This paper explores three different methods, employed separately and in combination, to improve the quality of video delivery on wireless local area networks. The approaches are: leader-driven multicast (LDM), monitor...
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ISBN:
(纸本)0780373715
This paper explores three different methods, employed separately and in combination, to improve the quality of video delivery on wireless local area networks. The approaches are: leader-driven multicast (LDM), monitoring MAC layer unicast (re)transmissions by other receivers; application-level forward error correction (FEC) using block erasure codes; negative feedback from selected receivers in the form of extra parity requests (EPR). The performance of these three methods is evaluated using both experiments on a mobile computing testbed and simulation. The results indicate that, while LDM is helpful in improving the raw packet reception rate, the combination of FEC and EPR is most effective in improving the frame delivery rate.
In softwareengineering, design patterns propose solution skeletons for common design problems. The solution skeleton is described in such a way that the design can be used for other projects, where each application t...
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In softwareengineering, design patterns propose solution skeletons for common design problems. The solution skeleton is described in such a way that the design can be used for other projects, where each application tailors the design to specific project constraints. This paper describes research into investigating how a similar approach to reuse can be applied to requirements specifications, which we term requirements patterns. Specifically, the paper explores how object-oriented modeling notations, such as the Unified Modeling Language (UML), can be used to represent common requirements patterns. Structural and behavioral information are captured as part of a requirements pattern. In order to maximise reuse, we focus on requirements patterns for embedded systems. This paper also describes case studies that illustrate how we have applied these general patterns to multiple embedded systems applications from the automotive industry.
software on wearable computers must adapt to dynamic environmental conditions, such as changes in packet loss behavior on wireless communication channels. This paper investigates the use of programming language constr...
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software on wearable computers must adapt to dynamic environmental conditions, such as changes in packet loss behavior on wireless communication channels. This paper investigates the use of programming language constructs to realize adaptive behavior. A prototype language, Adaptive Java, was used to construct MetaSocket components, whose composition and behavior can be adapted to changing conditions during execution. MetaSockets were then integrated into Pavilion, a web-based collaboration framework, and experiments were conducted on a mobile computing testbed containing Xybernaut MA-V wearable computersystems. Performance results demonstrate the utility of MetaSockets in reducing file transfer time and enhancing the quality of interactive audio streams.
Many middleware platforms use computational reflection to support adaptive functionality. Most approaches intertwine the activity of observing behavior (introspection) with the activity of changing behavior (intercess...
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Many middleware platforms use computational reflection to support adaptive functionality. Most approaches intertwine the activity of observing behavior (introspection) with the activity of changing behavior (intercession). This paper explores the use of language constructs to separate these parts of reflective functionality. This separation and "packaging" of reflective primitives is intended to facilitate the design of correct and consistent adaptive middleware. A prototype language, called Adaptive Java, is described in which this functionality is realized through extensions to the Java programming language. A case study is described in which "metamorphic" socket components are created from regular socket classes and used to realize adaptive behavior on wireless network connections.
A previously unknown form of compromising emanations has been discovered. LED status indicators on data communication equipment, under certain conditions, are shown to carry a modulated optical signal that is signific...
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Modern enterprises are irreversibly dependent on large-scale, adaptive, component-based information systems whose complexity frequently exceeds current engineering capabilities for intellectual control, resulting in p...
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Presents the design and preliminary evaluation of hierarchical partitioning and load-balancing techniques for distributed structured adaptive mesh refinement (SAMR) applications. The overall goal of these techniques i...
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Presents the design and preliminary evaluation of hierarchical partitioning and load-balancing techniques for distributed structured adaptive mesh refinement (SAMR) applications. The overall goal of these techniques is to enable the load distribution to reflect the state of the adaptive grid hierarchy and exploit it to reduce synchronization requirements, improve load-balance, and enable concurrent communications and incremental redistribution. The hierarchical partitioning algorithm (HPA) partitions the computational domain into subdomains and assigns them to hierarchical processor groups. Two variants of HPA are presented. The static hierarchical partitioning algorithm (SHRA) assigns portions of overall load to processor groups. In SHRA, the group size and the number of processors in each group is setup during initialization and remains unchanged during application execution. It is experimentally shown that SHRA reduces communication costs as compared to the Non-HPA scheme, and reduces overall application execution time by up to 41%. The adaptive hierarchical partitioning algorithm (AHRA) dynamically partitions the processor pool into hierarchical groups that match the structure of the adaptive grid hierarchy.
software inspections are regarded as an important technique to detect faults throughout the software development process. The individual preparation phase of software inspections has enlarged its focus from only compr...
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software inspections are regarded as an important technique to detect faults throughout the software development process. The individual preparation phase of software inspections has enlarged its focus from only comprehension to also include fault searching. Hence, reading techniques to support the reviewers on fault detection are needed. Usage-based reading (UBR) is a reading technique, which focuses on the important parts of a software document by using prioritized use cases. This paper presents a series of three UBR experiments on design specifications, with focus on the third. The first experiment evaluates the prioritization of UBR and the second compares UBR against checklist-based reading. The third experiment investigates the amount of information needed in the use cases and whether a more active approach helps the reviewers to detect more faults. The third study was conducted at two different places with a total of 82 subjects. The general result from the experiments is that UBR works as intended and is efficient as well as effective in guiding reviewers during the preparation phase of software inspections. Furthermore, the results indicate that use cases developed in advance are preferable compared to developing them as part of the preparation phase of the inspection.
Adaptive Quality-of-Service management is critical for enabling effective collaboration between distributed clients in a heterogeneous (wired and wireless) environment. This is because both client profiles (capabiliti...
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Adaptive Quality-of-Service management is critical for enabling effective collaboration between distributed clients in a heterogeneous (wired and wireless) environment. This is because both client profiles (capabilities, interests and resources) and system resources can be significantly different and highly dynamic. This paper presents the design and prototype implementation of an adaptive QoS management framework for collaborative multimedia applications in distributed, heterogeneous environments. The overall goal of the framework is to locally adapt the shared information to meet the capabilities, interests and current state of each collaborating client while preserving the semantic content of the information to maintain effective sharing. Transformations investigated in this paper include gradual gradations and modality transformations. The framework builds on a publisher-subscriber messaging substrate that uses semantic profiles and provides each client with direct and immediate access to all information defined by its needs and capabilities, without having to maintain and update global rosters. It interfaces with the Simple Network Management Protocol (SNMP) to determine the state of the network by directly querying network elements. An experimental evaluation of the framework for wired and wireless clients is also presented.
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