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ALTO                                                           S. Kiesel
Internet-Draft                                   University of Stuttgart
Intended status: Standards Track                            July 5, 2010
Expires: January 6, 2011


                  Using ALTO for ALTO server selection
                     draft-kiesel-alto-alto4alto-00

Abstract

   The goal of Application-Layer Traffic Optimization (ALTO) is to
   provide guidance to applications, which have to select one or several
   hosts from a set of candidates that are able to provide a desired
   resource.  Entities seeking guidance need to discover and possibly
   select an ALTO server to ask.

   This document proposes an ALTO-based scheme to select an ALTO server
   that can give guidance to a given ALTO client.  Unlike some other
   proposed ALTO discovery mechanisms, this solution works well if the
   client seeks guidance from a set of ALTO servers that are operated by
   an entity which is not the operator of the access network.

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on January 6, 2011.

Copyright Notice




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   Copyright (c) 2010 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
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   3.  Proposed Solution  . . . . . . . . . . . . . . . . . . . . . .  6
   4.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10




























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1.  Introduction

   The goal of Application-Layer Traffic Optimization (ALTO) is to
   provide guidance to applications, which have to select one or several
   hosts from a set of candidates, that are able to provide a desired
   resource.  ALTO is realized by a client-server protocol.  ALTO
   clients send queries to ALTO servers, in order to solicit guidance.
   Before sending these queries, ALTO clients need to discover and
   possibly select an appropriate destination ALTO server.

   The ALTO requirements document [I-D.ietf-alto-reqs] states two
   requirements that have an important impact on the ALTO server
   discovery mechanism:

   REQ.  ARv05-23: The ALTO client protocol MUST be designed in a way
   that the ALTO service can be provided by an entity which is not the
   operator of the IP access network.

   REQ.  ARv05-24: The ALTO client protocol MUST be designed in a way
   that different instances of the ALTO service operated by different
   providers can coexist.

   The rationale behind these requirements are trust issues.  Users may
   fear that the "official" ALTO service provided by their respective
   access network operator only optimizes traffic costs for the operator
   while penalizing performance.  Therefore, users may prefer to seek
   guidance from an "independent" entity providing ALTO service, e.g.,
   based on performance-related measurements.

   Simple ALTO server discovery mechanisms, such as having the network
   operator provide the ALTO server names (or IP addresses) by means of
   a DHCP option, are not in line with these requirements, as the user
   cannot influence the selection and switch to an independent entity's
   ALTO servers.

   Giving the user the ability to configure the name (or IP address) of
   an ALTO server in the ALTO client would solve this problem.  However,
   it is not a good solution, either: providers of ALTO service may wish
   to operate several regional ALTO servers, each being able to give
   guidance only to ALTO clients in its respective (topological)
   vicinity.  Requiring the user to know the "best" ALTO server for his
   client's topological position would be an inacceptable burden.  On
   the other hand, selecting the "best" server for a given client is
   very similar (see remark below) to the problem ALTO tries to solve.
   Therefore, we propose an ALTO-based scheme for selecting an ALTO
   server.

   Remark: in the normal mode of operation, ALTO gives guidance on



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   selecting among providers of an identical (copy of a) resource, based
   on connectivity-related parameters.  Here, in contrast, ALTO would
   give guidance on selecting the best resource (i.e., ALTO server that
   can give guidance to the client).  Giving guidance based on
   application knowledge is beyond the scope of ALTO for the general
   case with arbitrary applications.  However, in this special case
   where the application is ALTO, this approach seem feasible.

   Comments and discussions about this document should be directed to
   the ALTO working group: alto@ietf.org.









































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2.  Terminology

   This document uses the terminology introduced in [RFC5693].

   Furthermore, we define the term "ALTO service instance" as the ALTO
   service that is provided by one (legal) entity, such as a network
   operator, a CDN operator, an "independent" organization, etc.  This
   ALTO service instance is provided by one or more ALTO servers, which
   are under the control of this entity.  It is assumed that several
   ALTO service instance can coexist (see ARv05-24) and users should be
   able to select which ALTO service instance to ask for guidance.








































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3.  Proposed Solution

   The proposed solution requires 3 steps:

   Step 1  Get complete list of all ALTO servers that belong to the
      desired ALTO service instance.

      Thereto, ask user (may be a configuration file item, etc.) for the
      URI of a file with a list of addresses of all ALTO servers that
      constitute the desired ALTO service instance.  If the user has no
      specific wish, use as default choice the ALTO service provided by
      his access network operator.

      Because the ALTO client protocol [I-D.ietf-alto-protocol] itself
      is HTTP based, and because of the close interaction with Step 2 it
      seems advisable to host the abovementioned URI on an ALTO server.

      TBD: specify automatic retrieval of addresses for the default
      choice, maybe similar to the mechanism described in BEP 22
      [bep22].

   Step 2  Ask for ALTO guidance on that list.

      Randomly select an ALTO server from the list.  Ask for guidance,
      specify "ALTO server guidance quality" as the rating criterion.

      It is assumed that every ALTO server on the list knows the
      competences (wrt. giving guidance to specific clients) of all ALTO
      servers on the list.  That is, we assume that every ALTO server in
      one ALTO service instance can give guidance on which ALTO server
      from the same ALTO service instance can give the best guidance to
      a given client, for arbitrary ALTO queries.

   Step 3  Ask the recommended ALTO servers for guidance with respect to
      the resource provider selection the actual user application needs
      to make.















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4.  IANA Considerations

   This document proposes a new ALTO rating criterion "ALTO server
   guidance quality".  The ALTO requirements document mandates a
   registration procedure for such new rating criteria.  However, at
   this point in time it is unclear how these procedures will look like.
   If they will be implemented by an IANA registry, the proposed rating
   criterion will have to be registered there.











































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5.  Security Considerations

   This early version of this memo does not yet have any security
   considerations, but they will be added in future revision.















































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6.  References

   [I-D.ietf-alto-protocol]
              Alimi, R., Penno, R., and Y. Yang, "ALTO Protocol",
              draft-ietf-alto-protocol-04 (work in progress), May 2010.

   [I-D.ietf-alto-reqs]
              Kiesel, S., Previdi, S., Stiemerling, M., Woundy, R., and
              Y. Yang, "Application-Layer Traffic Optimization (ALTO)
              Requirements", draft-ietf-alto-reqs-05 (work in progress),
              June 2010.

   [RFC5693]  Seedorf, J. and E. Burger, "Application-Layer Traffic
              Optimization (ALTO) Problem Statement", RFC 5693,
              October 2009.

   [bep22]    Harrison, D., Shalunov, S., and G. Greg Hazel, "BitTorrent
              Local Tracker Discovery Protocol",
              BEP http://bittorrent.org/beps/bep_0022.html.
































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Author's Address

   Sebastian Kiesel
   University of Stuttgart Computing Center
   Allmandring 30
   Stuttgart  70550
   Germany

   Email: ietf-alto@skiesel.de
   URI:   http://www.rus.uni-stuttgart.de/nks/









































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