In wireless sensor networks, power is the most essential resource because each sensor node has limited batteries. Many kinds of existing clustering protocols have been developed to balance and maximize lifetime of the sensor nodes in wireless sensor networks. These protocols select cluster heads periodically, and they considered only 'How can we select cluster heads energy-efficiently?' or 'What is the best selection of cluster heads?' without considering energy-efficient period of the cluster heads replacement. Unnecessary head selection may dissipate limited battery power of the entire sensor networks. In this paper, we present T-LEACH, which is a threshold-based cluster head replacement scheme for clustering protocols of wireless sensor networks. T-LEACH minimizes the number of cluster head selection by using threshold of residual energy. Reducing the amount of head selection and replacement cost, the lifetime of the entire networks can be extended compared with the existing clustering protocols. Our simulation results show that T-LEACH outperformed LEACH in terms of balancing energy consumption and network lifetime.

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Generally, operating only a single host on a single server results in hardware underutilization. Thus, hypervisors (e.g., Xen) have been developed to allow several hosts to operate on a single server. The Xen hypervisor provides processor schedulers (e.g., Credit and Credit2 schedulers) to assign processors to each host. The Credit2 scheduler provides work assurance to the domain relative to latency and it evenly assigns processors to each domain. In addition, the Credit2 scheduler can assign a weight value to each host. A greater host weight value allows processors to be assigned to a host for longer periods. However, the Credit2 scheduler shows poorer performance than the basic Credit scheduler, which utilizes idle processors. In this paper, we propose the Mcredit2 scheduler, which improves the Credit2 scheduler. The Credit2 scheduler takes no action when the load on a specific domain causes increased processor usage. The proposed Mcredit2 scheduler allows a domain to quickly process loads by temporarily assigning a greater weight value to a host with high processor usage. In addition, we introduce a processor monitoring tool that visualizes the processor usage.

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