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Versions: 00 01 02 03                                                   
ALTO                                                               Y. Gu
Internet-Draft                                                    Huawei
Intended status: BCP                                            R. Alimi
Expires: January 13, 2011                                Yale University
                                                                 R. Even
                                                           July 12, 2010

                    ALTO Information Redistribution


   The ALTO protocol proposes several mechanisms to increase
   scalability.  One of the proposed mechanisms is ALTO information
   redistribution.  This document concretely defines ALTO Information
   Redistribution, indicates suggested extensions to the ALTO Protocol
   to support redistribution, and shows how redistribution could be used
   in practice.

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 January 13, 2011.

Copyright Notice

   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
   carefully, as they describe your rights and restrictions with respect

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   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 Simplified BSD License.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminologies and concepts . . . . . . . . . . . . . . . . . .  4
   3.  Redistribution Framework . . . . . . . . . . . . . . . . . . .  4
     3.1.  Basic Requirements . . . . . . . . . . . . . . . . . . . .  5
     3.2.  ALTO Information Types . . . . . . . . . . . . . . . . . .  5
     3.3.  Redistribution Scheme Design . . . . . . . . . . . . . . .  6
   4.  ALTO Redistribution Solutions Analysis . . . . . . . . . . . .  6
     4.1.  PUSH Information into Overlay  . . . . . . . . . . . . . .  7
       4.1.1.  General Requirements for PUSH  . . . . . . . . . . . .  7
       4.1.2.  Tracker Acts as Redistribution Proxy . . . . . . . . .  8
       4.1.3.  Supernode Acts as Redistribution Proxy . . . . . . . .  8
       4.1.4.  Advantages of PUSH . . . . . . . . . . . . . . . . . .  8
     4.2.  PULL Inforamtion into Overlay  . . . . . . . . . . . . . .  9
       4.2.1.  PULL Use Cases . . . . . . . . . . . . . . . . . . . .  9
   5.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 13
   6.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     6.1.  Normative References . . . . . . . . . . . . . . . . . . . 13
     6.2.  Informative References . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14

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1.  Introduction

   When providing an ALTO service, Network Providers offer information
   to clients with the goal of helping P2P applications to perform
   better peer selection and improving network efficiency.  The ALTO
   Service becomes a distribution point of network information for ALTO
   Clients within its network.  A Network Provider may deploy an ALTO
   Service using techniques such as load balancing and caching to handle
   a large number of subscribers.  In this document, we discuss an
   additional mechanism to distribute ALTO information to ALTO Clients:
   ALTO Information Redistribution.  Consider a scenario where a large
   number (e.g., millions) of users start their P2P live streaming
   clients just before the start of a popular event.  Each client
   requests ALTO information directly from the ALTO Service within their
   ISP if it has not yet been retrieved or needs to be refreshed.  For
   certain content (e.g., content with broad interest), even the number
   of streaming clients within a single ISP may be extremely large.  For
   example, tens of millions of people watched the United States
   Presidential Inauguration in Jan. 2009 via the Internet through such
   sites as CNN.  During the 2009 Spring Festival Evening in China, an
   audience of about 24 million watched the program on the Internet.  In
   such a case, an ISP's ALTO Service may not be able to handle the load
   and provide ALTO information directly to each client.

   Many mechanisms, such as load balancing, can be used to increase
   scalability of an ALTO Service.  [I-D.penno-alto-protocol] proposes
   ALTO Information Redistribution as one technique.  Using ALTO
   Information Redistribution, ALTO Clients may distribute ALTO
   information to each other instead of requesting directly from the
   ALTO Server.  For example, a P2P infrastructure can be used to
   distribute ALTO information to a large number of ALTO Clients with
   small load on the ALTO Server.

   This document serves three primary purposes:

   1)  Defines basic requirements for redistributing ALTO information,
       and considerations for developing a redistribution scheme.

   2)  Propose extensions to the ALTO Protocol to support ALTO
       Information redistribution to meet the defined requirements.

   3)  Provide use cases showing how redistribution may be applied in

   We envision that multiple redistribution schemes are possible, and
   the design may depend on the particular setting, such as scalability
   requirements and existing application protocols.  Thus,
   standardization of a redistribution scheme for all kinds of scenario

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   is not an object.  This BCP intends to extract the fundamental for
   real-world practice, and to provide use cases for most common
   scenario of ALTO Redistribution.

   Note that certain design changes during the development of the ALTO
   Protocol may affect ALTO information redistribution.  This document
   will be updated to track the progress of the ALTO Protocol.

2.  Terminologies and concepts

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in[RFC2119].

   The document uses terms defined in
   [I-D.ietf-alto-problem-statement]and [I-D.penno-alto-protocol].

3.  Redistribution Framework

   Before defining requirements for ALTO Information Redistribution, we
   first give a concrete model for ALTO Information Redistribution that
   we use in this document:

   1.  A set of ALTO Servers {S1, S2, S3, ...} are deployed, each
       possibly serving a different network region.

   2.  A set of ALTO Clients are running.  We assume that each ALTO
       Client can be mapped to one of the available ALTO Servers by the
       ALTO discovery process [I-D.song-alto-server-discovery].  Let
       Clients(Si) denote the set of ALTO Clients mapped to ALTO Server

   3.  An ALTO Client wishes to obtain a particular set of information
       from the ALTO Server.  The desired information is fully specified
       by: (1) the ALTO Server (hostname and port), and (2) the query
       and input parameters that would be sent to the ALTO Server.  See
       Section 6 for a discussion of behavior when criteria other than
       the input parameters are used by an ALTO Server to generate a

   4.  An ALTO Client may obtain the information either directly from
       its ALTO Server Si, or it may obtain the information from a
       member of Clients(Si).

   5.  For a particular query to ALTO Server Si, at least one member of
       Clients(Si) directly fetches from Si.  The remaining members of

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       Clients(Si) obtain the information from some other member in

3.1.  Basic Requirements

   A redistribution scheme should satisfy some basic requirements in
   order to successfully redistribute an ALTO Server's response to a set
   of ALTO Client.

   1.  The ALTO Client should be able to identify the desired
       redistributed data based only on the ALTO Server hostname and
       port, and the input parameters.

   2.  The ALTO Client should be able to check the validity of the
       information once it is retrieved.  That is, the ALTO Client
       should be able to determine if the retrieved information was
       indeed generated by its ALTO Server, , and is generated based on
       the particular input parameters.

3.2.  ALTO Information Types

   In general, it should be possible to redistribute the response from a
   particular ALTO Server that does not depend on anything except query
   input parameters.  However, redistribution may only be worthwhile for
   queries that are made by a large number of ALTO Clients.  In the
   context of [I-D.penno-alto-protocol], we provide an example list of
   information types that may be commonly used across many ALTO Clients,
   and hence benefit from redistribution.  The example list the most
   obvious examples to our best knowledge, and there might be other
   information types that are suitable for redistribution.

   o  Server Capability which indicates the capabilities implemented by
      an ALTO Server.

   o  Full Network Map which lists the PIDs and IP prefixes that are
      contained within each PID.

   o  Full Path Cost Map among all PIDs, which indicates the Path Cost
      between each pair of PIDs.

   [I-D.penno-alto-protocol]also specifies certain queries that may not
   benefit from redistribution.  For example, if a peer requests ordinal
   Path Costs (i.e., a ranked list) for a set of individual endpoint
   addresses (i.e., Resource Providers), the response may not be useful
   to other ALTO Clients.  This is because other ALTO Clients may be
   running different applications or have a different set of available
   peers (e.g., participating in a different swarm, or be in contact
   with a different set of peers within the same swarm).

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3.3.  Redistribution Scheme Design

   While this document does not fully specify a particular
   redistribution scheme, we provide a sampling of decisions that should
   be considered when designing an implementing a redistribution scheme.
   This list can be used as a guide for implementers when designing a
   redistribution scheme for a particular setting.  Considerations for a
   redistribution scheme include:

   o  Who places the ALTO Information onto overlay, and how the ALTO
      Information is published on the overlay

   o  How could peers decide whether to get ALTO Information from ALTO
      Server or to get from Overlay?

   o  What method is used for peers to locate redistributed ALTO

   o  What protocol is used for retrieving redistributed ALTO

   o  How could peers verify the Redistributed Information it obtained.

   o  How to update the Redistributed Information on time and who is
      responsible for updating.

   o  What naming scheme is used to specify the ALTO Server hostname,
      port, and input parameters in the protocol for locating
      redistributed ALTO information?  For example, the naming scheme
      could define how to compute the 'key' in a DHT.

   o  How is the redistributed information encoded?  Note that the
      original response from the ALTO Service may be reformatted (e.g.,
      compressed) for redistribution.  Note that if this approach is
      taken and ALTO Clients still wish to verify received information,
      ALTO Clients should be able to reconstruct the ALTO Service's
      original response (e.g., via decompression).  If a lossy
      transformation is used (e.g., filtering), ALTO Clients may not be
      able to verify the received information.

4.  ALTO Redistribution Solutions Analysis

   In this section, we present our considerations on Redistribution
   Implementation.  In the previous section, several questions have been
   enumerated, and the answer to the first question is the baseline of
   ALTO Redistribution.  There are two distinct ways to place the ALTO
   Information into the overlay: Redistribution Proxy PUSH the

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   Information into the overlay or components of the overlay PULL the
   Information into the Overlay.

   The main difference betwen PUSH and PULL is as follows.

   o  In PUSH, the Redistribution Proxy can publish the updated
      redistribution Information into the overlay.  Since the
      Redistribution Proxy can be much intelligent than a normal peer,
      e.g.  Redistribution Proxy has overall understanding of the
      overlay, it can make decision on how to distribute the Information
      in order to utilize the overlay much efficient.  For example,
      integration with DECADE, distribution via a CDN (many P2P apps are
      integrating CDNs now).  We will add more use case for PUSH in our
      later version.

   o  While In PULL, peers individually pull/request updated ALTO
      information from an overlay or ALTO server.  Considering the
      general size of a redistributable information, there might be an
      out-of-control flooding through the overlay.

   In the following text, we introduces some consideration of both PUSH
   and PULL, and conclude other features of PUSH and PULL.

4.1.  PUSH Information into Overlay

   In PUSH method, we introduce a new terminology, Redistribution Proxy.

   A Redistribution Proxy can be a Tracker in Tracker-based P2P Overlay
   or a supernode either in Tracker-based or Trackerless P2P Overlay.
   The duty of Redistribution Proxy to accecpt the redistributable
   information from ALTO Server and push the information into the
   overlay.  There are two options on obtaining redistributable
   inforamtion from ALTO Server.  One is Redistribution Proxy request
   and ALTO Server answers or ALTO Server positively update the
   information to the Redistribution Proxy.  Since the number of
   Redistribution Proxy is much fewer than the total number of ALTO
   Clients, so the latter option does not occupy much connection
   resources on ALTO Server.  In our draft, we introduce the PUSH based
   on the latter option, which is ALTO Server pushes the uptaed
   information to Redistribution Proxy positivly.

4.1.1.  General Requirements for PUSH

   To make PUSH feasible, the following requirements must be satisfied.

   o  Redistribution Proxy MUST has public IP Addresse, so that both
      ALTO server and Peers can connect with it without NAT issue.

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   o  ALTO server MUST know Redistribution proxy's IP Address.

   o  Redistribution Proxy MUST be reliable.

4.1.2.  Tracker Acts as Redistribution Proxy

   If Tracker is deployed as Redistribution Proxy, it has two choices.

   Tracker can publish the ALTO Information into overlay, then peers can
   search and obtain the Information through Overlay.

   Or Tracker can store the Information on itself, and answer peers'
   particular request based on the Information.  For those information
   that is not redistributable, peers can request directly from ALTO
   server or ask Tracker to request from ALTO server and answer.

   In both case, an indication is necessary for telling peers where to
   get ALTO Service.  For example, peers should know that for those
   redistributable type of Information, peers should first request from
   Tracker, and for those unredistributable, they should request from
   ALTO Sever.  Which can be configured by application.  The definition
   of indication configuration is out of the scope of ALTO.

4.1.3.  Supernode Acts as Redistribution Proxy

   If Supernode is deployed as Redistribution Proxy, it has two choices
   as well.

   Supernode store the Information and answer peers request.  In this
   case, peers should learn Supernode's IP Address in advance.

   Or Supernode just publish the Information into the overlay and then
   peers search and get the Information through the overlay.

   In both case, an indication is necessary as well.

4.1.4.  Advantages of PUSH

   The advantages of PUSH is obvious.

   1  Intelligence.  Refer to the text that explain the main difference
      between PUSH and PULL.

   2  Scalability.  PUSH can significantly reduce the request directly
      sent to ALTO Server, which can reduce the load on ALTO Server.

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   3  Quick updating.  Once the ALTO Information is updated in Server,
      ALTO server can notify the Redistribution Proxy with new

   4  Good Consistency, because redistributed Informaiton can be updated
      in time.

   5  Never expiration, because the redistributed Information is always
      as new as those in the server.

   6  Safe.  Redistribution Proxy is reliable.

   7  Low latency, because peers do not need to search and locate the
      redistribution Information on the overlay, which is extremely
      meaningful for time sensitive application, e.g.  Live streaming.

4.2.  PULL Inforamtion into Overlay

   There could be Tracker or peers who PULL the ALTO Information into
   the overlay.

   If it's peer that pull ALTO information into the overlay, several
   aspects should be considered.

   1  Where to request for ALTO Information first, ALTO server or
      overlay?  This can be configured by application, e.g. always
      request redistributable type of ALTO Information through Overlay
      first.  If appliction configuration recommends peer to request
      from ALTO Server first, this won't be any good to ALTO

   2  Publishing mechanism.  Should peer store the Information on itself
      and publish the resource into the overlay, or should peer store
      the Information on the corresponding responsible peer on the
      overlay?  However, this won't make much difference.

   3  How to authenticate the Information?  We have introduce a security
      method with Signature, which is now in ALTP Protocol, while the
      question is where to get the Public Key.

4.2.1.  PULL Use Cases

   The architecture of a particular P2P application will affect the
   redistribution mechanism.  Generally speaking, there are two kinds of
   P2P applications: trackerless, and those using a tracker.  In
   Tracker-based applications, a resource directory is maintained on a
   tracker, and peers contact the tracker to learn about new peers.  In
   a Trackerless overlay, peers are organized through a particular

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   algorithm, e.g.  DHT, and they publish or find resources by routing
   through the overlay.  Tracker-based redistribution

   1.  The Tracker finds the ALTO server on behalf of a peer, queries
       the necessary ALTO information and replies to the peer with the
       ALTO information as well as the candidate list.
       [I-D.kiesel-alto-3pdisc] describes several methods by which
       Tracker can find the right ALTO server.  Note that the Tracker
       might omit the 'more preferred' peers when making the original
       selection.  However, the ALTO Information can be applied to peers
       learned from other sources (e.g., Peer Exchange and/or DHT).

   2.  A peer asks for a Resource and Tracker replies without any ALTO
       information.  The peer queries the ALTO server for ALTO
       information, and selects peers.  In order to help lessen the
       burden on ALTO server, as well as to help other peers who want
       the same ALTO information, the peer publishes the ALTO
       information on the Tracker (if the Tracker allows this behavior).
       Peers may then distribute the ALTO information just as any other
       Resource.  The method introduced here can be regard as a
       complementary process to (1).

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                   |             |
                   |    ALTO     |
                   |   Server    |
                   |             |
                          | (1) Query
                          |     and
                          |     Response
           ^      +-----------------+    +----------------+           ^
           ^      |                 |    |                |           ^
           ^      |    Peer A       |    |  Peer B        |           ^
           ^      | (ALTO Client)   |    | (ALTO Client)  |           ^
           ^      +-----------------+    +----------------+           ^
           ^              * (3)                    * o                ^
           ^              * Redistribution         * o  (2)           ^
           ^              ************************** o   peer         ^
           ^                                         o  request       ^
           ^                                         o                ^
           ^                                         o                ^
           ^                                 +---------------+        ^
           ^                                 |               |        ^
           ^                                 |   Tracker     |        ^
           ^                                 |               |        ^
           ^                                 +---------------+        ^
               ---   ALTO query and response protocol
               ooo   peer request protocol in p2p overlay (out of scope)
               ***   ALTO information redistribution in overlay

        Information redistribution among peers in Tracker-based P2P
                                Application  Trackerless redistribution

   In a Trackerless overlay, peers obtain the ALTO information, then
   publish it via a P2P protocol (e.g., in a DHT).  Peers can also
   locate and retrieve ALTO information through the protocol.

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                   |            |
                   |    ALTO    |
                   |   Server   |
                   |            |
                          | (1) Query
                          |     and
                          |     Response
           ^      +------------------+    +-------------------+      ^
           ^      |                  |    |                   |      ^
           ^      |    Peer A        |    |     Peer B        |      ^
           ^      | (ALTO Client)    |    | (ALTO Client)     |      ^
           ^      +------------------+   +--------------------+      ^
           ^              * (2)                     *                ^
           ^              * Overlay redistribution  *                ^
           ^              ***************************                ^
                  ---   ALTO query and response protocol
                  ***   ALTO information searching and redistribution
                        by using P2P Protocol

     Information redistribution among peers in Trackerless P2P Overlay  Lookup in DHT

   When searching for a piece of data in a DHT, a node constructs an
   identifier for the desired data.  We propose here a simple naming
   scheme that can be used to lookup ALTO Information in a DHT.  This is
   provided as a suggestion for an implementation technique, and is not
   a requirement on redistribution implementations employing a DHT.

   Also note that the ALTO Information does not need to be included
   directly in the DHT.  A mechanism such as the Distributed Tracker
   implemented in Vuze [http://www.vuze.com] could be used to locate an
   ALTO Client that in turn provides access to the ALTO Information.

   This naming scheme allows redistribution of ALTO information
   requested using HTTP GET requests in [I-D.penno-alto-protocol] Since
   REST-style URLs are used, input parameters are included directly in
   the URL (along with ALTO Server hostname and port).  Thus, we compute
   a hash of the form:


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   where REQUEST_URL is the full HTTP URL that would have been used to
   request ALTO information from the ALTO Server directly.  The
   resulting string can be used as the lookup key in the DHT.

   The following simple examples show how the scheme applies to the
   Information Types in Section 3.2:

   1) Server Capability


   2) Full Network Map.


   3) Full Path Cost among all PIDs


5.  Acknowledgments

   The authors would like to give special thanks to Jan Seedorf and many
   others for the illuminative discussion in the mailing list.  The
   authors also thank David Bryan for providing comments on preliminary
   versions of the draft.

6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

              Seedorf, J. and E. Burger, "Application-Layer Traffic
              Optimization (ALTO) Problem Statement",
              draft-ietf-alto-problem-statement-04 (work in progress),
              September 2009.

6.2.  Informative References

              Penno, R. and Y. Yang, "ALTO Protocol",
              draft-penno-alto-protocol-04 (work in progress),

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              October 2009.

              Kiesel, S., Tomsu, M., Schwan, N., Scharf, M., and M.
              Stiemerling, "Third-party ALTO server discovery",
              draft-kiesel-alto-3pdisc-03 (work in progress), July 2010.

              Yongchao, S., Tomsu, M., Garcia, G., Wang, Y., and V.
              Avila, "ALTO Service Discovery",
              draft-song-alto-server-discovery-03 (work in progress),
              July 2010.

Authors' Addresses

   Gu Yingjie
   Baixia Road No. 91
   Nanjing, Jiangsu Province  210001

   Phone: +86-25-84565868
   Fax:   +86-25-84565888
   Email: guyingjie@huawei.com

   Richard Alimi
   Yale University

   Email: richard.alimi@yale.edu

   Roni Even

   Email: ron.even.tlv@gmail.com

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