Simple bounds for queueing systems with breakdowns

Computationally attractive and intuitively obvious simple bounds are proposed for finite service systems which are subject to random breakdowns. The services are assumed to be exponential. The up and down periods are allowed to be generally distributed. The bounds are based on product-form modifications and depend only on means. A formal proof is presented. This proof is of interest in itself. Numerical support indicates a potential usefulness for quick engineering and performance evaluation purposes

Extended Vacation Systems and the Universality of the M/G/1/K Blocking Formula

A simple blocking formula B(K) = (1 - p)EK [1 - pEK]- 1 relates the probability of blocking for the finite capacity M/G/1/K to EK, the steady state occupancy tail probability of the same system with infinite capacity. The validity of this formula is demonstrated for M/G/1 vacation systems augmented by an idle state, an umbrella for a host of priority systems and vacation systems related to M/G/1. A class of occupancy level dependent vacation systems introduced are shown to require a variant of this blocking formula

A study of some M[x]/G/1 type queues with random breakdowns and bernouilli schedule server vacations based on a single vacation policy

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Queueing systems arise in modelling of many practical applications related to computer sciences, telecommunication networks, manufacturing and production, human computer interaction, and so on. The classical queueing system, even vacation queues or queues subject to breakdown, might not be sufficiently realistic. The purpose of this research is to extend the work done on vacation queues and on unreliable queues by studying queueing systems which take into consideration both phenomena. We study the behavior of a batch arrival queueing system with a single server, where the system is subject to random breakdowns which require a repair process, and on the other hand, the server is allowed to take a vacation after finishing a service. The breakdowns are assumed to occur while serving a customer, and when the system breaks down, it enters a repair process immediately while the customer whose service is interrupted comes back to the head of the queue waiting for the service to resume. Server vacations are assumed to follow a Bernoulli schedule under single vacation policy. We consider the above assumptions for different queueing models: queues with generalized service time, queues with two-stages of heterogeneous service, queues with a second optional service, and queues with two types of service. For all the models mentioned above, it is assumed that the service times, vacation times, and repair times all have general arbitrary distributions. Applying the supplementary variable technique, we obtain probability generating functions of queue size at a random epoch for different states of the system, and some performance measures such as the mean queue length, mean waiting time in the queue, proportion of server's idle time, and the utilization factor. The results obtained in this research, show the effect of vacation and breakdown parameters upon main performance measures of interest. These effects are also illustrated using some numerical examples and graphs.This work is funded by the Ministry of Education, Kingdom of Bahrain

Queue-length balance equations in multiclass multiserver queues and their generalizations

A classical result for the steady-state queue-length distribution of single-class queueing systems is the following: the distribution of the queue length just before an arrival epoch equals the distribution of the queue length just after a departure epoch. The constraint for this result to be valid is that arrivals, and also service completions, with probability one occur individually, i.e., not in batches. We show that it is easy to write down somewhat similar balance equations for {\em multidimensional} queue-length processes for a quite general network of multiclass multiserver queues. We formally derive those balance equations under a general framework. They are called distributional relationships, and are obtained for any external arrival process and state dependent routing as long as certain stationarity conditions are satisfied and external arrivals and service completions do not simultaneously occur. We demonstrate the use of these balance equations, in combination with PASTA, by (i) providing very simple derivations of some known results for polling systems, and (ii) obtaining new results for some queueing systems with priorities. We also extend the distributional relationships for a non-stationary framework

The preemptive repeat hybrid server interruption model

We analyze a discrete-time queueing system with server interruptions and a hybrid preemptive repeat interruption discipline. Such a discipline encapsulates both the preemptive repeat identical and the preemptive repeat different disciplines. By the introduction and analysis of so-called service completion times, we significantly reduce the complexity of the analysis. Our results include a.o. the probability generating functions and moments of queue content and delay. Finally, by means of some numerical examples, we assess how performance measures are affected by the specifics of the interruption discipline

Exact Solutions for M/M/c/Setup Queues

Recently multiserver queues with setup times have been extensively studied because they have applications in power-saving data centers. The most challenging model is the M/M/$c$/Setup queue where a server is turned off when it is idle and is turned on if there are some waiting jobs. Recently, Gandhi et al.~(SIGMETRICS 2013, QUESTA 2014) present the recursive renewal reward approach as a new mathematical tool to analyze the model. In this paper, we derive exact solutions for the same model using two alternative methodologies: generating function approach and matrix analytic method. The former yields several theoretical insights into the systems while the latter provides an exact recursive algorithm to calculate the joint stationary distribution and then some performance measures so as to give new application insights.Comment: Submitted for revie

Mathematical Modeling of Multi-Server Queueing Model for Vacations and Impatient Customer

The combination of excursions and the powerful treatment of fretful clients are at the focal point of this review, which digs into the streamlining of multi-server queueing frameworks. Modified Priority Queue Algorithm (MPQA), Vacation Scheduling Algorithm (VSA), Impatience Handling Algorithm (IHA), and Server Utilization Balancing Algorithm (SUBA) are the four calculations that have been proposed and thoroughly assessed through recreations to decide their viability in decreasing line length, holding up time, and improving framework throughput and server usage. The MPQA shines on clients considering anxiety cutoff points and organization times, showing suitability in decreasing holding-up times. Then again, VSA continuously changes server get-away, yielding lower holding-up times during fame periods. IHA progressively oversees eagerness, diminishing takeoffs brought about by fretfulness and expanding framework throughput in general. SUBA in a perfect world adjusts server use, achieving additionally created throughput and system strength. The extraordinary commitments of each calculation are revealed in examinations with related work. VSA is in accordance with past examinations an extended get-away streamlining, while MPQA works on traditional ways to deal with prioritization. IHA presents dynamic energy dealing with, and SUBA lines up with liability careful server activation systems found in the composition. This assessment basically advances the appreciation of multi-server queueing systems, offering valuable solutions for organization arranged conditions. An establishment for future improvements in queueing hypothesis and genuine applications is given by the calculations, which were assessed with significant outcomes