The Experts below are selected from a list of 948 Experts worldwide ranked by ideXlab platform
Khurram Aziz - One of the best experts on this subject based on the ideXlab platform.
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Effect of Switchover Time in Cyclically Switched Systems
'IntechOpen', 2021Co-Authors: Khurram AzizAbstract:This chapter presented an overview of the various types of polling systems. Polling systems were classified and the existing work was summarized. Cyclic service queueing systems and their applications in modern day communication systems were then discussed. While a lot of work has been done on polling systems with exhaustive service and infinite queues, with several closed form solutions, the work on finite queue, non-exhaustive cyclic polling systems is very limited, and only approximate solutions are available. Starting with a simple two-queue cyclic polling model with Switchover Time ignored during service, various characteristic measures were studied, including the mean waiting Time and the blocking probability for the customers in the system. This simple two-queue model was then extended to an n-queue model and generalized formulae were developed.. In most of the studies, the Switchover Time an important parameter has been ignored. In order to see the effect of the Switchover Time, especially in optical communication systems where ever increasing speeds imply an ever diminishing ratio of service Time to Switchover Time, a two-stage service model was developed for a two-queue system with service followed by Switchover. This model was then compared with the model in which Switchover Time was ignored during service. Significant differences were noted when the ratio of service Time to Switchover Time was small. However, this difference was negligible where the ratio between service Time and Switchover Time was greater than 100. It can thus be concluded that it is not always safe to ignore the Switchover Times. It is important to note that the various techniques discussed here have been mostly for small systems with two, or three-queues. It is straightforward to extend this study to multiple queues with large queue sizes because of the symmetric nature of the systems. The practical limita
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Effect of Switchover Time in Cyclically Switched Systems
Switched Systems, 2009Co-Authors: Khurram AzizAbstract:Cyclic service queueing systems have a broad range of applications in communication systems. From legacy systems like the slotted ring networks and switching systems, to more recent ones like optical burst assembly, Ethernet over SDH/SONET mapping and traffic aggregation at the edge nodes, all may employ cyclic service as a means of providing fairness to incoming traffic. This would require the server to switch to the next traffic stream after serving one. This service can be exhaustive, in which all the packets in the queue are served before the server switches to the next queue, or non-exhaustive, in which the server serves just one packet (or in case of batch service, a group of packets) before switching to the next queue. Most of the study on systems with cyclic service has been performed on queues of unlimited size. Real systems always have finite buffers. In order to analyze real systems, we need to model queues with finite capacity. The analysis of such systems is among the most complicated as it is very difficult to obtain closed-form solutions to systems with finite capacity. An important parameter in cyclic service queueing systems with finite capacity is the Switchover Time, which is the Time taken for the server to switch to a different queue after a service completion. This is especially true for non-exhaustive cyclic service systems, in which the server has to switch to the next queue after serving each packet. The Switchover Time is usually very small as compared to the service Time, and is generally ignored during analysis. In such cases, the edge node can be modeled as a server, serving the various access nodes that can be modeled as queues in a cyclic manner. Hence, we assume that on finding an empty queue, the server will go to the next queue with a Switchover rate of, say e, but if the queue is not empty, we ignore the Switchover Time and assume that the server will switch to the next queue with rate μ after serving one packet in the queue. While this generally led to quite accurate results in the past due to a large difference in ratios between the service and Switchover Times, this might not be the case today as optical communication systems are getting faster and faster. Thus the Switchover Time cannot always be safely ignored as smaller differences between Switchover Times and service Times may introduce significant differences in the results. In order to analyze such systems, the Switchover process can be modeled as another phase in the service process. The focus of this chapter is on the analysis of non-exhaustive cyclic service systems with finite capacity using state space modeling technique. A brief summary on the work done to date, in cyclic service systems is presented in Section 2, while some applications of such systems 6
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Performance of Non-exhaustive Cyclic Service Systems with Finite Queues and Non-zero Switchover Times
2007 IEEE International Multitopic Conference, 2007Co-Authors: Khurram Aziz, H.r. Van As, Shahzad SarwarAbstract:Queueing systems with cyclic service have a broad range of applications in communication systems, e.g., in switching systems, ring networks, burst assembly in OBS and traffic aggregation in edge nodes. While such systems have been extensively studied, the buffer capacity is often assumed to be unlimited. In real systems, queue sizes are always limited. We present an analytical method using state-space modelling, for obtaining the performance of cyclic service systems with finite queues and non-exhaustive service. The effect of Switchover Time has also been taken into account. We also show the effect of varying traffic loads and queue sizes on the observed queue.
Mingshyan Huang - One of the best experts on this subject based on the ideXlab platform.
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cavity pressure based grey prediction of the filling to packing Switchover point for injection molding
Journal of Materials Processing Technology, 2007Co-Authors: Mingshyan HuangAbstract:Abstract Filling-to-packing Switchover control during injection molding plays a crucial role in ensuring the quality of the molded parts prior to production. Although this topic has been studied for years, traditional methods of filling-to-packing Switchover control, such as using screw cushioning or checking injection Time without indicating the actual behaviors of melt plastics being filled into the cavity, are still those mostly used in practice. The results of Switchover control, therefore, are often Times inaccurate while the variation in the quality of produced parts is not negligible. This study thus presents a novel method by which quick and accurate decisions concerning the ideal Switchover Time can be made. It has adopted a simple grey model, GM(1,1), to predict instantaneously the volumetric-filling point when monitoring the cavity pressure profile in each molding. Recently found to be a good indicator of product quality, cavity pressure profile is applied here to obtain more precise Switchover control. After the experimental verification is conducted, the results reveal that the innovative Switchover method yields a more uniform product weight than any traditional methods.
Jin-fu Chang - One of the best experts on this subject based on the ideXlab platform.
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Serving two correlated queues with a synchronous server under exhaustive service discipline and nonzero Switchover Time
IEEE Transactions on Communications, 1991Co-Authors: Jin-fu ChangAbstract:A system composed of two queues that accepts correlated inputs and receives services from a synchronous server is studied. An exhaustive service discipline is adopted in serving a queue. Nonzero Switchover Time for the server to change service from one queue to the other is assumed. A closed-form expression for mean waiting Time is obtained. The validity of the analysis if verified using the results of a computer simulation.
Perry Ohad - One of the best experts on this subject based on the ideXlab platform.
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Existence and Approximations of Moments for Polling Systems under the Binomial-Exhaustive Policy
2020Co-Authors: Hu Yue, Dong Jing, Perry OhadAbstract:We establish sufficient conditions for the existence of moments of the steady-state queue in polling systems operating under the binomial-exhaustive policy (BEP). We assume that the server switches between the different buffers according to a pre-specified table, and that Switchover Times are incurred whenever the server moves from one buffer to the next. We further assume that customers arrive according to independent Poisson processes, and that the service and Switchover Times are independent random variables with general distributions. We then propose a simple scheme to approximate the moments, which is shown to be asymptotically exact as the Switchover Times grow without bound, and whose computation complexity does not grow with the order of the moment. Finally, we demonstrate that the proposed asymptotic approximation for the moments is related to the fluid limit under a large-Switchover-Time scaling; thus, similar approximations can be easily derived for other server-switching policies, by simply identifying the fluid limits under those controls. Numerical examples demonstrate the effectiveness of our approximations for the moments under BEP and under other policies, and their increased accuracy as the Switchover Times increase.Comment: The current manuscript is based on material from the first version of arXiv:2005.08840. That material was removed from later versions of arXiv:2005.0884
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Asymptotic Optimality of the Binomial-Exhaustive Policy for Polling Systems with Large Switchover Times
2020Co-Authors: Hu Yue, Dong Jing, Perry OhadAbstract:We study an optimal-control problem of polling systems with large Switchover Times, when a holding cost is incurred on the queues. In particular, we consider a stochastic network with a single server that switches between several buffers (queues) according to a pre-specified order, assuming that the Switchover Times between the queues are large relative to the processing Times of individual jobs. Due to its complexity, computing an optimal control for such a system is prohibitive, and so we instead search for an asymptotically optimal control. To this end, we first solve an optimal control problem for a deterministic relaxation (namely, for a fluid model), that is represented as a hybrid dynamical system. We then "translate" the solution to that fluid problem to a binomial-exhaustive policy for the underlying stochastic system, and prove that this policy is asymptotically optimal in a large-Switchover-Time scaling regime, provided a certain uniform integrability (UI) condition holds. Finally, we demonstrate that the aforementioned UI condition holds in the following cases: (i) the holding cost has (at most) linear growth, and all service Times have finite second moments; (ii) the holding cost grows at most at a polynomial rate (of any degree), and the service-Time distributions possess finite moment generating functions
Hu Yue - One of the best experts on this subject based on the ideXlab platform.
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Existence and Approximations of Moments for Polling Systems under the Binomial-Exhaustive Policy
2020Co-Authors: Hu Yue, Dong Jing, Perry OhadAbstract:We establish sufficient conditions for the existence of moments of the steady-state queue in polling systems operating under the binomial-exhaustive policy (BEP). We assume that the server switches between the different buffers according to a pre-specified table, and that Switchover Times are incurred whenever the server moves from one buffer to the next. We further assume that customers arrive according to independent Poisson processes, and that the service and Switchover Times are independent random variables with general distributions. We then propose a simple scheme to approximate the moments, which is shown to be asymptotically exact as the Switchover Times grow without bound, and whose computation complexity does not grow with the order of the moment. Finally, we demonstrate that the proposed asymptotic approximation for the moments is related to the fluid limit under a large-Switchover-Time scaling; thus, similar approximations can be easily derived for other server-switching policies, by simply identifying the fluid limits under those controls. Numerical examples demonstrate the effectiveness of our approximations for the moments under BEP and under other policies, and their increased accuracy as the Switchover Times increase.Comment: The current manuscript is based on material from the first version of arXiv:2005.08840. That material was removed from later versions of arXiv:2005.0884
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Asymptotic Optimality of the Binomial-Exhaustive Policy for Polling Systems with Large Switchover Times
2020Co-Authors: Hu Yue, Dong Jing, Perry OhadAbstract:We study an optimal-control problem of polling systems with large Switchover Times, when a holding cost is incurred on the queues. In particular, we consider a stochastic network with a single server that switches between several buffers (queues) according to a pre-specified order, assuming that the Switchover Times between the queues are large relative to the processing Times of individual jobs. Due to its complexity, computing an optimal control for such a system is prohibitive, and so we instead search for an asymptotically optimal control. To this end, we first solve an optimal control problem for a deterministic relaxation (namely, for a fluid model), that is represented as a hybrid dynamical system. We then "translate" the solution to that fluid problem to a binomial-exhaustive policy for the underlying stochastic system, and prove that this policy is asymptotically optimal in a large-Switchover-Time scaling regime, provided a certain uniform integrability (UI) condition holds. Finally, we demonstrate that the aforementioned UI condition holds in the following cases: (i) the holding cost has (at most) linear growth, and all service Times have finite second moments; (ii) the holding cost grows at most at a polynomial rate (of any degree), and the service-Time distributions possess finite moment generating functions
