Matija Puzar

Data sharing in mobile ad-hoc networks - a study of replication and performance in the MIDAS data space

The dynamic nature of mobile ad-hoc networks (MANETs) can easily lead to data being inaccessible due to constant route changes and network partitions. One method often used for increasing reliability and availability of data is replication. However, replication comes with costs, those of transferring and storing data and keeping track of consistency between replicas. For that reason, we have identified the core factors impacting the resulting network traffic. We have performed experimental studies with a real world prototype of a distributed data management system for MANETs, called MIDAS data space. Furthermore, we have done an extensive simulation study showing where table replicas should be placed in the network, in order to minimise network traffic generated by access to the databases and by the synchronisation data. The results of the experiments are consistent and show that by using clustering techniques we can achieve close-to-optimal traffic by placing replicas on approximately 10% of nodes.

A Data Sharing Facility for Mobile Ad-Hoc Emergency and Rescue Applications

Efficient information sharing is very important for emergency and rescue operations. Mobile ad-hoc Networks (MANETs) are often the only network environment for such operations. We have developed the MIDAS data space (MDS) to transparently share information among rescue applications in such environments. To achieve the required level of availability for important information, MDS performs optimistic replication. The problems caused by optimistic replication, like consistency management, are not solved by standard solutions; instead we employ tailor-made solutions for emergency and rescue applications.

Middleware Services for Information Sharing in Mobile Ad-Hoc Networks

Information sharing is a mission critical key element in rescue and emergency operations. Mobile ad-hoc networks (MANETs) could provide a useful infrastructure to support information sharing, but appropriate applications are needed. To facilitate efficient application development for this type of infrastructure, middleware support is needed. In the Ad-Hoc InfoWare project, we are currently developing corresponding middleware services. In this paper, we discuss the application requirements that are imposed onto the middleware services, and we outline our technical approach to address the corresponding challenges. The architecture we propose comprises five main building blocks, namely knowledge management, a local and a distributed event notification service, resource management, and security and privacy management. We indicate design alternatives for these building blocks, identify open problems and relate our approach to the state-of-the-art.

Security and privacy issues in middleware for emergency and rescue applications

Mobile ad-hoc networks (MANETs) are a natural candidate for communication and information exchange in emergency and rescue operations. The personnelpsilas movements, network disruptions and other system dynamics make it hard to implement robust applications for such environments. The MIDAS project aims at creating a middleware platform to simplify the task of developing and deploying mobile and robust services for events in which the network might be set-up at short notice. MANETs may be used because infrastructure is non-existing, and the number of users might be very high. One of the application domains addressed by MIDAS are emergency and rescue operations. To get a broad acceptance of the MIDAS solutions, security and privacy issues need also to be addressed. In this paper, we analyze the security threats and present a two-way approach to securing the MIDAS architecture. In the bottom-up approach, we use an efficient key management protocol to establish trust, and in the top-down approach we use dynamic role based access control to secure the system and provide privacy.

Evaluation of Replica Placement Strategies for a Shared Data Space in Mobile Ad-Hoc Networks

The dynamic nature of mobile ad-hoc networks (MANETs) can easily lead to data being inaccessible due to constant route changes and network partitions. One method often used for increasing reliability and availability of data is replication. However, replication comes with costs, those of transferring and storing data and keeping track of consistency between replicas. For that reason, we have identified the core factors impacting the resulting network traffic. We have performed experimental studies with a real world prototype of a distributed data management system for MANETs. Further-more, we have done an extensive simulation study showing where table replicas should be placed in the network, in order to minimize network traffic generated by access to the data-bases and by the synchronization data. The results of the experiments are consistent and show that by using clustering techniques we can achieve close-to-optimal traffic by placing replicas on approximately 10 % of nodes.

Information Sharing in Mobile Ad-Hoc Networks: Evaluation of the MIDAS Data Space Prototype

Information sharing in dynamic mobile ad-hoc networks is a challenging task. High data availability in the presence of short and long term disconnections can be obtained by replicating shared data. The number of replicas must however be balanced against the cost of consistency management. In the MIDAS Data Space (MDS) we use optimistic replication together with internal versioning of data; this allows application-specific conflict resolution when reconciling replicas at network mergings. We have made a proof-of-concept implementation to perform experiments and to demonstrate through real-life field tests the usefulness of our design. In this paper we report our results. We have conducted a number of experiments on a small network formed by real devices to obtain a detailed performance evaluation. Using an emulation environment we have analysed and quantified the cost of consistency management, the impact of MDS operations, and the relationship between data availability and replication.

On the use of wireless sensor networks to cope with partitions in Mobile Ad-Hoc networks

Mobile ad-hoc networks have emerged as an efficient solution for communicating in critical scenarios, such as emergency and rescue operations. However, the infrastructure-less and dynamic nature of these networks make them vulnerable to network partitions, which directly affects the data delivery process. To mitigate the impact of partitioning, we introduce a new architecture that employs sensors to assist in forwarding the data. Such sensors are used whenever no route is found between two mobile nodes. We discuss the advantages and drawbacks of this architecture through extensive emulations. We believe that our results and discussions pave the way for the design of a new generation of ad-hoc networks.