We consider polling models consisting of a single server that visits the queues in a cyclic order. In the vast majority of papers that have appeared on polling models, it is assumed that at each of the individual queues, the customers are served on a first-come-first-served (FCFS) basis. In this paper, we study polling models where the local scheduling policy is not FCFS but instead is varied as last-come-first-served (LCFS), random order of service (ROS), processor sharing (PS), and shortest-job-first (SJF). The service policies are assumed to be either gated or globally gated. The main result of the paper is the derivation of asymptotic closed-form expressions for the Laplace–Stieltjes transform of the scaled waiting-time and sojourn-time distributions under heavy-traffic assumptions. For FCFS service, the asymptotic sojourn-time distribution is known to be of the form UΓ, where U and Γ are uniformly and gamma distributed with known parameters. In this paper, we show that the asymptotic sojourn-time distribution (1) for LCFS is also of the form UΓ, (2) for ROS is of the form ˜UΓ, where ˜U has a trapezoidal distribution, and (3) for PS and SJF is of the form ˜U∗Γ, where ˜U∗ has a generalized trapezoidal distribution. These results are rather intriguing and lead to new fundamental insight into the impact of the local scheduling policy on the performance of polling models. As a by-product, the heavy-traffic results suggest simple closed-form approximations for the complete waiting-time and sojourn-time distributions for stable systems with arbitrary load values. The accuracy of the approximations is evaluated by simulations.
Additional Metadata
THEME Logistics (theme 3)
Publisher Springer
Persistent URL dx.doi.org/10.1007/s11134-014-9416-8
Journal Queueing Systems
Citation
Bekker, R, Vis, P, Dorsman, J.-P.L, van der Mei, R.D, & Winands, E.M.M. (2015). The impact of scheduling policies on the waiting-time distributions in polling systems. Queueing Systems, 2, 145–172. doi:10.1007/s11134-014-9416-8