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    • 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.comAbstract - Peer-to-Peer (P2P) systems offer an Some important concepts in P2P systemsalternative 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 thatfor a long term presence in a network and to publish its applications cannot be set up by single node or singleown data to that network. These requirements can bedone by having some set of indexing and routing entity. It is the sharing of resources of different nodestechniques. For this solution, a sequence of approaches in a network.Decentralization means to avoid singlehas been already proposed by the existing researches. point of failures and bottlenecks. Self organizationResearchers proposed unstructured overlay–based means, based on whatever local information ispublish 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 ofand too complex.In order to solve this problem of all participating peers as network nodes. There areflexibility 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 ofapproach is to support the continuous queries inunstructured overlay networks. This approach another peer in the P2P network then there is acharacterized by 5 novel techniques , namely cluster directed edge from the former node to the latter in theresilient random walk algorithm, dynamic probability- overlay network. Based on how to each other, it canbased query registration scheme, develop efficient classify the P2P networks as unstructured orschemes for providing resilience to the churn of the P2P structured.network, fair distribution of the notification load among Structured P2P [2] network employ athe peers and finally consistency maintenance globally consistent protocol to ensure that any nodemechanism. It achieves high efficiency in consistency can efficiently route a search to some peer that hasmaintenance 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 thepublish-subscribe systems, random walks, consistency overlay links are established arbitrarily. Suchmaintenance 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 andnetwork, composed of a large number of distributed, Kazaa) have experienced tremendous growth in theheterogeneous peers, and they are highly dynamic past decade, and it is based on content or resourcepeers in which participants can share their own sharing. Simplicity of design and flexibility towardsresources. In P2P, the participants can act as a server node population are the attributes of the unstructuredand a client at the same time. They are directly P2P systems. A model for data sharing and discoveryaccessible by other nodes, without passing in unstructured P2P called adhoc query model. Itintermediatory entities. does not support for peers to advertise or announce the data items to other interested peers.Because of 84 All Rights Reserved © 2012 IJARCSEE
    • ISSN: 2277 – 9043 International Journal of Advanced Research in Computer Science and Electronics Engineering Volume 1, Issue 4, June 2012this limitation, it is inadequate for many advanced The continuous query model is a model thatP2P 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 theirpossible approach to address the limitations of adhoc queries, which are maintained in the network for longquery model. durations of time. The continuous query model The pub-sub system is a guaranteed provides a best effort of notification service for thenotification service so that the subscribers or confirmed queries that informing their source nodesconsumers to register their own interests in a of new content that may added to the former. So tonetwork. The alternate notification service of pub-sub implement this model, a middleware use calledsystem called continuous query model. To register CoQUOS.the continuous query on a set of peers that are locatedin various topological regions in the overlay. So the III. LIGHT WEIGHT SUPPORT FORreplicas of query are formed to notify the respective CONTINUOUS QUERIES IN UNSTRUCTUREDsource peers of matching advertisements that issued OVERLAY NETWORKby other peers. But this approach is not flexible forthese systems and too complex. So in order to solve P2P are distribution systems that stronglythis problem of flexibility and complexity, proposing enforced by their adhoc content discoveryan approach of CoQUOS with consistency mechanisms. It have two capabilities such asmaintenance mechanism. Instead of passively mechanism be capable that peers to register theiraccepting messages, this mechanism harmonically queries and receive the acknowledgements and peersintegrates file replication and consistency to advertise their content of information. Thesemaintenance 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 similar2.1 Pub-Sub System to publish-subscribe systems called CoQUOS[5].This CoQUOS provides best effort of notificationPub-Sub system is called Publish – Subscribe guarantees. CoQUOS is a scalable and lightweightsystems [6], [7]. It is a system that promising for middleware. It supports continuous queries inresource discovery in a distributed system. This pub- unstructured P2P networks. CoQUOS calledsub system also called producer –consumer system. It Continuous Queries in Unstructured OverlayScan be described as: (1) Subscribers called network. A key strength of the CoQUOS system isinformation consumers. The subscribers that express that, it can be implemented on any unstructuredtheir interests by subscribers that denote their own overlay network. Two important characteristics ininterests by specific subscriptions and register in the CoQUOS are: (1). It does not impose any topologicalevent based system. (2). Publishers called conditions on the P2P network and it does notinformation producers. When publishers publish implement dependent module in any unstructuredevents to the system, the system is responsible for networks.(2). The CoQUOS system is verydelivering the events to the corresponding lightweight, so it does not require complex indexsubscribers. Decoupling is one of responsible fact for structures. So it preserves design simplicity andthe 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 ofdecoupling, (2).space decoupling, and CoQUOS , it have two novel components, namely3).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 systemsare less flexible and lack of expressiveness.(2).Content based. The content based systems are IV. DESIGN OF CoQUOS SYSTEM MODELmore flexible for these systems , that allow thesubscribers to denote complex interests with the The goal of designing the CoQUOS systemcorresponding predicates on a set of attributes. is to design an effective service notification on the top of the unstructured overlay networks. CoOUOS2.2 Continuous Query Model can act as middleware, so it strives stronger 85 All Rights Reserved © 2012 IJARCSEE
    • ISSN: 2277 – 9043 International Journal of Advanced Research in Computer Science and Electronics Engineering Volume 1, Issue 4, June 2012notification success rates for each individual query of depthfirst traversal of the network and it has highthe 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 BASISpeer announcements. When a peer receives an OF QUERY REGISTRATIONannouncement message, it checks all queries that areregistered and check any of the queries match the The above process won’t be able to notify how toreceived 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 fixedannouncement – based data item discovery by beacon probability. But it cannot guarantee high notificationnodes. 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 registeringof the system are small, so the TTL of the query at a peer node is high if it is not alreadyannouncement of messages are set to very low registered.values. A peer that needs to announce a new dataitem creates an announcement message and sets the VIII. CHURN OVERLAYTTL value and then sends the message to allneighbors. Through the recipients receive the The information in nodes are entering andmessage, decrement the TTL and send it to the leaving frequently in P2P overlay called churnneighbors. This process is repeated until the TTL overlay. These affect success of the continuousreaches to zero. This peer announcement exploring queries and announcements. The entering and leavingsome strategies such as iterative deepening and mechanism would affect the churn in the overlay. Sodirected breadth first search. the churn overlay design as a low cost technique. V. HOW BEACON NODES SELECT IX. LOAD BALANCINGThe selection of beacon nodes has an important role The one of the important ingredients in theon 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 ofbasis of somekey features. First, the beacon nodes of continuous queries and numbers of notification senta query should be distributed in every major region of out per unit time by different nodes. These loadthe network. Second, the beacon nodes of a query metrics are used due to variety of reasons such asshould not be located very close to each other. The topological characteristics of the network, skewedCOQUOS system is a completely decentralized announcement and query popularities, variation in thetechnique that can use for the selection of beacon resource availabilities at peers or a combination ofnodes. So in this selection, a continuous query is these factors.circulated in the network and each peer receives thequery and it decides whether to register or store the X. IMPLEMENTATIONquery. The important feature of this is that each peermakes 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 frequentlyis 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 tosummarized as follows: When a peer receives a guarantee file fidelity of consistency at a low costmessage and its TTL value is not expired, it selects with file replication dynamism consideration. Itone of its neighbors at randomly and forwards the ensures timely update operation and avoidsmessage to that peer. So, each step the message is unnecessary updates. As a result, it achieves highforwarded to only one neighbor and the load impact efficiency. P2P systems are characterized byis very low.Thus random walk corresponds to a 86 All Rights Reserved © 2012 IJARCSEE
    • ISSN: 2277 – 9043 International Journal of Advanced Research in Computer Science and Electronics Engineering Volume 1, Issue 4, June 2012dynamism, in which node join and leave 11. CONCLUSIONcontinuously and rapidly. Fig. 1 shows an example for consistency Mechanisms that enable individual peers ofmaintenance. The nodes C and G in the middle unstructured P2P content sharing networks are toobserved frequent queries for the file, and nodes J register longstanding queries and receive notificationand 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 thenodes 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 unstructuredFor consistency maintenance, the replica nodes overlays is often a very complex endeavor. Theactively probe the file server for update. They probe continuous query paradigm studied in this, is similarthe server approximately at the rate of file change to pubsub, but it provides best-effort notificationrate. However, when their replica is visited at lower service and presented the design and middleware isfrequency 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 queriesvisited. This strategy reduces the overhead of in unstructured P2P networks. In order to solve thisconsistency maintenance while still guarantees the problem of flexibility and complexity, proposing anup-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 consistencymaintenance to cater the file replication dynamism. maintenance at a significantly low cost.The poll approach can achieve good consistency fordistant nodes and is less sensitive to P2P dynamism, REFERENCESnetwork size and connectivity of a node. We areproposing two main issues for consistency [1] S. Androutsellis-Theotokis and D. Spinellis,,maintenance. First is to determine the frequency that “A Survey of Peer-to-Peer ,” ACM Computingthe replica node probes a file owner in order to Surveys, vol. 36, pp. 335-371,2004.guarantee file update. Second is to reduce the number [2] Baldoni, C. Marchetti, A. Virgillito, and R.of polling operations so as to save cost and providing Vitenberg,, “Structuring Unstructured Peerto-the fidelity of consistency guarantees. Peer Networks,”Proc. 25th IEEE Int’l Conf. Distributed Computing Systems (ICDCS),2005. [3] C. Gkantsidis, M. Mikhail, and A. Saberi, “Random Walks in Peer-To-Peer Networks,” Proc.IEEE INFOCOM ’04, 2004. [4] Q. Lv, P. Cao, E. Cohen, K. Li, and S. Shenker, “Search and Replication in Unstructured Peer- to-Peer Networks,” Proc. 16th Ann. ACM Int’l Conf. Supercomputing, 2002. [5] L. Ramaswamy, J. Chen, and P. Parate, “CoQUOS: LightweightSupport for Continuous Queries in Unstructured Overlays,” Proc.IEEE Int’l Parallel and Distributed Processing Symp, 2007. [6] Shandong Zhang, Ji Wang, RuiShen, JieXuP. Triantafillou and I. Aekaterinidis, “Towards Building Efficient Content-Based Publish/Subscribe Systems over Structured P2P Overlays,” Proc.Third Int’lWorkshop Distributed Event-Based Systems (DEBS), 2010.Fig 1.Consistency Maintenance Mechanism 87 All Rights Reserved © 2012 IJARCSEE
    • ISSN: 2277 – 9043 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- Based Publish/Subscribe Services over Structured Peer-to-Peer Networks,” Proc.15th Euromicro Int’l Conf. Parallel, Distributed and Network-Based Processing (PDP),2007. 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 activedefense systems against DDoS attacks. Dr.S.Karthik publishedmore than 35 papers in refereed international journals and 25papers in conferences and has been involved many internationalconferences as Technical Chair and tutorial presenter. He is anactive member of IEEE, ISTE, IAENG, IACSIT and IndianComputer Society. 88 All Rights Reserved © 2012 IJARCSEE