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DOI: 10.1007/s00291-004-0165-7
OR Spectrum (2004) 26: 353376Salah Aguir1, Fikri Karaesmen2, O. Zeynep Aksin3, and Fabrice Chauvet41 Laboratoire G
enie Industriel, Ecole Centrale Paris, Grande Voie des Vignes,
92295 Chatenay-Malabry Cedex, France (e-mail: [email protected])2 Department of Industrial Engineering, Koc University, 34450 Sariyer, Istanbul, Turkey(e-mail: [email protected])3 Graduate School of Business, Koc University, 34450 Sariyer, Istanbul, Turkey(e-mail: [email protected])4 Bouygues Telecom R&D, 10 rue Paul Dautier, 78944 Velizy Cedex, France(e-mail: [email protected])Abstract. This paper models a call center as a Markovian queue with multiple
servers, where customer balking, impatience, and retrials are modeled explicitly.
The resulting queue is analyzed both in a stationary and non-stationary setting.
For the stationary setting a uid approximation is proposed, which overcomes the
computational burden of the continuous time markov chain analysis, and which is
shown to provide an accurate representation of the system for large call centers
with high system load. An insensitivity property of the retrial rate to key system
parameters is established. The uid approximation is shown to work equally well
for the non-stationary setting with time varying arrival rates. Using the uid approximation, the paper explores the retrial phenomenon for a real call center. The model
is used to estimate the real arrival rates based on demand data where retrials cannot
be distinguished from rst time calls. This is a common problem encountered in
call centers. Through numerical examples, it is shown that disregarding the retrial
phenomenon in call centers can lead to huge distortions in subsequent forecasting
and stafng analysis.Keywords: Call centers Multi-server queues Retrials1 IntroductionThis paper is motivated by the problem of a major European telecommunications
service providers call center. The call center is managed as a cost center, and
minimizing the stafng costs associated with this call center is an important business The authors would like to acknowledge helpful discussions with Yves Dallery (Ecole
Centrale Paris), Rabie Nait-Abdallah and Thierry Prat (Bouygues Telecom) during the course
of this project.Correspondence to: F. Karaesmenc
[circlecopyrt]Springer-Verlag 2004The impact of retrials on call center performance[star]354 S. Aguir et al.concern. At the same time, the mobile telephony market within which this call center
operates is a highly competitive one, and providing good service to customers
constitutes a competitive necessity. Good service is measured in many different
ways, but fundamentally it implies meeting the...