Information Sharing in Mobile Ad-Hoc Networks: Metadata Management in the MIDAS Dataspace

An approach to information sharing in mobile ad-hoc networks (MANETs) used e.g. in rescue operations, is to store on every node a small amount of metadata describing what information resources exist in the network and where they reside, allowing applications to first search locally for information about suitable resources, and next request relevant information from a node that contains the resource. The characteristics of MANETs in general and sparse, delay-tolerant networks in particular, make the task of maintaining and disseminating metadata across all nodes difficult, particularly in the presence of scarce resources. We have designed and implemented three protocols which use different approaches to metadata dissemination: epidemic one-to-one routing, one-to-many broadcasting that utilises the characteristics of the shared radio medium of wireless networks, and the semantic protocol where a group consisting of e.g. rescue team leaders is given priority in the dissemination process and afterwards serves as multiple starting points for further dissemination. In the MIDAS project we produce middleware that speeds up MANET application development. By prototyping the metadata management component of MIDAS and testing the prototype with each of the three protocols in the network emulator environment NEMAN, we have measured bandwidth usage and performance. The implemented broadcast protocol is measured to use substantially less bandwidth than epidemic routing. The semantic protocol shows that the group indeed gets priority; it is comparable to the broadcast protocol in terms of bandwidth usage. The broadcast protocol has been used successfully in field tests of the middleware.