Strong approximations for Markovian service networks
Queueing Systems: Theory and Applications
Heavy traffic resource pooling in parallel-server systems
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
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A Diffusion Approximation for the G/GI/n/m Queue
Operations Research
Heavy-Traffic Limits for the G/H2*/n/m Queue
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Optimal Routing In Output-Queued Flexible Server Systems
Probability in the Engineering and Informational Sciences
Maximizing Queueing Network Utility Subject to Stability: Greedy Primal-Dual Algorithm
Queueing Systems: Theory and Applications
Dynamic Routing in Large-Scale Service Systems with Heterogeneous Servers
Queueing Systems: Theory and Applications
Queueing Systems: Theory and Applications
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Operations Research
Optimal control of parallel server systems with many servers in heavy traffic
Queueing Systems: Theory and Applications
Service-Level Differentiation in Call Centers with Fully Flexible Servers
Management Science
Usage Restriction and Subscription Services: Operational Benefits with Rational Users
Manufacturing & Service Operations Management
Scheduling Flexible Servers with Convex Delay Costs in Many-Server Service Systems
Manufacturing & Service Operations Management
On a Data-Driven Method for Staffing Large Call Centers
Operations Research
Responding to Unexpected Overloads in Large-Scale Service Systems
Management Science
Shadow-Routing Based Control of Flexible Multiserver Pools in Overload
Operations Research
Robust Design and Control of Call Centers with Flexible Interactive Voice Response Systems
Manufacturing & Service Operations Management
Queueing Systems: Theory and Applications
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A general model with multiple input flows (classes) and several flexible multi-server pools is considered. We propose a robust, generic scheme for routing new arrivals, which optimally balances server pools' loads, without the knowledge of the flow input rates and without solving any optimization problem. The scheme is based on Shadow routing in a virtual queueing system. We study the behavior of our scheme in the Halfin---Whitt (or, QED) asymptotic regime, when server pool sizes and the input rates are scaled up simultaneously by a factor r growing to infinity, while keeping the system load within $O(\sqrt{r}\,)$ of its capacity.The main results are as follows. (i) We show that, in general, a system in a stationary regime has at least $O(\sqrt{r}\,)$ average queue lengths, even if the so called null-controllability (Atar et al., Ann. Appl. Probab. 16, 1764---1804, 2006) on a finite time interval is possible; strategies achieving this $O(\sqrt{r}\,)$ growth rate we call order-optimal. (ii) We show that some natural algorithms, such as MaxWeight, that guarantee stability, are not order-optimal. (iii) Under the complete resource pooling condition, we prove the diffusion limit of the arrival processes into server pools, under the Shadow routing. (We conjecture that result (iii) leads to order-optimality of the Shadow routing algorithm; a formal proof of this fact is an important subject of future work.) Simulation results demonstrate good performance and robustness of our scheme.