The IEEE 802.15.4 standard provides a flexible communication support for low-rate wireless personal area networks) applications. When active, the beacon-enabled mode provides a real-time communication to the supported application by adopting a guaranteed time slot (GTS) mechanism. However, this mechanism permits only up to seven real-time communicating devices. One way to deal with this limitation is to share the communication opportunities among the periodic tasks, by skipping some of the task activations in a controlled way. One of the widely accepted periodic task models that allows skips in periodic activations is the (m,k)-firm model. Motivated by this problem, this paper proposes the use of a dynamic GTS scheduling approach based on the (m,k)-firm task model, to deal with the GTS starvation problem. The proposed scheduling approach is based on pre-defined spins of the originally defined (m,k)-firm pattern. The use of an exact schedulability analysis test ensures that for each admitted message stream, at least m messages will be transmitted within each window of k consecutive deadlines. The schedulability analysis may be executed in polynomial time and therefore can be used as an online admission test for GTS requests. The effectiveness of the approach has been assessed both by a set of simulations and an experimental evaluation.
In some Wireless Sensor Network applications the sensor nodes share the same sensing activity, which means that for a considerable number of applications, not all nodes are required to perform sensing tasks during the network lifetime. Sleep-scheduling approaches can be applied in this scenario, enabling that some nodes turn off their radios, saving energy and bandwidth, as long as there are enough nodes to ensure the required Quality of Service (QoS) of the network. This paper presents a new adaptive approach for QoS and energy management in IEEE 802.15.4 networks, entitled Skip Game. This approach targets a trade-off between increasing the network lifetime and maintaining the QoS of the network, aiming a greater number of nodes to participate in the monitoring application. In order to evaluate the proposed approach, we performed some experiments using the OMNeT++ simulator tool under the MiXiM framework. The results show that the Skip Game outperforms both the traditional Gur Game and Gureen Game approaches in terms of QoS provision and network lifetime.
The IEEE 802.15.4 standard proposes a flexible communication solution for Low-Rate Wireless Personal Area Networks, including Wireless Sensor Networks. In these networks, the transmission of messages or the Guaranteed Time Slot allocation are coordinated by the traditional CSMA/CA scheme, which does not provide any additional traffic differentiation mechanism. In a previous work, we proposed an approach that assigns priorities to the messages based on the (m,k)-firm task model. This paper proposes, in a complementary way, an experimental assessment in order to define the best parameters for messages prioritization. The experimental assessment considers a realistic scenario in which a set of sensor nodes, implementing the proposed scheme works in the same coverage area of another set of nodes that does not belong to the same Wireless Sensor Networks infrastructure.
In this paper, adaptive scheduling based on dynamic priorities and imprecise computation is used in web servers. The goal is to keep proportional differentiation services. An approach with admission control has its properties of controllability and predictability evaluated. Another contribution is to show how to use and implement this approach in Apache web servers.
RESUMONeste artigo, técnicas de escalonamento adaptativo com prioridades dinâmicas e computação imprecisa são empregadas em servidores web. O principal objetivo é manter diferenciação de serviços proporcional. Um controle de admissão é adicionado à abordagem e suas propriedades de controlabilidade e previsibilidade são avaliadas. Outra contribuição do artigo é o de mostrar como implementar essas abordagens utilizando Apache.
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