rfc9621v3.txt		rfc9621.txt
	skipping to change at line 148 ¶		skipping to change at line 148 ¶
	to identify an optimal combination of a transport protocol instance		to identify an optimal combination of a transport protocol instance
	such as TCP, UDP, or another transport, together with configuration		such as TCP, UDP, or another transport, together with configuration
	of parameters and interfaces. A Connection represents an object		of parameters and interfaces. A Connection represents an object
	that, once established, can be used to send and receive messages. A		that, once established, can be used to send and receive messages. A
	Connection can also be created from another Connection, by cloning,		Connection can also be created from another Connection, by cloning,
	and then forms a part of a Connection Group whose Connections share		and then forms a part of a Connection Group whose Connections share
	properties.		properties.
	This document was developed in parallel with the specification of the		This document was developed in parallel with the specification of the
	Transport Services API [RFC9622] and implementation guidelines		Transport Services API [RFC9622] and implementation guidelines
	[RFC9623]. Although following the Transport Services architecture		[RFC9623]. Although following the Transport Services Architecture
	does not require all APIs and implementations to be identical, a		does not require all APIs and implementations to be identical, a
	common minimal set of features represented in a consistent fashion		common minimal set of features represented in a consistent fashion
	will enable applications to be easily ported from one implementation		will enable applications to be easily ported from one implementation
	of the Transport Services System to another.		of the Transport Services System to another.
	1.1. Background		1.1. Background
	The architecture of the Transport Services System is based on the		The architecture of the Transport Services System is based on the
	survey of services provided by IETF transport protocols and		survey of services provided by IETF transport protocols and
	congestion control mechanisms [RFC8095] and the distilled minimal set		congestion control mechanisms [RFC8095] and the distilled minimal set
	skipping to change at line 217 ¶		skipping to change at line 217 ¶
	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		"OPTIONAL" in this document are to be interpreted as described in
	BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all		BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
	capitals, as shown here.		capitals, as shown here.
	1.4. Glossary of Key Terms		1.4. Glossary of Key Terms
	This subsection provides a glossary of key terms related to the		This subsection provides a glossary of key terms related to the
	Transport Services architecture. It provides a short description of		Transport Services Architecture. It provides a short description of
	key terms that are defined later in this document.		key terms that are defined later in this document.
	Application: An entity that uses the transport layer for end-to-end		Application: An entity that uses the transport layer for end-to-end
	delivery of data across the network [RFC8095].		delivery of data across the network [RFC8095].
	Cached State: The state and history that the Transport Services		Cached State: The state and history that the Transport Services
	Implementation keeps for each set of the associated Endpoints that		Implementation keeps for each set of the associated Endpoints that
	have been used previously.		have been used previously.
	Candidate Path: One path that is available to an application and		Candidate Path: One path that is available to an application and
	skipping to change at line 351 ¶		skipping to change at line 351 ¶
	Transport Feature: A specific end-to-end feature that the transport		Transport Feature: A specific end-to-end feature that the transport
	layer provides to an application.		layer provides to an application.
	Transport Property: A property of a transport protocol and the		Transport Property: A property of a transport protocol and the
	services it provides [RFC8095].		services it provides [RFC8095].
	Transport Service: A set of transport features, not associated with		Transport Service: A set of transport features, not associated with
	any given framing protocol, that provides a complete service to an		any given framing protocol, that provides a complete service to an
	application.		application.
			Transport Services API: The abstract interface [RFC9622] to a
			Transport Services Implementation [RFC9623].
	Transport Services Implementation: All objects and protocol		Transport Services Implementation: All objects and protocol
	instances used internally to a system or library to implement the		instances used internally to a system or library to implement the
	functionality needed to provide a transport service across a		functionality needed to provide a transport service across a
	network, as required by the abstract interface.		network, as required by the abstract interface.
	Transport Services System: The Transport Services Implementation and		Transport Services System: The Transport Services Implementation and
	the Transport Services API.		the Transport Services API.
	2. API Model		2. API Model
	skipping to change at line 517 ¶		skipping to change at line 520 ¶
	* providing additional information to the Protocol Stack;		* providing additional information to the Protocol Stack;
	* the ability to associate deadlines with messages, for applications		* the ability to associate deadlines with messages, for applications
	that care about timing;		that care about timing;
	* the ability to control reliability, which messages to retransmit		* the ability to control reliability, which messages to retransmit
	when there is packet loss, and how best to make use of the data		when there is packet loss, and how best to make use of the data
	that arrived;		that arrived;
	* the ability to automatically assign messages and connections to		* the ability to automatically assign messages and connections to
	underlying transport connections to utilize multi-streaming and		underlying transport connections to utilize multistreaming and
	pooled connections.		pooled connections.
	Allowing applications to interact with messages is backward-		Allowing applications to interact with messages is backward-
	compatible with existing protocols and APIs because it does not		compatible with existing protocols and APIs because it does not
	change the wire format of any protocol. Instead, it provides the		change the wire format of any protocol. Instead, it provides the
	Protocol Stack with additional information to allow it to make better		Protocol Stack with additional information to allow it to make better
	use of modern Transport Services, while simplifying the application's		use of modern Transport Services, while simplifying the application's
	role in parsing data. For protocols that inherently use a streaming		role in parsing data. For protocols that inherently use a streaming
	abstraction, framers (Section 4.1.5) bridge the gap between the two		abstraction, framers (Section 4.1.5) bridge the gap between the two
	abstractions.		abstractions.
	2.3. Flexible Implementation		2.3. Flexible Implementation
	The Socket API for protocols like TCP is generally limited to		The Socket API for protocols like TCP is generally limited to
	connecting to a single address over a single interface (IP source		connecting to a single address over a single interface (IP source
	address). It also presents a single stream to the application.		address). It also presents a single stream to the application.
	Software layers built upon this API often propagate this limitation		Software layers built upon this API often propagate this limitation
	of a single-address single-stream model. The Transport Services		of a single-address single-stream model. The Transport Services
	architecture is designed to:		Architecture is designed to:
	* handle multiple candidate endpoints, protocols, and paths;		* handle multiple candidate endpoints, protocols, and paths;
	* support candidate protocol racing to select the most optimal stack		* support candidate protocol racing to select the most optimal stack
	in each situation;		in each situation;
	* support multipath and multistreaming protocols;		* support multipath and multistreaming protocols;
	* provide state caching and application control over it.		* provide state caching and application control over it.
	skipping to change at line 1000 ¶		skipping to change at line 1003 ¶
	transport protocol instances that can send and/or receive Messages		transport protocol instances that can send and/or receive Messages
	between Local and Remote Endpoints. It is an abstraction that		between Local and Remote Endpoints. It is an abstraction that
	represents the communication. The Connection object holds state		represents the communication. The Connection object holds state
	pertaining to the underlying transport protocol instances and any		pertaining to the underlying transport protocol instances and any
	ongoing data transfers. For example, an active Connection can		ongoing data transfers. For example, an active Connection can
	represent a connection-oriented protocol such as TCP, or it can		represent a connection-oriented protocol such as TCP, or it can
	represent a fully specified 5-tuple for a connectionless protocol		represent a fully specified 5-tuple for a connectionless protocol
	such as UDP, where the Connection remains an abstraction at the		such as UDP, where the Connection remains an abstraction at the
	endpoints. It can also represent a pool of transport protocol		endpoints. It can also represent a pool of transport protocol
	instances, e.g., a set of TCP and QUIC connections to equivalent		instances, e.g., a set of TCP and QUIC connections to equivalent
	endpoints, or a stream of a multi-streaming transport protocol		endpoints, or a stream of a multistreaming transport protocol
	instance. Connections can be created from a Preconnection or by a		instance. Connections can be created from a Preconnection or by a
	Listener.		Listener.
	Preconnection: A Preconnection object is a representation of a		Preconnection: A Preconnection object is a representation of a
	Connection that has not yet been established. It has state that		Connection that has not yet been established. It has state that
	describes parameters of the Connection: the Local Endpoint		describes parameters of the Connection: the Local Endpoint
	Identifier from which that Connection will be established, the		Identifier from which that Connection will be established, the
	Remote Endpoint Identifier to which it will connect, and Transport		Remote Endpoint Identifier to which it will connect, and Transport
	Properties that influence the paths and protocols a Connection		Properties that influence the paths and protocols a Connection
	will use. A Preconnection can be either fully specified		will use. A Preconnection can be either fully specified
	skipping to change at line 1247 ¶		skipping to change at line 1250 ¶
	The API allows a Connection to be created from another Connection.		The API allows a Connection to be created from another Connection.
	This adds the new Connection to the Connection Group. A change to		This adds the new Connection to the Connection Group. A change to
	one of the Connection Properties on any Connection in the Connection		one of the Connection Properties on any Connection in the Connection
	Group automatically changes the Connection Property for all others.		Group automatically changes the Connection Property for all others.
	All Connections in a Connection Group share the same set of		All Connections in a Connection Group share the same set of
	Connection Properties except for the Connection Priority. These		Connection Properties except for the Connection Priority. These
	Connection Properties are said to be entangled.		Connection Properties are said to be entangled.
	Passive Connections can also be added to a Connection Group, e.g.,		Passive Connections can also be added to a Connection Group, e.g.,
	when a Listener receives a new Connection that is just a new stream		when a Listener receives a new Connection that is just a new stream
	of an already-active multi-streaming protocol instance.		of an already-active multistreaming protocol instance.
	While Connection Groups are managed by the Transport Services		While Connection Groups are managed by the Transport Services
	Implementation, an application can define different Connection		Implementation, an application can define different Connection
	Contexts for different Connection Groups to explicitly control		Contexts for different Connection Groups to explicitly control
	caching boundaries, as discussed in Section 4.2.3.		caching boundaries, as discussed in Section 4.2.3.
	4.2. Transport Services Implementation		4.2. Transport Services Implementation
	This section defines the key architectural concepts for the Transport		This section defines the key architectural concepts for the Transport
	Services Implementation within the Transport Services System.		Services Implementation within the Transport Services System.
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