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Network Working Group                                               Liufei. Wen
Internet Draft                           Huawei Technologies Network Working Group
Intended status: Informational                              Yunfei. Zhang
Expires: February 1, 2009                                         China Mobile

                                                            July 4, 2008



               P2P Traffic Localization by Traceroute and 2-Means Classification
                       draft-zhang-alto-traceroute-00.txt


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   This Internet-Draft will expire on February 1, 2009.

Copyright Notice

   Copyright (C) The IETF Trust (2008)

Abstract

   Most P2P system performance suffers from the mismatch between the randomly
   constructed overlays topology and the underlying physical network topology,
   causing a large burden in the ISP and a long RTT time. This document



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   describes how DHT overlay peers can interact with the routers by traceroute to
   get the path information, and execute 2-Means Classification, thereafter peers
   leverage the DHT itself to build efficient "closer" cluster. This scheme only
      requires the infrastructure to enable traceroute queries.

Conventions used in this document

   In examples, "C:" and "S:" indicate lines sent by the client and
   server respectively.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119.

Table of Contents


   1. Introduction................................................2
      1.1. Terminology..............................................3
   2. Overview......................................................4
   3. Traceroute and Clustering........................................4
      3.1. Peer Traceroute...........................................4
      3.2. 2-Means Classification....................................5
      3.3. Form the Cluster...........................................6
      3.4. Update...................................................7
   4. Enhancement Examples............................................7
      4.1. Find the proximate candidates...........................7
      4.2. More Efficient Overlay Routing..........................7
      4.3. Placement of Cache......................................7
   5. Security Considerations......................................8
   6. IANA Considerations.........................................8
   References.....................................................9
   Author's Addresses.............................................9
   Intellectual Property Statement.................................9
   Disclaimer of Validity........................................10

1. Introduction

   This document describes how DHT overlay peers get the topology
   information and reduce the mismatch by traceroute and 2-Means
   classification. In particular, an assumption is made about the
   infrastructure routers support peers' traceroute requests, no
   matter what specific means(ICMP traceroute or TCP traceroute).

   In a P2P system, each end node provides services to other
   participating nodes as well as receives services from them. An


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   attractive feature of P2P is that peers do not need to directly
   interact with the underlying physical network, providing many
   new opportunities for user-level development and applications.
   Nevertheless, the mechanism for a peer to randomly choose logical
   neighbors, without any knowledge about the physical topology,
   causes a serious topology mismatch between the P2P overlay networks
   and the physical networks.

   The mismatch between physical topologies and logical overlays is a
   major factor that delays the lookup response time, which is determined
   by the product of the routing hops and the link latencies. Mismatch
   problem also causes a large volume of redundant traffic in
   inter-domain between the every ISP. These has constituted the
   motivation to the topology-aware P2P, which implies to mitigate such
   drawbacks.

   The purpose of this document is to specify a way to efficient topology
   matching technique. The DHT overlay peers' Traceroute result are used
   to get "near" clusters and Edge Gateway by execute 2-Means
   classification. This information will be put into the DHT. Two peers
   will be considered as to hava a close neighbor relationship, if they
   have at least one coomon router among their "near" clusters and Edge
      Gateways.

1.1. Terminology

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",
   "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
   RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
   described RFC 2119 [RFC2119].

   This section defines some key concepts using in this document.

   DHT  - distributed hash table (DHT).

    DHT Overlay :  An overlay network is a computer network which is
      built on top of another network. The peer-to-peer networks are
      overlay networks because they run on top of the Internet. And the
  peer-to-peer network which build with DHT is DHT Overlay.

   2-means classification: k-means classification is an algorithm to
      classify objects based on their attributes into K number of group.
      2-means classification algorithm is a special example of k-means


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      classification algorithm with k=2.
2. Overview

  Usually, to solve the mismatch problem, it needs three steps, first
   to estimate the physical network distance between two overlay peers
   through network probing or prediction. then,  based on this proximity
   information , to cluster "near" peers, so as to let peers can find a
   better candidate than the randomly chosen result. At last, such
   results are utilized to optimize P2P alogrithm. The "near" peers are
   the preferential choice in P2P lookup and maintenance, and these will
   impel the access and traffic localization and reduce delay.

   +-------------------------------------------------------------+
   |                    |                     |                  |
   |      Measure&      |     Clustering      |  Impelled local  |
   |      Predict       |                     |  access pattern  |
   |                    |                     |                  |
   +-------------------------------------------------------------+

    Figure 1 Basic Steps of P2P Traffic Localization

    In this document, an efficient topology matching technique is
    specified. First, before a peer joining the P2P networks, it
    randomly picks an Internet IP address and probes it using the
    traceroute tools. According to the measured data, the peer tracked
    the return information to a vector data. Then 2-means classification
    algorithm is used to classify the Internet routers into "near" and
    "remote" routers. Finally, peer chose the router with maximum Hops
    item in "near" set as a the Edge Gateway. The peer registers into
    the DHT overlays with the Edge Gateway the Key, then do same to the
    "near" set. Through shared vector cluster information such as "near"
    routers cluster and Edge Gateway, two peers were considered as a
    close neighbor relationship when their "near" routers cluster both
    had a same router's IP address at least and then gathered together
       to form a "close" peer clusters.

3. Traceroute and Clustering

3.1. Peer Traceroute

   As a rapid developed network, the Internet presents two kinds of
    basic characteristic. On one hand, with many end user hosts randomly
    join and leave the network, the topology of Internet is dynamic and
    variable,  but the routers constitute a much more stable


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    infrastructure topology. On the other hand, regarding Internet as a
    graph (V=routers, E=direct link between routers), we found that the
    edges between ASes constitutes a very small portion among the total
    edges, and usually the delay between ISP routers is more large than
    the delay between routers in the same AS domains.


   A peer need randomly picked an Internet IP address and probed it
    using the traceroute tools.  The peer tracked the return information
    to a vector data, with the data structure <IP, Hops, Latency>.

       5ms  10ms    100ms    6ms    150ms   20ms  8ms
      R1--R2---R3----------R4--R5----------R6---R7--R8
           Fig.2 The Traceroute Result

    Fig.2 is an example of path information by R1 traceroute to R8. As
    is clear from Fig.2, between the R3 and R4, R5 and R6, there are
    some huge latency leaps than the others. It possibly means that
    traceroute message across the different AS domains or different ISP
    ranges.
3.2. 2-Means Classification

   When the overlay peer gets the traceroute result through randomly
    probe, a 2-means classification algorithm is used to classify the
    Internet routers based on the Latency attribute in these traceroute
    result. The 2-means classification algorithm includes four steps as
    following:

    step1. Peer chooses the minimum latency item and maximum latency item
    in whole vectors as centroids for two initialization sets "first"
    and "second".

    As a example in Fig.2, <R1, 1, 5ms> and <R5, 5, 150ms> is selected
    as centroids for sets "first" and "second".

    step2. Peer takes the latency item in vector to make an absolute
    distance value with two centroids in turn, and then separately
    associated the corresponding vector to one vector cluster that has
    smaller absolute distance value.

    So for the Fig2. example, the vector of R2 is <R2, 2, 10ms>, and the
    distance between R2 and R1 is 10-5 = 5, and the distance between R2
    and R5 is 150-10 = 140. So <R2, 2, 10ms> belongs to the "first" set.


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    step3. Peer calculates the latency mean and variance value of two
    vector clusters. As in in Fig.2, the R1,R2,R4,R6,R7 belong to the
    "first" set, and R3,R5 belong to the "second" set and the mean and
    variance can be calculated.

    step4. If the variance value was larger than the threshold, peer
    picks two latency mean values as new centroids of "first" and
    "second" sets, then goto step2, otherwise finishes the classification
   and gets two "first" and "second" sets.

   Finally, peer chooses the router with minimum Hops item in "second"
    set as a hop threshold. This router and the other routers whose Hops
    item are larger than the hop threshold all divided into a "remote"
    router cluster. And then the remaining routers are gathered into
    another "near" cluster. and the router with maximum hops of the
    "near" cluster is regarded as overlay peer's Edge Gateway.

    So for the Fig.2 example, R1,R2,R3 are the "near" routers of overlay
    peer and others routers are the "remoter" routers of the overlay
    peer. R3 will be the Edge Gateway in this case.


3.3. Form the Cluster

   The peer registers into the P2P overlays with their Edge Gateway
    and "near" routers as the Key, and the DHT ID and IP of itself as
    the value.Due to the essence of DHT, if two item have the same Key,
    they will be routed to the same DHT peer. Thus it makes possible to
    let several peers to know each other, if they have some common
    elements of their "near" router set. Edge Gateway is more useful,
    so if the hosting DHT peers become overloaded, it will firstly
    deletes such non Edge Gateway routers item. The hosting DHT peer
    will notify those peers to form a "close" cluster, or join an
    existed cluster.

    Each peer clusters has a ClusterId generated by consistent hashing
    when the first two peers decided to form the cluster. The ClusterId
    and its member peer Ids will be PUT into the DHT, and the peer can
    find the other members within the same cluster by DHT GET with its
    ClusterId remembered during its last online life.





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3.4. Update

   During normal peer-to-peer interactions such as DHT lookup or
    maintenance, if peers belonging to different clusters found the
    delay between them were relatively low, then these two clusters
    should decide to combine a new bigger cluster. The mapping between
    those original ClusterIds and the new generated ClusterIds should
    also be registered into the DHT so as to let those peers belonging
    to old clusters could find and join the new cluster. This technique
    alleviates the problem occurred when peers belonging to same
    cluster get different Edge Gateways from their traceroute response,
       thus they can not form the ideal bigger cluster.

4. Enhancement Examples

4.1. Find the proximate candidates

   Peers register their resources to be shared as <Key, Value> pairs
    into the DHT. Usually the Key is generated by consistent hashing
   some information like the file name, and the Value is the IP address
   of the sharing peer. When use our scheme, we will also include the
    sharing peer's ClusterID in the Value.

    When a overlay peer wants to find a resource, it will raise a DHT
    get with the hashed Key and piggyback its ClusterID.  When getting
    the request, the peer hosting the Key k will check the list of <Key,
    Value> pairs registered by all the sharing candidates, then it will
    choose the sharing peer with the same ClusterId to be the preference
   result.

4.2. More Efficient Overlay Routing

   The delay between the ISP is larger more than the inner-domain delay.
    And if AS domain is big enough many resource can be found in the
    same AS domains. So a more efficient hierarchical P2P network is
    feasible. Each low layer (local) DHT is composed by the peers with
    same ClusterID. All the peers or some candidate peers from each
    local DHT will join the global DHT. Every peer firstly search in
    its local DHT for its desired resource, then it may switched to the
   glocal DHT only if the resource not available locally.

4.3. Placement of Cache

   In order to reduce the inter-domain traffic and delay, cache is


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    always considered in the P2P network. The placement strategy takes
    the cluster info into account. It will place caches to cover the
    peer clusters in the order of its population, the number of peers
    participating the cluster.

5. Security Considerations

   This document does not currently introduce security considerations.
6. IANA Considerations

   This document does not specify IANA considerations.




































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References

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

   [2]IFIP Networking 2008, Guangyu Shi, Youshui Long. "T2MC: A Peer-to
                           -Peer Mismatch Reduce Technique by Traceroute
                          and 2-Means Classification Algorithm."

Author's Addresses

   Yunfei Zhang
   China Mobile Communications Corporation

   Phone: +86 10 66006688
   Email: zhangyunfei@chinamobile.com


   Wen liufei
   Huawei Technologies Co. Ltd.

   Phone: +86 755 28977571
   Email: wenliufei@huawei.com


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Acknowledgment

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   Internet Society.























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