Mobile Ad-hoc NETworks (MANETs) are a type of infrastructure-less networks that are most useful in unprepared emergencies where critical applications must be launched quickly. However, they often operate in an adverse environment where endto -end connectivity is highly susceptible to various disruptions. Methods of adjusting the motion of existing nodes or deploying additional nodes can improve the connectivity under some circumstances, but there exist scenarios where connectivity cannot be immediately improved, and disruptions must be coped with properly. In this paper we propose an architecture of the Adhoc Storage Overlay System (ASOS). ASOS is a self-organized peer-to-peer (P2P) overlay, consisting of storage-abundant nodes that jointly provide distributed and reliable storage to disruptionaffected data flows. ASOS is a Delay-Tolerant Networking (DTN) approach that extends the conventional end-to-end data communication model in MANETs, and can significantly improve their applicability in practice.

Abstract—Data access is an important issue in Delay Tolerant Networks (DTNs), and a common technique to improve the performance of data access is cooperative caching. However, due to the unpredictable node mobility in DTNs, traditional caching schemes cannot be directly applied. In this paper, we propose DAC, a novel caching protocol adaptive to the challenging environment of DTNs. Specifically, we exploit the social community structure to combat the unstable network topology in DTNs. We propose a new centrality metric to evaluate the caching capability of each node within a community, and solutions based on this metric are proposed to determine where to cache. More importantly, we consider the impact of the contact duration limitation on cooperative caching, which has been ignored by the existing works. We prove that the marginal caching benefit that a node can provide diminishes when more data is cached. We derive an adaptive caching bound for each mobile node according to its specific contact patterns with others, to limit the amount of data it caches. In this way, both the storage space and the contact opportunities are better utilized. To mitigate the coupon collector’s problem, network coding techniques are used to further improve the caching efficiency. Extensive trace-driven simulations show that our cooperative caching protocol can significantly improve the performance of data access in DTNs.

Abstract—Information overload and convergence of devices aggravate the difficulties of accessing data distributed among various user devices especially when this is performed by mobile users and over heterogeneous wireless networks. Existing data replication systems help increase the performance of the distributed data system, but they do not consider users ’ different levels of interest in various pieces of data and neither heterogeneous wireless connectivity issues. This paper presents the Smart Personal Information Network (Smart PIN), a performance and cost-aware personal information network which uses a novel usercentric utility-based data replication scheme to exchange content automatically, based on both network performance and user interests. The proposed user-centric data replication scheme’s evaluation, through simulation, shows improved results in comparison with existing solutions.

Cooperative caching, which allows the sharing and coordination of cached data among multiple nodes, can be used to improve the performance of data access in ad hoc networks. When caching is used, data from the server is replicated on the caching nodes. Since a mobile node may return the cached data, or modify the route and forward a request to a caching node, it is very important that the mobile nodes do not maliciously modify data, drop or forward the request to the wrong destination. In this paper, we identify possible security attacks on cache consistency and propose a randomized grouping based schemes for intrusion detection, damage recovery and intruder identification. We also address other security issues in cooperative cache based data access.

A 3D framework provides a basis for designing, analyzing, and evaluating strategies to address data consistency issues in mobile wireless environments. A proposed relaypeer-based cache consistency protocol offers a generic and flexible method for carrying out cache invalidation. The trend toward wireless communications and advances in mobile technologies are increasing consumer demand for ubiquitous access to Internet-based information and services. However, due to battery power limitations, users often must disconnect mobile devices from the network to conserve energy. Moreover, wireless links have lower capacity than wired links and wireless channels are less stable, resulting in higher network congestion and packet loss. These challenges make mobile communication unreliable, emphasizing the need for efficient information-access mechanisms. 1-3 Cooperative caching improves system performance4,5 because it allows sharing and coordination of cached data among multiple mobile users in the network. By cooperatively caching frequently accessed information, mobile devices do not always have to send requests to the data source. In addition to reducing query latency, this technique can lower mobile host communication overhead and energy consumption. However, the unreliable communication and the user’s mobility make it difficult to maintain cache consistency. Mobile wireless environments can be broadly classified as either infrastructure based or ad hoc based. In the former scheme, shown in Figure 1a, a fixed network device such as a mobile support station forwards messages that mobile hosts send or receive. The MSS is sim-ilar to the server in a traditional client-server distributed system in that all source data is deployed on it. Other mobile hosts retrieve data from the MSS and can cache a replica by themselves. In contrast, ad hoc networks, like that shown in Figure 1b, do not store data on the MSS but use it only as the access point to the Internet. Ad hoc networks disperse all data items for searching and querying across the mobile hosts. Thus, the cache invalidation strategies employed in a single-hop wireless mobile network are not suitable for a multihop mobile ad hoc network.

Mobile Ad Hoc Networks (MANETs) provide an attractive solution for networking in the situations where network infrastructure or service subscription is not available. Cooperative caching scheme can improve the accessibility of data objects. In this paper, we proposed a neighbor group data caching scheme called Neighbor Group Data Caching (NGDC) for improving data access efficiency in MANETs. The objective is to improve data availability and access efficiency by collaborating local resources of mobile nodes. cache resolution and cache management are the two problems of cooperative caching. To improve data availability and access efficiency, cooperative caching discovers data sources which induce less communication cost by utilizing neighbor group nodes. For cache management, cooperative caching increases the effective capacity of cooperative caches by minimizing caching duplications within the cooperation zone and accommodating more data varieties.We evaluate the performance of the Neighbor Group Data Caching by using NS2 and compare it with the existing schemes such as Neighbor caching and ZoneCooperative. The experimental results show that the cache hit ratio is increased by about 4%~40 % and the average latency is reduced by about 5%~37 % compared with other schemes. Keywords:

MANETs or mobile ad hoc networks are a form of wireless networks which do not require a base station for providing network connectivity. Mobile adhoc networks have many characteristics which distinguish them from other wireless networks. Frequent network disconnection is one among various characteristics, due to which data availability is lower than traditional wired networks. Cooperative caching helps MANETs in alleviating from the situation of non data availability. In this paper we have proposed a cache cooperation strategy named global cluster cooperation (GCC) which is based on clusters. This approach fully exploits the pull mechanism to facilitate cache sharing in a MANET. For implementation we have evaluated the performance of our strategy based on global cooperation scheme with different cooperative caching schemes.

Abstract—The recent popularization of hand-held mobile devices, such as smartphones, enables the inter-connectivity among mobile users without the support of Internet infrastructure. When mobile users move and contact each other opportunistically, they form a Delay Tolerant Network (DTN), which can be exploited to share data among them. Data replication is one of the common techniques for such data sharing. However, the unstable network topology and limited contact duration in DTNs make it difficult to directly apply traditional data replication schemes. Although there are a few existing studies on data replication in DTNs, they generally ignore the contact duration limits. In this paper, we recognize the deficiency of existing data replication schemes which treat the complete data item as the replication unit, and propose to replicate data at the packet level. We analytically formulate the contact duration aware data replication problem and give a centralized solution to better utilize the limited storage buffers and the contact opportunities. We further propose a practical contact Duration Aware Replication Algorithm (DARA) which operates in a fully distributed manner and reduces the computational complexity. Extensive simulations on both synthetic and realistic traces show that our distributed scheme achieves close-to-optimal performance, and outperforms other existing replication schemes. I.

This paper investigates about the cooperative caching scheme which allows sharing their cache memory spaces among different node in ad-hoc network. We have applied trust model in cooperative caching which prevents malicious node from taking part in caching scenario and hence improves the reliability of the network. As routing protocol does not bother about the data accessibility and availability, instead their work mainly focus on finding the optimal route between the source and destination. To make routing more useful and reliable trust parameter can be used and to improve the data availability caching can be used. In this paper we apply the trust relationship among the nodes, and according to this trust relationship we take decision whether to make that node as a caching node or consider that node as a future threat in the network. Using this model, we can take more advantage of caching technique by neglecting the overhead generated by such malicious node.

The Mobile nodes are communicating with each other without centralized administration and data is accessed from the data source through multi-hop environment. The accessed data is stored in the mobile node’s cache for its own and neighbor’s future use. Caching is a significant process to store the frequently accessed data item in the MANET. Data availability and accessibility is a challenging task due to mobility of nodes, limited battery power and insufficient bandwidth. Cooperative caching addresses these challenges to improve the data availability and efficiency of data access by sharing and coordination among the mobile nodes. These challenges have received a tremendous amount of concentration from researchers and led to development of many different cooperative caching strategies. This paper attempts to provide the review and hypothetical analysis of various cooperative caching strategies in the mobile ad hoc networks based on their performance metrics such as cache hit ratio and average query delay with respect to cache size and number of mobile nodes. The Global Cluster Cooperative caching provides better performance than others in terms of cache hit and average query delay.