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Abstract-The analysis of the real-time properties of an embedded communication system relies on finding upper bounds on the Worst-Case Response Time (WCRT) of the messages that are exchanged among the nodes on the network. The classical WCRT analysis of Controller Area Network (CAN) implicitly assumes that at any given time, each node is able to enter its highest priority ready message into arbitration. However, in reality, CAN controllers may have some characteristics, such as nonabortable transmit buffers, which may break this assumption. This paper provides analysis for networks that contain nodes with non-abortable transmit buffers, as well as nodes that meet the requirements of the classical analysis. The impact on message WCRTs due to a limited number of transmission buffers with non-abortable behaviour is examined via two case-studies.

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In distributed real-time systems it is crucial to ensure the temporal validity of the data exchanged among the nodes. Classically, the frame Worst Case Response Time (WCRT) analyses, and the software tools which implement them, do not take into account the aperiodic traffic. One of the main reasons for this is that the aperiodic traffic is generally very difficult to characterize (i.e., the arrival patterns of the aperiodic frames). The consequence of this is that one tends to underestimate the WCRT, which may have an impact on the overall safety of the system. In this paper, we propose a probabilistic approach to model the aperiodic traffic and integrate it into response time analysis. The approach allows the system designer to choose the safety level of the analysis based on the system's dependability requirements. Compared to existing deterministic approaches the approach leads to more realistic WCRT evaluation and thus to a better dimensioning of the hardware platform. * Jörn MIGGE was with PSA Peugeot-Citroën at the time the study was undertaken.

Abstract-IEEE 802.15.4 standard specifies a beacon-enabled mode which provides a synchronization environment using beacon transmissions. However, this mode is designed for single hop networks and its use in multi-hop networks is not straightforward. The main challenges of using beacon-enabled mode in multi-hop networks are how to efficiently schedule beacon transmissions to avoid direct and indirect beacon collisions and how to make a schedule tolerant to the clock drifts due to the low cost components. In this paper, we present TBoPS, a novel technique for scheduling beacons in the cluster tree topology. TBoPS uses a dedicated period called beacon only period (BOP) to schedule beacons at the beginning of IEEE 802.15.4 superframe. The advantages of TBoPS is that every beacon-enabled node selects a beacon schedule distributively during association. We analysed the robustness of TBoPS to clock drifts. We also show through simulations that all nodes in the network are synchronized and follow the same superframe structure.

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Abstract. With this paper we offer an insight in designing and analyzing wireless sensor networks in a versatile manner. Our framework applies probabilistic and component-based design principles for the wireless sensor network modeling and consequently analysis; while maintaining flexibility and accuracy. In particular, we address the problem of allocating and reconfiguring the available bandwidth. The framework has been successfully implemented in IEEE 802.15.4 using an Admission Control Manager (ACM); which is a module of the MAC layer that guarantees that the nodes respect their probabilistic bandwidth assignment as well as the bandwidth assignment policy applied. The proposed framework also aims to accurately analyze the behaviors of communication protocols for energy-consumption and reliability purposes. We evaluate the probabilistic bandwidth assignment methods using CSMA/CA access protocol of IEEE 802.15.4. Furthermore, we analyze the behavior of the ACM and compare the performance of the network with and without using the ACM against the original standard. The simulation results show that the use of ACM increases the overall performance of the network. 4