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Application-Layer Traffic Optimization (ALTO) Problem Statement
RFC 5693

Network Working Group                                         J. Seedorf
Request for Comments: 5693                                           NEC
Category: Informational                                        E. Burger
                                                            Neustar Inc.
                                                            October 2009

    Application-Layer Traffic Optimization (ALTO) Problem Statement

Abstract

   Distributed applications -- such as file sharing, real-time
   communication, and live and on-demand media streaming -- prevalent on
   the Internet use a significant amount of network resources.  Such
   applications often transfer large amounts of data through connections
   established between nodes distributed across the Internet with little
   knowledge of the underlying network topology.  Some applications are
   so designed that they choose a random subset of peers from a larger
   set with which to exchange data.  Absent any topology information
   guiding such choices, or acting on suboptimal or local information
   obtained from measurements and statistics, these applications often
   make less than desirable choices.

   This document discusses issues related to an information-sharing
   service that enables applications to perform better-than-random peer
   selection.

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (c) 2009 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
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.

Seedorf & Burger             Informational                      [Page 1]
RFC 5693                 ALTO Problem Statement             October 2009

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Overview . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.2.  State-of-the-Art . . . . . . . . . . . . . . . . . . . . .  4
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  The Problem  . . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  Use Cases  . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     4.1.  File sharing . . . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  Cache/Mirror Selection . . . . . . . . . . . . . . . . . .  8
     4.3.  Live Media Streaming . . . . . . . . . . . . . . . . . . .  8
     4.4.  Real-Time Communications . . . . . . . . . . . . . . . . .  9
     4.5.  Distributed Hash Tables  . . . . . . . . . . . . . . . . .  9
   5.  Aspects of the Problem . . . . . . . . . . . . . . . . . . . .  9
     5.1.  Information Provided by an ALTO Service  . . . . . . . . .  9
     5.2.  ALTO Service Providers . . . . . . . . . . . . . . . . . . 10
     5.3.  ALTO Service Implementation  . . . . . . . . . . . . . . . 10
     5.4.  User Privacy . . . . . . . . . . . . . . . . . . . . . . . 10
     5.5.  Topology Hiding  . . . . . . . . . . . . . . . . . . . . . 11
     5.6.  Coexistence with Caching . . . . . . . . . . . . . . . . . 11
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   7.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 12
   8.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 12
   9.  Informative References . . . . . . . . . . . . . . . . . . . . 13

1.  Introduction

1.1.  Overview

   Distributed applications, both peer-to-peer (P2P) and client/server
   used for file sharing, real-time communication, and live and on-
   demand media streaming, use a significant amount of network capacity
   and CPU cycles in the routers [WWW.wired.fuel].  In contrast to
   centralized applications, distributed applications access resources
   such as files or media relays distributed across the Internet and
   exchange large amounts of data in connections that they establish
   directly with nodes sharing such resources.

   One advantage of highly distributed systems results from the fact
   that the resources such systems offer are often available through
   multiple replicas.  However, applications generally do not have
   reliable information of the underlying network and thus have to

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