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

of Operations Research, 108, 2002, 175–192.
Abstract. Motivated by a problem facing the Police Communication Centre in Auckland, New
Zealand, we consider the setting of staffing levels in a call centre with priority customers. The
choice of staffing level over any particular time period (e.g., Monday from 8am–9am) relies on
accurate arrival rate information. The usual method for identifying the arrival rate based on historical
data can, in some cases, lead to considerable errors in performance estimates for a given
staffing level. We explain why, identify three potential causes of the difficulty, and describe a
method for detecting and addressing such a problem.
112. Garnet, O., A. Mandelbaum and M. Reiman. Designing a call center with impatient customers,
Manufacturing & Service Operations Management, 4 (3), 2002, 208–227. Available
at http://ie.technion.ac.il/serveng.
Abstract. The most common model to support work force management of telephone call centers
is the M/M/N/B model, in particular its special cases M/M/N (Erlang C, which models out
busy-signals) and M/M/N/N (Erlang B, disallowing waiting). All of these models lack a central
prevalent feature, namely that impatient customers might decide to leave (abandon) before their
service begins.
In this paper we analyze the simplest abandonment model, in which customers’ patience is exponentially
distributed and the system’s waiting capacity is unlimited (M/M/N + M). Such a
model is both rich and analyzable enough to provide information that is practically important
for call center managers. We first outline a method for exact analysis of the M/M/N + M
model, that while numerically tractable is not very insightful. We then proceed with an asymptotic
analysis of the M/M/N + M model, in a regime that is appropriate for large call centers
(many agents, high efficiency, high service level). Guided by the asymptotic behavior, we derive
approximations for performance measures and propose “rules-of-thumb” for the design of large
call centers. We thus add support to the growing acknowledgment that insights from diffusion
approximations are directly applicable to management practice.
113. Koole, Ger and A. Mandelbaum. Queueing models of call centers: An introduction, Annals
of Operations Research, 113, 2002, 41–59. Special volume dedicated to a selection of papers
presented at the “First Madrid Conference on Queueing Theory” (MCQT ’02), July 2–5, 2002.
Abstract. This is a survey of some academic research on telephone call centers. The surveyed
research has its origin in, or is related to, queueing theory. Indeed, the “queueing-view” of call
centers is both natural and useful. Accordingly, queueing models have served as prevalent standard
support tools for call center management. However, the modern call center is a complex
socio-technical system. It thus enjoys central features that challenge existing queueing theory
to its limits, and beyond.
114. Mandelbaum, A., W.A. Massey, M.I. Reiman and B. Rider. Queue lengths and waiting times
for multiserver queues with abandonment and retrials, Telecommunication Systems, 21 (2–4),
2002, 149–171.
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