On reservation systems and queueing systems

Systems in which resources are shared can be operated either with reservation schedulers or as queueing systems. While reservation systems are the only option to support future start-time requests, both types of systems can be used when users want resources at the earliest available opportunity. The objective of this work is to determine the conditions under which a reservation scheduler is required versus when a queueing system is sufficient. The problem was motivated by a communication network service. A new scheduled dynamic circuit service that uses a reservation scheduler is being offered. It differs from plain old telephony service (POTS), which is operated as a queueing system. Three models of reservation systems are analyzed: (i) finite-window reservation system model, (ii) infinite-window reservation system model, and (iii) synchronized-server model. Our main finding is that if the number of servers is small, a reservation scheduler is required in both blocking-mode and waiting-mode systems. In blocking-mode systems, users should specify multiple start-time options in reservation requests to lower blocking rate while simultaneously operating the system at high utilization. In waiting-mode systems with small numbers of servers, since high-utilization system operation will cause large waiting times, a reservation system is preferred as it will allow customers to carry out other activities between their times of request and allocated start times rather than wait in a queue.