Impatient Customers Research Articles

Tandem queues with impatient customers

This paper studies a Markovian two-station tandem queueing network with impatient customers. Queueing networks with abandonment are common in many industries, e.g., call centers and healthcare. Therefore, their management has received much attention. The resulting model is a level-dependent quasi-birth-and-death (LDQBD) process. Such models are considered analytically intractable and require numerical methods for their solution. We study a specific type of LDQBD process, where the total abandonment rate increases with the number of waiting customers leading to the level-dependent feature. We analyze an equivalent last-come-first-serve system to develop a recursive relation in our LDQBD process, reducing the problem to solving quadratic matrix equations, for which efficient and exact numerical methods exist. We further simplify the analysis by combining the recursive renewal reward theorem with Queueing and Markov chain decomposition (QMCD), so that we only need to solve one quadratic matrix equation instead of infinite ones caused by the system’s level-dependent feature. We develop an exact numerical method to evaluate various performance measures of a tandem queueing network with abandonment. Our method is applicable to the analysis of queueing networks with abandonment under settings with diverse features and in various service disciplines.

Analysis of a Semi-Open Queuing Network with a State Dependent Marked Markovian Arrival Process, Customers Retrials and Impatience

We consider a queuing network with single-server nodes and heterogeneous customers. The number of customers, which can obtain service simultaneously, is restricted. Customers that cannot be admitted to the network upon arrival make repeated attempts to obtain service. The service time at the nodes is exponentially distributed. After service completion at a node, the serviced customer can transit to another node or leave the network forever. The main features of the model are the mutual dependence of processes of customer arrivals and retrials and the impatience and non-persistence of customers. Dynamics of the network are described by a multidimensional Markov chain with infinite state space, state inhomogeneous behavior and special structure of the infinitesimal generator. The explicit form of the generator is derived. An effective algorithm for computing the stationary distribution of this chain is recommended. The expressions for computation of the key performance measures of the network are given. Numerical results illustrating the importance of the account of the mentioned features of the model are presented. The model can be useful for capacity planning, performance evaluation and optimization of various wireless telecommunication networks, transportation and manufacturing systems.

Analysis of renewal input batch service queue with impatient customers and multiple working vacations

ABSTRACTThis paper presents a renewal input single server batch service queue with impatient customers and multiple working vacations. An arriving customer may join the system with probability or balk with probability . The service is carried out in batches with a maximum threshold limit . The server takes a working vacation when there are no customers in the system, and continues taking multiple working vacations as long as there are no customers at working vacation completion epochs. Applying the embedded Markov chain approach and the displacement operator method, we find the probability distribution of the queue-length at pre-arrival epoch. With the help of the Markov renewal theory and semi-Markov processes, we compute the probability distribution of the queue-length at an arbitrary epoch. We also obtain the system-length distributions at both pre-arrival and arbitrary epochs and present a potential application of the model in cloud systems. Some corresponding results underneath special cases are found by putting suitable values. We present various performance measures and waiting-time distributions in the queue. Numerical results are demonstrated to emphasize the qualitative features of the model.

The MX/M/c\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$M^{X}/M/c$$\\end{document} Bernoulli feedback queue with variant multiple working vacations and impatient customers: performance and economic analysis

The present paper deals with an MX/M/c\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$M^{X}/M/c$$\\end{document} Bernoulli feedback queueing system with variant multiple working vacations and impatience timers which depend on the states of the servers. Whenever a customer arrives at the system, he activates an random impatience timer. If his service has not been completed before his impatience timer expires, the customer may abandon the system. Using certain customer retention mechanism, the impatient customer can be retained in the system. After getting incomplete or unsatisfactory service, with some probability, each customer may comeback to the system as a Bernoulli feedback. Using the probability generating functions (PGFs), we derive the steady-state solution of the model. Then, we obtain useful performance measures. Moreover, we carry out an economic analysis. Finally, numerical study is performed to explore the effects of the model parameters on the behavior of the system.

Comparison results for M/G/1 queues with waiting and sojourn time deadlines

AbstractThis paper considers two variants of M/G/1 queues with impatient customers, which are denoted by M/G/1+Gw and M/G/1+Gs. In the M/G/1+Gw queue customers have deadlines for their waiting times, and they leave the system immediately if their services do not start before the expiration of their deadlines. On the other hand, in the M/G/1+Gs queue customers have deadlines for their sojourn times, where customers in service also immediately leave the system when their deadlines expire. In this paper we derive comparison results for performance measures of these models. In particular, we show that if the service time distribution is new better than used in expectation, then the loss probability in the M/G/1+Gs queue is greater than that in the M/G/1+Gw queue.

Time dependent of M/M/c/N an with discouragement arrivals and retention of impatient customers

Time dependent of M/M/c/N an with discouragement arrivals and retention of impatient customers

Impatient Customers in an M/M/1 Working Vacation Queue with a Waiting Server and Setup Time

Impatient Customers in an M/M/1 Working Vacation Queue with a Waiting Server and Setup Time

Analysis of a retrial queue with group service of impatient customers

A single-server retrial queue with a MAP flow, PH service times and a pool of finite capacity for accumulation of the customers and their group service is considered. Service to the next group is not provided until the number of customers in the pool will reach a certain predefined threshold value. The service time of a group depends on its size and it is less than the sum of the individual service times. The dependencies of the basic performance measures of the system on the capacity of the pool and the threshold are obtained. Numerical results are presented.

Coupling in the queue with impatience: case of several servers

We present the explicit construction of a stable queue with several servers and impatient customers, under stationary ergodic assumptions. Using a stochastic comparison of the (multivariate) workload sequence with two monotonic stochastic recursions, we propose a sufficient condition of existence of a unique stationary state of the system using Renovation theory. Whenever this condition is relaxed we use extension techniques to prove the existence of a stationary state in some cases.

On a queueing-inventory system with impatient customers, advanced reservation, cancellation, overbooking and common life time

We consider a queueing-inventory problem with Markovian arrival process, phase type distributed service time. The life time of items is exponentially distributed; all items perish together which means they have a common life time. Reservation (purchase) and cancellation of purchased items is permitted as long as the common life time is not realized. In addition overbooking of items upto a certain maximum is also permitted. When system is fully overbooked waiting customers tend to leave the system. On realization of common life time, instantly S items are procured resulting in the commencement of next cycle. In the particular case of Poisson process and exponentially distributed service time we show that the system admits asymptotic product form solution. System state characteristics are computed which are then numerically illustrated for different sets of values for the input parameters.

Analysis of Queueing System with Non-Preemptive Time Limited Service and Impatient Customers

We consider a single-server queueing system with server vacations as the important component of the polling queueing model of a real-world system. Period of continuous operation of the server (the maximum server attendance time) is restricted, but the service of a customer cannot be interrupted when this period expires. Such features are inherent for many real-world systems with resource sharing. We assume that the customers arrival is described by the Markovian Arrival Process and service, vacation and maximum server attendance times have a phase-type distribution. We derive the stationary distributions of the system states and waiting time. Taking in mind the necessity of further application of the results to modeling the polling queueing systems, the distribution of the server visiting time is derived. Extensive numerical results are presented. They highlight that an account of the coefficient of variation of vacation and maximum attendance time is very important for exact evaluation of the key performance measures of the system, while only the results for the coefficient of variation equal to zero or one are known in the literature. Impact of the possible customers impatience, which is intuitively important because the time-limited service is considered, is confirmed by the results of the numerical experiments. Optimization problem of matching the durations of vacation and maximum attendance time is considered.

Double-sided matching queues: Priority and impatient customers

We analyze a double-sided queue with priority that serves patient customers and customers with zero patience (i.e., impatient customers). In a two-sided market, high and low priority customers arrive to one side and match with queued customers on the opposite side. Impatient customers match with queued patient customers; when there is no queue, they leave the system unmatched. All arrivals follow independent Poisson processes. We derive exact formulae for the stationary queue length distribution and several steady-state performance measures.

Performance and economic analysis of a single server feedback queueing model with vacation and impatient customers

In this investigation, a single server M/M/1/N feedback queueing system with vacation, balking, reneging and retention of reneged customers is analyzed. By considering the mathematical modeling, we derive the steady state probabilities of the number of customers in the system. We obtain important measures of effectiveness of the model by using the stationary distribution, and develop a cost model of the queueing system. Further, a numerical study and a cost profit analysis are carried out.

Transient analysis of multi-server Markovian queueing system with synchronous multiple working vacations and impatience of customers

In this paper, we study an infinite capacity multi-server Markovian queue with synchronous multiple working vacations, balking and reneging. It is assumed that customers may balk and/or renege with some probability if all the c servers are busy serving customers either during the regular busy period or working vacation period. The reneging times follow an exponential distribution. The system is modeled by a quasi-birth-death process and the transient-state probabilities of the model are obtained in the Laplace domain using matrix geometric method.

Transient solution of an M/M/? queue with system's additional tasks and impatient customers

This paper studies the impatient behaviour in an infinite server queue with additional tasks assigned to the system. Whenever the system becomes empty, the system as a whole is assigned a secondary task of duration U whose distribution is exponential. Any arrival during the period U becomes impatient due to the unavailability of service facility. Each individual waiting customer activates an independent impatience timer of duration T which is exponentially distributed. When the system comes back after the completion of U, before T expires, the waiting customers are simultaneously taken for service and they leave the system after the completion of service. If T expires before the completion of task U, the customers abandon the system and never to return. The transient system size probabilities of this model are derived explicitly for both single and multiple task cases. The time-dependent mean and variance of system size are also derived. Further, numerical simulations are also presented to analyse the effect of system indices.

A multi-layer congested facility location problem with consideration of impatient customers in a queuing system

This study presents a novel multi-objective model for a facility location-allocation problem with congestion in a multi-layer network. The proposed model contemplates the existence of impatient customers within a classical queuing system, namely M/M/1. The network is configured by determining the optimal number of facilities in each layer and allocation of customers to the facilities in a hierarchy facilities problem. Regarding the first objective function of the model, we minimize the sum of aggregate costs related to the customers’ waiting times, as well as the costs imposed by the impatience of the customers. In the second objective function, the costs associated with the sum of aggregate idleness of facilities are minimized. The proposed multi-objective multi-layer facility location-allocation (MLFLA) problem is solved by an evolutionary approach according to the Pareto envelope-based selection algorithm II (PESA-II). Parameters of the algorithm are tuned by Taguchi method. Then, the performance of the algorithm is reported by four performance metrics introduced for multi-objective optimization problems. The computational run times of 10 test problems demonstrate that the solution methodology is capable of solving the problem with large network sizes.

Impatient Customers in a Markovian Queue with Multiple Working Vacation

Impatient Customers in a Markovian Queue with Multiple Working Vacation

Performance and economic analysis of Markovian Bernoulli feedback queueing system with vacations, waiting server and impatient customers

Abstract This paper concerns the analysis of a Markovian queueing system with Bernoulli feedback, single vacation, waiting server and impatient customers. We suppose that whenever the system is empty the sever waits for a random amount of time before he leaves for a vacation. Moreover, the customer’s impatience timer depends on the states of the server. If the customer’s service has not been completed before the impatience timer expires, the customer leaves the system, and via certain mechanism, impatient customer may be retained in the system. We obtain explicit expressions for the steady-state probabilities of the queueing model, using the probability generating function (PGF). Further, we obtain some important performance measures of the system and formulate a cost model. Finally, an extensive numerical study is illustrated.

Cost optimization analysis for an $$M^{X}/M/c$$ M X / M / c vacation queueing system with waiting servers and impatient customers

This paper deals with the study of an $$M^{X}/M/c$$ Bernoulli feedback queueing system with waiting servers and two different policies of synchronous vacations (single and multiple vacation policies). During vacation period, the customers may leave the system (reneging), and using certain customer retention mechanism, the reneged customers may be retained in the system. The probability generating function (PGF) has been used to obtain the steady state probabilities of the model. Various performances measures of the system are derived. Then, a cost model is developed. Further, a cost optimization problem is considered using quadratic fit search method. Finally, a variety of numerical illustrations are discussed for the applicability of the model.

Analysis of Customers’ Impatience in a Repairable Retrial Queue under Postponed Preventive Actions

SYNOPTIC ABSTRACTIn this article, we analyze an unreliable retrial queue with persistent and impatient customers having different general service distributions. The server is subject to active and passive breakdowns. A persistent customer whose service is interrupted enters the orbit, while an impatient one leaves the system. Two types of arbitrarily distributed maintenances are considered: preventive for improving system performances and preventing breakdowns, and corrective for restoring the service when a failure occurs. If a preventive maintenance occurs in a busy period, then it is postponed to an ulterior random date. We give the necessary and sufficient condition for the system to be stable. We obtain the joint probability distribution of the server state and the number of customers in orbit in terms of Laplace and z-transforms. Some performance measures are derived and numerical results are given. Moreover, a cost minimization problem is considered.