Proceedings of the 2005 Winter Simulation Conference
M. E. Kuhl, N. M. Steiger, F. B. Armstrong, and J. A. Joines, eds.
MODELING AND SIMULATION OF CALL CENTERS
Athanassios N. Avramidis
Pierre L’Ecuyer
Département d’Informatique et de Recherche Opérationnelle
Université de Montréal, C.P. 6128, Succ. Centre-Ville
Montréal (Québec), H3C 3J7, CANADA
ABSTRACT
In this review, we introduce key notions and describe the decision problems commonly encountered in call center management.
Main themes are the central role of uncertainty throughout the decision hierarchy and the many operational complexities and relationships between decisions. We make connections to analytical models in the literature, emphasizing insights gained and model limitations. The high operational complexity and the prevalent uncertainty suggest that simulation modeling and simulation-based decision-making could have a central role in the management of call centers.
We formulate some common decision problems and point to recently developed simulation-based solution techniques.
We review recent work that supports modeling the primitive inputs to a call center and highlight call center modeling difficulties. 1 INTRODUCTION
Call centers are an important component of the global economy. Around 3% of the workforce in the
United States and Canada works at a call center
(Call Center News Service 2001). More people in North
America work in call centers than in agriculture. Most of the operating cost of call centers (around 3/4) is labor costs.
These call centers handle customer support, phone orders and sales, marketing, governmental information services, emergency services (police, ambulance), etc. A current trend is the extension to a contact center, whereby telephone services are enhanced by services in other media such as e-mail, fax, or chat.
In this review, we introduce key notions and describe the decision problems commonly encountered in call center management. The main themes elaborated are: the central role of uncertainty throughout the decision hierarchy; the many operational complexities and relationships between decisions; and a review of work that supports modeling the primitive inputs to a call center. We also make connections to analytical models in the literature, emphasizing insights gained and model limitations. The high operational complexity and the prevalent uncertainty suggest that simulation modeling and simulation-based decision-making could have a central role in the management of call centers.
Mehrotra and Fama (2003) also discusses simulation-based decisions for call centers, from an applied point of view.
Gans et al. (2003) is an excellent, in-depth tutorial on call centers. 2 KEY NOTIONS
Acall center is a set of resources (communication equipment, employees, computers, etc.) which enable the delivery of services via the telephone. Inbound calls are those initiated by customers calling in to the center. A customer can be blocked, i.e., receive a busy signal, if all of the center’s phone lines are busy at the time he calls. At first, calls may be connected to an interactive voice response (IVR) unit. The latest generation of speech-recognition technology allows
IVRs to interpret complex user commands, so customers may be able to “self-serve”, i.e., complete the service interaction at the IVR. Otherwise, calls are passed from the IVR to an automatic call distributor (ACD). An ACD is a specialized switch designed to route each call to an individual agent; if no qualified agent is available, then the call is placed in a queue. Modern ACDs are sophisticated, allowing routing rules based on many criteria. A queued customer may abandon without receiving service.
In a multi-skill call center, we distinguish various call types (or skills), and we distinguish agents by their skill group, defined as the subset of call types they can handle. Skill-based routing (SBR), or simply routing, refers to rules (programmed in the ACD) that control in real time the agent-to-call and call-to-agent assignments.
There is a trend towards multi-skill centers with SBR (Koole and Mandelbaum 2002); according to
Mehrotra and Fama (2003), the multi-skill call center has become ubiquitous.
A blend center is one where inbound calls are blended with outbound calls; these are initiated by agents calling
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