Information sharing in mobile ad-hoc networks using a global metadata manager

Digital information sharing is vital to improve efficiency in rescue and emergency operations. In the absence of infrastructure, the devices brought into the area by rescue personnel, might be used to set up a mobile ad-hoc network. This application domain is dominated by frequent merges and departures of nodes, resulting in an unstable and ever changing topology. Information sharing can be handled by using metadata describing instances of tables in the network. We disseminate metadata to all nodes, so that each has its own local structure containting all metadata available. The structure enables nodes to search for table replicas, and query these over delay tolerant paths. Since metadata is small in size the structure will remain small even with many tables existing, and storing it on every device is feasible. The characteristics of mobile ad-hoc networks makes the task of disseminating metadata across all nodes difficult, in particular in the presence of scarce resources. We have looked into research coming from the domain of ad-hoc networks to reuse techniques applicable to information sharing. The techniques come mainly from routing in delay-tolerant networks, and routing protocols of dense networks. We have implemented three protocols which use different approaches to information sharing. The simple protocol uses a basic epidemic routing approach, propagating information from neighbor to neighbor. By using the broadcast protocol, we utilize the shared medium of wireless communication and its ability to send messages from one to many nodes, in addition to letting each node stop the synchronization if no metadata is needed, thus removing some of the redundant propagation paths. The semantic protocol utilizes the concept of groups amongst the nodes, by giving these first priority. If nodes of the same group are spread out through the network they will serve as multiple starting points for the following normal dissemination. By taking part in the implementation of the MIDAS middleware, real life scenarios have been acquired, and tested using the protocols developed in this thesis. MIDAS is a large reasearch project aiming to produce a middleware that speeds up MANET application development. By testing the implemented protocols in NEMAN, an emulator environment, we have measured both bandwidth usage and performance. The implemented broadcast protocol is measured to use 50 times less bandwidth than the simple implementation. Further the concept of groups of nodes is utilized to give certain nodes higher priority in the dissemination process, which results in multiple starting points for the normal dissemination techniques. This protocol has only shown that the group priority is working, however more research is needed to verify that the multiple starting points give an advantage to the global dissemination. As we can see from the results and the techniques used, routing principles in mobile ad-hoc networks can easily be applied to information sharing showing good performance optimization, resulting in fast dissemination and high availability of metadata information amoung the rescue personnel's devices