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Versions: 00 draft-trammell-taps-post-sockets

TAPS Working Group                                           B. Trammell
Internet-Draft                                                ETH Zurich
Intended status: Informational                                C. Perkins
Expires: April 30, 2017                            University of Glasgow
                                                                T. Pauly
                                                              Apple Inc.
                                                           M. Kuehlewind
                                                              ETH Zurich
                                                        October 27, 2016


Post Sockets, An Abstract Programming Interface for the Transport Layer
                     draft-trammell-post-sockets-00

Abstract

   This document describes Post Sockets, an asynchronous abstract
   programming interface for the atomic transmission of objects in an
   explicitly multipath environment.  Post replaces connections with
   long-lived associations between endpoints, with the possibility to
   cache cryptographic state in order to reduce amortized connection
   latency.  We present this abstract interface as an illustration of
   what is possible with present developments in transport protocols
   when freed from the strictures of the current sockets API.

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 http://datatracker.ietf.org/drafts/current/.

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

   This Internet-Draft will expire on April 30, 2017.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Abstractions and Terminology  . . . . . . . . . . . . . . . .   5
     2.1.  Association . . . . . . . . . . . . . . . . . . . . . . .   5
     2.2.  Listener  . . . . . . . . . . . . . . . . . . . . . . . .   5
     2.3.  Remote  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.4.  Local . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.5.  Path  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
     2.6.  Object  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     2.7.  Stream  . . . . . . . . . . . . . . . . . . . . . . . . .   9
   3.  Abstract Programming Interface  . . . . . . . . . . . . . . .   9
     3.1.  Active Association Creation . . . . . . . . . . . . . . .  10
     3.2.  Listener and Passive Association Creation . . . . . . . .  11
     3.3.  Sending Objects . . . . . . . . . . . . . . . . . . . . .  12
     3.4.  Receiving Objects . . . . . . . . . . . . . . . . . . . .  12
     3.5.  Creating and Destroying Streams . . . . . . . . . . . . .  13
     3.6.  Events  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     3.7.  Paths and Path Properties . . . . . . . . . . . . . . . .  14
     3.8.  Address Resolution  . . . . . . . . . . . . . . . . . . .  14
   4.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  15
   5.  Informative References  . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

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.  It
   would not be an overstatement to say that this simple API is the
   reason the Internet won the protocol wars of the 1980s.  SOCK_STREAM
   is tied to the Transmission Control Protocol (TCP), specified in 1981
   [RFC0793].  TCP has scaled remarkably well over the past three and a
   half decades, but its total ubiquity has hidden an uncomfortable
   fact: the network is not really a file, and stream abstractions are
   too simplistic for many modern application programming models.




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   In the meantime, the nature of Internet access is evolving.  Many
   end-user devices are connected to the Internet via multiple
   interfaces, which suggests it is time to promote the "path" by which
   a host is connected to a first-order object; we call this "path
   primacy".

   Implicit multipath communication is available for these multihomed
   nodes in the present Internet architecture with the Multipath TCP
   extension (MPTCP) [RFC6824].  Since many multihomed nodes are
   connected to the Internet through access paths with widely different
   properties with respect to bandwidth, latency and cost, adding
   explicit path control to MPTCP's API would be useful in many
   situations.  Path primacy for cooperation with path elements is also
   useful in single-homed architectures, such as the mechanism proposed
   by the Path Layer UDP Substrate (PLUS) effort (see
   [I-D.trammell-plus-statefulness] and
   [I-D.trammell-plus-abstract-mech]).

   Another trend straining the traditional layering of the transport
   stack associated with the SOCK_STREAM interface is the widespread
   interest in ubiquitous deployment of encryption to guarantee
   confidentiality, authenticity, and integrity, in the face of
   pervasive surveillance [RFC7258].  Layering the most widely deployed
   encryption technology, Transport Layer Security (TLS), strictly atop
   TCP (i.e., via a TLS library such as OpenSSL that uses the sockets
   API) requires the encryption-layer handshake to happen after the
   transport-layer handshake, which increases connection setup latency
   on the order of one or two round-trip times, an unacceptable delay
   for many applications.  Integrating cryptographic state setup and
   maintenance into the path abstraction naturally complements efforts
   in new protocols (e.g.  QUIC [I-D.hamilton-quic-transport-protocol])
   to mitigate this strict layering.

   From these three starting points - more flexible abstraction, path
   primacy, and encryption by default - we define the Post-Socket
   Application Programming Interface (API), described in detail in this
   work.  Post is designed to be language, transport protocol, and
   architecture independent, allowing applications to be written to a
   common abstract interface, easily ported among different platforms,
   and used even in environments where transport protocol selection may
   be done dynamically, as proposed in the IETF's Transport Services
   wotking group (see https://datatracker.ietf.org/wg/taps/charter).

   Post replaces the traditional SOCK_STREAM abstraction with an Object
   abstraction, which can be seen as a generalization of the Stream
   Control Transmission Protocol's [RFC4960] SOCK_SEQPACKET service.
   Objects can be small (e.g. messages in message-oriented protocols) or
   large (e.g. an HTTP response containing header and body).  It



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   replaces the notions of a socket address and connected socket with an
   Association with a remote endpoint via set of Paths.  Implementation
   and wire format for transport protocol(s) implementing the Post API
   are explicitly out of scope for this work; these abstractions need
   not map directly to implementation-level concepts, and indeed with
   various amounts of shimming and glue could be implemented with
   varying success atop any sufficiently flexible transport protocol.

   For compatibility with situations where only strictly stream-oriented
   transport protocols are available, applications with data streams
   that cannot be easily split into Objects at the sender, and and for
   easy porting of the great deal of existing stream-oriented
   application code to Post, Post also provides a SOCK_STREAM compatible
   abstraction, unimaginatively named Stream.

   The key features of Post as compared with the existing sockets API
   are:

   o  Explicit Object orientation, with framing and atomicity guarantees
      for Object transmission.

   o  Asynchronous reception, allowing all receiver-side interactions to
      be event-driven.

   o  Explicit support for multipath transport protocols and network
      architectures.

   o  Long-lived Associations, whose lifetimes may not be bound to
      underlying transport connections.  This allows associations to
      cache state and cryptographic key material to enable fast (0-rtt)
      resumption of communication.

   This work is the synthesis of many years of Internet transport
   protocol research and development.  It is heavily inspired by
   concepts from the Stream Control Transmission Protocol (SCTP)
   [RFC4960], TCP Minion [I-D.iyengar-minion-protocol],
   MinimaLT[MinimaLT], and various bulk object transports.

   We present Post Sockets as an illustration of what is possible with
   present developments in transport protocols when freed from the
   strictures of the current sockets API.  While much of the work for
   building parts of the protocols needed to implement Post are already
   ongoing in other IETF working groups (e.g.  TAPS, MPTCP, QUIC, TLS),
   we argue that an abstract programming interface unifying access all
   these efforts is necessary to fully exploit their potential.






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2.  Abstractions and Terminology

   gratuitously colorful SVG goes here; see slide six of

   https://www.ietf.org/proceedings/96/slides/slides-96-taps-2.pdf

   in the meantime

         Figure 1: Abstractions and relationships in Post Sockets

   Post is based on a small set of abstractions, the relationships among
   which are shown in Figure Figure 1 and detailed in this section.

2.1.  Association

   An Association is a container for all the state necessary for a local
   endpoint to communicate with a remote endpoint in an explicitly
   multipath environment.  It contains a set of Paths, certificate(s)
   for identifying the remote endpoint, certificate(s) and key(s) for
   identifying the local endpoint to the remote endpoint, and any cached
   cryptographic state for the communication to the remote endpoint.  An
   Association may have one or more Streams active at any given time.
   Objects are sent to Associations, as well.

   Note that, in contrast to current SOCK_STREAM sockets, Associations
   are meant to be relatively long-lived.  The lifetime of an
   Association is not bound to the lifetime of any transport-layer
   connection between the two endpoints; connections may be opened or
   closed as necessary to support the Streams and Object transmissions
   required by the application, and the application need not be bothered
   with the underlying connectivity state unless this is important to
   the application's semantics.

   Paths may be dynamically added or removed from an association, as
   well, as connectivity between the endpoints changes.  Cryptographic
   identifiers and state for endpoints may also be added and removed as
   necessary due to certificate lifetimes, key rollover, and revocation.

2.2.  Listener

   In many applications, there is a distinction between the active
   opener (or connection initiator, often a client), and the passive
   opener (often a server).  A Listener represents an endpoint's
   willingness to start Associations in this passive opener/server role.
   It is, in essence, a one-sided, Path-less Association from which
   fully-formed Associations can be created.





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   Listeners work very much like sockets on which the listen(2) call has
   been called in the SOCK_STREAM API.

2.3.  Remote

   A Remote represents all the information required to establish and
   maintain a connection with the far end of an Association: network-
   layer address, transport-layer port, information about public keys or
   certificate authorities used to identify the remote on connection
   establishment, etc.  Each Association is associated with a single
   Remote, either explicitly by the application (when created by active
   open) or by the Listener (when created by passive open).  The
   resolution of Remotes from higher-layer information (URIs, hostnames)
   is architecture-dependent.

2.4.  Local

   A Local represents all the information about the local endpoint
   necessary to establish an Association or a Listener: interface and
   port designators, as well as certificates and associated private
   keys.

2.5.  Path

   A Path represents a local and remote endpoint address, an optional
   set of intermediary path elements between the local and remote
   endpoint addresses, and a set of properties associated with the path.

   The set of available properties is a function of the underlying
   network-layer protocols used to expose the properties to the
   endpoint.  However, the following core properties are generally
   useful for applications and transport layer protocols to choose among
   paths for specific Objects:

   o  Maximum Transmission Unit (MTU): the maximum size of an Object's
      payload (subtracting transport, network, and link layer overhead)
      which will likely fit into a single frame.  Derived from signals
      sent by path elements, where available, and/or path MTU discovery
      processes run by the transport layer.

   o  Latency Expectation: expected one-way delay along the Path.
      Generally provided by inline measurements performed by the
      transport layer, as opposed to signaled by path elements.

   o  Loss Probability Expectation: expected probability of a loss of
      any given single frame along the Path.  Generally provided by
      inline measurements performed by the transport layer, as opposed
      to signaled by path elements.



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   o  Available Data Rate Expectation: expected maximum data rate along
      the Path.  May be derived from passive measurements by the
      transport layer, or from signals from path elements.

   o  Reserved Data Rate: Committed, reserved data rate for the given
      Association along the Path.  Requires a bandwidth reservation
      service in the underlying transport and network layer protocol.

   o  Path Element Membership: Identifiers for some or all nodes along
      the path, depending on the capabilities of the underlying network
      layer protocol to provide this.

   Path properties are generally read-only.  MTU is a property of the
   underlying link-layer technology on each link in the path; latency,
   loss, and rate expectations are dynamic properties of the network
   configuration and network traffic conditions; path element membership
   is a function of network topology.  In an explicitly multipath
   architecture, application and transport layer requirements are met by
   having multiple paths with different properties to select from.  Post
   can also provide signaling to the path, but this signaling is derived
   from information provided to the Object abstraction, below.

   Note that information about the path and signaling to path elements
   could be provided by a facility such as PLUS
   [I-D.trammell-plus-abstract-mech].

2.6.  Object

   Post provides two ways to send data over an Association.  We start
   with the Object abstraction, as a fundamental insight behind the
   interface is that most applications fundamentally deal in object
   transport.

   An Object is an atomic unit of communication between applications; or
   in other words, an ordered collection of bytes B0..Bm, such that
   every byte Bn depends on every other byte in the Object.  An object
   that cannot be delivered in its entirety within the constraints of
   the network connectivity and the requirements of the application is
   not delivered at all.

   Objects can represent both relatively small structures, such as
   messages in application-layer protocols built around datagram or
   message exchange, as well as relatively large structures, such files
   of arbitrary size in a filesystem.  Objects larger than the MTU on
   the Path on which they are sent will be segmented into multiple
   frames.  Multiple objects that will fit into a single frame may be
   concatenated into one frame.  There is no preference for transmitting
   the multiple frames for a given Object in any particular order, or by



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   default, that objects will be delivered in the order sent by the
   application.  This implies that both the sending and receiving
   endpoint, whether in the application layer or the transport layer,
   must guarantee storage for the full size of an object.

   Three object properties allow applications fine control ordering and
   reliability requirements in line with application semantics.  An
   Object may have a "lifetime" - a wallclock duration before which the
   object must be available to the application layer at the remote end.
   If a lifetime cannot be met, the object is discarded as soon as
   possible; therefore, Objects with lifetimes are implicitly sent non-
   reliably, and lifetimes are used to prioritize Object delivery.
   Lifetimes may be signaled to path elements by the underlying
   transport, so that path elements that realize a lifetime cannot be
   met can discard frames containing the object instead of forwarding
   them.

   Second, Objects may have a "niceness" - a category in an unbounded
   hierarchy most naturally represented as a non-negative integer.  By
   default, Objects are in niceness class 0, or highest priority.
   Niceness class 1 Objects will yield to niceness class 0 objects,
   class 2 to class 1, and so on.  Niceness may be translated to a
   priority signal for exposure to path elements (e.g.  DSCP codepoint)
   to allow prioritization along the path as well as at the sender and
   receiver.  This inversion of normal schemes for expressing priority
   has a convenient property: priority increases as both niceness and
   deadline decrease.

   An object may have both a niceness and a lifetime - objects with
   higher niceness classes will yield to lower classes if resource
   constraints mean only one can meet the lifetime.

   Third, an Object may have "antecedents" - other Objects on which it
   depends, which must be delivered before it (the "successor") is
   delivered.  The sending transport uses deadlines, niceness, and
   antecedents, along with information about the properties of the Paths
   available, to determine when to send which object down which Path.

   When an application has hard semantic requirements that all the
   frames of a given object be sent down a given Path or Paths, these
   hard constraints can also be expressed by the application.

   After calling the send function, the application can register event
   handlers to be informed of the transmission status of the object; the
   object can either be acknowledged (i.e., it has been received in full
   by the remote endpoint) or expired (its lifetime ran out before it
   was acknowledged).




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2.7.  Stream

   The Stream abstraction is provided for two reasons.  First, since it
   is the most like the existing SOCK_STREAM interface, it is the
   simplest abstraction to be used by applications ported to Post to
   take advantages of Path primacy.  Second, some environments have
   connectivity so impaired (by local network operation policy and/or
   accidental middlebox interference) that only stream- based transport
   protocols are available, and applications should have the option to
   use streams directly in these situations.

   A Stream is a sequence of bytes B0 .. Bm such that the reception (and
   delivery to the receiving application of) Bn always depends on Bn-1.
   This property is inherited from the BSD UNIX file abstraction, which
   in turn inherited it from the physical limitations of sequential
   access media (stacks of punch cards, paper and/or magnetic tape).

   A Stream is bound to an Association.  Writing a byte to the stream
   will cause it to be received by the remote, in order, or will cause
   an error condition and termination of the stream if the byte cannot
   be delivered.  Due to the strong sequential dependence on a stream,
   streams must always be reliable and ordered.  If frames containing
   Stream data are lost, these must be retransmitted or reconstructed
   using an error correction technique.  If frames containing Stream
   data arrive out of order, the remote end must buffer them until the
   unordered frames are received and reassembled.

   As with Objects, Streams may have a niceness for prioritization.
   When mixing Stream and Object data on the same Path in an
   association, the niceness classes for Streams and Objects are
   interleaved; e.g. niceness 2 Stream frames will yield to niceness 1
   Object frames.

   The underlying transport protocol may make whatever use of the Paths
   and known properties of those Paths it sees fit when transporting a
   Stream.

3.  Abstract Programming Interface

   We now turn to the design of an abstract programming interface to
   provide a simple interface to Post's abstractions, constrained by the
   following design principles:

   o  Flexibility is paramount.  So is simplicity.  Applications must be
      given as many controls and as much information as they may need,
      but they must be able to ignore controls and information
      irrelevant to their operation.  This implies that the "default"




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      interface must be no more complicated than BSD sockets, and must
      do something reasonable.

   o  A new API cannot be bound to a single transport protocol and
      expect wide deployment.  As the API is transport-independent and
      may support runtime transport selection, it must impose the
      minimum possible set of constraints on its underlying transports,
      though some API features may require underlying transport features
      to work optimally.  It must be possible to implement Post over
      vanilla TCP in the present Internet architecture.

   o  Reception is an inherently asynchronous activity.  While the API
      is designed to be as platform-independent as possible, one key
      insight it is based on is that an object receiver's behavior in a
      packet-switched network is inherently asynchronous, driven by the
      receipt of packets, and that this asynchronicity must be reflected
      in the API.  The actual implementation of receive and event
      callbacks will need to be aligned to the method a given platform
      provides for asynchronous I/O.

   The API we define consists of three classes (listener, association,
   and stream), four entry points (listen(), associate(), send(), and
   open_stream()) and a set of callbacks for handling events at each
   endpoint.  The details are given in the subsections below.

3.1.  Active Association Creation

   Associations can be created two ways: actively by a connection
   initiator, and passively by a Listener that accepts a connection.
   Connection initiation uses the associate() entry point:

   association = associate(local, remote, receive_handler)

   where:

   o  local: a resolved Local (see Section 3.8) describing the local
      identity and interface(s) to use

   o  remote: a resolved Remote (see Section 3.8) to associate with

   o  receive_handler: a callback to be invoked when new objects are
      received; see Section 3.4

   The returned association has the following additional properties:

   o  paths: a set of Paths that the Association can currently use to
      transport Objects.  When the underlying transport connection is
      closed, this set will be empty.  For explicitly multipath



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      architectures and transports, this set may change dynamically
      during the lifetime of an association, even while it remains
      connected.

   Since the existence of an association does not necessarily imply
   current connection state at both ends of the Association, these
   objects are durable, and can be cached, migrated, and restored, as
   long as the mappings to their event handlers are stable.  An attempts
   to send an object or open a stream on a dormant, previously actively-
   opened association will cause the underlying transport connection
   state to be resumed.

3.2.  Listener and Passive Association Creation

   In order to accept new Association requests from clients, a server
   must create a Listener object, using the listen() entry point:

   listener = listen(local, accept_handler)

   where:

   o  local: resolved Local (see Section 3.8) describing the local
      identity and interface(s) to use for Associations created by this
      listener.

   o  accept_handler: callback to be invoked each time an association is
      requested by a remote, to finalize setting the association up.
      Platforms may provide a default here for supporting synchronous
      association request handling via an object queue.

   The accept_handler has the following prototype:

   accepted = accept_handler(listener, local, remote)

   where:

   o  local: a resolved Local on which the association request was
      received.

   o  remote: a resolved Remote from which the association request was
      received.

   o  accepted: flag, true if the handler decided to accept the request,
      false otherwise.

   The accept_handler() calls the accept() entry point to finally create
   the association:




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   association = accept(listener, local, remote, receive_handler)

3.3.  Sending Objects

   Objects are sent using the send() entry point:

   send(association, bytes, [lifetime], [niceness], [oid],
   [antecedent_oids], [paths])}

   where:

   o  association: the association to send the object on

   o  bytes: sequence of bytes making up the object.  For platforms
      without bounded byte arrays, this may be implemented as a pointer
      and a length.

   o  lifetime: lifetime of the object in milliseconds.  This parameter
      is optional and defaults to infinity (for fully reliable object
      transport).

   o  niceness: the object's niceness class.  This parameter is optional
      and defaults to zero (for lowest niceness / highest priority)

   o  oid: opaque identifier for an object, assigned by the application.
      Used to refer to this object as a subsequently sent object's
      antecedent, or in an ack or expired handler (see Section 3.6).
      Optional, defaults to null.

   o  antecedent_oids: set of object identifiers on which this object
      depends and which must be sent before this object.  Optional,
      defaults to empty, meaning this object has no antecedent
      constraints.

   o  paths: set of paths, as a subset of those available to the
      association, to explicitly use for this object.  Optional,
      defaults to empty, meaning all paths are acceptable.

   Calls to send are non-blocking; a synchronous send which blocks on
   remote acknowledgment or expiry of an object can be implemented by a
   call to send() followed by a wait on the ack or expired events (see
   Section 3.6).

3.4.  Receiving Objects

   An application receives objects via its receive_handler callback,
   registered at association creation time.  This callback has the
   following prototype:



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   receive_handler(association, bytes)

   where: - association: the association the object was received from.
   - bytes: the sequence of bytes making up the object.

   For ease of porting synchronous datagram applications,
   implementations may make a default receive handler available, which
   allows messages to be synchronously polled from a per-association
   object queue.  If this default is available, the entry point for the
   polling call is:

   bytes = receive_next(association)

3.5.  Creating and Destroying Streams

   A stream may be created on an association via the open_stream() entry
   point:

   stream = open_stream(association, [sid])

   where:

   o  association: the association to open the stream on

   o  sid: opaque identifier for a stream.  For transport protocols
      which do not support multiple streaming, this argument has no
      effect.

   A stream with a given sid must be opened by both sides before it can
   be used.

   The stream object returned should act like a file descriptor or
   bidirectional I/O object, according to the conventions of the
   platform implementing Post.

3.6.  Events

   Message reception is a specific case of an event that can occur on an
   association.  Other events are also available, and the application
   can register event handlers for each of these.  Event handlers are
   registered via the handle() entry point:

   handle(association, event, handler) or

   handle(oid, event, handler)

   where




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   o  association: the association to register a handler on, or

   o  oid: the object identifier to register a handler on

   o  event: an identifier of the event to register a handler on

   o  handler: a callback to be invoked when the event occurs, or null
      if the event should be ignored.

   The following events are supported; every event handler takes the
   association on which it is registered as well as any additional
   arguments listed:

   o  receive (bytes): an object has been received

   o  path_up (path): a path is newly available

   o  path_down (path): a path is no longer available

   o  dormant: no more paths are available, the association is now
      dormant, and the connection will need to be resumed if further
      objects are to be sent

   o  ack (oid): an object was successfully received by the remote

   o  expired (oid): an object expired before being sent to the remote

   Handlers for the ack and expired events can be registered on an
   association (in which case they are called for all objects sent on
   the association) or on an oid (in which case they are only called for
   the oid).

3.7.  Paths and Path Properties

   As defined in Section 2.5, the properties of a path include both the
   addresses of elements along the path as well as measurement-derived
   latency and capacity characteristics.  The path_up and path_down
   events provide access to information about the paths available via
   the path argument to the event handler.  This argument encapsulates
   these properties in a platform and transport-specific way, depending
   on the availability of information about the path.

3.8.  Address Resolution

   Address resolution turns the name of a Remote into a resolved Remote
   object, which encapsulates all the information needed to connect
   (address, certificate parameters, cached cryptographic state, etc.);
   and an interface identifier on a local system to information needed



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   to connect.  Remote and local resolvers have the following entry
   points:

   remote = resolve(endpoint_name, configuration)

   local = resolve_local(endpoint_name, configuration)

   where:

   o  endpoint_name: a name identifying the remote or local endpoint,
      including port

   o  configuration: a platform-specific configuration object for
      configuring certificates, name resolution contexts, cached
      cryptographic state, etc.

4.  Acknowledgments

   Many thanks to Laurent Chuat and Jason Lee at the Network Security
   Group at ETH Zurich for contributions to the initial design of Post
   Sockets.

   This work is partially supported by the European Commission under
   Horizon 2020 grant agreement no. 688421 Measurement and Architecture
   for a Middleboxed Internet (MAMI), and by the Swiss State Secretariat
   for Education, Research, and Innovation under contract no. 15.0268.
   This support does not imply endorsement.

5.  Informative References

   [I-D.hamilton-quic-transport-protocol]
              Hamilton, R., Iyengar, J., Swett, I., and A. Wilk, "QUIC:
              A UDP-Based Multiplexed and Secure Transport", draft-
              hamilton-quic-transport-protocol-00 (work in progress),
              July 2016.

   [I-D.iyengar-minion-protocol]
              Jana, J., Cheshire, S., and J. Graessley, "Minion - Wire
              Protocol", draft-iyengar-minion-protocol-02 (work in
              progress), October 2013.

   [I-D.trammell-plus-abstract-mech]
              Trammell, B., "Abstract Mechanisms for a Cooperative Path
              Layer under Endpoint Control", draft-trammell-plus-
              abstract-mech-00 (work in progress), September 2016.






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   [I-D.trammell-plus-statefulness]
              Kuehlewind, M., Trammell, B., and J. Hildebrand,
              "Transport-Independent Path Layer State Management",
              draft-trammell-plus-statefulness-00 (work in progress),
              October 2016.

   [MinimaLT]
              Petullo, W., Zhang, X., Solworth, J., Bernstein, D., and
              T. Lange, "MinimaLT, Minimal-latency Networking Through
              Better Security", May 2013.

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

   [RFC4960]  Stewart, R., Ed., "Stream Control Transmission Protocol",
              RFC 4960, DOI 10.17487/RFC4960, September 2007,
              <http://www.rfc-editor.org/info/rfc4960>.

   [RFC6824]  Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
              "TCP Extensions for Multipath Operation with Multiple
              Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
              <http://www.rfc-editor.org/info/rfc6824>.

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <http://www.rfc-editor.org/info/rfc7258>.

Authors' Addresses

   Brian Trammell
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich
   Switzerland

   Email: ietf@trammell.ch


   Colin Perkins
   University of Glasgow
   School of Computing Science
   Glasgow  G12 8QQ
   United Kingdom

   Email: csp@cperkins.net





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   Tommy Pauly
   Apple Inc.
   1 Infinite Loop
   Cupertino, California 95014
   United States of America

   Email: tpauly@apple.com


   Mirja Kuehlewind
   ETH Zurich
   Gloriastrasse 35
   8092 Zurich
   Switzerland

   Email: mirja.kuehlewind@tik.ee.ethz.ch



































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