A fuzzy logic based similarity measure is introduced as a criterion for the identification of structure in data. An important characteristic of the proposed approach is that cluster prototypes are formed and evaluated...
详细信息
A fuzzy logic based similarity measure is introduced as a criterion for the identification of structure in data. An important characteristic of the proposed approach is that cluster prototypes are formed and evaluated in the course of the optimization without any a-priori assumptions about the number of clusters. The intuitively straightforward compound optimization criterion of maximizing the overall similarity between data and the prototypes while minimizing the similarity between the prototypes is adopted. It is shown that the partitioning of the pattern space obtained in the course of the optimization is more intuitive than the one obtained for the standard FCM. The local properties of clusters (in terms of the ranking order of features in the multidimensional pattern space) are captured by the weight vector associated with each cluster prototype. The weight vector is then used for the construction of interpretable information granules.
This paper uses analysis and experiments to study the minimal buffering requirements of congestion controlled multimedia applications. Applications in the Internet must use congestion control protocols, which vary tra...
详细信息
Transmission Control Protocol (TCP) is the dominant transport protocol in today's Internet. To maintain stability of the Internet, flows other than TCP must be "friendly" to TCP flows, or share network b...
详细信息
Transmission Control Protocol (TCP) is the dominant transport protocol in today's Internet. To maintain stability of the Internet, flows other than TCP must be "friendly" to TCP flows, or share network bandwidth fairly with TCP traffic. Usually a flow is claimed to be TCP-friendly when its throughput is theoretically the same as the throughput of a TCP flow when they experience the same congestion signals. However, when flows compete for bandwidth, they may not have the same perception of congestion. Therefore, measured bandwidth shares of flows are not necessarily equal, even when all flows are theoretically designed to be TCP-friendly. To study the effect on bandwidth sharing of interactions among a set of competing TCP-friendly flows, we built a hybrid state-space-based model of TCP using differential equations' and event-driven switches. We modified the TCP model, using TCP's additive-increase multiplicative-decrease (AIMD) congestion avoidance algorithm with different increase and decrease parameters, to create theoretically TCP-friendly protocols with various short-term transmission rates. We prove that TCP-friendly flows result in a stable attractor if the backing off of flow transmission rates is synchronized. Experiments using our model and using ns simulator with unsynchronized backing off show unfairness among competing flows with different short-term behaviors.
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...
详细信息
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...
详细信息
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...
详细信息
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...
详细信息
暂无评论