Service Systems with Outbound Work and Blending

Project: Research project

Project Details


Overview. The vast majority of the queueing literature on service systems is concerned with
systems that process inbound work only, typically assumed to arrive in accordance with some
stochastic arrival process. In particular, most of the contact-center literature deals with inbound
call centers. However, many service systems, and the majority of large contact centers, handle
outbound work in addition to their inbound work, and that outbound work typically requires a
substantial proportion of the total service capacity. We propose new stochastic models to investigate
and analyze large service systems with many agents that process these two types of jobs. Our focus
is on contact centers that handle inbound and outbound calls simultaneously, a process referred to
as blending in the contact-center literature. We aim to prove new many-server heavy-tra�c limits
in order to approximate those systems, and demonstrate the operational advantages that blending
o�ers to large-scale service systems. Those advantages are due to the
exibility in execution times of
outbound calls, in contrast to the inbound calls, which have to be replied within a short period. In
turn, this
exibility reduces the variability in the system, making stochastic
uctuations relatively
small. The goal of the proposed research is to study combined sta�ng and control problems in the
blending settings. If successful, we will prove that it is possible to provide excellent service levels,
in terms of waiting times for inbound work and throughput rate of outbound work, while achieving
signi�cant savings in sta�ng costs when compared to systems that handle both types of calls in
separate service pools.
Intellectual Merit. The proposed research aims to provide novel limit theorems to approximate
complex queueing systems that process outbound work and employs blending. We will consider (i)
multi-dimensional settings (i.e., stochastic networks); (ii) non-stationary settings with time-varying
arrival rates; and (iii) systems with uncertain arrival rates. E�ective routing and scheduling policies
are proposed so as to achieve optimality in the many-server heavy-tra�c limiting regime when
costs of abandonment (or dropped outbound calls) and pro�ts for successful outbound calls are
A challenging aspect of the systems we consider is that they comprise of processes that evolve in
di�erent orders of size, and therefore operate in di�erent time scales. Those smaller-order processes
require a re�ned analysis, which is relatively di�cult to carry out in heavy-tra�c asymptotic regimes
that provide a macroscopic approximation that is oblivious to small-order
Broader Impact. The proposed research will contribute to the academic literature on stochastic
queueing models, and in particular, to the relatively small literature on queueing systems with
outbound work and blending, and will rigorously demonstrate the operational advantages of blending.
Since most contact centers in practice process the two types of calls, and technology makes
blending simple to implement, our results could potentially have a large impact on contact-center
In addition, despite the fact that the focus of this research is on contact-center operations, the
results and methods extend to other queueing systems that process inbound work, but can also
\create" work whenever this is desired, e.g., large healthcare units that have scheduled patients.
Finally, we intend to involve graduate students in the project, and to integrate some of its
Effective start/end date9/1/148/31/18


  • National Science Foundation (CMMI-1436518)


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