Abstract—We investigate the problem of spreading information contents in a wireless ad hoc network. In our vision, information dissemination should satisfy the following requirements: (i) it should result in a desirable distribution of information replicas in the network and (ii) the information should be evenly and fairly carried by all nodes in their turn. In this paper, we show that these goals can be achieved by simple cache-andforward mechanisms inspired by well-known node mobility models, provided that a sufficient number of information replicas are injected into the network. The proposed approach works under different network scenarios, is fully distributed and comes at a very low cost in terms of protocol overhead. I.

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—Some recent studies have shown that cooperative cache can improve the system performance in wireless P2P networks such as ad hoc networks and mesh networks. However, all these studies are at a very high level, leaving many design and implementation issues unanswered. In this paper, we present our design and implementation of cooperative cache in wireless P2P networks, and propose solutions to find the best place to cache the data. We propose a novel asymmetric cooperative cache approach, where the data requests are transmitted to the cache layer on every node, but the data replies are only transmitted to the cache layer at the intermediate nodes that need to cache the data. This solution not only reduces the overhead of copying data between the user space and the kernel space, it also allows data pipelines to reduce the end-to-end delay. We also study the effects of different MAC layers, such as 802.11-based ad hoc networks and multi-interface-multichannel-based mesh networks, on the performance of cooperative cache. Our results show that the asymmetric approach outperforms the symmetric approach in traditional 802.11-based ad hoc networks by removing most of the processing overhead. In mesh networks, the asymmetric approach can significantly reduce the data access delay compared to the symmetric approach due to data pipelines. Index Terms—Wireless networks, P2P networks, cooperative cache. Ç

In mobile ad hoc networks (MANETs), nodes move freely and link/node failures are common, which leads to frequent network partitions. When a network partition occurs, mobile nodes in one partition are not able to access data hosted by nodes in other partitions, and hence significantly degrade the performance of data access. To deal with this problem, we apply data replication techniques. Existing data replication solutions in both wired or wireless networks aim at either reducing the query delay or improving the data availability, but not both. As both metrics are important for mobile nodes, we propose schemes to balance the tradeoffs between data availability and query delay under different system settings and requirements. Extensive simulation results show that the proposed schemes can achieve a balance between these two metrics and provide satisfying system performance.

Abstract — Data replication has been well adopted in data intensive scientific applications to reduce data file transfer time and bandwidth consumption. However, the problem of data replication in Data Grids, an enabling technology for data intensive applications, has proven to be NP-hard and even non-approximable, making this problem difficult to solve. Meanwhile, most of the previous research in this field is either theoretical investigation without practical consideration, or heuristics-based with little or no theoretical performance guarantee. In this paper, we propose a data replication algorithm that not only has a provable theoretical performance guarantee, but also can be implemented in a distributed and practical manner. Specifically, we design a polynomial time centralized replication algorithm that reduces the total data file access delay by at least half of that reduced by the optimal replication solution. Based on this centralized algorithm, we also design a distributed caching algorithm, which can be easily adopted in a distributed environment such as Data Grids. Extensive simulations are performed to validate the efficiency of our proposed algorithms. Using our own simulator, we show that our centralized replication algorithm performs comparably to the optimal algorithm and other intuitive heuristics under different network parameters. Using GridSim, a popular distributed Grid simulator, we demonstrate that the distributed caching technique significantly outperforms an existing popular file caching technique in Data Grids, and it is more scalable and adaptive to the dynamic change of file access patterns in Data Grids.

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Abstract — Extensive research has been performed to study selfish data caching in ad hoc networks using game-theoretic analysis. However, due to the caching problem’s theoretical root in classic facility location problem and k-median problem, most of the research assumes i), the data items are initially outside of the network, and ii), the caching cost is either a constant or not considered. In this paper, we study a general data caching model in which the data item is initially in the network, and both caching and access cost are distance-dependent in multi-hop ad hoc networks. We first show the studied problem is NP-hard. We construct a pure Nash Equilibrium, in which a node will not deviate its caching strategy if others remain theirs. However, a Nash Equilibrium may not guarantee social optimal cost – due to the selfishness of each node, the price of anarchy, which is the relative cost of the lack of cooperation among nodes, could be as large as O(N), where N is number of nodes in the network. Using an external incentive mechanism based upon a payment model, we construct a Nash Equilibrium wherein social optimal is also achieved.

This thesis studies the problem of determining achievable rates in heterogeneous wireless networks. We analyze the impact of location, traffic, and service heterogeneity. Consider a wireless network with n nodes located in a square area of size n communicating with each other over Gaussian fading channels. Location heterogeneity is modeled by allowing the nodes in the wireless network to be deployed in an arbitrary manner on the square area instead of the usual random uniform node placement. For traffic heterogeneity, we analyze the n × n dimensional unicast capacity region. For service heterogeneity, we consider the impact of multicasting and caching. This gives rise to the n × 2 n dimensional multicast capacity region and the 2 n × n dimensional caching capacity region. In each of these cases, we obtain an explicit informationtheoretic characterization of the scaling of achievable rates by providing a converse and a matching (in the scaling sense) communication architecture.

Abstract—We study the challenging problem of strategic content placement in a dynamic MANET. Existing content placement techniques cannot cope with such network dynamics since they are designed for fixed networks. Opportunistic caching approaches are insufficient as they do not actively manage contents for certain goals. In this paper, we present a novel content management approach, called LACMA, that leverages the location information available to mobile devices via GPS. The main insight behind LACMA is to bind data to geographic location (as opposed to network nodes). This location-based strategy decouples the content placement problem from the changing network topology, and allows us to design an optimization framework even in a dynamic MANET environment. We present key components of LACMA used for strategic content placement and contentlocation binding (through proactive content push). We evaluate LACMA and compare its performance with existing caching schemes and show that LACMA considerably outperforms existing schemes over a wide range of scenarios. I.

Abstract—As the day to day applications in mobile computing are increasing, different wireless peer-peer networks came into existence. There are several protocols and schemes are implemented to increase the network performance. The most implemented technique used to improve the performance of data access is Caching. Cooperative caching, which allows the sharing and coordination of cached data among multiple nodes, can further explore the potential of the caching techniques. Due to mobility and resource constraints of ad-hoc networks, cooperative caching techniques designed for wired network may not be applicable to ad-hoc networks. Hence, this paper presents a asymmetric cooperative caching scheme to efficiently support data access in ad-hoc networks. A Hybrid approach (Hybrid Cache) which can further improve the performance by taking advantage of Cache Data and Cache Path by avoiding general weaknesses. This proposed scheme increases the system performance in aspect of bandwidth, power utilization and end-end delay. Index Terms—Wireless networks, P2P networks, cooperative cache, Hybrid cache