[Docs] [txt|pdf|xml|html] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-trammell-taps-interface) 00 01 02

TAPS Working Group                                      B. Trammell, Ed.
Internet-Draft                                                ETH Zurich
Intended status: Informational                             M. Welzl, Ed.
Expires: January 3, 2019                              University of Oslo
                                                             T. Enghardt
                                                               TU Berlin
                                                            G. Fairhurst
                                                  University of Aberdeen
                                                           M. Kuehlewind
                                                              ETH Zurich
                                                              C. Perkins
                                                   University of Glasgow
                                                               P. Tiesel
                                                               TU Berlin
                                                                 C. Wood
                                                              Apple Inc.
                                                           July 02, 2018


     An Abstract Application Layer Interface to Transport Services
                      draft-ietf-taps-interface-01

Abstract

   This document describes an abstract programming interface to the
   transport layer, following the Transport Services Architecture.  It
   supports the asynchronous, atomic transmission of messages over
   transport protocols and network paths dynamically selected at
   runtime.  It is intended to replace the traditional BSD sockets API
   as the lowest common denominator interface to the transport layer, in
   an environment where endpoints have multiple interfaces and potential
   transport protocols to select from.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."




Trammell, et al.         Expires January 3, 2019                [Page 1]


Internet-Draft               TAPS Interface                    July 2018


   This Internet-Draft will expire on January 3, 2019.

Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   2.  Terminology and Notation  . . . . . . . . . . . . . . . . . .   5
   3.  Interface Design Principles . . . . . . . . . . . . . . . . .   6
   4.  API Summary . . . . . . . . . . . . . . . . . . . . . . . . .   7
   5.  Pre-Establishment Phase . . . . . . . . . . . . . . . . . . .   7
     5.1.  Specifying Endpoints  . . . . . . . . . . . . . . . . . .   8
     5.2.  Specifying Transport Properties . . . . . . . . . . . . .   9
     5.3.  Specifying Security Parameters and Callbacks  . . . . . .  10
       5.3.1.  Pre-Connection Parameters . . . . . . . . . . . . . .  11
       5.3.2.  Connection Establishment Callbacks  . . . . . . . . .  12
   6.  Establishing Connections  . . . . . . . . . . . . . . . . . .  12
     6.1.  Active Open: Initiate . . . . . . . . . . . . . . . . . .  12
     6.2.  Passive Open: Listen  . . . . . . . . . . . . . . . . . .  13
     6.3.  Peer-to-Peer Establishment: Rendezvous  . . . . . . . . .  14
     6.4.  Connection Groups . . . . . . . . . . . . . . . . . . . .  16
   7.  Sending Data  . . . . . . . . . . . . . . . . . . . . . . . .  16
     7.1.  Basic Sending . . . . . . . . . . . . . . . . . . . . . .  17
     7.2.  Send Events . . . . . . . . . . . . . . . . . . . . . . .  17
       7.2.1.  Sent  . . . . . . . . . . . . . . . . . . . . . . . .  18
       7.2.2.  Expired . . . . . . . . . . . . . . . . . . . . . . .  18
       7.2.3.  SendError . . . . . . . . . . . . . . . . . . . . . .  18
     7.3.  Message Context Parameters  . . . . . . . . . . . . . . .  18
       7.3.1.  Lifetime  . . . . . . . . . . . . . . . . . . . . . .  19
       7.3.2.  Niceness  . . . . . . . . . . . . . . . . . . . . . .  20
       7.3.3.  Ordered . . . . . . . . . . . . . . . . . . . . . . .  20
       7.3.4.  Idempotent  . . . . . . . . . . . . . . . . . . . . .  20
       7.3.5.  Final . . . . . . . . . . . . . . . . . . . . . . . .  20
       7.3.6.  Corruption Protection Length  . . . . . . . . . . . .  21
       7.3.7.  Transmission Profile  . . . . . . . . . . . . . . . .  21



Trammell, et al.         Expires January 3, 2019                [Page 2]


Internet-Draft               TAPS Interface                    July 2018


     7.4.  Partial Sends . . . . . . . . . . . . . . . . . . . . . .  22
     7.5.  Batching Sends  . . . . . . . . . . . . . . . . . . . . .  22
     7.6.  Sender-side Framing . . . . . . . . . . . . . . . . . . .  23
   8.  Receiving Data  . . . . . . . . . . . . . . . . . . . . . . .  23
     8.1.  Enqueuing Receives  . . . . . . . . . . . . . . . . . . .  23
     8.2.  Receive Events  . . . . . . . . . . . . . . . . . . . . .  24
       8.2.1.  Received  . . . . . . . . . . . . . . . . . . . . . .  24
       8.2.2.  ReceivedPartial . . . . . . . . . . . . . . . . . . .  24
       8.2.3.  ReceiveError  . . . . . . . . . . . . . . . . . . . .  25
     8.3.  Message Receive Context . . . . . . . . . . . . . . . . .  25
       8.3.1.  ECN . . . . . . . . . . . . . . . . . . . . . . . . .  26
       8.3.2.  Early Data  . . . . . . . . . . . . . . . . . . . . .  26
       8.3.3.  Receiving Final Messages  . . . . . . . . . . . . . .  26
     8.4.  Receiver-side De-framing over Stream Protocols  . . . . .  26
   9.  Setting and Querying Connection Properties  . . . . . . . . .  27
   10. Connection Termination  . . . . . . . . . . . . . . . . . . .  28
   11. Ordering of Operations and Events . . . . . . . . . . . . . .  29
   12. Transport Properties  . . . . . . . . . . . . . . . . . . . .  30
     12.1.  Transport Property Types . . . . . . . . . . . . . . . .  30
       12.1.1.  Boolean  . . . . . . . . . . . . . . . . . . . . . .  30
       12.1.2.  Enumeration  . . . . . . . . . . . . . . . . . . . .  31
       12.1.3.  Integer  . . . . . . . . . . . . . . . . . . . . . .  31
       12.1.4.  Preference . . . . . . . . . . . . . . . . . . . . .  31
     12.2.  Transport Property Classification  . . . . . . . . . . .  31
       12.2.1.  Selection Properties . . . . . . . . . . . . . . . .  32
       12.2.2.  Protocol Properties  . . . . . . . . . . . . . . . .  33
       12.2.3.  Control Properties . . . . . . . . . . . . . . . . .  33
       12.2.4.  Intents  . . . . . . . . . . . . . . . . . . . . . .  33
     12.3.  Mandatory Transport Properties . . . . . . . . . . . . .  34
       12.3.1.  Final  . . . . . . . . . . . . . . . . . . . . . . .  34
       12.3.2.  Reliable Data Transfer (Connection)  . . . . . . . .  34
       12.3.3.  Configure per-Message reliability  . . . . . . . . .  34
       12.3.4.  Reliable Data Transfer (Message) . . . . . . . . . .  35
       12.3.5.  Preservation of data ordering  . . . . . . . . . . .  35
       12.3.6.  Ordered  . . . . . . . . . . . . . . . . . . . . . .  35
       12.3.7.  Direction of communication . . . . . . . . . . . . .  36
       12.3.8.  Use 0-RTT session establishment with an idempotent
                Message  . . . . . . . . . . . . . . . . . . . . . .  36
       12.3.9.  Idempotent . . . . . . . . . . . . . . . . . . . . .  36
       12.3.10. Multistream Connections in Group . . . . . . . . . .  37
       12.3.11. Notification of excessive retransmissions  . . . . .  37
       12.3.12. Retransmission threshold before excessive
                retransmission notification  . . . . . . . . . . . .  37
       12.3.13. Notification of ICMP soft error message arrival  . .  38
       12.3.14. Control checksum coverage on sending or receiving  .  38
       12.3.15. Corruption Protection Length . . . . . . . . . . . .  38
       12.3.16. Required minimum coverage of the checksum for
                receiving  . . . . . . . . . . . . . . . . . . . . .  39



Trammell, et al.         Expires January 3, 2019                [Page 3]


Internet-Draft               TAPS Interface                    July 2018


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

1.  Introduction

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




Trammell, et al.         Expires January 3, 2019                [Page 4]


Internet-Draft               TAPS Interface                    July 2018


   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.





Trammell, et al.         Expires January 3, 2019                [Page 5]


Internet-Draft               TAPS Interface                    July 2018


   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




Trammell, et al.         Expires January 3, 2019                [Page 6]


Internet-Draft               TAPS Interface                    July 2018


      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.



Trammell, et al.         Expires January 3, 2019                [Page 7]


Internet-Draft               TAPS Interface                    July 2018


   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)




Trammell, et al.         Expires January 3, 2019                [Page 8]


Internet-Draft               TAPS Interface                    July 2018


   LocalSpecifier := NewLocalEndpoint()
   LocalSpecifier.WithStunServer(address, port, credentials)

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

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

   The transport services API will resolve names internally, when the
   Initiate(), Listen(), or Rendezvous() method is called establish a
   Connection.  The API does not need the application to resolve names,
   and premature name resolution can damage performance by limiting the
   scope for alternate path discovery during Connection establishment.
   The Resolve() method is, however, provided to resolve a Local
   Endpoint or a Remote Endpoint in cases where this is required, for
   example with some Network Address Translator (NAT) traversal
   protocols (see Section 6.3).

5.2.  Specifying Transport Properties

   A Preconnection Object holds properties reflecting the application's
   requirements and preferences for the transport.  These include
   Selection Properties (Protocol and Path Selection Properties), as
   well as Generic and Specific Protocol Properties for configuration of
   the detailed operation of the selected Protocol Stacks.

   The protocol(s) and path(s) selected as candidates during Connection
   establishment are determined by a set of properties.  Since there
   could be paths over which some transport protocols are unable to
   operate, or remote endpoints that support only specific network
   addresses or transports, transport protocol selection is necessarily
   tied to path selection.  This may involve choosing between multiple
   local interfaces that are connected to different access networks.

   Internally, the transport system will first exclude all protocols and
   paths that match a Prohibit, then exclude all protocols and paths
   that do not match a Require, then sort candidates according to
   Preferred properties, and then use Avoided properties as a
   tiebreaker.  In case of conflicts between Protocol and Path Selection
   Properties, Path Selection Properties take precedence.  For example,
   if an application indicates a preference for a specific path, but
   also a preference for a protocol not available on this path, the




Trammell, et al.         Expires January 3, 2019                [Page 9]


Internet-Draft               TAPS Interface                    July 2018


   transport system will try the path first, so the Protocol Selection
   Property might not have an effect.

   All Transport Properties used in the pre-establishment phase are
   collected in a TransportProperties Object that is passed to the
   Preconnection Object.

   TransportProperties := NewTransportProperties()

   The Individual properties are then added to the TransportProperties
   Object.

   TransportProperties.Add(property, value)

   Transport Properties of Preference Type, see Section 12.1.4, can use
   special calls to add a Property with a specific preference level,
   i.e, "TransportProperties.Add('some preference', avoid)" is
   equivalent to "TransportProperties.Avoid('some preference')"

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

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

   TransportProperties := Connection.GetTransportProperties()

   Section 12 provides a list of Transport Properties.

   Note that most properties are only considered for Connection
   establishment and can not be changed after a Connection is
   established; however, they can be queried.  See Section 9.

   A Connection gets its Transport Properties either by being explicitly
   configured via a Preconnection, or by inheriting them from an
   antecedent via cloning; see Section 6.4 for more.

5.3.  Specifying Security Parameters and Callbacks

   Most security parameters, e.g., TLS ciphersuites, local identity and
   private key, etc., may be configured statically.  Others are
   dynamically configured during connection establishment.  Thus, we
   partition security parameters and callbacks based on their place in
   the lifetime of connection establishment.  Similar to Transport




Trammell, et al.         Expires January 3, 2019               [Page 10]


Internet-Draft               TAPS Interface                    July 2018


   Properties, both parameters and callbacks are inherited during
   cloning (see Section 6.4).

5.3.1.  Pre-Connection Parameters

   Common parameters such as TLS ciphersuites are known to
   implementations.  Clients should use common safe defaults for these
   values whenever possible.  However, as discussed in
   [I-D.ietf-taps-transport-security], many transport security protocols
   require specific security parameters and constraints from the client
   at the time of configuration and actively during a handshake.  These
   configuration parameters are created as follows:

   SecurityParameters := NewSecurityParameters()

   Security configuration parameters and sample usage follow:

   o  Local identity and private keys: Used to perform private key
      operations and prove one's identity to the Remote Endpoint.
      (Note, if private keys are not available, e.g., since they are
      stored in HSMs, handshake callbacks must be used.  See below for
      details.)

   SecurityParameters.AddIdentity(identity)
   SecurityParameters.AddPrivateKey(privateKey, publicKey)

   o  Supported algorithms: Used to restrict what parameters are used by
      underlying transport security protocols.  When not specified,
      these algorithms should default to known and safe defaults for the
      system.  Parameters include: ciphersuites, supported groups, and
      signature algorithms.

SecurityParameters.AddSupportedGroup(secp256k1)
SecurityParameters.AddCiphersuite(TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256)
SecurityParameters.AddSignatureAlgorithm(ed25519)

   o  Session cache management: Used to tune cache capacity, lifetime,
      re-use, and eviction policies, e.g., LRU or FIFO.  Constants and
      policies for these interfaces are implementation-specific.

   SecurityParameters.SetSessionCacheCapacity(MAX_CACHE_ELEMENTS)
   SecurityParameters.SetSessionCacheLifetime(SECONDS_PER_DAY)
   SecurityParameters.SetSessionCachePolicy(CachePolicyOneTimeUse)

   o  Pre-Shared Key import: Used to install pre-shared keying material
      established out-of-band.  Each pre-shared keying material is
      associated with some identity that typically identifies its use or
      has some protocol-specific meaning to the Remote Endpoint.



Trammell, et al.         Expires January 3, 2019               [Page 11]


Internet-Draft               TAPS Interface                    July 2018


   SecurityParameters.AddPreSharedKey(key, identity)

5.3.2.  Connection Establishment Callbacks

   Security decisions, especially pertaining to trust, are not static.
   Once configured, parameters may also be supplied during connection
   establishment.  These are best handled as client-provided callbacks.
   Security handshake callbacks that may be invoked during connection
   establishment include:

   o  Trust verification callback: Invoked when a Remote Endpoint's
      trust must be validated before the handshake protocol can proceed.

   TrustCallback := NewCallback({
     // Handle trust, return the result
   })
   SecurityParameters.SetTrustVerificationCallback(trustCallback)

   o  Identity challenge callback: Invoked when a private key operation
      is required, e.g., when local authentication is requested by a
      remote.

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

6.  Establishing Connections

   Before a Connection can be used for data transfer, it must be
   established.  Establishment ends the pre-establishment phase; all
   transport properties and cryptographic parameter specification must
   be complete before establishment, as these will be used to select
   candidate Paths and Protocol Stacks for the Connection.
   Establishment may be active, using the Initiate() Action; passive,
   using the Listen() Action; or simultaneous for peer-to-peer, using
   the Rendezvous() Action.  These Actions are described in the
   subsections below.

6.1.  Active Open: Initiate

   Active open is the Action of establishing a Connection to a Remote
   Endpoint presumed to be listening for incoming Connection requests.
   Active open is used by clients in client-server interactions.  Active
   open is supported by this interface through the Initiate Action:

   Connection := Preconnection.Initiate()




Trammell, et al.         Expires January 3, 2019               [Page 12]


Internet-Draft               TAPS Interface                    July 2018


   Before calling Initiate, the caller must have populated a
   Preconnection Object with a Remote Endpoint specifier, optionally a
   Local Endpoint specifier (if not specified, the system will attempt
   to determine a suitable Local Endpoint), as well as all properties
   necessary for candidate selection.  After calling Initiate, no
   further properties may be added to the Preconnection.  The Initiate()
   call consumes the Preconnection and creates a Connection Object.  A
   Preconnection can only be initiated once.

   Once Initiate is called, the candidate Protocol Stack(s) may cause
   one or more candidate transport-layer connections to be created to
   the specified remote endpoint.  The caller may immediately begin
   sending Messages on the Connection (see Section 7) after calling
   Initate(); note that any idempotent data sent while the Connection is
   being established may be sent multiple times or on multiple
   candidates.

   The following Events may be sent by the Connection after Initiate()
   is called:

   Connection -> Ready<>

   The Ready Event occurs after Initiate has established a transport-
   layer connection on at least one usable candidate Protocol Stack over
   at least one candidate Path.  No Receive Events (see Section 8) will
   occur before the Ready Event for Connections established using
   Initiate.

   Connection -> InitiateError<>

   An InitiateError occurs either when the set of transport properties
   and cryptographic parameters cannot be fulfilled on a Connection for
   initiation (e.g. the set of available Paths and/or Protocol Stacks
   meeting the constraints is empty) or reconciled with the local and/or
   remote endpoints; when the remote specifier cannot be resolved; or
   when no transport-layer connection can be established to the remote
   endpoint (e.g. because the remote endpoint is not accepting
   connections, or the application is prohibited from opening a
   Connection by the operating system).

6.2.  Passive Open: Listen

   Passive open is the Action of waiting for Connections from remote
   endpoints, commonly used by servers in client-server interactions.
   Passive open is supported by this interface through the Listen
   Action:

   Preconnection.Listen()



Trammell, et al.         Expires January 3, 2019               [Page 13]


Internet-Draft               TAPS Interface                    July 2018


   Before calling Listen, the caller must have initialized the
   Preconnection during the pre-establishment phase with a Local
   Endpoint specifier, as well as all properties necessary for Protocol
   Stack selection.  A Remote Endpoint may optionally be specified, to
   constrain what Connections are accepted.  The Listen() Action
   consumes the Preconnection.  Once Listen() has been called, no
   further properties may be added to the Preconnection, and no
   subsequent establishment call may be made on the Preconnection.

   Listening continues until the global context shuts down, or until the
   Stop action is performed on the same Preconnection:

   Preconnection.Stop()

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

   Preconnection -> ConnectionReceived<Connection>

   The ConnectionReceived Event occurs when a Remote Endpoint has
   established a transport-layer connection to this Preconnection (for
   Connection-oriented transport protocols), or when the first Message
   has been received from the Remote Endpoint (for Connectionless
   protocols), causing a new Connection to be created.  The resulting
   Connection is contained within the ConnectionReceived event, and is
   ready to use as soon as it is passed to the application via the
   event.

   Preconnection -> ListenError<>

   A ListenError occurs either when the Preconnection cannot be
   fulfilled for listening, when the Local Endpoint (or Remote Endpoint,
   if specified) cannot be resolved, or when the application is
   prohibited from listening by policy.

   Preconnection -> Stopped<>

   A Stopped event occurs after the Preconnection has stopped listening.

6.3.  Peer-to-Peer Establishment: Rendezvous

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

   Preconnection.Rendezvous()

   The Preconnection Object must be specified with both a Local Endpoint
   and a Remote Endpoint, and also the transport properties and security
   parameters needed for Protocol Stack selection.



Trammell, et al.         Expires January 3, 2019               [Page 14]


Internet-Draft               TAPS Interface                    July 2018


   The Rendezvous() Action causes the Preconnection to listen on the
   Local Endpoint for an incoming Connection from the Remote Endpoint,
   while simultaneously trying to establish a Connection from the Local
   Endpoint to the Remote Endpoint.  This corresponds to a TCP
   simultaneous open, for example.

   The Rendezvous() Action consumes the Preconnection.  Once
   Rendezvous() has been called, no further properties may be added to
   the Preconnection, and no subsequent establishment call may be made
   on the Preconnection.

   Preconnection -> RendezvousDone<Connection>

   The RendezvousDone<> Event occurs when a Connection is established
   with the Remote Endpoint.  For Connection-oriented transports, this
   occurs when the transport-layer connection is established; for
   Connectionless transports, it occurs when the first Message is
   received from the Remote Endpoint.  The resulting Connection is
   contained within the RendezvousDone<> Event, and is ready to use as
   soon as it is passed to the application via the Event.

   Preconnection -> RendezvousError<msgRef, error>

   An RendezvousError occurs either when the Preconnection cannot be
   fulfilled for listening, when the Local Endpoint or Remote Endpoint
   cannot be resolved, when no transport-layer connection can be
   established to the Remote Endpoint, or when the application is
   prohibited from rendezvous by policy.

   When using some NAT traversal protocols, e.g., Interactive
   Connectivity Establishment (ICE) [RFC5245], it is expected that the
   Local Endpoint will be configured with some method of discovering NAT
   bindings, e.g., a Session Traversal Utilities for NAT (STUN) server.
   In this case, the Local Endpoint may resolve to a mixture of local
   and server reflexive addresses.  The Resolve() method on the
   Preconnection can be used to discover these bindings:

   PreconnectionBindings := Preconnection.Resolve()

   The Resolve() call returns a list of Preconnection Objects, that
   represent the concrete addresses, local and server reflexive, on
   which a Rendezvous() for the Preconnection will listen for incoming
   Connections.  This list can be passed to a peer via a signalling
   protocol, such as SIP [RFC3261] or WebRTC [RFC7478], to configure the
   remote.






Trammell, et al.         Expires January 3, 2019               [Page 15]


Internet-Draft               TAPS Interface                    July 2018


6.4.  Connection Groups

   Groups of Connections can be created using the Clone Action:

   Connection := Connection.Clone()

   Calling Clone on a Connection yields a group of two Connections: the
   parent Connection on which Clone was called, and the resulting clone
   Connection.  These connections are "entangled" with each other, and
   become part of a Connection group.  Calling Clone on any of these two
   Connections adds a third Connection to the group, and so on.
   Connections in a Connection Group share all their properties, and
   changing the properties on one Connection in the group changes the
   property for all others.

   If the underlying Protocol Stack does not support cloning, or cannot
   create a new stream on the given Connection, then attempts to clone a
   connection will result in a CloneError:

   Connection -> CloneError<>

   There is only one Protocol Property that is not entangled: niceness
   is kept as a separate per-Connection Property for individual
   Connections in the group.  Niceness works as in Section 12.3.21: when
   allocating available network capacity among Connections in a
   Connection Group, sends on Connections with higher Niceness values
   will be prioritized over sends on Connections with lower Niceness
   values.  An ideal transport system implementation would assign the
   Connection the capacity share (M-N) x C / M, where N is the
   Connection's Niceness value, M is the maximum Niceness value used by
   all Connections in the group and C is the total available capacity.
   However, the niceness setting is purely advisory, and no guarantees
   are given about the way capacity is shared.  Each implementation is
   free to implement a way it shares capacity that it sees fit.

7.  Sending Data

   Once a Connection has been established, it can be used for sending
   data.  Data is sent in terms of Messages, which allow the application
   to communicate the boundaries of the data being transferred.  By
   default, Send enqueues a complete Message, and takes optional per-
   Message properties (see Section 7.1).  All Send actions are
   asynchronous, and deliver events (see Section 7.2).  Sending partial
   Messages for streaming large data is also supported (see
   Section 7.4).






Trammell, et al.         Expires January 3, 2019               [Page 16]


Internet-Draft               TAPS Interface                    July 2018


7.1.  Basic Sending

   The most basic form of sending on a connection involves enqueuing a
   single Data block as a complete Message, with default Message
   Properties.  Message data is created as an array of octets, and the
   resulting object contains both the byte array and the length of the
   array.

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

   The interpretation of a Message to be sent is dependent on the
   implementation, and on the constraints on the Protocol Stacks implied
   by the Connection's transport properties.  For example, a Message may
   be a single datagram for UDP Connections; or an HTTP Request for HTTP
   Connections.

   Some transport protocols can deliver arbitrarily sized Messages, but
   other protocols constrain the maximum Message size.  Applications can
   query the protocol property Maximum Message Size on Send to determine
   the maximum size allowed for a single Message.  If a Message is too
   large to fit in the Maximum Message Size for the Connection, the Send
   will fail with a SendError event (Section 7.2.3).  For example, it is
   invalid to send a Message over a UDP connection that is larger than
   the available datagram sending size.

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

7.2.  Send Events

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

   Note that if partial Sends are used (Section 7.4), there will still
   be exactly one Send Event delivered for each call to Send.  For
   example, if a Message expired while two requests to Send data for
   that Message are outstanding, there will be two Expired events
   delivered.








Trammell, et al.         Expires January 3, 2019               [Page 17]


Internet-Draft               TAPS Interface                    July 2018


7.2.1.  Sent

   Connection -> Sent<msgRef>

   The Sent Event occurs when a previous Send Action has completed,
   i.e., when the data derived from the Message has been passed down or
   through the underlying Protocol Stack and is no longer the
   responsibility of the implementation of this interface.  The exact
   disposition of the Message (i.e., whether it has actually been
   transmitted, moved into a buffer on the network interface, moved into
   a kernel buffer, and so on) when the Sent Event occurs is
   implementation-specific.  The Sent Event contains an implementation-
   specific reference to the Message to which it applies.

   Sent Events allow an application to obtain an understanding of the
   amount of buffering it creates.  That is, if an application calls the
   Send Action multiple times without waiting for a Sent Event, it has
   created more buffer inside the transport system than an application
   that only issues a Send after this Event fires.

7.2.2.  Expired

   Connection -> Expired<msgRef>

   The Expired Event occurs when a previous Send Action expired before
   completion; i.e. when the Message was not sent before its Lifetime
   (see Section 12.3.28) expired.  This is separate from SendError, as
   it is an expected behavior for partially reliable transports.  The
   Expired Event contains an implementation-specific reference to the
   Message to which it applies.

7.2.3.  SendError

   Connection -> SendError<msgRef>

   A SendError occurs when a Message could not be sent due to an error
   condition: an attempt to send a Message which is too large for the
   system and Protocol Stack to handle, some failure of the underlying
   Protocol Stack, or a set of Message Properties not consistent with
   the Connection's transport properties.  The SendError contains an
   implementation-specific reference to the Message to which it applies.

7.3.  Message Context Parameters

   Applications may need to annotate the Messages they send with extra
   information to control how data is scheduled and processed by the
   transport protocols in the Connection.  A MessageContext object
   contains parameters for sending Messages, and can be passed to the



Trammell, et al.         Expires January 3, 2019               [Page 18]


Internet-Draft               TAPS Interface                    July 2018


   Send Action.  Some of these parameters are properties as defined in
   Section 12.  Note that these properties are per-Message, not per-Send
   if partial Messages are sent (Section 7.4).  All data blocks
   associated with a single Message share properties.  For example, it
   would not make sense to have the beginning of a Message expire, but
   allow the end of a Message to still be sent.

   messageData := "hello".octets()
   messageContext := NewMessageContext()
   messageContext.add(parameter, value)
   Connection.Send(messageData, messageContext)

   The simpler form of Send that does not take any MessageContext is
   equivalent to passing a default MessageContext with not values added.

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

   If an application wants to override Message Properties for a specific
   message, it can acquire an empty messageContext Object and add all
   desired Message Properties to that Object.  It can then reuse the
   same messageContext Object for sending multiple Messages with the
   same properties.

   Parameters may be added to a messageContext object only before the
   context is used for sending.  Once a messageContext has been used
   with a Send call, modifying any of its parameters is invalid.

   Message Properties may be inconsistent with the properties of the
   Protocol Stacks underlying the Connection on which a given Message is
   sent.  For example, a Connection must provide reliability to allow
   setting an infinitie value for the lifetime property of a Message.
   Sending a Message with Message Properties inconsistent with the
   Selection Properties of the Connection yields an error.

   The following Message Context Parameters are supported:

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

7.3.1.  Lifetime

   [TODO: De-Duplicate with Section 12.3.28]

   Lifetime specifies how long a particular Message can wait to be sent
   to the remote endpoint before it is irrelevant and no longer needs to
   be (re-)transmitted.  When a Message's Lifetime is infinite, it must



Trammell, et al.         Expires January 3, 2019               [Page 19]


Internet-Draft               TAPS Interface                    July 2018


   be transmitted reliably.  The type and units of Lifetime are
   implementation-specific.

7.3.2.  Niceness

   [TODO: De-Duplicate with Section 12.3.21]

   Niceness is a numeric (non-negative) value that represents an
   unbounded hierarchy of priorities of Messages, relative to other
   Messages sent over the same Connection and/or Connection Group (see
   Section 6.4).  A Message with Niceness 0 will yield to a Message with
   Niceness 1, which will yield to a Message with Niceness 2, and so on.
   Niceness may be used as a sender-side scheduling construct only, or
   be used to specify priorities on the wire for Protocol Stacks
   supporting prioritization.

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

7.3.3.  Ordered

   [TODO: De-Duplicate with Section 12.3.6]

   Ordered is a boolean property.  If true, this Message should be
   delivered after the last Message passed to the same Connection via
   the Send Action; if false, this Message may be delivered out of
   order.

7.3.4.  Idempotent

   [TODO: De-Duplicate with Section 12.3.9]

   Idempotent is a boolean property.  If true, the application-layer
   entity in the Message is safe to send to the remote endpoint more
   than once for a single Send Action.  It is used to mark data safe for
   certain 0-RTT establishment techniques, where retransmission of the
   0-RTT data may cause the remote application to receive the Message
   multiple times.

7.3.5.  Final

   [TODO: De-Duplicate with Section 12.3.1]

   Final is a boolean property.  If true, this Message is the last one
   that the application will send on a Connection.  This allows
   underlying protocols to indicate to the Remote Endpoint that the
   Connection has been effectively closed in the sending direction.  For
   example, TCP-based Connections can send a FIN once a Message marked



Trammell, et al.         Expires January 3, 2019               [Page 20]


Internet-Draft               TAPS Interface                    July 2018


   as Final has been completely sent, indicated by marking endOfMessage.
   Protocols that do not support signalling the end of a Connection in a
   given direction will ignore this property.

   Note that a Final Message must always be sorted to the end of a list
   of Messages.  The Final property overrides Niceness and any other
   property that would re-order Messages.  If another Message is sent
   after a Message marked as Final has already been sent on a
   Connection, the new Message will report an error.

7.3.6.  Corruption Protection Length

   [TODO: De-Duplicate with Section 12.3.15]

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

7.3.7.  Transmission Profile

   [TODO: De-Duplicate with Section 12.3.19]

   This enumerated property specifies the application's preferred
   tradeoffs for sending this Message; it is a per-Message override of
   the Capacity Profile protocol and path selection property (see
   Section 12.3.19).

   The following values are valid for Transmission Profile:

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

   Low Latency:  Response time (latency) should be optimized at the
      expense of efficiently using the available capacity when sending
      this message.  This can be used by the system to disable the
      coalescing of multiple small Messages into larger packets (Nagle's
      algorithm); to prefer immediate acknowledgment from the peer
      endpoint when supported by the underlying transport; to signal a
      preference for lower-latency, higher-loss treatment; and so on.






Trammell, et al.         Expires January 3, 2019               [Page 21]


Internet-Draft               TAPS Interface                    July 2018


7.4.  Partial Sends

   It is not always possible for an application to send all data
   associated with a Message in a single Send Action.  The Message data
   may be too large for the application to hold in memory at one time,
   or the length of the Message may be unknown or unbounded.

   Partial Message sending is supported by passing an endOfMessage
   boolean parameter to the Send Action.  This value is always true by
   default, and the simpler forms of send are equivalent to passing true
   for endOfMessage.

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

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

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

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

   All messageData sent with the same messageContext object will be
   treated as belonging to the same Message, and will constitute an in-
   order series until the endOfMessage is marked.  Once the end of the
   Message is marked, the messageContext object may be re-used as a new
   Message with identical parameters.

7.5.  Batching Sends

   In order to reduce the overhead of sending multiple small Messages on
   a Connection, the application may want to batch several Send actions
   together.  This provides a hint to the system that the sending of
   these Messages should be coalesced when possible, and that sending
   any of the batched Messages may be delayed until the last Message in
   the batch is enqueued.

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







Trammell, et al.         Expires January 3, 2019               [Page 22]


Internet-Draft               TAPS Interface                    July 2018


7.6.  Sender-side Framing

   Sender-side framing allows a caller to provide the interface with a
   function that takes a Message of an appropriate application-layer
   type and returns an array of octets, the on-the-wire representation
   of the Message to be handed down to the Protocol Stack.  It consists
   of a Framer Object with a single Action, Frame.  Since the Framer
   depends on the protocol used at the application layer, it is bound to
   the Preconnection during the pre-establishment phase:

   Preconnection.FrameWith(Framer)

   OctetArray := Framer.Frame(messageData)

   Sender-side framing is a convenience feature of the interface, for
   parity with receiver-side framing (see Section 8.4).

8.  Receiving Data

   Once a Connection is established, it can be used for receiving data.
   As with sending, data is received in terms of Messages.  Receiving is
   an asynchronous operation, in which each call to Receive enqueues a
   request to receive new data from the connection.  Once data has been
   received, or an error is encountered, an event will be delivered to
   complete the Receive request (see Section 8.2).

   As with sending, the type of the Message to be passed is dependent on
   the implementation, and on the constraints on the Protocol Stacks
   implied by the Connection's transport parameters.

8.1.  Enqueuing Receives

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

   Connection.Receive(minIncompleteLength, maxLength)

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

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



Trammell, et al.         Expires January 3, 2019               [Page 23]


Internet-Draft               TAPS Interface                    July 2018


   memory.  Applications should always check the length of the data
   delivered to the receive event and not assume it will be as long as
   minIncompleteLength in the case of shorter complete Messages or
   memory issues.

   The maxLength argument indicates the maximum size of a Message in
   bytes the application is currently prepared to receive.  The default
   value for maxLength is infinite.  If an incoming Message is larger
   than the minimum of this size and the maximum Message size on receive
   for the Connection's Protocol Stack, it will be delivered via
   ReceivedPartial events (Section 8.2.2).

   Note that maxLength does not guarantee that the application will
   receive that many bytes if they are available; the interface may
   return ReceivedPartial events with less data than maxLength according
   to implementation constraints.

8.2.  Receive Events

   Each call to Receive will be paired with a single Receive Event,
   which can be a success or an error.  This allows an application to
   provide backpressure to the transport stack when it is temporarily
   not ready to receive messages.

8.2.1.  Received

   Connection -> Received<messageData, messageContext>

   A Received event indicates the delivery of a complete Message.  It
   contains two objects, the received bytes as messageData, and the
   metadata and properties of the received Message as messageContext.
   See {#receive-context} for details about the received context.

   The messageData object provides access to the bytes that were
   received for this Message, along with the length of the byte array.

   See Section 8.4 for handling Message framing in situations where the
   Protocol Stack provides octet-stream transport only.

8.2.2.  ReceivedPartial

Connection -> ReceivedPartial<messageData, messageContext, endOfMessage>

   If a complete Message cannot be delivered in one event, one part of
   the Message may be delivered with a ReceivedPartial event.  In order
   to continue to receive more of the same Message, the application must
   invoke Receive again.




Trammell, et al.         Expires January 3, 2019               [Page 24]


Internet-Draft               TAPS Interface                    July 2018


   Multiple invocations of ReceivedPartial deliver data for the same
   Message by passing the same messageContext, until the endOfMessage
   flag is delivered.  All partial blocks of a single Message are
   delivered in order without gaps.  This event does not support
   delivering discontiguous partial Messages.

   If the minIncompleteLength in the Receive request was set to be
   infinite (indicating a request to receive only complete Messages),
   the ReceivedPartial event may still be delivered if one of the
   following conditions is true:

   o  the underlying Protocol Stack supports message boundary
      preservation, and the size of the Message is larger than the
      buffers available for a single message;

   o  the underlying Protocol Stack does not support message boundary
      preservation, and the deframer (see Section 8.4) cannot determine
      the end of the message using the buffer space it has available; or

   o  the underlying Protocol Stack does not support message boundary
      preservation, and no deframer was supplied by the application

   Note that in the absence of message boundary preservation or
   deframing, all bytes received on the Connection will be represented
   as one large message of indeterminate length.

8.2.3.  ReceiveError

   Connection -> ReceiveError<messageContext>

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

   The ReceiveError event passes an optional associated messageContext.
   This may indicate that a Message that was being partially received
   previously, but had not completed, encountered and error and will not
   be completed.

8.3.  Message Receive Context

   Each Received Message Context may contain metadata from protocols in
   the Protocol Stack; which metadata is available is Protocol Stack
   dependent.  The following metadata values are supported:




Trammell, et al.         Expires January 3, 2019               [Page 25]


Internet-Draft               TAPS Interface                    July 2018


8.3.1.  ECN

   When available, Message metadata carries the value of the Explicit
   Congestion Notification (ECN) field.  This information can be used
   for logging and debugging purposes, and for building applications
   which need access to information about the transport internals for
   their own operation.

8.3.2.  Early Data

   In some cases it may be valuable to know whether data was read as
   part of early data streams.  This is useful if applications need to
   treat early data separately, e.g., if early data has different
   security properties than data sent after connection establishment.
   In the case of TLS 1.3, client early data can be replayed maliciously
   (see [I-D.ietf-tls-tls13]).  Thus, receivers may wish to perform
   additional checks for early data to ensure it is idempotent or not
   replayed.  If TLS 1.3 is available and the recipient Message was sent
   as part of early data, the corresponding metadata carries a flag
   indicating as such.  If early data is enabled, applications should
   check this metadata field for Messages received during connection
   establishment and respond accordingly.

8.3.3.  Receiving Final Messages

   The Received Message Context can indicate whether or not this Message
   is the Final Message on a Connection.  For any Message that is marked
   as Final, the application can assume that there will be no more
   Messages received on the Connection once the Message has been
   completely delivered.  This corresponds to the Final property that
   may be marked on a sent Message Section 12.3.1.

   Some transport protocols and peers may not support signaling of the
   Final property.  Applications therefore should not rely on receiving
   a Message marked Final to know that the other endpoint is done
   sending on a connection.

   Any calls to Receive once the Final Message has been delivered will
   result in errors.

8.4.  Receiver-side De-framing over Stream Protocols

   The Receive Event is intended to be fired once per application-layer
   Message sent by the remote endpoint; i.e., it is a desired property
   of this interface that a Send at one end of a Connection maps to
   exactly one Receive on the other end.  This is possible with Protocol
   Stacks that provide message boundary preservation, but is not the




Trammell, et al.         Expires January 3, 2019               [Page 26]


Internet-Draft               TAPS Interface                    July 2018


   case over Protocol Stacks that provide a simple octet stream
   transport.

   For preserving message boundaries over stream transports, this
   interface provides receiver-side de-framing.  This facility is based
   on the observation that, since many of our current application
   protocols evolved over TCP, which does not provide message boundary
   preservation, and since many of these protocols require message
   boundaries to function, each application layer protocol has defined
   its own framing.  A Deframer allows an application to push this de-
   framing down into the interface, in order to transform an octet
   stream into a sequence of Messages.

   Concretely, receiver-side de-framing allows a caller to provide the
   interface with a function that takes an octet stream, as provided by
   the underlying Protocol Stack, reads and returns a single Message of
   an appropriate type for the application and platform, and leaves the
   octet stream at the start of the next Message to deframe.  It
   consists of a Deframer Object with a single Action, Deframe.  Since
   the Deframer depends on the protocol used at the application layer,
   it is bound to the Preconnection during the pre-establishment phase:

   Preconnection.DeframeWith(Deframer)

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

9.  Setting and Querying Connection Properties

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

   ConnectionProperties := Connection.GetProperties()

   Connection.SetProperty(property, value)

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

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

   o  Whether the connection can be used to send data.  A connection can
      not be used for sending if the connection was created with the
      Selection Property "Unidirectional Receive" or if a Message marked
      as "Final" was sent over this connection, see Section 12.3.1.

   o  Whether the connection can be used to receive data.  A connection
      can not be used for reading if the connection was created with the



Trammell, et al.         Expires January 3, 2019               [Page 27]


Internet-Draft               TAPS Interface                    July 2018


      Selection Property "Unidirectional: Send" or if a Message marked
      as "Final" was received, see Section 8.3.3.  The latter is only
      supported by certain transport protocols, e.g., by TCP as half-
      closed connection.

   o  For Connections that are Establishing: Transport Properties that
      the application specified on the Preconnection, see Section 5.2.
      Selection Properties of a Connection can only be queried, not set.

   o  For Connections that are Established, Closing, or Closed (TODO:
      double-check if closed belongs here): Transport Properties of the
      actual protocols that were selected and instantiated.  These
      features correspond to the properties given in Section 12 and
      include Selection Properties and Protocol Properties.

      *  Selection Properties indicate whether or not the Connection has
         or offers a certain Selection Property.  Note that the actually
         instantiated protocol stack may not match all Protocol
         Selection Properties that the application specified on the
         Preconnection.  For example, a certain Protocol Selection
         Property that an application specified as Preferred may not
         actually be present in the chosen protocol stack because none
         of the currently available transport protocols had this
         feature.  Selection Properties of a Connection can only be
         queried.

      *  Protocol Properties of the protocol stack in use (see
         Section 12.2.2 below).  These can be queried and set.  Certain
         specific Procotol Properties may be read-only, on a protocol-
         and property-specific basis.

   o  For Connections that are Established, properties of the path(s) in
      use.  These properties can be derived from the local provisioning
      domain [RFC7556], measurements by the Protocol Stack, or other
      sources.  They can only be queried.

10.  Connection Termination

   Close terminates a Connection after satisfying all the requirements
   that were specified regarding the delivery of Messages that the
   application has already given to the transport system.  For example,
   if reliable delivery was requested for a Message handed over before
   calling Close, the transport system will ensure that this Message is
   indeed delivered.  If the Remote Endpoint still has data to send, it
   cannot be received after this call.

   Connection.Close()




Trammell, et al.         Expires January 3, 2019               [Page 28]


Internet-Draft               TAPS Interface                    July 2018


   The Closed Event can inform the application that the Remote Endpoint
   has closed the Connection; however, there is no guarantee that a
   remote close will be signaled.

   Connection -> Closed<>

   Abort terminates a Connection without delivering remaining data:

   Connection.Abort()

   A ConnectionError can inform the application that the other side has
   aborted the Connection; however, there is no guarantee that an abort
   will be signaled:

   Connection -> ConnectionError<>

   A SoftError can inform the application about the receipt of an ICMP
   error message that does not force termination of the connection, if
   the underlying protocol stack supports access to soft errors;
   however, even if the underlying stack supports it, there is no
   guarantee that a soft error will be signaled.

   Connection -> SoftError<>

11.  Ordering of Operations and Events

   As this interface is designed to be independent of concurrency model,
   the details of how exactly actions are handled, and on which threads/
   callbacks events are dispatched, are implementation dependent.
   However, the interface does provide the following guarantees about
   the ordering of operations:

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

   o  No events will occur on a Connection after a Closed<> event, an
      InitiateError<> or ConnectionError<> on that connection.  To
      ensure this ordering, Closed<> will not occur on a Connection
      while other events on the Connection are still locally outstanding
      (i.e., known to the interface and waiting to be dealt with by the
      application).  ConnectionError<> may occur after Closed<>, but the
      interface must gracefully handle the application ignoring these
      errors.

   o  Sent<> events will occur on a Connection in the order in which the
      Messages were sent (i.e., delivered to the kernel or to the
      network interface, depending on implementation).



Trammell, et al.         Expires January 3, 2019               [Page 29]


Internet-Draft               TAPS Interface                    July 2018


12.  Transport Properties

   Transport Properties allow an application to control and introspect
   most aspects of the transport system and transport protocols.

   Properties are structured in two ways:

   o  By how they influence the transport system, which leads to a
      classification into "Selection Properties", "Protocol Properties",
      "Control Properties" and "Intents".

   o  By the object they can be applied to: Preconnections, see
      Section 5.2, Connections, see Section 9, and Messages, see
      Section 7.3.

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

   Note that it is possible for a set of specified Transport Properties
   to be internally inconsistent, or to be inconsistent with the later
   use of the API by the application.  Application developers can reduce
   inconsistency by only using the most stringent preference levels when
   failure to meet the property would break the application's
   functionality.  For example, it can set the Selection Property
   "Reliable Data Transfer", which is a core assumption of many
   application protocols, as Required.  Implementations of this
   interface should also raise any detected errors in configuration as
   early as possible, to help ensure that inconsistencies are caught
   early in the development process.

12.1.  Transport Property Types

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

12.1.1.  Boolean

   A boolean is a data type that can be either "true" or "false".
   Boolean transport properties should only be used for properties that
   can not be used in an optional way or to query the state of the
   transport implementation.  For optional features, especially in
   Selection Properties, the usage of the Preference type (see
   Section 12.1.4) is preferred.








Trammell, et al.         Expires January 3, 2019               [Page 30]


Internet-Draft               TAPS Interface                    July 2018


12.1.2.  Enumeration

   Enumeration types are used for transport properties that can take one
   value out of a limited set of choices.  The representation is
   implementation dependent.

12.1.3.  Integer

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

12.1.4.  Preference

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

   +------------+------------------------------------------------------+
   | Preference | Effect                                               |
   +------------+------------------------------------------------------+
   | Require    | Select only protocols/paths providing the property,  |
   |            | fail otherwise                                       |
   |            |                                                      |
   | Prefer     | Prefer protocols/paths providing the property,       |
   |            | proceed otherwise                                    |
   |            |                                                      |
   | Ignore     | Cancel any default preference for this property      |
   |            |                                                      |
   | Avoid      | Prefer protocols/paths not providing the property,   |
   |            | proceed otherwise                                    |
   |            |                                                      |
   | Prohibit   | Select only protocols/paths not providing the        |
   |            | property, fail otherwise                             |
   +------------+------------------------------------------------------+

   When used on a Connection, this type becomes a (read-only) Boolean
   representing whether the selected transport supports the requested
   feature.

12.2.  Transport Property Classification

   Note:  This section is subject to WG discussion on IETF-102.

   Transport Properties - whether they apply to connections,
   preconnections, or messages - differ in the way they affect the
   transport system and protocols exposed through the transport system.
   The classification proposed below emphasizes two aspects of how



Trammell, et al.         Expires January 3, 2019               [Page 31]


Internet-Draft               TAPS Interface                    July 2018


   properties affect the transport system, so applications know what to
   expect:

   o  Whether properties affect protocols exposed through the transport
      system (Protocol Properties) or the transport system itself
      (Control Properties)

   o  Whether properties have a clearly defined behavior that is likely
      to be invariant across implementations and environments (Protocol
      Properties and Control Properties) or whether the properties are
      interpreted by the transport system to provide a best effort
      service that matches the applications needs as well as possible
      (Intents).

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

      The classification in this version of the draft emphasizes the way
      the property affects the transport system and protocols.  It
      treats the aspect of whether properties are used on a connection,
      preconnection or message as an orthogonal dimension of
      classification.

      The "Message Properties" from I-D.ietf-taps-interface-00 therefore
      have been split into "Protocol Properties" - emphasizing that they
      affect the protocol configurations - and "Control Properties" -
      emphasizing that they control the local transport system itself.

12.2.1.  Selection Properties

   Selection Properties influence protocol and path selection.  Their
   value usually is or includes a Preference that constrains (in case of
   Require or Prohibit) or influences (Prefer, Ignore, Avoid) the
   selection of transport protocols and paths used.

   An implementation of this interface must provide sensible defaults
   for Selection Properties.  The defaults given for each property below
   represent a configuration that can be implemented over TCP.  An
   alternate set of default Protocol Selection Properties would
   represent a configuration that can be implemented over UDP.

   Protocol Selection Properties can only be set on Preconnections, see
   Section 5.2.  Path Selection Properties are usually used on
   Preconnections, but might also be used on messages to assist per-
   message path selection for multipath aware protocols.




Trammell, et al.         Expires January 3, 2019               [Page 32]


Internet-Draft               TAPS Interface                    July 2018


12.2.2.  Protocol Properties

   Protocol Properties represent the configuration of the selected
   Protocol Stacks backing a Connection.  Some properties apply
   generically across multiple transport protocols, while other
   properties only apply to specific protocols.  Generic properties will
   be passed to the selected candidate Protocol Stack(s) to configure
   them before candidate Connection establishment.  The default settings
   of these properties will vary based on the specific protocols being
   used and the system's configuration.

   Most Protocol Properties can be set on a Preconnection during pre-
   establishment to preconfigure Protocol Stacks during establishment.

   In order to specify Specific Protocol Properties, Transport System
   implementations may offer applications to attach a set of options to
   the Preconnection Object, associated with a specific protocol.  For
   example, an application could specify a set of TCP Options to use if
   and only if TCP is selected by the system.  Such properties must not
   be assumed to apply across different protocols.  Attempts to set
   specific protocol properties on a protocol stack not containing that
   specific protocol are simply ignored, and do not raise an error.

   Note that many protocol properties have a corresponding selection
   property which asks for a protocol providing a specific transport
   feature that is controlled by the protocol property.

12.2.3.  Control Properties

   [TODO: Discuss]

   Control properties manage the local transport system behavior or
   request state changes in the local transport system.  Depending on
   the protocols used, setting these properties might also influence the
   protocol state machine.  See Section 12.3.1 for an example.

12.2.4.  Intents

   [TODO: Discuss]

   Intents are hints to the transport system that do not directly map to
   a single protocol/transport feature or behavior of the transport
   system, but express a presumed application behavior or generic
   application needs.

   The application can expect the transport system to take appropriate
   actions involving protocol selection, path selection and, setting of
   protocol flags.  For example, if an application sets the "Capacity



Trammell, et al.         Expires January 3, 2019               [Page 33]


Internet-Draft               TAPS Interface                    July 2018


   Profile" to "bulk" on a Preconnection, this will likely influence
   path selection, DSCP flags in the IP header as well as niceness for
   multi-streaming connections.  When using Intents, the application
   must not expect consistent behavior across different environments,
   implementations or versions of the same implementation.

12.3.  Mandatory Transport Properties

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

12.3.1.  Final

   See Section 7.3.5.

   [TODO: Decide whether this is a property or a parameter]

12.3.2.  Reliable Data Transfer (Connection)

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection, Connection (read only)

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

12.3.3.  Configure per-Message reliability

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection, Connection (read only)

   This property specifies whether an application considers it useful to
   indicate its reliability requirements on a per-Message basis.  This
   property applies to Connections and Connection Groups.  The default
   is to not have this option.








Trammell, et al.         Expires January 3, 2019               [Page 34]


Internet-Draft               TAPS Interface                    July 2018


12.3.4.  Reliable Data Transfer (Message)

   Classification:  Protocol Property (Generic)

   Type:  Boolean

   Applicability:  Message

   This property specifies that a message should be sent in such a way
   that the transport protocol ensures all data is received on the other
   side without corruption.  Changing the 'Reliable Data Transfer'
   property on Messages is only possible if the transport protocol
   supports partial reliability (see Section 12.3.3).  Therefore, for
   protocols that always transfer data reliably, this property is always
   true and for protocols that always transfer data unreliably, this
   flag is always false.  Changing it may generate an error.

12.3.5.  Preservation of data ordering

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection, Connection (read only)

   This property specifies whether the application wishes to use a
   transport protocol that ensures that data is received by the
   application on the other end in the same order as it was sent.  The
   default is to preserve data ordering.

12.3.6.  Ordered

   Classification:  Protocol Property (Generic)

   Type:  Boolean

   Applicability:  Message

   This property specifies that a Message should be delivered to the
   other side after the previous Message which was passed to the same
   Connection via the Send Action.  It us used for protocols that
   support preservation of data ordering, see Section 12.3.5, but allow
   out-of-order delivery for certain messages.








Trammell, et al.         Expires January 3, 2019               [Page 35]


Internet-Draft               TAPS Interface                    July 2018


12.3.7.  Direction of communication

   Classification:  Selection Property, Control Property [TODO: Discuss]

   Type:  Enumeration

   Applicability:  Preconnection, Connection (read only)

   This property specifies whether an application wants to use the
   connection for sending and/or receiving data.  Possible values are:

   Bidirectional (default):  The connection must support sending and
      receiving data

   unidirectional send:  The connection must support sending data.

   unidirectional receive:  The connection must support receiving data

   In case a unidirectional connection is requested, but unidirectional
   connections are not supported by the transport protocol, the system
   should fall back to bidirectional transport.

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

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection, Connection (read only)

   This property specifies whether an application would like to supply a
   Message to the transport protocol before Connection establishment,
   which will then be reliably transferred to the other side before or
   during Connection establishment, potentially multiple times.  See
   also Section 12.3.9.  The default is to not have this option.

12.3.9.  Idempotent

   Classification:  Control Property

   Type:  Boolean

   Applicability:  Message

   This property specifies that a Message is safe to send to the remote
   endpoint more than once for a single Send Action.  It is used to mark
   data safe for certain 0-RTT establishment techniques, where




Trammell, et al.         Expires January 3, 2019               [Page 36]


Internet-Draft               TAPS Interface                    July 2018


   retransmission of the 0-RTT data may cause the remote application to
   receive the Message multiple times.

   The application can query the maximum size of a message that can be
   sent idempotent, see Section 12.3.24.

12.3.10.  Multistream Connections in Group

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection, Connection (read only)

   This property specifies that the application would prefer multiple
   Connections within a Connection Group to be provided by streams of a
   single underlying transport connection where possible.  The default
   is to not have this option.

12.3.11.  Notification of excessive retransmissions

   Classification:  Control Property [TODO: Discuss]

   Type:  Boolean

   Applicability:  Preconnection, Connection

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

   The default is to have this option.

12.3.12.  Retransmission threshold before excessive retransmission
          notification

   Classification:  Control Property [TODO: Discuss]

   Type:  Integer

   Applicability:  Preconnection, Connection




Trammell, et al.         Expires January 3, 2019               [Page 37]


Internet-Draft               TAPS Interface                    July 2018


   This property specifies after how many retransmissions to inform the
   application about "Excessive Retransmissions".

12.3.13.  Notification of ICMP soft error message arrival

   Classification:  Control Property [TODO: Discuss]

   Type:  Boolean

   Applicability:  Preconnection, Connection

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

   This property applies to Connections and Connection Groups.  The
   default is not to have this option.

12.3.14.  Control checksum coverage on sending or receiving

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection, Connection (read only)

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

12.3.15.  Corruption Protection Length

   Classification:  Protocol Property (Generic)

   Type:  Integer

   Applicability:  Message





Trammell, et al.         Expires January 3, 2019               [Page 38]


Internet-Draft               TAPS Interface                    July 2018


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

12.3.16.  Required minimum coverage of the checksum for receiving

   Classification:  Protocol Property (Generic)

   Type:  Integer

   Applicability:  Connection

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

12.3.17.  Interface Instance or Type

   Classification:  Selection Property

   Type:  Tuple (Enumeration, Preference)

   Applicability:  Preconnection, Connection (read only)

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

   If a system supports discovery of specific interface identifiers,
   such as "en0" or "eth0" on Unix-style systems, an implemention should
   allow using these identifiers to define path preferences.  Note that
   marking a specific interface as "Required" strictly limits path
   selection to a single interface, and leads to less flexible and
   resilient connection establishment.

   The set of valid interface types is implementation- and system-
   specific.  For example, on a mobile device, there may be "Wi-Fi" and
   "Cellular" interface types available; whereas on a desktop computer,
   there may be "Wi-Fi" and "Wired Ethernet" interface types available.
   Implementations should provide all types that are supported on some
   system to all systems, in order to allow applications to write
   generic code.  For example, if a single implementation is used on



Trammell, et al.         Expires January 3, 2019               [Page 39]


Internet-Draft               TAPS Interface                    July 2018


   both mobile devices and desktop devices, it should define the
   "Cellular" interface type for both systems, since an application may
   want to always "Prohibit Cellular".  Note that marking a specific
   interface type as "Required" limits path selection to a small set of
   interfaces, and leads to less flexible and resilient connection
   establishment.

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

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

12.3.18.  Provisioning Domain Instance or Type

   Classification:  Selection Property

   Type:  Tuple (Enumeration, Preference)

   Applicability:  Preconnection, Connection (read only)

   Similar to interface instances and types Section 12.3.17, this
   property allows the application to control path selection by
   selecting which specific Provisioning Domains or categories of
   Provisioning Domains it wants to "Require", "Prohibit", "Prefer", or
   "Avoid".  Provisioning Domains define consistent sets of network
   properties that may be more specific than network interfaces
   [RFC7556].

   The identification of a specific Provisioning Domain (PvD) is defined
   to be implementation- and system-specific, since there is not a
   portable standard format for a PvD identitfier.  For example, this
   identifier may be a string name or an integer.  As with requiring
   specific interfaces, requiring a specific PvD strictly limits path
   selection.

   Categories or types of PvDs are also defined to be implementation-
   and system-specific.  These may be useful to identify a service that
   is provided by a PvD.  For example, if an application wants to use a
   PvD that provides a Voice-Over-IP service on a Cellular network, it
   can use the relevant PvD type to require some PvD that provides this
   service, without needing to look up a particular instance.  While
   this does restrict path selection, it is more broad than requiring
   specific PvD instances or interface instances, and should be
   preferred over those options.



Trammell, et al.         Expires January 3, 2019               [Page 40]


Internet-Draft               TAPS Interface                    July 2018


12.3.19.  Capacity Profile

   Classification:  Intent [TODO: Discuss]

   Type:  Enumeration

   Applicability:  Preconnection, Connection, Message

   This property specifies the application's expectation of the
   dominating traffic pattern for this Connection.  This implies that
   the transport system should optimize for the capacity profile
   specified.  This can influence path and protocol selection.  The
   following values are valid for the Capacity Profile:

   Default:  The application makes no representation about its expected
      capacity profile.  No special optimizations of the tradeoff
      between delay, delay variation, and bandwidth efficiency should be
      made when selecting and configuring stacks.

   Low Latency:  Response time (latency) should be optimized at the
      expense of bandwidth efficiency and delay variation when sending
      this message.  This can be used by the system to disable the
      coalescing of multiple small Messages into larger packets (Nagle's
      algorithm); to prefer immediate acknowledgment from the peer
      endpoint when supported by the underlying transport; to signal a
      preference for lower-latency, higher-loss treatment; and so on.

   Constant Rate:  The application expects to send/receive data at a
      constant rate after Connection establishment.  Delay and delay
      variation should be minimized at the expense of bandwidth
      efficiency.  This implies that the Connection may fail if the
      desired rate cannot be maintained across the Path.  A transport
      may interpret this capacity profile as preferring a circuit
      breaker [RFC8084] to a rate-adaptive congestion controller.

   Scavenger/Bulk:  The application is not interactive.  It expects to
      send/receive a large amount of data, without any urgency.  This
      can, for example, be used to select protocol stacks with scavenger
      transmission control, to signal a preference for less-than-best-
      effort treatment, or to assign the traffic to a lower-effort
      service.

12.3.20.  Congestion control

   Classification:  Selection Property

   Type:  Preference




Trammell, et al.         Expires January 3, 2019               [Page 41]


Internet-Draft               TAPS Interface                    July 2018


   Applicability:  Preconnection, Connection (read only)

   This property specifies whether the application would like the
   Connection to be congestion controlled or not.  Note that if a
   Connection is not congestion controlled, an application using such a
   Connection should itself perform congestion control in accordance
   with [RFC2914].  Also note that reliability is usually combined with
   congestion control in protocol implementations, rendering "reliable
   but not congestion controlled" a request that is unlikely to succeed.
   The default is that the Connection is congestion controlled.

12.3.21.  Niceness

   Classification:  Protocol Property (Generic)

   Type:  Integer

   Applicability:  Connection, Message

   This property is a numeric (non-negative) value that represents an
   unbounded hierarchy of priorities.  It can specify the priority of a
   Message, relative to other Messages sent over the same Connection
   and/or Connection Group (see Section 6.4), or the priority of a
   Connection, relative to other Connections in the same Connection
   Group.

   A Message with Niceness 0 will yield to a Message with Niceness 1,
   which will yield to a Message with Niceness 2, and so on.  Niceness
   may be used as a sender-side scheduling construct only, or be used to
   specify priorities on the wire for Protocol Stacks supporting
   prioritization.

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

   As noted in Section 6.4, when set on a Connection, this property is
   not entangled when Connections are cloned.

12.3.22.  Timeout for aborting Connection

   Classification:  Control Property [TODO: Discuss]

   Type:  Integer

   Applicability:  Preconnection, Connection






Trammell, et al.         Expires January 3, 2019               [Page 42]


Internet-Draft               TAPS Interface                    July 2018


   This property specifies how long to wait before aborting a Connection
   during establishment, or before deciding that a Connection has failed
   after establishment.  It is given in seconds.

12.3.23.  Connection group transmission scheduler

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

   Type:  Enum

   Applicability:  Preconnection, Connection

   This property specifies which scheduler should be used among
   Connections within a Connection Group, see Section 6.4.  The set of
   schedulers can be taken from [I-D.ietf-tsvwg-sctp-ndata].

12.3.24.  Maximum message size concurrent with Connection establishment

   Classification:  Protocol Property (Generic)

   Type:  Integer

   Applicability:  Connection (read only)

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

12.3.25.  Maximum Message size before fragmentation or segmentation

   Classification:  Protocol Property (Generic)

   Type:  Integer

   Applicability:  Connection (read only)

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

12.3.26.  Maximum Message size on send

   Classification:  Protocol Property (Generic)

   Type:  Integer




Trammell, et al.         Expires January 3, 2019               [Page 43]


Internet-Draft               TAPS Interface                    July 2018


   Applicability:  Connection (read only)

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

12.3.27.  Maximum Message size on receive

   Classification:  Protocol Property (Generic)

   Type:  Integer

   Applicability:  Connection (read only)

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

12.3.28.  Lifetime

   Classification:  Protocol Property (Generic)

   Type:  Integer

   Applicability:  Message

   Lifetime specifies how long a particular Message can wait to be sent
   to the remote endpoint before it is irrelevant and no longer needs to
   be (re-)transmitted.  When a Message's Lifetime is infinite, it must
   be transmitted reliably.  The type and units of Lifetime are
   implementation-specific.

12.4.  Optional Transport Properties

   TODO: Maybe move some of the above properties here.

12.5.  Experimental Transport Properties

   TODO: Move Appendix A here.

13.  IANA Considerations

   RFC-EDITOR: Please remove this section before publication.

   This document has no Actions for IANA.








Trammell, et al.         Expires January 3, 2019               [Page 44]


Internet-Draft               TAPS Interface                    July 2018


14.  Security Considerations

   This document describes a generic API for interacting with a
   transport services (TAPS) system.  Part of this API includes
   configuration details for transport security protocols, as discussed
   in Section Section 5.3.  It does not recommend use (or disuse) of
   specific algorithms or protocols.  Any API-compatible transport
   security protocol should work in a TAPS system.

15.  Acknowledgements

   This work has received funding from the European Union's Horizon 2020
   research and innovation programme under grant agreements No. 644334
   (NEAT) and No. 688421 (MAMI).

   This work has been supported by Leibniz Prize project funds of DFG -
   German Research Foundation: Gottfried Wilhelm Leibniz-Preis 2011 (FKZ
   FE 570/4-1).

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

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

16.  References

16.1.  Normative References

   [I-D.ietf-taps-arch]
              Pauly, T., Trammell, B., Brunstrom, A., Fairhurst, G.,
              Perkins, C., Tiesel, P., and C. Wood, "An Architecture for
              Transport Services", draft-ietf-taps-arch-01 (work in
              progress), July 2018.

   [I-D.ietf-taps-minset]
              Welzl, M. and S. Gjessing, "A Minimal Set of Transport
              Services for End Systems", draft-ietf-taps-minset-04 (work
              in progress), June 2018.

   [I-D.ietf-tls-tls13]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", draft-ietf-tls-tls13-28 (work in progress),
              March 2018.




Trammell, et al.         Expires January 3, 2019               [Page 45]


Internet-Draft               TAPS Interface                    July 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.  Informative References

   [I-D.ietf-taps-transport-security]
              Pauly, T., Perkins, C., Rose, K., and C. Wood, "A Survey
              of Transport Security Protocols", draft-ietf-taps-
              transport-security-02 (work in progress), June 2018.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <https://www.rfc-editor.org/info/rfc793>.

   [RFC2914]  Floyd, S., "Congestion Control Principles", BCP 41,
              RFC 2914, DOI 10.17487/RFC2914, September 2000,
              <https://www.rfc-editor.org/info/rfc2914>.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              DOI 10.17487/RFC3261, June 2002,
              <https://www.rfc-editor.org/info/rfc3261>.

   [RFC5245]  Rosenberg, J., "Interactive Connectivity Establishment
              (ICE): A Protocol for Network Address Translator (NAT)
              Traversal for Offer/Answer Protocols", RFC 5245,
              DOI 10.17487/RFC5245, April 2010,
              <https://www.rfc-editor.org/info/rfc5245>.





Trammell, et al.         Expires January 3, 2019               [Page 46]


Internet-Draft               TAPS Interface                    July 2018


   [RFC7478]  Holmberg, C., Hakansson, S., and G. Eriksson, "Web Real-
              Time Communication Use Cases and Requirements", RFC 7478,
              DOI 10.17487/RFC7478, March 2015,
              <https://www.rfc-editor.org/info/rfc7478>.

   [RFC7556]  Anipko, D., Ed., "Multiple Provisioning Domain
              Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
              <https://www.rfc-editor.org/info/rfc7556>.

   [RFC8084]  Fairhurst, G., "Network Transport Circuit Breakers",
              BCP 208, RFC 8084, DOI 10.17487/RFC8084, March 2017,
              <https://www.rfc-editor.org/info/rfc8084>.

   [RFC8095]  Fairhurst, G., Ed., Trammell, B., Ed., and M. Kuehlewind,
              Ed., "Services Provided by IETF Transport Protocols and
              Congestion Control Mechanisms", RFC 8095,
              DOI 10.17487/RFC8095, March 2017,
              <https://www.rfc-editor.org/info/rfc8095>.

Appendix A.  Additional Properties

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

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

A.1.  Experimental Transport Properties

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






Trammell, et al.         Expires January 3, 2019               [Page 47]


Internet-Draft               TAPS Interface                    July 2018


A.1.1.  Suggest a timeout to the Remote Endpoint

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection

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

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

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

   Classification:  Protocol Property

   Type:  Integer

   Applicability:  Preconnection, Connection

   This numeric property specifies the timeout to propose to the Remote
   Endpoint.  It is given in seconds.

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

A.1.3.  Request not to delay acknowledgment of Message

   Classification:  Selection Property

   Type:  Preference

   Applicability:  Preconnection

   This property specifies whether an application considers it useful to
   be able to request for a Message that its acknowledgment be sent out
   as early as possible instead of potentially being bundled with other
   acknowledgments.  The default is to not have this option.

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







Trammell, et al.         Expires January 3, 2019               [Page 48]


Internet-Draft               TAPS Interface                    July 2018


A.1.4.  Traffic Category

   Classification:  Intent

   Type:  Enumeration

   Applicability:  Preconnection

   This property specifies what the application expect the dominating
   traffic pattern to be.  Possible values are:

   Query:  Single request / response style workload, latency bound

   Control:  Long lasting low bandwidth control channel, not bandwidth
      bound

   Stream:  Stream of data with steady data rate

   Bulk:  Bulk transfer of large Messages, presumably bandwidth bound

   The default is to not assume any particular traffic pattern.  Most
   categories suggest the use of other intents to further describe the
   traffic pattern anticipated, e.g., the bulk category suggesting the
   use of the Message Size intents or the stream category suggesting the
   Stream Bitrate and Duration intents.

A.1.5.  Size to be Sent or Received

   Classification:  Intent

   Type:  Integer

   Applicability:  Preconnection, Message

   This property specifies how many bytes the application expects to
   send (Size to be Sent) or how many bytes the application expects to
   receive in response (Size to be Received).

A.1.6.  Duration

   Classification:  Intent

   Type:  Integer

   Applicability:  Preconnection

   This Intent specifies what the application expects the lifetime of a
   connection to be.  It is given in milliseconds.



Trammell, et al.         Expires January 3, 2019               [Page 49]


Internet-Draft               TAPS Interface                    July 2018


A.1.7.  Send or Receive Bit-rate

   Classification:  Intent

   Type:  Integer

   Applicability:  Preconnection, Message

   This Intent specifies what the application expects the bit-rate of a
   transfer to be.  It is given in Bytes per second.

   On a message, this property specifies at what bitrate the application
   wishes the Message to be sent.  A transport system supporting this
   feature will not exceed the requested Send Bitrate even if flow-
   control and congestion control allow higher bitrates.  This helps to
   avoid bursty traffic pattern on busy video streaming servers.

A.1.8.  Cost Preferences

   Classification:  Intent

   Type:  Enumeration

   Applicability:  Preconnection, Message

   This property describes what an application prefers regarding
   monetary costs, e.g., whether it considers it acceptable to utilize
   limited data volume.  It provides hints to the transport system on
   how to handle trade-offs between cost and performance or reliability.

   Possible values are:

   No Expense:  Avoid transports associated with monetary cost

   Optimize Cost:  Prefer inexpensive transports and accept service
      degradation

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

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

   The default is "Balance Cost".








Trammell, et al.         Expires January 3, 2019               [Page 50]


Internet-Draft               TAPS Interface                    July 2018


A.1.9.  Immediate

   Classification:  Protocol Property (Generic)

   Type:  Boolean

   Applicability:  Message

   This property specifies whether the caller prefers immediacy to
   efficient capacity usage for this Message.  For example, this means
   that the Message should not be bundled with other Message into the
   same transmission by the underlying Protocol Stack.

Appendix B.  Sample API definition in Go

   This document defines an abstract interface.  To illustrate how this
   would map concretely into a programming language, an API interface
   definition in Go is available online at https://github.com/mami-
   project/postsocket.  Documentation for this API - an illustration of
   the documentation an application developer would see for an instance
   of this interface - is available online at
   https://godoc.org/github.com/mami-project/postsocket.  This API
   definition will be kept largely in sync with the development of this
   abstract interface definition.

Authors' Addresses

   Brian Trammell (editor)
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich
   Switzerland

   Email: ietf@trammell.ch


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

   Email: michawe@ifi.uio.no








Trammell, et al.         Expires January 3, 2019               [Page 51]


Internet-Draft               TAPS Interface                    July 2018


   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







Trammell, et al.         Expires January 3, 2019               [Page 52]


Internet-Draft               TAPS Interface                    July 2018


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

   Email: cawood@apple.com












































Trammell, et al.         Expires January 3, 2019               [Page 53]


Html markup produced by rfcmarkup 1.129b, available from https://tools.ietf.org/tools/rfcmarkup/