Mobile Information Systems 3 (2007) 107-132 107 IOS Press High performance publish/subscribe middleware for mobile wireless networks

Abstract. Decoupling, flexible, scalable and asynchronous nature of publish/subscribe paradigms makes them a good choice for mobile wireless networks. However, our research shows that current implementations of publish/subscribe systems as well as the traditional solutions for extending publish/subscribe systems to the mobile domain do not perform well in highly mobile and unreliable wireless settings. We present semi-durable subscriptions, a technique that we have developed to overcome the challenges and the performance concerns publish/subscribe systems face in mobile wireless settings. We discuss the architecture of semi-durable subscriptions and study in detail the effect of various mobility parameters on the performance of semi-durable subscriptions to demonstrate their efficacy in mobile wireless settings. We also discuss system parameters for semi-durable subscriptions and with the help of experimental results demonstrate how these parameters can be controlled to configure a system according to a set of desired characteristics

Similarity-Based Clustering Strategy for Mobile Ad Hoc Multimedia Databases

Multimedia data are becoming popular in wireless ad hoc environments. However, the traditional content-based retrieval techniques are inefficient in ad hoc networks due to the multiple limitations such as node mobility, computation capability, memory space, network bandwidth, and data heterogeneity. To provide an efficient platform for multimedia retrieval, we propose to cluster ad hoc multimedia databases based on their semantic contents, and construct a virtual hierarchical indexing infrastructure overlaid on the mobile databases. This content-aware clustering scheme uses a semantic-aware framework as the theoretical foundation for data organization. Several novel techniques are presented to facilitate the representation and manipulation of multimedia data in ad hoc networks: 1) using concise distribution expressions to represent the semantic similarity of multimedia data, 2) constructing clusters based on the semantic relationships between multimedia entities, 3) reducing the cost of content-based multimedia retrieval through the restriction of semantic distances, and 4) employing a self-adaptive mechanism that dynamically adjusts to the content and topology changes of the ad hoc networks. The proposed scheme is scalable, fault-tolerant, and efficient in performing content-based multimedia retrieval as demonstrated in our combination of theoretical analysis and extensive experimental studies