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Carrier-sense Medium Access Control (MAC) protocols such as the IEEE 802,11 Distributed Coordination Function (DCF) avoid collisions by holding up pending packet transmission requests when a carrier signal is observed above a certain threshold. However, this often results in unnecessarily conservative communication, thus making it difficult to maximize the utilization of the spatial spectral resource. This paper shows that a higher aggregate throughput can be achieved by allowing more concurrent communications and adjusting the communication distance on the fly, which needs provisions for the following two areas: On the one hand, carrier sense-based MAC protocols do not allow aggressive communication attempts when they are within the carrier senseable area. On the other hand, the communication distance is generally neither short nor adjustable because multihop routing protocols strive for providing minimum hop paths, This paper proposes a new MAC algorithm, called Multiple Access with Salvation Army (MASA), which adopts less sensitive carrier sensing to promote more concurrent communications and adjusts the communication distance adaptively via "packet salvaging* at the MAC layer. Extensive simulation based on the ns-2 has shown MASA to outperform the DCF, particularly in terms of packet delay. We also discuss the implementation of MASA based on the DCF specification. [ABSTRACT FROM AUTHOR]

This paper presents a performance study of UDP/IP, TCP/IP, and M‐VIA using Linux/SimOS. Linux/SimOS is a Linux operating system port to a complete machine simulator SimOS. A complete machine simulator includes all the system components, such as CPU, memory, I/O devices, etc., and models them in sufficient detail to run an operating system. Therefore, a real program execution environment can be set up on the simulator to perform detailed system evaluation in a non‐intrusive manner. The motivation for Linux/SimOS is to alleviate the limitations of SimOS (and its variants), which only support proprietary operating systems. Therefore, the availability of the popular Linux operating system for a complete machine simulator will make it an extremely effective and flexible simulation environment for studying all aspects of computer system performance, especially evaluating communication protocols and network interfaces. The contributions made in this paper are two‐fold: First, the major modifications that were necessary to run Linux on SimOS are described. These modifications are specific to SimOS I/O device models and thus any future operating system porting efforts to SimOS will experience similar challenges. Second, a detailed analysis of UDP/IP, TCP/IP, and M‐VIA is performed to demonstrate the capabilities of Linux/SimOS. The simulation study shows that Linux/SimOS is capable of capturing all aspects communication performance, including the effects of the kernel, device driver, and network interface. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a comparison of power-aware video decoding techniques that utilize dynamic voltage scaling (DVS). These techniques reduce the power consumption of a processor by exploiting high frame variability within a video stream. This is done through scaling of the voltage and frequency of the processor during the video decoding process. However, DVS causes frame deadline misses due to inaccuracies in decoding time predictions and granularity of processor settings used. Four techniques were simulated and compared in terms of power consumption, accuracy, and deadline misses. In addition, this paper proposes the frame-data computation aware (FDCA) technique, which is a useful power-saving technique not only for stored video but also for real-time video applications. The FDCA method is compared with the GOP, Direct, and Dynamic methods, which tend to be more suited for stored video applications. The simulation results indicated that the Dynamic per-frame technique, where the decoding time prediction adapts to the particular video being decoded, provides the most power saving with performance comparable to the ideal case. On the other hand, the FDCA method consumes more power than the Dynamic method but can be used for stored video and real-time time video scenarios without the need for any preprocessing. Our findings also indicate that, in general, DVS improves power savings, but the number of deadline misses also increase as the number of available processor settings increases. More importantly, most of these deadline misses are within 10–20% of the playout interval and thus have minimal affect on video quality. However, video clips with high variability in frame complexities combined with inaccurate decoding time predictions may degrade the video quality. Finally, our results show that a processor with 13 voltage/frequency settings is sufficient to achieve near maximum performance with the experimental environment and the video workloads we have used. [Copyright &y& Elsevier]