[Search] [txt|xml|pdf|bibtex] [Tracker] [Email] [Nits]

Versions: 00                                                            
TAPS                                                            M. Welzl
Internet-Draft                                        University of Oslo
Intended status: Informational                                 M. Tuexen
Expires: March 24, 2016                 Muenster Univ. of Appl. Sciences
                                                              N. Khademi
                                                      University of Oslo
                                                      September 21, 2015


 An Approach to Identify Services Provided by IETF Transport Protocols
                   and Congestion Control Mechanisms
                     draft-welzl-taps-transports-00

Abstract

   This document describes a method to identify services in transport
   protocols and congestion control mechanisms.  It shows the approach
   using TCP and SCTP (base protocol) as examples.

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 March 24, 2016.

Copyright Notice

   Copyright (c) 2015 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



Welzl, et al.            Expires March 24, 2016                 [Page 1]


Internet-Draft             Transport Services             September 2015


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


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  General Considerations . . . . . . . . . . . . . . . . . . . .  3
   3.  Pass 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Services Provided by TCP . . . . . . . . . . . . . . . . .  4
       3.1.1.  Excluded Services  . . . . . . . . . . . . . . . . . .  7
     3.2.  Services Provided by SCTP  . . . . . . . . . . . . . . . .  7
       3.2.1.  Excluded Services  . . . . . . . . . . . . . . . . . . 10
   4.  Pass 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     4.1.  CONNECTION Related Services  . . . . . . . . . . . . . . . 11
     4.2.  DATA Transfer Related Services . . . . . . . . . . . . . . 15
   5.  Pass 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     5.1.  CONNECTION Related Services  . . . . . . . . . . . . . . . 17
     5.2.  DATA Transfer Related Services . . . . . . . . . . . . . . 20
       5.2.1.  Sending Data . . . . . . . . . . . . . . . . . . . . . 20
       5.2.2.  Receiving Data . . . . . . . . . . . . . . . . . . . . 21
       5.2.3.  Errors . . . . . . . . . . . . . . . . . . . . . . . . 21
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
   7.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 22
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 22
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 22
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 22
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23






















Welzl, et al.            Expires March 24, 2016                 [Page 2]


Internet-Draft             Transport Services             September 2015


1.  Introduction

   This document considers every form of defined interaction between a
   transport protocol and its user ("upper layer protocol" or
   "application") as a "service".  Here, the term "service" is NOT the
   same as the term used to specify the entire "above transport"
   protocol that maps to a port number or service name (which is another
   common meaning of the term "service" in the context of transport
   protocols).

   The list of services in this document is strictly based on the parts
   of relevant protocol specifications that relate to what the protocol
   provides to an application using it and how the application interacts
   with it.  It is based on text that describes what a protocol provides
   to the upper layer and how it is used (abstract API descriptions),
   given for the base protocols in [RFC0793], [RFC1122] and [RFC4960].
   It does not cover API instances, for example the one given for SCTP
   in [RFC6458].  It also does not cover parts of the protocol that are
   explicitly stated as optional to implement.

   The document presents a three-pass process to arrive at a list of
   transport protocol services.  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 services that are uniformly categorized
   across protocols.  Here, an attempt is made to present services in a
   slightly generalized form to highlight similarities.  This is, for
   example, achieved by renaming "commands" (or "transport primitives")
   of protocols or by avoiding a strict 1:1-mapping between these
   commands and services in the list.  Finally, the third pass presents
   all services from pass 2, identifying which protocol implements them.

   In the list resulting from the second pass, some services are missing
   because they are implicit in some protocols, and they only become
   explicit when we consider the superset of all services 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 to consider an always-on checksum as a service (it would not be
   a service if no protocol would allow to disable / configure the
   checksum).  Similar arguments apply to other protocol functions (e.g.
   congestion control).  The complete list of services across all
   protocols is therefore only available after pass 3.


2.  General Considerations

   This document discusses unicast [AUTHOR'S NOTE: for simplicity, for
   now.  Hopefully forever, for simplicity.] transport protocols.



Welzl, et al.            Expires March 24, 2016                 [Page 3]


Internet-Draft             Transport Services             September 2015


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

   Some protocols are connection-oriented.  Connection-orientation, to
   the user of an application, means that there is state shared between
   the endpoints that persists across messages.  Connection-oriented
   protocols often use an initial call to "open" a connection before
   communication can progress, and require communication to be
   explicitly terminated by issuing a "close" call.  Moreover, a
   "connection" is the common state that some transport primitives refer
   to, e.g. to adjust general configuration settings.  Connections
   establishment, maintenance and termination are therefore used to
   categorize certain services of connection-oriented transport
   protocols in pass 2 and 3.


3.  Pass 1

   In this first iteration, the relevant text parts of the RFCs
   describing the protocols are summarized, focusing on what a protocol
   provides to the upper layer and how it is used (abstract API
   descriptions).  The resulting text is somewhat heterogeneous in
   terminology - e.g. the user of the protocol is called "Application"
   in TCP and "Upper-Layer Protocol (ULP)" in SCTP, and TCP's "user
   commands" are called "ULP primitives" in SCTP.

3.1.  Services Provided by TCP

   [RFC0793] states: "TCP is a connection-oriented, end-to-end reliable
   protocol (..)".  Section 3.8 in [RFC0793] further specifies the
   interaction with the application by listing several user commands.
   It is also assumed that the Operating System provides a means for TCP
   to asynchronously signal the user program.  Here, we describe the
   relevant user commands and notifications to the application.

   open:  this is either active or passive, to initiate a connection or
      listen for incoming connections.  All other commands are
      associated with a specific connection, which is assumed to first
      have been opened.  An active open call contains a fully specified
      foreign socket (IP address + port number).  A passive open call
      with a fully specified foreign socket waits for a particular



Welzl, et al.            Expires March 24, 2016                 [Page 4]


Internet-Draft             Transport Services             September 2015


      connection; alternatively, a passive open call can leave the
      foreign socket unspecified to accept any incoming connection.  A
      fully specified passive call can later be made active by executing
      'send'.  Optionally, a timeout can be specified, after which TCP
      will abort the connection if data is not 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 let the application specify IP
      options such as source route, record route, or timestamp.  (It is
      not stated on which segments of a connection these options should
      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]).  As the only non-optional IP option in this
      parameter, an application can specify a source route when it
      actively opens a TCP connection.

   send:  this command hands over a provided number of bytes that TCP
      should reliably send to the other side of the connection.  The
      PUSH flag, if set, requires data to be promptly transmitted to the
      receiver without delaying it.  Conversely, not using PUSH can
      reduce the number of unnecessary wakeup calls to the receiving
      application process.  [RFC1122] states that "Generally, an
      interactive application protocol must set the PUSH flag at least
      in the last SEND call in each command or response sequence.  A
      bulk transfer protocol like FTP should set the PUSH flag on the
      last segment of a file or when necessary to prevent buffer
      deadlock."  An optional timeout parameter can be provided that
      updates the connection's timeout (see "open").

   receive:  This command 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.





Welzl, et al.            Expires March 24, 2016                 [Page 5]


Internet-Draft             Transport Services             September 2015


   close:  This command 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 handed over to TCP (and if that fails,
      'close' becomes 'abort').  Close also implies push function.

   abort:  This command causes all pending SENDs and RECEIVES to be
      aborted, the TCB to be removed, and a special RESET message to be
      sent to the TCP on the other side of the connection.  See
      [RFC0793].

   close event:  TCP will signal a user, even if no RECEIVEs are
      outstanding, that the other side has closed, so the user can
      terminate his/her side 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 user is signaled "error: connection
      aborted due to user timeout".

   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, 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, parts of the TOS field have been assigned to ECN
      [RFC3168] and the six most significant bits have been assigned to
      DiffServ by the name of 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).  [AUTHOR's NOTE: text trying to "read between the lines"
      of RFCs here... this perhaps calls for an update to [RFC1122]?]







Welzl, et al.            Expires March 24, 2016                 [Page 6]


Internet-Draft             Transport Services             September 2015


   Nagle:  An application can disable the Nagle algorithm on an
      individual connection.  This algorithm delays sending data for
      some time to increase the likelihood of sending a full-sized
      segment.


3.1.1.  Excluded Services

   The 'send' and 'receive' commands include usage of an "URGENT"
   mechanism, which SHOULD NOT be implemented according to [RFC6093] and
   is therefore not described here.  This also concerns the notification
   "Urgent pointer advance" in the ERROR_REPORT described in Section
   4.2.4.1 of [RFC1122].

   The 'open' command specified in [RFC0793] can be handed optional
   Precedence or security/compartment information according to
   [RFC0793], but this was not incuded here because it is mostly
   irrelevant today, as explained in [RFC7414].  The 'open' command also
   includes a parameter "options" that is explained in [RFC1122] to let
   the application specify IP options such as source route, record
   route, or timestamp.  This parameter was not included here because it
   is not clear which segments of a connection (all?) these options
   would then be applied to.

   The 'status' command was not included because [RFC0793] calls this
   command "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 'receive'
   command can (under some conditions) yield the status of the PUSH flag
   according to [RFC0793], but this TCP functionality is made optional
   in [RFC1122] and hence not considered here.  Generally, section
   4.2.2.2 of [RFC1122] says that PUSH on send calls MAY be implemented,
   which could be a reason not to consider it here.  However, the text
   then explains that "an interactive application protocol must set the
   PUSH flag at least in the last SEND call in each command or response
   sequence", and most implementations provide some option to cause a
   behavior that is in some way similar to PUSH.  Therefore PUSH is
   described as a part of SEND here.  [RFC1122] also introduces keep-
   alives to TCP, but these are optional and hence not considered here.
   [RFC1122] describes that "some TCP implementations have included a
   FLUSH call", indicating that this call is optional to implement.  It
   is therefore not considered here.

3.2.  Services 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



Welzl, et al.            Expires March 24, 2016                 [Page 7]


Internet-Draft             Transport Services             September 2015


   service that is 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 transport addresses at each end point.
   For SCTP running over IP, [RFC4960] defines a "transport address" as
   "the combination of an IP address and an SCTP port number (where SCTP
   is the transport protocol)".

   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 user program.  Here, we describe
   the relevant ULP primitives and notifications to the ULP process:

   Initialize:  Initialize creates a local SCTP instance which 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 transport
      addresses from the returned destination addresses 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 ULP
      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.

   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).  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
      destination transport address, and the message can be delivered
      out-of-order if the unordered flag is set.  Another advisory flag
      indicates the ULP's preference to avoid bundling user data with
      other outbound DATA chunks (i.e., in the same packet).  The
      handling of this no-bundle flags is similar to the sender side



Welzl, et al.            Expires March 24, 2016                 [Page 8]


Internet-Draft             Transport Services             September 2015


      handling of the TCP PUSH flag.  A payload protocol-id can be
      provided to pass a value that indicates the type of payload
      protocol data to the peer.

   Receive:  Messages are received from an association, and optionally a
      stream within the association, with their size returned.  The ULP
      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 ULP.

   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 ULP.  A return code informs about success
      or failure of this procedure.

   Change Heartbeat / Request Heartbeat:  This allows the ULP 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 transport address.  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.

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

   Status:  The 'Status' primitive returns a data block with information
      about a specified association, containing: association connection
      state; destination transport address 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.



Welzl, et al.            Expires March 24, 2016                 [Page 9]


Internet-Draft             Transport Services             September 2015


   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 ULP process about the
      affected association, the type of event that has occurred, the
      complete set of transport addresses 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 ULP process 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 ULP about a transport address 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 ULP process of the
      affected association and the type of event (failure OR termination
      in response to a shutdown or abort request).

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


3.2.1.  Excluded Services

   For the 'Set Primary' primitive, an optional possibility to specify
   the source transport address to be used in outgoing IP datagrams is
   described, but the RFC text says "some implementations may allow you
   to", indicating that implementing this in SCTP is optional.  This
   functionality is therefore not considered here.  The 'Receive'
   primitive can also return certain additional information, but this is
   also left up to the implementation and therefore not considered.
   With a COMMUNICATION LOST notification, some more information may
   optionally be passed to the ULP (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



Welzl, et al.            Expires March 24, 2016                [Page 10]


Internet-Draft             Transport Services             September 2015


   be provided.  The primitive 'Get SRTT Report' returns information
   that is included in what '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' primitive was excluded: it erases the
   SCTP instance that was created by 'Initialize', but this does not
   translate into a service for the ULP.


4.  Pass 2

   Here we categorize the services from pass 1 based on whether they
   relate to a connection or to data transmission.  Services are
   presented following the nomenclature
   "CATEGORY.[SUBCATEGORY].SERVICENAME.PROTOCOL".  We present
   "connection" as a general protocol-independent concept and use it to
   refer to both TCP's connections (which are identifiable by a unique
   socket pair, where a socket is defined as an IP address and TCP port)
   and SCTP's associations (which are identifiable by multiple IP
   address and port number pairs).  We define the "transport address" as
   "the combination of an IP address and a transport protocol's port
   number".  The "application" is the user of the protocol (called
   "Upper-Level Protocol (ULP)" in SCTP).

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

4.1.  CONNECTION Related Services

   ESTABLISHMENT:
   Active creation of a connection from one transport address to one or
   more transport addresses.

   o  CONNECT.TCP:
      Command / event: 'open' (active) or 'open' (passive) with
      destination transport address, followed by 'send'
      Parameters: 1 local IP address (optional); 1 destination transport
      address (for active open; else the destination transport address
      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.  [AUTHOR'S NOTE: [RFC1122] does
      not clearly state this, but it seems to be the implication of some
      text there.]  The timeout can also be a retransmission count.  The



Welzl, et al.            Expires March 24, 2016                [Page 11]


Internet-Draft             Transport Services             September 2015


      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:
      Command / event: 'initialize', followed by 'associate'
      Parameters: list of local transport addresses (initialize); 1
      destination transport address; outbound stream count
      Returns: destination transport address list
      Comments: 'initialize' needs to be called only once per local
      transport address list.  One destination transport address will
      automatically be chosen; it can later be changed in MAINTENANCE.


   AVAILABILITY:
   Preparing to receive incoming connection requests.

   o  LISTEN.TCP:
      Command / event: 'open' (passive)
      Parameters: 1 local IP address (optional); 1 destination transport
      address (optional); timeout (optional)
      Comments: if the transport address 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 without this / these restraint(s).  ESTABLISHMENT can
      later be done with 'send'.

   o  LISTEN.SCTP:
      Command / event: 'initialize', followed by 'COMMUNICATION UP'
      notification
      Parameters: list of local transport addresses (initialize)
      Returns: destination transport address list; outbound stream
      count; inbound stream count
      Comments: initialize needs to be called only once per local
      transport address list.  COMMUNICATION UP can also follow a
      COMMUNICATION LOST notification, indicating that the lost
      communication is restored.


   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 when new data are handed over for sending).






Welzl, et al.            Expires March 24, 2016                [Page 12]


Internet-Draft             Transport Services             September 2015


   o  CHANGE-TIMEOUT.TCP:
      Command / event: 'send'
      Parameters: timeout value
      Comments: when sending data, the connection's timeout value (time
      after which the connection will be aborted if data cannot be
      delivered) can be adjusted.

   o  CHANGE-TIMEOUT.SCTP:
      Command / 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 transport address)
      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
      commands / parameters together can yield a similar behavior to
      CHANGE-TIMEOUT.TCP.

   o  DISABLE-NAGLE.TCP:
      Command / 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.  This is related
      to the no-bundle flag in DATA.SEND.SCTP.

   o  REQUESTHEARTBEAT.SCTP:
      Command / event: 'Request HeartBeat'
      Parameters: destination transport address
      Returns: success or failure
      Comments: requests a heartbeat to be immediately carried out on a
      path, returning success or failure.

   o  SETPROTOCOLPARAMETERS.SCTP:
      Command / 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

   o  SETPRIMARY.SCTP:
      Command / event: 'Set Primary'
      Parameters: destination transport address
      Returns: result of attempting this operation
      Comments: update the current primary address to be used, based on
      the set of available destination transport addresses of the
      association.



Welzl, et al.            Expires March 24, 2016                [Page 13]


Internet-Draft             Transport Services             September 2015


   o  ERROR.TCP:
      Command / 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:
      Excessive Retransmissions and ICMP error message arrived.

   o  STATUS.SCTP:
      Command / event: 'Status' and 'NETWORK STATUS CHANGE' notification
      Returns: data block with information about a specified
      association, containing: association connection state; destination
      transport address 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 transport address becoming active/inactive.

   o  CHANGE-DSCP.TCP:
      Command / event: not specified
      Parameters: DSCP value
      Comments: This allows an application to change the DSCP value.  It
      was only specified for the TOS field in [RFC1122], which is here
      interpreted to refer to the DSField as per [RFC3260].


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

   o  CLOSE.TCP:
      Command / event: 'close'
      Comments: this terminates the sending side of a connection after
      reliably delivering all remaining data.  Close also implies push
      function (see DATA.SEND.TCP).

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

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



Welzl, et al.            Expires March 24, 2016                [Page 14]


Internet-Draft             Transport Services             September 2015


   o  ABORT.SCTP:
      Command / 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:
      Command / event: 'USER TIMEOUT' event
      Comments: the application is informed that the connection is
      aborted.  This event is executed when the timeout set in
      CONNECTION.ESTABLISHMENT.CONNECT.TCP (and possibly adjusted in
      CONNECTION.MAINTENANCE.CHANGE-TIMEOOUT.TCP) expires.

   o  TIMEOUT.SCTP:
      Command / event: 'COMMUNICATION LOST' event
      Comments: the application is informed that the connection is
      aborted. this event is executed when 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 expires.

   o  ABORT-EVENT.TCP:
      Command / event: not specified

   o  ABORT-EVENT.SCTP:
      Command / 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:
      Command / event: not specified

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


4.2.  DATA Transfer Related Services

   All commands in this section refer to an existing connection, i.e. a
   connection that was either established or made available for
   receiving data.  In addition to the listed parameters, all sending
   commands contain a reference to a data block and all receiving
   commands contain a reference to available buffer space for the data.





Welzl, et al.            Expires March 24, 2016                [Page 15]


Internet-Draft             Transport Services             September 2015


   o  SEND.TCP:
      Command / event: 'send'
      Parameters: PUSH flag (optional); timeout (optional)
      Comments: If the push flag is set, the data block should promptly
      be transmitted to the receiver without waiting.  The timeout can
      be configured with this call whenever data are sent (see also
      CONNECTION.MAINTENANCE.CHANGE-TIMEOUT.TCP).

   o  SEND.SCTP:
      Command / event: 'Send'
      Parameters: stream number; context (optional); life time
      (optional); destination transport address (optional); unordered
      flag (optional); no-bundle flag (optional); payload protocol-id
      (optional)
      Comments: 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 'life time' specifies a time after
      which this data block will not be sent.  The 'destination
      transport address' 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
      (this is related to CONNECTION.MAINTENANCE.DISABLE-NAGLE.TCP).
      The 'payload protocol-id' is a number that will, if it was
      provided, be handed over to the receiving application.

   o  RECEIVE.TCP:
      Command / event: 'receive'

   o  RECEIVE.SCTP:
      Command / 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 an entire message
      consists of.

   o  SENDFAILURE-EVENT.SCTP:
      Command / 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



Welzl, et al.            Expires March 24, 2016                [Page 16]


Internet-Draft             Transport Services             September 2015


      'context' is the context number if such a number has been provided
      in DATA.SEND.SCTP, for later use with 'Receive Unsent Message' or
      'Receive Unacknowledged Message', respectively.  These commands
      can be used to retrieve the complete unsent or unacknowledged
      message if desired.



5.  Pass 3

   Here we present the superset of all services in all protocols, based
   on the list in pass 2 but also on text in pass 1 to include services
   that can be configured in one protocol and are static properties in
   another.  Again, some minor details are omitted for the sake of
   generalization -- e.g., TCP may provide various different IP options
   but only supporting source route is mandatory to implement, and this
   detail is no longer visible in "Specify IP Options".  The detail was
   removed because no other protocols provide this features.  [AUTHOR'S
   NOTE: and if we find another one that does, we need that detail
   again.]

   [AUTHOR'S NOTE: the list here looks pretty similar to the list in
   pass 2 for now.  This will change as more protocols are added.  For
   example, if we add UDP, we will find that UDP does not do congestion
   control, which is relevant to the application using it.  This will
   have to be reflected in pass 1 and pass 2, only for UDP.  In pass 3,
   we can derive "congestion control" as a service of TCP and SCTP
   because it probably does not make much sense to write that only UDP
   provides a congestion control related service: the "service" of not
   doing it -- meaning that it may require more work from the
   application developer.]

5.1.  CONNECTION Related Services

   ESTABLISHMENT:
   Active creation of a connection from one transport address to one or
   more transport addresses.

   o  Specify IP Options
      Protocols: TCP

   o  Request multiple streams
      Protocols: SCTP

   o  Obtain multiple destination transport addresses
      Protocols: SCTP





Welzl, et al.            Expires March 24, 2016                [Page 17]


Internet-Draft             Transport Services             September 2015


   AVAILABILITY:
   Preparing to receive incoming connection requests.

   o  Listen, 1 specified local interface
      Protocols: TCP, SCTP

   o  Listen, N specified local interfaces
      Protocols: SCTP

   o  Listen, all local interfaces (unspecified)
      Protocols: TCP, SCTP

   o  Obtain requested number of streams
      Protocols: SCTP


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

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

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

   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
      Comments: in future versions of this document, it might make sense
      to split out some of these parameters -- e.g., if a different
      protocol provides means to adjust the RTO calculation there could
      be a common service for them called "adjust RTO calculation".

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



Welzl, et al.            Expires March 24, 2016                [Page 18]


Internet-Draft             Transport Services             September 2015


   o  Notification of ICMP error message arrival
      Protocols: TCP

   o  Status (query or notification)
      Protocols: SCTP
      SCTP parameters: association connection state; destination
      transport address 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;
      transport address becoming active / inactive

   o  Set primary path
      Protocols: SCTP

   o  Change DSCP
      Protocols: TCP
      Comments: This is described to be changeable for SCTP too in
      [RFC6458].


   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: TCP's 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.

   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)".







Welzl, et al.            Expires March 24, 2016                [Page 19]


Internet-Draft             Transport Services             September 2015


5.2.  DATA Transfer Related Services

   All services in this section refer to an existing connection, i.e. a
   connection that was either established or made available for
   receiving data.  In addition to the listed parameters, all sending
   commands contain a reference to a data block and all receiving
   commands contain a reference to available buffer space for the 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 services 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".

   o  Reliably transfer data
      Protocols: TCP, SCTP

   o  Notifying the receiver to promptly hand over data to application
      Protocols: TCP
      Comments: This seems unnecessary in SCTP, where data arrival
      causes an event for the application.

   o  Message identification
      Protocols: SCTP

   o  Choice of stream
      Protocols: SCTP

   o  Choice of path (destination address)
      Protocols: SCTP

   o  Message lifetime
      Protocols: SCTP

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

   o  Request not to bundle messages
      Protocols: SCTP

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





Welzl, et al.            Expires March 24, 2016                [Page 20]


Internet-Draft             Transport Services             September 2015


5.2.2.  Receiving Data

   All services in this section are provided by DATA.RECEIVE from pass
   2.  DATA.RECEIVE fills a buffer provided to the application, with
   what we here call a "message".

   o  Receive data
      Protocols: TCP, SCTP

   o  Choice of stream to receive on
      Protocols: SCTP

   o  Message identification
      Protocols: SCTP
      Comments: In SCTP, this is optionally achieved with a "stream
      sequence number".  The stream sequence number is always provided
      in case of partial message arrival.

   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.


5.2.3.  Errors

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

   o  Notification of unsent messages
      Protocols: SCTP

   o  Notification of unacknowledged messages
      Protocols: SCTP



6.  Acknowledgements

   The authors would like to thank Joe Touch for comments on the TCP
   part.  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).






Welzl, et al.            Expires March 24, 2016                [Page 21]


Internet-Draft             Transport Services             September 2015


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

   [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,
              <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>.

9.2.  Informative References

   [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>.

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

   [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>.



Welzl, et al.            Expires March 24, 2016                [Page 22]


Internet-Draft             Transport Services             September 2015


   [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>.

   [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>.


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


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

   Email: naeemk@ifi.uio.no










Welzl, et al.            Expires March 24, 2016                [Page 23]