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rfc:rfc6875

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

Abstract

 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
 http://www.rfc-editor.org/info/rfc6875.

Kamei, et al. Informational [Page 1] RFC 6875 P2P Experiments in Japan February 2013

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
 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.

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

Kamei, et al. Informational [Page 2] RFC 6875 P2P Experiments in Japan February 2013

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
 effectiveness.
 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.

Kamei, et al. Informational [Page 3] RFC 6875 P2P Experiments in Japan February 2013

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
 effectively.

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

Kamei, et al. Informational [Page 4] RFC 6875 P2P Experiments in Japan February 2013

 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
 applications.
 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.

Kamei, et al. Informational [Page 5] RFC 6875 P2P Experiments in Japan February 2013

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

Kamei, et al. Informational [Page 6] RFC 6875 P2P Experiments in Japan February 2013

    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.

Kamei, et al. Informational [Page 7] RFC 6875 P2P Experiments in Japan February 2013

 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
 server.
 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
 generally.
 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
 network.
 +----------------------+
 |+--------------------+|
 ||+------------------+||
 ||| P2P Application  |||
 |||    Windows XP    |||
 |||        +--+      |||
 ||+--------|N |------+||
 ||  VMware |e |       ||
 |+---------|t |-------+|
 |   Linux  |IF| capture|
 +----------|  |--------+
           +--+
                         Figure 1: Dummy node

Kamei, et al. Informational [Page 8] RFC 6875 P2P Experiments in Japan February 2013

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
 optimization.
 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.

Kamei, et al. Informational [Page 9] RFC 6875 P2P Experiments in Japan February 2013

 +---------+   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
 district.
 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.

Kamei, et al. Informational [Page 10] RFC 6875 P2P Experiments in Japan February 2013

                  +--------------------+------------+
                  | 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

Kamei, et al. Informational [Page 11] RFC 6875 P2P Experiments in Japan February 2013

    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={no|upnp|unknown}]
    [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
   ttl=ttl
   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

Kamei, et al. Informational [Page 12] RFC 6875 P2P Experiments in Japan February 2013

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.

Kamei, et al. Informational [Page 13] RFC 6875 P2P Experiments in Japan February 2013

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
     link.
 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
 networks.
 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.

Kamei, et al. Informational [Page 14] RFC 6875 P2P Experiments in Japan February 2013

 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
    peer.

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.

Kamei, et al. Informational [Page 15] RFC 6875 P2P Experiments in Japan February 2013

 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
 standard.

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,
       <http://www.sandvine.com/news/global_broadband_trends.asp>.
 [4]   Wikipedia, "Winny", July 2012, <http://en.wikipedia.org/w/
       index.php?title=Winny&oldid=500744660>.
 [5]   Wikipedia, "Share (P2P)", January 2013,
       <http://en.wikipedia.org/w/
       index.php?title=Share_(P2P)&oldid=532999898>.
 [6]   Taniwaki, Y., "Broadband Competition Policy in Japan",
       March 2008, <http://unpan1.un.org/intradoc/groups/public/
       documents/apcity/unpan040329.pdf>.

Kamei, et al. Informational [Page 16] RFC 6875 P2P Experiments in Japan February 2013

 [7]   Ministry of Internal Affairs and Communications, "Disclosure of
       the Report 'Working Group on P2P Networks'" (in Japanese),
       2007,
       <http://www.soumu.go.jp/menu_news/s-news/2007/070629_11.html>.
 [8]   The Foundation for MultiMedia Communications, "The P2P Network
       Experiment Council" (in Japanese), 2007,
       <http://www.fmmc.or.jp/P2P/about.htm>.
 [9]   Ministry of Internal Affairs and Communications, "P2P Network
       Experiment Council Symposium to Be Held", February 2008,
       <http://www.soumu.go.jp/main_sosiki/joho_tsusin/eng/Releases/
       Telecommunications/news080201_1.html>.
 [10]  The Foundation for MultiMedia Communications, "The Aim of P2P
       Network Experiment Council" (in Japanese), 2007,
       <http://www.fmmc.or.jp/p2p_web/aim.html>.
 [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,
       <http://www.ietf.org/proceedings/76/slides/SAMRG-6.pdf>.
 [12]  TV Bank Corp., "Live Delivery Using 'BB Broadcast' Achieved a
       96% Saving in Traffic!" (in Japanese), October 2008,
       <http://www.tv-bank.com/jp/20081031.html>.
 [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/
       projects/p4p/p4p-sigcomm08.pdf>.
 [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.

Kamei, et al. Informational [Page 17] RFC 6875 P2P Experiments in Japan February 2013

 [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
 Japan
 Phone: +81-50-3812-4697
 EMail: skame@nttv6.jp
 Tsuyoshi Momose
 Cisco Systems G.K.
 9-7-1 Akasaka
 Minato-ku, Tokyo  107-6227
 Japan
 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
 Japan
 Phone: +81-82-563-5030
 EMail: inoue@jp.ntt.net
 Tomohiro Nishitani
 NTT Communications Corporation
 1-1-6, Uchisaiwaicho
 Chiyodaku, Tokyo  100-8019
 Japan
 Phone: +81-50-3812-4742
 EMail: tomohiro.nishitani@ntt.com

Kamei, et al. Informational [Page 18]

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