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Versions: 00 01 02                                                      
Network Working Group                                      Liufei. Wen
Internet Draft                                     Huawei Technologies
Intended status: Informational                              Yunfei.Zhang
Expires: April 23, 2009                                     China Mobile
                                                      October 23, 2008

     P2P Traffic Localization by Traceroute and 2-Means Classification
                    draft-zhang-alto-traceroute-02.txt


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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 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




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   build efficient "closer" cluster. This scheme only requires the
   infrastructure to enable traceroute queries.

Table of Contents


   1. Introduction................................................2
      1.1. Terminology............................................3
   2. Overview....................................................3
   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.................................................6
   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......................................7
   6. IANA Considerations.........................................7
   7. Conclusions.................................................8
   8. References..................................................9
      8.1. Normative References....................................9
      8.2. Informative 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).This operation
   is reasonable for ISP in its network when it builds up a P2P overlay
   and provides measurement services for themselves or for clients which
   are defined in P2P SIP[3].

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



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   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 [1].

   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 builds 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
   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


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   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 tracks 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 chooses 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
    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>.





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          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[2]:

       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.

        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 finishs the
        classification and gets two "first" and "second" sets.



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        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.

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.







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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 global 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
   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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7. Conclusions

   This document 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.









































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8. References

8.1. Normative References

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

8.2. Informative References

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

   [3]  V. Pascual et.al," P2PSIP Clients",IETF draft, February 2008.

Author's Addresses

   Yunfei Zhang
   China Mobile Communications Corporation

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


   Liufei Wen
   Huawei Technologies Co. Ltd

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


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