Group communication is a useful abstraction in the development of highly available distributed and communication-oriented applications in wide area networks (WANs). The most important aspects of this abstraction are the dynamic maintenance of group membership and its diverse semantics for interleaving membership change noti cations within the ow of regular messages. In this paper we propose a new architecture for a scalable group membership service for wide area environments. Our architecture provides two di erent service levels and their semantics, each geared to di erent applications with di erent needs: The congress membership service which provides simple semantics of membership approximation, and the moshe service, which extends congress, provides full virtual synchrony semantics. The novelty of our design is in its client-server approach, which allows lightweight clients to bene t from advanced membership services. Furthermore, our design supports the coexistence of full-edged clients along with thin clients.

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In recent years, the demand for high-precision tracking systems has significantly increased in the field of Wireless Sensor Network (WSN). A new tracking system based on exploitation of Received Signal Strength Indicator (RSSI) measurements in WSN is proposed. The proposed system is designed in particular for WSNs that are deployed in close proximity and can transmit data at a high transmission rate. The close proximity and an optimized transmit power level enable accurate conversion of RSSI measurements to range estimates. Having an adequate transmission rate enables spatial-temporal correlation between consecutive RSSI measurements. In addition, advanced statistical and signal processing methods are used to mitigate channel distortion and to compensate for packet loss. The system is evaluated in indoor conditions and achieves tracking resolution of a few centimeters which is compatible with theoretical bounds.

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