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標題: 周期性重組光封包交換之模型化及效能分析
Modeling and Performance Analysis of Optical Packet Switching with Periodic Reconfiguration
作者: 林偉 
關鍵字: 基礎研究;資訊工程--硬體工程

Recently, optical switching technology is becoming an attractive alternative to electronicswitches. Optical switches operate in a very different way than their electronic counterpart.They are periodically reconfigured through mechanical settling and synchronization, with asignificant delay ranging from tens of nanoseconds to several milliseconds. Duringreconfiguration, an optical switch temporarily suspends packets transmission and holds themin buffers. Reconfiguration causes extra delay for packets departure in addition to the queueingdelay due to output contention. In this proposal, we address the issue that reconfigurationfrequency in fact has a crucial effect on reconfiguration delay and queueing delay. Loweringreconfiguration frequency helps reduce the reconfiguration delay on average, but this mayprolong the queueing time of packets in buffers and waste switch bandwidth especially underlight load. On the other hand, raising reconfiguration frequency cuts down the queueing timeof packets, but it increases the reconfiguration delay in all. Therefore, we propose toanalytically study the impact of reconfiguration frequency on the optical switch performance.We intend to use the analytical results to find the proper frequency for optical switches tooperate with peak performance.In the past, several reconfiguration schemes have been proposed in an attempt tominimize reconfiguration delay. The main idea behind these schemes is to group arrivingpackets in one batch at a time and to deterministically schedule the packets with a minimumset of configurations. These deterministic scheduling schemes, however, can only achieve alocal optimization for one single batch. Here we propose a different approach to investigatingthe performance optimization problem. We consider switch reconfiguration as a stochasticprocess with random variables that characterize packets arrival and queueing. In other words,we are looking for statistic optimization instead. With the introduction of reconfiguration delayas well as VOQs, the conventional queueing models, e.g. Geox/G/1, flatly unfit for theperformance analysis of optical packet switches under consideration. Here we propose todevelop a new discrete-time queueing system that observes the time-limited service disciplinewith variable vacation time. By means of stochastic decomposition, we will construct ananalytical model with nested Markov chains and proceed to analyze the switch performance.Through the analysis, we will be able to quantify the impact of major system parameters onthe switch performance in closed forms. In this proposal, we sketch a computational methodfor generating numerical results from these closed forms. Using the numerical results, we canspecifically locate the optimum reconfiguration frequency at which optical switches transmitpackets with the minimum delay time. We will implement a simulator for validating theanalytical results produced by the queueing system. The proposed research is of greatsignificance to the performance enhancement of optical packet switches. With the finding ofoptimum frequency, we are capable of dynamically tuning up the performance of opticalswitches in response to varying loading conditions.
其他識別: NSC100-2221-E005-066
Appears in Collections:資訊科學與工程學系所

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