rfc9621.original   rfc9621.txt 
TAPS Working Group T. Pauly, Ed. Internet Engineering Task Force (IETF) T. Pauly, Ed.
Internet-Draft Apple Inc. Request for Comments: 9621 Apple Inc.
Intended status: Standards Track B. Trammell, Ed. Category: Standards Track B. Trammell, Ed.
Expires: 12 May 2024 Google Switzerland GmbH ISSN: 2070-1721 Google Switzerland GmbH
A. Brunstrom A. Brunstrom
Karlstad University Karlstad University
G. Fairhurst G. Fairhurst
University of Aberdeen University of Aberdeen
C. Perkins C. S. Perkins
University of Glasgow University of Glasgow
9 November 2023 November 2024
Architecture and Requirements for Transport Services Architecture and Requirements for Transport Services
draft-ietf-taps-arch-19
Abstract Abstract
This document describes an architecture for exposing transport This document describes an architecture that exposes transport
protocol features to applications for network communication. This protocol features to applications for network communication. The
system exposes transport protocol features to applications for Transport Services Application Programming Interface (API) is based
network communication. The Transport Services Application on an asynchronous, event-driven interaction pattern. This API uses
Programming Interface (API) is based on an asynchronous, event-driven messages for representing data transfer to applications and describes
interaction pattern. This API uses messages for representing data how a Transport Services Implementation can use multiple IP
transfer to applications, and describes how a Transport Services addresses, multiple protocols, and multiple paths and can provide
Implementation can use multiple IP addresses, multiple protocols, and multiple application streams. This document provides the
multiple paths, and provide multiple application streams. This architecture and requirements. It defines common terminology and
document provides the architecture and requirements. It defines concepts to be used in definitions of a Transport Services API and a
common terminology and concepts to be used in definitions of 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 is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 12 May 2024. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9621.
Copyright Notice Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction
1.1. Background . . . . . . . . . . . . . . . . . . . . . . . 4 1.1. Background
1.2. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Overview
1.3. Specification of Requirements . . . . . . . . . . . . . . 5 1.3. Specification of Requirements
1.4. Glossary of Key Terms . . . . . . . . . . . . . . . . . . 5 1.4. Glossary of Key Terms
2. API Model . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2. API Model
2.1. Event-Driven API . . . . . . . . . . . . . . . . . . . . 10 2.1. Event-Driven API
2.2. Data Transfer Using Messages . . . . . . . . . . . . . . 11 2.2. Data Transfer Using Messages
2.3. Flexible Implementation . . . . . . . . . . . . . . . . . 12 2.3. Flexible Implementation
2.4. Coexistence . . . . . . . . . . . . . . . . . . . . . . . 13 2.4. Coexistence
3. API and Implementation Requirements . . . . . . . . . . . . . 13 3. API and Implementation Requirements
3.1. Provide Common APIs for Common Features . . . . . . . . . 14 3.1. Provide Common APIs for Common Features
3.2. Allow Access to Specialized Features . . . . . . . . . . 15 3.2. Allow Access to Specialized Features
3.3. Select Between Equivalent Protocol Stacks . . . . . . . . 16 3.3. Select Between Equivalent Protocol Stacks
3.4. Maintain Interoperability . . . . . . . . . . . . . . . . 17 3.4. Maintain Interoperability
3.5. Support Monitoring . . . . . . . . . . . . . . . . . . . 17 3.5. Support Monitoring
4. Transport Services Architecture and Concepts . . . . . . . . 18 4. Transport Services Architecture and Concepts
4.1. Transport Services API Concepts . . . . . . . . . . . . . 20 4.1. Transport Services API Concepts
4.1.1. Endpoint Objects . . . . . . . . . . . . . . . . . . 22 4.1.1. Endpoint Objects
4.1.2. Connections and Related Objects . . . . . . . . . . . 22 4.1.2. Connections and Related Objects
4.1.3. Pre-establishment . . . . . . . . . . . . . . . . . . 24 4.1.3. Preestablishment
4.1.4. Establishment Actions . . . . . . . . . . . . . . . . 24 4.1.4. Establishment Actions
4.1.5. Data Transfer Objects and Actions . . . . . . . . . . 25 4.1.5. Data Transfer Objects and Actions
4.1.6. Event Handling . . . . . . . . . . . . . . . . . . . 26 4.1.6. Event Handling
4.1.7. Termination Actions . . . . . . . . . . . . . . . . . 27 4.1.7. Termination Actions
4.1.8. Connection Groups . . . . . . . . . . . . . . . . . . 28 4.1.8. Connection Groups
4.2. Transport Services Implementation . . . . . . . . . . . . 28 4.2. Transport Services Implementation
4.2.1. Candidate Gathering . . . . . . . . . . . . . . . . . 30 4.2.1. Candidate Gathering
4.2.2. Candidate Racing . . . . . . . . . . . . . . . . . . 30 4.2.2. Candidate Racing
4.2.3. Separating Connection Contexts . . . . . . . . . . . 30 4.2.3. Separating Connection Contexts
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31 5. IANA Considerations
6. Security and Privacy Considerations . . . . . . . . . . . . . 31 6. Security and Privacy Considerations
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 32 7. References
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 32 7.1. Normative References
8.1. Normative References . . . . . . . . . . . . . . . . . . 32 7.2. Informative References
8.2. Informative References . . . . . . . . . . . . . . . . . 33 Acknowledgements
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35 Authors' Addresses
1. Introduction 1. Introduction
Many application programming interfaces (APIs) to provide transport Many Application Programming Interfaces (APIs) to provide transport
interfaces to networks have been deployed, perhaps the most widely interfaces to networks have been deployed, perhaps the most widely
known and imitated being the BSD Socket [POSIX] interface (Socket known and imitated being the Socket interface (Socket API) [POSIX].
API). The naming of objects and functions across these APIs is not The naming of objects and functions across these APIs is not
consistent and varies depending on the protocol being used. For consistent and varies, depending on the protocol being used. For
example, sending and receiving streams of data is conceptually the example, the concept of sending and receiving streams of data is the
same for both an unencrypted Transmission Control Protocol (TCP) same for both an unencrypted Transmission Control Protocol (TCP)
stream and operating on an encrypted Transport Layer Security (TLS) stream and operating on an encrypted Transport Layer Security (TLS)
[RFC8446] stream over TCP, but applications cannot use the same stream [RFC8446] over TCP, but applications cannot use the same
socket send() and recv() calls on top of both kinds of connections. socket send() and recv() calls on top of both kinds of connections.
Similarly, terminology for the implementation of transport protocols Similarly, terminology for the implementation of transport protocols
varies based on the context of the protocols themselves: terms such varies based on the context of the protocols themselves: terms such
as "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 System architecture is to provide The goal of the Transport Services System architecture is to provide
a flexible and reusable system with a common interface for transport a flexible and reusable system with a common interface for transport
protocols. An application uses the Transport Services System through protocols. An application uses the Transport Services System through
an abstract Connection (we use capitalization to distinguish these an abstract Connection (we use capitalization to distinguish these
from the underlying connections of, e.g., TCP). This provides from the underlying connections of, for example, TCP). This provides
flexible connection establishment allowing an application to request flexible connection establishment allowing an application to request
or require a set of properties. or require a set of properties.
As applications adopt this interface, they will benefit from a wide As applications adopt this interface, they will benefit from a wide
set of transport features that can evolve over time, and ensure that set of transport features that can evolve over time and will ensure
the system providing the interface can optimize its behavior based on that the system providing the interface can optimize its behavior
the application requirements and network conditions, without based on the application requirements and network conditions, without
requiring changes to the applications. This flexibility enables requiring changes to the applications. This flexibility enables
faster deployment of new features and protocols. faster deployment of new features and protocols.
This architecture can also support applications by offering racing 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). Racing selects one or application separately (see Section 4.2.2). Racing selects one or
more candidates each with equivalent protocol stacks that are used to more candidates, each with equivalent Protocol Stacks that are used
identify an optimal combination of transport protocol instance such to identify an optimal combination of a transport protocol instance
as TCP, UDP, or another transport, together with configuration of such as TCP, UDP, or another transport, together with configuration
parameters and interfaces. A Connection represents an object that, of parameters and interfaces. A Connection represents an object
once established, can be used to send and receive messages. A that, once established, can be used to send and receive messages. A
Connection can also be created from another Connection, by cloning, Connection can also be created from another Connection, by cloning,
and then forms a part of a Connection Group whose Connections share and then forms a part of a Connection Group whose Connections share
properties. 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 [RFC9622] and implementation guidelines
guidelines [I-D.ietf-taps-impl]. Although following the Transport [RFC9623]. Although following the Transport Services architecture
Services architecture does not require all APIs and implementations does not require all APIs and implementations to be identical, a
to be identical, a common minimal set of features represented in a common minimal set of features represented in a consistent fashion
consistent fashion will enable applications to be easily ported from will enable applications to be easily ported from one implementation
one implementation of the Transport Services System to another. of the Transport Services System to another.
1.1. Background 1.1. Background
The architecture of the Transport Services System is based on the The architecture of the Transport Services System is based on the
survey of services provided by IETF transport protocols and survey of services provided by IETF transport protocols and
congestion control mechanisms [RFC8095], and the distilled minimal congestion control mechanisms [RFC8095] and the distilled minimal set
set of the features offered by transport protocols [RFC8923]. These of the features offered by transport protocols [RFC8923]. These
documents identified common features and patterns across all documents identified common features and patterns across all
transport protocols developed thus far in the IETF. transport protocols developed thus far in the IETF.
Since transport security is an increasingly relevant aspect of using Since transport security is an increasingly relevant aspect of using
transport protocols on the Internet, this document also considers the transport protocols on the Internet, this document also considers the
impact of transport security protocols on the feature-set exposed by impact of transport security protocols on the feature set exposed 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 (1) require application interaction and guidance (referred to
that document as Functional or Optimizing Features), or else can be in that document as Functional or Optimizing Features) or (2) can be
handled automatically by an implementation of the Transport Services handled automatically by an implementation of the Transport Services
System (referred to as Automatable Features). Among the identified System (referred to as Automatable Features). Among the identified
Functional and Optimizing Features, some are common across all or Functional and Optimizing Features, some are common across all or
nearly all transport protocols, while others present features that, nearly all transport protocols, while others present features that,
if specified, would only be useful with a subset of protocols, but if specified, would only be useful with a subset of protocols, but
would not harm the functionality of other protocols. For example, would not harm the functionality of other protocols. For example,
some protocols can deliver messages faster for applications that do some protocols can deliver messages more quickly for applications
not require messages to arrive in the order in which they were sent. that do not require messages to arrive in the order in which they
This functionality needs to be explicitly allowed by the application, were sent. This functionality needs to be explicitly allowed by the
since reordering messages would be undesirable in many cases. application, since reordering messages would be undesirable in many
cases.
1.2. Overview 1.2. Overview
This document describes the Transport Services System in three The following sections describe the Transport Services System:
sections:
* Section 2 describes how the Transport Services API model differs * Section 2 describes how the Transport Services API model differs
from that of traditional socket-based APIs. Specifically, it from that of traditional socket-based APIs. Specifically, it
offers asynchronous event-driven interaction, the use of messages offers asynchronous event-driven interaction, the use of messages
for data transfer, and the flexibility to use different transport for data transfer, and the flexibility to use different transport
protocols and paths without requiring major changes to the protocols and paths without requiring major 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 the Transport Services Implementation and * Section 4 presents the Transport Services Implementation and
defines the concepts that are used by the API defines the concepts that are used by the API [RFC9622] and
[I-D.ietf-taps-interface] and described in the implementation described in the implementation guidelines [RFC9623]. This
guidelines [I-D.ietf-taps-impl]. This introduces the introduces the Preconnection, which allows applications to
Preconnection, which allows applications to configure Connection configure Connection Properties.
Properties.
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
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 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 defined later 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
end delivery of data across the network [RFC8095]. delivery of data across the network [RFC8095].
* Cached State: The state and history that the Transport Services Cached State: The state and history that the Transport Services
Implementation keeps for each set of the associated Endpoints that Implementation keeps for each set of the associated Endpoints that
have been used 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
an application for a Connection during racing. 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. that 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 Context: A set of stored properties across Connections, Connection Context: A set of stored properties across Connections,
such as cached protocol state, cached path state, and heuristics, such as cached protocol state, cached path state, and heuristics,
which can include one or more Connection Groups. which can include one or more Connection Groups.
* Connection Group: A set of Connections that share properties and 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 entity that communicates with one or more other Endpoint: An entity that communicates with one or more other
endpoints using a transport protocol. endpoints using a transport protocol.
* Endpoint Identifier: An identifier that specifies one side of a Endpoint Identifier: An identifier that specifies one side of a
Connection (local or remote), such as a hostname or URL. 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: The local Endpoint. Local Endpoint: The local Endpoint.
* Local Endpoint Identifier: A representation of the application's Local Endpoint Identifier: A representation of the application's
identifier for itself that it uses for a Connection. 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 for prohibiting, avoiding, ignoring,
require a specific Transport Feature. preferring, or requiring 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
any state necessary to establish connectivity or send and receive 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
based on the Selection and Connection Properties communicated by on the Selection and Connection Properties communicated by the
the application, along with any Security Parameters. application, along with any Security Parameters.
* Remote Endpoint: The peer that a local Endpoint can communicate Remote Endpoint: The peer that a local Endpoint can communicate with
with when a Connection is established. when a Connection is established.
* Remote Endpoint Identifier: A representation of the application's Remote Endpoint Identifier: A representation of the application's
identifier for a peer that can participate in establishing a identifier for a peer that can participate in establishing a
Connection. 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 Selection Property: A Transport Property that can be set to
influence the selection of paths between the Local and Remote
Endpoints.
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
destination port number [RFC8303]. destination port number [RFC8303].
* System Policy: The input from an operating system or other global System Policy: The input from an operating system or other global
preferences that can constrain or influence how an implementation preferences that can constrain or influence how an implementation
will gather Candidate Paths and Protocol Stacks and race the will gather Candidate Paths and Protocol Stacks and race the
candidates during establishment of a Connection. candidates during establishment of a Connection.
* Selection Property: A Transport Property that can be set to Transport Feature: A specific end-to-end feature that the transport
influence the selection of paths between the Local and Remote layer provides to an application.
Endpoints.
* Transport Feature: A specific end-to-end feature that the
transport layer provides to an application.
* Transport Property: A property that expresses requirements, Transport Property: A property of a transport protocol and the
prohibitions and preferences [RFC8095]. services it provides [RFC8095].
* Transport Service: A set of transport features, without an Transport Service: A set of transport features, not associated with
association to any given framing protocol, that provides a any given framing protocol, that provides a complete service to an
complete service to an application. application.
* Transport Services Implementation: This consists of all objects Transport Services Implementation: All objects and protocol
and protocol instances used internally to a system or library to instances used internally to a system or library to implement the
implement the functionality needed to provide a transport service functionality needed to provide a transport service across a
across a network, as required by the abstract interface. network, as required by the abstract interface.
* Transport Services System: The Transport Services Implementation Transport Services System: The Transport Services Implementation and
and the Transport Services API. the Transport Services API.
2. API Model 2. API Model
The traditional model of using sockets can be represented as follows The traditional model of using sockets can be represented as follows
(see figure 1): (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 DNS stub resolver. performed by a system-provided DNS stub resolver.
+-----------------------------------------------------+ +-----------------------------------------------------+
| Application | | Application |
+-----------------------------------------------------+ +-----------------------------------------------------+
| | | | | |
+------------+ +------------+ +--------------+ +------------+ +------------+ +--------------+
| DNS 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 architecture of the Transport Services System is an evolution of The architecture of the Transport Services System is an evolution of
this general model of interaction. It both modernizes the API this general model of interaction. It both modernizes the API
presented to applications by the transport layer and enriches the presented to applications by the transport layer and enriches the
capabilities of the Transport Services Implementation below this API. capabilities of the Transport Services Implementation below this API.
The Transport Services API [RFC9622] defines the interface for an
application to create Connections and transfer data. It combines
interfaces for multiple interaction patterns into a unified whole
(see Figure 2). This offers generic functions and also the protocol-
specific mappings for TCP, UDP, UDP-Lite, and other protocol layers.
These mappings are extensible. Future documents could define similar
mappings for new layers and for other transport protocols, such as
QUIC [RFC9000].
+-----------------------------------------------------+ +-----------------------------------------------------+
| Application | | Application |
+-----------------------------------------------------+ +-----------------------------------------------------+
| |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Transport Services API | | Transport Services API |
+-----------------------------------------------------+ +-----------------------------------------------------+
| |
+-----------------------------------------------------+ +-----------------------------------------------------+
| Transport Services Implementation | | Transport Services Implementation |
| (Using: DNS, UDP, TCP, SCTP, DCCP, TLS, QUIC, etc) | | (Using DNS, UDP, TCP, SCTP, DCCP, TLS, QUIC, etc.) |
+-----------------------------------------------------+ +-----------------------------------------------------+
| |
+-----------------------------------------------------+ +-----------------------------------------------------+
| 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 By combining name resolution with connection establishment and data
interface for an application to create Connections and transfer data. transfer in a single API, it allows for more flexible implementations
It combines interfaces for multiple interaction patterns into a to provide path and transport protocol agility on the application's
unified whole (see figure 2). This offers generic functions and also behalf.
the protocol-specific mappings for TCP, UDP, UDP-Lite, and other
protocol layers. These mapping are extensible. Future documents
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] is the The Transport Services Implementation [RFC9623] is the component of
component of the Transport Services System that implements the the Transport Services System that implements the transport-layer
transport layer protocols and other functions needed to send and protocols and other functions needed to send and receive data. It is
receive data. It is responsible for mapping the API to a specific responsible for mapping the API to a specific available transport
available transport Protocol Stack and managing the available network Protocol Stack and managing the available network interfaces and
interfaces and paths. paths.
There are key differences between the architecture of the Transport There are key differences between the architecture of the Transport
Services System and the architecture of the Socket API: the API of Services System and the architecture of the Socket API. The API of
the Transport Services System is asynchronous and event-driven; it the Transport Services System:
uses messages for representing data transfer to applications; and it
describes how a Transport Services Implementation can resolve * is asynchronous and driven by events;
Endpoint Identifiers to use multiple IP addresses, multiple
protocols, multiple paths, and provide multiple application streams. * uses messages for representing data transfer to applications;
* describes how a Transport Services Implementation can resolve
Endpoint Identifiers to use multiple IP addresses, multiple
protocols, and multiple paths and to 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 can use a try-and-fail an asynchronous interface using the Socket API can use a try-and-fail
model: If the application wants to read, but data has not yet been model: if the application wants to read but data has not yet been
received from the peer, the call to read will fail. The application received from the peer, the call to read will fail. The application
then waits and can try again later. then waits and can try again later.
In contrast to the Socket API, all interactions using the Transport In contrast to the Socket API, all interactions using the Transport
Services API are 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), which models this around an event-driven model (see Section 4.1.6), which models this
asynchronous interaction. Other forms of asynchronous communication asynchronous interaction. Other forms of asynchronous communication
could also be available to applications, depending on the platform could also be available to applications, depending on the platform
implementing the interface. implementing the interface.
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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.
Separate from events, callbacks are also provided for asynchronous Separate from events, callbacks are also provided for asynchronous
interactions with the Transport Services API that are not directly interactions with the Transport Services API that are not directly
related to events on the network or network interfaces. related to events on the network or network interfaces.
2.2. Data Transfer Using Messages 2.2. Data Transfer Using Messages
The Socket API provides a message interface for datagram protocols The Socket API provides a message interface for datagram protocols
like UDP, but provides an unstructured stream abstraction for TCP. like UDP but provides an unstructured stream abstraction for TCP.
While TCP has the ability to send and receive data as a byte-stream, While TCP has the ability to send and receive data as a byte-stream,
most applications need to interpret structure within this byte- most applications need to interpret structure within this byte-
stream. For example, HTTP/1.1 uses character delimiters to segment stream. For example, HTTP/1.1 uses character delimiters to segment
messages over a byte-stream [RFC9112]; TLS record headers carry a messages over a byte-stream [RFC9112]; TLS record headers carry a
version, content type, and length [RFC8446]; and HTTP/2 uses frames version, content type, and length [RFC8446]; and HTTP/2 uses frames
to segment its headers and bodies [RFC9113]. to segment its headers and bodies [RFC9113].
The Transport Services API represents data as messages, so that it The Transport Services API represents data as messages, so that it
more closely matches the way applications use the network. A more closely matches the way applications use the network. A
message-based abstraction provides many benefits, such as: message-based abstraction provides many benefits, such as:
skipping to change at page 12, line 5 skipping to change at line 520
that care about timing; that care about timing;
* the ability to control reliability, which messages to retransmit * the ability to control reliability, which messages to retransmit
when there is packet loss, and how best to make use of the data when there is packet loss, and how best to make use of the data
that arrived; that arrived;
* 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 backward-
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 inherently 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 (IP source connecting to a single address over a single interface (IP source
address). It also presents a single stream to the application. address). It also presents a single stream to the application.
Software layers built upon this API often propagate this limitation Software layers built upon this API often propagate this limitation
of a single-address single-stream model. The Transport Services of a single-address single-stream model. The Transport Services
architecture is designed: architecture is designed to:
* to handle multiple candidate endpoints, protocols, and paths; * handle multiple candidate endpoints, protocols, and paths;
* to support candidate protocol racing to select the most optimal * support candidate protocol racing to select the most optimal stack
stack in each situation; in each situation;
* to support multipath and multistreaming protocols; * support multipath and multistreaming protocols;
* to provide state caching and application control over it. * 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 Sections 4.2.1 and 4.2.2). This requires
requires applications to specify identifiers for the Local and Remote applications to specify identifiers for the Local and Remote Endpoint
Endpoint that are higher-level than IP addresses, such as a hostname that are at a higher level than IP addresses, such as a hostname or
or URL, which are used by a Transport Services Implementation for URL. These identifiers are used by a Transport Services
resolution, path selection, and racing. An implementation can Implementation for resolution, path selection, and racing. An
further implement fallback mechanisms if connection establishment of implementation can further implement fallback mechanisms if
one protocol fails or performance is detected to be unsatisfactory. connection establishment for one protocol fails or performance is
determined 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) is 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 trade-offs 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
While the architecture of the Transport Services System is designed While the architecture of the Transport Services System is designed
as an 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, coexistence has been entirely on a system or platform; indeed, coexistence has been
recommended for incremental deployability [RFC8170]. The recommended for incremental deployability [RFC8170]. The
architecture is therefore designed such that it can run alongside architecture is therefore designed such that it can run alongside
(or, indeed, on top of) an existing Socket API implementation; only (or, indeed, on top of) an existing Socket API implementation; only
applications built to the Transport Services API are managed by the applications built on the Transport Services API are managed by the
system's Transport Services Implementation. system's Transport Services Implementation.
3. API and Implementation Requirements 3. API and Implementation Requirements
One goal of the architecture is to redefine the interface between One goal of the architecture is to redefine the interface between
applications and transports in a way that allows the transport layer applications and transports in a way that allows the transport layer
to evolve and improve without fundamentally changing the contract to evolve and improve without fundamentally changing the contract
with the application. This requires a careful consideration of how with the application. This requires careful consideration of how to
to expose the capabilities of protocols. The architecture also expose the capabilities of protocols. The architecture also
encompasses system policies that can influence and inform how encompasses system policies that can influence and 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:
protocols and protocol features; it can use these protocols across
multiple paths that could have different performance and functional * provide access to transport protocols and protocol features;
characteristics; and it can communicate with different remote systems
to optimize performance, robustness to failure, or some other metric. * use these protocols across multiple paths that could have
different performance and functional characteristics;
* communicate with different remote systems 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 the Transport Services Implementation to provide
functionality without causing incompatibility or introducing security this functionality without causing incompatibility or introducing
vulnerabilities. security 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
expanded in the future, the Transport Services API ought to be expanded in the future, the Transport Services API ought to be
extended to match. extended to match.
An application can specify constraints and preferences for the An application can specify constraints and preferences for the
protocols, features, and network interfaces it will use via protocols, features, and network interfaces it will use via
Properties. Properties are used by an application to declare its Properties. Properties are used by an application to declare its
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 the following:
Protocol Stacks can be used and are preferred by the application;
Connection Properties, which inform decisions made during connection
establishment and fine-tune the established connection; and Message
Properties, set on individual Messages.
It is RECOMMENDED that the Transport Services API offers properties * Selection Properties, which specify which paths and Protocol
Stacks can be used and are preferred by the application;
* Connection Properties, which inform decisions made during
connection establishment and fine-tune the established connection;
and
* Message Properties, which can be set on individual Messages.
It is RECOMMENDED that the Transport Services API offer properties
that are common to multiple transport protocols. This enables a that are common to multiple transport protocols. This enables a
Transport Services System to appropriately select between protocols Transport Services System to appropriately select between protocols
that offer equivalent features. Similarly, it is RECOMMENDED that that offer equivalent features. Similarly, it is RECOMMENDED that
the Properties offered by the Transport Services API are applicable the Properties offered by the Transport Services API be applicable to
to a variety of network layer interfaces and paths, which permits a variety of network-layer interfaces and paths, to permit racing of
racing of different network paths without affecting the applications different network paths without affecting the applications using the
using the API. Each is expected to have a default value. API. Each is expected to have a default value.
It is RECOMMENDED that the default values for Properties are selected It is RECOMMENDED that the default values for Properties be 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 need to be designed to Applications using the Transport Services API need to be designed to
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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 Some specialized features 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
if an application is using TCP, it could require control over the an application is using TCP, it could require control over the User
User Timeout Option for TCP [RFC5482]; these options would not take Timeout Option for TCP [RFC5482]. Such features 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 for using the User Timeout
communication would not fail when a protocol such as UDP is selected. Option, communication would not fail when a protocol such as UDP is
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 preestablishment 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 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 to use, and select
multiple Protocol Stacks based on the Selection and Connection between, multiple Protocol Stacks based on the Selection and
Properties communicated by the application, along with any Security Connection Properties communicated by the application, along with any
Parameters. The implementation can only attempt to use multiple Security Parameters. The implementation can only attempt to use
Protocol Stacks when they are "equivalent", which means that the multiple Protocol Stacks when they are "equivalent", which means that
stacks can provide the same Transport Properties and interface the 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
application is not equivalent to a Protocol Stack that runs TCP as application is not equivalent to a Protocol Stack that runs TCP as
the top-level interface. A UDP stack would allow an application the top-level interface. A UDP stack would allow an application
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.
A Transport Services Implementation can race different security A Transport Services Implementation can race different security
protocols, e.g., if the System Policy is explicitly configured to protocols, e.g., if the System Policy is explicitly configured to
consider them equivalent. A Transport Services implementation SHOULD consider them equivalent. A Transport Services Implementation SHOULD
only race Protocol Stacks where the transport security protocols only race Protocol Stacks where the transport security protocols
within the stacks are identical. To ensure that security protocols within the stacks are identical. To ensure that security protocols
are not incorrectly swapped, a Transport Services Implementation MUST are not incorrectly swapped, a Transport Services Implementation MUST
only select Protocol Stacks that meet application requirements only select Protocol Stacks that meet application requirements
([RFC8922]). A Transport Services Implementation MUST NOT [RFC8922]. A Transport Services Implementation MUST NOT
automatically fall back from secure protocols to insecure protocols, automatically fall back from secure protocols to insecure protocols
or to weaker versions of secure protocols. A Transport Services or fall back to weaker versions of secure protocols. A Transport
Implementation MAY allow applications to explicitly specify which Services Implementation MAY allow applications to explicitly specify
versions of a protocol ought to be permitted, e.g., to allow a 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. minimum version of TLS 1.2 if TLS 1.3 is not available.
A Transport Services Implementation MAY specify security properties A Transport Services Implementation MAY specify security properties
relating to how the system operates (e.g., requirements, relating to how the system operates (e.g., requirements,
prohibitions, and preferences for the use of DNS Security Extensions prohibitions, and preferences for the use of DNS Security Extensions
(DNSSEC) or DNS over HTTPS (DoH)). (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 implementation of [RFC9622] nor the guidelines for implementation of the Transport
the Transport Service System [I-D.ietf-taps-impl] define new Services System [RFC9623] define new protocols or protocol
protocols or protocol capabilities that affect what is communicated capabilities that affect what is communicated across the network. A
across the network. A Transport Services System MUST NOT require Transport Services System MUST NOT require that a peer on the other
that a peer on the other side of a connection uses the same API or side of a connection use the same API or implementation. A Transport
implementation. A Transport Services Implementation acting as a Services Implementation acting as a connection initiator is able to
connection initiator is able to communicate with any existing communicate with any existing Endpoint that implements the transport
Endpoint that implements the transport protocol(s) and all the protocol(s) and all the required properties selected. Similarly, a
required properties selected. Similarly, a Transport Services Transport Services Implementation acting as a Listener can receive
Implementation acting as a Listener can receive connections for any connections for any protocol that is supported from an existing
protocol that is supported from an existing initiator that implements initiator that implements the protocol, independently of whether or
the protocol, independent of whether the initiator uses the Transport not the initiator uses the Transport Services System.
Services System or not.
A Transport Services Implemenation makes decisions that select A Transport Services Implementation makes decisions that select
protocols and interfaces. In normal use, a given version of a protocols and interfaces. In normal use, a given version of a
Transport Services System SHOULD result in consistent protocol and Transport Services System SHOULD result in consistent protocol and
interface selection decisions for the same network conditions given interface selection decisions for the same network conditions, given
the same set of Properties. This is intended to provide predictable the same set of Properties. This is intended to provide predictable
outcomes to the application using the API. outcomes to the application using the API.
3.5. Support Monitoring 3.5. Support Monitoring
The Transport Services API increases the layer of abstraction for The Transport Services API increases the layer of abstraction for
applications, and it enables greater automation below the API. Such applications, and it enables greater automation below the API. Such
increased abstraction comes at the cost of increased complexity when increased abstraction comes at the cost of increased complexity when
application programmers, users or system administrators try to application programmers, users, or system administrators try to
understand why any issues and failures may be happening. Transport understand why any issues and failures may be happening. Transport
Services systems should therefore offer monitoring functions that Services systems should therefore offer monitoring functions that
provide relevant debug and diagnostics information. For example, provide relevant debug and diagnostics information. For example,
such monitoring functions could indicate the protocol(s) in use, the such monitoring functions could indicate the protocol(s) in use, the
number of open connections per protocol, and any statistics that number of open connections per protocol, and any statistics that
these protocols may offer. these protocols may offer.
4. Transport Services Architecture and Concepts 4. Transport Services Architecture and Concepts
This section of the document describes the architecture non- This section describes the architecture non-normatively and explains
normatively and explains the operation of a Transport Services the operation of a Transport Services Implementation. The concepts
Implementation. The concepts defined in this document are intended defined in this document are intended primarily for use in the
primarily for use in the documents and specifications that describe documents and specifications that describe the Transport Services
the Transport Services System. This includes the architecture, the System. This includes the architecture, the Transport Services API,
Transport Services API and the associated Transport Services and the associated Transport Services Implementation. While the
Implementation. While the specific terminology can be used in some specific terminology can be used in some implementations, it is
implementations, it is expected that there will remain a variety of expected that there will remain a variety of terms used by running
terms used by running code. code.
The architecture divides the concepts for Transport Services System The architecture divides the concepts for the Transport Services
into two categories: System 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 a The following diagram summarizes the top-level concepts in a
Transport Services System and how they relate to one another. Transport Services System and how they relate to one another.
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| | | | | |
| (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 Architecture of the Figure 3: Concepts and Relationships in the Architecture of the
Transport Services System 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 dependent
and implementation- dependent, and do not affect application-level on the platform and implementation and do not affect application-
interoperability, the Transport Services API level interoperability, the Transport Services API [RFC9622] does not
[I-D.ietf-taps-interface] does not specify an interface for reading specify an interface for reading or writing System Policy.
or writing System Policy.
The Cached State is the state and history that the Transport Services The Cached State is the state and history that the Transport Services
Implementation keeps for each set of associated Endpoints that have Implementation keeps for each set of associated Endpoints that have
previously been used. An application ought to explicitly request any previously been used. An application ought to explicitly request any
required or desired properties via the Transport Services API. 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
exposed as handles or referenced objects, depending on the chosen as handles or referenced objects, depending on the chosen programming
programming language. 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 * Preestablishment (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 preestablishment
establishment can have a large impact on the rest of the can have a large impact on the rest of the interface: they modify
interface: they modify how establishment occurs, they influence how establishment occurs, influence the expectations around data
the expectations around data transfer, and they determine the set transfer, and 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
to interact with the underlying transport by querying state or to interact with the underlying transport by querying state or
updating maintenance options. updating maintenance options.
* Termination (Section 4.1.7) focuses on the methods by which data * Termination (Section 4.1.7) focuses on the methods by which data
transmission is stopped, and connection state is torn down. transmission is stopped and connection state is torn down.
The diagram below provides a high-level view of the actions and The diagram below provides a high-level view of the actions and
events during the lifetime of a Connection object. Note that some events during the lifetime of a Connection object. Note that some
actions are alternatives (e.g., whether to initiate a connection or actions are alternatives (e.g., whether to initiate a connection or
to listen for incoming connections), while others are optional (e.g., listen for incoming connections), while others are optional (e.g.,
setting Connection and Message Properties in pre-establishment) or setting Connection and Message Properties in preestablishment) or
have been omitted for brevity and simplicity. have been omitted for brevity and simplicity.
Pre-establishment : Established : Termination Preestablishment : Established : Termination
----------------- : ----------- : ----------- ----------------- : ----------- : -----------
: : : :
+-- Local Endpoint : Message : +-- Local Endpoint : Message :
+-- Remote Endpoint : Receive() | : +-- Remote Endpoint : Receive() | :
+-- Transport Properties : Send() | : +-- Transport Properties : Send() | :
+-- Security Parameters : | : +-- Security Parameters : | :
| : | : | : | :
| InitiateWithSend() | Close() : | InitiateWithSend() | Close() :
| +---------------+ Initiate() +-----+------+ Abort() : | +---------------+ Initiate() +-----+------+ Abort() :
+---+ Preconnection |------------->| Connection |-----------> Closed +---+ Preconnection |------------->| Connection |-----------> Closed
+---------------+ Rendezvous() +------------+ : +---------------+ Rendezvous() +------------+ :
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 divided into In this diagram, the lifetime of a Connection object is divided into
three phases: pre-establishment, the Established state, and three phases: preestablishment, the Established state, and
Termination. termination of a connection.
Pre-establishment is based around a Preconnection object, that Preestablishment is based around a Preconnection object containing
contains various sub-objects that describe the properties and various sub-objects that describe the properties and parameters of
parameters of desired Connections (Local and Remote Endpoints, desired Connections (Local and Remote Endpoints, Transport
Transport Properties, and Security Parameters). A Preconnection can Properties, and Security Parameters). A Preconnection can be used to
be used to start listening for inbound connections, in which case a start listening for inbound connections -- in which case a Listener
Listener object is created, or can be used to establish a new object is created -- or can be used to establish a new connection
connection directly using Initiate (for outbound connections) or directly using Initiate (for outbound connections) or Rendezvous (for
Rendezvous (for peer-to-peer connections). 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 can 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
An Endpoint Identifier specifies one side of a transport connection. An Endpoint Identifier specifies one side of a transport connection.
Endpoints can be Local Endpoints or Remote Endpoints, and the Endpoints can be Local Endpoints or Remote Endpoints, and the
Endpoint Identifiers can 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. An application uses for the source or destination of a connection. An
Endpoint Identifier can be specified at various levels of Endpoint Identifier can be specified at various levels of
abstraction. An Endpoint Identifier at a higher level of abstraction abstraction. An Endpoint Identifier at a higher level of abstraction
(such as a hostname) can be resolved to more concrete identities (such as a hostname) can be resolved to more concrete identities
(such as IP addresses). A Remote Endpoint Identifier can also (such as IP addresses). A Remote Endpoint Identifier can also
represent a multicast group or anycast address. In the case of represent a multicast group or anycast address. In the case of
multicast, this selects a multicast transport for communication. multicast, a multicast transport will be selected for communication.
* Remote Endpoint Identifier: The Remote Endpoint Identifier Remote Endpoint Identifier: The Remote Endpoint Identifier
represents the application's identifier for a peer that can represents the application's identifier for a peer that can
participate in a transport connection; for example, the participate in a transport connection, for example, the
combination of a DNS name for the peer and a service name/port. combination of a DNS name for the peer and a service name/port.
* Local Endpoint Identifier: The Local Endpoint Identifier Local Endpoint Identifier: The Local Endpoint Identifier represents
represents the application's identifier for itself that it uses the application's identifier for itself that it uses for transport
for transport connections; for example, a local IP address and connections, for example, a local IP address and port.
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 it 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 describes parameters of the Connection: the Local Endpoint
Identifier from which that Connection will be established, the Identifier from which that Connection will be established, the
Remote Endpoint Identifier (Section 4.1.3) to which it will Remote Endpoint Identifier to which it will connect, and Transport
connect, and Transport Properties that influence the paths and Properties that influence the paths and protocols a Connection
protocols a Connection will use. A Preconnection can be either will use. A Preconnection can be either fully specified
fully specified (representing a single possible Connection), or it (representing a single possible Connection) or partially specified
can be partially specified (representing a family of possible (representing a family of possible Connections). The Local
Connections). The Local Endpoint (Section 4.1.3) is required for Endpoint (Section 4.1.3) is required for a Preconnection used to
a Preconnection used to Listen for incoming Connections, but Listen for incoming Connections but is optional if it is used to
optional if it is used to Initiate a Connection. The Remote Initiate a Connection. The Remote Endpoint Identifier is required
Endpoint Identifier is required in a Preconnection that used to in a Preconnection that is used to Initiate a Connection but is
Initiate a Connection, but is optional if it is used to Listen for optional if it is used to Listen for incoming Connections. The
incoming Connections. The Local Endpoint Identifier and the Local Endpoint Identifier and the Remote Endpoint Identifier are
Remote Endpoint Identifier are both required if a peer-to-peer both required if a peer-to-peer Rendezvous is to occur based on
Rendezvous is to occur based on the Preconnection. the Preconnection.
* Transport Properties: Transport Properties allow the application Transport Properties: Transport Properties allow the application to
to express their requirements, prohibitions, and preferences and express requirements, prohibitions, and preferences and configure
configure a Transport Services Implementation. There are three a Transport Services Implementation. There are three kinds of
kinds of Transport Properties: 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
can be specified on a Preconnection and changed on the 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
can also be specified during data transfer to affect specific can also be specified during data transfer to affect specific
Messages. Messages.
* Listener: A Listener object accepts incoming transport protocol Listener: A Listener object accepts incoming transport protocol
connections from Remote Endpoints and generates corresponding connections from Remote Endpoints and generates corresponding
Connection objects. It is created from a Preconnection object Connection objects. It is created from a Preconnection object
that specifies the type of incoming Connections it will accept. that specifies the type of incoming Connections it will accept.
4.1.3. Pre-establishment 4.1.3. Preestablishment
* Selection Properties: The Selection Properties consist of the Selection Properties: Selection Properties consist of the properties
properties that an application can set to influence the selection that an application can set to influence the selection of paths
of paths between the Local and Remote Endpoints, to influence the between the Local and Remote Endpoints, influence the selection of
selection of transport protocols, or to configure the behavior of transport protocols, or configure the behavior of generic
generic transport protocol features. These properties can take transport protocol features. These properties can take the form
the form of requirements, prohibitions, or preferences. Examples of requirements, prohibitions, or preferences. Examples of
of properties that influence path selection include the interface 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
open support. support for TCP Fast Open.
* Connection Properties: The Connection Properties are used to Connection Properties: Connection Properties are used to configure
configure protocol-specific options and control per-connection protocol-specific options and control per-connection behavior of a
behavior of a Transport Services Implementation; for example, a Transport Services Implementation; for example, a protocol-
protocol-specific Connection Property can express that if TCP is specific Connection Property can express that if TCP is used, the
used, the implementation ought to use the User Timeout Option. implementation ought to use the User Timeout Option. Note that
Note that the presence of such a property does not require that a the presence of such a property does not require that a specific
specific protocol will be used. In general, these properties do protocol be used. In general, these properties do not explicitly
not explicitly determine the selection of paths or protocols, but determine the selection of paths or protocols but can be used by
can be used by an implementation during connection establishment. an implementation during connection establishment. Connection
Connection Properties are specified on a Preconnection prior to Properties are specified on a Preconnection prior to Connection
Connection establishment, and can be modified on the Connection establishment and can be modified on the Connection later.
later. Changes made to Connection Properties after Connection 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
create a Connection to a Remote Endpoint, and prepare any required a Connection to a Remote Endpoint and prepare any required local
local or remote state to enable the transmission of Messages. For or remote state to enable the transmission of Messages. For some
some protocols, this will initiate a client-to-server style protocols, this will initiate a client-to-server-style handshake;
handshake; for other protocols, this will just establish local for other protocols, this will just establish local state (e.g.,
state (e.g., with connectionless protocols such as UDP). The with connectionless protocols such as UDP). The process of
process of identifying options for connecting, such as resolution identifying options for connecting, such as resolution of the
of the Remote Endpoint Identifier, occurs in response to the Remote Endpoint Identifier, occurs in response to the Initiate
Initiate call. 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 Identifier(s). Connections can be accepted on any Local Endpoint Identifier(s). Connections can be accepted on any
of the 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
Identifier(s), occurs in response to the Rendezvous call. As with Identifier(s), occurs in response to the Rendezvous call. As with
Listeners, the set of local paths and endpoints is constrained by Listeners, the set of local paths and endpoints is constrained by
Selection Properties. If successful, the Rendezvous call Selection Properties. If successful, the Rendezvous call
generates and asynchronously returns a Connection object to generates and asynchronously returns a Connection object to
represent the established peer-to-peer connection. The processes represent the established peer-to-peer connection. The processes
by which connections are initiated during a Rendezvous action will by which connections are initiated during a Rendezvous action will
depend on the set of Local and Remote Endpoints configured on the depend on the set of Local and Remote Endpoints configured on the
Preconnection. For example, if the Local and Remote Endpoints are Preconnection. For example, if the Local and Remote Endpoints are
TCP host candidates, then a TCP simultaneous open [RFC9293] might TCP host candidates, then a TCP simultaneous open [RFC9293] might
be performed. However, if the set of Local Endpoints includes be performed. However, if the set of Local Endpoints includes
server reflexive candidates, such as those provided by STUN server-reflexive candidates, such as those provided by STUN
(Session Traversal Utilities for NAT) [RFC5389], a Rendezvous (Session Traversal Utilities for NAT) [RFC8489], a Rendezvous
action will race candidates in the style of the ICE (Interactive action will race candidates in the style of the ICE (Interactive
Connection Establishment) algorithm [RFC8445] to perform NAT Connectivity Establishment) algorithm [RFC8445] to perform NAT
binding discovery and initiate a peer-to-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
represented as bytes that can be transferred between two endpoints as bytes that can be transferred between two endpoints over a
over a transport connection. The bytes within a Message are transport connection. The bytes within a Message are assumed to
assumed to be ordered. If an application does not care about the be ordered. If an application does not care about the order in
order in which a peer receives two distinct spans of bytes, those which a peer receives two distinct spans of bytes, those spans of
spans of bytes are considered independent Messages. Messages are bytes are considered independent Messages. Messages are sent in
sent in the payload of IP packets. One packet can carry one or the payload of IP packets. One packet can carry one or more
more Messages or parts of a Message. 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
Connection as defaults. These properties might only apply to how as defaults. These properties might only apply to how a Message
a Message is sent (such as how the transport will treat is sent (such as how the transport will treat prioritization and
prioritization and reliability), but can also include properties reliability) but can also include properties that specific
that specific protocols encode and communicate to the Remote protocols encode and communicate to the Remote Endpoint. When
Endpoint. When receiving Messages, Message Properties can contain receiving Messages, Message Properties can contain information
information about the received Message, such as metadata generated about the received Message, such as metadata generated at the
at the receiver and information signalled by the Remote Endpoint. receiver and information signaled by the Remote Endpoint. For
For example, a Message can be marked with a Message Property example, a Message can be marked with a Message Property
indicating that it is the final Message on a Connection. indicating that it is the final Message on a Connection.
* Send: The action to transmit a Message over a Connection to the Send: The Send action transmits a Message over a Connection to the
Remote Endpoint. The interface to Send can accept Message Remote Endpoint. The interface to Send can accept Message
Properties specific to how the Message content is to be sent. The Properties specific to how the Message content is to be sent. The
status of the Send operation is delivered back to the sending status of the Send operation is delivered back to the sending
application in an event (Section 4.1.6). application in an event (Section 4.1.6).
* Receive: An action that indicates that the application is ready to Receive: The Receive action indicates that the application is ready
asynchronously accept a Message over a Connection from a Remote to asynchronously accept a Message over a Connection from a Remote
Endpoint, while the Message content itself will be delivered in an Endpoint, while the Message content itself will be delivered in an
event (Section 4.1.6). The interface to Receive can include event (Section 4.1.6). The interface to Receive can include
Message Properties specific to the Message that is to be delivered Message Properties specific to the Message that is to be delivered
to the application. to the application.
* Framer: A Framer is a data translation layer that can be added to Framer: A Framer is a data translation layer that can be added to a
a Connection. Framers allow extending a Connection's Protocol Connection. Framers allow extending a Connection's Protocol Stack
Stack to define how to encapsulate or encode outbound Messages, to define how to encapsulate or encode outbound Messages and how
and how to decapsulate or decode inbound data into Messages. In to decapsulate or decode inbound data into Messages. In this way,
this way, message boundaries can be preserved when using a message boundaries can be preserved when using a Connection
Connection object, even with a protocol that otherwise presents object, even with a protocol that otherwise presents unstructured
unstructured streams, such as TCP. This is designed based on the streams, such as TCP. This is designed based on the fact that
fact that many of the current application protocols evolved over many of the current application protocols evolved over TCP, which
TCP, which does not provide message boundary preservation, and does not provide message boundary preservation, and since many of
since many of these protocols require message boundaries to these protocols require message boundaries to function, each
function, each application layer protocol has defined its own application-layer protocol has defined its own framing. For
framing. For example, when an HTTP application sends and receives example, when an HTTP application sends and receives HTTP messages
HTTP messages over a byte-stream transport, it must parse the over a byte-stream transport, it must parse the boundaries of HTTP
boundaries of HTTP messages from the stream of bytes. messages from the stream of bytes.
4.1.6. Event Handling 4.1.6. Event Handling
The following categories of events can be delivered to an The following categories of events can be delivered to an
application: application:
* Connection Ready: Signals to an application that a given Connection Ready: Signals to an application that a given Connection
Connection is ready to send and/or receive Messages. If the is ready to send and/or receive Messages. If the Connection
Connection relies on handshakes to establish state between peers, relies on handshakes to establish state between peers, then it is
then it is assumed that these steps have been taken. assumed that these steps have been taken.
* Connection Closed: Signals to an application that a given Connection Closed: Signals to an application that a given Connection
Connection is no longer usable for sending or receiving Messages. is no longer usable for sending or receiving Messages. The event
The event delivers a reason or error to the application that delivers a reason or error to the application that describes the
describes the nature of the termination. nature of the termination.
* Connection Received: Signals to an application that a given Connection Received: Signals to an application that a given Listener
Listener has received a Connection. 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. To allow an application application, based on a Receive action. To allow an application
to limit the occurrence of such events, each call to Receive will to limit the occurrence of such events, each call to Receive will
be paired with a single Receive event. This can include an error be paired with a single Receive event. This can include an error
if the Receive action cannot be satisfied, e.g., due to the if the Receive action cannot be satisfied, e.g., due to the
Connection being closed. 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 might indicate 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
of the Connection has changed that might influence how and where the Connection has changed that might influence how and where data
data is sent and/or received. 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 or is no longer willing to
receive data, and that the protocol should signal this state to receive data. The protocol should signal this state to the Remote
the Remote Endpoint if the transport protocol allows this. (Note Endpoint if the transport protocol permits it. (Note that this is
that this is distinct from the concept of "half-closing" a distinct from the concept of "half-closing" a bidirectional
bidirectional connection, such as when a FIN is sent in one connection, such as when a FIN is sent in one direction of a TCP
direction of a TCP connection [RFC9293]. The end of a stream can connection [RFC9293]. The end of a stream can also be indicated
also be indicated using Message Properties when sending.) 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
indicate a Close and also indicate that the Transport Services that the Transport Services System should not attempt to deliver
System should not attempt to deliver any outstanding data, and any outstanding data and that it should immediately close and drop
immediately drop the connection. This is intended for immediate, the connection. This is intended for immediate, usually abnormal,
usually abnormal, termination of a connection. 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
transport protocols that support multiplexing, only Connections transport protocols that support multiplexing, only Connections
within the same Connection Group are allowed to be multiplexed within the same Connection Group are allowed to be multiplexed
together. 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.
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 While Connection Groups are managed by the Transport Services
Implementation, an application can define different Connection Implementation, an application can define different Connection
Contexts for different Connection Groups to explicitly control Contexts for different Connection Groups to explicitly control
caching boundaries, as 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 architectural concepts for the Transport This section defines the key architectural concepts for the Transport
Services Implementation within the Transport Services System. Services Implementation within the Transport Services System.
The Transport Services System consists of the Transport Services The Transport Services System consists of the Transport Services
Implementation and the Transport Services API. The Transport Implementation and the Transport Services API. The Transport
Services Implementation consists of all objects and protocol Services Implementation consists of all objects and protocol
instances used internally to a system or library to implement the instances used internally to a system or library to implement the
functionality needed to provide a transport service across a network, functionality needed to provide a transport service across a network,
as required by the abstract interface. as required by the abstract interface.
* 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
any state necessary to establish connectivity or send and receive 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
used together to establish connectivity or send and receive used together to establish connectivity or send and receive
Messages. A single stack can be simple (a single transport Messages. A single stack can be simple (e.g., one application
protocol instance over IP), or it can be complex (multiple stream carried TCP running over IP) or complex (e.g,. multiple
application protocol streams going through a single security and application streams carried over a multipath transport protocol
transport protocol, over IP; or, a multi-path transport protocol using multiple subflows over IP).
over multiple transport sub-flows).
* 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, of which conforms to the Selection Properties and System Policy, of which
there can be several. Candidate Paths are identified during the there can be several. Candidate Paths are identified during the
gathering phase (Section 4.2.1) and can be used during the racing gathering phase (Section 4.2.1) and can be used during the racing
phase (Section 4.2.2). phase (Section 4.2.2).
* Candidate Protocol Stack: One Protocol Stack that can be used by Candidate Protocol Stack: One Protocol Stack that can be used by an
an application for a Connection, for which there can be several application for a Connection, for which there can be several
candidates. Candidate Protocol Stacks are identified during the candidates. Candidate Protocol Stacks are identified during the
gathering phase (Section 4.2.1) and are started during the racing gathering phase (Section 4.2.1) and are started during the racing
phase (Section 4.2.2). phase (Section 4.2.2).
* System Policy: The input from an operating system or other global System Policy: The input from an operating system or other global
preferences that can constrain or influence how an implementation preferences that can constrain or influence how an implementation
will gather candidate paths and Protocol Stacks (Section 4.2.1) will gather candidate paths and Protocol Stacks (Section 4.2.1)
and race the candidates during establishment (Section 4.2.2). and race the candidates during establishment (Section 4.2.2).
Specific aspects of the System Policy either apply to all Specific aspects of the System Policy apply to either all
Connections or only certain ones, depending on the runtime context Connections or only certain Connections, depending on the runtime
and properties of the Connection. context 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 a connections; rather, it means that cached state is used by a
Transport Services Implementation 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 behavior; 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
Endpoint Identifiers provided by the application, as well as the Endpoint Identifiers provided by the application, as well as the
policies and 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 (see [RFC7556]) different Paths will have distinct configurations (see [RFC7556])
for local addresses and DNS servers, attempts across different for local addresses and DNS servers, attempts across different
Paths will perform separate DNS resolution steps, which can lead Paths will perform separate DNS resolution steps, which can lead
to further racing of the resolved Remote Endpoint Identifiers. 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 Identifier, such as a representation of the Remote Endpoint Identifier, such as a
particular IP 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 regarding:
* Privacy concerns about re-using cached protocol state that can * reusing cached protocol state, as this can lead to linkability.
lead to linkability. Sensitive state could include TLS session Sensitive state could include TLS session state [RFC8446] and HTTP
state [RFC8446] and HTTP cookies [RFC6265]. These concerns could cookies [RFC6265]. These concerns could be addressed using
be addressed using Connection Contexts with separate caches, such Connection Contexts with separate caches, such as for different
as for different browser tabs. browser tabs.
* Privacy concerns about allowing Connections to multiplex together, * allowing Connections to multiplex together, which can tell a
which can tell a Remote Endpoint that all of the Connections are Remote Endpoint that all of the Connections are coming from the
coming from the same application. Using Connection Contexts same application. Using Connection Contexts avoids the
avoids the Connections being multiplexed in a HTTP/2 or QUIC Connections being multiplexed in an HTTP/2 or QUIC stream.
stream.
5. IANA Considerations 5. IANA Considerations
This document has no actions for IANA. This document has no IANA actions.
6. Security and Privacy Considerations 6. Security and Privacy Considerations
The Transport Services System does not recommend use of specific The Transport Services System does not recommend the use of specific
security protocols or algorithms. Its goal is to offer ease of use security protocols or algorithms. Its goal is to offer ease 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 trade-offs 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 the cache toward an on-path observer). Some applications have
features (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). security protocol handshakes that are 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 fall back to weaker
secure protocols (see Section 3.3). For example, if an application versions of secure protocols (see Section 3.3). For example, if an
requests a specific version of TLS, but the desired version of TLS is application requests a specific version of TLS but the desired
not available, its connection will fail. As described in version of TLS is not available, its connection will fail. As
Section 3.3, the Transport Services API can allow applications to described in Section 3.3, the Transport Services API can allow
specify minimum versions that are allowed to be used by the Transport applications to specify minimum versions that are allowed to be used
Services System. by the Transport Services System.
7. Acknowledgements
This work has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreements No. 644334
(NEAT), No. 688421 (MAMI) and No 815178 (5GENESIS).
This work has been supported by Leibniz Prize project funds of DFG -
German Research Foundation: Gottfried Wilhelm Leibniz-Preis 2011 (FKZ
FE 570/4-1).
This work has been supported by the UK Engineering and Physical
Sciences Research Council under grant EP/R04144X/1.
Thanks to Reese Enghardt, Max Franke, Mirja Kuehlewind, Jonathan
Lennox, and Michael Welzl for the discussions and feedback that
helped shape the architecture of the system described here.
Particular thanks is also due to Philipp S. Tiesel and Christopher
A. Wood, who were both co-authors of this specification as it
progressed through the TAPS working group. Thanks as well to Stuart
Cheshire, Josh Graessley, David Schinazi, and Eric Kinnear for their
implementation and design efforts, including Happy Eyeballs, that
heavily influenced this work.
8. References 7. References
8.1. Normative References 7.1. 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,
<https://www.rfc-editor.org/rfc/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[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/info/rfc8174>.
8.2. Informative References
[I-D.ietf-taps-impl]
Brunstrom, A., Pauly, T., Enghardt, R., Tiesel, P. S., and
M. Welzl, "Implementing Interfaces to Transport Services",
Work in Progress, Internet-Draft, draft-ietf-taps-impl-16,
5 June 2023, <https://datatracker.ietf.org/doc/html/draft-
ietf-taps-impl-16>.
[I-D.ietf-taps-interface]
Trammell, B., Welzl, M., Enghardt, R., Fairhurst, G.,
Kühlewind, M., Perkins, C., Tiesel, P. S., and T. Pauly,
"An Abstract Application Layer Interface to Transport
Services", Work in Progress, Internet-Draft, draft-ietf-
taps-interface-22, 6 July 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-taps-
interface-22>.
[POSIX] "IEEE Std. 1003.1-2008 Standard for Information Technology 7.2. Informative References
-- Portable Operating System Interface (POSIX). Open
group Technical Standard: Base Specifications, Issue 7",
2008.
[RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, [POSIX] "IEEE Standard for Information Technology -- Portable
"Session Traversal Utilities for NAT (STUN)", RFC 5389, Operating System Interface (POSIX(R))", IEEE
DOI 10.17487/RFC5389, October 2008, Std 1003.1-2008, DOI 10.1109/IEEESTD.2008.4694976, 2008,
<https://www.rfc-editor.org/rfc/rfc5389>. <https://ieeexplore.ieee.org/document/4694976>.
[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/info/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/info/rfc6265>.
[RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain [RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain
Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015, Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
<https://www.rfc-editor.org/rfc/rfc7556>. <https://www.rfc-editor.org/info/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/info/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/info/rfc8170>.
[RFC8303] Welzl, M., Tuexen, M., and N. Khademi, "On the Usage of [RFC8303] Welzl, M., Tuexen, M., and N. Khademi, "On the Usage of
Transport Features Provided by IETF Transport Protocols", Transport Features Provided by IETF Transport Protocols",
RFC 8303, DOI 10.17487/RFC8303, February 2018, RFC 8303, DOI 10.17487/RFC8303, February 2018,
<https://www.rfc-editor.org/rfc/rfc8303>. <https://www.rfc-editor.org/info/rfc8303>.
[RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: [RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
Better Connectivity Using Concurrency", RFC 8305, Better Connectivity Using Concurrency", RFC 8305,
DOI 10.17487/RFC8305, December 2017, DOI 10.17487/RFC8305, December 2017,
<https://www.rfc-editor.org/rfc/rfc8305>. <https://www.rfc-editor.org/info/rfc8305>.
[RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive [RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445, Address Translator (NAT) Traversal", RFC 8445,
DOI 10.17487/RFC8445, July 2018, DOI 10.17487/RFC8445, July 2018,
<https://www.rfc-editor.org/rfc/rfc8445>. <https://www.rfc-editor.org/info/rfc8445>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[RFC8489] Petit-Huguenin, M., Salgueiro, G., Rosenberg, J., Wing,
D., Mahy, R., and P. Matthews, "Session Traversal
Utilities for NAT (STUN)", RFC 8489, DOI 10.17487/RFC8489,
February 2020, <https://www.rfc-editor.org/info/rfc8489>.
[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/info/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/info/rfc8923>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based [RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000, Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021, DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>. <https://www.rfc-editor.org/info/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/info/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/info/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,
<https://www.rfc-editor.org/rfc/rfc9293>. <https://www.rfc-editor.org/info/rfc9293>.
[RFC9622] Trammell, B., Ed., Welzl, M., Ed., Enghardt, R.,
Fairhurst, G., Kühlewind, M., Perkins, C. S., Tiesel, P.,
and T. Pauly, "An Abstract Application-Layer Interface to
Transport Services", RFC 9622, DOI 10.17487/RFC9622,
November 2024, <https://www.rfc-editor.org/info/rfc9622>.
[RFC9623] Brunstrom, A., Ed., Pauly, T., Ed., Enghardt, R., Tiesel,
P., and M. Welzl, "Implementing Interfaces to Transport
Services", RFC 9623, DOI 10.17487/RFC9623, November 2024,
<https://www.rfc-editor.org/info/rfc9623>.
Acknowledgements
This work has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreements No. 644334
(NEAT), No. 688421 (MAMI), and No. 815178 (5GENESIS).
This work has been supported by:
* Leibniz Prize project funds from the DFG - German Research
Foundation: Gottfried Wilhelm Leibniz-Preis 2011 (FKZ FE 570/4-1).
* the UK Engineering and Physical Sciences Research Council under
grant EP/R04144X/1.
Thanks to Reese Enghardt, Max Franke, Mirja Kühlewind, Jonathan
Lennox, and Michael Welzl for the discussions and feedback that
helped shape the architecture of the system described here.
Particular thanks are also due to Philipp S. Tiesel and Christopher
A. Wood, who were both coauthors of this specification as it
progressed through the Transport Services (TAPS) Working Group.
Thanks as well to Stuart Cheshire, Josh Graessley, David Schinazi,
and Eric Kinnear for their implementation and design efforts,
including Happy Eyeballs, that heavily influenced this work.
Authors' Addresses Authors' Addresses
Tommy Pauly (editor) Tommy Pauly (editor)
Apple Inc. Apple Inc.
One Apple Park Way One Apple Park Way
Cupertino, California 95014, Cupertino, CA 95014
United States of America United States of America
Email: tpauly@apple.com Email: tpauly@apple.com
Brian Trammell (editor) Brian Trammell (editor)
Google Switzerland GmbH Google Switzerland GmbH
Gustav-Gull-Platz 1 Gustav-Gull-Platz 1
CH- 8004 Zurich CH-8004 Zurich
Switzerland Switzerland
Email: ietf@trammell.ch Email: ietf@trammell.ch
Anna Brunstrom Anna Brunstrom
Karlstad University Karlstad University
Universitetsgatan 2 Universitetsgatan 2
651 88 Karlstad 651 88 Karlstad
Sweden Sweden
Email: anna.brunstrom@kau.se Email: anna.brunstrom@kau.se
Godred Fairhurst Godred Fairhurst
University of Aberdeen University of Aberdeen
Fraser Noble Building Fraser Noble Building
Aberdeen, AB24 3UE Aberdeen, AB24 3UE
United Kingdom
Email: gorry@erg.abdn.ac.uk Email: gorry@erg.abdn.ac.uk
URI: http://www.erg.abdn.ac.uk/ URI: https://erg.abdn.ac.uk/
Colin Perkins Colin S. Perkins
University of Glasgow University of Glasgow
School of Computing Science School of Computing Science
Glasgow G12 8QQ Glasgow G12 8QQ
United Kingdom United Kingdom
Email: csp@csperkins.org Email: csp@csperkins.org
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