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TAPS                                                            M. Welzl
Internet-Draft                                        University of Oslo
Intended status: Informational                                 M. Tuexen
Expires: May 4, 2017                    Muenster Univ. of Appl. Sciences
                                                              N. Khademi
                                                      University of Oslo
                                                        October 31, 2016


 On the Usage of Transport Service Features Provided by IETF Transport
                               Protocols
                  draft-ietf-taps-transports-usage-02

Abstract

   This document describes how transport protocols expose services to
   applications and how an application can configure and use the
   features of a transport service.

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 May 4, 2017.

Copyright Notice

   Copyright (c) 2016 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
   (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



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Pass 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Primitives Provided by TCP . . . . . . . . . . . . . . . .  5
       3.1.1.  Excluded Primitives or Parameters  . . . . . . . . . .  7
     3.2.  Primitives Provided by MPTCP . . . . . . . . . . . . . . .  8
     3.3.  Primitives Provided by SCTP  . . . . . . . . . . . . . . .  9
       3.3.1.  Excluded Primitives or Parameters  . . . . . . . . . . 13
     3.4.  Primitives Provided by UDP and UDP-Lite  . . . . . . . . . 14
   4.  Pass 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     4.1.  CONNECTION Related Primitives  . . . . . . . . . . . . . . 14
     4.2.  DATA Transfer Related Primitives . . . . . . . . . . . . . 23
   5.  Pass 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
     5.1.  CONNECTION Related Transport Service Features  . . . . . . 25
     5.2.  DATA Transfer Related Transport Service Features . . . . . 30
       5.2.1.  Sending Data . . . . . . . . . . . . . . . . . . . . . 30
       5.2.2.  Receiving Data . . . . . . . . . . . . . . . . . . . . 31
       5.2.3.  Errors . . . . . . . . . . . . . . . . . . . . . . . . 31
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 32
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 32
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 32
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 32
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 33
   Appendix A.  Overview of RFCs used as input for pass 1 . . . . . . 35
   Appendix B.  How to contribute . . . . . . . . . . . . . . . . . . 36
   Appendix C.  Revision information  . . . . . . . . . . . . . . . . 37
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 38

















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1.  Terminology

   Transport Service Feature:  a specific end-to-end feature that a
      transport service provides to its clients.  Examples include
      confidentiality, reliable delivery, ordered delivery, message-
      versus-stream orientation, etc.
   Transport Service:  a set of transport service features, without an
      association to any given framing protocol, which provides a
      complete service to an application.
   Transport Protocol:  an implementation that provides one or more
      different transport services using a specific framing and header
      format on the wire.
   Transport Protocol Component:  an implementation of a transport
      service feature within a protocol.
   Transport Service Instance:  an arrangement of transport protocols
      with a selected set of features and configuration parameters that
      implements a single transport service, e.g., a protocol stack (RTP
      over UDP).
   Application:  an entity that uses the transport layer for end-to-end
      delivery of data across the network (this may also be an upper
      layer protocol or tunnel encapsulation).
   Endpoint:  an entity that communicates with one or more other
      endpoints using a transport protocol.
   Connection:  shared state of two or more endpoints that persists
      across messages that are transmitted between these endpoints.
   Primitive:  a function call that is used to locally communicate
      between an application and a transport endpoint and is related to
      one or more Transport Service Features.
   Parameter:  a value passed between an application and a transport
      protocol by a primitive.
   Socket:  the combination of a destination IP address and a
      destination port number.
   Transport Address:  the combination of an IP address, transport
      protocol and the port number used by the transport protocol.


2.  Introduction

   This document presents defined interactions between transport
   protocols and applications in the form of 'primitives' (function
   calls).  Primitives can be invoked by an application or a transport
   protocol; the latter type is called an "event".  The list of
   transport service features and primitives in this document is
   strictly based on the parts of protocol specifications that relate to
   what the protocol provides to an application using it and how the
   application interacts with it.  It does not cover parts of a protocol
   that are explicitly stated as optional to implement.




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   The document presents a three-pass process to arrive at a list of
   transport service features.  In the first pass, the relevant RFC text
   is discussed per protocol.  In the second pass, this discussion is
   used to derive a list of primitives that are uniformly categorized
   across protocols.  Here, an attempt is made to present or -- where
   text describing primitives does not yet exist -- construct primitives
   in a slightly generalized form to highlight similarities.  This is,
   for example, achieved by renaming primitives of protocols or by
   avoiding a strict 1:1-mapping between the primitives in the protocol
   specification and primitives in the list.  Finally, the third pass
   presents transport service features based on pass 2, identifying
   which protocols implement them.

   In the list resulting from the second pass, some transport service
   features are missing because they are implicit in some protocols, and
   they only become explicit when we consider the superset of all
   features offered by all protocols.  For example, TCP's reliability
   includes integrity via a checksum, but we have to include a protocol
   like UDP-Lite as specified in [RFC3828] (which has a configurable
   checksum) in the list before we can consider an always-on checksum as
   a transport service feature.  Similar arguments apply to other
   protocol functions (e.g. congestion control).  The complete list of
   features across all protocols is therefore only available after pass
   3.

   This document discusses unicast transport protocols.  [AUTHOR'S NOTE:
   we skip "congestion control mechanisms" for now.  This simplifies the
   discussion; the congestion control mechanisms part is about LEDBAT,
   which should be easy to add later.]  Transport protocols provide
   communication between processes that operate on network endpoints,
   which means that they allow for multiplexing of communication between
   the same IP addresses, and normally this multiplexing is achieved
   using port numbers.  Port multiplexing is therefore assumed to be
   always provided and not discussed in this document.

   Some protocols are connection-oriented.  Connection-oriented
   protocols often use an initial call to a specific transport primitive
   to open a connection before communication can progress, and require
   communication to be explicitly terminated by issuing another call to
   a transport primitive (usually called "close").  A "connection" is
   the common state that some transport primitives refer to, e.g., to
   adjust general configuration settings.  Connection establishment,
   maintenance and termination are therefore used to categorize
   transport primitives of connection-oriented transport protocols in
   pass 2 and pass 3.






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3.  Pass 1

   This first iteration summarizes the relevant text parts of the RFCs
   describing the protocols, focusing on what each transport protocol
   provides to the application and how it is used (abstract API
   descriptions, where they are available).

3.1.  Primitives Provided by TCP

   [RFC0793] states: "The Transmission Control Protocol (TCP) is
   intended for use as a highly reliable host-to-host protocol between
   hosts in packet-switched computer communication networks, and in
   interconnected systems of such networks".  Section 3.8 in [RFC0793]
   further specifies the interaction with the application by listing
   several transport primitives.  It is also assumed that an Operating
   System provides a means for TCP to asynchronously signal the
   application; the primitives representing such signals are called
   'events' in this section.  This section describes the relevant
   primitives.

   open:  this is either active or passive, to initiate a connection or
      listen for incoming connections.  All other primitives are
      associated with a specific connection, which is assumed to first
      have been opened.  An active open call contains a socket.  A
      passive open call with a socket waits for a particular connection;
      alternatively, a passive open call can leave the socket
      unspecified to accept any incoming connection.  A fully specified
      passive call can later be made active by calling 'send'.
      Optionally, a timeout can be specified, after which TCP will abort
      the connection if data has not been successfully delivered to the
      destination (else a default timeout value is used).  [RFC1122]
      describes a procedure for aborting the connection that must be
      used to avoid excessive retransmissions, and states that an
      application must be able to control the threshold used to
      determine the condition for aborting -- and that this threshold
      may be measured in time units or as a count of retransmission.
      This indicates that the timeout could also be specified as a count
      of retransmission.

      Also optional, for multihomed hosts, the local IP address can be
      provided [RFC1122].  If it is not provided, a default choice will
      be made in case of active open calls.  A passive open call will
      await incoming connection requests to all local addresses and then
      maintain usage of the local IP address where the incoming
      connection request has arrived.  Finally, the 'options' parameter
      is explained in [RFC1122] to allow the application to specify IP
      options such as source route, record route, or timestamp.  It is
      not stated on which segments of a connection these options should



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      be applied, but probably all segments, as this is also stated in a
      specification given for the usage of source route (section 4.2.3.8
      of [RFC1122]).  Source route is the only non-optional IP option in
      this parameter, allowing an application to specify a source route
      when it actively opens a TCP connection.

   send:  this is the primitive that an application uses to give the
      local TCP transport endpoint a number of bytes that TCP should
      reliably send to the other side of the connection.  The URGENT
      flag, if set, states that the data handed over by this send call
      is urgent and this urgency should be indicated to the receiving
      process in case the receiving application has not yet consumed all
      non-urgent data preceding it.  An optional timeout parameter can
      be provided that updates the connection's timeout (see 'open').

   receive:  This primitive allocates a receiving buffer for a provided
      number of bytes.  It returns the number of received bytes provided
      in the buffer when these bytes have been received and written into
      the buffer by TCP.  The application is informed of urgent data via
      an URGENT flag: if it is on, there is urgent data.  If it is off,
      there is no urgent data or this call to 'receive' has returned all
      the urgent data.

   close:  This primitive closes one side of a connection.  It is
      semantically equivalent to "I have no more data to send" but does
      not mean "I will not receive any more", as the other side may
      still have data to send.  This call reliably delivers any data
      that has already been given to TCP (and if that fails, 'close'
      becomes 'abort').

   abort:  This primitive causes all pending 'send' and 'receive' calls
      to be aborted.  A TCP RESET message is sent to the TCP endpoint on
      the other side of the connection [RFC0793].

   close event:  TCP uses this primitive to inform an application that
      the application on the other side has called the 'close'
      primitive, so the local application can also issue a 'close' and
      terminate the connection gracefully.  See [RFC0793], Section 3.5.

   abort event:  When TCP aborts a connection upon receiving a "Reset"
      from the peer, it "advises the user and goes to the CLOSED state."
      See [RFC0793], Section 3.4.

   USER TIMEOUT event:  This event, described in Section 3.9 of
      [RFC0793], is executed when the user timeout expires (see 'open').
      All queues are flushed and the application is informed that the
      connection had to be aborted due to user timeout.




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   ERROR_REPORT event:  This event, described in Section 4.2.4.1 of
      [RFC1122], informs the application of "soft errors" that can be
      safely ignored [RFC5461], including the arrival of an ICMP error
      message or excessive retransmissions (reaching a threshold below
      the threshold where the connection is aborted).

   Type-of-Service:  Section 4.2.4.2 of [RFC1122] states that the
      application layer MUST be able to specify the Type-of-Service
      (TOS) for segments that are sent on a connection.  The application
      should be able to change the TOS during the connection lifetime,
      and the TOS value should be passed to the IP layer unchanged.
      Since then the TOS field has been redefined.  A part of the field
      has been assigned to ECN [RFC3168] and the six most significant
      bits have been assigned to carry the DiffServ CodePoint, DSField
      [RFC3260].  Staying with the intention behind the application's
      ability to specify the "Type of Service", this should probably be
      interpreted to mean the value in the DSField, which is the
      Differentiated Services Codepoint (DSCP).

   Nagle:  The Nagle algorithm, described in Section 4.2.3.4 of
      [RFC1122], delays sending data for some time to increase the
      likelihood of sending a full-sized segment.  An application can
      disable the Nagle algorithm for an individual connection.

   User Timeout Option:  The User Timeout Option (UTO) [RFC5482] allows
      one end of a TCP connection to advertise its current user timeout
      value so that the other end of the TCP connection can adapt its
      own user timeout accordingly.  In addition to the configurable
      value of the User Timeout (see 'send'), [RFC5482] introduces three
      per-connection state variables that an application can adjust to
      control the operation of the User Timeout Option (UTO): ADV_UTO is
      the value of the UTO advertised to the remote TCP peer (default:
      system-wide default user timeout); ENABLED (default false) is a
      boolean-type flag that controls whether the UTO option is enabled
      for a connection.  This applies to both sending and receiving.
      CHANGEABLE is a boolean-type flag (default true) that controls
      whether the user timeout may be changed based on a UTO option
      received from the other end of the connection.  CHANGEABLE becomes
      false when an application explicitly sets the user timeout (see
      'send').


3.1.1.  Excluded Primitives or Parameters

   The 'open' primitive specified in [RFC0793] can be handed optional
   Precedence or security/compartment information according to
   [RFC0793], but this was not included here because it is mostly
   irrelevant today, as explained in [RFC7414].



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   The 'status' primitive was not included because [RFC0793] describes
   this primitive as "implementation dependent" and states that it
   "could be excluded without adverse effect".  Moreover, while a data
   block containing specific information is described, it is also stated
   that not all of this information may always be available.  The 'send'
   primitive described in [RFC0793] includes an optional PUSH flag
   which, if set, requires data to be promptly transmitted to the
   receiver without delay; the 'receive' primitive described in
   [RFC0793] can (under some conditions) yield the status of the PUSH
   flag.  Because PUSH functionality is made optional to implement for
   both the 'send' and 'receive' primitives in [RFC1122], this
   functionality is not included here.  [RFC1122] also introduces keep-
   alives to TCP, but these are optional to implement and hence not
   considered here.  [RFC1122] describes that "some TCP implementations
   have included a FLUSH call", indicating that this call is also
   optional to implement.  It is therefore not considered here.

3.2.  Primitives Provided by MPTCP

   Multipath TCP (MPTCP) is an extension to TCP that allows the use of
   multiple paths for a single data-stream.  It achieves this by
   creating different so-called TCP subflows for each of the interfaces
   and scheduling the traffic across these TCP subflows.  The service
   provided by MPTCP is described in [RFC6182] "Multipath TCP MUST
   follow the same service model as TCP [RFC0793]: in- order, reliable,
   and byte-oriented delivery.  Furthermore, a Multipath TCP connection
   SHOULD provide the application with no worse throughput or resilience
   than it would expect from running a single TCP connection over any
   one of its available paths."

   Further, [RFC6182] states constraints on the API exposed by MPTCP: "A
   multipath-capable equivalent of TCP MUST retain some level of
   backward compatibility with existing TCP APIs, so that existing
   applications can use the newer merely by upgrading the operating
   systems of the end hosts."  As such, the primitives provided by MPTCP
   are equivalent to the ones provided by TCP.  Nevertheless, [RFC6824]
   and [RFC6897] clarify some parts of TCP's primitives with respect to
   MPTCP and add some extensions for better control on MPTCP's subflows.
   Hereafter is a list of the clarifications and extensions the above
   cited RFCs provide to TCP's primitives.

   open:  [RFC6897] states "An application should be able to request to
      turn on or turn off the usage of MPTCP.".  The RFC states that
      this functionality can be provided through a socket-option called
      TCP_MULTIPATH_ENABLE.  Further, [RFC6897] says that MPTCP must be
      disabled in case the application is binding to a specific address.





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   send/receive:  [RFC6824] states that the sending and receiving of
      data does not require any changes to the application when MPTCP is
      being used.  The MPTCP-layer will "take one input data stream from
      an application, and split it into one or more subflows, with
      sufficient control information to allow it to be reassembled and
      delivered reliably and in order to the recipient application."
      The use of the Urgent-Pointer is special in MPTCP and [RFC6824]
      says "a TCP subflow MUST NOT use the Urgent Pointer to interrupt
      an existing mapping."

   address and subflow management:  MPTCP uses different addresses and
      allows a host to announce these addresses as part of the protocol.
      [RFC6897] says "An application should be able to restrict MPTCP to
      binding to a given set of addresses." and thus allows applications
      to limit the set of addresses that are being used by MPTCP.
      Further, "An application should be able to obtain information on
      the pairs of addresses used by the MPTCP subflows.".


3.3.  Primitives Provided by SCTP

   Section 1.1 of [RFC4960] lists limitations of TCP that SCTP removes.
   Three of the four mentioned limitations directly translate into a
   transport service features that are visible to an application using
   SCTP: 1) it allows for preservation of message delineations; 2) these
   messages, while reliably transferred, do not require to be in order
   unless the application wants it; 3) multi-homing is supported.  In
   SCTP, connections are called "association" and they can be between
   not only two (as in TCP) but multiple addresses at each endpoint.

   Section 10 of [RFC4960] further specifies the interaction with the
   application (which RFC [RFC4960] calls the "Upper Layer Protocol"
   (ULP)).  It is assumed that the Operating System provides a means for
   SCTP to asynchronously signal the application; the primitives
   representing such signals are called 'events' in this section.  Here,
   we describe the relevant primitives.  In addition to the abstract API
   described in Section 10 of [RFC4960], an extension to the socket API
   is described in [RFC6458] covering the functionality of the base
   protocol specified in [RFC4960] and its extensions specified in
   [RFC3758], [RFC4895], and [RFC5061].  For the protocol extensions
   specified in [RFC6525], [RFC6951], [RFC7053], [RFC7496], and
   [RFC7829] the corresponding extensions of the socket API are
   specified in these protocol specifications.  The functionality
   exposed to the ULP through this socket API is considered here in
   addition to the abstract API specified in Section 10 of [RFC4960].






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   Initialize:  Initialize creates a local SCTP instance that it binds
      to a set of local addresses (and, if provided, port number).
      Initialize needs to be called only once per set of local
      addresses.

   Associate:  This creates an association (the SCTP equivalent of a
      connection) between the local SCTP instance and a remote SCTP
      instance.  Most primitives are associated with a specific
      association, which is assumed to first have been created.
      Associate can return a list of destination transport addresses so
      that multiple paths can later be used.  One of the returned
      sockets will be selected by the local endpoint as default primary
      path for sending SCTP packets to this peer, but this choice can be
      changed by the application using the list of destination
      addresses.  Associate is also given the number of outgoing streams
      to request and optionally returns the number of outgoing streams
      negotiated.  An optional parameter of 32-bits, the adaptation
      layer indication, can be provided, as specified in [RFC5061].  If
      the extension specified in [RFC4895] is used, the chunk types
      required to be sent authenticated by the peer can be provided.

   Send:  This sends a message of a certain length in bytes over an
      association.  A number can be provided to later refer to the
      correct message when reporting an error, and a stream id is
      provided to specify the stream to be used inside an association
      (we consider this as a mandatory parameter here for simplicity: if
      not provided, the stream id defaults to 0).  A condition to
      abandon the message can be specified (for example limiting the
      number of retransmissions or the lifetime of the user message).
      This allows to control the partial reliability extension specified
      in [RFC3758] and [RFC7496].  An optional maximum life time can
      specify the time after which the message should be discarded
      rather than sent.  A choice (advisory, i.e. not guaranteed) of the
      preferred path can be made by providing a socket, and the message
      can be delivered out-of-order if the unordered flag is set.  An
      advisory flag indicates that the peer should not delay the
      acknowledgement of the user message provided by making use of the
      I-bit specified in [RFC7053].  Another advisory flag indicates
      whether the application prefers to avoid bundling user data with
      other outbound DATA chunks (i.e., in the same packet).  A payload
      protocol-id can be provided to pass a value that indicates the
      type of payload protocol data to the peer.  If the extension
      specified in [RFC4895] is used, the key identifier used for
      authenticating the DATA chunks can be provided.







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   Receive:  Messages are received from an association, and optionally a
      stream within the association, with their size returned.  The
      application is notified of the availability of data via a DATA
      ARRIVE notification.  If the sender has included a payload
      protocol-id, this value is also returned.  If the received message
      is only a partial delivery of a whole message, a partial flag will
      indicate so, in which case the stream id and a stream sequence
      number are provided to the application.  A delivery number lets
      the application detect reordering.

   Shutdown:  This primitive gracefully closes an association, reliably
      delivering any data that has already been handed over to SCTP.  A
      return code informs about success or failure of this procedure.

   Abort:  This ungracefully closes an association, by discarding any
      locally queued data and informing the peer that the association
      was aborted.  Optionally, an abort reason to be passed to the peer
      may be provided by the application.  A return code informs about
      success or failure of this procedure.

   Change Heartbeat / Request Heartbeat:  This allows the application to
      enable/disable heartbeats and optionally specify a heartbeat
      frequency as well as requesting a single heartbeat to be carried
      out upon a function call, with a notification about success or
      failure of transmitting the HEARTBEAT chunk to the destination.

   Set Protocol Parameters:  This allows to set values for protocol
      parameters per association; for some parameters, a setting can be
      made per socket.  The set listed in [RFC4960] is: RTO.Initial;
      RTO.Min; RTO.Max; Max.Burst; RTO.Alpha; RTO.Beta;
      Valid.Cookie.Life; Association.Max.Retrans; Path.Max.Retrans;
      Max.Init.Retransmits; HB.interval; HB.Max.Burst.  In addition to
      these, the Quick Failover Algorithm specified in [RFC7829] can be
      controlled by the PotentiallyFailed.Max.Retrans and
      Primary.Switchover.Max.Retrans parameter.  A remote UDP
      encapsulation port can be set for using UDP encapsulation as
      specified in [RFC6951].

   Set Primary:  This allows to set a new primary default path for an
      association by providing a socket.  Optionally, a default source
      address to be used in IP datagrams can be provided.

   Set / Get Authentication Parameters:  This allows an endpoint to add/
      remove key material to/from an association.  In addition, the
      chunk types being authenticated can be queried.  This is provided
      by the protocol extension defined in [RFC4895].





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   Change Local Address / Set Peer Primary:  This allows an endpoint to
      add/remove local addresses to/from an association.  In addition,
      the peer can be given a hint which address to use as the primary
      address.  This is provided by the protocol extension defined in
      [RFC5061].

   Add / Reset Streams, Reset Association:  This allows an endpoint to
      add streams to an existing association or or to reset them
      individually.  Additionally, the association can be reset.  This
      is provided by the protocol extension defined in [RFC6525].

   Status:  The 'Status' primitive returns a data block with information
      about a specified association, containing: association connection
      state; socket list; destination transport address reachability
      states; current receiver window size; current congestion window
      sizes; number of unacknowledged DATA chunks; number of DATA chunks
      pending receipt; primary path; most recent SRTT on primary path;
      RTO on primary path; SRTT and RTO on other destination addresses.

   COMMUNICATION UP notification:  When a lost communication to an
      endpoint is restored or when SCTP becomes ready to send or receive
      user messages, this notification informs the application process
      about the affected association, the type of event that has
      occurred, the complete set of sockets of the peer, the maximum
      number of allowed streams and the inbound stream count (the number
      of streams the peer endpoint has requested).

   DATA ARRIVE notification:  When a message is ready to be retrieved
      via the Receive primitive, the application is informed by this
      notification.

   SEND FAILURE notification / Receive Unsent Message / Receive
   Unacknowledged Message:  When a message cannot be delivered via an
      association, the sender can be informed about it and learn whether
      the message has just not been acknowledged or (e.g. in case of
      lifetime expiry) if it has not even been sent.

   NETWORK STATUS CHANGE notification:  The NETWORK STATUS CHANGE
      notification informs the application about a socket becoming
      active/inactive.

   COMMUNICATION LOST notification:  When SCTP loses communication to an
      endpoint (e.g. via Heartbeats or excessive retransmission) or
      detects an abort, this notification informs the application
      process of the affected association and the type of event (failure
      OR termination in response to a shutdown or abort request).





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   SHUTDOWN COMPLETE notification:  When SCTP completes the shutdown
      procedures, this notification is passed to the upper layer,
      informing it about the affected assocation.

   AUTHENICATION notification:  When SCTP wants to notify the upper
      layer regarding the key management related to the extension
      defined in [RFC4895], this notification is passed to the upper
      layer.

   ADAPTATION LAYER INDICATION notification:  When SCTP completes the
      association setup and the peer provided an adaptation layer
      indication, this is passed to the upper layer.  This extension is
      defined in [RFC5061] and [RFC6458].

   STREAM RESET notification:  When SCTP completes the procedure for
      resetting streams as specified in [RFC6525], this notification is
      passed to the upper layer, informing it about the result.

   ASSOCIATION RESET notification:  When SCTP completes the association
      reset procedure as specified in [RFC6525], this notification is
      passed to the upper layer, informing it about the result.

   STREAM CHANGE notification:  When SCTP completes the procedure used
      to increase the number of streams as specified in [RFC6525], this
      notification is passed to the upper layer, informing it about the
      result.


3.3.1.  Excluded Primitives or Parameters

   The 'Receive' primitive can return certain additional information,
   but this is optional to implement and therefore not considered.  With
   a COMMUNICATION LOST notification, some more information may
   optionally be passed to the application (e.g., identification to
   retrieve unsent and unacknowledged data).  SCTP "can invoke" a
   COMMUNICATION ERROR notification and "may send" a RESTART
   notification, making these two notifications optional to implement.
   The list provided under 'Status' includes "etc", indicating that more
   information could be provided.  The primitive 'Get SRTT Report'
   returns information that is included in the information that 'Status'
   provides and is therefore not discussed.  Similarly, 'Set Failure
   Threshold' sets only one out of various possible parameters included
   in 'Set Protocol Parameters'.  The 'Destroy SCTP Instance' API
   function was excluded: it erases the SCTP instance that was created
   by 'Initialize', but is not a Primitive as defined in this document
   because it does not relate to a Transport Service Feature.





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3.4.  Primitives Provided by UDP and UDP-Lite

   The primitives provided by UDP and UDP-Lite are described in [FJ16].


4.  Pass 2

   This pass categorizes the primitives from pass 1 based on whether
   they relate to a connection or to data transmission.  Primitives are
   presented following the nomenclature
   "CATEGORY.[SUBCATEGORY].PRIMITIVENAME.PROTOCOL".  The CATEGORY can be
   CONNECTION or DATA.  Within the CONNECTION category, ESTABLISHMENT,
   AVAILABILITY, MAINTENANCE and TERMINATION subcategories can be
   considered.  The DATA category does not have any SUBCATEGORY (as of
   now).  The PROTOCOL name "UDP(-Lite)" is used when primitives are
   equivalent for UDP and UDP-Lite; the PROTOCOL name "TCP" refers to
   both TCP and MPTCP.  We present "connection" as a general protocol-
   independent concept and use it to refer to, e.g., TCP connections
   (identifiable by a unique pair of IP addresses and TCP port numbers),
   SCTP associations (identifiable by multiple IP address and port
   number pairs), as well UDP and UDP-Lite connections (identifiable by
   a unique socket pair).

   Some minor details are omitted for the sake of generalization --
   e.g., SCTP's 'close' [RFC4960] returns success or failure, whereas
   this is not described in the same way for TCP in [RFC0793], but this
   detail plays no significant role for the primitives provided by
   either TCP or SCTP.

   The TCP 'send' and 'receive' primitives include usage of an "URGENT"
   mechanism.  This mechanism is required to implement the "synch
   signal" used by telnet [RFC0854], but SHOULD NOT be used by new
   applications [RFC6093].  Because pass 2 is meant as a basis for the
   creation of TAPS systems, the "URGENT" mechanism is excluded.  This
   also concerns the notification "Urgent pointer advance" in the
   ERROR_REPORT described in Section 4.2.4.1 of [RFC1122].

4.1.  CONNECTION Related Primitives

   ESTABLISHMENT:
   Active creation of a connection from one transport endpoint to one or
   more transport endpoints.
   Interfaces to UDP and UDP-Lite allow both connection-oriented and
   connection-less usage of the API [I-D.ietf-tsvwg-rfc5405bis]

   o  CONNECT.TCP:
      Pass 1 primitive / event: 'open' (active) or 'open' (passive) with
      socket, followed by 'send'



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      Parameters: 1 local IP address (optional); 1 destination transport
      address (for active open; else the socket and the local IP address
      of the succeeding incoming connection request will be maintained);
      timeout (optional); options (optional)
      Comments: If the local IP address is not provided, a default
      choice will automatically be made.  The timeout can also be a
      retransmission count.  The options are IP options to be used on
      all segments of the connection.  At least the Source Route option
      is mandatory for TCP to provide.

   o  CONNECT.SCTP:
      Pass 1 primitive / event: 'initialize', followed by 'associate'
      Parameters: list of local SCTP port number / IP address pairs
      (initialize); 1 socket; outbound stream count; adaptation layer
      indication; chunk types required to be authenticated
      Returns: socket list
      Comments: 'initialize' needs to be called only once per list of
      local SCTP port number / IP address pairs.  One socket will
      automatically be chosen; it can later be changed in MAINTENANCE.

   o  CONNECT.MPTCP:
      This is similar to CONNECT.TCP except for one additional boolean
      parameter that allows to enable or disable MPTCP for a particular
      connection or socket (default: enabled).

   o  CONNECT.UDP(-Lite):
      Pass 1 primitive / event: 'connect' followed by 'send'.
      Parameters: 1 local IP address (default (ANY), or specified); 1
      destination transport address; 1 local port (default (OS chooses),
      or specified); 1 destination port (default (OS chooses), or
      specified).
      Comments: Associates a transport address creating a UDP(-Lite)
      socket connection.  This can be called again with a new transport
      address to create a new connection.  The CONNECT function allows
      an application to receive errors from messages sent to a transport
      address.


   AVAILABILITY:
   Preparing to receive incoming connection requests.

   o  LISTEN.TCP:
      Pass 1 primitive / event: 'open' (passive)
      Parameters: 1 local IP address (optional); 1 socket (optional);
      timeout (optional)
      Comments: if the socket and/or local IP address is provided, this
      waits for incoming connections from only and/or to only the
      provided address.  Else this waits for incoming connections



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      without this / these constraint(s).  ESTABLISHMENT can later be
      performed with 'send'.

   o  LISTEN.SCTP:
      Pass 1 primitive / event: 'initialize', followed by 'COMMUNICATION
      UP' notification and possibly 'ADAPTATION LAYER' notification
      Parameters: list of local SCTP port number / IP address pairs
      (initialize)
      Returns: socket list; outbound stream count; inbound stream count;
      adaptation layer indication; chunks required to be authenticated
      Comments: initialize needs to be called only once per list of
      local SCTP port number / IP address pairs.  COMMUNICATION UP can
      also follow a COMMUNICATION LOST notification, indicating that the
      lost communication is restored.  If the peer has provided an
      adaptation layer indication, an 'ADAPTATION LAYER' notification is
      issued.

   o  LISTEN.MPTCP:
      This is similar to LISTEN.TCP except for one additional boolean
      parameter that allows to enable or disable MPTCP for a particular
      connection or socket (default: enabled).

   o  LISTEN.UDP(-Lite):
      Pass 1 primitive / event: 'receive'.
      Parameters: 1 local IP address (default (ANY), or specified); 1
      destination transport address; local port (default (OS chooses),
      or specified); destination port (default (OS chooses), or
      specified).
      Comments: The receive function registers the application to listen
      for incoming UDP(-Lite) datagrams at an endpoint.


   MAINTENANCE:
   Adjustments made to an open connection, or notifications about it.
   These are out-of-band messages to the protocol that can be issued at
   any time, at least after a connection has been established and before
   it has been terminated (with one exception: CHANGE-TIMEOUT.TCP can
   only be issued for an open connection when DATA.SEND.TCP is called).
   In some cases, these primitives can also be immediately issued during
   ESTABLISHMENT or AVAILABILITY, without waiting for the connection to
   be opened (e.g.  CHANGE-TIMEOUT.TCP can be done using TCP's 'open'
   primitive).  For UDP and UDP-Lite, these functions may establish a
   setting per connection, but may also be changed per datagram message.

   o  CHANGE-TIMEOUT.TCP:
      Pass 1 primitive / event: 'open' or 'send' combined with
      unspecified control of per-connection state variables
      Parameters: timeout value (optional); ADV_UTO (optional); boolean



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      UTO_ENABLED (optional, default false); boolean CHANGEABLE
      (optional, default true)
      Comments: when sending data, an application can adjust the
      connection's timeout value (time after which the connection will
      be aborted if data could not be delivered).  If UTO_ENABLED is
      true, the user timeout value (or, if provided, the value ADV_UTO)
      will be advertised for the TCP on the other side of the connection
      to adapt its own user timeout accordingly.  UTO_ENABLED controls
      whether the UTO option is enabled for a connection.  This applies
      to both sending and receiving.  CHANGEABLE controls whether the
      user timeout may be changed based on a UTO option received from
      the other end of the connection; it becomes false when 'timeout
      value' is used.

   o  CHANGE-TIMEOUT.SCTP:
      Pass 1 primitive / event: 'Change HeartBeat' combined with 'Set
      Protocol Parameters'
      Parameters: 'Change HeartBeat': heartbeat frequency; 'Set Protocol
      Parameters': Association.Max.Retrans (whole association) or
      Path.Max.Retrans (per socket)
      Comments: Change Heartbeat can enable / disable heartbeats in SCTP
      as well as change their frequency.  The parameter
      Association.Max.Retrans defines after how many unsuccessful
      heartbeats the connection will be terminated; thus these two
      primitives / parameters together can yield a similar behavior to
      CHANGE-TIMEOUT.TCP.

   o  DISABLE-NAGLE.TCP:
      Pass 1 primitive / event: not specified
      Parameters: one boolean value
      Comments: the Nagle algorithm delays data transmission to increase
      the chance to send a full-sized segment.  An application must be
      able to disable this algorithm for a connection.

   o  REQUESTHEARTBEAT.SCTP:
      Pass 1 primitive / event: 'Request HeartBeat'
      Parameters: socket
      Returns: success or failure
      Comments: requests an immediate heartbeat on a path, returning
      success or failure.

   o  SETPROTOCOLPARAMETERS.SCTP:
      Pass 1 primitive / event: 'Set Protocol Parameters'
      Parameters: RTO.Initial; RTO.Min; RTO.Max; Max.Burst; RTO.Alpha;
      RTO.Beta; Valid.Cookie.Life; Association.Max.Retrans;
      Path.Max.Retrans; Max.Init.Retransmits; HB.interval; HB.Max.Burst;
      PotentiallyFailed.Max.Retrans; Primary.Switchover.Max.Retrans;
      Remote.UDPEncapsPort.



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   o  SETPRIMARY.SCTP:
      Pass 1 primitive / event: 'Set Primary'
      Parameters: socket
      Returns: result of attempting this operation
      Comments: update the current primary address to be used, based on
      the set of available sockets of the association.

   o  SETPEERPRIMARY.SCTP:
      Pass 1 primitive / event: Change Local Address / Set Peer Primary
      Parameters: local IP address
      Comments: this is only advisory for the peer.

   o  SETAUTH.SCTP:
      Pass 1 primitive / event: Set / Get Authentication Parameters
      Parameters: key_id, key, hmac_id

   o  GETAUTH.SCTP:
      Pass 1 primitive / event: Set / Get Authentication Parameters
      Parameters: key_id, chunk_list

   o  RESETSTREAM.SCTP:
      Pass 1 primitive / event: Add / Reset Streams, Reset Association
      Parameters: sid, direction

   o  RESETSTREAM-EVENT.SCTP:
      Pass 1 primitive / event: STREAM RESET notification
      Parameters: information about the result of RESETSTREAM.SCTP.
      Comments: This is issued when the procedure for resetting streams
      has completed.

   o  RESETASSOC.SCTP:
      Pass 1 primitive / event: Add / Reset Streams, Reset Association
      Parameters: information related to the extension defined in
      [RFC3260].

   o  RESETASSOC-EVENT.SCTP:
      Pass 1 primitive / event: ASSOCIATION RESET notification
      Parameters: information about the result of RESETASSOC.SCTP.
      Comments: This is issued when the procedure for resetting an
      association has completed.

   o  ADDSTREAM.SCTP:
      Pass 1 primitive / event: Add / Reset Streams, Reset Association
      Parameters: number if outgoing and incoming streams to be added

   o  ADDSTREAM-EVENT.SCTP:
      Pass 1 primitive / event: STREAM CHANGE notification
      Parameters: information about the result of ADDSTREAM.SCTP.



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      Comments: This is issued when the procedure for adding a stream
      has completed.

   o  ERROR.TCP:
      Pass 1 primitive / event: 'ERROR_REPORT'
      Returns: reason (encoding not specified); subreason (encoding not
      specified)
      Comments: soft errors that can be ignored without harm by many
      applications; an application should be able to disable these
      notifications.  The reported conditions include at least: ICMP
      error message arrived; Excessive Retransmissions.

   o  ERROR.UDP(-Lite):
      Pass 1 primitive / event: 'ERROR_REPORT'.
      Returns: Error report
      Comments: This returns soft errors that may be ignored without
      harm by many applications; An application must connect to be able
      receive these notifications.

   o  STATUS.SCTP:
      Pass 1 primitive / event: 'Status' and 'NETWORK STATUS CHANGE'
      notification
      Returns: data block with information about a specified
      association, containing: association connection state; socket
      list; destination transport address reachability states; current
      receiver window size; current congestion window sizes; number of
      unacknowledged DATA chunks; number of DATA chunks pending receipt;
      primary path; most recent SRTT on primary path; RTO on primary
      path; SRTT and RTO on other destination addresses.  The NETWORK
      STATUS CHANGE notification informs the application about a socket
      becoming active/inactive.

   o  STATUS.MPTCP:
      Pass 1 primitive / event: not specified
      Returns: list of pairs of tuples of IP address and TCP port number
      of each subflow.  The first of the pair is the local IP and port
      number, while the second is the remote IP and port number.

   o  SET_DSCP.TCP:
      Pass 1 primitive / event: not specified
      Parameters: DSCP value
      Comments: this allows an application to change the DSCP value for
      outgoing segments.  For TCP this was originally specified for the
      TOS field [RFC1122], which is here interpreted to refer to the
      DSField [RFC3260].






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   o  SET_DSCP.UDP(-Lite):
      Pass 1 primitive / event: 'SET_DSCP'
      Parameter: DSCP value
      Comments: This allows an application to change the DSCP value for
      outgoing UDP(-Lite) datagrams.  [RFC7657] and
      [I-D.ietf-tsvwg-rfc5405bis] provide current guidance on using this
      value with UDP.

   o  ADD_SUBFLOW.MPTCP:
      Pass 1 primitive / event: not specified
      Parameters: local IP address and optionally the local port number
      Comments: the application specifies the local IP address and port
      number that must be used for a new subflow.

   o  ADD_ADDR.SCTP:
      Pass 1 primitive / event: Change Local Address / Set Peer Primary
      Parameters: local IP address

   o  REM_SUBFLOW.MPTCP:
      Pass 1 primitive / event: not specified
      Parameters: local IP address, local port number, remote IP
      address, remote port number
      Comments: the application removes the subflow specified by the IP/
      port-pair.  The MPTCP implementation must trigger a removal of the
      subflow that belongs to this IP/port-pair.

   o  REM_ADDR.SCTP:
      Pass 1 primitive / event: Change Local Address / Set Peer Primary
      Parameters: local IP address

   o  CHECKSUM.UDP:
      Pass 1 primitive / event: 'DISABLE_CHECKSUM'.
      Parameters: 0 when no checksum is used at sender, 1 for checksum
      at sender (default).

   o  CHECKSUM_REQUIRED.UDP:
      Pass 1 primitive / event: 'REQUIRE_CHECKSUM'.
      Parameter: 0 when checksum is required at receiver, 1 to allow
      zero checksum at receiver (default).

   o  SET_CHECKSUM_COVERAGE.UDP-Lite:
      Pass 1 primitive / event: 'SET_CHECKSUM_COVERAGE'.
      Parameters: Coverage length at sender (default maximum coverage)

   o  SET_MIN_CHECKSUM_COVERAGE.UDP-Lite:
      Pass 1 primitive / event: 'SET_MIN_COVERAGE'.
      Parameter: Coverage length at receiver (default minimum coverage)




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   o  SET_DF.UDP(-Lite):
      Pass 1 primitive event: 'SET_DF'.
      Parameter: 0 when DF is not set (default), 1 when DF is set.

   o  SET_TTL.UDP(-Lite) (IPV6_UNICAST_HOPS):
      Pass 1 primitive / event: 'SET_TTL' and 'SET_IPV6_UNICAST_HOPS'
      Parameters: IPv4 TTL value or IPv6 Hop Count value
      Comments: This allows an application to change the IPv4 TTL of
      IPv6 Hop count value for outgoing UDP(-Lite) datagrams.

   o  GET_TTL.UDP(-Lite) (IPV6_UNICAST_HOPS):
      Pass 1 primitive / event: 'GET_TTL' and 'GET_IPV6_UNICAST_HOPS'
      Returns: IPv4 TTL value or IPv6 Hop Count value
      Comments: This allows an application to read the the IPv4 TTL of
      IPv6 Hop count value from a received UDP(-Lite) datagram.

   o  SET_ECN.UDP(-Lite):
      Pass 1 primitive / event: 'SET_ECN'
      Parameters: ECN value
      Comments: This allows a UDP(-Lite) application to set the ECN
      codepoint field for outgoing UDP(-Lite) datagrams.

   o  GET_ECN.UDP(-Lite):
      Pass 1 primitive / event: 'GET_ECN'
      Parameters: ECN value
      Comments: This allows a UDP(-Lite) application to read the ECN
      codepoint field from a received UDP(-Lite) datagram.

   o  SET_IP_OPTIONS.UDP(-Lite):
      Pass 1 primitive / event: 'SET_IP_OPTIONS'
      Parameters: options
      Comments: This allows a UDP(-Lite) application to set IP Options
      for outgoing UDP(-Lite) datagrams.  These options can at least be
      the Source Route, Record Route, and Time Stamp option.

   o  GET_IP_OPTIONS.UDP(-Lite):
      Pass 1 primitive / event: 'GET_IP_OPTIONS'
      Returns: options
      Comments: This allows a UDP(-Lite) application to receive any IP
      options that are contained in a received UDP(-Lite) datagram.

   o  AUTHENTICATION_NOTIFICATION-EVENT.SCTP:
      Pass 1 primitive / event: 'AUTHENTICATION notification'
      Returns: information regarding key management.


   TERMINATION:
   Gracefully or forcefully closing a connection, or being informed



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   about this event happening.

   o  CLOSE.TCP:
      Pass 1 primitive / event: 'close'
      Comments: this terminates the sending side of a connection after
      reliably delivering all remaining data.

   o  CLOSE.SCTP:
      Pass 1 primitive / event: 'Shutdown'
      Comments: this terminates a connection after reliably delivering
      all remaining data.

   o  CLOSE.UDP(-Lite):
      Pass 1 primitive event: 'CLOSE'
      Comments: No further UDP(-Lite) datagrams are sent/received on
      this connection.

   o  ABORT.TCP:
      Pass 1 primitive / event: 'abort'
      Comments: this terminates a connection without delivering
      remaining data and sends an error message to the other side.

   o  ABORT.SCTP:
      Pass 1 primitive / event: 'abort'
      Parameters: abort reason to be given to the peer (optional)
      Comments: this terminates a connection without delivering
      remaining data and sends an error message to the other side.

   o  TIMEOUT.TCP:
      Pass 1 primitive / event: 'USER TIMEOUT' event
      Comments: the application is informed that the connection is
      aborted.  This event is executed on expiration of the timeout set
      in CONNECTION.ESTABLISHMENT.CONNECT.TCP (possibly adjusted in
      CONNECTION.MAINTENANCE.CHANGE-TIMEOUT.TCP).

   o  TIMEOUT.SCTP:
      Pass 1 primitive / event: 'COMMUNICATION LOST' event
      Comments: the application is informed that the connection is
      aborted. this event is executed on expiration of the timeout that
      should be enabled by default (see beginning of section 8.3 in
      [RFC4960]) and was possibly adjusted in
      CONNECTION.MAINTENANCE.CHANGE-TIMEOOUT.SCTP.

   o  ABORT-EVENT.TCP:
      Pass 1 primitive / event: not specified.






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   o  ABORT-EVENT.SCTP:
      Pass 1 primitive / event: 'COMMUNICATION LOST' event
      Returns: abort reason from the peer (if available)
      Comments: the application is informed that the other side has
      aborted the connection using CONNECTION.TERMINATION.ABORT.SCTP.

   o  CLOSE-EVENT.TCP:
      Pass 1 primitive / event: not specified.

   o  CLOSE-EVENT.SCTP:
      Pass 1 primitive / event: 'SHUTDOWN COMPLETE' event
      Comments: the application is informed that
      CONNECTION.TERMINATION.CLOSE.SCTP was successfully completed.


4.2.  DATA Transfer Related Primitives

   All primitives in this section refer to an existing connection, i.e.
   a connection that was either established or made available for
   receiving data (although this is optional for the primitives of UDP(-
   Lite)).  In addition to the listed parameters, all sending primitives
   contain a reference to a data block and all receiving primitives
   contain a reference to available buffer space for the data.

   o  SEND.TCP:
      Pass 1 primitive / event: 'send'
      Parameters: timeout (optional)
      Comments: this gives TCP a data block for reliable transmission to
      the TCP on the other side of the connection.  The timeout can be
      configured with this call whenever data are sent (see also
      CONNECTION.MAINTENANCE.CHANGE-TIMEOUT.TCP).

   o  SEND.SCTP:
      Pass 1 primitive / event: 'Send'
      Parameters: stream number; context (optional); socket (optional);
      unordered flag (optional); no-bundle flag (optional); payload
      protocol-id (optional); pr-policy (optional) pr-value (optional);
      sack-immediately flag (optional); key-id (optional)
      Comments: this gives SCTP a data block for transmission to the
      SCTP on the other side of the connection (SCTP association).  The
      'stream number' denotes the stream to be used.  The 'context'
      number can later be used to refer to the correct message when an
      error is reported.  The 'socket' can be used to state which path
      should be preferred, if there are multiple paths available (see
      also CONNECTION.MAINTENANCE.SETPRIMARY.SCTP).  The data block can
      be delivered out-of-order if the 'unordered flag' is set.  The
      'no-bundle flag' can be set to indicate a preference to avoid
      bundling.  The 'payload protocol-id' is a number that will, if



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      provided, be handed over to the receiving application.  Using pr-
      policy and pr-value the level of reliability can be controlled.
      The sack-immediately flag can be used to indicate that the peer
      should not delay the sending of a SACK corresponding to the
      provided user message.  If specified, the provided key-id is used
      for authenticating the user message.

   o  SEND.UDP(-Lite):
      Pass 1 primitive / event: 'SEND'
      Parameters: IP Address and Port Number of the destination endpoint
      (optional if connected).
      Comments: This provides a message for unreliable transmission
      using UDP(-Lite) to the specified transport address.  IP address
      and Port may be omitted for connected UDP(-Lite) sockets.  All
      CONNECTION.MAINTENANCE.SET_*.UDP(-Lite) primitives apply per
      message sent.

   o  RECEIVE.TCP:
      Pass 1 primitive / event: 'receive'.

   o  RECEIVE.SCTP:
      Pass 1 primitive / event: 'DATA ARRIVE' notification, followed by
      'Receive'
      Parameters: stream number (optional)
      Returns: stream sequence number (optional), partial flag
      (optional)
      Comments: if the 'stream number' is provided, the call to receive
      only receives data on one particular stream.  If a partial message
      arrives, this is indicated by the 'partial flag', and then the
      'stream sequence number' must be provided such that an application
      can restore the correct order of data blocks that comprise an
      entire message.  Additionally, a delivery number lets the
      application detect reordering.

   o  RECEIVE.UDP(-Lite):
      Pass 1 primitive / event: 'RECEIVE',
      Parameters: Buffer for received datagram.
      Comments: All CONNECTION.MAINTENANCE.GET_*.UDP(-Lite) primitives
      apply per message received.

   o  SENDFAILURE-EVENT.SCTP:
      Pass 1 primitive / event: 'SEND FAILURE' notification, optionally
      followed by 'Receive Unsent Message' or 'Receive Unacknowledged
      Message'
      Returns: cause code; context; unsent or unacknowledged message
      (optional)
      Comments: 'cause code' indicates the reason of the failure, and
      'context' is the context number if such a number has been provided



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      in DATA.SEND.SCTP, for later use with 'Receive Unsent Message' or
      'Receive Unacknowledged Message', respectively.  These primitives
      can be used to retrieve the complete unsent or unacknowledged
      message if desired.

   o  SEND_FAILURE.UDP(-Lite):
      Pass 1 primitive / event: 'SEND'
      Comment: This may be used to probe for the effective PMTU when
      using in combination with the 'MAINTENANCE.SET_DF' primitive.



5.  Pass 3

   This section presents the superset of all transport service features
   in all protocols that were discussed in the preceding sections, based
   on the list of primitives in pass 2 but also on text in pass 1 to
   include features that can be configured in one protocol and are
   static properties in another (congestion control, for example).
   Again, some minor details are omitted for the sake of generalization
   -- e.g., TCP may provide various different IP options, but only
   source route is mandatory to implement, and this detail is not
   visible in the Pass 3 feature "Specify IP Options".

5.1.  CONNECTION Related Transport Service Features

   ESTABLISHMENT:
   Active creation of a connection from one transport endpoint to one or
   more transport endpoints.

   o  Connect
      Protocols: TCP, SCTP, UDP(-Lite)

   o  Specify which IP Options must always be used
      Protocols: TCP

   o  Request multiple streams
      Protocols: SCTP

   o  Obtain multiple sockets
      Protocols: SCTP

   o  Disable MPTCP
      Protocols: MPTCP

   o  Specify which chunk types must always be authenticated
      Protocols: SCTP
      Comments: DATA, ACK etc. are different 'chunks' in SCTP; one or



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      more chunks may be included in a single packet.

   o  Indicate an Adaptation Layer (via an adaptation code point)
      Protocols: SCTP


   AVAILABILITY:
   Preparing to receive incoming connection requests.

   o  Listen, 1 specified local interface
      Protocols: TCP, SCTP, UDP(-Lite)

   o  Listen, N specified local interfaces
      Protocols: SCTP, UDP(-Lite)

   o  Listen, all local interfaces
      Protocols: TCP, SCTP, UDP(-Lite)

   o  Obtain requested number of streams
      Protocols: SCTP

   o  Specify which IP Options must always be used
      Protocols: TCP

   o  Disable MPTCP
      Protocols: MPTCP

   o  Specify which chunk types must always be authenticated
      Protocols: SCTP
      Comments: DATA, ACK etc. are different 'chunks' in SCTP; one or
      more chunks may be included in a single packet.

   o  Indicate an Adaptation Layer (via an adaptation code point)
      Protocols: SCTP


   MAINTENANCE:
   Adjustments made to an open connection, or notifications about it.
   NOTE: all features except "set primary path" in this category apply
   to one out of multiple possible paths (identified via sockets) in
   SCTP, whereas TCP uses only one path (one socket).

   o  Change timeout for aborting connection (using retransmit limit or
      time value)
      Protocols: TCP, SCTP






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   o  Control advertising timeout for aborting connection to remote
      endpoint
      Protocols: TCP

   o  Disable Nagle algorithm
      Protocols: TCP, SCTP
      Comments: This is not specified in [RFC4960] but in [RFC6458].

   o  Request an immediate heartbeat, returning success/failure
      Protocols: SCTP

   o  Set protocol parameters
      Protocols: SCTP
      SCTP parameters: RTO.Initial; RTO.Min; RTO.Max; Max.Burst;
      RTO.Alpha; RTO.Beta; Valid.Cookie.Life; Association.Max.Retrans;
      Path.Max.Retrans; Max.Init.Retransmits; HB.interval; HB.Max.Burst;
      PotentiallyFailed.Max.Retrans; Primary.Switchover.Max.Retrans;
      Remote.UDPEncapsPort
      Comments: as transport layer features from other protocols are
      added, it might make sense to separate out some of these
      parameters -- e.g., if a different protocol provides means to
      adjust the RTO calculation there could be a common feature for
      them called "adjust RTO calculation".

   o  Notification of Excessive Retransmissions (early warning below
      abortion threshold)
      Protocols: TCP

   o  Notification of ICMP error message arrival
      Protocols: TCP, UDP(-Lite)

   o  Obtain status (query or notification)
      Protocols: SCTP, MPTCP
      SCTP parameters: association connection state; socket list; socket
      reachability states; current receiver window size; current
      congestion window sizes; number of unacknowledged DATA chunks;
      number of DATA chunks pending receipt; primary path; most recent
      SRTT on primary path; RTO on primary path; SRTT and RTO on other
      destination addresses; socket becoming active / inactive
      MPTCP parameters: subflow-list (identified by source-IP; source-
      Port; destination-IP; destination-Port)

   o  Change authentication parameters
      Protocols: SCTP

   o  Obtain authentication information
      Protocols: SCTP




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   o  Set primary path
      Protocols: SCTP

   o  Reset Stream
      Protocols: SCTP

   o  Notification of Stream Reset
      Protocols: STCP

   o  Reset Association
      Protocols: SCTP

   o  Notification of Association Reset
      Protocols: STCP

   o  Add Streams
      Protocols: SCTP

   o  Notification of Added Stream
      Protocols: STCP

   o  Set peer primary path
      Protocols: SCTP

   o  Specify DSCP field
      Protocols: TCP, SCTP, UDP(-Lite)

   o  Add subflow
      Protocols: MPTCP
      MPTCP Parameters: source-IP; source-Port; destination-IP;
      destination-Port

   o  Remove subflow
      Protocols: MPTCP
      MPTCP Parameters: source-IP; source-Port; destination-IP;
      destination-Port

   o  Add local address
      Protocols: SCTP

   o  Remove local address
      Protocols: SCTP

   o  Disable checksum when sending
      Protocols: UDP






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   o  Disable checksum requirement when receiving
      Protocols: UDP

   o  Specify checksum coverage used by the sender
      Protocols: UDP-Lite

   o  Specify minimum checksum coverage required by receiver
      Protocols: UDP-Lite

   o  Specify DF field
      Protocols: UDP(-Lite)

   o  Specify TTL/Hop count field
      Protocols: UDP(-Lite)

   o  Obtain TTL/Hop count field
      Protocols: UDP(-Lite)

   o  Specify ECN field
      Protocols: UDP(-Lite)

   o  Obtain ECN field
      Protocols: UDP(-Lite)

   o  Specify IP Options
      Protocols: UDP(-Lite)

   o  Obtain IP Options
      Protocols: UDP(-Lite)


   TERMINATION:
   Gracefully or forcefully closing a connection, or being informed
   about this event happening.

   o  Close after reliably delivering all remaining data, causing an
      event informing the application on the other side
      Protocols: TCP, SCTP
      Comments: A TCP endpoint locally only closes the connection for
      sending; it may still receive data afterwards.

   o  Abort without delivering remaining data, causing an event
      informing the application on the other side
      Protocols: TCP, SCTP
      Comments: In SCTP a reason can optionally be given by the
      application on the aborting side, which can then be received by
      the application on the other side.




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   o  Timeout event when data could not be delivered for too long
      Protocols: TCP, SCTP
      Comments: the timeout is configured with CONNECTION.MAINTENANCE
      "Change timeout for aborting connection (using retransmit limit or
      time value)".


5.2.  DATA Transfer Related Transport Service Features

   All features in this section refer to an existing connection, i.e. a
   connection that was either established or made available for
   receiving data.  Reliable data transfer entails delay -- e.g. for the
   sender to wait until it can transmit data, or due to retransmission
   in case of packet loss.

5.2.1.  Sending Data

   All features in this section are provided by DATA.SEND from pass 2.
   DATA.SEND is given a data block from the application, which we here
   call a "message" if the beginning and end of the data block can be
   identified at the receiver, and "data" otherwise.

   o  Reliably transfer data, with congestion control
      Protocols: TCP

   o  Reliably transfer a message, with congestion control
      Protocols: SCTP

   o  Unreliably transfer a message, with congestion control
      Protocols: SCTP

   o  Unreliably transfer a message, without congestion control
      Protocols: UDP(-Lite)

   o  Configurable Message Reliability
      Protocols: SCTP

   o  Choice of stream
      Protocols: SCTP

   o  Choice of path (destination address)
      Protocols: SCTP

   o  Choice between unordered (potentially faster) or ordered delivery
      of messages
      Protocols: SCTP





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   o  Request not to bundle messages
      Protocols: SCTP

   o  Specifying a "payload protocol-id" (handed over as such by the
      receiver)
      Protocols: SCTP

   o  Specifying a key id to be used to authenticate a message
      Protocols: SCTP

   o  Request not to delay the acknowledgement (SACK) of a message
      Protocols: SCTP


5.2.2.  Receiving Data

   All features in this section are provided by DATA.RECEIVE from pass
   2.  DATA.RECEIVE fills a buffer provided by the application, with
   what we here call a "message" if the beginning and end of the data
   block can be identified at the receiver, and "data" otherwise.

   o  Receive data
      Protocols: TCP

   o  Receive a message
      Protocols: SCTP, UDP(-Lite)

   o  Choice of stream to receive from
      Protocols: SCTP

   o  Information about partial message arrival
      Protocols: SCTP
      Comments: In SCTP, partial messages are combined with a stream
      sequence number so that the application can restore the correct
      order of data blocks an entire message consists of.

   o  Obtain a message delivery number
      Protocols: SCTP
      Comments: This number can let applications detect and, if desired,
      correct reordering.


5.2.3.  Errors

   This section describes sending failures that are associated with a
   specific call to DATA.SEND from pass 2.





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   o  Notification of unsent messages
      Protocols: SCTP, UDP(-Lite)

   o  Notification of unacknowledged messages
      Protocols: SCTP



6.  Acknowledgements

   The authors would like to thank (in alphabetical order) Bob Briscoe,
   Gorry Fairhurst, David Hayes, Tom Jones, Karen Nielsen and Joe Touch
   for providing valuable feedback on this document.  We especially
   thank to Christoph Paasch for providing input related to Multipath
   TCP.  This work has received funding from the European Union's
   Horizon 2020 research and innovation programme under grant agreement
   No. 644334 (NEAT).  The views expressed are solely those of the
   author(s).


7.  IANA Considerations

   XX RFC ED - PLEASE REMOVE THIS SECTION XXX

   This memo includes no request to IANA.


8.  Security Considerations

   Security will be considered in future versions of this document.


9.  References

9.1.  Normative References

   [I-D.ietf-tsvwg-rfc5405bis]
              Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
              Guidelines", draft-ietf-tsvwg-rfc5405bis-07 (work in
              progress), November 2015.

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

   [RFC1122]  Braden, R., Ed., "Requirements for Internet Hosts -
              Communication Layers", STD 3, RFC 1122, DOI 10.17487/
              RFC1122, October 1989,



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              <http://www.rfc-editor.org/info/rfc1122>.

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

   [RFC5482]  Eggert, L. and F. Gont, "TCP User Timeout Option",
              RFC 5482, DOI 10.17487/RFC5482, March 2009,
              <http://www.rfc-editor.org/info/rfc5482>.

9.2.  Informative References

   [FA16]     Fairhurst, Ed., G., Trammell, Ed., B., and M. Kuehlewind,
              Ed., "Services provided by IETF transport protocols and
              congestion control mechanisms",
              draft-ietf-taps-transports-12.txt (work in progress),
              October 2016.

   [FJ16]     Fairhurst, G. and T. Jones, "Features of the User Datagram
              Protocol (UDP) and Lightweight UDP (UDP-Lite) Transport
              Protocols", draft-fairhurst-taps-transports-usage-udp-03
              (work in progress), October 2016.

   [RFC0854]  Postel, J. and J. Reynolds, "Telnet Protocol
              Specification", STD 8, RFC 854, DOI 10.17487/RFC0854,
              May 1983, <http://www.rfc-editor.org/info/rfc854>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
              RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP",
              RFC 3168, DOI 10.17487/RFC3168, September 2001,
              <http://www.rfc-editor.org/info/rfc3168>.

   [RFC3260]  Grossman, D., "New Terminology and Clarifications for
              Diffserv", RFC 3260, DOI 10.17487/RFC3260, April 2002,
              <http://www.rfc-editor.org/info/rfc3260>.

   [RFC3758]  Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
              Conrad, "Stream Control Transmission Protocol (SCTP)
              Partial Reliability Extension", RFC 3758, DOI 10.17487/
              RFC3758, May 2004,
              <http://www.rfc-editor.org/info/rfc3758>.

   [RFC3828]  Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., Ed.,



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              and G. Fairhurst, Ed., "The Lightweight User Datagram
              Protocol (UDP-Lite)", RFC 3828, DOI 10.17487/RFC3828,
              July 2004, <http://www.rfc-editor.org/info/rfc3828>.

   [RFC4895]  Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
              "Authenticated Chunks for the Stream Control Transmission
              Protocol (SCTP)", RFC 4895, DOI 10.17487/RFC4895,
              August 2007, <http://www.rfc-editor.org/info/rfc4895>.

   [RFC5061]  Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
              Kozuka, "Stream Control Transmission Protocol (SCTP)
              Dynamic Address Reconfiguration", RFC 5061, DOI 10.17487/
              RFC5061, September 2007,
              <http://www.rfc-editor.org/info/rfc5061>.

   [RFC5461]  Gont, F., "TCP's Reaction to Soft Errors", RFC 5461,
              DOI 10.17487/RFC5461, February 2009,
              <http://www.rfc-editor.org/info/rfc5461>.

   [RFC6093]  Gont, F. and A. Yourtchenko, "On the Implementation of the
              TCP Urgent Mechanism", RFC 6093, DOI 10.17487/RFC6093,
              January 2011, <http://www.rfc-editor.org/info/rfc6093>.

   [RFC6182]  Ford, A., Raiciu, C., Handley, M., Barre, S., and J.
              Iyengar, "Architectural Guidelines for Multipath TCP
              Development", RFC 6182, DOI 10.17487/RFC6182, March 2011,
              <http://www.rfc-editor.org/info/rfc6182>.

   [RFC6458]  Stewart, R., Tuexen, M., Poon, K., Lei, P., and V.
              Yasevich, "Sockets API Extensions for the Stream Control
              Transmission Protocol (SCTP)", RFC 6458, DOI 10.17487/
              RFC6458, December 2011,
              <http://www.rfc-editor.org/info/rfc6458>.

   [RFC6525]  Stewart, R., Tuexen, M., and P. Lei, "Stream Control
              Transmission Protocol (SCTP) Stream Reconfiguration",
              RFC 6525, DOI 10.17487/RFC6525, February 2012,
              <http://www.rfc-editor.org/info/rfc6525>.

   [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>.

   [RFC6897]  Scharf, M. and A. Ford, "Multipath TCP (MPTCP) Application
              Interface Considerations", RFC 6897, DOI 10.17487/RFC6897,
              March 2013, <http://www.rfc-editor.org/info/rfc6897>.




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   [RFC6951]  Tuexen, M. and R. Stewart, "UDP Encapsulation of Stream
              Control Transmission Protocol (SCTP) Packets for End-Host
              to End-Host Communication", RFC 6951, DOI 10.17487/
              RFC6951, May 2013,
              <http://www.rfc-editor.org/info/rfc6951>.

   [RFC7053]  Tuexen, M., Ruengeler, I., and R. Stewart, "SACK-
              IMMEDIATELY Extension for the Stream Control Transmission
              Protocol", RFC 7053, DOI 10.17487/RFC7053, November 2013,
              <http://www.rfc-editor.org/info/rfc7053>.

   [RFC7414]  Duke, M., Braden, R., Eddy, W., Blanton, E., and A.
              Zimmermann, "A Roadmap for Transmission Control Protocol
              (TCP) Specification Documents", RFC 7414, DOI 10.17487/
              RFC7414, February 2015,
              <http://www.rfc-editor.org/info/rfc7414>.

   [RFC7496]  Tuexen, M., Seggelmann, R., Stewart, R., and S. Loreto,
              "Additional Policies for the Partially Reliable Stream
              Control Transmission Protocol Extension", RFC 7496,
              DOI 10.17487/RFC7496, April 2015,
              <http://www.rfc-editor.org/info/rfc7496>.

   [RFC7657]  Black, D., Ed. and P. Jones, "Differentiated Services
              (Diffserv) and Real-Time Communication", RFC 7657,
              DOI 10.17487/RFC7657, November 2015,
              <http://www.rfc-editor.org/info/rfc7657>.

   [RFC7829]  Nishida, Y., Natarajan, P., Caro, A., Amer, P., and K.
              Nielsen, "SCTP-PF: A Quick Failover Algorithm for the
              Stream Control Transmission Protocol", RFC 7829,
              DOI 10.17487/RFC7829, April 2016,
              <http://www.rfc-editor.org/info/rfc7829>.


Appendix A.  Overview of RFCs used as input for pass 1

   TCP:  [RFC0793], [RFC1122], [RFC5482]
   MPTCP:  [RFC6182], [RFC6824], [RFC6897]
   SCTP:  RFCs without a socket API specification: [RFC3758], [RFC4895],
      [RFC4960], [RFC5061].  RFCs that include a socket API
      specification: [RFC6458], [RFC6525], [RFC6951], [RFC7053],
      [RFC7496] [RFC7829].
   UDP(-Lite):  See [FJ16]







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Appendix B.  How to contribute

   This document is only concerned with transport service features that
   are explicitly exposed to applications via primitives.  It also
   strictly follows RFC text: if a feature is truly relevant for an
   application, the RFCs better say so and in some way describe how to
   use and configure it.  Thus, the approach to follow for contributing
   to this document is to identify the right RFCs, then analyze and
   process their text.

   Experimental RFCs are excluded, and so are primitives that MAY be
   implemented (by the transport protocol).  To be included, the minimum
   requirement level for a primitive to be implemented by a protocol is
   SHOULD.  If [RFC2119]-style requirements levels are not used,
   primitives should be excluded when they are described in conjunction
   with statements like, e.g.: "some implementations also provide" or
   "an implementation may also".  Briefly describe excluded primitives
   in a subsection called "excluded primitives".

   Pass 1: Identify text that talks about primitives.  An API
   specification, abstract or not, obviously describes primitives -- but
   note that we are not *only* interested in API specifications.  The
   text describing the 'send' primitive in the API specified in
   [RFC0793], for instance, does not say that data transfer is reliable.
   TCP's reliability is clear, however, from this text in Section 1 of
   [RFC0793]: "The Transmission Control Protocol (TCP) is intended for
   use as a highly reliable host-to-host protocol between hosts in
   packet-switched computer communication networks, and in
   interconnected systems of such networks."

   For the new pass 1 subsection about the protocol you're describing,
   it is recommendable to begin by copy+pasting all the relevant text
   parts from the relevant RFCs, then adjust terminology to match the
   terminology in Section 1 and adjust (shorten!) phrasing to match the
   general style of the document.  Try to formulate everything as a
   primitive description to make the primitive description as complete
   as possible (e.g., the "SEND.TCP" primitive in pass 2 is explicitly
   described as reliably transferring data); if there is text that is
   relevant for the primitives presented in this pass but still does not
   fit directly under any primitive, use it as an introduction for your
   subsection.  However, do note that document length is a concern and
   all the protocols and their services / features are already described
   in [FA16].

   Pass 2: The main goal of this pass is unification of primitives.  As
   input, use your own text from Pass 1, no exterior sources.  If you
   find that something is missing there, fix the text in Pass 1.  The
   list in pass 2 is not done by protocol ("first protocol X, here are



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   all the primitives; then protocol Y, here are all the primitives,
   ..") but by primitive ("primitive A, implemented this way in protocol
   X, this way in protocol Y, ...").  We want as many similar pass 2
   primitives as possible.  This can be achieved, for instance, by not
   always maintaining a 1:1 mapping between pass 1 and pass 2
   primitives, renaming primitives etc.  Please consider the primitives
   that are already there and try to make the ones of the protocol you
   are describing as much in line with the already existing ones as
   possible.  In other words, we would rather have a primitive with new
   parameters than a new primitive that allows to send in a particular
   way.

   Please make primitives fit within the already existing categories and
   subcategories.  For each primitive, please follow the style:

   o  PRIMITIVENAME.PROTOCOL:
      Pass 1 primitive / event:
      Parameters:
      Returns:
      Comments:

   The entries "Parameters", "Returns" and "Comments" may be skipped if
   a primitive has no parameters, no described return value or no
   comments seem necessary, respectively.  Optional parameters must be
   followed by "(optional)".  If a default value is known, provide it
   too.

   Pass 3: the main point of this pass is to identify features that are
   the result of static properties of protocols, for which all protocols
   have to be listed together; this is then the final list of all
   available features.  For this, we need a list of features per
   category (similar categories as in pass 2) along with the protocol
   supporting it.  This should be primarily based on text from pass 2 as
   input, but text from pass 1 can also be used.  Do not use external
   sources.


Appendix C.  Revision information

   XXX RFC-Ed please remove this section prior to publication.

   -00 (from draft-welzl-taps-transports): this now covers TCP based on
   all TCP RFCs (this means: if you know of something in any TCP RFC
   that you think should be addressed, please speak up!) as well as
   SCTP, exclusively based on [RFC4960].  We decided to also incorporate
   [RFC6458] for SCTP, but this hasn't happened yet.  Terminology made
   in line with [FA16].  Addressed comments by Karen Nielsen and Gorry
   Fairhurst; various other fixes.  Appendices (TCP overview and how-to-



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   contribute) added.

   -01: this now also covers MPTCP based on [RFC6182], [RFC6824] and
   [RFC6897].

   -02: included UDP, UDP-Lite, and all extensions of SCTPs.  This
   includes fixing the [RFC6458] omission from -00.

   TODO: security considerations (see review in ML); the "how to
   contribute" section (which, at some point, should be updated to
   reflect how the document WAS created, not how it SHOULD BE created)
   still says "Experimental RFCs are excluded".  This is wrong, and
   accordingly, Experimental RFCs must also be considered - thus, TFO
   (are there more Experimental ones for TCP?).  Also, include LEDBAT.
   SCTP: DSCP and SCTP_NODELAY (equivalent to Nagle) are missing in pass
   1 and 2.  Are we missing more (DF, TTL, ..)?  What about e.g.
   "notification of ICMP error message arrival"?  Also consider
   draft-ietf-tsvwg-sctp-ndata.


Authors' Addresses

   Michael Welzl
   University of Oslo
   PO Box 1080 Blindern
   Oslo,   N-0316
   Norway

   Phone: +47 22 85 24 20
   Email: michawe@ifi.uio.no


   Michael Tuexen
   Muenster University of Applied Sciences
   Stegerwaldstrasse 39
   Steinfurt  48565
   Germany

   Email: tuexen@fh-muenster.de












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   Naeem Khademi
   University of Oslo
   PO Box 1080 Blindern
   Oslo,   N-0316
   Norway

   Email: naeemk@ifi.uio.no












































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