Published

2010-05-01

The consequences of heavy-tailed service time distribution on a basic queuing model and its performance indicators

Efecto del uso de tiempos de atención heavy-tailed sobre el modelo básico de líneas de espera y sus medidas de desempeño

DOI:

https://doi.org/10.15446/ing.investig.v30n2.15744

Keywords:

queuing system, heavy-tailed distribution, service time, Pareto distribution, generative model (en)
líneas de espera, distribuciones heavy-tailed, tiempos de servicio, distribución de Pareto, modelos generatrices (es)

Authors

  • Lina M. Rangel Martínez Pontificia Universidad Javeriana
  • Jorge A. Alvarado Valencia Pontificia Universidad Javeriana

Recent research showing theoretical generative models for heavy-tailed service time queues and its empirical validation implies the need for a better knowledge of the key performance indicators' behaviour under such assumption. The behaviour of the average length of the queue (Lp) and the average waiting-time (Wp)were analysed through simulation, varying system capacity, average service utilisation factor (r) and the number of servers in the systems as parameters. Comparisons were also made with service times based on Poisson processes. The results showed more sensitive variations Lq and Wq heavy-tailed service times than for Poisson-based service times. Systems having a capacity of over 1,000 entities might be considered as being systems having infinity capacity and the number of servers has a greater importance in heavy-tailed ruled processes than in Poisson processes. There was a lack adequacy Lq and Wq as key performance indicators for heavy-tailed service times, leading to unexpected and unstable results.

La reciente aparición de modelos generatrices de líneas de espera con tiempos de atención heavy-tailed y su comprobación empírica implican la necesidad de conocer el comportamiento de las medidas clásicas de desempeño de una línea de espera bajo estas condiciones. El objetivo del estudio fue el de analizar el comportamiento de Lp (longitud promedio de la fila) y Wp (tiempo promedio de espera en fila) variando los parámetros capacidad del sistema, nivel de utilización promedio (r) y número de servidores para líneas de espera con tiempos de atención heavy-tailed, y contrastar dicho comportamiento con los resultados clásicos basados en procesos de Poisson, usando para ello la simulación de eventos discretos. Los resultados mostraron que la sensibilidad de los modelos con tiempos de atención heavy-tailed a variaciones en los parámetros es mayor que la de los modelos basados en procesos de Poisson. En particular, a partir de capacidades de sistema de 1.000 entidades ciertos procesos heay-tailed pueden considerarse infinitos, y la importancia del número de servidores es mayor en los procesos heavy-tailed analizados que en los procesos de Poisson. Por último, la utilización de Lp y Wp como medidas de desempeño es inadecuada para tiempos de atención heavy-tailed al generar resultados inestables y contraintuitivos.

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