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TAPS                                                         S. Gjessing
Internet-Draft                                                  M. Welzl
Intended status: Informational                        University of Oslo
Expires: September 19, 2016                               March 18, 2016


          A Minimal Set of Transport Services for TAPS Systems
                     draft-gjessing-taps-minset-01

Abstract

   This draft will eventually recommend a minimal set of IETF Transport
   Services offered by end systems supporting TAPS, and give guidance on
   choosing among the available mechanisms and protocols.  It
   categorizes the set of transport services given in the TAPS document
   draft-ietf-taps-transports-usage-00, assuming that the eventual
   minimal set of transport services will be based on a similar form of
   categorization.

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 September 19, 2016.

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
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   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology (as defined by draft-ietf-taps-transports-10) . .   4
   3.  The superset of transport service features  . . . . . . . . .   4
     3.1.  CONNECTION Related Transport Service Features . . . . . .   5
     3.2.  DATA Transfer Related Transport Service Features  . . . .   9
       3.2.1.  Sending Data  . . . . . . . . . . . . . . . . . . . .   9
       3.2.2.  Receiving Data  . . . . . . . . . . . . . . . . . . .  10
       3.2.3.  Errors  . . . . . . . . . . . . . . . . . . . . . . .  11
   4.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  12
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  Informative References  . . . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   An application has an intended usage and demands for transport
   services, and the task of any system that implements TAPS is to offer
   these services to its applications, i.e. the applications running on
   top of TAPS, without binding an application to a particular transport
   protocol.

   The present draft is based on [TAPS1] and [TAPS2]  and follows the
   same terminology (also listed below).  The purpose of these two
   drafts is, according to the TAPS charter, to "Define a set of
   Transport Services, identifying the services provided by existing
   IETF protocols and congestion control mechanisms."  This is item 1 in
   the list of working group tasks.  Also according to the TAPS charter,
   the working group will then "Specify the subset of those Transport
   Services, as identified in item 1, that end systems supporting TAPS
   will provide, and give guidance on choosing among available
   mechanisms and protocols.  Note that not all the capabilities of IETF
   Transport protocols need to be exposed as Transport Services."  Hence
   it is necessary to minimize the number of services that are offered.
   We begin this by grouping the transport features.

   Following [TAPS2], we divide the transport service features into two
   main groups as follows:

   1.  Connection related transport service features
       - Establishment
       - Availability



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       - Maintenance
       - Termination

   2.  Data Transfer Related Transport Service Features
       - Sending Data
       - Receiving Data
       - Errors


   Because QoS is out of scope of TAPS, this document assumes a "best
   effort" service model [RFC5290], [RFC7305].  Applications using a
   TAPS system can therefore not make any assumptions about e.g. the
   time it will take to send a message.  There are however certain
   requirements that are strictly kept by transport protocols today, and
   these must also be kept by a TAPS system.  Some of these requirements
   relate to features that we call "Functional".

   Functional features provide functionality that cannot be used without
   the application knowing about them, or else they violate assumptions
   that might cause the application to break.  For example, unordered
   message delivery is a functional feature: it cannot be used without
   the application knowing about it because the application's assumption
   could be that messages arrive in-order, and in this case unordered
   delivery could cause the application to break.  Change DSCP and data
   bundling (Nagle in TCP) are optimizing features: if a TAPS system
   autonomously decides to enable or disable them, an application will
   not break, but a TAPS system may be able to communicate more
   efficiently if the application is in control of this optimizing
   feature.  Change DSCP and data bundling are examples of features that
   require application-specific knowledge (about delay/bandwidth
   requirements and the length of future data blocks that are to be
   transmitted, respectively).  Some features, however, do not always
   require application-specific knowledge, and could therefore sometimes
   be used by a TAPS system without exposing them to the application.
   We call these features potentially automatable.

   To summarize, features offered to applications are divided into two
   groups as follows:

   o  Potentially automatable
      It may sometimes be possible to use this feature without support
      by the application.
   o  Application-specific
      It is not possible to use this feature without support by the
      application.

   The Application-specific features are further divided into two
   groups:



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   o  Functional
      This feature is application-specific, and using it without
      explicitly involving the application could lead to incorrect
      operation.
   o  Optimizing
      This feature is application-specific, and can allow an application
      to improve its performance.

   In the following, some features are additionally marked as DELETED.
   These features are IETF Transport protocol features that are not
   exposed to the TAPS user because they include functionality that is
   automatable.  A few features are marked as "ADDED".  These provide
   non-automatable functionality of DELETED features.

2.  Terminology (as defined by draft-ietf-taps-transports-10)

   The following terms are used throughout this document, and in
   subsequent documents produced by TAPS that describe the composition
   and decomposition of transport services.

   Transport Service Feature:  a specific end-to-end feature that the
      transport layer provides to an application.  Examples include
      confidentiality, reliable delivery, ordered delivery, message-
      versus-stream orientation, etc.
   Transport Service:  a set of Transport 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 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 data across the network (this may also be an upper layer
      protocol or tunnel encapsulation).

3.  The superset of transport service features

   This section is based on the classification of the transport service
   features in pass 3 of [TAPS2].  As noted earlier, whether the usage
   of potentially automatable features can be automatized in a TAPS
   system depends on how much network-specific information an
   application wants to manipulate (e.g., to directly expose to its
   user).  Therefore, in the following, "application-specific knowledge"
   refers to knowledge that only applications have, as opposed to all
   knowledge that applications may want to have.



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3.1.  CONNECTION Related Transport Service Features

   ESTABLISHMENT:

   o  Connect
      Protocols: TCP, SCTP
      Functional because the notion of a connection is often reflected
      in applications as an expectation to be able to communicate after
      a "Connect" succeeded, with a communication sequence relating to
      this feature that is defined by the application protocol.
      ADDED.



   o  Specify IP Options
      Protocols: TCP
      Potentially automatable because IP Options relate to knowledge
      about the network, not the application.
      DELETED.



   o  Request multiple streams
      Protocols: SCTP
      Potentially automatable because using multi-streaming does not
      require application-specific knowledge.
      DELETED.



   o  Obtain multiple sockets
      Protocols: SCTP
      Potentially automatable because the usage of multiple paths to
      communicate to the same end host relates to knowledge about the
      network, not the application.
      DELETED.




   AVAILABILITY:

   o  Listen
      Protocols: All
      Functional because the notion of accepting connection requests is
      often reflected in application as an expectation to be able to
      communicate after a "Listen" succeeded, with a communication




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      sequence relating to this feature that is defined by the
      application protocol.
      ADDED.



   o  Listen, 1 specified local interface
      Protocols: TCP, SCTP
      Potentially automatable because decisions about local interfaces
      relate to knowledge about the network and the Operating System,
      not the application.
      DELETED.



   o  Listen, N specified local interfaces
      Protocols: SCTP
      Potentially automatable because decisions about local interfaces
      relate to knowledge about the network and the Operating System,
      not the application.
      DELETED.



   o  Listen, all local interfaces (unspecified)
      Protocols: TCP, SCTP
      Potentially automatable because decisions about local interfaces
      relate to knowledge about the network and the Operating System,
      not the application.
      DELETED.



   o  Obtain requested number of streams
      Protocols: SCTP
      Potentially automatable because using multi-streaming does not
      require application-specific knowledge.




   MAINTENANCE:

   o  Change timeout for aborting connection (using retransmit limit or
      time value)
      Protocols: TCP, SCTP
      Functional because this is closely related to potentially assumed
      reliable data delivery.



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   o  Control advertising timeout for aborting connection to remote
      endpoint
      Protocols: TCP
      Functional because this is closely related to potentially assumed
      reliable data delivery.



   o  Disable Nagle algorithm
      Protocols: TCP, SCTP
      Optimizing because this decision depends on knowledge about the
      size of future data blocks and the delay between them.



   o  Request an immediate heartbeat, returning success/failure
      Protocols: SCTP
      Potentially automatable because this informs about network-
      specific knowledge.



   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
      Potentially automatable because these parameters relate to
      knowledge about the network, not the application.



   o  Notification of Excessive Retransmissions (early warning below
      abortion threshold)
      Protocols: TCP
      Optimizing because it is an early warning to the application,
      informing it of an impending functional event.



   o  Notification of ICMP error message arrival
      Protocols: TCP
      Optimizing because these messages can inform about success or
      failure of functional features (e.g., host unreachable relates to
      "Connect")






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   o  Status (query or notification)
      Protocols: SCTP
      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
      Potentially automatable because these parameters relate to
      knowledge about the network, not the application.



   o  Set primary path
      Protocols: SCTP
      Potentially automatable because it requires using multiple
      sockets, but obtaining multiple sockets in the
      CONNECTION.ESTABLISHMENT category is potentially automatable.



   o  Change DSCP
      Protocols: TCP
      Optimizing because choosing a suitable DSCP value requires
      application-specific knowledge.




   TERMINATION:

   o  Close after reliably delivering all remaining data, causing an
      event informing the application on the other side
      Protocols: TCP, SCTP
      Functional because the notion of a connection is often reflected
      in applications as an expectation to have all outstanding data
      delivered and no longer be able to communicate after a "Close"
      succeeded, with a communication sequence relating to this feature
      that is defined by the application protocol.



   o  Abort without delivering remaining data, causing an event
      informing the application on the other side
      Protocols: TCP, SCTP
      Functional because the notion of a connection is often reflected
      in applications as an expectation to potentially not have all
      outstanding data delivered and no longer be able to communicate



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      after an "Abort" succeeded, with a communication sequence relating
      to this feature that is defined by the application protocol.



   o  Timeout event when data could not be delivered for too long
      Protocols: TCP, SCTP
      Functional because this notifies that potentially assumed reliable
      data delivery is no longer provided.



3.2.  DATA Transfer Related Transport Service Features

3.2.1.  Sending Data

   o  Reliably transfer data
      Protocols: TCP, SCTP
      Functional because this is closely tied to properties of the data
      that an application sends or expects to receive.



   o  Notifying the receiver to promptly hand over data to application
      Protocols: TCP
      Optimizing because this is meant to control sleep times of the
      application's receiving process.



   o  Message identification
      Protocols: SCTP
      Functional because this is closely tied to properties of the data
      that an application sends or expects to receive.



   o  Choice of stream
      Protocols: SCTP
      Potentially automatable because it requires using multiple
      streams, but requesting multiple streams in the
      CONNECTION.ESTABLISHMENT category is potentially automatable.


   o  Choice of path (destination address)
      Protocols: SCTP





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      Potentially automatable because it requires using multiple
      sockets, but obtaining multiple sockets in the
      CONNECTION.ESTABLISHMENT category is potentially automatable.


   o  Message lifetime
      Protocols: SCTP
      Optimizing because only applications know about the time
      criticality of their communication.



   o  Choice between unordered (potentially faster) or ordered delivery
      Protocols: SCTP
      Functional because this is closely tied to properties of the data
      that an application sends or expects to receive.



   o  Request not to bundle messages
      Protocols: SCTP
      Optimizing because this decision depends on knowledge about the
      size of future data blocks and the delay between them.



   o  Specifying a "payload protocol-id" (handed over as such by the
      receiver)
      Protocols: SCTP
      Functional because it allows application data with every message,
      for the sake of identification of data, which by itself is
      application-specific.




3.2.2.  Receiving Data

   o  Receive data
      Protocols: TCP, SCTP
      Functional because a TAPS system must be able to send and receive
      data.



   o  Choice of stream to receive from
      Protocols: SCTP




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      Potentially automatable because it requires using multiple
      streams, but requesting multiple streams in the
      CONNECTION.ESTABLISHMENT category is potentially automatable.



   o  Message identification
      Protocols: SCTP
      Functional because this is closely tied to properties of the data
      that an application sends or expects to receive.



   o  Information about partial message arrival
      Protocols: SCTP
      Functional because this is closely tied to properties of the data
      that an application sends or expects to receive.




3.2.3.  Errors

   o  Notification of send failures
      Protocols: All
      Functional because this notifies that potentially assumed reliable
      data delivery is no longer provided.
      ADDED.



   o  Notification of unsent messages
      Protocols: SCTP
      Automatable because the distinction between unsent and
      unacknowledged is network-specific.
      DELETED.



   o  Notification of unacknowledged messages
      Protocols: SCTP
      Automatable because the distinction between unsent and
      unacknowledged is network-specific.
      DELETED.







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4.  Conclusion

   The eventual recommendations are:

   o  A TAPS system should exhibit all functional features that are
      offered by the transport protocols that it uses because these
      features could otherwise not be utilized by the TAPS system.  It
      can still be possible to implement a TAPS system that does not
      offer all functional features, e.g. for the sake of uniform
      application operation across a broader set of protocols, but then
      the corresponding functionality of transport protocols is not
      exploited.
   o  A TAPS system should exhibit all application-specific optimizing
      features.  If an application-specific optimizing feature is only
      available in a subset of the transport protocols used by the TAPS
      system, it should be acceptable for the TAPS system to ignore its
      usage when the transport protocol that is currently used does not
      provide it because of the performance-optimizing nature of the
      feature and the initially mentioned assumption of "best effort"
      operation.
   o  By hiding potentially automatable features from the application, a
      TAPS system can gain opportunities to automatize network-related
      functionality.  This can facilitate using the TAPS system for the
      application programmer and it allows for optimizations that may
      not be possible for an application.  For instance, a kernel-level
      TAPS system that hides SCTP multi-streaming from applications
      could theoretically map application-level connections from
      multiple applications onto the same SCTP association.  Similarly,
      system-wide configurations regarding the usage of multiple
      interfaces could be exploited if the choice of the interface is
      not given to the application.  However, if an application wants to
      directly expose such choices to its user, not offering this
      functionality can become a disadvantage of a TAPS system.  This is
      a trade-off that must be considered in TAPS system design.

   Given that the intention of TAPS is to break the design-time binding
   between applications and transport protocols, the decision on which
   features a TAPS system provides should also depend on the protocols
   that support them.  Features that are provided by only one particular
   transport protocol have the potential to tie applications to that
   protocol.  They should either not be offered, or replaced by fall-
   back functionality that allows for semantically correct operation
   (for example, ordered data delivery is correct but potentially slower
   for an application that requests unordered data delivery.
   "Potentially slower" is not a hindrance to correct operation within
   the "best effort" service model).





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5.  Acknowledgements

   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).

6.  IANA Considerations

   XX RFC ED - PLEASE REMOVE THIS SECTION XXX

   This memo includes no request to IANA.

7.  Security Considerations

   Security will be considered in future versions of this document.

8.  Informative References

   [RFC5290]  Floyd, S. and M. Allman, "Comments on the Usefulness of
              Simple Best-Effort Traffic", RFC 5290,
              DOI 10.17487/RFC5290, July 2008,
              <http://www.rfc-editor.org/info/rfc5290>.

   [RFC7305]  Lear, E., Ed., "Report from the IAB Workshop on Internet
              Technology Adoption and Transition (ITAT)", RFC 7305,
              DOI 10.17487/RFC7305, July 2014,
              <http://www.rfc-editor.org/info/rfc7305>.

   [TAPS1]    Fairhurst, G., Trammell, B., and M. Kuehlewind, "Services
              provided by IETF transport protocols and congestion
              control mechanisms", Internet-draft draft-ietf-taps-
              transports-10, March 2016.

   [TAPS2]    Welzl, M., Tuexen, M., and N. Khademi, "An Approach to
              Identify Services Provided by IETF Transport Protocols and
              Congestion Control Mechanisms", Internet-draft draft-ietf-
              taps-transports-usage-00, June 2015.

Authors' Addresses

   Stein Gjessing
   University of Oslo
   PO Box 1080 Blindern
   Oslo  N-0316
   Norway

   Phone: +47 22 85 24 44
   Email: steing@ifi.uio.no



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

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











































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