On the invariance principle for the first passage time
Mathematics of Operations Research
On the M(n)/M(n)/s queue with impatient calls
Performance Evaluation
Asymptotic Results and a Markovian Approximation for the M(n)/M(n)/s+GI System
Queueing Systems: Theory and Applications
Designing a Call Center with Impatient Customers
Manufacturing & Service Operations Management
Commissioned Paper: Telephone Call Centers: Tutorial, Review, and Research Prospects
Manufacturing & Service Operations Management
Dimensioning Large Call Centers
Operations Research
Engineering Solution of a Basic Call-Center Model
Management Science
Call Centers with Impatient Customers: Many-Server Asymptotics of the M/M/n + G Queue
Queueing Systems: Theory and Applications
Fluid Models for Multiserver Queues with Abandonments
Operations Research
Service-Level Agreements in Call Centers: Perils and Prescriptions
Management Science
Staffing of Time-Varying Queues to Achieve Time-Stable Performance
Management Science
Call Center Outsourcing Contract Analysis and Choice
Management Science
Call Center Outsourcing: Coordinating Staffing Level and Service Quality
Management Science
Manufacturing & Service Operations Management
Markov Chains and Stochastic Stability
Markov Chains and Stochastic Stability
Two fluid approximations for multi-server queues with abandonments
Operations Research Letters
Nurse Staffing in Medical Units: A Queueing Perspective
Operations Research
Service-Level Variability of Inbound Call Centers
Manufacturing & Service Operations Management
Computers and Industrial Engineering
Computers and Operations Research
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To ensure quality from outsourced call centers, firms sign service-level agreements (SLAs). These define service measures such as what constitutes an acceptable delay or an acceptable abandonment rate. They may also dictate penalties for failing to meet agreed-upon targets. We introduce a period-based SLA that measures performance over a short duration such as a rush hour. We compare it to alternate SLAs that measure service by individual and over a long horizon. To measure the service levels for these SLAs, we develop several approximations. We approximate the probability an acceptable delay is met by generalizing the heavy-traffic quality and efficiency driven regime. We also provide a new approximation for the abandonment rate. Further, we prove a central limit theorem for the probability of meeting a service level measured by the percentage of customers acceptably served during a period. We demonstrate how an outsourced call center operating in an environment with uncertain demand and abandonment can determine its staffing policy to maximize the expected profit for these SLAs. Numerical experiments demonstrate a high degree of accuracy for the approximations and the resulting staffing levels. We indicate several salient features of the behavior of the period-based SLA.