Despite the many research efforts addressing the integration of mobile nodes into grids, only a few of them have considered the establishment of mobile grids over wireless ad hoc networks (hereafter, mobile ad hoc grids). Clearly, such grids need specialized resource discovery and scheduling mechanisms. To the best of our knowledge, though, the research on these mechanisms for mobile ad hoc grids is still preliminary. Besides, and more importantly, it has approached discovery and scheduling as separate mechanisms, which, we argue, is not suitable for mobile ad hoc grids. In this paper, we propose the integration of resource discovery and scheduling for mobile ad hoc grids into a single protocol called DICHOTOMY (DIscovery and sCHeduling prOTOcol for MobilitY). This protocol allows computational tasks to be distributed appropriately in a mobile ad hoc grid, while mitigating the overhead of discovery messages exchanged among the nodes. Our experiments show that the protocol: (i) does proper scheduling, allowing an efficient load balancing among the nodes and helping with lowering the average completion time of tasks; (ii) keeps the discovery efficiency at acceptable levels in mobility scenarios and (iii) scales very well with respect to an increasing number of nodes, both in the total amount of energy savings due to packet transmissions and the distribution of such savings among the nodes.

The potential loss of privacy due to the use of location-based applications may be one of the greatest obstacles to their wider acceptance. Nevertheless, most research about privacy management to-date has not taken into consideration the complexity in the utilization of collaborative applications that may require users' location sharing among participants. In this article, we propose a privacy service that helps users to maintain their privacy policy in a flexible and incremental way. We also carried out a qualitative evaluation study whose results illustrate several challenges that should be handled in the design of such a service.

As networks with mobile devices becorne commonplace, many new applications for those networks arisc, including some that require coordination among groups of mobile clients. One basic tool for implementing coordination is reliable multicast, where delivery of a multicast message is atomic, i.e. cither all or none of the group members deliver the message. While several multicast protocols have been proposed for mobile networks, only a few works have considered reliable multicats. In this paper we present and compare two protocols based on Two-Phase-Commit that implement reliable multicast for structured mobile networks. Protocol iAM²C is a variant of protocol AM2C that employs a two-level hierarchical location management scheme to locate and route messages to the mobile hosts addressed by a multicast. Although hierarchical location management is not new in the context of mobile and cellular networks, we are unaware of any other work which combines hierarchical location management with protocols for reliable multicast. We have prototyped, simulated and evaluated both protocols using the MobiCS simulation enviromment. Our experiments indicate that despite some overhead incurred by the location management and the additional level of message redirection, iAM2C is more efficient than the AM² C protocol and scales well with the size of the wired network infra-structure.

In distributed applications based on mobile agents, coordination and synchronization of the actions executed by a team of mobile agents are difficult tasks. The main difficulty comes from the fact that coordination requires the agents to interact with each other in spite of their dynamically changing locations. In this paper we present a mechanism for coordinating mobile agents which handles the problem of locating and addressing members in a group of mobile agents. This mechanism, which we called Broadcast Channel, implements reliable broadcasts of messages to a group of mobile agents, independently of their current locations.