CALL CENTERS (CENTRES) - Faculty of Industrial Engineering and ...

104. Feng, W. and R.T. Hurley. Birth-death models for a class of service systems. Proceedings of the
IASTED International Conference Applied Informatics. International Symposium on Parallel
and Distributed Computing and Networks. ACTA Press, Anaheim, CA, USA, 2001, 320–325.
Abstract. In this paper, we discussed three birth-death models for service systems, such as
telephone call centers of Internet access points. The first model assumes that customers have
no information about the system and so they may balk or renege upon arrival. The other two
models assume that customers receive the state information as they arrive and thus, the balking
probability is state-dependent. Model 2 uses the assumption that the balking probabilities depend
on a waiting time threshold while model 3 assumes that the balking probabilities depend
directly on the number of customers in the waiting queue. Both analysis and simulation are
used to investigate the performance of the systems based on the three models. We compare the
server utilization and mean response time. Our results indicate that model 2 tends to have a
lower response time than model 1 and the performance of a system based on model 3 greatly
depends on the sequence of balking probabilities. We show the results for two such scenarios.
105. Green, Linda V., Peter J. Kolesar and Joao Soares. Improving the SIPP approach for staffing
service systems that have cyclic demands, Operations Research, 49 (4), 2001, 549–564.
Abstract. This paper evaluates the practice of determining staffing requirements in service systems
with random cyclic demands by using a series of stationary queueing models. We consider
Markovian models with sinusoidal arrival rates and use numerical methods to show that the
commonly used “stationary independent period by period” (SIPP) approach to setting staffing
requirements is inaccurate for parameter values corresponding to many real situations. Specifically,
using the SIPP approach can result in staffing levels that do not meet specified period
by period probability of delay targets during a significant fraction of the cycle. We determine
the manner in which the various system parameters affect SIPP reliability and identify domains
for which SIPP will be accurate. After exploring several alternatives, we propose two simple
modifications of SIPP that will produce reliable staffing levels in models whose parameters span
a broad range of practical situations. Our conclusions from the sinusoidal model are tested
against some empirical data.
Keywords: Service systems, Staffing: Use of queueing models, Queueing systems, Cyclic: Accuracy
of stationary models, Call centers
106. Green, Linda V., Peter J. Kolesar and Joao Soares. An improved heuristic for staffing telephone
call centers with limited operating hours. Report, Centre for Mathematics, University of Coimbra
(CMUC), Portugal, 2001.
107. Grossman, Thomas A., Douglas A. Samuelson, Sherry L. Oh and Thomas R. Rohleder. Call
centers. In Encyclopedia of Operations Research and Management Science, Centennial edition,
Saul I. Gass and Carl M. Harris (Eds.). Norwell: Kluwer Academic Publishers, 2001.
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