An Abstract Application Layer Interface to Transport Services
draft-ietf-taps-interface-02
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| Authors | Brian Trammell , Michael Welzl , Reese Enghardt , Gorry Fairhurst , Mirja Kühlewind , Colin Perkins , Philipp S. Tiesel , Christopher A. Wood | ||
| Last updated | 2018-10-22 (Latest revision 2018-07-02) | ||
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draft-ietf-taps-interface-02
TAPS Working Group B. Trammell, Ed.
Internet-Draft ETH Zurich
Intended status: Standards Track M. Welzl, Ed.
Expires: April 25, 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.
October 22, 2018
An Abstract Application Layer Interface to Transport Services
draft-ietf-taps-interface-02
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 April 25, 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
4.1. Transport Properties . . . . . . . . . . . . . . . . . . 7
4.2. Scope of the Interface Definition . . . . . . . . . . . . 8
5. Pre-Establishment Phase . . . . . . . . . . . . . . . . . . . 9
5.1. Specifying Endpoints . . . . . . . . . . . . . . . . . . 9
5.2. Specifying Transport Properties . . . . . . . . . . . . . 11
5.2.1. Reliable Data Transfer (Connection) . . . . . . . . . 13
5.2.2. Configure per-Message reliability . . . . . . . . . . 13
5.2.3. Preservation of data ordering . . . . . . . . . . . . 13
5.2.4. Use 0-RTT session establishment with an idempotent
Message . . . . . . . . . . . . . . . . . . . . . . . 13
5.2.5. Multistream Connections in Group . . . . . . . . . . 13
5.2.6. Control checksum coverage on sending or receiving . . 13
5.2.7. Congestion control . . . . . . . . . . . . . . . . . 14
5.2.8. Interface Instance or Type . . . . . . . . . . . . . 14
5.2.9. Provisioning Domain Instance or Type . . . . . . . . 15
5.3. Specifying Security Parameters and Callbacks . . . . . . 15
5.3.1. Pre-Connection Parameters . . . . . . . . . . . . . . 16
5.3.2. Connection Establishment Callbacks . . . . . . . . . 17
6. Establishing Connections . . . . . . . . . . . . . . . . . . 17
6.1. Active Open: Initiate . . . . . . . . . . . . . . . . . . 17
6.2. Passive Open: Listen . . . . . . . . . . . . . . . . . . 18
6.3. Peer-to-Peer Establishment: Rendezvous . . . . . . . . . 19
6.4. Connection Groups . . . . . . . . . . . . . . . . . . . . 21
7. Sending Data . . . . . . . . . . . . . . . . . . . . . . . . 22
7.1. Basic Sending . . . . . . . . . . . . . . . . . . . . . . 22
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7.2. Send Events . . . . . . . . . . . . . . . . . . . . . . . 22
7.2.1. Sent . . . . . . . . . . . . . . . . . . . . . . . . 23
7.2.2. Expired . . . . . . . . . . . . . . . . . . . . . . . 23
7.2.3. SendError . . . . . . . . . . . . . . . . . . . . . . 23
7.3. Message Properties . . . . . . . . . . . . . . . . . . . 24
7.3.1. Lifetime . . . . . . . . . . . . . . . . . . . . . . 24
7.3.2. Niceness . . . . . . . . . . . . . . . . . . . . . . 25
7.3.3. Ordered . . . . . . . . . . . . . . . . . . . . . . . 25
7.3.4. Idempotent . . . . . . . . . . . . . . . . . . . . . 25
7.3.5. Final . . . . . . . . . . . . . . . . . . . . . . . . 25
7.3.6. Corruption Protection Length . . . . . . . . . . . . 26
7.3.7. Reliable Data Transfer (Message) . . . . . . . . . . 26
7.3.8. Transmission Profile . . . . . . . . . . . . . . . . 26
7.3.9. Singular Transmission . . . . . . . . . . . . . . . . 27
7.4. Partial Sends . . . . . . . . . . . . . . . . . . . . . . 27
7.5. Batching Sends . . . . . . . . . . . . . . . . . . . . . 28
7.6. Send on Active Open: InitiateWithIdempotentSend . . . . . 28
7.7. Sender-side Framing . . . . . . . . . . . . . . . . . . . 29
8. Receiving Data . . . . . . . . . . . . . . . . . . . . . . . 29
8.1. Enqueuing Receives . . . . . . . . . . . . . . . . . . . 30
8.2. Receive Events . . . . . . . . . . . . . . . . . . . . . 30
8.2.1. Received . . . . . . . . . . . . . . . . . . . . . . 30
8.2.2. ReceivedPartial . . . . . . . . . . . . . . . . . . . 31
8.2.3. ReceiveError . . . . . . . . . . . . . . . . . . . . 32
8.3. Message Receive Context . . . . . . . . . . . . . . . . . 32
8.3.1. ECN . . . . . . . . . . . . . . . . . . . . . . . . . 32
8.3.2. Early Data . . . . . . . . . . . . . . . . . . . . . 32
8.3.3. Receiving Final Messages . . . . . . . . . . . . . . 33
8.4. Receiver-side De-framing over Stream Protocols . . . . . 33
9. Managing Connections . . . . . . . . . . . . . . . . . . . . 34
9.1. Generic Connection Properties . . . . . . . . . . . . . . 35
9.1.1. Notification of excessive retransmissions . . . . . . 35
9.1.2. Retransmission threshold before excessive
retransmission notification . . . . . . . . . . . . . 36
9.1.3. Notification of ICMP soft error message arrival . . . 36
9.1.4. Required minimum coverage of the checksum for
receiving . . . . . . . . . . . . . . . . . . . . . . 36
9.1.5. Niceness (Connection) . . . . . . . . . . . . . . . . 36
9.1.6. Timeout for aborting Connection . . . . . . . . . . . 37
9.1.7. Connection group transmission scheduler . . . . . . . 37
9.1.8. Maximum message size concurrent with Connection
establishment . . . . . . . . . . . . . . . . . . . . 37
9.1.9. Maximum Message size before fragmentation or
segmentation . . . . . . . . . . . . . . . . . . . . 37
9.1.10. Maximum Message size on send . . . . . . . . . . . . 37
9.1.11. Maximum Message size on receive . . . . . . . . . . . 37
9.1.12. Capacity Profile . . . . . . . . . . . . . . . . . . 38
9.2. Soft Errors . . . . . . . . . . . . . . . . . . . . . . . 39
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10. Connection Termination . . . . . . . . . . . . . . . . . . . 39
11. Connection State and Ordering of Operations and Events . . . 40
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 41
13. Security Considerations . . . . . . . . . . . . . . . . . . . 41
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 41
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 42
15.1. Normative References . . . . . . . . . . . . . . . . . . 42
15.2. Informative References . . . . . . . . . . . . . . . . . 43
Appendix A. Additional Properties . . . . . . . . . . . . . . . 44
A.1. Experimental Transport Properties . . . . . . . . . . . . 45
A.1.1. Direction of communication . . . . . . . . . . . . . 45
A.1.2. Suggest a timeout to the Remote Endpoint . . . . . . 45
A.1.3. Abort timeout to suggest to the Remote Endpoint . . . 46
A.1.4. Traffic Category . . . . . . . . . . . . . . . . . . 46
A.1.5. Size to be Sent or Received . . . . . . . . . . . . . 46
A.1.6. Duration . . . . . . . . . . . . . . . . . . . . . . 47
A.1.7. Send or Receive Bit-rate . . . . . . . . . . . . . . 47
A.1.8. Cost Preferences . . . . . . . . . . . . . . . . . . 47
Appendix B. Sample API definition in Go . . . . . . . . . . . . 48
Appendix C. Relationship to the Minimal Set of Transport
Services for End Systems . . . . . . . . . . . . . . 48
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
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
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provided in [RFC8095], [I-D.ietf-taps-minset], and
[I-D.ietf-taps-transport-security].
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 creates an array of Objects:
[]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.
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 callbacks, communicating sequential
processes, or other asynchronous calling conventions. The method for
dispatching and handling Events 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).
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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 Message- as opposed to stream-orientation, using application-
assisted framing and deframing where the underlying transport does
not provide these;
o Asynchronous Connection establishment, transmission, and
reception, allowing concurrent operations during establishment and
supporting event-driven application interactions with the
transport layer, in line with developments in modern platforms and
programming languages;
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; and
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
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take full advantage of new transport protocols supporting these
features.
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.
Section 5, Section 6, Section 7, Section 8, and Section 10 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].
4.1. Transport Properties
Each application using the Transport Services Interface declares its
preferences for how the transport service should operate using
properties at each stage of the lifetime of a connection. During
pre-establishment, Selection Properties Section 5.2 are used to
specify which paths and protocol stacks can be used and are preferred
by the application, and Connection Properties Section 9.1 can be used
to fine-tune the eventually established connection. These Connection
Properties can also be used to monitor and fine-tune established
connections. The behavior of the selected protocol stack(s) when
sending Messages is controlled by Message Properties Section 7.3.
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Collectively, Selection, Connection, and Message Properties can be
referred to as Transport Properties. All Transport Properties,
regardless of the phase in which they are used, are organized within
a single namespace. This enables setting them as defaults in earlier
stages and querying them in later stages: - Connection Properties can
be set on Preconnections - Message Properties can be set on
Preconnections and Connections - The effect of Selection Properties
can be queried on Connections and Messages
Transport Properties can have one of a set of data types:
o Boolean: can take the values "true" and "false"; representation is
implementation-dependent.
o Integer: can take positive or negative numeric values; range and
representation is implementation-dependent.
o Enumeration: can take one value of a finite set of values,
dependent on the property itself. The representation is
implementation dependent; however, implementations MUST provide a
method for the application to determine the entire set of possible
values for each property.
o Preference: can take one of five values (Prohibit, Avoid, Ignore,
Prefer, Require) for the level of preference of a given property
during protocol selection; see Section 5.2.
4.2. Scope of the Interface Definition
This document defines a language- and platform-independent interface
to a Transport Services system. Given the wide variety of languages
and language conventions used to write applications that use the
transport layer to connect to other applications over the Internet,
this independence makes this interface necessarily abstract. While
there is no interoperability benefit to tightly defining how the
interface be presented to application programmers in diverse
platforms, maintaining the "shape" of the abstract interface across
these platforms reduces the effort for programmers who learn the
transport services interface to apply their knowledge in multiple
platforms. We therefore make the following recommendations:
o Actions, Events, and Errors in implementations of this interface
SHOULD carry the names given for them in the document, subject to
capitalization and punctuation conventions in the language of the
implementation, unless the implementation itself uses different
names for substantially equivalent objects for networking by
convention.
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o Implementations of this interface SHOULD implement each Selection
Property, Connection Property, and Message Context Property
specified in this document, exclusive of appendices, even if said
implementation is a non-operation, e.g. because transport
protocols implementing a given Property are not available on the
platform.
5. Pre-Establishment Phase
The pre-establishment phase allows applications to specify properties
for the Connections they are about to make, or to query the API about
potential connections they could make.
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 Selection Properties (see Section 5.2), any
preconfigured Connection Properties (Section 9.1), 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 if 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 7.7) 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.
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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)
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 Remote Endpoint. 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 resolves names internally, when the
Initiate(), Listen(), or Rendezvous() method is called establish a
Connection. The API explicitly does not require the application to
resolve names, though there is a tradeoff between early and late
binding of addresses to names. Early binding allows the API
implementation to reduce connection setup latency, at the cost of
potentially limited scope for alternate path discovery during
Connection establishment, as well as potential additional information
leakage about application interest when used with a resolution method
(such as DNS without TLS) which does not protect query
confidentiality.
The Resolve() action on Preconnection can be used by the application
to force early binding when required, for example with some Network
Address Translator (NAT) traversal protocols (see Section 6.3).
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5.2. Specifying Transport Properties
A Preconnection Object holds properties reflecting the application's
requirements and preferences for the transport. These include
Selection Properties for selecting protocol stacks and paths, as well
as Connection Properties for configuration of the detailed operation
of the selected Protocol Stacks.
The protocol(s) and path(s) selected as candidates during
establishment are determined and configured using these 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.
Selection properties are represented as preferences, which can have
one of five 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 system 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 |
+------------+------------------------------------------------------+
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. Selection Properties which select paths take preference
over those which select protocols. For example, if an application
indicates a preference for a specific path by specifying an
interface, but also a preference for a protocol not available on this
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path, the transport system will try the path first, ignoring the
preference.
Both Selection and Connection Properties can be added to a
Preconnection to configure the selection process, and to further
configure the eventually selected protocol stack(s). They are
collected into a TransportProperties object to be passed into a
Preconnection object:
TransportProperties := NewTransportProperties()
Individual properties are then added to the TransportProperties
Object:
TransportProperties.Add(property, value)
Selection Properties can be added to a TransportProperties object
using special actions for each preference level i.e,
"TransportProperties.Add(some_property, avoid)" is equivalent to
"TransportProperties.Avoid(some_property)":
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()
A Connection gets its Transport Properties either by being explicitly
configured via a Preconnection, by configuration after establishment,
or by inheriting them from an antecedent via cloning; see Section 6.4
for more.
Section 9.1 provides a list of Connection Properties, while Selection
Properties are listed in the subsections below. Note that many
properties are only considered during establishment, and can not be
changed after a Connection is established; however, they can be
queried. Querying a Selection Property after establishment yields
the value Required for properties of the selected protocol and path,
Avoid for properties avoided during selection, and Ignore for all
other properties.
An implementation of this interface must provide sensible defaults
for Selection Properties. The recommended defaults given for each
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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.
5.2.1. Reliable Data Transfer (Connection)
This property specifies whether the application needs 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 recommended default is to
enable Reliable Data Transfer.
5.2.2. Configure per-Message reliability
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
recommended default is to not have this option.
5.2.3. Preservation of data ordering
This property specifies whether the application wishes to use a
transport protocol that can ensure that data is received by the
application on the other end in the same order as it was sent. The
recommended default is to preserve data ordering.
5.2.4. Use 0-RTT session establishment with an idempotent Message
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 7.3.4. The recommended default is to not have this
option.
5.2.5. Multistream Connections in Group
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
recommended default is to not have this option.
5.2.6. Control checksum coverage on sending or receiving
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.
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The recommended default is full checksum coverage without the option
to configure it, and requiring a checksum when receiving.
5.2.7. Congestion control
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 recommended default is that the Connection is congestion
controlled.
5.2.8. Interface Instance or Type
This property allows the application to select which specific network
interfaces or categories of interfaces it wants to "Require",
"Prohibit", "Prefer", or "Avoid".
In contrast to other Selection Properties, this property is tuple of
an (Enumerated) interface identifier and a preference, and can either
be implemented directly as such, or for making one preference
available for each interface and interface type available on the
system.
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
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.
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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 (see Section 5.2.9) or
another specific property.
5.2.9. Provisioning Domain Instance or Type
Similar to interface instances and types (see Section 5.2.8), 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].
As with interface instances and types, this property is tuple of an
(Enumerated) PvD identifier and a preference, and can either be
implemented directly as such, or for making one preference available
for each interface and interface type available on the system.
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 broader than requiring
specific PvD instances or interface instances, and should be
preferred over these options.
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
Properties, both parameters and callbacks are inherited during
cloning (see Section 6.4).
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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 hardware security modules (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.
SecurityParameters.AddPreSharedKey(key, identity)
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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()
Before calling Initiate, the caller must have populated a
Preconnection Object with a Remote Endpoint specifier, optionally a
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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.
The Initiate() Action consumes the Preconnection. Once Initiate()
has been called, no further properties may be added to the
Preconnection, and no subsequent establishment call may be made on
the Preconnection.
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 security 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).
See also Section 7.6 to combine Connection establishment and
transmission of the first message in a single action.
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.
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Passive open is supported by this interface through the Listen
Action:
Preconnection.Listen()
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:
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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.
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() action on the
Preconnection can be used to discover these bindings:
[]Preconnection := 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
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Connections. These resolved Preconnections will share all other
Properties with the Preconnection from which they are derived, though
some Properties may be made more-specific by the resolution process.
This list can be passed to a peer via a signalling protocol, such as
SIP [RFC3261] or WebRTC [RFC7478], to configure the remote.
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 cloned
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 Connection Group, and so
on. Connections in a Connection Group share all Protocol Properties
that are not applicable to a Message.
Changing one of these Protocol Properties on one Connection in the
group changes it for all others. Per-Message Protocol Properties,
however, are not entangled. For example, changing "Timeout for
aborting Connection" (see Section 9.1.6) on one Connection in a group
will automatically change this Protocol Property for all Connections
in the group in the same way. However, changing "Lifetime" (see
Section 7.3.1) of a Message will only affect a single Message on a
single Connection, entangled or not.
If the underlying protocol supports multi-streaming, it is natural to
use this functionality to implement Clone. In that case, entangled
Connections are multiplexed together, giving them similar treatment
not only inside endpoints but also across the end-to-end Internet
path.
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<>
The Protocol Property "Niceness" operates on entangled Connections as
in Section 7.3.2: 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 each Connection the capacity share (M-N) x C / M, where
N is the Connection's Niceness value, M is the maximum Niceness value
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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 to share 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).
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.
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.
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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.
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 always waits for the Sent Event before calling the next Send
Action.
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 7.3.1) 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.
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7.3. Message Properties
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 properties for sending Messages, and can be passed to the
Send Action. 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.
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.
Properties 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 properties 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 Properties are supported:
7.3.1. Lifetime
Type: Integer
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.
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7.3.2. Niceness
Type: Integer (non-negative)
This property represents an unbounded hierarchy of priorities. It
can specify the priority of a Message, relative to other Messages
sent over the same Connection.
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.
Note that this property is not a per-message override of the
connection Niceness - see Section 9.1.5. Both Niceness properties
may interact, but can be used independently and be realized by
different mechanisms.
7.3.3. Ordered
Type: Boolean
If true, it specifies that the receiver-side transport protocol stack
only deliver the Message to the receiving application after the
previous ordered Message which was passed to the same Connection via
the Send Action, when such a Message exists. If false, the Message
may be delivered to the receiving application out of order. This
property is used for protocols that support preservation of data
ordering, see Section 5.2.3, but allow out-of-order delivery for
certain messages.
7.3.4. Idempotent
Type: Boolean
If true, it 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
retransmission of the 0-RTT data may cause the remote application to
receive the Message multiple times.
7.3.5. Final
Type: Boolean
If true, this Message is the last one that the application will send
on a Connection. This allows underlying protocols to indicate to the
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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 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 Send Action for the new Message will cause a
SendError Event.
7.3.6. Corruption Protection Length
Type: Integer (non-negative with -1 as special value)
This property specifies the length of the section of the Message,
starting from byte 0, that the application requires to be delivered
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 a 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. Reliable Data Transfer (Message)
Type: Boolean
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 Connection supports
reliability. When this is not the case, changing it will generate an
error.
7.3.8. Transmission Profile
Type: Enumeration
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 9.1.12).
The following values are valid for Transmission Profile:
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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.
[TODO: This is inconsistent with {prop-cap-profile}} - needs to be
fixed]
7.3.9. Singular Transmission
Type: Boolean
This property specifies that a message should be sent and received as
a single packet without transport-layer segmentation or network-layer
fragmentation. Attempts to send a message with this property set
with a size greater to the transport's current estimate of its
maximum transmission segment size will result in a "SendError". When
used with transports supporting this functionality and running over
IP version 4, the Don't Fragment bit will be set.
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.
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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 data 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)
)
7.6. Send on Active Open: InitiateWithIdempotentSend
For application-layer protocols where the Connection initiator also
sends the first message, the InitiateWithIdempotentSend() action
combines Connection initiation with a first Message sent, provided
that message is idempotent.
Without a message context (as in Section 7.1):
Connection := Preconnection.InitiateWithIdempotentSend(messageData)
With a message context (as in Section 7.3):
Connection := Preconnection.InitiateWithIdempotentSend(messageData, messageContext)
The message passed to InitiateWithIdempotentSend() is, as suggested
by the name, considered to be idempotent (see Section 7.3.4)
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regardless of declared message properties or defaults. If protocol
stacks supporting 0-RTT establishment with idempotent data are
available on the Preconnection, then 0-RTT establishment may be used
with the given message when establishing candidate connections. For
a non-idemponent initial message, or when the selected stack(s) do
not support 0-RTT establishment, InitiateWithIdempotentSend is
identical to Initiate() followed by Send().
Neither partial sends nor send batching are supported by
InitiateWithIdempotentSend().
The Events that may be sent after InitiateWithIdempotentSend() are
equivalent to those that would be sent by an invocation of Initate()
followed immediately by an invocation of Send(), with the caveat that
a send failure that occurs because the Connection could not be
established will not result in a SendError separate from the
InitiateError signaling the failure of Connection establishment.
7.7. 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.
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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 (see
Section 8.2.2 and Section 8.4 for more information on how this is
accomplished). 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 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>
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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.
Multiple invocations of ReceivedPartial deliver data for the same
Message by passing the same MessageContext, until the endOfMessage
flag is delivered or a ReceiveError occurs. 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.
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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 to 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 an 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:
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 transfer (before connection establishment has
finished). 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.
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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 7.3.5.
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
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:
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Preconnection.DeframeWith(Deframer)
{messageData} := Deframer.Deframe(OctetStream, ...)
9. Managing Connections
After establishment, connections can be configured and queried using
Connection Properties, and asynchronous information may be available
about the state of the connection via Soft Errors.
Connection Properties represent the configuration and state of the
selected Protocol Stack(s) backing a Connection. These Connection
Properties may be Generic, applying regardless of transport protocol,
or Specific, applicable to a single implementation of a single
transport protocol stack. Generic Connection Properties are defined
in Section 9.1 below. Specific Protocol Properties are defined in a
transport- and implementation-specific way, and 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; however, too
much reliance by an application on Specific Protocol Properties may
significantly reduce the flexibility of a transport services
implementation.
The application can set and query Connection Properties on a per-
Connection basis. Connection Properties that are not read-only can
be set during pre-establishment (see Section 5.2), as well as on
connections directly using the SetProperty action: ~~~
Connection.SetProperty(property, value) ~~~
At any point, the application can query Connection Properties. ~~~
ConnectionProperties := Connection.GetProperties() ~~~
Depending on the status of the connection, the queried Connection
Properties will include different information:
o The connection state, 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 "Direction of Communication" set to
"unidirectional receive" or if a Message marked as "Final" was
sent over this connection, see Section 7.3.5.
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
Selection Property "Direction of Communication" set to
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"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.
o For Connections that are Established, Closing, or Closed:
Selection (Section 5.2) and Connection Properties (Section 9.1) of
the actual protocols that were selected and instantiated.
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.
o For Connections that are Established, additional 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.
9.1. Generic Connection Properties
The Connection Properties defined as independent, and available on
all Connections are defined in the subsections below.
Note that many protocol properties have a corresponding selection
property, which prefers protocols providing a specific transport
feature that controlled by that protocol property. [EDITOR'S NOTE:
todo: add these cross-references up to Section 5.2]
9.1.1. Notification of excessive retransmissions
Type: Boolean
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.
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The recommended default is to have this option.
9.1.2. Retransmission threshold before excessive retransmission
notification
Type: Integer
This property specifies after how many retransmissions to inform the
application about "Excessive Retransmissions".
9.1.3. Notification of ICMP soft error message arrival
Type: Boolean
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
recommended default is not to have this option.
9.1.4. Required minimum coverage of the checksum for receiving
Type: Integer
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.
9.1.5. Niceness (Connection)
Type: Integer
This Property is a non-negative integer representing the relative
inverse priority of this Connection relative to other Connections in
the same Connection Group. It has no effect on Connections not part
of a Connection Group. As noted in Section 6.4, this property is not
entangled when Connections are cloned.
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9.1.6. Timeout for aborting Connection
Type: Integer
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.
9.1.7. Connection group transmission scheduler
Type: Enum
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].
9.1.8. Maximum message size concurrent with Connection establishment
Type: Integer (read only)
This property represents the maximum Message size that can be sent
before or during Connection establishment, see also Section 7.3.4.
It is given in Bytes.
9.1.9. Maximum Message size before fragmentation or segmentation
Type: Integer (read only)
This property, if applicable, represents the maximum Message size
that can be sent without incurring network-layer fragmentation or
transport layer segmentation at the sender.
9.1.10. Maximum Message size on send
Type: Integer (read only)
This property represents the maximum Message size that can be sent.
9.1.11. Maximum Message size on receive
Type: Integer (read only)
This numeric property represents the maximum Message size that can be
received.
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9.1.12. Capacity Profile
This property specifies the desired network treatment for traffic
sent by the application and the tradeoffs the application is prepared
to make in path and protocol selection to receive that desired
treatment. When the capacity profile is set to a value other than
Default, the transport system should select paths and profiles to
optimize for the capacity profile specified. 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 transport protocol stacks.
Transport system implementations that map the requested capacity
profile onto per-connection DSCP signaling without multiplexing
SHOULD assign the DSCP Default Forwarding [RFC2474] PHB; when the
Connection is multiplexed, the guidelines in section 6 of
[RFC7657] apply.
Scavenger: The application is not interactive. It expects to send
and/or receive data without any urgency. This can, for example,
be used to select protocol stacks with scavenger transmission
control and/or to assign the traffic to a lower-effort service.
Transport system implementations that map the requested capacity
profile onto per-connection DSCP signaling without multiplexing
SHOULD assign the DSCP Less than Best Effort [LE-PHB] PHB; when
the Connection is multiplexed, the guidelines in section 6 of
[RFC7657] apply.
Low Latency/Interactive: The application is interactive, and prefers
loss to latency. Response time should be optimized at the expense
of bandwidth efficiency and delay variation when sending on this
connection. 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; and so on.
Transport system implementations that map the requested capacity
profile onto per-connection DSCP signaling without multiplexing
SHOULD assign the DSCP Expedited Forwarding [RFC3246] PHB; when
the Connection is multiplexed, the guidelines in section 6 of
[RFC7657] apply.
Low Latency/Non-Interactive: The application prefers loss to latency
but is not interactive. Response time should be optimized at the
expense of bandwidth efficiency and delay variation when sending
on this connection.Transport system implementations that map the
requested capacity profile onto per-connection DSCP signaling
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without multiplexing SHOULD assign a DSCP Assured Forwarding
(AF21,AF22,AF23,AF24) [RFC2597] PHB; when the Connection is
multiplexed, the guidelines in section 6 of [RFC7657] apply.
Constant-Rate Streaming: 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.
Transport system implementations that map the requested capacity
profile onto per-connection DSCP signaling without multiplexing
SHOULD assign a DSCP Assured Forwarding (AF31,AF32,AF33,AF34)
[RFC2597] PHB; when the Connection is multiplexed, the guidelines
in section 6 of [RFC7657] apply.
High Throughput Data: The application expects to send/receive data
at the maximum rate allowed by its congestion controller over a
relatively long period of time. Transport system implementations
that map the requested capacity profile onto per-connection DSCP
signaling without multiplexing SHOULD assign a DSCP Assured
Forwarding (AF11,AF12,AF13,AF14) [RFC2597] PHB per section 4.8 of
[RFC4594]. When the Connection is multiplexed, the guidelines in
section 6 of [RFC7657] apply.
The Capacity Profile for a selected protocol stack may be modified on
a per-Message basis using the Transmission Profile Message Property;
see Section 7.3.8.
9.2. Soft Errors
Asynchronous introspection is also possible, via the SoftError Event.
This event informing the application about the receipt of an ICMP
error message related to the Connection. This will only happen 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<>
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
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indeed delivered. If the Remote Endpoint still has data to send, it
cannot be received after this call.
Connection.Close()
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 indeed 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 indeed be signaled.
Connection -> ConnectionError<>
11. Connection State and Ordering of Operations and Events
As this interface is designed to be independent of an
implementation's concurrency model, the details of how exactly
actions are handled, and on which threads/callbacks events are
dispatched, are implementation dependent.
Each transition of connection state is associated with one of more
events:
o Ready<> occurs when a Connection created with Initiate() or
InitiateWithIdempotentData() transitions to Established state.
o ConnectionReceived<> occurs when a Connection created with
Listen() transitions to Established state.
o RendezvousDone<> occurs when a Connection created with
Rendezvous() transitions to Established state.
o Closed<> occurs when a Connection transitions to Closed state
without error.
o InitiateError<> occurs when a Connection created with Initiate()
transitions from Establishing state to Closed state due to an
error.
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o ConnectionError<> occurs when a Connection transitions to Closed
state due to an error in all other circumstances.
The interface provides the following guarantees about the ordering of
operations:
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).
o Received<> will never occur on a Connection before it is
Established; i.e. before a Ready<> event on that Connection, or a
ConnectionReceived<> or RendezvousDone<> containing that
Connection.
o No events will occur on a Connection after it is Closed; i.e.,
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 all cases
where application ignores these errors.
12. IANA Considerations
RFC-EDITOR: Please remove this section before publication.
This document has no Actions for IANA.
13. 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 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.
14. 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).
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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.
15. References
15.1. 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-11 (work
in progress), September 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.
[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>.
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15.2. 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.
[LE-PHB] Bless, R., "A Lower Effort Per-Hop Behavior (LE PHB)",
draft-ietf-tsvwg-le-phb-06 (work in progress), October
2018.
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/info/rfc793>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[RFC2597] Heinanen, J., Baker, F., Weiss, W., and J. Wroclawski,
"Assured Forwarding PHB Group", RFC 2597,
DOI 10.17487/RFC2597, June 1999,
<https://www.rfc-editor.org/info/rfc2597>.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41,
RFC 2914, DOI 10.17487/RFC2914, September 2000,
<https://www.rfc-editor.org/info/rfc2914>.
[RFC3246] Davie, B., Charny, A., Bennet, J., Benson, K., Le Boudec,
J., Courtney, W., Davari, S., Firoiu, V., and D.
Stiliadis, "An Expedited Forwarding PHB (Per-Hop
Behavior)", RFC 3246, DOI 10.17487/RFC3246, March 2002,
<https://www.rfc-editor.org/info/rfc3246>.
[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>.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594,
DOI 10.17487/RFC4594, August 2006,
<https://www.rfc-editor.org/info/rfc4594>.
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[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>.
[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>.
[RFC7657] Black, D., Ed. and P. Jones, "Differentiated Services
(Diffserv) and Real-Time Communication", RFC 7657,
DOI 10.17487/RFC7657, November 2015,
<https://www.rfc-editor.org/info/rfc7657>.
[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
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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 5.2, Section 9.1, and
Section 7.3.
A.1.1. 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.
A.1.2. 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]
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A.1.3. 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.1.4. Traffic Category
Classification: Intent
Type: Enumeration
Applicability: Preconnection
This property specifies what the application expects 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
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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.
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 a bursty traffic pattern on busy streaming video 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
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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".
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.
Appendix C. Relationship to the Minimal Set of Transport Services for
End Systems
[I-D.ietf-taps-minset] identifies a minimal set of transport services
that end systems should offer. These services make all transport
features offered by TCP, MPTCP, UDP, UDP-Lite, SCTP and LEDBAT
available that 1) require interaction with the application, and 2) do
not get in the way of a possible implementation over TCP or, with
limitations, UDP. The following text explains how this minimal set
is reflected in the present API. For brevity, this uses the list in
Section 4.1 of [I-D.ietf-taps-minset], updated according to the
discussion in Section 5 of [I-D.ietf-taps-minset].
[EDITOR'S NOTE: This is early text. In the future, this section will
contain backward references, which we currently avoid because things
are still being moved around and names / categories etc. are
changing. Also, clearly, the intention is for the full minset to be
reflected by the API at some point.]
o Connect:
"Initiate" Action.
o Listen:
"Listen" Action.
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o Specify number of attempts and/or timeout for the first
establishment message:
TODO.
o Disable MPTCP:
TODO.
o Hand over a message to reliably transfer (possibly multiple times)
before connection establishment:
"InitiateWithIdempotentSend" Action.
o Hand over a message to reliably transfer during connection
establishment:
TODO.
o Change timeout for aborting connection (using retransmit limit or
time value):
"Timeout for aborting Connection" property, using a time value in
seconds.
o Timeout event when data could not be delivered for too long:
TODO: this should probably be covered by the "ConnectionError"
Event, but the text above it currently reads: "...can inform the
application that the other side has aborted the Connection". In
this case, it is the local side.
o Suggest timeout to the peer:
"Suggest a timeout to the Remote Endpoint" and "Abort timeout to
suggest to the Remote Endpoint" Selection property. [EDITOR'S
NOTE: For discussion of this option, see https://github.com/taps-
api/drafts/issues/109].
o Notification of Excessive Retransmissions (early warning below
abortion threshold):
"Notification of excessive retransmissions" property.
o Notification of ICMP error message arrival:
"Notification of ICMP soft error message arrival" property.
o Choose a scheduler to operate between streams of an association:
"Connection group transmission scheduler" property.
o Configure priority or weight for a scheduler:
"Niceness (Connection)" property.
o "Specify checksum coverage used by the sender" and "Disable
checksum when sending":
"Corruption Protection Length" property (value 0 to disable).
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o "Specify minimum checksum coverage required by receiver" and
"Disable checksum requirement when receiving":
"Required minimum coverage of the checksum for receiving" property
(value 0 to disable).
o "Specify DF" field and "Request not to bundle messages:"
The "Singular Transmission" Message property combines both of
these requests, i.e. if a request not to bundle messages is made,
this also turns off DF in case of protocols that allow this (only
UDP and UDP-Lite, which cannot bundle messages anyway).
o Get max. transport-message size that may be sent using a non-
fragmented IP packet from the configured interface:
"Maximum Message size before fragmentation or segmentation"
property.
o Get max. transport-message size that may be received from the
configured interface:
"Maximum Message size on receive" property.
o Obtain ECN field:
"ECN" is a defined metadata value as part of the Message Receive
Context.
o "Specify DSCP field", "Disable Nagle algorithm", "Enable and
configure a 'Low Extra Delay Background Transfer'":
As suggested in Section 5.5 of [I-D.ietf-taps-minset], these
transport features are collectively offered via the "Capacity
profile" property.
o Close after reliably delivering all remaining data, causing an
event informing the application on the other side:
This is offered by the "Close" Action with slightly changed
semantics in line with the discussion in Section 5.2 of
[I-D.ietf-taps-minset].
o "Abort without delivering remaining data, causing an event
informing the application on the other side" and "Abort without
delivering remaining data, not causing an event informing the
application on the other side":
This is offered by the "Abort" action without promising that this
is signaled to the other side. If it is, a "ConnectionError"
Event will fire at the peer.
o "Reliably transfer data, with congestion control", "Reliably
transfer a message, with congestion control" and "Unreliably
transfer a message":
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Reliability is controlled via the "Reliable Data Transfer
(Message)" Message property. Transmitting data without delimiters
is done by not using a Framer. The choice of congestion control
is provided via the "Congestion control" property.
o Configurable Message Reliability:
The "Lifetime" Message Property implements a time-based way to
configure message reliability.
o "Ordered message delivery (potentially slower than unordered)" and
"Unordered message delivery (potentially faster than ordered)":
The two transport features are controlled via the Message property
"Ordered".
o Request not to delay the acknowledgement (SACK) of a message:
Should the protocol support it, this is one of the transport
features the transport system can use when an application uses the
Capacity Profile Property with value "Low Latency/Interactive".
o Receive data (with no message delimiting):
"Received" Event without using a Deframer.
o Receive a message:
"Received" Event. Section 5.1 of [I-D.ietf-taps-minset] discusses
how messages can be obtained from a bytestream in case of
implementation over TCP. Here, this is dealt with by Framers and
Deframers.
o Information about partial message arrival:
"ReceivedPartial" Event.
o Notification of send failures:
"Expired" and "SendError" Events.
o Notification that the stack has no more user data to send:
Applications can obtain this information via the "Sent" Event.
o Notification to a receiver that a partial message delivery has
been aborted:
"ReceiveError" Event.
Authors' Addresses
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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
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
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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
Chris Wood
Apple Inc.
1 Infinite Loop
Cupertino, California 95014
United States of America
Email: cawood@apple.com
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