1. RFC 6875
Internet Research Task Force (IRTF)                             S. Kamei
Request for Comments: 6875                            NTT Communications
Category: Informational                                        T. Momose
ISSN: 2070-1721                                            Cisco Systems
                                                                T. Inoue
                                                            T. Nishitani
                                                      NTT Communications
                                                           February 2013

  The P2P Network Experiment Council's Activities and Experiments with
         Application-Layer Traffic Optimization (ALTO) in Japan


   This document describes experiments that clarify how an approach
   similar to Application-Layer Traffic Optimization (ALTO) was
   effective in reducing network traffic.  These experiments were
   performed in Japan by the P2P Network Experiment Council in an
   attempt to harmonize peer-to-peer (P2P) technology with network
   infrastructure.  Based on what was learned from these experiments,
   this document provides some suggestions that might be useful for the
   ALTO architecture and especially for application-independent ALTO-
   like server operation.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Research Task Force
   (IRTF).  The IRTF publishes the results of Internet-related research
   and development activities.  These results might not be suitable for
   deployment.  This RFC represents the individual opinion(s) of one or
   more members of the Peer-to-Peer Research Group of the Internet
   Research Task Force (IRTF).  Documents approved for publication by
   the IRSG are not a candidate for any level of Internet Standard; see
   Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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Copyright Notice

   Copyright (c) 2013 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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   (http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Background in Japan  . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  P2P Traffic  . . . . . . . . . . . . . . . . . . . . . . .  4
     2.2.  Impact on Network Infrastructure . . . . . . . . . . . . .  4
     2.3.  Overview of the P2P Network Experiment Council . . . . . .  5
   3.  Objectives of the P2P Network Experiment Council . . . . . . .  6
   4.  Details of the Experiment  . . . . . . . . . . . . . . . . . .  7
     4.1.  Dummy Node . . . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Hint Servers . . . . . . . . . . . . . . . . . . . . . . . . .  9
   6.  High-Level Trial Results . . . . . . . . . . . . . . . . . . . 13
     6.1.  Peer Selection with P2P  . . . . . . . . . . . . . . . . . 13
     6.2.  Peer Selection with the Hint Server  . . . . . . . . . . . 13
   7.  Considerations . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.1.  Next Steps . . . . . . . . . . . . . . . . . . . . . . . . 14
     7.2.  Feedback to the ALTO WG  . . . . . . . . . . . . . . . . . 15
       7.2.1.  Hierarchical Architecture for ALTO Servers . . . . . . 15
       7.2.2.  Measurement Mechanism  . . . . . . . . . . . . . . . . 15
   8.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   9.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 16
   10. Informative References . . . . . . . . . . . . . . . . . . . . 16

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1.  Introduction

   An overlay network, which is used by P2P and other applications,
   offers the advantage of allowing flexible provisioning of services
   while hiding the lower-layer network.  The disadvantage is that
   inefficient routing without considering the lower-layer network may
   cause increasing the network load.  Several proposals have been made
   to build an overlay network that takes into account the information
   about the lower-layer network [1] [2].  Since the management of the
   Internet is highly distributed, it is difficult to implement such
   proposals, and thus to optimize a network, without the cooperation of
   network providers.

   Recently, the controversy between the overlay network and the network
   providers about network resource wastefulness has been rekindled.
   Under these circumstances, some researchers have studied overlay-
   network control technology that takes into account the network
   topology information obtained from network providers.

   One research effort regarding this issue were experiments planned and
   performed by the P2P Network Experiment Council in Japan.  This
   document reports on these experiments and the issues they addressed.

   These experiments were performed from 2007 to 2008, because P2P
   traffic decreased after Japanese copyright law was revised.  While
   more recently, the dominant traffic in Japan, the United States, and
   elsewhere has been HTTP-based flash streaming, a large amount of
   traffic in Asia (outside Japan) is still P2P traffic, like P2P
   streaming [3], and P2P technology is very useful in such a real-time
   streaming area.

   Our experience in this experiment might be useful for ALTO
   architecture, especially for application-independent and multi-
   application ALTO-like server operations.  We suggest that a generic
   measurement mechanism is important because each application has
   different mechanism, which makes it difficult to compare their

   This document is a product of the P2P Research Group (RG).  The views
   in this document were considered controversial by the P2P RG, but the
   RG reached a consensus that the document should still be published.

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2.  Background in Japan

2.1.  P2P Traffic

   As of 2008, the world's most popular P2P file-sharing application,
   BitTorrent, was not widely deployed in Japan.  Instead, other file-
   sharing P2P applications specific to Japan, such as Winny [4] and
   Share [5], still account for 40% of the Internet traffic in Japan,
   even though many those P2P users were arrested for sharing illegal
   files with these P2P applications.

   Each P2P file-sharing application has a unique protocol and none have
   a large market share, therefore making it hard to control them

2.2.  Impact on Network Infrastructure

   One advantage of using P2P technology for content delivery is that
   peers exchange content directly among themselves without server
   bottleneck.  This reduces the load on servers.  Also, P2P
   applications can reduce upstream traffic from an origin content
   server.  This reduces server cost dramatically.

   It is also known that server cost could be reduced with P2P
   technology.  However, the story is quite different for network
   providers.  From the viewpoint of network providers, the traffic that
   content servers generate has shifted to the edge network and the
   amount of traffic has not necessarily been reduced by using P2P
   technology for reducing server cost.  Another problem for network
   providers is that extremely inefficient routing may be selected
   because overlay network systems are configured without any regard to
   the structure of the lower-layer network or network geometry.

   In some cases, the total amount of traffic on the Internet used to be
   limited by the capacity of servers.  For those cases, P2P technology
   can improve the scalability of servers; however, it may exhaust
   network resources.  Moreover, using P2P applications remarkably
   increases the volume of traffic per user.

   Faced with an increase in the load on network infrastructure, network
   providers are compelled to take actions to overcome the sudden
   increase in facilities' costs.  Representative actions include
   placing content in Internet Exchanges (IXs) or data centers,
   introducing bandwidth control, and raising access fees [6].

   As mentioned above, the dominant traffic currently in Japan, the US,
   and elsewhere, is HTTP-based flash streaming.  However, a large
   amount of traffic in Asia (outside Japan) is P2P traffic, like P2P

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   Streaming [3], and P2P technology is very useful in such real-time
   streaming.  The increase in traffic arising from such a shift may be
   a great threat to the network.

2.3.  Overview of the P2P Network Experiment Council

   In order to reduce Internet traffic and encourage legitimate use of
   P2P technologies, in 2006 the Japanese government established a new
   council called the P2P Network Experiment Council, in conjunction
   with commercial P2P application vendors and ISPs.

   The council developed regulations that include guidelines such as
   giving advance notice to heavy users before restricting their
   bandwidth.  In accordance with the regulations, some ISPs introduced
   solutions that reduce traffic caused by P2P file-sharing

   In addition, the council, along with ISPs, carriers, contents
   providers, and P2P system vendors, looked for new ways to control
   traffic by commercial P2P applications.  In this work, the council
   performed experiments that introduced an ALTO-like system and
   observed how the traffic was reduced when it was redirected to proper
   peers on the real Internet in Japan.

   In our experiment, the council deployed hint servers, which are
   described in Section 5.  Hint servers run a protocol that offers
   network distances to peers, and these distances are disclosed to P2P
   application vendors.

   Using hint servers, P2P application vendors can introduce ALTO
   concepts easily into their P2P distribution systems.  Because the
   protocol used by hint servers, as defined by the council, is
   independent of specific P2P application vendors like BitTorrent.  The
   protocol needs to gather network information from ISPs so it can
   provide network distance to peers.  However, many ISPs dislike
   disclosing such information to others.  Therefore, hint servers are
   designed to offer little information about an ISP's network
   architecture to P2P application vendors.

   To monitor the traffic of peers, the council also deployed a dummy
   node, which is described in Section 4.1.

   The remainder of this memo provides an overview of the experiments.

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3.  Objectives of the P2P Network Experiment Council

   The Japanese Ministry of Internal Affairs and Communications, which
   has jurisdiction over information and communication systems in Japan,
   held meetings of an advisory panel on network neutrality in 2006 and
   2007 in order to study issues related to next-generation networks,
   such as how to ensure fairness in the use of networks and how to
   define fairness in the cost burden.  The panel took an interest in
   P2P technology as a solution to the impending traffic saturation in
   the backbone network resulting from the rapid expansion of broadband
   access in Japan, and it formed a "Working Group on the P2P Network",
   which carried out an intensive study of P2P networks.

   The working group reported that it would be necessary to undertake
   the following four activities, which are intended to encourage the
   government to adopt relevant policies [7]:

   o  Formulate guidelines on P2P file-delivery applications to be self-
      imposed by the industry.

   o  Promote feasibility tests of P2P networks.

   o  Study the current state of traffic control and promote the sharing
      of information.

   o  Hold working group meetings about traffic control.

   The first two proposals led to the establishment of the P2P Network
   Experiment Council, supported by the Japanese Ministry of Internal
   Affairs and Communications [8] [9].  The Council, with membership
   from P2P delivery providers, content holders, and network providers,
   began a variety of delivery experiments, which were expected to
   strengthen cooperative control between different layers.  In contrast
   to P4P (Proactive Network Provider Participation for P2P), which
   takes a relatively top-down approach of adopting an architecture
   based on a proposal from a university, the Council is characterized
   by its bottom-up approach.  The aim of establishing the Council was
   described as follows (translated from [10]).

      The rapid growth of broadband access enables content delivery
      systems to deliver high-quality and high-volume videos securely
      and efficiently.  Although P2P technology is an effective
      technology for this requirement, it still has some issues to be
      coped with.  Therefore, the "P2P Network Experiment Council" was
      established with the support of the Japanese Ministry of Internal
      Affairs and Communications, with its secretariat set up within the

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      Foundation for MultiMedia Communications (FMMC), in order to
      formulate guidelines for providers and conduct feasibility tests
      so that users can receive video delivery services safely.

   The activities of the P2P Network Experiment Council can be
   classified into two categories.  The first is formulating guidelines
   for promoting the commercial use of P2P technology.  These guidelines
   will enable users to use P2P technology safely and will give
   providers clear rules they must observe.  The second is feasibility
   testing of P2P technology.  Section 4 describes experiments conducted
   in 2007 and 2008.

4.  Details of the Experiment

   The Council investigated data offered by the members of the Council
   and learned that the server cost could be reduced by using P2P
   technology for content delivery.  For example, the data from the
   vendors showed the following:

      Traffic was reduced by 90% with UGLive by Utagoe, Inc. [11].

      The cost of delivering to tens of thousands of subscribers was
      reduced by 80% with BBbroadcast with TV Bank Corp. [12]

   On the other hand, these reduced server costs may have affected the
   network load.  One of the goals of our experiments was to visualize
   the impact and propose an architecture to reduce network load caused
   by these new technologies.

   In order to visualize the reduction of network cost, we modeled P2P
   applications and a multi-ISP environment.  This model was also needed
   for visualizing the effectiveness of the ALTO-like approach.

4.1.  Dummy Node

   As mentioned above, while the effect of using P2P technology to
   reduce the traffic and the load on servers is well known; however,
   traffic behavior in the inter-ISP area is not known.  In Japan, the
   ISPs and IXes cooperated to create a backbone traffic report [13].
   However, the measurements gathered for that report required capturing
   packets on subscribers' lines in order to determine the end users'
   activities.  It is not realistic to measure the behavior of P2P
   applications at user terminals connected to the Internet because that
   would require a large-scale arrangement for measurement, such as
   using deep packet inspection (DPI) on aggregated lines.

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   To solve these problems, we put several nodes called 'dummy nodes' in
   the ISP's networks.  The dummy nodes emulate an end user's PC running
   P2P applications.  Every P2P node provided by participating vendors
   in the experiment was configured so it always contacted the hint

   By introducing dummy nodes and measuring the traffic on them, we were
   able to observe and evaluate how much the P2P applications affected
   the networks.  Since this method can't measure every subscriber's
   traffic, the accuracy is less than other methods.  However, using
   dummy nodes makes it possible to adapt to situations in which many
   different P2P applications coexist on a network.  We decided that
   using dummy nodes was suitable for these experiments.

   A dummy node consisted of an Intel PC server running Linux (CentOS),
   VMWare, and Windows XP on VMWare.  With this configuration, all
   packets can be captured without any impact on the behavior of the
   network, nodes, or applications.  Also, this configuration enabled us
   to use different P2P applications for Windows and evaluate them

   To see behaviors of the node, incoming and outgoing packets are
   captured on Linux because every packet is transmitted through it.  To
   see flow information in these experiments, we captured the source and
   destination addresses, port number, amount of traffic, and start and
   end times.

   We placed 60 dummy nodes on access networks of 40 different ISPs.
   They were placed as close as possible to the subscriber in each

   ||| P2P Application  |||
   |||    Windows XP    |||
   |||        +--+      |||
   ||+--------|N |------+||
   ||  VMware |e |       ||
   |+---------|t |-------+|
   |   Linux  |IF| capture|
   +----------|  |--------+

                           Figure 1: Dummy node

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5.  Hint Servers

   Since fiber to the home (FTTH) has rapidly spread all over Japan,
   bottlenecks in IP networks have been shifting from access networks to
   backbone networks and equipment, such as bandwidth between ISPs and
   capacity in IXs.  Under these circumstances, the Council proposed
   less restrictive and more flexible cooperation between ISPs than
   existent P4P experiments [14].  The proposed method consists of the
   following elements: (1) P2P clients, (2) P2P control servers, and (3)
   a hint server (specifically, a peer selection hint server).  P2P
   clients and control servers are existing systems, but whether the P2P
   control servers exist is application dependent.  The hint server is a
   server that provides a hint for peer selection and plays a role
   equivalent to that of the ALTO server.  Note that this proposal was
   based on results of experiments using dummy nodes.  The results
   showed that it was possible to reduce unnecessary traffic that flows
   across the boundaries of geographical districts or ISPs by providing
   information about the physical network to P2P applications.

   When a peer joins the network, it registers its location information
   (IP address) and supplementary information (line speed, etc.) with
   the hint server.  The hint server calculates the network distance
   between peers (P2P clients) based on network topology information
   obtained from the ISP and generates a priority table for peer
   selection.  The hint server returns the table to the peer.

   If all information is public, the above procedure can produce results
   that are nearly optimal.  However, some information held by ISPs is
   often confidential.  Also, in some cases, the volume of calculation
   required to process all information can be excessive.  To avoid these
   problems, the plan is to conduct experiments with a limited set of
   functions, analyze the results, and gradually expand the scope of

   A control mechanism that makes use of all possible information is
   difficult not only technically but also because it requires
   coordination among providers.  In light of these difficulties, the
   council has been limiting the implementation and experiments to the
   technical scope.

   Figure 2 shows an outline of the hint server.

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   +---------+   GetLocation    +-------------GeoIP DB Server---------+
   |         |  +-----------+   |   +----------+      +-----------+   |
   |         |--|IP Address |-->|   | GeoIP DB |      |BGP daemon |   |
   |         |  +-----------+   |   +----------+      +-----------+   |
   |         |                  | +-------------+  +----------------+ |
   |         |  +-----------+   | |  District   |  |    Routing     | |
   |         |--|AS Code:   |---| | Information |  |Information(BGP)| |
   |         |  |Regional   |   | |             |  |                | |
   |P2P Peers|  |Information|   | |   Range of  |  |AS Code(origin) | |
   |   or    |  +-----------+   | | IP Addresses|  |                | |
   | Control |                  | +-------------+  +----------------+ |
   | Server  |                  +-------------------------------------+
   |         |                                  |      ^
   |         |  PeerSelection                   v      |
   |         |  +-----------+   +--------------------------------------+
   |         |--|IP Address |-->| +--Priority Node Selection System--+ |
   |         |  |    List   |   | |                                  | |
   |         |  +-----------+   | |     Peer Candidate Ranking       | |
   |         |  +-----------+   | |                                  | |
   |         |--|  Ranking  |-->| +----------------------------------+ |
   |         |  +-----------+   +--------------------------------------+

                 Figure 2: Hint server for peer selection

   The network information used by the hint server is not information
   solicited from individual ISPs but is the Autonomous System (AS)
   number and district information, which are more or less public
   already.  Routing tables are not generated.  Instead, peers within
   the same ISP or the same district are selected with higher priority
   in order to confine traffic to within the same ISP or the same

   When the hint server receives an IP address, it returns its attribute
   information, in order to confine the traffic to within the nearer ISP
   or district.  A peer can select another based on the returned
   information.  This operation is called GetLocation.  However, in
   preparation for the time when it becomes necessary to hide topology
   information, an interface is provided through which a priority order
   is returned in response to an input of a list of candidate peers.
   This operation is called PeerSelection.

   Although the target node is selected based on the criterion that it
   is within the same ISP or the same district, this type of selection
   is not very effective if the number of participating peers is small.
   Table 1 shows the percentage of peers within the same AS or the same
   prefecture calculated from the distribution of ASes and prefectures
   in the IP address space from one-day data on a Winny network.

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                    | Conditions         | Percentage |
                    | AS matches         |    6.70%   |
                    | Prefecture matches |   12.76%   |
                    | Both match         |    2.09%   |
                    | Neither match      |   78.45%   |

                 Table 1: AS and prefecture distributions

   Because, in addition to the above, the presence or absence of content
   affects the results, controlling peer selection within the same
   district may be inadequate.  Therefore, it is necessary to introduce
   the weight of a continuous quantity that reflects the physical
   distance or the AS path length as an indicator of the proximity of
   the areas involved.

   In consideration of this, the following two measures are used to
   evaluate the proximity of peers in a hint server.

   o  AS path length (distance between ISPs)

      AS path length is calculated from BGP full routes.  Since a full
      routing table retrieved at an ISP can show only a best path, it
      may not get an accurate length if the AS hop count of both ISPs is
      too large.  To avoid this, we use BGP information received from
      different ISPs and combine them.  Based on this concept, we used
      BGP routing information offered by three ISPs operated by big
      telecommunication couriers and made a topology tree.  Then, we
      were able to calculate the shortest path between two given ASes.

   o  Geographical distance

      Distances between peers are measured using the physical distance
      between the capitals of the prefectures to which the peers belong.
      Distances between prefectural capitals are sorted into ascending
      order, and then into bands, with weights 1 to 15 assigned to them
      so that each band contains roughly the same number of "capital
      pairs".  If either of the peer's locations is indefinite, the
      distance is equal to 15; if they are in the same prefecture, the
      distance is equal to 0.

      Evaluation of distances between peers showed that the distribution
      of distances was almost uniform when distances between peers are
      normalized.  This result suggests that using normalized distances

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      expands the area where the control by a hint server is effective.
      The geographical distance is used only when the AS path length is
      the same between some candidates.

   An example of the request and the response follows.

   o Request

      POST /PeerSelection HTTP/1.1
      Host: ServerName
      User-Agent: ClientName
      Content-Type: text/plain; charset=utf-8

      v=Version number
      [application=Application identifier]
      ip=IP address of physical interface
      port=Port number of physical interface
      [nat_ip=Global IP address using UPnP]
      [nat_port= Global port number using UPnP]
      [trans_id=transaction ID]
      [pt=Flag of port type]
      [ub=upload bandwidth]
      [db=download bandwidth]

   o Response

     HTTP/1.1 200 OK
     Date: Timestamp
     Content-Type: text/plain; charset=utf-8
     Cache-control: max-age=max age
     Connection: close

     v=Version number
     server=hint server name
     trans_id=transaction ID
     pt=Flag of port type
     client_ip=Peer IP address observed from server
     client_port=Peer port number observed from server
     numpeers=number of responding peers
     n=[src address] dst address / cost / option

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6.  High-Level Trial Results

6.1.  Peer Selection with P2P

   Table 2 shows the result of the analysis of communication in a node
   of an ISP in Tokyo, as an example of measurement results.

   In these two experiments, we evaluated different P2P applications.
   In the first experiment, the P2P topology was generated by a tree
   algorithm; in the second experiment, it was generated by a mesh
   algorithm.  Both resulted in similar performance.

   | Conditions                              | Experiment | Experiment |
   |                                         |      1     |      2     |
   | Peers selected within the same ISP      |     22%    |     29%    |
   |                                         |            |            |
   | Peers selected within the same district |     19%    |     23%    |
   |                                         |            |            |
   | Peers selected within the same district |     5%     |     7%     |
   | and the same ISP                        |            |            |

         Table 2: Percentage of communication within the same ISP

   Table 2 shows that the probability of communication with peers in the
   same ISP is proportional to the population size and the share of the
   ISP in each district.  The data show that peers were selected at
   random.  Note that the vendor of a P2P application used in these
   experiments demonstrated that the mechanism for selecting a peer
   using network information can be implemented.  However, peer
   selection is normally based on past information because users often
   cannot actually perceive the effect of using network information.

6.2.  Peer Selection with the Hint Server

   The main objective of these experiments was to verify the operation
   of the hint server and P2P applications.  The distances between a
   dummy node and a peer were obtained from data on the dummy nodes.  An
   examination of the distances between a dummy node and a peer revealed
   that the mean value of distance after the hint server was introduced
   was reduced by 10% and that the 95th percentile was reduced by 5%.
   The results show that introducing a hint server can reduce the
   network loads that result from P2P applications.

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7.  Considerations

   We clarified the following during our experiments.

   1.  Dispersed dummy nodes can determine the behavior of peers and
       traffic between inter-ISP networks and can determine the peer
       that each peer selects.  Therefore, this result proves the
       importance of the peer-selection control mechanism that is
       proposed by ALTO.

   2.  Using our peer-selection control mechanism, called hint servers,
       can result in significant differences.  Hint servers can lead
       each peer to select a closer peer.

   3.  The 10% reduction of network cost is not satisfactory for ISPs,
       but the controllability of P2P applications is the most important
       point.  When ISPs apply this mechanism to their real networks,
       they will set a very large cost for the most expensive network

   In the experimental results for peer-selection control, the selection
   is smaller in intra-ISP traffic than in other experiments [15].  We
   think this is because there are fewer peers in each area of traffic
   control.  When there are many peers in one ISP, it is easy to select
   peers in the same ISP.  However, when there are fewer peers in one
   ISP, it is difficult to select peers in the same ISP.  In our
   experiments, most of the ISPs had many peers in their networks, i.e.,
   there were a small number of ISPs that had few peers in their

   Moreover, we didn't force P2P vendors to limit their implementation
   policy; therefore, we observed differences in how each implementation
   weighs the information from the hint servers.  Specifically, in P2P
   applications when a tree topology is used, the hint-server mechanism
   is very effective; on the other hand, when a mesh topology is used,
   it less effective.

7.1.  Next Steps

   In recent research, we've changed to an ALTO-based communication
   protocol on hint servers because the requirements of ALTO are
   documented in RFC 6708 [16] and the ALTO protocol is a work in
   progress [17].  In our implementation, protocol identifiers (PIDs)
   and the cost value are mapped to ISP subnets and to ISP distance,
   respectively.  We also implement services for compatibility required
   by ALTO such as Map Services and Endpoint Cost Service.  The Endpoint
   Cost Service (defined in [17]) is mainly used because of backward
   compatibility with our experiments.

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   We are also studying a hierarchical structure of hint servers, in
   order to control traffic at a coarse level (in inter-ISP areas) and
   at a finer level (in intra-ISP areas).  It is also effective for
   limiting the areas where information is disclosed.

7.2.  Feedback to the ALTO WG

   This section describes what the authors learned from these
   experiments that might be useful to the ALTO WG.

7.2.1.  Hierarchical Architecture for ALTO Servers

   In our experiments, we present the possibility of traffic control
   among multiple ISPs and multiple P2P applications using an ALTO
   mechanism.  We found several problems when ISPs try to adopt the
   mechanism.  One is the granularity of network information from
   Council members.  Among inter-ISP areas, it is relatively easy to
   handle information for public purposes by using BGP full routes.  On
   the other hand, among the intra-ISP areas, it may be difficult to
   disclose the private information of each ISP.  Kiesel [18] proposes
   some modifications for the ALTO protocol in order to hide ISP
   information.  We propose hierarchical structures.  From the viewpoint
   of cooperation between ISPs, fine-grained information is not
   necessarily required.  Moreover, it is difficult to exchange the
   fine-grained information between ISPs.  Considering this situation,
   we used only coarse-grained information to control backbone traffic
   in these experiments; however, in the future, there may be a demand
   for controlling traffic within an ISP using fine-grained information.
   Therefore, we decided to introduce hierarchical structures into ALTO
   in order to cope with both situations.  Actually, adopting a
   hierarchical control mechanism that includes the following two steps
   will be useful.

   o  First, use coarse-grained information about whole the network to
      select ISPs.

   o  Second, use fine-grained information within the ISP to select a

7.2.2.  Measurement Mechanisms

   In these experiments, there were two difficulties as follows.

   o  Evaluating the effect of introducing a hint server was difficult
      because the P2P applications had their own measurement mechanisms.

   o  How to treat the priority order of peers suggested by a hint
      server could not be predetermined for P2P applications.

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   From these experiences, the authors consider that clarifying the
   requirements about measurement mechanisms for P2P applications is
   necessary in ALTO.

8.  Security Considerations

   This document does not propose any kind of protocol, practice, or

9.  Acknowledgments

   The P2P Network Experiment Council was established thanks to strong
   support by the Japanese Ministry of Internal Affairs and
   Communications.  These experiments were performed with cooperation
   among the P2P Network Experiment Council members.  DREAMBOAT Co.,
   Ltd., Bitmedia, Inc., Utagoe, Inc., and Toyama IX have especially
   supported the analyses of the experiments.  The authors appreciate
   Tohru Asami, Hiroshi Esaki, and Tatsuya Yamashita for their
   constructive comments.

   The authors would also like to thank Martin Stiemerling, Stefano
   Previdi, and Vijay K. Gurbani for their comments on this document.

10.  Informative References

   [1]   Kawahara, R., Lua, E., Uchida, M., Kamei, S., and H. Yoshino,
         "On the Quality of Triangle Inequality Violation Aware Routing
         Overlay Architecture", INFOCOM 2009, pages 2761-2765.

   [2]   Li, Z. and P. Mohapatra, "QRON: QoS-aware routing in overlay
         networks", IEEE Journal on Selected Areas in
         Communications, Vol. 22, No. 1, January 2004.

   [3]   Sandvine, Inc., "Global Internet Phenomena Report: 2H 2012",
         September 2012,

   [4]   Wikipedia, "Winny", July 2012, <http://en.wikipedia.org/w/

   [5]   Wikipedia, "Share (P2P)", January 2013,

   [6]   Taniwaki, Y., "Broadband Competition Policy in Japan",
         March 2008, <http://unpan1.un.org/intradoc/groups/public/

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   [7]   Ministry of Internal Affairs and Communications, "Disclosure of
         the Report 'Working Group on P2P Networks'" (in Japanese),

   [8]   The Foundation for MultiMedia Communications, "The P2P Network
         Experiment Council" (in Japanese), 2007,

   [9]   Ministry of Internal Affairs and Communications, "P2P Network
         Experiment Council Symposium to Be Held", February 2008,

   [10]  The Foundation for MultiMedia Communications, "The Aim of P2P
         Network Experiment Council" (in Japanese), 2007,

   [11]  Shudo, K., "A Review of ALM Software in Practical Use", IRTF
         SAMRG (Scalable Adaptive Multicast Research Group)
         meeting, Proceedings of IETF 76, November 2009,

   [12]  TV Bank Corp., "Live Delivery Using 'BB Broadcast' Achieved a
         96% Saving in Traffic!" (in Japanese), October 2008,

   [13]  Cho, K., Fukuda, K., Esaki, H., and A. Kato, "The Impact and
         Implications of the Growth in Residential User-to-User
         Traffic", SIGCOMM '06, pages 207-218, September 2006.

   [14]  Xie, H., Yang, R., Krishnamurthy, A., Liu, Y., and A.
         Silberscatz, "P4P: Provider Portal for Applications", SIGCOMM
         '08, pages 351-362, 2008, <http://www.cs.yale.edu/homes/yry/

   [15]  Griffiths, C., Livingood, J., Popkin, L., Woundy, R., and Y.
         Yang, "Comcast's ISP Experiences in a Proactive Network
         Provider Participation for P2P (P4P) Technical Trial",
         RFC 5632, September 2009.

   [16]  Kiesel, S., Previdi, S., Stiemerling, M., Woundy, R., and Y.
         Yang, "Application-Layer Traffic Optimization (ALTO)
         Requirements", RFC 6708, September 2012.

   [17]  Alimi, R., Ed., Penno, R., Ed., and Y. Yang, Ed., "ALTO
         Protocol", Work in Progress, September 2012.

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   [18]  Kiesel, S. and M. Stiemerling, "ALTO H12", Work in Progress,
         March 2010.

Authors' Addresses

   Satoshi Kamei
   NTT Communications Corporation
   Granpark Tower 16F, 3-4-1 Shibaura
   Minato-ku, Tokyo  108-8118

   Phone: +81-50-3812-4697
   EMail: skame@nttv6.jp

   Tsuyoshi Momose
   Cisco Systems G.K.
   9-7-1 Akasaka
   Minato-ku, Tokyo  107-6227

   Phone: +81-3-6738-5154
   EMail: tmomose@cisco.com

   Takeshi Inoue
   NTT Communications Corporation
   Kuredo Hakushima Building 3F, 14-15 Higashihakushimacho
   Chuo-ku, Hiroshima-City, Hiroshima  730-0004

   Phone: +81-82-563-5030
   EMail: inoue@jp.ntt.net

   Tomohiro Nishitani
   NTT Communications Corporation
   1-1-6, Uchisaiwaicho
   Chiyodaku, Tokyo  100-8019

   Phone: +81-50-3812-4742
   EMail: tomohiro.nishitani@ntt.com

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  1. RFC 6875