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

Abstract. Motivated by the development of complex telephone call center networks, we present
a general framework for decompositions to approximately solve Markovian queueing networks
with time-dependent and state-dependent transition rates. The decompositions are based on
assuming either full or partial product form for the time-dependent probability vectors at each
time. These decompositions reduce the number of time-dependent ordinary differential equations
that must be solved. We show how special structure in the transition rates can be exploited to
speed up computation. There is extra theoretical support for the decomposition approximation
when the steady-state distribution of the time-homogeneous version of the model has product
form.
Keywords: Time-dependent queues, Time-dependent Markovian queueing networks, Time-dependent
Markov chains, Markovian queueing networks, Decomposition approximations, Systems of ordinary
differential equations, Product-form queueing networks, Product-form approximations,
Telephone call centers, Air traffic management, Decompositions, Transition rates, Probability
vectors, Differential equations
82. Zhou, Yong-Pin and Noah Gans. A single-server queue with Markov modulated service times.
Working Paper, The Wharton School, The University of Pennsylvania, October 1999.
Abstract. We study an M/MMPP/1 queuing system, where the arrival process is Poisson and
service requirements are Markov modulated. When the Markov Chain modulating service times
has two states, we show that the distribution of the number-in-system is a superposition of two
matrix-geometric series and provide a simple algorithm for computing the rate and coefficient
matrices. These results hold for both finite and infinite waiting space systems and extend results
obtained in Neuts [5] and Naoumov [4].
Numerical comparisons between the performance of the M/MMPP/1 system and its M/G/1
analogue lead us to make the conjecture that the M/MMPP/1 system performs better if and
only if the total switching probabilities between the two states satisfy a simple condition. We
give an intuitive argument to support this conjecture.
83. Weidong Xu. Long range planning for call centers at FedEx, The Journal of Business Forecasting
Methods & Systems, 18 (4), Winter 1999/2000, 7–11.
Abstract. FedEx is the world’s largest express transportation company, generating $14 billion
in annual revenue. To support the global transportation network, FedEx has established 51
worldwide customer service call centers. The customer service at FedEx in the US handles about
500,000 calls per day. There are three major networks: 1. Domestic, 2. International, and 3.
Freight. For each network, the company has developed four different types of forecasts based on
different forecasting horizons: 1. Strategic Plan, 2. Business Plan, 3. Tactical Forecast, and 4.
Operational Forecast. Different methodologies are adopted for different levels of forecasts. An
overview of these methodologies is presented.
Keywords: Postal & delivery services, Forecasting techniques, Customer services, Case studies
(Appears also in Sections VIII and II.)
84. Aksin, O.Z. and P.T. Harker. Computing performance measures in a multi-class multi-resource
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