Path probing is essential to maintain an efficient overlay network topology. However, the cost of complete probing can be as high as O(n/sup 2/), which is prohibitive in large-scale overlay networks. Recently we propo...
详细信息
Path probing is essential to maintain an efficient overlay network topology. However, the cost of complete probing can be as high as O(n/sup 2/), which is prohibitive in large-scale overlay networks. Recently we proposed a method that trades probing overhead for inference accuracy in sparse networks such as the Internet. The method uses physical path information to infer path quality for all of the n/spl times/(n-1) overlay paths, while actually probing only a subset of the paths. We propose and evaluate a distributed approach to implement this method. We describe a minimum diameter, link-stress bounded overlay spanning tree, which is used to collect and disseminate path quality information. All nodes in the tree collaborate to infer the quality of all paths. Simulation results show this approach can achieve a high-level of inference accuracy while reducing probing overhead and balancing link stress on the spanning tree.
We address a key issue that arises in run-time recomposition of software: the transfer of nontransient state between old components and their replacements. We focus on the concept of collateral change, which refers to...
详细信息
We address a key issue that arises in run-time recomposition of software: the transfer of nontransient state between old components and their replacements. We focus on the concept of collateral change, which refers to the set of recomposition actions that must be applied atomically for continued correct execution of the system. We describe Perimorph, a system that supports compositional adaptation of both functional and nonfunctional concerns by explicitly addressing collateral change. The operation of Perimorph is demonstrated through the implementation and testing of a 2D/3D digital elevation mapping application that supports recomposition and handoff among networked devices with varying capabilities.
Various anatomical objects are tubular in shape. These structures can be modeled by describing their curvilinear path and the cross-sectional shape along the path. However, most research on tubular object segmentation...
详细信息
Various anatomical objects are tubular in shape. These structures can be modeled by describing their curvilinear path and the cross-sectional shape along the path. However, most research on tubular object segmentation has focused on vascular systems, and often assumes a circular cross-section. These techniques are not readily applicable to anatomy such as the cochlea, which has a non-circular cross-sectional shape. We present the principal flow filter, which calculates the flow vector (tangential to the path) in a local region of a tubular object with a non-circular cross-section. It can be used to extract the centerline orientation and thus incrementally track along the tube. We present results from generated data with a variety of cross-sectional shapes. The filter is shown to rapidly and robustly converge to the true orientation. We also analyse a CT scan of a human cochlea, with promising results.
This paper addresses the energy consumption of forward error correction (FEC) protocols as used to improve quality-of-service (QoS) for wireless computing devices. The paper also characterizes the effect on energy con...
详细信息
This paper addresses the energy consumption of forward error correction (FEC) protocols as used to improve quality-of-service (QoS) for wireless computing devices. The paper also characterizes the effect on energy consumption and QoS of the power saving mode in 802.11 wireless local area networks (WLANs). Experiments are described in which FEC-encoded audio streams are multicast to mobile computers across a WLAN. Results of these experiments quantify the tradeoffs between improved QoS, due to FEC, and additional energy consumption caused by receiving and decoding redundant packets. Two different approaches to FEC are compared relative to these metrics. The results of this study enable the development of adaptive software mechanisms that attempt to manage these tradeoffs in the presence of highly dynamic wireless environments.
This paper addresses the design of adaptive middleware to support autonomic computing in pervasive computing environments. The particular problem we address here is how to support self-optimization to changing network...
详细信息
This paper addresses the design of adaptive middleware to support autonomic computing in pervasive computing environments. The particular problem we address here is how to support self-optimization to changing network connection capabilities as a mobile user interacts with heterogeneous elements in a wireless network infrastructure. The goal is to enable self-optimization to such changes transparently with respect to the core application code. We propose a solution based on the use of the generic proxy, which is a specific CORBA object that can intercept and process any CORBA request using rules and actions that can be introduced to the knowledge base of the proxy during execution. To explore its design and operation, we have incorporated the generic proxy into ACT (Sadjadi and McKinley, 2004), an adaptive middleware framework we designed previously to support adaptation in CORBA applications. Details of the generic proxy are presented. A case study is described in which a generic proxy is used to support self-optimization in an existing image retrieval application, when executed in a heterogeneous wireless environment.
Adaptable applications are difficult to develop and maintain especially if adaptive code, which implements the adaptive behavior, is tangled into functional code, which implements the imperative behavior. Our work inv...
详细信息
Adaptable applications are difficult to develop and maintain especially if adaptive code, which implements the adaptive behavior, is tangled into functional code, which implements the imperative behavior. Our work investigates how to wrap existing applications transparently to generate such management components. Developing manageable components requires some mechanism to support adaptation in behavior. The predominant mechanism for implementing adaptation in object-oriented software is behavioral reflection, which can be used to modify how an object responds to a message. This work describes the application of TRAP/J to a multicast audio application. The audio-streaming application (ASA) is designed to deliver interactive audio from a microphone at one network node to multiple receiving nodes.
This work introduces an approach to adding timing information to UML diagrams for modeling embedded systems. In order to perform automated formal analysis of these UML diagrams with timing information, we extend a pre...
详细信息
ISBN:
(纸本)9780769521312
This work introduces an approach to adding timing information to UML diagrams for modeling embedded systems. In order to perform automated formal analysis of these UML diagrams with timing information, we extend a previously developed UML formalization framework to provide Promela semantics for the timing elements of the UML diagrams. The paper describes the application of our approach to an electronically controlled steering system obtained from one of our industrial collaborators.
This work presents an approach for dynamic software reconfiguration in sensor networks. Our approach utilizes explicit models of the design space of the embedded application. The design space is captured by formally m...
详细信息
This work presents an approach for dynamic software reconfiguration in sensor networks. Our approach utilizes explicit models of the design space of the embedded application. The design space is captured by formally modeling all the software components, their interfaces, and their composition. System requirements are expressed as formal constraints on QoS parameters that are measured at runtime. Reconfiguration is performed by transitioning from one point of the operation space to another based on the constraints. We demonstrate our approach using simulation results for a simple sensor network that performs one-dimensional tracking.
The emergence of pervasive wide-area distributed computing environments, such as pervasive information systems and computational grids, has enabled new generations of applications that are based on seamless access, ag...
详细信息
The emergence of pervasive wide-area distributed computing environments, such as pervasive information systems and computational grids, has enabled new generations of applications that are based on seamless access, aggregation and interaction. However, the inherent complexity, heterogeneity and dynamism of these systems require a change in how the applications are developed and managed. In this paper we present a component-based programming framework to support the development of autonomic self-managed applications. The framework enables the development of autonomic components and the formulation of autonomic applications as the dynamic composition and management of autonomic components. The operation of the proposed framework is illustrated using a forest fire application.
The problem of locating a semi-desirable facility on a plane is considered. A bi-criteria model is used. One of the criteria is well known minimum criterion. The second criterion is a weighted sum of Euclidean distanc...
详细信息
The problem of locating a semi-desirable facility on a plane is considered. A bi-criteria model is used. One of the criteria is well known minimum criterion. The second criterion is a weighted sum of Euclidean distances raised to the power of negative one. This function represents the aggregate undesirable effects of the facility and it is also a minimization problem. The bi-criteria model consists of a linear combination of these two criteria. The proposed model solved by particle swarm optimization provides better results than a previously proposed heuristic.
暂无评论