TAPS Working Group                                      B. Trammell, Ed.
Internet-Draft                                                ETH Zurich
Intended status: Informational Standards Track                           M. Welzl, Ed.
Expires: January 3, 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.
                                                           July 02,
                                                        October 22, 2018

     An Abstract Application Layer Interface to Transport Services
                      draft-ietf-taps-interface-01
                      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."
   This Internet-Draft will expire on January 3, 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 . . . . . . . . . . . . . . . . . . .   7   9
     5.1.  Specifying Endpoints  . . . . . . . . . . . . . . . . . .   8   9
     5.2.  Specifying Transport Properties . . . . . . . . . . . . .   9  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  . . . . . .  10  15
       5.3.1.  Pre-Connection Parameters . . . . . . . . . . . . . .  11  16
       5.3.2.  Connection Establishment Callbacks  . . . . . . . . .  12  17
   6.  Establishing Connections  . . . . . . . . . . . . . . . . . .  12  17
     6.1.  Active Open: Initiate . . . . . . . . . . . . . . . . . .  12  17
     6.2.  Passive Open: Listen  . . . . . . . . . . . . . . . . . .  13  18
     6.3.  Peer-to-Peer Establishment: Rendezvous  . . . . . . . . .  14  19
     6.4.  Connection Groups . . . . . . . . . . . . . . . . . . . .  16  21
   7.  Sending Data  . . . . . . . . . . . . . . . . . . . . . . . .  16  22
     7.1.  Basic Sending . . . . . . . . . . . . . . . . . . . . . .  17  22
     7.2.  Send Events . . . . . . . . . . . . . . . . . . . . . . .  17  22
       7.2.1.  Sent  . . . . . . . . . . . . . . . . . . . . . . . .  18  23
       7.2.2.  Expired . . . . . . . . . . . . . . . . . . . . . . .  18  23
       7.2.3.  SendError . . . . . . . . . . . . . . . . . . . . . .  18  23
     7.3.  Message Context Parameters Properties  . . . . . . . . . . . . . . .  18 . . . .  24
       7.3.1.  Lifetime  . . . . . . . . . . . . . . . . . . . . . .  19  24
       7.3.2.  Niceness  . . . . . . . . . . . . . . . . . . . . . .  20  25
       7.3.3.  Ordered . . . . . . . . . . . . . . . . . . . . . . .  20  25
       7.3.4.  Idempotent  . . . . . . . . . . . . . . . . . . . . .  20  25
       7.3.5.  Final . . . . . . . . . . . . . . . . . . . . . . . .  20  25
       7.3.6.  Corruption Protection Length  . . . . . . . . . . . .  21  26
       7.3.7.  Transmission Profile  Reliable Data Transfer (Message)  . . . . . . . . . .  26
       7.3.8.  Transmission Profile  . . . . . .  21

     7.4.  Partial Sends . . . . . . . . . .  26
       7.3.9.  Singular Transmission . . . . . . . . . . . .  22 . . . .  27
     7.4.  Partial Sends . . . . . . . . . . . . . . . . . . . . . .  27
     7.5.  Batching Sends  . . . . . . . . . . . . . . . . . . . . .  22  28
     7.6.  Send on Active Open: InitiateWithIdempotentSend . . . . .  28
     7.7.  Sender-side Framing . . . . . . . . . . . . . . . . . . .  23  29
   8.  Receiving Data  . . . . . . . . . . . . . . . . . . . . . . .  23  29
     8.1.  Enqueuing Receives  . . . . . . . . . . . . . . . . . . .  23  30
     8.2.  Receive Events  . . . . . . . . . . . . . . . . . . . . .  24  30
       8.2.1.  Received  . . . . . . . . . . . . . . . . . . . . . .  24  30
       8.2.2.  ReceivedPartial . . . . . . . . . . . . . . . . . . .  24  31
       8.2.3.  ReceiveError  . . . . . . . . . . . . . . . . . . . .  25  32
     8.3.  Message Receive Context . . . . . . . . . . . . . . . . .  25  32
       8.3.1.  ECN . . . . . . . . . . . . . . . . . . . . . . . . .  26  32
       8.3.2.  Early Data  . . . . . . . . . . . . . . . . . . . . .  26  32
       8.3.3.  Receiving Final Messages  . . . . . . . . . . . . . .  26  33
     8.4.  Receiver-side De-framing over Stream Protocols  . . . . .  26  33
   9.  Setting and Querying Connection Properties  Managing Connections  . . . . . . . . .  27
   10. Connection Termination . . . . . . . . . . .  34
     9.1.  Generic Connection Properties . . . . . . . .  28
   11. Ordering of Operations and Events . . . . . .  35
       9.1.1.  Notification of excessive retransmissions . . . . . .  35
       9.1.2.  Retransmission threshold before excessive
               retransmission notification . .  29
   12. Transport Properties . . . . . . . . . . .  36
       9.1.3.  Notification of ICMP soft error message arrival . . .  36
       9.1.4.  Required minimum coverage of the checksum for
               receiving . . . . . .  30
     12.1.  Transport Property Types . . . . . . . . . . . . . . . .  30
       12.1.1.  Boolean  36
       9.1.5.  Niceness (Connection) . . . . . . . . . . . . . . . .  36
       9.1.6.  Timeout for aborting Connection . . . . . .  30
       12.1.2.  Enumeration . . . . .  37
       9.1.7.  Connection group transmission scheduler . . . . . . .  37
       9.1.8.  Maximum message size concurrent with Connection
               establishment . . . . . . . .  31
       12.1.3.  Integer . . . . . . . . . . . .  37
       9.1.9.  Maximum Message size before fragmentation or
               segmentation  . . . . . . . . . .  31
       12.1.4.  Preference . . . . . . . . . .  37
       9.1.10. Maximum Message size on send  . . . . . . . . . . .  31
     12.2.  Transport Property Classification .  37
       9.1.11. Maximum Message size on receive . . . . . . . . . .  31
       12.2.1.  Selection Properties .  37
       9.1.12. Capacity Profile  . . . . . . . . . . . . . . .  32
       12.2.2.  Protocol Properties . . .  38
     9.2.  Soft Errors . . . . . . . . . . . . .  33
       12.2.3.  Control Properties . . . . . . . . . .  39

   10. Connection Termination  . . . . . . .  33
       12.2.4.  Intents . . . . . . . . . . . .  39
   11. Connection State and Ordering of Operations and Events  . . .  40
   12. IANA Considerations . . . . . . .  33
     12.3.  Mandatory Transport Properties . . . . . . . . . . . . .  34
       12.3.1.  Final .  41
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  41
   14. Acknowledgements  . . .  34
       12.3.2.  Reliable Data Transfer (Connection) . . . . . . . .  34
       12.3.3.  Configure per-Message reliability . . . . . . . . .  34
       12.3.4.  Reliable Data Transfer (Message) . .  41
   15. References  . . . . . . . .  35
       12.3.5.  Preservation of data ordering . . . . . . . . . . .  35
       12.3.6.  Ordered . . . . . .  42
     15.1.  Normative References . . . . . . . . . . . . . . . .  35
       12.3.7.  Direction of communication . .  42
     15.2.  Informative References . . . . . . . . . . .  36
       12.3.8.  Use 0-RTT session establishment with an idempotent
                Message  . . . . . . . . . . . . . . . . . . . . . .  36
       12.3.9.  Idempotent . . . . . . .  43
   Appendix A.  Additional Properties  . . . . . . . . . . . . . .  36
       12.3.10. Multistream Connections in Group . . . . . . . . . .  37
       12.3.11. Notification of excessive retransmissions  . . . . .  37
       12.3.12. Retransmission threshold before excessive
                retransmission notification  44
     A.1.  Experimental Transport Properties . . . . . . . . . . . .  37
       12.3.13. Notification  45
       A.1.1.  Direction of ICMP soft error message arrival  . .  38
       12.3.14. Control checksum coverage on sending or receiving communication  .  38
       12.3.15. Corruption Protection Length . . . . . . . . . . . .  38
       12.3.16. Required minimum coverage of  45
       A.1.2.  Suggest a timeout to the checksum for
                receiving  . . . . . . . Remote Endpoint  . . . . . .  45
       A.1.3.  Abort timeout to suggest to the Remote Endpoint . . .  46
       A.1.4.  Traffic Category  . . . . .  39

       12.3.17. Interface Instance or Type . . . . . . . . . . . . .  39
       12.3.18. Provisioning Domain Instance  46
       A.1.5.  Size to be Sent or Type . . . . . . . .  40
       12.3.19. Capacity Profile . . . . . . . . . . . . . . Received . . . .  41
       12.3.20. Congestion control . . . . . . . . .  46
       A.1.6.  Duration  . . . . . . . .  41
       12.3.21. Niceness . . . . . . . . . . . . . .  47
       A.1.7.  Send or Receive Bit-rate  . . . . . . . .  42
       12.3.22. Timeout for aborting Connection . . . . . .  47
       A.1.8.  Cost Preferences  . . . .  42
       12.3.23. Connection group transmission scheduler . . . . . .  43
       12.3.24. Maximum message size concurrent with Connection
                establishment . . . . . . . .  47
   Appendix B.  Sample API definition in Go  . . . . . . . . . . .  43
       12.3.25. Maximum Message size before fragmentation or
                segmentation .  48
   Appendix C.  Relationship to the Minimal Set of Transport
                Services for End Systems . . . . . . . . . . . . . .  48
   Authors' Addresses  . . . . .  43
       12.3.26. Maximum Message size on send . . . . . . . . . . . .  43
       12.3.27. Maximum Message size on receive . . . . . . . . . .  44
       12.3.28. Lifetime . . . . . . . . . . . . . . . . . . . . . .  44
     12.4.  Optional Transport Properties  . . . . . . . . . . . . .  44
     12.5.  Experimental Transport Properties  . . . . . . . . . . .  44
   13. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  44
   14. Security Considerations . . . . . . . . . . . . . . . . . . .  45
   15. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  45
   16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  45
     16.1.  Normative References . . . . . . . . . . . . . . . . . .  45
     16.2.  Informative References . . . . . . . . . . . . . . . . .  46
   Appendix A.  Additional Properties  . . . . . . . . . . . . . . .  47
     A.1.  Experimental Transport Properties . . . . . . . . . . . .  47
       A.1.1.  Suggest a timeout to the Remote Endpoint  . . . . . .  48
       A.1.2.  Abort timeout to suggest to the Remote Endpoint . . .  48
       A.1.3.  Request not to delay acknowledgment of Message  . . .  48
       A.1.4.  Traffic Category  . . . . . . . . . . . . . . . . . .  49
       A.1.5.  Size to be Sent or Received . . . . . . . . . . . . .  49
       A.1.6.  Duration  . . . . . . . . . . . . . . . . . . . . . .  49
       A.1.7.  Send or Receive Bit-rate  . . . . . . . . . . . . . .  50
       A.1.8.  Cost Preferences  . . . . . . . . . . . . . . . . . .  50
       A.1.9.  Immediate . . . . . . . . . . . . . . . . . . . . . .  51
   Appendix B.  Sample API definition in Go  . . . . . . . . . . . .  51
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  51

1.  Introduction

   The BSD Unix Sockets API's SOCK_STREAM abstraction, by bringing
   network sockets into the UNIX programming model, allowing anyone who
   knew how to write programs that dealt with sequential-access files to
   also write network applications, was a revolution in simplicity.  The
   simplicity of this API is a key reason the Internet won the protocol
   wars of the 1980s.  SOCK_STREAM is tied to the Transmission Control
   Protocol (TCP), specified in 1981 [RFC0793].  TCP has scaled
   remarkably well over the past three and a half decades, but its total
   ubiquity has hidden an uncomfortable fact: the network is not really
   a file, and stream abstractions are too simplistic for many modern
   application programming models.

   In the meantime, the nature of Internet access, and the variety of
   Internet transport protocols, is evolving.  The challenges that new
   protocols and access paradigms present to the sockets API and to
   programming models based on them inspire the design principles of a
   new approach, which we outline in Section 3.

   As a first step to realizing this design, [I-D.ietf-taps-arch]
   describes a high-level architecture for transport services.  This
   document builds a modern abstract programming interface atop this
   architecture, deriving specific path and protocol selection
   properties and supported transport features from the analysis
   provided in [RFC8095] and [I-D.ietf-taps-minset].

2.  Terminology and Notation

   This API is described in terms of Objects, which an application can
   interact with; Actions the application can perform on these Objects;
   Events, which an Object can send to an application asynchronously;
   and Parameters associated with these Actions and Events.

   The following notations, which can be combined, are used in this
   document:

   o  An Action creates an Object:

   Object := Action()

   o  An Action is performed on an Object:

   Object.Action()

   o  An Object sends an Event:

   Object -> Event<>

   o  An Action takes a set of Parameters; an Event contains a set of
      Parameters:

   Action(parameter, parameter, ...) / Event<parameter, parameter, ...>

   Actions associated with no Object are Actions on the abstract
   interface itself; they are equivalent to Actions on a per-application
   global context.

   How these abstract concepts map into concrete implementations of this
   API in a given language on a given platform is largely dependent on
   the features of the language and the platform.  Actions could be
   implemented as functions or method calls, for instance, and Events
   could be implemented via callback passing or other asynchronous
   calling conventions.  The method for registering callbacks and
   handlers is left as an implementation detail, with the caveat that
   the interface for receiving Messages must require the application to
   invoke the Connection.Receive() Action once per Message to be
   received (see Section 8).

   This specification treats Events and errors similarly.  Errors, just
   as any other Events, may occur asynchronously in network
   applications.  However, it is recommended that implementations of
   this interface also return errors immediately, according to the error
   handling idioms of the implementation platform, for errors which can
   be immediately detected, such as inconsistency in Transport
   Properties.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Interface Design Principles

   The design of the interface specified in this document is based on a
   set of princples, themselves an elaboration on the architectural
   design principles defined in [I-D.ietf-taps-arch].  The interface
   defined in this document provides:

   o  A single interface to a variety of transport protocols to be used
      in a variety of application design patterns, independent of the
      properties of the application and the Protocol Stacks that will be
      used at runtime, such that all common specialized features of
      these protocol stacks are made available to the application as
      necessary in a transport-independent way, to enable applications
      written to a single API to make use of transport protocols in
      terms of the features they provide;

   o  Explicit support for security properties as first-order transport
      features, and for long-term caching of cryptographic identities
      and parameters for associations among endpoints;

   o  Asynchronous Connection establishment, transmission, and
      reception, allowing most application interactions with the
      transport layer to be Event-driven, in line with developments in
      modern platforms and programming languages;

   o  Explicit support for multistreaming and multipath transport
      protocols, and the grouping of related Connections into Connection
      Groups through cloning of Connections, to allow applications to
      take full advantage of new transport protocols supporting these
      features; and

   o  Atomic transmission of data, using application-assisted framing
      and deframing where the underlying transport does not provide
      these.

4.  API Summary

   The Transport Services Interface is the basic common abstract
   application programming interface to the Transport Services
   Architecture defined in [I-D.ietf-taps-arch].  An application
   primarily interacts with this interface through two Objects,
   Preconnections and Connections.  A Preconnection represents a set of
   properties and constraints on the selection and configuration of
   paths and protocols to establish a Connection with a remote endpoint.
   A Connection represents a transport Protocol Stack on which data can
   be sent to and/or received from a remote endpoint (i.e., depending on
   the kind of transport, connections can be bi-directional or
   unidirectional).  Connections can be created from Preconnections in
   three ways: by initiating the Preconnection (i.e., actively opening,
   as in a client), through listening on the Preconnection (i.e.,
   passively opening, as in a server), or rendezvousing on the
   Preconnection (i.e. peer to peer establishment).

   Once a Connection is established, data can be sent on it in the form
   of Messages.  The interface supports the preservation of message
   boundaries both via explicit Protocol Stack support, and via
   application support through a deframing callback which finds message
   boundaries in a stream.  Messages are received asynchronously through
   a callback registered by the application.  Errors and other
   notifications also happen asynchronously on the Connection.

   In the following sections, we describe the details of application
   interaction with Objects through Actions and Events in each phase of
   a Connection, following the phases described in [I-D.ietf-taps-arch].

5.  Pre-Establishment Phase

   The pre-establishment phase allows applications to specify properties
   for the Connections they're about to make, or to query the API about
   potential connections they could make.

   A Preconnection Object represents a potential Connection.  It has
   state that describes properties of a Connection that might exist in
   the future.  This state comprises Local Endpoint and Remote Endpoint
   Objects that denote the endpoints of the potential Connection (see
   Section 5.1), the transport properties (see Section 12), and the
   security parameters (see Section 5.3):

      Preconnection := NewPreconnection(LocalEndpoint,
                                        RemoteEndpoint,
                                        TransportProperties,
                                        SecurityParams)

   The Local Endpoint MUST be specified if the Preconnection is used to
   Listen() for incoming Connections, but is OPTIONAL if it is used to
   Initiate() connections.  The Remote Endpoint MUST be specified in the
   Preconnection is used to Initiate() Connections, but is OPTIONAL if
   it is used to Listen() for incoming Connections.  The Local Endpoint
   and the Remote Endpoint MUST both be specified if a peer-to-peer
   Rendezvous is to occur based on the Preconnection.

   Framers (see Section 7.6) and deframers (see Section 8.4), if
   necessary, should be bound to the Preconnection during pre-
   establishment.

5.1.  Specifying Endpoints

   The transport services API uses the Local Endpoint and Remote
   Endpoint types to refer to the endpoints of a transport connection.
   Subtypes of these represent various different types of endpoint
   identifiers, such as IP addresses, DNS names, and interface names, as
   well as port numbers and service names.

   RemoteSpecifier := NewRemoteEndpoint()
   RemoteSpecifier.WithHostname("example.com")
   RemoteSpecifier.WithService("https")

   RemoteSpecifier := NewRemoteEndpoint()
   RemoteSpecifier.WithIPv6Address(2001:db8:4920:e29d:a420:7461:7073:0a)
   RemoteSpecifier.WithPort(443)

   RemoteSpecifier := NewRemoteEndpoint()
   RemoteSpecifier.WithIPv4Address(192.0.2.21)
   RemoteSpecifier.WithPort(443)

   LocalSpecifier := NewLocalEndpoint()
   LocalSpecifier.WithInterface("en0")
   LocalSpecifier.WithPort(443)
   LocalSpecifier := NewLocalEndpoint()
   LocalSpecifier.WithStunServer(address, port, credentials)

   Implementations may also support additional endpoint representations
   and provide a single NewEndpoint() call that takes different endpoint
   representations.

   Multiple endpoint identifiers can be specified for each Local
   Endpoint and RemoteEndoint.  For example, a Local Endpoint could be
   configured with two interface names, or a Remote Endpoint could be
   specified via both IPv4 and IPv6 addresses.  These multiple
   identifiers refer to the same transport endpoint.

   The transport services API will resolve names internally, when the
   Initiate(), Listen(), or Rendezvous() method is called establish a
   Connection.  51

1.  Introduction

   The API does not need the application to resolve names,
   and premature name resolution can damage performance BSD Unix Sockets API's SOCK_STREAM abstraction, by limiting bringing
   network sockets into the
   scope for alternate path discovery during Connection establishment.
   The Resolve() method is, however, provided UNIX programming model, allowing anyone who
   knew how to resolve a Local
   Endpoint or write programs that dealt with sequential-access files to
   also write network applications, was a Remote Endpoint revolution in cases where simplicity.  The
   simplicity of this API is required, for
   example with some Network Address Translator (NAT) traversal
   protocols (see Section 6.3).

5.2.  Specifying Transport Properties

   A Preconnection Object holds properties reflecting a key reason the application's
   requirements and preferences for Internet won the transport.  These include
   Selection Properties (Protocol and Path Selection Properties), as
   well as Generic and Specific Protocol Properties for configuration protocol
   wars of the detailed operation of 1980s.  SOCK_STREAM is tied to the selected Transmission Control
   Protocol Stacks.

   The protocol(s) (TCP), specified in 1981 [RFC0793].  TCP has scaled
   remarkably well over the past three and path(s) selected as candidates during Connection
   establishment are determined by a set of properties.  Since there
   could be paths over which some transport protocols are unable to
   operate, or remote endpoints that support only specific half decades, but its total
   ubiquity has hidden an uncomfortable fact: the network
   addresses or transports, transport protocol selection is necessarily
   tied to path selection.  This may involve choosing between multiple
   local interfaces that not really
   a file, and stream abstractions are connected to different access networks.

   Internally, too simplistic for many modern
   application programming models.

   In the transport system will first exclude all protocols meantime, the nature of Internet access, and
   paths the variety of
   Internet transport protocols, is evolving.  The challenges that match a Prohibit, then exclude all new
   protocols and paths
   that do not match a Require, then sort candidates according to
   Preferred properties, and then use Avoided properties as a
   tiebreaker.  In case of conflicts between Protocol access paradigms present to the sockets API and Path Selection
   Properties, Path Selection Properties take precedence.  For example,
   if an application indicates to
   programming models based on them inspire the design principles of a preference for
   new approach, which we outline in Section 3.

   As a specific path, but
   also first step to realizing this design, [I-D.ietf-taps-arch]
   describes a preference high-level architecture for transport services.  This
   document builds a protocol not available on modern abstract programming interface atop this path, the
   transport system will try the
   architecture, deriving specific path first, so and protocol selection
   properties and supported transport features from the Protocol Selection
   Property might not have an effect.

   All Transport Properties used analysis
   provided in the pre-establishment phase are
   collected [RFC8095], [I-D.ietf-taps-minset], and
   [I-D.ietf-taps-transport-security].

2.  Terminology and Notation

   This API is described in a TransportProperties terms of Objects, which an application can
   interact with; Actions the application can perform on these Objects;
   Events, which an Object that is passed can send to the
   Preconnection Object.

   TransportProperties := NewTransportProperties() an application asynchronously;
   and Parameters associated with these Actions and Events.

   The Individual properties following notations, which can be combined, are then added to the TransportProperties
   Object.

   TransportProperties.Add(property, value)

   Transport Properties used in this
   document:

   o  An Action creates an Object:

   Object := Action()

   o  An Action creates an array of Preference Type, see Section 12.1.4, can use
   special calls 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 add Actions on a Property with per-application
   global context.

   How these abstract concepts map into concrete implementations of this
   API in a specific preference level,
   i.e, "TransportProperties.Add('some preference', avoid)" given language on a given platform is
   equivalent to "TransportProperties.Avoid('some preference')"

   TransportProperties.Require(property)
   TransportProperties.Prefer(property)
   TransportProperties.Ignore(property)
   TransportProperties.Avoid(property)
   TransportProperties.Prohibit(property)

   For an existing Connection, the Transport Properties can be queried
   any time by using the following call largely dependent on
   the Connection Object:

   TransportProperties := Connection.GetTransportProperties()

   Section 12 provides a list features of Transport Properties.

   Note that most properties are only considered for Connection
   establishment the language and can not the platform.  Actions could be changed after a Connection is
   established; however, they can
   implemented as functions or method calls, for instance, and Events
   could be queried.  See Section 9.

   A Connection gets its Transport Properties either by being explicitly
   configured implemented via a Preconnection, callbacks, communicating sequential
   processes, or by inheriting them from an
   antecedent via cloning; see Section 6.4 other asynchronous calling conventions.  The method for more.

5.3.  Specifying Security Parameters and Callbacks

   Most security parameters, e.g., TLS ciphersuites, local identity
   dispatching and
   private key, etc., may 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 configured statically.  Others are
   dynamically configured during connection establishment.  Thus, we
   partition security parameters received (see Section 8).

   This specification treats Events and callbacks based on their place errors similarly.  Errors, just
   as any other Events, may occur asynchronously in
   the lifetime network
   applications.  However, it is recommended that implementations of connection establishment.  Similar
   this interface also return errors immediately, according to Transport
   Properties, both parameters and callbacks are inherited during
   cloning (see Section 6.4).

5.3.1.  Pre-Connection Parameters

   Common parameters the error
   handling idioms of the implementation platform, for errors which can
   be immediately detected, such as TLS ciphersuites 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 known to
   implementations.  Clients should use common safe defaults for these
   values whenever possible.  However, be interpreted as discussed described in
   [I-D.ietf-taps-transport-security], many 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 security protocols
   require specific security parameters to be used
      in a variety of application design patterns, independent of the
      properties of the application and constraints from the client Protocol Stacks that will be
      used at the time runtime, such that all common specialized features of configuration and actively during a handshake.  These
   configuration parameters
      these protocol stacks are created made available to the application as follows:

   SecurityParameters := NewSecurityParameters()

   Security configuration parameters and sample usage follow:

   o  Local identity and private keys: Used
      necessary in a transport-independent way, to perform private key
      operations and prove one's identity enable applications
      written to the Remote Endpoint.
      (Note, if private keys are not available, e.g., since they are
      stored a single API to make use of transport protocols in HSMs, handshake callbacks must be used.  See below for
      details.)

   SecurityParameters.AddIdentity(identity)
   SecurityParameters.AddPrivateKey(privateKey, publicKey)
      terms of the features they provide;

   o  Supported algorithms: Used  Message- as opposed to restrict what parameters are used by stream-orientation, using application-
      assisted framing and deframing where the underlying transport security protocols.  When does
      not specified,
      these algorithms should default to known provide these;

   o  Asynchronous Connection establishment, transmission, and safe defaults for
      reception, allowing concurrent operations during establishment and
      supporting event-driven application interactions with the
      system.  Parameters include: ciphersuites, supported groups,
      transport layer, in line with developments in modern platforms and
      signature algorithms.

SecurityParameters.AddSupportedGroup(secp256k1)
SecurityParameters.AddCiphersuite(TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256)
SecurityParameters.AddSignatureAlgorithm(ed25519)
      programming languages;

   o  Session cache management: Used to tune cache capacity, lifetime,
      re-use,  Explicit support for security properties as first-order transport
      features, and eviction policies, e.g., LRU or FIFO.  Constants for long-term caching of cryptographic identities
      and
      policies parameters for these interfaces are implementation-specific.

   SecurityParameters.SetSessionCacheCapacity(MAX_CACHE_ELEMENTS)
   SecurityParameters.SetSessionCacheLifetime(SECONDS_PER_DAY)
   SecurityParameters.SetSessionCachePolicy(CachePolicyOneTimeUse) associations among endpoints; and

   o  Pre-Shared Key import: Used  Explicit support for multistreaming and multipath transport
      protocols, and the grouping of related Connections into Connection
      Groups through cloning of Connections, to install pre-shared keying material
      established out-of-band.  Each pre-shared keying material allow applications to
      take full advantage of new transport protocols supporting these
      features.

4.  API Summary

   The Transport Services Interface is
      associated with some identity that typically identifies its use or
      has some protocol-specific meaning the basic common abstract
   application programming interface to the Remote Endpoint.

   SecurityParameters.AddPreSharedKey(key, identity)

5.3.2.  Connection Establishment Callbacks

   Security decisions, especially pertaining 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 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 establish a Remote Endpoint's
      trust must Connection with a
   remote endpoint.  A Connection represents a transport Protocol Stack
   on which data can be validated before sent to and/or received from a remote endpoint
   (i.e., depending on the handshake protocol kind of transport, connections can proceed.

   TrustCallback := NewCallback({
     // Handle trust, return be bi-
   directional or unidirectional).  Connections can be created from
   Preconnections in three ways: by initiating the result
   })
   SecurityParameters.SetTrustVerificationCallback(trustCallback)

   o  Identity challenge callback: Invoked when Preconnection (i.e.,
   actively opening, as in a private key operation
      is required, e.g., when local authentication is requested by client), through listening on the
   Preconnection (i.e., passively opening, as in a
      remote.

   ChallengeCallback := NewCallback({
     // Handle challenge
   })
   SecurityParameters.SetIdentityChallengeCallback(challengeCallback)

6.  Establishing Connections

   Before server), or
   rendezvousing on the Preconnection (i.e.  peer to peer
   establishment).

   Once a Connection is established, data can be used 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 data transfer, it must be
   established.  Establishment ends how the pre-establishment phase; all 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 cryptographic parameter specification must
   be complete before establishment, as these will protocol stacks can be used to select
   candidate Paths and Protocol Stacks for are preferred
   by the Connection.
   Establishment may application, and Connection Properties Section 9.1 can be active, using the Initiate() Action; passive,
   using the Listen() Action; or simultaneous for peer-to-peer, using used
   to fine-tune the Rendezvous() Action. eventually established connection.  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
   Properties can also be listening for incoming Connection requests.
   Active open is used by clients in client-server interactions.  Active
   open to monitor and fine-tune established
   connections.  The behavior of the selected protocol stack(s) when
   sending Messages is supported controlled by this interface through Message Properties Section 7.3.

   Collectively, Selection, Connection, and Message Properties can be
   referred to as Transport Properties.  All Transport Properties,
   regardless of the Initiate Action: 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 := Preconnection.Initiate()
   Before calling Initiate, the caller must 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 populated one of a
   Preconnection Object with 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 Remote Endpoint specifier, optionally finite set of values,
      dependent on the property itself.  The representation is
      implementation dependent; however, implementations MUST provide a
   Local Endpoint specifier (if not specified,
      method for the system will attempt application to determine a suitable Local Endpoint), as well as all properties
   necessary the entire set of possible
      values for each property.

   o  Preference: can take one of five values (Prohibit, Avoid, Ignore,
      Prefer, Require) for candidate selection.  After calling Initiate, no
   further properties may be added to the Preconnection.  The Initiate()
   call consumes level of preference of a given property
      during protocol selection; see Section 5.2.

4.2.  Scope of the Preconnection Interface Definition

   This document defines a language- and creates platform-independent interface
   to a Connection Object.  A
   Preconnection can only be initiated once.

   Once Initiate is called, Transport Services system.  Given the candidate Protocol Stack(s) may cause
   one or more candidate transport-layer connections 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 created presented to application programmers in diverse
   platforms, maintaining the specified remote endpoint.  The caller may immediately begin
   sending Messages on "shape" of the Connection (see Section 7) after calling
   Initate(); note that any idempotent data sent while abstract interface across
   these platforms reduces the Connection is
   being established may be sent multiple times or on effort for programmers who learn the
   transport services interface to apply their knowledge in multiple
   candidates.

   The
   platforms.  We therefore make the following Events may be sent by 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.

   o  Implementations of this interface SHOULD implement each Selection
      Property, Connection after Initiate() Property, and Message Context Property
      specified in this document, exclusive of appendices, even if said
      implementation is called:

   Connection -> Ready<>

   The Ready Event occurs after Initiate has established a transport-
   layer connection non-operation, e.g.  because transport
      protocols implementing a given Property are not available 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
      platform.

5.  Pre-Establishment Phase

   The pre-establishment phase allows applications to specify properties
   for the Connections established using
   Initiate.

   Connection -> InitiateError<>

   An InitiateError occurs either when they are about to make, or to query the set of transport API about
   potential connections they could make.

   A Preconnection Object represents a potential Connection.  It has
   state that describes properties
   and cryptographic parameters cannot be fulfilled on of a Connection for
   initiation (e.g. that might exist in
   the set future.  This state comprises Local Endpoint and Remote Endpoint
   Objects that denote the endpoints of available Paths and/or Protocol Stacks
   meeting the constraints is empty) or reconciled with potential Connection (see
   Section 5.1), the local and/or
   remote endpoints; when Selection Properties (see Section 5.2), any
   preconfigured Connection Properties (Section 9.1), and the remote specifier cannot be resolved; or
   when no transport-layer connection can security
   parameters (see Section 5.3):

      Preconnection := NewPreconnection(LocalEndpoint,
                                        RemoteEndpoint,
                                        TransportProperties,
                                        SecurityParams)

   The Local Endpoint MUST be established to the remote
   endpoint (e.g. because specified if the remote endpoint Preconnection is not accepting
   connections, or the application used to
   Listen() for incoming Connections, but is prohibited from opening a
   Connection by the operating system).

6.2.  Passive Open: Listen

   Passive open OPTIONAL if it is used to
   Initiate() connections.  The Remote Endpoint MUST be specified if the Action of waiting for Connections from remote
   endpoints, commonly
   Preconnection is used by servers in client-server interactions.
   Passive open to Initiate() Connections, but is supported by this interface through OPTIONAL if
   it is used to Listen() for incoming Connections.  The Local Endpoint
   and the Listen
   Action:

   Preconnection.Listen()
   Before calling Listen, Remote Endpoint MUST both be specified if a peer-to-peer
   Rendezvous is to occur based on the caller must have initialized 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 pre-establishment phase with a Local Endpoint specifier, 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 all properties necessary port numbers and service names.

   RemoteSpecifier := NewRemoteEndpoint()
   RemoteSpecifier.WithHostname("example.com")
   RemoteSpecifier.WithService("https")

   RemoteSpecifier := NewRemoteEndpoint()
   RemoteSpecifier.WithIPv6Address(2001:db8:4920:e29d:a420:7461:7073:0a)
   RemoteSpecifier.WithPort(443)

   RemoteSpecifier := NewRemoteEndpoint()
   RemoteSpecifier.WithIPv4Address(192.0.2.21)
   RemoteSpecifier.WithPort(443)

   LocalSpecifier := NewLocalEndpoint()
   LocalSpecifier.WithInterface("en0")
   LocalSpecifier.WithPort(443)

   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 Protocol
   Stack selection.  A each Local
   Endpoint and Remote Endpoint.  For example, a Local Endpoint may optionally could be specified, to
   constrain what Connections are accepted.  The Listen() Action
   consumes the Preconnection.  Once Listen() has been called, no
   further properties may
   configured with two interface names, or a Remote Endpoint could be added to the Preconnection,
   specified via both IPv4 and no
   subsequent establishment call may be made on IPv6 addresses.  These multiple
   identifiers refer to the Preconnection.

   Listening continues until same transport endpoint.

   The transport services API resolves names internally, when the global context shuts down,
   Initiate(), Listen(), or until the
   Stop action Rendezvous() method is performed on called establish a
   Connection.  The API explicitly does not require the same Preconnection:

   Preconnection.Stop()

   After Stop() application to
   resolve names, though there is called, a tradeoff between early and late
   binding of addresses to names.  Early binding allows the preconnection can be disposed of.

   Preconnection -> ConnectionReceived<Connection>

   The ConnectionReceived Event occurs 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 Remote Endpoint has
   established a transport-layer connection to this resolution method
   (such as DNS without TLS) which does not protect query
   confidentiality.

   The Resolve() action on Preconnection (for
   Connection-oriented transport protocols), or 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).

5.2.  Specifying Transport Properties

   A Preconnection Object holds properties reflecting the first Message
   has been received from application's
   requirements and preferences for the Remote Endpoint (for Connectionless
   protocols), causing a new Connection to be created.  The resulting transport.  These include
   Selection Properties for selecting protocol stacks and paths, as well
   as Connection is contained within Properties for configuration of the ConnectionReceived event, detailed operation
   of the selected Protocol Stacks.

   The protocol(s) and path(s) selected as candidates during
   establishment are determined and is
   ready configured using these properties.
   Since there could be paths over which some transport protocols are
   unable to use as soon as it operate, or remote endpoints that support only specific
   network addresses or transports, transport protocol selection is passed
   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 application via the
   event.

   Preconnection -> ListenError<>

   A ListenError occurs either when property,  |
   |            | fail otherwise                                       |
   |            |                                                      |
   | Prefer     | Prefer protocols/paths providing the Preconnection cannot be
   fulfilled property,       |
   |            | proceed otherwise                                    |
   |            |                                                      |
   | Ignore     | Cancel any system default preference for listening, when the Local Endpoint (or Remote Endpoint,
   if specified) cannot be resolved, or when this        |
   |            | property                                             |
   |            |                                                      |
   | Avoid      | Prefer protocols/paths not providing the application is
   prohibited from listening by policy.

   Preconnection -> Stopped<>

   A Stopped event occurs after property,   |
   |            | proceed otherwise                                    |
   |            |                                                      |
   | Prohibit   | Select only protocols/paths not providing the Preconnection has stopped listening.

6.3.  Peer-to-Peer Establishment: Rendezvous

   Simultaneous peer-to-peer Connection establishment is supported by        |
   |            | property, fail otherwise                             |
   +------------+------------------------------------------------------+

   Internally, the Rendezvous() Action:

   Preconnection.Rendezvous()

   The Preconnection Object must be specified with both transport system will first exclude all protocols and
   paths that match a Local Endpoint Prohibit, then exclude all protocols and paths
   that do not match a Remote Endpoint, Require, then sort candidates according to
   Preferred properties, and also the transport then use Avoided properties and security
   parameters needed for Protocol Stack selection.

   The Rendezvous() Action causes the Preconnection to listen on the
   Local Endpoint 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 incoming Connection from the Remote Endpoint,
   while simultaneously trying to establish
   interface, but also a Connection from preference for a protocol not available on this
   path, the Local
   Endpoint to transport system will try the Remote Endpoint.  This corresponds to a TCP
   simultaneous open, for example.

   The Rendezvous() Action consumes path first, ignoring the Preconnection.  Once
   Rendezvous() has been called, no further properties may
   preference.

   Both Selection and Connection Properties can be added to a
   Preconnection to configure the Preconnection, selection process, and no subsequent establishment call may be made
   on to further
   configure the Preconnection.

   Preconnection -> RendezvousDone<Connection>

   The RendezvousDone<> Event occurs when eventually selected protocol stack(s).  They are
   collected into 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 TransportProperties object to use as
   soon as it is be passed to the application via the Event.

   Preconnection -> RendezvousError<msgRef, error>

   An RendezvousError occurs either when the into a
   Preconnection cannot be
   fulfilled for listening, when the Local Endpoint or Remote Endpoint
   cannot be resolved, when no transport-layer connection object:

   TransportProperties := NewTransportProperties()

   Individual properties are then added to the TransportProperties
   Object:

   TransportProperties.Add(property, value)

   Selection Properties can be
   established added to the Remote Endpoint, or when the application is
   prohibited from rendezvous by policy.

   When a TransportProperties object
   using some NAT traversal protocols, e.g., Interactive
   Connectivity Establishment (ICE) [RFC5245], it special actions for each preference level i.e,
   "TransportProperties.Add(some_property, avoid)" is expected that 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
   Local Endpoint will 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 with some method of discovering NAT
   bindings, e.g., via a Session Traversal Utilities Preconnection, by configuration after establishment,
   or by inheriting them from an antecedent via cloning; see Section 6.4
   for NAT (STUN) server.
   In this case, more.

   Section 9.1 provides a list of Connection Properties, while Selection
   Properties are listed in the Local Endpoint may resolve to subsections below.  Note that many
   properties are only considered during establishment, and can not be
   changed after a mixture Connection is established; however, they can be
   queried.  Querying a Selection Property after establishment yields
   the value Required for properties of local the selected protocol and server reflexive addresses. 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 Resolve() method on recommended defaults given for each
   property below represent a configuration that can be implemented over
   TCP.  An alternate set of default Protocol Selection Properties would
   represent a configuration that can be implemented over UDP.

5.2.1.  Reliable Data Transfer (Connection)

   This property specifies whether the
   Preconnection can be used application needs to discover these bindings:

   PreconnectionBindings := Preconnection.Resolve()

   The Resolve() call returns use a list of Preconnection Objects,
   transport protocol that
   represent the concrete addresses, local and server reflexive, ensures that all data is received on
   which a Rendezvous() for the Preconnection will listen for incoming
   Connections.
   other side without corruption.  This list can be passed to a peer via also entails being notified when
   a signalling
   protocol, such as SIP [RFC3261] Connection is closed or WebRTC [RFC7478], aborted.  The recommended default is to configure the
   remote.

6.4.  Connection Groups

   Groups of Connections can be created using the Clone Action:

   Connection := Connection.Clone()

   Calling Clone
   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 yields a group Groups.  The
   recommended default is to not have this option.

5.2.3.  Preservation of two Connections: data ordering

   This property specifies whether the
   parent Connection application wishes to use a
   transport protocol that can ensure that data is received by the
   application on which Clone was called, and the resulting clone
   Connection.  These connections are "entangled" 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 each other, and
   become part of an idempotent Message

   This property specifies whether an application would like to supply a
   Message to the transport protocol before Connection group.  Calling Clone on any of these two
   Connections adds a third 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 the group, and so on. not have this
   option.

5.2.5.  Multistream Connections in a Connection Group share all their properties, and
   changing the properties on one Connection in the group changes the

   This property for all others.

   If specifies that the application would prefer multiple
   Connections within a Connection Group to be provided by streams of a
   single underlying Protocol Stack does transport connection where possible.  The
   recommended default is to not support cloning, or cannot
   create a new stream have this option.

5.2.6.  Control checksum coverage on sending or receiving

   This property specifies whether the given Connection, then attempts application considers it useful
   to clone enable, disable, or configure a
   connection will result in checksum when sending a CloneError:

   Connection -> CloneError<>

   There is only one Protocol Property that is Message,
   or configure whether to require a checksum or not entangled: niceness when receiving.

   The recommended default is kept as a separate per-Connection Property for individual
   Connections in full checksum coverage without the group.  Niceness works as in Section 12.3.21: when
   allocating available network capacity among Connections in option
   to configure it, and requiring 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 checksum when receiving.

5.2.7.  Congestion control

   This property specifies whether the application would assign like the
   Connection the capacity share (M-N) x C / M, where N to be congestion controlled or not.  Note that if a
   Connection is the
   Connection's Niceness value, M not congestion controlled, an application using such a
   Connection should itself perform congestion control in accordance
   with [RFC2914].  Also note that reliability is the maximum Niceness value used by
   all Connections usually combined with
   congestion control in the group and C protocol implementations, rendering "reliable
   but not congestion controlled" a request that is the total available capacity.
   However, the niceness setting unlikely to succeed.
   The recommended default is purely advisory, and no guarantees
   are given about that the way capacity is shared.  Each implementation Connection is
   free congestion
   controlled.

5.2.8.  Interface Instance or Type

   This property allows the application to implement a way it shares capacity that select which specific network
   interfaces or categories of interfaces it sees fit.

7.  Sending Data

   Once wants to "Require",
   "Prohibit", "Prefer", or "Avoid".

   In contrast to other Selection Properties, this property is tuple of
   an (Enumerated) interface identifier and a Connection has been established, it preference, and can either
   be used implemented directly as such, or for sending
   data.  Data is sent in terms of Messages, which allow making one preference
   available for each interface and interface type available on the application
   system.

   Note that marking a specific interface as "Required" strictly limits
   path selection to communicate the boundaries of the data being transferred.  By
   default, Send enqueues a complete Message, single interface, and takes optional per-
   Message properties (see Section 7.1).  All Send actions are
   asynchronous, leads to less flexible and deliver events (see Section 7.2).  Sending partial
   Messages for streaming large data
   resilient connection establishment.

   The set of valid interface types is also 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 (see
   Section 7.4).

7.1.  Basic Sending

   The most basic form of sending on a connection involves enqueuing some
   system to all systems, in order to allow applications to write
   generic code.  For example, if a single Data block as a complete Message, with default Message
   Properties.  Message data implementation is created as an array of octets, and the
   resulting object contains used on
   both the byte array mobile devices and desktop devices, it should define the length
   "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 the
   array.

   messageData := "hello".octets()
   Connection.Send(messageData)
   interfaces, and leads to less flexible and resilient connection
   establishment.

   The interpretation set of interface types is expected to change over time as new
   access technologies become available.

   Interface types should not be treated as a Message proxy for properties of
   interfaces such as metered or unmetered network access.  If an
   application needs to prohibit metered interfaces, this should be sent is dependent on the
   implementation,
   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 on the constraints on types (see Section 5.2.8), this
   property allows the Protocol Stacks implied application to control path selection by the Connection's transport properties.  For example,
   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 Message may preference, and can either be a single datagram for UDP Connections;
   implemented directly as such, 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 making one preference available
   for each interface and interface type available on Send to determine the maximum size allowed for a single Message.  If system.

   The identification of a Message specific Provisioning Domain (PvD) is too
   large defined
   to fit in the Maximum Message Size be implementation- and system-specific, since there is not a
   portable standard format for the Connection, the Send
   will fail with a SendError event (Section 7.2.3). PvD identitfier.  For example, it is
   invalid to send a Message over a UDP connection that is larger than
   the available datagram sending size.

   If Send is called on this
   identifier may be a Connection which has not yet been established, string name or an Initiate Action will be implicitly performed simultaneously with
   the Send.  Together integer.  As with the Idempotent property (see
   Section 12.3.9), this can be used to send data during establishment
   for 0-RTT session resumption on Protocol Stacks that support it.

7.2.  Send Events

   Like all Actions in this interface, the Send Action is asynchronous.
   There are several events that can be delivered in response to Sending requiring
   specific interfaces, requiring a Message.

   Note that if partial Sends specific PvD strictly limits path
   selection.

   Categories or types of PvDs are used (Section 7.4), there will still also defined to be exactly one Send Event delivered for each call implementation-
   and system-specific.  These may be useful to Send. identify a service that
   is provided by a PvD.  For example, if a Message expired while two requests an application wants to Send data for use a
   PvD that Message are outstanding, there will be two Expired events
   delivered.

7.2.1.  Sent

   Connection -> Sent<msgRef>

   The Sent Event occurs when provides 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 Voice-Over-IP service on a Cellular network, it
   can use the implementation of relevant PvD type to require some PvD that provides this interface.  The exact
   disposition of the Message (i.e., whether it has actually been
   transmitted, moved into
   service, without needing to look up a buffer 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 network interface, moved into
   a kernel buffer, lifetime of connection establishment.  Similar to Transport
   Properties, both parameters and so on) when the Sent Event occurs is
   implementation-specific.  The Sent Event contains an implementation- callbacks are inherited during
   cloning (see Section 6.4).

5.3.1.  Pre-Connection Parameters

   Common parameters such as TLS ciphersuites are known to
   implementations.  Clients should use common safe defaults for these
   values whenever possible.  However, as discussed in
   [I-D.ietf-taps-transport-security], many transport security protocols
   require specific reference to security parameters and constraints from the Message 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 which it applies.

   Sent Events allow an application perform private key
      operations and prove one's identity to obtain an understanding of the
   amount of buffering it creates.  That is, Remote Endpoint.
      (Note, if an application calls 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
   Send Action multiple times without waiting
      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 a Sent Event, it 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
   created more buffer inside some protocol-specific meaning to the transport system than an application Remote Endpoint.

   SecurityParameters.AddPreSharedKey(key, identity)

5.3.2.  Connection Establishment Callbacks

   Security decisions, especially pertaining to trust, are not static.
   Once configured, parameters may also be supplied during connection
   establishment.  These are best handled as client-provided callbacks.
   Security handshake callbacks that only issues a Send after this Event fires.

7.2.2.  Expired

   Connection -> Expired<msgRef>

   The Expired Event occurs may be invoked during connection
   establishment include:

   o  Trust verification callback: Invoked when a previous Send Action expired Remote Endpoint's
      trust must be validated before
   completion; i.e. when the Message was not sent before its Lifetime
   (see Section 12.3.28) expired.  This is separate from SendError, as
   it is an expected behavior for partially reliable transports.  The
   Expired Event contains an implementation-specific reference to handshake protocol can proceed.

   TrustCallback := NewCallback({
     // Handle trust, return the
   Message to which it applies.

7.2.3.  SendError

   Connection -> SendError<msgRef>

   A SendError occurs result
   })
   SecurityParameters.SetTrustVerificationCallback(trustCallback)

   o  Identity challenge callback: Invoked when a Message could not be sent due to an error
   condition: an attempt to send a Message which private key operation
      is too large 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
   system pre-establishment phase; all
   transport properties and Protocol Stack cryptographic parameter specification must
   be complete before establishment, as these will be used to handle, some failure of the underlying select
   candidate Paths and Protocol Stack, or a set of Message Properties not consistent with
   the Connection's transport properties.  The SendError contains an
   implementation-specific reference to Stacks for the Message to which it applies.

7.3.  Message Context Parameters

   Applications Connection.
   Establishment may need to annotate the Messages they send with extra
   information to control how data is scheduled and processed by be active, using the
   transport protocols in Initiate() Action; passive,
   using the Connection.  A MessageContext object
   contains parameters Listen() Action; or simultaneous for sending Messages, and can be passed to peer-to-peer, using
   the
   Send Rendezvous() Action.  Some of these parameters  These Actions are properties as defined described in
   Section 12.  Note that these properties are per-Message, not per-Send
   if partial Messages are sent (Section 7.4).  All data blocks
   associated with a single Message share properties.  For example, it
   would not make sense to have the beginning of a Message expire, but
   allow
   subsections below.

6.1.  Active Open: Initiate

   Active open is the end Action of establishing a Message Connection to a Remote
   Endpoint presumed 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 listening for incoming Connection requests.
   Active open is
   equivalent to passing 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 default MessageContext
   Preconnection Object with not values added.

   Message Properties share a single namespace with Transport Properties
   (see Section 12).  This allows the specification of per-Connection
   Protocol Properties that can be overridden on Remote Endpoint specifier, optionally a per-Message basis.

   If an application wants
   Local Endpoint specifier (if not specified, the system will attempt
   to override Message Properties for determine a specific
   message, it can acquire an empty messageContext Object and add suitable Local Endpoint), as well as all
   desired Message Properties to that Object.  It can then reuse the
   same messageContext Object properties
   necessary for sending multiple Messages with candidate selection.

   The Initiate() Action consumes the
   same properties.

   Parameters Preconnection.  Once Initiate()
   has been called, no further properties may be added to a messageContext object only before the
   context is used for sending.
   Preconnection, and no subsequent establishment call may be made on
   the Preconnection.

   Once a messageContext has been used
   with a Send call, modifying any of its parameters Initiate is invalid.

   Message Properties called, the candidate Protocol Stack(s) may cause
   one or more candidate transport-layer connections to be inconsistent with created to
   the properties of specified remote endpoint.  The caller may immediately begin
   sending Messages on the
   Protocol Stacks underlying 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 which a given Message multiple
   candidates.

   The following Events may be sent by the Connection after Initiate()
   is
   sent.  For example, a called:

   Connection must provide reliability to allow
   setting an infinitie value -> 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 lifetime property set of transport properties
   and security parameters cannot be fulfilled on a Message.
   Sending a Message with Message Properties inconsistent with Connection for
   initiation (e.g. the
   Selection Properties set of available Paths and/or Protocol Stacks
   meeting the Connection yields an error.

   The following Message Context Parameters are supported:

   [TODO: De-Duplicate with Properties in Section 12, find consensus on
   which Section to put them]

7.3.1.  Lifetime

   [TODO: De-Duplicate with Section 12.3.28]

   Lifetime specifies how long a particular Message 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 wait to be sent established to the remote
   endpoint before it (e.g. because the remote endpoint is irrelevant and no longer needs to
   be (re-)transmitted.  When a Message's Lifetime not accepting
   connections, or the application is infinite, it must
   be transmitted reliably.  The type prohibited from opening a
   Connection by the operating system).

   See also Section 7.6 to combine Connection establishment and units
   transmission of Lifetime are
   implementation-specific.

7.3.2.  Niceness

   [TODO: De-Duplicate with Section 12.3.21]

   Niceness is the first message in a numeric (non-negative) value that represents an
   unbounded hierarchy of priorities single action.

6.2.  Passive Open: Listen

   Passive open is the Action of Messages, relative to other
   Messages sent over waiting for Connections from remote
   endpoints, commonly used by servers in client-server interactions.

   Passive open is supported by this interface through the same Connection and/or Connection Group (see
   Section 6.4).  A Message Listen
   Action:

   Preconnection.Listen()

   Before calling Listen, the caller must have initialized the
   Preconnection during the pre-establishment phase with Niceness 0 will yield to a Message with
   Niceness 1, which will yield Local
   Endpoint specifier, as well as all properties necessary for Protocol
   Stack selection.  A Remote Endpoint may optionally be specified, to a Message with Niceness 2,
   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 so on.
   Niceness no
   subsequent establishment call may be used as a sender-side scheduling construct only, made on the Preconnection.

   Listening continues until the global context shuts down, or
   be used to specify priorities until the
   Stop action is performed on the wire for Protocol Stacks
   supporting prioritization.

   This encoding of same Preconnection:

   Preconnection.Stop()

   After Stop() is called, the priority has preconnection can be disposed of.

   Preconnection -> ConnectionReceived<Connection>

   The ConnectionReceived Event occurs when a convenient property that the
   priority increases as both Niceness and Lifetime decrease.

7.3.3.  Ordered

   [TODO: De-Duplicate with Section 12.3.6]

   Ordered is Remote Endpoint has
   established a boolean property.  If true, transport-layer connection to this Message should be
   delivered after Preconnection (for
   Connection-oriented transport protocols), or when the last first Message passed to
   has been received from the same Remote Endpoint (for Connectionless
   protocols), causing a new Connection via
   the Send Action; if false, this Message may to be delivered out of
   order.

7.3.4.  Idempotent

   [TODO: De-Duplicate with Section 12.3.9]

   Idempotent created.  The resulting
   Connection is a boolean property.  If true, the application-layer
   entity in contained within the Message ConnectionReceived event, and is safe to send
   ready to the remote endpoint more
   than once for a single Send Action.  It use as soon as it is used passed to mark data safe the application via the
   event.

   Preconnection -> ListenError<>

   A ListenError occurs either when the Preconnection cannot be
   fulfilled for
   certain 0-RTT establishment techniques, where retransmission of listening, when the
   0-RTT data may cause Local Endpoint (or Remote Endpoint,
   if specified) cannot be resolved, or when the remote application to receive is
   prohibited from listening by policy.

   Preconnection -> Stopped<>

   A Stopped event occurs after the Message
   multiple times.

7.3.5.  Final

   [TODO: De-Duplicate with Section 12.3.1]

   Final Preconnection has stopped listening.

6.3.  Peer-to-Peer Establishment: Rendezvous

   Simultaneous peer-to-peer Connection establishment is supported by
   the Rendezvous() Action:

   Preconnection.Rendezvous()

   The Preconnection Object must be specified with both a boolean property.  If true, this Message is Local Endpoint
   and a Remote Endpoint, and also the last one
   that transport properties and security
   parameters needed for Protocol Stack selection.

   The Rendezvous() Action causes the application will send on a Connection.  This allows
   underlying protocols to indicate Preconnection to listen on the Remote
   Local Endpoint that the for an incoming 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 from the end of Remote Endpoint,
   while simultaneously trying to establish a Connection in a
   given direction will ignore this property.

   Note that a Final Message must always be sorted from the Local
   Endpoint to the end of Remote Endpoint.  This corresponds to a list
   of Messages. TCP
   simultaneous open, for example.

   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 Rendezvous() Action consumes the Preconnection.  Once
   Rendezvous() has already been sent called, no further properties may be added to
   the Preconnection, and no subsequent establishment call may be made
   on a
   Connection, the new Message will report an error.

7.3.6.  Corruption Protection Length

   [TODO: De-Duplicate Preconnection.

   Preconnection -> RendezvousDone<Connection>

   The RendezvousDone<> Event occurs when a Connection is established
   with Section 12.3.15]

   This numeric property specifies the length of the section of the
   Message, starting from byte 0, that Remote Endpoint.  For Connection-oriented transports, this
   occurs when the application assumes will be
   received without corruption due to lower layer errors.  It transport-layer connection is used to
   specify options for simple integrity protection via checksums.  By
   default, established; for
   Connectionless transports, it occurs when the entire first Message is protected by checksum.  A value of 0
   means that no checksum is required, and a special value (e.g. -1) can
   be used to indicate
   received from the default.  Only full coverage Remote Endpoint.  The resulting Connection is guaranteed,
   any other requests are advisory.

7.3.7.  Transmission Profile

   [TODO: De-Duplicate with Section 12.3.19]

   This enumerated property specifies
   contained within the application's preferred
   tradeoffs for sending this Message; RendezvousDone<> Event, and is ready to use as
   soon as it is a per-Message override of passed to the Capacity Profile protocol and path selection property (see
   Section 12.3.19).

   The following values are valid application via the Event.

   Preconnection -> RendezvousError<msgRef, error>

   An RendezvousError occurs either when the Preconnection cannot be
   fulfilled for Transmission Profile:

   Default:  No special optimizations of listening, when the tradeoff between delay,
      delay variation, and bandwidth efficiency should Local Endpoint or Remote Endpoint
   cannot be made resolved, when
      sending this message.

   Low Latency:  Response time (latency) should no transport-layer connection can be optimized at
   established to the
      expense of efficiently 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 available capacity when sending
      this message.  This can
   Local Endpoint will be used by configured with some method of discovering NAT
   bindings, e.g., a Session Traversal Utilities for NAT (STUN) server.
   In this case, the system Local Endpoint may resolve to disable the
      coalescing a mixture of multiple small Messages into larger packets (Nagle's
      algorithm); to prefer immediate acknowledgment from the peer
      endpoint when supported by local
   and server reflexive addresses.  The Resolve() action on the underlying transport;
   Preconnection can be used to signal discover these bindings:

   []Preconnection := Preconnection.Resolve()

   The Resolve() call returns a
      preference for lower-latency, higher-loss treatment; list of Preconnection Objects, that
   represent the concrete addresses, local and so on.

7.4.  Partial Sends

   It is not always possible server reflexive, on
   which a Rendezvous() for an application to send the Preconnection will listen for incoming
   Connections.  These resolved Preconnections will share all data
   associated other
   Properties with a Message in a single Send Action.  The Message data the Preconnection from which they are derived, though
   some Properties may be too large for made more-specific by the application resolution process.
   This list can be passed to hold in memory at one time, a peer via a signalling protocol, such as
   SIP [RFC3261] or WebRTC [RFC7478], to configure the length remote.

6.4.  Connection Groups

   Groups of the Message may Connections can be unknown or unbounded.

   Partial Message sending is supported by passing an endOfMessage
   boolean parameter to created using the Send Action.  This value is always true by
   default, 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 simpler forms of send resulting cloned
   Connection.  These connections are equivalent to passing true
   for endOfMessage.

   The following example sends a Message in two separate calls to Send.

   messageContext := NewMessageContext()
   messageContext.add(parameter, value)

   messageData := "hel".octets()
   endOfMessage := false
   Connection.Send(messageData, messageContext, endOfMessage)

   messageData := "lo".octets()
   endOfMessage := true
   Connection.Send(messageData, messageContext, endOfMessage)

   All messageData sent "entangled" with the same messageContext object will be
   treated as belonging each other, and
   become part of a Connection Group.  Calling Clone on any of these two
   Connections adds a third Connection to the same Message, 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 constitute an in-
   order series until automatically change this Protocol Property for all Connections
   in the endOfMessage is marked.  Once group in the end same way.  However, changing "Lifetime" (see
   Section 7.3.1) of the a Message is marked, the messageContext object may be re-used as will only affect a new single Message with identical parameters.

7.5.  Batching Sends

   In order to reduce the overhead of sending multiple small Messages on a
   single Connection, entangled or not.

   If the application may want underlying protocol supports multi-streaming, it is natural to batch several Send actions
   together.  This provides a hint
   use this functionality to the system that the sending of
   these Messages should be coalesced when possible, and implement Clone.  In that sending
   any of the batched Messages may be delayed until the last Message in case, entangled
   Connections are multiplexed together, giving them similar treatment
   not only inside endpoints but also across the batch is enqueued.

   Connection.Batch(
       Connection.Send(messageData)
       Connection.Send(messageData)
   )

7.6.  Sender-side Framing

   Sender-side framing allows a caller to provide end-to-end Internet
   path.

   If the interface with a
   function that takes underlying Protocol Stack does not support cloning, or cannot
   create a Message of an appropriate application-layer
   type and returns an array of octets, the on-the-wire representation
   of new stream on the Message to be handed down given Connection, then attempts to the clone a
   connection will result in a CloneError:

   Connection -> CloneError<>

   The Protocol Stack.  It consists
   of Property "Niceness" operates on entangled Connections as
   in Section 7.3.2: when allocating available network capacity among
   Connections in a Framer Object Connection Group, sends on Connections with a single Action, Frame.  Since the Framer
   depends higher
   Niceness values will be prioritized over sends on Connections with
   lower Niceness values.  An ideal transport system implementation
   would assign each Connection the protocol capacity share (M-N) x C / M, where
   N is the Connection's Niceness value, M is the maximum Niceness value
   used at by all Connections in the application layer, it group and C is bound to the Preconnection during total available
   capacity.  However, the pre-establishment phase:

   Preconnection.FrameWith(Framer)

   OctetArray := Framer.Frame(messageData)

   Sender-side framing Niceness setting is a convenience feature of purely advisory, and no
   guarantees are given about the interface, for
   parity with receiver-side framing (see Section 8.4).

8.  Receiving 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 is has been established, it can be used for receiving sending
   data.
   As with sending, data  Data is received sent in terms of Messages.  Receiving is
   an asynchronous operation, in Messages, which each call allow the application
   to Receive communicate the boundaries of the data being transferred.  By
   default, Send enqueues a
   request to receive new 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 from the connection.  Once 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 has been
   received, or an error is encountered, created as an event will be delivered to
   complete array of octets, and the Receive request (see Section 8.2).

   As with sending,
   resulting object contains both the type byte array and the length of the
   array.

   messageData := "hello".octets()
   Connection.Send(messageData)

   The interpretation of a Message to be passed sent is dependent on the
   implementation, and on the constraints on the Protocol Stacks implied
   by the Connection's transport parameters.

8.1.  Enqueuing Receives

   Receive takes two parameters to specify the length of data that an
   application is willing to receive, both of which are optional and
   have default values if not specified.

   Connection.Receive(minIncompleteLength, maxLength)

   By default, Receive will try to deliver complete Messages in a single
   event (Section 8.2.1).

   The application can set properties.  For example, a minIncompleteLength value to indicates the
   smallest partial Message data size in bytes that should be delivered
   in response to this Receive.  By default, this value is infinite,
   which means that only complete Messages should be delivered.  If this
   value is set to some smaller value, the associated receive event will may
   be triggered only when at least that many bytes are available, 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 is complete with fewer bytes, or the system needs to free up
   memory. size.  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 can
   query the case of shorter complete Messages or
   memory issues.

   The maxLength argument indicates protocol property Maximum Message Size on Send to determine
   the maximum size of allowed for a single Message.  If a Message in
   bytes the application is currently prepared too
   large to receive.  The default
   value fit in the Maximum Message Size for maxLength the Connection, the Send
   will fail with a SendError event (Section 7.2.3).  For example, it is infinite.  If an incoming
   invalid to send a Message over a UDP connection that is larger than
   the minimum of available datagram sending size.

7.2.  Send Events

   Like all Actions in this size and the maximum Message size on receive
   for interface, the Connection's Protocol Stack, it will Send Action is asynchronous.
   There are several events that can be delivered via
   ReceivedPartial events (Section 8.2.2). in response to Sending
   a Message.

   Note that maxLength does not guarantee that the application if partial Sends are used (Section 7.4), there will
   receive that many bytes still
   be exactly one Send Event delivered for each call to Send.  For
   example, if they a Message expired while two requests to Send data for
   that Message are available; the interface may
   return ReceivedPartial outstanding, there will be two Expired events with less
   delivered.

7.2.1.  Sent

   Connection -> Sent<msgRef>

   The Sent Event occurs when a previous Send Action has completed,
   i.e., when the data than maxLength according 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 implementation constraints.

8.2.  Receive Events

   Each call the Message to Receive will be paired with a single Receive Event, which can be a success or an error.  This allows it applies.

   Sent Events allow an application to
   provide backpressure to obtain an understanding of the transport stack when
   amount of buffering it is temporarily
   not ready to receive messages.

8.2.1.  Received

   Connection -> Received<messageData, messageContext>

   A Received event indicates creates.  That is, if an application calls the delivery of
   Send Action multiple times without waiting for a complete Message.  It
   contains two objects, Sent Event, it has
   created more buffer inside the received bytes as messageData, and transport system than an application
   that always waits for the
   metadata and properties of 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 received Message was not sent before its Lifetime
   (see Section 7.3.1) expired.  This is separate from SendError, as messageContext.
   See {#receive-context} it
   is an expected behavior for details about the received context. partially reliable transports.  The messageData object provides access
   Expired Event contains an implementation-specific reference 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 to which it applies.

7.2.3.  SendError

   Connection -> ReceivedPartial<messageData, messageContext, endOfMessage>

   If SendError<msgRef>

   A SendError occurs when a complete Message cannot could not be delivered in one event, one part 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 may be delivered Properties not consistent with a ReceivedPartial event.  In order
   to continue
   the Connection's transport properties.  The SendError contains an
   implementation-specific reference to receive more of the same Message, Message to which it applies.

7.3.  Message Properties

   Applications may need to annotate the application must
   invoke Receive again.

   Multiple invocations of ReceivedPartial deliver Messages they send with extra
   information to control how data for the same
   Message is scheduled and processed by passing the same messageContext, until
   transport protocols in the endOfMessage
   flag is delivered.  All 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 of
   associated with a single Message are
   delivered in order without gaps.  This event does share properties.  For example, it
   would not support
   delivering discontiguous partial Messages.

   If make sense to have the minIncompleteLength in beginning of a Message expire, but
   allow the Receive request was set end of a Message to still be
   infinite (indicating 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 request 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 receive a MessageContext object only complete Messages), before the ReceivedPartial event
   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 still be delivered if one of inconsistent with the
   following conditions is true:

   o properties of the underlying
   Protocol Stack supports message boundary
      preservation, and the size of Stacks underlying the Connection on which a given Message is larger than the
      buffers available for
   sent.  For example, a single message;

   o  the underlying Protocol Stack does not support message boundary
      preservation, and the deframer (see Section 8.4) cannot determine Connection must provide reliability to allow
   setting an infinitie value for the end lifetime property of a Message.
   Sending a Message with Message Properties inconsistent with 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
   Selection Properties of message boundary preservation or
   deframing, all bytes received on the Connection will 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 represented
   as one large message of indeterminate length.

8.2.3.  ReceiveError

   Connection -> ReceiveError<messageContext>

   A ReceiveError occurs when data is received by sent
   to the underlying
   Protocol Stack that cannot be fully retrieved or deframed, or when
   some other indication remote endpoint before it is received that reception has failed.  Such
   conditions that irrevocably lead the the termination 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 the
   Connection Lifetime are signaled using ConnectionError instead (see
   Section 10).

   The ReceiveError event passes an optional associated messageContext.
   implementation-specific.

7.3.2.  Niceness

   Type:  Integer (non-negative)

   This may indicate that 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 that was being partially received
   previously, but had not completed, encountered and error and with Niceness 0 will not
   be completed.

8.3. yield to a Message Receive Context

   Each Received with Niceness 1,
   which will yield to a Message Context with Niceness 2, and so on.  Niceness
   may contain metadata from protocols in be used as a sender-side scheduling construct only, or be used to
   specify priorities on the wire for Protocol Stack; which metadata is available Stacks supporting
   prioritization.

   Note that this property is Protocol Stack
   dependent.  The following metadata values are supported:

8.3.1.  ECN

   When available, Message metadata carries the value not a per-message override of the Explicit
   Congestion Notification (ECN) field.  This information
   connection Niceness - see Section 9.1.5.  Both Niceness properties
   may interact, but can be used
   for logging and debugging purposes, independently and for building applications 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 need access was passed to information about the transport internals for
   their own operation.

8.3.2.  Early Data

   In some cases it same Connection via
   the Send Action, when such a Message exists.  If false, the Message
   may be valuable delivered to know whether data was read as
   part the receiving application out of early data streams. order.  This
   property is useful if applications need to
   treat early data separately, e.g., if early used for protocols that support preservation of data has different
   security properties
   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 sent after connection establishment.
   In the case safe for certain 0-RTT establishment techniques, where
   retransmission of TLS 1.3, client early the 0-RTT data can be replayed maliciously
   (see [I-D.ietf-tls-tls13]).  Thus, receivers may wish to perform
   additional checks for early data cause the remote application to ensure it is idempotent or not
   replayed.
   receive the Message multiple times.

7.3.5.  Final

   Type:  Boolean

   If TLS 1.3 true, this Message is available and the recipient Message was sent
   as part of early data, last one that the corresponding metadata carries application will send
   on a flag
   indicating Connection.  This allows underlying protocols to indicate to the
   Remote Endpoint that the Connection has been effectively closed in
   the sending direction.  For example, TCP-based Connections can send a
   FIN once a Message marked as such.  If early data is enabled, applications should
   check this metadata field for Messages received during connection
   establishment and respond accordingly.

8.3.3.  Receiving Final Messages

   The Received Message Context can indicate whether or 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
   is must always be sorted to the Final Message on end of a Connection.  For list
   of Messages.  The Final property overrides Niceness and any Message other
   property that would re-order Messages.  If another Message is sent
   after a Message marked as Final, the application can assume that there will be no more
   Messages received Final has already been sent on a
   Connection, the Connection once Send Action for the new Message has been
   completely delivered. will cause a
   SendError Event.

7.3.6.  Corruption Protection Length

   Type:  Integer (non-negative with -1 as special value)

   This corresponds to the Final property specifies the length of the section of the Message,
   starting from byte 0, that
   may the application requires to be marked on a sent 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 Section 12.3.1.

   Some transport protocols and peers may not support signaling 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
   Final property.  Applications therefore 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 not rely on receiving be sent in such a Message marked Final to know way
   that the other endpoint transport protocol ensures all data is done
   sending received 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 other
   side without corruption.  Changing the 'Reliable Data Transfer'
   property on Messages is only possible if the Connection supports
   reliability.  When this is intended to be fired once per application-layer
   Message sent by not the remote endpoint; i.e., 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 desired 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:

   Default:  No special optimizations of the tradeoff between delay,
      delay variation, and bandwidth efficiency should be made when
      sending this interface that a Send message.

   Low Latency:  Response time (latency) should be optimized at one end the
      expense of a Connection maps efficiently using the available capacity when sending
      this message.  This can be used by the system to
   exactly one Receive on disable the other end.
      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 possible inconsistent with Protocol
   Stacks that provide message boundary preservation, but is not the
   case over Protocol Stacks {prop-cap-profile}} - needs to be
   fixed]

7.3.9.  Singular Transmission

   Type:  Boolean

   This property specifies 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, should be sent 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 received as
   a single packet without transport-layer segmentation or network-layer
   fragmentation.  Attempts to push send a message with this de-
   framing down into the interface, in order to transform an octet
   stream into property set
   with a sequence size greater to the transport's current estimate of Messages.

   Concretely, receiver-side de-framing allows its
   maximum transmission segment size will result in a caller to provide "SendError".  When
   used with transports supporting this functionality and running over
   IP version 4, the
   interface 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 function that takes an octet stream, as provided by
   the underlying Protocol Stack, reads and returns Message in a single Send Action.  The Message of
   an appropriate type data
   may be too large for the application and platform, and leaves the
   octet stream to hold in memory at one time,
   or the start length 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 may be unknown or unbounded.

   Partial Message sending is bound supported by passing an endOfMessage
   boolean parameter to the Preconnection during the pre-establishment phase:

   Preconnection.DeframeWith(Deframer)

   {messageData} := Deframer.Deframe(OctetStream, ...)

9.  Setting Send Action.  This value is always true by
   default, and Querying Connection Properties

   At any point, the application can query Connection Properties.  It
   can also set per-connection Protocol Properties.

   ConnectionProperties := Connection.GetProperties()

   Connection.SetProperty(property, value)

   Depending on the status of the connection, the queried Connection
   Properties will include different information:

   o  The status of the connection, which can be one simpler forms of the following:
      Establishing, Established, Closing, or Closed.

   o  Whether the connection can be used Send are equivalent to send data.  A connection can
      not be used passing true
   for sending if the connection was created with the
      Selection Property "Unidirectional Receive" or if endOfMessage.

   The following example sends a Message marked
      as "Final" was in two separate calls to Send.

   messageContext := NewMessageContext()
   messageContext.add(parameter, value)

   messageData := "hel".octets()
   endOfMessage := false
   Connection.Send(messageData, messageContext, endOfMessage)

   messageData := "lo".octets()
   endOfMessage := true
   Connection.Send(messageData, messageContext, endOfMessage)

   All data sent over this connection, see Section 12.3.1.

   o  Whether with the connection can same MessageContext object will be used treated as
   belonging to receive data.  A connection
      can not be used for reading if the connection was created with same Message, and will constitute an in-order series
   until the endOfMessage is marked.  Once the end of the
      Selection Property "Unidirectional: Send" or if a Message marked
      as "Final" was received, see Section 8.3.3.  The latter is only
      supported by certain transport protocols, e.g., by TCP as half-
      closed connection.

   o  For Connections that are Establishing: Transport Properties that
   marked, the application specified on MessageContext object may be re-used as a new Message
   with identical parameters.

7.5.  Batching Sends

   In order to reduce the Preconnection, see Section 5.2.
      Selection Properties overhead of sending multiple small Messages on
   a Connection can only be queried, not set.

   o  For Connections that are Established, Closing, or Closed (TODO:
      double-check if closed belongs here): Transport Properties of Connection, the
      actual protocols that were selected and instantiated.  These
      features correspond application may want to batch several Send actions
   together.  This provides a hint to the properties given in Section 12 and
      include Selection Properties and Protocol Properties.

      *  Selection Properties indicate whether or not system that the Connection has
         or offers a certain Selection Property.  Note sending of
   these Messages should be coalesced when possible, and that sending
   any of the actually
         instantiated protocol stack batched Messages may not match all Protocol
         Selection Properties that be delayed until the application specified on last Message in
   the
         Preconnection. batch is enqueued.

   Connection.Batch(
       Connection.Send(messageData)
       Connection.Send(messageData)
   )

7.6.  Send on Active Open: InitiateWithIdempotentSend

   For example, application-layer protocols where the Connection initiator also
   sends the first message, the InitiateWithIdempotentSend() action
   combines Connection initiation with a certain Protocol Selection
         Property first Message sent, provided
   that an application specified as Preferred may not
         actually be present message is idempotent.

   Without a message context (as in the chosen protocol stack because none
         of the currently available transport protocols had this
         feature.  Selection Properties of Section 7.1):

   Connection := Preconnection.InitiateWithIdempotentSend(messageData)

   With a message context (as in Section 7.3):

Connection can only be
         queried.

      *  Protocol Properties of := Preconnection.InitiateWithIdempotentSend(messageData, messageContext)

   The message passed to InitiateWithIdempotentSend() is, as suggested
   by the protocol stack in use name, considered to be idempotent (see Section 12.2.2 below).  These can be queried and set.  Certain
         specific Procotol Properties 7.3.4)
   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 read-only, on a protocol-
         and property-specific basis.

   o used
   with the given message when establishing candidate connections.  For Connections
   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 Established, properties of the path(s) in
      use.  These properties can
   equivalent to those that would be derived from the local provisioning
      domain [RFC7556], measurements sent by an invocation of Initate()
   followed immediately by an invocation of Send(), with the caveat that
   a send failure that occurs because the Protocol Stack, or other
      sources.  They can only be queried.

10. Connection Termination

   Close terminates could not be
   established will not result in a Connection after satisfying all SendError separate from the requirements
   that were specified regarding
   InitiateError signaling the delivery failure of Messages that the
   application has already given Connection establishment.

7.7.  Sender-side Framing

   Sender-side framing allows a caller to provide the transport system.  For example,
   if reliable delivery was requested for interface with a Message handed over before
   calling Close, the transport system will ensure
   function that this takes a Message is
   indeed delivered.  If of an appropriate application-layer
   type and returns an array of octets, the Remote Endpoint still has data on-the-wire representation
   of the Message to send, it
   cannot be received after this call.

   Connection.Close()
   The Closed Event can inform 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 that layer, it is bound to
   the Remote Endpoint
   has closed Preconnection during the Connection; however, there pre-establishment phase:

   Preconnection.FrameWith(Framer)

   OctetArray := Framer.Frame(messageData)

   Sender-side framing is no guarantee that a
   remote close will be signaled.

   Connection -> Closed<>

   Abort terminates convenience feature of the interface, for
   parity with receiver-side framing (see Section 8.4).

8.  Receiving Data

   Once a Connection without delivering remaining data:

   Connection.Abort()

   A ConnectionError is established, it can inform the application that 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 other side connection.  Once data has
   aborted the Connection; however, there been
   received, or an error is no guarantee that encountered, an abort event will be signaled:

   Connection -> ConnectionError<>

   A SoftError can inform delivered to
   complete the application about Receive request (see Section 8.2).

   As with sending, the receipt of an ICMP
   error message that does not force termination type of the connection, if
   the underlying protocol stack supports access Message to soft errors;
   however, even if the underlying stack supports it, there is no
   guarantee that a soft error will be signaled.

   Connection -> SoftError<>

11.  Ordering of Operations and Events

   As this interface passed is designed to be independent of concurrency model, dependent on
   the details of how exactly actions are handled, implementation, and on which threads/
   callbacks events are dispatched, are implementation dependent.
   However, the interface does provide constraints on the following guarantees about Protocol Stacks
   implied by the ordering Connection's transport parameters.

8.1.  Enqueuing Receives

   Receive takes two parameters to specify the length of operations:

   o  Received<> will never occur on a Connection before a Ready<> event
      on that Connection, or a ConnectionReceived<> or RendezvousDone<>
      containing data that Connection.

   o  No events will occur on a Connection after a Closed<> event, an
      InitiateError<> or ConnectionError<> on that connection.  To
      ensure this ordering, Closed<> will not occur on a Connection
      while other events on the Connection are still locally outstanding
      (i.e., known
   application is willing to the interface receive, both of which are optional and waiting
   have default values if not specified.

   Connection.Receive(minIncompleteLength, maxLength)

   By default, Receive will try to be dealt with by the
      application).  ConnectionError<> may occur after Closed<>, but the
      interface must gracefully handle the deliver complete Messages in a single
   event (Section 8.2.1).

   The application ignoring these
      errors.

   o  Sent<> events will occur on can set a Connection in minIncompleteLength value to indicates the order
   smallest partial Message data size in bytes that should be delivered
   in response to this Receive.  By default, this value is infinite,
   which the means that only complete Messages were sent (i.e., 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 kernel
   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
      network interface, depending on implementation).

12.  Transport Properties

   Transport Properties allow an application length of the data delivered to control the receive event
   and introspect
   most aspects not assume it will be as long as minIncompleteLength in the case
   of shorter complete Messages or memory issues.

   The maxLength argument indicates the transport system and transport protocols.

   Properties are structured maximum size of a Message in two ways:

   o  By how they influence
   bytes the transport system, which leads application is currently prepared to a
      classification into "Selection Properties", "Protocol Properties",
      "Control Properties" receive.  The default
   value for maxLength is infinite.  If an incoming Message is larger
   than the minimum of this size and "Intents".

   o  By the object they can maximum Message size on receive
   for the Connection's Protocol Stack, it will be applied to: Preconnections, see
      Section 5.2, Connections, see Section 9, and Messages, see
      Section 7.3.

   Because some properties can 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 applied or queried on multiple
   objects, all Transport Properties are organized within paired with a single
   namespace.

   Note that it is possible for a set of specified Transport Properties
   to Receive Event,
   which can be internally inconsistent, a success or an error.  This allows an application to be inconsistent with the later
   use of the API by the application.  Application developers can reduce
   inconsistency by only using the most stringent preference levels when
   failure
   provide backpressure to meet the property would break the application's
   functionality.  For example, transport stack when it can set the Selection Property
   "Reliable Data Transfer", which is a core assumption temporarily
   not ready to receive messages.

8.2.1.  Received

   Connection -> Received<messageData, messageContext>
   A Received event indicates the delivery of many
   application protocols, a complete Message.  It
   contains two objects, the received bytes as Required.  Implementations messageData, and the
   metadata and properties of this
   interface should also raise any detected errors in configuration as
   early the received Message as possible, messageContext.
   See {#receive-context} for details about the received context.

   The messageData object provides access to help ensure the bytes that inconsistencies are caught
   early in were
   received for this Message, along with the development process.

12.1.  Transport Property Types

   Each Transport Property takes a value length of a property-specific type.

12.1.1.  Boolean

   A boolean is a data type that can be either "true" or "false".
   Boolean transport properties should only be used the byte array.

   See Section 8.4 for properties that
   can not 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 used delivered in an optional way or one event, one part of
   the Message may be delivered with a ReceivedPartial event.  In order
   to query the state continue to receive more of the
   transport implementation.  For optional features, especially in
   Selection Properties, same Message, the usage application must
   invoke Receive again.

   Multiple invocations of ReceivedPartial deliver data for the Preference type (see
   Section 12.1.4) same
   Message by passing the same MessageContext, until the endOfMessage
   flag is preferred.

12.1.2.  Enumeration

   Enumeration types are used for transport properties that can take one
   value out of delivered or a limited set ReceiveError occurs.  All partial blocks of choices.  The representation is
   implementation dependent.

12.1.3.  Integer

   Integer types a
   single Message are used to represent integer numbers.  The
   representation is implementation dependent.

12.1.4.  Preference

   The Preference type is used delivered in most Selection properties on a
   Preconnection object to constrain Path Selection and Protocol
   Selection.  It is a specific instance of the "Enum" type and has five
   different preference levels:

   +------------+------------------------------------------------------+
   | Preference | Effect                                               |
   +------------+------------------------------------------------------+
   | Require    | Select only protocols/paths providing the property,  |
   |            | fail otherwise                                       |
   |            |                                                      |
   | Prefer     | Prefer protocols/paths providing the property,       |
   |            | proceed otherwise                                    |
   |            |                                                      |
   | Ignore     | Cancel any default preference for this property      |
   |            |                                                      |
   | Avoid      | Prefer protocols/paths order without gaps.  This event does
   not providing support delivering discontiguous partial Messages.

   If the property,   |
   |            | proceed otherwise                                    |
   |            |                                                      |
   | Prohibit   | Select only protocols/paths not providing minIncompleteLength in the        |
   |            | property, fail otherwise                             |
   +------------+------------------------------------------------------+

   When used on a Connection, this type becomes Receive request was set to be
   infinite (indicating a (read-only) Boolean
   representing whether request to receive only complete Messages),
   the ReceivedPartial event may still be delivered if one of the selected transport
   following conditions is true:

   o  the underlying Protocol Stack supports message boundary
      preservation, and the requested
   feature.

12.2.  Transport Property Classification

   Note:  This section size of the Message is subject to WG discussion on IETF-102.

   Transport Properties - whether they apply to connections,
   preconnections, or messages - differ in larger than the way they affect
      buffers available for a single message;

   o  the
   transport system underlying Protocol Stack does not support message boundary
      preservation, and protocols exposed through the transport system.
   The classification proposed below emphasizes two aspects deframer (see Section 8.4) cannot determine
      the end of how
   properties affect the transport system, so applications know what to
   expect:

   o  Whether properties affect protocols exposed through message using the transport
      system (Protocol Properties) buffer space it has available; or the transport system itself
      (Control Properties)

   o  Whether properties have a clearly defined behavior that is likely
      to be invariant across implementations and environments (Protocol
      Properties and Control Properties) or whether  the properties are
      interpreted underlying Protocol Stack does not support message boundary
      preservation, and no deframer was supplied by the transport system to provide a best effort
      service application

   Note that matches the applications needs as well as possible
      (Intents).

   Note:  in I-D.ietf-taps-interface-00, we had a classification into
      Connection Properties and Message Properties, whereby Connection
      Properties where itself were sub-classified in Protocol-Selection,
      Path-Selection and Protocol properties.

      The classification in this version of the draft emphasizes the way absence of message boundary preservation or
   deframing, all bytes received on the property affects Connection will be represented
   as one large message of indeterminate length.

8.2.3.  ReceiveError

   Connection -> ReceiveError<messageContext>

   A ReceiveError occurs when data is received by the transport system and protocols.  It
      treats 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 aspect termination of whether properties the Connection
   are used on signaled using ConnectionError instead (see Section 10).

   The ReceiveError event passes an optional associated MessageContext.
   This may indicate that a connection,
      preconnection or message as Message that was being partially received
   previously, but had not completed, encountered an orthogonal dimension of
      classification.

      The "Message Properties" error and will not
   be completed.

8.3.  Message Receive Context

   Each Received Message Context may contain metadata from I-D.ietf-taps-interface-00 therefore
      have been split into "Protocol Properties" - emphasizing that they
      affect protocols in
   the protocol configurations - and "Control Properties" -
      emphasizing that they control 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 local transport system itself.

12.2.1.  Selection Properties

   Selection Properties influence protocol and path selection.  Their value usually is or includes a Preference that constrains (in case of
   Require or Prohibit) or influences (Prefer, Ignore, Avoid) the
   selection of transport protocols Explicit
   Congestion Notification (ECN) field.  This information can be used
   for logging and debugging purposes, and paths used.

   An implementation of this interface must provide sensible defaults for Selection Properties.  The defaults given building applications
   which need access to information about the transport internals for each property below
   represent a configuration that can
   their own operation.

8.3.2.  Early Data

   In some cases it may be implemented over TCP.  An
   alternate set valuable to know whether data was read as
   part of default Protocol Selection Properties would
   represent a configuration that can be implemented over UDP.

   Protocol Selection Properties 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 only be set on Preconnections, see
   Section 5.2.  Path Selection Properties are usually used on
   Preconnections, but might also be used on messages replayed maliciously (see
   [I-D.ietf-tls-tls13]).  Thus, receivers may wish to assist per-
   message path selection perform
   additional checks for multipath aware protocols.

12.2.2.  Protocol Properties

   Protocol Properties represent early data to ensure it is idempotent or not
   replayed.  If TLS 1.3 is available and the configuration recipient Message was sent
   as part of early data, the selected
   Protocol Stacks backing corresponding metadata carries a flag
   indicating as such.  If early data is enabled, applications should
   check this metadata field for Messages received during connection
   establishment and respond accordingly.

8.3.3.  Receiving Final Messages

   The Received Message Context can indicate whether or not this Message
   is the Final Message on a Connection.  Some properties apply
   generically across multiple transport protocols, while other
   properties only apply to specific protocols.  Generic properties  For any Message that is marked
   as Final, the application can assume that there will be passed to no more
   Messages received on the selected candidate Protocol Stack(s) to configure
   them before candidate Connection establishment.  The default settings
   of these properties will vary based on once the specific protocols being
   used and Message has been
   completely delivered.  This corresponds to the system's configuration.

   Most Protocol Properties can Final property that
   may be set marked on a Preconnection during pre-
   establishment to preconfigure Protocol Stacks during establishment.

   In order to specify Specific Protocol Properties, Transport System
   implementations sent Message Section 7.3.5.

   Some transport protocols and peers may offer applications to attach a set not support signaling of options the
   Final property.  Applications therefore should not rely on receiving
   a Message marked Final to know that the Preconnection Object, associated with a specific protocol.  For
   example, an application could specify other endpoint is done
   sending on a set of TCP Options connection.

   Any calls to use if
   and only if TCP 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 selected intended to be fired once per application-layer
   Message sent by the system.  Such properties must not
   be assumed to apply across different protocols.  Attempts to set
   specific protocol properties on a protocol stack not containing that
   specific protocol are simply ignored, and do not raise an error.

   Note that many protocol properties have remote endpoint; i.e., it is a corresponding selection desired property which asks for
   of this interface that a protocol providing Send at one end of a specific transport
   feature Connection maps to
   exactly one Receive on the other end.  This is possible with Protocol
   Stacks that provide message boundary preservation, but is controlled by the protocol property.

12.2.3.  Control Properties

   [TODO: Discuss]

   Control properties manage the local transport system behavior or
   request state changes in not the local transport system.  Depending
   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 used, setting evolved over TCP, which does not provide message boundary
   preservation, and since many of these properties might also influence the protocols require message
   boundaries to function, each application layer protocol state machine.  See Section 12.3.1 for an example.

12.2.4.  Intents

   [TODO: Discuss]

   Intents are hints has defined
   its own framing.  A Deframer allows an application to push this de-
   framing down into the transport system that do not directly map interface, in order to transform an octet
   stream into a single protocol/transport feature or behavior sequence of the transport
   system, but express Messages.

   Concretely, receiver-side de-framing allows a presumed application behavior or generic
   application needs.

   The application can expect the transport system caller to take appropriate
   actions involving protocol selection, path selection and, setting of
   protocol flags.  For example, if an application sets provide the "Capacity
   Profile" to "bulk" on
   interface with a Preconnection, this will likely influence
   path selection, DSCP flags in the IP header as well function that takes an octet stream, as niceness provided by
   the underlying Protocol Stack, reads and returns a single Message of
   an appropriate type for
   multi-streaming connections.  When using Intents, the application
   must not expect consistent behavior across different environments,
   implementations or versions and platform, and leaves the
   octet stream at the start of the same implementation.

12.3.  Mandatory Transport Properties

   The following properties are mandatory next Message to implement in a transport
   system:

12.3.1.  Final

   See Section 7.3.5.

   [TODO: Decide whether this is deframe.  It
   consists of a property or Deframer Object with a parameter]

12.3.2.  Reliable Data Transfer (Connection)

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection, Connection (read only)

   This property specifies whether single Action, Deframe.  Since
   the application wishes to use a
   transport protocol that ensures that all data is received Deframer depends on the
   other side without corruption.  This also entails being notified when
   a Connection is closed or aborted.  The default is to enable Reliable
   Data Transfer.

12.3.3.  Configure per-Message reliability

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection, Connection (read only)

   This property specifies whether an protocol used at the application considers layer,
   it useful to
   indicate its reliability requirements on a per-Message basis.  This
   property applies is bound to the Preconnection during the pre-establishment phase:

   Preconnection.DeframeWith(Deframer)

   {messageData} := Deframer.Deframe(OctetStream, ...)

9.  Managing Connections

   After establishment, connections can be configured and queried using
   Connection Groups.  The default
   is to not have this option.

12.3.4.  Reliable Data Transfer (Message)

   Classification:  Protocol Property (Generic)

   Type:  Boolean

   Applicability:  Message

   This property specifies that a message should Properties, and asynchronous information may be sent in such a way
   that available
   about the transport protocol ensures all data is received on state of the other
   side without corruption.  Changing connection via Soft Errors.

   Connection Properties represent the 'Reliable Data Transfer'
   property on Messages is only possible if 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
   supports partial reliability (see stack.  Generic Connection Properties are defined
   in Section 12.3.3).  Therefore, for
   protocols that always transfer data reliably, this property is always
   true 9.1 below.  Specific Protocol Properties are defined in a
   transport- and for protocols 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 always transfer data unreliably, this
   flag is always false.  Changing it may generate specific
   protocol are simply ignored, and do not raise an error.

12.3.5.  Preservation error; however, too
   much reliance by an application on Specific Protocol Properties may
   significantly reduce the flexibility of data ordering

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection, a transport services
   implementation.

   The application can set and query Connection (read only)

   This property specifies whether 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 application wishes to use a
   transport protocol that ensures that data is received by SetProperty action: ~~~
   Connection.SetProperty(property, value) ~~~

   At any point, the application can query Connection Properties.  ~~~
   ConnectionProperties := Connection.GetProperties() ~~~

   Depending on the other end in status of the same order as it was sent. connection, the queried Connection
   Properties will include different information:

   o  The
   default is to preserve data ordering.

12.3.6.  Ordered

   Classification:  Protocol Property (Generic)

   Type:  Boolean

   Applicability:  Message

   This property specifies that a Message should connection state, which can be delivered to one of the
   other side after following:
      Establishing, Established, Closing, or Closed.

   o  Whether the previous Message which was passed connection can be used to the same
   Connection via the Send Action.  It us send data.  A connection can
      not be used for protocols that
   support preservation of data ordering, see Section 12.3.5, but allow
   out-of-order delivery for certain messages.

12.3.7.  Direction of communication

   Classification: sending if the connection was created with the
      Selection Property, Control Property [TODO: Discuss]

   Type:  Enumeration

   Applicability:  Preconnection, Connection (read only)

   This property specifies whether an application wants "Direction of Communication" set to use
      "unidirectional receive" or if a Message marked as "Final" was
      sent over this connection, see Section 7.3.5.

   o  Whether 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 can be used to receive data.

   unidirectional receive:  The connection must support receiving data

   In case a unidirectional  A connection is requested, but unidirectional
   connections are
      can not supported by the transport protocol, be used for reading if the connection was created with the system
   should fall back to bidirectional transport.

12.3.8.  Use 0-RTT session establishment with an idempotent Message

   Classification:
      Selection Property

   Type:  Preference

   Applicability:  Preconnection, Connection (read only)

   This property specifies whether an application would like "Direction of Communication" set to supply
      "unidirectional send" or if a Message to the marked as "Final" was
      received, see Section 8.3.3.  The latter is only supported by
      certain transport protocol before Connection establishment,
   which will then be reliably transferred to protocols, e.g., by TCP as half-closed
      connection.

   o  For Connections that are Establishing: Transport Properties that
      the other side before application specified on the Preconnection, see Section 5.2.

   o  For Connections that are Established, Closing, or
   during Closed:
      Selection (Section 5.2) and Connection establishment, potentially multiple times.  See
   also Section 12.3.9.  The default is to not have this option.

12.3.9.  Idempotent

   Classification:  Control Property

   Type:  Boolean

   Applicability:  Message

   This property specifies Properties (Section 9.1) of
      the actual protocols that a Message is safe to send to were selected and instantiated.
      Selection Properties indicate whether or not the remote
   endpoint more than once for Connection has or
      offers a single Send Action.  It is used to mark
   data safe for certain 0-RTT establishment techniques, where
   retransmission of Selection Property.  Note that the 0-RTT data actually
      instantiated protocol stack may cause not match all Protocol Selection
      Properties that the remote application to
   receive specified on the Message multiple times.

   The Preconnection.
      For example, a certain Protocol Selection Property that an
      application can query specified as Preferred may not actually be present in
      the maximum size chosen protocol stack because none of a message 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
   sent idempotent, see Section 12.3.24.

12.3.10.  Multistream 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 Group

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection, Connection (read only)

   This property specifies that the application would prefer multiple
   Connections within subsections below.

   Note that many protocol properties have a Connection Group to be provided by streams of corresponding selection
   property, which prefers protocols providing a
   single underlying specific transport connection where possible.  The default
   is
   feature that controlled by that protocol property.  [EDITOR'S NOTE:
   todo: add these cross-references up to not have this option.

12.3.11. Section 5.2]

9.1.1.  Notification of excessive retransmissions

   Classification:  Control Property [TODO: Discuss]

   Type:  Boolean

   Applicability:  Preconnection, Connection

   This property specifies whether an application considers it useful to
   be informed in case sent data was retransmitted more often than a
   certain threshold.  When set to true, the effect is twofold: The
   application may receive events in case excessive retransmissions.  In
   addition, the transport system considers this as a preference to use
   transports stacks that can provide this notification.  This is not a
   strict requirement.  If set to false, no notification of excessive
   retransmissions will be sent and this transport feature is ignored
   for protocol selection.

   The default is to have this option.

12.3.12.  Retransmission threshold before excessive retransmission
          notification

   Classification:  Control Property [TODO: Discuss]

   Type:  Integer

   Applicability:  Preconnection, Connection
   This property specifies after how many retransmissions to inform the
   application about "Excessive Retransmissions".

12.3.13.  Notification of ICMP soft error message arrival

   Classification:  Control Property [TODO: Discuss]

   Type:  Boolean

   Applicability:  Preconnection, Connection

   This property specifies whether an application considers it useful to
   be informed when an ICMP error message arrives that does not force
   termination of a connection.  When set to true, received ICMP errors
   will be available as SoftErrors.  Note that even if a protocol
   supporting this property is selected, not all ICMP errors will
   necessarily be delivered, so applications cannot rely on receiving
   them.  Setting this option also implies a preference to prefer
   transports stacks that can provide this notification.  If not set, no
   events will be sent for ICMP soft error message sent 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.

12.3.14.  Control checksum coverage on sending or receiving

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection, Connection (read only)

   This property specifies whether the application considers it useful
   to enable, disable, or configure a checksum when sending a Message,
   or configure whether to require a checksum or not when receiving.
   The default is full checksum coverage without the option to configure
   it, and requiring a checksum when receiving.

12.3.15.  Corruption Protection Length

   Classification:  Protocol Property (Generic)

9.1.2.  Retransmission threshold before excessive retransmission
        notification

   Type:  Integer

   Applicability:  Message

   This numeric property specifies the length of the section of the
   Message, starting from byte 0, that the application assumes will be
   received without corruption due to lower layer errors.  It is used to
   specify options for simple integrity protection via checksums.  By
   default, the entire Message is protected by the checksum.  A value of
   0 means that no checksum is required, and a special value (e.g. -1)
   can be used after how many retransmissions to indicate inform the default.  Only full coverage is
   guaranteed, any other requests are advisory.

12.3.16.  Required minimum coverage
   application about "Excessive Retransmissions".

9.1.3.  Notification of the checksum for receiving

   Classification:  Protocol Property (Generic) ICMP soft error message arrival

   Type:  Integer

   Applicability:  Connection  Boolean

   This property specifies the part of the received data that needs to
   be covered by a checksum.  It is given in Bytes.  A value of 0 means
   that no checksum is required, and a special value (e.g., -1)
   indicates full checksum coverage.

12.3.17.  Interface Instance or Type

   Classification:  Selection Property

   Type:  Tuple (Enumeration, Preference)

   Applicability:  Preconnection, Connection (read only)

   This property allows the whether an application to select which specific network
   interfaces or categories of interfaces considers it wants useful to "Require",
   "Prohibit", "Prefer", or "Avoid".

   If a system supports discovery of specific interface identifiers,
   such as "en0" or "eth0" on Unix-style systems,
   be informed when an implemention should
   allow using these identifiers to define path preferences.  Note ICMP error message arrives 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 does not force
   termination 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 connection.  When set to true, received ICMP errors
   will be "Wi-Fi" and "Wired Ethernet" interface types available.
   Implementations should provide all types available as SoftErrors.  Note that are supported on some
   system to all systems, in order to allow applications to write
   generic code.  For example, even if a single implementation protocol
   supporting this property is used selected, not all ICMP errors will
   necessarily be delivered, so applications cannot rely 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 receiving
   them.  Setting this option also implies a specific
   interface type as "Required" limits path selection preference to a small set of
   interfaces, prefer
   transports stacks that can provide this notification.  If not set, no
   events will be sent for ICMP soft error message and leads this transport
   feature is ignored for protocol selection.

   This property applies to less flexible Connections and resilient connection
   establishment. Connection Groups.  The set of interface types
   recommended default is expected to change over time as new
   access technologies become available.

   Interface types should not be treated as a proxy for properties of
   interfaces such as metered or unmetered network access.  If an
   application needs to prohibit metered interfaces, have this should be
   specified via Provisioning Domain attributes Section 12.3.18 or
   another specific property.

12.3.18.  Provisioning Domain Instance or Type

   Classification:  Selection Property option.

9.1.4.  Required minimum coverage of the checksum for receiving

   Type:  Tuple (Enumeration, Preference)

   Applicability:  Preconnection, Connection (read only)

   Similar to interface instances and types Section 12.3.17, this  Integer

   This property allows specifies 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 part of network
   properties the received data that may needs to
   be more specific than network interfaces
   [RFC7556].

   The identification of covered by a specific Provisioning Domain (PvD) checksum.  It is defined
   to be implementation- and system-specific, since there given in Bytes.  A value of 0 means
   that no checksum is not a
   portable standard format for a PvD identitfier.  For example, this
   identifier may be required, and a string name or an integer.  As with requiring
   specific interfaces, requiring special value (e.g., -1)
   indicates full checksum coverage.

9.1.5.  Niceness (Connection)

   Type:  Integer

   This Property is a specific PvD strictly limits path
   selection.

   Categories or types non-negative integer representing the relative
   inverse priority of PvDs are also defined to be implementation-
   and system-specific.  These may be useful this Connection relative to identify other Connections in
   the same Connection Group.  It has no effect on Connections not part
   of a service that Connection Group.  As noted in Section 6.4, this property is provided by a PvD.  For example, if an application wants not
   entangled when Connections are cloned.

9.1.6.  Timeout for aborting Connection

   Type:  Integer

   This property specifies how long to use wait before aborting a
   PvD Connection
   during establishment, or before deciding that provides a Voice-Over-IP service on 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 Cellular network, it Connection Group, see Section 6.4.  The set of
   schedulers can use 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 relevant PvD type to require some PvD maximum Message size that provides this
   service, without needing to look up a particular instance.  While
   this does restrict path selection, it can be sent
   before or during Connection establishment, see also Section 7.3.4.
   It is more broad than requiring
   specific PvD instances given in Bytes.

9.1.9.  Maximum Message size before fragmentation or interface instances, and should segmentation

   Type:  Integer (read only)

   This property, if applicable, represents the maximum Message size
   that can be
   preferred over those options.

12.3.19.  Capacity Profile

   Classification:  Intent [TODO: Discuss] sent without incurring network-layer fragmentation or
   transport layer segmentation at the sender.

9.1.10.  Maximum Message size on send

   Type:  Enumeration

   Applicability:  Preconnection, Connection,  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.

9.1.12.  Capacity Profile

   This property specifies the application's expectation of the
   dominating traffic pattern desired network treatment for this Connection.  This implies 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.  This can influence path and protocol selection.  The following values
   are valid for the Capacity Profile:

   Default:  The application makes no representation about its expected
      capacity profile.  No special optimizations of the tradeoff
      between delay, delay variation, and bandwidth efficiency should be
      made when selecting and configuring 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: Latency/Interactive:  The application is interactive, and prefers
      loss to latency.  Response time (latency) should be optimized at the expense
      of bandwidth efficiency and delay variation when sending on this message.
      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; to signal a
      preference for lower-latency, higher-loss treatment; and so on.

   Constant Rate:
      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
      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.

   Scavenger/Bulk:
      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 is not interactive.  It expects to send/receive data
      at the maximum rate allowed by its congestion controller over a large amount
      relatively long period of data, time.  Transport system implementations
      that map the requested capacity profile onto per-connection DSCP
      signaling without any urgency.  This
      can, 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 example, be used to select a selected protocol stacks with scavenger
      transmission control, to signal stack may be modified on
   a preference for less-than-best-
      effort treatment, or to assign per-Message basis using the traffic to a lower-effort
      service.

12.3.20.  Congestion control

   Classification:  Selection Property

   Type:  Preference
   Applicability:  Preconnection, Connection (read only) Transmission Profile Message Property;
   see Section 7.3.8.

9.2.  Soft Errors

   Asynchronous introspection is also possible, via the SoftError Event.
   This property specifies whether event informing the application would like about the
   Connection receipt of an ICMP
   error message related to be congestion controlled or not.  Note that 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 is not congestion controlled, an application using such -> SoftError<>

10.  Connection Termination

   Close terminates a Connection should itself perform congestion control in accordance
   with [RFC2914].  Also note after satisfying all the requirements
   that reliability is usually combined with
   congestion control in protocol implementations, rendering "reliable
   but not congestion controlled" 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 request Message handed over before
   calling Close, the transport system will ensure that this Message is unlikely
   indeed delivered.  If the Remote Endpoint still has data to succeed. send, it
   cannot be received after this call.

   Connection.Close()

   The default is Closed Event can inform the application that the Connection is congestion controlled.

12.3.21.  Niceness

   Classification:  Protocol Property (Generic)

   Type:  Integer

   Applicability:  Connection, Message

   This property Remote Endpoint
   has closed the Connection; however, there is a numeric (non-negative) value no guarantee that represents an
   unbounded hierarchy of priorities.  It a
   remote Close will indeed be signaled.

   Connection -> Closed<>

   Abort terminates a Connection without delivering remaining data:

   Connection.Abort()

   A ConnectionError can specify inform the application that the priority of a
   Message, relative to other Messages sent over side has
   aborted the same Connection; however, there is no guarantee that an Abort
   will indeed be signaled.

   Connection
   and/or -> ConnectionError<>

11.  Connection Group (see Section 6.4), or the priority State and Ordering of a
   Connection, relative Operations and Events

   As this interface is designed to other Connections in be independent of an
   implementation's concurrency model, the same Connection
   Group.

   A Message with Niceness 0 will yield to a Message with Niceness 1, details of how exactly
   actions are handled, and on which will yield to a Message threads/callbacks events are
   dispatched, are implementation dependent.

   Each transition of connection state is associated with Niceness 2, and so on.  Niceness
   may be used as one of more
   events:

   o  Ready<> occurs when a sender-side scheduling construct only, Connection created with Initiate() or be used
      InitiateWithIdempotentData() transitions to
   specify priorities on the wire for Protocol Stacks supporting
   prioritization.

   This encoding of the priority has a convenient property that the
   priority increases as both Niceness and Lifetime decrease.

   As noted in Section 6.4, Established state.

   o  ConnectionReceived<> occurs when set on a Connection, this property is
   not entangled when Connections are cloned.

12.3.22.  Timeout for aborting Connection

   Classification:  Control Property [TODO: Discuss]

   Type:  Integer

   Applicability:  Preconnection, Connection
   This property specifies how long created with
      Listen() transitions to wait before aborting Established state.

   o  RendezvousDone<> occurs when a Connection
   during establishment, or before deciding that created with
      Rendezvous() transitions to Established state.

   o  Closed<> occurs when a Connection has failed
   after establishment.  It is given in seconds.

12.3.23.  Connection group transmission scheduler

   Classification:  Protocol Property (Generic) / Control Property
      [TODO: Discuss]

   Type:  Enum

   Applicability:  Preconnection, Connection

   This property specifies which scheduler should be used among
   Connections within transitions to Closed state
      without error.

   o  InitiateError<> occurs when a Connection Group, see Section 6.4.  The set of
   schedulers can be taken from [I-D.ietf-tsvwg-sctp-ndata].

12.3.24.  Maximum message size concurrent created with Initiate()
      transitions from Establishing state to Closed state due to an
      error.

   o  ConnectionError<> occurs when a Connection establishment

   Classification:  Protocol Property (Generic)

   Type:  Integer

   Applicability:  Connection (read only)

   This property represents the maximum Message size that can be sent
   before or during Connection establishment, see also Section 12.3.9.
   It is given transitions to Closed
      state due to an error in Bytes.  This property is read-only.

12.3.25.  Maximum Message size before fragmentation or segmentation

   Classification:  Protocol Property (Generic)

   Type:  Integer

   Applicability:  Connection (read only)

   This property, if applicable, represents the maximum Message size
   that can be sent without incurring network-layer fragmentation and/or
   transport layer segmentation at the sender.  This property is read-
   only.

12.3.26.  Maximum Message size on send

   Classification:  Protocol Property (Generic)

   Type:  Integer
   Applicability:  Connection (read only)

   This property represents the maximum Message size that can be sent.
   This property is read-only.

12.3.27.  Maximum Message size all other circumstances.

   The interface provides the following guarantees about the ordering of
   operations:

   o  Sent<> events will occur on receive

   Classification:  Protocol Property (Generic)

   Type:  Integer

   Applicability: a Connection (read only)

   This numeric property represents in the maximum Message size that can be
   received.  This property is read-only.

12.3.28.  Lifetime

   Classification:  Protocol Property (Generic)

   Type:  Integer

   Applicability:  Message

   Lifetime specifies how long a particular Message can wait to be order in which the
      Messages were sent (i.e., delivered to the remote endpoint kernel or to the
      network interface, depending on implementation).

   o  Received<> will never occur on a Connection before it is irrelevant and no longer needs to
   be (re-)transmitted.  When
      Established; i.e.  before a Message's Lifetime is infinite, Ready<> event on that Connection, or a
      ConnectionReceived<> or RendezvousDone<> containing that
      Connection.

   o  No events will occur on a Connection after it must
   be transmitted reliably.  The type and units of Lifetime 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
   implementation-specific.

12.4.  Optional Transport Properties

   TODO: Maybe move some of still
      locally outstanding (i.e., known to the above properties here.

12.5.  Experimental Transport Properties

   TODO: Move Appendix A here.

13. 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.

14.

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 Section 5.3.  It does not recommend use (or disuse) of specific
   algorithms or protocols.  Any API-compatible transport security
   protocol should work in a TAPS system.

15.

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).

   This work has been supported by the UK Engineering and Physical
   Sciences Research Council under grant EP/R04144X/1.

   Thanks to Stuart Cheshire, Josh Graessley, David Schinazi, and Eric
   Kinnear for their implementation and design efforts, including Happy
   Eyeballs, that heavily influenced this work.  Thanks to Laurent Chuat
   and Jason Lee for initial work on the Post Sockets interface, from
   which this work has evolved.

16.

15.  References

16.1.

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-04 draft-ietf-taps-minset-11 (work
              in progress), June 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>.

16.2.

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>.

   [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 interface specified by this document represents the minimal
   common interface to an endpoint in the transport services
   architecture [I-D.ietf-taps-arch], based upon that architecture and
   on the minimal set of transport service features elaborated in
   [I-D.ietf-taps-minset].  However, the interface has been designed
   with extension points to allow the implementation of features beyond
   those in the minimal common interface: Protocol Selection Properties,
   Path Selection Properties, and Message Properties are open sets.
   Implementations of the interface are free to extend these sets to
   provide additional expressiveness to applications written on top of
   them.

   This appendix enumerates a few additional properties that could be
   used to enhance transport protocol and/or path selection, or the
   transmission of messages given a Protocol Stack that implements them.
   These are not part of the interface, and may be removed from the
   final document, but are presented here to support discussion within
   the TAPS working group as to whether they should be added to a future
   revision of the base specification.

A.1.  Experimental Transport Properties

   The following Transport Properties might be made available in
   addition to those specified in Section 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 this document represents the minimal
   common interface transport protocol, the system
   should fall back to bidirectional transport.

A.1.2.  Suggest a timeout to an endpoint in the transport services
   architecture [I-D.ietf-taps-arch], based upon that architecture and
   on Remote Endpoint

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection

   This property specifies whether an application considers it useful to
   propose a timeout until the minimal set Connection is assumed to be lost.  The
   default is to have this option.

   [EDITOR'S NOTE: For discussion of transport service features elaborated this option, see
   https://github.com/taps-api/drafts/issues/109]

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
   [I-D.ietf-taps-minset].  However, 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 interface has been designed 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 extension points steady data rate

   Bulk:  Bulk transfer of large Messages, presumably bandwidth bound

   The default is to allow 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 implementation of features beyond
   those in stream category suggesting the minimal common interface: Protocol Selection Properties,
   Path Selection Properties,
   Stream Bitrate and Duration intents.

A.1.5.  Size to be Sent or Received

   Classification:  Intent

   Type:  Integer

   Applicability:  Preconnection, Message Properties are open sets.
   Implementations of
   This property specifies how many bytes the interface are free application expects to extend these sets
   send (Size to
   provide additional expressiveness be Sent) or how many bytes the application expects to applications written on top of
   them.
   receive in response (Size to be Received).

A.1.6.  Duration

   Classification:  Intent

   Type:  Integer

   Applicability:  Preconnection

   This appendix enumerates Intent specifies what the application expects the lifetime of a few additional properties that could be
   used
   Connection to enhance transport protocol and/or path selection, 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
   transmission application expects the bit-rate of messages a
   transfer to be.  It is given in Bytes per second.

   On a Protocol Stack that implements them.
   These are not part of the interface, and may be removed from Message, this property specifies at what bitrate the
   final document, but are presented here to support discussion within application
   wishes the TAPS working group as Message to whether they should be added to a future
   revision of sent.  A transport system supporting this
   feature will not exceed the base specification.

A.1.  Experimental Transport Properties

   The following Transport Properties might be made available in
   addition to those specified in Section 12:

A.1.1.  Suggest a timeout requested Send Bitrate even if flow-
   control and congestion control allow higher bitrates.  This helps to the Remote Endpoint
   avoid a bursty traffic pattern on busy streaming video servers.

A.1.8.  Cost Preferences

   Classification:  Selection Property  Intent

   Type:  Preference  Enumeration

   Applicability:  Preconnection  Preconnection, Message

   This property specifies whether describes what an application prefers regarding
   monetary costs, e.g., whether it considers it useful acceptable to utilize
   limited data volume.  It provides hints to
   propose a timeout until the Connection is assumed transport system on
   how to be lost. handle trade-offs between cost and performance or reliability.

   Possible values are:

   No Expense:  Avoid transports associated with monetary cost
   Optimize Cost:  Prefer inexpensive transports and accept service
      degradation

   Balance Cost:  Use system policy to balance cost and other criteria

   Ignore Cost:  Ignore cost, choose transport solely based on other
      criteria

   The default is to have this option.

   [EDITOR'S NOTE: For discussion of this option, see
   https://github.com/taps-api/drafts/issues/109]

A.1.2.  Abort timeout to suggest to the Remote Endpoint

   Classification:  Protocol Property

   Type:  Integer

   Applicability:  Preconnection, Connection "Balance Cost".

Appendix B.  Sample API definition in Go

   This numeric property specifies the timeout to propose to the Remote
   Endpoint.  It is given document defines an abstract interface.  To illustrate how this
   would map concretely into a programming language, an API interface
   definition in seconds.

   [EDITOR'S NOTE: For discussion of Go is available online at https://github.com/mami-
   project/postsocket.  Documentation for this property, see
   https://github.com/taps-api/drafts/issues/109]

A.1.3.  Request not to delay acknowledgment API - an illustration of Message

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection

   This property specifies whether
   the documentation an application considers it useful to 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 able kept largely in sync with the development of this
   abstract interface definition.

Appendix C.  Relationship to request the Minimal Set of Transport Services for
             End Systems

   [I-D.ietf-taps-minset] identifies a Message minimal set of transport services
   that its acknowledgment be sent out
   as early as possible instead 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 potentially being bundled a possible implementation over TCP or, with other
   acknowledgments.
   limitations, UDP.  The default is to not have following text explains how this option.

   [EDITOR'S NOTE: 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 this option, see
   https://github.com/taps-api/drafts/issues/90]

A.1.4.  Traffic Category

   Classification:  Intent

   Type:  Enumeration

   Applicability:  Preconnection [I-D.ietf-taps-minset].

   [EDITOR'S NOTE: This property specifies what is early text.  In the application expect 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 dominating
   traffic pattern intention is for the full minset 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 be
   reflected by the API at some point.]

   o  Connect:
      "Initiate" Action.

   o  Listen:
      "Listen" Action.

   o  Specify number of data with steady data rate

   Bulk:  Bulk attempts and/or timeout for the first
      establishment message:
      TODO.

   o  Disable MPTCP:
      TODO.

   o  Hand over a message to reliably transfer of large Messages, presumably bandwidth bound

   The default is (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 assume any particular traffic pattern.  Most
   categories suggest be delivered for too long:
      TODO: this should probably be covered by the "ConnectionError"
      Event, but the use of other intents to further describe text above it currently reads: "...can inform the
   traffic pattern anticipated, e.g.,
      application that the bulk category suggesting other side has aborted the
   use of Connection".  In
      this case, it is the Message Size intents or local side.

   o  Suggest timeout to the stream category suggesting peer:
      "Suggest a timeout to the
   Stream Bitrate Remote Endpoint" and Duration intents.

A.1.5.  Size "Abort timeout to be Sent
      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 Received

   Classification:  Intent

   Type:  Integer

   Applicability:  Preconnection, Message

   This weight for a scheduler:
      "Niceness (Connection)" property.

   o  "Specify checksum coverage used by the sender" and "Disable
      checksum when sending":
      "Corruption Protection Length" property specifies how many bytes (value 0 to disable).

   o  "Specify minimum checksum coverage required by receiver" and
      "Disable checksum requirement when receiving":
      "Required minimum coverage of the application expects checksum for receiving" property
      (value 0 to
   send (Size disable).

   o  "Specify DF" field and "Request not to be Sent) or how many bytes the application expects bundle messages:"
      The "Singular Transmission" Message property combines both of
      these requests, i.e. if a request not to
   receive bundle messages is made,
      this also turns off DF in response (Size to 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 Received).

A.1.6.  Duration

   Classification:  Intent

   Type:  Integer

   Applicability:  Preconnection

   This Intent specifies what sent using a non-
      fragmented IP packet from the application expects configured interface:
      "Maximum Message size before fragmentation or segmentation"
      property.

   o  Get max. transport-message size that may be received from the lifetime
      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
   connection to be.  It is given 'Low Extra Delay Background Transfer'":
      As suggested in milliseconds.

A.1.7.  Send or Receive Bit-rate

   Classification:  Intent

   Type:  Integer

   Applicability:  Preconnection, Message

   This Intent specifies what 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 expects on the bit-rate of a
   transfer to be.  It other side:
      This is given offered by the "Close" Action with slightly changed
      semantics in Bytes per second.

   On a message, this property specifies at what bitrate 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
   wishes on the Message to be sent.  A transport system supporting this
   feature will other side" and "Abort without
      delivering remaining data, not exceed causing an event informing the requested Send Bitrate even if flow-
   control and congestion control allow higher bitrates.  This helps to
   avoid bursty traffic pattern
      application on busy video streaming servers.

A.1.8.  Cost Preferences

   Classification:  Intent

   Type:  Enumeration

   Applicability:  Preconnection, Message the other side":
      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 is offered by the transport system on
   how to handle trade-offs between cost and performance or reliability.

   Possible values are:

   No Expense:  Avoid transports associated with monetary cost

   Optimize Cost:  Prefer inexpensive transports and accept service
      degradation

   Balance Cost:  Use system policy "Abort" action without promising that this
      is signaled to balance cost and other criteria

   Ignore Cost:  Ignore cost, choose transport solely based on the other
      criteria

   The default 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":

      Reliability is "Balance Cost".

A.1.9.  Immediate

   Classification:  Protocol Property (Generic)

   Type:  Boolean

   Applicability: controlled via the "Reliable Data Transfer
      (Message)" Message

   This property specifies whether property.  Transmitting data without delimiters
      is done by not using a Framer.  The choice of congestion control
      is provided via the caller prefers immediacy "Congestion control" property.

   o  Configurable Message Reliability:
      The "Lifetime" Message Property implements a time-based way to
   efficient capacity usage for this Message.  For example, this means
   that
      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 should property
      "Ordered".

   o  Request not be bundled with other Message into to delay the
   same transmission by acknowledgement (SACK) of a message:
      Should the underlying Protocol Stack.

Appendix B.  Sample API definition in Go

   This document defines an abstract interface.  To illustrate how protocol support it, 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 one of the documentation transport
      features the transport system can use when an application developer would see for an instance 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 this interface - is available online at
   https://godoc.org/github.com/mami-project/postsocket.  This API
   definition will [I-D.ietf-taps-minset] discusses
      how messages can be kept largely obtained from a bytestream in sync case of
      implementation over TCP.  Here, this is dealt with the development 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
   abstract interface definition. information via the "Sent" Event.

   o  Notification to a receiver that a partial message delivery has
      been aborted:
      "ReceiveError" Event.

Authors' Addresses
   Brian Trammell (editor)
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich
   Switzerland

   Email: ietf@trammell.ch

   Michael Welzl (editor)
   University of Oslo
   PO Box 1080 Blindern
   0316  Oslo
   Norway

   Email: michawe@ifi.uio.no

   Theresa Enghardt
   TU Berlin
   Marchstrasse 23
   10587 Berlin
   Germany

   Email: theresa@inet.tu-berlin.de

   Godred Fairhurst
   University of Aberdeen
   Fraser Noble Building
   Aberdeen, AB24 3UE
   Scotland

   Email: gorry@erg.abdn.ac.uk
   URI:   http://www.erg.abdn.ac.uk/

   Mirja Kuehlewind
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich
   Switzerland

   Email: mirja.kuehlewind@tik.ee.ethz.ch
   Colin Perkins
   University of Glasgow
   School of Computing Science
   Glasgow  G12 8QQ
   United Kingdom

   Email: csp@csperkins.org

   Philipp S. Tiesel
   TU Berlin
   Marchstrasse 23
   10587 Berlin
   Germany

   Email: philipp@inet.tu-berlin.de

   Chris Wood
   Apple Inc.
   1 Infinite Loop
   Cupertino, California 95014
   United States of America

   Email: cawood@apple.com