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Essays on Queueing Systems with Endogenous Service Times

  • Author / Creator
    Delasay Sorkhab, Mohammad
  • Service rates in many real queueing systems, e.g., call centers and emergency departments, change with the system conditions. We investigate and model load-dependant service rates in this dissertation. First, we propose a general framework that explains different mechanisms that cause service rates to change in response to the system load. We use the framework to categorize and explain the results of published empirical papers that document dependence of service times on load. We employ the framework to analyze the effect of load on service times of an Emergency Medical Services (EMS) system based on a data set for emergency calls received by the Calgary EMS system in 2009. Second, we propose a state-dependent queueing model in which servers speed up in response to the system “load,” but eventually slow down as a result of “overwork,” a situation where the system has been under a heavy load for an extended time period. We quantify load as the fraction of occupied servers and we operationalize overwork as the number of users served so far in the current high-load period. Our model is a quasi-birth-and-death process with a special structure that we exploit to develop efficient algorithms to compute system performance measures. We use the model and simulation to demonstrate how using models that ignore adaptive server behavior can result in inconsistencies between planned and realized performance and can lead to suboptimal, unstable, or oscillatory staffing decisions.

  • Subjects / Keywords
  • Graduation date
    2014-11
  • Type of Item
    Thesis
  • Degree
    Doctor of Philosophy
  • DOI
    https://doi.org/10.7939/R3T14TW4P
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.
  • Language
    English
  • Institution
    University of Alberta
  • Degree level
    Doctoral
  • Department
    • Faculty of Business
  • Specialization
    • Operations and Information Systems
  • Supervisor / co-supervisor and their department(s)
    • Ingolfsson, Armann (School of Business)
    • Kolfal, Bora (School of Business)
  • Examining committee members and their departments
    • Hagtvedt, Reidar (School of Business)