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 trade-offs 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.

Content sharing through vehicle-to-vehicle communication can help people find their interested content on the road. In VANETs, due to limited contact duration and unreliable wireless connection, a vehicle can get the useful data only when it meets another vehicle and the encountered vehicle has the exactly matched data. However, the probability of such case is very low. To improve the performance of content sharing in intermittently connected VANETs, we propose a novel P2P content sharing scheme called Roadcast. Roadcast ensures popular data is more likely to be shared with other vehicles so that the overall query delay and the query hit ratio can be improved. Roadcast consists of two components called popularity aware content retrieval and popularity aware data replacement. The popularity aware content retrieval scheme makes use of information retrieval (IR) techniques to find the most relevant and popular data towards user's query. The popularity aware data replacement algorithm ensures that the density of different data is proportional to their popularity in the system steady state, which firmly obeys the optimal "square-root" replication rule. Results based on real city map and real traffic model show that Roadcast outperforms other content sharing schemes in VANETs.

To disseminate content with content-based routing (CBR), the routing paths of subscription and publication cannot be determined a priori and have to be computed hop-by-hop, which brings in scalability and robustness challenges in large scale mobile ad hoc networks (MANETs). In this paper, we propose a novel two-tier content-based routing protocol called CLONE (Community and Location aware content based routing). In CLONE, we map the human community structure of social networks to MANETs. The whole network can be self-organized into communities based on the interest locality, so that most subscriptions inside a community can be served in an intra-community fashion, reducing the communication overhead and the response delay. Community construction is self-organized and completely distributed. Analytical and simulation results demonstrate the effectiveness of CLONE in large-scale MANETs.

Different from existing mobility-assisted data access techniques, we propose to use data diffusion to reduce the query delay in DTNs. We use social network analysis to classify and study four diffusion schemes based on the homophily phenomenon in social network. Theoretical models are further developed to analyze the data diffusion process and compare the performance of the four proposed diffusion schemes in terms of diffusion speed and query delay.

Abstract In a Grid‐based services system facing a large number of requests with different services and profits significance, there is always a trade‐off between the system profits and the Quality of Service (QoS). In such systems, admission control plays an important role: the system has to employ a proper strategy to make admission control decisions and reserve resources for the coming requests thus to achieve greater profits without violating the QoS of the requests already admitted. In this paper, we introduce three essential admission control strategies with threshold on resource reservation and a newly proposed strategy with layered threshold. Through comprehensive theoretical analyses and extensive simulations, we demonstrate that the strategy with layered threshold is more efficient and flexible than the existing strategies for Grid‐based multimedia services systems. Copyright © 2006 John Wiley & Sons, Ltd.