Some background

Call centers are systems that deliver services by telephone. People are of course the prime resource, and they account for 60 to 70% of the operational costs. Another important resource is communication and computer equipment. Without computers call centers would have been impossible: they replaced the paper files allowing for immediate access to customer data. The successors of call centers are often called contact centers, because of the shift of communication towards fax, email, and internet. However, in most contact centers inbound calls still form the majority of contacts with customers. Inbound calls are also the most demanding when it comes to waiting times or response times: nobody expects an email to be answered within minutes, but waiting on the telephone for several minutes is usually considered unacceptable.

Most companies nowadays have call centers, or hire specialized firms to handle their communications with customers through call centers. As such there is an enormous financial interest in call centers. Current trends are towards an increase in size and in complexity.

The management of call centers can be split in two parts. Issues related to the effectiveness of the services offered by the call center require ICT and product-related skills. The efficiency is for a considerable part the domain of mathematics. Because the costs are dominated by personnel costs, this amounts to an efficient use of the workforce. The basis of workforce management in call centers is the well-known Erlang formula [3]: it allows one to calculate the waiting time distribution under given load and number of servers. It is used in call centers to calculate the number of servers needed to meet the required waiting time objectives. From this daily requirements are calculated which form the basis of the agent schedules. The research projects that we discuss in the next section can all be seen as extensions of the Erlang formula.

For an extensive overview of call center research, see Gans et al. [4].