CALL CENTERS (CENTRES) - Faculty of Industrial Engineering and ...

Keywords: Exponential (Markovian) queues, Abandonments, Equilibrium analysis, Invisible
queues, Performance-dependent behavior, Tele-services, Tele-queues, Call centers
(Appears also in Section III.)
117. Aksin, O. Zeynep and Patrick T. Harker. Capacity sizing in the presence of a common shared
resource: Dimensioning an inbound call center, European Journal of Operational Research, 147
(3), 2003, 464–483.
Abstract. This paper studies a capacity sizing problem for service systems where capacity is
determined by multiple types of resources that are required simultaneously in order to provide
service. In addition to the simultaneous use of resources, the systems are characterized by the
presence of a common resource that is shared across multiple types of customers. The paper
focuses on inbound call centers as an important example of such systems. The capacity sizing
problem in this context is one where the optimal number of servers that need to be allocated to
different call types is determined. Optimality is defined as the number of servers that maximize
revenues net of staffing costs. For the case where customers do not wait, it is shown that a
greedy allocation procedure yields the optimal server allocation. Heuristics are proposed for
the case with waiting customers that can exhibit impatience. The numerical analysis illustrates
that for systems experiencing heavy loads and serving a diverse set of customers, the proposed
heuristics outperform current methods that ignore the role of a shared resource in these types
of dimensioning problems.
Keywords: Queueing, Staff dimensioning, Resource sharing, Call center design
118. Bhulai, S. and G. Koole. A queueing model for call blending in call centers, IEEE Transactions
on Automatic Control, 48 (8), 2003, 1434–1438.
Abstract. Call centers that apply call blending obtain high productivity and high service levels
by dynamically mixing inbound and outbound traffic. We show that agents should be assigned
to outbound calls if the number of available agents exceeds a certain threshold. This control
policy is optimal for equal service time distributions and a very good approximation otherwise.
Keywords: Call centres, Decision theory, Dynamic programming, Markov processes, Queueing
theory, Stochastic processes
119. Chevalier, P. and N. Tabordon. Overflow analysis and cross-trained servers, International Journal
of Production Economics, 85 (1), 2003, 47–60.
Abstract. In this paper, we evaluate the performance of a call center composed of specialized
and cross-trained operators (i.e., operators trained to answer different classes of calls). The
paper focuses on the approximation of the loss probability of a call center where the different
classes of calls arrive according to a Poisson distribution and service time distribution is exponential.
We make the simplifying assumption that calls not immediately answered are lost. Our
closed form approximation is based on an approximation for hierarchical overflow systems in
telecommunication developed by Hayward and later extended by Fredericks (1980).
Keywords: Statistical decision theory, Operations research, Personnel management, Executive
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