is being offered by the
Transport Services system, as opposed to more generic uses of the Transport Services system, as opposed to more generic uses of the
word "connection". word "connection".
* Connection Group: A set of Connections that shares properties and * Connection Context: A set of stored properties across Connections,
such as cached protocol state, cached path state, and heuristics,
which can include one or more Connection Groups.
* Connection Group: A set of Connections that share properties and
caches. caches.
* Connection Property: A Transport Property that controls per- * Connection Property: A Transport Property that controls per-
Connection behavior of a Transport Services implementation. Connection behavior of a Transport Services implementation.
* Endpoint: An identifier for one side of a Connection (local or * Endpoint: An entity that communicates with one or more other
remote), such as a hostnames or URL. endpoints using a transport protocol.
* Endpoint Identifier: An identifier that specifies one side of a
Connection (local or remote), such as a hostname or URL.
* Equivalent Protocol Stacks: Protocol Stacks that can be safely * Equivalent Protocol Stacks: Protocol Stacks that can be safely
swapped or raced in parallel during establishment of a Connection. swapped or raced in parallel during establishment of a Connection.
* Event: A primitive that is invoked by an endpoint [RFC8303]. * Event: A primitive that is invoked by an Endpoint [RFC8303].
* Framer: A data translation layer that can be added to a Connection * Framer: A data translation layer that can be added to a Connection
to define how application-layer Messages are transmitted over a to define how application-layer Messages are transmitted over a
Protocol Stack. Protocol Stack.
* Local Endpoint: A representation of the application's identifier * Local Endpoint: The local Endpoint.
for itself that it uses for a Connection.
* Local Endpoint Identifier: A representation of the application's
identifier for itself that it uses for a Connection.
* Message: A unit of data that can be transferred between two * Message: A unit of data that can be transferred between two
Endpoints over a Connection. Endpoints over a Connection.
* Message Property: A property that can be used to specify details * Message Property: A property that can be used to specify details
about Message transmission, or obtain details about the about Message transmission, or obtain details about the
transmission after receiving a Message. transmission after receiving a Message.
* Parameter: A value passed between an application and a transport * Parameter: A value passed between an application and a transport
protocol by a primitive [RFC8303]. protocol by a primitive [RFC8303].
* Path: A representation of an available set of properties that a * Path: A representation of an available set of properties that a
Local Endpoint can use to communicate with a Remote Endpoint. Local Endpoint can use to communicate with a Remote Endpoint.
* Peer: An endpoint application party to a Connection. * Peer: An Endpoint application party to a Connection.
* Preconnection: an object that represents a Connection that has not * Preconnection: an object that represents a Connection that has not
yet been established. yet been established.
* Preference: A preference to prohibit, avoid, ignore, prefer, or * Preference: A preference to prohibit, avoid, ignore, prefer, or
require a specific Transport Feature. require a specific Transport Feature.
* Primitive: A function call that is used to locally communicate * Primitive: A function call that is used to locally communicate
between an application and an endpoint, which is related to one or between an application and an Endpoint, which is related to one or
more Transport Features [RFC8303]. more Transport Features [RFC8303].
* Protocol Instance: A single instance of one protocol, including * Protocol Instance: A single instance of one protocol, including
any state necessary to establish connectivity or send and receive any state necessary to establish connectivity or send and receive
Messages. Messages.
* Protocol Stack: A set of Protocol Instances that are used together * Protocol Stack: A set of Protocol Instances that are used together
to establish connectivity or send and receive Messages. to establish connectivity or send and receive Messages.
* Racing: The attempt to select between multiple Protocol Stacks * Racing: The attempt to select between multiple Protocol Stacks
based on the Selection and Connection Properties communicated by based on the Selection and Connection Properties communicated by
the application, along with any security parameters. the application, along with any Security Parameters.
* Remote Endpoint: A representation of the application's identifier * Remote Endpoint: The peer that a local Endpoint can communicate
for a peer that can participate in establishing a Connection. with when a Connection is established.
* Remote Endpoint Identifier: A representation of the application's
identifier for a peer that can participate in establishing a
Connection.
* Rendezvous: The action of establishing a peer-to-peer Connection * Rendezvous: The action of establishing a peer-to-peer Connection
with a Remote Endpoint. with a Remote Endpoint.
* Security Parameters: Parameters that define an application's * Security Parameters: Parameters that define an application's
requirements for authentication and encryption on a Connection. requirements for authentication and encryption on a Connection.
* Server: The peer responsible for responding to a Connection * Server: The peer responsible for responding to a Connection
initiation. initiation.
* Socket: The combination of a destination IP address and a * Socket: The combination of a destination IP address and a
skipping to change at page 8, line 5 skipping to change at page 8, line 24
* Transport Feature: A specific end-to-end feature that the * Transport Feature: A specific end-to-end feature that the
transport layer provides to an application. transport layer provides to an application.
* Transport Property: A property that expresses requirements, * Transport Property: A property that expresses requirements,
prohibitions and preferences [RFC8095]. prohibitions and preferences [RFC8095].
* Transport Service: A set of transport features, without an * Transport Service: A set of transport features, without an
association to any given framing protocol, that provides a association to any given framing protocol, that provides a
complete service to an application. complete service to an application.
* Transport Services System: The Transport Services implementation * Transport Services Implementation: This consists of all objects
and the Transport Services API and protocol instances used internally to a system or library to
implement the functionality needed to provide a transport service
across a network, as required by the abstract interface.
* Transport Services System: The Transport Services Implementation
and the Transport Services API.
2. API Model 2. API Model
The traditional model of using sockets for networking can be The traditional model of using sockets can be represented as follows
represented as follows: (see figure 1):
* Applications create connections and transfer data using the Socket * Applications create connections and transfer data using the Socket
API. API.
* The Socket API provides the interface to the implementations of * The Socket API provides the interface to the implementations of
TCP and UDP (typically implemented in the system's kernel). TCP and UDP (typically implemented in the system's kernel).
* TCP and UDP in the kernel send and receive data over the available * TCP and UDP in the kernel send and receive data over the available
network-layer interfaces. network-layer interfaces.
* Sockets are bound directly to transport-layer and network-layer * Sockets are bound directly to transport-layer and network-layer
addresses, obtained via a separate resolution step, usually addresses, obtained via a separate resolution step, usually
performed by a system-provided stub resolver. performed by a system-provided DNS stub resolver.
+-----------------------------------------------------+ +-----------------------------------------------------+
| Application | | Application |
+-----------------------------------------------------+ +-----------------------------------------------------+
| | | | | |
+------------+ +------------+ +--------------+ +------------+ +------------+ +--------------+
| stub | | Stream API | | Datagram API | | DNS stub | | Stream API | | Datagram API |
| resolver | +------------+ +--------------+ | resolver | +------------+ +--------------+
+------------+ | | +------------+ | |
+---------------------------------+ +---------------------------------+
| TCP UDP | | TCP UDP |
| Kernel Networking Stack | | Kernel Networking Stack |
+---------------------------------+ +---------------------------------+
| |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Network Layer Interface | | Network Layer Interface |
+-----------------------------------------------------+ +-----------------------------------------------------+
Figure 1: Socket API Model Figure 1: Socket API Model
The Transport Services architecture evolves this general model of The architecture of the Transport Services System is an evolution of
interaction, to both modernize the API surface presented to this general model of interaction. It both modernizes the API
applications by the transport layer and to enrich the capabilities of presented to applications by the transport layer and enriches the
the implementation below the API. capabilities of the Transport Services Implementation below this API.
+-----------------------------------------------------+ +-----------------------------------------------------+
| Application | | Application |
+-----------------------------------------------------+ +-----------------------------------------------------+
| |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Transport Services API | | Transport Services API |
+-----------------------------------------------------+ +-----------------------------------------------------+
| |
+-----------------------------------------------------+ +-----------------------------------------------------+
skipping to change at page 9, line 27 skipping to change at page 9, line 51
| |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Network Layer Interface | | Network Layer Interface |
+-----------------------------------------------------+ +-----------------------------------------------------+
Figure 2: Transport Services API Model Figure 2: Transport Services API Model
The Transport Services API [I-D.ietf-taps-interface] defines the The Transport Services API [I-D.ietf-taps-interface] defines the
interface for an application to create Connections and transfer data. interface for an application to create Connections and transfer data.
It combines interfaces for multiple interaction patterns into a It combines interfaces for multiple interaction patterns into a
unified whole. By combining name resolution with connection unified whole (see figure 2). This offers generic functions and also
establishment and data transfer in a single API, it allows for more the protocol-specific mappings for TCP, UDP, UDP-Lite, and other
flexible implementations to provide path and transport protocol protocol layers. These mapping are extensible. Future documents
agility on the application's behalf. could define similar mappings for new layers and for other transport
protocols, such as QUIC [RFC9000]. By combining name resolution with
connection establishment and data transfer in a single API, it allows
for more flexible implementations to provide path and transport
protocol agility on the application's behalf.
The Transport Services implementation [I-D.ietf-taps-impl] implements The Transport Services Implementation [I-D.ietf-taps-impl] is the
the transport layer protocols and other functions needed to send and component of the Transport Services System that implements the
transport layer protocols and other functions needed to send and
receive data. It is responsible for mapping the API to a specific receive data. It is responsible for mapping the API to a specific
available transport Protocol Stack and managing the available network available transport Protocol Stack and managing the available network
interfaces and paths. interfaces and paths.
There are key differences between the Transport Services architecture There are key differences between the architecture of the Transport
and the architecture of the Socket API: the API of the Transport Services System and the architecture of the Socket API: the API of
Services architecture is asynchronous and event-driven; it uses the Transport Services System is asynchronous and event-driven; it
messages for representing data transfer to applications; and it uses messages for representing data transfer to applications; and it
describes how implementations can use multiple IP addresses, multiple describes how a Transport Services Implementation can resolve
Endpoint Identifiers to use multiple IP addresses, multiple
protocols, multiple paths, and provide multiple application streams. protocols, multiple paths, and provide multiple application streams.
2.1. Event-Driven API 2.1. Event-Driven API
Originally, the Socket API presented a blocking interface for Originally, the Socket API presented a blocking interface for
establishing connections and transferring data. However, most modern establishing connections and transferring data. However, most modern
applications interact with the network asynchronously. Emulation of applications interact with the network asynchronously. Emulation of
an asynchronous interface using the Socket API generally uses a try- an asynchronous interface using the Socket API can use a try-and-fail
and-fail model. If the application wants to read, but data has not model: If the application wants to read, but data has not yet been
yet been received from the peer, the call to read will fail. The received from the peer, the call to read will fail. The application
application then waits and can try again later. then waits and can try again later.
In contrast to the Socket API, all interaction using the Transport In contrast to the Socket API, all interactions using the Transport
Services API is expected to be asynchronous. The API is defined Services API are expected to be asynchronous. The API is defined
around an event-driven model (see Section 4.1.6) in order to model around an event-driven model (see Section 4.1.6), which models this
this asynchronous interaction, though other forms of asynchronous asynchronous interaction. Other forms of asynchronous communication
communication may be available to applications depending on the could also be available to applications, depending on the platform
platform implementing the interface. implementing the interface.
For example, an application first issues a call to receive new data For example, when an application that uses the Transport Services API
from the connection. When delivered data becomes available, this wants to receive data, it issues an asynchronous call to receive new
data is delivered to the application using asynchronous events that data from the Connection. When delivered data becomes available,
contain the data. Error handling is also asynchronous; a failure to this data is delivered to the application using asynchronous events
send data results in an asynchronous error event. that contain the data. Error handling is also asynchronous,
resulting in asynchronous error events.
This API also delivers events regarding the lifetime of a connection This API also delivers events regarding the lifetime of a connection
and changes in the available network links, which were not previously and changes in the available network links, which were not previously
made explicit in the Socket API. made explicit in the Socket API.
Using asynchronous events allows for a more natural interaction model Using asynchronous events allows for a more natural interaction model
when establishing connections and transferring data. Events in time when establishing connections and transferring data. Events in time
more closely reflect the nature of interactions over networks, as more closely reflect the nature of interactions over networks, as
opposed to how the Socket API represents network resources as file opposed to how the Socket API represents network resources as file
system objects that may be temporarily unavailable. system objects that may be temporarily unavailable.
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* the ability to automatically assign messages and connections to * the ability to automatically assign messages and connections to
underlying transport connections to utilize multi-streaming and underlying transport connections to utilize multi-streaming and
pooled connections. pooled connections.
Allowing applications to interact with messages is backwards- Allowing applications to interact with messages is backwards-
compatible with existing protocols and APIs because it does not compatible with existing protocols and APIs because it does not
change the wire format of any protocol. Instead, it provides the change the wire format of any protocol. Instead, it provides the
Protocol Stack with additional information to allow it to make better Protocol Stack with additional information to allow it to make better
use of modern transport services, while simplifying the application's use of modern transport services, while simplifying the application's
role in parsing data. For protocols that natively use a streaming role in parsing data. For protocols that inherently use a streaming
abstraction, framers (Section 4.1.5) bridge the gap between the two abstraction, framers (Section 4.1.5) bridge the gap between the two
abstractions. abstractions.
2.3. Flexible Implementation 2.3. Flexible Implementation
The Socket API for protocols like TCP is generally limited to The Socket API for protocols like TCP is generally limited to
connecting to a single address over a single interface. It also connecting to a single address over a single interface (IP source
presents a single stream to the application. Software layers built address). It also presents a single stream to the application.
upon this API often propagate this limitation of a single-address Software layers built upon this API often propagate this limitation
single-stream model. The Transport Services architecture is of a single-address single-stream model. The Transport Services
designed: architecture is designed:
* to handle multiple candidate endpoints, protocols, and paths; * to handle multiple candidate endpoints, protocols, and paths;
* to support candidate protocol racing to select the most optimal * to support candidate protocol racing to select the most optimal
stack in each situation; stack in each situation;
* to support multipath and multistreaming protocols; * to support multipath and multistreaming protocols;
* to provide state caching and application control over it. * to provide state caching and application control over it.
A Transport Services implementation is intended to be flexible at A Transport Services Implementation is intended 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 by racing them and trying to select the most optimal combinations by racing them and
measuring the results (see Section 4.2.1 and Section 4.2.2). This measuring the results (see Section 4.2.1 and Section 4.2.2). This
requires applications to provide higher-level endpoints than IP requires applications to specify identifiers for the Local and Remote
addresses, such as hostnames and URLs, which are used by a Transport Endpoint that are higher-level than IP addresses, such as a hostname
Services implementation for resolution, path selection, and racing. or URL, which are used by a Transport Services Implementation for
An implementation can further implement fallback mechanisms if resolution, path selection, and racing. An implementation can
connection establishment of one protocol fails or performance is further implement fallback mechanisms if connection establishment of
detected to be unsatisfactory. one protocol fails or performance is detected to be unsatisfactory.
Information used in connection establishment (e.g. cryptographic Information used in connection establishment (e.g. cryptographic
resumption tokens, information about usability of certain protocols resumption tokens, information about usability of certain protocols
on the path, results of racing in previous connections) are cached in on the path, results of racing in previous connections) are cached in
the Transport Services implementation. Applications have control the Transport Services Implementation. Applications have control
over whether this information is used for a specific establishment, over whether this information is used for a specific establishment,
in order to allow tradeoffs between efficiency and linkability. in order to allow tradeoffs between efficiency and linkability.
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.
2.4. Coexistence 2.4. Coexistence
Note that while the Transport Service architecture is designed as an While the architecture of the Transport Services System is designed
enhanced replacement for the Socket API, it need not replace it as an enhanced replacement for the Socket API, it need not replace it
entirely on a system or platform; indeed, incremental deployability entirely on a system or platform; indeed, coexistence has been
[RFC8170] requires coexistence. The architecture is therefore recommended for incremental deployability [RFC8170]. The
designed such that it can run alongside (or, indeed, on top of) an architecture is therefore designed such that it can run alongside
existing Socket API implementation; only applications built to the (or, indeed, on top of) an existing Socket API implementation; only
Transport Services API are managed by the system's Transport Services applications built to the Transport Services API are managed by the
implementation. system's Transport Services Implementation.
3. API and Implementation Requirements 3. API and Implementation Requirements
A goal of the Transport Services architecture is to redefine the One goal of the architecture is to redefine the interface between
interface between applications and transports in a way that allows applications and transports in a way that allows the transport layer
the transport layer to evolve and improve without fundamentally to evolve and improve without fundamentally changing the contract
changing the contract with the application. This requires a careful with the application. This requires a careful consideration of how
consideration of how to expose the capabilities of protocols. This to expose the capabilities of protocols. The architecture also
architecture also encompasses system policies that can influence and encompasses system policies that can influence and inform how
inform how transport protocols use a network path or interface. transport protocols use a network path or interface.
There are several ways the Transport Services system can offer There are several ways the Transport Services System can offer
flexibility to an application: it can provide access to transport flexibility to an application: it can provide access to transport
protocols and protocol features; it can use these protocols across protocols and protocol features; it can use these protocols across
multiple paths that could have different performance and functional multiple paths that could have different performance and functional
characteristics; and it can communicate with different remote systems characteristics; and it can communicate with different remote systems
to optimize performance, robustness to failure, or some other metric. to optimize performance, robustness to failure, or some other metric.
Beyond these, if the Transport Services API remains the same over Beyond these, if the Transport Services API remains the same over
time, new protocols and features can be added to the Transport time, new protocols and features can be added to the Transport
Services implementation without requiring changes in applications for Services Implementation without requiring changes in applications for
adoption. Similarly, this can provide a common basis for utilizing adoption. Similarly, this can provide a common basis for utilizing
information about a network path or interface, enabling evolution information about a network path or interface, enabling evolution
below the transport layer. below the transport layer.
The normative requirements described in this section allow Transport The normative requirements described in this section allow Transport
Services APIs and Transport Services implementation to provide this Services APIs and Transport Services Implementation to provide this
functionality without causing incompatibility or introducing security functionality without causing incompatibility or introducing security
vulnerabilities. vulnerabilities.
3.1. Provide Common APIs for Common Features 3.1. Provide Common APIs for Common Features
Any functionality that is common across multiple transport protocols Any functionality that is common across multiple transport protocols
SHOULD be made accessible through a unified set of calls using the SHOULD be made accessible through a unified set of calls using the
Transport Services API. As a baseline, any Transport Services API Transport Services API. As a baseline, any Transport Services API
SHOULD allow access to the minimal set of features offered by SHOULD allow access to the minimal set of features offered by
transport protocols [RFC8923]. If that minimal set is updated or transport protocols [RFC8923]. If that minimal set is updated or
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preferences for how the transport service should operate at each preferences for how the transport service should operate at each
stage in the lifetime of a connection. Transport Properties are stage in the lifetime of a connection. Transport Properties are
subdivided into Selection Properties, which specify which paths and subdivided into Selection Properties, which specify which paths and
Protocol Stacks can be used and are preferred by the application; Protocol Stacks can be used and are preferred by the application;
Connection Properties, which inform decisions made during connection Connection Properties, which inform decisions made during connection
establishment and fine-tune the established connection; and Message establishment and fine-tune the established connection; and Message
Properties, set on individual Messages. Properties, set on individual Messages.
It is RECOMMENDED that the Transport Services API offers properties It is RECOMMENDED that the Transport Services API offers properties
that are common to multiple transport protocols. This enables a that are common to multiple transport protocols. This enables a
Transport Services implementation to appropriately select between Transport Services System to appropriately select between protocols
protocols that offer equivalent features. Similarly, it is that offer equivalent features. Similarly, it is RECOMMENDED that
RECOMMENDED that the Properties offered by the Transport Services API the Properties offered by the Transport Services API are applicable
are applicable to a variety of network layer interfaces and paths, to a variety of network layer interfaces and paths, which permits
which permits racing of different network paths without affecting the racing of different network paths without affecting the applications
applications using the API. Each is expected to have a default using the API. Each is expected to have a default value.
value.
It is RECOMMENDED that the default values for Properties are selected It is RECOMMENDED that the default values for Properties are selected
to ensure correctness for the widest set of applications, while to ensure correctness for the widest set of applications, while
providing the widest set of options for selection. For example, providing the widest set of options for selection. For example,
since both applications that require reliability and those that do since both applications that require reliability and those that do
not require reliability can function correctly when a protocol not require reliability can function correctly when a protocol
provides reliability, reliability ought to be enabled by default. As provides reliability, reliability ought to be enabled by default. As
another example, the default value for a Property regarding the another example, the default value for a Property regarding the
selection of network interfaces ought to permit as many interfaces as selection of network interfaces ought to permit as many interfaces as
possible. possible.
Applications using the Transport Services API are REQUIRED to be Applications using the Transport Services API need to be designed to
robust to the automated selection provided by the Transport Services be robust to the automated selection provided by the Transport
implementation. This automated selection is constrained by the Services System. This automated selection is constrained by the
properties and preferences expressed by the application and requires properties and preferences expressed by the application and requires
applications to explicitly set properties that define any necessary applications to explicitly set properties that define any necessary
constraints on protocol, path, and interface selection. constraints on protocol, path, and interface selection.
3.2. Allow Access to Specialized Features 3.2. Allow Access to Specialized Features
There are applications that will need to control fine-grained details There are applications that will need to control fine-grained details
of transport protocols to optimize their behavior and ensure of transport protocols to optimize their behavior and ensure
compatibility with remote systems. It is therefore RECOMMENDED that compatibility with remote systems. It is therefore RECOMMENDED that
the Transport Services API and the Transport Services implementation the Transport Services API and the Transport Services Implementation
permit more specialized protocol features to be used. permit more specialized protocol features to be used.
A specialized feature could be needed by an application only when A specialized feature could be needed 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 TCP, it could require control over the if an application is using TCP, it could require control over the
User Timeout Option for TCP [RFC5482]; these options would not take User Timeout Option for TCP [RFC5482]; these options would not take
effect for other transport protocols. In such cases, the API ought effect for other transport protocols. In such cases, the API ought
to expose the features in such a way that they take effect when a to expose the features in such a way that they take effect when a
particular protocol is selected, but do not imply that only that particular protocol is selected, but do not imply that only that
protocol could be used. For example, if the API allows an protocol could be used. For example, if the API allows an
application to specify a preference to use the User Timeout Option, application to specify a preference to use the User Timeout Option,
communication would not fail when a protocol such as QUIC is communication would not fail when a protocol such as UDP is selected.
selected.
Other specialized features, however, can also be strictly required by Other specialized features, however, can also be strictly required by
an application and thus further constrain the set of protocols that an application and thus further constrain the set of protocols that
can be used. For example, if an application requires support for can be used. For example, if an application requires support for
automatic handover or failover for a connection, only Protocol Stacks automatic handover or failover for a connection, only Protocol Stacks
that provide this feature are eligible to be used, e.g., Protocol that provide this feature are eligible to be used, e.g., Protocol
Stacks that include a multipath protocol or a protocol that supports Stacks that include a multipath protocol or a protocol that supports
connection migration. A Transport Services API needs to allow connection migration. A Transport Services API needs to allow
applications to define such requirements and constrain the options applications to define such requirements and constrain the options
available to a Transport Services implementation. Since such options available to a Transport Services Implementation. Since such options
are not part of the core/common features, it will generally be simple are not part of the core/common features, it will generally be simple
for an application to modify its set of constraints and change the for an application to modify its set of constraints and change the
set of allowable protocol features without changing the core set of allowable protocol features without changing the core
implementation. implementation.
To control these specialized features, the application can declare To control these specialized features, the application can declare
its preference – whether the presence of a specific feature is its preference – whether the presence of a specific feature is
prohibited, should be avoided, can be ignored, is preferred, or is prohibited, should be avoided, can be ignored, is preferred, or is
required in the pre-establishment phase. An implementation of a required in the pre-establishment phase. An implementation of a
Transport Services API would honor this preference and allow the Transport Services API would honor this preference and allow the
application to query the availability of each specialized feature application to query the availability of each specialized feature
after a successful establishment. after a successful establishment.
3.3. Select Between Equivalent Protocol Stacks 3.3. Select Between Equivalent Protocol Stacks
A Transport Services implementation can attempt and select between A Transport Services Implementation can attempt and select between
multiple Protocol Stacks based on the Selection and Connection multiple Protocol Stacks based on the Selection and Connection
Properties communicated by the application, along with any security Properties communicated by the application, along with any Security
parameters. The implementation can only attempt to use multiple Parameters. The implementation can only attempt to use multiple
Protocol Stacks when they are "equivalent", which means that the Protocol Stacks when they are "equivalent", which means that the
stacks can provide the same Transport Properties and interface stacks can provide the same Transport Properties and interface
expectations as requested by the application. Equivalent Protocol expectations as requested by the application. Equivalent Protocol
Stacks can be safely swapped or raced in parallel (see Section 4.2.2) Stacks can be safely swapped or raced in parallel (see Section 4.2.2)
during connection establishment. during connection establishment.
The following two examples show non-equivalent Protocol Stacks: The following two examples show non-equivalent Protocol Stacks:
* If the application requires preservation of message boundaries, a * If the application requires preservation of message boundaries, a
Protocol Stack that runs UDP as the top-level interface to the Protocol Stack that runs UDP as the top-level interface to the
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to read out message boundaries based on datagrams sent from the to read out message boundaries based on datagrams sent from the
remote system, whereas TCP does not preserve message boundaries on remote system, whereas TCP does not preserve message boundaries on
its own, but needs a framing protocol on top to determine message its own, but needs a framing protocol on top to determine message
boundaries. boundaries.
* If the application specifies that it requires reliable * If the application specifies that it requires reliable
transmission of data, then a Protocol Stack using UDP without any transmission of data, then a Protocol Stack using UDP without any
reliability layer on top would not be allowed to replace a reliability layer on top would not be allowed to replace a
Protocol Stack using TCP. Protocol Stack using TCP.
The following example shows equivalent Protocol Stacks: The following example shows Equivalent Protocol Stacks:
* If the application does not require reliable transmission of data, * If the application does not require reliable transmission of data,
then a Protocol Stack that adds reliability could be regarded as then a Protocol Stack that adds reliability could be regarded as
an equivalent Protocol Stack as long as providing this would not an Equivalent Protocol Stack as long as providing this would not
conflict with any other application-requested properties. conflict with any other application-requested properties.
To ensure that security protocols are not incorrectly swapped, a A Transport Services Implementation can race different security
Transport Services implementation MUST only select Protocol Stacks protocols, e.g., if the System Policy is explicitly configured to
that meet application requirements ([RFC8922]). A Transport Services consider them equivalent. A Transport Services implementation SHOULD
implementation SHOULD only race Protocol Stacks where the transport only race Protocol Stacks where the transport security protocols
security protocols within the stacks are identical. A Transport within the stacks are identical. To ensure that security protocols
Services implementation MUST NOT automatically fall back from secure are not incorrectly swapped, a Transport Services Implementation MUST
protocols to insecure protocols, or to weaker versions of secure only select Protocol Stacks that meet application requirements
protocols. A Transport Services implementation MAY allow ([RFC8922]). A Transport Services Implementation MUST NOT
applications to explicitly specify which versions of a protocol ought automatically fall back from secure protocols to insecure protocols,
to be permitted, e.g., to allow a minimum version of TLS 1.2 in case or to weaker versions of secure protocols. A Transport Services
TLS 1.3 is not available. Implementation MAY allow applications to explicitly specify which
versions of a protocol ought to be permitted, e.g., to allow a
minimum version of TLS 1.2 in case TLS 1.3 is not available.
A Transport Services Implementation MAY specify security properties
relating to how the system operates (e.g., requirements,
prohibitions, and preferences for the use of DNS Security Extensions
(DNSSEC) or DNS over HTTPS (DoH)).
3.4. Maintain Interoperability 3.4. Maintain Interoperability
It is important to note that neither the Transport Services API It is important to note that neither the Transport Services API
[I-D.ietf-taps-interface] nor the guidelines for the Transport [I-D.ietf-taps-interface] nor the guidelines for implementation of
Service implementation [I-D.ietf-taps-impl] define new protocols or the Transport Service System [I-D.ietf-taps-impl] define new
protocol capabilities that affect what is communicated across the protocols or protocol capabilities that affect what is communicated
network. A Transport Services system MUST NOT require that a peer on across the network. A Transport Services System MUST NOT require
the other side of a connection uses the same API or implementation. that a peer on the other side of a connection uses the same API or
A Transport Services implementation acting as a connection initiator implementation. A Transport Services Implementation acting as a
is able to communicate with any existing endpoint that implements the connection initiator is able to communicate with any existing
transport protocol(s) and all the required properties selected. Endpoint that implements the transport protocol(s) and all the
Similarly, a Transport Services implementation acting as a Listener required properties selected. Similarly, a Transport Services
can receive connections for any protocol that is supported from an Implementation acting as a Listener can receive connections for any
existing initiator that implements the protocol, independent of protocol that is supported from an existing initiator that implements
whether the initiator uses the Transport Services architecture or the protocol, independent of whether the initiator uses the Transport
not. Services System or not.
A Transport Services system makes decisions that select protocols and A Transport Services Implemenation makes decisions that select
interfaces. In normal use, a given version of a Transport Services protocols and interfaces. In normal use, a given version of a
system SHOULD result in consistent protocol and interface selection Transport Services System SHOULD result in consistent protocol and
decisions for the same network conditions given the same set of interface selection decisions for the same network conditions given
Properties. This is intended to provide predictable outcomes to the the same set of Properties. This is intended to provide predictable
application using the API. outcomes to the application using the API.
3.5. Support Monitoring
The Transport Services API increases the layer of abstraction for
applications, and it enables greater automation below the API. Such
increased abstraction comes at the cost of increased complexity when
application programmers, users or system administrators try to
understand why any issues and failures may be happening. Transport
Services systems should therefore offer monitoring functions that
provide relevant debug and diagnostics information. For example,
such monitoring functions could indicate the protocol(s) in use, the
number of open connections per protocol, and any statistics that
these protocols may offer.
4. Transport Services Architecture and Concepts 4. Transport Services Architecture and Concepts
This section and the remainder of this document describe the This section of the document describes the architecture non-
architecture non-normatively. The concepts defined in this document normatively and explains the operation of a Transport Services
are intended primarily for use in the documents and specifications Implementation. The concepts defined in this document are intended
that describe the Transport Services system. This includes the primarily for use in the documents and specifications that describe
architecture, the Transport Services API and the associated Transport the Transport Services System. This includes the architecture, the
Services implementation. While the specific terminology can be used Transport Services API and the associated Transport Services
in some implementations, it is expected that there will remain a Implementation. While the specific terminology can be used in some
variety of terms used by running code. implementations, it is expected that there will remain a variety of
terms used by running code.
The architecture divides the concepts for Transport Services system The architecture divides the concepts for Transport Services System
into two categories: into two categories:
1. API concepts, which are intended to be exposed to applications; 1. API concepts, which are intended to be exposed to applications;
and and
2. System-implementation concepts, which are intended to be 2. System-implementation concepts, which are intended to be
internally used by a Transport Services implementation. internally used by a Transport Services Implementation.
The following diagram summarizes the top-level concepts in the The following diagram summarizes the top-level concepts in a
architecture and how they relate to one another. Transport Services System 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+ |
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| (Candidate Gathering) | +-----------------+ | | (Candidate Gathering) | +-----------------+ |
| | | | | |
| (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 3: Concepts and Relationships in the Transport Services Figure 3: Concepts and Relationships in the Architecture of the
Architecture Transport Services System
The Transport Services Implementation includes the Cached State and The Transport Services Implementation includes the Cached State and
System Policy. System Policy.
The System Policy provides input from an operating system or other The System Policy provides input from an operating system or other
global preferences that can constrain or influence how an global preferences that can constrain or influence how an
implementation will gather Candidate Paths and Protocol Stacks and implementation will gather Candidate Paths and Protocol Stacks and
race the candidates when establishing a Connection. As the details race the candidates when establishing a Connection. As the details
of System Policy configuration and enforcement are largely platform- of System Policy configuration and enforcement are largely platform-
and implementation- dependent, and do not affect application-level and implementation- dependent, and do not affect application-level
interoperability, the Transport Services API interoperability, the Transport Services API
[I-D.ietf-taps-interface] does not specify an interface for reading [I-D.ietf-taps-interface] does not specify an interface for reading
or writing System Policy. or writing System Policy.
The Cached State is the state and history that the implementation The Cached State is the state and history that the Transport Services
keeps for each set of associated endpoints that have previously been Implementation keeps for each set of associated Endpoints that have
used. previously been used. An application ought to explicitly request any
required or desired properties via the Transport Services API.
4.1. Transport Services API Concepts 4.1. Transport Services API Concepts
Fundamentally, a Transport Services API needs to provide connection Fundamentally, a Transport Services API needs to provide Connection
objects (Section 4.1.2) that allow applications to establish objects (Section 4.1.2) that allow applications to establish
communication, and then send and receive data. These could be communication, and then send and receive data. These could be
exposed as handles or referenced objects, depending on the chosen exposed as handles or referenced objects, depending on the chosen
programming language. programming language.
Beyond the connection objects, there are several high-level groups of Beyond the Connection objects, there are several high-level groups of
actions that any Transport Services API needs to provide: actions that any Transport Services API needs to provide:
* Pre-establishment (Section 4.1.3) encompasses the properties that * Pre-establishment (Section 4.1.3) 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. prohibitions, and preferences for its networking operations.
These properties apply to multiple transport protocols, unless These properties apply to multiple transport protocols, unless
otherwise specified. Properties specified during pre- otherwise specified. Properties specified during pre-
establishment can have a large impact on the rest of the establishment can have a large impact on the rest of the
interface: they modify how establishment occurs, they influence interface: they modify how establishment occurs, they influence
the expectations around data transfer, and they determine the set the expectations around data transfer, and they determine the set
of events that will be supported. of events that will be supported.
* Establishment (Section 4.1.4) focuses on the actions that an * Establishment (Section 4.1.4) focuses on the actions that an
application takes on the connection objects to prepare for data application takes on the Connection objects to prepare for data
transfer. transfer.
* Data Transfer (Section 4.1.5) consists of how an application * Data Transfer (Section 4.1.5) consists of how an application
represents the data to be sent and received, the functions represents the data to be sent and received, the functions
required to send and receive that data, and how the application is required to send and receive that data, and how the application is
notified of the status of its data transfer. notified of the status of its data transfer.
* Event Handling (Section 4.1.6) defines categories of notifications * Event Handling (Section 4.1.6) defines categories of notifications
that an application can receive during the lifetime of a that an application can receive during the lifetime of a
Connection. Events also provide opportunities for the application Connection. Events also provide opportunities for the application
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Listen() | : | | : Listen() | : | | :
| : | v : | : | v :
v : | Connection : v : | Connection :
+----------+ : | Ready : +----------+ : | Ready :
| Listener |----------------------+ : | Listener |----------------------+ :
+----------+ Connection Received : +----------+ Connection Received :
: : : :
Figure 4: The lifetime of a Connection object Figure 4: The lifetime of a Connection object
In this diagram, the lifetime of a Connection object is broken into In this diagram, the lifetime of a Connection object is divided into
three phases: pre-establishment, the Established state, and three phases: pre-establishment, the Established state, and
Termination. Termination.
Pre-establishment is based around a Preconnection object, that Pre-establishment is based around a Preconnection object, that
contains various sub-objects that describe the properties and contains various sub-objects that describe the properties and
parameters of desired Connections (Local and Remote Endpoints, parameters of desired Connections (Local and Remote Endpoints,
Transport Properties, and Security Parameters). A Preconnection can Transport Properties, and Security Parameters). A Preconnection can
be used to start listening for inbound connections, in which case a be used to start listening for inbound connections, in which case a
Listener object is created, or can be used to establish a new Listener object is created, or can be used to establish a new
connection directly using Initiate (for outbound connections) or connection directly using Initiate (for outbound connections) or
Rendezvous (for peer-to-peer connections). Rendezvous (for peer-to-peer connections).
Once a Connection is in the Established state, an application can Once a Connection is in the Established state, an application can
send and receive Message objects, and receive state updates. send and receive Message objects, and receive state updates.
Closing or aborting a connection, either locally or from the peer, Closing or aborting a connection, either locally or from the peer,
can terminate a connection. can terminate a connection.
4.1.1. Endpoint Objects 4.1.1. Endpoint Objects
* Endpoint: An endpoint represents an identifier for one side of a An Endpoint Identifier specifies one side of a transport connection.
transport connection. Endpoints can be Local Endpoints or Remote Endpoints can be Local Endpoints or Remote Endpoints, and the
Endpoints, and respectively represent an identity that the Endpoint Identifiers can respectively represent an identity that the
application uses for the source or destination of a connection. application uses for the source or destination of a connection. An
An endpoint can be specified at various levels of abstraction. An Endpoint Identifier can be specified at various levels of
endpoint at a higher level of abstraction (such as a hostname) can abstraction. An Endpoint Identifier at a higher level of abstraction
be resolved to more concrete identities (such as IP addresses). (such as a hostname) can be resolved to more concrete identities
An endpoint may also represent a multicast group, in which case it (such as IP addresses). A Remote Endpoint Identifier can also
selects a multicast transport for communication. represent a multicast group or anycast address. In the case of
multicast, this selects a multicast transport for communication.
* Remote Endpoint: The Remote Endpoint represents the application's * Remote Endpoint Identifier: The Remote Endpoint Identifier
identifier for a peer that can participate in a transport represents the application's identifier for a peer that can
connection; for example, the combination of a DNS name for the participate in a transport connection; for example, the
peer and a service name/port. combination of a DNS name for the peer and a service name/port.
* Local Endpoint: The Local Endpoint represents the application's * Local Endpoint Identifier: The Local Endpoint Identifier
identifier for itself that it uses for transport connections; for represents the application's identifier for itself that it uses
example, a local IP address and port. for transport connections; for example, a local IP address and
port.
4.1.2. Connections and Related Objects 4.1.2. Connections and Related Objects
* Connection: A Connection object represents one or more active * Connection: A Connection object represents one or more active
transport protocol instances that can send and/or receive Messages transport protocol instances that can send and/or receive Messages
between Local and Remote Endpoints. It is an abstraction that between Local and Remote Endpoints. It is an abstraction that
represents the communication. The Connection object holds state represents the communication. The Connection object holds state
pertaining to the underlying transport protocol instances and any pertaining to the underlying transport protocol instances and any
ongoing data transfers. For example, an active Connection can ongoing data transfers. For example, an active Connection can
represent a connection-oriented protocol such as TCP, or can represent a connection-oriented protocol such as TCP, or can
represent a fully-specified 5-tuple for a connectionless protocol represent a fully-specified 5-tuple for a connectionless protocol
such as UDP, where the Connection remains an abstraction at the such as UDP, where the Connection remains an abstraction at the
endpoints. It can also represent a pool of transport protocol endpoints. It can also represent a pool of transport protocol
instances, e.g., a set of TCP and QUIC connections to equivalent instances, e.g., a set of TCP and QUIC connections to equivalent
endpoints, or a stream of a multi-streaming transport protocol endpoints, or a stream of a multi-streaming transport protocol
instance. Connections can be created from a Preconnection or by a instance. Connections can be created from a Preconnection or by a
Listener. Listener.
* Preconnection: A Preconnection object is a representation of a * Preconnection: A Preconnection object is a representation of a
Connection that has not yet been established. It has state that Connection that has not yet been established. It has state that
describes parameters of the Connection: the Local Endpoint from describes parameters of the Connection: the Local Endpoint
which that Connection will be established, the Remote Endpoint Identifier from which that Connection will be established, the
(Section 4.1.3) to which it will connect, and Transport Properties Remote Endpoint Identifier (Section 4.1.3) to which it will
that influence the paths and protocols a Connection will use. A connect, and Transport Properties that influence the paths and
Preconnection can be either fully specified (representing a single protocols a Connection will use. A Preconnection can be either
possible Connection), or it can be partially specified fully specified (representing a single possible Connection), or it
(representing a family of possible Connections). The Local can be partially specified (representing a family of possible
Endpoint (Section 4.1.3) is required for a Preconnection used to Connections). The Local Endpoint (Section 4.1.3) is required for
Listen for incoming Connections, but optional if it is used to a Preconnection used to Listen for incoming Connections, but
Initiate a Connection. The Remote Endpoint is required in a optional if it is used to Initiate a Connection. The Remote
Preconnection that used to Initiate a Connection, but is optional Endpoint Identifier is required in a Preconnection that used to
if it is used to Listen for incoming Connections. The Local Initiate a Connection, but is optional if it is used to Listen for
Endpoint and the Remote Endpoint are both required if a peer-to- incoming Connections. The Local Endpoint Identifier and the
peer Rendezvous is to occur based on the Preconnection. Remote Endpoint Identifier are both required if a peer-to-peer
Rendezvous is to occur based on the Preconnection.
* Transport Properties: Transport Properties allow the application * Transport Properties: Transport Properties allow the application
to express their requirements, prohibitions, and preferences and to express their requirements, prohibitions, and preferences and
configure a Transport Services system. There are three kinds of configure a Transport Services Implementation. There are three
Transport Properties: kinds of Transport Properties:
- Selection Properties (Section 4.1.3): Selection Properties can - Selection Properties (Section 4.1.3): Selection Properties can
only be specified on a Preconnection. only be specified on a Preconnection.
- Connection Properties (Section 4.1.3): Connection Properties - Connection Properties (Section 4.1.3): Connection Properties
can be specified on a Preconnection and changed on the can be specified on a Preconnection and changed on the
Connection. Connection.
- Message Properties (Section 4.1.5): Message Properties can be - Message Properties (Section 4.1.5): Message Properties can be
specified as defaults on a Preconnection or a Connection, and specified as defaults on a Preconnection or a Connection, and
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of properties that influence path selection include the interface of properties that influence path selection include the interface
type (such as a Wi-Fi connection, or a Cellular LTE connection), type (such as a Wi-Fi connection, or a Cellular LTE connection),
requirements around the largest Message that can be sent, or requirements around the largest Message that can be sent, or
preferences for throughput and latency. Examples of properties preferences for throughput and latency. Examples of properties
that influence protocol selection and configuration of transport that influence protocol selection and configuration of transport
protocol features include reliability, multipath support, and fast protocol features include reliability, multipath support, and fast
open support. open support.
* Connection Properties: The Connection Properties are used to * Connection Properties: The Connection Properties are used to
configure protocol-specific options and control per-connection configure protocol-specific options and control per-connection
behavior of a Transport Services implementation; for example, a behavior of a Transport Services Implementation; for example, a
protocol-specific Connection Property can express that if TCP is protocol-specific Connection Property can express that if TCP is
used, the implementation ought to use the User Timeout Option. used, the implementation ought to use the User Timeout Option.
Note that the presence of such a property does not require that a Note that the presence of such a property does not require that a
specific protocol will be used. In general, these properties do specific protocol will be used. In general, these properties do
not explicitly determine the selection of paths or protocols, but not explicitly determine the selection of paths or protocols, but
can be used by an implementation during connection establishment. can be used by an implementation during connection establishment.
Connection Properties are specified on a Preconnection prior to Connection Properties are specified on a Preconnection prior to
Connection establishment, and can be modified on the Connection Connection establishment, and can be modified on the Connection
later. Changes made to Connection Properties after Connection later. Changes made to Connection Properties after Connection
establishment take effect on a best-effort basis. establishment take effect on a best-effort basis.
* Security Parameters: Security Parameters define an application's * Security Parameters: Security Parameters define an application's
requirements for authentication and encryption on a Connection. requirements for authentication and encryption on a Connection.
They are used by Transport Security protocols (such as those They are used by Transport Security protocols (such as those
described in [RFC8922]) to establish secure Connections. Examples described in [RFC8922]) to establish secure Connections. Examples
of parameters that can be set include local identities, private of parameters that can be set include local identities, private
keys, supported cryptographic algorithms, and requirements for keys, supported cryptographic algorithms, and requirements for
validating trust of remote identities. Security Parameters are validating trust of remote identities. Security Parameters are
primarily associated with a Preconnection object, but properties primarily associated with a Preconnection object, but properties
related to identities can be associated directly with endpoints. related to identities can be associated directly with Endpoints.
4.1.4. Establishment Actions 4.1.4. Establishment Actions
* Initiate: The primary action that an application can take to * 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 enable the transmission of Messages. For local or remote state to enable the transmission of Messages. For
some protocols, this will initiate a client-to-server style some protocols, this will initiate a client-to-server style
handshake; for other protocols, this will just establish local handshake; for other protocols, this will just establish local
state (e.g., with connectionless protocols such as UDP). The state (e.g., with connectionless protocols such as UDP). The
process of identifying options for connecting, such as resolution process of identifying options for connecting, such as resolution
of the Remote Endpoint, occurs in response to the Initiate call. of the Remote Endpoint Identifier, occurs in response to the
Initiate call.
* Listen: Enables a Listener to accept incoming connections. The * Listen: Enables a Listener to accept incoming connections. The
Listener will then create Connection objects as incoming Listener will then create Connection objects as incoming
connections are accepted (Section 4.1.6). Listeners by default connections are accepted (Section 4.1.6). Listeners by default
register with multiple paths, protocols, and Local Endpoints, register with multiple paths, protocols, and Local Endpoints,
unless constrained by Selection Properties and/or the specified unless constrained by Selection Properties and/or the specified
Local Endpoint(s). Connections can be accepted on any of the Local Endpoint Identifier(s). Connections can be accepted on any
available paths or endpoints. of the available paths or endpoints.
* Rendezvous: The action of establishing a peer-to-peer connection * 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
connection to a Remote Endpoint while listening for an incoming connection to a Remote Endpoint while listening for an incoming
connection from that endpoint. The process of identifying options connection from that Endpoint. The process of identifying options
for the connection, such as resolution of the Remote Endpoint, for the connection, such as resolution of the Remote Endpoint
occurs in response to the Rendezvous call. As with Listeners, the Identifier(s), occurs in response to the Rendezvous call. As with
set of local paths and endpoints is constrained by Selection Listeners, the set of local paths and endpoints is constrained by
Properties. If successful, the Rendezvous call returns a Selection Properties. If successful, the Rendezvous call
Connection object to represent the established peer-to-peer generates and asynchronously returns a Connection object to
connection. The processes by which connections are initiated represent the established peer-to-peer connection. The processes
during a Rendezvous action will depend on the set of Local and by which connections are initiated during a Rendezvous action will
Remote Endpoints configured on the Preconnection. For example, if depend on the set of Local and Remote Endpoints configured on the
the Local and Remote Endpoints are TCP host candidates, then a TCP Preconnection. For example, if the Local and Remote Endpoints are
simultaneous open [RFC9293] will be performed. However, if the TCP host candidates, then a TCP simultaneous open [RFC9293] might
set of Local Endpoints includes server reflexive candidates, such be performed. However, if the set of Local Endpoints includes
as those provided by STUN (Session Traversal Utilities for NAT) server reflexive candidates, such as those provided by STUN
[RFC5389], a Rendezvous action will race candidates in the style (Session Traversal Utilities for NAT) [RFC5389], a Rendezvous
of the ICE (Interactive Connection Establishment) algorithm action will race candidates in the style of the ICE (Interactive
[RFC8445] to perform NAT binding discovery and initiate a peer-to- Connection Establishment) algorithm [RFC8445] to perform NAT
peer connection. binding discovery and initiate a peer-to-peer connection.
4.1.5. Data Transfer Objects and Actions 4.1.5. Data Transfer Objects and Actions
* Message: A Message object is a unit of data that can be * 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 endpoints
over a transport connection. The bytes within a Message are over a transport connection. The bytes within a Message are
assumed to be ordered. If an application does not care about the assumed to be ordered. If an application does not care about the
order in which a peer receives two distinct spans of bytes, those order in which a peer receives two distinct spans of bytes, those
spans of bytes are considered independent Messages. Messages are spans of bytes are considered independent Messages. Messages are
sent in the payload of IP packet. One packet can carry one or sent in the payload of IP packets. One packet can carry one or
more Messages or parts of a Message. more Messages or parts of a Message.
* Message Properties: Message Properties are used to specify details * Message Properties: Message Properties are used to specify details
about Message transmission. They can be specified directly on about Message transmission. They can be specified directly on
individual Messages, or can be set on a Preconnection or individual Messages, or can be set on a Preconnection or
Connection as defaults. These properties might only apply to how Connection as defaults. These properties might only apply to how
a Message is sent (such as how the transport will treat a Message is sent (such as how the transport will treat
prioritization and reliability), but can also include properties prioritization and reliability), but can also include properties
that specific protocols encode and communicate to the Remote that specific protocols encode and communicate to the Remote
Endpoint. When receiving Messages, Message Properties can contain Endpoint. When receiving Messages, Message Properties can contain
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* Connection Closed: Signals to an application that a given * Connection Closed: Signals to an application that a given
Connection is no longer usable for sending or receiving Messages. Connection is no longer usable for sending or receiving Messages.
The event delivers a reason or error to the application that The event delivers a reason or error to the application that
describes the nature of the termination. describes the nature of the termination.
* Connection Received: Signals to an application that a given * Connection Received: Signals to an application that a given
Listener has received a Connection. Listener has received a Connection.
* Message Received: Delivers received Message content to the * Message Received: Delivers received Message content to the
application, based on a Receive action. This can include an error application, based on a Receive action. To allow an application
if the Receive action cannot be satisfied due to the Connection to limit the occurrence of such events, each call to Receive will
being closed. be paired with a single Receive event. This can include an error
if the Receive action cannot be satisfied, e.g., due to the
Connection being closed.
* Message Sent: Notifies the application of the status of its Send * Message Sent: Notifies the application of the status of its Send
action. This might indicate a failure if the Message cannot be action. This might indicate a failure if the Message cannot be
sent, or an indication that the Message has been processed by the sent, or an indication that the Message has been processed by the
Transport Services system. Transport Services System.
* Path Properties Changed: Notifies the application that a property * Path Properties Changed: Notifies the application that a property
of the Connection has changed that might influence how and where of the Connection has changed that might influence how and where
data is sent and/or received. data is sent and/or received.
4.1.7. Termination Actions 4.1.7. Termination Actions
* Close: The action an application takes on a Connection to indicate * Close: The action an application takes on a Connection to indicate
that it no longer intends to send data, is no longer willing to that it no longer intends to send data, is no longer willing to
receive data, and that the protocol should signal this state to receive data, and that the protocol should signal this state to
the Remote Endpoint if the transport protocol allows this. (Note the Remote Endpoint if the transport protocol allows this. (Note
that this is distinct from the concept of "half-closing" a that this is distinct from the concept of "half-closing" a
bidirectional connection, such as when a FIN is sent in one bidirectional connection, such as when a FIN is sent in one
direction of a TCP connection [RFC9293]. The end of a stream can direction of a TCP connection [RFC9293]. The end of a stream can
also be indicated using Message Properties when sending.) also be indicated using Message Properties when sending.)
* Abort: The action the application takes on a Connection to * Abort: The action the application takes on a Connection to
indicate a Close and also indicate that a Transport Services indicate a Close and also indicate that the Transport Services
system should not attempt to deliver any outstanding data, and System should not attempt to deliver any outstanding data, and
immediately drop the connection. This is intended for immediate, immediately drop the connection. This is intended for immediate,
usually abnormal, termination of a connection. usually abnormal, termination of a connection.
4.1.8. Connection Groups 4.1.8. Connection Groups
A Connection Group is a set of Connections that shares Connection A Connection Group is a set of Connections that shares Connection
Properties and cached state generated by protocols. A Connection Properties and cached state generated by protocols. A Connection
Group represents state for managing Connections within a single Group represents state for managing Connections within a single
application, and does not require end-to-end protocol signaling. For application, and does not require end-to-end protocol signaling. For
multiplexing transport protocols, only Connections within the same transport protocols that support multiplexing, only Connections
Connection Group are allowed to be multiplexed together. within the same Connection Group are allowed to be multiplexed
together.
The API allows a Connection to be created from another Connection. The API allows a Connection to be created from another Connection.
This adds the new Connection to the Connection Group. A change to This adds the new Connection to the Connection Group. A change to
one of the Connection Properties on any Connection in the Connection one of the Connection Properties on any Connection in the Connection
Group automatically changes the Connection Property for all others. Group automatically changes the Connection Property for all others.
All Connections in a Connection Group share the same set of All Connections in a Connection Group share the same set of
Connection Properties except for the Connection Priority. These Connection Properties except for the Connection Priority. These
Connection Properties are said to be entangled. Connection Properties are said to be entangled.
For multiplexing transport protocols, only Connections within the
same Connection Group are allowed to be multiplexed together.
Passive Connections can also be added to a Connection Group, e.g., Passive Connections can also be added to a Connection Group, e.g.,
when a Listener receives a new Connection that is just a new stream when a Listener receives a new Connection that is just a new stream
of an already active multi-streaming protocol instance. of an already active multi-streaming protocol instance.
While Connection Groups are managed by the Transport Services system, While Connection Groups are managed by the Transport Services
an application can define different Connection Contexts for different Implementation, an application can define different Connection
Connection Groups to explicitly control caching boundaries, as Contexts for different Connection Groups to explicitly control
discussed in Section 4.2.3. caching boundaries, as discussed in Section 4.2.3.
4.2. Transport Services Implementation 4.2. Transport Services Implementation
This section defines the key concepts of the Transport Services This section defines the key architectural concepts for the Transport
architecture. Services Implementation within the Transport Services System.
* Transport Service implementation: This consists of all objects and The Transport Services System consists of the Transport Services
protocol instances used internally to a system or library to Implementation and the Transport Services API. The Transport
implement the functionality needed to provide a transport service Services Implementation consists of all objects and protocol
across a network, as required by the abstract interface. instances used internally to a system or library to implement the
functionality needed to provide a transport service across a network,
as required by the abstract interface.
* Transport Services system: This consists of the Transport Service
implementation and the Transport Services API.
* Path: Represents an available set of properties that a Local * Path: Represents an available set of properties that a Local
Endpoint can use to communicate with a Remote Endpoint, such as Endpoint can use to communicate with a Remote Endpoint, such as
routes, addresses, and physical and virtual network interfaces. routes, addresses, and physical and virtual network interfaces.
* Protocol Instance: A single instance of one protocol, including * Protocol Instance: A single instance of one protocol, including
any state necessary to establish connectivity or send and receive any state necessary to establish connectivity or send and receive
Messages. Messages.
* Protocol Stack: A set of Protocol Instances (including relevant * 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
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Specific aspects of the System Policy either apply to all Specific aspects of the System Policy either apply to all
Connections or only certain ones, depending on the runtime context Connections or only certain ones, depending on the runtime context
and properties of the Connection. and properties of the Connection.
* Cached State: The state and history that the implementation keeps * 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, as well as other information. This caching does not imply paths, as well as other information. This caching does not imply
that the same decisions are necessarily made for subsequent that the same decisions are necessarily made for subsequent
connections, rather, it means that cached state is used by the connections, rather, it means that cached state is used by a
Transport Services architecture to inform functions such as Transport Services Implementation to inform functions such as
choosing the candidates to be raced, selecting appropriate choosing the candidates to be raced, selecting appropriate
transport parameters, etc. An application SHOULD NOT rely on transport parameters, etc. An application SHOULD NOT rely on
specific caching behaviour, instead it ought to explicitly request specific caching behaviour, instead it ought to explicitly request
any required or desired properties via the Transport Services API. any required or desired properties via the Transport Services API.
4.2.1. Candidate Gathering 4.2.1. Candidate Gathering
* Candidate Path Selection: Candidate Path Selection represents the * Candidate Path Selection: Candidate Path Selection represents the
act of choosing one or more paths that are available to use based act of choosing one or more paths that are available to use based
on the Selection Properties and any available Local and Remote on the Selection Properties and any available Local and Remote
Endpoints provided by the application, as well as the policies and Endpoint Identifiers provided by the application, as well as the
heuristics of a Transport Services implementation. policies and heuristics of a Transport Services implementation.
* Candidate Protocol Selection: Candidate Protocol Selection * Candidate Protocol Selection: Candidate Protocol Selection
represents the act of choosing one or more sets of Protocol Stacks represents the act of choosing one or more sets of Protocol Stacks
that are available to use based on the Transport Properties that are available to use based on the Transport Properties
provided by the application, and the heuristics or policies within provided by the application, and the heuristics or policies within
the Transport Services implementation. the Transport Services Implementation.
4.2.2. Candidate Racing 4.2.2. Candidate Racing
Connection establishment attempts for a set of candidates may be Connection establishment attempts for a set of candidates may be
performed simultaneously, synchronously, serially, or using some performed simultaneously, synchronously, serially, or using some
combination of all of these. We refer to this process as racing, combination of all of these. We refer to this process as racing,
borrowing terminology from Happy Eyeballs [RFC8305]. borrowing terminology from Happy Eyeballs [RFC8305].
* Protocol Option Racing: Protocol Option Racing is the act of * Protocol Option Racing: Protocol Option Racing is the act of
attempting to establish, or scheduling attempts to establish, attempting to establish, or scheduling attempts to establish,
multiple Protocol Stacks that differ based on the composition of multiple Protocol Stacks that differ based on the composition of
protocols or the options used for protocols. protocols or the options used for protocols.
* Path Racing: Path Racing is the act of attempting to establish, or * 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. Since differ based on a selection from the available Paths. Since
different Paths will have distinct configurations for local different Paths will have distinct configurations (see [RFC7556])
addresses and DNS servers, attempts across different Paths will for local addresses and DNS servers, attempts across different
perform separate DNS resolution steps, which can lead to further Paths will perform separate DNS resolution steps, which can lead
racing of the resolved Remote Endpoints. to further racing of the resolved Remote Endpoint Identifiers.
* Remote Endpoint Racing: Remote Endpoint Racing is the act of * Remote Endpoint Racing: Remote Endpoint Racing is the act of
attempting to establish, or scheduling attempts to establish, attempting to establish, or scheduling attempts to establish,
multiple Protocol Stacks that differ based on the specific multiple Protocol Stacks that differ based on the specific
representation of the Remote Endpoint, such as a particular IP representation of the Remote Endpoint Identifier, such as a
address that was resolved from a DNS hostname. particular IP address that was resolved from a DNS hostname.
4.2.3. Separating Connection Contexts 4.2.3. Separating Connection Contexts
A Transport Services implementation can by default share stored A Transport Services Implementation can by default share stored
properties across Connections within an application, such as cached properties across Connections within an application, such as cached
protocol state, cached path state, and heuristics. This provides protocol state, cached path state, and heuristics. This provides
efficiency and convenience for the application, since the Transport efficiency and convenience for the application, since the Transport
Services system can automatically optimize behavior. Services System can automatically optimize behavior.
The Transport Services API can allow applications to explicitly The Transport Services API can allow applications to explicitly
define Connection Contexts that force separation of Cached State and define Connection Contexts that force separation of Cached State and
Protocol Stacks. For example, a web browser application could use Protocol Stacks. For example, a web browser application could use
Connection Contexts with separate caches when implementing different Connection Contexts with separate caches when implementing different
tabs. Possible reasons to isolate Connections using separate tabs. Possible reasons to isolate Connections using separate
Connection Contexts include: Connection Contexts include:
* Privacy concerns about re-using cached protocol state that can * Privacy concerns about re-using cached protocol state that can
lead to linkability. Sensitive state could include TLS session lead to linkability. Sensitive state could include TLS session
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as for different browser tabs. as for different browser tabs.
* Privacy concerns about allowing Connections to multiplex together, * Privacy concerns about allowing Connections to multiplex together,
which can tell a Remote Endpoint that all of the Connections are which can tell a Remote Endpoint that all of the Connections are
coming from the same application. Using Connection Contexts coming from the same application. Using Connection Contexts
avoids the Connections being multiplexed in a HTTP/2 or QUIC avoids the Connections being multiplexed in a HTTP/2 or QUIC
stream. stream.
5. IANA Considerations 5. IANA Considerations
RFC-EDITOR: Please remove this section before publication.
This document has no actions for IANA. This document has no actions for IANA.
6. Security and Privacy Considerations 6. Security and Privacy Considerations
The Transport Services architecture does not recommend use of The Transport Services System does not recommend use of specific
specific security protocols or algorithms. Its goal is to offer ease security protocols or algorithms. Its goal is to offer ease of use
of use for existing protocols by providing a generic security-related for existing protocols by providing a generic security-related
interface. Each provided interface translates to an existing interface. Each provided interface translates to an existing
protocol-specific interface provided by supported security protocols. protocol-specific interface provided by supported security protocols.
For example, trust verification callbacks are common parts of TLS For example, trust verification callbacks are common parts of TLS
APIs; a Transport Services API exposes similar functionality APIs; a Transport Services API exposes similar functionality
[RFC8922]. [RFC8922].
As described above in Section 3.3, if a Transport Services As described above in Section 3.3, if a Transport Services
implementation races between two different Protocol Stacks, both need Implementation races between two different Protocol Stacks, both need
to use the same security protocols and options. However, a Transport to use the same security protocols and options. However, a Transport
Services implementation can race different security protocols, e.g., Services Implementation can race different security protocols, e.g.,
if the application explicitly specifies that it considers them if the application explicitly specifies that it considers them
equivalent. equivalent.
The application controls whether information from previous racing The application controls whether information from previous racing
attempts, or other information about past communications that was attempts, or other information about past communications that was
cached by the Transport Services system is used during establishment. cached by the Transport Services System is used during establishment.
This allows applications to make tradeoffs between efficiency This allows applications to make tradeoffs between efficiency
(through racing) and privacy (via information that might leak from (through racing) and privacy (via information that might leak from
the cache toward an on-path observer). Some applications have native the cache toward an on-path observer). Some applications have
concepts (e.g. "incognito mode") that align with this functionality. features (e.g. "incognito mode") that align with this functionality.
Applications need to ensure that they use security APIs Applications need to ensure that they use security APIs
appropriately. In cases where applications use an interface to appropriately. In cases where applications use an interface to
provide sensitive keying material, e.g., access to private keys or provide sensitive keying material, e.g., access to private keys or
copies of pre-shared keys (PSKs), key use needs to be validated and copies of pre-shared keys (PSKs), key use needs to be validated and
scoped to the intended protocols and roles. For example, if an scoped to the intended protocols and roles. For example, if an
application provides a certificate to only be used as client application provides a certificate to only be used as client
authentication for outbound TLS and QUIC connections, the Transport authentication for outbound TLS and QUIC connections, the Transport
Services system MUST NOT use this automatically in other contexts Services System MUST NOT use this automatically in other contexts
(such as server authentication for inbound connections, or in other (such as server authentication for inbound connections, or in other
another security protocol handshake that is not equivalent to TLS). another security protocol handshake that is not equivalent to TLS).
A Transport Services system MUST NOT automatically fall back from A Transport Services System MUST NOT automatically fall back from
secure protocols to insecure protocols, or to weaker versions of secure protocols to insecure protocols, or to weaker versions of
secure protocols (see Section 3.3). For example, if an application secure protocols (see Section 3.3). For example, if an application
requests a specific version of TLS, but the desired version of TLS is requests a specific version of TLS, but the desired version of TLS is
not available, its connection will fail. As described in not available, its connection will fail. As described in
Section 3.3, the Transport Services API can allow applications to Section 3.3, the Transport Services API can allow applications to
specify minimum versions that are allowed to be used by the Transport specify minimum versions that are allowed to be used by the Transport
Services system. Services System.
7. Acknowledgements 7. Acknowledgements
This work has received funding from the European Union's Horizon 2020 This work has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreements No. 644334 research and innovation programme under grant agreements No. 644334
(NEAT), No. 688421 (MAMI) and No 815178 (5GENESIS). (NEAT), No. 688421 (MAMI) and No 815178 (5GENESIS).
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 Reese Enghardt, Max Franke, Mirja Kuehlewind, Jonathan Thanks to Reese Enghardt, Max Franke, Mirja Kuehlewind, Jonathan
Lennox, and Michael Welzl for the discussions and feedback that Lennox, and Michael Welzl for the discussions and feedback that
helped shape the architecture described here. Particular thanks is helped shape the architecture of the system described here.
also due to Philipp S. Tiesel and Christopher A. Wood, who were Particular thanks is also due to Philipp S. Tiesel and Christopher
both co-authors of this architecture specification as it progressed A. Wood, who were both co-authors of this specification as it
through the TAPS working group. Thanks as well to Stuart Cheshire, progressed through the TAPS working group. Thanks as well to Stuart
Josh Graessley, David Schinazi, and Eric Kinnear for their Cheshire, Josh Graessley, David Schinazi, and Eric Kinnear for their
implementation and design efforts, including Happy Eyeballs, that implementation and design efforts, including Happy Eyeballs, that
heavily influenced this work. heavily influenced this work.
8. References 8. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
skipping to change at page 30, line 46 skipping to change at page 33, line 19
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>. May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
8.2. Informative References 8.2. Informative References
[I-D.ietf-taps-impl] [I-D.ietf-taps-impl]
Brunstrom, A., Pauly, T., Enghardt, R., Tiesel, P. S., and Brunstrom, A., Pauly, T., Enghardt, R., Tiesel, P. S., and
M. Welzl, "Implementing Interfaces to Transport Services", M. Welzl, "Implementing Interfaces to Transport Services",
Work in Progress, Internet-Draft, draft-ietf-taps-impl-15, Work in Progress, Internet-Draft, draft-ietf-taps-impl-16,
9 March 2023, <https://datatracker.ietf.org/doc/html/ 5 June 2023, <https://datatracker.ietf.org/doc/html/draft-
draft-ietf-taps-impl-15>. ietf-taps-impl-16>.
[I-D.ietf-taps-interface] [I-D.ietf-taps-interface]
Trammell, B., Welzl, M., Enghardt, R., Fairhurst, G., Trammell, B., Welzl, M., Enghardt, R., Fairhurst, G.,
Kühlewind, M., Perkins, C., Tiesel, P. S., and T. Pauly, Kühlewind, M., Perkins, C., Tiesel, P. S., and T. Pauly,
"An Abstract Application Layer Interface to Transport "An Abstract Application Layer Interface to Transport
Services", Work in Progress, Internet-Draft, draft-ietf- Services", Work in Progress, Internet-Draft, draft-ietf-
taps-interface-20, 29 March 2023, taps-interface-22, 6 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-taps- <https://datatracker.ietf.org/doc/html/draft-ietf-taps-
interface-20>. interface-22>.
[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",
2008. 2008.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC 5389, "Session Traversal Utilities for NAT (STUN)", RFC 5389,
DOI 10.17487/RFC5389, October 2008, DOI 10.17487/RFC5389, October 2008,
<https://www.rfc-editor.org/rfc/rfc5389>. <https://www.rfc-editor.org/rfc/rfc5389>.
[RFC5482] Eggert, L. and F. Gont, "TCP User Timeout Option", [RFC5482] Eggert, L. and F. Gont, "TCP User Timeout Option",
RFC 5482, DOI 10.17487/RFC5482, March 2009, RFC 5482, DOI 10.17487/RFC5482, March 2009,
<https://www.rfc-editor.org/rfc/rfc5482>. <https://www.rfc-editor.org/rfc/rfc5482>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011, DOI 10.17487/RFC6265, April 2011,
<https://www.rfc-editor.org/rfc/rfc6265>. <https://www.rfc-editor.org/rfc/rfc6265>.
[RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain
Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
<https://www.rfc-editor.org/rfc/rfc7556>.
[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/rfc/rfc8095>. <https://www.rfc-editor.org/rfc/rfc8095>.
[RFC8170] Thaler, D., Ed., "Planning for Protocol Adoption and [RFC8170] Thaler, D., Ed., "Planning for Protocol Adoption and
Subsequent Transitions", RFC 8170, DOI 10.17487/RFC8170, Subsequent Transitions", RFC 8170, DOI 10.17487/RFC8170,
May 2017, <https://www.rfc-editor.org/rfc/rfc8170>. May 2017, <https://www.rfc-editor.org/rfc/rfc8170>.
skipping to change at page 32, line 25 skipping to change at page 34, line 45
[RFC8922] Enghardt, T., Pauly, T., Perkins, C., Rose, K., and C. [RFC8922] Enghardt, T., Pauly, T., Perkins, C., Rose, K., and C.
Wood, "A Survey of the Interaction between Security Wood, "A Survey of the Interaction between Security
Protocols and Transport Services", RFC 8922, Protocols and Transport Services", RFC 8922,
DOI 10.17487/RFC8922, October 2020, DOI 10.17487/RFC8922, October 2020,
<https://www.rfc-editor.org/rfc/rfc8922>. <https://www.rfc-editor.org/rfc/rfc8922>.
[RFC8923] Welzl, M. and S. Gjessing, "A Minimal Set of Transport [RFC8923] Welzl, M. and S. Gjessing, "A Minimal Set of Transport
Services for End Systems", RFC 8923, DOI 10.17487/RFC8923, Services for End Systems", RFC 8923, DOI 10.17487/RFC8923,
October 2020, <https://www.rfc-editor.org/rfc/rfc8923>. October 2020, <https://www.rfc-editor.org/rfc/rfc8923>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>.
[RFC9112] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke, [RFC9112] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112, Ed., "HTTP/1.1", STD 99, RFC 9112, DOI 10.17487/RFC9112,
June 2022, <https://www.rfc-editor.org/rfc/rfc9112>. June 2022, <https://www.rfc-editor.org/rfc/rfc9112>.
[RFC9113] Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113, [RFC9113] Thomson, M., Ed. and C. Benfield, Ed., "HTTP/2", RFC 9113,
DOI 10.17487/RFC9113, June 2022, DOI 10.17487/RFC9113, June 2022,
<https://www.rfc-editor.org/rfc/rfc9113>. <https://www.rfc-editor.org/rfc/rfc9113>.
[RFC9293] Eddy, W., Ed., "Transmission Control Protocol (TCP)", [RFC9293] Eddy, W., Ed., "Transmission Control Protocol (TCP)",
STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022, STD 7, RFC 9293, DOI 10.17487/RFC9293, August 2022,
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