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Hiệu suất của hệ thống thông tin máy tính P9

These days, intelligent file or computing servers via a shared communication medium that grants access using a polling scheme. Also in other fields, e.g., manufacturing, logistics and maintenance, the principle of polling is often encountered. When trying to analyse systems that operate along some polling scheme, so-called polling models are needed. In this chapter we provide a concise overview of the theory and application of polling models. Although we do provide some mathematical derivations, sometimes polling our main aim is. | Performance of Computer Communication Systems A Model-Based Approach. Boudewijn R. Haverkort Copyright 1998 John Wiley Sons Ltd ISBNs 0-471-97228-2 Hardback 0-470-84192-3 Electronic Chapter 9 Polling models THE principle of polling is well-known in many branches of computer science applications. In early timed-sharing computers terminals were polled in order to investigate whether they had any processing to be done. These days intelligent workstations access file or computing servers via a shared communication medium that grants access using a polling scheme. Also in other fields e.g. manufacturing logistics and maintenance the principle of polling is often encountered. When trying to analyse systems that operate along some polling scheme so-called polling models are needed. In this chapter we provide a concise overview of the theory and application of polling models. Although we do provide some mathematical derivations our main aim is to show how relatively simple models can be used albeit sometimes approximately for the analysis of fairly complex systems. This chapter is further organised as follows. In Section 9.1 we characterise polling models and introduce notation and terminology. In Section 9.2 we address some important general results for polling models. Symmetric and asymmetric count-based polling models are addressed in Section 9.3 and 9.4 respectively. Using these models the IBM token ring system is analysed in Section 9.5. Time-based polling models both symmetric and asymmetric are finally discussed in Section 9.6. 9.1 Characterisation of polling models In polling models there is a single server which visits polls a number of queues in some predefined order. Customers arrive at the queues following some arrival process. Upon visiting a particular queue queued customers are being served according to some scheduling strategy. After that the server leaves the queue and visits the next queue. Going from 174 9 Polling models one queue to another takes some .