Sameer Tuladhar, L. Sumalatha / International Journal of Engineering Research and                   Applications (IJERA) I...
Sameer Tuladhar, L. Sumalatha / International Journal of Engineering Research and                               Applicatio...
Sameer Tuladhar, L. Sumalatha / International Journal of Engineering Research and                   Applications (IJERA) I...
Sameer Tuladhar, L. Sumalatha / International Journal of Engineering Research and                     Applications (IJERA)...
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  1. 1. Sameer Tuladhar, L. Sumalatha / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.1063-1066 Replication of Query Messages in the Unstructured Overlays Peer-to-Peer Network Sameer Tuladhar, L. Sumalatha M.Tech.(Student), JNTUK, Kakinada,AP,India. Assistant Professor, JNTUK, Kakinada, AP,India.Abstract— Unstructured peer–to-peer (P2P) In each of the P2P networks, a search mechanismnetworks are attractive because they impose few needs to be defined so that resources need to beconstraints to the participating peers and have a known to be of importance to be used by users. Butlow maintenance overhead. It provides high the problem arises because of the dynamic nature ofresilience and tolerance to the continuous arrival the P2P network which lacks central directory forand departure of nodes. However the current resource location. Moreover current P2P contentP2P networks are mostly constricted by on- distribution systems suffer from limitations such asdemand content discovery mechanism. The content discovery mechanism only when requestedCoQUOS Approach has been suggested over and have no provision for declarations of data itemspublish-subscribe systems which can they own to other interested peers. Participatingcontinuously notify the new data items, and a peers in the P2P network discover data bymeans for the peers to advertise contents. circulating queries which are received by other peersAnother point that should be considered is churn and respond back if it has any matching data. Butwhich is the phenomenon of dynamic nature of the shortcoming is that these queries are not cachedentry and departure of peers in the P2P network. in the overlays network which results in the networkThus the churn significantly affects the search to forget the query once it completed circulation.mechanism in the P2P networks leading to Besides these limitations P2P networks must alsoquestion the effectiveness and reliability of P2P deal with the churn which is the instantaneousnetworks. In addition to the two novel connectivity of the peers and intentionally ortechniques, namely cluster-resilient random walk unintentionally departing from the network at anyalgorithm for queries propagation and dynamic instance of time. The more the churn is prevailing inprobability-based query registration scheme as the network lesser will be the reliability of thesuggested in CoQUOS approach, we suggest the network.message replication of query registrationspresent on a peer to one or more of its 1.1 Paper Contributionsneighbouring peers. For this, a technique called In a P2P network, data and other necessaryFrequency Aware Search is suggested that resources are stored in a distributed fashion by thedefines a policy for partitioning the search space participating peers of the network which has to be ofand a replication policy of keys. This paper any interest to others. However to know whether theelaborates the suggested algorithms through data is available or not and also to inform thetheoretical analysis and also reports the interested peers that requested data is available,effectiveness proposed schemes through flooding of message seems to be an easy way out.experimental evaluations. But it results in unnecessary traffic in the network. In this paper we discuss about the CoQUOSKeywords— Peer-to-Peer networks, CoQUOS approach for unstructured overlays network whichApproach, Random Walks, Churn, Message not only implements the message forwardingreplication without flooding to all the peers but also provides best-effort notification service for the registered1. INTRODUCTION queries from the peers about the discovery of the Unstructured peer-to-peer networks have required data. The main advantage of this approachbeen use for quite a long time for content sharing or is that it doesn’t enforce any topological constraintsfile sharing by the participating nodes. Searching in on the underlying network structure and doesn’tthese types of networks is very popular these days. require any complex index structures of routingOverlays networks form virtual topologies on top of mechanism. On top of these features, this paperan underlying network as the links in the overlay deals with a search algorithm to improve thenetworks have no correspondence with links negative impacts of the churn by replicating theestablished in the underlying network. P2P networks messages to the neighbouring peers. This algorithmare the best example of such overlays network. is Frequency-Aware Search (FASE) which is basically a search space partitioning mechanism, 1063 | P a g e
  2. 2. Sameer Tuladhar, L. Sumalatha / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.1063-1066 combined with a replication policy. It also doesn’t in black i.e. {P2, P8, P11} are the beacon nodes and require the rigid network structure or any pre P0 is the requesting peer which may receive multiple routing informations. notifications. The Beacon nodes should be selected in such a manner that they are distributed in every 2. THE CoQUOS SYSTEM OVERVIEW major region of the network such that every other The CoQUOS system is a lightweight peer in the network can reach them in a very small middleware that supports continuous queries and number of hops and they should not be located very announcements/advertisements about discovery of close to each other. data to the requesting peers in the unstructured overlays or simply saying P2P networks. The key 2.2 Cluster Resilient Random Walk features of this system include Cluster Resilient In P2P networks Random Walk message Random Walk (CRW) [3] for forwarding the propagation are more popular than flooding. In this messages to other peers in the network and a approach a peer receives and forwards the message dynamic probability scheme for the registration of to another neighbouring peer at random if its Time- queries in the peers. Continuous query is the means To-Live (TTL) is not expired. Since this message of communication through which the peer registers forwarding is done only one at a time so it reduces its interest to the network. It can be represented as the message traffic in the network in comparison to Q=(SID, Predicate, VTime), which is actually a the flooding. However with the networks with high tuple consisting of SourceID(SID) that identifies the degree of clustering of nodes, there is a greater requesting peer, a query predicate(Predicate) for chance the message gets trapped within the cluster matching condition of the query with the requested and its TTL gets expired before it come outs of the data and validity time(VTime) which is the lifetime cluster. To overcome this drawback, CoQUOS of interest of the requesting peer. system suggests a technique called Cluster Resilient Random Walk (CRW). This technique considers the 2.1.1 Design concept of two peers being in the same cluster if The CoQUOS system maintains each they have the large number of common neighbours. continuous query at one or more peers in the So CRW forwards messages to those nodes which network. The main objective of this system is to have less neighbours in common by calculating the achieve high notification success rate for the query probability of nodes being not in the same cluster. individually for the peer as well as overall for the Thus a peer has to compute the overlap between its complete network. The figure below shows the neighbours list and those of each of its neighbours, design of the CoQUOS system. and make message forwarding decisions. Let NbrList(Pj) denote the list of A Announcement neighbours of Pj and Pk,Pk+1,Pk+2...,Pk+l denote the neighbours of the node Pj. UniqueNbrs(Pk+1,Pj) N Notification denote the set of neighbouring peers of Pk+1 that are 5 not the neighbours of Pj. Suppose the node Pj A receives a query message from a neighbouring peer Beacon A 1 Pk. The probability[3] of a neighbour Pk+1 receiving 2 6 4 A the message in the next hop can be calculated as UniqueNbrs P k +1 ,P j A λ 1 NbrsList P k +1Source 0 7 5 FwdProbability(Pk+1) =C 3 Beacon A A UniqueNbrs P l ,P j λ NbrList Pl N 1 A The propagation of query in CRW starts with source A 1 4 peer creating a query message initializing its TTL to 1 1 1 6 A a default value. Each peer along the query’s path Beacon 2 9 1 forward the message to one of their neighbours 8 1 2 according to their FwdProbability values. The TTL 3 Fig.1. CoQUOS System 0 Overview is then decremented at each hop until it becomesE zero. The Fig. 2. [3] given below illustrates CRW If a continuous query Qm is registered at a peer Pi, message forwarding in a single step. The query then Pi is called beacon node which implicitly takes message is at the node p4 and λ which controls the the responsibility of notifying the source node of extent of the bias is set to 2. The numbers on the any matching data items that it might discover edges indicate the probabilities of forwarding the through incoming peer advertisements and checks query along that link. It has been observed that with the registered query if anything matches to CRW is better than normal random walks and provide notification to the requesting node about the flooding techniques in forwarding messages to availability of the data. In the figure the peers shown various regions of the P2P overlays. 1064 | P a g e
  3. 3. Sameer Tuladhar, L. Sumalatha / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.1063-1066 over unstructured network which works well by replication of queries with CRW technique. 4. FREQUENCY AWARE SEARCH This technique defines a policy for dividing the search space in the network and a key replication policy. The term frequency [6] is defined to be any element of a finite and discrete set Φ. We define functions fN: N→ Φ and fK: K→ Φ mapping respectively the set of nodes (N) and keys (K) in frequencies. A pointer is a tuple defined as follows:2.3 Dynamic Query Registration Pointer: <Key,URL> This technique is based on the dynamicprobability of the peers to decide the registration of In a pointer, a key identifies the item and anqueries on their own will. The registration URL is an unique node address where the query willprobability of a query varies as the query traverses be replicated. FASE improves search results byalong its path depending on whether the query has having nodes to forward random walks preferably tobeen registered or not at the nodes it visited in the nodes in the same frequency of the search key. Thisrecent past. Thus if it has been registered at the node algorithm assumes that majority of nodes in thein the recent past the probability of getting overlay have a constant degree.registered in the next hop will be low and vice versa. The registration probability [3] value of 4.1. Pointer Replicationeach message Qm is denoted as (Rp(Qm)). This value In order to reduce the impact of churn andis set to an initial value when a peer issues a query. properly facilitate item location, nodes replicateIf a peer registers this query, then it resets the value pointers using replication messages which carry oneof Rp(Qm) to the default initial value, before or more pointers with keys of the same frequency.forwarding to its neighbours. However if the peer For the message MR let fK(MR) be the frequency ofchoose not to register the query then it increments the keys being carried. These replication messagesRp(Qm) by a pre-specified amount and forwards to carry a counter that defines the maximum number ofthe neighbour. That means the Rp(Qm) value keeps replicas of each pointer to be stored. Every peer thaton incrementing until it gets registered wherein decides to store pointer decrements the replicathere will be sudden fall of point to the initial value. counter and when the counter becomes 0 theThis technique helps in controlling the number of message is discarded. Replication messages arebeacon nodes where such query registration is done. forwarded to those neighbours who have not been visited previously. Since the replication message is3. NETWORK OVERLAY CHURN preferably forwarded to nodes labelled with the The very dynamic nature of P2P networks same frequency of the item, only one pointer ismeans that there will be number of nodes that will stored for the whole path that contains number ofbe entering and leaving the network at will. This nodes. This leads to the efficiency in storing themeans besides the resource location, P2P networks pointer. The main purpose of this replication methodmust also cope with the intermittent connectivity of is to make items well available for searches at anythe peers in the network to ensure the reliability of point.the overall network and data transfer. If this churn The pointer replication process isis not handled well it can impact the success of illustrated in the Fig. 3 given below.continuous queries and announcements as well.When a node leaves the system properly, itsresponsibilities are well taken care by theneighbouring peers, but when it happens abruptly,all the query registrations are lost thus it will hamperthe notification success rates of the respectivequeries and the matching announcements will bedropped. In order to resolve this problem onesolution is the replication of queries on one or moreof its neighbours. For this, the technique called Fig.3. Pointer Replication [6]Frequency- Aware Search (FASE) algorithm can beimplemented which is basically a search protocol The above figure shows the path of a replication 1065 | P a g e
  4. 4. Sameer Tuladhar, L. Sumalatha / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 Vol. 2, Issue 5, September- October 2012, pp.1063-1066message MR starting at node S. The dotted circlesare the nodes in the same frequency of the message.Here node S forwards message to a randomneighbour as it has no neighbour in MR frequency,fK(MR) and thus the neighbour in the following hopwith fN(n) = fK(MR) will store a pointer. The figureshows that a replication message is alwaysforwarded to unvisited nodes of the same frequency.The nodes labelled with P store the pointer carriedby MR. These pointers are stored once per path andthe forwarding of MR is stopped once the replicacounter reaches 0 or when all the neighbours of thecurrent node have been visited before by MR. Fig.5. Effectiveness of FASE to tackle churn 5. EXPERIMENTAL EVALUATION This section shows the experimental results The mean NSRs which were measuredof the simulation of FASE algorithm with CRW when the churn rate is set to 10%, 20% and 30%technique. For this we have simulated a network show that NSRs are high when using FASE thanconsisting of 1000 nodes. The simulation created without using it.100 unique data items, from a group of data items inexcess of 4000, each advertised by a distinct node 6. CONCLUSIONselected at random to the beacon nodes. For Maintaining the network reliability and dataevaluation of the algorithm, queries are performed resources available in a P2P network is a challengefor items that are present in the network and are provided its dynamic nature i.e. churns. Althoughselected uniformly at random. there may not be any perfect solution to tackle this We measured the difference in the problem but the presented Frequency-Aware SearchNotification Success Rates (NSR) of overlay algorithm helps to reliably search the data item innetwork with and without the application of FASE the unstructured overlays networks to very goodalgorithm with CRW. The Fig.4. and Fig.5. shows extent. Like CoQUOS approach FASE doesn’tthe NSRs of the two approaches for which the enforce any restriction on the network structure orregistration probability value is set to 0.3. topology. Our evalution shows that with the use of FASE, we can achieve high NSRs even on increasing the churn rate. The results suggest that, the replication policy like FASW helps to increase the availability of searched items. REFERENCES [1] Gnutella P2P Network. www.gnutella .com [2] Wikipedia. [3] L. Ramaswamy, J. Chen. The CoQUOS Approach to Continuous Queries inFig.4. Comparison of minimum NSR of CRW with Unstructured Overlays. IEEE Transactionsand without use of FASE on Knowledge and Data Engineering, 2011. In this experiment, the minimum NSRs of [4] L. Ramaswamy, J. Chen and Piyush Parate.CRW were set to different values with the use of CoQUOS: Lightweight Support forFASE and without FASE and the results show that Continuous Queries in Unstructuredthere is significant benefit in the NSR with the use Overlays. IEEE 2007.of FASE yielding reasonable NSR even at relatively [5] J. Chen, L. Ramaswamy and A. Meka.low initial TTL values. Message Diffusion in Unstructured We also checked the effectiveness of the Overlay Networks. In Proceedings of NCA,CRW with and without using FASE to evaluate the 2007effect of churn. The Fig.5. shows the results of the [6] Pedro Fonseca. Search Strategies inexperiment. Unstructured Overlays 1066 | P a g e