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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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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