Telephone call centers are an integral part of many businesses, and their economic role is significant and growing. They are also fascinating sociotechnical systems in which the behavior of customers and employees is closely intertwined with physical performance measures. In these environments traditional operational models are of great value--and at the same time fundamentally limited--in their ability to characterize system performance.We review the state of research on telephone call centers. We begin with a tutorial on how call centers function and proceed to survey academic research devoted to the management of their operations. We then outline important problems that have not been addressed and identify promising directions for future research.

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Commissioned Paper: Telephone Call Centers: Tutorial, Review, and Research Prospects

A call center is a service network in which agents provide telephone-based services. Customers who seek these services are delayed in tele-queues. This article summarizes an analysis of a unique record of call center operations. The data comprise a complete operational history of a small banking call center, call by call, over a full year. Taking the perspective of queueing theory, we decompose the service process into three fundamental components: arrivals, customer patience, and service durations. Each component involves different basic mathematical structures and requires a different style of statistical analysis. Some of the key empirical results are sketched, along with descriptions of the varied techniques required. Several statistical techniques are developed for analysis of the basic components. One of these techniques is a test that a point process is a Poisson process. Another involves estimation of the mean function in a nonparametric regression with lognormal errors. A new graphical technique ...

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Statistical Analysis of a Telephone Call Center: A Queueing-Science Perspective

The most common model to support workforce management of telephone call centers is theM/ M/ N/ B model, in particular its special casesM/ M/ N (Erlang C, which models out busy signals) andM/ 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 theM/ M/ N +M model, that while numerically tractable is not very insightful. We then proceed with an asymptotic analysis of theM/ 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.

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Designing a Call Center with Impatient Customers

Computational methods for rostering and personnel scheduling has been a subject of continued research and commercial interest since the 1950s. This annotated bibliography puts together a comprehensive collection of some 700 references in this area, focusing mainly on algorithms for generating rosters and personnel schedules but also covering related areas such as workforce planning and estimating staffing requirements. We classify these papers according to the type of problem addressed, the application areas covered and the methods used. In addition, a short summary is provided for each paper.

http://www3.eng.cam.ac.uk/~hj231/Papers/AORRosteringPaper.pdf

An Annotated Bibliography of Personnel Scheduling and Rostering

Total Care Products (Functional Products) are integrated systems comprising hardware and support services. The Functional Product supplier provides all the support systems that are required to keep the hardware operable. The support systems are often referred to as ‘services’. The success of Total Care Products depends upon both hardware and services. Well established methods exist for the design of hardware. In comparison, design processes and methods for services are not so well developed. This paper is concerned with the definition and design of functional Products, in particular design of services in the context of Total Care Products. Literature from the service sector is reviewed exten-sively to identify the principal components of service design. The information required for the execution of each component of the process, and outputs of each component, are considered with respect to the design of Total Care Products. Of particular interest is the customer-supplier relationship throughout the design...

The Design of Functional (Total Care) Products

This paper describes a queueing model of telephone operator staffing and the application of the model. The Bell System has used the model to reduce the cost of meeting its service criteria, for planning purposes, and to help explain to regulatory agencies changes in service measurement criteria. The model deals with large server team sizes, bimodal service time distributions, nonstationary arrivals, customer abandonments and reattempts, and certain priority queueing structures.

David Y. Sze

Papers

OR Practice-A Queueing Model for Telephone Operator Staffing