rfc9622.original   rfc9622.txt 
TAPS Working Group B. Trammell, Ed. Internet Engineering Task Force (IETF) B. Trammell, Ed.
Internet-Draft Google Switzerland GmbH Request for Comments: 9622 Google Switzerland GmbH
Intended status: Standards Track M. Welzl, Ed. Category: Standards Track M. Welzl, Ed.
Expires: 18 September 2024 University of Oslo ISSN: 2070-1721 University of Oslo
R. Enghardt R. Enghardt
Netflix Netflix
G. Fairhurst G. Fairhurst
University of Aberdeen University of Aberdeen
M. Kuehlewind M. Kühlewind
Ericsson Ericsson
C. Perkins C. S. Perkins
University of Glasgow University of Glasgow
P. Tiesel P. Tiesel
SAP SE SAP SE
T. Pauly T. Pauly
Apple Inc. Apple Inc.
17 March 2024 November 2024
An Abstract Application Layer Interface to Transport Services An Abstract Application-Layer Interface to Transport Services
draft-ietf-taps-interface-26
Abstract Abstract
This document describes an abstract application programming This document describes an abstract Application Programming Interface
interface, API, to the transport layer that enables the selection of (API) to the transport layer that enables the selection of transport
transport protocols and network paths dynamically at runtime. This protocols and network paths dynamically at runtime. This API enables
API enables faster deployment of new protocols and protocol features faster deployment of new protocols and protocol features without
without requiring changes to the applications. The specified API requiring changes to the applications. The specified API follows the
follows the Transport Services architecture by providing Transport Services architecture by providing asynchronous, atomic
asynchronous, atomic transmission of messages. It is intended to transmission of messages. It is intended to replace the BSD Socket
replace the BSD sockets API as the common interface to the transport API as the common interface to the transport layer, in an environment
layer, in an environment where endpoints could select from multiple where endpoints could select from multiple network paths and
network paths and potential transport protocols. potential transport protocols.
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-
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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 18 September 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/rfc9622.
Copyright Notice Copyright Notice
Copyright (c) 2024 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 . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction
1.1. Terminology and Notation . . . . . . . . . . . . . . . . 5 1.1. Terminology and Notation
1.2. Specification of Requirements . . . . . . . . . . . . . . 7 1.2. Specification of Requirements
2. Overview of the API Design . . . . . . . . . . . . . . . . . 7 2. Overview of the API Design
3. API Summary . . . . . . . . . . . . . . . . . . . . . . . . . 8 3. API Summary
3.1. Usage Examples . . . . . . . . . . . . . . . . . . . . . 9 3.1. Usage Examples
3.1.1. Server Example . . . . . . . . . . . . . . . . . . . 10 3.1.1. Server Example
3.1.2. Client Example . . . . . . . . . . . . . . . . . . . 11 3.1.2. Client Example
3.1.3. Peer Example . . . . . . . . . . . . . . . . . . . . 13 3.1.3. Peer Example
4. Transport Properties . . . . . . . . . . . . . . . . . . . . 14 4. Transport Properties
4.1. Transport Property Names . . . . . . . . . . . . . . . . 15 4.1. Transport Property Names
4.2. Transport Property Types . . . . . . . . . . . . . . . . 16 4.2. Transport Property Types
5. Scope of the API Definition . . . . . . . . . . . . . . . . . 17 5. Scope of the API Definition
6. Pre-Establishment Phase . . . . . . . . . . . . . . . . . . . 18 6. Preestablishment Phase
6.1. Specifying Endpoints . . . . . . . . . . . . . . . . . . 19 6.1. Specifying Endpoints
6.1.1. Using Multicast Endpoints . . . . . . . . . . . . . . 21 6.1.1. Using Multicast Endpoints
6.1.2. Constraining Interfaces for Endpoints . . . . . . . . 23 6.1.2. Constraining Interfaces for Endpoints
6.1.3. Protocol-Specific Endpoints . . . . . . . . . . . . . 23 6.1.3. Protocol-Specific Endpoints
6.1.4. Endpoint Examples . . . . . . . . . . . . . . . . . . 24 6.1.4. Endpoint Examples
6.1.5. Multicast Examples . . . . . . . . . . . . . . . . . 25 6.1.5. Multicast Examples
6.2. Specifying Transport Properties . . . . . . . . . . . . . 27 6.2. Specifying Transport Properties
6.2.1. Reliable Data Transfer (Connection) . . . . . . . . . 30 6.2.1. Reliable Data Transfer (Connection)
6.2.2. Preservation of Message Boundaries . . . . . . . . . 30 6.2.2. Preservation of Message Boundaries
6.2.3. Configure Per-Message Reliability . . . . . . . . . . 30 6.2.3. Configure Per-Message Reliability
6.2.4. Preservation of Data Ordering . . . . . . . . . . . . 31 6.2.4. Preservation of Data Ordering
6.2.5. Use 0-RTT Session Establishment with a Safely 6.2.5. Use 0-RTT Session Establishment with a Safely
Replayable Message . . . . . . . . . . . . . . . . . 31 Replayable Message
6.2.6. Multistream Connections in Group . . . . . . . . . . 31 6.2.6. Multistream Connections in a Group
6.2.7. Full Checksum Coverage on Sending . . . . . . . . . . 31 6.2.7. Full Checksum Coverage on Sending
6.2.8. Full Checksum Coverage on Receiving . . . . . . . . . 32 6.2.8. Full Checksum Coverage on Receiving
6.2.9. Congestion control . . . . . . . . . . . . . . . . . 32 6.2.9. Congestion Control
6.2.10. Keep alive . . . . . . . . . . . . . . . . . . . . . 32 6.2.10. Keep-Alive Packets
6.2.11. Interface Instance or Type . . . . . . . . . . . . . 33 6.2.11. Interface Instance or Type
6.2.12. Provisioning Domain Instance or Type . . . . . . . . 34 6.2.12. Provisioning Domain Instance or Type
6.2.13. Use Temporary Local Address . . . . . . . . . . . . . 35 6.2.13. Use Temporary Local Address
6.2.14. Multipath Transport . . . . . . . . . . . . . . . . . 35 6.2.14. Multipath Transport
6.2.15. Advertisement of Alternative Addresses . . . . . . . 36 6.2.15. Advertisement of Alternative Addresses
6.2.16. Direction of communication . . . . . . . . . . . . . 36 6.2.16. Direction of Communication
6.2.17. Notification of ICMP soft error message arrival . . . 37 6.2.17. Notification of ICMP Soft Error Message Arrival
6.2.18. Initiating side is not the first to write . . . . . . 37 6.2.18. Initiating Side Is Not the First to Write
6.3. Specifying Security Parameters and Callbacks . . . . . . 38 6.3. Specifying Security Parameters and Callbacks
6.3.1. Allowed security protocols . . . . . . . . . . . . . 39 6.3.1. Allowed Security Protocols
6.3.2. Certificate bundles . . . . . . . . . . . . . . . . . 40 6.3.2. Certificate Bundles
6.3.3. Pinned server certificate . . . . . . . . . . . . . . 40 6.3.3. Pinned Server Certificate
6.3.4. Application-layer protocol negotiation . . . . . . . 40 6.3.4. Application-Layer Protocol Negotiation
6.3.5. Groups, ciphersuites, and signature algorithms . . . 41 6.3.5. Groups, Ciphersuites, and Signature Algorithms
6.3.6. Session cache options . . . . . . . . . . . . . . . . 41 6.3.6. Session Cache Options
6.3.7. Pre-shared key . . . . . . . . . . . . . . . . . . . 41 6.3.7. Pre-Shared Key
6.3.8. Connection Establishment Callbacks . . . . . . . . . 42 6.3.8. Connection Establishment Callbacks
7. Establishing Connections . . . . . . . . . . . . . . . . . . 42 7. Establishing Connections
7.1. Active Open: Initiate . . . . . . . . . . . . . . . . . . 43 7.1. Active Open: Initiate
7.2. Passive Open: Listen . . . . . . . . . . . . . . . . . . 44 7.2. Passive Open: Listen
7.3. Peer-to-Peer Establishment: Rendezvous . . . . . . . . . 45 7.3. Peer-to-Peer Establishment: Rendezvous
7.4. Connection Groups . . . . . . . . . . . . . . . . . . . . 47 7.4. Connection Groups
7.5. Adding and Removing Endpoints on a Connection . . . . . . 49 7.5. Adding and Removing Endpoints on a Connection
8. Managing Connections . . . . . . . . . . . . . . . . . . . . 50 8. Managing Connections
8.1. Generic Connection Properties . . . . . . . . . . . . . . 51 8.1. Generic Connection Properties
8.1.1. Required Minimum Corruption Protection Coverage for 8.1.1. Required Minimum Corruption Protection Coverage for
Receiving . . . . . . . . . . . . . . . . . . . . . . 52 Receiving
8.1.2. Connection Priority . . . . . . . . . . . . . . . . . 52 8.1.2. Connection Priority
8.1.3. Timeout for Aborting Connection . . . . . . . . . . . 52 8.1.3. Timeout for Aborting Connection
8.1.4. Timeout for keep alive packets . . . . . . . . . . . 53 8.1.4. Timeout for Keep-Alive Packets
8.1.5. Connection Group Transmission Scheduler . . . . . . . 53 8.1.5. Connection Group Transmission Scheduler
8.1.6. Capacity Profile . . . . . . . . . . . . . . . . . . 53 8.1.6. Capacity Profile
8.1.7. Policy for using Multipath Transports . . . . . . . . 55 8.1.7. Policy for Using Multipath Transports
8.1.8. Bounds on Send or Receive Rate . . . . . . . . . . . 56 8.1.8. Bounds on Send or Receive Rate
8.1.9. Group Connection Limit . . . . . . . . . . . . . . . 56 8.1.9. Group Connection Limit
8.1.10. Isolate Session . . . . . . . . . . . . . . . . . . . 57 8.1.10. Isolate Session
8.1.11. Read-only Connection Properties . . . . . . . . . . . 57 8.1.11. Read-Only Connection Properties
8.2. TCP-specific Properties: User Timeout Option (UTO) . . . 59 8.2. TCP-Specific Properties: User Timeout Option (UTO)
8.2.1. Advertised User Timeout . . . . . . . . . . . . . . . 59 8.2.1. Advertised User Timeout
8.2.2. User Timeout Enabled . . . . . . . . . . . . . . . . 60 8.2.2. User Timeout Enabled
8.2.3. Timeout Changeable . . . . . . . . . . . . . . . . . 60 8.2.3. Timeout Changeable
8.3. Connection Lifecycle Events
8.3. Connection Lifecycle Events . . . . . . . . . . . . . . . 60 8.3.1. Soft Errors
8.3.1. Soft Errors . . . . . . . . . . . . . . . . . . . . . 60 8.3.2. Path Change
8.3.2. Path change . . . . . . . . . . . . . . . . . . . . . 60 9. Data Transfer
9. Data Transfer . . . . . . . . . . . . . . . . . . . . . . . . 61 9.1. Messages and Framers
9.1. Messages and Framers . . . . . . . . . . . . . . . . . . 61 9.1.1. Message Contexts
9.1.1. Message Contexts . . . . . . . . . . . . . . . . . . 61 9.1.2. Message Framers
9.1.2. Message Framers . . . . . . . . . . . . . . . . . . . 61 9.1.3. Message Properties
9.1.3. Message Properties . . . . . . . . . . . . . . . . . 64 9.2. Sending Data
9.2. Sending Data . . . . . . . . . . . . . . . . . . . . . . 70 9.2.1. Basic Sending
9.2.1. Basic Sending . . . . . . . . . . . . . . . . . . . . 70 9.2.2. Send Events
9.2.2. Send Events . . . . . . . . . . . . . . . . . . . . . 71 9.2.3. Partial Sends
9.2.3. Partial Sends . . . . . . . . . . . . . . . . . . . . 72 9.2.4. Batching Sends
9.2.4. Batching Sends . . . . . . . . . . . . . . . . . . . 73 9.2.5. Send on Active Open: InitiateWithSend
9.2.5. Send on Active Open: InitiateWithSend . . . . . . . . 73 9.2.6. Priority and the Transport Services API
9.2.6. Priority and the Transport Services API . . . . . . . 74 9.3. Receiving Data
9.3. Receiving Data . . . . . . . . . . . . . . . . . . . . . 74 9.3.1. Enqueuing Receives
9.3.1. Enqueuing Receives . . . . . . . . . . . . . . . . . 75 9.3.2. Receive Events
9.3.2. Receive Events . . . . . . . . . . . . . . . . . . . 75 9.3.3. Receive Message Properties
9.3.3. Receive Message Properties . . . . . . . . . . . . . 78 10. Connection Termination
10. Connection Termination . . . . . . . . . . . . . . . . . . . 80 11. Connection State and Ordering of Operations and Events
11. Connection State and Ordering of Operations and Events . . . 81 12. IANA Considerations
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 83 13. Privacy and Security Considerations
13. Privacy and Security Considerations . . . . . . . . . . . . . 83 14. References
14. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 85 14.1. Normative References
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 85 14.2. Informative References
15.1. Normative References . . . . . . . . . . . . . . . . . . 85 Appendix A. Implementation Mapping
15.2. Informative References . . . . . . . . . . . . . . . . . 86 A.1. Types
Appendix A. Implementation Mapping . . . . . . . . . . . . . . . 90 A.2. Events and Errors
A.1. Types . . . . . . . . . . . . . . . . . . . . . . . . . . 90 A.3. Time Duration
A.2. Events and Errors . . . . . . . . . . . . . . . . . . . . 91 Appendix B. Convenience Functions
A.3. Time Duration . . . . . . . . . . . . . . . . . . . . . . 91 B.1. Adding Preference Properties
Appendix B. Convenience Functions . . . . . . . . . . . . . . . 91 B.2. Transport Property Profiles
B.1. Adding Preference Properties . . . . . . . . . . . . . . 91 B.2.1. reliable-inorder-stream
B.2. Transport Property Profiles . . . . . . . . . . . . . . . 92 B.2.2. reliable-message
B.2.1. reliable-inorder-stream . . . . . . . . . . . . . . . 92 B.2.3. unreliable-datagram
B.2.2. reliable-message . . . . . . . . . . . . . . . . . . 92
B.2.3. unreliable-datagram . . . . . . . . . . . . . . . . . 93
Appendix C. Relationship to the Minimal Set of Transport Services Appendix C. Relationship to the Minimal Set of Transport Services
for End Systems . . . . . . . . . . . . . . . . . . . . . 94 for End Systems
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 97 Acknowledgements
Authors' Addresses
1. Introduction 1. Introduction
This document specifies an abstract application programming interface This document specifies an abstract Application Programming Interface
(API) that describes the interface component of the high-level (API) that describes the interface component of the high-level
Transport Services architecture defined in [I-D.ietf-taps-arch]. A Transport Services architecture defined in [RFC9621]. A Transport
Transport Services system supports asynchronous, atomic transmission Services system supports asynchronous, atomic transmission of
of messages over transport protocols and network paths dynamically messages over transport protocols and network paths dynamically
selected at runtime, in environments where an endpoint selects from selected at runtime, in environments where an endpoint selects from
multiple network paths and potential transport protocols. multiple network paths and potential transport protocols.
Applications that adopt this API will benefit from a wide set of Applications that adopt this API will benefit from a wide set of
transport features that can evolve over time. This protocol- transport features that can evolve over time. This protocol-
independent API ensures that the system providing the API can independent API ensures that the system providing the API can
optimize its behavior based on the application requirements and optimize its behavior based on the application requirements and
network conditions, without requiring changes to the applications. network conditions, without requiring changes to the applications.
This flexibility enables faster deployment of new features and This flexibility enables faster deployment of new features and
protocols, and can support applications by offering racing and protocols and can support applications by offering racing and
fallback mechanisms, which otherwise need to be separately fallback mechanisms, which otherwise need to be separately
implemented in each application. Transport Services Implementations implemented in each application. Transport Services Implementations
are free to take any desired form as long as the API specification in are free to take any desired form as long as the API specification in
this document is honored; a nonprescriptive guide to implementing a this document is honored; a non-prescriptive guide to implementing a
Transport Services system is available [I-D.ietf-taps-impl]. Transport Services system is available (see [RFC9623]).
The Transport Services system derives specific path and protocol The Transport Services system derives specific path and Protocol
selection properties and supported transport features from the Selection Properties and supported transport features from the
analysis provided in [RFC8095], [RFC8923], and [RFC8922]. The analysis provided in [RFC8095], [RFC8923], and [RFC8922]. The
Transport Services API enables an implementation to dynamically Transport Services API enables an implementation to dynamically
choose a transport protocol rather than statically binding choose a transport protocol rather than statically binding
applications to a protocol at compile time. The Transport Services applications to a protocol at compile time. The Transport Services
API also provides applications with a way to override transport API also provides applications with a way to override transport
selection and instantiate a specific stack, e.g., to support servers selection and instantiate a specific stack, e.g., to support servers
wishing to listen to a specific protocol. However, forcing a choice wishing to listen to a specific protocol. However, forcing a choice
to use a specific transport stack is discouraged for general use, to use a specific transport stack is discouraged for general use
because it can reduce portability. because it can reduce portability.
1.1. Terminology and Notation 1.1. Terminology and Notation
The Transport Services API is described in terms of The Transport Services API is described in terms of:
* Objects with which an application can interact; * Objects with which an application can interact;
* Actions the application can perform on these objects; * Actions the application can perform on these objects;
* Events, which an object can send to an application to be processed * Events, which an object can send to an application to be processed
asynchronously; and asynchronously; and
* Parameters associated with these actions and events. * Parameters associated with these actions and events.
skipping to change at page 6, line 24 skipping to change at line 247
[]Object := Action() []Object := Action()
* An action that is performed on an object: * An action that is performed on an object:
Object.Action() Object.Action()
* An object sends an event: * An object sends an event:
Object -> Event<> Object -> Event<>
* An action takes a set of Parameters; an event contains a set of * An action takes a set of parameters; an event contains a set of
Parameters. action and event parameters whose names are suffixed parameters. Action and event parameters whose names are suffixed
with a question mark are optional. with a question mark are optional:
Action(param0, param1?, ...) Action(param0, param1?, ...)
Event<param0, param1?, ...> Event<param0, param1?, ...>
Objects that are passed as parameters to actions use call-by-value Objects that are passed as parameters to actions use call-by-value
behavior. Actions associated with no object are actions on the API; behavior. Actions associated with no object are actions on the API;
they are equivalent to actions on a per-application global context. they are equivalent to actions on a per-application global context.
Events are sent to the application or application-supplied code (e.g. Events are sent to the application or application-supplied code
framers, see Section 9.1.2) for processing; the details of event (e.g., framers; see Section 9.1.2) for processing; the details of
interfaces are platform- and implementation-specific, and can be event interfaces are specific to the platform or implementation and
implemented using other forms of asynchronous processing, as can be implemented using other forms of asynchronous processing, as
idiomatic for the implementing platform. idiomatic for the implementing platform.
We also make use of the following basic types: We also make use of the following basic types:
* Boolean: Instances take the value true or false. Boolean: Instances take the value true or false.
* Integer: Instances take integer values. Integer: Instances take integer values.
* Numeric: Instances take real number values. Numeric: Instances take real number values.
* String: Instances are represented in UTF-8. String: Instances are represented in UTF-8.
* IP Address: An IPv4 [RFC791] or IPv6 [RFC4291] address. IP Address: An IPv4 address [RFC791] or IPv6 address [RFC4291].
* Enumeration: A family of types in which each instance takes one of Enumeration: A family of types in which each instance takes one of a
a fixed, predefined set of values specific to a given enumerated fixed, predefined set of values specific to a given enumerated
type. type.
* Tuple: An ordered grouping of multiple value types, represented as Tuple: An ordered grouping of multiple value types, represented as a
a comma-separated list in parentheses, e.g., (Enumeration, comma-separated list in parentheses, e.g., (Enumeration,
Preference). Instances take a sequence of values each valid for Preference). Instances take a sequence of values, each valid for
the corresponding value type. the corresponding value type.
* Array: Denoted []Type, an instance takes a value for each of zero Array: Denoted []Type, an instance takes a value for each of zero or
or more elements in a sequence of the given Type. An array can be more elements in a sequence of the given Type. An array can be of
of fixed or variable length. fixed or variable length.
* Set: An unordered grouping of one or more different values of the Set: An unordered grouping of one or more different values of the
same type. same type.
For guidance on how these abstract concepts can be implemented in For guidance on how these abstract concepts can be implemented in
languages in accordance with language-specific design patterns and languages in accordance with language-specific design patterns and
platform features, see Appendix A. platform features, see Appendix A.
1.2. Specification of Requirements 1.2. 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.
2. Overview of the API Design 2. Overview of the API Design
The design of the API specified in this document is based on a set of The design of the API specified in this document is based on a set of
principles, themselves an elaboration on the architectural design principles, themselves an elaboration on the architectural design
principles defined in [I-D.ietf-taps-arch]. The API defined in this principles defined in [RFC9621]. The API defined in this document
document provides: provides:
* A Transport Services system that can offer a variety of transport * A Transport Services system that can offer a variety of transport
protocols, independent of the Protocol Stacks that will be used at protocols, independent of the Protocol Stacks that will be used at
runtime. To the degree possible, all common features of these runtime. To the degree possible, all common features of these
protocol stacks are made available to the application in a Protocol Stacks are made available to the application in a
transport-independent way. This enables applications written to a transport-independent way. This enables applications written to a
single API to make use of transport protocols in terms of the single API to make use of transport protocols in terms of the
features they provide. features they provide.
* A unified API to datagram and stream-oriented transports, allowing * A unified API to datagram and stream-oriented transports, allowing
use of a common API for Connection establishment and closing. the use of a common API for Connection establishment and closing.
* Message-orientation, as opposed to stream-orientation, using * Message orientation, as opposed to stream orientation, using
application-assisted framing and deframing where the underlying application-assisted framing and deframing where the underlying
transport does not provide these. transport does not provide these.
* Asynchronous Connection establishment, transmission, and * Asynchronous Connection establishment, transmission, and
reception. This allows concurrent operations during establishment reception. This allows concurrent operations during establishment
and event-driven application interactions with the transport and event-driven application interactions with the transport
layer. layer.
* Selection between alternate network paths, using additional * Selection between alternate network paths, using additional
information about the networks over which a Connection can operate information about the networks over which a Connection can operate
(e.g. Provisioning Domain (PvD) information [RFC7556]) where (e.g., Provisioning Domain (PvD) information [RFC7556]) where
available. available.
* Explicit support for transport-specific features to be applied, * Explicit support for transport-specific features to be applied,
when that particular transport is part of a chosen Protocol Stack. when that particular transport is part of a chosen Protocol Stack.
* Explicit support for security properties as first-order transport * Explicit support for security properties as first-order transport
features. features.
* Explicit support for configuration of cryptographic identities and * Explicit support for configuration of cryptographic identities and
transport security parameters persistent across multiple transport security parameters persistent across multiple
skipping to change at page 8, line 44 skipping to change at line 361
3. API Summary 3. API Summary
An application primarily interacts with this API through two objects: An application primarily interacts with this API through two objects:
Preconnections and Connections. A Preconnection object (Section 6) Preconnections and Connections. A Preconnection object (Section 6)
represents a set of properties and constraints on the selection and represents a set of properties and constraints on the selection and
configuration of paths and protocols to establish a Connection with configuration of paths and protocols to establish a Connection with
an Endpoint. A Connection object represents an instance of a an Endpoint. A Connection object represents an instance of a
transport Protocol Stack on which data can be sent to and/or received transport Protocol Stack on which data can be sent to and/or received
from a Remote Endpoint (i.e., a logical connection that, depending on from a Remote Endpoint (i.e., a logical connection that, depending on
the kind of transport, can be bi-directional or unidirectional, and the kind of transport, can be bidirectional or unidirectional, and
that can use a stream protocol or a datagram protocol). Connections that can use a stream protocol or a datagram protocol). Connections
are presented consistently to the application, irrespective of are presented consistently to the application, irrespective of
whether the underlying transport is connection-less or connection- whether the underlying transport is connectionless or connection
oriented. Connections can be created from Preconnections in three oriented. Connections can be created from Preconnections in three
ways: ways:
* by initiating the Preconnection (i.e., creating a Connection from * initiating the Preconnection (i.e., creating a Connection from the
the Preconnection, actively opening, as in a client; see Preconnection, actively opening, as in a client; see Initiate() in
Initiate() in Section 7.1), Section 7.1),
* by listening on the Preconnection (i.e., creating a Listener based * listening on the Preconnection (i.e., creating a Listener based on
on the Preconnection, passively opening, as in a server; see the Preconnection, passively opening, as in a server; see Listen()
Listen() in Section 7.2), in Section 7.2), or
* or by a rendezvous for the Preconnection (i.e., peer to peer * a rendezvous for the Preconnection (i.e., peer-to-peer connection
establishment; see Rendezvous() in Section 7.3). establishment; see Rendezvous() in Section 7.3).
Once a Connection is established, data can be sent and received on it Once a Connection is established, data can be sent and received on it
in the form of Messages. The API supports the preservation of in the form of Messages. The API supports the preservation of
message boundaries both via explicit Protocol Stack support, and via message boundaries via both explicit Protocol Stack support and
application support through a Message Framer that finds message application support through a Message Framer that finds message
boundaries in a stream. Messages are received asynchronously through boundaries in a stream. Messages are received asynchronously through
event handlers registered by the application. Errors and other event handlers registered by the application. Errors and other
notifications also happen asynchronously on the Connection. It is notifications also happen asynchronously on the Connection. It is
not necessary for an application to handle all events; some events not necessary for an application to handle all events; some events
can have implementation-specific default handlers. can have implementation-specific default handlers.
The application SHOULD NOT assume that ignoring events (e.g., errors) The application SHOULD NOT assume that ignoring events (e.g., errors)
is always safe. is always safe.
3.1. Usage Examples 3.1. Usage Examples
The following usage examples illustrate how an application might use The following usage examples illustrate how an application might use
the Transport Services API to: the Transport Services API to act as:
* Act as a server, by listening for incoming Connections, receiving * a server, by listening for incoming Connections, receiving
requests, and sending responses, see Section 3.1.1. requests, and sending responses; see Section 3.1.1.
* Act as a client, by connecting to a Remote Endpoint using * a client, by connecting to a Remote Endpoint using Initiate,
Initiate, sending requests, and receiving responses, see sending requests, and receiving responses; see Section 3.1.2.
Section 3.1.2.
* Act as a peer, by connecting to a Remote Endpoint using Rendezvous * a peer, by connecting to a Remote Endpoint using Rendezvous while
while simultaneously waiting for incoming Connections, sending simultaneously waiting for incoming Connections, sending Messages,
Messages, and receiving Messages, see Section 3.1.3. and receiving Messages; see Section 3.1.3.
The examples in this section presume that a transport protocol is The examples in this section presume that a transport protocol is
available between the Local and Remote Endpoints that provides available between the Local and Remote Endpoints and that this
Reliable Data Transfer, Preservation of Data Ordering, and protocol provides reliable data transfer, preservation of data
Preservation of Message Boundaries. In this case, the application ordering, and preservation of message boundaries. In this case, the
can choose to receive only complete Messages. application can choose to receive only complete Messages.
If none of the available transport protocols provides Preservation of If none of the available transport protocols provide preservation of
Message Boundaries, but there is a transport protocol that provides a message boundaries, but there is a transport protocol that provides a
reliable ordered byte-stream, an application could receive this byte- reliable ordered byte-stream, an application could receive this byte-
stream as partial Messages and transform it into application-layer stream as partial Messages and transform it into application-layer
Messages. Alternatively, an application might provide a Message Messages. Alternatively, an application might provide a Message
Framer, which can transform a sequence of Messages into a byte-stream Framer, which can transform a sequence of Messages into a byte-stream
and vice versa (Section 9.1.2). and vice versa (Section 9.1.2).
3.1.1. Server Example 3.1.1. Server Example
This is an example of how an application might listen for incoming This is an example of how an application might listen for incoming
Connections using the Transport Services API, receive a request, and Connections using the Transport Services API, receive a request, and
send a response. send a response.
LocalSpecifier := NewLocalEndpoint() LocalSpecifier := NewLocalEndpoint()
LocalSpecifier.WithInterface("any") LocalSpecifier.WithInterface("any")
LocalSpecifier.WithService("https") LocalSpecifier.WithService("https")
TransportProperties := NewTransportProperties() TransportProperties := NewTransportProperties()
TransportProperties.Require(preserveMsgBoundaries) TransportProperties.Require(preserveMsgBoundaries)
// Reliable Data Transfer and Preserve Order are Required by default // Reliable data transfer and preserve order are required by default
SecurityParameters := NewSecurityParameters() SecurityParameters := NewSecurityParameters()
SecurityParameters.Set(serverCertificate, myCertificate) SecurityParameters.Set(serverCertificate, myCertificate)
// Specifying a Remote Endpoint is optional when using Listen // Specifying a Remote Endpoint is optional when using Listen
Preconnection := NewPreconnection(LocalSpecifier, Preconnection := NewPreconnection(LocalSpecifier,
TransportProperties, TransportProperties,
SecurityParameters) SecurityParameters)
Listener := Preconnection.Listen() Listener := Preconnection.Listen()
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Connection.Close() Connection.Close()
// Stop listening for incoming Connections // Stop listening for incoming Connections
// (this example supports only one Connection) // (this example supports only one Connection)
Listener.Stop() Listener.Stop()
//---- Receive event handler end ---- //---- Receive event handler end ----
3.1.2. Client Example 3.1.2. Client Example
This is an example of how an application might open two Connections This is an example of how an application might open two Connections
to a remote application using the Transport Services API, and send a to a remote application using the Transport Services API and send a
request as well as receive a response on each of them. The code request as well as receive a response on each of them. The code
designated with comments as "Ready event handler" could, e.g., be designated with comments as "Ready event handler" could, for example,
implemented as a callback function, for example. This function would be implemented as a callback function. This function would receive
receive the Connection that it expects to operate on ("Connection" the Connection that it expects to operate on ("Connection" and
and "Connection2" in the example), handed over using the variable "Connection2" in the example) handed over using the variable name
name "C". "C".
RemoteSpecifier := NewRemoteEndpoint() RemoteSpecifier := NewRemoteEndpoint()
RemoteSpecifier.WithHostName("example.com") RemoteSpecifier.WithHostName("example.com")
RemoteSpecifier.WithService("https") RemoteSpecifier.WithService("https")
TransportProperties := NewTransportProperties() TransportProperties := NewTransportProperties()
TransportProperties.Require(preserve-msg-boundaries) TransportProperties.Require(preserve-msg-boundaries)
// Reliable Data Transfer and Preserve Order are Required by default // Reliable data transfer and preserve order are required by default
SecurityParameters := NewSecurityParameters() SecurityParameters := NewSecurityParameters()
TrustCallback := NewCallback({ TrustCallback := NewCallback({
// Verify identity of the Remote Endpoint, return the result // Verify the identity of the Remote Endpoint and return the result
}) })
SecurityParameters.SetTrustVerificationCallback(TrustCallback) SecurityParameters.SetTrustVerificationCallback(TrustCallback)
// Specifying a Local Endpoint is optional when using Initiate // Specifying a Local Endpoint is optional when using Initiate
Preconnection := NewPreconnection(RemoteSpecifier, Preconnection := NewPreconnection(RemoteSpecifier,
TransportProperties, TransportProperties,
SecurityParameters) SecurityParameters)
Connection := Preconnection.Initiate() Connection := Preconnection.Initiate()
Connection2 := Connection.Clone() Connection2 := Connection.Clone()
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Connection2 -> Received<messageDataResponse, messageContext> Connection2 -> Received<messageDataResponse, messageContext>
// Close the Connection in a Receive event handler // Close the Connection in a Receive event handler
Connection.Close() Connection.Close()
Connection2.Close() Connection2.Close()
A Preconnection serves as a template for creating a Connection via A Preconnection serves as a template for creating a Connection via
initiating, listening, or via rendezvous. Once a Connection has been initiating, listening, or via rendezvous. Once a Connection has been
created, changes made to the Preconnection that was used to create it created, changes made to the Preconnection that was used to create it
do not affect this Connection. Preconnections are reusable after do not affect this Connection. Preconnections are reusable after
being used to create a Connection, whether this Connection was closed being used to create a Connection, whether or not this Connection was
or not. Hence, in the above example, it would be correct for the closed. Hence, in the above example, it would be correct for the
client to initiate a third Connection to the example.com server by client to initiate a third Connection to the example.com server by
continuing as follows: continuing as follows:
//.. carry out adjustments to the Preconnection, if desired //.. carry out adjustments to the Preconnection, if desired
Connection3 := Preconnection.Initiate() Connection3 := Preconnection.Initiate()
3.1.3. Peer Example 3.1.3. Peer Example
This is an example of how an application might establish a Connection This is an example of how an application might establish a Connection
with a peer using Rendezvous, send a Message, and receive a Message. with a peer using Rendezvous, send a Message, and receive a Message.
// Configure local candidates: a port on the Local Endpoint // Configure local candidates: a port on the Local Endpoint
// and via a STUN server // and via a Session Traversal Utilities for NAT (STUN) server
HostCandidate := NewLocalEndpoint() HostCandidate := NewLocalEndpoint()
HostCandidate.WithPort(9876) HostCandidate.WithPort(9876)
StunCandidate := NewLocalEndpoint() StunCandidate := NewLocalEndpoint()
StunCandidate.WithStunServer(address, port, credentials) StunCandidate.WithStunServer(address, port, credentials)
LocalCandidates = [HostCandidate, StunCandidate] LocalCandidates = [HostCandidate, StunCandidate]
TransportProperties := // ...Configure transport properties TransportProperties := // ...Configure transport properties
SecurityParameters := // ...Configure security properties SecurityParameters := // ...Configure security properties
Preconnection := NewPreconnection(LocalCandidates, Preconnection := NewPreconnection(LocalCandidates,
[], // No remote candidates yet [], // No remote candidates yet
TransportProperties, TransportProperties,
SecurityParameters) SecurityParameters)
// Resolve the LocalCandidates. The Preconnection.Resolve() // Resolve the LocalCandidates. The Preconnection.Resolve()
// call resolves both local and remote candidates but, since // call resolves both local and remote candidates; however,
// the remote candidates have not yet been specified, the // because the remote candidates have not yet been specified,
// ResolvedRemote list returned will be empty and is not // the ResolvedRemote list returned will be empty and is not
// used. // used.
ResolvedLocal, ResolvedRemote = Preconnection.Resolve() ResolvedLocal, ResolvedRemote = Preconnection.Resolve()
// Application-specific code goes here to send the ResolvedLocal // Application-specific code goes here to send the ResolvedLocal
// list to peer via some out-of-band signalling channel (e.g., // list to the peer via some out-of-band signaling channel (e.g.,
// in a SIP message) // in a SIP message).
... ...
// Application-specific code goes here to receive RemoteCandidates // Application-specific code goes here to receive RemoteCandidates
// (type []RemoteEndpoint, a list of RemoteEndpoint objects) from // (type []RemoteEndpoint, a list of RemoteEndpoint objects) from
// the peer via the signalling channel // the peer via the signaling channel.
... ...
// Add remote candidates and initiate the rendezvous: // Add remote candidates and initiate the rendezvous:
Preconnection.AddRemote(RemoteCandidates) Preconnection.AddRemote(RemoteCandidates)
Preconnection.Rendezvous() Preconnection.Rendezvous()
Preconnection -> RendezvousDone<Connection> Preconnection -> RendezvousDone<Connection>
//---- RendezvousDone event handler begin ---- //---- RendezvousDone event handler begin ----
Connection.Send(messageDataRequest) Connection.Send(messageDataRequest)
Connection.Receive() Connection.Receive()
//---- RendezvousDone event handler end ---- //---- RendezvousDone event handler end ----
Connection -> Received<messageDataResponse, messageContext> Connection -> Received<messageDataResponse, messageContext>
// If new Remote Endpoint candidates are received from the // If new Remote Endpoint candidates are received from the
// peer over the signalling channel, for example if using // peer over the signaling channel -- for example, if using
// Trickle ICE, then add them to the Connection: // Trickle Interactive Connectivity Establishment (ICE) --
// then add them to the Connection:
Connection.AddRemote(NewRemoteCandidates) Connection.AddRemote(NewRemoteCandidates)
// On a PathChange<> event, resolve the Local Endpoint Identifiers to // On a PathChange<> event, resolve the Local Endpoint Identifiers to
// see if a new Local Endpoint has become available and, if // see if a new Local Endpoint has become available and, if
// so, send to the peer as a new candidate and add to the // so, send to the peer as a new candidate and add to the
// Connection: // Connection:
Connection -> PathChange<> Connection -> PathChange<>
//---- PathChange event handler begin ---- //---- PathChange event handler begin ----
ResolvedLocal, ResolvedRemote = Preconnection.Resolve() ResolvedLocal, ResolvedRemote = Preconnection.Resolve()
if ResolvedLocal has changed: if ResolvedLocal has changed:
// Application-specific code goes here to send the // Application-specific code goes here to send the
// ResolvedLocal list to peer via signalling channel // ResolvedLocal list to the peer via the signaling channel
... ...
// Add the new Local Endpoints to the Connection: // Add the new Local Endpoints to the Connection:
Connection.AddLocal(ResolvedLocal) Connection.AddLocal(ResolvedLocal)
//---- PathChange event handler end ---- //---- PathChange event handler end ----
// Close the Connection in a Receive event handler // Close the Connection in a Receive event handler:
Connection.Close() Connection.Close()
4. Transport Properties 4. Transport Properties
Each application using the Transport Services API declares its Each application using the Transport Services API declares its
preferences for how the Transport Services system is to operate. preferences for how the Transport Services system is to operate.
This is done by using Transport Properties, as defined in This is done by using Transport Properties, as defined in [RFC9621],
[I-D.ietf-taps-arch], at each stage of the lifetime of a Connection. at each stage of the lifetime of a Connection.
Transport Properties are divided into Selection, Connection, and Transport Properties are divided into Selection, Connection, and
Message Properties. Message Properties.
Selection Properties (see Section 6.2) can only be set during pre- Selection Properties (see Section 6.2) can only be set during
establishment. They are only used to specify which paths and preestablishment. They are only used to specify which paths and
Protocol Stacks can be used and are preferred by the application. Protocol Stacks can be used and are preferred by the application.
Calling Initiate on a Preconnection creates an outbound Connection, Calling Initiate on a Preconnection creates an outbound Connection,
and the Selection Properties remain readable from the Connection, but and the Selection Properties remain readable from the Connection but
become immutable. Selection Properties can be set on Preconnections, become immutable. Selection Properties can be set on Preconnections,
and the effect of Selection Properties can be queried on Connections and the effect of Selection Properties can be queried on Connections
and Messages. and Messages.
Connection Properties (see Section 8.1) are used to inform decisions Connection Properties (see Section 8.1) are used to inform decisions
made during establishment and to fine-tune the established made during establishment and to fine-tune the established
Connection. They can be set during pre-establishment, and can be Connection. They can be set during preestablishment and can be
changed later. Connection Properties can be set on Connections and changed later. Connection Properties can be set on Connections and
Preconnections; when set on Preconnections, they act as an initial Preconnections; when set on Preconnections, they act as an initial
default for the resulting Connections. default for the resulting Connections.
Message Properties (see Section 9.1.3) control the behavior of the Message Properties (see Section 9.1.3) control the behavior of the
selected protocol stack(s) when sending Messages. Message Properties selected Protocol Stack(s) when sending Messages. Message Properties
can be set on Messages, Connections, and Preconnections; when set on can be set on Messages, Connections, and Preconnections; when set on
the latter two, they act as an initial default for the Messages sent the latter two, they act as an initial default for the Messages sent
over those Connections. over those Connections.
Note that configuring Connection Properties and Message Properties on Note that configuring Connection Properties and Message Properties on
Preconnections is preferred over setting them later. Early Preconnections is preferred over setting them later. Early
specification of Connection Properties allows their use as additional specification of Connection Properties allows their use as additional
input to the selection process. Protocol-specific Properties, which input to the selection process. Protocol-specific Properties, which
enable configuration of specialized features of a specific protocol enable configuration of specialized features of a specific protocol
(see Section 3.2 of [I-D.ietf-taps-arch]) are not used as an input to (see Section 3.2 of [RFC9621]), are not used as input to the
the selection process, but only support configuration if the selection process; they only support configuration if the respective
respective protocol has been selected. protocol has been selected.
4.1. Transport Property Names 4.1. Transport Property Names
Transport Properties are referred to by property names, represented Transport Properties are referred to by property names, represented
as case-insensitive strings. These names serve two purposes: as case-insensitive strings. These names serve two purposes:
* Allowing different components of a Transport Services * Allowing different components of a Transport Services
Implementation to pass Transport Properties, e.g., between a Implementation to pass Transport Properties, e.g., between a
language frontend and a policy manager, or as a representation of language front end and a policy manager or as a representation of
properties retrieved from a file or other storage. properties retrieved from a file or other storage.
* Making the code of different Transport Services Implementations * Making the code of different Transport Services Implementations
look similar. While individual programming languages might look similar. While individual programming languages might
preclude strict adherence to the aforementioned naming convention preclude strict adherence to the aforementioned naming convention
(for instance, by prohibiting the use of hyphens in symbols), (for instance, by prohibiting the use of hyphens in symbols),
users interacting with multiple implementations will still benefit users interacting with multiple implementations will still benefit
from the consistency resulting from the use of visually similar from the consistency resulting from the use of visually similar
symbols. symbols.
Transport Property Names are hierarchically organized in the form Transport Property Names are hierarchically organized in the form
[<Namespace>.]<PropertyName>. [<Namespace>.]<PropertyName>.
* The optional Namespace component and its trailing character . MUST * The optional Namespace component and its trailing character . MUST
be omitted for well-known, generic properties, i.e., for be omitted for well-known, generic properties, i.e., for
properties that are not specific to a protocol. properties that are not specific to a protocol.
* Protocol-specific Properties MUST use the protocol acronym as the * Protocol-specific Properties MUST use the protocol acronym as the
Namespace (e.g., a Connection that uses TCP could support a TCP- Namespace (e.g., a Connection that uses TCP could support a TCP-
specific Transport Property, such as the TCP user timeout value, specific Transport Property, such as the TCP User Timeout value,
in a Protocol-specific Property called tcp.userTimeoutValue (see in a Protocol-specific Property called tcp.userTimeoutValue (see
Section 8.2)). Section 8.2)).
* Vendor or implementation specific properties MUST be placed in a * Vendor-specific or implementation-specific properties MUST be
Namespace starting with the underscore _ character and SHOULD use placed in a Namespace starting with the underscore _ character and
a string identifying the vendor or implementation. SHOULD use a string identifying the vendor or implementation.
* For IETF protocols, the name of a Protocol-specific Property MUST * For IETF protocols, the name of a Protocol-specific Property MUST
be specified in an IETF document published in the RFC Series after be specified in an IETF document published in the RFC Series after
IETF review. An IETF protocol Namespace does not start with an IETF review. An IETF protocol Namespace does not start with an
underscore character. underscore character.
Namespaces for each of the keywords provided in the IANA protocol Namespaces for each of the keywords provided in the "Protocol
numbers registry (see https://www.iana.org/assignments/protocol- Numbers" registry (see <https://www.iana.org/assignments/protocol-
numbers/protocol-numbers.xhtml) are reserved for Protocol-specific numbers/>) are reserved for Protocol-specific Properties and MUST NOT
Properties and MUST NOT be used for vendor or implementation-specific be used for vendor-specific or implementation-specific properties.
properties. Terms listed as keywords as in the protocol numbers Terms listed as keywords, as in the "Protocol Numbers" registry,
registry SHOULD be avoided as any part of a vendor- or SHOULD be avoided as any part of a vendor-specific or implementation-
implementation-specific property name. specific property name.
Though Transport Property Names are case-insensitive, it is Though Transport Property Names are case insensitive, it is
recommended to use camelCase to improve readability. Implementations recommended to use camelCase to improve readability. Implementations
may transpose Transport Property Names into snake_case or PascalCase may transpose Transport Property Names into snake_case or PascalCase
to blend into the language environment. to blend into the language environment.
4.2. Transport Property Types 4.2. Transport Property Types
Each Transport Property has one of the basic types described in Each Transport Property has one of the basic types described in
Section 1.1. Section 1.1.
Most Selection Properties (see Section 6.2) are of the Enumeration Most Selection Properties (see Section 6.2) are of the Enumeration
type, and use the Preference Enumeration, which takes one of five type, and they use the Preference Enumeration, which takes one of
possible values (Prohibit, Avoid, No Preference, Prefer, or Require) five possible values (Prohibit, Avoid, No Preference, Prefer, or
denoting the level of preference for a given property during protocol Require) denoting the level of preference for a given property during
selection. protocol selection.
5. Scope of the API Definition 5. Scope of the API Definition
This document defines a language- and platform-independent API of a This document defines a language- and platform-independent API of a
Transport Services system. Given the wide variety of languages and Transport Services system. Given the wide variety of languages and
language conventions used to write applications that use the language conventions used to write applications that use the
transport layer to connect to other applications over the Internet, transport layer to connect to other applications over the Internet,
this independence makes this API necessarily abstract. this independence makes this API necessarily abstract.
There is no interoperability benefit in tightly defining how the API There is no interoperability benefit in tightly defining how the API
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* Actions, events, and errors in implementations of the Transport * Actions, events, and errors in implementations of the Transport
Services API SHOULD use the names given for them in the document, Services API SHOULD use the names given for them in the document,
subject to capitalization, punctuation, and other typographic subject to capitalization, punctuation, and other typographic
conventions in the language of the implementation, unless the conventions in the language of the implementation, unless the
implementation itself uses different names for substantially implementation itself uses different names for substantially
equivalent objects for networking by convention. equivalent objects for networking by convention.
* Transport Services systems SHOULD implement each Selection * Transport Services systems SHOULD implement each Selection
Property, Connection Property, and Message Context Property Property, Connection Property, and Message Context Property
specified in this document. These features SHOULD be implemented specified in this document. These features SHOULD be implemented
even when in a specific implementation it will always result in no even when, in a specific implementation, it will always result in
operation, e.g. there is no action when the API specifies a no operation, e.g., there is no action when the API specifies a
Property that is not available in a transport protocol implemented Property that is not available in a transport protocol implemented
on a specific platform. For example, if TCP is the only on a specific platform. For example, if TCP is the only
underlying transport protocol, the Message Property msgOrdered can underlying transport protocol, the Message Property msgOrdered can
be implemented (trivially, as a no-op) as disabling the be implemented (trivially, as a no-op) as disabling the
requirement for ordering will not have any effect on delivery requirement for ordering will not have any effect on delivery
order for Connections over TCP. Similarly, the msgLifetime order for Connections over TCP. Similarly, the msgLifetime
Message Property can be implemented but ignored, as the Message Property can be implemented but ignored, as the
description of this Property states that "it is not guaranteed description of this Property (Section 9.1.3.1) states that "it is
that a Message will not be sent when its Lifetime has expired". not guaranteed that a Message will not be sent when its Lifetime
has expired".
* Implementations can use other representations for Transport * Implementations can use other representations for Transport
Property Names, e.g., by providing constants, but should provide a Property Names, e.g., by providing constants, but should provide a
straight-forward mapping between their representation and the straightforward mapping between their representation and the
property names specified here. property names specified here.
6. Pre-Establishment Phase 6. Preestablishment Phase
The pre-establishment phase allows applications to specify properties The preestablishment phase allows applications to specify properties
for the Connections that they are about to make, or to query the API for the Connections that they are about to make or to query the API
about potential Connections they could make. about potential Connections they could make.
A Preconnection object represents a potential Connection. It is a A Preconnection object represents a potential Connection. It is a
passive object (a data structure) that merely maintains the state passive object (a data structure) that merely maintains the state
that describes the properties of a Connection that might exist in the that describes the properties of a Connection that might exist in the
future. This state comprises Local Endpoint and Remote Endpoint future. This state comprises Local Endpoint and Remote Endpoint
objects that denote the endpoints of the potential Connection (see objects that denote the endpoints of the potential Connection (see
Section 6.1), the Selection Properties (see Section 6.2), any Section 6.1), the Selection Properties (see Section 6.2), any
preconfigured Connection Properties (Section 8.1), and the security preconfigured Connection Properties (Section 8.1), and the security
parameters (see Section 6.3): parameters (see Section 6.3):
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on the appropriate interface(s). At least one Remote Endpoint MUST on the appropriate interface(s). At least one Remote Endpoint MUST
be specified if the Preconnection is used to Initiate Connections, be specified if the Preconnection is used to Initiate Connections,
but the list of Remote Endpoints MAY be empty if the Preconnection is but the list of Remote Endpoints MAY be empty if the Preconnection is
used to Listen for incoming Connections. At least one Local Endpoint used to Listen for incoming Connections. At least one Local Endpoint
and one Remote Endpoint MUST be specified if a peer-to-peer and one Remote Endpoint MUST be specified if a peer-to-peer
Rendezvous is to occur based on the Preconnection. Rendezvous is to occur based on the Preconnection.
If more than one Local Endpoint is specified on a Preconnection, then If more than one Local Endpoint is specified on a Preconnection, then
the application is indicating that all of the Local Endpoints are the application is indicating that all of the Local Endpoints are
eligible to be used for Connections. For example, their Endpoint eligible to be used for Connections. For example, their Endpoint
Identifiers might correspond to different interfaces on a multi-homed Identifiers might correspond to different interfaces on a multihomed
host, or their Endpoint Identifiers might correspond to local host or their Endpoint Identifiers might correspond to local
interfaces and a STUN server that can be resolved to a server interfaces and a STUN server that can be resolved to a server-
reflexive address for a Preconnection used to make a peer-to-peer reflexive address for a Preconnection used to make a peer-to-peer
Rendezvous. Rendezvous.
If more than one Remote Endpoint is specified on the Preconnection, If more than one Remote Endpoint is specified on the Preconnection,
the application is indicating that it expects all of the Remote the application is indicating that it expects all of the Remote
Endpoints to offer an equivalent service, and that the Transport Endpoints to offer an equivalent service and that the Transport
Services system can choose any of them for a Connection. For Services system can choose any of them for a Connection. For
example, a Remote Endpoint might represent various network interfaces example, a Remote Endpoint might represent various network interfaces
of a host, or a server reflexive address that can be used to reach a of a host, or a server-reflexive address that can be used to reach a
host, or a set of hosts that provide equivalent local balanced host, or a set of hosts that provide equivalent local balanced
service. service.
In most cases, it is expected that a single Remote Endpoint will be In most cases, it is expected that a single Remote Endpoint will be
specified by name, and a later call to Initiate on the Preconnection specified by name, and a later call to Initiate on the Preconnection
(see Section 7.1) will internally resolve that name to a list of (see Section 7.1) will internally resolve that name to a list of
concrete Endpoint Identifers. Specifying multiple Remote Endpoints concrete Endpoint Identifiers. Specifying multiple Remote Endpoints
on a Preconnection allows applications to override this for more on a Preconnection allows applications to override this for more
detailed control. detailed control.
If Message Framers are used (see Section 9.1.2), they MUST be added If Message Framers are used (see Section 9.1.2), they MUST be added
to the Preconnection during pre-establishment. to the Preconnection during preestablishment.
6.1. Specifying Endpoints 6.1. Specifying Endpoints
The Transport Services API uses the Local Endpoint and Remote The Transport Services API uses the Local Endpoint and Remote
Endpoint objects to refer to the endpoints of a Connection. Endpoint objects to refer to the endpoints of a Connection.
Endpoints can be created as either remote or local: Endpoints can be created as either remote or local:
RemoteSpecifier := NewRemoteEndpoint() RemoteSpecifier := NewRemoteEndpoint()
LocalSpecifier := NewLocalEndpoint() LocalSpecifier := NewLocalEndpoint()
A single Endpoint object represents the identity of a network host. A single Endpoint object represents the identity of a network host.
That endpoint can be more or less specific depending on which That endpoint can be more or less specific, depending on which
Endpoint Identifiers are set. For example, an Endpoint that only Endpoint Identifiers are set. For example, an Endpoint that only
specifies a hostname can, in fact, finally correspond to several specifies a hostname can, in fact, finally correspond to several
different IP addresses on different hosts. different IP addresses on different hosts.
An Endpoint object can be configured with the following identifiers: An Endpoint object can be configured with the following identifiers:
* HostName (string): * HostName (string):
RemoteSpecifier.WithHostName("example.com") RemoteSpecifier.WithHostName("example.com")
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An Endpoint object can be configured with the following identifiers: An Endpoint object can be configured with the following identifiers:
* HostName (string): * HostName (string):
RemoteSpecifier.WithHostName("example.com") RemoteSpecifier.WithHostName("example.com")
* Port (a 16-bit unsigned Integer): * Port (a 16-bit unsigned Integer):
RemoteSpecifier.WithPort(443) RemoteSpecifier.WithPort(443)
* Service (an identifier string that maps to a port; either a * Service (an identifier string that maps to a port; either a
service name associated with a port number, from service name associated with a port number (from
https://www.iana.org/assignments/service-names-port-numbers/ <https://www.iana.org/assignments/service-names-port-numbers/>) or
service-names-port-numbers.xhtml, or a DNS SRV service name to be a DNS SRV service name to be resolved):
resolved):
RemoteSpecifier.WithService("https") RemoteSpecifier.WithService("https")
* IP address (an IPv4 or IPv6 address type; note that the examples * IP address (an IPv4 or IPv6 address type; note that the examples
here show the human-readable form of the IP addresses, but the here show the human-readable form of the IP addresses, but the
functions can take a binary encoding of the addresses): functions can take a binary encoding of the addresses):
RemoteSpecifier.WithIPAddress(192.0.2.21) RemoteSpecifier.WithIPAddress(192.0.2.21)
RemoteSpecifier.WithIPAddress(2001:db8:4920:e29d:a420:7461:7073:a) RemoteSpecifier.WithIPAddress(2001:db8:4920:e29d:a420:7461:7073:a)
* Interface identifier (which can be a string name or other * Interface identifier (which can be a string name or other
platform-specific identifier), e.g., to qualify link-local platform-specific identifier), e.g., to qualify link-local
addresses (see Section 6.1.2 for details): addresses (see Section 6.1.2 for details):
LocalSpecifier.WithInterface("en0") LocalSpecifier.WithInterface("en0")
The Resolve action on a Preconnection can be used to obtain a list of The Resolve action on a Preconnection can be used to obtain a list of
available local interfaces. available local interfaces.
Note that an IPv6 address specified with a scope zone ID (e.g. Note that an IPv6 address specified with a scope zone ID (e.g.,
fe80::2001:db8%en0) is equivalent to WithIPAddress with an unscoped fe80::2001:db8%en0) is equivalent to WithIPAddress with an unscoped
address and WithInterface together. address and WithInterface together.
Applications creating Endpoint objects using WithHostName SHOULD Applications creating Endpoint objects using WithHostName SHOULD
provide fully-qualified domain names (FQDNs). Not providing an FQDN provide Fully Qualified Domain Names (FQDNs). Not providing an FQDN
will result in the Transport Services Implementation needing to use will result in the Transport Services Implementation needing to use
DNS search domains for name resolution, which might lead to DNS search domains for name resolution, which might lead to
inconsistent or unpredictable behavior. inconsistent or unpredictable behavior.
The design of the API MUST NOT permit an Endpoint object to be The design of the API MUST NOT permit an Endpoint object to be
configured with multiple Endpoint Identifiers of the same type. For configured with multiple Endpoint Identifiers of the same type. For
example, an Endpoint object cannot specify two IP addresses. Two example, an Endpoint object cannot specify two IP addresses. Two
separate IP addresses are represented as two Endpoint objects. If a separate IP addresses are represented as two Endpoint objects. If a
Preconnection specifies a Remote Endpoint with a specific IP address Preconnection specifies a Remote Endpoint with a specific IP address
set, it will only establish Connections to that IP address. If, on set, it will only establish Connections to that IP address. If, on
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resolution and attempt using any address derived from the original resolution and attempt using any address derived from the original
hostname of the Remote Endpoint. Note that multiple Remote Endpoints hostname of the Remote Endpoint. Note that multiple Remote Endpoints
can be added to a Preconnection, as discussed in Section 7.5. can be added to a Preconnection, as discussed in Section 7.5.
The Transport Services system resolves names internally, when the The Transport Services system resolves names internally, when the
Initiate, Listen, or Rendezvous method is called to establish a Initiate, Listen, or Rendezvous method is called to establish a
Connection. Privacy considerations for the timing of this resolution Connection. Privacy considerations for the timing of this resolution
are given in Section 13. are given in Section 13.
The Resolve action on a Preconnection can be used by the application The Resolve action on a Preconnection can be used by the application
to force early binding when required, for example with some Network to force early binding when required, for example, with some Network
Address Translator (NAT) traversal protocols (see Section 7.3). Address Translator (NAT) traversal protocols (see Section 7.3).
6.1.1. Using Multicast Endpoints 6.1.1. Using Multicast Endpoints
To use multicast, a Preconnection is first created with the Local/ To use multicast, a Preconnection is first created with the Local/
Remote Endpoint Identifer specifying the any-source multicast (ASM) Remote Endpoint Identifier specifying the Any-Source Multicast (ASM)
or source-specific multicast (SSM) multicast group and destination or Source-Specific Multicast (SSM) multicast group and destination
port number. This is then followed by a call to either Initiate, port number. This is then followed by a call to either Initiate,
Listen, or Rendezvous depending on whether the resulting Connection Listen, or Rendezvous, depending on whether the resulting Connection
is to be used to send messages to the multicast group, receive is to be used to send messages to the multicast group, receive
messages from the group, or, for an any-source multicast group, to messages from the group, or both send and receive messages (as is the
both send and receive messages. case for an ASM group).
Note that the Transport Services API has separate specifier calls for Note that the Transport Services API has separate specifier calls for
multicast groups to avoid introducing filter properties for single- multicast groups to avoid introducing filter properties for single-
source multicast and seeks to avoid confusion that can be caused by source multicast and seeks to avoid confusion that can be caused by
overloading the unicast specifiers. overloading the unicast specifiers.
Calling Initiate on that Preconnection creates a Connection that can Calling Initiate on that Preconnection creates a Connection that can
be used to send Messages to the multicast group. The Connection be used to send Messages to the multicast group. The Connection
object that is created will support Send but not Receive. Any object that is created will support Send but not Receive. Any
Connections created this way are send-only, and do not join the Connections created this way are send-only and do not join the
multicast group. The resulting Connection will have a Local Endpoint multicast group. The resulting Connection will have a Local Endpoint
identifying the local interface to which the Connection is bound and identifying the local interface to which the Connection is bound and
a Remote Endpoint identifying the multicast group. a Remote Endpoint identifying the multicast group.
The following API calls can be used to configure a Preconnection The following API calls can be used to configure a Preconnection
before calling Initiate: before calling Initiate:
RemoteSpecifier.WithMulticastGroupIP(GroupAddress) RemoteSpecifier.WithMulticastGroupIP(GroupAddress)
RemoteSpecifier.WithPort(PortNumber) RemoteSpecifier.WithPort(PortNumber)
RemoteSpecifier.WithHopLimit(HopLimit) RemoteSpecifier.WithHopLimit(HopLimit)
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multicast group. The resulting Connection will have a Local Endpoint multicast group. The resulting Connection will have a Local Endpoint
identifying the local interface to which the Connection is bound and identifying the local interface to which the Connection is bound and
a Remote Endpoint identifying the multicast group. a Remote Endpoint identifying the multicast group.
The following API calls can be used to configure a Preconnection The following API calls can be used to configure a Preconnection
before calling Initiate: before calling Initiate:
RemoteSpecifier.WithMulticastGroupIP(GroupAddress) RemoteSpecifier.WithMulticastGroupIP(GroupAddress)
RemoteSpecifier.WithPort(PortNumber) RemoteSpecifier.WithPort(PortNumber)
RemoteSpecifier.WithHopLimit(HopLimit) RemoteSpecifier.WithHopLimit(HopLimit)
Calling Listen on a Preconnection with a multicast group specified on Calling Listen on a Preconnection with a multicast group specified on
the Remote Endpoint will join the multicast group to receive the Remote Endpoint will join the multicast group to receive
Messages. This Listener will create one Connection for each Remote Messages. This Listener will create one Connection for each Remote
Endpoint sending to the group, with the Local Endpoint Identifer Endpoint sending to the group, with the Local Endpoint Identifier
specified as a group address. The set of Connection objects created specified as a group address. The set of Connection objects created
forms a Connection Group. The receiving interface can be restricted forms a Connection Group. The receiving interface can be restricted
by passing it as part of the LocalSpecifier or queried through the by passing it as part of the LocalSpecifier or queried through the
Message Context on the Messages received (see Section 9.1.1 for Message Context on the Messages received (see Section 9.1.1 for
further details). further details).
Specifying WithHopLimit sets the Time To Live (TTL) field in the Specifying WithHopLimit sets the Time To Live (TTL) field in the
header of IPv4 packets or the Hop Count field in the header of IPv6 header of IPv4 packets or the Hop Count field in the header of IPv6
packets. packets.
The following API calls can be used to configure a Preconnection The following API calls can be used to configure a Preconnection
before calling Listen: before calling Listen:
LocalSpecifier.WithSingleSourceMulticastGroupIP(GroupAddress, LocalSpecifier.WithSingleSourceMulticastGroupIP(GroupAddress,
SourceAddress) SourceAddress)
LocalSpecifier.WithAnySourceMulticastGroupIP(GroupAddress) LocalSpecifier.WithAnySourceMulticastGroupIP(GroupAddress)
LocalSpecifier.WithPort(PortNumber) LocalSpecifier.WithPort(PortNumber)
Calling Rendezvous on a Preconnection with an any-source multicast Calling Rendezvous on a Preconnection with an ASM group address as
group address as the Remote Endpoint Identifer will join the the Remote Endpoint Identifier will join the multicast group, and
multicast group, and also indicates that the resulting Connection can also indicates that the resulting Connection can be used to send
be used to send Messages to the multicast group. The Rendezvous call Messages to the multicast group. The Rendezvous call will return
will return both a Connection that can be used to send to the group, both:
that acts the same as a Connection returned by calling Initiate with
a multicast Remote Endpoint, and a Listener that acts as if Listen 1. a Connection that can be used to send to the group and that acts
had been called with a multicast Remote Endpoint. Calling Rendezvous the same as a Connection returned by calling Initiate with a
on a Preconnection with a source-specific multicast group address as multicast Remote Endpoint and
the Local Endpoint Identifer results in an EstablishmentError.
2. a Listener that acts as if Listen had been called with a
multicast Remote Endpoint.
Calling Rendezvous on a Preconnection with an SSM group address as
the Local Endpoint Identifier results in an EstablishmentError.
The following API calls can be used to configure a Preconnection The following API calls can be used to configure a Preconnection
before calling Rendezvous: before calling Rendezvous:
RemoteSpecifier.WithMulticastGroupIP(GroupAddress) RemoteSpecifier.WithMulticastGroupIP(GroupAddress)
RemoteSpecifier.WithPort(PortNumber) RemoteSpecifier.WithPort(PortNumber)
RemoteSpecifier.WithHopLimit(HopLimit) RemoteSpecifier.WithHopLimit(HopLimit)
LocalSpecifier.WithAnySourceMulticastGroupIP(GroupAddress) LocalSpecifier.WithAnySourceMulticastGroupIP(GroupAddress)
LocalSpecifier.WithPort(PortNumber) LocalSpecifier.WithPort(PortNumber)
LocalSpecifier.WithHopLimit(HopLimit) LocalSpecifier.WithHopLimit(HopLimit)
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* Specifying an interface on a Local Endpoint explicitly binds all * Specifying an interface on a Local Endpoint explicitly binds all
candidates derived from this Endpoint to use the specified candidates derived from this Endpoint to use the specified
interface. interface.
* Specifying an interface using the interface Selection Property * Specifying an interface using the interface Selection Property
(Section 6.2.11) or indirectly via the pvd Selection Property (Section 6.2.11) or indirectly via the pvd Selection Property
(Section 6.2.12) influences the selection among the available (Section 6.2.12) influences the selection among the available
candidates. candidates.
While specifying an Interface on an Endpoint restricts the candidates While specifying an Interface on an Endpoint restricts the candidates
available for Connection establishment in the Pre-Establishment available for Connection establishment in the preestablishment phase,
Phase, the Selection Properties prioritize and constrain the the Selection Properties prioritize and constrain the Connection
Connection establishment. establishment.
6.1.3. Protocol-Specific Endpoints 6.1.3. Protocol-Specific Endpoints
An Endpoint can have an alternative definition when using different An Endpoint can have an alternative definition when using different
protocols. For example, a server that supports both TLS/TCP and QUIC protocols. For example, a server that supports both TLS/TCP and QUIC
could be accessible on two different port numbers depending on which could be accessible on two different port numbers, depending on which
protocol is used. protocol is used.
To scope an Endpoint to apply conditionally to a specific transport To scope an Endpoint to apply conditionally to a specific transport
protocol (such as defining an alternate port to use when QUIC is protocol (such as defining an alternate port to use when QUIC is
selected, as opposed to TCP), an Endpoint can be associated with a selected, as opposed to TCP), an Endpoint can be associated with a
protocol identifier. Protocol identifiers are objects or enumeration protocol identifier. Protocol identifiers are objects or enumeration
values provided by the Transport Services API, which will vary based values provided by the Transport Services API that will vary based on
on which protocols are implemented in a particular system. which protocols are implemented in a particular system.
AlternateRemoteSpecifier.WithProtocol(QUIC) AlternateRemoteSpecifier.WithProtocol(QUIC)
The following example shows a case where example.com has a server The following example shows a case where example.com has a server
running on port 443, with an alternate port of 8443 for QUIC. Both running on port 443 with an alternate port of 8443 for QUIC. Both
endpoints can be passed when creating a Preconnection. endpoints can be passed when creating a Preconnection.
RemoteSpecifier := NewRemoteEndpoint() RemoteSpecifier := NewRemoteEndpoint()
RemoteSpecifier.WithHostName("example.com") RemoteSpecifier.WithHostName("example.com")
RemoteSpecifier.WithPort(443) RemoteSpecifier.WithPort(443)
QUICRemoteSpecifier := NewRemoteEndpoint() QUICRemoteSpecifier := NewRemoteEndpoint()
QUICRemoteSpecifier.WithHostName("example.com") QUICRemoteSpecifier.WithHostName("example.com")
QUICRemoteSpecifier.WithPort(8443) QUICRemoteSpecifier.WithPort(8443)
QUICRemoteSpecifier.WithProtocol(QUIC) QUICRemoteSpecifier.WithProtocol(QUIC)
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RemoteSpecifier.WithIPAddress(2001:db8:4920:e29d:a420:7461:7073:a) RemoteSpecifier.WithIPAddress(2001:db8:4920:e29d:a420:7461:7073:a)
RemoteSpecifier.WithPort(443) RemoteSpecifier.WithPort(443)
Specify a Remote Endpoint using an IPv4 address and remote port: Specify a Remote Endpoint using an IPv4 address and remote port:
RemoteSpecifier := NewRemoteEndpoint() RemoteSpecifier := NewRemoteEndpoint()
RemoteSpecifier.WithIPAddress(192.0.2.21) RemoteSpecifier.WithIPAddress(192.0.2.21)
RemoteSpecifier.WithPort(443) RemoteSpecifier.WithPort(443)
Specify a Local Endpoint using a local interface name and no local Specify a Local Endpoint using a local interface name and no local
port, to let the system assign an ephemeral local port: port to let the system assign an ephemeral local port:
LocalSpecifier := NewLocalEndpoint() LocalSpecifier := NewLocalEndpoint()
LocalSpecifier.WithInterface("en0") LocalSpecifier.WithInterface("en0")
Specify a Local Endpoint using a local interface name and local port: Specify a Local Endpoint using a local interface name and local port:
LocalSpecifier := NewLocalEndpoint() LocalSpecifier := NewLocalEndpoint()
LocalSpecifier.WithInterface("en0") LocalSpecifier.WithInterface("en0")
LocalSpecifier.WithPort(443) LocalSpecifier.WithPort(443)
As an alternative to specifying an interface name for the Local As an alternative to specifying an interface name for the Local
Endpoint, an application can express more fine-grained preferences Endpoint, an application can express more fine-grained preferences
using the Interface Instance or Type Selection Property, see using the Interface Instance or Type Selection Property; see
Section 6.2.11. However, if the application specifies Selection Section 6.2.11. However, if the application specifies Selection
Properties that are inconsistent with the Local Endpoint, this will Properties that are inconsistent with the Local Endpoint, this will
result in an error once the application attempts to open a result in an error once the application attempts to open a
Connection. Connection.
Specify a Local Endpoint using a STUN server: Specify a Local Endpoint using a STUN server:
LocalSpecifier := NewLocalEndpoint() LocalSpecifier := NewLocalEndpoint()
LocalSpecifier.WithStunServer(address, port, credentials) LocalSpecifier.WithStunServer(address, port, credentials)
6.1.5. Multicast Examples 6.1.5. Multicast Examples
The following examples show how multicast groups can be used. The following examples show how multicast groups can be used.
Join an Any-Source Multicast group in receive-only mode, bound to a Join an ASM group in receive-only mode, bound to a known port on a
known port on a named local interface: named local interface:
RemoteSpecifier := NewRemoteEndpoint() RemoteSpecifier := NewRemoteEndpoint()
LocalSpecifier := NewLocalEndpoint() LocalSpecifier := NewLocalEndpoint()
LocalSpecifier.WithAnySourceMulticastGroupIP(233.252.0.0) LocalSpecifier.WithAnySourceMulticastGroupIP(233.252.0.0)
LocalSpecifier.WithPort(5353) LocalSpecifier.WithPort(5353)
LocalSpecifier.WithInterface("en0") LocalSpecifier.WithInterface("en0")
TransportProperties := ... TransportProperties := ...
SecurityParameters := ... SecurityParameters := ...
Preconnection := NewPreconnection(LocalSpecifier, Preconnection := NewPreconnection(LocalSpecifier,
RemoteSpecifier, RemoteSpecifier,
TransportProperties, TransportProperties,
SecurityProperties) SecurityProperties)
Listener := Preconnection.Listen() Listener := Preconnection.Listen()
Join a Source-Specific Multicast group in receive-only mode, bound to Join an SSM group in receive-only mode, bound to a known port on a
a known port on a named local interface: named local interface:
RemoteSpecifier := NewRemoteEndpoint() RemoteSpecifier := NewRemoteEndpoint()
LocalSpecifier := NewLocalEndpoint() LocalSpecifier := NewLocalEndpoint()
LocalSpecifier.WithSingleSourceMulticastGroupIP(233.252.0.0, LocalSpecifier.WithSingleSourceMulticastGroupIP(233.252.0.0,
198.51.100.10) 198.51.100.10)
LocalSpecifier.WithPort(5353) LocalSpecifier.WithPort(5353)
LocalSpecifier.WithInterface("en0") LocalSpecifier.WithInterface("en0")
TransportProperties := ... TransportProperties := ...
SecurityParameters := ... SecurityParameters := ...
Preconnection := NewPreconnection(LocalSpecifier, Preconnection := NewPreconnection(LocalSpecifier,
RemoteSpecifier, RemoteSpecifier,
TransportProperties, TransportProperties,
SecurityProperties) SecurityProperties)
Listener := Preconnection.Listen() Listener := Preconnection.Listen()
Create a Source-Specific Multicast group as a sender: Create an SSM group as a sender:
RemoteSpecifier := NewRemoteEndpoint() RemoteSpecifier := NewRemoteEndpoint()
RemoteSpecifier.WithMulticastGroupIP(233.251.240.1) RemoteSpecifier.WithMulticastGroupIP(233.251.240.1)
RemoteSpecifier.WithPort(5353) RemoteSpecifier.WithPort(5353)
RemoteSpecifier.WithHopLimit(8) RemoteSpecifier.WithHopLimit(8)
LocalSpecifier := NewLocalEndpoint() LocalSpecifier := NewLocalEndpoint()
LocalSpecifier.WithIPAddress(192.0.2.22) LocalSpecifier.WithIPAddress(192.0.2.22)
LocalSpecifier.WithInterface("en0") LocalSpecifier.WithInterface("en0")
TransportProperties := ... TransportProperties := ...
SecurityParameters := ... SecurityParameters := ...
Preconnection := NewPreconnection(LocalSpecifier, Preconnection := NewPreconnection(LocalSpecifier,
RemoteSpecifier, RemoteSpecifier,
TransportProperties, TransportProperties,
SecurityProperties) SecurityProperties)
Connection := Preconnection.Initiate() Connection := Preconnection.Initiate()
Join an any-source multicast group as both a sender and a receiver: Join an ASM group as both a sender and a receiver:
RemoteSpecifier := NewRemoteEndpoint() RemoteSpecifier := NewRemoteEndpoint()
RemoteSpecifier.WithMulticastGroupIP(233.252.0.0) RemoteSpecifier.WithMulticastGroupIP(233.252.0.0)
RemoteSpecifier.WithPort(5353) RemoteSpecifier.WithPort(5353)
RemoteSpecifier.WithHopLimit(8) RemoteSpecifier.WithHopLimit(8)
LocalSpecifier := NewLocalEndpoint() LocalSpecifier := NewLocalEndpoint()
LocalSpecifier.WithAnySourceMulticastGroupIP(233.252.0.0) LocalSpecifier.WithAnySourceMulticastGroupIP(233.252.0.0)
LocalSpecifier.WithIPAddress(192.0.2.22) LocalSpecifier.WithIPAddress(192.0.2.22)
LocalSpecifier.WithPort(5353) LocalSpecifier.WithPort(5353)
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The protocol(s) and path(s) selected as candidates during The protocol(s) and path(s) selected as candidates during
establishment are determined and configured using these properties. establishment are determined and configured using these properties.
Since there could be paths over which some transport protocols are Since there could be paths over which some transport protocols are
unable to operate, or Remote Endpoints that support only specific unable to operate, or Remote Endpoints that support only specific
network addresses or transports, transport protocol selection is network addresses or transports, transport protocol selection is
necessarily tied to path selection. This could involve choosing necessarily tied to path selection. This could involve choosing
between multiple local interfaces that are connected to different between multiple local interfaces that are connected to different
access networks. access networks.
When additional information (such as Provisioning Domain (PvD) When additional information (such as PvD information [RFC7556]) is
information [RFC7556]) is available about the networks over which an available about the networks over which an endpoint can operate, this
endpoint can operate, this can inform the selection between alternate can inform the selection between alternate network paths. Path
network paths. Path information can include PMTU, set of supported information can include the Path MTU (PMTU), the set of supported
DSCPs, expected usage, cost, etc. The usage of this information by Differentiated Services Code Points (DSCPs), expected usage, cost,
the Transport Services System is generally independent of the etc. The usage of this information by the Transport Services System
specific mechanism/protocol used to receive the information (e.g. is generally independent of the specific mechanism/protocol used to
zero-conf, DHCP, or IPv6 RA). receive the information (e.g., zero-conf, DHCP, or IPv6 Router
Advertisements (RAs)).
Most Selection Properties are represented as Preferences, which can Most Selection Properties are represented as Preferences, which can
take one of five values: take one of five values:
+============+========================================+ +============+=========================================+
| Preference | Effect | | Preference | Effect |
+============+========================================+ +============+=========================================+
| Require | Select only protocols/paths providing | | Require | Select only protocols/paths providing |
| | the property, fail otherwise | | | the property; otherwise, fail |
+------------+----------------------------------------+ +------------+-----------------------------------------+
| Prefer | Prefer protocols/paths providing the | | Prefer | Prefer protocols/paths providing the |
| | property, proceed otherwise | | | property; otherwise, proceed |
+------------+----------------------------------------+ +------------+-----------------------------------------+
| No | No preference | | No | No preference |
| Preference | | | Preference | |
+------------+----------------------------------------+ +------------+-----------------------------------------+
| Avoid | Prefer protocols/paths not providing | | Avoid | Prefer protocols/paths not providing |
| | the property, proceed otherwise | | | the property; otherwise, proceed |
+------------+----------------------------------------+ +------------+-----------------------------------------+
| Prohibit | Select only protocols/paths not | | Prohibit | Select only protocols/paths not |
| | providing the property, fail otherwise | | | providing the property; otherwise, fail |
+------------+----------------------------------------+ +------------+-----------------------------------------+
Table 1: Selection Property Preference Levels Table 1: Selection Property Preference Levels
The implementation MUST ensure an outcome that is consistent with all The implementation MUST ensure an outcome that is consistent with all
application requirements expressed using Require and Prohibit. While application requirements expressed using Require and Prohibit. While
preferences expressed using Prefer and Avoid influence protocol and preferences expressed using Prefer and Avoid influence protocol and
path selection as well, outcomes can vary given the same Selection path selection as well, outcomes can vary, even given the same
Properties, because the available protocols and paths can differ Selection Properties, because the available protocols and paths can
across systems and contexts. However, implementations are differ across systems and contexts. However, implementations are
RECOMMENDED to seek to provide a consistent outcome to an RECOMMENDED to seek to provide a consistent outcome to an
application, when provided with the same set of Selection Properties. application, when provided with the same set of Selection Properties.
Note that application preferences can conflict with each other. For Note that application preferences can conflict with each other. For
example, if an application indicates a preference for a specific path example, if an application indicates a preference for a specific path
by specifying an interface, but also a preference for a protocol, a by specifying an interface, but also a preference for a protocol, a
situation might occur in which the preferred protocol is not situation might occur in which the preferred protocol is not
available on the preferred path. In such cases, applications can available on the preferred path. In such cases, applications can
expect properties that determine path selection to be prioritized expect properties that determine path selection to be prioritized
over properties that determine protocol selection. The transport over properties that determine protocol selection. The transport
system SHOULD determine the preferred path first, regardless of system SHOULD determine the preferred path first, regardless of
protocol preferences. This ordering is chosen to provide consistency protocol preferences. This ordering is chosen to provide consistency
across implementations, based on the fact that it is more common for across implementations; this is based on the fact that it is more
the use of a given network path to determine cost to the user (i.e., common for the use of a given network path to determine cost to the
an interface type preference might be based on a user's preference to user (i.e., an interface type preference might be based on a user's
avoid being charged more for a cellular data plan). preference to avoid being charged more for a cellular data plan).
Selection and Connection Properties, as well as defaults for Message Selection and Connection Properties, as well as defaults for Message
Properties, can be added to a Preconnection to configure the Properties, can be added to a Preconnection to configure the
selection process and to further configure the eventually selected selection process and to further configure the eventually selected
Protocol Stack(s). They are collected into a TransportProperties Protocol Stack(s). They are collected into a TransportProperties
object to be passed into a Preconnection object: object to be passed into a Preconnection object:
TransportProperties := NewTransportProperties() TransportProperties := NewTransportProperties()
Individual properties are then set on the TransportProperties object. Individual properties are then set on the TransportProperties object.
Setting a Transport Property to a value overrides the previous value Setting a Transport Property to a value overrides the previous value
of this Transport Property. of this Transport Property.
TransportProperties.Set(property, value) TransportProperties.Set(property, value)
To aid readability, implementations MAY provide additional To aid readability, implementations MAY provide additional
convenience functions to simplify use of Selection Properties: see convenience functions to simplify the use of Selection Properties:
Appendix B.1 for examples. In addition, implementations MAY provide see Appendix B.1 for examples. In addition, implementations MAY
a mechanism to create TransportProperties objects that are provide a mechanism to create TransportProperties objects that are
preconfigured for common use cases, as outlined in Appendix B.2. preconfigured for common use cases, as outlined in Appendix B.2.
Transport Properties for an established Connection can be queried via Transport Properties for an established Connection can be queried via
the Connection object, as outlined in Section 8. the Connection object, as outlined in Section 8.
A Connection gets its Transport Properties either by being explicitly A Connection gets its Transport Properties by either being explicitly
configured via a Preconnection, by configuration after establishment, configured via a Preconnection, being configured after establishment,
or by inheriting them from an antecedent via cloning; see Section 7.4 or inheriting them from an antecedent via cloning; see Section 7.4
for more. for more details.
Section 8.1 provides a list of Connection Properties, while Selection Section 8.1 provides a list of Connection Properties, while Selection
Properties are listed in the subsections below. Selection Properties Properties are listed in the subsections below. Selection Properties
are only considered during establishment, and can not be changed are only considered during establishment and cannot be changed after
after a Connection is established. After a Connection is a Connection is established. At which point, Selection Properties
established, Selection Properties can only be read to check the can only be read to check the properties used by the Connection.
properties used by the Connection. Upon reading, the Preference type Upon reading, the Preference type of a Selection Property changes
of a Selection Property changes into Boolean, where true means that into Boolean, where:
the selected Protocol Stack supports the feature or uses the path
associated with the Selection Property, and false means that the * true means that the selected Protocol Stack supports the feature
Protocol Stack does not support the feature or use the path. or uses the path associated with the Selection Property, and
* false means that the Protocol Stack does not support the feature
or use the path.
Implementations of Transport Services systems could alternatively use Implementations of Transport Services systems could alternatively use
the two Preference values Require and Prohibit to represent true and the Require and Prohibit Preference values to represent true and
false, respectively. Other types of Selection Properties remain false, respectively. Other types of Selection Properties remain
unchanged when they are made available for reading after a Connection unchanged when they are made available for reading after a Connection
is established. is established.
An implementation of the Transport Services API needs to provide An implementation of the Transport Services API needs to provide
sensible defaults for Selection Properties. The default values for sensible defaults for Selection Properties. The default values for
each property below represent a configuration that can be implemented each property below represent a configuration that can be implemented
over TCP. If these default values are used and TCP is not supported over TCP. If these default values are used and TCP is not supported
by a Transport Services system, then an application using the default by a Transport Services system, then an application using the default
set of Properties might not succeed in establishing a Connection. set of Properties might not succeed in establishing a Connection.
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6.2.1. Reliable Data Transfer (Connection) 6.2.1. Reliable Data Transfer (Connection)
Name: reliability Name: reliability
Type: Preference Type: Preference
Default: Require Default: Require
This property specifies whether the application needs to use a This property specifies whether the application needs to use a
transport protocol that ensures that all data is received at the transport protocol that ensures that all data is received at the
Remote Endpoint in order without loss or duplication. When reliable Remote Endpoint in order, without loss or duplication. When reliable
data transfer is enabled, this also entails being notified when a data transfer is enabled, this also entails being notified when a
Connection is closed or aborted. Connection is closed or aborted.
6.2.2. Preservation of Message Boundaries 6.2.2. Preservation of Message Boundaries
Name: preserveMsgBoundaries Name: preserveMsgBoundaries
Type: Preference Type: Preference
Default: No Preference Default: No Preference
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6.2.5. Use 0-RTT Session Establishment with a Safely Replayable Message 6.2.5. Use 0-RTT Session Establishment with a Safely Replayable Message
Name: zeroRttMsg Name: zeroRttMsg
Type: Preference Type: Preference
Default: No Preference Default: No Preference
This property specifies whether an application would like to supply a This property specifies whether an application would like to supply a
Message to the transport protocol before connection establishment Message to the transport protocol before connection establishment,
that will then be reliably transferred to the Remote Endpoint before which will then be reliably transferred to the Remote Endpoint before
or during connection establishment. This Message can potentially be or during connection establishment. This Message can potentially be
received multiple times (i.e., multiple copies of the Message data received multiple times (i.e., multiple copies of the Message data
could be passed to the Remote Endpoint). See also Section 9.1.3.4. could be passed to the Remote Endpoint). See also Section 9.1.3.4.
6.2.6. Multistream Connections in Group 6.2.6. Multistream Connections in a Group
Name: multistreaming Name: multistreaming
Type: Preference Type: Preference
Default: Prefer Default: Prefer
This property specifies whether the application would prefer multiple This property specifies whether the application would prefer multiple
Connections within a Connection Group to be provided by streams of a Connections within a Connection Group to be provided by streams of a
single underlying transport connection where possible. single underlying transport connection, where possible.
6.2.7. Full Checksum Coverage on Sending 6.2.7. Full Checksum Coverage on Sending
Name: fullChecksumSend Name: fullChecksumSend
Type: Preference Type: Preference
Default: Require Default: Require
This property specifies the application's need for protection against This property specifies the application's need for protection against
corruption for all data transmitted on this Connection. Disabling corruption for all data transmitted on this Connection. Disabling
this property could enable the application to influence the sender this property could enable the application to influence the sender
checksum coverage after Connection establishment (see checksum coverage after Connection establishment (see
Section 9.1.3.6). Section 9.1.3.6).
6.2.8. Full Checksum Coverage on Receiving 6.2.8. Full Checksum Coverage on Receiving
Name: fullChecksumRecv Name: fullChecksumRecv
Type: Preference Type: Preference
Default: Require Default: Require
This property specifies the application's need for protection against This property specifies the application's need for protection against
corruption for all data received on this Connection. Disabling this corruption for all data received on this Connection. Disabling this
property could enable the application to influence the required property could enable the application to influence the required
minimum receiver checksum coverage after Connection establishment minimum receiver checksum coverage after Connection establishment
(see Section 8.1.1). (see Section 8.1.1).
6.2.9. Congestion control 6.2.9. Congestion Control
Name: congestionControl Name: congestionControl
Type: Preference Type: Preference
Default: Require Default: Require
This property specifies whether the application would like the This property specifies whether or not the application would like the
Connection to be congestion controlled or not. Note that if a Connection to be congestion controlled. Note that if a Connection is
Connection is not congestion controlled, an application using such a not congestion controlled, an application using such a Connection
Connection SHOULD itself perform congestion control in accordance SHOULD itself perform congestion control in accordance with [RFC2914]
with [RFC2914] or use a circuit breaker in accordance with [RFC8084], or use a circuit breaker in accordance with [RFC8084], whichever is
whichever is appropriate. Also note that reliability is usually appropriate. Also note that reliability is usually combined with
combined with congestion control in protocol implementations, congestion control in protocol implementations rendering "reliable
rendering "reliable but not congestion controlled" a request that is but not congestion controlled", a request that is unlikely to
unlikely to succeed. If the Connection is congestion controlled, succeed. If the Connection is congestion controlled, performing
performing additional congestion control in the application can have additional congestion control in the application can have negative
negative performance implications. performance implications.
6.2.10. Keep alive 6.2.10. Keep-Alive Packets
Name: keepAlive Name: keepAlive
Type: Preference Type: Preference
Default: No Preference Default: No Preference
This property specifies whether the application would like the
Connection to send keep-alive packets or not. Note that if a This property specifies whether or not the application would like the
Connection determines that keep-alive packets are being sent, the Connection to send keep-alive packets. Note that if a Connection
application SHOULD itself avoid generating additional keep-alive determines that keep-alive packets are being sent, the application
messages. Note that when supported, the system will use the default itself SHOULD avoid generating additional keep-alive messages. Note
period for generation of the keep alive-packets. (See also that, when supported, the system will use the default period for
Section 8.1.4). generation of the keep-alive packets. (See also Section 8.1.4.)
6.2.11. Interface Instance or Type 6.2.11. Interface Instance or Type
Name: interface Name: interface
Type: Set of (Preference, Enumeration) Type: Set of (Preference, Enumeration)
Default: Empty (not setting a preference for any interface) Default: Empty (not setting a preference for any interface)
This property allows the application to select any specific network This property allows the application to select any specific network
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Prefer, or Avoid. Note that marking a specific interface as Require Prefer, or Avoid. Note that marking a specific interface as Require
strictly limits path selection to that single interface, and often strictly limits path selection to that single interface, and often
leads to less flexible and resilient connection establishment. leads to less flexible and resilient connection establishment.
In contrast to other Selection Properties, this property is a set of In contrast to other Selection Properties, this property is a set of
tuples of (Enumerated) interface identifier and preference. It can tuples of (Enumerated) interface identifier and preference. It can
either be implemented directly as such, or for making one preference either be implemented directly as such, or for making one preference
available for each interface and interface type available on the available for each interface and interface type available on the
system. system.
The set of valid interface types is implementation- and system- The set of valid interface types is specific to the implementation or
specific. For example, on a mobile device, there could be Wi-Fi and system. For example, on a mobile device, there could be Wi-Fi and
Cellular interface types available; whereas on a desktop computer, Cellular interface types available; whereas, on a desktop computer,
Wi-Fi and Wired Ethernet interface types might be available. An Wi-Fi and Wired Ethernet interface types might be available. An
implementation should provide all types that are supported on the implementation should provide all types that are supported on the
local system, to allow applications to be written generically. For local system to allow applications to be written generically. For
example, if a single implementation is used on both mobile devices example, if a single implementation is used on both mobile devices
and desktop devices, it ought to define the Cellular interface type and desktop devices, it ought to define the Cellular interface type
for both systems, since an application might wish to always prohibit for both systems, since an application might wish to always prohibit
cellular. cellular.
The set of interface types is expected to change over time as new The set of interface types is expected to change over time as new
access technologies become available. The taxonomy of interface access technologies become available. The taxonomy of interface
types on a given Transport Services system is implementation- types on a given Transport Services system is implementation
specific. specific.
Interface types SHOULD NOT be treated as a proxy for properties of Interface types SHOULD NOT be treated as a proxy for properties of
interfaces such as metered or unmetered network access. If an interfaces, such as metered or unmetered network access. If an
application needs to prohibit metered interfaces, this should be application needs to prohibit metered interfaces, this should be
specified via Provisioning Domain attributes (see Section 6.2.12) or specified via Provisioning Domain attributes (see Section 6.2.12) or
another specific property. another specific property.
Note that this property is not used to specify an interface scope Note that this property is not used to specify an interface scope
zone for a particular Endpoint. Section 6.1.2 provides details about zone for a particular Endpoint. Section 6.1.2 provides details about
how to qualify endpoint candidates on a per-interface basis. how to qualify endpoint candidates on a per-interface basis.
6.2.12. Provisioning Domain Instance or Type 6.2.12. Provisioning Domain Instance or Type
Name: pvd Name: pvd
Type: Set of (Preference, Enumeration) Type: Set of (Preference, Enumeration)
Default: Empty (not setting a preference for any PvD) Default: Empty (not setting a preference for any PvD)
Similar to interface (see Section 6.2.11), this property allows the Similar to interface (see Section 6.2.11), this property allows the
application to control path selection by selecting which specific application to control path selection by selecting which specific PvD
Provisioning Domain (PvD) or categories of PVDs it wants to Require, or categories of PvDs it wants to Require, Prohibit, Prefer, or
Prohibit, Prefer, or Avoid. Provisioning Domains define consistent Avoid. Provisioning Domains define consistent sets of network
sets of network properties that might be more specific than network properties that might be more specific than network interfaces
interfaces [RFC7556]. [RFC7556].
As with interface instances and types, this property is a set of As with interface instances and types, this property is a set of
tuples of (Enumerated) PvD identifier and preference. It can either tuples of (Enumerated) PvD identifier and preference. It can either
be implemented directly as such, or for making one preference be implemented directly as such, or for making one preference
available for each interface and interface type available on the available for each interface and interface type available on the
system. system.
The identification of a specific PvD is implementation- and system- The identification of a specific PvD is specific to the
specific. [RFC8801] defines how to use an FQDN to identify a PvD implementation or system. [RFC8801] defines how to use an FQDN to
when advertised by a network, but systems might also use other identify a PvD when advertised by a network, but systems might also
locally-relevant identifiers such as string names or Integers to use other locally relevant identifiers such as string names or
identify PvDs. As with requiring specific interfaces, requiring a Integers to identify PvDs. As with requiring specific interfaces,
specific PvD strictly limits the path selection. requiring a specific PvD strictly limits the path selection.
Categories or types of PvDs are also defined to be implementation- Categories or types of PvDs are also defined to be specific to the
and system-specific. These can be useful to identify a service that implementation or system. These can be useful to identify a service
is provided by a PvD. For example, if an application wants to use a that is provided by a PvD. For example, if an application wants to
PvD that provides a Voice-Over-IP service on a Cellular network, it use a PvD that provides a Voice-Over-IP (VoIP) service on a Cellular
can use the relevant PvD type to require a PvD that provides this network, it can use the relevant PvD type to require a PvD that
service, without needing to look up a particular instance. While provides this service, without needing to look up a particular
this does restrict path selection, it is broader than requiring instance. While this does restrict path selection, it is broader
specific PvD instances or interface instances, and should be than requiring specific PvD instances or interface instances and
preferred over these options. should be preferred over these options.
6.2.13. Use Temporary Local Address 6.2.13. Use Temporary Local Address
Name: useTemporaryLocalAddress Name: useTemporaryLocalAddress
Type: Preference Type: Preference
Default: Avoid for Listeners and Rendezvous Connections. Prefer for Default: Avoid for Listeners and Rendezvous Connections; Prefer for
other Connections. other Connections
This property allows the application to express a preference for the This property allows the application to express a preference for the
use of temporary local addresses, sometimes called "privacy" use of temporary local addresses, sometimes called "privacy"
addresses [RFC8981]. Temporary addresses are generally used to addresses [RFC8981]. Temporary addresses are generally used to
prevent linking connections over time when a stable address, prevent linking connections over time when a stable address,
sometimes called "permanent" address, is not needed. There are some sometimes called a "permanent" address, is not needed. There are
caveats to note when specifying this property. First, if an some caveats to note when specifying this property. First, if an
application Requires the use of temporary addresses, the resulting application Requires the use of temporary addresses, the resulting
Connection cannot use IPv4, because temporary addresses do not exist Connection cannot use IPv4 because temporary addresses do not exist
in IPv4. Second, temporary local addresses might involve trading off in IPv4. Second, temporary local addresses might involve trading off
privacy for performance. For instance, temporary addresses (e.g., privacy for performance. For instance, temporary addresses (e.g.,
[RFC8981]) can interfere with resumption mechanisms that some [RFC8981]) can interfere with resumption mechanisms that some
protocols rely on to reduce initial latency. protocols rely on to reduce initial latency.
6.2.14. Multipath Transport 6.2.14. Multipath Transport
Name: multipath Name: multipath
Type: Enumeration Type: Enumeration
Default: Disabled for Connections created through initiate and Default: Disabled for Connections created through initiate and
rendezvous, Passive for Listeners rendezvous; Passive for Listeners
This property specifies whether and how applications want to take This property specifies whether, and how, applications want to take
advantage of transferring data across multiple paths between the same advantage of transferring data across multiple paths between the same
end hosts. Using multiple paths allows Connections to migrate end hosts. Using multiple paths allows Connections to migrate
between interfaces or aggregate bandwidth as availability and between interfaces or aggregate bandwidth as availability and
performance properties change. Possible values are: performance properties change. Possible values are as follows:
Disabled: The Connection will not use multiple paths once Disabled: The Connection will not use multiple paths once
established, even if the chosen transport supports using multiple established, even if the chosen transport supports using multiple
paths. paths.
Active: The Connection will negotiate the use of multiple paths if Active: The Connection will negotiate the use of multiple paths if
the chosen transport supports this. the chosen transport supports it.
Passive: The Connection will support the use of multiple paths if Passive: The Connection will support the use of multiple paths if
the Remote Endpoint requests it. the Remote Endpoint requests it.
The policy for using multiple paths is specified using the separate The policy for using multiple paths is specified using the separate
multipathPolicy property, see Section 8.1.7 below. To enable the multipathPolicy property; see Section 8.1.7. To enable the peer
peer endpoint to initiate additional paths towards a local address endpoint to initiate additional paths toward a local address other
other than the one initially used, it is necessary to set the than the one initially used, it is necessary to set the
advertisesAltaddr property (see Section 6.2.15 below). advertisesAltaddr property (see Section 6.2.15).
Setting this property to Active can have privacy implications: It Setting this property to Active can have privacy implications. It
enables the transport to establish connectivity using alternate paths enables the transport to establish connectivity using alternate paths
that might result in users being linkable across the multiple paths, that might result in users being linkable across the multiple paths,
even if the advertisesAltaddr property (see Section 6.2.15 below) is even if the advertisesAltaddr property (see Section 6.2.15) is set to
set to false. false.
Note that Multipath Transport has no corresponding Selection Property Note that Multipath Transport has no corresponding Selection Property
of type Preference. Enumeration values other than Disabled are of type Preference. Enumeration values other than Disabled are
interpreted as a preference for choosing protocols that can make use interpreted as a preference for choosing protocols that can make use
of multiple paths. The Disabled value implies a requirement not to of multiple paths. The Disabled value implies a requirement not to
use multiple paths in parallel but does not prevent choosing a use multiple paths in parallel but does not prevent choosing a
protocol that is capable of using multiple paths, e.g., it does not protocol that is capable of using multiple paths, e.g., it does not
prevent choosing TCP, but prevents sending the MP_CAPABLE option in prevent choosing TCP but prevents sending the MP_CAPABLE option in
the TCP handshake. the TCP handshake.
6.2.15. Advertisement of Alternative Addresses 6.2.15. Advertisement of Alternative Addresses
Name: advertisesAltaddr Name: advertisesAltaddr
Type: Boolean Type: Boolean
Default: false Default: false
This property specifies whether alternative addresses, e.g., of other This property specifies whether alternative addresses, e.g., of other
interfaces, ought to be advertised to the peer endpoint by the interfaces, ought to be advertised to the peer endpoint by the
Protocol Stack. Advertising these addresses enables the peer Protocol Stack. Advertising these addresses enables the peer
endpoint to establish additional connectivity, e.g., for Connection endpoint to establish additional connectivity, e.g., for Connection
migration or using multiple paths. migration or using multiple paths.
Note that this can have privacy implications because it might result Note that this can have privacy implications because it might result
in users being linkable across the multiple paths. Also, note that in users being linkable across the multiple paths. Also, note that
setting this to false does not prevent the local Transport Services setting this to false does not prevent the local Transport Services
system from _establishing_ connectivity using alternate paths (see system from _establishing_ connectivity using alternate paths (see
Section 6.2.14 above); it only prevents _proactive advertisement_ of Section 6.2.14); it only prevents _proactive advertisement_ of
addresses. addresses.
6.2.16. Direction of communication 6.2.16. Direction of Communication
Name: direction Name: direction
Type: Enumeration Type: Enumeration
Default: Bidirectional Default: Bidirectional
This property specifies whether an application wants to use the This property specifies whether an application wants to use the
Connection for sending and/or receiving data. Possible values are: Connection for sending and/or receiving data. Possible values are as
follows:
Bidirectional: The Connection must support sending and receiving Bidirectional: The Connection must support sending and receiving
data data.
Unidirectional send: The Connection must support sending data, and Unidirectional send: The Connection must support sending data, and
the application cannot use the Connection to receive any data the application cannot use the Connection to receive any data.
Unidirectional receive: The Connection must support receiving data, Unidirectional receive: The Connection must support receiving data,
and the application cannot use the Connection to send any data and the application cannot use the Connection to send any data.
Since unidirectional communication can be supported by transports Since unidirectional communication can be supported by transports
offering bidirectional communication, specifying unidirectional offering bidirectional communication, specifying unidirectional
communication might cause a transport stack that supports communication might cause a transport stack that supports
bidirectional communication to be selected. bidirectional communication to be selected.
6.2.17. Notification of ICMP soft error message arrival 6.2.17. Notification of ICMP Soft Error Message Arrival
Name: softErrorNotify Name: softErrorNotify
Type: Preference Type: Preference
Default: No Preference Default: No Preference
This property specifies whether an application considers it useful to This property specifies whether an application considers it useful to
be informed when an ICMP error message arrives that does not force be informed when an ICMP error message arrives that does not force
termination of a connection. When set to true, received ICMP errors termination of a connection. When set to true, received ICMP errors
are available as SoftError events, see Section 8.3.1. Note that even are available as SoftError events; see Section 8.3.1. Note that even
if a protocol supporting this property is selected, not all ICMP if a protocol supporting this property is selected, not all ICMP
errors will necessarily be delivered, so applications cannot rely errors will necessarily be delivered, so applications cannot rely
upon receiving them [RFC8085]. upon receiving them [RFC8085].
6.2.18. Initiating side is not the first to write 6.2.18. Initiating Side Is Not the First to Write
Name: activeReadBeforeSend Name: activeReadBeforeSend
Type: Preference Type: Preference
Default: No Preference Default: No Preference
The most common client-server communication pattern involves the The most common client-server communication pattern involves the
client actively opening a Connection, then sending data to the client actively opening a Connection, then sending data to the
server. The server listens (passive open), reads, and then answers. server. The server listens (passive open), reads, and then answers.
This property specifies whether an application wants to diverge from This property specifies whether an application wants to diverge from
this pattern -- either by actively opening with Initiate, immediately this pattern by either:
followed by reading, or passively opening with Listen, immediately
followed by writing. This property is ignored when establishing 1. actively opening with Initiate, immediately followed by reading
connections using Rendezvous. Requiring this property limits the or
choice of mappings to underlying protocols, which can reduce
efficiency. For example, it prevents the Transport Services system 2. passively opening with Listen, immediately followed by writing.
from mapping Connections to SCTP streams, where the first transmitted
data takes the role of an active open signal. This property is ignored when establishing connections using
Rendezvous. Requiring this property limits the choice of mappings to
underlying protocols, which can reduce efficiency. For example, it
prevents the Transport Services system from mapping Connections to
Stream Control Transmission Protocol (SCTP) streams, where the first
transmitted data takes the role of an active open signal.
6.3. Specifying Security Parameters and Callbacks 6.3. Specifying Security Parameters and Callbacks
Most security parameters, e.g., TLS ciphersuites, local identity and Most security parameters, e.g., TLS ciphersuites, local identity and
private key, etc., can be configured statically. Others are private key, etc., can be configured statically. Others are
dynamically configured during Connection establishment. Security dynamically configured during Connection establishment. Security
parameters and callbacks are partitioned based on their place in the parameters and callbacks are partitioned based on their place in the
lifetime of Connection establishment. Similar to Transport lifetime of Connection establishment. Similar to Transport
Properties, both parameters and callbacks are inherited during Properties, both parameters and callbacks are inherited during
cloning (see Section 7.4). cloning (see Section 7.4).
This document specifies an abstract API, which could appear to This document specifies an abstract API, which could appear to
conflict with the need for security parameters to be unambiguous. conflict with the need for security parameters to be unambiguous.
The Transport Services System SHOULD provide reasonable, secure The Transport Services System SHOULD provide reasonable, secure
defaults for each enumerated security parameter, such that users of defaults for each enumerated security parameter, such that users of
the system only need to specify parameters required to establish a the system only need to specify parameters required to establish a
secure connection (e.g., serverCertificate, clientCertificate). secure connection (e.g., serverCertificate or clientCertificate).
Specifying security parameters from enumerated values (e.g., specific Specifying security parameters from enumerated values (e.g., specific
ciphersuites) might constrain which transport protocols can be ciphersuites) might constrain which transport protocols can be
selected during Connection establishment. selected during Connection establishment.
Security configuration parameters are specified in the pre- Security configuration parameters are specified in the
establishment phase and are created as follows: preestablishment phase and are created as follows:
SecurityParameters := NewSecurityParameters() SecurityParameters := NewSecurityParameters()
Specific parameters are added using a call to Set() on the Specific parameters are added using a call to Set() on the
SecurityParameters. SecurityParameters.
As with the rest of the Transport Services API, the exact names of As with the rest of the Transport Services API, the exact names of
parameters and/or values of enumerations (e.g., ciphersuites) used in parameters and/or values of enumerations (e.g., ciphersuites) used in
the security parameters are system- and implementation-specific, and the security parameters are specific to the system or implementation
ought to be chosen to follow the principle of least surprise for and ought to be chosen to follow the principle of least surprise for
users of the platform / language environment in question. users of the platform/language environment in question.
For security parameters that are enumerations of known values, such For security parameters that are enumerations of known values, such
as TLS ciphersuites, implementations are responsible for exposing the as TLS ciphersuites, implementations are responsible for exposing the
set of values they support. For security parameters that are not set of values they support. For security parameters that are not
simple value types, such as certificates and keys, implementations simple value types, such as certificates and keys, implementations
are responsible for exposing types appropriate for the platform / are responsible for exposing types appropriate for the platform/
language environment. language environment.
Applications SHOULD use common safe defaults for values such as TLS Applications SHOULD use common safe defaults for values such as TLS
ciphersuites whenever possible. However, as discussed in [RFC8922], ciphersuites whenever possible. However, as discussed in [RFC8922],
many transport security protocols require specific security many transport security protocols require specific security
parameters and constraints from the client at the time of parameters and constraints from the client at the time of
configuration and actively during a handshake. configuration and actively during a handshake.
The set of security parameters defined here is not exhaustive, but The set of security parameters defined here is not exhaustive, but
illustrative. Implementations SHOULD expose an equivalent to the illustrative. Implementations SHOULD expose an equivalent to the
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Services System will use. Services System will use.
Representation of security parameters in implementations ought to Representation of security parameters in implementations ought to
parallel that chosen for Transport Property names as suggested in parallel that chosen for Transport Property names as suggested in
Section 5. Section 5.
Connections that use Transport Services SHOULD use security in Connections that use Transport Services SHOULD use security in
general. However, for compatibility with endpoints that do not general. However, for compatibility with endpoints that do not
support transport security protocols (such as a TCP endpoint that support transport security protocols (such as a TCP endpoint that
does not support TLS), applications can initialize their security does not support TLS), applications can initialize their security
parameters to indicate that security can be disabled, or can be parameters to indicate that security can be disabled or
opportunistic. If security is disabled, the Transport Services opportunistic. If security is disabled, the Transport Services
system will not attempt to add transport security automatically. If system will not attempt to add transport security automatically. If
security is opportunistic, it will allow Connections without security is opportunistic, it will allow Connections without
transport security, but will still attempt to use unauthenticated transport security, but it will still attempt to use unauthenticated
security if available. security if available.
SecurityParameters := NewDisabledSecurityParameters() SecurityParameters := NewDisabledSecurityParameters()
SecurityParameters := NewOpportunisticSecurityParameters() SecurityParameters := NewOpportunisticSecurityParameters()
6.3.1. Allowed security protocols 6.3.1. Allowed Security Protocols
Name: allowedSecurityProtocols Name: allowedSecurityProtocols
Type: Implementation-specific enumeration of security protocol names Type: Implementation-specific enumeration of security protocol names
and/or versions. and/or versions
Default: Implementation-specific best available security protocols Default: Implementation-specific best available security protocols
This property allows applications to restrict which security This property allows applications to restrict which security
protocols and security protocol versions can be used in the protocol protocols and security protocol versions can be used in the Protocol
stack. Applications MUST be able to constrain the security protocols Stack. Applications MUST be able to constrain the security protocols
used by this or an equivalent mechanism, in order to prevent the use used by this or an equivalent mechanism, in order to prevent the use
of security protocols with unknown or weak security properties. of security protocols with unknown or weak security properties.
SecurityParameters.Set(allowedSecurityProtocols, [ tls_1_2, tls_1_3 ]) SecurityParameters.Set(allowedSecurityProtocols, [ tls_1_2, tls_1_3 ])
6.3.2. Certificate bundles 6.3.2. Certificate Bundles
Names: serverCertificate, clientCertificate Names: serverCertificate, clientCertificate
Type: Array of certificate objects Type: Array of certificate objects
Default: Empty array Default: Empty array
One or more certificate bundles identifying the Local Endpoint, One or more certificate bundles identifying the Local Endpoint as a
whether as a server certificate or a client certificate. Multiple server certificate or a client certificate. Multiple bundles may be
bundles may be provided to allow selection among different protocol provided to allow selection among different Protocol Stacks that may
stacks that may require differently formatted bundles. The form and require differently formatted bundles. The form and format of the
format of the certificate bundle is implementation-specific. Note certificate bundle are implementation specific. Note that if the
that if the private keys associated with a bundle are not available, private keys associated with a bundle are not available, e.g., since
e.g., since they are stored in hardware security modules (HSMs), they are stored in Hardware Security Modules (HSMs), handshake
handshake callbacks are necessary. See below for details. callbacks are necessary. See below for details.
SecurityParameters.Set(serverCertificate, myCertificateBundle[]) SecurityParameters.Set(serverCertificate, myCertificateBundle[])
SecurityParameters.Set(clientCertificate, myCertificateBundle[]) SecurityParameters.Set(clientCertificate, myCertificateBundle[])
6.3.3. Pinned server certificate 6.3.3. Pinned Server Certificate
Name: pinnedServerCertificate Name: pinnedServerCertificate
Type: Array of certificate chain objects Type: Array of certificate chain objects
Default: Empty array Default: Empty array
Zero or more certificate chains to use as pinned server certificates, Zero or more certificate chains to use as pinned server certificates,
such that connecting will fail if the presented server certificate such that connecting will fail if the presented server certificate
does not match one of the supplied pinned certificates. The form and does not match one of the supplied pinned certificates. The form and
format of the certificate chain is implementation-specific. format of the certificate chain are implementation specific.
SecurityParameters.Set(pinnedServerCertificate, yourCertificateChain[]) SecurityParameters.Set(pinnedServerCertificate, yourCertificateChain[])
6.3.4. Application-layer protocol negotiation 6.3.4. Application-Layer Protocol Negotiation
Name: alpn Name: alpn
Type: Array of Strings Type: Array of Strings
Default: Automatic selection Default: Automatic selection
Application-layer protocol negotiation (ALPN) values: used to Application-Layer Protocol Negotiation (ALPN) values: used to
indicate which application-layer protocols are negotiated by the indicate which application-layer protocols are negotiated by the
security protocol layer. See [ALPN] for definition of the ALPN security protocol layer. See [ALPN] for a definition of the ALPN
field. Note that the Transport Services System can provide ALPN field. Note that the Transport Services System can provide ALPN
values automatically, based on the protocols being used, if not values automatically based on the protocols being used, if not
explicitly specified by the application. explicitly specified by the application.
SecurityParameters.Set(alpn, ["h2"]) SecurityParameters.Set(alpn, ["h2"])
6.3.5. Groups, ciphersuites, and signature algorithms 6.3.5. Groups, Ciphersuites, and Signature Algorithms
Names: supportedGroup, ciphersuite, signatureAlgorithm Names: supportedGroup, ciphersuite, signatureAlgorithm
Types: Arrays of implementation-specific enumerations Types: Arrays of implementation-specific enumerations
Default: Automatic selection Default: Automatic selection
These are used to restrict what cryptographic parameters are used by These are used to restrict what cryptographic parameters are used by
underlying transport security protocols. When not specified, these underlying transport security protocols. When not specified, these
algorithms should use known and safe defaults for the system. algorithms should use known and safe defaults for the system.
SecurityParameters.Set(supportedGroup, secp256r1) SecurityParameters.Set(supportedGroup, secp256r1)
SecurityParameters.Set(ciphersuite, TLS_AES_128_GCM_SHA256) SecurityParameters.Set(ciphersuite, TLS_AES_128_GCM_SHA256)
SecurityParameters.Set(signatureAlgorithm, ecdsa_secp256r1_sha256) SecurityParameters.Set(signatureAlgorithm, ecdsa_secp256r1_sha256)
6.3.6. Session cache options 6.3.6. Session Cache Options
Names: maxCachedSessions, cachedSessionLifetimeSeconds Names: maxCachedSessions, cachedSessionLifetimeSeconds
Type: Integer Type: Integer
Default: Automatic selection Default: Automatic selection
These values are used to tune session cache capacity and lifetime, These values are used to tune session cache capacity and lifetime and
and can be extended to include other policies. can be extended to include other policies.
SecurityParameters.Set(maxCachedSessions, 16) SecurityParameters.Set(maxCachedSessions, 16)
SecurityParameters.Set(cachedSessionLifetimeSeconds, 3600) SecurityParameters.Set(cachedSessionLifetimeSeconds, 3600)
6.3.7. Pre-shared key 6.3.7. Pre-Shared Key
Name: preSharedKey Name: preSharedKey
Type: Key and identity (platform-specific) Type: Key and identity (platform specific)
Default: None Default: None
Used to install pre-shared keying material established out-of-band. Used to install pre-shared keying material established out of band.
Each instance of pre-shared keying material is associated with some Each instance of pre-shared keying material is associated with some
identity that typically identifies its use or has some protocol- identity that typically identifies its use or has some protocol-
specific meaning to the Remote Endpoint. Note that use of a pre- specific meaning to the Remote Endpoint. Note that the use of a pre-
shared key will tend to select a single security protocol, and shared key will tend to select a single security protocol and,
therefore directly select a single underlying protocol stack. A therefore, directly select a single underlying Protocol Stack. A
Transport Services API could express None in an environment-typical Transport Services API could express None in an environment-typical
way, e.g., as a Union type or special value. way, e.g., as a Union type or special value.
SecurityParameters.Set(preSharedKey, key, myIdentity) SecurityParameters.Set(preSharedKey, key, myIdentity)
6.3.8. Connection Establishment Callbacks 6.3.8. Connection Establishment Callbacks
Security decisions, especially pertaining to trust, are not static. Security decisions, especially pertaining to trust, are not static.
Once configured, parameters can also be supplied during Connection Once configured, parameters can also be supplied during Connection
establishment. These are best handled as client-provided callbacks. establishment. These are best handled as client-provided callbacks.
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callbacks and events are implemented is specific to each callbacks and events are implemented is specific to each
implementation. Security handshake callbacks that could be invoked implementation. Security handshake callbacks that could be invoked
during Connection establishment include: during Connection establishment include:
* Trust verification callback: Invoked when a Remote Endpoint's * Trust verification callback: Invoked when a Remote Endpoint's
trust must be verified before the handshake protocol can continue. trust must be verified before the handshake protocol can continue.
For example, the application could verify an X.509 certificate as For example, the application could verify an X.509 certificate as
described in [RFC5280]. described in [RFC5280].
TrustCallback := NewCallback({ TrustCallback := NewCallback({
// Handle trust, return the result // Handle the trust and return the result
}) })
SecurityParameters.SetTrustVerificationCallback(TrustCallback) SecurityParameters.SetTrustVerificationCallback(TrustCallback)
* Identity challenge callback: Invoked when a private key operation * Identity challenge callback: Invoked when a private key operation
is required, e.g., when local authentication is requested by a is required, e.g., when local authentication is requested by a
Remote Endpoint. Remote Endpoint.
ChallengeCallback := NewCallback({ ChallengeCallback := NewCallback({
// Handle challenge // Handle the challenge
}) })
SecurityParameters.SetIdentityChallengeCallback(ChallengeCallback) SecurityParameters.SetIdentityChallengeCallback(ChallengeCallback)
7. Establishing Connections 7. Establishing Connections
Before a Connection can be used for data transfer, it needs to be Before a Connection can be used for data transfer, it needs to be
established. Establishment ends the pre-establishment phase; all established. Establishment ends the preestablishment phase; all
transport properties and cryptographic parameter specification must transport properties and cryptographic parameter specification must
be complete before establishment, as these will be used to select be complete before establishment, as these will be used to select
candidate Paths and Protocol Stacks for the Connection. candidate Paths and Protocol Stacks for the Connection.
Establishment can be active, using the Initiate action; passive, Establishment can be active, using the Initiate action; passive,
using the Listen action; or simultaneous for peer-to-peer, using the using the Listen action; or simultaneous for peer-to-peer
Rendezvous action. These actions are described in the subsections connections, using the Rendezvous action. These actions are
below. described in the subsections below.
7.1. Active Open: Initiate 7.1. Active Open: Initiate
Active open is the action of establishing a Connection to a Remote Active open is the action of establishing a Connection to a Remote
Endpoint presumed to be listening for incoming Connection requests. Endpoint presumed to be listening for incoming Connection requests.
Active open is used by clients in client-server interactions. Active Active open is used by clients in client-server interactions. Active
open is supported by the Transport Services API through the Initiate open is supported by the Transport Services API through the Initiate
action: action:
Connection := Preconnection.Initiate(timeout?) Connection := Preconnection.Initiate(timeout?)
skipping to change at page 43, line 48 skipping to change at line 1955
Connection -> Ready<> Connection -> Ready<>
The Ready event occurs after Initiate has established a transport- The Ready event occurs after Initiate has established a transport-
layer connection on at least one usable candidate Protocol Stack over layer connection on at least one usable candidate Protocol Stack over
at least one candidate Path. No Receive events (see Section 9.3) at least one candidate Path. No Receive events (see Section 9.3)
will occur before the Ready event for Connections established using will occur before the Ready event for Connections established using
Initiate. Initiate.
Connection -> EstablishmentError<reason?> Connection -> EstablishmentError<reason?>
An EstablishmentError occurs either when the set of transport An EstablishmentError occurs when:
properties and security parameters cannot be fulfilled on a
Connection for initiation (e.g., the set of available Paths and/or * the set of transport properties and security parameters cannot be
Protocol Stacks meeting the constraints is empty) or reconciled with fulfilled on a Connection for initiation (e.g., the set of
the Local and/or Remote Endpoints; when a remote Endpoint Identifier available Paths and/or Protocol Stacks meeting the constraints is
cannot be resolved; or when no transport-layer connection can be empty) or reconciled with the Local and/or Remote Endpoints,
established to the Remote Endpoint (e.g., because the Remote Endpoint
is not accepting connections, the application is prohibited from * a Remote Endpoint Identifier cannot be resolved, or
opening a Connection by the operating system, or the establishment
attempt has timed out for any other reason). * no transport-layer connection can be established to the Remote
Endpoint (e.g., because the Remote Endpoint is not accepting
connections, the application is prohibited from opening a
Connection by the operating system, or the establishment attempt
has timed out for any other reason).
Connection establishment and transmission of the first Message can be Connection establishment and transmission of the first Message can be
combined in a single action (Section 9.2.5). combined in a single action (Section 9.2.5).
7.2. Passive Open: Listen 7.2. Passive Open: Listen
Passive open is the action of waiting for Connections from Remote Passive open is the action of waiting for Connections from Remote
Endpoints, commonly used by servers in client-server interactions. Endpoints, commonly used by servers in client-server interactions.
Passive open is supported by the Transport Services API through the Passive open is supported by the Transport Services API through the
Listen action and returns a Listener object: Listen action and returns a Listener object:
Listener := Preconnection.Listen() Listener := Preconnection.Listen()
Before calling Listen, the caller must have initialized the Before calling Listen, the caller must have initialized the
Preconnection during the pre-establishment phase with a Local Preconnection during the preestablishment phase with a Local Endpoint
Endpoint object, as well as all properties necessary for Protocol object, as well as all properties necessary for Protocol Stack
Stack selection. A Remote Endpoint can optionally be specified, to selection. A Remote Endpoint can optionally be specified, to
constrain what Connections are accepted. constrain what Connections are accepted.
The Listen action returns a Listener object. Once Listen has been The Listen action returns a Listener object. Once Listen has been
called, any changes to the Preconnection MUST NOT have any effect on called, any changes to the Preconnection MUST NOT have any effect on
the Listener. The Preconnection can be disposed of or reused, e.g., the Listener. The Preconnection can be disposed of or reused, e.g.,
to create another Listener. to create another Listener.
Listener.Stop() Listener.Stop()
Listening continues until the global context shuts down, or until the Listening continues until the global context shuts down or until the
Stop action is performed on the Listener object. Stop action is performed on the Listener object.
Listener -> ConnectionReceived<Connection> Listener -> ConnectionReceived<Connection>
The ConnectionReceived event occurs when a Remote Endpoint has The ConnectionReceived event occurs when:
established or cloned (e.g., by creating a new stream in a multi-
stream transport; see Section 7.4) a transport-layer connection to * a Remote Endpoint has established or cloned (e.g., by creating a
this Listener (for Connection-oriented transport protocols), or when new stream in a multi-stream transport; see Section 7.4) a
the first Message has been received from the Remote Endpoint (for transport-layer connection to this Listener (for Connection-
Connectionless protocols or streams of a multi-streaming transport), oriented transport protocols), or
causing a new Connection to be created. The resulting Connection is
contained within the ConnectionReceived event, and is ready to use as * the first Message has been received from the Remote Endpoint (for
soon as it is passed to the application via the event. Connectionless protocols or streams of a multi-streaming
transport) causing a new Connection to be created.
The resulting Connection is contained within the ConnectionReceived
event and is ready to use as soon as it is passed to the application
via the event.
Listener.SetNewConnectionLimit(value) Listener.SetNewConnectionLimit(value)
If the caller wants to rate-limit the number of inbound Connections If the caller wants to rate-limit the number of inbound Connections
that will be delivered, it can set a cap using SetNewConnectionLimit. that will be delivered, it can set a cap using SetNewConnectionLimit.
This mechanism allows a server to protect itself from being drained This mechanism allows a server to protect itself from being drained
of resources. Each time a new Connection is delivered by the of resources. Each time a new Connection is delivered by the
ConnectionReceived event, the value is automatically decremented. ConnectionReceived event, the value is automatically decremented.
Once the value reaches zero, no further Connections will be delivered Once the value reaches zero, no further Connections will be delivered
until the caller sets the limit to a higher value. By default, this until the caller sets the limit to a higher value. By default, this
value is Infinite. The caller is also able to reset the value to value is Infinite. The caller is also able to reset the value to
Infinite at any point. Infinite at any point.
Listener -> EstablishmentError<reason?> Listener -> EstablishmentError<reason?>
An EstablishmentError occurs either when the Properties and security An EstablishmentError occurs when:
parameters of the Preconnection cannot be fulfilled for listening or
cannot be reconciled with the Local Endpoint (and/or Remote Endpoint, * the Properties and security parameters of the Preconnection cannot
if specified), when the Local Endpoint (or Remote Endpoint, if be fulfilled for listening or cannot be reconciled with the Local
specified) cannot be resolved, or when the application is prohibited Endpoint (and/or Remote Endpoint, if specified),
from listening by policy.
* the Local Endpoint (or Remote Endpoint, if specified) cannot be
resolved, or
* the application is prohibited from listening by policy.
Listener -> Stopped<> Listener -> Stopped<>
A Stopped event occurs after the Listener has stopped listening. A Stopped event occurs after the Listener has stopped listening.
7.3. Peer-to-Peer Establishment: Rendezvous 7.3. Peer-to-Peer Establishment: Rendezvous
Simultaneous peer-to-peer Connection establishment is supported by Simultaneous peer-to-peer Connection establishment is supported by
the Rendezvous action: the Rendezvous action:
Preconnection.Rendezvous() Preconnection.Rendezvous()
A Preconnection object used in a Rendezvous MUST have both the Local A Preconnection object used in a Rendezvous MUST have both the Local
Endpoint candidates and the Remote Endpoint candidates specified, Endpoint candidates and the Remote Endpoint candidates specified,
along with the Transport Properties and security parameters needed along with the Transport Properties and security parameters needed
for Protocol Stack selection, before the Rendezvous action is for Protocol Stack selection before the Rendezvous action is
initiated. initiated.
The Rendezvous action listens on the Local Endpoint candidates for an The Rendezvous action listens on the Local Endpoint candidates for an
incoming Connection from the Remote Endpoint candidates, while also incoming Connection from the Remote Endpoint candidates, while also
simultaneously trying to establish a Connection from the Local simultaneously trying to establish a Connection from the Local
Endpoint candidates to the Remote Endpoint candidates. Endpoint candidates to the Remote Endpoint candidates.
If there are multiple Local Endpoints or Remote Endpoints configured, If there are multiple Local Endpoints or Remote Endpoints configured,
then initiating a Rendezvous action will cause the Transport Services then initiating a Rendezvous action will cause the Transport Services
Implementation to systematically probe the reachability of those Implementation to systematically probe the reachability of those
endpoint candidates following an approach such as that used in endpoint candidates following an approach such as that used in
Interactive Connectivity Establishment (ICE) [RFC8445]. Interactive Connectivity Establishment (ICE) [RFC8445].
If the endpoints are suspected to be behind a NAT, and the Local If the endpoints are suspected to be behind a NAT, and the Local
Endpoint supports a method of discovering NAT bindings, such as Endpoint supports a method of discovering NAT bindings, such as STUN
Session Traversal Utilities for NAT (STUN) [RFC8489] or Traversal [RFC8489] or Traversal Using Relays around NAT (TURN) [RFC8656], then
Using Relays around NAT (TURN) [RFC8656], then the Resolve action on the Resolve action on the Preconnection can be used to discover such
the Preconnection can be used to discover such bindings: bindings:
[]LocalEndpoint, []RemoteEndpoint := Preconnection.Resolve() []LocalEndpoint, []RemoteEndpoint := Preconnection.Resolve()
The Resolve call returns lists of Local Endpoints and Remote The Resolve call returns lists of Local Endpoints and Remote
Endpoints that represent the concrete addresses, local and server Endpoints that represent the concrete addresses, local and server
reflexive, on which a Rendezvous for the Preconnection will listen reflexive, on which a Rendezvous for the Preconnection will listen
for incoming Connections, and to which it will attempt to establish for incoming Connections and to which it will attempt to establish
Connections. Connections.
Note that the set of Local Endpoints returned by Resolve might or Note that the set of Local Endpoints returned by Resolve might or
might not contain information about all possible local interfaces might not contain information about all possible local interfaces,
depending on how the Preconnection is configured. The set of depending on how the Preconnection is configured. The set of
available local interfaces can also change over time so care needs to available local interfaces can also change over time, so care needs
be taken when using stored interface names. to be taken when using stored interface names.
An application that uses Rendezvous to establish a peer-to-peer An application that uses Rendezvous to establish a peer-to-peer
Connection in the presence of NATs will configure the Preconnection Connection in the presence of NATs will configure the Preconnection
object with at least one Local Endpoint that supports NAT binding object with at least one Local Endpoint that supports NAT binding
discovery. It will then Resolve the Preconnection, and pass the discovery. It will then Resolve the Preconnection and pass the
resulting list of Local Endpoint candidates to the peer via a resulting list of Local Endpoint candidates to the peer via a
signalling protocol, for example as part of an ICE [RFC8445] exchange signaling protocol, for example, as part of an ICE exchange [RFC8445]
within SIP [RFC3261] or WebRTC [RFC7478]. The peer will then, via within SIP [RFC3261] or WebRTC [RFC7478]. The peer will then, via
the same signalling channel, return the Remote Endpoint candidates. the same signaling channel, return the Remote Endpoint candidates.
The set of Remote Endpoint candidates are then configured onto the The set of Remote Endpoint candidates is then configured on the
Preconnection: Preconnection:
Preconnection.AddRemote([]RemoteEndpoint) Preconnection.AddRemote([]RemoteEndpoint)
The Rendezvous action is initiated, and causes the Transport Services Once the application has added both the Local Endpoint candidates and
Implementation to begin connectivity checks, once the application has the Remote Endpoint candidates retrieved from the peer via the
added both the Local Endpoint candidates and the Remote Endpoint signaling channel to the Preconnection, the Rendezvous action is
candidates retrieved from the peer via the signalling channel to the initiated and causes the Transport Services Implementation to begin
Preconnection. connectivity checks.
If successful, the Rendezvous action returns a Connection object via If successful, the Rendezvous action returns a Connection object via
a RendezvousDone<> event: a RendezvousDone<> event:
Preconnection -> RendezvousDone<Connection> Preconnection -> RendezvousDone<Connection>
The RendezvousDone<> event occurs when a Connection is established The RendezvousDone<> event occurs when a Connection is established
with the Remote Endpoint. For Connection-oriented transports, this with the Remote Endpoint. For Connection-oriented transports, this
occurs when the transport-layer connection is established; for occurs when the transport-layer connection is established; for
Connectionless transports, it occurs when the first Message is Connectionless transports, it occurs when the first Message is
received from the Remote Endpoint. The resulting Connection is received from the Remote Endpoint. The resulting Connection is
contained within the RendezvousDone<> event, and is ready to use as contained within the RendezvousDone<> event and is ready to use as
soon as it is passed to the application via the event. Changes made soon as it is passed to the application via the event. Changes made
to a Preconnection after Rendezvous has been called MUST NOT have any to a Preconnection after Rendezvous has been called MUST NOT have any
effect on existing Connections. effect on existing Connections.
An EstablishmentError occurs either when the Properties and Security An EstablishmentError occurs when:
Parameters of the Preconnection cannot be fulfilled for rendezvous or
cannot be reconciled with the Local and/or Remote Endpoints, when the * the Properties and Security Parameters of the Preconnection cannot
Local Endpoint or Remote Endpoint cannot be resolved, when no be fulfilled for rendezvous or cannot be reconciled with the Local
transport-layer connection can be established to the Remote Endpoint, and/or Remote Endpoints,
or when the application is prohibited from rendezvous by policy:
* the Local Endpoint or Remote Endpoint cannot be resolved,
* no transport-layer connection can be established to the Remote
Endpoint, or
* the application is prohibited from rendezvous by policy.
Preconnection -> EstablishmentError<reason?> Preconnection -> EstablishmentError<reason?>
7.4. Connection Groups 7.4. Connection Groups
Connection Groups can be created using the Clone action: Connection Groups can be created using the Clone action:
Connection := Connection.Clone(framer?, connectionProperties?) Connection := Connection.Clone(framer?, connectionProperties?)
Calling Clone on a Connection yields a Connection Group containing Calling Clone on a Connection yields a Connection Group containing
two Connections: the parent Connection on which Clone was called, and two Connections: the parent Connection on which Clone was called and
a resulting cloned Connection. The new Connection is actively a resulting cloned Connection. The new Connection is actively
opened, and it will locally send a Ready event or an opened, and it will locally send a Ready event or an
EstablishmentError event. Calling Clone on any of these Connections EstablishmentError event. Calling Clone on any of these Connections
adds another Connection to the Connection Group. Connections in a adds another Connection to the Connection Group. Connections in a
Connection Group share all Connection Properties except connPriority Connection Group share all Connection Properties except connPriority
(see Section 8.1.2), and these Connection Properties are entangled: (see Section 8.1.2), and these Connection Properties are entangled:
Changing one of the Connection Properties on one Connection in the changing one of the Connection Properties on one Connection in the
Connection Group automatically changes the Connection Property for Connection Group automatically changes the Connection Property for
all others. For example, changing connTimeout (see Section 8.1.3) on all others. For example, changing connTimeout (see Section 8.1.3) on
one Connection in a Connection Group will automatically make the same one Connection in a Connection Group will automatically make the same
change to this Connection Property for all other Connections in the change to this Connection Property for all other Connections in the
Connection Group. Like all other Properties, connPriority is copied Connection Group. Like all other Properties, connPriority is copied
to the new Connection when calling Clone, but in this case, a later to the new Connection when calling Clone, but, in this case, a later
change to the connPriority on one Connection does not change it on change to the connPriority on one Connection does not change it on
the other Connections in the same Connection Group. the other Connections in the same Connection Group.
The optional connectionProperties parameter allows passing Transport The optional connectionProperties parameter allows passing Transport
Properties that control the behavior of the underlying stream or Properties that control the behavior of the underlying stream or
connection to be created, e.g., Protocol-specific Properties to connection to be created, e.g., Protocol-specific Properties to
request specific stream IDs for SCTP or QUIC. request specific stream IDs for SCTP or QUIC.
Message Properties set on a Connection also apply only to that Message Properties set on a Connection also apply only to that
Connection. Connection.
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Framers can internally maintain per-Connection state. Framers can internally maintain per-Connection state.
It is also possible to check which Connections belong to the same It is also possible to check which Connections belong to the same
Connection Group. Calling GroupedConnections on a specific Connection Group. Calling GroupedConnections on a specific
Connection returns a set of all Connections in the same group. Connection returns a set of all Connections in the same group.
[]Connection := Connection.GroupedConnections() []Connection := Connection.GroupedConnections()
Connections will belong to the same group if the application Connections will belong to the same group if the application
previously called Clone. Passive Connections can also be added to previously called Clone. Passive Connections can also be added to
the same group -- e.g., when a Listener receives a new Connection the same group, e.g., when a Listener receives a new Connection that
that is just a new stream of an already active multi-streaming is just a new stream of an already-active multi-streaming protocol
protocol instance. instance.
If the underlying protocol supports multi-streaming, it is natural to If the underlying protocol supports multi-streaming, it is natural to
use this functionality to implement Clone. In that case, Connections use this functionality to implement Clone. In that case, Connections
in a Connection Group are multiplexed together, giving them similar in a Connection Group are multiplexed together, giving them similar
treatment not only inside Endpoints, but also across the end-to-end treatment not only inside Endpoints, but also across the end-to-end
Internet path. Internet path.
Note that calling Clone can result in on-the-wire signaling, e.g., to Note that calling Clone can result in on-the-wire signaling, e.g., to
open a new transport connection, depending on the underlying Protocol open a new transport connection, depending on the underlying Protocol
Stack. When Clone leads to the opening of multiple such connections, Stack. When Clone leads to the opening of multiple such connections,
the Transport Services system will ensure consistency of Connection the Transport Services system will ensure consistency of Connection
Properties by uniformly applying them to all underlying connections Properties by uniformly applying them to all underlying connections
in a group. Even in such a case, there are possibilities for a in a group. Even in such a case, it is possible for a Transport
Transport Services system to implement prioritization within a Services system to implement prioritization within a Connection Group
Connection Group [TCP-COUPLING] [RFC8699]. (see [TCP-COUPLING] and [RFC8699]).
Attempts to clone a Connection can result in a CloneError: Attempts to clone a Connection can result in a CloneError:
Connection -> CloneError<reason?> Connection -> CloneError<reason?>
A CloneError can also occur later, after Clone was successfully A CloneError can also occur later, after Clone was successfully
called. In this case, it informs the application that the Connection called. In this case, it informs the application that the Connection
that sends the CloneError is no longer a part of any Connection that sends the CloneError is no longer a part of any Connection
Group. For example, this can occur when the Transport Services Group. For example, this can occur when the Transport Services
system is unable to implement entanglement (a Connection Property was system is unable to implement entanglement (a Connection Property was
changed on a different Connection in the Connection Group, but this changed on a different Connection in the Connection Group, but this
change could not be successfully applied to the Connection that sends change could not be successfully applied to the Connection that sends
the CloneError). the CloneError).
The connPriority Connection Property operates on Connections in a The connPriority Connection Property operates on Connections in a
Connection Group using the same approach as in Section 9.1.3.2: when Connection Group using the same approach as that used in
allocating available network capacity among Connections in a Section 9.1.3.2: when allocating available network capacity among
Connection Group, sends on Connections with numerically lower Connections in a Connection Group, sends on Connections with
Priority values will be prioritized over sends on Connections that numerically lower Priority values will be prioritized over sends on
have numerically higher Priority values. Capacity will be shared Connections that have numerically higher Priority values. Capacity
among these Connections according to the connScheduler property will be shared among these Connections according to the connScheduler
(Section 8.1.5). See Section 9.2.6 for more. property (Section 8.1.5). See Section 9.2.6 for more details.
7.5. Adding and Removing Endpoints on a Connection 7.5. Adding and Removing Endpoints on a Connection
Transport protocols that are explicitly multipath aware are expected Transport protocols that are explicitly multipath aware are expected
to automatically manage the set of Remote Endpoints that they are to automatically manage the set of Remote Endpoints that they are
communicating with, and the paths to those endpoints. A PathChange<> communicating with and the paths to those endpoints. A PathChange<>
event, described in Section 8.3.2, will be generated when the path event, described in Section 8.3.2, will be generated when the path
changes. changes.
In some cases, however, it is necessary to explicitly indicate to a However, in some cases, it is necessary to explicitly indicate to a
Connection that a new Remote Endpoint has become available for use, Connection that a new Remote Endpoint has become available for use or
or to indicate that a Remote Endpoint is no longer available. This indicate that a Remote Endpoint is no longer available. This is most
is most common in the case of peer to peer connections using Trickle common in the case of peer-to-peer connections using Trickle ICE
ICE [RFC8838]. [RFC8838].
The AddRemote action can be used to add one or more new Remote The AddRemote action can be used to add one or more new Remote
Endpoints to a Connection: Endpoints to a Connection:
Connection.AddRemote([]RemoteEndpoint) Connection.AddRemote([]RemoteEndpoint)
Endpoints that are already known to the Connection are ignored. A Endpoints that are already known to the Connection are ignored. A
call to AddRemote makes the new Remote Endpoints available to the call to AddRemote makes the new Remote Endpoints available to the
Connection, but whether the Connection makes use of those Endpoints Connection, but whether the Connection makes use of those Endpoints
will depend on the underlying transport protocol. will depend on the underlying transport protocol.
Similarly, the RemoveRemote action can be used to tell a Connection Similarly, the RemoveRemote action can be used to tell a Connection
to stop using one or more Remote Endpoints: to stop using one or more Remote Endpoints:
Connection.RemoveRemote([]RemoteEndpoint) Connection.RemoveRemote([]RemoteEndpoint)
Removing all known Remote Endpoints can have the effect of aborting Removing all known Remote Endpoints can have the effect of aborting
the connection. The effect of removing the active Remote Endpoint(s) the connection. The effect of removing the active Remote Endpoint(s)
depends on the underlying transport: multipath aware transports might depends on the underlying transport: multipath-aware transports might
be able to switch to a new path if other reachable Remote Endpoints be able to switch to a new path if other reachable Remote Endpoints
exist, or the connection might abort. exist or the connection might abort.
Similarly, the AddLocal and RemoveLocal actions can be used to add Similarly, the AddLocal and RemoveLocal actions can be used to add
and remove Local Endpoints to/from a Connection. and remove Local Endpoints to or from a Connection.
8. Managing Connections 8. Managing Connections
During pre-establishment and after establishment, (Pre-)Connections During preestablishment and after establishment, Preconnections or
can be configured and queried using Connection Properties, and Connections can be configured and queried using Connection
asynchronous information could be available about the state of the Properties, and asynchronous information could be available about the
Connection via SoftError events. state of the Connection via SoftError events.
Connection Properties represent the configuration and state of the Connection Properties represent the configuration and state of the
selected Protocol Stack(s) backing a Connection. These Connection selected Protocol Stack(s) backing a Connection. These Connection
Properties can be generic, applying regardless of transport protocol, Properties can be generic (applying regardless of transport protocol)
or specific, applicable to a single implementation of a single or specific (applicable to a single implementation of a single
transport Protocol Stack. Generic Connection Properties are defined transport Protocol Stack). Generic Connection Properties are defined
in Section 8.1 below. in Section 8.1.
Protocol-specific Properties are defined in a transport- and Protocol-specific Properties are defined in a way that is specific to
implementation-specific way to permit more specialized protocol the transport or implementation to permit more specialized protocol
features to be used. Too much reliance by an application on features to be used. Too much reliance by an application on
Protocol-specific Properties can significantly reduce the flexibility Protocol-specific Properties can significantly reduce the flexibility
of a transport services system to make appropriate selection and of a Transport Services system to make appropriate selection and
configuration choices. Therefore, it is RECOMMENDED that Generic configuration choices. Therefore, it is RECOMMENDED that Generic
Connection Properties are used for properties common across different Connection Properties be used for properties common across different
protocols and that Protocol-specific Connection Properties are only protocols and that Protocol-specific Connection Properties are only
used where specific protocols or properties are necessary. used where specific protocols or properties are necessary.
The application can set and query Connection Properties on a per- The application can set and query Connection Properties on a per-
Connection basis. Connection Properties that are not read-only can Connection basis. Connection Properties that are not read-only can
be set during pre-establishment (see Section 6.2), as well as on be set during preestablishment (see Section 6.2), as well as on
Connections directly using the SetProperty action: Connections directly using the SetProperty action:
ErrorCode := Connection.SetProperty(property, value) ErrorCode := Connection.SetProperty(property, value)
If an error is encountered in setting a property (for example, if the If an error is encountered in setting a property (for example, if the
application tries to set a TCP-specific property on a Connection that application tries to set a TCP-specific property on a Connection that
is not using TCP), the application MUST be informed about this error is not using TCP), the application MUST be informed about this error
via the ErrorCode Object. Such errors MUST NOT cause the Connection via the ErrorCode Object. Such errors MUST NOT cause the Connection
to be terminated. Note that changing one of the Connection to be terminated. Note that changing one of the Connection
Properties on one Connection in a Connection Group will also change Properties on one Connection in a Connection Group will also change
it for all other Connections of that group; see further Section 7.4. it for all other Connections of that group; see Section 7.4.
At any point, the application can query Connection Properties. At any point, the application can query Connection Properties.
ConnectionProperties := Connection.GetProperties() ConnectionProperties := Connection.GetProperties()
value := ConnectionProperties.Get(property) value := ConnectionProperties.Get(property)
if ConnectionProperties.Has(boolean_or_preference_property) then ... if ConnectionProperties.Has(boolean_or_preference_property) then...
Depending on the status of the Connection, the queried Connection Depending on the status of the Connection, the queried Connection
Properties will include different information: Properties will include different information:
* The Connection state, which can be one of the following: * The Connection state, which can be one of the following:
Establishing, Established, Closing, or Closed (see Establishing, Established, Closing, or Closed (see
Section 8.1.11.1). Section 8.1.11.1).
* Whether the Connection can be used to send data (see * Whether the Connection can be used to send data (see
Section 8.1.11.2). A Connection can not be used for sending if Section 8.1.11.2). A Connection cannot be used for sending if the
the Connection was created with the Selection Property direction Connection was created with the Selection Property direction set
set to unidirectional receive or if a Message marked as Final was to unidirectional receive or if a Message marked as Final was sent
sent over this Connection. See also Section 9.1.3.5. over this Connection. See also Section 9.1.3.5.
* Whether the Connection can be used to receive data (see * Whether the Connection can be used to receive data (see
Section 8.1.11.3). A Connection cannot be used for receiving if Section 8.1.11.3). A Connection cannot be used for receiving if
the Connection was created with the Selection Property direction the Connection was created with the Selection Property direction
set to unidirectional send or if a Message marked as Final was set to unidirectional send or if a Message marked as Final was
received. See Section 9.3.3.3. The latter is only supported by received (see Section 9.3.3.3). The latter is only supported by
certain transport protocols, e.g., by TCP as half-closed certain transport protocols, e.g., by TCP as a half-closed
connection. connection.
* For Connections that are Established, Closing, or Closed: * For Connections that are Established, Closing, or Closed:
Connection Properties (Section 8.1) of the actual protocols that Connection Properties (Section 8.1) of the actual protocols that
were selected and instantiated, and Selection Properties that the were selected and instantiated, and Selection Properties that the
application specified on the Preconnection. Selection Properties application specified on the Preconnection. Selection Properties
of type Preference will be exposed as boolean values indicating of type Preference will be exposed as boolean values indicating
whether or not the property applies to the selected transport. whether or not the property applies to the selected transport.
Note that the instantiated Protocol Stack might not match all Note that the instantiated Protocol Stack might not match all
Protocol Selection Properties that the application specified on Protocol Selection Properties that the application specified on
the Preconnection. the Preconnection.
* For Connections that are Established: Transport Services system * For Connections that are Established: Transport Services system
implementations ought to provide information concerning the implementations ought to provide information concerning the
path(s) used by the Protocol Stack. This can be derived from path(s) used by the Protocol Stack. This can be derived from
local PVD information, measurements by the Protocol Stack, or local PvD information, measurements by the Protocol Stack, or
other sources. For example, a Transport System that is configured other sources. For example, a transport system that is configured
to receive and process PVD information [RFC7556] could also to receive and process PvD information [RFC7556] could also
provide network configuration information for the chosen path(s). provide network configuration information for the chosen path(s).
8.1. Generic Connection Properties 8.1. Generic Connection Properties
Generic Connection Properties are defined independent of the chosen Generic Connection Properties are defined independently of the chosen
Protocol Stack and therefore available on all Connections. Protocol Stack; therefore, they are available on all Connections.
Many Connection Properties have a corresponding Selection Property Many Connection Properties have a corresponding Selection Property
that enables applications to express their preference for protocols that enables applications to express their preference for protocols
providing a supporting transport feature. providing a supporting transport feature.
8.1.1. Required Minimum Corruption Protection Coverage for Receiving 8.1.1. Required Minimum Corruption Protection Coverage for Receiving
Name: recvChecksumLen Name: recvChecksumLen
Type: Integer (non-negative) or Full Coverage Type: Integer (non-negative) or Full Coverage
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Connection Priority are given; a Transport Services system could Connection Priority are given; a Transport Services system could
ignore this property. See Section 9.2.6 for more details. ignore this property. See Section 9.2.6 for more details.
8.1.3. Timeout for Aborting Connection 8.1.3. Timeout for Aborting Connection
Name: connTimeout Name: connTimeout
Type: Numeric (positive) or Disabled Type: Numeric (positive) or Disabled
Default: Disabled Default: Disabled
If this property is Numeric, it specifies how long to wait before If this property is Numeric, it specifies how long to wait before
deciding that an active Connection has failed when trying to reliably deciding that an active Connection has failed when trying to reliably
deliver data to the Remote Endpoint. Adjusting this property will deliver data to the Remote Endpoint. Adjusting this property will
only take effect when the underlying stack supports reliability. If only take effect when the underlying stack supports reliability. If
this property has the enumerated value Disabled, it means that no this property has the enumerated value Disabled, it means that no
timeout is scheduled. A Transport Services API could express timeout is scheduled. A Transport Services API could express
Disabled in an environment-typical way, e.g., as a Union type or Disabled in an environment-typical way, e.g., as a Union type or
special value. special value.
8.1.4. Timeout for keep alive packets 8.1.4. Timeout for Keep-Alive Packets
Name: keepAliveTimeout Name: keepAliveTimeout
Type: Numeric (positive) or Disabled Type: Numeric (positive) or Disabled
Default: Disabled Default: Disabled
A Transport Services API can request a protocol that supports sending A Transport Services API can request a protocol that supports sending
keep alive packets (Section 6.2.10). If this property is Numeric, it keep-alive packets (Section 6.2.10). If this property is Numeric, it
specifies the maximum length of time an idle Connection (one for specifies the maximum length of time an idle Connection (one for
which no transport packets have been sent) ought to wait before the which no transport packets have been sent) ought to wait before the
Local Endpoint sends a keep-alive packet to the Remote Endpoint. Local Endpoint sends a keep-alive packet to the Remote Endpoint.
Adjusting this property will only take effect when the underlying Adjusting this property will only take effect when the underlying
stack supports sending keep-alive packets. Guidance on setting this stack supports sending keep-alive packets. Guidance on setting this
value for connection-less transports is provided in [RFC8085]. A value for connectionless transports is provided in [RFC8085]. A
value greater than the Connection timeout (Section 8.1.3) or the value greater than the Connection timeout (Section 8.1.3) or the
enumerated value Disabled will disable the sending of keep-alive enumerated value Disabled will disable the sending of keep-alive
packets. A Transport Services API could express Disabled in an packets. A Transport Services API could express Disabled in an
environment-typical way, e.g., as a Union type or special value. environment-typical way, e.g., as a Union type or special value.
8.1.5. Connection Group Transmission Scheduler 8.1.5. Connection Group Transmission Scheduler
Name: connScheduler Name: connScheduler
Type: Enumeration Type: Enumeration
Default: Weighted Fair Queueing (see Section 3.6 of [RFC8260]) Default: Weighted Fair Queueing (see Section 3.6 of [RFC8260])
This property specifies which scheduler is used among Connections This property specifies which scheduler is used among Connections
within a Connection Group to apportion the available capacity within a Connection Group to apportion the available capacity
according to Connection priorities (see Section 7.4 and according to Connection priorities (see Sections 7.4 and 8.1.2). A
Section 8.1.2). A set of schedulers is described in [RFC8260]. set of schedulers is described in [RFC8260].
8.1.6. Capacity Profile 8.1.6. Capacity Profile
Name: connCapacityProfile Name: connCapacityProfile
Type: Enumeration Type: Enumeration
Default: Default Profile (Best Effort) Default: Default Profile (Best Effort)
This property specifies the desired network treatment for traffic This property specifies the desired network treatment for traffic
sent by the application and the tradeoffs the application is prepared sent by the application and the trade-offs the application is
to make in path and protocol selection to receive that desired prepared to make in path and protocol selection to receive that
treatment. When the capacity profile is set to a value other than desired treatment. When the capacity profile is set to a value other
Default, the Transport Services system SHOULD select paths and than Default, the Transport Services system SHOULD select paths and
configure protocols to optimize the tradeoff between delay, delay configure protocols to optimize the trade-off between delay, delay
variation, and efficient use of the available capacity based on the variation, and efficient use of the available capacity based on the
capacity profile specified. How this is realized is implementation- capacity profile specified. How this is realized is implementation
specific. The capacity profile MAY also be used to set markings on specific. The capacity profile MAY also be used to set markings on
the wire for Protocol Stacks supporting this. Recommendations for the wire for Protocol Stacks supporting this action. Recommendations
use with DSCP are provided below for each profile; note that when a for use with DSCPs are provided below for each profile; note that
Connection is multiplexed, the guidelines in Section 6 of [RFC7657] when a Connection is multiplexed, the guidelines in Section 6 of
apply. [RFC7657] apply.
The following values are valid for the capacity profile: The following values are valid for the capacity profile:
Default: The application provides no information about its expected Default: The application provides no information about its expected
capacity profile. Transport Services systems that map the capacity profile. Transport Services systems that map the
requested capacity profile onto per-connection DSCP signaling requested capacity profile to per-connection DSCP signaling SHOULD
SHOULD assign the DSCP Default Forwarding [RFC2474] Per Hop assign the DSCP Default Forwarding Per Hop Behavior (PHB)
Behaviour (PHB). [RFC2474].
Scavenger: The application is not interactive. It expects to send Scavenger: The application is not interactive. It expects to send
and/or receive data without any urgency. This can, for example, and/or receive data without any urgency. This can, for example,
be used to select Protocol Stacks with scavenger transmission be used to select Protocol Stacks with scavenger transmission
control and/or to assign the traffic to a lower-effort service. control and/or to assign the traffic to a lower-effort service.
Transport Services systems that map the requested capacity profile Transport Services systems that map the requested capacity profile
onto per-connection DSCP signaling SHOULD assign the DSCP Less to per-connection DSCP signaling SHOULD assign the DSCP "Less than
than Best Effort [RFC8622] PHB. best effort" PHB [RFC8622].
Low Latency/Interactive: The application is interactive, and prefers Low Latency/Interactive: The application is interactive and prefers
loss to latency. Response time SHOULD be optimized at the expense loss to latency. Response time SHOULD be optimized at the expense
of delay variation and efficient use of the available capacity of delay variation and efficient use of the available capacity
when sending on this Connection. This can be used by the system when sending on this Connection. This can be used by the system
to disable the coalescing of multiple small Messages into larger to disable the coalescing of multiple small Messages into larger
packets (Nagle's algorithm); to prefer immediate acknowledgment packets (Nagle's algorithm); to prefer immediate acknowledgement
from the peer endpoint when supported by the underlying transport; from the peer endpoint when supported by the underlying transport;
and so on. Transport Services systems that map the requested and so on. Transport Services systems that map the requested
capacity profile onto per-connection DSCP signaling without capacity profile to per-connection DSCP signaling without
multiplexing SHOULD assign a DSCP Assured Forwarding multiplexing SHOULD assign a DSCP Assured Forwarding
(AF41,AF42,AF43,AF44) [RFC2597] PHB. Inelastic traffic that is (AF41,AF42,AF43,AF44) PHB [RFC2597]. Inelastic traffic that is
expected to conform to the configured network service rate could expected to conform to the configured network service rate could
be mapped to the DSCP Expedited Forwarding [RFC3246] or [RFC5865] be mapped to the DSCP Expedited Forwarding PHBs [RFC3246] or PHBs
PHBs. as discussed in [RFC5865].
Low Latency/Non-Interactive: The application prefers loss to Low Latency/Non-Interactive: The application prefers loss to latency
latency, but is not interactive. Response time SHOULD be but is not interactive. Response time SHOULD be optimized at the
optimized at the expense of delay variation and efficient use of expense of delay variation and efficient use of the available
the available capacity when sending on this Connection. Transport capacity when sending on this Connection. Transport system
system implementations that map the requested capacity profile implementations that map the requested capacity profile to per-
onto per-connection DSCP signaling without multiplexing SHOULD connection DSCP signaling without multiplexing SHOULD assign a
assign a DSCP Assured Forwarding (AF21,AF22,AF23,AF24) [RFC2597] DSCP Assured Forwarding (AF21,AF22,AF23,AF24) PHB [RFC2597].
PHB.
Constant-Rate Streaming: The application expects to send/receive Constant-Rate Streaming: The application expects to send/receive
data at a constant rate after Connection establishment. Delay and data at a constant rate after Connection establishment. Delay and
delay variation SHOULD be minimized at the expense of efficient delay variation SHOULD be minimized at the expense of efficient
use of the available capacity. This implies that the Connection use of the available capacity. This implies that the Connection
might fail if the Path is unable to maintain the desired rate. A might fail if the Path is unable to maintain the desired rate. A
transport can interpret this capacity profile as preferring a transport can interpret this capacity profile as preferring a
circuit breaker [RFC8084] to a rate-adaptive congestion circuit breaker [RFC8084] to a rate-adaptive congestion
controller. Transport system implementations that map the controller. Transport system implementations that map the
requested capacity profile onto per-connection DSCP signaling requested capacity profile to per-connection DSCP signaling
without multiplexing SHOULD assign a DSCP Assured Forwarding without multiplexing SHOULD assign a DSCP Assured Forwarding
(AF31,AF32,AF33,AF34) [RFC2597] PHB. (AF31,AF32,AF33,AF34) PHB [RFC2597].
Capacity-Seeking: The application expects to send/receive data at Capacity-Seeking: The application expects to send/receive data at
the maximum rate allowed by its congestion controller over a the maximum rate allowed by its congestion controller over a
relatively long period of time. Transport Services systems that relatively long period of time. Transport Services systems that
map the requested capacity profile onto per-connection DSCP map the requested capacity profile to per-connection DSCP
signaling without multiplexing SHOULD assign a DSCP Assured signaling without multiplexing SHOULD assign a DSCP Assured
Forwarding (AF11,AF12,AF13,AF14) [RFC2597] PHB per Section 4.8 of Forwarding (AF11,AF12,AF13,AF14) PHB [RFC2597] per Section 4.8 of
[RFC4594]. [RFC4594].
The capacity profile for a selected Protocol Stack may be modified on The capacity profile for a selected Protocol Stack may be modified on
a per-Message basis using the Transmission Profile Message Property; a per-Message basis using the Transmission Profile Message Property;
see Section 9.1.3.8. see Section 9.1.3.8.
8.1.7. Policy for using Multipath Transports 8.1.7. Policy for Using Multipath Transports
Name: multipathPolicy Name: multipathPolicy
Type: Enumeration Type: Enumeration
Default: Handover Default: Handover
This property specifies the local policy for transferring data across This property specifies the local policy for transferring data across
multiple paths between the same end hosts if Multipath Transport is multiple paths between the same end hosts if Multipath Transport is
not set to Disabled (see Section 6.2.14). Possible values are: not set to Disabled (see Section 6.2.14). Possible values are as
follows:
Handover: The Connection ought only to attempt to migrate between Handover: The Connection ought only to attempt to migrate between
different paths when the original path is lost or becomes different paths when the original path is lost or becomes
unusable. The thresholds used to declare a path unusable are unusable. The thresholds used to declare a path unusable are
implementation specific. implementation specific.
Interactive: The Connection ought only to attempt to minimize the Interactive: The Connection ought only to attempt to minimize the
latency for interactive traffic patterns by transmitting data latency for interactive traffic patterns by transmitting data
across multiple paths when this is beneficial. The goal of across multiple paths when this is beneficial. The goal of
minimizing the latency will be balanced against the cost of each minimizing the latency will be balanced against the cost of each
of these paths. Depending on the cost of the lower-latency path, of these paths. Depending on the cost of the lower-latency path,
the scheduling might choose to use a higher-latency path. Traffic the scheduling might choose to use a higher-latency path. Traffic
can be scheduled such that data may be transmitted on multiple can be scheduled such that data may be transmitted on multiple
paths in parallel to achieve a lower latency. The specific paths in parallel to achieve a lower latency. The specific
scheduling algorithm is implementation-specific. scheduling algorithm is implementation specific.
Aggregate: The Connection ought to attempt to use multiple paths in Aggregate: The Connection ought to attempt to use multiple paths in
parallel to maximize available capacity and possibly overcome the parallel to maximize available capacity and possibly overcome the
capacity limitations of the individual paths. The actual strategy capacity limitations of the individual paths. The actual strategy
is implementation specific. is implementation specific.
Note that this is a local choice – the Remote Endpoint can choose a Note that this is a local choice: the Remote Endpoint can choose a
different policy. different policy.
8.1.8. Bounds on Send or Receive Rate 8.1.8. Bounds on Send or Receive Rate
Name: minSendRate / minRecvRate / maxSendRate / maxRecvRate Name: minSendRate / minRecvRate / maxSendRate / maxRecvRate
Type: Numeric (positive) or Unlimited / Numeric (positive) or Type: Numeric (positive) or Unlimited / Numeric (positive) or
Unlimited / Numeric (positive) or Unlimited / Numeric (positive) Unlimited / Numeric (positive) or Unlimited / Numeric (positive)
or Unlimited or Unlimited
Default: Unlimited / Unlimited / Unlimited / Unlimited Default: Unlimited / Unlimited / Unlimited / Unlimited
Numeric values of these properties specify an upper-bound rate that a Numeric values of these properties specify an upper-bound rate that a
transfer is not expected to exceed (even if flow control and transfer is not expected to exceed (even if flow control and
congestion control allow higher rates), and/or a lower-bound congestion control allow higher rates) and/or a lower-bound
application-layer rate below which the application does not deem it application-layer rate below which the application does not deem it
will be useful. These rate values are measured at the application will be useful. These rate values are measured at the application
layer, i.e. do not consider the header overhead from protocols used layer, i.e., do not consider the header overhead from protocols used
by the Transport Services system. The values are specified in bits by the Transport Services system. The values are specified in bits
per second, and assumed to be measured over one-second time per second and assumed to be measured over one-second time intervals.
intervals. E.g., specifying a maxSendRate of X bits per second means For example, specifying a maxSendRate of X bits per second means
that, from the moment at which the property value is chosen, not more that, from the moment at which the property value is chosen, not more
than X bits will be send in any following second. The enumerated than X bits will be sent in any following second. The enumerated
value Unlimited indicates that no bound is specified. A Transport value Unlimited indicates that no bound is specified. A Transport
Services API could express Unlimited in an environment-typical way, Services API could express Unlimited in an environment-typical way,
e.g., as a Union type or special value. e.g., as a Union type or special value.
8.1.9. Group Connection Limit 8.1.9. Group Connection Limit
Name: groupConnLimit Name: groupConnLimit
Type: Numeric (positive) or Unlimited Type: Numeric (positive) or Unlimited
Default: Unlimited Default: Unlimited
If this property is Numeric, it controls the number of Connections If this property is Numeric, it controls the number of Connections
that can be accepted from a peer as new members of the Connection's that can be accepted from a peer as new members of the Connection's
group. Similar to SetNewConnectionLimit, this limits the number of group. Similar to SetNewConnectionLimit, this limits the number of
ConnectionReceived events that will occur, but constrained to the ConnectionReceived events that will occur, but constrained to the
group of the Connection associated with this property. For a multi- group of the Connection associated with this property. For a multi-
streaming transport, this limits the number of allowed streams. A streaming transport, this limits the number of allowed streams. A
Transport Services API could express Unlimited in an environment- Transport Services API could express Unlimited in an environment-
typical way, e.g., as a Union type or special value. typical way, e.g., as a Union type or special value.
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Default: false Default: false
When set to true, this property will initiate new Connections using When set to true, this property will initiate new Connections using
as little cached information (such as session tickets or cookies) as as little cached information (such as session tickets or cookies) as
possible from previous Connections that are not in the same possible from previous Connections that are not in the same
Connection Group. Any state generated by this Connection will only Connection Group. Any state generated by this Connection will only
be shared with Connections in the same Connection Group. Cloned be shared with Connections in the same Connection Group. Cloned
Connections will use saved state from within the Connection Group. Connections will use saved state from within the Connection Group.
This is used for separating Connection Contexts as specified in This is used for separating Connection Contexts as specified in
Section 4.2.3 of [I-D.ietf-taps-arch]. Section 4.2.3 of [RFC9621].
Note that this does not guarantee no leakage of information, as Note that this does not guarantee no leakage of information, as
implementations might not be able to fully isolate all caches (e.g. implementations might not be able to fully isolate all caches (e.g.,
RTT estimates). Note that this property could degrade Connection RTT estimates). Note that this property could degrade Connection
performance. performance.
8.1.11. Read-only Connection Properties 8.1.11. Read-Only Connection Properties
The following generic Connection Properties are read-only, i.e. they The following generic Connection Properties are read-only, i.e., they
cannot be changed by an application. cannot be changed by an application.
8.1.11.1. Connection state 8.1.11.1. Connection State
Name: connState Name: connState
Type: Enumeration Type: Enumeration
This property informs about the current state of the Connection. This property provides information about the current state of the
Possible values are: Establishing, Established, Closing or Closed; Connection. Possible values are Establishing, Established, Closing,
for more details on Connection state, see Section 11. or Closed. For more details on Connection state, see Section 11.
8.1.11.2. Can Send Data 8.1.11.2. Can Send Data
Name: canSend Name: canSend
Type: Boolean Type: Boolean
This property can be queried to learn whether the Connection can be This property can be queried to learn whether the Connection can be
used to send data. used to send data.
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Name: singularTransmissionMsgMaxLen Name: singularTransmissionMsgMaxLen
Type: Integer (non-negative) or Not applicable Type: Integer (non-negative) or Not applicable
This property, if applicable, represents the maximum Message size This property, if applicable, represents the maximum Message size
that can be sent without incurring network-layer fragmentation at the that can be sent without incurring network-layer fragmentation at the
sender. It is specified as a number of bytes and is less than or sender. It is specified as a number of bytes and is less than or
equal to the Maximum Message Size on Send. It exposes a readable equal to the Maximum Message Size on Send. It exposes a readable
value to the application based on the Maximum Packet Size (MPS). The value to the application based on the Maximum Packet Size (MPS). The
value of this property can change over time (and can be updated by value of this property can change over time (and can be updated via
Datagram PLPMTUD [RFC8899]). This value allows a sending stack to Datagram Packetization Layer Path MTU Discovery (DPLPMTUD)
avoid unwanted fragmentation at the network-layer or segmentation by [RFC8899]). This value allows a sending stack to avoid unwanted
the transport layer before choosing the message size and/or after a fragmentation at the network layer or segmentation by the transport
SendError occurs indicating an attempt to send a Message that is too layer before choosing the message size and/or after a SendError
large. A Transport Services API could express Not applicable in an occurs indicating an attempt to send a Message that is too large. A
Transport Services API could express Not applicable in an
environment-typical way, e.g., as a Union type or special value environment-typical way, e.g., as a Union type or special value
(e.g., 0). (e.g., 0).
8.1.11.5. Maximum Message Size on Send 8.1.11.5. Maximum Message Size on Send
Name: sendMsgMaxLen Name: sendMsgMaxLen
Type: Integer (non-negative) Type: Integer (non-negative)
This property represents the maximum Message size that an application This property represents the maximum Message size that an application
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8.1.11.6. Maximum Message Size on Receive 8.1.11.6. Maximum Message Size on Receive
Name: recvMsgMaxLen Name: recvMsgMaxLen
Type: Integer (non-negative) Type: Integer (non-negative)
This property represents the maximum Message size that an application This property represents the maximum Message size that an application
can receive. It is specified as the number of bytes. A value of 0 can receive. It is specified as the number of bytes. A value of 0
indicates that receiving is not possible. indicates that receiving is not possible.
8.2. TCP-specific Properties: User Timeout Option (UTO) 8.2. TCP-Specific Properties: User Timeout Option (UTO)
These properties specify configurations for the TCP User Timeout These properties specify configurations for the TCP User Timeout
Option (UTO). This is a TCP-specific property, that is only used in Option (UTO). This is a TCP-specific property that is only used in
the case that TCP becomes the chosen transport protocol and useful the case that TCP becomes the chosen transport protocol. It is
only if TCP is implemented in the Transport Services system. useful only if TCP is implemented in the Transport Services system.
Protocol-specific options could also be defined for other transport Protocol-specific options could also be defined for other transport
protocols. protocols.
These are included here because the feature Suggest timeout to the These properties are included here because the feature Suggest
peer is part of the minimal set of transport services [RFC8923], timeout to the peer is part of the minimal set of Transport Services
where this feature was categorized as "functional". This means that [RFC8923], where this feature was categorized as "functional". This
when a Transport Services system offers this feature, the Transport means that when a Transport Services system offers this feature, the
Services API has to expose an interface to the application. Transport Services API has to expose an interface to the application.
Otherwise, the implementation might violate assumptions by the Otherwise, the implementation might violate assumptions by the
application, which could cause the application to fail. application, which could cause the application to fail.
All of the below properties are optional (e.g., it is possible to All of the below properties are optional (e.g., it is possible to
specify User Timeout Enabled as true, but not specify an Advertised specify User Timeout Enabled as true but not specify an Advertised
User Timeout value; in this case, the TCP default will be used). User Timeout value; in this case, the TCP default will be used).
These properties reflect the API extension specified in Section 3 of These properties reflect the API extension specified in Section 3 of
[RFC5482]. [RFC5482].
8.2.1. Advertised User Timeout 8.2.1. Advertised User Timeout
Name: tcp.userTimeoutValue Name: tcp.userTimeoutValue
Type: Integer (positive) Type: Integer (positive)
Default: the TCP default Default: the TCP default
This time value is advertised via the TCP User Timeout Option (UTO) This time value is advertised via the TCP User Timeout Option (UTO)
[RFC5482] to the Remote Endpoint which can use it to adapt its own [RFC5482] to the Remote Endpoint, which can use it to adapt its own
Timeout for aborting Connection (see Section 8.1.3) value. Timeout for aborting the Connection (see Section 8.1.3) value.
8.2.2. User Timeout Enabled 8.2.2. User Timeout Enabled
Name: tcp.userTimeoutEnabled Name: tcp.userTimeoutEnabled
Type: Boolean Type: Boolean
Default: false Default: false
This property controls whether the TCP UTO option is enabled for a This property controls whether the TCP UTO is enabled for a
connection. This applies to both sending and receiving. connection. This applies to both sending and receiving.
8.2.3. Timeout Changeable 8.2.3. Timeout Changeable
Name: tcp.userTimeoutChangeable Name: tcp.userTimeoutChangeable
Type: Boolean Type: Boolean
Default: true Default: true
This property controls whether the TCP connTimeout (see This property controls whether the TCP connTimeout (see
Section 8.1.3) can be changed based on a UTO option received from the Section 8.1.3) can be changed based on a UTO received from the remote
remote peer. This boolean becomes false when connTimeout (see peer. This boolean becomes false when connTimeout (see
Section 8.1.3) is used. Section 8.1.3) is used.
8.3. Connection Lifecycle Events 8.3. Connection Lifecycle Events
During the lifetime of a Connection there are events that can occur During the lifetime of a Connection there are events that can occur
when configured. when configured.
8.3.1. Soft Errors 8.3.1. Soft Errors
Asynchronous introspection is also possible, via the SoftError event. Asynchronous introspection is also possible, via the SoftError event.
This event informs the application about the receipt and contents of This event informs the application about the receipt and contents of
an ICMP error message related to the Connection. This will only an ICMP error message related to the Connection. This will only
happen if the underlying Protocol Stack supports access to soft happen if the underlying Protocol Stack supports access to soft
errors; however, even if the underlying stack supports it, there is errors; however, even if the underlying stack supports it, there is
no guarantee that a soft error will be signaled. no guarantee that a soft error will be signaled.
Connection -> SoftError<> Connection -> SoftError<>
8.3.2. Path change 8.3.2. Path Change
This event notifies the application when at least one of the paths This event notifies the application when at least one of the paths
underlying a Connection has changed. Changes occur on a single path underlying a Connection has changed. Changes occur on a single path
when the PMTU changes as well as when multiple paths are used and when the PMTU changes as well as when multiple paths are used and
paths are added or removed, the set of local endpoints changes, or a paths are added or removed, the set of local endpoints changes, or a
handover has been performed. handover has been performed.
Connection -> PathChange<> Connection -> PathChange<>
9. Data Transfer 9. Data Transfer
Data is sent and received as Messages, which allows the application Data is sent and received as Messages, which allows the application
to communicate the boundaries of the data being transferred. to communicate the boundaries of the data being transferred.
9.1. Messages and Framers 9.1. Messages and Framers
Each Message has an optional Message Context, which allows adding Each Message has an optional Message Context, which allows adding
Message Properties, identify Send events related to a specific Message Properties, identify Send events related to a specific
Message or to inspect meta-data related to the Message sent. Framers Message or to inspect metadata related to the Message sent. Framers
can be used to extend or modify the Message data with additional can be used to extend or modify the Message data with additional
information that can be processed at the receiver to detect message information that can be processed at the receiver to detect message
boundaries. boundaries.
9.1.1. Message Contexts 9.1.1. Message Contexts
Using the MessageContext object, the application can set and retrieve Using the MessageContext object, the application can set and retrieve
meta-data of the Message, including Message Properties (see metadata of the Message, including Message Properties (see
Section 9.1.3) and framing meta-data (see Section 9.1.2.2). Section 9.1.3) and framing metadata (see Section 9.1.2.2).
Therefore, a MessageContext object can be passed to the Send action Therefore, a MessageContext object can be passed to the Send action
and is returned by each Send and Receive related event. and is returned by each event related to Send and Receive.
Message Properties can be set and queried using the Message Context: Message Properties can be set and queried using the Message Context:
MessageContext.add(property, value) MessageContext.add(property, value)
PropertyValue := MessageContext.get(property) PropertyValue := MessageContext.get(property)
These Message Properties can be generic properties or Protocol- These Message Properties can be generic properties or Protocol-
specific Properties. specific Properties.
For MessageContexts returned by Send events (see Section 9.2.2) and For MessageContexts returned by Send events (see Section 9.2.2) and
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9.1.2. Message Framers 9.1.2. Message Framers
Although most applications communicate over a network using well- Although most applications communicate over a network using well-
formed Messages, the boundaries and metadata of the Messages are formed Messages, the boundaries and metadata of the Messages are
often not directly communicated by the transport protocol itself. often not directly communicated by the transport protocol itself.
For example, HTTP applications send and receive HTTP messages over a For example, HTTP applications send and receive HTTP messages over a
byte-stream transport, requiring that the boundaries of HTTP messages byte-stream transport, requiring that the boundaries of HTTP messages
be parsed from the stream of bytes. be parsed from the stream of bytes.
Message Framers allow extending a Connection's Protocol Stack to Message Framers allow extending a Connection's Protocol Stack to
define how to encapsulate or encode outbound Messages, and how to define how to encapsulate or encode outbound Messages and how to
decapsulate or decode inbound data into Messages. Message Framers decapsulate or decode inbound data into Messages. Message Framers
allow message boundaries to be preserved when using a Connection allow message boundaries to be preserved when using a Connection
object, even when using byte-stream transports. This is designed object, even when using byte-stream transports. This is designed
based on the fact that many of the current application protocols based on the fact that many of the application protocols in use at
evolved over TCP, which does not provide message boundary the time of writing evolved over TCP, which does not provide message
preservation, and since many of these protocols require message boundary preservation; because many of these protocols require
boundaries to function, each application layer protocol has defined message boundaries to function, each application-layer protocol has
its own framing. defined its own framing.
To use a Message Framer, the application adds it to its Preconnection To use a Message Framer, the application adds it to its Preconnection
object. Then, the Message Framer can intercept all calls to Send or object. Then, the Message Framer can intercept all calls to Send or
Receive on a Connection to add Message semantics, in addition to Receive on a Connection to add Message semantics, in addition to
interacting with the setup and teardown of the Connection. A Framer interacting with the setup and teardown of the Connection. A Framer
can start sending data before the application sends data if the can start sending data before the application sends data if the
framing protocol requires a prefix or handshake (see [RFC9329] for an framing protocol requires a prefix or handshake (see [RFC9329] for an
example of such a framing protocol). example of such a framing protocol).
Initiate() Send() Receive() Close() Initiate() Send() Receive() Close()
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+----+----------+---------^----------+-----+ +----+----------+---------^----------+-----+
| | | | | | | |
| +-----------------+ | | +-----------------+ |
| | Byte-stream | | | | Byte-stream | |
| +-----------------+ | | +-----------------+ |
| | | | | | | |
+----v----------v---------+----------v-----+ +----v----------v---------+----------v-----+
| Transport Protocol Stack | | Transport Protocol Stack |
+------------------------------------------+ +------------------------------------------+
Figure 1: Protocol Stack showing a Message Framer Figure 1: Protocol Stack Showing a Message Framer
Note that while Message Framers add the most value when placed above Note that while Message Framers add the most value when placed above
a protocol that otherwise does not preserve message boundaries, they a protocol that otherwise does not preserve message boundaries, they
can also be used with datagram- or message-based protocols. In these can also be used with datagram- or message-based protocols. In these
cases, they add a transformation to further encode or encapsulate, cases, they add a transformation to further encode or encapsulate and
and can potentially support packing multiple application-layer can potentially support packing multiple application-layer Messages
Messages into individual transport datagrams. into individual transport datagrams.
The API to implement a Message Framer can vary depending on the The API to implement a Message Framer can vary, depending on the
implementation; guidance on implementing Message Framers can be found implementation; guidance on implementing Message Framers can be found
in [I-D.ietf-taps-impl]. in [RFC9623].
9.1.2.1. Adding Message Framers to Pre-Connections 9.1.2.1. Adding Message Framers to Preconnections
The Message Framer object can be added to one or more Preconnections The Message Framer object can be added to one or more Preconnections
to run on top of transport protocols. Multiple Framers can be added to run on top of transport protocols. Multiple Framers can be added
to a Preconnection; in this case, the Framers operate as a framing to a Preconnection; in this case, the Framers operate as a framing
stack, i.e. the last one added runs first when framing outbound stack, i.e., the last one added runs first when framing outbound
Messages, and last when parsing inbound data. Messages, and last when parsing inbound data.
The following example adds a basic HTTP Message Framer to a The following example adds a basic HTTP Message Framer to a
Preconnection: Preconnection:
framer := NewHTTPMessageFramer() framer := NewHTTPMessageFramer()
Preconnection.AddFramer(framer) Preconnection.AddFramer(framer)
Since Message Framers pass from Preconnection to Listener or Since Message Framers pass from Preconnection to Listener or
Connection, addition of Framers must happen before any operation that Connection, addition of Framers must happen before any operation that
might result in the creation of a Connection. might result in the creation of a Connection.
9.1.2.2. Framing Meta-Data 9.1.2.2. Framing Metadata
When sending Messages, applications can add Framer-specific When sending Messages, applications can add Framer-specific
properties to a MessageContext (Section 9.1.1) with the add action. properties to a MessageContext (Section 9.1.1) with the add action.
To avoid naming conflicts, the property names SHOULD be prefixed with To avoid naming conflicts, the property names SHOULD be prefixed with
a namespace referencing the framer implementation or the protocol it a namespace referencing the framer implementation or the protocol it
implements as described in Section 4.1. implements as described in Section 4.1.
This mechanism can be used, for example, to set the type of a Message This mechanism can be used, for example, to set the type of a Message
for a TLV format. The namespace of values is custom for each unique for a TLV format. The namespace of values is custom for each unique
Message Framer. Message Framer.
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messageContext.add(httpFramer, "accept", "text/html") messageContext.add(httpFramer, "accept", "text/html")
9.1.3. Message Properties 9.1.3. Message Properties
Applications needing to annotate the Messages they send with extra Applications needing to annotate the Messages they send with extra
information (for example, to control how data is scheduled and information (for example, to control how data is scheduled and
processed by the transport protocols supporting the Connection) can processed by the transport protocols supporting the Connection) can
include this information in the Message Context passed to the Send include this information in the Message Context passed to the Send
action. For other uses of the Message Context, see Section 9.1.1. action. For other uses of the Message Context, see Section 9.1.1.
Message Properties are per-Message, not per-Send if partial Messages Message Properties are per-Message, not per-Send, if partial Messages
are sent (Section 9.2.3). All data blocks associated with a single are sent (Section 9.2.3). All data blocks associated with a single
Message share properties specified in the Message Contexts. For Message share properties specified in the Message Contexts. For
example, it would not make sense to have the beginning of a Message example, it would not make sense to have the beginning of a Message
expire, but allow the end of a Message to still be sent. expire but allow the end of the Message to still be sent.
A MessageContext object contains metadata for the Messages to be sent A MessageContext object contains metadata for the Messages to be sent
or received. or received.
messageData := "hello" messageData := "hello"
messageContext := NewMessageContext() messageContext := NewMessageContext()
messageContext.add(parameter, value) messageContext.add(parameter, value)
Connection.Send(messageData, messageContext) Connection.Send(messageData, messageContext)
The simpler form of Send, which does not take any MessageContext, is The simpler form of Send, which does not take any MessageContext, is
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set to Require and a protocol with configurable per-Message set to Require and a protocol with configurable per-Message
reliability is used, setting msgReliable to false for a particular reliability is used, setting msgReliable to false for a particular
Message will allow this Message to be sent without any reliability Message will allow this Message to be sent without any reliability
guarantees. Changing the msgReliable Message Property is only guarantees. Changing the msgReliable Message Property is only
possible for Connections that were established enabling the Selection possible for Connections that were established enabling the Selection
Property perMsgReliability. If the contradicting Message Property Property perMsgReliability. If the contradicting Message Property
cannot be supported by the Connection (such as requiring reliability cannot be supported by the Connection (such as requiring reliability
on a Connection that uses an unreliable protocol), the Send action on a Connection that uses an unreliable protocol), the Send action
will result in a SendError event. will result in a SendError event.
The following Message Properties are supported: The Message Properties in the following subsections are supported.
9.1.3.1. Lifetime 9.1.3.1. Lifetime
Name: msgLifetime Name: msgLifetime
Type: Numeric (positive) Type: Numeric (positive)
Default: infinite Default: infinite
The Lifetime specifies how long a particular Message can wait in the The Lifetime specifies how long a particular Message can wait in the
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After this time, it is irrelevant and no longer needs to be After this time, it is irrelevant and no longer needs to be
(re-)transmitted. This is a hint to the Transport Services system -- (re-)transmitted. This is a hint to the Transport Services system --
it is not guaranteed that a Message will not be sent when its it is not guaranteed that a Message will not be sent when its
Lifetime has expired. Lifetime has expired.
Setting a Message's Lifetime to infinite indicates that the Setting a Message's Lifetime to infinite indicates that the
application does not wish to apply a time constraint on the application does not wish to apply a time constraint on the
transmission of the Message, but it does not express a need for transmission of the Message, but it does not express a need for
reliable delivery; reliability is adjustable per Message via the reliable delivery; reliability is adjustable per Message via the
perMsgReliability property (see Section 9.1.3.7). The type and units perMsgReliability property (see Section 9.1.3.7). The type and units
of Lifetime are implementation-specific. of Lifetime are implementation specific.
9.1.3.2. Priority 9.1.3.2. Priority
Name: msgPriority Name: msgPriority
Type: Integer (non-negative) Type: Integer (non-negative)
Default: 100 Default: 100
This property specifies the priority of a Message, relative to other This property specifies the priority of a Message, relative to other
Messages sent over the same Connection. A numerically lower value Messages sent over the same Connection. A numerically lower value
represents a higher priority. represents a higher priority.
A Message with Priority 2 will yield to a Message with Priority 1, A Message with Priority 2 will yield to a Message with Priority 1,
which will yield to a Message with Priority 0, and so on. Priorities which will yield to a Message with Priority 0, and so on. Priorities
can be used as a sender-side scheduling construct only, or be used to can be used as a sender-side scheduling construct only or be used to
specify priorities on the wire for Protocol Stacks supporting specify priorities on the wire for Protocol Stacks supporting
prioritization. prioritization.
Note that this property is not a per-Message override of connPriority Note that this property is not a per-Message override of
- see Section 8.1.2. The priority properties might interact, but can connPriority; see Section 8.1.2. The priority properties might
be used independently and be realized by different mechanisms; see interact, but they can be used independently and be realized by
Section 9.2.6. different mechanisms; see Section 9.2.6.
9.1.3.3. Ordered 9.1.3.3. Ordered
Name: msgOrdered Name: msgOrdered
Type: Boolean Type: Boolean
Default: the queried Boolean value of the Selection Property Default: the queried Boolean value of the Selection Property
preserveOrder (Section 6.2.4) preserveOrder (Section 6.2.4)
The order in which Messages were submitted for transmission via the The order in which Messages were submitted for transmission via the
Send action will be preserved on delivery via Receive events for all Send action will be preserved on delivery via Receive events for all
Messages on a Connection that have this Message Property set to true. Messages on a Connection that have this Message Property set to true.
If false, the Message is delivered to the receiving application If false, the Message is delivered to the receiving application
without preserving the ordering. This property is used for protocols without preserving the ordering. This property is used for protocols
that support preservation of data ordering, see Section 6.2.4, but that support preservation of data ordering (see Section 6.2.4) but
allow out-of-order delivery for certain Messages, e.g., by allow out-of-order delivery for certain Messages, e.g., by
multiplexing independent Messages onto different streams. multiplexing independent Messages onto different streams.
If it is not configured by the application before sending, this If it is not configured by the application before sending, this
property's default value will be based on the Selection Property property's default value will be based on the Selection Property
preserveOrder of the Connection associated with the Send action. preserveOrder of the Connection associated with the Send action.
9.1.3.4. Safely Replayable 9.1.3.4. Safely Replayable
Name: safelyReplayable Name: safelyReplayable
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Type: Boolean Type: Boolean
Default: false Default: false
If true, this indicates a Message is the last that the application If true, this indicates a Message is the last that the application
will send on a Connection. This allows underlying protocols to will send on a Connection. This allows underlying protocols to
indicate to the Remote Endpoint that the Connection has been indicate to the Remote Endpoint that the Connection has been
effectively closed in the sending direction. For example, TCP-based effectively closed in the sending direction. For example, TCP-based
Connections can send a FIN once a Message marked as Final has been Connections can send a FIN once a Message marked as Final has been
completely sent, indicated by marking endOfMessage. Protocols that completely sent, indicated by marking endOfMessage. Protocols that
do not support signalling the end of a Connection in a given do not support signaling the end of a Connection in a given direction
direction will ignore this property. will ignore this property.
A Final Message must always be sorted to the end of a list of A Final Message must always be sorted to the end of a list of
Messages. The Final property overrides Priority and any other Messages. The Final property overrides Priority and any other
property that would re-order Messages. If another Message is sent property that would reorder Messages. If another Message is sent
after a Message marked as Final has already been sent on a after a Message marked as Final has already been sent on a
Connection, the Send action for the new Message will cause a Connection, the Send action for the new Message will cause a
SendError event. SendError event.
9.1.3.6. Sending Corruption Protection Length 9.1.3.6. Sending Corruption Protection Length
Name: msgChecksumLen Name: msgChecksumLen
Type: Integer (non-negative) or Full Coverage Type: Integer (non-negative) or Full Coverage
Default: Full Coverage Default: Full Coverage
If this property is an Integer, it specifies the minimum length of If this property is an Integer, it specifies the minimum length of
the section of a sent Message, starting from byte 0, that the the section of a sent Message, starting from byte 0, that the
application requires to be delivered without corruption due to lower application requires to be delivered without corruption due to lower-
layer errors. It is used to specify options for simple integrity layer errors. It is used to specify options for simple integrity
protection via checksums. A value of 0 means that no checksum needs protection via checksums. A value of 0 means that no checksum needs
to be calculated, and the enumerated value Full Coverage means that to be calculated, and the enumerated value Full Coverage means that
the entire Message needs to be protected by a checksum. Only Full the entire Message needs to be protected by a checksum. Only Full
Coverage is guaranteed, any other requests are advisory, which may Coverage is guaranteed: any other requests are advisory, which may
result in Full Coverage being applied. result in Full Coverage being applied.
9.1.3.7. Reliable Data Transfer (Message) 9.1.3.7. Reliable Data Transfer (Message)
Name: msgReliable Name: msgReliable
Type: Boolean Type: Boolean
Default: the queried Boolean value of the Selection Property Default: the queried Boolean value of the Selection Property
reliability (Section 6.2.1) reliability (Section 6.2.1)
When true, this property specifies that a Message should be sent in When true, this property specifies that a Message should be sent in
such a way that the transport protocol ensures all data is received such a way that the transport protocol ensures that all data is
by the Remote Endpoint. Changing the msgReliable property on received by the Remote Endpoint. Changing the msgReliable property
Messages is only possible for Connections that were established on Messages is only possible for Connections that were established
enabling the Selection Property perMsgReliability. When this is not enabling the Selection Property perMsgReliability. When this is not
the case, changing msgReliable will generate an error. the case, changing msgReliable will generate an error.
Disabling this property indicates that the Transport Services system Disabling this property indicates that the Transport Services system
could disable retransmissions or other reliability mechanisms for could disable retransmissions or other reliability mechanisms for
this particular Message, but such disabling is not guaranteed. this particular Message, but such disabling is not guaranteed.
If it is not configured by the application before sending, this If it is not configured by the application before sending, this
property's default value will be based on the Selection Property property's default value will be based on the Selection Property
reliability of the Connection associated with the Send action. reliability of the Connection associated with the Send action.
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If it is not configured by the application before sending, this If it is not configured by the application before sending, this
property's default value will be based on the Selection Property property's default value will be based on the Selection Property
reliability of the Connection associated with the Send action. reliability of the Connection associated with the Send action.
9.1.3.8. Message Capacity Profile Override 9.1.3.8. Message Capacity Profile Override
Name: msgCapacityProfile Name: msgCapacityProfile
Type: Enumeration Type: Enumeration
Default: inherited from the Connection Property connCapacityProfile Default: inherited from the Connection Property connCapacityProfile
(Section 8.1.6) (Section 8.1.6)
This enumerated property specifies the application's preferred This enumerated property specifies the application's preferred trade-
tradeoffs for sending this Message; it is a per-Message override of offs for sending this Message; it is a per-Message override of the
the connCapacityProfile Connection Property (see Section 8.1.6). If connCapacityProfile Connection Property (see Section 8.1.6). If it
it is not configured by the application before sending, this is not configured by the application before sending, this property's
property's default value will be based on the Connection Property default value will be based on the Connection Property
connCapacityProfile of the Connection associated with the Send connCapacityProfile of the Connection associated with the Send
action. action.
9.1.3.9. No Network-Layer Fragmentation 9.1.3.9. No Network-Layer Fragmentation
Name: noFragmentation Name: noFragmentation
Type: Boolean Type: Boolean
Default: false Default: false
This property specifies that a Message should be sent and received This property specifies that a Message should be sent and received
without network-layer fragmentation, if possible. It can be used to without network-layer fragmentation, if possible. It can be used to
avoid network layer fragmentation when transport segmentation is avoid network-layer fragmentation when transport segmentation is
preferred. preferred.
This only takes effect when the transport uses a network layer that This only takes effect when the transport uses a network layer that
supports this functionality. When it does take effect, setting this supports this functionality. When it does take effect, setting this
property to true will cause the sender to avoid network-layer source property to true will cause the sender to avoid network-layer source
fragmentation. When using IPv4, this will result in the Don't fragmentation. When using IPv4, this will result in the Don't
Fragment bit being set in the IP header. Fragment (DF) bit being set in the IP header.
Attempts to send a Message with this property that result in a size Attempts to send a Message with this property that result in a size
greater than the transport's current estimate of its maximum packet greater than the transport's current estimate of its maximum packet
size (singularTransmissionMsgMaxLen) can result in transport size (singularTransmissionMsgMaxLen) can result in transport
segmentation when permitted, or in a SendError. segmentation when permitted or in a SendError.
Note: noSegmentation is used when it is desired to only send a Note: noSegmentation is used when it is desired to only sending a
Message within a single network packet. Message within a single network packet.
9.1.3.10. No Segmentation 9.1.3.10. No Segmentation
Name: noSegmentation Name: noSegmentation
Type: Boolean Type: Boolean
Default: false Default: false
When set to true, this property requests the transport layer to not
When set to true, this property requests that the transport layer not
provide segmentation of Messages larger than the maximum size provide segmentation of Messages larger than the maximum size
permitted by the network layer, and also to avoid network-layer permitted by the network layer and that it avoid network-layer source
source fragmentation of Messages. When running over IPv4, setting fragmentation of Messages. When running over IPv4, setting this
this property to true will result in a sending endpoint setting the property to true will result in a sending endpoint setting the Don't
Don't Fragment bit in the IPv4 header of packets generated by the Fragment bit in the IPv4 header of packets generated by the transport
transport layer. layer.
An attempt to send a Message that results in a size greater than the An attempt to send a Message that results in a size greater than the
transport's current estimate of its maximum packet size transport's current estimate of its maximum packet size
(singularTransmissionMsgMaxLen) will result in a SendError. This (singularTransmissionMsgMaxLen) will result in a SendError. This
only takes effect when the transport and network layer support this only takes effect when the transport and network layers support this
functionality. functionality.
9.2. Sending Data 9.2. Sending Data
Once a Connection has been established, it can be used for sending Once a Connection has been established, it can be used for sending
Messages. By default, Send enqueues a complete Message, and takes Messages. By default, Send enqueues a complete Message and takes
optional per-Message properties (see Section 9.2.1). All Send optional per-Message properties (see Section 9.2.1). All Send
actions are asynchronous, and deliver events (see Section 9.2.2). actions are asynchronous and deliver events (see Section 9.2.2).
Sending partial Messages for streaming large data is also supported Sending partial Messages for streaming large data is also supported
(see Section 9.2.3). (see Section 9.2.3).
Messages are sent on a Connection using the Send action: Messages are sent on a Connection using the Send action:
Connection.Send(messageData, messageContext?, endOfMessage?) Connection.Send(messageData, messageContext?, endOfMessage?)
where messageData is the data object to send, and messageContext where messageData is the data object to send and messageContext
allows adding Message Properties, identifying Send events related to allows adding Message Properties, identifying Send events related to
a specific Message or inspecting meta-data related to the Message a specific Message or inspecting metadata related to the Message sent
sent (see Section 9.1.1). (see Section 9.1.1).
The optional endOfMessage parameter supports partial sending and is The optional endOfMessage parameter supports partial sending and is
described in Section 9.2.3. described in Section 9.2.3.
9.2.1. Basic Sending 9.2.1. Basic Sending
The most basic form of sending on a Connection involves enqueuing a The most basic form of sending on a Connection involves enqueuing a
single Data block as a complete Message with default Message single Data block as a complete Message with default Message
Properties. Properties.
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described in Section 9.2.3. described in Section 9.2.3.
9.2.1. Basic Sending 9.2.1. Basic Sending
The most basic form of sending on a Connection involves enqueuing a The most basic form of sending on a Connection involves enqueuing a
single Data block as a complete Message with default Message single Data block as a complete Message with default Message
Properties. Properties.
messageData := "hello" messageData := "hello"
Connection.Send(messageData) Connection.Send(messageData)
The interpretation of a Message to be sent is dependent on the The interpretation of a Message to be sent is dependent on the
implementation, and on the constraints on the Protocol Stacks implied implementation and on the constraints on the Protocol Stacks implied
by the Connection’s transport properties. For example, a Message by the Connection's transport properties. For example, a Message
could be the payload of a single datagram for a UDP Connection; or an could be the payload of a single datagram for a UDP Connection; or an
HTTP Request for an HTTP Connection. HTTP Request for an HTTP Connection.
Some transport protocols can deliver arbitrarily sized Messages, but Some transport protocols can deliver arbitrarily sized Messages, but
other protocols constrain the maximum Message size. Applications can other protocols constrain the maximum Message size. Applications can
query the Connection Property sendMsgMaxLen (Section 8.1.11.5) to query the Connection Property sendMsgMaxLen (Section 8.1.11.5) to
determine the maximum size allowed for a single Message. If a determine the maximum size allowed for a single Message. If a
Message is too large to fit in the Maximum Message Size for the Message is too large to fit in the Maximum Message Size for the
Connection, the Send will fail with a SendError event Connection, the Send will fail with a SendError event
(Section 9.2.2.3). For example, it is invalid to send a Message over (Section 9.2.2.3). For example, it is invalid to send a Message over
a UDP connection that is larger than the available datagram sending a UDP connection that is larger than the available datagram sending
size. size.
9.2.2. Send Events 9.2.2. Send Events
Like all actions in Transport Services API, the Send action is Like all actions in the Transport Services API, the Send action is
asynchronous. There are several events that can be delivered in asynchronous. There are several events that can be delivered in
response to sending a Message. Exactly one event (Sent, Expired, or response to sending a Message. Exactly one event (Sent, Expired, or
SendError) will be delivered in response to each call to Send. SendError) will be delivered in response to each call to Send.
Note that if partial Send calls are used (Section 9.2.3), there will Note that, if partial Send calls are used (Section 9.2.3), there will
still be exactly one Send event delivered for each call to Send. For still be exactly one Send event delivered for each call to Send. For
example, if a Message expired while two requests to Send data for example, if a Message expired while two requests to Send data for
that Message are outstanding, there will be two Expired events that Message are outstanding, there will be two Expired events
delivered. delivered.
The Transport Services API should allow the application to correlate The Transport Services API should allow the application to correlate
which Send action resulted in a particular Send event. The manner in which Send action resulted in a particular Send event. The manner in
which this correlation is indicated is implementation-specific. which this correlation is indicated is implementation specific.
9.2.2.1. Sent 9.2.2.1. Sent
Connection -> Sent<messageContext> Connection -> Sent<messageContext>
The Sent event occurs when a previous Send call has completed, i.e., The Sent event occurs when a previous Send call has completed, i.e.,
when the data derived from the Message has been passed down or when the data derived from the Message has been passed down or
through the underlying Protocol Stack and is no longer the through the underlying Protocol Stack and is no longer the
responsibility of the Transport Services API. The exact disposition responsibility of the Transport Services API. The exact disposition
of the Message (i.e., whether it has actually been transmitted, moved of the Message (i.e., whether it has actually been transmitted, moved
into a buffer on the network interface, moved into a kernel buffer, into a buffer on the network interface, moved into a kernel buffer,
and so on) when the Sent event occurs is implementation-specific. and so on) when the Sent event occurs is implementation specific.
The Sent event contains a reference to the Message Context of the The Sent event contains a reference to the Message Context of the
Message to which it applies. Message to which it applies.
Sent events allow an application to obtain an understanding of the Sent events allow an application to obtain an understanding of the
amount of buffering it creates. That is, if an application calls the amount of buffering it creates. That is, if an application calls the
Send action multiple times without waiting for a Sent event, it has Send action multiple times without waiting for a Sent event, it has
created more buffer inside the Transport Services system than an created more buffer inside the Transport Services system than an
application that always waits for the Sent event before calling the application that always waits for the Sent event before calling the
next Send action. next Send action.
9.2.2.2. Expired 9.2.2.2. Expired
Connection -> Expired<messageContext> Connection -> Expired<messageContext>
The Expired event occurs when a previous Send action expired before The Expired event occurs when a previous Send action expired before
completion; i.e. when the Message was not sent before its Lifetime completion, i.e., when the Message was not sent before its Lifetime
(see Section 9.1.3.1) expired. This is separate from SendError, as (see Section 9.1.3.1) expired. This is separate from SendError, as
it is an expected behavior for partially reliable transports. The it is an expected behavior for partially reliable transports. The
Expired event contains a reference to the Message Context of the Expired event contains a reference to the Message Context of the
Message to which it applies. Message to which it applies.
9.2.2.3. SendError 9.2.2.3. SendError
Connection -> SendError<messageContext, reason?> Connection -> SendError<messageContext, reason?>
A SendError occurs when a Message was not sent due to an error A SendError occurs when a Message was not sent due to an error
condition: an attempt to send a Message that is too large for the condition: an attempt to send a Message that is too large for the
system and Protocol Stack to handle, some failure of the underlying system and Protocol Stack to handle, some failure of the underlying
Protocol Stack, or a set of Message Properties not consistent with Protocol Stack, or a set of Message Properties not consistent with
the Connection's transport properties. The SendError contains a the Connection's transport properties. The SendError contains a
reference to the Message Context of the Message to which it applies. reference to the Message Context of the Message to which it applies.
9.2.3. Partial Sends 9.2.3. Partial Sends
It is not always possible for an application to send all data It is not always possible for an application to send all data
associated with a Message in a single Send action. The Message data associated with a Message in a single Send action. The Message data
might be too large for the application to hold in memory at one time, might be too large for the application to hold in memory at one time
or the length of the Message might be unknown or unbounded. or the length of the Message might be unknown or unbounded.
Partial Message sending is supported by passing an endOfMessage Partial Message sending is supported by passing an endOfMessage
Boolean parameter to the Send action. This value is always true by Boolean parameter to the Send action. This value is always true by
default, and the simpler forms of Send are equivalent to passing true default, and the simpler forms of Send are equivalent to passing true
for endOfMessage. for endOfMessage.
The following example sends a Message in two separate calls to Send. The following example sends a Message in two separate calls to Send:
messageContext := NewMessageContext() messageContext := NewMessageContext()
messageContext.add(parameter, value) messageContext.add(parameter, value)
messageData := "hel" messageData := "hel"
endOfMessage := false endOfMessage := false
Connection.Send(messageData, messageContext, endOfMessage) Connection.Send(messageData, messageContext, endOfMessage)
messageData := "lo" messageData := "lo"
endOfMessage := true endOfMessage := true
Connection.Send(messageData, messageContext, endOfMessage) Connection.Send(messageData, messageContext, endOfMessage)
All data sent with the same MessageContext object will be treated as All data sent with the same MessageContext object will be treated as
belonging to the same Message, and will constitute an in-order series belonging to the same Message and will constitute an in-order series
until the endOfMessage is marked. until the endOfMessage is marked.
9.2.4. Batching Sends 9.2.4. Batching Sends
To reduce the overhead of sending multiple small Messages on a To reduce the overhead of sending multiple small Messages on a
Connection, the application could batch several Send actions Connection, the application could batch several Send actions
together. This provides a hint to the system that the sending of together. This provides a hint to the system that the sending of
these Messages ought to be coalesced when possible, and that sending these Messages ought to be coalesced when possible and that sending
any of the batched Messages can be delayed until the last Message in any of the batched Messages can be delayed until the last Message in
the batch is enqueued. the batch is enqueued.
The semantics for starting and ending a batch can be implementation- The semantics for starting and ending a batch can be implementation
specific, but need to allow multiple Send actions to be enqueued. specific but need to allow multiple Send actions to be enqueued.
Connection.StartBatch() Connection.StartBatch()
Connection.Send(messageData) Connection.Send(messageData)
Connection.Send(messageData) Connection.Send(messageData)
Connection.EndBatch() Connection.EndBatch()
9.2.5. Send on Active Open: InitiateWithSend 9.2.5. Send on Active Open: InitiateWithSend
For application-layer protocols where the Connection initiator also For application-layer protocols where the Connection initiator also
sends the first Message, the InitiateWithSend action combines sends the first Message, the InitiateWithSend action combines
Connection initiation with a first Message sent: Connection initiation with a first Message sent:
Connection := Preconnection.InitiateWithSend(messageData, Connection := Preconnection.InitiateWithSend(messageData,
messageContext?, messageContext?,
timeout?) timeout?)
Whenever possible, a MessageContext should be provided to declare the Whenever possible, a MessageContext should be provided to declare the
Message passed to InitiateWithSend as "safely replayable" using the Message passed to InitiateWithSend as "safely replayable" using the
safelyReplayable property. This allows the Transport Services system safelyReplayable property. This allows the Transport Services system
to make use of 0-RTT establishment in case this is supported by the to make use of 0-RTT establishment in case this is supported by the
available Protocol Stacks. When the selected stack(s) do not support available Protocol Stacks. When the selected stack or stacks do not
transmitting data upon connection establishment, InitiateWithSend is support transmitting data upon connection establishment,
identical to Initiate followed by Send. InitiateWithSend is identical to Initiate followed by Send.
Neither partial sends nor send batching are supported by Neither partial sends nor send batching are supported by
InitiateWithSend. InitiateWithSend.
The events that are sent after InitiateWithSend are equivalent to The events that are sent after InitiateWithSend are equivalent to
those that would be sent by an invocation of Initiate followed those that would be sent by an invocation of Initiate followed
immediately by an invocation of Send, with the caveat that a send immediately by an invocation of Send, with the caveat that a send
failure that occurs because the Connection could not be established failure that occurs because the Connection could not be established
will not result in a SendError separate from the EstablishmentError will not result in a SendError separate from the EstablishmentError
signaling the failure of Connection establishment. signaling the failure of Connection establishment.
9.2.6. Priority and the Transport Services API 9.2.6. Priority and the Transport Services API
The Transport Services API provides two properties to allow a sender The Transport Services API provides two properties to allow a sender
to signal the relative priority of data transmission: msgPriority to signal the relative priority of data transmission: msgPriority
Section 9.1.3.2 and connPriority Section 8.1.2. These properties are (see Section 9.1.3.2) and connPriority (see Section 8.1.2). These
designed to allow the expression and implementation of a wide variety properties are designed to allow the expression and implementation of
of approaches to transmission priority in the transport and a wide variety of approaches to transmission priority in the
application layer, including those which do not appear on the wire transport and application layers, including those that do not appear
(affecting only sender-side transmission scheduling) as well as those on the wire (affecting only sender-side transmission scheduling) as
that do (e.g. [RFC9218]. A Transport Services system gives no well as those that do (e.g., [RFC9218]). A Transport Services system
guarantees about how its expression of relative priorities will be gives no guarantees about how its expression of relative priorities
realized. will be realized.
The Transport Services API does order connPriority over msgPriority. The Transport Services API does order connPriority over msgPriority.
In the absence of other externalities (e.g., transport-layer flow In the absence of other externalities (e.g., transport-layer flow
control), a priority 1 Message on a priority 0 Connection will be control), a priority 1 Message on a priority 0 Connection will be
sent before a priority 0 Message on a priority 1 Connection in the sent before a priority 0 Message on a priority 1 Connection in the
same group. same group.
9.3. Receiving Data 9.3. Receiving Data
Once a Connection is established, it can be used for receiving data Once a Connection is established, it can be used for receiving data
(unless the direction property is set to unidirectional send). As (unless the direction property is set to unidirectional send). As
with sending, the data is received in Messages. Receiving is an with sending, the data is received in Messages. Receiving is an
asynchronous operation, in which each call to Receive enqueues a asynchronous operation in which each call to Receive enqueues a
request to receive new data from the Connection. Once data has been request to receive new data from the Connection. Once data has been
received, or an error is encountered, an event will be delivered to received, or an error is encountered, an event will be delivered to
complete any pending Receive requests (see Section 9.3.2). If complete any pending Receive requests (see Section 9.3.2). If
Messages arrive at the Transport Services system before Receive Messages arrive at the Transport Services system before Receive
requests are issued, ensuing Receive requests will first operate on requests are issued, ensuing Receive requests will first operate on
these Messages before awaiting any further Messages. these Messages before awaiting any further Messages.
9.3.1. Enqueuing Receives 9.3.1. Enqueuing Receives
Receive takes two parameters to specify the length of data that an Receive takes two parameters to specify the length of data that an
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have default values if not specified. have default values if not specified.
Connection.Receive(minIncompleteLength?, maxLength?) Connection.Receive(minIncompleteLength?, maxLength?)
By default, Receive will try to deliver complete Messages in a single By default, Receive will try to deliver complete Messages in a single
event (Section 9.3.2.1). event (Section 9.3.2.1).
The application can set a minIncompleteLength value to indicate the The application can set a minIncompleteLength value to indicate the
smallest partial Message data size in bytes to be delivered in smallest partial Message data size in bytes to be delivered in
response to this Receive. By default, this value is infinite, which response to this Receive. By default, this value is infinite, which
means that only complete Messages should be delivered (see means that only complete Messages should be delivered. See
Section 9.3.2.2 and Section 9.1.2 for more information on how this is Sections 9.3.2.2 and 9.1.2 for more information on how this is
accomplished). If this value is set to some smaller value, the accomplished. If this value is set to some smaller value, the
associated receive event will be triggered only when at least that associated receive event will be triggered only:
many bytes are available, or the Message is complete with fewer
bytes, or the system needs to free up memory. Applications SHOULD 1. when at least that many bytes are available,
always check the length of the data delivered to the receive event
and not assume it will be as long as minIncompleteLength in the case 2. the Message is complete with fewer bytes, or
of shorter complete Messages or memory issues.
3. the system needs to free up memory.
Applications SHOULD always check the length of the data delivered to
the receive event and not assume it will be as long as
minIncompleteLength in the case of shorter complete Messages or
memory issues.
The maxLength argument indicates the maximum size of a Message in The maxLength argument indicates the maximum size of a Message in
bytes that the application is currently prepared to receive. The bytes that the application is currently prepared to receive. The
default value for maxLength is infinite. If an incoming Message is default value for maxLength is infinite. If an incoming Message is
larger than the minimum of this size and the maximum Message size on larger than the minimum of this size and the maximum Message size on
receive for the Connection's Protocol Stack, it will be delivered via receive for the Connection's Protocol Stack, it will be delivered via
ReceivedPartial events (Section 9.3.2.2). ReceivedPartial events (Section 9.3.2.2).
Note that maxLength does not guarantee that the application will Note that maxLength does not guarantee that the application will
receive that many bytes if they are available; the Transport Services receive that many bytes if they are available; the Transport Services
API could return ReceivedPartial events with less data than maxLength API could return ReceivedPartial events with less data than maxLength
according to implementation constraints. Note also that maxLength according to implementation constraints. Note also that maxLength
and minIncompleteLength are intended only to manage buffering, and and minIncompleteLength are intended only to manage buffering and are
are not interpreted as a receiver preference for Message reordering. not interpreted as a receiver preference for Message reordering.
9.3.2. Receive Events 9.3.2. Receive Events
Each call to Receive will be paired with a single Receive event. Each call to Receive will be paired with a single Receive event.
This allows an application to provide backpressure to the transport This allows an application to provide backpressure to the transport
stack when it is temporarily not ready to receive Messages. For stack when it is temporarily not ready to receive Messages. For
example, an application that will later be able to handle multiple example, an application that will later be able to handle multiple
receive events at the same time can make multiple calls to Receive receive events at the same time can make multiple calls to Receive
without waiting for, or processing, any receive events. An without waiting for, or processing, any receive events. An
application that is temporarily unable to process received events for application that is temporarily unable to process received events for
a connection could refrain from calling Receive or delay calling it. a connection could refrain from calling Receive or could delay
This would lead to a build-up of unread data, which, in turn, could calling it. This would lead to a buildup of unread data, which, in
result in backpressure to the sender via a transport protocol's flow turn, could result in backpressure to the sender via a transport
control. protocol's flow control.
The Transport Services API should allow the application to correlate The Transport Services API should allow the application to correlate
which call to Receive resulted in a particular Receive event. The which call to Receive resulted in a particular Receive event. The
manner in which this correlation is indicated is implementation- manner in which this correlation is indicated is implementation
specific. specific.
9.3.2.1. Received 9.3.2.1. Received
Connection -> Received<messageData, messageContext> Connection -> Received<messageData, messageContext>
A Received event indicates the delivery of a complete Message. It A Received event indicates the delivery of a complete Message. It
contains two objects, the received bytes as messageData, and the contains two objects: the received bytes as messageData and the
metadata and properties of the received Message as messageContext. metadata and properties of the received Message as messageContext.
The messageData value provides access to the bytes that were received The messageData value provides access to the bytes that were received
for this Message, along with the length of the byte array. The for this Message, along with the length of the byte array. The
messageContext value is provided to enable retrieving metadata about messageContext value is provided to enable retrieving metadata about
the Message and referring to the Message. The MessageContext object the Message and referring to the Message. The MessageContext object
is described in Section 9.1.1. is described in Section 9.1.1.
See Section 9.1.2 for handling Message framing in situations where See Section 9.1.2 regarding how to handle Message framing in
the Protocol Stack only provides a byte-stream transport. situations where the Protocol Stack only provides a byte-stream
transport.
9.3.2.2. ReceivedPartial 9.3.2.2. ReceivedPartial
Connection -> ReceivedPartial<messageData, messageContext, Connection -> ReceivedPartial<messageData, messageContext,
endOfMessage> endOfMessage>
If a complete Message cannot be delivered in one event, one part of If a complete Message cannot be delivered in one event, one part of
the Message can be delivered with a ReceivedPartial event. To the Message can be delivered with a ReceivedPartial event. To
continue to receive more of the same Message, the application must continue to receive more of the same Message, the application must
invoke Receive again. invoke Receive again.
Multiple invocations of ReceivedPartial deliver data for the same Multiple invocations of ReceivedPartial deliver data for the same
Message by passing the same MessageContext, until the endOfMessage Message by passing the same MessageContext until the endOfMessage
flag is delivered or a ReceiveError occurs. All partial blocks of a flag is delivered or a ReceiveError occurs. All partial blocks of a
single Message are delivered in order without gaps. This event does single Message are delivered in order without gaps. This event does
not support delivering non-contiguous partial Messages. If, for not support delivering non-contiguous partial Messages. For example,
example, Message A is divided into three pieces (A1, A2, A3) and if Message A is divided into three pieces (A1, A2, A3), Message B is
Message B is divided into three pieces (B1, B2, B3), and divided into three pieces (B1, B2, B3), and preserveOrder is not
preserveOrder is not Required, the ReceivedPartial could deliver them Required, the ReceivedPartial could deliver them in a sequence like
in a sequence like this: A1, B1, B2, A2, A3, B3, because the this: A1, B1, B2, A2, A3, B3. This is because the MessageContext
MessageContext allows the application to identify the pieces as allows the application to identify the pieces as belonging to Message
belonging to Message A and B, respectively. However, a sequence A and B, respectively. However, a sequence like A1, A3 will never
like: A1, A3 will never occur. occur.
If the minIncompleteLength in the Receive request was set to be If the minIncompleteLength in the Receive request was set to be
infinite (indicating a request to receive only complete Messages), infinite (indicating a request to receive only complete Messages),
the ReceivedPartial event could still be delivered if one of the the ReceivedPartial event could still be delivered if one of the
following conditions is true: following conditions is true:
* the underlying Protocol Stack supports message boundary * the underlying Protocol Stack supports message boundary
preservation, and the size of the Message is larger than the preservation and the size of the Message is larger than the
buffers available for a single Message; buffers available for a single Message;
* the underlying Protocol Stack does not support message boundary * the underlying Protocol Stack does not support message boundary
preservation, and the Message Framer (see Section 9.1.2) cannot preservation and the Message Framer (see Section 9.1.2) cannot
determine the end of the Message using the buffer space it has determine the end of the Message using the buffer space it has
available; or available; or
* the underlying Protocol Stack does not support message boundary * the underlying Protocol Stack does not support message boundary
preservation, and no Message Framer was supplied by the preservation and no Message Framer was supplied by the
application application.
Note that in the absence of message boundary preservation or a Note that, in the absence of message boundary preservation or a
Message Framer, all bytes received on the Connection will be Message Framer, all bytes received on the Connection will be
represented as one large Message of indeterminate length. represented as one large Message of indeterminate length.
In the following example, an application only wants to receive up to In the following example, an application only wants to receive up to
1000 bytes at a time from a Connection. If a 1500-byte Message 1000 bytes at a time from a Connection. If a 1500-byte Message
arrives, it would receive the Message in two separate ReceivedPartial arrives, it would receive the Message in two separate ReceivedPartial
events. events.
Connection.Receive(1, 1000) Connection.Receive(1, 1000)
// Receive first 1000 bytes, message is incomplete // Receive the first 1000 bytes; message is incomplete
Connection -> ReceivedPartial<messageData(1000 bytes), Connection -> ReceivedPartial<messageData(1000 bytes),
messageContext, false> messageContext, false>
Connection.Receive(1, 1000) Connection.Receive(1, 1000)
// Receive last 500 bytes, message is now complete // Receive the last 500 bytes; message is now complete
Connection -> ReceivedPartial<messageData(500 bytes), Connection -> ReceivedPartial<messageData(500 bytes),
messageContext, true> messageContext, true>
9.3.2.3. ReceiveError 9.3.2.3. ReceiveError
Connection -> ReceiveError<messageContext, reason?> Connection -> ReceiveError<messageContext, reason?>
A ReceiveError occurs when data is received by the underlying A ReceiveError occurs when:
Protocol Stack that cannot be fully retrieved or parsed, and when it
is useful for the application to be notified of such errors. For * data is received by the underlying Protocol Stack that cannot be
example, a ReceiveError can indicate that a Message (identified via fully retrieved or parsed, and
the messageContext value) that was being partially received
* it is useful for the application to be notified of such errors.
For example, a ReceiveError can indicate that a Message (identified
via the messageContext value) that was being partially received
previously, but had not completed, encountered an error and will not previously, but had not completed, encountered an error and will not
be completed. This can be useful for an application, which might be completed. This can be useful for an application, which might
wish to use this error as a hint to remove previously received wish to use this error as a hint to remove previously received
Message parts from memory. As another example, if an incoming Message parts from memory. As another example, if an incoming
Message does not fulfill the recvChecksumLen property (see Message does not fulfill the recvChecksumLen property (see
Section 8.1.1), an application can use this error as a hint to inform Section 8.1.1), an application can use this error as a hint to inform
the peer application to adjust the msgChecksumLen property (see the peer application to adjust the msgChecksumLen property (see
Section 9.1.3.6). Section 9.1.3.6).
In contrast, internal protocol reception errors (e.g., loss causing In contrast, internal protocol reception errors (e.g., loss causing
retransmissions in TCP) are not signalled by this event. Conditions retransmissions in TCP) are not signaled by this event. Conditions
that irrevocably lead to the termination of the Connection are that irrevocably lead to the termination of the Connection are
signaled using ConnectionError (see Section 10). signaled using ConnectionError (see Section 10).
9.3.3. Receive Message Properties 9.3.3. Receive Message Properties
Each Message Context could contain metadata from protocols in the Each Message Context could contain metadata from protocols in the
Protocol Stack; which metadata is available is Protocol Stack Protocol Stack; which metadata is available is Protocol Stack
dependent. These are exposed through additional read-only Message dependent. These are exposed through additional read-only Message
Properties that can be queried from the MessageContext object (see Properties that can be queried from the MessageContext object (see
Section 9.1.1) passed by the receive event. The following metadata Section 9.1.1) passed by the receive event. The metadata values in
values are supported: the following subsections are supported.
9.3.3.1. UDP(-Lite)-specific Property: ECN 9.3.3.1. Property Specific to UDP and UDP-Lite: ECN
When available, Message metadata carries the value of the Explicit When available, Message metadata carries the value of the Explicit
Congestion Notification (ECN) field. This information can be used Congestion Notification (ECN) field. This information can be used
for logging and debugging, and for building applications that need for logging and debugging as well as building applications that need
access to information about the transport internals for their own access to information about the transport internals for their own
operation. This property is specific to UDP and UDP-Lite because operation. This property is specific to UDP and UDP-Lite, because
these protocols do not implement congestion control, and hence expose these protocols do not implement congestion control; hence, they
this functionality to the application (see [RFC8293], following the expose this functionality to the application (see [RFC8293],
guidance in [RFC8085]) following the guidance in [RFC8085]).
9.3.3.2. Early Data 9.3.3.2. Early Data
In some cases it can be valuable to know whether data was read as In some cases, it can be valuable to know whether data was read as
part of early data transfer (before Connection establishment has part of early data transfer (before Connection establishment has
finished). This is useful if applications need to treat early data finished). This is useful if applications need to treat early data
separately, e.g., if early data has different security properties separately, e.g., if early data has different security properties
than data sent after connection establishment. In the case of TLS than data sent after connection establishment. In the case of TLS
1.3, client early data can be replayed maliciously (see [RFC8446]). 1.3, client early data can be replayed maliciously (see [RFC8446]).
Thus, receivers might wish to perform additional checks for early Thus, receivers might wish to perform additional checks for early
data to ensure it is safely replayable. If TLS 1.3 is available and data to ensure that it is safely replayable. If TLS 1.3 is available
the recipient Message was sent as part of early data, the and the recipient Message was sent as part of early data, the
corresponding metadata carries a flag indicating as such. If early corresponding metadata carries a flag indicating as such. If early
data is enabled, applications should check this metadata field for data is enabled, applications should check this metadata field for
Messages received during Connection establishment and respond Messages received during Connection establishment and respond
accordingly. accordingly.
9.3.3.3. Receiving Final Messages 9.3.3.3. Receiving Final Messages
The Message Context can indicate whether or not this Message is the The Message Context can indicate whether or not this Message is the
Final Message on a Connection. For any Message that is marked as Final Message on a Connection. For any Message that is marked as
Final, the application can assume that there will be no more Messages Final, the application can assume that there will be no more Messages
received on the Connection once the Message has been completely received on the Connection once the Message has been completely
delivered. This corresponds to the final property that can be marked delivered. This corresponds to the final property that can be marked
on a sent Message, see Section 9.1.3.5. on a sent Message; see Section 9.1.3.5.
Some transport protocols and peers do not support signaling of the Some transport protocols and peers do not support signaling of the
final property. Applications therefore SHOULD NOT rely on receiving final property. Therefore, applications SHOULD NOT rely on receiving
a Message marked Final to know that the sending endpoint is done a Message marked Final to know that the sending endpoint is done
sending on a Connection. sending on a Connection.
Any calls to Receive once the Final Message has been delivered will Any calls to Receive once the Final Message has been delivered will
result in errors. result in errors.
10. Connection Termination 10. Connection Termination
A Connection can be terminated i) by the Local Endpoint (i.e., the A Connection can be terminated:
application calls the Close, CloseGroup, Abort or AbortGroup action),
ii) by the Remote Endpoint (i.e., the remote application calls the 1. by the Local Endpoint (i.e., the application calls the Close,
Close, CloseGroup, Abort or AbortGroup action), or iii) because of an CloseGroup, Abort, or AbortGroup action),
error (e.g., a timeout). A local call of the Close action will cause
the Connection to either send a Closed event or a ConnectionError 2. by the Remote Endpoint (i.e., the remote application calls the
event, and a local call of the CloseGroup action will cause all of Close, CloseGroup, Abort, or AbortGroup action), or
the Connections in the group to either send a Closed event or a
ConnectionError event. A local call of the Abort action will cause 3. because of an error (e.g., a timeout).
the Connection to send a ConnectionError event, indicating local
Abort as a reason, and a local call of the AbortGroup action will A local call of the Close action will cause the Connection to send
cause all of the Connections in the group to send a ConnectionError either a Closed event or a ConnectionError event; a local call of the
event, indicating local Abort as a reason. CloseGroup action will cause all of the Connections in the group to
send either a Closed event or a ConnectionError event. A local call
of the Abort action will cause the Connection to send a
ConnectionError event, indicating local Abort as a reason; a local
call of the AbortGroup action will cause all of the Connections in
the group to send a ConnectionError event, indicating local Abort as
a reason.
Remote action calls map to events similar to local calls (e.g., a Remote action calls map to events similar to local calls (e.g., a
remote Close causes the Connection to either send a Closed event or a remote Close causes the Connection to send either a Closed event or a
ConnectionError event), but, different from local action calls, it is ConnectionError event), but in contrast to local action calls, it is
not guaranteed that such events will indeed be invoked. When an not guaranteed that such events will indeed be invoked. When an
application needs to free resources associated with a Connection, it application needs to free resources associated with a Connection, it
ought not to therefore rely on the invocation of such events due to ought not rely on the invocation of such events due to termination
termination calls from the Remote Endpoint, but instead use the local calls from the Remote Endpoint; instead, it should use the local
termination actions. termination actions.
Close terminates a Connection after satisfying all the requirements Close terminates a Connection after satisfying all the requirements
that were specified regarding the delivery of Messages that the that were specified regarding the delivery of Messages that the
application has already given to the Transport Services system. Upon application has already given to the Transport Services system. Upon
successfully satisfying all these requirements, the Connection will successfully satisfying all these requirements, the Connection will
send the Closed event. For example, if reliable delivery was send the Closed event. For example, if reliable delivery was
requested for a Message handed over before calling Close, the Closed requested for a Message handed over before calling Close, the Closed
event will signify that this Message has indeed been delivered. This event will signify that this Message has indeed been delivered. This
action does not affect any other Connection in the same Connection action does not affect any other Connection in the same Connection
Group. Group.
An application MUST NOT assume that it can receive any further data An application MUST NOT assume that it can receive any further data
on a Connection for which it has called Close, even if such data is on a Connection for which it has called Close, even if such data is
already in flight. already in flight.
Connection.Close() Connection.Close()
The Closed event informs the application that a Close action has The Closed event informs the application that a Close action has
successfully completed, or that the Remote Endpoint has closed the successfully completed or that the Remote Endpoint has closed the
Connection. There is no guarantee that a remote Close will be Connection. There is no guarantee that a remote Close will be
signaled. signaled.
Connection -> Closed<> Connection -> Closed<>
Abort terminates a Connection without delivering any remaining Abort terminates a Connection without delivering any remaining
Messages. This action does not affect any other Connection that is Messages. This action does not affect any other Connection that is
entangled with this one in a Connection Group. When the Abort action entangled with this one in a Connection Group. When the Abort action
has finished, the Connection will send a ConnectionError event, has finished, the Connection will send a ConnectionError event,
indicating local Abort as a reason. indicating local Abort as a reason.
Connection.Abort() Connection.Abort()
CloseGroup gracefully terminates a Connection and any other CloseGroup gracefully terminates a Connection and any other
Connections in the same Connection Group. For example, all of the Connections in the same Connection Group. For example, all of the
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Connection.CloseGroup() Connection.CloseGroup()
AbortGroup terminates a Connection and any other Connections that are AbortGroup terminates a Connection and any other Connections that are
in the same Connection Group without delivering any remaining in the same Connection Group without delivering any remaining
Messages. When the AbortGroup action has finished, all Connections Messages. When the AbortGroup action has finished, all Connections
in the group will send a ConnectionError event, indicating local in the group will send a ConnectionError event, indicating local
Abort as a reason. Abort as a reason.
Connection.AbortGroup() Connection.AbortGroup()
A ConnectionError informs the application that: 1) data could not be A ConnectionError informs the application that:
delivered to the peer after a timeout, or 2) the Connection has been
aborted (e.g., because the peer has called Abort). There is no 1. data could not be delivered to the peer after a timeout or
guarantee that an Abort from the peer will be signaled.
2. the Connection has been aborted (e.g., because the peer has
called Abort).
There is no guarantee that an Abort from the peer will be signaled.
Connection -> ConnectionError<reason?> Connection -> ConnectionError<reason?>
11. Connection State and Ordering of Operations and Events 11. Connection State and Ordering of Operations and Events
This Transport Services API is designed to be independent of an This Transport Services API is designed to be independent of an
implementation's concurrency model. The details of how exactly implementation's concurrency model. The exact details regarding how
actions are handled, and how events are dispatched, are actions are handled, and how events are dispatched, are
implementation dependent. implementation dependent.
Some transitions of Connection states are associated with events: Some transitions of Connection states are associated with events:
* Ready<> occurs when a Connection created with Initiate or * Ready<> occurs when a Connection created with Initiate or
InitiateWithSend transitions to Established state. InitiateWithSend transitions to Established state.
* ConnectionReceived<> occurs when a Connection created with Listen * ConnectionReceived<> occurs when a Connection created with Listen
transitions to Established state. transitions to Established state.
skipping to change at page 82, line 38 skipping to change at line 3799
(*) Ready<>, ConnectionReceived<>, RendezvousDone<> (*) Ready<>, ConnectionReceived<>, RendezvousDone<>
(**) Closed<>, ConnectionError<> (**) Closed<>, ConnectionError<>
Figure 2: Connection State Diagram Figure 2: Connection State Diagram
The Transport Services API provides the following guarantees about The Transport Services API provides the following guarantees about
the ordering of operations: the ordering of operations:
* Sent<> events will occur on a Connection in the order in which the * Sent<> events will occur on a Connection in the order in which the
Messages were sent (i.e., delivered to the kernel or to the Messages were sent (i.e., delivered to the kernel or to the
network interface, depending on implementation). network interface, depending on the implementation).
* Received<> will never occur on a Connection before it is * Received<> will never occur on a Connection before it is
Established; i.e. before a Ready<> event on that Connection, or a Established, i.e., before a Ready<> event on that Connection or a
ConnectionReceived<> or RendezvousDone<> containing that ConnectionReceived<> or RendezvousDone<> containing that
Connection. Connection.
* No events will occur on a Connection after it is closed; i.e., * No events will occur on a Connection after it is closed, i.e.,
after a Closed<> event, an EstablishmentError<> or after a Closed<> event, an EstablishmentError<> or
ConnectionError<> will not occur on that Connection. To ensure ConnectionError<> will not occur on that Connection. To ensure
this ordering, Closed<> will not occur on a Connection while other this ordering, Closed<> will not occur on a Connection while other
events on the Connection are still locally outstanding (i.e., events on the Connection are still locally outstanding (i.e.,
known to the Transport Services API and waiting to be dealt with known to the Transport Services API and waiting to be dealt with
by the application). by the application).
12. IANA Considerations 12. IANA Considerations
This document has no actions for IANA. Later versions of this This document has no IANA actions.
document might create IANA registries for generic transport property
names and transport property namespaces (see Section 4.1). Future works might create IANA registries for generic transport
property names and transport property namespaces (see Section 4.1).
13. Privacy and Security Considerations 13. Privacy and Security Considerations
This document describes a generic API for interacting with a This document describes a generic API for interacting with a
Transport Services system. Part of this API includes configuration Transport Services system. Part of this API includes configuration
details for transport security protocols, as discussed in details for transport security protocols, as discussed in
Section 6.3. It does not recommend use (or disuse) of specific Section 6.3. It does not recommend use (or disuse) of specific
algorithms or protocols. Any API-compatible transport security algorithms or protocols. Any API-compatible transport security
protocol ought to work in a Transport Services system. Security protocol ought to work in a Transport Services system. Security
considerations for these protocols are discussed in the respective considerations for these protocols are discussed in the respective
specifications. specifications.
[I-D.ietf-taps-arch] provides general security considerations and [RFC9621] provides general security considerations and requirements
requirements for any system that implements the Transport Services for any system that implements the Transport Services architecture.
architecture. These include recommendations of relevance to the API, These include recommendations of relevance to the API, e.g.,
e.g. regarding the use of keying material. regarding the use of keying material.
The described API is used to exchange information between an The described API is used to exchange information between an
application and the Transport Services system. While it is not application and the Transport Services system. While it is not
necessarily expected that both systems are implemented by the same necessarily expected that both systems are implemented by the same
authority, it is expected that the Transport Services Implementation authority, it is expected that the Transport Services Implementation
is either provided as a library that is selected by the application is provided as a library either that is selected by the application
from a trusted party, or that it is part of the operating system that from a trusted party or that it is part of the operating system that
the application also relies on for other tasks. the application also relies on for other tasks.
In either case, the Transport Services API is an internal interface In either case, the Transport Services API is an internal interface
that is used to exchange information locally between two systems. that is used to exchange information locally between two systems.
However, as the Transport Services system is responsible for network However, as the Transport Services system is responsible for network
communication, it is in the position to potentially share any communication, it is in the position to potentially share any
information provided by the application with the network or another information provided by the application with the network or another
communication peer. Most of the information provided over the communication peer. Most of the information provided over the
Transport Services API are useful to configure and select protocols Transport Services API is useful to configure and select protocols
and paths and are not necessarily privacy-sensitive. Still, some and paths and is not necessarily privacy sensitive. Still, some
information could be privacy sensitive because it might reveal usage information could be privacy sensitive because it might reveal usage
characteristics and habits of the user of an application. characteristics and habits of the user of an application.
Of course any communication over a network reveals usage Of course, any communication over a network reveals usage
characteristics, because all packets, as well as their timing and characteristics, because all packets, as well as their timing and
size, are part of the network-visible wire image [RFC8546]. However, size, are part of the network-visible wire image [RFC8546]. However,
the selection of a protocol and its configuration also impacts which the selection of a protocol and its configuration also impacts which
information is visible, potentially in clear text, and which other information is visible, potentially in clear text, and which other
entities can access it. How Transport Services systems ought to entities can access it. How Transport Services systems ought to
choose protocols depending on the security properties required is out choose protocols -- depending on the security properties required --
of scope of this specification, as it is limited to transport is out of scope for this specification, as it is limited to transport
protocols. The choice of a security protocol can be informed by the protocols. The choice of a security protocol can be informed by the
survey provided in [RFC8922]. survey provided in [RFC8922].
In most cases, information provided for protocol and path selection In most cases, information provided for protocol and path selection
does not directly translate to information that can be observed by does not directly translate to information that can be observed by
network devices on the path. However, there might be specific network devices on the path. However, there might be specific
configuration information that is intended for path exposure, e.g., a configuration information that is intended for path exposure, e.g., a
DiffServ codepoint setting, that is either provided directly by the Diffserv codepoint setting that is either provided directly by the
application or indirectly configured for a traffic profile. application or indirectly configured for a traffic profile.
Applications should be aware that a single communication attempt can Applications should be aware that a single communication attempt can
lead to more than one connection establishment procedure. This is lead to more than one connection establishment procedure. For
the case, for example, when the Transport Services system also example, this is the case when:
executes name resolution, when support mechanisms such as TURN or ICE
are used to establish connectivity, if protocols or paths are raced, * the Transport Services system also executes name resolution,
or if a path fails and fallback or re-establishment is supported in
the Transport Services system. Applications should take special care * support mechanisms such as TURN or ICE are used to establish
when using 0-RTT session resumption (see Section 6.2.5), as early connectivity if protocols or paths are raced or if a path fails
data sent across multiple paths during connection establishment could and fallback or re-establishment is supported in the Transport
reveal information that can be used to correlate endpoints on these Services system.
paths.
Applications should take special care when using 0-RTT session
resumption (see Section 6.2.5), as early data sent across multiple
paths during connection establishment could reveal information that
can be used to correlate endpoints on these paths.
Applications should also take care to not assume that all data Applications should also take care to not assume that all data
received using the Transport Services API is always complete or well- received using the Transport Services API is always complete or well-
formed. Specifically, Messages that are received partially formed. Specifically, Messages that are received partially (see
Section 9.3.2.2 could be a source of truncation attacks if Section 9.3.2.2 )could be a source of truncation attacks if
applications do not distinguish between partial Messages and complete applications do not distinguish between partial Messages and complete
Messages. Messages.
The Transport Services API explicitly does not require the The Transport Services API explicitly does not require the
application to resolve names, though there is a tradeoff between application to resolve names, though there is a trade-off between
early and late binding of addresses to names. Early binding allows early and late binding of addresses to names. Early binding allows
the Transport Services Implementation to reduce Connection setup the Transport Services Implementation to reduce Connection setup
latency, at the cost of potentially limited scope for alternate path latency. This is at the cost of potentially limited scope for
discovery during Connection establishment, as well as potential alternate path discovery during Connection establishment as well as
additional information leakage about application interest when used potential additional information leakage about application interest
with a resolution method (such as DNS without TLS) which does not when used with a resolution method (such as DNS without TLS) that
protect query confidentiality. Names used with the Transport does not protect query confidentiality. Names used with the
Services API SHOULD be fully-qualified domain names (FQDNs); not Transport Services API SHOULD be FQDNs; not providing an FQDN will
providing an FQDN will result in the Transport Services result in the Transport Services Implementation needing to use DNS
Implementation needing to to use DNS search domains for name search domains for name resolution, which might lead to inconsistent
resolution, which might lead to inconsistent or unpredictable or unpredictable behavior.
behavior.
These communication activities are not different from what is used
today. However, the goal of a Transport Services system is to
support such mechanisms as a generic service within the transport
layer. This enables applications to more dynamically benefit from
innovations and new protocols in the transport, although it reduces
transparency of the underlying communication actions to the
application itself. The Transport Services API is designed such that
protocol and path selection can be limited to a small and controlled
set if the application requires this or to implement a security
policy. can be limited to a small and controlled set if required by
the application to perform a function or to provide security.
Further, introspection on the properties of Connection objects allows
an application to determine which protocol(s) and path(s) are in use.
A Transport Services system SHOULD provide a facility logging the
communication events of each Connection.
14. Acknowledgments
This work has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreements No. 644334
(NEAT) and No. 688421 (MAMI).
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.
This work has been supported by the Research Council of Norway under
its "Toppforsk" programme through the "OCARINA" project.
Thanks to Stuart Cheshire, Josh Graessley, David Schinazi, and Eric These communication activities are not different from what is used at
Kinnear for their implementation and design efforts, including Happy the time of writing. However, the goal of a Transport Services
Eyeballs, that heavily influenced this work. Thanks to Laurent Chuat system is to support such mechanisms as a generic service within the
and Jason Lee for initial work on the Post Sockets interface, from transport layer. This enables applications to more dynamically
which this work has evolved. Thanks to Maximilian Franke for asking benefit from innovations and new protocols in the transport, although
good questions based on implementation experience and for it reduces transparency of the underlying communication actions to
contributing text, e.g., on multicast. the application itself. The Transport Services API is designed such
that protocol and path selection can be limited to a small and
controlled set, if the application requires this, or to implement a
security policy can be limited to a small and controlled set if
required by the application to perform a function or to provide
security. Further, introspection on the properties of Connection
objects allows an application to determine which protocol(s) and
path(s) are in use. A Transport Services system SHOULD provide a
facility logging the communication events of each Connection.
15. References 14. References
15.1. Normative References 14.1. Normative References
[ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan, [ALPN] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol "Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301, Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/rfc/rfc7301>. July 2014, <https://www.rfc-editor.org/info/rfc7301>.
[I-D.ietf-taps-arch]
Pauly, T., Trammell, B., Brunstrom, A., Fairhurst, G., and
C. Perkins, "Architecture and Requirements for Transport
Services", Work in Progress, Internet-Draft, draft-ietf-
taps-arch-19, 9 November 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-taps-
arch-19>.
[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>.
15.2. Informative References [RFC9621] Pauly, T., Ed., Trammell, B., Ed., Brunstrom, A.,
Fairhurst, G., and C. S. Perkins, "Architecture and
Requirements for Transport Services", RFC 9621,
DOI 10.17487/RFC9621, November 2024,
<https://www.rfc-editor.org/info/RFC9621>.
[I-D.ietf-taps-impl] 14.2. Informative References
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-18,
14 December 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-taps-impl-18>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS "Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998, DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/rfc/rfc2474>. <https://www.rfc-editor.org/info/rfc2474>.
[RFC2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski, [RFC2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
"Assured Forwarding PHB Group", RFC 2597, "Assured Forwarding PHB Group", RFC 2597,
DOI 10.17487/RFC2597, June 1999, DOI 10.17487/RFC2597, June 1999,
<https://www.rfc-editor.org/rfc/rfc2597>. <https://www.rfc-editor.org/info/rfc2597>.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, [RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, DOI 10.17487/RFC2914, September 2000, RFC 2914, DOI 10.17487/RFC2914, September 2000,
<https://www.rfc-editor.org/rfc/rfc2914>. <https://www.rfc-editor.org/info/rfc2914>.
[RFC3246] Davie, B., Charny, A., Bennet, J.C.R., Benson, K., Le [RFC3246] Davie, B., Charny, A., Bennet, J.C.R., Benson, K., Le
Boudec, J.Y., Courtney, W., Davari, S., Firoiu, V., and D. Boudec, J.Y., Courtney, W., Davari, S., Firoiu, V., and D.
Stiliadis, "An Expedited Forwarding PHB (Per-Hop Stiliadis, "An Expedited Forwarding PHB (Per-Hop
Behavior)", RFC 3246, DOI 10.17487/RFC3246, March 2002, Behavior)", RFC 3246, DOI 10.17487/RFC3246, March 2002,
<https://www.rfc-editor.org/rfc/rfc3246>. <https://www.rfc-editor.org/info/rfc3246>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E. A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261, Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002, DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/rfc/rfc3261>. <https://www.rfc-editor.org/info/rfc3261>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/rfc/rfc4291>. 2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration [RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594, Guidelines for DiffServ Service Classes", RFC 4594,
DOI 10.17487/RFC4594, August 2006, DOI 10.17487/RFC4594, August 2006,
<https://www.rfc-editor.org/rfc/rfc4594>. <https://www.rfc-editor.org/info/rfc4594>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/rfc/rfc5280>. <https://www.rfc-editor.org/info/rfc5280>.
[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>.
[RFC5865] Baker, F., Polk, J., and M. Dolly, "A Differentiated [RFC5865] Baker, F., Polk, J., and M. Dolly, "A Differentiated
Services Code Point (DSCP) for Capacity-Admitted Traffic", Services Code Point (DSCP) for Capacity-Admitted Traffic",
RFC 5865, DOI 10.17487/RFC5865, May 2010, RFC 5865, DOI 10.17487/RFC5865, May 2010,
<https://www.rfc-editor.org/rfc/rfc5865>. <https://www.rfc-editor.org/info/rfc5865>.
[RFC7478] Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real- [RFC7478] Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real-
Time Communication Use Cases and Requirements", RFC 7478, Time Communication Use Cases and Requirements", RFC 7478,
DOI 10.17487/RFC7478, March 2015, DOI 10.17487/RFC7478, March 2015,
<https://www.rfc-editor.org/rfc/rfc7478>. <https://www.rfc-editor.org/info/rfc7478>.
[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>.
[RFC7657] Black, D., Ed. and P. Jones, "Differentiated Services [RFC7657] Black, D., Ed. and P. Jones, "Differentiated Services
(Diffserv) and Real-Time Communication", RFC 7657, (Diffserv) and Real-Time Communication", RFC 7657,
DOI 10.17487/RFC7657, November 2015, DOI 10.17487/RFC7657, November 2015,
<https://www.rfc-editor.org/rfc/rfc7657>. <https://www.rfc-editor.org/info/rfc7657>.
[RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791, [RFC791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981, DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/rfc/rfc791>. <https://www.rfc-editor.org/info/rfc791>.
[RFC8084] Fairhurst, G., "Network Transport Circuit Breakers", [RFC8084] Fairhurst, G., "Network Transport Circuit Breakers",
BCP 208, RFC 8084, DOI 10.17487/RFC8084, March 2017, BCP 208, RFC 8084, DOI 10.17487/RFC8084, March 2017,
<https://www.rfc-editor.org/rfc/rfc8084>. <https://www.rfc-editor.org/info/rfc8084>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage [RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085, Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/rfc/rfc8085>. March 2017, <https://www.rfc-editor.org/info/rfc8085>.
[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>.
[RFC8260] Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann, [RFC8260] Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann,
"Stream Schedulers and User Message Interleaving for the "Stream Schedulers and User Message Interleaving for the
Stream Control Transmission Protocol", RFC 8260, Stream Control Transmission Protocol", RFC 8260,
DOI 10.17487/RFC8260, November 2017, DOI 10.17487/RFC8260, November 2017,
<https://www.rfc-editor.org/rfc/rfc8260>. <https://www.rfc-editor.org/info/rfc8260>.
[RFC8293] Ghanwani, A., Dunbar, L., McBride, M., Bannai, V., and R. [RFC8293] Ghanwani, A., Dunbar, L., McBride, M., Bannai, V., and R.
Krishnan, "A Framework for Multicast in Network Krishnan, "A Framework for Multicast in Network
Virtualization over Layer 3", RFC 8293, Virtualization over Layer 3", RFC 8293,
DOI 10.17487/RFC8293, January 2018, DOI 10.17487/RFC8293, January 2018,
<https://www.rfc-editor.org/rfc/rfc8293>. <https://www.rfc-editor.org/info/rfc8293>.
[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>.
[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, [RFC8489] Petit-Huguenin, M., Salgueiro, G., Rosenberg, J., Wing,
D., Mahy, R., and P. Matthews, "Session Traversal D., Mahy, R., and P. Matthews, "Session Traversal
Utilities for NAT (STUN)", RFC 8489, DOI 10.17487/RFC8489, Utilities for NAT (STUN)", RFC 8489, DOI 10.17487/RFC8489,
February 2020, <https://www.rfc-editor.org/rfc/rfc8489>. February 2020, <https://www.rfc-editor.org/info/rfc8489>.
[RFC8546] Trammell, B. and M. Kuehlewind, "The Wire Image of a [RFC8546] Trammell, B. and M. Kuehlewind, "The Wire Image of a
Network Protocol", RFC 8546, DOI 10.17487/RFC8546, April Network Protocol", RFC 8546, DOI 10.17487/RFC8546, April
2019, <https://www.rfc-editor.org/rfc/rfc8546>. 2019, <https://www.rfc-editor.org/info/rfc8546>.
[RFC8622] Bless, R., "A Lower-Effort Per-Hop Behavior (LE PHB) for [RFC8622] Bless, R., "A Lower-Effort Per-Hop Behavior (LE PHB) for
Differentiated Services", RFC 8622, DOI 10.17487/RFC8622, Differentiated Services", RFC 8622, DOI 10.17487/RFC8622,
June 2019, <https://www.rfc-editor.org/rfc/rfc8622>. June 2019, <https://www.rfc-editor.org/info/rfc8622>.
[RFC8656] Reddy, T., Ed., Johnston, A., Ed., Matthews, P., and J. [RFC8656] Reddy, T., Ed., Johnston, A., Ed., Matthews, P., and J.
Rosenberg, "Traversal Using Relays around NAT (TURN): Rosenberg, "Traversal Using Relays around NAT (TURN):
Relay Extensions to Session Traversal Utilities for NAT Relay Extensions to Session Traversal Utilities for NAT
(STUN)", RFC 8656, DOI 10.17487/RFC8656, February 2020, (STUN)", RFC 8656, DOI 10.17487/RFC8656, February 2020,
<https://www.rfc-editor.org/rfc/rfc8656>. <https://www.rfc-editor.org/info/rfc8656>.
[RFC8699] Islam, S., Welzl, M., and S. Gjessing, "Coupled Congestion [RFC8699] Islam, S., Welzl, M., and S. Gjessing, "Coupled Congestion
Control for RTP Media", RFC 8699, DOI 10.17487/RFC8699, Control for RTP Media", RFC 8699, DOI 10.17487/RFC8699,
January 2020, <https://www.rfc-editor.org/rfc/rfc8699>. January 2020, <https://www.rfc-editor.org/info/rfc8699>.
[RFC8801] Pfister, P., Vyncke, É., Pauly, T., Schinazi, D., and W. [RFC8801] Pfister, P., Vyncke, É., Pauly, T., Schinazi, D., and W.
Shao, "Discovering Provisioning Domain Names and Data", Shao, "Discovering Provisioning Domain Names and Data",
RFC 8801, DOI 10.17487/RFC8801, July 2020, RFC 8801, DOI 10.17487/RFC8801, July 2020,
<https://www.rfc-editor.org/rfc/rfc8801>. <https://www.rfc-editor.org/info/rfc8801>.
[RFC8838] Ivov, E., Uberti, J., and P. Saint-Andre, "Trickle ICE: [RFC8838] Ivov, E., Uberti, J., and P. Saint-Andre, "Trickle ICE:
Incremental Provisioning of Candidates for the Interactive Incremental Provisioning of Candidates for the Interactive
Connectivity Establishment (ICE) Protocol", RFC 8838, Connectivity Establishment (ICE) Protocol", RFC 8838,
DOI 10.17487/RFC8838, January 2021, DOI 10.17487/RFC8838, January 2021,
<https://www.rfc-editor.org/rfc/rfc8838>. <https://www.rfc-editor.org/info/rfc8838>.
[RFC8899] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T. [RFC8899] Fairhurst, G., Jones, T., Tüxen, M., Rüngeler, I., and T.
Völker, "Packetization Layer Path MTU Discovery for Völker, "Packetization Layer Path MTU Discovery for
Datagram Transports", RFC 8899, DOI 10.17487/RFC8899, Datagram Transports", RFC 8899, DOI 10.17487/RFC8899,
September 2020, <https://www.rfc-editor.org/rfc/rfc8899>. September 2020, <https://www.rfc-editor.org/info/rfc8899>.
[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>.
[RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves, [RFC8981] Gont, F., Krishnan, S., Narten, T., and R. Draves,
"Temporary Address Extensions for Stateless Address "Temporary Address Extensions for Stateless Address
Autoconfiguration in IPv6", RFC 8981, Autoconfiguration in IPv6", RFC 8981,
DOI 10.17487/RFC8981, February 2021, DOI 10.17487/RFC8981, February 2021,
<https://www.rfc-editor.org/rfc/rfc8981>. <https://www.rfc-editor.org/info/rfc8981>.
[RFC9218] Oku, K. and L. Pardue, "Extensible Prioritization Scheme [RFC9218] Oku, K. and L. Pardue, "Extensible Prioritization Scheme
for HTTP", RFC 9218, DOI 10.17487/RFC9218, June 2022, for HTTP", RFC 9218, DOI 10.17487/RFC9218, June 2022,
<https://www.rfc-editor.org/rfc/rfc9218>. <https://www.rfc-editor.org/info/rfc9218>.
[RFC9329] Pauly, T. and V. Smyslov, "TCP Encapsulation of Internet [RFC9329] Pauly, T. and V. Smyslov, "TCP Encapsulation of Internet
Key Exchange Protocol (IKE) and IPsec Packets", RFC 9329, Key Exchange Protocol (IKE) and IPsec Packets", RFC 9329,
DOI 10.17487/RFC9329, November 2022, DOI 10.17487/RFC9329, November 2022,
<https://www.rfc-editor.org/rfc/rfc9329>. <https://www.rfc-editor.org/info/rfc9329>.
[RFC9623] Brunstrom, A., Ed., Pauly, T., Ed., Enghardt, R., Tiesel,
P. S., and M. Welzl, "Implementing Interfaces to Transport
Services", RFC 9623, DOI 10.17487/RFC9623, November 2024,
<https://www.rfc-editor.org/info/rfc9623>.
[TCP-COUPLING] [TCP-COUPLING]
Islam, S., Welzl, M., Hiorth, K., Hayes, D., Armitage, G., Islam, S., Welzl, M., Hiorth, K., Hayes, D., Armitage, G.,
and S. Gjessing, "ctrlTCP: Reducing Latency through and S. Gjessing, "ctrlTCP: Reducing latency through
Coupled, Heterogeneous Multi-Flow TCP Congestion Control", coupled, heterogeneous multi-flow TCP congestion control",
IEEE INFOCOM Global Internet Symposium (GI) workshop (GI IEEE INFOCOM 2018 - IEEE Conference on Computer
2018) , 2018. Communications Workshops (INFOCOM WKSHPS),
DOI 10.1109/INFCOMW.2018.8406887, 2018,
<https://ieeexplore.ieee.org/document/8406887>.
Appendix A. Implementation Mapping Appendix A. Implementation Mapping
The way the concepts from this abstract API map into concrete APIs in The way the concepts from this abstract API map to concrete APIs in a
a given language on a given platform largely depends on the features given language on a given platform largely depends on the features
and norms of the language and the platform. Actions could be and norms of the language and the platform. For instance, actions
implemented as functions or method calls, for instance, and events could be implemented as functions or method calls and events could be
could be implemented via event queues, handler functions or classes, implemented via event queues, handler functions or classes,
communicating sequential processes, or other asynchronous calling communicating sequential processes, or other asynchronous calling
conventions. conventions.
A.1. Types A.1. Types
The basic types mentioned in Section 1.1 typically have natural The basic types mentioned in Section 1.1 typically have natural
correspondences in practical programming languages, perhaps correspondences in practical programming languages, perhaps
constrained by implementation-specific limitations. For example: constrained by implementation-specific limitations. For example:
* An Integer can typically be represented in C by an int or long, * Typically, an Integer can be represented in C by an int or long;
subject to the underlying platform's ranges for each. this is subject to the underlying platform's ranges for each.
* In C, a Tuple may be represented as a struct with one member for * In C, a Tuple may be represented as a struct with one member for
each of the value types in the ordered grouping. In Python, by each of the value types in the ordered grouping. However, in
contrast, a Tuple may be represented as a tuple, a sequence of Python, a Tuple may be represented as a tuple, which is a sequence
dynamically-typed elements. of dynamically typed elements.
* A Set may be represented as a std::set in C++ or as a set in * A Set may be represented as a std::set in C++ or as a set in
Python. In C, it may be represented as an array or as a higher- Python. In C, it may be represented as an array or as a higher-
level data structure with appropriate accessors defined. level data structure with appropriate accessors defined.
The objects described in Section 1.1 can similarly be represented in The objects described in Section 1.1 can also be represented in
different ways depending on which programming language is used. different ways, depending on which programming language is used.
Objects like Preconnections, Connections, and Listeners can be long- Objects like Preconnections, Connections, and Listeners can be long-
lived, and benefit from using object-oriented constructs. Note that lived and benefit from using object-oriented constructs. Note that,
in C, these objects may need to provide a way to release or free in C, these objects may need to provide a way to release or free
their underlying memory when the application is done using them. For their underlying memory when the application is done using them. For
example, since a Preconnection can be used to initiate multiple example, since a Preconnection can be used to initiate multiple
Connections, it is the responsibility of the application to clean up Connections, it is the responsibility of the application to clean up
the Preconnection memory if necessary. the Preconnection memory if necessary.
A.2. Events and Errors A.2. Events and Errors
This specification treats events and errors similarly. Errors, just This specification treats events and errors similarly. Errors, just
as any other events, may occur asynchronously in network as any other events, may occur asynchronously in network
applications. However, implementations of this API may report errors applications. However, implementations of this API may report errors
synchronously, according to the error handling idioms of the synchronously. This is done according to the error-handling idioms
implementation platform, where they can be immediately detected, such of the implementation platform, where they can be immediately
as by generating an exception when attempting to initiate a detected. An example of this being generating an exception when
Connection with inconsistent Transport Properties. An error can attempting to initiate a Connection with inconsistent Transport
provide an optional reason to the application with further details Properties. An error can provide an optional reason to the
about why the error occurred. application with further details about why the error occurred.
A.3. Time Duration A.3. Time Duration
Time duration types are implementation-specific. For instance, it Time duration types are implementation specific. For instance, it
could be a number of seconds, number of milliseconds, or a struct could be a number of seconds, a number of milliseconds, or a struct
timeval in C or a user-defined Duration class in C++. timeval in C; in C++, it could be a user-defined Duration class.
Appendix B. Convenience Functions Appendix B. Convenience Functions
B.1. Adding Preference Properties B.1. Adding Preference Properties
TransportProperties will frequently need to set Selection Properties TransportProperties will frequently need to set Selection Properties
of type Preference, therefore implementations can provide special of type Preference; therefore, implementations can provide special
actions for adding each preference level i.e, actions for adding each preference level, i.e.,
TransportProperties.Set(some_property, avoid) is equivalent TransportProperties.Set(some_property, avoid) is equivalent to
toTransportProperties.Avoid(some_property)`: TransportProperties.Avoid(some_property):
TransportProperties.Require(property) TransportProperties.Require(property)
TransportProperties.Prefer(property) TransportProperties.Prefer(property)
TransportProperties.NoPreference(property) TransportProperties.NoPreference(property)
TransportProperties.Avoid(property) TransportProperties.Avoid(property)
TransportProperties.Prohibit(property) TransportProperties.Prohibit(property)
B.2. Transport Property Profiles B.2. Transport Property Profiles
To ease the use of the Transport Services API, implementations can To ease the use of the Transport Services API, implementations can
provide a mechanism to create Transport Property objects (see provide a mechanism to create Transport Property objects (see
Section 6.2) that are preconfigured with frequently used sets of Section 6.2) that are preconfigured with frequently used sets of
properties; the following are in common use in current applications: properties; the following subsections list those that are in common
use in applications at the time of writing.
B.2.1. reliable-inorder-stream B.2.1. reliable-inorder-stream
This profile provides reliable, in-order transport service with This profile provides reliable, in-order transport service with
congestion control. TCP is an example of a protocol that provides congestion control. TCP is an example of a protocol that provides
this service. It should consist of the following properties: this service. It should consist of the following properties:
+=======================+===============+ +=======================+===============+
| Property | Value | | Property | Value |
+=======================+===============+ +=======================+===============+
| reliability | require | | reliability | require |
+-----------------------+---------------+ +-----------------------+---------------+
| preserveOrder | require | | preserveOrder | require |
+-----------------------+---------------+ +-----------------------+---------------+
| congestionControl | require | | congestionControl | require |
+-----------------------+---------------+ +-----------------------+---------------+
| preserveMsgBoundaries | no preference | | preserveMsgBoundaries | no preference |
+-----------------------+---------------+ +-----------------------+---------------+
Table 2: reliable-inorder-stream Table 2: reliable-inorder-stream
preferences Preferences
B.2.2. reliable-message B.2.2. reliable-message
This profile provides message-preserving, reliable, in-order This profile provides message-preserving, reliable, in-order
transport service with congestion control. SCTP is an example of a transport service with congestion control. SCTP is an example of a
protocol that provides this service. It should consist of the protocol that provides this service. It should consist of the
following properties: following properties:
+=======================+=========+ +=======================+=========+
| Property | Value | | Property | Value |
skipping to change at page 93, line 18 skipping to change at line 4262
| reliability | require | | reliability | require |
+-----------------------+---------+ +-----------------------+---------+
| preserveOrder | require | | preserveOrder | require |
+-----------------------+---------+ +-----------------------+---------+
| congestionControl | require | | congestionControl | require |
+-----------------------+---------+ +-----------------------+---------+
| preserveMsgBoundaries | require | | preserveMsgBoundaries | require |
+-----------------------+---------+ +-----------------------+---------+
Table 3: reliable-message Table 3: reliable-message
preferences Preferences
B.2.3. unreliable-datagram B.2.3. unreliable-datagram
This profile provides a datagram transport service without any This profile provides a datagram transport service without any
reliability guarantee. An example of a protocol that provides this reliability guarantee. An example of a protocol that provides this
service is UDP. It consists of the following properties: service is UDP. It consists of the following properties:
+=======================+===============+ +=======================+===============+
| Property | Value | | Property | Value |
+=======================+===============+ +=======================+===============+
skipping to change at page 93, line 40 skipping to change at line 4284
+-----------------------+---------------+ +-----------------------+---------------+
| preserveOrder | avoid | | preserveOrder | avoid |
+-----------------------+---------------+ +-----------------------+---------------+
| congestionControl | no preference | | congestionControl | no preference |
+-----------------------+---------------+ +-----------------------+---------------+
| preserveMsgBoundaries | require | | preserveMsgBoundaries | require |
+-----------------------+---------------+ +-----------------------+---------------+
| safelyReplayable | true | | safelyReplayable | true |
+-----------------------+---------------+ +-----------------------+---------------+
Table 4: unreliable-datagram preferences Table 4: unreliable-datagram Preferences
Applications that choose this Transport Property Profile would avoid Applications that choose this Transport Property Profile would avoid
the additional latency that could be introduced by retransmission or the additional latency that could be introduced by retransmission or
reordering in a transport protocol. reordering in a transport protocol.
Applications that choose this Transport Property Profile to reduce Applications that choose this Transport Property Profile to reduce
latency should also consider setting an appropriate capacity profile latency should also consider setting an appropriate capacity profile
Property, see Section 8.1.6 and might benefit from controlling Property (see Section 8.1.6) and might benefit from controlling
checksum coverage, see Section 6.2.7 and Section 6.2.8. checksum coverage (see Sections 6.2.7 and 6.2.8).
Appendix C. Relationship to the Minimal Set of Transport Services for Appendix C. Relationship to the Minimal Set of Transport Services for
End Systems End Systems
[RFC8923] identifies a minimal set of transport services that end [RFC8923] identifies a minimal set of Transport Services that end
systems should offer. These services make all non-security-related systems should offer. These services make all non-security-related
transport features of TCP, MPTCP, UDP, UDP-Lite, SCTP and LEDBAT transport features of TCP, Multipath TCP (MPTCP), UDP, UDP-Lite,
available that 1) require interaction with the application, and 2) do SCTP, and Low Extra Delay Background Transport (LEDBAT) available
not get in the way of a possible implementation over TCP (or, with that:
limitations, UDP). The following text explains how this minimal set
is reflected in the present API. For brevity, it is based on the 1. require interaction with the application and
list in Section 4.1 of [RFC8923], updated according to the discussion
in Section 5 of [RFC8923]. The present API covers all elements of 2. do not get in the way of a possible implementation over TCP (or,
this section. This list is a subset of the transport features in with limitations, UDP).
Appendix A of [RFC8923], which refers to the primitives in "pass 2"
(Section 4) of [RFC8303] for further details on the implementation The following text explains how this minimal set is reflected in the
with TCP, MPTCP, UDP, UDP-Lite, SCTP and LEDBAT. This facilitates present API. For brevity, it is based on the list in Section 4.1 of
finding the specifications for implementing the services listed below [RFC8923] and updated according to the discussion in Section 5 of
with these protocols. [RFC8923]. The present API covers all elements of this section.
This list is a subset of the transport features in Appendix A of
[RFC8923], which refers to the primitives in "pass 2" (see Section 4
of [RFC8303]) for further details on the implementation with TCP,
MPTCP, UDP, UDP-Lite, SCTP, and LEDBAT. This facilitates finding the
specifications for implementing the services listed below with these
protocols.
* Connect: Initiate action (Section 7.1). * Connect: Initiate action (Section 7.1).
* Listen: Listen action (Section 7.2). * Listen: Listen action (Section 7.2).
* Specify number of attempts and/or timeout for the first * Specify number of attempts and/or timeout for the first
establishment Message: timeout parameter of Initiate (Section 7.1) establishment Message: timeout parameter of Initiate (Section 7.1)
or InitiateWithSend action (Section 9.2.5). or InitiateWithSend action (Section 9.2.5).
* Disable MPTCP: multipath property (Section 6.2.14). * Disable MPTCP: multipath property (Section 6.2.14).
skipping to change at page 94, line 45 skipping to change at line 4341
before connection establishment: InitiateWithSend action before connection establishment: InitiateWithSend action
(Section 9.2.5). (Section 9.2.5).
* Change timeout for aborting connection (using retransmit limit or * Change timeout for aborting connection (using retransmit limit or
time value): connTimeout property, using a time value time value): connTimeout property, using a time value
(Section 8.1.3). (Section 8.1.3).
* Timeout event when data could not be delivered for too long: * Timeout event when data could not be delivered for too long:
ConnectionError event (Section 10). ConnectionError event (Section 10).
* Suggest timeout to the peer: See "TCP-specific Properties: User * Suggest timeout to the peer: See "TCP-Specific Properties: User
Timeout Option (UTO)" (Section 8.2). Timeout Option (UTO)" (Section 8.2).
* Notification of ICMP error message arrival: softErrorNotify * Notification of ICMP error message arrival: softErrorNotify
(Section 6.2.17) and SoftError event (Section 8.3.1). (Section 6.2.17) and SoftError event (Section 8.3.1).
* Choose a scheduler to operate between streams of an association: * Choose a scheduler to operate between streams of an association:
connScheduler property (Section 8.1.5). connScheduler property (Section 8.1.5).
* Configure priority or weight for a scheduler: connPriority * Configure priority or weight for a scheduler: connPriority
property (Section 8.1.2). property (Section 8.1.2).
skipping to change at page 95, line 19 skipping to change at line 4364
checksum when sending": msgChecksumLen property (Section 9.1.3.6) checksum when sending": msgChecksumLen property (Section 9.1.3.6)
and fullChecksumSend property (Section 6.2.7). and fullChecksumSend property (Section 6.2.7).
* "Specify minimum checksum coverage required by receiver" and * "Specify minimum checksum coverage required by receiver" and
"Disable checksum requirement when receiving": recvChecksumLen "Disable checksum requirement when receiving": recvChecksumLen
property (Section 8.1.1) and fullChecksumRecv property property (Section 8.1.1) and fullChecksumRecv property
(Section 6.2.8). (Section 6.2.8).
* "Specify DF field": noFragmentation property (Section 9.1.3.9). * "Specify DF field": noFragmentation property (Section 9.1.3.9).
* Get max. transport-message size that may be sent using a non- * Get maximum transport-message size that may be sent using a non-
fragmented IP packet from the configured interface: fragmented IP packet from the configured interface:
singularTransmissionMsgMaxLen property (Section 8.1.11.4). singularTransmissionMsgMaxLen property (Section 8.1.11.4).
* Get max. transport-message size that may be received from the * Get maximum transport-message size that may be received from the
configured interface: recvMsgMaxLen property (Section 8.1.11.6). configured interface: recvMsgMaxLen property (Section 8.1.11.6).
* Obtain ECN field: This is a read-only Message Property of the * Obtain ECN field: This is a read-only Message Property of the
MessageContext object (see "UDP(-Lite)-specific Property: ECN" MessageContext object (see "Property Specific to UDP and UDP-Lite:
Section 9.3.3.1). ECN" (Section 9.3.3.1)).
* "Specify DSCP field", "Disable Nagle algorithm", "Enable and * "Specify DSCP field", "Disable Nagle algorithm", and "Enable and
configure a Low Extra Delay Background Transfer": as suggested in configure a Low Extra Delay Background Transfer": as suggested in
Section 5.5 of [RFC8923], these transport features are Section 5.5 of [RFC8923], these transport features are
collectively offered via the connCapacityProfile property collectively offered via the connCapacityProfile property
(Section 8.1.6). Per-Message control ("Request not to bundle (Section 8.1.6). Per-Message control ("Request not to bundle
messages") is offered via the msgCapacityProfile property messages") is offered via the msgCapacityProfile property
(Section 9.1.3.8). (Section 9.1.3.8).
* Close after reliably delivering all remaining data, causing an * Close after reliably delivering all remaining data, causing an
event informing the application on the other side: this is offered event informing the application on the other side: this is offered
by the Close action with slightly changed semantics in line with by the Close action with slightly changed semantics in line with
the discussion in Section 5.2 of [RFC8923] (Section 10). the discussion in Section 5.2 of [RFC8923] (see also Section 10).
* "Abort without delivering remaining data, causing an event * "Abort without delivering remaining data, causing an event
informing the application on the other side" and "Abort without informing the application on the other side" and "Abort without
delivering remaining data, not causing an event informing the delivering remaining data, not causing an event informing the
application on the other side": this is offered by the Abort application on the other side": this is offered by the Abort
action without promising that this is signaled to the other side. action without promising that this is signaled to the other side.
If it is, a ConnectionError event will be invoked at the peer If it is, a ConnectionError event will be invoked at the peer
(Section 10). (Section 10).
* "Reliably transfer data, with congestion control", "Reliably * "Reliably transfer data, with congestion control", "Reliably
transfer a message, with congestion control" and "Unreliably transfer a message, with congestion control", and "Unreliably
transfer a message": data is transferred via the Send action transfer a message": data is transferred via the Send action
(Section 9.2). Reliability is controlled via the reliability (Section 9.2). Reliability is controlled via the reliability
(Section 6.2.1) property and the msgReliable Message Property (Section 6.2.1) property and the msgReliable Message Property
(Section 9.1.3.7). Transmitting data as a Message or without (Section 9.1.3.7). Transmitting data as a Message or without
delimiters is controlled via Message Framers (Section 9.1.2). The delimiters is controlled via Message Framers (Section 9.1.2). The
choice of congestion control is provided via the congestionControl choice of congestion control is provided via the congestionControl
property (Section 6.2.9). property (Section 6.2.9).
* Configurable Message Reliability: the msgLifetime Message Property * Configurable Message Reliability: the msgLifetime Message Property
implements a time-based way to configure message reliability implements a time-based way to configure message reliability
(Section 9.1.3.1). (Section 9.1.3.1).
* "Ordered message delivery (potentially slower than unordered)" and * "Ordered message delivery (potentially slower than unordered)" and
"Unordered message delivery (potentially faster than ordered)": "Unordered message delivery (potentially faster than ordered)":
these two transport features are controlled via the Message these two transport features are controlled via the Message
Property msgOrdered (Section 9.1.3.3). Property msgOrdered (Section 9.1.3.3).
* Request not to delay the acknowledgment (SACK) of a message: * Request not to delay the acknowledgement (SACK) of a message:
should the protocol support it, this is one of the transport should the protocol support it, this is one of the transport
features the Transport Services system can apply when an features the Transport Services system can apply when an
application uses the connCapacityProfile Property (Section 8.1.6) application uses the connCapacityProfile Property (Section 8.1.6)
or the msgCapacityProfile Message Property (Section 9.1.3.8) with or the msgCapacityProfile Message Property (Section 9.1.3.8) with
value Low Latency/Interactive. value Low Latency/Interactive.
* Receive data (with no message delimiting): Receive action * Receive data (with no message delimiting): Receive action
(Section 9.3.1) and Received event (Section 9.3.2.1). (Section 9.3.1) and Received event (Section 9.3.2.1).
* Receive a message: Receive action (Section 9.3.1) and Received * Receive a message: Receive action (Section 9.3.1) and Received
event (Section 9.3.2.1), using Message Framers (Section 9.1.2). event (Section 9.3.2.1) using Message Framers (Section 9.1.2).
* Information about partial message arrival: Receive action * Information about partial message arrival: Receive action
(Section 9.3.1) and ReceivedPartial event (Section 9.3.2.2). (Section 9.3.1) and ReceivedPartial event (Section 9.3.2.2).
* Notification of send failures: Expired event (Section 9.2.2.2) and * Notification of send failures: Expired event (Section 9.2.2.2) and
SendError event (Section 9.2.2.3). SendError event (Section 9.2.2.3).
* Notification that the stack has no more user data to send: * Notification that the stack has no more user data to send:
applications can obtain this information via the Sent event applications can obtain this information via the Sent event
(Section 9.2.2.1). (Section 9.2.2.1).
* Notification to a receiver that a partial message delivery has * Notification to a receiver that a partial message delivery has
been aborted: ReceiveError event (Section 9.3.2.3). been aborted: ReceiveError event (Section 9.3.2.3).
* Notification of Excessive Retransmissions (early warning below * Notification of Excessive Retransmissions (early warning below
abortion threshold): SoftError event (Section 8.3.1). abortion threshold): SoftError event (Section 8.3.1).
Acknowledgements
This work has received funding from the European Union's Horizon 2020
research and innovation programme under grant agreements No. 644334
(NEAT) and No. 688421 (MAMI).
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.
* the Research Council of Norway under its "Toppforsk" programme
through the "OCARINA" project.
Thanks to Stuart Cheshire, Josh Graessley, David Schinazi, and Eric
Kinnear for their implementation and design efforts, including Happy
Eyeballs, that heavily influenced this work. Thanks to Laurent Chuat
and Jason Lee for initial work on the Post Sockets interface, from
which this work has evolved. Thanks to Maximilian Franke for asking
good questions based on implementation experience and for
contributing text, e.g., on multicast.
Authors' Addresses Authors' Addresses
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
Michael Welzl (editor) Michael Welzl (editor)
University of Oslo University of Oslo
PO Box 1080 Blindern PO Box 1080 Blindern
0316 Oslo 0316 Oslo
Norway Norway
Email: michawe@ifi.uio.no Email: michawe@ifi.uio.no
Reese Enghardt Reese Enghardt
Netflix Netflix
121 Albright Way 121 Albright Way
Los Gatos, CA 95032, Los Gatos, CA 95032
United States of America United States of America
Email: ietf@tenghardt.net Email: ietf@tenghardt.net
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/
Mirja Kuehlewind Mirja Kühlewind
Ericsson Ericsson
Ericsson-Allee 1 Ericsson-Allee 1
Herzogenrath Herzogenrath
Germany Germany
Email: mirja.kuehlewind@ericsson.com Email: mirja.kuehlewind@ericsson.com
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
Philipp S. Tiesel Philipp S. Tiesel
SAP SE SAP SE
George-Stephenson-Straße 7-13 George-Stephenson-Straße 7-13
10557 Berlin 10557 Berlin
Germany Germany
Email: philipp@tiesel.net Email: philipp@tiesel.net
Tommy Pauly Tommy Pauly
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
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