We present the concept of mobile groups as a basic mechanism for the reliable coordination of mobile agents. Analogously to traditional group systems, mobile groups also provide message delivery guarantees and virtual synchrony. Furthermore, they make agent mobility not only visible for the group, but also consistently ordered with other group actions (such as crashes, joins, leaves, and other migrations). The mobile groups approach represents a novel mobility support mechanism, which can be used to handle reliability of mobile agents required at both, the application and system level (e.g., for coordinating distributed agents and for reliable agent migration, respectively). In this paper, we discuss the motivations for the mobile groups approach, formally define their properties, and present a membership protocol for such groups. We also discuss some implementation issues and related performance data, and present the advantages of mobile groups against mechanisms commonly employed for the coordination of mobile agents.

Abstract-Topology control is one of the main techniques that can be used to decrease energy spenditure in wireless sensor networks. Although it has been the subject of much research, less attention has been devoted to study the effects of overhearing on topology control, i.e., the effects of the cost implied by nodes hearing transmissions even if these transmissions were not intended to them. In this paper we describe a distributed (localized) algorithm for topology control in wireless sensor networks. Our approach differs from previous work mainly in the sense that it takes the effects of overhearing into consideration and that it might eliminate more communication links from a given connectivity graph, and thus possibly assign lower transmission power to some nodes. This is done by eliminating so-called k-redundant edges, instead of eliminating only tworedundant edges. We present the sketch of the proof of properties of the algorithm and simulation results.

Support for transactional behaviour and fault tolerant executions of mobile agent-based applications is a fundamental issue in the development of mobile agent systems. We are developing the MARES platform, which supports the modelling of mobile agent-based applications as distributed transactions. The executions of mobile agent-based transactions on top of the MARES platform are fault-tolerant, in the sense that if the location in the distributed environment where a part of a global transaction is being executed becomes faulty for a long time, the system performs a recovery procedure to resume the execution of that part of the transaction at another location. In this paper we present the transaction model used in the MARES platform, we outline the interface for modelling mobile agent-based transactions, and we discuss alternatives for implementing mobile agent fault tolerance that increase the level of flexibility for modelling reliable mobile agent-based applications when compared with previously proposed approaches.