Motivated by call centers, we study large-scale service systems with homogeneous customers and heterogeneous servers. The servers differ with respect to their speed of service. This model arises naturally in situations with various servers' experience levels (trainees vs. experienced / expert servers). It can also be used as a stylized model to capture natural heterogeneity in server population. We ask the following two questions: 1) Given a fixed set of servers, how to assign customers to servers so as to optimize system performance, and 2) How many servers of each pool are required in order to minimize staffing costs while maintaining pre-specified performance goals. We propose staffing and routing rules that are jointly asymptotically optimal as the system approaches the heavy-traffic many-server Halfin-Whitt (QED) regime. The talk is based on three papers:

Armony M., (2005) "Dynamic Routing in Large-Scale Service Systems with Heterogeneous Servers", Queueing Systems, 51(3-4), 287-329

Armony, M., Mandelbaum, A., (2008) "Routing and Staffing in Large-Scale Service Systems: The Case of Homogeneous Impatient Customers and Heterogeneous Servers", working paper

Armony, M., Ward, A.R., (2008) "Fair Dynamic Routing in Large-Scale Heterogeneous-Server Systems", working paper