Avishai Mandelbaum

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Telephone call centers are an integral part of many businesses, and their economic role is significant and growing. They are also fascinating socio-technical 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(More)
T he most common model to support workforce 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(More)
A call center is a service network in which agents provide telephone-based services. Customers that seek these services are delayed in tele-queues. This paper 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(More)
We develop a framework for asymptotic optimization of a queueing system. The motivation is the staffing problem of large call centers, which we have modeled as M/M/N queues with N , the number of agents, being large. Within our framework, we determine the asymptotically optimal staffing level N ∗ that trades off agents’ costs with service quality: the(More)
Avi Mandelbaum , William A. Massey b and Martin I. Reiman c Davidson Faculty of Industrial Engineering and Management, Technion Institute, Haifa 32000, Israel E-mail: avim@tx.technion.ac.il b Bell Laboratories, Lucent Technologies, Office 2C-320, Murray Hill, NJ 07974, USA E-mail: will@research.bell-labs.com c Bell Laboratories, Lucent Technologies, Office(More)
We consider a queueing system with multitype customers and flexible (multiskilled) servers that work in parallel. If Qi is the queue length of type i customers, this queue incurs cost at the rate of Ci Qi , where Ci · is increasing and convex. We analyze the system in heavy traffic (Harrison and Lopez 1999) and show that a very simple generalized c -rule(More)
Patient flow in hospitals can be naturally modeled as a queueing network, where patients are the customers, and medical staff, beds and equipment are the servers. But are there special features of such a network that sets it apart from prevalent models of queueing networks? To address this question, we use Exploratory Data Analysis (EDA) to study detailed(More)
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(More)