Effect of parameters on Geoa/Geob/1 Queues: theoretical analysis and simulation results

This paper analyzes a discrete-time Geoa/Geob/1 queuing system with batch arrivals of fixed size a , and batch services of fixed size b. Both arrivals and services occur randomly following a geometric distribution. The steady-state queue length distribution is obtained as the solution of a system of difference equations. Necessary and sufficient conditions are given for the system to be stationary. Besides, the uniqueness of the root of the characteristic polynomial in the interval (0, 1) is proven which is the only root needed for the computation of the theoretical solution with the proposed procedure. The theoretical results are compared with the ones observed in some simulations of the queuing system under different sets of parameters. The agreement of the results encourages the use of simulation for more complex systems. Finally, we explore the effect of parameters on the mean length of the queue as well as on the mean waiting time

Analysis of a discrete-time queue with general independent arrivals, general service demands and fixed service capacity

This paper analyzes a single-server discrete-time queueing model with general independent arrivals, where the service process of the server is characterized in two steps. Specifically, the model assumes that (1) each customer represents a random, arbitrarily distributed, amount of work for the server, the service demand, and (2) the server disposes of a fixed number of work units that can be executed per slot, the service capacity. For this non-classical queueing model, we obtain explicit closed-form results for the probability generating functions (pgf's) of the unfinished work in the system (expressed in work units) and the queueing delay of an arbitrary customer (expressed in time slots). Deriving the pgf of the number of customers in the system turns out to be hard, in general. Nevertheless, we derive this pgf explicitly in a number of special cases, i.e., either for geometrically distributed service demands, and/or for Bernoulli arrivals or geometric arrivals. The obtained results show that the tail distributions of the unfinished work, the customer delay and the system content all exhibit a geometric decay, with semi-analytic formulas for the decay rates available. Another interesting conclusion is that, for a given system load, the mean customer delay converges to constant limiting values when the service capacity per slot goes to infinity, and either the mean arrival rate or the mean service demand increases proportionally. Accurate approximative analytical expressions are available for these limiting values

Sistemas de colas en tiempo discreto con entradas y servicios en bloque: estudio teórico y simulaciones comparativas

Los sistemas de colas se vienen estudiando desde inicios del siglo XX. Suele formarse una cola ante una instalación que proporciona determinado servicio. La teoría de colas pretende estudiar las fluctuaciones que se producen en estas situaciones: el número de clientes, el tiempo que debe esperar cada uno antes de ser atendido, la duración del tiempo de servicio … En este trabajo se plantean algunos modelos de colas con un solo servidor en los que los clientes llegan y son atendidos en grupos, no necesariamente del mismo tamaño. El estudio se hace mediante simulación y mediante análisis probabilístico y se comparan los resultados obtenidos por ambos procedimientos. Se mide la eficiencia de cada modelo en términos de acumulación de clientes y tiempos de espera de acuerdo con los parámetros que los gobiernan. También se comparan las eficiencias de los modelos planteados