An Optimal Replica Relocation Scheme for Improving Service Availability in Mobile Ad Hoc Networks K. Muralidhar Department of Computer Science & Engineering Ananthalakshmi Institute of Technology & Sciences Anantapuramu, Andhra Pradesh, India muralidhar.kurni@gmail.com N. Prathibha Bharathi Department of Computer Science & Engineering Dr.K.V.S.R.C.E. for Women Kurnool, Andhra Pradesh, India prathibha.nuvvula@gmail.com Abstract—This paper proposes an optimal replica relocation scheme improving service availability in Mobile Ad Hoc Networks (MANETs) that relocates replicas as necessary so that the actual data items are available to the nodes which are in need of them. Since MANET’s topology is highly dynamic, data items should be made available to the nodes that are required by them in a minimum distance. The nodes which initially store data may move far because of the dynamic topology and the nodes that are selected for relocation should be nearer to the nodes that are in need of them. Also the nodes which store the replicas may drain out in servicing excessive data access requests. This proposed scheme not only considers the minimum distance parameter, but also considers the vital parameters like storage availability, and residual energy parameters in selecting the node for relocation. The proposed scheme was implemented in NS2 and when compared to the no relocation scheme, our proposed scheme proved to be superior. Keywords—relocation; service availability; MANETs; replicas; storage; residual energy; distance. I. INTRODUCTION In a mobile ad-hoc network (MANET) data caching is crucial to cut back rivalry within the network, increasing the likelihood of mobile nodes to possess access to desired data, and up system performance, by primarily reducing access delay [1], [2] and [3]. Since in MANETs, some nodes could be part of the network others could leave, whereas most nodes can amendment location. This makes some cached data unavailable or inaccessible for nodes within the network. Replicating cached data within the network can thus improve data accessibility and availability, and lowers access delays by reducing pricey requests to servers behind the MANET. The replica allocation strategy should contemplate the varied conditions of the network to produce acceptable quality of service, reflected by data availability and consequently there will be low access delays. Since MANET’s topology is extremely dynamic, the nodes which initially store the replicated data might move far. However the nodes that store the replicas ought to be nearer to the nodes that are in need of them. Conjointly the nodes that store the replicas ought to be available for a long period of time, but not possible since they have to service excessive data access requests, they’ll drain out. By reallocating replicas frequently as per the nodes mobility and request pattern, helps in reducing the communication cost of accessing replicas. But reallocating replicas involves much overhead. In order to reduce this overhead we prefer replica relocation than replica reallocation. In this work, we propose a replica relocation scheme, which not only considers the minimum distance parameter, but also considers the vital parameters like storage availability and residual energy parameters in selecting the node for replica relocation. II. ISSUES TO BE THOUGHT-ABOUT WHILE RELOCATING REPLICAS The following issues need to be thought-about [4] in choosing a node for the replica relocation. A. Power Consumption Since all the mobile nodes in a MANET are battery powered, if a node with less power is chosen for replica relocation then it soon gets drained in servicing requests for data items, and it cannot give services any longer. Therefore replica relocation algorithm should relocate replicate data within the nodes that has sufficient power, by periodically checking the remaining power of every node. B. Node mobility Since nodes in the MANET are mobile, replica relocation algorithms has to support mobility prediction specified if a node is probably going far away from its original location, its replicas will be relocated in some another nodes that are anticipated to stay nearer to the specified nodes for a specific amount of time. C. Resource availability Since nodes in MANETs have limited memory, the replica relocation algorithms have to choose nodes with comfortable memory to hold relocated replicas. 978-1-4799-3972-5/14/$31.00 ©2014 IEEE 397