Interactive multimedia and sensor-based real-time applications on the Internet must be delivered to the receiver at the sender's transmission rate and have bounded end-to-end delay requirements. We call such flows...
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Interactive multimedia and sensor-based real-time applications on the Internet must be delivered to the receiver at the sender's transmission rate and have bounded end-to-end delay requirements. We call such flows real-rate flows. The resource requirements of such flows can not be met in many environments. Researchers have proposed selectively dropping data in the flow so that the data rate matches available resource capacity (i.e., QoS adaptive, real-rate flows). Application-level QoS adaptation is not well integrated with network scheduling mechanisms and resource management, resulting in slow and inaccurate QoS adaptation, poor flow quality, and unpredictable interactions between adaptive mechanisms. Our proposed resource management service integrates QoS adaptation and network/CPU scheduling mechanisms to offer support for QoS adaptive, real-rate flows. Its goal is to deliver the highest quality flow to the receiver within a bounded delay at the sender's real rate. This service combines two techniques - both based on feedback real-rate scheduling and QoS adaptation. Real-rate scheduling uses packet time-stamps to schedule flows along the flow path at the sender's real rate. QoS adaptation drops data at a node when the node's resources are limited, in application-specified priority order. System modeling issues are discussed and a controller structure is proposed.
We present new simulation results, in which a computational model of interacting visual neurons simultaneously predicts the modulation of spatial vision thresholds by focal visual attention, for five dual-task human p...
We present new simulation results, in which a computational model of interacting visual neurons simultaneously predicts the modulation of spatial vision thresholds by focal visual attention, for five dual-task human psychophysics experiments. This new study complements our previous findings that attention activates a winner-take-all competition among early visual neurons within one cortical hypercolumn. This "intensified competition" hypothesis assumed that attention equally affects all neurons, and yielded two single-unit predictions: an increase in gain and a sharpening of tuning with attention. While both effects have been separately observed in electrophysiology, no single-unit study has yet shown them simultaneously. Hence, we here explore whether our model could still predict our data if attention might only modulate neuronal gain, but do so non-uniformly across neurons and tasks. Specifically, we investigate whether modulating the gain of only the neurons that are loudest, best-tuned, or most informative about the stimulus, or of all neurons equally but in a task-dependent manner, may account for the data. We find that none of these hypotheses yields predictions as plausible as the intensified competition hypothesis, hence providing additional support for our original findings.
Commonplace computer applications on general-purpose computers increasingly are expected to meet "real-rate" requirements, processing or displaying data or images at an externally driven "rate". We...
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ISBN:
(纸本)0780366387
Commonplace computer applications on general-purpose computers increasingly are expected to meet "real-rate" requirements, processing or displaying data or images at an externally driven "rate". We describe a feedback-control-based resource manager design approach, allowing the computer system to allocate resources such as CPU and network bandwidth based on the measured "progress" of the applications. Progress is measured by separating a complex application into a number of simpler applications separated by buffers. The resource scheduler measures the buffer fill levels to determine whether the rates of data coming in and going out of each buffer are matched. Feedback controllers keep the buffer levels around a certain fill level. We have developed prototype systems in the Linux environment that demonstrate that (classical) feedback control can be used to match the real rates. However, more formal methods, such as those that can be developed by the control theory community, are needed to help with the analysis and design of such systems to make them commercially viable. This paper presents the computer system problems, results from the prototype designs showing feasibility, some preliminary modeling results, and demonstrations and discussions of which control modeling, analysis and design results and techniques appear to be relevant to this computer system problem, and why.
Hierarchical WWW cache formation which provides both higher hit rates and saves overall bandwidth consumption through fetching WWW objects and periodically redistributing them among member caches is proposed as an app...
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Transaction management is required to maintain data consistency in any system with concurrent access to its information. The Object Transaction Service (OTS) is a CORBA service that brings transactional semantics to d...
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We investigate the asymptotic dynamics of on-line learning for neural networks, and provide an exact solution to the network dynamics at late times under various annealing schedules. The dynamics is solved using two d...
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We investigate the asymptotic dynamics of on-line learning for neural networks, and provide an exact solution to the network dynamics at late times under various annealing schedules. The dynamics is solved using two different frameworks: the master equation and order parameter dynamics, which concentrate on microscopic and macroscopic parameters, respectively. The two approaches provide complementary descriptions of the dynamics. Optimal annealing rates and the corresponding prefactors are derived for soft committee machine networks with hidden layers of arbitrary size.
Transaction management is required to maintain data consistency in any system with concurrent access to its information. The Object Transaction Service (OTS) is a CORBA service that brings transactional semantics to d...
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Transaction management is required to maintain data consistency in any system with concurrent access to its information. The Object Transaction Service (OTS) is a CORBA service that brings transactional semantics to distributed object oriented applications. We report our experience of developing a prototype using OTS. We present results from our scaling experiments and analyze the overheads incurred by the components of an OTS based distributed transaction. We also highlight issues that need to be addressed if OTS is to be used in large distributed systems such as those in Boeing.
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