1. ISSN: 2277 – 9043
International Journal of Advanced Research in Computer Science and Electronics Engineering
Volume 1, Issue 4, June 2012
Consistency Maintenance Of Continuous
Queries In Unstructured Overlay Networks
Annie Chacko,M.Sadish Sendil, DR. S Karthik
#
II ME/Department of Computer Science and Engineering
SNS College of Technology, Coimbatore
1
annievargh@gmail.com
*
Professor/Department of Computer Science and Engineering
SNS College of Technology, Coimbatore
2
sadishsendil@yahoo.com
#
H.O.D/Department of Computer Science and Engineering
SNS College of Technology, Coimbatore
3
kkarthikraja@yahoo.com
Abstract - Peer-to-Peer (P2P) systems offer an Some important concepts in P2P systems
alternative to client-server systems. The main objectives are: sharing resources, decentralization, and self-
of the P2P content distribution systems are to register organization. Resource sharing means that
for a long term presence in a network and to publish its applications cannot be set up by single node or single
own data to that network. These requirements can be
done by having some set of indexing and routing
entity. It is the sharing of resources of different nodes
techniques. For this solution, a sequence of approaches in a network.Decentralization means to avoid single
has been already proposed by the existing researches. point of failures and bottlenecks. Self organization
Researchers proposed unstructured overlay–based means, based on whatever local information is
publish subscribe system that offer the above objectives. available and interacting with locally.
But these approaches are not flexible for these systems The P2P overlay is the network consists of
and too complex.In order to solve this problem of all participating peers as network nodes. There are
flexibility and complexity proposing, an approach of links between any two nodes that know each other.
CoQUOS with consistency maintenance. The CoQUOS That is, if a participating peer knows the location of
approach is to support the continuous queries in
unstructured overlay networks. This approach
another peer in the P2P network then there is a
characterized by 5 novel techniques , namely cluster directed edge from the former node to the latter in the
resilient random walk algorithm, dynamic probability- overlay network. Based on how to each other, it can
based query registration scheme, develop efficient classify the P2P networks as unstructured or
schemes for providing resilience to the churn of the P2P structured.
network, fair distribution of the notification load among Structured P2P [2] network employ a
the peers and finally consistency maintenance globally consistent protocol to ensure that any node
mechanism. It achieves high efficiency in consistency can efficiently route a search to some peer that has
maintenance at a significantly low cost. the desired file , even if the file is extremely rare.
Keywords – Peer-to-peer networks,continuous queries,
And Unstructured P2P network is formed when the
publish-subscribe systems, random walks, consistency overlay links are established arbitrarily. Such
maintenance mechanism. networks can be easily constructed as a peer that
wants to join the network can copy existing links of
I. INTRODUCTION another node and forms its own links overtime.
A Peer-to-Peer (P2P) network [1] is a Unstructured P2P (such as Gnutella and
network, composed of a large number of distributed, Kazaa) have experienced tremendous growth in the
heterogeneous peers, and they are highly dynamic past decade, and it is based on content or resource
peers in which participants can share their own sharing. Simplicity of design and flexibility towards
resources. In P2P, the participants can act as a server node population are the attributes of the unstructured
and a client at the same time. They are directly P2P systems. A model for data sharing and discovery
accessible by other nodes, without passing in unstructured P2P called adhoc query model. It
intermediatory entities. does not support for peers to advertise or announce
the data items to other interested peers.Because of
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International Journal of Advanced Research in Computer Science and Electronics Engineering
Volume 1, Issue 4, June 2012
this limitation, it is inadequate for many advanced The continuous query model is a model that
P2P applications. So another systems called pub-sub is similar to publish-subscribe system. This model
(Publish –Subscribe) systems [6], is one of the provides a mechanism that peers can register their
possible approach to address the limitations of adhoc queries, which are maintained in the network for long
query model. durations of time. The continuous query model
The pub-sub system is a guaranteed provides a best effort of notification service for the
notification service so that the subscribers or confirmed queries that informing their source nodes
consumers to register their own interests in a of new content that may added to the former. So to
network. The alternate notification service of pub-sub implement this model, a middleware use called
system called continuous query model. To register CoQUOS.
the continuous query on a set of peers that are located
in various topological regions in the overlay. So the III. LIGHT WEIGHT SUPPORT FOR
replicas of query are formed to notify the respective CONTINUOUS QUERIES IN UNSTRUCTURED
source peers of matching advertisements that issued OVERLAY NETWORK
by other peers. But this approach is not flexible for
these systems and too complex. So in order to solve P2P are distribution systems that strongly
this problem of flexibility and complexity, proposing enforced by their adhoc content discovery
an approach of CoQUOS with consistency mechanisms. It have two capabilities such as
maintenance mechanism. Instead of passively mechanism be capable that peers to register their
accepting messages, this mechanism harmonically queries and receive the acknowledgements and peers
integrates file replication and consistency to advertise their content of information. These
maintenance file popularity is not uniform. capabilities are based on publish-subscribe systems.
It developing a paradigm of publish-subscribe
II. RELATED WORKS systems on top of unstructured P2P networks. For
these type of applications, another paradigm similar
2.1 Pub-Sub System to publish-subscribe systems called CoQUOS[5].This
CoQUOS provides best effort of notification
Pub-Sub system is called Publish – Subscribe guarantees. CoQUOS is a scalable and lightweight
systems [6], [7]. It is a system that promising for middleware. It supports continuous queries in
resource discovery in a distributed system. This pub- unstructured P2P networks. CoQUOS called
sub system also called producer –consumer system. It Continuous Queries in Unstructured OverlayS
can be described as: (1) Subscribers called network. A key strength of the CoQUOS system is
information consumers. The subscribers that express that, it can be implemented on any unstructured
their interests by subscribers that denote their own overlay network. Two important characteristics in
interests by specific subscriptions and register in the CoQUOS are: (1). It does not impose any topological
event based system. (2). Publishers called conditions on the P2P network and it does not
information producers. When publishers publish implement dependent module in any unstructured
events to the system, the system is responsible for networks.(2). The CoQUOS system is very
delivering the events to the corresponding lightweight, so it does not require complex index
subscribers. Decoupling is one of responsible fact for structures. So it preserves design simplicity and
the pub-sub systems. There are three types of flexibility of the unstructured overlay network.
decoupling in the pub-sub systems. (1).time Because of the light weight support of
decoupling, (2).space decoupling, and CoQUOS , it have two novel components, namely
3).synchronization decoupling. cluster resilient random walk algorithm [3] and
Pub-sub systems are mainly classified as dynamic probability based query registration.
two types: (1). Topic based. The topic based systems
are less flexible and lack of expressiveness.
(2).Content based. The content based systems are IV. DESIGN OF CoQUOS SYSTEM MODEL
more flexible for these systems , that allow the
subscribers to denote complex interests with the The goal of designing the CoQUOS system
corresponding predicates on a set of attributes. is to design an effective service notification on the
top of the unstructured overlay networks. CoOUOS
2.2 Continuous Query Model can act as middleware, so it strives stronger
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International Journal of Advanced Research in Computer Science and Electronics Engineering
Volume 1, Issue 4, June 2012
notification success rates for each individual query of depthfirst traversal of the network and it has high
the system. If a continuous query is registered at a probability than flooding based broadcast.
peer, that peer called the beacon node of the query.
The beacon nodes can discover new data through VII. DYNAMIC PROBABILITY ON THE BASIS
peer announcements. When a peer receives an OF QUERY REGISTRATION
announcement message, it checks all queries that are
registered and check any of the queries match the The above process won’t be able to notify how to
received announcement. receive a notification to register. Each and every peer
In this design, we consider peer receiving a query can decide to register with a fixed
announcement – based data item discovery by beacon probability. But it cannot guarantee high notification
nodes. The peer announcement is on the basis of TTL rates of each query. So the idea behind the of this
(Time to Live) value. The communication overheads scheme as follows: The probability of registering
of the system are small, so the TTL of the query at a peer node is high if it is not already
announcement of messages are set to very low registered.
values. A peer that needs to announce a new data
item creates an announcement message and sets the VIII. CHURN OVERLAY
TTL value and then sends the message to all
neighbors. Through the recipients receive the The information in nodes are entering and
message, decrement the TTL and send it to the leaving frequently in P2P overlay called churn
neighbors. This process is repeated until the TTL overlay. These affect success of the continuous
reaches to zero. This peer announcement exploring queries and announcements. The entering and leaving
some strategies such as iterative deepening and mechanism would affect the churn in the overlay. So
directed breadth first search. the churn overlay design as a low cost technique.
V. HOW BEACON NODES SELECT IX. LOAD BALANCING
The selection of beacon nodes has an important role The one of the important ingredients in the
on the notification of the success rates of a performance of COQUOS is the good load balancing.
continuous query. The selection can be done on the The metrics of load in CoQUOS are number of
basis of somekey features. First, the beacon nodes of continuous queries and numbers of notification sent
a query should be distributed in every major region of out per unit time by different nodes. These load
the network. Second, the beacon nodes of a query metrics are used due to variety of reasons such as
should not be located very close to each other. The topological characteristics of the network, skewed
COQUOS system is a completely decentralized announcement and query popularities, variation in the
technique that can use for the selection of beacon resource availabilities at peers or a combination of
nodes. So in this selection, a continuous query is these factors.
circulated in the network and each peer receives the
query and it decides whether to register or store the X. IMPLEMENTATION
query. The important feature of this is that each peer
makes a local decision regarding the registration. 10.1 Consistency Maintenance Mechanism
VI. IMPLEMENTING CLUSTER -RESILENT To solve the replication between the files in
RANDOM WALK the peers, an approach called consistency
maintenance mechanism. This mechanism can be
Implementation the random walk technique used to maintain the consistency of the frequently
is based on flooding-based broadcast. The idea of updated or even infrequently updated files.
implementing the random walk technique can be Consistency maintenance mechanism in turn aims to
summarized as follows: When a peer receives a guarantee file fidelity of consistency at a low cost
message and its TTL value is not expired, it selects with file replication dynamism consideration. It
one of its neighbors at randomly and forwards the ensures timely update operation and avoids
message to that peer. So, each step the message is unnecessary updates. As a result, it achieves high
forwarded to only one neighbor and the load impact efficiency. P2P systems are characterized by
is very low.Thus random walk corresponds to a
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International Journal of Advanced Research in Computer Science and Electronics Engineering
Volume 1, Issue 4, June 2012
dynamism, in which node join and leave 11. CONCLUSION
continuously and rapidly.
Fig. 1 shows an example for consistency Mechanisms that enable individual peers of
maintenance. The nodes C and G in the middle unstructured P2P content sharing networks are to
observed frequent queries for the file, and nodes J register longstanding queries and receive notification
and M queried for the file frequently. Therefore, they when new matching items can appear significantly,
made a copy of the file in themselves. The replica improve their utility and effectiveness. While the
nodes periodically check the query rate. When their pub-sub paradigm can provide this capability,
replicas are underutilized, they remove the replicas. implementing pub-sub systems on unstructured
For consistency maintenance, the replica nodes overlays is often a very complex endeavor. The
actively probe the file server for update. They probe continuous query paradigm studied in this, is similar
the server approximately at the rate of file change to pubsub, but it provides best-effort notification
rate. However, when their replica is visited at lower service and presented the design and middleware is
frequency than the file’s change frequency, they used for the evaluation of a lightweight system,
probe the server at the frequency that the replica is called CoQUOS, which supports continuous queries
visited. This strategy reduces the overhead of in unstructured P2P networks. In order to solve this
consistency maintenance while still guarantees the problem of flexibility and complexity, proposing an
up-to-date status of the visited replicas. Here we approach of CoQUOS with consistency maintenance.
employing adaptive polling for file consistency It achieves high efficiency in consistency
maintenance to cater the file replication dynamism. maintenance at a significantly low cost.
The poll approach can achieve good consistency for
distant nodes and is less sensitive to P2P dynamism, REFERENCES
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Fig 1.Consistency Maintenance Mechanism
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International Journal of Advanced Research in Computer Science and Electronics Engineering
Volume 1, Issue 4, June 2012
[7] X. Yang, Y. Zhu, and Y. Hu,“Scalable Content-
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Annie Chacko received her
B.Tech degree in Information
Technology from TKM Institute
of Technology, Kollam, Kerala
under Cochin University of
Science & Technology in 2006.
Currently she is pursuing her
ME degree in CSE from SNS
College of Technology,
Coimbatore under Anna
University.
M.Sadish Serdil is currently working
as a Professor in CSE department in
SNS College of Technology,
Coimbatore. He got Ph.D from Anna
University. He received ME degree in
CSE from Anna University Chennai. He
had published more than 15
International Journals and about more
than 20 international conferences. He
has done research in distributed
networks, computed Networks and
database.
Professor Dr.S.Karthik is presently
Professor & Dean in the Department of
Computer Science & Engineering, SNS
College of Technology, affiliated to
Anna University- Coimbatore,
Tamilnadu, India.. He received the M.E
degree from the Anna University
Chennai and PhD degree from Ann
University of Technology, Coimbatore.
His research interests include network
security, web services and wireless
systems. In particular ,he is currently
working in a research group developing
new security architectures and active
defense systems against DDoS attacks. Dr.S.Karthik published
more than 35 papers in refereed international journals and 25
papers in conferences and has been involved many international
conferences as Technical Chair and tutorial presenter. He is an
active member of IEEE, ISTE, IAENG, IACSIT and Indian
Computer Society.
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