7 research outputs found
Operational Analysis Revisited: Error Measure Limits of Assumptions
The assumptions used to develop operational analysiscomputer performance measures, such as number of jobs at adevice or response times, are stated in terms of the data itself,rather than the underlying system which produces the data. Inspite of claims of validity and as an aid in introducing queueingtheory in teaching, little has been written about operationalanalysis in the past ten years. Accuracy of operational analysisperformance measures depend on data behavior assumptionswhich can be validated with data based error measures.Increased soundness of the operational analysis approach may beobtained by determining the limits of assumption errors as thetime period of observation increases. Part I of this paper is areview of operational analysis and addresses some of the previousconcerns with its approach. Part II develops furtherunderstanding of operational analysis assumption errors byexamining their limits. Limits are found for the assumptionerrors of job flow balance, homogeneous arrivals andhomogenous services. While the job flow balance assumptionerror measure is shown to approach zero over time, thehomogeneity assumption error measures, in general, do not
A Fixed-Point Algorithm for Closed Queueing Networks
In this paper we propose a new efficient iterative scheme for solving closed queueing networks with phase-type service time distributions. The method is especially efficient and accurate in case of large numbers of nodes and large customer populations. We present the method, put it in perspective, and validate it through a large number of test scenarios. In most cases, the method provides accuracies within 5% relative error (in comparison to discrete-event simulation)
Stochastic analyses arising from a new approach for closed queueing networks
Analyses are addressed for a number of problems in queueing systems and
stochastic modeling that arose due to an investigation into techniques that could
be used to approximate general closed networks.
In Chapter II, a method is presented to calculate the system size distribution at
an arbitrary point in time and at departures for a (n)/G/1/N queue. The analysis
is carried out using an embedded Markov chain approach. An algorithm is also
developed that combines our analysis with the recursive method of Gupta and Rao.
This algorithm compares favorably with that of Gupta and Rao and will solve some
situations when Gupta and Rao's method fails or becomes intractable.
In Chapter III, an approach is developed for generating exact solutions of the
time-dependent conditional joint probability distributions for a phase-type renewal
process. Closed-form expressions are derived when a class of Coxian distributions
are used for the inter-renewal distribution. The class of Coxian distributions was
chosen so that solutions could be obtained for any mean and variance desired in the
inter-renewal times.
In Chapter IV, an algorithm is developed to generate numerical solutions for
the steady-state system size probabilities and waiting time distribution functions of
the SM/PH/1/N queue by using the matrix-analytic method. Closed form results are also obtained for particular situations of the preceding queue. In addition, it
is demonstrated that the SM/PH/1/N model can be implemented to the analysis
of a sequential two-queue system. This is an extension to the work by Neuts and
Chakravarthy.
In Chapter V, principal results developed in the preceding chapters are employed
for approximate analysis of the closed network of queues with arbitrary service
times. Specifically, the (n)/G/1/N queue is applied to closed networks of a
general topology, and a sequential two-queue model consisting of the (n)/G/1/N
and SM/PH/1/N queues is proposed for tandem queueing networks
Throughput Analysis of Manual Order Picking Systems with Congestion Consideration
Throughput in manual order picking systems with narrow aisles suffers from congestion as pickers cannot pass each other. Only few models incorporate congestion but they have very strict assumptions. In this work, queueing theory is used to analyze systems with traversal routing as well as different storage policies. The models are able to estimate throughput for many alternative designs in a relatively short amount of time. New guidelines for narrow-aisle order picking systems are introduced