An Abstract Application Layer Interface to Transport Services
draft-ietf-taps-interface-01
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| Authors | Brian Trammell , Michael Welzl , Reese Enghardt , Gorry Fairhurst , Mirja Kühlewind , Colin Perkins , Philipp S. Tiesel , Christopher A. Wood | ||
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draft-ietf-taps-interface-01
TAPS Working Group B. Trammell, Ed.
Internet-Draft ETH Zurich
Intended status: Informational M. Welzl, Ed.
Expires: January 3, 2019 University of Oslo
T. Enghardt
TU Berlin
G. Fairhurst
University of Aberdeen
M. Kuehlewind
ETH Zurich
C. Perkins
University of Glasgow
P. Tiesel
TU Berlin
C. Wood
Apple Inc.
July 02, 2018
An Abstract Application Layer Interface to Transport Services
draft-ietf-taps-interface-01
Abstract
This document describes an abstract programming interface to the
transport layer, following the Transport Services Architecture. It
supports the asynchronous, atomic transmission of messages over
transport protocols and network paths dynamically selected at
runtime. It is intended to replace the traditional BSD sockets API
as the lowest common denominator interface to the transport layer, in
an environment where endpoints have multiple interfaces and potential
transport protocols to select from.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on January 3, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology and Notation . . . . . . . . . . . . . . . . . . 5
3. Interface Design Principles . . . . . . . . . . . . . . . . . 6
4. API Summary . . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Pre-Establishment Phase . . . . . . . . . . . . . . . . . . . 7
5.1. Specifying Endpoints . . . . . . . . . . . . . . . . . . 8
5.2. Specifying Transport Properties . . . . . . . . . . . . . 9
5.3. Specifying Security Parameters and Callbacks . . . . . . 10
5.3.1. Pre-Connection Parameters . . . . . . . . . . . . . . 11
5.3.2. Connection Establishment Callbacks . . . . . . . . . 12
6. Establishing Connections . . . . . . . . . . . . . . . . . . 12
6.1. Active Open: Initiate . . . . . . . . . . . . . . . . . . 12
6.2. Passive Open: Listen . . . . . . . . . . . . . . . . . . 13
6.3. Peer-to-Peer Establishment: Rendezvous . . . . . . . . . 14
6.4. Connection Groups . . . . . . . . . . . . . . . . . . . . 16
7. Sending Data . . . . . . . . . . . . . . . . . . . . . . . . 16
7.1. Basic Sending . . . . . . . . . . . . . . . . . . . . . . 17
7.2. Send Events . . . . . . . . . . . . . . . . . . . . . . . 17
7.2.1. Sent . . . . . . . . . . . . . . . . . . . . . . . . 18
7.2.2. Expired . . . . . . . . . . . . . . . . . . . . . . . 18
7.2.3. SendError . . . . . . . . . . . . . . . . . . . . . . 18
7.3. Message Context Parameters . . . . . . . . . . . . . . . 18
7.3.1. Lifetime . . . . . . . . . . . . . . . . . . . . . . 19
7.3.2. Niceness . . . . . . . . . . . . . . . . . . . . . . 20
7.3.3. Ordered . . . . . . . . . . . . . . . . . . . . . . . 20
7.3.4. Idempotent . . . . . . . . . . . . . . . . . . . . . 20
7.3.5. Final . . . . . . . . . . . . . . . . . . . . . . . . 20
7.3.6. Corruption Protection Length . . . . . . . . . . . . 21
7.3.7. Transmission Profile . . . . . . . . . . . . . . . . 21
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7.4. Partial Sends . . . . . . . . . . . . . . . . . . . . . . 22
7.5. Batching Sends . . . . . . . . . . . . . . . . . . . . . 22
7.6. Sender-side Framing . . . . . . . . . . . . . . . . . . . 23
8. Receiving Data . . . . . . . . . . . . . . . . . . . . . . . 23
8.1. Enqueuing Receives . . . . . . . . . . . . . . . . . . . 23
8.2. Receive Events . . . . . . . . . . . . . . . . . . . . . 24
8.2.1. Received . . . . . . . . . . . . . . . . . . . . . . 24
8.2.2. ReceivedPartial . . . . . . . . . . . . . . . . . . . 24
8.2.3. ReceiveError . . . . . . . . . . . . . . . . . . . . 25
8.3. Message Receive Context . . . . . . . . . . . . . . . . . 25
8.3.1. ECN . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.3.2. Early Data . . . . . . . . . . . . . . . . . . . . . 26
8.3.3. Receiving Final Messages . . . . . . . . . . . . . . 26
8.4. Receiver-side De-framing over Stream Protocols . . . . . 26
9. Setting and Querying Connection Properties . . . . . . . . . 27
10. Connection Termination . . . . . . . . . . . . . . . . . . . 28
11. Ordering of Operations and Events . . . . . . . . . . . . . . 29
12. Transport Properties . . . . . . . . . . . . . . . . . . . . 30
12.1. Transport Property Types . . . . . . . . . . . . . . . . 30
12.1.1. Boolean . . . . . . . . . . . . . . . . . . . . . . 30
12.1.2. Enumeration . . . . . . . . . . . . . . . . . . . . 31
12.1.3. Integer . . . . . . . . . . . . . . . . . . . . . . 31
12.1.4. Preference . . . . . . . . . . . . . . . . . . . . . 31
12.2. Transport Property Classification . . . . . . . . . . . 31
12.2.1. Selection Properties . . . . . . . . . . . . . . . . 32
12.2.2. Protocol Properties . . . . . . . . . . . . . . . . 33
12.2.3. Control Properties . . . . . . . . . . . . . . . . . 33
12.2.4. Intents . . . . . . . . . . . . . . . . . . . . . . 33
12.3. Mandatory Transport Properties . . . . . . . . . . . . . 34
12.3.1. Final . . . . . . . . . . . . . . . . . . . . . . . 34
12.3.2. Reliable Data Transfer (Connection) . . . . . . . . 34
12.3.3. Configure per-Message reliability . . . . . . . . . 34
12.3.4. Reliable Data Transfer (Message) . . . . . . . . . . 35
12.3.5. Preservation of data ordering . . . . . . . . . . . 35
12.3.6. Ordered . . . . . . . . . . . . . . . . . . . . . . 35
12.3.7. Direction of communication . . . . . . . . . . . . . 36
12.3.8. Use 0-RTT session establishment with an idempotent
Message . . . . . . . . . . . . . . . . . . . . . . 36
12.3.9. Idempotent . . . . . . . . . . . . . . . . . . . . . 36
12.3.10. Multistream Connections in Group . . . . . . . . . . 37
12.3.11. Notification of excessive retransmissions . . . . . 37
12.3.12. Retransmission threshold before excessive
retransmission notification . . . . . . . . . . . . 37
12.3.13. Notification of ICMP soft error message arrival . . 38
12.3.14. Control checksum coverage on sending or receiving . 38
12.3.15. Corruption Protection Length . . . . . . . . . . . . 38
12.3.16. Required minimum coverage of the checksum for
receiving . . . . . . . . . . . . . . . . . . . . . 39
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12.3.17. Interface Instance or Type . . . . . . . . . . . . . 39
12.3.18. Provisioning Domain Instance or Type . . . . . . . . 40
12.3.19. Capacity Profile . . . . . . . . . . . . . . . . . . 41
12.3.20. Congestion control . . . . . . . . . . . . . . . . . 41
12.3.21. Niceness . . . . . . . . . . . . . . . . . . . . . . 42
12.3.22. Timeout for aborting Connection . . . . . . . . . . 42
12.3.23. Connection group transmission scheduler . . . . . . 43
12.3.24. Maximum message size concurrent with Connection
establishment . . . . . . . . . . . . . . . . . . . 43
12.3.25. Maximum Message size before fragmentation or
segmentation . . . . . . . . . . . . . . . . . . . . 43
12.3.26. Maximum Message size on send . . . . . . . . . . . . 43
12.3.27. Maximum Message size on receive . . . . . . . . . . 44
12.3.28. Lifetime . . . . . . . . . . . . . . . . . . . . . . 44
12.4. Optional Transport Properties . . . . . . . . . . . . . 44
12.5. Experimental Transport Properties . . . . . . . . . . . 44
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
14. Security Considerations . . . . . . . . . . . . . . . . . . . 45
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 45
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 45
16.1. Normative References . . . . . . . . . . . . . . . . . . 45
16.2. Informative References . . . . . . . . . . . . . . . . . 46
Appendix A. Additional Properties . . . . . . . . . . . . . . . 47
A.1. Experimental Transport Properties . . . . . . . . . . . . 47
A.1.1. Suggest a timeout to the Remote Endpoint . . . . . . 48
A.1.2. Abort timeout to suggest to the Remote Endpoint . . . 48
A.1.3. Request not to delay acknowledgment of Message . . . 48
A.1.4. Traffic Category . . . . . . . . . . . . . . . . . . 49
A.1.5. Size to be Sent or Received . . . . . . . . . . . . . 49
A.1.6. Duration . . . . . . . . . . . . . . . . . . . . . . 49
A.1.7. Send or Receive Bit-rate . . . . . . . . . . . . . . 50
A.1.8. Cost Preferences . . . . . . . . . . . . . . . . . . 50
A.1.9. Immediate . . . . . . . . . . . . . . . . . . . . . . 51
Appendix B. Sample API definition in Go . . . . . . . . . . . . 51
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51
1. Introduction
The BSD Unix Sockets API's SOCK_STREAM abstraction, by bringing
network sockets into the UNIX programming model, allowing anyone who
knew how to write programs that dealt with sequential-access files to
also write network applications, was a revolution in simplicity. The
simplicity of this API is a key reason the Internet won the protocol
wars of the 1980s. SOCK_STREAM is tied to the Transmission Control
Protocol (TCP), specified in 1981 [RFC0793]. TCP has scaled
remarkably well over the past three and a half decades, but its total
ubiquity has hidden an uncomfortable fact: the network is not really
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a file, and stream abstractions are too simplistic for many modern
application programming models.
In the meantime, the nature of Internet access, and the variety of
Internet transport protocols, is evolving. The challenges that new
protocols and access paradigms present to the sockets API and to
programming models based on them inspire the design principles of a
new approach, which we outline in Section 3.
As a first step to realizing this design, [I-D.ietf-taps-arch]
describes a high-level architecture for transport services. This
document builds a modern abstract programming interface atop this
architecture, deriving specific path and protocol selection
properties and supported transport features from the analysis
provided in [RFC8095] and [I-D.ietf-taps-minset].
2. Terminology and Notation
This API is described in terms of Objects, which an application can
interact with; Actions the application can perform on these Objects;
Events, which an Object can send to an application asynchronously;
and Parameters associated with these Actions and Events.
The following notations, which can be combined, are used in this
document:
o An Action creates an Object:
Object := Action()
o An Action is performed on an Object:
Object.Action()
o An Object sends an Event:
Object -> Event<>
o An Action takes a set of Parameters; an Event contains a set of
Parameters:
Action(parameter, parameter, ...) / Event<parameter, parameter, ...>
Actions associated with no Object are Actions on the abstract
interface itself; they are equivalent to Actions on a per-application
global context.
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How these abstract concepts map into concrete implementations of this
API in a given language on a given platform is largely dependent on
the features of the language and the platform. Actions could be
implemented as functions or method calls, for instance, and Events
could be implemented via callback passing or other asynchronous
calling conventions. The method for registering callbacks and
handlers is left as an implementation detail, with the caveat that
the interface for receiving Messages must require the application to
invoke the Connection.Receive() Action once per Message to be
received (see Section 8).
This specification treats Events and errors similarly. Errors, just
as any other Events, may occur asynchronously in network
applications. However, it is recommended that implementations of
this interface also return errors immediately, according to the error
handling idioms of the implementation platform, for errors which can
be immediately detected, such as inconsistency in Transport
Properties.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Interface Design Principles
The design of the interface specified in this document is based on a
set of princples, themselves an elaboration on the architectural
design principles defined in [I-D.ietf-taps-arch]. The interface
defined in this document provides:
o A single interface to a variety of transport protocols to be used
in a variety of application design patterns, independent of the
properties of the application and the Protocol Stacks that will be
used at runtime, such that all common specialized features of
these protocol stacks are made available to the application as
necessary in a transport-independent way, to enable applications
written to a single API to make use of transport protocols in
terms of the features they provide;
o Explicit support for security properties as first-order transport
features, and for long-term caching of cryptographic identities
and parameters for associations among endpoints;
o Asynchronous Connection establishment, transmission, and
reception, allowing most application interactions with the
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transport layer to be Event-driven, in line with developments in
modern platforms and programming languages;
o Explicit support for multistreaming and multipath transport
protocols, and the grouping of related Connections into Connection
Groups through cloning of Connections, to allow applications to
take full advantage of new transport protocols supporting these
features; and
o Atomic transmission of data, using application-assisted framing
and deframing where the underlying transport does not provide
these.
4. API Summary
The Transport Services Interface is the basic common abstract
application programming interface to the Transport Services
Architecture defined in [I-D.ietf-taps-arch]. An application
primarily interacts with this interface through two Objects,
Preconnections and Connections. A Preconnection represents a set of
properties and constraints on the selection and configuration of
paths and protocols to establish a Connection with a remote endpoint.
A Connection represents a transport Protocol Stack on which data can
be sent to and/or received from a remote endpoint (i.e., depending on
the kind of transport, connections can be bi-directional or
unidirectional). Connections can be created from Preconnections in
three ways: by initiating the Preconnection (i.e., actively opening,
as in a client), through listening on the Preconnection (i.e.,
passively opening, as in a server), or rendezvousing on the
Preconnection (i.e. peer to peer establishment).
Once a Connection is established, data can be sent on it in the form
of Messages. The interface supports the preservation of message
boundaries both via explicit Protocol Stack support, and via
application support through a deframing callback which finds message
boundaries in a stream. Messages are received asynchronously through
a callback registered by the application. Errors and other
notifications also happen asynchronously on the Connection.
In the following sections, we describe the details of application
interaction with Objects through Actions and Events in each phase of
a Connection, following the phases described in [I-D.ietf-taps-arch].
5. Pre-Establishment Phase
The pre-establishment phase allows applications to specify properties
for the Connections they're about to make, or to query the API about
potential connections they could make.
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A Preconnection Object represents a potential Connection. It has
state that describes properties of a Connection that might exist in
the future. This state comprises Local Endpoint and Remote Endpoint
Objects that denote the endpoints of the potential Connection (see
Section 5.1), the transport properties (see Section 12), and the
security parameters (see Section 5.3):
Preconnection := NewPreconnection(LocalEndpoint,
RemoteEndpoint,
TransportProperties,
SecurityParams)
The Local Endpoint MUST be specified if the Preconnection is used to
Listen() for incoming Connections, but is OPTIONAL if it is used to
Initiate() connections. The Remote Endpoint MUST be specified in the
Preconnection is used to Initiate() Connections, but is OPTIONAL if
it is used to Listen() for incoming Connections. The Local Endpoint
and the Remote Endpoint MUST both be specified if a peer-to-peer
Rendezvous is to occur based on the Preconnection.
Framers (see Section 7.6) and deframers (see Section 8.4), if
necessary, should be bound to the Preconnection during pre-
establishment.
5.1. Specifying Endpoints
The transport services API uses the Local Endpoint and Remote
Endpoint types to refer to the endpoints of a transport connection.
Subtypes of these represent various different types of endpoint
identifiers, such as IP addresses, DNS names, and interface names, as
well as port numbers and service names.
RemoteSpecifier := NewRemoteEndpoint()
RemoteSpecifier.WithHostname("example.com")
RemoteSpecifier.WithService("https")
RemoteSpecifier := NewRemoteEndpoint()
RemoteSpecifier.WithIPv6Address(2001:db8:4920:e29d:a420:7461:7073:0a)
RemoteSpecifier.WithPort(443)
RemoteSpecifier := NewRemoteEndpoint()
RemoteSpecifier.WithIPv4Address(192.0.2.21)
RemoteSpecifier.WithPort(443)
LocalSpecifier := NewLocalEndpoint()
LocalSpecifier.WithInterface("en0")
LocalSpecifier.WithPort(443)
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LocalSpecifier := NewLocalEndpoint()
LocalSpecifier.WithStunServer(address, port, credentials)
Implementations may also support additional endpoint representations
and provide a single NewEndpoint() call that takes different endpoint
representations.
Multiple endpoint identifiers can be specified for each Local
Endpoint and RemoteEndoint. For example, a Local Endpoint could be
configured with two interface names, or a Remote Endpoint could be
specified via both IPv4 and IPv6 addresses. These multiple
identifiers refer to the same transport endpoint.
The transport services API will resolve names internally, when the
Initiate(), Listen(), or Rendezvous() method is called establish a
Connection. The API does not need the application to resolve names,
and premature name resolution can damage performance by limiting the
scope for alternate path discovery during Connection establishment.
The Resolve() method is, however, provided to resolve a Local
Endpoint or a Remote Endpoint in cases where this is required, for
example with some Network Address Translator (NAT) traversal
protocols (see Section 6.3).
5.2. Specifying Transport Properties
A Preconnection Object holds properties reflecting the application's
requirements and preferences for the transport. These include
Selection Properties (Protocol and Path Selection Properties), as
well as Generic and Specific Protocol Properties for configuration of
the detailed operation of the selected Protocol Stacks.
The protocol(s) and path(s) selected as candidates during Connection
establishment are determined by a set of properties. Since there
could be paths over which some transport protocols are unable to
operate, or remote endpoints that support only specific network
addresses or transports, transport protocol selection is necessarily
tied to path selection. This may involve choosing between multiple
local interfaces that are connected to different access networks.
Internally, the transport system will first exclude all protocols and
paths that match a Prohibit, then exclude all protocols and paths
that do not match a Require, then sort candidates according to
Preferred properties, and then use Avoided properties as a
tiebreaker. In case of conflicts between Protocol and Path Selection
Properties, Path Selection Properties take precedence. For example,
if an application indicates a preference for a specific path, but
also a preference for a protocol not available on this path, the
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transport system will try the path first, so the Protocol Selection
Property might not have an effect.
All Transport Properties used in the pre-establishment phase are
collected in a TransportProperties Object that is passed to the
Preconnection Object.
TransportProperties := NewTransportProperties()
The Individual properties are then added to the TransportProperties
Object.
TransportProperties.Add(property, value)
Transport Properties of Preference Type, see Section 12.1.4, can use
special calls to add a Property with a specific preference level,
i.e, "TransportProperties.Add('some preference', avoid)" is
equivalent to "TransportProperties.Avoid('some preference')"
TransportProperties.Require(property)
TransportProperties.Prefer(property)
TransportProperties.Ignore(property)
TransportProperties.Avoid(property)
TransportProperties.Prohibit(property)
For an existing Connection, the Transport Properties can be queried
any time by using the following call on the Connection Object:
TransportProperties := Connection.GetTransportProperties()
Section 12 provides a list of Transport Properties.
Note that most properties are only considered for Connection
establishment and can not be changed after a Connection is
established; however, they can be queried. See Section 9.
A Connection gets its Transport Properties either by being explicitly
configured via a Preconnection, or by inheriting them from an
antecedent via cloning; see Section 6.4 for more.
5.3. Specifying Security Parameters and Callbacks
Most security parameters, e.g., TLS ciphersuites, local identity and
private key, etc., may be configured statically. Others are
dynamically configured during connection establishment. Thus, we
partition security parameters and callbacks based on their place in
the lifetime of connection establishment. Similar to Transport
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Properties, both parameters and callbacks are inherited during
cloning (see Section 6.4).
5.3.1. Pre-Connection Parameters
Common parameters such as TLS ciphersuites are known to
implementations. Clients should use common safe defaults for these
values whenever possible. However, as discussed in
[I-D.ietf-taps-transport-security], many transport security protocols
require specific security parameters and constraints from the client
at the time of configuration and actively during a handshake. These
configuration parameters are created as follows:
SecurityParameters := NewSecurityParameters()
Security configuration parameters and sample usage follow:
o Local identity and private keys: Used to perform private key
operations and prove one's identity to the Remote Endpoint.
(Note, if private keys are not available, e.g., since they are
stored in HSMs, handshake callbacks must be used. See below for
details.)
SecurityParameters.AddIdentity(identity)
SecurityParameters.AddPrivateKey(privateKey, publicKey)
o Supported algorithms: Used to restrict what parameters are used by
underlying transport security protocols. When not specified,
these algorithms should default to known and safe defaults for the
system. Parameters include: ciphersuites, supported groups, and
signature algorithms.
SecurityParameters.AddSupportedGroup(secp256k1)
SecurityParameters.AddCiphersuite(TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256)
SecurityParameters.AddSignatureAlgorithm(ed25519)
o Session cache management: Used to tune cache capacity, lifetime,
re-use, and eviction policies, e.g., LRU or FIFO. Constants and
policies for these interfaces are implementation-specific.
SecurityParameters.SetSessionCacheCapacity(MAX_CACHE_ELEMENTS)
SecurityParameters.SetSessionCacheLifetime(SECONDS_PER_DAY)
SecurityParameters.SetSessionCachePolicy(CachePolicyOneTimeUse)
o Pre-Shared Key import: Used to install pre-shared keying material
established out-of-band. Each pre-shared keying material is
associated with some identity that typically identifies its use or
has some protocol-specific meaning to the Remote Endpoint.
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SecurityParameters.AddPreSharedKey(key, identity)
5.3.2. Connection Establishment Callbacks
Security decisions, especially pertaining to trust, are not static.
Once configured, parameters may also be supplied during connection
establishment. These are best handled as client-provided callbacks.
Security handshake callbacks that may be invoked during connection
establishment include:
o Trust verification callback: Invoked when a Remote Endpoint's
trust must be validated before the handshake protocol can proceed.
TrustCallback := NewCallback({
// Handle trust, return the result
})
SecurityParameters.SetTrustVerificationCallback(trustCallback)
o Identity challenge callback: Invoked when a private key operation
is required, e.g., when local authentication is requested by a
remote.
ChallengeCallback := NewCallback({
// Handle challenge
})
SecurityParameters.SetIdentityChallengeCallback(challengeCallback)
6. Establishing Connections
Before a Connection can be used for data transfer, it must be
established. Establishment ends the pre-establishment phase; all
transport properties and cryptographic parameter specification must
be complete before establishment, as these will be used to select
candidate Paths and Protocol Stacks for the Connection.
Establishment may be active, using the Initiate() Action; passive,
using the Listen() Action; or simultaneous for peer-to-peer, using
the Rendezvous() Action. These Actions are described in the
subsections below.
6.1. Active Open: Initiate
Active open is the Action of establishing a Connection to a Remote
Endpoint presumed to be listening for incoming Connection requests.
Active open is used by clients in client-server interactions. Active
open is supported by this interface through the Initiate Action:
Connection := Preconnection.Initiate()
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Before calling Initiate, the caller must have populated a
Preconnection Object with a Remote Endpoint specifier, optionally a
Local Endpoint specifier (if not specified, the system will attempt
to determine a suitable Local Endpoint), as well as all properties
necessary for candidate selection. After calling Initiate, no
further properties may be added to the Preconnection. The Initiate()
call consumes the Preconnection and creates a Connection Object. A
Preconnection can only be initiated once.
Once Initiate is called, the candidate Protocol Stack(s) may cause
one or more candidate transport-layer connections to be created to
the specified remote endpoint. The caller may immediately begin
sending Messages on the Connection (see Section 7) after calling
Initate(); note that any idempotent data sent while the Connection is
being established may be sent multiple times or on multiple
candidates.
The following Events may be sent by the Connection after Initiate()
is called:
Connection -> Ready<>
The Ready Event occurs after Initiate has established a transport-
layer connection on at least one usable candidate Protocol Stack over
at least one candidate Path. No Receive Events (see Section 8) will
occur before the Ready Event for Connections established using
Initiate.
Connection -> InitiateError<>
An InitiateError occurs either when the set of transport properties
and cryptographic parameters cannot be fulfilled on a Connection for
initiation (e.g. the set of available Paths and/or Protocol Stacks
meeting the constraints is empty) or reconciled with the local and/or
remote endpoints; when the remote specifier cannot be resolved; or
when no transport-layer connection can be established to the remote
endpoint (e.g. because the remote endpoint is not accepting
connections, or the application is prohibited from opening a
Connection by the operating system).
6.2. Passive Open: Listen
Passive open is the Action of waiting for Connections from remote
endpoints, commonly used by servers in client-server interactions.
Passive open is supported by this interface through the Listen
Action:
Preconnection.Listen()
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Before calling Listen, the caller must have initialized the
Preconnection during the pre-establishment phase with a Local
Endpoint specifier, as well as all properties necessary for Protocol
Stack selection. A Remote Endpoint may optionally be specified, to
constrain what Connections are accepted. The Listen() Action
consumes the Preconnection. Once Listen() has been called, no
further properties may be added to the Preconnection, and no
subsequent establishment call may be made on the Preconnection.
Listening continues until the global context shuts down, or until the
Stop action is performed on the same Preconnection:
Preconnection.Stop()
After Stop() is called, the preconnection can be disposed of.
Preconnection -> ConnectionReceived<Connection>
The ConnectionReceived Event occurs when a Remote Endpoint has
established a transport-layer connection to this Preconnection (for
Connection-oriented transport protocols), or when the first Message
has been received from the Remote Endpoint (for Connectionless
protocols), 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.
Preconnection -> ListenError<>
A ListenError occurs either when the Preconnection cannot be
fulfilled for listening, when the Local Endpoint (or Remote Endpoint,
if specified) cannot be resolved, or when the application is
prohibited from listening by policy.
Preconnection -> Stopped<>
A Stopped event occurs after the Preconnection has stopped listening.
6.3. Peer-to-Peer Establishment: Rendezvous
Simultaneous peer-to-peer Connection establishment is supported by
the Rendezvous() Action:
Preconnection.Rendezvous()
The Preconnection Object must be specified with both a Local Endpoint
and a Remote Endpoint, and also the transport properties and security
parameters needed for Protocol Stack selection.
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The Rendezvous() Action causes the Preconnection to listen on the
Local Endpoint for an incoming Connection from the Remote Endpoint,
while simultaneously trying to establish a Connection from the Local
Endpoint to the Remote Endpoint. This corresponds to a TCP
simultaneous open, for example.
The Rendezvous() Action consumes the Preconnection. Once
Rendezvous() has been called, no further properties may be added to
the Preconnection, and no subsequent establishment call may be made
on the Preconnection.
Preconnection -> RendezvousDone<Connection>
The RendezvousDone<> Event occurs when a Connection is established
with the Remote Endpoint. For Connection-oriented transports, this
occurs when the transport-layer connection is established; for
Connectionless transports, it occurs when the first Message is
received from the Remote Endpoint. The resulting Connection is
contained within the RendezvousDone<> Event, and is ready to use as
soon as it is passed to the application via the Event.
Preconnection -> RendezvousError<msgRef, error>
An RendezvousError occurs either when the Preconnection cannot be
fulfilled for listening, when the Local Endpoint or Remote Endpoint
cannot be resolved, when no transport-layer connection can be
established to the Remote Endpoint, or when the application is
prohibited from rendezvous by policy.
When using some NAT traversal protocols, e.g., Interactive
Connectivity Establishment (ICE) [RFC5245], it is expected that the
Local Endpoint will be configured with some method of discovering NAT
bindings, e.g., a Session Traversal Utilities for NAT (STUN) server.
In this case, the Local Endpoint may resolve to a mixture of local
and server reflexive addresses. The Resolve() method on the
Preconnection can be used to discover these bindings:
PreconnectionBindings := Preconnection.Resolve()
The Resolve() call returns a list of Preconnection Objects, that
represent the concrete addresses, local and server reflexive, on
which a Rendezvous() for the Preconnection will listen for incoming
Connections. This list can be passed to a peer via a signalling
protocol, such as SIP [RFC3261] or WebRTC [RFC7478], to configure the
remote.
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6.4. Connection Groups
Groups of Connections can be created using the Clone Action:
Connection := Connection.Clone()
Calling Clone on a Connection yields a group of two Connections: the
parent Connection on which Clone was called, and the resulting clone
Connection. These connections are "entangled" with each other, and
become part of a Connection group. Calling Clone on any of these two
Connections adds a third Connection to the group, and so on.
Connections in a Connection Group share all their properties, and
changing the properties on one Connection in the group changes the
property for all others.
If the underlying Protocol Stack does not support cloning, or cannot
create a new stream on the given Connection, then attempts to clone a
connection will result in a CloneError:
Connection -> CloneError<>
There is only one Protocol Property that is not entangled: niceness
is kept as a separate per-Connection Property for individual
Connections in the group. Niceness works as in Section 12.3.21: when
allocating available network capacity among Connections in a
Connection Group, sends on Connections with higher Niceness values
will be prioritized over sends on Connections with lower Niceness
values. An ideal transport system implementation would assign the
Connection the capacity share (M-N) x C / M, where N is the
Connection's Niceness value, M is the maximum Niceness value used by
all Connections in the group and C is the total available capacity.
However, the niceness setting is purely advisory, and no guarantees
are given about the way capacity is shared. Each implementation is
free to implement a way it shares capacity that it sees fit.
7. Sending Data
Once a Connection has been established, it can be used for sending
data. Data is sent in terms of Messages, which allow the application
to communicate the boundaries of the data being transferred. By
default, Send enqueues a complete Message, and takes optional per-
Message properties (see Section 7.1). All Send actions are
asynchronous, and deliver events (see Section 7.2). Sending partial
Messages for streaming large data is also supported (see
Section 7.4).
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7.1. Basic Sending
The most basic form of sending on a connection involves enqueuing a
single Data block as a complete Message, with default Message
Properties. Message data is created as an array of octets, and the
resulting object contains both the byte array and the length of the
array.
messageData := "hello".octets()
Connection.Send(messageData)
The interpretation of a Message to be sent is dependent on the
implementation, and on the constraints on the Protocol Stacks implied
by the Connection's transport properties. For example, a Message may
be a single datagram for UDP Connections; or an HTTP Request for HTTP
Connections.
Some transport protocols can deliver arbitrarily sized Messages, but
other protocols constrain the maximum Message size. Applications can
query the protocol property Maximum Message Size on Send to determine
the maximum size allowed for a single Message. If a Message is too
large to fit in the Maximum Message Size for the Connection, the Send
will fail with a SendError event (Section 7.2.3). For example, it is
invalid to send a Message over a UDP connection that is larger than
the available datagram sending size.
If Send is called on a Connection which has not yet been established,
an Initiate Action will be implicitly performed simultaneously with
the Send. Together with the Idempotent property (see
Section 12.3.9), this can be used to send data during establishment
for 0-RTT session resumption on Protocol Stacks that support it.
7.2. Send Events
Like all Actions in this interface, the Send Action is asynchronous.
There are several events that can be delivered in response to Sending
a Message.
Note that if partial Sends are used (Section 7.4), there will 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
that Message are outstanding, there will be two Expired events
delivered.
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7.2.1. Sent
Connection -> Sent<msgRef>
The Sent Event occurs when a previous Send Action has completed,
i.e., when the data derived from the Message has been passed down or
through the underlying Protocol Stack and is no longer the
responsibility of the implementation of this interface. The exact
disposition of the Message (i.e., whether it has actually been
transmitted, moved into a buffer on the network interface, moved into
a kernel buffer, and so on) when the Sent Event occurs is
implementation-specific. The Sent Event contains an implementation-
specific reference to the Message to which it applies.
Sent Events allow an application to obtain an understanding of 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
created more buffer inside the transport system than an application
that only issues a Send after this Event fires.
7.2.2. Expired
Connection -> Expired<msgRef>
The Expired Event occurs when a previous Send Action expired before
completion; i.e. when the Message was not sent before its Lifetime
(see Section 12.3.28) expired. This is separate from SendError, as
it is an expected behavior for partially reliable transports. The
Expired Event contains an implementation-specific reference to the
Message to which it applies.
7.2.3. SendError
Connection -> SendError<msgRef>
A SendError occurs when a Message could not be sent due to an error
condition: an attempt to send a Message which is too large for the
system and Protocol Stack to handle, some failure of the underlying
Protocol Stack, or a set of Message Properties not consistent with
the Connection's transport properties. The SendError contains an
implementation-specific reference to the Message to which it applies.
7.3. Message Context Parameters
Applications may need to annotate the Messages they send with extra
information to control how data is scheduled and processed by the
transport protocols in the Connection. A MessageContext object
contains parameters for sending Messages, and can be passed to the
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Send Action. Some of these parameters are properties as defined in
Section 12. Note that these properties are per-Message, not per-Send
if partial Messages are sent (Section 7.4). All data blocks
associated with a single Message share properties. For 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.
messageData := "hello".octets()
messageContext := NewMessageContext()
messageContext.add(parameter, value)
Connection.Send(messageData, messageContext)
The simpler form of Send that does not take any MessageContext is
equivalent to passing a default MessageContext with not values added.
Message Properties share a single namespace with Transport Properties
(see Section 12). This allows the specification of per-Connection
Protocol Properties that can be overridden on a per-Message basis.
If an application wants to override Message Properties for a specific
message, it can acquire an empty messageContext Object and add all
desired Message Properties to that Object. It can then reuse the
same messageContext Object for sending multiple Messages with the
same properties.
Parameters may be added to a messageContext object only before the
context is used for sending. Once a messageContext has been used
with a Send call, modifying any of its parameters is invalid.
Message Properties may be inconsistent with the properties of the
Protocol Stacks underlying the Connection on which a given Message is
sent. For example, a Connection must provide reliability to allow
setting an infinitie value for the lifetime property of a Message.
Sending a Message with Message Properties inconsistent with the
Selection Properties of the Connection yields an error.
The following Message Context Parameters are supported:
[TODO: De-Duplicate with Properties in Section 12, find consensus on
which Section to put them]
7.3.1. Lifetime
[TODO: De-Duplicate with Section 12.3.28]
Lifetime specifies how long a particular Message can wait to be sent
to the remote endpoint before it is irrelevant and no longer needs to
be (re-)transmitted. When a Message's Lifetime is infinite, it must
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be transmitted reliably. The type and units of Lifetime are
implementation-specific.
7.3.2. Niceness
[TODO: De-Duplicate with Section 12.3.21]
Niceness is a numeric (non-negative) value that represents an
unbounded hierarchy of priorities of Messages, relative to other
Messages sent over the same Connection and/or Connection Group (see
Section 6.4). A Message with Niceness 0 will yield to a Message with
Niceness 1, which will yield to a Message with Niceness 2, and so on.
Niceness may be used as a sender-side scheduling construct only, or
be used to specify priorities on the wire for Protocol Stacks
supporting prioritization.
This encoding of the priority has a convenient property that the
priority increases as both Niceness and Lifetime decrease.
7.3.3. Ordered
[TODO: De-Duplicate with Section 12.3.6]
Ordered is a boolean property. If true, this Message should be
delivered after the last Message passed to the same Connection via
the Send Action; if false, this Message may be delivered out of
order.
7.3.4. Idempotent
[TODO: De-Duplicate with Section 12.3.9]
Idempotent is a boolean property. If true, the application-layer
entity in the Message is safe to send to the remote endpoint more
than once for a single Send Action. It is used to mark data safe for
certain 0-RTT establishment techniques, where retransmission of the
0-RTT data may cause the remote application to receive the Message
multiple times.
7.3.5. Final
[TODO: De-Duplicate with Section 12.3.1]
Final is a boolean property. If true, this Message is the last one
that the application will send on a Connection. This allows
underlying protocols to indicate to the Remote Endpoint that the
Connection has been effectively closed in the sending direction. For
example, TCP-based Connections can send a FIN once a Message marked
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as Final has been completely sent, indicated by marking endOfMessage.
Protocols that do not support signalling the end of a Connection in a
given direction will ignore this property.
Note that a Final Message must always be sorted to the end of a list
of Messages. The Final property overrides Niceness and any other
property that would re-order Messages. If another Message is sent
after a Message marked as Final has already been sent on a
Connection, the new Message will report an error.
7.3.6. Corruption Protection Length
[TODO: De-Duplicate with Section 12.3.15]
This numeric property specifies the length of the section of the
Message, starting from byte 0, that the application assumes will be
received without corruption due to lower layer errors. It is used to
specify options for simple integrity protection via checksums. By
default, the entire Message is protected by checksum. A value of 0
means that no checksum is required, and a special value (e.g. -1) can
be used to indicate the default. Only full coverage is guaranteed,
any other requests are advisory.
7.3.7. Transmission Profile
[TODO: De-Duplicate with Section 12.3.19]
This enumerated property specifies the application's preferred
tradeoffs for sending this Message; it is a per-Message override of
the Capacity Profile protocol and path selection property (see
Section 12.3.19).
The following values are valid for Transmission Profile:
Default: No special optimizations of the tradeoff between delay,
delay variation, and bandwidth efficiency should be made when
sending this message.
Low Latency: Response time (latency) should be optimized at the
expense of efficiently using the available capacity when sending
this message. This can be used by the system to disable the
coalescing of multiple small Messages into larger packets (Nagle's
algorithm); to prefer immediate acknowledgment from the peer
endpoint when supported by the underlying transport; to signal a
preference for lower-latency, higher-loss treatment; and so on.
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7.4. Partial Sends
It is not always possible for an application to send all data
associated with a Message in a single Send Action. The Message data
may be too large for the application to hold in memory at one time,
or the length of the Message may be unknown or unbounded.
Partial Message sending is supported by passing an endOfMessage
boolean parameter to the Send Action. This value is always true by
default, and the simpler forms of send are equivalent to passing true
for endOfMessage.
The following example sends a Message in two separate calls to Send.
messageContext := NewMessageContext()
messageContext.add(parameter, value)
messageData := "hel".octets()
endOfMessage := false
Connection.Send(messageData, messageContext, endOfMessage)
messageData := "lo".octets()
endOfMessage := true
Connection.Send(messageData, messageContext, endOfMessage)
All messageData sent with the same messageContext object will be
treated as belonging to the same Message, and will constitute an in-
order series until the endOfMessage is marked. Once the end of the
Message is marked, the messageContext object may be re-used as a new
Message with identical parameters.
7.5. Batching Sends
In order to reduce the overhead of sending multiple small Messages on
a Connection, the application may want to batch several Send actions
together. This provides a hint to the system that the sending of
these Messages should be coalesced when possible, and that sending
any of the batched Messages may be delayed until the last Message in
the batch is enqueued.
Connection.Batch(
Connection.Send(messageData)
Connection.Send(messageData)
)
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7.6. Sender-side Framing
Sender-side framing allows a caller to provide the interface with a
function that takes a Message of an appropriate application-layer
type and returns an array of octets, the on-the-wire representation
of the Message to be handed down to the Protocol Stack. It consists
of a Framer Object with a single Action, Frame. Since the Framer
depends on the protocol used at the application layer, it is bound to
the Preconnection during the pre-establishment phase:
Preconnection.FrameWith(Framer)
OctetArray := Framer.Frame(messageData)
Sender-side framing is a convenience feature of the interface, for
parity with receiver-side framing (see Section 8.4).
8. Receiving Data
Once a Connection is established, it can be used for receiving data.
As with sending, data is received in terms of Messages. Receiving is
an asynchronous operation, in which each call to Receive enqueues a
request to receive new data from the connection. Once data has been
received, or an error is encountered, an event will be delivered to
complete the Receive request (see Section 8.2).
As with sending, the type of the Message to be passed is dependent on
the implementation, and on the constraints on the Protocol Stacks
implied by the Connection's transport parameters.
8.1. Enqueuing Receives
Receive takes two parameters to specify the length of data that an
application is willing to receive, both of which are optional and
have default values if not specified.
Connection.Receive(minIncompleteLength, maxLength)
By default, Receive will try to deliver complete Messages in a single
event (Section 8.2.1).
The application can set a minIncompleteLength value to indicates the
smallest partial Message data size in bytes that should be delivered
in response to this Receive. By default, this value is infinite,
which means that only complete Messages should be delivered. If this
value is set to some smaller value, the associated receive event will
be triggered only when at least that many bytes are available, or the
Message is complete with fewer bytes, or the system needs to free up
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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
bytes the application is currently prepared to receive. The default
value for maxLength is infinite. If an incoming Message is 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
ReceivedPartial events (Section 8.2.2).
Note that maxLength does not guarantee that the application will
receive that many bytes if they are available; the interface may
return ReceivedPartial events with less data than maxLength according
to implementation constraints.
8.2. Receive Events
Each call to Receive will be paired with a single Receive Event,
which can be a success or an error. This allows an application to
provide backpressure to the transport stack when it is temporarily
not ready to receive messages.
8.2.1. Received
Connection -> Received<messageData, messageContext>
A Received event indicates the delivery of a complete Message. It
contains two objects, the received bytes as messageData, and the
metadata and properties of the received Message as messageContext.
See {#receive-context} for details about the received context.
The messageData object provides access to the bytes that were
received for this Message, along with the length of the byte array.
See Section 8.4 for handling Message framing in situations where the
Protocol Stack provides octet-stream transport only.
8.2.2. ReceivedPartial
Connection -> ReceivedPartial<messageData, messageContext, endOfMessage>
If a complete Message cannot be delivered in one event, one part of
the Message may be delivered with a ReceivedPartial event. In order
to continue to receive more of the same Message, the application must
invoke Receive again.
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Multiple invocations of ReceivedPartial deliver data for the same
Message by passing the same messageContext, until the endOfMessage
flag is delivered. All partial blocks of a single Message are
delivered in order without gaps. This event does not support
delivering discontiguous partial Messages.
If the minIncompleteLength in the Receive request was set to be
infinite (indicating a request to receive only complete Messages),
the ReceivedPartial event may still be delivered if one of the
following conditions is true:
o the underlying Protocol Stack supports message boundary
preservation, and the size of the Message is larger than the
buffers available for a single message;
o the underlying Protocol Stack does not support message boundary
preservation, and the deframer (see Section 8.4) cannot determine
the end of the message using the buffer space it has available; or
o the underlying Protocol Stack does not support message boundary
preservation, and no deframer was supplied by the application
Note that in the absence of message boundary preservation or
deframing, all bytes received on the Connection will be represented
as one large message of indeterminate length.
8.2.3. ReceiveError
Connection -> ReceiveError<messageContext>
A ReceiveError occurs when data is received by the underlying
Protocol Stack that cannot be fully retrieved or deframed, or when
some other indication is received that reception has failed. Such
conditions that irrevocably lead the the termination of the
Connection are signaled using ConnectionError instead (see
Section 10).
The ReceiveError event passes an optional associated messageContext.
This may indicate that a Message that was being partially received
previously, but had not completed, encountered and error and will not
be completed.
8.3. Message Receive Context
Each Received Message Context may contain metadata from protocols in
the Protocol Stack; which metadata is available is Protocol Stack
dependent. The following metadata values are supported:
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8.3.1. ECN
When available, Message metadata carries the value of the Explicit
Congestion Notification (ECN) field. This information can be used
for logging and debugging purposes, and for building applications
which need access to information about the transport internals for
their own operation.
8.3.2. Early Data
In some cases it may be valuable to know whether data was read as
part of early data streams. This is useful if applications need to
treat early data separately, e.g., if early data has different
security properties than data sent after connection establishment.
In the case of TLS 1.3, client early data can be replayed maliciously
(see [I-D.ietf-tls-tls13]). Thus, receivers may wish to perform
additional checks for early data to ensure it is idempotent or not
replayed. If TLS 1.3 is available and the recipient Message was sent
as part of early data, the corresponding metadata carries a flag
indicating as such. If early data is enabled, applications should
check this metadata field for Messages received during connection
establishment and respond accordingly.
8.3.3. Receiving Final Messages
The Received Message Context can indicate whether or not this Message
is the Final Message on a Connection. For any Message that is marked
as Final, the application can assume that there will be no more
Messages received on the Connection once the Message has been
completely delivered. This corresponds to the Final property that
may be marked on a sent Message Section 12.3.1.
Some transport protocols and peers may not support signaling of the
Final property. Applications therefore should not rely on receiving
a Message marked Final to know that the other endpoint is done
sending on a connection.
Any calls to Receive once the Final Message has been delivered will
result in errors.
8.4. Receiver-side De-framing over Stream Protocols
The Receive Event is intended to be fired once per application-layer
Message sent by the remote endpoint; i.e., it is a desired property
of this interface that a Send at one end of a Connection maps to
exactly one Receive on the other end. This is possible with Protocol
Stacks that provide message boundary preservation, but is not the
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case over Protocol Stacks that provide a simple octet stream
transport.
For preserving message boundaries over stream transports, this
interface provides receiver-side de-framing. This facility is based
on the observation that, since many of our current application
protocols evolved over TCP, which does not provide message boundary
preservation, and since many of these protocols require message
boundaries to function, each application layer protocol has defined
its own framing. A Deframer allows an application to push this de-
framing down into the interface, in order to transform an octet
stream into a sequence of Messages.
Concretely, receiver-side de-framing allows a caller to provide the
interface with a function that takes an octet stream, as provided by
the underlying Protocol Stack, reads and returns a single Message of
an appropriate type for the application and platform, and leaves the
octet stream at the start of the next Message to deframe. It
consists of a Deframer Object with a single Action, Deframe. Since
the Deframer depends on the protocol used at the application layer,
it is bound to the Preconnection during the pre-establishment phase:
Preconnection.DeframeWith(Deframer)
{messageData} := Deframer.Deframe(OctetStream, ...)
9. Setting and Querying Connection Properties
At any point, the application can query Connection Properties. It
can also set per-connection Protocol Properties.
ConnectionProperties := Connection.GetProperties()
Connection.SetProperty(property, value)
Depending on the status of the connection, the queried Connection
Properties will include different information:
o The status of the connection, which can be one of the following:
Establishing, Established, Closing, or Closed.
o Whether the connection can be used to send data. A connection can
not be used for sending if the connection was created with the
Selection Property "Unidirectional Receive" or if a Message marked
as "Final" was sent over this connection, see Section 12.3.1.
o Whether the connection can be used to receive data. A connection
can not be used for reading if the connection was created with the
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Selection Property "Unidirectional: Send" or if a Message marked
as "Final" was received, see Section 8.3.3. The latter is only
supported by certain transport protocols, e.g., by TCP as half-
closed connection.
o For Connections that are Establishing: Transport Properties that
the application specified on the Preconnection, see Section 5.2.
Selection Properties of a Connection can only be queried, not set.
o For Connections that are Established, Closing, or Closed (TODO:
double-check if closed belongs here): Transport Properties of the
actual protocols that were selected and instantiated. These
features correspond to the properties given in Section 12 and
include Selection Properties and Protocol Properties.
* Selection Properties indicate whether or not the Connection has
or offers a certain Selection Property. Note that the actually
instantiated protocol stack may not match all Protocol
Selection Properties that the application specified on the
Preconnection. For example, a certain Protocol Selection
Property that an application specified as Preferred may not
actually be present in the chosen protocol stack because none
of the currently available transport protocols had this
feature. Selection Properties of a Connection can only be
queried.
* Protocol Properties of the protocol stack in use (see
Section 12.2.2 below). These can be queried and set. Certain
specific Procotol Properties may be read-only, on a protocol-
and property-specific basis.
o For Connections that are Established, properties of the path(s) in
use. These properties can be derived from the local provisioning
domain [RFC7556], measurements by the Protocol Stack, or other
sources. They can only be queried.
10. Connection Termination
Close terminates a Connection after satisfying all the requirements
that were specified regarding the delivery of Messages that the
application has already given to the transport system. For example,
if reliable delivery was requested for a Message handed over before
calling Close, the transport system will ensure that this Message is
indeed delivered. If the Remote Endpoint still has data to send, it
cannot be received after this call.
Connection.Close()
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The Closed Event can inform the application that the Remote Endpoint
has closed the Connection; however, there is no guarantee that a
remote close will be signaled.
Connection -> Closed<>
Abort terminates a Connection without delivering remaining data:
Connection.Abort()
A ConnectionError can inform the application that the other side has
aborted the Connection; however, there is no guarantee that an abort
will be signaled:
Connection -> ConnectionError<>
A SoftError can inform the application about the receipt of an ICMP
error message that does not force termination of the connection, if
the underlying protocol stack supports access to soft errors;
however, even if the underlying stack supports it, there is no
guarantee that a soft error will be signaled.
Connection -> SoftError<>
11. Ordering of Operations and Events
As this interface is designed to be independent of concurrency model,
the details of how exactly actions are handled, and on which threads/
callbacks events are dispatched, are implementation dependent.
However, the interface does provide the following guarantees about
the ordering of operations:
o Received<> will never occur on a Connection before a Ready<> event
on that Connection, or a ConnectionReceived<> or RendezvousDone<>
containing that Connection.
o No events will occur on a Connection after a Closed<> event, an
InitiateError<> or ConnectionError<> on that connection. To
ensure this ordering, Closed<> will not occur on a Connection
while other events on the Connection are still locally outstanding
(i.e., known to the interface and waiting to be dealt with by the
application). ConnectionError<> may occur after Closed<>, but the
interface must gracefully handle the application ignoring these
errors.
o 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
network interface, depending on implementation).
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12. Transport Properties
Transport Properties allow an application to control and introspect
most aspects of the transport system and transport protocols.
Properties are structured in two ways:
o By how they influence the transport system, which leads to a
classification into "Selection Properties", "Protocol Properties",
"Control Properties" and "Intents".
o By the object they can be applied to: Preconnections, see
Section 5.2, Connections, see Section 9, and Messages, see
Section 7.3.
Because some properties can be applied or queried on multiple
objects, all Transport Properties are organized within a single
namespace.
Note that it is possible for a set of specified Transport Properties
to be internally inconsistent, or to be inconsistent with the later
use of the API by the application. Application developers can reduce
inconsistency by only using the most stringent preference levels when
failure to meet the property would break the application's
functionality. For example, it can set the Selection Property
"Reliable Data Transfer", which is a core assumption of many
application protocols, as Required. Implementations of this
interface should also raise any detected errors in configuration as
early as possible, to help ensure that inconsistencies are caught
early in the development process.
12.1. Transport Property Types
Each Transport Property takes a value of a property-specific type.
12.1.1. Boolean
A boolean is a data type that can be either "true" or "false".
Boolean transport properties should only be used for properties that
can not be used in an optional way or to query the state of the
transport implementation. For optional features, especially in
Selection Properties, the usage of the Preference type (see
Section 12.1.4) is preferred.
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12.1.2. Enumeration
Enumeration types are used for transport properties that can take one
value out of a limited set of choices. The representation is
implementation dependent.
12.1.3. Integer
Integer types are used to represent integer numbers. The
representation is implementation dependent.
12.1.4. Preference
The Preference type is used in most Selection properties on a
Preconnection object to constrain Path Selection and Protocol
Selection. It is a specific instance of the "Enum" type and has five
different preference levels:
+------------+------------------------------------------------------+
| Preference | Effect |
+------------+------------------------------------------------------+
| Require | Select only protocols/paths providing the property, |
| | fail otherwise |
| | |
| Prefer | Prefer protocols/paths providing the property, |
| | proceed otherwise |
| | |
| Ignore | Cancel any default preference for this property |
| | |
| Avoid | Prefer protocols/paths not providing the property, |
| | proceed otherwise |
| | |
| Prohibit | Select only protocols/paths not providing the |
| | property, fail otherwise |
+------------+------------------------------------------------------+
When used on a Connection, this type becomes a (read-only) Boolean
representing whether the selected transport supports the requested
feature.
12.2. Transport Property Classification
Note: This section is subject to WG discussion on IETF-102.
Transport Properties - whether they apply to connections,
preconnections, or messages - differ in the way they affect the
transport system and protocols exposed through the transport system.
The classification proposed below emphasizes two aspects of how
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properties affect the transport system, so applications know what to
expect:
o Whether properties affect protocols exposed through the transport
system (Protocol Properties) or the transport system itself
(Control Properties)
o Whether properties have a clearly defined behavior that is likely
to be invariant across implementations and environments (Protocol
Properties and Control Properties) or whether the properties are
interpreted by the transport system to provide a best effort
service that matches the applications needs as well as possible
(Intents).
Note: in I-D.ietf-taps-interface-00, we had a classification into
Connection Properties and Message Properties, whereby Connection
Properties where itself were sub-classified in Protocol-Selection,
Path-Selection and Protocol properties.
The classification in this version of the draft emphasizes the way
the property affects the transport system and protocols. It
treats the aspect of whether properties are used on a connection,
preconnection or message as an orthogonal dimension of
classification.
The "Message Properties" from I-D.ietf-taps-interface-00 therefore
have been split into "Protocol Properties" - emphasizing that they
affect the protocol configurations - and "Control Properties" -
emphasizing that they control the local transport system itself.
12.2.1. Selection Properties
Selection Properties influence protocol and path selection. Their
value usually is or includes a Preference that constrains (in case of
Require or Prohibit) or influences (Prefer, Ignore, Avoid) the
selection of transport protocols and paths used.
An implementation of this interface must provide sensible defaults
for Selection Properties. The defaults given for each property below
represent a configuration that can be implemented over TCP. An
alternate set of default Protocol Selection Properties would
represent a configuration that can be implemented over UDP.
Protocol Selection Properties can only be set on Preconnections, see
Section 5.2. Path Selection Properties are usually used on
Preconnections, but might also be used on messages to assist per-
message path selection for multipath aware protocols.
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12.2.2. Protocol Properties
Protocol Properties represent the configuration of the selected
Protocol Stacks backing a Connection. Some properties apply
generically across multiple transport protocols, while other
properties only apply to specific protocols. Generic properties will
be passed to the selected candidate Protocol Stack(s) to configure
them before candidate Connection establishment. The default settings
of these properties will vary based on the specific protocols being
used and the system's configuration.
Most Protocol Properties can be set on a Preconnection during pre-
establishment to preconfigure Protocol Stacks during establishment.
In order to specify Specific Protocol Properties, Transport System
implementations may offer applications to attach a set of options to
the Preconnection Object, associated with a specific protocol. For
example, an application could specify a set of TCP Options to use if
and only if TCP is selected by the system. Such properties must not
be assumed to apply across different protocols. Attempts to set
specific protocol properties on a protocol stack not containing that
specific protocol are simply ignored, and do not raise an error.
Note that many protocol properties have a corresponding selection
property which asks for a protocol providing a specific transport
feature that is controlled by the protocol property.
12.2.3. Control Properties
[TODO: Discuss]
Control properties manage the local transport system behavior or
request state changes in the local transport system. Depending on
the protocols used, setting these properties might also influence the
protocol state machine. See Section 12.3.1 for an example.
12.2.4. Intents
[TODO: Discuss]
Intents are hints to the transport system that do not directly map to
a single protocol/transport feature or behavior of the transport
system, but express a presumed application behavior or generic
application needs.
The application can expect the transport system to take appropriate
actions involving protocol selection, path selection and, setting of
protocol flags. For example, if an application sets the "Capacity
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Profile" to "bulk" on a Preconnection, this will likely influence
path selection, DSCP flags in the IP header as well as niceness for
multi-streaming connections. When using Intents, the application
must not expect consistent behavior across different environments,
implementations or versions of the same implementation.
12.3. Mandatory Transport Properties
The following properties are mandatory to implement in a transport
system:
12.3.1. Final
See Section 7.3.5.
[TODO: Decide whether this is a property or a parameter]
12.3.2. Reliable Data Transfer (Connection)
Classification: Selection Property
Type: Preference
Applicability: Preconnection, Connection (read only)
This property specifies whether the application wishes to use a
transport protocol that ensures that all data is received on the
other side without corruption. This also entails being notified when
a Connection is closed or aborted. The default is to enable Reliable
Data Transfer.
12.3.3. Configure per-Message reliability
Classification: Selection Property
Type: Preference
Applicability: Preconnection, Connection (read only)
This property specifies whether an application considers it useful to
indicate its reliability requirements on a per-Message basis. This
property applies to Connections and Connection Groups. The default
is to not have this option.
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12.3.4. Reliable Data Transfer (Message)
Classification: Protocol Property (Generic)
Type: Boolean
Applicability: Message
This property specifies that a message should be sent in such a way
that the transport protocol ensures all data is received on the other
side without corruption. Changing the 'Reliable Data Transfer'
property on Messages is only possible if the transport protocol
supports partial reliability (see Section 12.3.3). Therefore, for
protocols that always transfer data reliably, this property is always
true and for protocols that always transfer data unreliably, this
flag is always false. Changing it may generate an error.
12.3.5. Preservation of data ordering
Classification: Selection Property
Type: Preference
Applicability: Preconnection, Connection (read only)
This property specifies whether the application wishes to use a
transport protocol that ensures that data is received by the
application on the other end in the same order as it was sent. The
default is to preserve data ordering.
12.3.6. Ordered
Classification: Protocol Property (Generic)
Type: Boolean
Applicability: Message
This property specifies that a Message should be delivered to the
other side after the previous Message which was passed to the same
Connection via the Send Action. It us used for protocols that
support preservation of data ordering, see Section 12.3.5, but allow
out-of-order delivery for certain messages.
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12.3.7. Direction of communication
Classification: Selection Property, Control Property [TODO: Discuss]
Type: Enumeration
Applicability: Preconnection, Connection (read only)
This property specifies whether an application wants to use the
connection for sending and/or receiving data. Possible values are:
Bidirectional (default): The connection must support sending and
receiving data
unidirectional send: The connection must support sending data.
unidirectional receive: The connection must support receiving data
In case a unidirectional connection is requested, but unidirectional
connections are not supported by the transport protocol, the system
should fall back to bidirectional transport.
12.3.8. Use 0-RTT session establishment with an idempotent Message
Classification: Selection Property
Type: Preference
Applicability: Preconnection, Connection (read only)
This property specifies whether an application would like to supply a
Message to the transport protocol before Connection establishment,
which will then be reliably transferred to the other side before or
during Connection establishment, potentially multiple times. See
also Section 12.3.9. The default is to not have this option.
12.3.9. Idempotent
Classification: Control Property
Type: Boolean
Applicability: Message
This property specifies that a Message is safe to send to the remote
endpoint more than once for a single Send Action. It is used to mark
data safe for certain 0-RTT establishment techniques, where
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retransmission of the 0-RTT data may cause the remote application to
receive the Message multiple times.
The application can query the maximum size of a message that can be
sent idempotent, see Section 12.3.24.
12.3.10. Multistream Connections in Group
Classification: Selection Property
Type: Preference
Applicability: Preconnection, Connection (read only)
This property specifies that the application would prefer multiple
Connections within a Connection Group to be provided by streams of a
single underlying transport connection where possible. The default
is to not have this option.
12.3.11. Notification of excessive retransmissions
Classification: Control Property [TODO: Discuss]
Type: Boolean
Applicability: Preconnection, Connection
This property specifies whether an application considers it useful to
be informed in case sent data was retransmitted more often than a
certain threshold. When set to true, the effect is twofold: The
application may receive events in case excessive retransmissions. In
addition, the transport system considers this as a preference to use
transports stacks that can provide this notification. This is not a
strict requirement. If set to false, no notification of excessive
retransmissions will be sent and this transport feature is ignored
for protocol selection.
The default is to have this option.
12.3.12. Retransmission threshold before excessive retransmission
notification
Classification: Control Property [TODO: Discuss]
Type: Integer
Applicability: Preconnection, Connection
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This property specifies after how many retransmissions to inform the
application about "Excessive Retransmissions".
12.3.13. Notification of ICMP soft error message arrival
Classification: Control Property [TODO: Discuss]
Type: Boolean
Applicability: Preconnection, Connection
This property specifies whether an application considers it useful to
be informed when an ICMP error message arrives that does not force
termination of a connection. When set to true, received ICMP errors
will be available as SoftErrors. Note that even if a protocol
supporting this property is selected, not all ICMP errors will
necessarily be delivered, so applications cannot rely on receiving
them. Setting this option also implies a preference to prefer
transports stacks that can provide this notification. If not set, no
events will be sent for ICMP soft error message and this transport
feature is ignored for protocol selection.
This property applies to Connections and Connection Groups. The
default is not to have this option.
12.3.14. Control checksum coverage on sending or receiving
Classification: Selection Property
Type: Preference
Applicability: Preconnection, Connection (read only)
This property specifies whether the application considers it useful
to enable, disable, or configure a checksum when sending a Message,
or configure whether to require a checksum or not when receiving.
The default is full checksum coverage without the option to configure
it, and requiring a checksum when receiving.
12.3.15. Corruption Protection Length
Classification: Protocol Property (Generic)
Type: Integer
Applicability: Message
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This numeric property specifies the length of the section of the
Message, starting from byte 0, that the application assumes will be
received without corruption due to lower layer errors. It is used to
specify options for simple integrity protection via checksums. By
default, the entire Message is protected by the checksum. A value of
0 means that no checksum is required, and a special value (e.g. -1)
can be used to indicate the default. Only full coverage is
guaranteed, any other requests are advisory.
12.3.16. Required minimum coverage of the checksum for receiving
Classification: Protocol Property (Generic)
Type: Integer
Applicability: Connection
This property specifies the part of the received data that needs to
be covered by a checksum. It is given in Bytes. A value of 0 means
that no checksum is required, and a special value (e.g., -1)
indicates full checksum coverage.
12.3.17. Interface Instance or Type
Classification: Selection Property
Type: Tuple (Enumeration, Preference)
Applicability: Preconnection, Connection (read only)
This property allows the application to select which specific network
interfaces or categories of interfaces it wants to "Require",
"Prohibit", "Prefer", or "Avoid".
If a system supports discovery of specific interface identifiers,
such as "en0" or "eth0" on Unix-style systems, an implemention should
allow using these identifiers to define path preferences. Note that
marking a specific interface as "Required" strictly limits path
selection to a single interface, and leads to less flexible and
resilient connection establishment.
The set of valid interface types is implementation- and system-
specific. For example, on a mobile device, there may be "Wi-Fi" and
"Cellular" interface types available; whereas on a desktop computer,
there may be "Wi-Fi" and "Wired Ethernet" interface types available.
Implementations should provide all types that are supported on some
system to all systems, in order to allow applications to write
generic code. For example, if a single implementation is used on
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both mobile devices and desktop devices, it should define the
"Cellular" interface type for both systems, since an application may
want to always "Prohibit Cellular". Note that marking a specific
interface type as "Required" limits path selection to a small set of
interfaces, and leads to less flexible and resilient connection
establishment.
The set of interface types is expected to change over time as new
access technologies become available.
Interface types should not be treated as a proxy for properties of
interfaces such as metered or unmetered network access. If an
application needs to prohibit metered interfaces, this should be
specified via Provisioning Domain attributes Section 12.3.18 or
another specific property.
12.3.18. Provisioning Domain Instance or Type
Classification: Selection Property
Type: Tuple (Enumeration, Preference)
Applicability: Preconnection, Connection (read only)
Similar to interface instances and types Section 12.3.17, this
property allows the application to control path selection by
selecting which specific Provisioning Domains or categories of
Provisioning Domains it wants to "Require", "Prohibit", "Prefer", or
"Avoid". Provisioning Domains define consistent sets of network
properties that may be more specific than network interfaces
[RFC7556].
The identification of a specific Provisioning Domain (PvD) is defined
to be implementation- and system-specific, since there is not a
portable standard format for a PvD identitfier. For example, this
identifier may be a string name or an integer. As with requiring
specific interfaces, requiring a specific PvD strictly limits path
selection.
Categories or types of PvDs are also defined to be implementation-
and system-specific. These may be useful to identify a service that
is provided by a PvD. For example, if an application wants to use a
PvD that provides a Voice-Over-IP service on a Cellular network, it
can use the relevant PvD type to require some PvD that provides this
service, without needing to look up a particular instance. While
this does restrict path selection, it is more broad than requiring
specific PvD instances or interface instances, and should be
preferred over those options.
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12.3.19. Capacity Profile
Classification: Intent [TODO: Discuss]
Type: Enumeration
Applicability: Preconnection, Connection, Message
This property specifies the application's expectation of the
dominating traffic pattern for this Connection. This implies that
the transport system should optimize for the capacity profile
specified. This can influence path and protocol selection. The
following values are valid for the Capacity Profile:
Default: The application makes no representation about its expected
capacity profile. No special optimizations of the tradeoff
between delay, delay variation, and bandwidth efficiency should be
made when selecting and configuring stacks.
Low Latency: Response time (latency) should be optimized at the
expense of bandwidth efficiency and delay variation when sending
this message. This can be used by the system to disable the
coalescing of multiple small Messages into larger packets (Nagle's
algorithm); to prefer immediate acknowledgment from the peer
endpoint when supported by the underlying transport; to signal a
preference for lower-latency, higher-loss treatment; and so on.
Constant Rate: The application expects to send/receive data at a
constant rate after Connection establishment. Delay and delay
variation should be minimized at the expense of bandwidth
efficiency. This implies that the Connection may fail if the
desired rate cannot be maintained across the Path. A transport
may interpret this capacity profile as preferring a circuit
breaker [RFC8084] to a rate-adaptive congestion controller.
Scavenger/Bulk: The application is not interactive. It expects to
send/receive a large amount of data, without any urgency. This
can, for example, be used to select protocol stacks with scavenger
transmission control, to signal a preference for less-than-best-
effort treatment, or to assign the traffic to a lower-effort
service.
12.3.20. Congestion control
Classification: Selection Property
Type: Preference
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Applicability: Preconnection, Connection (read only)
This property specifies whether the application would like the
Connection to be congestion controlled or not. Note that if a
Connection is not congestion controlled, an application using such a
Connection should itself perform congestion control in accordance
with [RFC2914]. Also note that reliability is usually combined with
congestion control in protocol implementations, rendering "reliable
but not congestion controlled" a request that is unlikely to succeed.
The default is that the Connection is congestion controlled.
12.3.21. Niceness
Classification: Protocol Property (Generic)
Type: Integer
Applicability: Connection, Message
This property is a numeric (non-negative) value that represents an
unbounded hierarchy of priorities. It can specify the priority of a
Message, relative to other Messages sent over the same Connection
and/or Connection Group (see Section 6.4), or the priority of a
Connection, relative to other Connections in the same Connection
Group.
A Message with Niceness 0 will yield to a Message with Niceness 1,
which will yield to a Message with Niceness 2, and so on. Niceness
may be used as a sender-side scheduling construct only, or be used to
specify priorities on the wire for Protocol Stacks supporting
prioritization.
This encoding of the priority has a convenient property that the
priority increases as both Niceness and Lifetime decrease.
As noted in Section 6.4, when set on a Connection, this property is
not entangled when Connections are cloned.
12.3.22. Timeout for aborting Connection
Classification: Control Property [TODO: Discuss]
Type: Integer
Applicability: Preconnection, Connection
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This property specifies how long to wait before aborting a Connection
during establishment, or before deciding that a Connection has failed
after establishment. It is given in seconds.
12.3.23. Connection group transmission scheduler
Classification: Protocol Property (Generic) / Control Property
[TODO: Discuss]
Type: Enum
Applicability: Preconnection, Connection
This property specifies which scheduler should be used among
Connections within a Connection Group, see Section 6.4. The set of
schedulers can be taken from [I-D.ietf-tsvwg-sctp-ndata].
12.3.24. Maximum message size concurrent with Connection establishment
Classification: Protocol Property (Generic)
Type: Integer
Applicability: Connection (read only)
This property represents the maximum Message size that can be sent
before or during Connection establishment, see also Section 12.3.9.
It is given in Bytes. This property is read-only.
12.3.25. Maximum Message size before fragmentation or segmentation
Classification: Protocol Property (Generic)
Type: Integer
Applicability: Connection (read only)
This property, if applicable, represents the maximum Message size
that can be sent without incurring network-layer fragmentation and/or
transport layer segmentation at the sender. This property is read-
only.
12.3.26. Maximum Message size on send
Classification: Protocol Property (Generic)
Type: Integer
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Applicability: Connection (read only)
This property represents the maximum Message size that can be sent.
This property is read-only.
12.3.27. Maximum Message size on receive
Classification: Protocol Property (Generic)
Type: Integer
Applicability: Connection (read only)
This numeric property represents the maximum Message size that can be
received. This property is read-only.
12.3.28. Lifetime
Classification: Protocol Property (Generic)
Type: Integer
Applicability: Message
Lifetime specifies how long a particular Message can wait to be sent
to the remote endpoint before it is irrelevant and no longer needs to
be (re-)transmitted. When a Message's Lifetime is infinite, it must
be transmitted reliably. The type and units of Lifetime are
implementation-specific.
12.4. Optional Transport Properties
TODO: Maybe move some of the above properties here.
12.5. Experimental Transport Properties
TODO: Move Appendix A here.
13. IANA Considerations
RFC-EDITOR: Please remove this section before publication.
This document has no Actions for IANA.
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14. Security Considerations
This document describes a generic API for interacting with a
transport services (TAPS) system. Part of this API includes
configuration details for transport security protocols, as discussed
in Section Section 5.3. It does not recommend use (or disuse) of
specific algorithms or protocols. Any API-compatible transport
security protocol should work in a TAPS system.
15. 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 of DFG -
German Research Foundation: Gottfried Wilhelm Leibniz-Preis 2011 (FKZ
FE 570/4-1).
This work has been supported by the UK Engineering and Physical
Sciences Research Council under grant EP/R04144X/1.
Thanks to 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.
16. References
16.1. Normative References
[I-D.ietf-taps-arch]
Pauly, T., Trammell, B., Brunstrom, A., Fairhurst, G.,
Perkins, C., Tiesel, P., and C. Wood, "An Architecture for
Transport Services", draft-ietf-taps-arch-01 (work in
progress), July 2018.
[I-D.ietf-taps-minset]
Welzl, M. and S. Gjessing, "A Minimal Set of Transport
Services for End Systems", draft-ietf-taps-minset-04 (work
in progress), June 2018.
[I-D.ietf-tls-tls13]
Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", draft-ietf-tls-tls13-28 (work in progress),
March 2018.
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[I-D.ietf-tsvwg-rtcweb-qos]
Jones, P., Dhesikan, S., Jennings, C., and D. Druta, "DSCP
Packet Markings for WebRTC QoS", draft-ietf-tsvwg-rtcweb-
qos-18 (work in progress), August 2016.
[I-D.ietf-tsvwg-sctp-ndata]
Stewart, R., Tuexen, M., Loreto, S., and R. Seggelmann,
"Stream Schedulers and User Message Interleaving for the
Stream Control Transmission Protocol", draft-ietf-tsvwg-
sctp-ndata-13 (work in progress), September 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
16.2. Informative References
[I-D.ietf-taps-transport-security]
Pauly, T., Perkins, C., Rose, K., and C. Wood, "A Survey
of Transport Security Protocols", draft-ietf-taps-
transport-security-02 (work in progress), June 2018.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, DOI 10.17487/RFC2914, September 2000,
<https://www.rfc-editor.org/info/rfc2914>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/info/rfc3261>.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
DOI 10.17487/RFC5245, April 2010,
<https://www.rfc-editor.org/info/rfc5245>.
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[RFC7478] Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real-
Time Communication Use Cases and Requirements", RFC 7478,
DOI 10.17487/RFC7478, March 2015,
<https://www.rfc-editor.org/info/rfc7478>.
[RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain
Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
<https://www.rfc-editor.org/info/rfc7556>.
[RFC8084] Fairhurst, G., "Network Transport Circuit Breakers",
BCP 208, RFC 8084, DOI 10.17487/RFC8084, March 2017,
<https://www.rfc-editor.org/info/rfc8084>.
[RFC8095] Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind,
Ed., "Services Provided by IETF Transport Protocols and
Congestion Control Mechanisms", RFC 8095,
DOI 10.17487/RFC8095, March 2017,
<https://www.rfc-editor.org/info/rfc8095>.
Appendix A. Additional Properties
The interface specified by this document represents the minimal
common interface to an endpoint in the transport services
architecture [I-D.ietf-taps-arch], based upon that architecture and
on the minimal set of transport service features elaborated in
[I-D.ietf-taps-minset]. However, the interface has been designed
with extension points to allow the implementation of features beyond
those in the minimal common interface: Protocol Selection Properties,
Path Selection Properties, and Message Properties are open sets.
Implementations of the interface are free to extend these sets to
provide additional expressiveness to applications written on top of
them.
This appendix enumerates a few additional properties that could be
used to enhance transport protocol and/or path selection, or the
transmission of messages given a Protocol Stack that implements them.
These are not part of the interface, and may be removed from the
final document, but are presented here to support discussion within
the TAPS working group as to whether they should be added to a future
revision of the base specification.
A.1. Experimental Transport Properties
The following Transport Properties might be made available in
addition to those specified in Section 12:
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A.1.1. Suggest a timeout to the Remote Endpoint
Classification: Selection Property
Type: Preference
Applicability: Preconnection
This property specifies whether an application considers it useful to
propose a timeout until the Connection is assumed to be lost. The
default is to have this option.
[EDITOR'S NOTE: For discussion of this option, see
https://github.com/taps-api/drafts/issues/109]
A.1.2. Abort timeout to suggest to the Remote Endpoint
Classification: Protocol Property
Type: Integer
Applicability: Preconnection, Connection
This numeric property specifies the timeout to propose to the Remote
Endpoint. It is given in seconds.
[EDITOR'S NOTE: For discussion of this property, see
https://github.com/taps-api/drafts/issues/109]
A.1.3. Request not to delay acknowledgment of Message
Classification: Selection Property
Type: Preference
Applicability: Preconnection
This property specifies whether an application considers it useful to
be able to request for a Message that its acknowledgment be sent out
as early as possible instead of potentially being bundled with other
acknowledgments. The default is to not have this option.
[EDITOR'S NOTE: For discussion of this option, see
https://github.com/taps-api/drafts/issues/90]
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A.1.4. Traffic Category
Classification: Intent
Type: Enumeration
Applicability: Preconnection
This property specifies what the application expect the dominating
traffic pattern to be. Possible values are:
Query: Single request / response style workload, latency bound
Control: Long lasting low bandwidth control channel, not bandwidth
bound
Stream: Stream of data with steady data rate
Bulk: Bulk transfer of large Messages, presumably bandwidth bound
The default is to not assume any particular traffic pattern. Most
categories suggest the use of other intents to further describe the
traffic pattern anticipated, e.g., the bulk category suggesting the
use of the Message Size intents or the stream category suggesting the
Stream Bitrate and Duration intents.
A.1.5. Size to be Sent or Received
Classification: Intent
Type: Integer
Applicability: Preconnection, Message
This property specifies how many bytes the application expects to
send (Size to be Sent) or how many bytes the application expects to
receive in response (Size to be Received).
A.1.6. Duration
Classification: Intent
Type: Integer
Applicability: Preconnection
This Intent specifies what the application expects the lifetime of a
connection to be. It is given in milliseconds.
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A.1.7. Send or Receive Bit-rate
Classification: Intent
Type: Integer
Applicability: Preconnection, Message
This Intent specifies what the application expects the bit-rate of a
transfer to be. It is given in Bytes per second.
On a message, this property specifies at what bitrate the application
wishes the Message to be sent. A transport system supporting this
feature will not exceed the requested Send Bitrate even if flow-
control and congestion control allow higher bitrates. This helps to
avoid bursty traffic pattern on busy video streaming servers.
A.1.8. Cost Preferences
Classification: Intent
Type: Enumeration
Applicability: Preconnection, Message
This property describes what an application prefers regarding
monetary costs, e.g., whether it considers it acceptable to utilize
limited data volume. It provides hints to the transport system on
how to handle trade-offs between cost and performance or reliability.
Possible values are:
No Expense: Avoid transports associated with monetary cost
Optimize Cost: Prefer inexpensive transports and accept service
degradation
Balance Cost: Use system policy to balance cost and other criteria
Ignore Cost: Ignore cost, choose transport solely based on other
criteria
The default is "Balance Cost".
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A.1.9. Immediate
Classification: Protocol Property (Generic)
Type: Boolean
Applicability: Message
This property specifies whether the caller prefers immediacy to
efficient capacity usage for this Message. For example, this means
that the Message should not be bundled with other Message into the
same transmission by the underlying Protocol Stack.
Appendix B. Sample API definition in Go
This document defines an abstract interface. To illustrate how this
would map concretely into a programming language, an API interface
definition in Go is available online at https://github.com/mami-
project/postsocket. Documentation for this API - an illustration of
the documentation an application developer would see for an instance
of this interface - is available online at
https://godoc.org/github.com/mami-project/postsocket. This API
definition will be kept largely in sync with the development of this
abstract interface definition.
Authors' Addresses
Brian Trammell (editor)
ETH Zurich
Gloriastrasse 35
8092 Zurich
Switzerland
Email: ietf@trammell.ch
Michael Welzl (editor)
University of Oslo
PO Box 1080 Blindern
0316 Oslo
Norway
Email: michawe@ifi.uio.no
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Theresa Enghardt
TU Berlin
Marchstrasse 23
10587 Berlin
Germany
Email: theresa@inet.tu-berlin.de
Godred Fairhurst
University of Aberdeen
Fraser Noble Building
Aberdeen, AB24 3UE
Scotland
Email: gorry@erg.abdn.ac.uk
URI: http://www.erg.abdn.ac.uk/
Mirja Kuehlewind
ETH Zurich
Gloriastrasse 35
8092 Zurich
Switzerland
Email: mirja.kuehlewind@tik.ee.ethz.ch
Colin Perkins
University of Glasgow
School of Computing Science
Glasgow G12 8QQ
United Kingdom
Email: csp@csperkins.org
Philipp S. Tiesel
TU Berlin
Marchstrasse 23
10587 Berlin
Germany
Email: philipp@inet.tu-berlin.de
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Chris Wood
Apple Inc.
1 Infinite Loop
Cupertino, California 95014
United States of America
Email: cawood@apple.com
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