Real-time scheduling theory has shown an impressive evolution in the past few years. As a consequence of the intensive research done in this area a lot of new scheduling policies had been proposed to date. Nevertheless, just a few of such scheduling policies are available in existing Real-Time Operating Systems (RTOS). In this paper, we describe Realtss, an open source realtime scheduling simulator which is suited to simulate real-time scheduling algorithms without the need of implement them in a RTOS. Realtss is an invaluable teaching and researching tool since existing and new real-time scheduling policies can be easily evaluated.

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The performance of wireless sensor networks (WSNs) at monitoring time-critical events is an important research topic, mainly due to the need to ensure that the actions to be taken upon these events are timely. To determine the effectiveness of the IEEE 802.15.4 standard at monitoring time-critical events in WSNs, we introduce a routing scheme based on drain announcements that seeks minimum routing overhead. We carried out a novel performance evaluation of the IEEE 802.15.4 technology under different conditions, to determine whether or not near-real-time event monitoring is feasible. By analyzing different simulation metrics such as packet loss rate, average end-to-end delay, and routing overhead, we determine the degree of effectiveness of the IEEE 802.15.4 standard at supporting time-critical tasks in multi-hop WSNs, evidencing its limitations upon the size and the amount of traffic flowing through the network.

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